Preparation method of'monatomic + cluster 'co-modified CdS photocatalyst capable of decomposing pure water into hydrogen

Abstract

The invention discloses a preparation method of a'monatomic + cluster 'co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen, and relates to the field of catalyst hydrogen production. Cadmium-containing wastewater and H2S-containing waste gas are used as raw materials, cheap metals such as Fe, Ni and Co are further introduced, and by means of a precipitation-photoreduction strategy, the single atom and cluster co-modified CdS photocatalyst is prepared. The cadmium sulfide catalyst material which internally contains a twin crystal structure, has Fe, Ni and Co monatomic on the surface layer and is co-modified by catalytic sites such as clusters formed by the transition metals is prepared, and the cadmium sulfide catalyst material is marked as Z / W-CdS (FeCoNi) SA + C. XRD, diffuse reflection, Mott-Schottky, SEM, EDS and HRTEM are used for analyzing the crystal structure, the energy band energy level position and the morphology microstructure of a prepared sample, and it is proved that the Z / W-CdS (FeCoNi) SA + C material is successfully prepared. A hydrogen production test shows that under the condition of visible light irradiation, the hydrogen production rate of the Z / W-CdS (FeCoNi) SA + C material reaches 3.0253 mmol.h <-1 >. G <-1 >, which is far superior to the performance of various unitary and binary transition metal modified catalysts, and the hydrogen production performance of the Z / W-CdS (FeCoNi) SA + C material is improved by 87.9 times compared with that of a transition metal-free modified Z / W-CdS catalyst.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst hydrogen production, and specifically relates to a method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen. Background Art

[0002] To achieve the goals of carbon peak and carbon neutrality and address energy shortages and environmental pollution, developing clean, green, and sustainable new energy sources is crucial. Hydrogen, with its abundant resources (water is rich in hydrogen), high calorific value (combustion heat is three times that of gasoline of the same mass), and zero-pollution combustion products (combustion products are water, with no carbon emissions), is widely considered the ideal green energy carrier of the new century. Therefore, how to scientifically identify and find reliable hydrogen production routes to ensure an environmentally friendly, economical, safe, and efficient hydrogen supply has become a key scientific issue. This is also fundamental to ensuring that the industrial chain of a "hydrogen energy society" is both well-developed and well-established. Compared to numerous gray and blue hydrogen production technologies, hydrogen production technology that utilizes solar energy as a power source to drive catalytic water splitting is considered humanity's ultimate dream of new energy because it can truly achieve "zero energy consumption" and "zero pollution" hydrogen production. However, preparing highly active photocatalysts remains a long-term and arduous challenge. Among various photocatalytic materials, CdS catalyst is considered one of the most promising due to its suitable band structure and high visible light response. However, in the application of photocatalytic decomposition of pure water to produce hydrogen, the defects of easily causing photocorrosion and rapid recombination of photogenerated carriers have restricted the research and development of CdS catalysts. This is the key and difficult problem in realizing the actual development and application of "solar hydrogen".

[0003] In recent years, the international academic community has conducted a series of fruitful explorations into functional modification strategies, such as the construction of protective layers and the combination of co-catalysts. However, protective layer materials have also been found to be a double-edged sword. While they can alleviate the problem of photocorrosion of the catalyst, they also increase the difficulty for photogenerated carriers to penetrate the protective layer and reach the reaction sites. Considering that CdS is often used as the core material in core-shell photocatalytic systems, the designed protective layer material should be thin. If assembled to a thickness of several atoms, it is expected to significantly reduce the negative impact of the protective layer material on the water splitting process. In addition, the surface atomic ratio of the active component in traditional nanoparticle-based co-catalyst materials is relatively low, resulting in fewer active sites and limited addition effect to the catalytic system. Theoretically, if the active component in the co-catalyst material is reduced to a single atom, the utilization rate of the surface active sites on the catalyst can be increased to 100%. In recent years, single-atom catalysts (SACs) have shown great potential in improving the performance of photocatalytic hydrogen production and have made significant progress. Compared with traditional nanoparticle-type co-catalysts, the atomically dispersed single-atom active sites on the surface of photocatalysts can effectively enhance the separation of charge carriers and provide efficient hydrogen evolution sites. Therefore, the work of optimizing the performance of photocatalysts using precious metal SACs such as Au, P, and Pd has been widely recognized. However, in order to efficiently and stably decompose water to produce hydrogen, it is necessary to take into account the rate-controlling steps such as water adsorption and dissociation. Zhang Jiankang's research group used atomic layer deposition technology (ALD) to implant Pt clusters (C) and Pt single atoms (SA) within a certain distance on the surface of CdS catalysts. The two significantly improved the adsorption, dissociation and desorption of water, respectively. Ultimately, this "SA+C" dual active site efficiently and synergistically promoted the photocatalytic hydrogen production process. However, the ALD synthesis process requires highly precise control and strict synthesis conditions, which is obviously contrary to the green production concept of energy saving, environmental protection, and easy operation. And considering the problems of limited reserves and high costs of precious metals, how to use a simple and economical synthesis method to prepare cheap metal "SA+C" dual active sites is obviously more practical. Summary of the Invention

