A preparation method of CdS-TA-PEI and its application in photocatalytic synthesis of hydrogen peroxide

Abstract

This invention discloses a method for preparing CdS-TA-PEI and its application in the photocatalytic synthesis of hydrogen peroxide. Under weakly alkaline conditions, this method utilizes a catechol and amine monomer to generate polyphenolic amines on the surface of CdS via oxidation-polymerization, constructing a novel heterojunction. In the presence of only water and oxygen, CdS-TA-PEI produces 4.01 mM H2O2 after 5 h of visible light irradiation, nearly 10 times that of CdS (0.43 mM). Experimental results demonstrate that the TA-PEI coating improves the hydrophilicity and charge mobility of CdS and inhibits photocorrosion, thereby effectively improving the stability and photoactivity of the photocatalyst. This structural design allows for the generation of H2O2 without sacrificing reagents, providing a green, sustainable, and environmentally friendly pathway for the efficient production of H2O2.

Description

Technical Field

[0001] This invention relates to the preparation of CdS-TA-PEI, which is applied to the field of green energy, represented by photocatalytic synthesis of hydrogen peroxide. Background Technology

[0002] H₂O₂ is a highly efficient and environmentally friendly oxidant, considered one of the world's 100 most important chemical substances, with an annual production exceeding 5.5 million tons. It has a high reactive oxygen species content, and in reactions it participates in, the only products are water (H₂O) and oxygen (O₂). As an environmentally friendly oxidant, H₂O₂ has wide applications in chemical synthesis, bleaching, water treatment, and disinfection. H₂O₂ is also considered an alternative liquid fuel with a higher energy density than compressed H₂, and is used in compact thin-film fuel cells.

[0003] Currently, over 95% of commercially available hydrogen peroxide is produced using the traditional anthraquinone (AQ) method (e.g.) Figure 1 This includes alkyl AQ hydrogenation and alkyl-anthracene hydroquinone (AHQ) oxidation using Pd as a catalyst. The disadvantages of the AQ method are the use of organic solvents and precious metals, involving expensive hydrogen intake, waste solvent treatment, and significant energy consumption. Furthermore, H2O2 can also be synthesized from H2 and O2 in the presence of a metal catalyst. However, the use of expensive precious metals and H2 gas limits its widespread application. Other methods for producing H2O2 include alcohol oxidation and electrochemical synthesis. However, these methods have drawbacks: they consume large amounts of energy, pollute the environment, and the mixing of organic impurities with H2O2 in the solution increases the difficulty of H2O2 purification.

[0004] Photocatalytic synthesis of H₂O₂ is a promising and cost-effective approach. Under the influence of sunlight and oxygen, a photocatalyst reacts in water to produce hydrogen peroxide. The synthesis requires only light, water, and oxygen. The photocatalyst converts green solar energy into chemical energy stored in H₂O₂. Cadmium sulfide, due to its suitable band edge position and narrow band gap, is suitable for photocatalytic hydrogen peroxide production. However, cadmium sulfide suffers from severe surface photocorrosion and rapid charge recombination, resulting in low photocatalytic efficiency and poor catalytic stability. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention constructs a protective layer on the surface of cadmium sulfide to reduce surface photocorrosion and improve the efficiency of photocatalytic hydrogen peroxide production. Tannic acid (TA) is a common natural polyphenol compound found in fruits and trees, possessing excellent metal chelating ability and strong interaction with amine-containing compounds. Therefore, this invention uses tannic acid (TA) crosslinked with polyethyleneimine (PEI) to prepare a polymer coating on the surface of cadmium sulfide, synthesizing a CdS-TA-PEI heterojunction catalyst. In the photocatalytic hydrogen peroxide production process, the TA-PEI coating can also serve as a protective layer to inhibit surface photocorrosion of cadmium sulfide, improving hydrophilicity and carrier transfer rate, providing a new strategy for developing artificial photosynthesis of hydrogen peroxide. In view of this, this invention provides a method for preparing CdS-TA-PEI, which includes the following steps:

[0006] Preparation of S1 and CdS: First, cadmium acetate dihydrate and sodium sulfide nonahydrate are uniformly dispersed in ethylene glycol and stirred evenly. Then, the mixture is transferred to a reaction vessel and subjected to hydrothermal reaction. After centrifugation, washing and drying, CdS is obtained.

