Enhanced photocatalytic activity of zinc sulfide nanoparticles toward visible region

Abstract

The patent application pertains to enhancing the photocatalytic activity of zinc sulfide nanoparticles in the visible light spectrum by utilizing a hybrid material comprising hexamine, silicotungstic acid, and nickel. This innovative approach aims to overcome the traditional limitations associated with zinc sulfide nanoparticles' suboptimal performance in response to visible light. The hybrid material's unique composition alters the optical response range of the zinc sulfide nanoparticles, enhancing their efficiency in utilizing visible light for photocatalysis. By incorporating hexamine, silicotungstic acid, and nickel onto the surface of the zinc sulfide nanoparticles, the resultant hybrid material demonstrates improved photocatalytic activity towards visible light, surpassing the constraints of unmodified zinc sulfide nanoparticles.

Description

DescriptionTitle of Invention: ENHANCED PHOTOCATALYTIC ACTIVITY OF ZINCSULFIDE NANOPARTICLES TOWARD VISIBLE REGION.Technical Field

[0001] The present disclosure generally relates to modifying zinc sulfide nanoparticles and more specifically, modifying zinc sulfide nanoparticles with hexamine- silicotungstic acid-nickel hybrid to enter the visible region.Background Art

[0002] This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.

[0003] Zinc sulfide (ZnS) is recognized as a significant semiconductor photocatalyst renowned for its band gap energy of 3.54 eV. Zinc sulfide nanoparticles have garnered attention as potent photocatalysts due to their unique properties and potential applications in various fields. However, a limitation often observed with zinc sulfide nanoparticles is their suboptimal photocatalytic activity in the visible region of the light spectrum, thereby restricting their overall efficiency.

[0004] In efforts to address the responsivity to the visible region, researchers have explored surface modifications of zinc sulfide nanoparticles with various materials to enhance their photocatalytic performance in the visible region.

[0005] In a study by Yu and colleagues, significant efforts were made to enhance the responsiveness of zinc sulfide to visible light. Yu et al. (2021 ) highlighted zinc sulfide's potential as a photocatalyst for water purification, despite its drawbacks of low photon efficiency and weak response to visible light. To overcome these challenges, the researchers introduced Ag2O to zinc sulfide, leveraging their respective energy band properties to create a novel ZnS / Ag2O composite photocatalyst. This composite structure not only enables efficient separation and transfer of charge carriers but also extends the optical response range of the catalyst, although it does not achieve complete responsiveness to visible light.

[0006] The preceding art has pinpointed a common challenge associated with zinc sulfide (ZnS) photocatalysts, specifically their low efficiency or limited response inthe visible region of the light spectrum. This limitation has led to rigorous exploration of methodologies to enhance the photocatalytic performance of ZnS, especially within the visible light range, to expand its utility in various applications such as water purification and environmental remediation.

[0007] One new approach to enhance ZnS's photocatalytic activity involves using a hybrid material comprising hexamine, silicotungstic acid, and nickel. This novel hybrid surface modification has shown potential in significantly improving the photocatalytic activity of zinc sulfide nanoparticles towards the visible region of the spectrum.

[0008] The hybrid material's unique composition and properties play a pivotal role in altering the optical response range of the zinc sulfide nanoparticles, thereby increasing their efficiency in harnessing visible light for photocatalysis. By effectively incorporating hexamine, silicotungstic acid, and nickel onto the surface of zinc sulfide nanoparticles, the resultant hybrid material demonstrates enhanced photocatalytic activity and extended functionality towards visible light, surpassing conventional limitations associated with unmodified zinc sulfide nanoparticles.Summary of Invention

[0009] The following provides a simplified summary of various aspects of the present disclosure to offer a basic understanding of such aspects. This summary is not an extensive overview of the disclosure and is not intended to identify key or critical elements of the disclosure, nor delineate any scope of the particular embodiments of the disclosure or any scope of the claims. Its sole purpose is to present some concepts of the disclosure in a simplified form as a prelude to the more detailed description that follows.

[0010] The present invention discloses a method for enhancing the photocatalytic activity of zinc sulfide nanoparticles in visible light using a hybrid of hexamine, silicotungstic acid, and nickel. The method involves preparing a hybrid precipitate of hexamine-silicotungstic acid-nickel and modifying zinc sulfide by combining the prepared precipitate with a cationic dye and zinc sulfide powder. The preparation of the hybrid precipitate involves dissolving hexamine, silicotungstic acid, and a colored nickel salt in a solvent to form a mixture. The modification of zinc sulfideincludes adjusting the acidity of the mixture with methyl blue, introducing nano zinc sulfide, and separating the formed precipitate using the coprecipitation method.

