Preparation method and application of ZIS / CdS / CQDs ternary composite photocatalyst

Abstract

The invention discloses a preparation method and application of a ZIS / CdS / CQDs ternary composite photocatalyst, relates to the field of photocatalytic materials, and aims to solve the problem of low photocatalytic hydrogen production efficiency of an existing photocatalytic hydrogen production catalyst. The method comprises the following steps: 1, adding a metal sulfide CdS into a methanol solution, sequentially adding zinc acetate dihydrate, indium chloride tetrahydrate and thioacetamide, carrying out ultrasonic treatment, and adding Na2CO3 to obtain a mixed solution; 2, transferring the mixed solution into a reaction kettle for reaction, cooling, washing and drying to obtain ZIS / CdS; and 3, mixing the ZIS / CdS powder and the CQDs powder for reaction, cooling, washing and drying to obtain the ZIS / CdS / CQDs. According to the invention, ZnInS and CdS are compounded, so that the photocatalytic activity is obviously enhanced. The visible light response range of the composite material can be expanded by the broadband spectrum absorption capacity of the CQDs, and the light capture efficiency is improved by cooperating with the narrow band gap of the CdS. The method is used for photocatalytic hydrogen production.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials, specifically to a method for preparing and applying a Zn4In2S7 / CdS / CQDs ternary composite photocatalyst. Background Technology

[0002] With the rapid development of the global economy, addressing the increasingly serious energy shortage and environmental pollution has become a hot topic. Solar-driven photocatalytic hydrogen production technology, due to its clean and renewable characteristics, is considered one of the key pathways to meet future energy demands.

[0003] Photocatalytic hydrogen production uses water as a raw material and utilizes renewable solar energy to generate hydrogen under the action of a photocatalyst. Water is widely available, and the reaction process does not produce gases such as carbon dioxide. The hydrogen product is burned to produce only water, making it an ideal clean energy production method that helps reduce dependence on traditional fossil fuels and thus alleviate the energy crisis. Some photocatalytic materials (such as titanium dioxide) are widely available, low in cost, and possess good chemical stability and photocatalytic activity, making photocatalytic hydrogen evolution economically feasible for large-scale industrial production.

[0004] However, the field of photocatalysis still faces severe challenges. Photocatalysts for hydrogen production suffer from the following shortcomings: During photocatalysis, the catalyst generates photogenerated electron-hole pairs upon photoexcitation. However, these photogenerated charge carriers are highly susceptible to recombination, releasing energy as heat or other forms of energy. This reduces the number of effective charges participating in the photocatalytic hydrogen evolution reaction, thus lowering the efficiency of photocatalytic hydrogen production. Furthermore, some catalysts have a limited number of active sites or low utilization rates of these sites, resulting in a slow reaction rate for photocatalytic hydrogen production. Summary of the Invention

[0005] This invention aims to address the problem of low efficiency in photocatalytic hydrogen production from existing photocatalytic hydrogen production catalysts, and provides a method for preparing and applying a ZIS / CdS / CQDs ternary composite photocatalyst. Here, ZIS is short for Zn4In2S7, and CQDs is short for Carbon Quantum Dots.

[0006] The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst of the present invention includes the following steps:

[0007] 1. Add CdS to a methanol solution, then add Zn(CH3COO)2•2H2O, InCl3•4H2O and thioacetamide in sequence, sonicate and stir; then add Na2CO3 to obtain a mixed solution.

[0008] 2. The obtained mixture is transferred to a reaction vessel and kept at 160~200℃ for 10~14h. After naturally cooling to room temperature, the obtained product is washed and dried to obtain ZIS / CdS binary composite material.

[0009] 3. Mix the ZIS / CdS binary composite material from step 2 with the freeze-dried CQDs powder, put it into a reaction vessel, keep it at 160~200℃ for 10~14h, cool it naturally to room temperature, wash it, and dry it to obtain the ZIS / CdS / CQDs ternary composite photocatalyst.

