Description:TECHNICAL FIELD
[0001] The present disclosure relates to polymer composite nanofibers, in particular, the present disclosure relates to a nanofiber composite, a method for preparing the nanofiber composite, and a method for removing lead from wastewater.
BACKGROUND
[0002] Water pollution due to heavy metal contamination presents a significant environmental and public health challenge worldwide. Heavy metals, including for example, lead, cadmium, mercury, and chromium, readily persist in the environment and bioaccumulate in living organisms, posing substantial threats to ecosystem health and human well-being. The heavy metals act as contaminants and enter water bodies through various industrial processes, mining activities, agricultural runoff, and improper waste disposal, necessitating effective and economical remediation technologies for their removal from wastewater and contaminated water sources.
[0003] Existing methods for heavy metal removal include chemical precipitation, ion exchange, membrane filtration, coagulation, and adsorption. While the existing methods have been implemented in various industrial settings, they suffer from significant limitations. The chemical precipitation generates secondary waste that requires further treatment, membrane technologies often involve high operational costs and frequent fouling issues, and the ion exchange materials exhibit limited selectivity and regeneration capabilities. Furthermore, the adsorbents frequently demonstrate inadequate adsorption capacities, poor stability in aqueous environments, and insufficient regeneration potential, limiting their practical application in sustainable water treatment processes. The development of advanced materials that combine high adsorption capacity, selectivity, mechanical stability, and reusability remains a significant challenge in the field of water remediation.
[0004] Several materials, including activated carbon, clay minerals, metal oxides, and various polymeric adsorbents, have been investigated for heavy metal removal applications. While showing promise in laboratory settings, these materials often exhibit diminished performance under real-world conditions, particularly when confronted with complex water matrices containing multiple contaminants. Additionally, many existing adsorbents suffer from poor mechanical integrity, leading to material loss during treatment processes and compromised performance over repeated use cycles. The synthesis of the existing materials frequently involves complex procedures requiring harsh chemicals, high energy inputs, or specialised equipment, further limiting their cost-effectiveness and environmental sustainability for large-scale implementation.
[0005] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.
SUMMARY
[0006] The present disclosure provides a nanofiber composite, a method for preparing the nanofiber composite, and a method for removing lead from wastewater. The present disclosure addresses the technical problem of how to remove heavy metals by using an adsorbent material with enhanced adsorption capacity and structural stability. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provides an improved nanofiber composite and an improved method for preparing the nanofiber composite featuring a three-dimensional fibrous network for lead adsorption from water.
[0007] One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
[0008] In one aspect, the present disclosure provides a nanofiber composite, comprising:
zeolitic imidazolate framework-67 nanoparticles; and
polyvinyl alcohol fibres encapsulating the zeolitic imidazolate framework-67 nanoparticles,
wherein the nanofiber composite has an adsorption capacity for lead ions of at least 100 milligrams per gram.
[0009] The inclusion of ZIF-67 nanoparticles introduces a high surface area and a porous crystalline structure containing well-defined micropores, facilitating selective adsorption of lead ions through pore-filling, electrostatic attraction, and ion exchange with cobalt ions. The ZIF-67 framework offers high affinity sites for lead ions due to accessible nitrogen cavities, thereby enabling rapid and efficient capture of lead ions. The encapsulation of ZIF-67 within PVA nanofibers provides mechanical stability and processability to the overall nanofiber composite. The PVA matrix acts as a structural support, providing flexibility, robustness, and compatibility with electrospinning while preserving the active surface functionality of the encapsulated ZIF-67. The PVA also contributes functional hydroxyl groups that participate in hydrogen bonding or electrostatic interactions with metal ions, further enhancing the overall adsorption capacity of the nanofiber composite.
[0010] The combination of ZIF-67 nanoparticles and PVA nanofibers improves the adsorption capacity of the nanofiber composite. The ZIF-67 framework provides a high internal surface area with accessible metal coordination sites suitable for lead ion capture, while the PVA ensures structural support, mechanical flexibility, and additional functional groups (e.g., hydroxyl groups) that further contribute to adsorption through hydrogen bonding and electrostatic interactions. When integrated, the PVA matrix stabilises and disperses the ZIF-67 nanoparticles uniformly across the fibrous network of the nanofiber composite. Furthermore, the ZIF-67 nanoparticles enhance the accessibility to adsorption sites and prevent nanoparticle agglomeration or leaching.
[0011] In another aspect, the present disclosure provides a method for preparing a nanofiber composite for lead adsorption from water, comprising:
mixing zeolitic imidazolate framework-67 nanoparticles with polyvinyl alcohol in a solvent to form a precursor solution with a weight ratio of 1:4; and
electrospinning the precursor solution at a voltage of 8-12 kilovolts to form nanofibers,
wherein the mixing and electrospinning create a three-dimensional fibrous network that positions nitrogen atoms of the zeolitic imidazole framework-67 at predetermined intervals, creating coordination sites that facilitate electrostatic and hydrogen bonding interactions with lead ions for lead adsorption from water.
[0012] The method for preparing a nanofiber composite for lead adsorption from water achieves all the advantages and technical effects of the nanofiber composite formed in the present disclosure.
[0013] In yet another aspect, the present disclosure provides a method for removing lead from wastewater, comprising:
contacting wastewater containing lead ions with a nanofiber composite comprising zeolitic imidazolate framework-67 nanoparticles encapsulated in polyvinyl alcohol fibres;
allowing the nanofiber composite to adsorb the lead ions by maintaining a pH of 5-7 that promotes deprotonation of hydroxyl groups and nitrogen sites, creating adsorption sites that attract lead ions and facilitate chelation and ion exchange mechanisms; and
separating the nanofiber composite from the wastewater,
wherein the nanofiber composite removes lead ions through a combination of electrostatic attraction via deprotonated sites, chelation between lead ions and hydroxyl functionalities, and ion exchange between lead ions and cobalt ions within the zeolitic imidazolate framework-67 structure.
[0014] The precisely controlled pH range approximately ranging between 5-7, acts as a useful condition to activate ion-exchange and adsorption surfaces of the nanofiber composite. At such pH range, the hydroxyl groups present in the PVA matrix undergo partial deprotonation, yielding negatively charged oxygen sites capable of attracting positively charged lead ions through electrostatic interactions. Simultaneously, the nitrogen-containing moieties within the imidazole rings of ZIF-67 also become partially deprotonated or exposed, enhancing the capacity of the ZIF-67 framework to interact with cationic metal species. Following adsorption, the lead-loaded nanofiber composite can be easily separated from the aqueous phase through a combination of electrostatic attraction via deprotonated sites, chelation between lead ions and hydroxyl functionalities. Collectively, the method offers a high-throughput, reusable, and scalable approach to wastewater remediation by leveraging the structural and chemical properties of both ZIF-67 and PVA under carefully controlled conditions.
[0015] Additional aspects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
[0017] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
FIG.1 is a flowchart illustrating a method for preparing a nanofiber composite for lead adsorption from water, in accordance with an embodiment of the present disclosure;
FIG. 2 is a graphical representation illustrating Fourier transform infrared (FTIR) spectroscopy, in accordance with an embodiment of the present disclosure;
FIG. 3 is a graphical representation illustrating an X-ray diffraction (XRD) pattern of the nanofiber composite before and after lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 4A is a diagram illustrating a scanning electron microscope (SEM) image of the nanofiber composite, in accordance with an embodiment of the present disclosure;
FIG. 4B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of the network of interwoven nanoparticles, in accordance with an embodiment of present disclosure;
FIG. 5A is a diagram illustrating a scanning electron microscope (SEM) image of the nanofiber composite after lead ion adsorption, in accordance with an embodiment of the present disclosure;
FIG. 5B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of the nanofiber composite after lead ion adsorption, in accordance with an embodiment of present disclosure;
FIG.6 is a flowchart illustrating a method for removing lead from wastewater, in accordance with an embodiment of the present disclosure;
FIG. 7A is a graphical representation illustrating the raman spectroscopy analysis of the nanofiber composite before lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 7B is a graphical representation illustrating the raman spectroscopy analysis of the nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 8A is a graphical representation illustrating an ultraviolet-visible (UV-Vis) absorption spectrum of zeolitic imidazolate framework-67 (ZIF-67), in accordance with an embodiment of the present disclosure;
FIG. 8B is a graphical representation illustrating an ultraviolet-visible (UV-Vis) absorption spectrum of polyvinyl alcohol (PVA), in accordance with an embodiment of the present disclosure;
FIG. 8C is a graphical representation illustrating an ultraviolet-visible (UV-Vis) absorption spectrum of a nanofiber composite before lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 8D is a graphical representation illustrating an ultraviolet-visible (UV-Vis) absorption spectrum of the nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 9A is a graphical representation illustrating an X-ray photoelectron spectroscopy (XPS) survey spectrum of zeolitic imidazolate framework-67 (ZIF-67), in accordance with an embodiment of the present disclosure;
FIG. 9B is a graphical representation illustrating an X-ray photoelectron spectroscopy (XPS) survey spectrum of nanofiber composite material, in accordance with an embodiment of the present disclosure;
FIG. 9C is a graphical representation illustrating an X-ray photoelectron spectroscopy (XPS) survey spectrum of the nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 9D is a graphical representation illustrating a high-resolution X-ray photoelectron spectroscopy (XPS) spectrum of a nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure;
FIG. 10A is a graphical representation illustrating the effect of pH on removal efficiency of ions using the nanofiber composite, in accordance with an embodiment of the present disclosure;
FIG. 10B is a graphical representation illustrating the determination of point of zero charge (PZC) for the nanofiber composite, in accordance with an embodiment of the present disclosure;
FIG. 10C is a graphical representation illustrating the effect nanofiber composite dosage on removal efficiency and adsorption capacity, in accordance with an embodiment of the present disclosure;
FIG. 10D is a graphical representation illustrating the effect of initial lead ion concentration on removal efficiency and adsorption capacity, in accordance with an embodiment of the present disclosure; and
FIG. 11 is a graphical representation illustrating the regeneration efficiency of the nanofiber composite over multiple regeneration cycles using different regeneration agents, in accordance with an embodiment of the present disclosure.
