1. A process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles comprising the steps: - Preparing seed extract of Citrus sinensis seeds by, - Drying the seeds of Citrus sinensis under specific conditions, - Removing husk from the dried seed, - Crushing the husk free seeds in acetone to prepare a seed paste, - Carrying out two-stage centrifugation of the seed paste, by centrifuging the seed paste at a specific speed and time, followed by separating the supernatant and centrifuging the supernatant at a specific speed and time to obtain the seed extract of Citrus sinensis, - Preparing an alkaline solution of seed extract and metal salt by, - Mixing the seeds extract with 0.1M Mn (CH3CO2)2.4H2O followed by centrifugation at specific conditions of speed, time and temperature to obtain a solution of seed extract and metal salt, - Adding freshly prepared 5M NaOH in the solution of seed extract and metal salt to obtain an alkaline solution of seed extract and metal salt with pH 9, - Centrifuging the alkaline solution of seed extract and metal salt at specific conditions of speed, time and temperature to obtain the crude form of CS-MnO2-NPs, - Purifying the crude form of CS-MnO2-NPs to obtain CS-MnO2-NPs by, - washing the crude form of CS-MnO2-NPs with ethanol, - drying the ethanol washed CS-MnO2-NPs over a water bath, at a specific temperature to obtain dried CS-MnO2-NPs, - calcinating the dried CS-MnO2-NPs in a muffle furnace at a specific temperature and time to obtain pure black coloured CS-MnO2-NPs, wherein said CS-MnO2-NPs are used as a photocatalyst for the degradation of methylene blue dye in wastewater treatment.

2. The process as claimed in claim 1, wherein the specific conditions for drying the seeds of Citrus sinensis is temperature in the range of 105 oC to 110 oC for a period of 1 to 2 days.

3. The process as claimed in claim 1, wherein the specific speed and time of two stage centrifugation of the seed paste is 150 to 250 rpm for 3 h and of the supernatant is 2600 rpm to 2800 rpm for 20 min to 30 min.

4. The process as claimed in claim 1, wherein specific conditions of centrifugation speed, time and temperature to obtain a solution of seed extract and metal salt are 1100 to 1300 rpm for 45 min at a temperature in the range of 40 oC to 60 oC.

5. The process as claimed in claim 1, wherein specific conditions of centrifugation speed, time and temperature to obtain crude form of CS-MnO2-NPs are 2300 rpm to 2600 rpm at RT for a duration of 20 min to 30 min.

6. The process as claimed in claim 1, wherein a specific temperature of drying the ethanol washed CS-MnO2-NPs over water bath to obtain dried CS-MnO2-NPs temperature in the range of 105 oC to 110 oC for a period of 25-30 min.

7. The process as claimed in claim 1, wherein specific temperature and time of calcinating the dried CS-MnO2-NPs in a muffle furnace at a temperature of 300 oC for 2 h.

8. The process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles comprising the steps: - Preparing seed extract of Citrus sinensis seeds by, - Drying the seeds of Citrus sinensis at a temperature in the range of 105 oC to 110 oC for a period of 1 to 2 days, - Removing husk from the dried seed, - Crushing the husk free seeds in acetone to prepare a seed paste, - Centrifuging the seed paste at 200 rpm for 3 h and separating the supernatant which is the seed extract of Citrus sinensis, and centrifuging the supernatant at 2800 rpm for 25 min, - Preparing alkaline solution of seed extract and metal salt by, - Mixing the seeds extract with 0.1M Mn (CH3CO2)2.4H2O followed by centrifugation at 1200 rpm for 45 min at a temperature of 45 oC to obtain a solution of seed extract and metal salt, - Adding freshly prepared 5M NaOH in the solution of seed extract and metal salt to obtain an alkaline solution of seed extract and metal salt with pH 9, - Centrifuging the alkaline solution of seed extract and metal salt at 2500 rpm at RT for 25 min to obtain the crude form of CS-MnO2-NPs, - Purifying the crude form of CS-MnO2-NPs to obtain CS-MnO2-NPs by, - washing the crude form of CS-MnO2-NPs with ethanol, - drying the ethanol washed CS-MnO2-NPs over a water bath, at a temperature in the range of 105 oC to 110 oC to obtain dried CS-MnO2-NPs, - calcinating the dried CS-MnO2-NPs in a muffle furnace at a temperature of 300 oC for 2 h to obtain pure black coloured CS-MnO2-NPs, wherein said CS-MnO2-NPs are used as photocatalysts for the degradation of methylene blue dye in wastewater treatment.