[0010] Furthermore, the volume concentration of the methanol solution in step one is 40% to 60%.

[0011] Furthermore, in step one, the mass ratio of CdS to the volume ratio of the methanol solution is (0.05~0.06) g: 70 mL.

[0012] Furthermore, in step one, the molar ratio of CdS to Zn(CH3COO)2•2H2O, InCl3•4H2O and thioacetamide is 1:(4~4.2):(6.5~7):(3~3.2).

[0013] Furthermore, in step one, the mass ratio of CdS to Na2CO3 is 1:(2~2.2).

[0014] Furthermore, in step three, the mass ratio of the ZIS / CdS binary composite material to the freeze-dried CQDs powder is 247.6: (11~15).

[0015] This invention also provides the application of ZIS / CdS / CQDs ternary composite photocatalysts in photocatalytic hydrogen production.

[0016] The beneficial effects of this invention are:

[0017] The method of this invention forms an S-type heterojunction by matching the energy levels of ZIS and CdS, which promotes the transfer of photogenerated electrons from CdS to ZIS and the reverse migration of holes, significantly improving the carrier separation efficiency. This not only enhances the photocatalytic activity, but also suppresses the photocorrosion of CdS by using ZIS as a protective layer, thereby improving the stability of the material.

[0018] CQDs possess high electron mobility and conductivity, which can act as a "bridge" to accelerate charge transfer at heterojunction interfaces and reduce recombination losses. The broad-spectral absorption capability of CQDs can also extend the visible light response range of composite materials, synergistically improving light capture efficiency with the narrow bandgap (2.26 eV) of CdS.

[0019] This invention combines ZIS / CdS binary composite material with CQDs to form a ternary composite system, which significantly improves hydrogen production performance through the coupling of multiple interface effects (charge separation, light absorption, and active sites). Attached Figure Description

[0020] Figure 1 TEM image of CQDs (scale bar is 50 nm);

[0021] Figure 2 The particle size distribution histogram of CQDs;

[0022] Figure 3 High-resolution transmission electron microscopy image of sp2-type carbon nuclei in CQDs;

[0023] Figure 4 The XRD results are for X-ZIS / CdS prepared in Examples 1-4;

[0024] Figure 5 The XRD results of 2-ZIS / CdS after in-situ loading with CQDs in Example 2 are shown.

[0025] Figure 6 The nitrogen adsorption-desorption isotherms for ZIS, CdS, and 2-ZIS / CdS in Example 2 are shown.

[0026] Figure 7 Nitrogen adsorption-desorption isotherms for 2-ZIS / CdS and 2-ZIS / CdS / CQDs-2;

[0027] Figure 8 The pore size distribution curves of ZIS, CdS, and 2-ZIS / CdS in Example 2 are shown.

[0028] Figure 9 Pore ​​size distribution curves for 2-ZIS / CdS and 2-ZIS / CdS / CQDs-2;

[0029] Figure 10 Morphological images of ZIS, CdS, X-ZIS / CdS, and X-ZIS / CdS / CQDs-X;

[0030] Figure 11 TEM image of 2-ZIS / CdS / CQDs-2 and elemental distribution map of the region obtained by EDS energy dispersive spectroscopy.

[0031] Figure 12 The full scan spectrum of 2-ZIS / CdS;

[0032] Figure 13 Comparison of XPS binding energies of sulfur in catalysts;

[0033] Figure 14 XPS binding energy comparison of In element in catalysts;

[0034] Figure 15 Comparison of XPS binding energies of Zn element in catalysts;

[0035] Figure 16 XPS binding energy comparison of Cd element in catalysts;

[0036] Figure 17 Comparison of S-element binding energy before and after in-situ XPS illumination of 2-ZIS / CdS;

[0037] Figure 18 Comparison of In element binding energy before and after in-situ XPS illumination of 2-ZIS / CdS;

[0038] Figure 19 Comparison of Cd element binding energy before and after 2-ZIS / CdS in-situ XPS illumination;

[0039] Figure 20 Comparison of Zn element binding energy before and after 2-ZIS / CdS in-situ XPS illumination;

[0040] Figure 21 For ZIS, CdS and X-ZIS / CdS (X=1, 2, 4, 6) solid UV absorption edges;

[0041] Figure 22 The UV absorption band gaps of ZIS, CdS, and X-ZIS / CdS (X=1, 2, 4, 6) solids are represented.