[0018] In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
[0019] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognise that other embodiments for carrying out or practicing the present disclosure are also possible.
[0020] FIG.1 is a flowchart illustrating a method for preparing a nanofiber composite for lead adsorption from water, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, a method 100 includes steps 102 to 104.
[0021] At step 102, the method 100 includes mixing zeolitic imidazolate framework-67 (ZIF-67) nanoparticles with polyvinyl alcohol (PVA) in a solvent to form a precursor solution with a weight ratio of 1:4. The zeolitic imidazolate framework-67 (ZIF-67) is a type of metal-organic framework (MOF) with a cobalt-based structure, where cobalt ions are linked to 2-methylimidazole ligands. The ZIF-67 is known for its high surface area, thermal and chemical stability, and porous structure, making it a versatile material for various applications such as gas storage, catalysis, sensing, water purification, and as a precursor for other nanomaterials. The ZIF-67 is synthesised through a simple room-temperature solution-based method involving the reaction of cobalt nitrate hexahydrate with 2-methylimidazole in a suitable solvent (for example, methanol or deionised water). For example, a predetermined amount of cobalt nitrate hexahydrate is dissolved in methanol using a magnetic stirrer to ensure uniform dispersion and dissolution of the cobalt nitrate hexahydrate, forming a clear pink solution. Separately, 2-methylimidazole is also dissolved in methanol under magnetic stirring to prepare a colourless solution. Once the solution of cobalt nitrate hexahydrate dissolved in methanol and the colourless solution of the 2-methylimidazole dissolved in methanol are completely homogeneous, they are combined slowly while continuously stirring using a magnetic stirrer at ambient temperature. The coordination reaction between cobalt ions and imidazole ligands initiates the formation of purple-coloured ZIF-67 crystals. The reaction mixture is stirred continuously for 12 to 24 hours to allow sufficient time for crystal growth and uniform particle formation. The formed particles are then collected via centrifugation or vacuum filtration, followed by washing several times with methanol to remove unreacted precursors and any soluble by-products. Finally, the purified ZIF-67 crystals are dried under vacuum or in a hot air oven at a moderate temperature (60–80°C), yielding a fine crystalline ZIF-67 powder.
[0022] The Polyvinyl alcohol (PVA) is a synthetic polymer (also known as PVOH) that is water-soluble, colourless, and odourless. The PVA is made from the polymerisation of vinyl acetate. The PVA is widely used in various applications, including adhesives, films, and biomedical applications like hydrogels. A specific quantity of PVA powder is dissolved in deionised water under magnetic stirring and gentle heating. The solution of deionised water and PVA powder is stirred at a temperature of around 80–90°C for 2 to 4 hours until a clear, viscous PVA solution is formed, indicating complete dissolution of the PVA. The concentration of PVA is maintained within an optimal range (e.g., 8–12% weight/volume) to ensure proper viscosity and electrospinnability.
[0023] In an implementation, the mixing includes dissolving the zeolitic imidazolate framework-67 and polyvinyl alcohol in deionised water. The deionised water is selected as the solvent due to its ability to dissolve PVA effectively while allowing for proper dispersion of the ZIF-67 nanoparticles without chemical degradation. Once the PVA solution is ready, a predetermined amount of synthesised ZIF-67 powder is gradually added to the PVA solution under continuous stirring. For example, 3 g of ZIF-67 was mixed with 12 g of PVA in 0.150 L of deionised water. The mixing of the ZIF-67 and PVA is done in the weight ratio of 1:4. The ratio of 1:4 ensures optimal distribution of ZIF-67 nanoparticles throughout the PVA matrix while maintaining sufficient polymer content to form stable nanofibers. In an implementation, the mixing includes sonicating the mixture for a period of 5-15 minutes. To ensure uniform dispersion of the ZIF-67 particles within the PVA matrix, the mixture of the ZIF-67 and PVA in deionised water is subjected to sonication using a probe or bath sonicator for 10-15 minutes. The sonication helps in breaking any particle agglomerates and promotes homogeneous distribution throughout the solution. The sonicated mixture is further stirred magnetically for an additional 1–2 hours at room temperature to stabilise the suspension and ensure consistency in composition, thereby forming a homogenous solution.
[0024] In an implementation, the stirring further includes stirring the mixture at 80-90 degrees Celsius for 3-5 hours. After sonication, the sonicated mixture is stirred at an elevated temperature of 80-90 degrees Celsius for 3-5 hours using a magnetic stirrer with heating capability. The extended heating and stirring period promote the complete dissolution of the PVA polymer chains and allow for optimal interaction between the PVA and the ZIF-67 nanoparticles. The temperature range is carefully selected to be below the degradation temperature of the PVA while being sufficiently high to reduce solution viscosity and enhance molecular mobility, resulting in a homogeneous precursor solution with ideal rheological properties for the subsequent electrospinning process.
[0025] At step 104, the method 100 includes electrospinning the precursor solution at a voltage of 8-12 kilovolts to form nanofibers. The precursor solution, formed by sonication and then continuous stirring at high temperature, is subjected to electrospinning at a voltage between 10-20 kilovolts. The precursor solution is loaded into a syringe equipped with a blunt-end stainless steel needle (18-22 gauge), which is connected to a high-voltage power supply. The syringe is mounted on a syringe pump to control the feed rate of the precursor solution. For example, a 20-gauge syringe is loaded with the precursor solution and mounted on a syringe pump to control the feed rate of the precursor solution. In an implementation, the feed rate of the precursor solution is maintained at approximately 0.2 to 0.5 millilitres per hour. The feed rate range of 0.2 to 0.5 millilitres per hour balances the requirements of continuous nanofiber production and adequate solvent evaporation. Feeding the precursor solution too rapidly would result in insufficient solvent evaporation and potentially lead to beaded or fused nanofibers, while excessively slow feed rates might cause needle clogging due to premature drying at the tip or produce nanofibers with inconsistent diameters. A voltage in the range of 10–20 kV is applied between the needle and a grounded collector plate placed at a fixed distance. For example, at a lower voltage of around 10 kV, the electric field may be just sufficient to initiate the ejection of the precursor solution from the needle tip (forming a taylor cone), but may produce thicker nanofibers due to slower jet acceleration and limited stretching.
[0026] In another example, a higher voltage of 18 kV increases the electric field strength, leading to greater stretching of the polymer jet, resulting in finer nanofibers with smaller diameters. In an implementation, the distance between the needle and the grounded collector plate (examples of grounded collector plate are aluminium foil or a rotating drum) is approximately ranging between 10–15 cm. The distance range of 10–15 cm provides the optimal flight path for the jet of the precursor solution, allowing sufficient time for solvent evaporation while ensuring that the electrostatic field strength remains adequate for nanofiber formation. At distances shorter than 10 centimetres, incomplete solvent evaporation might occur, leading to wet fibres and potential fusion at contact points, while distances exceeding 15 centimetres may result in insufficient electrostatic forces, causing jet instability or even preventing nanofiber formation altogether.
[0027] The voltage range of 10-20 kilovolts generates an electrostatic field strong enough to overcome the surface tension of the precursor solution, resulting in the ejection of a charged jet that stretches and thins as it travels towards the grounded collector plate. During the transfer of the precursor solution from the tip of the needle to the grounded collector plate, the deionised water evaporates, leading to the formation of solid nanofibers with diameters approximately ranging from 100 to 300 nanometers. The electrospinning is allowed to continue for a sufficient period (t 2 to 4 hours) to accumulate a nanofiber mat. After electrospinning, the nanofiber mat is carefully peeled from the grounded collector plate. In an implementation, the nanofiber mat is dried in a vacuum oven at 40–60°C to remove any residual moisture or solvent, forming a nanofiber composite. The nanofiber composite formed is stable and is composed of uniformly embedded ZIF-67 particles within a PVA fibrous matrix. The nanofiber composite is then stored in a desiccator until further use in adsorption experiments or characterisation procedures. The combination of mixing and electrospinning processes creates a three-dimensional fibrous network with high surface area and porosity, where the nitrogen atoms of the ZIF-67 structure are positioned at predetermined intervals within the nanofiber composite matrix. The arrangement of nitrogen atoms creates well-distributed coordination sites throughout the nanofiber composite, facilitating multiple interaction mechanisms, including electrostatic attraction between the nitrogen atoms and lead ions, as well as hydrogen bonding interactions. Such interaction mechanisms significantly enhance the capability of the nanofiber composite to adsorb lead ions from water.