[0004] The purpose of the present invention is to solve the above technical problems and provide a method for preparing a "single atom + cluster" co-modified CdS photocatalyst that can decompose pure water to produce hydrogen.

[0005] The preparation method of the "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen of the present invention is carried out according to the following steps:

[0006] Cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate were added to a reactor and stirred evenly. A 1% hydrogen sulfide / argon mixture was introduced and reacted under light conditions until the solution became a suspension. The solution was allowed to stand until the layers separated. The lower layer of suspension was removed, washed, centrifuged, and dried to obtain Z / W-CdS(FeCoNi). SA+C catalyst.

[0007] Furthermore, the mass volume ratio of the cadmium acetate, deionized water, nickel sulfate, cobalt nitrate and ferric nitrate is 0.1-1 g:50-100 mL:0.016-0.16 g:0.014-0.14 g:0.013-0.13 g.

[0008] Furthermore, the mass volume ratio of the cadmium acetate, deionized water, nickel sulfate, cobalt nitrate and ferric nitrate is 0.5 g:80 mL:0.026 g:0.024 g:0.033 g.

[0009] Furthermore, the mass concentration of the cadmium acetate solution is 0.00125-0.0125 g / mL.

[0010] Furthermore, the flow rate of the hydrogen sulfide / argon mixed gas is controlled to be 0.1-0.5 mL·min -1 .

[0011] Furthermore, the washing and centrifugation are both performed using deionized water for washing and centrifugation, the deionized water washing is repeated twice, and the third time the washing and centrifugation is performed using anhydrous ethanol.

[0012] The present invention uses cadmium-containing wastewater and H2S-containing waste gas as raw materials, further introduces cheap metals such as Fe, Ni, and Co, and uses a precipitation-photoreduction strategy to prepare a cadmium sulfide catalyst material with catalytic sites co-modified with a twin structure (Z / W) inside, Fe, Ni, and Co single atoms (SA) on the surface, and clusters (C) formed by the above transition metals. The material is labeled Z / W-CdS(FeCoNi). SA+C The crystal structure, energy band position, morphology and microstructure of the prepared samples were analyzed by XRD, diffuse reflectance, Mott-Schottky, SEM, EDS and HRTEM, which confirmed that Z / W-CdS(FeCoNi) SA+C The material was successfully prepared. Compared with Z / W-CdS material, Z / W-CdS(FeCoNi) SA+C The material exhibits a narrower band gap of 2.3eV and a more suitable band structure E CB (vs SHE)=-0.36V,E VB (vs SHE)=+1.94V. When excited by light, Z / W-CdS(FeCoNi) SA+CThe internal electric field formed by the twin structure inside the material provides the thermodynamic driving force for the reaction, and the ternary metal clusters and single-atom catalytic sites on the surface provide active sites for the kinetic processes such as "water adsorption-water dissociation-hydrogen and hydrogen peroxide generation". This dual optimization of thermodynamics and kinetics was further tested on the prepared catalyst material for photocatalytic decomposition of seawater to produce hydrogen. It was found that under visible light irradiation, Z / W-CdS(FeCoNi) SA+C The hydrogen production rate of the material reached 3.0253mmol·h -1 ·g -1 , which is far superior to the performance of various single and binary transition metal modified catalysts, and its hydrogen production performance is 87.9 times higher than that of the Z / W-CdS catalyst without transition metal modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Z / W-CdS(A) and Z / W-CdS(FeCoNi) SA+C (B) XRD pattern of the catalyst;