9. A green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) obtained by the process as claimed in claim 1, wherein said green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) are used as photocatalyst for degradation of methylene blue dye in the wastewater treatment.

10. The green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) obtained by the process as claimed in claim 1, wherein said green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) have 97% removal efficiency of 100 ppm methylene blue dye at optimum conditions of pH 3 at contact time of 90 minutes with the CS-MnO2-NPs dosage of 50 mg.

Description:FIELD OF THE INVENTION:
The present invention relates to the field of wastewater treatment. Particularly, the present invention relates to a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles. More particularly, the present invention relates to a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles for use as photocatalyst for the degradation of methylene blue dye in wastewater treatment.

BACKGROUND OF THE INVENTION:
There is substantial growth in the demand for new wastewater treatment technologies that are being driven by population growth and increasing volumes of wastewater produced, tighter wastewater quality regulations, increasing cost of clean water and water shortages, awareness for the protection of clean water sources and replacement of aging wastewater systems.

For the last few decades, synthetic dyes have not only widely employed in the industry, such as textiles, leather, paper, dyeing/printing, and plastic industries, and have also been extensively utilized in food handling and agriculture research. The above industries cause the discharge of dyes into the environment and generate a considerable amount of dye wastewater, which can do great harm to human beings and the environment due to its toxicity and non-biodegradability.

Many organic dyes are toxic/carcinogenic in nature and show resistance to degradation due to high stability towards light and oxidation. The presence of even very small amounts of dyes in water is visible and undesirable. For example, exposure to basic dyes like methylene blue (MB), is a cationic dyestuff, which is particularly resistant to biodegradation, commonly used for dying cotton, wood and silk or methyl orange (MO), widely used in textile, printing, paper, food and pharmaceutical industries, research laboratories etc., causes eye burns, breathing difficulties, burning sensation, nausea, vomiting, profuse sweating, mental confusion and methemoglobinemia.

Industries are specifically being forced both by tougher discharge standards and cost pressures to eliminate their recalcitrant wastewater pollutants before discharge, and to adopt on-site water reuse and recycling systems to avoid rising water supply and effluent discharge costs. The requirement is for cost-effective, sustainable water treatment technology that does not require the addition of chemicals and does not produce secondary pollution, is compliant with stringent water quality standards, and has minimal operational and maintenance requirements. Industrial wastewater can contain organic compounds, many of which are toxic, persistent and resist conventional biological and chemical wastewater treatment.

The presence of dyes in water changes colour, taste, and order, and also may inhibit sunlight penetration, consume oxygen of the water, and ultimately, enhance the chemical, and biological oxygen demands of water, thus reducing the dissolved oxygen for aquatic animals and plants, which may kill the aquatic life. Moreover, when inhaled, through contaminated water, dyes cause adverse health effects towards the human body which include increased heartbeat, nausea, jaundice, tissue necrosis, and quadriplegia. Synthetic dyes, particularly basic dyes, such as Methylene blue, and MB, have stable, non-biodegradable, aromatic molecular structures which pose a large threat to the ecological system.

The non-ionic existence form of dispersed dyes in solution, bioaccumulation, and stable chemical structure produce a great challenge to traditional sewage treatment systems. Our Existing processing technology cannot decompose dyes in the wastewater effectively. So, it is vital to find a novel and valid process to dispel the dyes from the contaminated water.

Decolorization of colored water via photodegradation of dye molecules/ions is another demanding water purification technique. The semiconductor photocatalysts can remove the organic effluent through their mineralization and decolorization abilities. The incorporation of inorganic photocatalysts into cellulosic carbon framework also generates photocatalytic properties in the visible region which represents an advancement in water treatment technology. Nontoxic TiO2 is the most utilized photocatalyst for UV-light-driven photodegradation of organic pollutants but has a large band gap energy (approximately, 3.2?eV) and thus only shows the catalytic activity in the UV region. Besides the commonly used titanium dioxide (TiO2), manganese dioxide (MnO2) is a potential photocatalyst for wastewater treatment. In numerous catalyst materials, MnO2 has been a very promising candidate because of its high activation properties, low toxicity, and especially its large natural abundance. MnO2 has a narrow bandgap energy of 1~2 eV. Thus, it possesses a high possibility of being driven by visible light and infrared light for dye degradation.