[0028] The present disclosure provides the nanofiber composite configured for the effective adsorption of lead ions from aqueous solutions. The nanofiber composite includes zeolitic imidazolate framework-67 (ZIF-67) nanoparticles uniformly embedded within the polyvinyl alcohol (PVA) matrix. The ZIF-67 nanoparticles serve as the active adsorbent component due to their high surface area and porous structure, while the PVA matrix acts as a flexible, hydrophilic support matrix. The structural configuration of the nanofiber composite ensures that the ZIF-67 particles are well-dispersed and accessible for lead ion interaction. In an implementation, the nanofiber composite exhibits a lead adsorption capacity of at least 100 milligrams of lead per gram of nanofiber composite. The led adsorption capacity represents a significant enhancement compared to conventional polymer-only systems and confirms the high-efficiency adsorption behaviour of the nanofiber composite.
[0029] In an implementation, the weight ratio of zeolitic imidazolate framework-67 to polyvinyl alcohol is from 1:2 to 1:6. The ratio range from 1:2 to 1:6 ensures optimal dispersion of ZIF-67 particles within the polymer matrix while maintaining the mechanical integrity and electrospinnability of the solution. For example, a 1:4 weight ratio provides a balance between maximising the number of active sites from ZIF-67 and maintaining nanofiber uniformity during electrospinning. The compositions outside the range from 1:2 to 1:6 either lead to poor nanofiber formation (when ZIF-67 is too high) or reduced adsorption efficiency (when the content of the PVA dominates). Thus, the ratio ranges from 1:2 to 1:6, enables high-performance nanofibers with retained flexibility and active site accessibility.
[0030] In an implementation, the nanofiber composite has a fibrous structure with diameters in the range of 100-500 nanometers. The diameter range of the nanofiber composite ensures a high surface area-to-volume ratio. The high surface area-to-volume ratio improves the kinetics of lead adsorption by enhancing diffusion and surface contact with the contaminated water. Moreover, the interconnected network of nanofibers facilitates rapid percolation of water through the nanofiber composite, ensuring uniform exposure of the nanofibers to lead ions and maximising adsorption throughout the nanofiber composite.
[0031] In an implementation, the zeolitic imidazolate framework-67 nanoparticles have a rhombic dodecahedral shape. The rhombic dodecahedral shape is characteristic of ZIF-67 and provides a stable three-dimensional framework with uniform micropores. The rhombic dodecahedral structure ensures consistent pore distribution and maximised surface exposure, which contributes to the high uptake of lead ions. Moreover, the geometric uniformity aids in reproducible nanofiber formation during electrospinning, supporting uniform composite morphology.
[0032] In an implementation, the adsorption of lead ions occurs through electrostatic interaction, surface precipitation, chelation, or ion exchange between lead ions and cobalt ions. The electrostatic attraction is initiated when deprotonated hydroxyl and nitrogen sites on the nanofiber composite interact with positively charged lead ions in the water. The chelation occurs between lead ions and oxygen or nitrogen donor atoms within the PVA and ZIF-67 structure, forming stable complexes. The ion exchange involves the substitution of cobalt ions (Co²⁺) in ZIF-67 with lead ions, while surface precipitation may result from localised supersaturation near the active sites.
[0033] In an implementation, the binding energy between the nanofiber composite and lead ions is between -3.0 and -3.5 kilocalories per mole. The binding energy indicates a stable yet reversible adsorption interaction, useful for potential regeneration and reuse of the nanofiber composite. The binding energy range reflects a strong affinity between lead ions and the active binding sites, without leading to irreversible chemisorption that would hinder the recovery of the nanofiber composite. Thus, the binding energy range between -3.0 and -3.5 kilocalories per mole ensures both high selectivity and reusability, supporting sustainable wastewater treatment applications.
[0034] FIG. 2 is a graphical representation illustrating Fourier transform infrared (FTIR) spectroscopy, in accordance with an embodiment of the present disclosure. FIG 2 is described in conjunction with elements from FIG 1. With reference to FIG. 2, there is shown a graphical representation 200 depicting the absorption of infrared light by permanent epoxy and uncured epoxy at different wavelengths, measured in wavenumbers. The transmittance is measured in arbitrary units (A.U.) represented on the ordinate axis. The wavenumber is measured in centimetres inverse (cm⁻¹) on the abscissa axis. Transmittance quantifies the amount of light that passes through a sample or material, expressed as a percentage of the original light intensity. The wavenumber is defined as the number of wavelengths per unit distance. The graphical representation 200 includes a curve 202 depicting the behaviour of ZIF-67, a curve 204 depicting the behaviour of PVA, a curve 206 depicting the behaviour of nanofiber composite before lead adsorption, and a curve 208 depicting the behaviour of nanofiber composite after lead adsorption. Each peak or band in the curve 202 to the curve 208 corresponds to the vibration of specific chemical bonds within the curves shown in the graphical representation 200.
[0035] The curve 202 exhibits strong absorption bands in a region 210 approximately ranging between 1580–500 cm⁻¹. The region 210 is associated to the stretching and bending vibrations of imidazolate linkers coordinated with cobalt ions. The curve 202 further includes a plurality of peaks 202A in the region 210 confirming the presence of characteristic chemical bonds within ZIF-67, including cobalt–nitrogen (Co–N) coordination and ring-based skeletal vibrations associated with the organic ligand, indicating the structural stability of the ZIF-67 material prior to integration into the PVA or exposure to lead ions.
[0036] The curve 204 exhibits a first dip 204A and a second dip 204B in a region approximately ranging between 2500-3500 cm⁻¹ due to O–H stretching vibrations and C–H stretching vibrations respectively. Further, the curve 204 includes additional dips in a region 212 approximately ranging between 1400–800 cm⁻¹ associated with C–O stretching and C–H bending vibrations. The additional dips in the region 212 confirm the presence of hydroxyl and alkyl groups in the chemical composition of PVA.
[0037] The curve 206 exhibits characteristics of the curve 202 and the curve 204, indicating the successful incorporation of ZIF-67 into the PVA. Additionally, the curve 206 exhibits peaks similar to the curve 202 though slightly shifted and with altered intensities due to interactions between the ZIF-67 framework and PVA chains in a region 214 approximately ranging between 1580-500 cm⁻¹. Similarly, the O-H stretching vibrations from PVA remain visible indicated by a first dip 206A and a firts peak 206B.
[0038] The curve 208 in comparison to the curve 206, exhibits reduction in intensity of a first dip 208A approximately ranging between 3000-3500 cm⁻¹ as compared to the first dip 206A indicating interaction between lead ions and the hydroxyl groups of PVA. Furthermore, a marked decrease in transmittance in a region 216 approximately ranging between 1500-500 cm⁻¹ indicating formation of Pb-N coordination bonds as lead ions interact with the nitrogen sites of the imidazolate linkers in ZIF-67. Additionally, shifts are observed in the Co-N stretching vibrations approximately ranging between 1200-1000 cm⁻¹, suggesting structural rearrangements in the ZIF-67 framework upon lead ion capture. The broadening of a second peak 208B in the curve 208 further indicating increased disorder in the ZIF-67/PVA nanofiber composite structure following lead adsorption.
[0039] FIG. 3 is a graphical representation illustrating an X-ray diffraction (XRD) pattern of the nanofiber composite before and after lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements of FIGs. 1 and 2. With reference to FIG. 3, there is shown a graphical representation 300 including a first XRD pattern 302 of the nanofiber composite before lead adsorption and a second XRD pattern 304 of the ZIF-67/PVA nanofiber composite after lead adsorption.
[0040] XRD is used to identify the crystallographic structure, composition, and physical properties of materials. Peaks in the XRD pattern correspond to atomic planes in a crystal lattice, and their intensities relate to the number of such atomic planes and the orientation of the crystals. The diffraction angle denoted by 2θ is measured in degrees in an abscissa axis. The intensity is expressed in arbitrary units (A.U.) in an ordinate axis. Peaks at specific 2θ degrees values indicate the presence of specific crystallographic planes. Higher peaks indicate more atoms arranged in the corresponding crystallographic plane. The graphical representation 300 illustrating the XRD pattern includes peaks at 2θ values corresponding to specific crystallographic planes of the zinc oxide films.
[0041] The first XRD pattern 302 exhibits a dominant peak 302A approximately ranging between 15-20 degrees. The dominant peak 302A indicates the semi-crystalline nature of the polyvinyl alcohol (PVA) matrix. Furthermore, a minor peak 302B corresponds to the embedded ZIF-67 particles within the nanofiber composite structure, confirming the successful integration of the ZIF-67 framework into the PVA network. The sharpness and intensity of the dominant peak 302A indicate the structural stability and preserved crystallinity of the nanofiber composite prior to adsorption.
[0042] The second XRD pattern 304 exhibits a reduction in the intensity of a dominant peak 304A approximately ranging between 15-20 degrees as compared to the dominant peak 302A. The decrease in intensity of the dominant peak 304A suggests partial disruption or occupation of crystalline sites due to the interaction of lead ions with the nanofiber composite.
[0043] FIG. 4A is a diagram 400A illustrating a scanning electron microscope (SEM) image of nanofiber composite, in accordance with an embodiment of the present disclosure. FIG. 4A is described in conjunction with elements from FIGs. 1 to 3. With reference to FIG. 4A, the diagram 400A provides insight into the morphological characteristics and surface topology of the nanofiber composite. The SEM image enables visualisation at the micro- and nanoscale to confirm the crystalline architecture of the material.
[0044] The scanning electron microscopy (SEM) is a high-resolution imaging technique used to examine the surface morphology and microstructure of solid materials.
