A zinc cadmium sulfide solid solution, its preparation method and application

Abstract

This invention discloses a zinc-cadmium sulfide solid solution, its preparation method, and its applications. The preparation method of the zinc-cadmium sulfide solid solution of this invention includes the following steps: 1) dissolving a zinc source and a cadmium source in water to obtain a zinc-cadmium source solution; 2) dissolving a sulfur source in the zinc-cadmium source solution to obtain a precursor solution; 3) adding an alkaline solution to the precursor solution, followed by a hydrothermal reaction, and then separating, purifying, and drying the product to obtain the zinc-cadmium sulfide solid solution. The zinc-cadmium sulfide solid solution of this invention has advantages such as high catalytic efficiency and good stability, making it suitable for photocatalytic water splitting to produce hydrogen. Furthermore, its preparation method is simple, the reaction conditions are mild, the reproducibility is good, and the production cost is low, making it suitable for large-scale industrial production and application.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic water splitting for hydrogen production, specifically to a zinc cadmium sulfide solid solution, its preparation method, and its application. Background Technology

[0002] With the acceleration of global industrialization and the continuous growth of energy consumption, the depletion of traditional fossil fuels and environmental pollution are becoming increasingly serious problems. To address this issue, using solar energy to drive semiconductor photocatalytic water splitting to produce hydrogen (hydrogen is a clean fuel with high energy density) is recognized as one of the most promising solutions.

[0003] Zinc cadmium sulfide (Zn) x Cd 1-x Solid solutions (S) possess advantages such as tunable band gap (2.4 eV–3.6 eV), strong visible light response, suitable conduction band position, and low cost, making them ideal photocatalytic materials for visible light-based water splitting to produce hydrogen. However, the photocatalytic efficiency of pure-phase (cubic and hexagonal) zinc cadmium sulfide solid solutions falls far short of practical application requirements due to: 1) the rapid recombination rate of photogenerated electron-hole pairs within the bulk phase; and 2) the slow redox reaction kinetics on the material surface. To address these issues, researchers have employed modification strategies such as morphology control, elemental doping, defect engineering, and heterostructure construction, but the actual technical effects achieved have been limited and still cannot fully meet practical application needs.

[0004] Therefore, it is of great significance to develop a zinc cadmium sulfide solid solution with high catalytic efficiency and good stability for photocatalytic water splitting to produce hydrogen. Summary of the Invention

[0005] The purpose of this invention is to provide a zinc cadmium sulfide solid solution, its preparation method, and its application.

[0006] The technical solution adopted in this invention is: A method for preparing a zinc cadmium sulfide solid solution includes the following steps: 1) Dissolve the zinc source and cadmium source in water to obtain a zinc source-cadmium source solution; 2) Dissolve the sulfur source in a zinc-cadmium source solution to obtain a precursor solution; 3) Add the alkaline solution to the precursor solution, then carry out a hydrothermal reaction, and then separate, purify and dry the product to obtain zinc cadmium sulfide solid solution.

[0007] Preferably, the molar ratio of the zinc source and the cadmium source in step 1) is 1:1 to 2.

[0008] Preferably, the zinc source in step 1) is at least one of zinc acetate, zinc chloride, zinc nitrate, and zinc carbonate.

[0009] Preferably, the cadmium source in step 1) is at least one of cadmium acetate, cadmium chloride, cadmium nitrate, and cadmium carbonate.

[0010] Preferably, the total concentration of zinc source and cadmium source in the zinc source-cadmium source solution in step 1) is 0.2 mol / L to 1.0 mol / L.

[0011] Preferably, the amount of sulfur source used in step 2) is 2 to 4 times the molar amount of zinc source.

[0012] Preferably, the sulfur source in step 2) is at least one of sodium sulfide, thiourea, sodium thiosulfate, thioacetamide, and L-cysteine.

[0013] More preferably, the sulfur source in step 2) is thioacetamide (C2H5NS, TAA).

[0014] Preferably, the alkaline solution in step 3) is at least one of ammonia water, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and calcium hydroxide aqueous solution.

[0015] More preferably, the alkaline solution in step 3) is an aqueous solution of sodium hydroxide.