[0014] Figure 2 Z / W-CdS and Z / W-CdS(FeCoNi) SA+C UV-visible diffuse reflectance spectrum of the sample (A) and the corresponding energy band conversion spectrum (B); Z / W-CdS(FeCoNi) SA+C Mott-Schottky curve of the sample (C); Z / W-CdS(FeCoNi) SA+C Distribution diagram of energy level and band positions within the sample (D);

[0015] Figure 3 SEM images (A, B), EDX-Mapping images (CE) and EDS images (F) of the Z / W-CdS sample;

[0016] Figure 4 Z / W-CdS(FeCoNi) SA+C SEM images (A, B), EDX-Mapping images (CH) and EDS images (I) of the samples;

[0017] Figure 5 Z / W-CdS(FeCoNi) SA+C HRTEM images (A, B), HAADF-STEM (C), and EDX-Mapping images (DH) of the samples;

[0018] Figure 6 The performance diagram of photocatalytic decomposition of pure water to produce hydrogen for different samples;

[0019] Figure 7 Z / W-CdS(FeCoNi) SA+CDiagram of the material's photocatalytic decomposition of pure water to produce hydrogen. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention more clearly understood, the spirit of the contents disclosed in the present invention will be described in detail below. After understanding the embodiments of the contents of the present invention, any technician in the relevant technical field can change and modify the contents of the present invention based on the techniques taught by the contents of the present invention without departing from the spirit and scope of the contents of the present invention.

[0021] The exemplary embodiments of the present invention and the description thereof are used to explain the present invention but are not intended to limit the present invention.

[0022] Example 1

[0023] Preparation of catalyst materials by "precipitation-photochemical reduction" method

[0024] 1. Preparation of Z / W-CdS catalyst

[0025] In this example, cadmium sulfide catalyst was prepared by chemical precipitation. 0.5 g of cadmium acetate was added to 80 mL of water and placed in a reactor. The reactor was placed on a magnetic stirrer and stirred evenly. At the same time, a 1% hydrogen sulfide / argon mixed gas was introduced from the reactor inlet (the flow rate was controlled at 0.2 mL min). -1 ) and allowed to react at room temperature for one hour. The solution gradually changed from a colorless, clear solution to a yellow suspension. After the reaction was complete, the reactor was allowed to stand for one hour. Once the solution clearly separated, the supernatant was poured out and the lower suspension was poured into a centrifuge tube. The tube was then washed with deionized water and centrifuged. This was repeated twice with deionized water, followed by a third wash and centrifugation with anhydrous ethanol. After centrifugation, the tube was oven-dried to obtain the Z / W-CdS powder catalyst.

[0026] 2. Preparation of Z / W-CdS(FeCoNi)SA+C catalyst

[0027] The Z / W-CdS(FeCoNi)SA+C catalyst was prepared by precipitation-photoreduction strategy. 0.5 g of cadmium acetate, 80 mL of deionized water, 0.026 g of nickel sulfate, 0.024 g of cobalt nitrate, and 0.033 g of ferric nitrate were weighed and added to a reactor. The reactor was placed on a magnetic stirrer and stirred evenly. At the same time, a 1% hydrogen sulfide / argon mixture was introduced from the reactor inlet (the flow rate was controlled at 0.2 mL min). -1) and reacted under light for one hour. The solution was observed to gradually transform from a colorless, clear solution into a turbid suspension. After the reaction was completed, the reactor was allowed to stand for one hour. Once the solution clearly separated into separate layers, the supernatant was poured out and the lower suspension was poured into a centrifuge tube. The tube was then washed with deionized water and centrifuged. This was repeated twice with deionized water, followed by a third wash and centrifugation with anhydrous ethanol. After centrifugation, the tube was oven-dried to obtain a Z / W-CdS(FeCoNi)SA+C powder catalyst.

