Claims:We Claim:

1. A process of preparation of a sericin doped Graphene Oxide (GO) membrane for Forward Osmosis (FO), wherein the process (100) comprises the steps of:
a. isolating the GO flakes based on the flake size by centrifuging the pristine GO dispersion at 2000 rpm for 10 mins (101);
b. collecting a supernatant comprising the medium GO flakes with sizes in the range between 1 µm to 2 µm (102);
c. pouring the sericin solution on top of the nylon support by using a filtration setup without vacuum pressure (103);
d. pouring the medium GO flake dispersion at a concentration of 1 mg/ml on top of sericin doped nylon support by means of a filtration setup under vacuum pressure (104);
e. heating the GO coated sericin doped nylon support to promote the crosslinking of GO and sericin for obtaining a partially reduced GO (PrGO) membrane (105);
f. immersing the sericin doped partially reduced GO (SPrGO) membrane in Deionized (DI) water for a duration of 24 hours (106); and
g. drying the sericin doped partially reduced Graphene Oxide membrane (107).
2. The process as claimed in claim 1, wherein the GO coated sericin-nylon membrane is heated at a temperature in the range between 140oC and 160oC, preferably at 150oC for optimum annealing of the GO-sericin doped on the nylon support.
3. The process as claimed in claim 1, wherein the GO coated on sericin-nylon composite membrane is heated for a duration in the range between 2 and 3 hours, preferably for 2.5 hours to achieve optimum crosslinking of GO-sericin with the nylon support.
4. The process as claimed in claim 1, wherein the sericin solution at a concentration in the range between 20 g/l to 30 g/l is doped on the nylon support, preferably at an optimum concentration of 25 g/l for doping on the nylon support.
5. The process as claimed in claim 1, wherein the sericin coating on the nylon support is replaced with GO coating followed by sericin doping to form a PrGO-sericin membrane.
6. A sericin doped Graphene Oxide (GO) membrane for Forward Osmosis (FO), wherein the membrane comprises sericin as the material for doping on a nylon support to obtain sericin first doped on nylon support and then GO coated on the sericin-nylon support membrane to obtain a sericin doped partially reduced graphene oxide (SPrGO).
7. The sericin doped GO membrane as claimed in claim 6, wherein the FO membrane alternatively comprises GO doped first on the nylon support and then sericin coated on the GO-nylon support to obtain a PrGO-sericin membrane.
8. The sericin doped GO membrane as claimed in claim 6, wherein the nylon support is replaced preferably with the polymers such as polyester, Polypropylene (PP) and Polyvinylidene fluoride (PVDF).
9. The sericin doped GO membrane as claimed in claim 6, wherein the sericin doped PrGO membrane exhibits higher water flux of around 80-100 LMH compared to the pristine GO membrane.
10. The sericin doped GO membrane as claimed in claim 6, wherein the sericin doped PrGO membrane exhibits higher salt rejection of up to 99.5%.
11. The sericin doped GO membrane as claimed in claim 6, wherein the sericin doped PrGO membrane exhibits lower salt flux of around 5-6 gMH.
12. The sericin doped GO membrane as claimed in claim 6, wherein the FO membrane is effective for water desalination, wastewater treatment and to prepare concentrates such as juice concentrates, beverage concentrates and pharmaceutical concentrates.
, Description:Preamble to the Description
[0001] The following specification describes the invention and the manner in which is to be performed:
DESCRIPTION OF THE INVENTION
Technical field of the invention
[0002] The present invention relates to a sericin doped Graphene Oxide (GO) membrane for Forward Osmosis (FO). More particularly, the invention relates to a process of preparation of sericin doped partially reduced Graphene Oxide (SPrGO) membrane for FO.
Background of the invention
[0003] Although the planet is covered with 70% water, the freshwater suitable for drinking and other needs is available at a mere 3%, leading to water scarcity all over the world. In addition to the existing water scarcity issues that are affecting many countries, the freshwater sources are drying up apart from being polluted. Consequently, resulting in scarcity of potable water.
[0004] Millions of people die every year due to the scarcity of potable water and water-related diseases. Earlier, conventional methods of water treatment such as coagulation, sedimentation, etc, were used to purify water. However, due to many limitations, these treatment methods are not feasible for further applications. Therefore, researchers have advanced the treatment methods to improve the quality of potable water utilizing membrane technology.