[0007] Preparation of S2 and CdS-TA-PEI: CdS was dispersed in Tris-HCl solution, ultrasonically dispersed and stirred, and tannic acid was added to make it evenly mixed in water. Then, polyethyleneimine was added, and after stirring, it was filtered and dried to obtain CdS-TA-PEI.

[0008] The mass ratio of cadmium acetate dihydrate to sodium sulfide nonahydrate in S1 is 0.3-0.6:0.4-0.5.

[0009] The hydrothermal reaction temperature in S1 is 180-200℃, and the hydrothermal reaction time is 20-28h.

[0010] The mass ratio of CdS, tannic acid, and polyethyleneimine in S2 is 200-250:30-40:10-15.

[0011] The concentration of the Tris-HCl solution is 30-50 mM, and the pH is 8.5-9.5.

[0012] The stirring temperature is 10-70℃, and the stirring time is 6-24h.

[0013] The method described describes the application of CdS-TA-PEI in the photocatalytic synthesis of hydrogen peroxide from oxygen.

[0014] The method described describes the application of CdS-TA-PEI prepared in the photocatalytic synthesis of hydrogen peroxide from water.

[0015] The photocatalytic process is performed under visible light or the full spectrum, with a light intensity of 50-200 mW / cm².2 .

[0016] Based on the above research, this invention prepares CdS using a hydrothermal method, and then coats the CdS surface with a TA-PEI coating by adding tannic acid and polyethyleneimine monomer to a Tris-HCl buffer solution and undergoing oxidation-polymerization under specific temperature conditions. This method, by coating the CdS surface with the TA-PEI polymer, increases its hydrophilicity and carrier separation efficiency, thus inhibiting the decomposition of hydrogen peroxide by CdS. During the photocatalytic process, the interconversion of phenolic and quinone structures on the CdS-TA-PEI significantly improves the yield of hydrogen peroxide synthesized by photocatalysis. Compared to CdS, CdS-TA-PEI shows a significant improvement in both yield and stability per unit time. Attached Figure Description

[0017] Figure 1 Transmission electron microscopy (TEM) images of CdS-TA-PEI prepared in Example 1 and CdS prepared in Comparative Example 1.

[0018] Figure 2 The X-ray diffraction patterns of CdS-TA-PEI prepared in Example 1 and CdS prepared in Comparative Example 1 are shown.

[0019] Figure 3 Fourier transform infrared spectra of CdS-TA-PEI prepared in Example 1 and CdS prepared in Comparative Example 1.

[0020] Figure 4 The UV-Vis diffuse reflectance spectra of CdS-TA-PEI prepared in Example 1 and CdS prepared in Comparative Example 1 are shown.

[0021] Figure 5 The graph shows the performance of CdS-TA-PEI, CdS, and CdS / TA-PEI in the photocatalytic synthesis of hydrogen peroxide within 5 hours in Example 2.

[0022] Figure 6 The diagram shows the cycle performance of CdS-TA-PEI photocatalytic synthesis of hydrogen peroxide in Example 3.

[0023] Figure 7 The electrochemical impedance spectroscopy (EIS), transient photocurrent spectrum, and Mott-Schottky diagrams of CdS prepared by CdS-TA-PEI in Example 4 and Comparative Example 1 are shown.

[0024] Figure 8 The diagrams show the water contact angles of CdS-TA-PEI and CdS in Example 5. A represents the water contact angle of CdS-TA-PEI, and B represents the water contact angle of CdS.

[0025] Figure 9 The graph shows the performance of CdS-TA-PEI in the photocatalytic hydrogen peroxide production process during oxygen reduction and water oxidation in Example 6. Detailed Implementation

[0026] Comparative Example 1

[0027] 0.533 g of cadmium acetate dihydrate and 0.480 g of sodium sulfide nonahydrate were uniformly dispersed in 30 ml of ethylene glycol and stirred until homogeneous. The mixture was then transferred to a reactor and hydrothermally reacted at 180 °C for 24 h. After cooling, CdS was obtained by centrifugation, washing, and drying. CdS without TA-PEI coating was used as a comparative catalyst.