[0016] Preferably, the concentration of the sodium hydroxide aqueous solution is 1 mol / L to 5 mol / L.

[0017] Preferably, the alkaline solution in step 3) is added at a constant flow rate of 0.8 mL / min to 1.2 mL / min.

[0018] Preferably, the hydrothermal reaction in step 3) is carried out at a temperature of 150℃ to 250℃ for a reaction time of 10h to 30h.

[0019] Preferably, the product separation, purification and drying in step 3) includes the following operations: centrifuging the reaction solution, washing the solid with water and ethanol in sequence, and then freeze-drying.

[0020] Preferably, the centrifugation is carried out at a centrifuge speed of 5000 rpm to 20000 rpm.

[0021] Preferably, the freeze-drying time is 20h to 30h.

[0022] A zinc cadmium sulfide solid solution is prepared by the above-described preparation method.

[0023] A photocatalyst comprising the aforementioned zinc cadmium sulfide solid solution.

[0024] A photocatalytic water splitting method for hydrogen production uses the aforementioned zinc cadmium sulfide solid solution as the photocatalyst.

[0025] The beneficial effects of the present invention are: the zinc cadmium sulfide solid solution of the present invention has the advantages of high catalytic efficiency and good stability, and is suitable for photocatalytic water splitting to produce hydrogen. Moreover, its preparation method is simple, the reaction conditions are mild, the reproducibility is good, and the production cost is low, making it suitable for large-scale industrial production and application.

[0026] Specifically: 1) This invention synthesizes zinc cadmium sulfide solid solution rich in twin interfaces in one step via hydrothermal method. It utilizes stacking fault induction to form an atomically coherent homojunction structure with alternating zincblende phase (ZB) and wurtzite phase (WZ). This homojunction constructs a periodic built-in electric field inside the material, which can drive the directional separation and migration of photogenerated electrons and holes in the bulk phase, effectively suppressing bulk carrier recombination. 2) This invention can precisely control sulfur vacancies (V) by adjusting the concentration of the alkali solution. s The concentration and distribution of sulfur vacancies can be monitored. An appropriate amount of sulfur vacancies can act as selective charge traps to further capture photogenerated electrons and prolong carrier lifetime. At the same time, sulfur vacancies can also serve as reactive sites to optimize the adsorption and activation of reactants and improve the surface reaction kinetic rate. 3) This invention achieves synergistic optimization of homojunction and sulfur vacancy: the homojunction dominates the spatial separation and migration of bulk carriers, and the sulfur vacancy serves as a shallow energy level trap to optimize the utilization of surface charge. The synergistic effect of the two achieves precise control of carriers throughout the entire chain of "bulk separation-interface transfer-surface reaction". 4) The zinc cadmium sulfide solid solution of the present invention can be used for photocatalytic hydrogen production under visible light irradiation. The hydrogen production rate can reach 192.05 mmol / h / g, and the hydrogen production performance does not show significant decay after 36h (9 cycles) of continuous testing, showing excellent stability. Its performance is better than that of the zinc cadmium sulfide solid solutions reported in the past, and it has a very broad application prospect in the field of solar photocatalytic water splitting for hydrogen production. 5) The preparation process of the zinc cadmium sulfide solid solution of the present invention is simple, the reaction conditions are mild, and the reproducibility is good, making it suitable for large-scale industrial production and application. Attached Figure Description

[0027] Figure 1 For T-ZCS1, T-ZCS3, T-ZCS5, ZB-ZCS, WZ-ZCS, TZ 0.7 C 0.3 Photocatalytic hydrogen production effects of S and T-CdS.

[0028] Figure 2 This is a test diagram of the photocatalytic hydrogen production cycle of T-ZCS3.

[0029] Figure 3 Electron paramagnetic resonance spectra of T-ZCS1, T-ZCS3, and T-ZCS5.

[0030] Figure 4 The image shows a scanning transmission microscope image of T-ZCS3 with double spherical aberration correction and a schematic diagram of the atomic arrangement of the homojunction. Detailed Implementation

[0031] The present invention will be further explained and described below with reference to specific embodiments.