[0011] Furthermore, the disclosure describes a modified zinc sulfide powder exhibiting photocatalytic activity in the visible spectrum, composed of zinc sulfide, hexamine, silicotungstic acid, and nickel. The particle size of the zinc sulfide powder ranges from 90-150 nanometers, with zinc sulfide, silicotungstic acid, and hexamine composition percentages in the modified powder falling in the ranges of 45-55%, 35-43%, and 7-8%, respectively.Technical Problem

[0012] The primary technical problem addressed by the present invention involves the suboptimal photocatalytic activity of zinc sulfide (ZnS) nanoparticles in the visible region of the light spectrum, which limits their overall efficiency as photocatalysts.

[0013] Researchers have recognized this limitation and have undertaken efforts to enhance the responsivity of zinc sulfide to visible light in order to broaden its utility in applications such as water purification and environmental remediation. This problem has led to extensive exploration of surface modifications and hybrid material compositions to improve the photocatalytic performance of zinc sulfide nanoparticles within the visible light range, thus overcoming the challenges of low efficiency and weak response to visible light exhibited by unmodified zinc sulfide photocatalyst.Solution to Problem

[0014] The present invention provides an innovative solution to the technical problems associated with the photocatalytic activity of zinc sulfide nanoparticles in the visible region of the light spectrum, leading to a limitation in their overall efficiency. Despite being recognized for their band gap energy and potential applications, zinc sulfide nanoparticles exhibit weak responsiveness to visible light, hindering their effectiveness as photocatalysts for various purposes.

[0015] Researchers have recognized this challenge and have explored surface modifications using different materials to enhance the photocatalytic performance of zinc sulfide nanoparticles, particularly in the visible light range, in this patent, efforts have been made to overcome the limitations of zinc sulfide's low efficiency and weak response to visible light through innovative approaches like introducinghybrid materials such as hexamine, silicotungstic acid, and nickel. These surface modifications aim to alter the optical response range of zinc sulfide nanoparticles, thereby improving their photocatalytic activity and expanding their utility in applications such as water purification and environmental remediation.Advantageous Effects of Invention

[0016] The advantageous effect of the invention described in the text is the significant improvement in the photocatalytic activity of zinc sulfide nanoparticles, particularly in the visible region of the light spectrum. Introducing a hybrid material comprising hexamine, silicotungstic acid, and nickel onto the surface of zinc sulfide nanoparticles, enhance the efficiency of these nanoparticles in harnessing visible light for photocatalysis. This modification not only alters the optical response range of the zinc sulfide nanoparticles, but also extends their functionality towards visible light, surpassing the limitations typically associated with unmodified zinc sulfide nanoparticles.

[0017] Furthermore, the hybrid material's unique composition and properties play a crucial role in boosting the photocatalytic performance of zinc sulfide nanoparticles, potentially enabling their application in various fields requiring efficient photocatalysis, such as water purification and environmental remediation. This enhanced efficiency in utilizing visible light for photocatalysis represents a significant advancement in the field, offering a solution to the suboptimal photocatalytic activity of zinc sulfide nanoparticles in the visible region and thereby expanding their potential utility and effectiveness in practical applications.Brief Description of Drawings

[0018] New features of the present invention are set forth with characteristic features in the attached claims. A better understanding of the features and advantages of the present invention will be available through reference to the following detailed description, which sets forth representative embodiments in which the principles of the present invention are utilized, and to the accompanying drawings

[0019] [FIG. 1] illustrates a flowchart of a method for modifying zinc sulfide by using hexamine- silicotungstate acid -nickel hybrid, consistent with one or more exemplary embodiments of the present disclosure.

[0020] [FIG. 2] illustrates an infra-red (IR) spectrum of ZnS, STA, ZnS-STA-HMT and HMT respectively from top to bottom, consistent with one or more exemplary embodiments of the present disclosure

[0021] [FIG. 3] illustrates an XRD pattern of ZnS-STA-HMT-Ni, ZnS and STA-HMT respectively from top to bottom, consistent with one or more exemplary embodiments of the present disclosure.