[0005] Membrane technology relates to the use of membrane as a separation barrier to remove small particles such as salt, ions, etc from water. Water treatment facilities use various types of membranes and processes to clean surface water, groundwater and wastewater to produce water that serves for industrial and drinking purposes, but membrane technology is mainly used for desalination. The desalination process is generally carried out using membranes in Reverse Osmosis (RO), Nanofiltration (NF), Ultrafiltration (UF), Microfiltration (MF), etc. However, due to high energy consumption and fouling of the RO membrane as well as drawbacks such as low water flux and salt rejection of NF and UF membrane, the use of these membranes was restricted.
[0006] Consequently, researchers have opted for the application of membrane technology using Forward Osmosis (FO). FO is a pressure-driven process and hence requires less energy, thus resulting in lower membrane fouling. In the FO process, water molecules transport from lower concentration (feed side) to higher concentration (draw side) through the FO membrane. At the same time, reverse salt transport occurs from the draw side to the feed side. Since polymeric and ceramic membranes produce low water flux, the reverse salt flux is high for such membranes, which results in internal concentration polarization and membrane fouling. In order to overcome the above drawback, a 2D nanomaterial such as Graphene Oxide (GO), which is a derivative of graphene is applied on the polymeric membrane to enhance desalination in the FO process. The GO material comprises functional groups such as carboxyl, hydroxyl and epoxy group, hence it is high in oxygen, and due to the presence of multiple functional groups, the GO material is hydrophilic and helps in faster transport of water. Simultaneously, the salt ions are separated during the filtration process due to the tortuous pathway of nano-channels of the GO flakes from the higher concentration to lower concentration thus reducing the salt concentration in the treated water. Therefore, the GO membrane enhances the water flux as well as decreases the salt flux during FO.
[0007] Another derivative of graphene is reduced graphene oxide (rGO), which has narrower inter-layer spacing between the sheets compared to GO. As a result of narrower inter layer spacing, the rate of salt rejection is higher than GO. Thus, providing a forward osmosis membrane with enhanced water flux. Many researchers have prepared the GO membrane doped with certain materials to enhance desalination. However, the doping materials were not high enough to increase the water flux. The prior arts listed below discloses different ways and means of desalination using membrane technology.
[0008] The patent application “CN105854630B” entitled “A kind of forward osmosis membrane and preparation method thereof” discloses a forward osmosis membrane and method of preparation of the membrane which includes a supporting layer. The supporting layer is the blend of ultrafiltration membrane, graphene oxide, the polyamide-amide in 0~2 generation. The forward osmosis membrane has higher water flux, the interlamellar spacing of the graphene oxide interlayer is relatively stable and the membrane does not easily drop-off from the ultrafiltration membrane. Further, the interlamellar spacing of graphene oxide is adjustable. The forward osmosis membrane has higher interception capacity to the anions and cations in the solution, to improve the whole cutoff performance of the film.
[0009] The patent application “US20190070566A1” entitled “Techniques for performing diffusion-based filtration using nanoporous membranes and related systems and methods” discloses a semi-permeable membrane provided for performing separation processes as well as the method of manufacture. The membrane may comprise a porous substrate, and an active layer disposed upon the substrate. The active layer may further comprise at least one atomically thin layer having a plurality of open pores that allow transport of some species through the membrane while restricting transport of other species through the membrane.
[0010] The patent application CN109529623A entitled “A kind of high-intensity high-throughput antibacterial forward osmosis membrane of no fabric and preparation method thereof” discloses the preparation of an antibacterial forward osmosis membrane. The main objective of the invention is to prepare a kind of forward osmosis membrane without enhancing the fabric and eliminate the osmotic resistance to water, reduce the integral thickness of the film and promote the water flux of the film. The mechanical performance of graphene oxide is excellent and meets the intensity of the forward osmosis membrane after removing fabric. The hydrophilic and antibiotic property of graphene oxide is utilized for preparing a nano combined forward osmosis membrane exhibiting high-intensities, high-throughput and stable against biological contamination.