In the past, several methods have been adopted for the removal of dyes from wastewater, including for example, photocatalytic degradation, cation exchange membranes, electrochemical degradation, and adsorption/precipitation processes. Although viable dye removal processes are to an extent, these existing processes are limited by disadvantages including energy cost, secondary pollution, and safety of operation.

Green synthesis of nanoparticles, rooted in nanobiotechnology, has become a central area of focus in nanotechnology research. The biosynthesis of nanoparticles stands out due to its environmentally friendly, pure, cost-effective, and versatile nature, often carried out at room temperature. The adoption of biosynthesis is crucial in avoiding the generation of toxic or hazardous byproducts, emphasizing the need for straightforward and benign production techniques. Practically, green synthesis of nanoparticles is not only cost-effective but can also be efficiently conducted under ambient conditions. During a one-step synthesis process, a natural bio-reductant extract is mixed with a metallic salt solution. The ensuing redox reaction rapidly produces nanomaterials.

Green synthesis offers a superior alternative to traditional methods for producing metal and metal oxide nanoparticles. This approach is not only benign and safe but also cost-effective, scalable, and straightforward, operating under ambient conditions.

Cited prior art “Nigella sativa seed based nanocomposite-MnO2/BC: An antibacterial material for photocatalytic degradation, and adsorptive removal of Methylene blue from water” discloses the Antimicrobial Nigella sativa seed-based nanocomposite, MnO2/BC was synthesized by co-precipitation method and utilized for the water purification through adsorption, and the photocatalytic degradation.
Another cited prior art “Recent developments in MnO2-based photocatalysts for organic dye removal: a review” discusses the effect of various factors that could affect the photocatalytic performance of MnO2 nanostructures, followed by the future prospects of the development of semiconductor photocatalysts towards commercialization.
Therefore, there exists a need for a novel composition and an efficient process for treating dye effluents or pollutants. There is also a need for a composition that consumes less time, and energy and allows easy retrieval of the catalyst from the reaction mixture for subsequent uses.

In view of the above, the present invention provides a process for the green synthesis of Citrus sinensis Seed Extract Assisted MnO2 Nanoparticles, and a nanostructured MnO2 as a potential photocatalyst which is an affordable, effective, eco-friendly, benign, cost-effective and sustainable catalyst for the degradation of methylene blue dye in the wastewater treatment.

OBJECTS OF THE INVENTION:
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

The main object of the present invention is to provide a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles.

Another object of the present invention is to provide a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles for use as photocatalyst for the degradation of methylene blue dye in wastewater treatment.

Yet another object of the present invention is to provide a green synthesized MnO2 nanoparticle.

Yet another object of the present invention is to provide green synthesized MnO2 nanoparticles which are used as photocatalysts for the degradation of methylene blue dye in wastewater treatment.

Yet another object of the present invention is to provide a green synthesized MnO2 nanoparticle which is an affordable, effective, eco-friendly, benign, cost-effective and sustainable catalyst for the degradation of methylene blue dye in wastewater treatment.

Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

SUMMARY OF THE INVENTION:
Accordingly, the present invention provides a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles which is used as a photocatalyst for the degradation of methylene blue dye in wastewater treatment.
In one of the aspects of the present disclosure, there is provided a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles of the present invention. The process comprises mixing the Citrus sinensis seed paste with acetone to prepare the aqueous extract using an orbital shaker, centrifuging the aqueous extract, collecting supernatant and mixing with 0.1M Mn (CH3CO2)2.4H2O in a sterile conical flask then adding a freshly prepared 5M NaOH solution dropwise to the sterile conical flask while constant stirring until the pale-yellow color solution changed into an amber-precipitated solution. The supernatant is separated after centrifugation for a specific time, and washing the precipitates with ethanol to eliminate impurities and then centrifuged again to obtain a precipitate. The resulting precipitate is dried through a water bath and in the oven to dry completely, and then calcinates in a muffle furnace to obtain a black-colored green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles.

In one of the aspects of the present disclosure, there is provided a green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles, for use as a photocatalyst for degradation of methylene blue dye in the wastewater treatment.