[0022] [FIG. 4] illustrates a scanning electron microscopy (SEM) image of zinc sulfide and zinc sulfide-silicotungstic acid-hexamine-nickel, consistent with one or more exemplary embodiments of the present disclosure.

[0023] [FIG. 5] illustrates EDS in conjunction with SEM of zinc sulfide-silicotungstic acid-hexamine-nickel, consistent with one or more exemplary embodiments of the present disclosure.

[0024] [FIG. 6] illustrates a diffuse reflectance spectrum (DRS) of zinc sulfide photocatalyst, zinc sulfide-silicotungstic acid-hexamine-nickel (ZnS-STA-HMT-Ni) photocatalyst and silicotungstic acid-hexamine-nickel (STA-HMT-Ni), consistent with one or more exemplary embodiments of the present disclosure.

[0025] [FIG. 7] illustrates a Tauc plot for zinc sulfide photocatalyst zinc sulfide- silicotungstic acid-hexamine-nickel (ZnS-STA-HMT-Ni) and silicotungstic acid- hexamine-nickel (STA-HMT- Ni), consistent with one or more exemplary embodiments of the present disclosure.

[0026] [FIG. 8] illustrates a gap energy and excitation wavelength of silicotungstic acid, silicotungstic acid-hexamine-nickel zinc sulfide and zinc sulfide-silicotungstic acid- hexamine-nickel, consistent with one or more exemplary embodiments of the present disclosure.

[0027] [FIG. 9] illustrates an absorption spectrum of 25 ml Rhodamine B solution (15 mg / l) with pH equal to 9 in the presence of 0.02 g zinc sulfide under sunlight, consistent with one or more exemplary embodiments of the present disclosure.

[0028] [FIG. 10] illustrate an absorption spectrum of 25 ml Rhodamine-B solution with a concentration of 5 ppm at pH 9 under sunlight, consistent with one or more exemplary embodiments of the present disclosure.Description of Embodiments

[0029] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the relevant teachings. However, it should be apparent that the present teachings may be practiced without such specific details. In other instances, well-known methods, procedures, components, and circuitry have been described in a manner that will be readily understood by those skilled in the art, in order to avoid unnecessarily obscuring aspects of the present teachings.

[0030] This detailed description is intended to enable a person skilled in the art to make and use the methods and devices disclosed in exemplary embodiments of the present invention. For explanatory purposes, specific nomenclature is used to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not required to practice the disclosed exemplary embodiments. Descriptions of specific exemplary embodiments are provided as representative examples. Various modifications to the exemplary embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the present invention. The present invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0031] The following detailed description provides a comprehensive overview of the novel material and method disclosed for enhancing the photocatalytic activity of zinc sulfide nanoparticles in the visible region through surface modification with a hybrid of hexamine, silicotungstic acid, and nickel. The process involves the precise utilization of hexamine (HMT), silicotungstic acid (ST A), and nickel to modify zinc sulfide and enhance its photocatalytic properties.

[0032] FIG. 1 presents an overview of the method for modifying zinc sulfide using the hexamine- silicotungstate acid -nickel hybrid serving as a reference for the subsequent detailed description. The exemplary method outlined in FIG. 1 entails essential steps including the preparation of a precipitate of the hexamine- silicotungstic acid-nickel hybrid 110, and the modification of zinc sulfide nanoparticles by mixing the prepared precipitate from step 110, with a cationic dye and zinc sulfide nanoparticles120.

[0033] The comprehensive method outlined in FIG.1 serves as a foundational guide for modifying zinc sulfide nanoparticles in accordance with one or more embodiments of the disclosed invention. It provides a comprehensive overview of the key steps involved in the process, starting from the preparation of the hybrid precipitate to the final modification of zinc sulfide nanoparticles. Further elucidation of each step will be provided in the subsequent sections to ensure clarity and understanding.

[0034] The process of producing the precipitate of the hexamine-silicotungstic acid- nickel hybrid, as depicted in FIG. 1 , initiates with step 110. In this step, hexamethylenetetramine (HMT) is dissolved in ethanol to create mixture No.1 , while nickel salts are dissolved in distilled water to form mixture No.2. Various colored nickel salts can be employed, including but not limited to nickel acetate, nickel nitrate, nickel chloride, nickel nitrate hexahydrate, nickel hydroxide, and nickel fluoride. In a specific embodiment, nickel (II) nitrate hexahydrate (Ni (NO3)2.6H2O) is utilized as the nickel salt.

