Preparation method and application of N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst
N-doping ZnCdS catalysts address the limitations of ZnCdS by creating internal dipole fields, improving visible light response and electron-hole separation, resulting in high photocatalytic activity and stability for hydrogen production.
Patent Information
- Application Number
- CN202510479375.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-17
- Publication Date
- 2025-07-15
AI Technical Summary
The existing ZnCdS photocatalysts have photocorrosion problems and low electron hole separation efficiency in photohydrogen analysis reactions, which limit their application in visible light utilization and stability.
By introducing organic nitrogen sources such as triethylenetetramine as N dopants, N-doped ZnCdS catalysts are prepared by solvothermal method to form an internal dipole electric field, promote the separation of photogenerated electrons and holes, and improve catalytic activity and stability.
The catalyst has achieved high-efficiency photohydrogen analysis under visible light, with an average hydrogen evolution amount greater than 100 mmol/g/h, and maintained good activity in 5 cycles, showing excellent photohydrogen analysis performance and stability.
Smart Images
Figure CN120306008A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of photocatalyst preparation, in particular to the preparation of N-doped ZnCdS catalyst, which is applied to photolysis of water for hydrogen evolution. Background Art
[0002] With the development of industry and the continuous increase in population density, the energy gap of mankind is increasing. However, the main source of energy is still non-renewable fossil energy. However, the use of fossil fuels will cause a series of environmental pollution problems. Therefore, the development of renewable energy is a scientific problem that needs to be solved urgently. Solar energy and hydrogen energy are both potential green energy sources to solve the current energy crisis and have great research potential. Since the pioneering research of Fujishima et al. in 1972, semiconductor photocatalytic technology has been widely studied, and a large number of researchers have made great efforts to improve the performance of photocatalysts. So far, a variety of photocatalysts such as TiO2, ZnS, CdS, g-C3N4 and other materials have shown great potential in the direction of photocatalytic water splitting to produce hydrogen.
[0003] Metal sulfides show strong reactivity in the photocatalytic hydrogen evolution reaction of water splitting, among which CdS is the most representative. CdS has a band gap of 2.4eV, a light absorption edge of 520nm, and excellent visible light responsiveness. However, CdS is easily corroded by light during photoreaction, which is the bottleneck of the development of CdS catalysts. ZnS has a strong ability to separate electrons and holes, but its band gap is about 3.7eV, and its utilization rate of visible light is low. ZnS and CdS have the same crystal structure and have the conditions to form a solid solution. Zn 0.5 Cd 0.5 The S (ZCS) ternary solid solution is a hexagonal phase CdS in which half of the Cd atoms are replaced with Zn atoms of the same coordination number. Experimental results show that the ZCS solid solution can simultaneously have the wide visible light response range of CdS and the high separation efficiency of photogenerated electrons and holes of ZnS. Studies have found that the ZCS solid solution has a suitable band structure, high separation efficiency of electrons and holes, and better stability. However, the ability of ZCS solid solution to generate hydrogen by photolysis of water is still insufficient for large-scale application.
[0004] To solve the above problems, many researchers have made great efforts to improve the photocatalytic activity of ZCS. Generally speaking, one of the effective methods to improve the photocatalytic activity of a catalyst is to introduce a metal cocatalyst as an active site, such as Pt, Pd, Ni, etc. In addition, the construction of a heterojunction interface is also an effective means to improve photocatalytic activity. The key to the strategy of constructing a heterojunction is a tight interface connection. However, this method has the problem of being difficult to control at the microscale, and the imbalance of carriers on both sides of the heterojunction interface also makes the electron transport path not match the ideal state. Recently, scientists have regarded element doping as an effective method to improve the performance of catalytic materials. Element doping can adjust the energy band structure of the catalyst, form impurity energy levels in the forbidden band of the semiconductor, enhance the visible light response, and promote the separation and migration of carriers. In addition, the introduced elements can also become the active centers of the reaction. This modification method has a positive effect on electron migration and improves the catalytic activity.