[0032] Example 1: A zinc cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 10 mmol of zinc acetate dihydrate ((CH3COO)2Zn·2H2O) and 10 mmol of cadmium acetate dihydrate ((CH3COO)2Cd·2H2O) in 35 mL of deionized water to obtain a zinc source-cadmium source solution. 2) Add 25 mmol of thioacetamide (TAA) to the zinc-cadmium source solution and stir for 30 min to obtain the precursor solution; 3) Add 10 mL of 1 mol / L NaOH aqueous solution to the precursor solution under stirring at a constant flow rate of 1 mL / min. After the addition is complete, continue stirring for 30 min. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, place it in an oven at 180°C for 24 h. After naturally cooling to room temperature, centrifuge at 12000 rpm. Take the solid and wash it three times with deionized water and anhydrous ethanol respectively. Then dry it in a vacuum freeze dryer for 24 h to obtain zinc cadmium sulfide solid solution (denoted as T-ZCS1).

[0033] Example 2: A zinc cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 10 mmol of zinc acetate dihydrate and 10 mmol of cadmium acetate dihydrate in 35 mL of deionized water to obtain a zinc source-cadmium source solution. 2) Add 25 mmol of thioacetamide to the zinc-cadmium source solution and stir for 30 min to obtain the precursor solution; 3) Add 10 mL of 3 mol / L NaOH aqueous solution to the precursor solution under stirring at a constant flow rate of 1 mL / min. After the addition is complete, continue stirring for 30 min. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, place it in an oven at 180°C for 24 h. After naturally cooling to room temperature, centrifuge at 12000 rpm. Take the solid and wash it three times with deionized water and anhydrous ethanol respectively. Then dry it in a vacuum freeze dryer for 24 h to obtain zinc cadmium sulfide solid solution (denoted as T-ZCS3).

[0034] Example 3: A zinc cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 10 mmol of zinc acetate dihydrate and 10 mmol of cadmium acetate dihydrate in 35 mL of deionized water to obtain a zinc source-cadmium source solution. 2) Add 25 mmol of thioacetamide to the zinc-cadmium source solution and stir for 30 min to obtain the precursor solution; 3) Add 10 mL of 5 mol / L NaOH aqueous solution to the precursor solution under stirring at a constant flow rate of 1 mL / min. After the addition is complete, continue stirring for 30 min. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, place it in an oven and react at 180°C for 24 h. After naturally cooling to room temperature, centrifuge at 12000 rpm. Take the solid and wash it three times with deionized water and anhydrous ethanol respectively. Then dry it in a vacuum freeze dryer for 24 h to obtain zinc cadmium sulfide solid solution (denoted as T-ZCS5).

[0035] Comparative Example 1: A zinc cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 2 mmol of zinc acetate dihydrate and 2 mmol of cadmium acetate dihydrate in 50 mL of deionized water to obtain a zinc source-cadmium source solution. 2) Add 6 mmol of sodium sulfide nonahydrate to the zinc-cadmium source solution and stir for 30 min to obtain the precursor solution; 3) The precursor solution was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, it was placed in an oven at 180°C for 24 hours. After naturally cooling to room temperature, it was centrifuged at 12,000 rpm. The solid was washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum freeze dryer for 24 hours to obtain zinc cadmium sulfide solid solution (denoted as ZB-ZCS; pure cubic phase).

[0036] Comparative Example 2: A zinc cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 2 mmol of zinc acetate dihydrate and 2 mmol of cadmium acetate dihydrate in 50 mL of deionized water to obtain a zinc source-cadmium source solution. 2) Add 6 mmol of thiourea to the zinc-cadmium source solution and stir for 30 min to obtain the precursor solution; 3) The precursor solution was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, it was placed in an oven at 180°C for 24 hours. After naturally cooling to room temperature, it was centrifuged at 12,000 rpm. The solid was washed three times with deionized water and anhydrous ethanol, and then dried in a vacuum freeze dryer for 24 hours to obtain zinc cadmium sulfide solid solution (denoted as WZ-ZCS; pure hexagonal phase).