[0028] Comparative Example 2

[0029] Take 50 ml of 50 mM Tris-HCl solution in a beaker, add 0.4 g of tannic acid (TA), stir for two minutes, then add 0.133 g of polyethyleneimine (PEI), maintain the temperature at 30 °C, and stir for 24 hours. Collect the TA-PEI solution in the beaker by filtration and washing, and then place it in a vacuum oven to dry.

[0030] Comparative Example 3

[0031] Take 0.2g of CdS from Comparative Example 1 and 53.3mg of TA-PEI from Comparative Example 2 and put them into a mortar. Grind for 5 minutes and collect the resulting CdS / TA-PEI sample as Comparative Example 3.

[0032] Example 1

[0033] 0.533 g of cadmium acetate dihydrate and 0.480 g of sodium sulfide nonahydrate were uniformly dispersed in 30 ml of ethylene glycol and stirred until homogeneous. The mixture was then transferred to a reaction vessel and subjected to hydrothermal reaction at 180 °C for 24 h. After cooling, CdS was obtained by centrifugation, washing, and drying.

[0034] Take 50 ml of 50 mM Tris-HCl solution in a beaker, add 0.2 g of CdS, and sonicate for 1 h. Then add 40 mg of tannic acid (TA), stir for 2 minutes, and then add 13.3 mg of polyethyleneimine (PEI). Maintain the temperature at 30 °C and stir for 24 h. Collect the CdS-TA-PEI solution by filtration and washing, and then dry it in a vacuum oven.

[0035] Figure 1The images are transmission electron microscope (TEM) images of CdS-TA-PEI in Example 1 and CdS in Comparative Example 1. It can be observed that TA-PEI polyphenol amine is coated on the outer layer of cadmium sulfide.

[0036] Figure 2 The X-ray diffraction patterns of CdS-TA-PEI in Example 1 and CdS in Comparative Example 1 show that the synthesized catalyst has the corresponding crystal plane of CdS.

[0037] Figure 3 The Fourier transform infrared spectra of CdS-TA-PEI in Example 1 and CdS in Comparative Example 1 show absorption peaks corresponding to CN and CO, indicating that polyphenol amine was successfully synthesized and coated on the surface of cadmium sulfide.

[0038] Figure 4 The UV-Vis diffuse reflectance spectra of CdS-TA-PEI in Example 1 and CdS in Comparative Example 1 show that CdS-TA-PEI still has strong light absorption in the range of 600nm to 1000nm.

[0039] Example 2

[0040] The application of the catalysts CdS, CdS / TA-PEI, and CdS-TA-PEI of Comparative Examples 1, 3, and 1 of this invention in the photocatalytic synthesis of hydrogen peroxide.

[0041] The photocatalytic synthesis of hydrogen peroxide using the catalyst is as follows:

[0042] Step 1: Add 20ml of water to a 25ml beaker, weigh out 30mg of catalyst and add it to the beaker, sonicate for two minutes, then introduce oxygen and stir for 20 minutes in the absence of light.

[0043] Step 2: Take a certain sample, set it to 0 min, perform color development using the DPD-POD method, and finally calculate its hydrogen peroxide concentration;

[0044] Step 3: Turn on the xenon lamp and maintain its light intensity at 100mW / cm². 2 Under these conditions, samples are taken every 1 hour, and the process ends after 5 hours;

[0045] Step 4: Turn off the xenon lamp, develop the color of the sample using the DPD-POD method, record the peak value of its UV-Vis absorption spectrum using a UV-Vis spectrophotometer, and then calculate the concentration of hydrogen peroxide.

[0046] Figure 5The graph shows the photocatalytic synthesis of hydrogen peroxide by CdS-TA-PEI, CdS, and CdS / TA-PEI in Example 2 within 5 hours. It can be seen that the photocatalytic performance of CdS coated with TA-PEI is the best.

[0047] Example 3

[0048] The cyclic performance of the CdS-TA-PEI catalyst in photocatalytic hydrogen peroxide production was measured using the catalyst of Example 1 of this invention.