[0045] The SEM operates by directing a focused beam of electrons onto the sample surface and detecting the secondary or backscattered electrons emitted. The interaction between the electrons and the sample generates high-magnification images that reveal detailed surface features, including shape, texture, porosity, and crystal geometry. SEM is commonly used in material characterisation to verify particle size, distribution, and synthesis uniformity.
[0046] The diagram 400A exhibits the three-dimensional nanofibrous structure of the nanofiber composite at a microscopic scale. The diagram 400A displays an intricate network of interwoven nanofibers where each nanofiber (for example a first nanofiber 402A) is characterised by their elongated, cylindrical morphology with varying diameters approximately ranging between 100 and 300 nanometres.
[0047] The network of interwoven nanofibers exhibits a high degree of interconnectivity, forming a porous mesh-like architecture with substantial void spaces between adjacent nanofibers. The nanofibers demonstrate a predominantly smooth surface texture with occasional surface irregularities that may be attributed to the integration of ZIF-67 nanoparticles within the PVA polymer matrix. The diagram 400A includes a plurality of junction points 404A where multiple nanofibers intersect, contributing to the structural stability and mechanical integrity of the nanofiber composite.
[0048] The random orientation of the nanofibers creates a three-dimensional network with a high surface-area-to-volume ratio. The high surface-area-to-volume ratio is advantageous for adsorption applications. The uniform distribution of the nanofibers throughout the imaged area indicates the homogeneity of the electrospinning process employed for fabricating the nanofiber composite.
[0049] FIG. 4B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of the network of interwoven nanoparticles, in accordance with an embodiment of present disclosure. FIG. 4B is described in conjunction with FIGs. 1 to 4A. With reference to FIG. 4B, there is shown a graphical representation 400B depicting an energy dispersive spectroscopy (EDS) analysis of the network of interwoven nanofibers. Specifically, the graphical representation 400B depicts the absorption of high energy electron beam by the network of interwoven nanofibers (for example the first nanofiber 402A) and the intensity (also called x-ray counts) corresponding to an element present in the first nanofiber 402A. The high energy electron beam is measured in kilo electron volt (keV) in an abscissa axis. The intensity is expressed in arbitrary units in an ordinate axis.
[0050] The graphical representation 400B includes a first peak 402B, a second peak 404B, a third peak 406B, and a fourth peak 408B. Each peak corresponds to the characteristic X-ray energy emitted by a particular element present in the first nanofiber 402A, and the height of each peak reflects the relative abundance of that element in the first nanofiber 402A. For example, the first peak 402B depicts the presence of carbon (C) element in the first nanofiber 402A, and the height of the first peak 402B reflects the high abundance of the carbon in the first nanofiber 402A approximately 69.20% by weight. Similarly, the second peak 404B indicates the presence of nitrogen (N). The third peak 406B indicates the presence of oxygen (O). The fourth peak 408B depict the presence of cobalt (Co). The presence and relative intensities of the Carbon, Nitrogen, Oxygen, and Cobalt peaks confirm the successful synthesis of the first nanofiber 402A.
[0051] FIG. 5A is a diagram 500A illustrating a scanning electron microscope (SEM) image of the nanofiber composite after lead ion adsorption, in accordance with an embodiment of the present disclosure. FIG. 5A is described in conjunction with elements from FIGs. 1 to 4B. With reference to FIG. 5A, the diagram 500A provides insight into the morphological characteristics and surface topology of the nanofiber composite following its interaction with lead ions in an aqueous solution.
[0052] The diagram 500A indicates morphological changes in the structure of the nanofiber composite compared to its pre-adsorption state depicted in the FIG. 4A. The diagram 500A shows a substantial presence of spherical and quasi-spherical particles (for example, a first particle 502A and a second particle 504A) distributed across the surface of the nanofibers. Such spherical and quasi-spherical particles, appear as bright, rounded structures with diameters approximately ranging between 200 and 500 nanometers representing lead compounds that have been adsorbed onto the active sites of the nanofiber composite.
[0053] The underlying nanofibrous network remains partially visible beneath the adsorbed particles, indicating that while significant adsorption has occurred, the fundamental structure of the nanofiber composite has been preserved. The distribution pattern of the adsorbed particles suggests a heterogeneous adsorption mechanism, with certain regions of the nanofiber composite exhibiting higher concentrations of lead compounds than others. The heterogeneity may be attributed to variations in the local density of active sites or differing accessibility of these sites due to the three-dimensional architecture of the nanofiber network.
[0054] FIG. 5B is a graphical representation illustrating an energy dispersive spectroscopy (EDS) analysis of the nanofiber composite after lead ion adsorption, in accordance with an embodiment of present disclosure. FIG. 5B is described in conjunction with FIGs. 1 to 5A. With reference to FIG. 5B, there is shown a graphical representation 500B depicting an energy dispersive spectroscopy (EDS) analysis of the nanofiber composite following lead ion adsorption. Specifically, the graphical representation 500B depicts the absorption of high energy electron beam by the nanofiber composite and the intensity (also called x-ray counts) corresponding to elements present in the composite. The high energy electron beam is measured in kilo electron volt (keV) in an abscissa axis (X-axis). The intensity is expressed in arbitrary units in an ordinate axis (Y-axis).
[0055] The graphical representation 500B includes a plurality of peaks such as a first peak 502B, a second peak 504B, a third peak 506B, a fourth peak 508B, and a fifth peak 510B. Each peak of the plurality of peaks corresponds to the characteristic X-ray energy emitted by a particular element present in the nanofiber composite, and the height of each peak reflects the relative abundance of that element in the composite. For example, the first peak 502B depicts the presence of carbon (C) element in the nanofiber composite, and the height of the first peak 502B reflects the high abundance of carbon in the composite at approximately 53.03% by weight and 60.76% by atomic percentage, which is notably lower than the 69.20% by weight observed in the pre-adsorption state (as explained in the FIG. 4B).
[0056] Similarly, the second peak 504B indicates the presence of nitrogen (N) at approximately 9.86% by weight and 9.69% by atomic percentage, which is higher than the 5.07% by weight recorded before adsorption. The third peak 506B indicates the presence of oxygen (O) at approximately 33.59% by weight and 28.89% by atomic percentage, significantly higher than the 24.71% by weight in the pre-adsorption state. The fourth peak 508B depicts the presence of cobalt (Co) at approximately 2.56% by weight and 0.60% by atomic percentage, which is higher than the 1.02% by weight observed before adsorption.
[0057] Most significantly, the fifth peak 510B confirms the presence of lead (Pb) at approximately 0.96% by weight and 0.06% by atomic percentage. The detection of lead in the EDS analysis provides definitive evidence of successful lead ion adsorption by the nanofiber composite. The relative changes in the elemental composition, particularly the increased percentages of nitrogen, oxygen, and cobalt, alongside the appearance of lead, suggest that the adsorption process involves complex interactions between the lead ions and multiple functional groups within the composite structure.
[0058] FIG.6 is a flowchart illustrating a method for removing lead from wastewater, in accordance with an embodiment of the present disclosure. With reference to FIG. 6, a method 600 includes steps 602 to 606.
[0059] At step 602, the method 600 includes contacting wastewater containing lead ions with a nanofiber composite comprising zeolitic imidazolate framework-67 nanoparticles encapsulated in polyvinyl alcohol fibres. The nanofiber composite is immersed or suspended in the contaminated solution under controlled conditions. Specifically, the contacting can be performed using batch adsorption systems where a predetermined amount of the nanofiber composite is added to a fixed volume of wastewater containing lead concentrations ranging from 10-50 mg/L. During contact, the wastewater-nanofiber mixture is maintained at a controlled pH and agitated at 150-200 rpm using an orbital shaker to ensure uniform distribution of the nanofibers throughout the wastewater and maximise the exposure of active sites to lead ions. The contact duration is maintained for 2 hours, which provides sufficient time for the adsorption equilibrium to be established.
[0060] Upon contact with the wastewater, multiple adsorption mechanisms are simultaneously activated. The nitrogen atoms in the imidazole ligands of the ZIF-67 structure function as lewis base sites, forming coordination bonds with lead ions (Pb²⁺) which act as lewis acids. Concurrently, the cobalt metal centres in the ZIF-67 framework can undergo ion exchange with lead ions, while the hydroxyl groups of the PVA polymer chains form hydrogen bonds with water molecules surrounding the hydrated lead ions, further facilitating the capture of the lead ions. The high surface area of the nanofiber composite provides numerous accessible adsorption sites, while the three-dimensional porous structure allows for efficient mass transfer of lead ions from the bulk solution to such active adsorption sites.
[0061] In an implementation, the nanofiber composite dosage is 15-25 milligrams per liter. The nanofiber composite dosage range was optimised based on batch adsorption trials, where increasing the composite concentration beyond 25 mg/L resulted in minimal additional lead removal, indicating saturation of active binding sites. Conversely, nanofiber composite dosages below 15 mg/L were insufficient to provide a surface area capable of removing the target lead concentration (10 mg/L) within the desired time frame. The dosage range of 15-25 milligrams per litre balances adsorption efficiency, material economy, and treatment scalability, thereby ensuring practical utility for both laboratory and field-scale applications.
[0062] At step 604, the method 600 includes allowing the nanofiber composite to adsorb the lead ions by maintaining a pH of 5-7 that promotes deprotonation of hydroxyl groups and nitrogen sites, creating adsorption sites that attract lead ions and facilitate chelation and ion exchange mechanisms. The pH range is precisely controlled through the addition of dilute solutions of either sodium hydroxide (NaOH) or nitric acid (HNO₃) in small increments (0.1 M concentrations), with continuous monitoring using a calibrated pH meter. The pH control can be achieved using automated pH controllers with feedback systems for large-scale applications or manual adjustment for laboratory-scale treatments. The pH range of 5-7 has been experimentally determined to be optimal (as explained in FIG. 10A).