[0037] Comparative Example 3: A zinc cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 14 mmol of zinc acetate dihydrate and 6 mmol of cadmium acetate dihydrate in 35 mL of deionized water to obtain a zinc source-cadmium source solution. 2) Add 25 mmol of thioacetamide to the zinc-cadmium source solution and stir for 30 min to obtain the precursor solution; 3) Add 10 mL of a 3 mol / L NaOH aqueous solution to the precursor solution under stirring at a constant flow rate of 1 mL / min. After the addition is complete, continue stirring for 30 min. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, place it in an oven at 180°C for 24 h and allow it to cool naturally to room temperature. Centrifuge at 12000 rpm and take the solid. Wash the solid three times with deionized water and anhydrous ethanol, respectively. Then dry it in a vacuum freeze dryer for 24 h to obtain zinc cadmium sulfide solid solution (denoted as TZ). 0.7 C 0.3 S).

[0038] Comparative Example 4: A cadmium sulfide solid solution is prepared by the following method: 1) Dissolve 20 mmol of cadmium acetate dihydrate in 35 mL of deionized water to obtain a cadmium source solution; 2) Add 25 mmol of thioacetamide to the cadmium source solution and stir for 30 min to obtain the precursor solution; 3) Add 10 mL of 3 mol / L NaOH aqueous solution to the precursor solution under stirring at a constant flow rate of 1 mL / min. After the addition is complete, continue stirring for 30 min. Then transfer the solution to a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After sealing the reactor, place it in an oven at 180°C for 24 h. After naturally cooling to room temperature, centrifuge at 12000 rpm. Take the solid and wash it three times with deionized water and anhydrous ethanol respectively. Then dry it in a vacuum freeze dryer for 24 h to obtain cadmium sulfide solid solution (denoted as T-CdS).

[0039] Performance testing: 1) Add 35 mmol of sodium sulfide nonahydrate (sacrificial agent) and 25 mmol of sodium sulfite (sacrificial agent) to 100 mL of deionized water, then add 5 mg of photocatalyst (T-ZCS1, T-ZCS3, T-ZCS5, ZB-ZCS, WZ-ZCS, TZ 0.7 C 0.3 The reaction system (S and T-CdS) was kept at 6℃ using circulating condensate. Argon gas was introduced for 30 minutes before testing to remove dissolved gases from the solution. During testing, a 300W xenon lamp (PLS-SXE300+; Beijing Pofilai Technology Co., Ltd.; equipped with an AM 1.5G filter and a 420nm cutoff filter) was used for 3.5 hours of irradiation. The resulting photocatalytic hydrogen production effect is shown in the figure below. Figure 1 As shown.

[0040] Depend on Figure 1 It can be known that: a) Compared with ZB-ZCS (pure cubic phase) and WZ-ZCS (pure hexagonal phase), T-ZCS1, T-ZCS3 and T-ZCS5 all showed significantly improved photocatalytic hydrogen production performance; b) The hydrogen production rate of T-ZCS3 (Zn:Cd=1:1) is as high as 192.05 mmol·h -1 ·g -1 These figures are approximately 8 times and 60 times that of ZB-ZCS and WZ-ZCS, respectively, while TZ 0.7 C 0.3 The hydrogen production rates of S (Zn:Cd=0.7:0.3) and T-CdS were only 82.67 mmol·h. -1 ·g -1 and 12.82 mmol·h -1 ·g -1 .

[0041] 2) Add 35 mmol of sodium sulfide nonahydrate and 25 mmol of sodium sulfite to 100 mL of deionized water, then add 5 mg of photocatalyst (T-ZCS3). Irradiate with a 300 W xenon lamp (PLS-SXE300+; Beijing Pofilai Technology Co., Ltd.; equipped with an AM 1.5G filter and a 420 nm cutoff filter) for 4 h, let stand for 2 h, then irradiate with the xenon lamp for another 4 h, and repeat the cycle. The resulting photocatalytic hydrogen production cycle test graph is shown below. Figure 2 As shown.

[0042] Depend on Figure 2It can be seen that after nine consecutive cycles (a total of 36 hours) of photocatalytic reaction, the hydrogen production rate of T-ZCS3 did not show a significant decrease, indicating that T-ZCS3 has excellent cycle stability. During each cycle test, the hydrogen production rate showed a slight decreasing trend with the extension of reaction time. This is mainly attributed to the gradual consumption of the sacrificial agent and the competitive consumption of photogenerated electrons during the formation of the byproduct thiosulfate. The hydrogen production activity of the catalyst can be restored to the initial level by simply replenishing fresh sacrificial agent after the cycle ends, which further confirms the stability of the catalyst.