[0042] Figure 23 The UV absorption edges of 2-ZIS / CdS and 2-ZIS / CdS / CQDs-X (X=1, 2, 3) solids are represented.

[0043] Figure 24 The UV absorption band gaps of 2-ZIS / CdS and 2-ZIS / CdS / CQDs-X (X=1, 2, 3) solids are represented.

[0044] Figure 25 For ZIS Mott-Schottky diagrams;

[0045] Figure 26 CdS Mott-Schottky spectrum;

[0046] Figure 27 Band structures of ZIS and CdS;

[0047] Figure 28 This is a diagram of the catalytic mechanism;

[0048] Figure 29The it curves are for ZIS, CdS, and X-ZIS / CdS (X=1, 2, 4, 6);

[0049] Figure 30 The it curves for 2-ZIS / CdS and 2-ZIS / CdS / CQDs-X (X=1, 2, 3);

[0050] Figure 31 EIS curves for ZIS, CdS, and X-ZIS / CdS (X=1, 2, 4, 6);

[0051] Figure 32 EIS curves for 2-ZIS / CdS and 2-ZIS / CdS / CQDs-X (X=1, 2, 3);

[0052] Figure 33 PL curves for ZIS, CdS, 2-ZIS / CdS, and 2-ZIS / CdS / CQDs-2;

[0053] Figure 34 The curves show the hydrogen production over time for ZIS, CdS, and X-ZIS / CdS (X=1, 2, 4, 6);

[0054] Figure 35 The hydrogen production curves of 2-ZIS / CdS and 2-ZIS / CdS / CQDs-X (X=1, 2, 3) as a function of time are shown.

[0055] Figure 36 The hydrogen production rates are denoted as ZIS, CdS, and X-ZIS / CdS (X=1, 2, 4, 6).

[0056] Figure 37 Hydrogen production rates for 2-ZIS / CdS and 2-ZIS / CdS / CQDs-X (X=1, 2, 3);

[0057] Figure 38 The change in hydrogen production over time after 5 cycles of the 2-ZIS / CdS / CQDs-2 photocatalyst;

[0058] Figure 39 XRD comparison images before and after 5 cycles of 2-ZIS / CdS / CQDs-2;

[0059] Figure 40 SEM image before 2-ZIS / CdS / CQDs-3 illumination;

[0060] Figure 41 SEM images after 2-ZIS / CdS / CQDs-3 illumination. Detailed Implementation

[0061] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0062] Specific Implementation Method 1: The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst in this implementation method includes the following steps:

[0063] 1. Add CdS to a methanol solution, then add Zn(CH3COO)2•2H2O, InCl3•4H2O and thioacetamide in sequence, sonicate and stir; then add Na2CO3 to obtain a mixed solution.

[0064] 2. The obtained mixture is transferred to a reaction vessel and kept at 160~200℃ for 10~14h. After naturally cooling to room temperature, the obtained product is washed and dried to obtain ZIS / CdS.

[0065] 3. Mix the ZIS / CdS binary composite material from step 2 with the freeze-dried CQDs powder, put it into a reaction vessel, keep it at 160~200℃ for 10~14h, cool it naturally to room temperature, wash it, and dry it to obtain the ZIS / CdS / CQDs ternary composite photocatalyst.