[0011] The publication titled “Progress of Nanocomposite Membranes for Water Treatment” by Claudia Ursino et al., relates to the application of membrane-based technologies for water treatment, wherein nanocomposite membranes are studied in detail. The study draws more insights into the use of nanomembranes for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes provide added advantage such as enhances the hydrophilicity, suppresses the accumulation of pollutants and foulants, enhances rejection efficiencies and improves the mechanical properties and thermal stabilities. Thus, the purpose of the study is to provide up-to-date information related to the novel nanocomposite membranes and their contribution for water treatment applications.
[0012] The publication titled “Separation and purification using GO and r-GO membranes” by J. Lyu et al discusses the use of graphene oxide membrane for water purification. Graphene oxide (GO), a two-dimensional derivative of graphene is considered as a promising membrane material for water purification due to its excellent hydrophilicity, high water permeability, and excellent ionic or molecular separation properties. The evaluation is intensive on the possible multipurpose applicability of GO membranes. The selective reduction of GO results in membranes with a pore size of ~0.35 nm, ideally suited for desalination purposes. The publication presents the applicability of graphene-based membranes for multiple separation applications. The study outlines a comparison of GO and reduced GO (r-GO) membranes and discusses the suitability for applications based on the porosity of the membranes.
[0013] The publication titled “Fabrication of reduced graphene oxide membranes for highly efficient water desalination” by Junxian Pei et al, discloses the use of graphene-based membrane for desalination. The study involves the use of reduced graphene membrane fabricated using dopamine followed by vacuum filtration. The resultant membrane allows faster permeation of water compared to the pristine graphene oxide membrane, but a higher retention rate of solutes. The increase of interaction between functional groups of reduced graphene oxide and the ions or water molecules is responsible for these excellent performances, which make the graphene-based membranes promising materials for their usage in desalination and water treatment.
[0014] The publication titled “Thermally Reduced Nanoporous Graphene Oxide Membrane for Desalination” by Yang Li et al, discusses graphene-based laminar membranes. Such membranes open new avenues for water treatment, particularly, reduced graphene oxide (rGO) membranes with high stability in aqueous solutions are gaining increased attention for desalination. However, the low water permeability of these membranes significantly limits their applications. In the study, the water permeability of thermally reduced GO membrane was increased by a factor of 26 times by creating in-plane nanopores with an average diameter of ~3 nm and a high density of 2.89 × 1015 m–2 via H2O2 oxidation. These in-plane nanopores offer additional transport channels and reduce the transport distance for water molecules. Meanwhile, salt rejection of this membrane is dominated by both the Donnan effect and the size exclusion of the interspaces. Besides the thermal treatment time, membrane thickness can be adjusted to alter the permeability of the water and salt rejection of the thermally reduced nanoporous GO membrane. Moreover, the fabricated membrane exhibits a relatively stable rejection of Na2SO4 during long-term testing. The study demonstrates a novel and effective strategy for fabricating high-performance laminar rGO membranes for desalination applications.
[0015] The publication titled “Enhanced desalination performance of forward osmosis membranes based on reduced graphene oxide laminates coated with hydrophilic polydopamine” by Euntae Yang et al, relates to Forward osmosis (FO) membranes. Although FO processes are known to be low energy consuming next-generation desalination technology, the low performance of polymeric membranes remains a bottleneck in the practical application of FO. Graphene oxide (GO) membranes possess a huge potential as an alternative to polymeric membranes because of their facile fabrication procedure, ultra-thin thickness, controllable pore size, and out the performance of competing materials in terms of water transport rate. The low stability of GO laminates underwater and their hydrophobic property (if GO laminates are reduced) remain as problems necessitating solutions before their practical implementation. In order to address the above issue, the chemical reduction of GO laminates along with a hydrophilic adhesive polydopamine (pDA) layer is applied. Reduced GO (rGO) laminates sustainably retained their compacted nanochannels (3.45 Å) compared to pristine GO laminates, which increased the selectivity of hydrated ions. Besides, adding a pDA coating onto the rGO laminates improves the hydrophilicity of the rGO laminate surface, which accelerated the water absorption speed. As a result of these synergistic effects, pDA-coated rGO (pDA-rGO) membranes achieved an outstanding water flux and high salt rejection.