[0005] In summary, we designed and proposed an N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst, which has an internal dipole electric field and thus has high activity and stability in the hydrogen evolution reaction. Summary of the Invention
[0006] The purpose of the present invention is to improve the problems existing in the current ZnCdS material in photocatalytic water splitting, and provide a new method for modifying ZnCdS. The preparation process of this method is simple and easy to operate, and the cost is low. Due to the existence of the internal dipole electric field of the material, the prepared catalyst has good visible light response ability and high separation efficiency of photo-generated electrons and holes, and shows excellent photocatalytic water splitting activity and stability. This design idea of constructing a dipole field inside the material can be applied to a variety of catalysts.
[0007] To achieve the above object, the present invention provides the following scheme:
[0008] A preparation method of an N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst, comprising the following steps:
[0009] (1) Prepare a reaction solution by mixing an inorganic zinc salt, an inorganic cadmium salt, an organic sulfur source, an organic nitrogen source and deionized water. The molar ratio of zinc ions to cadmium ions in the reaction solution is 1:1, and the molar ratio of the organic sulfur source to the total amount of zinc ions and cadmium ions is 1:(4 - 10), specifically 1:4, 1:6, 1:8, 1:10. The volume ratio of the organic nitrogen source to deionized water is (1 - 3):(3 - 1), specifically 1:3, 1:1, 1:3;
[0010] (2) Transfer the reaction solution obtained in step (1) to a reaction kettle, carry out a solvothermal reaction at 180 - 220 °C for 18 - 24 h. After the heat treatment is completed, wait for the reaction kettle to cool to room temperature completely, and then wash, centrifuge and dry the product to obtain the N-doped ZnCdS.
[0011] Specifically, in step (1), the organic nitrogen source is one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. The organic nitrogen source is preferably triethylenetetramine. Preferably, the volume ratio of triethylenetetramine to deionized water is 1:1.
[0012] Specifically, in step (2), the reaction solution is transferred to a polytetrafluoroethylene reaction kettle, with an external stainless steel reaction jacket, and placed in an oven for solvothermal reaction at 180 - 220 °C for 18 - 24 h. After the heat treatment is completed, wait for the reaction kettle to cool to room temperature, and then wash the product alternately with deionized water and ethanol, centrifuge, and dry to obtain the N-doped ZnCdS.
[0013] Preferably, in step (2), the heat treatment temperature is 220 °C, the reaction time is 24 h, and the heating rate is 5 °C / min.
[0014] Step (1) specifically includes:
[0015] (101) Weigh inorganic zinc salt and inorganic cadmium salt and add them to deionized water, stir to dissolve the two to obtain the precursor solution A;
[0016] (102) Weigh the organic sulfur source and add it to deionized water, stir to dissolve to obtain the precursor solution B;
[0017] (103) Mix the precursor solutions A and B obtained in steps (1) and (2), then add triethylenetetramine, and stir to make them evenly mixed to obtain the reaction solution.
[0018] Among them, in step (101), the concentrations of both the zinc salt and the cadmium salt are 0.2 - 0.5 mol / L, in step (2), the concentration of thiourea is 1.5 - 4.0 mol / L; in step (3), the volume ratio of solution A to solution B is 1:1 - 1:3.
[0019] The inorganic zinc salt is one or more of zinc acetate, zinc nitrate, and zinc chloride; the inorganic cadmium salt is one or more of cadmium acetate, cadmium nitrate, and cadmium chloride; the organic sulfur source includes one or more of thiourea and thioacetamide.
[0020] The beneficial effects of the present invention are as follows:
[0021] Based on the above technical solutions, the present invention provides a method for realizing N doping and morphology control of ZnCdS by using an organic nitrogen source as an N source and a capping agent during the heat treatment process. When triethylenetetramine is used as the organic nitrogen source, the catalyst involved has a high hydrogen evolution activity under the irradiation of an LED light source, the average hydrogen evolution amount is greater than 100 mmol / g / h within 4 h, and it has good cycle stability. This method of modifying the catalyst is relatively novel and can provide a new idea for catalyst design.
[0022] The present invention discloses a strategy for preparing N-doped ZnCdS nanoparticle catalysts with high hydrogen evolution activity through a one-pot hydrothermal method. Since N has a relatively high electronegativity, the introduction of N into the ZnCdS lattice can cause a displacement of the positive and negative charge centers of the material, thereby generating dipole polarization to form an internal polarization electric field. The existence of the internal dipole polarization electric field can promote the separation of photogenerated electrons and holes and improve the performance of hydrogen production by photocatalytic water splitting. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 Scanning electron microscope and transmission electron microscope images of ZCS and ZCS-TETA-50% samples.