[0063] At pH values above 5.18 (the point of zero charge), the hydroxyl (-OH) groups present in the polyvinyl alcohol (PVA) component of the nanofiber composite undergo deprotonation, transforming from -OH to -O⁻. The deprotonation creates negatively charged sites throughout the polymeric network that electrostatically attract the positively charged lead ions (Pb²⁺) in the wastewater. Simultaneously, the nitrogen atoms in the imidazole ligands of the ZIF-67 framework, which possess lone pairs of electrons, become more available for coordination interactions at the pH range of 5-7 due to reduced competition with hydrogen ions.
[0064] The deprotonated hydroxyl groups and nitrogen sites serve as electron-rich centres that can form coordination bonds with lead ions through the vacant orbitals. The chelation process involves the formation of multiple coordinate bonds between a single lead ion and several ligand sites, creating stable complexes. Additionally, the cobalt ions in the ZIF-67 framework can undergo ion exchange with lead ions, particularly at the pH range of 5-7, where lead ions remain soluble.
[0065] In an implementation, the contact time between the nanofiber composite and the wastewater is 1-3 hours. Due to the high surface accessibility and porous nature of the nanofiber composite, significant adsorption of the wastewater occurs within the first hour. However, allowing up to 3 hours ensures complete interaction between lead ions and the active sites of the nanofiber composite.
[0066] In an implementation, the method 600 further includes regenerating the nanofiber composite by treating with 0.01 molar sodium hydroxide solution to desorb the adsorbed lead ions. The mild alkaline treatment of the nanofiber composite promotes desorption of adsorbed lead ions from the nanofiber composite by disrupting electrostatic and chelation-based interactions and restoring the original binding sites. The nanofiber composite is soaked in the NaOH solution for a fixed duration (e.g., 30 minutes), followed by washing with deionised water to neutralise the surface and remove residual NaOH. The treatment with NaOH enables the nanofiber composite to be reused in subsequent adsorption cycles with minimal structural or functional degradation.
[0067] At step 606, the method 600 includes separating the nanofiber composite from the wastewater. The separation of the nanofiber composite from the wastewater is accomplished through a multi-stage filtration approach that efficiently recovers the lead-laden nanofiber composite while minimising material loss. The initial separation can be performed using a vacuum filtration system employing a buchner funnel fitted with a membrane filter (e.g., polytetrafluoroethylene or cellulose acetate) with pore sizes of 0.45-1.0 μm. The nanofiber composite is substantially larger than the pore size of the membrane filter and is, therefore, effectively retained on the filter surface while allowing the treated water to pass through.
[0068] In an implementation, for larger-scale applications, centrifugation can be employed at speeds of 3000-5000 rpm for 10-15 minutes, causing the nanofiber composite to form a pellet at the bottom of the centrifuge tube due to its higher density compared to water, particularly after lead adsorption. Alternatively, a continuous-flow separation system utilising cross-flow filtration or hydrocyclone technology can be implemented for industrial-scale wastewater treatment, where the nanofiber composite is continuously recovered while the treated effluent is directed to further processing or discharge.
[0069] In an implementation, maintaining the pH at 5-7 and using a nanofiber composite dosage of 15-25 milligrams per litre with a contact time of 1-3 hours structurally facilitates a lead removal efficiency of more than 83% at initial lead concentrations of 10 milligrams per litre. The nanofiber composite dosage of 15-25 milligrams per litre provides optimal surface area and active site availability without excessive material usage. The contact time of 1-3 hours allows sufficient interaction between lead ions and active sites on the nanofiber composite for equilibrium adsorption to occur. For example, the nanofiber composite dosage of 20 milligrams per litre with a contact time of 1-3 hours provides suitable conditions where deprotonated hydroxyl groups and nitrogen sites in the nanofiber composite effectively bind with lead ions through coordination bonding and electrostatic attraction.
[0070] In an implementation, the regenerated nanofiber composite can be reused for at least four adsorption-desorption cycles with an adsorption efficiency of at least 60%. The regeneration of the nanofiber composite preserves the structural integrity and functional groups of the nanofiber composite, allowing it to be reused for at least four consecutive adsorption-desorption cycles while maintaining an adsorption efficiency of at least 60% (as explained in FIG. 11). The reusability of the nanofiber composite enhances the cost-effectiveness and sustainability of the treatment process by reducing the need for fresh adsorbent material.
[0071] FIG. 7A is a graphical representation illustrating the raman spectroscopy analysis of the nanofiber composite before lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 7A is described in conjunction with elements from FIGs. 1 to 6. With reference to FIG. 7A, the graphical representation 700A depicts raman spectra of the nanofiber composite before lead adsorption. Intensity measured in arbitrary units (A.U.) on the ordinate axis against raman shift measured in wavenumbers (cm⁻¹) on the abscissa axis. The raman spectrum provides detailed information about the vibrational and rotational modes of the molecular bonds present in the nanofiber composite, offering crucial insights into its chemical structure and composition.
[0072] The graphical representation 700A exhibits a first peak 702A at approximately 1000 cm⁻¹. The first peak 702A is attributed to the C-N stretching vibrations in the imidazole rings of the ZIF-67 framework. The first peak 702A serves as a distinctive feature of the ZIF-67, confirming its presence within the nanofiber composite. Further, a second peak 704A is observed at approximately 1500 cm⁻¹, corresponding to the C=N stretching modes of the imidazole ligands, further corroborating the incorporation of the ZIF-67 framework within the nanofiber composite.
[0073] Additionally, the graphical representation 700A includes a third peak 706A at approximately ranging from 2900-3000 cm⁻¹. The third peak 706A is assigned to the C-H stretching vibrations primarily associated with the PVA polymer fibers and the methyl groups of the 2-methylimidazole ligands in the ZIF-67 structure. The presence of multiple lower-intensity peaks in the range of 400-700 cm⁻¹ can be attributed to metal-nitrogen (Co-N) coordination bonds. The overall spectral pattern, with its well-defined peaks and relatively low background noise, indicates the high crystallinity and structural integrity of the nanofiber composite before its application in lead adsorption processes.
[0074] FIG. 7B is a graphical representation 700B illustrating the raman spectroscopy analysis of the nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 7B is described in conjunction with elements from FIGs. 1 to 7A. With reference to FIG. 7B, the graphical representation 700B plots intensity measured in arbitrary units (A.U.) on the ordinate axis against raman shift measured in wavenumbers (cm⁻¹) on the abscissa axis, providing information about the structural and compositional changes in the nanofiber composite after the adsorption of lead ions.
[0075] In stark contrast to the graphical representation 700A, the graphical representation 700B indicates significant alterations in peak intensities and overall spectral pattern, indicating substantial chemical and structural modifications resulting from lead adsorption. The graphical representation 700B shows a dominant peak 702B at approximately ranging between 1050-1100 cm⁻¹. The dominant peak 702B can be attributed to the formation of lead-nitrogen coordination bonds and lead-oxygen interactions with the functional groups of the nanofiber composite.
[0076] The disappearance of the second peak 704A associated with the imidazole C=N stretching and the third peak 706A associated with the C-H stretching vibrations indicates that such functional groups have become heavily involved in lead coordination or have experienced electronic environment alterations due to lead adsorption. The overall simplification of the spectrum with increased background noise suggests a reduction in the crystallinity of the composite structure, which is consistent with the incorporation of lead ions disrupting the original molecular arrangement of the ZIF-67.
[0077] FIG. 8A is a graphical representation illustrating an ultraviolet-visible absorption spectrum of zeolitic imidazolate framework-67 (ZIF-67), in accordance with an embodiment of the present disclosure. FIG. 8A is described in conjunction with elements from FIGs. 1 to 7B. With reference to FIG. 8A, there is shown the graphical representation 800A depicting the absorption intensity measured in arbitrary units (A.U.) on the ordinate axis against wavenumber measured in centimetres inverse (cm⁻¹) on the abscissa axis. The graphical representation 800A includes a curve 802A depicting a relationship between adsorption and wavenumber for ZIF-67.
[0078] The ultraviolet-visible spectroscopy is an analytical technique used to measure the absorption of ultraviolet and visible light by a material as a function of wavelength or wavenumber. When light passes through or reflects off a sample, certain wavelengths are absorbed due to electronic transitions between molecular or atomic energy levels. The resulting absorption spectrum provides information about the electronic structure, conjugation, and chemical environment of the material.
[0079] The curve 802A includes an absorption peak 804A approximately centred around 220 nm, which corresponds to pi to pi star (π→π*) electronic transitions occurring within the aromatic imidazole rings of the 2-methylimidazole linker. The π→π* electronic transition occurs when electrons of a molecule of the nanofiber composite jumps from a bonding pi orbital (π) to a higher-energy antibonding pi star (π*) orbital. The π→π* electronic transition reflects the presence of conjugated π-electron systems within the ZIF-67.