[0016] Although, there are several methods and membranes available for the desalination process, the existing doping materials do not provide high water flux and large quantities of such doping materials are required for preparing such chemical doped graphene oxide membranes. Despite doping the GO membrane with chemicals, the mechanical strength of the membrane is low, associated with moderate water flux, uneven distribution of GO on the support layer as well as low life cycle studies were observed. Hence, there is a need for a membrane with higher water flux, superior salt rejection as well as filters with increased mechanical strength for FO process.
Summary of the invention
[0017] The invention overcomes the drawbacks in the existing prior arts by providing a sericin doped Graphene Oxide (GO) membrane to exhibit higher water flux, lower salt flux, increased salt rejection as well as improved mechanical strength of the Forward Osmosis (FO) membrane.
[0018] The invention discloses a sericin doped Graphene Oxide membrane for FO. The invention also discloses a process of preparation of the sericin doped GO membrane. More particularly, the invention discloses a process of preparation of sericin doped on partially reduced graphene oxide (SPrGO) membrane for FO.
[0019] The invention discloses a process of preparation of the SPrGO membrane. The process comprises the steps of isolation of GO flakes of medium size in the range between 1 µm and 2 µm by centrifuging the pristine GO dispersion at 2000 rpm for 10 mins, pouring the sericin solution on top of the nylon support to form a sericin coating, pouring the medium GO flake dispersion on top of the sericin coated nylon support, heating the coated membrane to promote the crosslinking of sericin-GO for obtaining a partially reduced GO (PrGO) membrane to form a Sericin-PrGO or SPrGO membrane, immersing the SPrGO membrane in Deionized (DI) water to obtain a membrane coated with sericin first and then coating with GO on the nylon support and finally drying the membrane for FO. The SPrGO membrane thus obtained exhibits higher water flux, increased salt rejection, along with an easy and feasible preparation process to obtain sericin solution.
[0020] The invention further discloses a sericin doped on the GO coated nylon membrane (PrGO-sericin) for FO. The process of preparation of PrGO-sericin membrane comprises the steps of isolation of GO flakes of medium size in the range between 1 µm and 2 µm by centrifuging the pristine GO dispersion at 2000 rpm for 10 mins, pouring the medium GO flake dispersion on top of nylon support to form a GO coating, pouring sericin solution on top of the GO coated nylon support, heating the coated membrane to promote the crosslinking of GO for obtaining the PrGO membrane to form PrGO-sericin membrane, immersing the PrGO-sericin membrane in DI water to obtain a membrane coated with GO first and then doping sericin on GO coated nylon support and finally drying the membrane for FO. The PrGO-sericin membrane thus obtained exhibits improved water flux, increased salt rejection when compared to only GO coated nylon membrane or PrGO coated nylon membrane.
[0021] The membrane prepared from medium GO solution provides better water flux than that of pristine GO due to the smaller flake size as compared to the original dispersion. Further, the addition of sericin enhances water flux due to the hydrophilic or the hygroscopic nature of sericin and availability of the polar group. Thus, the invention provides a protein doped GO membrane for FO by utilizing a safe doping material, as sericin is non-toxic compared to other doping materials and results in uniform deposition of GO on the substrate using vacuum filtration, which enhances the transport of water across the membrane quicker and consumes less energy as FO is pressure driven. Further, the FO membrane is applicable for water desalination, wastewater remediation, food and pharmaceutical processing, etc.
Brief description of the drawings
[0022] The foregoing and other features of embodiments will become more apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings.
[0023] Figure 1 illustrates a flow chart for a process of preparation of sericin doped partially reduced Graphene Oxide (SPrGO) membrane for Forward Osmosis (FO).
[0024] Figure 2 illustrates the results of surface morphology of the different membranes.
[0025] Figure 3 illustrates the results of Transmission Electron Microscope (TEM) of sericin and medium GO flakes.
[0026] Figure 4 illustrates the results of Energy Dispersive X-Ray (EXD) analysis of different membranes.
[0027] Figure 5a illustrates the comparison graph of the membranes against water flux.
[0028] Figure 5b illustrates the comparison graph of the membranes against salt flux.
[0029] Figure 6 illustrates the results of leachability study of the prepared sericin solution.
[0030] Figure 7a illustrates the life cycle studies of the SPrGO and the PrGO membranes with respect to the water flux.
[0031] Figure 7b illustrates the life cycle studies of the SPrGO and the PrGO membranes with respect to the salt flux.