[0049] The steps for measuring the cyclic performance of the CdS-TA-PEI catalyst in photocatalytic hydrogen peroxide production are as follows:

[0050] Step 1: Prepare a piranha solution by adding a 30% hydrogen peroxide solution to concentrated sulfuric acid at a volume ratio of 3:7. Before loading the photocatalyst, immerse a glass slide in the solution for hydroxylation. After treatment with the piranha solution, rinse the glass slide with deionized water and then dry it with high-purity nitrogen.

[0051] Step 2: Disperse the photocatalyst (2 mg) in a solution containing 50 μL of 5% Nafion solution and 150 μL of ethanol, and sonicate for 30 min;

[0052] Step 3: Drop the solution obtained in step 2 onto the glass slide prepared in step 1 and let it air dry naturally;

[0053] Step 4: Place the glass slide with the catalyst supported in Step 3 into a beaker containing 20ml of water, turn on the xenon lamp, and circulate dry air to maintain its light intensity at 100mW / cm². 2 Under these conditions, samples are taken every 20 minutes, and the testing time is 40 minutes for one cycle;

[0054] Step 5: Turn off the xenon lamp, develop the color of the sample using the DPD-POD method, record the peak value of its UV-Vis absorption spectrum using a UV-Vis spectrophotometer, and then calculate the concentration of hydrogen peroxide.

[0055] Step 6: Take out the glass slide loaded with catalyst from Step 4 and place it in a beaker containing 20ml of pure water. Under the same light conditions, start the second cycle test. Repeat this cycle for a total of 7 times and measure the concentration of H2O2 produced by photocatalysis after each cycle.

[0056] Figure 6 The diagram shows the cyclic performance of CdS-TA-PEI photocatalytic synthesis of hydrogen peroxide in Example 3. It can be seen that the photocatalytic performance of CdS-TA-PEI did not show significant decay and the performance was relatively stable, which confirms that the coating of TA-PEI polyphenol amine material effectively improved the stability of the catalyst.

[0057] Example 4

[0058] The basic electrochemical properties of the catalysts CdS and CdS-TA-PEI prepared in Comparative Example 1 and Example 1 were measured using the present invention.

[0059] The steps for measuring the basic electrochemical properties of the catalysts CdS and CdS-TA-PEI are as follows:

[0060] Step 1: Add 10 mg of catalyst and 1 mg of ethyl cellulose to 5 ml of anhydrous ethanol and sonicate for 30 min;

[0061] Step 2: Slowly drop the solution obtained in Step 1 into a mortar and grind it. When it is almost dry, use a glass rod to evenly spread it on a conductive glass sheet, put it in an oven, and dry it at 120℃ for 3 hours.

[0062] Step 3: Prepare a 0.5M Na2SO4 solution as the electrolyte, and use an electrochemical workstation to measure its electrochemical impedance spectroscopy (EIS), transient photocurrent spectrum, and Mott-Schottky diagram.

[0063] Figure 7 The images show the electrochemical impedance spectroscopy (EIS), transient photocurrent spectrum, and Mott-Schottky diagram of CdS prepared in Example 4 with CdS-TA-PEI and CdS prepared in Comparative Example 1. It can be seen that after coating with TA-PEI, the photocurrent increases and the electrochemical impedance decreases. The decrease in electrochemical impedance and increase in photocurrent indicate an increase in carrier transport rate. Carriers are key factors participating in photocatalytic reactions; the higher the carrier concentration, the higher the efficiency of photocatalytic reactions.

[0064] Example 5

[0065] The water contact angles of the catalysts CdS and CdS-TA-PEI prepared in Comparative Example 1 and Example 1 were measured using the present invention.

[0066] The steps for measuring the water contact angle of the catalysts CdS and CdS-TA-PEI are as follows:

[0067] Step 1: Place the sample on the measurement platform and adjust the viewing angle. During placement, ensure the sample surface is clean and that the platform remains stable.

[0068] Step 2: Select a suitable solution and drop three water droplets onto the sample surface, keeping the droplets as steady as possible.

[0069] Step 3: Observe the water droplets and calculate the contact angle based on the results. The results need to be averaged three times to ensure data accuracy.