[0066] CQDs possess excellent electron conductivity and abundant surface functional groups (such as -COOH, -OH, and -NH2), enabling them to construct "electron bridges" between two semiconductor materials. They can achieve close contact between the two semiconductors, effectively reducing the contact resistance and electron transfer barrier at the interface, and promoting faster transfer of photogenerated electrons from the conduction band of the reduced semiconductor to the valence band of the oxidized semiconductor. As a highly efficient electron transport medium, CQDs ensure that electrons from the conduction band of the reduced semiconductor can be efficiently and selectively transferred to the half-valence band of the oxidized semiconductor, where they recombine with holes. This directional transfer process is crucial, preventing undesirable type II heterojunction electron transfer (i.e., electrons from the reduced semiconductor to the conduction band of the oxidized semiconductor) between the two semiconductors, thus maximizing the preservation of the strong redox potentials of both semiconductors.

[0067] Specific Implementation Method Two: In this implementation method, the volume concentration of the methanol solution in step one is 40%~60%. Other steps and parameters are the same as in Specific Implementation Method One.

[0068] Specific Implementation Method 3: In step one of this implementation method, the mass ratio of CdS to the volume ratio of the methanol solution is (0.05~0.06) g: 70 mL. Other steps and parameters are the same as in Specific Implementation Method 1 or 2.

[0069] Specific Implementation Method Four: In step one of this implementation method, the molar ratio of CdS to Zn(CH3COO)2•2H2O, InCl3•4H2O, and thioacetamide is 1:(4~4.2):(6.5~7):(3~3.2). Other steps and parameters are the same as in any of Specific Implementation Methods One to Three.

[0070] Specific Implementation Method 5: In step one of this implementation method, the mass ratio of CdS to Na2CO3 is 1:(2~2.2). Other steps and parameters are the same as in any of Specific Implementation Methods 1 to 4.

[0071] Specific Implementation Method Six: In step three of this implementation method, the mass ratio of ZIS / CdS binary composite material to freeze-dried CQDs powder is 247.6:(11~15). Other steps and parameters are the same as in any of Specific Implementation Methods One to Five.

[0072] Specific Implementation Method Seven: Application of ZIS / CdS / CQDs ternary composite photocatalyst in photocatalytic hydrogen production.

[0073] The embodiments of the present invention will be described in detail below. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation schemes and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0074] Example 1:

[0075] The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst in this embodiment includes the following steps:

[0076] I. Hydrothermal Preparation of CQDs

[0077] At room temperature, 1 g of alkali lignin was added to 50 mL of distilled aqueous solution and stirred for 30 min until the alkali lignin was completely dispersed. The resulting dispersion was then transferred to a 100 mL polytetrafluoroethylene reactor and kept at 180 °C for 12 h. After cooling to room temperature, the brown liquid was filtered through a 0.22 μm aqueous filter membrane and dialyzed using a 3500 Da dialysis membrane for 48 h, with the deionized water replaced every 6 h. The solution was then freeze-dried to obtain CQDs.

[0078] II. Simplified Solvothermal Hydrothermal Synthesis of CdS

[0079] At room temperature, 15.65 mmol of thiourea and 5.19 mmol of Cd(NO3)2•6H2O were added to 25 mL of methanol solvent and stirred for 30 min. The mixture was then transferred to a 50 mL polytetrafluoroethylene (PTFE) reactor and kept at 200 °C for 24 h to obtain a precipitate. The precipitate was washed several times with deionized water and ethanol. It was then vacuum dried at 60 °C for 12 h and ground into powder, which is CdS.

[0080] III. Synthesis of 1-ZIS / CdS binary composite materials

[0081] 0.055 g of CdS was added to a mixed solution of 35 mL H2O and 35 mL methanol. Then, 0.8 mmol Zn(CH3COO)2•2H2O, 1.6 mmol InCl3•4H2O, and 3.2 mmol thioacetamide were added sequentially. The mixture was sonicated for 10 min and stirred for 20 min. Further, 0.11 g Na2CO3 was added to the above system to obtain a mixed solution. The resulting mixture was immediately transferred to a stainless steel autoclave and kept at 180 °C for 12 h in a forced-air drying oven. After natural cooling to room temperature, the product was washed three times alternately with deionized water and ethanol, and then dried in a vacuum oven at 60 °C for 12 h. The obtained product was named 1-ZIS / CdS.