[0028] Figure 1 Figure A shows the XRD pattern of the Z / W-CdS catalyst synthesized by the precipitation-photoreduction method. By comparing with the cubic sphalerite card (PDF#10-0454) and the hexagonal wurtzite card (PDF#41-1049), it can be seen that the Z / W-CdS catalyst has characteristic peaks of both cubic and hexagonal phases. The 2θ values are 24.8°, 28.5°, 36.5°, 43.7°, 47.8°, 51.8°, and 66.9°, which correspond to the (100), (101), (102), (110), (103), (102), and (203) crystal planes of hexagonal CdS, respectively. At the same time, we note that the peak intensity at 26.5° is significantly greater than the peak intensities at 24.8° and 28.5°. This is due to the superposition of the peaks of the (111) crystal plane of the cubic phase and the (002) crystal plane of the hexagonal phase in Z / W-CdS. According to the Bragg equation, the interplanar spacing of the dominant growth plane (111) or (002) is 0.336nm. Figure 1 B found that after loading active sites such as Fe, Co, and Ni single atoms and clusters, the peak intensities of the cubic (111) and hexagonal (002) planes in Z / W-CdS were further enhanced, indicating that the modification of transition metal elements induced the further growth of these planes. Due to the low content of the two active species, single atoms and clusters, their characteristic peaks were not detected.

[0029] Figure 2 A shows: Compared with Z / W-CdS, Z / W-CdS(FeCoNi) SA+C The absorption edge of the catalyst has a significant red shift, indicating that the light absorption range of the modified cadmium sulfide catalyst is significantly larger than that of the pure cadmium sulfide catalyst. The Tauc plot method is used to calculate the energy band conversion spectrum of the sample ( Figure 2 B), we can see that the band gap of pure CdS catalyst sample is 2.34eV, and Z / W-CdS(FeCoNi) SA+C The band gap of the catalyst is 2.30eV. According to literature research, the narrower the band gap, the easier it is to absorb visible light. Therefore, the Z / W-CdS (FeCoNi) prepared in this example SA+CThe catalyst has better efficiency in utilizing sunlight.

[0030] In order to further understand the energy level and band position information of the catalyst, the Mott-Schottky test was performed on the catalyst. Figure 2 As shown in C, the slope of the test curve is positive, indicating that Z / W-CdS(FeCoNi) SA+C The catalyst is an n-type semiconductor. According to the band edge of the test curve, the conduction band position of the catalyst is deduced as: E CB (vs SHE) = -0.36V, and the valence band position is deduced from the bandgap width: E VB (vs SHE) = +1.94V. Since the Z / W-CdS material contains two crystal phases, the energy band position should be attributed to the average conversion value of the cubic phase and hexagonal phase CdS conduction band and valence band respectively. According to the literature research, H + / H2 reduction potential and H2O / H2O2 oxidation potential are 0V (vs SHE) and 1.80V (vs SHE), respectively. SA+C The catalyst has sufficient reduction and oxidation capabilities ( Figure 2 D), can decompose pure water into H2 and H2O2.

[0031] Figure 3 The SEM images (A, B), EDX-Mapping images (CE) and EDS images of the Z / W-CdS sample are shown. Figure 3 A shows that the morphology of Z / W-CdS catalyst is mainly agglomerate. Figure 3 The magnified part of the red circle in A shows that the particle size of the agglomerated material is relatively large, ranging from about 150 to 300 nm ( Figure 3 B). Figure 3 CE shows the distribution of Cd and S elements in the Z / W-CdS sample. It can be observed that the two elements are uniformly and orderly distributed inside the sample, proving that the preparation of the Z / W-CdS sample is successful. EDS test results ( Figure 3 F) further confirms this point.