Detailed description of the invention
[0032] In order to make the matter of the invention clear and concise, the following definitions are provided for specific terms used in the following description.
[0033] The term “Dispersion” refers to a process wherein agglomerated particles are separated from each other.
[0034] The term “Forward osmosis” or FO refers to an osmotic process by means of a semipermeable membrane to effect separation of water from dissolved solutes, driven by the osmotic pressure gradient.
[0035] The term “Sericin” refers to a protein synthesized by Bombyx mori also called as silkworm.
[0036] The term “Desalination” refers to a process of removal of dissolved salts and other minerals from water.
[0037] The invention relates to sericin doped graphene oxide membrane for forward osmosis. More particularly, the invention relates to the use of sericin as a doping material to prepare a sericin doped FO membrane. The invention also discloses a process of preparation of the sericin doped GO membrane for FO. The resulting membrane exhibits higher water flux and lower salt flux during the water desalination in FO.
[0038] According to an embodiment of the invention, the process of preparation of a membrane for FO comprises doping the nylon support with sericin solution and then coating with GO to obtain a sericin first doped on nylon support and then GO coated on sericin-nylon support to form a SPrGO. Figure 1 illustrates a flow chart for the process of preparation of a sericin doped partially reduced graphene oxide (SPrGO) membrane for forward osmosis. The process (100) of preparation of the FO membrane comprises a step (101) of isolating the medium size GO flakes by centrifuging the pristine GO dispersion at 2000 rpm for 10 minutes. At step (102), the supernatant comprising the medium GO dispersion with flake sizes ranging from 1 µm to 2 µm is collected and subjected to vacuum filtration. At step (103), the sericin solution at a concentration in the range between 20 g/l and 30 g/l is subjected to filtration without vacuum pressure and poured on top of nylon support. At step (104), the medium GO flake dispersion at a concentration of 1mg/ml is poured on top of sericin doped nylon support by using vacuum pressure filtration. At step (105), the resulting membrane comprising sericin doped first on nylon support followed by GO coated on the sericin-nylon support is heated at a temperature in the range between 140oC and 160oC for a duration of around 2 to 3 hours to promote the crosslinking of GO-sericin on the surface of the nylon support. The color of the membrane changes from brown to black as GO is partially reduced to form a sericin doped on partially reduced GO membrane. At step (106), the sericin-PrGO (SPrGO) membrane is immersed in DI water for a duration of 24 hours. At step (107), the membrane thus obtained is subjected to drying before using for FO process.
[0039] According to another embodiment of the invention, the process of preparation of a FO membrane comprises doping the nylon support with medium GO dispersion first and then coating with sericin solution to obtain a GO first doped on nylon support and then sericin coated on the GO-nylon support to form a PrGO-sericin membrane. The process of preparation of FO membrane comprises a step of isolating the medium size GO flakes by centrifuging the pristine GO dispersion at 2000 rpm for 10 minutes, the supernatant comprising the medium GO dispersion with flake sizes ranging from 1 µm to 2 µm is collected and subjected to vacuum filtration, the medium GO flake dispersion at a concentration of 1mg/ml is poured on top of nylon support. Subsequently, a sericin solution at a concentration in the range between 20 g/l and 30 g/l is filtered and poured on top of the GO-coated nylon support by vacuum filtration. The resulting membrane comprising GO doped first on nylon support followed by sericin coated on the GO-nylon support is heated at a temperature in the range between 140oC and 160oC for a duration of around 2 to 3 hours to promote the crosslinking of sericin-GO on top of the nylon support. The color of the membrane changes from brown to black as the GO is partially reduced forming a partially reduced GO doped with sericin (PrGO-sericin) membrane. Finally, the PrGO-sericin membrane is immersed in DI for a duration of 24 hours. The membrane thus obtained is subjected to drying before using for the FO process.
[0040] In addition to nylon, the support membrane for sericin doped PrGO membrane for forward osmosis is also prepared using the other suitable materials such as polyester, Polyethersulfone (PES), Polypropylene (PP) or Polyvinylidene fluoride (PVDF).
[0041] The addition of sericin solution to the medium GO flakes dispersion enhances the water flux as sericin is hydrophilic and tends to adhere to medium GO flakes due to the presence of polar groups such as hydroxyl, carboxyl, etc. Further, due to the hydrophilic and hygroscopic nature the sericin doped PrGO membrane helps in better water transport compared to the pristine GO membrane during FO for water desalination.