[0035] In one exemplary embodiment according to the present disclosure, mixture No.2 may be added drop by drop to mixture No.1 over the controlled duration of 10 minutes to form mixture No.3.

[0036] Continuing to Step 110, silicotungstic acid may be dissolved in ethanol to prepare a mixture No.4, which is gradually added drop by drop to mixture No.3 over a specified period of 10 minutes with continuous stirring to create mixture No.5. Mixture No.5 is stirred for 3 hours at 900 rpm, and the resulting precipitate is separated by centrifuge, then dried at 100°C for 3 hours to obtain the desired precipitate of the hexamine-silicotungstic acid-nickel hybrid.

[0037] Moving on to step 120, for modifying nano zinc sulfide, the prepared precipitate may be added to a solution containing methyl blue to adjust the PH within the range of 2-4.

[0038] In one specific embodiment, the prepared precipitate is added to a solution containing methyl blue to precisely adjust the pH to 2.5, forming mixture No.6, which is then stirred for 45 minutes. Subsequently, zinc sulfide nanoparticles with a particle size of 40 nm are introduced into mixture No.6 and stirred for 6 hours toform a precipitate. The resulting precipitate is separated and dried at a controlled temperature of 100°C for 3 hours to produce the modified zinc sulfide.

[0039] Subsequent experiments were conducted to analyze the structure of the modified zinc sulfide and its response to visible light compared to unmodified zinc sulfide.

[0040] FIG. 2 presents the infra-red (IR) spectrum of ZnS, STA, ZnS-STA-HMT and HMT arranged from top to bottom, in accordance with one or more exemplary embodiments of the present disclosure.

[0041] In a specific exemplary embodiment, the modified zinc sulfide's IR spectrum, as depicted in FIG. 2, showcases distinctive peaks associated with hexamine and silicotungstic acid. Notably, strong absorption peaks in the range of 750-1 100 cm-1indicate the presence of SiW^C o4-anions featuring the Keggin structure. Specific peaks at 795, 885, 970, and 920 cm-1correspond to W-Oc-W, W-Ob-W, W-Od, and Si-0 stretching modes. Furthermore, the peak at around 1260cm-1corresponds to the CH2 vibration of hexamine.

[0042] FIG. 3 depicts an XRD pattern of ZnS-STA-HMT-Ni, ZnS and STA-HMT displayed from top to bottom. In a particular exemplary embodiment, to verify structural modifications, X-ray diffraction patterns of zinc sulfide, silicotungstic acid- hexamine, and zinc sulfide-silicotungstic acid-hexamine-nickel have been examined. The peaks attributed to silicotungstic acid-hexamine are denoted as S- H, while those corresponding to zinc sulfide are labeled as Z in FIG. 3, aligning with one or more exemplary embodiments of the present disclosure.

[0043] FIG. 4 presents scanning electron microscopy (SEM) images of zinc sulfide and zinc sulfide-silicotungstic acid-hexamine-nickel at different magnifications. Specifically, SEM image of zinc sulfide at a magnification of 25600x (420), SEM image of Zinc sulfide at a magnification of 51200x 440, SEM image of zinc sulfide- silicotungstic acid-hexamine-nickel at a magnification of 25600x 410, and SEM image of zinc sulfide-silicotungstic acid-hexamine-nickel at a magnification of 51200x 430 are presented. The scanning electron microscope (SEM) images provide insight into the morphology of the hybrid structure, revealing the composition and arrangement of nanoparticles. A comparative analysis of these images aids in comprehending the distribution of the silicotungstic acid-hexamine-nickel hybrid on the zinc sulfide nanoparticle surface, in line with one or more exemplary embodiments of the present disclosure.

[0044] FIG. 5 illustrate an Energy Dispersive X-ray Spectroscopy (EDS) analysis, in conjunction with Scanning electron Microscopy (SEM). The EDS and SEM tests was conducted at two specific points on the hybrid zinc sulfide hexamine silicotungstic acid nickel. The analysis revealed the presence of zinc, sulfide, nickel, tungstate, and hexamine in the modified zinc sulfide powder at these two points.