[0082] IV. Preparation of X-ZIS / CdS / CQDs ternary composite photocatalysts

[0083] Using the optimal ratio of the 1-ZIS-CdS binary composite material from step three, 3.2 mg, 6.9 mg, and 12 mg of lyophilized CQDs powder were added respectively. The preparation method was similar to step three. The mixture was placed in a polytetrafluoroethylene high-pressure reactor and kept at 180°C for 12 h. After naturally cooling to room temperature, the mixture was washed three times with deionized water and ethanol respectively, and then placed in a vacuum oven at 60°C for 12 h. The resulting products were named 1-ZIS-CdS / CQDs-1, 1-ZIS-CdS / CQDs-2, and 1-ZIS-CdS / CQDs-3 respectively.

[0084] Example 2:

[0085] The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst in this embodiment includes the following steps:

[0086] I. Hydrothermal Preparation of CQDs

[0087] At room temperature, 1 g of alkali lignin was added to 50 mL of distilled aqueous solution and stirred for 30 min until the alkali lignin was completely dispersed. The resulting dispersion was then transferred to a 100 mL polytetrafluoroethylene reactor and kept at 180 °C for 12 h. After cooling to room temperature, the brown liquid was filtered through a 0.22 μm aqueous filter membrane and dialyzed using a 3500 Da dialysis membrane for 48 h, with the deionized water replaced every 6 h. The solution was then freeze-dried to obtain CQDs.

[0088] II. Simplified Solvothermal Hydrothermal Synthesis of CdS

[0089] At room temperature, 15.65 mmol of thiourea and 5.19 mmol of Cd(NO3)2•6H2O were added to 25 mL of methanol solvent and stirred for 30 min. The mixture was then transferred to a 50 mL polytetrafluoroethylene (PTFE) reactor and kept at 200 °C for 24 h to obtain a precipitate. The precipitate was washed several times with deionized water and ethanol. It was then vacuum dried at 60 °C for 12 h and ground into powder, which is CdS.

[0090] III. Synthesis of 2-ZIS / CdS binary composite materials

[0091] 0.055 g of CdS was added to a mixed solution of 35 mL H2O and 35 mL methanol. Then, 1.6 mmol Zn(CH3COO)2•2H2O, 3.2 mmol InCl3•4H2O, and 6.4 mmol thioacetamide were added sequentially. The mixture was sonicated for 10 min and stirred for 20 min. Further, 0.11 g Na2CO3 was added to the above system to obtain a mixed solution. The resulting mixture was immediately transferred to a stainless steel autoclave and kept at 180 °C for 12 h in a forced-air drying oven. After natural cooling to room temperature, the product was washed three times alternately with deionized water and ethanol, and then dried in a vacuum oven at 60 °C for 12 h. The obtained product was named 2-ZIS / CdS.

[0092] IV. Preparation of 2-ZIS / CdS / CQDs-X ternary composite photocatalyst

[0093] Using the optimal ratio of the 2-ZIS-CdS binary composite material from step three, 3.2 mg, 6.9 mg, and 12 mg of lyophilized CQDs powder were added respectively. The preparation method was similar to step three. The mixture was placed in a polytetrafluoroethylene high-pressure reactor and kept at 180°C for 12 h. After naturally cooling to room temperature, the mixture was washed three times with deionized water and ethanol respectively, and then placed in a vacuum oven at 60°C for 12 h. The resulting products were named 2-ZIS-CdS / CQDs-1, 2-ZIS-CdS / CQDs-2, and 2-ZIS-CdS / CQDs-3 respectively.