These and other aspects herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention herein without departing from the spirit thereof.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps, does not include only those steps but may include other steps not expressly listed or inherent to such a process or method. Similarly, one or more steps of the process or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other steps or components. Appearances of the phrase "in a preferred embodiment”, “in an embodiment", “in another embodiment” and similar language throughout this specification may, but not necessarily do, all refer to the same embodiment.
BRIEF DESCRIPTION OF THE FIGURES
Fig. 1 depicts the green synthesis of Citrus sinensis seed extract-assisted MnO2 nanoparticles (CS-MnO2-NPs).
Fig. 2 depicts the mechanism for photocatalytic degradation of methylene blue.
Fig.3 depicts the XRD graph of CS-MnO2-NPs.
Fig. 4 (a) and (b) depicts SEM images for CS-MnO2-NPs at different magnification levels.
Fig. 5(a) and (b) depict TEM images of CS-MnO2-NPs and the SAED pattern of CS-MnO2-NPs, respectively.
Fig. 6 depicts the analysis of methylene blue dye degradation at 2 and 3 pH.
Fig. 7 depicts the analysis of MB dye using a 1mg catalyst.

DETAILED DESCRIPTION OF THE INVENTION WITH NON-LIMITING EMBODIMENTS AND EXAMPLES

In the following detailed description of the invention, numerous specific details are outlined to provide a thorough understanding of the invention. However, it will be obvious to a person skilled in the art that the invention may be practiced with or without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the invention.

Furthermore, it will be clear that the invention is not limited to these alternatives only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art, without parting from the scope of the invention.

Accordingly, the present invention provides a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles which are used as a photocatalyst for the degradation of methylene blue dye in wastewater treatment.

As shown in Fig. 1. in an aspect of the present disclosure, the process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles of the present invention comprises preparing seeds extract of Citrus sinensis seeds, mixing the seeds extract with 0.1M Mn (CH3CO2)2.4H2O to obtain a solution of seed extract and metal salt, adding freshly prepared 5M NaOH solution dropwise in the solution of seed extract and metal salt to bring the pH of the solution of seed extract and metal salt at pH 9 to obtain alkaline solution of seed extract and metal salt, centrifuging the alkaline solution of seed extract and metal salt and separating the precipitate, purification of the precipitate through washing, drying and heating to obtain CS-MnO2-NPs.

In one of the embodiments of the present disclosure, the seeds of Citrus sinensis are dried at a temperature in the range of 105 oC to 110 oC for a period of 1 to 2 days. Husk is removed from the dried seeds and the seeds are then crushed in acetone to prepare a paste. The paste is centrifuged at 150 to 250 rpm for 3 h and the supernatant is separated. The supernatant is again centrifuged at 2600 rpm to 2800 rpm for 20 min to 30 min.
In one of the embodiments of the present disclosure, the seeds extract is mixed with the 0.1M Mn (CH3CO2)2.4H2O and centrifuged at 1100 to 1300 rpm for 45 min at a temperature in the range of 40 oC to 60 oC to obtain a solution of seed extract and a metal salt.

In one of the embodiments of the present disclosure, the colour of the solution of seed extract and metal salt is pale yellow, which turns to an amber colour with the addition of NaOH due to a pH change from 7.4 to 9.

In one of the embodiments of the present disclosure, the alkaline solution of seed extract and metal salt is centrifuged at 2300 rpm to 2600 rpm at RT for a duration of 20 min to 30 min to obtain the crude form of CS-MnO2-NPs.

In one of the embodiments of the present disclosure, a crude form of CS-MnO2-NPs undergoes a three-step purification process. The first step of purification is washing with ethanol. The second step of purification is drying the ethanol washed CS-MnO2-NPs over a water bath, at a temperature in the range of 105 oC to 110 oC. The third step of purification is the calcination of dried CS-MnO2-NPs in a muffle furnace at a temperature of 300 oC for 2 h to obtain pure black coloured CS-MnO2-NPs.

In one embodiment, a green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) obtained by the process of the present invention, which are used as a photocatalyst for degradation of methylene blue dye in the wastewater treatment.