[0080] Following the absorption peak 804A, a broad absorption tail extends approximately ranging between 250–500 nm in a region 806A, associated with “n” to pi star (n→π*) transitions and metal-ligand charge transfer (MLCT) interactions between the cobalt ions and the imidazolate nitrogen atoms. The n→π* transition refers to an electronic transition where a non-bonding (n) electron on a heteroatom, like oxygen or nitrogen, is promoted to a higher energy π* (anti-bonding) orbital. The MLCT interactions are characteristic of the Co–N coordination environment found in the ZIF-67 structure. Moreover, a small peak 808A approximately ranging between 580-620 nm is attributed to d–d transitions of cobalt ions in the tetrahedral coordination geometry, further supporting the presence of cobalt within the ZIF-67 structure.
[0081] FIG. 8B is a graphical representationillustrating an ultraviolet-visible (UV-Vis) absorption spectrum of polyvinyl alcohol (PVA) in accordance with an embodiment of the present disclosure. FIG. 8B is described in conjunction with elements from FIGs. 1 to 8A. With reference to FIG. 8B, there is shown the graphical representation 800B depicting the absorption intensity measured in arbitrary units (A.U.) on the ordinate axis plotted against wavenumber measured in centimetres inverse (cm⁻¹) on the abscissa axis. The graphical representation 800B includes a curve 802B depicting a relationship between adsorption and wavenumber for PVA.
[0082] The curve 802B includes a sharp peak 804B approximately around 220 nm. The sharp peak 804B is primarily attributed to pi to pi star (π→π*) transitions originating from the residual acetate groups or unsaturated impurities within the PVA. The residual acetate groups may remain from the incomplete hydrolysis of polyvinyl acetate during the preparation of PVA and absorb in the ultraviolet range.
[0083] Following the sharp peak 804B, the curve 802B exhibits a steep decline in absorption intensity beyond 250 nm and exhibits a relatively flat profile throughout a region 806B approximately ranging between 300–800 nm. The absence of absorption bands in the region 806B is consistent with the non-conjugated, saturated hydrocarbon nature of PVA, which lacks extensive π-electron systems or transition metal centres that would otherwise contribute to visible-range absorption. The flat profile throughout the region 806B confirms the optical transparency and chemical purity of the PVA.
[0084] FIG. 8C is a graphical representation 800C illustrating an ultraviolet-visible (UV-Vis) absorption spectrum of a nanofiber composite before lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 8C is described in conjunction with elements from FIGs. 1 to 8B. The graphical representation 800C shows the absorption intensity measured in arbitrary units (A.U.) on the ordinate axis plotted against wavenumber measured in centimetre inverse (cm⁻¹) on the abscissa axis. The graphical representation 800C includes a curve 802C.
[0085] The curve 802C includes a peak 804C at approximately around 220 nm, corresponding to pi to pi star (π→π*) electronic transitions associated with the aromatic imidazole rings present in the ZIF-67. Further, the curve 802C shows a broader absorption profile in a region approximately ranging between 250-560 nm, with a subtle peak 808C appearing approximately ranging between 580–620 nm, attributed to d–d transitions of cobalt ions coordinated within the ZIF-67. The peak 804C and the subtle peak 808C confirm the incorporation of ZIF-67 into the PVA matrix without substantial alteration of the optical properties, thereby validating the integrity of the nanofiber composite prior to lead ion exposure.
[0086] FIG. 8D is a graphical representation illustrating an ultraviolet-visible (UV-Vis) absorption spectrum of the nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 8D is described in conjunction with elements from FIGs. 1 to 8C. The graphical representation 800D depicts the absorption intensity measured in arbitrary units (A.U.) on the ordinate axis plotted against wavenumber measured in centimetres inverse (cm⁻¹) on the abscissa axis. The graphical representation 800D includes a curve 802D depicting a relationship between adsorption and wavenumber for the nanofiber composite after lead ion adsorption.
[0087] The curve 802D shows a reduced absorption intensity of a peak 804D as compared to the curve 802C approximately around 220 nm. The reduction in intensity of the peak 804D is due to the interaction of lead ions with the active sites in the nanofiber composite, including coordination with nitrogen atoms in the ZIF-67 framework and hydroxyl groups in the PVA matrix. The spectral shift and reduction in absorption intensity in a lead ion transition region 806D approximately ranging between 580-620 nm, further indicate potential ion exchange between cobalt and lead within the nanofiber composite. The overall decrease in absorbance confirms the engagement of the functional groups of the nanofiber composite with lead ions adsorption.
[0088] FIG. 9A is a graphical representation illustrating an X-ray photoelectron spectroscopy (XPS) survey spectrum of zeolitic imidazolate framework-67 (ZIF-67), in accordance with an embodiment of the present disclosure. FIG. 9A is described in conjunction with elements from FIGs. 1 to 8D. With reference to FIG. 9A, the graphical representation 900A plots intensity measured in counts per second on the ordinate axis against binding energy measured in electron volts (eV) on the abscissa axis. The graphical representation includes a curve 902A representing the XPS spectrum of ZIF-67.
[0089] XPS is used to determine the elemental composition and chemical states of atoms present on the surface of a material. The XPS works by bombarding the material with X-rays, which eject core electrons from atoms, and then measuring the kinetic energy of the ejected electrons. By analysing the kinetic energy, the elemental composition and chemical state of the surface of material is determined.
[0090] The curve 902A shows a first peak 904A approximately ranging between 700-800 eV. The first peak 904A is characteristic of the Co 2p core level, confirming the presence of cobalt as the central metal ion within the ZIF-67. The intensity and sharpness of the first peak 904A indicate a high surface concentration of cobalt in its oxidation state.
[0091] Further, a second peak 906A is present approximately ranging between 500-550 eV, corresponding to the N 1s orbital. The second peak 906A is attributed to nitrogen atoms from the imidazole-based organic linkers that coordinate with cobalt ions, forming the Co–N bonding network that defines the structural framework of ZIF-67. The presence of the second peak 906A affirms the integrity of the organic ligand in the ZIF-67.
[0092] Furthermore, a third peak 908A is present approximately ranging between 250-300 eV representing the C 1s orbital, arising from the carbon atoms within the imidazole ring structures. The third peak 908A may consist of multiple overlapping components reflecting different carbon environments, such as C=C, C–N, or C–H bonds, all of which are consistent with the structure of the organic ligand used in the synthesis of ZIF-67.
[0093] FIG. 9B is a graphical representation 900B illustrating an X-ray photoelectron spectroscopy (XPS) survey spectrum of nanofiber composite material, in accordance with an embodiment of the present disclosure. FIG. 9B is described in conjunction with elements from FIGs. 1 to 9A. With reference to FIG. 9B, the graphical representation 900B plots intensity measured in counts per second on the ordinate axis against binding energy measured in electron volts (eV) on the abscissa axis. The graphical representation includes a curve 902B representing the XPS spectrum of the nanofiber composite.
[0094] The curve 902B shows a first peak 904B approximately ranging between 700–800 eV, which corresponds to the Cobalt 2p orbital. The first peak 904B confirms the presence of cobalt within the nanofiber composite, indicating that the ZIF-67 remains chemically intact following its encapsulation in the PVA matrix.
[0095] Further, a second peak 906B is observed approximately ranging between 500–550 eV, which is characteristic of the Nitrogen 1s orbital. The second peak 906B arises from the nitrogen atoms in the imidazole-based organic linkers of the ZIF-67 structure. The preservation of the second peak 906B within the nanofiber composite spectrum indicates the continued structural role of the Co–N coordination bonds, even after the integration of the ZIF-67 into the PVA matrix.
[0096] Furthermore, a third peak 908B is present approximately ranging between 250–300 eV, corresponding to the C 1s orbital. The third peak 908B is attributed to carbon atoms found in the organic backbone of the imidazole ligand and possibly the PVA chains. This peak may include overlapping signals from C–N, C–C, and C–O bonding environments, all of which are consistent with the composition of both the ZIF-67 and the PVA.
[0097] FIG. 9C is a graphical representation 900C illustrating an X-ray photoelectron spectroscopy (XPS) survey spectrum of the nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 9C is described in conjunction with elements from FIGs. 1 to 9B. With reference to FIG. 9C, the graphical representation 900C plots intensity measured in counts per second on the ordinate axis against binding energy measured in electron volts (eV) on the abscissa axis. The graphical representation 900C includes a curve 902C representing the XPS spectrum of the nanofiber composite following adsorption of lead ions from water.
[0098] The curve 902C shows a first peak 904C approximately ranging between 500–550 eV, which is characteristic of the N 1s orbital. The persistence of the first peak 904C indicates the continued presence of nitrogen atoms from the imidazole rings of ZIF-67 even after lead ion interaction, confirming the structural retention of the nanofiber composite structure post- lead adsorption. However, minor changes in intensity of the first peak 904C may suggest partial involvement of nitrogen atoms in lead ion coordination.
[0099] Further, a second peak 906C is observed approximately ranging between 250–300 eV, representing the C 1s orbital. The second peak 906C corresponds to the carbon atoms within the imidazole ligand and possibly from the PVA matrix. The visibility of the second peak 906C in the after lead adsorption indicates the structural stability of the nanofiber composite and indicates no significant decomposition of the organic components of the nanofiber composite during lead adsorption.
[0100] Furthermore, a third peak 908C is present approximately ranging between 100–150 eV, which is characteristic of Pb 4f orbitals. The third peak 908C indicates that lead ion is adsorbed onto the composite surface. The appearance of the Pb 4f orbitals confirms that lead ions are successfully captured and retained within the nanofiber composite structure through coordination with nitrogen sites of ZIF-67 and hydroxyl groups of the PVA matrix.