[0094] Example 3:

[0095] The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst in this embodiment includes the following steps:

[0096] I. Hydrothermal Preparation of CQDs

[0097] At room temperature, 1 g of alkali lignin was added to 50 mL of distilled aqueous solution and stirred for 30 min until the alkali lignin was completely dispersed. The resulting dispersion was then transferred to a 100 mL polytetrafluoroethylene reactor and kept at 180 °C for 12 h. After cooling to room temperature, the brown liquid was filtered through a 0.22 μm aqueous filter membrane and dialyzed using a 3500 Da dialysis membrane for 48 h, with the deionized water replaced every 6 h. The solution was then freeze-dried to obtain CQDs.

[0098] II. Simplified Solvothermal Hydrothermal Synthesis of CdS

[0099] At room temperature, 15.65 mmol of thiourea and 5.19 mmol of Cd(NO3)2•6H2O were added to 25 mL of methanol solvent and stirred for 30 min. The mixture was then transferred to a 50 mL polytetrafluoroethylene (PTFE) reactor and kept at 200 °C for 24 h to obtain a precipitate. The precipitate was washed several times with deionized water and ethanol. It was then vacuum dried at 60 °C for 12 h and ground into powder, which is CdS.

[0100] III. Synthesis of 4-ZIS / CdS binary composite materials

[0101] 0.055 g of CdS was added to a mixed solution of 35 mL H2O and 35 mL methanol. Then, 3.2 mmol Zn(CH3COO)2•2H2O, 6.4 mmol InCl3•4H2O, and 12.8 mmol thioacetamide were added sequentially. The mixture was sonicated for 10 min and stirred for 20 min. Further, 0.11 g Na2CO3 was added to the above system to obtain a mixed solution. The resulting mixture was immediately transferred to a stainless steel autoclave and kept at 180 °C for 12 h in a forced-air drying oven. After natural cooling to room temperature, the product was washed three times alternately with deionized water and ethanol, and then dried in a vacuum oven at 60 °C for 12 h. The obtained product was named 4-ZIS / CdS.

[0102] IV. Preparation of 4-ZIS / CdS / CQDs ternary composite photocatalysts

[0103] Using the optimal ratio of the 4-ZIS-CdS binary composite material from step three, 3.2 mg, 6.9 mg, and 12 mg of lyophilized CQDs powder were added respectively. The preparation method was similar to step three. The mixture was placed in a polytetrafluoroethylene high-pressure reactor and kept at 180°C for 12 h. After naturally cooling to room temperature, the mixture was washed three times with deionized water and ethanol respectively, and then placed in a vacuum oven at 60°C for 12 h. The resulting products were named 4-ZIS-CdS / CQDs-1, 4-ZIS-CdS / CQDs-2, and 4-ZIS-CdS / CQDs-3 respectively.

[0104] Example 4:

[0105] The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst in this embodiment includes the following steps:

[0106] I. Hydrothermal Preparation of Carbon Quantum Dots (CQDs)

[0107] At room temperature, 1 g of alkali lignin was added to 50 mL of distilled aqueous solution and stirred for 30 min until the alkali lignin was completely dispersed. The resulting dispersion was then transferred to a 100 mL polytetrafluoroethylene reactor and kept at 180 °C for 12 h. After cooling to room temperature, the brown liquid was filtered through a 0.22 μm aqueous filter membrane and dialyzed using a 3500 Da dialysis membrane for 48 h, with the deionized water replaced every 6 h. The solution was then freeze-dried to obtain CQDs.

[0108] II. Simplified Solvothermal Hydrothermal Synthesis of CdS

[0109] At room temperature, 15.65 mmol of thiourea and 5.19 mmol of Cd(NO3)2•6H2O were added to 25 mL of methanol solvent and stirred for 30 min. The mixture was then transferred to a 50 mL polytetrafluoroethylene (PTFE) reactor and kept at 200 °C for 24 h to obtain a precipitate. The precipitate was washed several times with deionized water and ethanol. It was then vacuum dried at 60 °C for 12 h and ground into powder, which is CdS.