[0032] Figure 4 Demonstrated Z / W-CdS(FeCoNi) SA+C SEM images (A, B), EDX-Mapping images (CE) and EDS images of the samples. Figure 4 A can be seen that Z / W-CdS(FeCoNi) SA+C The sample showed the morphology of nanoparticles. To further observe the particle size, we Figure 4 Magnified observation of the red circle in A reveals: Z / W-CdS(FeCoNi)SA+C The particle size distribution of the samples is between 20 and 40 nm ( Figure 4 B), the particle size is significantly smaller than that of Z / W-CdS sample. This indicates that Z / W-CdS(FeCoNi) SA+C The sample has a larger specific surface area and exhibits more active sites, which will be more conducive to the photocatalytic decomposition of pure water. Figure 4 CH demonstrated Z / W-CdS(FeCoNi) SA+C The distribution of various elements in the sample shows that Cd and S are uniformly and orderly distributed in the interior of the sample, while part of Fe, Co, and Ni are evenly distributed on the surface of the sample, and the other part is slightly agglomerated on the surface of the sample. This may be because Fe, Co, and Ni elements form single atom and cluster active sites on the surface of CdS, further confirming that Z / W-CdS(FeCoNi) SA+C The sample preparation was successful.

[0033] Figure 5 Demonstrated Z / W-CdS(FeCoNi) SA+C HRTEM images (A, B), HAADF-STEM (C), and EDX-Mapping images (DH) of the samples. SA+C Internal crystal structure observation of the sample ( Figure 5 A), it can be seen that the sample contains a twin structure (clear twin interface and SAED pattern with twin characteristics in the upper right corner), and the interplanar spacing is 0.336nm, which corresponds to the (111) crystal plane of the cubic phase or the (002) crystal plane of the hexagonal phase, which is consistent with the XRD observation results, indicating that CdS grows preferentially along the

[111] or

[002] direction, and once again confirms the Z / W-CdS(FeCoNi) SA+C The sample was successfully prepared. Z / W-CdS(FeCoNi) was further observed using a spherical aberration high-resolution electron microscope. SA+C Sample, found: the particle size of the species marked by the red circle in the sample is slightly larger than the size of the Cd atom ( Figure 5 B), indicating that the species may be a FeCoNi ternary metal cluster adsorbed on the surface of the CdS material. In addition, the atomic contrast of the blue circle marked area is low ( Figure 5 B), which may be caused by the formation of cadmium vacancies on the surface of CdS material. In order to further verify whether there are single-atom sites filling the cadmium vacancies, we further conducted EDX-Mapping observations ( Figure 5 CH), the study found that the large particle size material marked by the red circle is indeed composed of three elements: Fe, Co, and Ni ( Figure 5C, FH), confirming the existence of the ternary cluster structure; in the area marked by the blue circle, the three elements Fe, Co, and Ni are evenly distributed, confirming that the cadmium vacancies in this area are indeed filled with single atoms such as Fe, Co, and Ni ( Figure 5 C, FH). This research result once again confirmed that Z / W-CdS(FeCoNi) SA+C The material was prepared successfully.

[0034] Figure 6 The photocatalytic decomposition of pure water to produce hydrogen was demonstrated. Calculations show that the hydrogen production rate of the Z / W-CdS sample is only 0.0344 mmol·h -1 ·g -1 ; Z / W-CdS(Fe) modified with ferric nitrate SA+C The hydrogen production rate of the sample is 0.5695 mmol·h -1 ·g -1 ; Z / W-CdS(Co) modified with cobalt nitrate SA+C The hydrogen production rate of the sample is 0.7961 mmol·h -1 ·g -1 ; Z / W-CdS(Ni) modified with nickel sulfate SA+C The hydrogen production rate of the sample is 0.9399 mmol·h -1 ·g -1 ; Z / W-CdS(FeCo) modified by adding ferric nitrate and cobalt nitrate SA+C The hydrogen production rate of the sample is 0.823 mmol·h -1 ·g -1 ; Z / W-CdS(FeNi) modified with ferric nitrate and nickel sulfate SA+C The hydrogen production rate of the sample is 1.0329 mmol·h -1 ·g -1 ; Z / W-CdS(CoNi) modified with cobalt nitrate and nickel sulfate SA+C The hydrogen production rate of the sample is 1.1412 mmol·h -1 ·g -1 ; Z / W-CdS (FeCoNi) modified with Fe, Co, and Ni SA+C The hydrogen production rate of the sample is 3.0253 mmol·h -1 ·g -1 Compared with the samples modified with single metal, Z / W-CdS(FeCoNi) SA+C The hydrogen production performance of the samples was improved by more than 4 times; compared with the samples modified with binary metals, Z / W-CdS(FeCoNi) SA+CThe hydrogen production performance of each sample increased by more than 3 times, and was 87.9 times higher than that of the unmodified Z / W-CdS sample. Literature research indicates that metal clusters can efficiently adsorb and dissociate water molecules, and single-atom active sites can accelerate the hydrogen production reaction. The results of this test indicate that ternary metal clusters may exhibit higher water adsorption energies and lower water dissociation energies than mono- and binary metal clusters. Whether the three types of mixed single-atom sites exhibit lower Gibbs free energies for hydrogen production than mono- and binary single-atom sites requires further experimental and theoretical confirmation.