[0101] FIG. 9D is a graphical representation illustrating a high-resolution X-ray photoelectron spectroscopy (XPS) spectrum of a nanofiber composite after lead adsorption, in accordance with an embodiment of the present disclosure. FIG. 9D is described in conjunction with elements from FIGs. 1 to 9C. With reference to FIG. 9D, the graphical representation 900D plots intensity measured in counts per second on the ordinate axis against binding energy measured in electron volts (eV) on the abscissa axis. The graphical representation includes a curve 902D representing the localised XPS spectrum.
[0102] The curve 902D shows two distinct peaks (a first peak 904D and a second peak 906D) that confirm the presence of lead on the surface of the nanofiber composite after adsorption. The first peak 904D is present approximately ranging between 138-141 eV, which corresponds to the lead 4f5/2 orbital. The first peak 904D confirms that lead ions have been successfully adsorbed onto the nanofiber composite surface. A binding energy region 908D is associated with lead in its divalent oxidation state (Pb²⁺), indicating electrostatic or coordination-based interactions with active sites on the nanofiber composite.
[0103] The second peak 906D is observed approximately ranging between 143-146 eV and is attributed to the Pb 4f5/2 orbital. The second peak 906D, results from spin-orbit splitting of the 4f electrons and is a characteristic feature of lead ions. The consistent energy gap between the first peak 904D and the second peak 906D further substantiates that lead exists in its expected oxidation state (i.e. Pb²⁺) and is stably adsorbed within the nanofiber composite.
[0104] FIG. 10A is a graphical representation illustrating the effect of pH on removal efficiency of ions using the nanofiber composite, in accordance with an embodiment of the present disclosure. FIG. 10A is described in conjunction with elements from FIGs. 1 to 9D. With reference to FIG. 10A, a graphical representation 1000A plots removal efficiency measured in percentage (%) on the ordinate axis against pH values on the abscissa axis. The graphical representation 1000A includes a curve 1002A representing the relationship between the pH of the water containing lead ions and the corresponding ion removal efficiency achieved by the nanofiber composite under controlled experimental conditions.
[0105] The curve 1002A shows that the removal efficiency of the nanofiber composite is pH-dependent, exhibiting a non-linear relationship across the tested pH range of approximately 2 to 7. At the lower end of the pH spectrum, specifically at approximately pH 2, the removal efficiency is at its lowest value, approximately ranging between 50% and 55%. As the pH increases from approximately 2 to 3, the curve 1002A shows an upward trend, with removal efficiency increasing to approximately ranging between 58% and 62%.
[0106] Further, as the pH continues to increase from approximately 3 to 4, the curve 1002A maintains its ascending trajectory, with the removal efficiency reaching approximately ranging between 68% and 72%. The positive correlation between pH and removal efficiency continues as the pH increases from approximately 4 to 5, and the removal efficiency reaches approximately ranging between 76% and 79%.
[0107] The curve 1002A reaches the highest value of removal efficiency at approximately pH 6, where the removal efficiency attains a maximum value of approximately ranging between 83% and 86%. The value of removal efficiency indicates an optimal pH condition for the ion removal capability of the nanofiber composite. However, as the pH further increases to approximately 7, the curve 1002A exhibits a downward trend, with the removal efficiency decreasing to approximately ranging between 70% and 73%, thereby indicating that excessively alkaline conditions may adversely affect the ion removal performance of the nanofiber composite.
[0108] The experimental conditions for obtaining the data represented in the graphical representation 1000A include the nanofiber composite dosage of 20 mg/L, an initial ion concentration of 10 mg/L, and a contact time of 2 hours. The controlled parameters ensure the reliability and reproducibility of the relationship depicted by the curve 1002A between pH and removal efficiency.
[0109] FIG. 10B is a graphical representation 1000B illustrating the determination of point of zero charge (PZC) for the nanofiber composite, in accordance with an embodiment of the present disclosure. FIG. 10B is described in conjunction with elements from FIGs. 1 to 10A. With reference to FIG. 10B, the graphical representation 1000B plots change in pH (ΔpH) on the ordinate axis against initial pH on the abscissa axis. The graphical representation 1000B includes a curve 1002B representing the relationship between the initial pH values and the corresponding changes in pH after equilibration with the nanofiber composite.
[0110] The curve 1002B demonstrates a systematic variation in the surface charge characteristics of the nanofiber composite across different pH values. At the lower end of the pH spectrum, specifically at approximately pH 1, the change in pH exhibits its maximum positive value of approximately ranging between 4.5 and 5.0. The significant positive change in pH value indicates that the nanofiber composite strongly attracts hydroxide ions (OH-) and/or releases hydrogen ions (H+) at highly acidic conditions.
[0111] As the initial pH increases from approximately 2 to 4, the curve 1002B shows a notable downward trend, with the change in pH decreasing to approximately ranging between 1.5 and 2.0 units, while still remaining positive. The curve 1002B continues its descending trajectory as the initial pH increases from approximately 4 to approximately 4.5, where the change in pH further reduces to approximately ranging between 0.5 and 1.0 units.
[0112] Significantly, the curve 1002B intersects the abscissa axis at a point 1004B where the change in pH equals zero, corresponding to an initial pH value of approximately 5.18. The point 1004B represents the point of zero charge (PZC) of the nanofiber composite, a critical parameter indicating the pH at which the net surface charge of the material is zero. At pH values below the PZC, the nanofiber composite exhibits a net positive surface charge, whereas at pH values above the PZC, the nanofiber composite possesses a net negative surface charge.
[0113] As the initial pH further increases beyond the PZC, specifically from approximately 6 to approximately 11, the curve 1002B continues its descending trend, with the change in pH becoming increasingly negative, reaching approximately ranging between -4.0 and -4.5 units at an initial pH of approximately 11. The progressively negative change in pH indicates that the nanofiber composite increasingly attracts hydrogen ions (H+) and/or releases hydroxide ions (OH-) as the water containing led ions becomes more alkaline.
[0114] FIG. 10C is a graphical representation 1000C illustrating the effect nanofiber composite dosage on removal efficiency and adsorption capacity, in accordance with an embodiment of the present disclosure. FIG. 10C is described in conjunction with elements from FIGs. 1 to 10B. With reference to FIG. 10C, the graphical representation 1000C plots removal efficiency measured in percentage (%) on the primary ordinate axis and adsorption capacity measured in milligrams per gram (mg/g) on the secondary ordinate axis, against nanofiber dosage measured in milligrams per liter (mg/L) on the abscissa axis. The graphical representation 1000C includes a solid curve 1002C representing the relationship between nanofiber dosage and removal efficiency, and a dashed curve 1004C representing the relationship between nanofiber dosage and adsorption capacity.
[0115] The solid curve 1002C demonstrates that the removal efficiency of lead ions increases with increasing dosage of the nanofiber composite. At the lower end of the dosage spectrum, specifically at approximately 20 mg/L, the removal efficiency is at its lowest value, approximately ranging between 57% and 60%. As the nanofiber dosage increases from approximately 20 mg/L to approximately 40 mg/L, the solid curve 1002C shows a significant upward trend with removal efficiency increasing to approximately ranging between 69% and 72%.
[0116] Further, as the dosage of the nanofiber composite increases from approximately 40 mg/L to approximately 60 mg/L, the solid curve 1002C continues its ascending trajectory, with the removal efficiency reaching approximately ranging between 80% and 83%. The positive correlation between dosage of the nanofiber composite and removal efficiency persists throughout the range in the graphical representation 1000C, with the removal efficiency reaching approximately ranging between 84% and 87% at a dosage of approximately 80 mg/L, and attaining its maximum value of approximately ranging between 89% and 91% at the highest tested dosage of approximately 100 mg/L.
[0117] Concurrently, the dashed curve 1004C illustrates an inverse relationship between the nanofiber dosage and adsorption capacity. At the lowest tested dosage of approximately 20 mg/L, the adsorption capacity is at its maximum value of approximately ranging between 42 and 45 mg/g. As the nanofiber dosage increases to approximately 40 mg/L, the adsorption capacity decreases to approximately ranging between 22 and 25 mg/g. The decreasing trend in adsorption capacity continues, as the nanofiber dosage further increases, with the adsorption capacity reducing to approximately ranging between 17 and 20 mg/g at a dosage of approximately 60 mg/L, to approximately ranging between 13 and 16 mg/g at a dosage of approximately 80 mg/L, and to its lowest value of approximately ranging between 10 and 13 mg/g at the highest tested dosage of approximately 100 mg/L.
[0118] The experimental conditions for obtaining the data represented in the graphical representation 1000C include a pH value of 6, an initial lead ion concentration of 10 mg/L, and a contact time of 2 hours. Such experimental conditions ensure the reliability and reproducibility of the relationships depicted by the solid curve 1002C and the dashed curve 1004C between nanofiber dosage, removal efficiency, and adsorption capacity.
[0119] FIG. 10D is a graphical representation 1000D illustrating the effect of initial lead ion concentration on removal efficiency and adsorption capacity, in accordance with an embodiment of the present disclosure. FIG. 10D is described in conjunction with elements from FIGs. 1 to 10C. With reference to FIG. 10D, the graphical representation 1000D plots removal efficiency measured in percentage (%) on the primary ordinate axis and adsorption capacity measured in milligrams per gram (mg/g) on the secondary ordinate axis, against initial lead ion concentration measured in milligrams per liter (mg/L) on the abscissa axis. The graphical representation 1000D includes two curves: a solid curve 1002D representing the relationship between initial lead ion concentration and removal efficiency, and a dashed curve 1004D representing the relationship between initial lead ion concentration and adsorption capacity.