[0045] The average nanoparticle size was determined using the Debye-Scherrer formula alongside the diffraction pattern analysis(X-ray). The Debye-Scherrer formula is:

[0046] In the Debye-Scherrer formula D is the nanoparticles crystalline size, K represents the Scherrer constant (0.98), A denotes the wavelength (1.54) and [3 denotes the full width at half maximum (FWHM). In one embodiment, the average size range of the modified nanoparticles is between 90-150 nanometers.

[0047] FIG. 6 illustrates a diffuse reflectance spectrum (DRS) of zinc sulfide photocatalyst 610, zinc sulfide-silicotungstic acid-hexamine-nickel (ZnS-STA- HMT-Ni) photocatalyst 620 and silicotungstic acid-hexamine-nickel (STA-HMT-Ni) 630.

[0048] band gap energy calculated by using Tauc's diagram FIG. 7, which is drawn from the diffuse reflection spectrum FIG. 6. The band gap energy indicating a shift towards visible light for the modified zinc sulfide compared to its unmodified counterpart.

[0049] FIG. 7 displays the Tauc diagram drawn using the diffuse reflectance spectrum. The gap energy is determined through the Tauke diagram. The Tauc diagram for the zinc sulfide photocatalyst 710, zinc sulfide-silicotungstic acid-hexamine-nickel (ZnS-STA-HMT-Ni) 720, and silicotungstic acid-hexamine-nickel (STA-HMT-Ni) 730.

[0050] The desired spectrum is recorded in the wavelength range of 300 to 900 nm.The Tauc diagram is drawn in the form of (c / itf)2in terms of M, where a represents the absorption coefficient and h-9 represents the excitation energy. To calculate theband gap energy, a tangent line is drawn on the Tauc curve and the horizontal axis. The point of their intersection signifies the band gap energy. FIG. 8 illustrates the values of gap energy and corresponding wavelengths for Silicotungstate acid, silicotungstic acid-hexamine-nickel, zinc sulfide, and Zinc sulfide-silicotungstic acid-hexamine-nickel.

[0051] In the described embodiment, zinc sulfide-silicotungstic acid-hexamine-nickel exhibits a reduced band gap energy compared to unmodified zinc sulfide photocatalyst. Furthermore, the wavelengths were determined using the formula A=1240 / Eg, where Egrepresents the band gap energy in electron volts (eV) and A denotes the wavelength in nanometers. The calculated wavelength for zinc sulfide photocatalyst is 775 nm in the visible spectrum, indicating a shift in its photocatalytic efficiency from the ultraviolet to the visible range due to the modification with silicotungstic acid-hexamine-nickel. This shift suggests an enhancement in the material's photocatalytic properties for processes reliant on visible light. In FIG. 8, more detailed information on the band gap energies and corresponding wavelengths for both materials is depicted.ExamplesEXAMPLE 1 : Preparation of Modified Zinc Sulfide:

[0052] In a particular embodiment as illustrated in FIG.1 , the method in step 110 may begin by dissolving 0.1 g of hexamethylenetetramine (HMT) in 5ml of ethanol to create mixture No.1. Following this, 0.2066g of nickel (II) nitrate hexahydrate (Ni (NO3)2.6H2O) may be dissolved in 5ml of distilled water to generate mixture No.2. The mixture No.2 can be gradually added drop by drop to mixture No.1 over a controlled duration of 10 minutes, resulting in mixture No.3. Subsequently, 1.03g of silicotungstic acid (ST A) may be dissolved in 5ml of ethanol to prepare mixture No.4. Mixture No.4 can be added drop by drop to mixture No.3 over a specified period of 10 minutes with continuous stirring to create mixture No.5.

[0053] Mixture No.5 may be stirred for 3 hours at 900 rpm, following which the precipitate is separated from mixture No.5 through centrifugation and dried at 100°C for 3 hours to obtain the desired HMT-STA-nickel hybrid precipitate.