[0035] Figure 7 Demonstrated Z / W-CdS(FeCoNi) SA+C The photocatalytic decomposition of pure water to produce hydrogen by the sample is illustrated as follows: (1) When the catalyst is excited by light, the electrons inside the CdS material jump from the valence band to the conduction band, forming electron-hole pairs with the holes in the valence band. Driven by the type II homojunction electric field formed by the internal twin structure, the photogenerated electrons and holes are efficiently separated and transported to the surface of the material; (2) The photogenerated holes are further transferred to the ternary metal clusters. Since the ternary metal clusters have lower adsorption and dissociation energies for water, Z / W-CdS(FeCoNi) SA+C The ternary metal clusters on the surface of the material preferentially adsorb water molecules and dissociate them. The hydroxide ions generated by the dissociation react with the photogenerated holes in situ to produce hydrogen peroxide; (3) The hydrogen ions generated by the dissociation of water by the ternary metal clusters diffuse to the single-atom catalytic sites (Fe, Co, Ni); (4) At the same time, the photogenerated electrons transfer to the single-atom catalytic sites and react with the diffused hydrogen ions to produce hydrogen gas.

[0036] In summary, the internal electric field formed by the twin structure provides the thermodynamic driving force for the reaction; the ternary metal clusters and single-atom catalytic sites provide active sites for the kinetic processes of "water adsorption-water dissociation-hydrogen and hydrogen peroxide generation". This dual optimization of thermodynamics and kinetics ensures the Z / W-CdS(FeCoNi) SA+C The material can carry out photocatalytic decomposition of pure water efficiently and stably.

Claims

1. A method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen, characterized in that: It is done in the following steps: Cadmium acetate, deionized water, nickel sulfate, cobalt nitrate, and ferric nitrate were added to a reactor and stirred evenly. A 1% hydrogen sulfide / argon mixture was introduced and reacted under light conditions until the solution became a suspension. The solution was allowed to stand until the layers separated. The lower layer of suspension was removed, washed, centrifuged, and dried to obtain Z / W-CdS(FeCoNi). SA+C catalyst.

2. The method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen according to claim 1, characterized in that: The mass volume ratio of the cadmium acetate, deionized water, nickel sulfate, cobalt nitrate and ferric nitrate is 0.1-1 g:50-100 mL:0.016-0.16 g:0.014-0.14 g:0.013-0.13 g.

3. The method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen according to claim 1 or 2, characterized in that: The mass volume ratio of the cadmium acetate, deionized water, nickel sulfate, cobalt nitrate and ferric nitrate is 0.5 g:80 mL:0.026 g:0.024 g:0.033 g.

4. The method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen according to claim 1, characterized in that: The mass concentration of the cadmium acetate solution is 0.00125-0.0125 g / mL.

5. The method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen according to claim 1, characterized in that: The flow rate of the hydrogen sulfide / argon mixed gas was controlled to be 0.1-0.5 mL·min -1 .

6. The method for preparing a "single atom + cluster" co-modified CdS photocatalyst capable of decomposing pure water to produce hydrogen according to claim 1, characterized in that: The washing and centrifugation were both performed using deionized water for washing and centrifugation, and the deionized water was repeatedly used for washing twice, and anhydrous ethanol was used for washing and centrifugation for the third time.

Images