[0024] Figure 2 X-ray diffraction patterns of ZCS and ZCS-TETA-50% samples.
[0025] Figure 3 X-ray photoelectron spectroscopy diagrams of ZCS and ZCS-TETA-50% samples.
[0026] Figure 4 Hydrogen evolution efficiency diagrams of photocatalytic water splitting for ZCS and a series of ZCS-TETA samples.
[0027] Figure 5 Hydrogen evolution efficiency diagram of photocatalytic water splitting for Example 5.
[0028] Figure 6 Hydrogen evolution efficiency diagrams of photocatalytic water splitting for Examples 6-7. DETAILED DESCRIPTION OF THE INVENTION
[0029] The principles involved in the present invention will be further described in detail below with reference to the accompanying drawings. This embodiment is implemented on the premise of the technology of the present invention, and detailed implementation methods and specific operation processes are now given to illustrate the creativity of the present invention. However, the protection scope of the present invention is not limited to the following embodiments. All the reagents used in the present invention are conventional commercially available reagents.
[0030] Example 1:
[0031] Weigh 0.274 g of zinc acetate dihydrate and 0.333 g of cadmium acetate dihydrate, dissolve them in 5 mL of deionized water to obtain solution A. Dissolve 1.522 g of thiourea in 10 mL of deionized water to obtain solution B. After stirring them evenly respectively, mix solution A and B, then add 15 mL of triethylenetetramine. After stirring the mixed solution for 30 min, transfer the solution to a 50 mL polytetrafluoroethylene reaction kettle, heat it to 200 °C at a rate of 5 °C / min and keep it for 24 h. After the solvothermal reaction is completed and the reaction kettle is cooled to room temperature, wash the synthesized catalyst by centrifugation with anhydrous ethanol and deionized water alternately for 3 times. Before each centrifugation, put the solid-liquid mixture into an ultrasonic dispersion instrument for ultrasonic treatment. The ultrasonic power is 400 W, ultrasonic for 20 s and then centrifuge at a rotation speed of 8000 r / min. After washing, put it into an oven at 60 °C and dry for 12 h. After drying, N-doped ZnCdS is obtained, and the product is denoted as ZCS-TETA-50%.
[0032] Example 2:
[0033] The difference between this example and Example 1 is that the volume ratio of water to triethylenetetramine is changed. The volume of triethylenetetramine is 7.5 mL and the total volume of deionized water is 22.5 mL. The other conditions remain unchanged, and the obtained target product is denoted as ZCS-TETA-25%.
[0034] Example 3:
[0035] The difference between this example and Example 1 is that the volume ratio of water to triethylenetetramine is changed. The volume of triethylenetetramine is 22.5 mL and the volume of deionized water is 7.5 mL. The other conditions remain unchanged, and the obtained target product is denoted as ZCS-TETA-75%.
[0036] Example 4:
[0037] The difference between this example and Example 1 is that the volume ratio of water to triethylenetetramine is changed. The volume of triethylenetetramine is 0 mL and the volume of deionized water is 30 mL. The other conditions remain unchanged, and the obtained target product is denoted as ZCS.
[0038] Example 5:
[0039] The difference between this example and Example 1 is that thiourea is replaced by thioacetamide, and the other conditions remain unchanged.
[0040] Example 6:
[0041] The difference between this example and Example 1 is that triethylenetetramine is replaced by ethylenediamine, and the other conditions remain unchanged.
[0042] Example 7:
[0043] The difference between this example and Example 1 is that triethylenetetramine is replaced by diethylenetriamine, and the other conditions remain unchanged.
[0044] The SEM images of ZCS-TETA-50% and ZCS are shown in Figure 1 , Figure 1 a is the SEM image of ZCS, Figure 1 d is the SEM image of ZCS-TETA-50%. It can be seen that the addition of TETA makes ZnCdS present a uniform nanoparticle morphology, while the ZCS sample presents a non-uniform block structure. Figure 1 b and Figure 1 c are the TEM images of the ZCS sample, where Figure 1 the 0.313 nm lattice fringe in b corresponds to the (101) crystal plane of ZnCdS; Figure 1 e and Figure 1 f are the TEM images of the ZCS-TETA-50% sample. Figure 1 The 0.311 nm lattice fringe in e corresponds to the (101) crystal plane of ZnCdS. The decrease in the lattice spacing proves that the introduction of the low-radius element N causes lattice contraction of the (101) crystal plane of ZnCdS. Figure 2 are the XRD patterns of the samples ZCS-TETA-50% and ZCS. The XRD results show that ZCS-TETA-50% and ZCS match well with the hexagonal ZnCdS standard card. In addition, the (101) crystal plane of ZCS-TETA-50% is slightly shifted towards a higher angle, which is consistent with the result of the smaller lattice spacing in TEM.