[0042] Having generally described this invention, a further understanding can be obtained by reference to certain specific examples, which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.
Example 1: Preparation of GO coated on sericin membrane for water desalination in FO
[0043] The preparation of GO coated on sericin membrane comprises preparing the sericin solution at a concentration of about 25 g/l. The sericin solution is subjected to filtration without vacuum pressure and poured on top of the nylon support. Subsequently, the medium flake GO dispersion at a concentration of about 1 mg/ml is subjected to vacuum filtration and poured on the obtained sericin-nylon support, annealing the sericin (first)-GO (second) membrane by heating at a temperature of around 150oC for a duration of 2.5 hours to promote the crosslinking of the GO-sericin on top of the nylon support. The resultant membrane is a sericin doped partially reduced graphene oxide membrane, which changes the color of the membrane from brown to black as GO is partially reduced. The SPrGO membrane is immersed in DI water for 24 hours before using for FO.
Example 2: Preparation of sericin coated on GO membrane for water desalination in FO
[0044] The preparation of the sericin coated GO membrane comprises preparing medium GO flake dispersion at a concentration of about 1 mg/ml and subjected to vacuum filtration and pouring 1 ml of the medium GO dispersion on the nylon support. Sericin solution at a concentration of about 25g/l is subjected to filtration and poured on top of the GO coated nylon support. Annealing the GO (first)-sericin (second) membrane by heating at a temperature of 150oC for a duration of 2.5 hours to promote the crosslinking of the sericin-GO membrane on top of the nylon support. The resulting membrane is a partially reduced Graphene Oxide (PrGO) coated with sericin, which changes the color of the membrane from brown to black as GO is partially reduced. The PrGO-sericin membrane is immersed in DI water for 24 hrs before using for FO.
[0045] The resulting SPrGO membrane and PrGO-sericin membrane are individually analyzed for water and salt flux during the FO. The experiment is carried out by preparing a draw solution and feed solution. A 1liter conical flask is filled with around 1M Sodium chloride (NaCl) solution as a draw solution and another conical flask is filled with de-ionized water as the feed solution. The feed and draw solutions are prepared in duplicates to analyze SPrGO and PrGO-sericin membranes separately. In order to measure the weight change during the FO process, a digital electronic weighing balance is placed under each flask for analyzing the SPrGO and PrGO-sericin membranes. The salt concentration is measured in each flask by placing a conductivity meter in the flasks containing the draw solution as well as feed solution. Further, to measure the pressure, the digital pressure gauges are placed on both the sides of the SPrGO membrane and PrGO-sericin membrane. Reverse Osmosis (RO) booster pumps are used to circulate the solutions on each side of the SPrGO and PrGO-sericin membrane separately, wherein the SPrGO and PrGO-sericin membrane is placed inside a module made of nylon 6,6. The draw and feed solutions are circulated across the membrane by means of a Polyvinyl Chloride (PVC) pipes of 0.3 cm diameter. Further, in order to secure the flow between the flasks containing the draw and feed solution and to promote continuous flow, the valves and connectors are used to connect the PVC pipes. The salt flux and water flux are determined for both the SPrGO and PrGO membrane individually.
[0046] Figure 2 illustrates the results of surface morphology of the different membranes. The test is helpful to understand the pore size and pore distribution on the membrane, which directly influence the selectivity and permeation rate and is determined by the surface morphology data. Figure 2(a) illustrates the surface morphology of the nylon support alone. Figure 2(b) illustrates the surface morphology of GO coated on top of the nylon support. Figure 2(c) illustrates the surface morphology of the nylon support doped with sericin first and then GO coated on top of the sericin-nylon support (SPrGO). Figure 2(d) illustrates the surface morphology of the nylon support first coated with GO and then sericin doped on top of the GO-nylon support (PrGO-sericin). The uniformity in distribution of sericin is observed in the SPrGO and PrGO-sericin membranes.