[0120] The solid curve 1002D demonstrates that the removal efficiency of lead ions is inversely related to the initial lead ion concentration beyond a certain threshold. At the lowest tested initial concentration of approximately 10 mg/L, the removal efficiency is at a relatively high value of approximately ranging between 82% and 85%. As the initial concentration increases to approximately 20 mg/L, the solid curve 1002D shows a significant downward trend with removal efficiency decreasing to approximately ranging between 58% and 61%.
[0121] As the initial lead ion concentration further increases from approximately 20 mg/L to approximately 30 mg/L, the solid curve 1002D continues its descending trajectory, albeit at a reduced rate, with the removal efficiency reaching approximately ranging between 55% and 58%. From approximately 30 mg/L to approximately 40 mg/L of initial lead ion concentration, the curve 1002D exhibits a plateau, with the removal efficiency remaining relatively constant at approximately ranging between 56% and 59%. However, as the initial concentration increases to approximately 50 mg/L, the curve 1002D shows a slight further decrease in removal efficiency to approximately ranging between 54% and 57%.
[0122] In contrast, the dashed curve 1004D illustrates a positive correlation between the initial lead ion concentration and adsorption capacity. At the lowest tested initial concentration of approximately 10 mg/L, the adsorption capacity is at its minimum value of approximately ranging between 40 and 45 mg/g. As the initial concentration increases to approximately 20 mg/L, the adsorption capacity increases substantially to approximately ranging between 58 and 63 mg/g. This increasing trend continues as the initial concentration further increases, with the adsorption capacity rising to approximately ranging between 80 and 85 mg/g at an initial concentration of approximately 30 mg/L, to approximately ranging between 110 and 115 mg/g at an initial concentration of approximately 40 mg/L, and to its maximum value of approximately ranging between 135 and 140 mg/g at the highest tested initial concentration of approximately 50 mg/L.
[0123] The experimental conditions for obtaining the data represented in the graphical representation 1000D include a pH value of 6, a ZIF-67/PVA nanofiber dosage of 20 mg/L, and a contact time of 2 hours. Such experimental conditions ensure the reliability and reproducibility of the relationships depicted by the solid curve 1002D and the dashed curve 1004D between initial lead ion concentration, removal efficiency, and adsorption capacity.
[0124] FIG. 11 is a graphical representation 1100 illustrating the regeneration efficiency of the nanofiber composite over multiple regeneration cycles using different regeneration agents, in accordance with an embodiment of the present disclosure. FIG. 11 is described in conjunction with elements from FIGs. 1 to 10D. With reference to FIG. 11, the graphical representation 1100 plots regeneration efficiency measured in percentage (%) on the ordinate axis against the number of regeneration cycles on the abscissa axis. The graphical representation 1100 includes wide-spaced diagonallly hatched bars representing 0.01 M NaOH, narrow spaced horizontally hatched bars representing 0.01 M HNO₃, and unfilled bars representing deionised (DI) water.
[0125] The wide-spaced diagonallly hatched bars corresponding to 0.01 M NaOH demonstrate the highest regeneration efficiency among the tested regeneration agents (NaOH, HNO₃, and DI water) across all regeneration cycles. During the first regeneration cycle, the regeneration efficiency with 0.01 M NaOH is approximately ranging between 83% and 87%. As the number of regeneration cycles increases, the regeneration efficiency with 0.01 M NaOH exhibits a gradual decreasing trend, reducing to approximately ranging between 78% and 82% in the second cycle, approximately ranging between 73% and 77% in the third cycle, approximately ranging between 70% and 74% in the fourth cycle, approximately ranging between 65% and 69% in the fifth cycle, and finally to approximately ranging between 60% and 64% in the sixth cycle.
[0126] The narrow spaced horizontally hatched bars corresponding to 0.01 M HNO₃ illustrate moderate regeneration efficiency that decreases more rapidly with increasing regeneration cycles compared to 0.01 M NaOH. In the first regeneration cycle, the regeneration efficiency with 0.01 M HNO₃ is approximately ranging between 57% and 61%. The regeneration efficiency decreases to approximately ranging between 43% and 47% in the second cycle, approximately ranging between 37% and 41% in the third cycle, approximately ranging between 27% and 31% in the fourth cycle, approximately ranging between 22% and 26% in the fifth cycle, and reaches its lowest value of approximately ranging between 10% and 14% in the sixth cycle.
[0127] The unfilled bars corresponding to DI water exhibit the lowest regeneration efficiency among the tested regeneration agents across all regeneration cycles. In the first regeneration cycle, the regeneration efficiency with DI water is approximately ranging between 9% and 13%. The regeneration efficiency shows a gradual decrease through subsequent cycles, reducing to approximately ranging between 8% and 12% in the second cycle, approximately ranging between 6% and 10% in the third cycle, approximately ranging between 3% and 7% in the fourth cycle, approximately ranging between 2% and 6% in the fifth cycle, and to approximately ranging between 1% and 3% in the sixth cycle.
[0128] The graphical representation 1100 indicates that 0.01 M NaOH is the most effective regeneration agent for the nanofiber composite, maintaining a regeneration efficiency of nanofiber composite approximately 60% even after six regeneration cycles. In contrast, 0.01 M HNO₃ shows moderate effectiveness with a significant decrease in regeneration efficiency over multiple cycles, while DI water exhibits minimal regeneration capability, rendering it least effective among the tested regeneration agents.
[0129] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure. , Claims:CLAIMS
We claim:
1. A nanofiber composite for lead adsorption from water, comprising:
zeolitic imidazolate framework-67 nanoparticles; and
polyvinyl alcohol fibres encapsulating the zeolitic imidazolate framework-67 nanoparticles,
wherein the nanofiber composite has an adsorption capacity for lead ions of at least 100 milligrams per gram.
2. The nanofiber composite as claimed in claim 1, wherein the weight ratio of zeolitic imidazolate framework-67 to polyvinyl alcohol is from 1:2 to 1:6.
3. The nanofiber composite as claimed in claim 1, wherein the nanofiber composite has a fibrous structure with diameters in the range of 100-500 nanometers.
4. The nanofiber composite as claimed in claim 1, wherein the zeolitic imidazolate framework-67 nanoparticles have a rhombic dodecahedral shape.
5. The nanofiber composite as claimed in claim 1, wherein the adsorption of lead ions occurs through electrostatic interaction, surface precipitation, chelation, or ion exchange between lead ions and cobalt ions.
6. The nanofiber composite as claimed in claim 1, wherein the binding energy between the nanofiber composite and lead ions is between -3.0 and -3.5 kilocalories per mole.
7. A method (100) for preparing a nanofiber composite for lead adsorption from water, comprising:
mixing zeolitic imidazolate framework-67 nanoparticles with polyvinyl alcohol in a solvent to form a precursor solution with a weight ratio of 1:4; and
electrospinning the precursor solution at a voltage of 8-12 kilovolts to form nanofibers,
wherein the mixing and electrospinning creates a three-dimensional fibrous network that positions nitrogen atoms of the zeolitic imidazole framework-67 at predetermined intervals, creating coordination sites that facilitate electrostatic and hydrogen bonding interactions with lead ions for lead adsorption from water.
8. The method (100) as claimed in claim 7, wherein the mixing comprises:
dissolving the zeolitic imidazolate framework-67 and polyvinyl alcohol in deionised water;
sonicating the mixture for a period of 5-15 minutes; and
stirring the mixture at 80-90 degrees Celsius for 3-5 hours.
9. The method (100) as claimed in claim 7, wherein the electrospinning further comprises:
maintaining a distance of 10-15 centimetres between the needle tip and a collector; and
feeding the solution at a rate of 0.2-0.5 millilitres per hour.
10. A method (600) for removing lead from wastewater, comprising:
contacting wastewater containing lead ions with a nanofiber composite comprising zeolitic imidazolate framework-67 nanoparticles encapsulated in polyvinyl alcohol fibres;
allowing the nanofiber composite to adsorb the lead ions by maintaining a pH of 5-7 that promotes deprotonation of hydroxyl groups and nitrogen sites, creating adsorption sites that attract lead ions and facilitate chelation and ion exchange mechanisms; and
separating the nanofiber composite from the wastewater,
wherein the nanofiber composite removes lead ions through a combination of electrostatic attraction via deprotonated sites, chelation between lead ions and hydroxyl functionalities, and ion exchange between lead ions and cobalt ions within the zeolitic imidazolate framework-67 structure.
11. The method (600) as claimed in claim 10, wherein the nanofiber composite dosage is 15-25 milligrams per litre.
12. The method (600) as claimed in claim 10, wherein the contact time between the nanofiber composite and the wastewater is 1-3 hours.
13. The method (600) as claimed in claim 10, further comprising regenerating the nanofiber composite by treating with 0.01 molar sodium hydroxide solution to desorb the adsorbed lead ions.
14. The method (600) as claimed in claim 13, wherein the regenerated nanofiber composite can be reused for at least four adsorption-desorption cycles with an adsorption efficiency of at least 60%.
15. The method (600) as claimed in claim 10, wherein maintaining the pH at 5-7 and using a nanofiber composite dosage of 15-25 milligrams per litre with a contact time of 1-3 hours structurally facilitates a lead removal efficiency of more than 83% at initial lead concentrations of 10 milligrams per litre.