[0054] In another embodiment depicted in FIG. 1 (step120), to modify nano zinc sulfide, 0.195g of the hybrid material is introduced into a solution comprising 50ml of methylblue (134mg / l) to adjust the solution's pH to 2.5, forming mixture No.6, which is then stirred for 45 minutes. Subsequently, 0.195g of zinc sulfide nanoparticles with a particle size of 40 nm are added to mixture No.6 and stirred for 6 hours to induce precipitation. The resulting precipitate from mixture No.6 is separated and dried at 100°C for 3 hours to obtain the modified zinc sulfide.EXAMPLE 2: percentage of materials in modified zinc sulfide powder:

[0055] In a specific embodiment, the composition of modified zinc sulfide powder includes 50.3% ZnS, 39.1 % STA, 7.6% HMT, 1.6% nickel, and 1.4% other compounds.EXAMPLE 3: Decolorization Using Zinc Sulfide:

[0056] The decolorization procedure entailed treating a 25 ml solution of Rhodamine B with a concentration of 5 mg / l at pH 0.9 while utilizing 0.02 g of zinc sulfide photocatalyst, as illustrated in FIG. 9. The results indicate that zinc sulfide exhibits restricted photocatalytic effectiveness against Rhodamine B at pH 0.9.EXAMPLE 4: Decolorization Utilizing Zinc Sulfide-Silicotungstic Acid- Hexamine-Nickel Hybrid:

[0057] Rhodamine B, with a pKa of 3.1 , predominantly exists in its neutral state at pH levels above 3.1 , leading to minimal adsorption on the surface of the compound. However, at acidic pH levels below 3.1 , Rhodamine B transforms into a cationic form, enhancing its affinity for surface adsorption.

[0058] To assess the photocatalytic performance of the zinc sulfide-silicotungstic acid- hexamine-nickel hybrid, decolorization trials of Rhodamine B solution were carried out under sunlight at pH 9 to confirm that color elimination solely resulted from the photocatalyst and not surface adsorption.

[0059] Three comparative experiments were conducted to assess the photocatalytic efficiency of the modified zinc sulfide in degrading Rhodamine B dye at a concentration of 5 ppm and pH 9, utilizing varying quantities of the modified zinc sulfide, specifically 0.01 and 0.02 grams. These experiments were performed under sunlight conditions, and the results are elaborated in FIG. 10 of the patent document.

Claims

AMENDED CLAIMS received by the International Bureau on 01 March 2025 (01.03.2025)

1. A method for enhancing the photocatalytic activity of zinc sulfide nanoparticles to the visible region by modifying them with a hexamine-silicotungstic acid-nickel hybrid, comprising steps of: a) preparing a precipitate of hexamine-silicotungstic acid-nickel hybrid utilized co-precipitation method; and b) modifying zinc sulfide nanoparticles by mixing the prepared precipitate from step (a) with a cationic dye and zinc sulfide nanoparticles to prepare modified zinc sulfide nanoparticles, wherein the hexamine-silicotungstic acid-nickel precipitate is prepared using at least one colored nickel salts; wherein the modified zinc sulfide nanoparticles, demonstrating photocata lytic activity in the visible region, comprise zinc sulfide, hexamine, silicotungstic acid, and nickel.

2. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claim 1, wherein the colored nickel salts further comprising nickel acetate, nickel nitrate, nickel chloride, nickel nitrate hexahydrate, nickel hydroxide, and nickel fluoride.

3. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claims 1 and 2, wherein the utilized nickel salt is nickel nitrate hexahydrate.

4. The method for enhancing the photocatalytic activity of zinc sulfide nanoparticles according to claim 1, wherein modifying zinc sulfide nanoparticles further comprises steps of: c) mixing the prepared precipitate from step (a) with the cationic dye to form a mixture No.1; d) adding zinc sulfide nanoparticles to mixture No.l, separating a precipitate, and preparing modified ZnS nanoparticles.

5. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claims 1 and 4, wherein the mixture No.l has a pH range between 2 and 4.

6. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claims 1 and 4 , wherein the utilized cationic dye is methyl blue.

7. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claim 1, wherein the modified zinc sulfide nanoparticles have a particle size in the range of 90-150 nanometers.

8. The method for enhancing the photocatalytic activity of zinc sulfide nanoparticles according to claim 1, wherein the modified zinc sulfide nanoparticles contain zinc sulfide in an amount ranging from 45% to 55% by weight.

9. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claim 1, wherein the modified zinc sulfide nanoparticles contain silicotungstic acid in an amount ranging from 35% to 43% by weight.

10. The method for enhancing the photocatalytic activity of zinc sulfide nanoparticles according to claim 1, wherein the modified zinc sulfide nanoparticles contain hexamine in an amount ranging from 7% to 8% by weight.

11. The method for enhancing the photocata lytic activity of zinc sulfide nanoparticles according to claim 1, wherein the modified zinc sulfide nanoparticles contain nickel in an amount ranging from 1% to 2.5% by weight.

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