In one embodiment, the CS-MnO2-NPs obtained by the process of the present invention which are used as photocatalysts for the degradation of methylene blue dye in the wastewater treatment shown in Fig. 2 in which the CS-MnO2-NPs mixed with Methylene Blue (MB) dye in the sunlight to degrade under visible light from water with an excellent degradation capacity.
In one example, the green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles comprises:
- Preparing seed extract of Citrus sinensis seeds by,
- Drying the seeds of Citrus sinensis at a temperature in the range of 105 oC to 110 oC for a period of 1 to 2 days,
- Removing husk from the dried seed,
- Crushing the husk-free seeds in acetone to prepare a seed paste,
- Centrifuging the seed paste at 200 rpm for 3 h and separating the supernatant which is the seed extract of Citrus sinensis, and centrifuging the supernatant at 2800 rpm for 25 min,
- Preparing an alkaline solution of seed extract and metal salt by,
- Mixing the seeds extract with 0.1M Mn (CH3CO2)2.4H2O followed by centrifugation at 1200 rpm for 45 min at a temperature of 45 oC to obtain a solution of seed extract and metal salt,
- Adding freshly prepared 5M NaOH in the solution of seed extract and metal salt to obtain an alkaline solution of seed extract and metal salt with pH 9,
- Centrifuging the alkaline solution of seed extract and metal salt at 2500 rpm at RT for 25 min to obtain the crude form of CS-MnO2-NPs,
- Purifying the crude form of CS-MnO2-NPs to obtain CS-MnO2-NPs by,
- washing the crude form of CS-MnO2-NPs with ethanol,
- drying the ethanol washed CS-MnO2-NPs over a water bath, at a temperature in the range of 105 oC to 110 oC to obtain dried CS-MnO2-NPs,
- calcinating the dried CS-MnO2-NPs in a muffle furnace at a temperature of 300 oC for 2 h to obtain pure black coloured CS-MnO2-NPs,
wherein said CS-MnO2-NPs are used as a photocatalyst for the degradation of methylene blue dye in wastewater treatment.

Experiments
Citrus sinensis seeds were procured from the juice shop of Banasthali Vidyapith, Newai, Tonk, Rajasthan, India as waste part of orange.
Characterization of Citrus sinensis Seed Extract Assisted MnO2 Nanoparticles
X-ray diffraction (XRD)
A characterization method for examining the crystallographic structure of materials is XRD. XRD analysis was used to verify the crystallinity of the green synthesized Citrus sinensis seed extract assisted nanoparticles (CS-MnO2-NPs), as shown in Fig. 3. The green synthesized CS-MnO2-NPs displayed clear diffraction peaks at 2?˜18.2, 28.9, 31.1, 32.6, 36.2, and 38.3 degrees. The strongest peak was observed at 2? values of 18.2 and 36.2 degrees, with 100% and 99.1% MnO2 intensity counts, respectively. The peaks show that the MnO2 crystallized properly. These peaks showed hkl values of 200, 310, 112, 220, 400, and 211, which matched particular crystallographic planes. Using the Derby-Scherrer equation, the crystal size was estimated:
?? = ?? ?/ ß.cos ? (1)
Where K is the shape factor with a value of 0.9; ? is the X-ray wavelength (for copper, ? =1.5406 Å), ß (2?) is the full width at half-maximum (FWHM) of a particular diffraction peak in radians; and ? is the Bragg angle. The CS-MnO2-NPs within the nanoscale range were confirmed by the X-ray diffractogram, which showed that the average size (15.23 nm) of the synthesized CS-MnO2-NPs utilizing the FWHM of the (200) and (400) peaks was 12.77 nm and 17.69 nm, respectively. It indicated that the nanoparticles were synthesized within the nanoscale range.
Field emission scanning electron microscopy (FESEM)
The green synthesized CS-MnO2-NPs morphology was determined using a FESEM analysis. Green synthesized CS-MnO2-NPs were visible in FESEM pictures at various magnification levels. Sharp grain boundaries and a variety of shapes and sizes are displayed by the randomly oriented MnO2 grains in Fig. 4(a) and (b). Additionally, a significant number of voids, micro-cracks, and MnO2-NPs clusters are easily visible in between the grains. Large grains have developed, with smooth borders and virtually no spaces or fissures at the grain boundaries or in between the grains.
Transmission electron microscopy (TEM)
The size and shape of the synthesized CS-MnO2-NPs were further characterized using TEM analysis. The TEM images of CS-MnO2-NPs indicate that they are not clumped together. The green synthesized CS-MnO2-NPs spherical shape was found by TEM investigation, as shown in Fig. 5 (a). The nanoparticle sizes range from 30 to 50 nm, as shown in Fig. 5 (b). CS-MnO2-NPs crystalline nature was investigated using selected area electron diffraction (SAED) pattern analysis.