[0047] Figure 3 illustrates the images from Transmission Electron Microscope (TEM) of sericin and medium GO flakes. The test provides highly magnified internal structure of the samples and particle size of each sample is determined using TEM. Figure 3(a) illustrates the TEM image of sericin. The result interpreted that the size of sericin is around 300 nm. Figure 3(b) illustrates the TEM image of sericin at varying size range. The result interpreted that the size of the sample is 0.5 ?m. Figure 3(c) illustrates the TEM image of medium GO flake. The result interpreted that the size of the GO flakes is between 3 ?m and 4 ?m.
[0048] Figure 4 illustrates the results of Energy Dispersive X-Ray (EXD) analysis of different membranes. The analysis is used to confirm the bonding of sericin with GO by determining the nitrogen and oxygen concentrations in the serine doped GO membrane. Figure 4(a) illustrates the result of EDX analysis of GO membrane alone. The analysis determines the presence of around 22.3% of oxygen and 4.6% of nitrogen concentration. Figure 4(b) illustrates the result of EDX analysis of the sericin doped GO (SGO) membrane. The analysis determines the presence of around 31.6% of oxygen and 10.3% of nitrogen concentration. Figure 4(c) illustrates the result of EDX analysis of PrGO membrane. The analysis determines the presence of around 22.1% of oxygen and 5.8% of nitrogen concentration. Figure 4(d) illustrates the result of EDX analysis of the SPrGO membrane. The analysis determines the presence of around 33.2% of oxygen and 11.0% of nitrogen concentration. The increase in the percentage of the oxygen and nitrogen content in the SGO and SPrGO membrane confirms the bonding of the sericin on the GO and PrGO membrane respectively.
[0049] Figure 5a illustrates the comparison graph of the membranes against water flux. The graph illustrates the water flux limit of the PrGO in comparison with the water flux limit of the PrGO-sericin membrane and SPrGO membrane. The SPrGO exhibited high water flux around 80-100 LMH, thus proves to be an efficient membrane for desalination with increased water flux compared to the PrGO-sericin and PrGO membranes.
[0050] Figure 5b illustrates the comparison graph of the membranes against salt flux. The graph illustrates the salt flux limit of the PrGO in comparison with the salt flux limit of the PrGO-sericin membrane and SPrGO membrane. The SPrGO exhibited lower salt flux around 5-6 gMH, thus proves to be an efficient membrane for desalination with higher salt rejection of up to 99.5% compared to the other two membranes.
[0051] Figure 6 illustrates the results of leachability study of sericin, draw and feed solutions. The sericin solutions at a concentration of 1mg/ml and a concentration of 0.25 mg/ml are prepared and compared with the samples collected from the draw and feed solutions after the experimentation of the FO membranes obtained from the process as disclosed in Example 1 and Example 2.
[0052] Figure 7a illustrates the life cycle studies of SPrGO and PrGO membranes with respect to the water flux. The graph illustrates the life cycle of the SPrGO membrane versus the PrGO membrane for water flux. The SPrGO membrane exhibited higher water flux than PrGO membrane.
[0053] Figure 7b illustrates the life cycle studies of SPrGO and PrGO membranes with respect to the salt flux. The graph illustrates the life cycle of SPrGO membrane versus the PrGO membrane for salt flux. The SPrGO membrane exhibited lower salt flux compared to PrGO membrane.
[0054] Thus, the invention provides a sericin doped PrGO membrane exhibiting increased water flux, lower salt flux with increased salt rejection. The medium GO dispersion provides high water flux than mixed flakes of GO dispersion due to the presence of smaller GO flakes compared to original GO dispersion. Further, the addition of sericin on the GO membrane enhances water flux due to the hydrophilic or hygroscopic nature of sericin and availability of the polar group. Basically, sericin is discarded as effluent during silk processing. Thus, the sericin doped GO membrane is cost effective and sericin being non-toxic compared to other doping materials is a reliable alternate. Sericin results in uniform deposition of GO on the nylon support, which enhances the transport of water across the membrane and consumes less energy as FO is pressure-driven, Further, the resulting membrane exhibits better mechanical strength compared to other GO membranes.
[0055] The resulting membrane for FO is applicable for water desalination, wastewater treatment, preparation of juice concentrate and beverage concentrates. The juice concentrates such as sucrose concentrate, and beverage concentrate such as caffeine and catechin concentrate are prepared using the FO membrane. Further, the membrane also is applicable to prepare pharmaceutical based product concentrates such as enzymes and antibiotic.