[0043] 3) The electron paramagnetic resonance spectra of the zinc cadmium sulfide solid solutions (T-ZCS1, T-ZCS3, and T-ZCS5) of Examples 1-3 are as follows: Figure 3 (g=2.004 is the sulfur vacancy signal) as shown.

[0044] Depend on Figure 3 It can be seen that in T-ZCS1, the peak near g factor 2.064 belongs to the defect center related to metal vacancy, and the peak near g factor 1.947 belongs to the surface adsorbed O2. - The remaining peaks are attributed to distance-dependent electron-hole exchange generated by different termination edges in Shockley partial dislocations, which are related to stacking faults. As the concentration of NaOH solution added during the preparation of zinc cadmium sulfide solid solution increases, the ultrafine peaks of zinc cadmium sulfide solid solution rapidly broaden, and isolated sulfur vacancy signals appear (g=2.004). The strongest isolated sulfur vacancy signal is obtained when the concentration of NaOH solution is 3 mol / L.

[0045] 4) Double aberration corrected scanning transmission microscope image (atomic resolution HAADF-STEM image taken along the

[001] zone axis) and schematic diagram of the atomic arrangement of the homojunction of the zinc cadmium sulfide solid solution (T-ZCS3) in Example 3 are shown below. Figure 4 (The cubic phase and the hexagonal phase are named ZB and WZ, respectively.) As shown.

[0046] Depend on Figure 4 As shown in the left image, the atomic pillars are clearly mirror-symmetrically distributed on both sides of the interface marked by the white dashed line, confirming the existence of twins.

[0047] Depend on Figure 4 As shown in the right figure, on both sides far from the interface, the atomic layer stacking order is a cubic close-packed mode of AaBbCc…, corresponding to the zincblende phase; at the twin interface, due to the slip of atoms along the close-packed plane {111} direction, the slip direction is

[112] , and the local stacking order changes to the hexagonal close-packed mode of the wurtzite phase of ABAB….

[0048] In summary, T-ZCS3 contains an atomically coherent homojunction structure of alternating wurtzite and zincblende within the same grain (formed by stacking fault induction).

[0049] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a zinc cadmium sulfide solid solution, characterized in that, Includes the following steps: 1) Dissolve the zinc source and cadmium source in water to obtain a zinc source-cadmium source solution; 2) Dissolve the sulfur source in a zinc-cadmium source solution to obtain a precursor solution; 3) Add the alkaline solution to the precursor solution, then carry out a hydrothermal reaction, and then separate, purify and dry the product to obtain zinc cadmium sulfide solid solution.

2. The preparation method according to claim 1, characterized in that: Step 1) The molar ratio of the zinc source and the cadmium source is 1:1 to 2.

3. The preparation method according to claim 1 or 2, characterized in that: Step 1) The zinc source is at least one of zinc acetate, zinc chloride, zinc nitrate, and zinc carbonate; and / or, Step 1) The cadmium source is at least one of cadmium acetate, cadmium chloride, cadmium nitrate, and cadmium carbonate.

4. The preparation method according to claim 1, characterized in that: Step 2) The amount of sulfur source used is 2 to 4 times the molar amount of zinc source.

5. The preparation method according to claim 1 or 4, characterized in that: Step 2) The sulfur source is at least one of sodium sulfide, thiourea, sodium thiosulfate, thioacetamide, and L-cysteine.

6. The preparation method according to claim 1, characterized in that: Step 3) The alkaline solution is at least one of ammonia water, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and calcium hydroxide aqueous solution.

7. The preparation method according to claim 1 or 6, characterized in that: Step 3) The hydrothermal reaction is carried out at a temperature of 150℃~250℃ for a reaction time of 10h~30h.

8. A zinc cadmium sulfide solid solution, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

9. A photocatalyst, characterized in that, It includes the zinc cadmium sulfide solid solution as described in claim 8.

10. A method for producing hydrogen through photocatalytic water splitting, characterized in that, The photocatalyst used is the zinc cadmium sulfide solid solution as described in claim 8.

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