Photocatalytic degradation of Methylene Blue
Photocatalytic activity
The variations in various experimental parameters such as dye concentration, catalyst amount, and pH value affect the photocatalytic activity of methylene blue (MB) using photocatalyst CS-MnO2-NPs. At definite time intervals, a sample of 3 mL was taken out from the reaction mixture, and the absorbance was analyzed at 664 nm. It was observed that as the time intervals increased, the absorbance of the reaction mixture decreased, indicating that the concentration of MB dye decreased with longer exposure time. The dye's degradation efficiency has been calculated using the Equation:

To determine the kinetics of the photocatalytic process, contact time has been labelled in the range of 0-90 minutes (at 10 minutes intervals). The rate constant was then calculated using the following expression:

Effect of pH
The effect of pH on the photocatalytic degradation rate was investigated in the range of 2-3 at dye concentration 1×10-6-7×10-6 M and 1 mg amount of photocatalyst (CS-MnO2-NPs). It has a significant effect on the surface charge of the photocatalyst. The pH of MB dye was adjusted by using 0.1 N H2SO4. It has been observed that at pH 3, the reaction rate also increases compared to pH 2, due to the greater availability of OH- ions as the pH rises as shown in Fig. 6. A low pH range makes it more challenging to generate hydroxyl radicals. In the reaction between OH- and H+ (hole), more hydroxyl radicals are generated, which interact with dye molecules to degrade them. As a result, pH rises to 3 the negative surface of the photocatalyst enhances electrostatic interactions with MB cation, improving the reaction rate.
Effect of the amount of catalyst
The catalyst amount for the degradation efficiency of MB dye has been observed to range from 1-3mg. It was found that the percentage of MB degradation strongly depends on the amount of catalyst. The increasing amount of catalyst enhances the surface area, a larger surface area provides more active sites for the generation of hydroxyl radicals (•OH). The CS-MnO2-NPs catalyst significantly affects the photocatalytic degradation activity by increasing the amount of catalyst, leading to a decrease in the photodegradation rate constant (k×10-4) value as shown in Fig.7.
The band gap of CS-MnO2-NPs of the present invention is 4.2eV, therefore this is a very effective photocatalyst for the degradation of methylene blue. The removal efficiency of 100 ppm methylene blue dye was found to be 97% at optimum conditions of pH 3, contact time of 90 minutes, and catalyst (CS-MnO2-NPs) dosage of 50 mg.

Therefore, the present invention provides a process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles which are used as a photocatalyst for the degradation of methylene blue dye in wastewater treatment. The green synthesized MnO2 nanoparticle of the present invention is an affordable, effective, eco-friendly, benign, cost-effective and sustainable catalyst for the degradation of methylene blue dye in wastewater treatment.

From the features, as applied to various alternatives, it can be understood that various omissions, substitutions, and changes in the form and details of the present disclosure can be made without departing from the scope of the disclosure. As can be recognized, certain alternatives described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others.
, C , Claims:I/We claim:
1. A process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles comprising the steps:
- Preparing seed extract of Citrus sinensis seeds by,
- Drying the seeds of Citrus sinensis under specific conditions,
- Removing husk from the dried seed,
- Crushing the husk free seeds in acetone to prepare a seed paste,
- Carrying out two-stage centrifugation of the seed paste, by centrifuging the seed paste at a specific speed and time, followed by separating the supernatant and centrifuging the supernatant at a specific speed and time to obtain the seed extract of Citrus sinensis,
- Preparing an alkaline solution of seed extract and metal salt by,
- Mixing the seeds extract with 0.1M Mn (CH3CO2)2.4H2O followed by centrifugation at specific conditions of speed, time and temperature to obtain a solution of seed extract and metal salt,
- Adding freshly prepared 5M NaOH in the solution of seed extract and metal salt to obtain an alkaline solution of seed extract and metal salt with pH 9,
- Centrifuging the alkaline solution of seed extract and metal salt at specific conditions of speed, time and temperature to obtain the crude form of CS-MnO2-NPs,
- Purifying the crude form of CS-MnO2-NPs to obtain CS-MnO2-NPs by,
- washing the crude form of CS-MnO2-NPs with ethanol,
- drying the ethanol washed CS-MnO2-NPs over a water bath, at a specific temperature to obtain dried CS-MnO2-NPs,
- calcinating the dried CS-MnO2-NPs in a muffle furnace at a specific temperature and time to obtain pure black coloured CS-MnO2-NPs,
wherein said CS-MnO2-NPs are used as a photocatalyst for the degradation of methylene blue dye in wastewater treatment.