[0070] Figure 8The image shows the water contact diagrams of CdS-TA-PEI prepared in Example 4 and CdS prepared in Comparative Example 1. It can be seen that the hydrophilicity increases after coating with TA-PEI, which is beneficial for catalyst dispersion. The decrease in the water contact angle indicates increased hydrophilicity, as water is a reactant and facilitates sufficient contact between the catalyst and reactants, thus improving reaction efficiency.

[0071] Example 6

[0072] The photocatalyst CdS-TA-PEI prepared in this invention was used to study its effects on photocatalytic oxygen reduction and water oxidation reactions.

[0073] The steps of the photocatalytic oxygen reduction reaction of the catalyst CdS-TA-PEI are studied as follows:

[0074] Step 1: Add 20 mg of 0.1 M methanol solution to a 25 ml beaker, weigh 30 mg of catalyst and add it to the beaker, sonicate for two minutes, then purge with air and stir for 20 minutes in the absence of light.

[0075] Step 2: Take a certain amount of sample and set the time to 0 min;

[0076] Step 3: Turn on the xenon lamp and maintain its light intensity at 100mW / cm². 2 Under the condition of air circulation, samples were taken every 30 minutes for a total of 120 minutes.

[0077] Step 4: Record the peak value of the UV-Vis absorption spectrum of each sampling point using a UV-Vis spectrophotometer, and then calculate the concentration of hydrogen peroxide.

[0078] The catalyst CdS-TA-PEI was studied in the photocatalytic water oxidation reaction step, in which 0.1M potassium bromate replaced methanol, argon replaced air, and the remaining steps were similar to the oxygen reduction reaction.

[0079] Figure 9 The graph shows the oxygen reduction and water oxidation performance of CdS-TA-PEI. The graph shows the oxygen reduction (O2 + 2e2) performance. - +2H + →H2O2) and water oxidation reaction (2H2O+2h) + →H₂O₂ + 2H⁺ + Both of these processes produce hydrogen peroxide, indicating that CdS-TA-PEI is a dual-channel, highly efficient hydrogen peroxide synthesis process in photocatalytic hydrogen peroxide production.

Claims

1. A method for preparing CdS-TA-PEI, characterized in that, The specific preparation method is as follows: Preparation of S1 and CdS: First, cadmium acetate dihydrate and sodium sulfide nonahydrate are uniformly dispersed in ethylene glycol and stirred evenly. Then, the resulting mixture is transferred to a reaction vessel and subjected to hydrothermal reaction. After centrifugation, washing and drying, CdS is obtained. Preparation of S2 and CdS-TA-PEI: CdS was dispersed in Tris-HCl solution, ultrasonically dispersed and stirred, and tannic acid was added to mix it evenly in water. Then, polyethyleneimine was added, and after stirring, it was filtered and dried to obtain CdS-TA-PEI. The mass ratio of CdS, tannic acid and polyethyleneimine used was 200-250:30-40:10-15.

2. The preparation method of CdS-TA-PEI according to claim 1, characterized in that, The mass ratio of cadmium acetate dihydrate to sodium sulfide nonahydrate in S1 is 0.3-0.6:0.4-0.

5.

3. The preparation method of CdS-TA-PEI according to claim 1, characterized in that, The hydrothermal reaction temperature in S1 is 180-200℃, and the hydrothermal reaction time is 20-28h.

4. The preparation method of CdS-TA-PEI according to claim 1, characterized in that, The concentration of the Tris-HCl solution is 30-50 mM, and the pH is 8.5-9.

5.

5. The preparation method of CdS-TA-PEI according to claim 1, characterized in that, After adding polyethyleneimine, the stirring temperature is 10-70℃, and the stirring time is 6-24h.

6. The application of CdS-TA-PEI prepared by the method according to any one of claims 1-5 in the photocatalytic synthesis of hydrogen peroxide from oxygen, wherein phenolic and quinone structures on CdS-TA-PEI interconvert during the photocatalytic process.

7. The application of CdS-TA-PEI prepared by the method according to any one of claims 1-5 in the photocatalytic synthesis of hydrogen peroxide from water, wherein phenolic and quinone structures on CdS-TA-PEI interconvert during the photocatalytic process.

8. The application according to claim 6 or 7, wherein the photocatalytic process is performed under visible light or the full spectrum, and the light intensity is 50-200 mW / cm². 2 .

Images