[0045] The surface elements of ZCS and ZCS-TETA-50% were analyzed by X-ray photoelectron spectroscopy (XPS). As Figure 3 shown in a, these two samples are mainly composed of Zn, Cd, and S. Figure 3 In b, the Zn 2p spectra of ZCS and ZCS-TETA-50% are divided into two peaks, corresponding to Zn 2p 3 / 2 and Zn 2p 1 / 2 . Figure 3 In c, the two signal peaks in the Cd 3d spectrum correspond to Cd 3d 3 / 2 and Cd3d 5 / 2 . Figure 3 In d, the S2p spectrum can be divided into two peaks corresponding to S2p 1 / 2 and S2p 1 / 2 . Figure 3 b, 3c, and 3d show that the signal peaks of Cd 3d, Zn 2p, and S2p in ZCS-TETA-50% shift significantly towards lower binding energies. It is worth noting that the presence of the N signal in ZCS-TETA-50% indicates the existence of metal-N bonds in the material, confirming the successful incorporation of N ( Figure 3 e). The small-radius element N has successfully replaced the S atom in the ZCS unit cell, resulting in electron enrichment and an increase in electron cloud density. This is also the reason for the change in the binding energy of each element.
[0046] The highly electronegative element N with a small radius successfully replaced the S atom in the ZCS framework, resulting in a significant separation of the positive and negative charge centers within the ZCS, electron enrichment, and increased electron cloud density. At the same time, the introduction of the N element generated an induced dipole and formed a built-in electric field. This greatly promoted the migration of photogenerated carriers within the material and was beneficial to the precipitation of H2.
[0047] In the photocatalytic hydrogen evolution experiment, a 10W LED (400-780nm) lamp was used as the light source, and a 50mL quartz reaction bottle was used as the reactor. The specific experimental steps are as follows: First, 2mg of the photocatalyst was dispersed in 30mL of a mixed solution of 0.12MNa2S and 0.2M Na2SO3 by ultrasound. Before the reaction, the gas in the reaction bottle was replaced 10 times with high-purity nitrogen to ensure that the system was in an oxygen-free environment. The reaction was carried out in a multi-channel photocatalytic reaction system, and a constant temperature (20°C) was maintained during the illumination process. 0.1mL of the gas in the bottle was extracted every 1h, and the hydrogen content was detected using a gas chromatograph (GC7900) column with a TCD detector to calculate the hydrogen yield. Figure 4 The photocatalytic hydrogen evolution performance of Examples 1-4 under LED light irradiation. ZCS-TETA-50% has the highest hydrogen evolution performance (115.7 mmol / g / h), which is 4.1 times that of ZCS. In addition, ZCS-TETA-50% maintained good activity during 5 cycles. The improvement in activity is mainly attributed to the addition of the highly electronegative element N to the ZCS framework. This addition generates a built-in electric field, enhances the electron mobility of the material, and reduces the possibility of photogenerated electron-hole recombination. In addition, the optimal ratio of water and TETA was explored. Figure 4 As shown, its performance presents a volcanic shape. The average hydrogen evolution rate of ZCS-TETA-25% is 53.6mmol / g / h; the average hydrogen evolution rate of ZCS-TETA-75% is 101.9mmol / g / h. This is because when the proportion of water in the solution is large, the NH2 content is low and the coordination ability with metal ions is poor. On the contrary, as the water content decreases, the solubility of metal salts and thiourea deteriorates, resulting in poor controllability of sulfide synthesis. It is worth noting that the present invention shows a more significant performance improvement without the need to design a complex heterogeneous structure or add precious metal loads.