2. The process as claimed in claim 1, wherein the specific conditions for drying the seeds of Citrus sinensis is temperature in the range of 105 oC to 110 oC for a period of 1 to 2 days.

3. The process as claimed in claim 1, wherein the specific speed and time of two stage centrifugation of the seed paste is 150 to 250 rpm for 3 h and of the supernatant is 2600 rpm to 2800 rpm for 20 min to 30 min.

4. The process as claimed in claim 1, wherein specific conditions of centrifugation speed, time and temperature to obtain a solution of seed extract and metal salt are 1100 to 1300 rpm for 45 min at a temperature in the range of 40 oC to 60 oC.

5. The process as claimed in claim 1, wherein specific conditions of centrifugation speed, time and temperature to obtain crude form of CS-MnO2-NPs are 2300 rpm to 2600 rpm at RT for a duration of 20 min to 30 min.

6. The process as claimed in claim 1, wherein a specific temperature of drying the ethanol washed CS-MnO2-NPs over water bath to obtain dried CS-MnO2-NPs temperature in the range of 105 oC to 110 oC for a period of 25-30 min.

7. The process as claimed in claim 1, wherein specific temperature and time of calcinating the dried CS-MnO2-NPs in a muffle furnace at a temperature of 300 oC for 2 h.

8. The process of green synthesis of Citrus sinensis seed extract assisted MnO2 nanoparticles comprising the steps:
- Preparing seed extract of Citrus sinensis seeds by,
- Drying the seeds of Citrus sinensis at a temperature in the range of 105 oC to 110 oC for a period of 1 to 2 days,
- Removing husk from the dried seed,
- Crushing the husk free seeds in acetone to prepare a seed paste,
- Centrifuging the seed paste at 200 rpm for 3 h and separating the supernatant which is the seed extract of Citrus sinensis, and centrifuging the supernatant at 2800 rpm for 25 min,
- Preparing alkaline solution of seed extract and metal salt by,
- Mixing the seeds extract with 0.1M Mn (CH3CO2)2.4H2O followed by centrifugation at 1200 rpm for 45 min at a temperature of 45 oC to obtain a solution of seed extract and metal salt,
- Adding freshly prepared 5M NaOH in the solution of seed extract and metal salt to obtain an alkaline solution of seed extract and metal salt with pH 9,
- Centrifuging the alkaline solution of seed extract and metal salt at 2500 rpm at RT for 25 min to obtain the crude form of CS-MnO2-NPs,
- Purifying the crude form of CS-MnO2-NPs to obtain CS-MnO2-NPs by,
- washing the crude form of CS-MnO2-NPs with ethanol,
- drying the ethanol washed CS-MnO2-NPs over a water bath, at a temperature in the range of 105 oC to 110 oC to obtain dried CS-MnO2-NPs,
- calcinating the dried CS-MnO2-NPs in a muffle furnace at a temperature of 300 oC for 2 h to obtain pure black coloured CS-MnO2-NPs,
wherein said CS-MnO2-NPs are used as photocatalysts for the degradation of methylene blue dye in wastewater treatment.

9. A green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) obtained by the process as claimed in claim 1, wherein said green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) are used as photocatalyst for degradation of methylene blue dye in the wastewater treatment.

10. The green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) obtained by the process as claimed in claim 1, wherein said green synthesized Citrus sinensis seed extract assisted MnO2 nanoparticles (CS-MnO2-NPs) have 97% removal efficiency of 100 ppm methylene blue dye at optimum conditions of pH 3 at contact time of 90 minutes with the CS-MnO2-NPs dosage of 50 mg.