[0048] Figure 5 This is the photocatalytic hydrogen evolution performance of Example 5. As shown in the figure, when the sulfur source is replaced with thioacetamide (TAA), the average hydrogen evolution rate within 4 hours is 92.6 mmol / g / h.
[0049] Figure 6It is the photocatalytic hydrogen evolution performance of Examples 6-7. As shown in the figure, when the organic nitrogen source is changed to ethylenediamine (EN) and diethylenetriamine (DETA), the average hydrogen evolution rate within 4 h is 71.4 mmol / g / h and 68.5 mmol / g / h.
[0050] By changing the volume ratio of deionized water to the capping agent triethylenetetramine in the solvothermal synthesis of ZnCdS, the present invention can obtain nano-ZnCdS particles with different N doping amounts and uniform morphologies. XPS analysis proves the successful doping of the highly electronegative element N, and the introduction of the highly electronegative element N induces the generation of a dipole polarization electric field inside ZnCdS, enhancing the separation efficiency of electrons and holes.
[0051] The test results of the photocatalytic water splitting hydrogen evolution performance show that under the irradiation of 10 W LED (400-700 nm) light, the average hydrogen evolution activity of this catalyst within 4 hours is 115.7 mmol / g / h, the sacrificial agents are 0.11 mol / L Na2S and 0.2 mol / L Na2SO3, the temperature during the hydrogen evolution process is maintained at 20 °C, and the activity remains good during 5 hydrogen evolution cycles, proving that this catalyst has excellent photocatalytic water splitting hydrogen evolution activity and stability under visible light irradiation.
[0052] The above-described embodiments are only descriptions of the preferred modes of the present invention and do not limit the present invention. Any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A preparation method of an N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst, characterized in that, It includes the following steps: (1) Prepare a reaction solution by mixing an inorganic zinc salt, an inorganic cadmium salt, an organic sulfur source, an organic nitrogen source, and deionized water. The molar ratio of zinc ions to cadmium ions in the reaction solution is 1:1, the molar ratio of the organic sulfur source to the total amount of zinc ions and cadmium ions is 1:(4 - 10), and the volume ratio of the organic nitrogen source to deionized water is (1 - 3):(3 - 1); (2) Transfer the reaction solution obtained in step (1) to a reaction kettle, carry out a solvothermal reaction at 180 - 220 °C for 18 - 24 h. After the heat treatment is completed, wait for the reaction kettle to cool to room temperature completely, and then wash the product, centrifuge, and dry it to obtain the N-doped ZnCdS.
2. The preparation method of the N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst according to claim 1, characterized in that, In step (1), the organic nitrogen source is one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.
3. The preparation method of the N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst according to claim 1, characterized in that, The organic nitrogen source is triethylenetetramine.
4. The preparation method of the N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst according to claim 1, wherein, In step (2), the heat treatment temperature is 220 °C, the reaction time is 24 h, and the heating rate is 5 °C / min.
5. The preparation method of the N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst according to claim 1, characterized in that, Step (1) specifically includes: (101) Weigh the inorganic zinc salt and the inorganic cadmium salt, add them to deionized water, and stir to dissolve them to obtain the precursor solution A; (102) Weigh the organic sulfur source, add it to deionized water, and stir to dissolve it to obtain the precursor solution B; (103) Mix the precursor solutions A and B obtained in steps (1) and (2), add triethylenetetramine, and stir to make them evenly mixed to obtain the reaction solution.
6. The preparation method of the N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst according to claim 5, characterized in that, In step (101), the concentrations of the zinc salt and the cadmium salt are both 0.2 - 0.5 mol / L. In step (2), the concentration of thiourea is 1.5 - 4.0 mol / L. In step (3), the volume ratio of solution A to solution B is 1:1 - 1:
3.
7. The preparation method of the N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst according to claim 6, characterized in that, The inorganic zinc salt is one or more of zinc acetate, zinc nitrate, and zinc chloride; the inorganic cadmium salt is one or more of cadmium acetate, cadmium nitrate, and cadmium chloride; the organic sulfur source includes one or more of thiourea and thioacetamide.
8. The N-doped ZnCdS photocatalytic water splitting hydrogen evolution catalyst prepared by the method according to any one of claims 1 - 7.
9. The application of the catalyst according to claim 8 in photocatalytic hydrogen evolution, using a 10 W LED lamp with a wavelength of 400 - 780 nm as the light source.