[0110] III. Synthesis of 6-ZIS / CdS binary composite materials

[0111] 0.055 g of CdS was added to a mixed solution of 35 mL H2O and 35 mL methanol. Then, 4.8 mmol Zn(CH3COO)2•2H2O, 9.6 mmol InCl3•4H2O, and 19.2 mmol thioacetamide were added sequentially. The mixture was sonicated for 10 min and stirred for 20 min. Further, 0.11 g Na2CO3 was added to the above system to obtain a mixed solution. The resulting mixture was immediately transferred to a stainless steel autoclave and kept at 180 °C for 12 h in a forced-air drying oven. After natural cooling to room temperature, the product was washed three times alternately with deionized water and ethanol, and then dried in a vacuum oven at 60 °C for 12 h. The obtained product was named 6-ZIS / CdS.

[0112] IV. Preparation of 6-ZIS / CdS / CQDs ternary composite photocatalyst

[0113] Using the optimal ratio of the 6-ZIS-CdS binary composite material from step three, 3.2 mg, 6.9 mg, and 12 mg of lyophilized CQDs powder were added respectively. The preparation method was similar to step three. The mixture was placed in a polytetrafluoroethylene high-pressure reactor and kept at 180°C for 12 h. After naturally cooling to room temperature, the mixture was washed three times with deionized water and ethanol respectively, and then placed in a vacuum oven at 60°C for 12 h. The resulting products were named 6-ZIS-CdS / CQDs-1, 6-ZIS-CdS / CQDs-2, and 6-ZIS-CdS / CQDs-3 respectively.

[0114] The photocatalysts prepared in the above examples were tested, and the results are as follows:

[0115] (a) Microscopic morphology of CQDs

[0116] Figure 1 TEM images of CQDs prepared by the above method (scale bar is 50 nm). Figure 2 This is a histogram of the particle size distribution of CQDs. (From...) Figure 1 As can be seen, CQDs are spherical particles, and the high-resolution transmission electron microscope (HRTEM) image of their sp2-type carbon core is shown below. Figure 3 As shown, the interplanar spacing is 0.21 nm, corresponding to the (100) crystal plane of graphitic carbon. From Figure 2 It is known that the average particle size of CQDs is 0.21 nm. Generally, CQDs synthesized from natural carbon sources have an amorphous carbon structure, and the entire CQD structure is amorphous, or CQDs have a crystalline nucleus and an amorphous shell. The CQDs prepared by the method of this invention have a well-crystallized structure, which is sufficient to prove that the alkaline lignin reacts completely during the hydrothermal process.

[0117] (II) XRD Analysis

[0118] The X-ray powder diffraction (XRD) results of the X-ZIS / CdS binary composite material prepared in step three of the above embodiments are as follows: Figure 4 As shown, the diffraction peaks of the X-ZIS / CdS binary composite material belong to the space group Fd-3m, and its ZIS and CdS diffraction peaks correspond one by one to standard card 00-0244-1447 and 97-060-2958. Figure 4The diffraction peaks at 22.20°, 27.81°, and 31.62° shown can be located to the (008), (102), and (106) planes of the cubic ZIS phase, respectively (PDF number 00-0244-1447). Furthermore, the characteristic peaks of CdS at 24.89°, 26.53°, and 28.32° correspond to preferred orientations in the (100), (002), and (101) lattice planes. The diffraction peaks match those of hexagonal CdS (97-060-2958). The phase structures of ZIS, CdS, X-ZIS / CdS-X binary composites, and 2-ZIS / CdS / CQDs-2 ternary composite photocatalysts were analyzed using XRD. Figure 4 As shown, the diffraction peak at 27.5° after CdS and ZIS are combined gradually disappears with increasing ZIS content. This is because the formation of the solid solution in the X-ZIS / CdS binary composite material generates a new compound phase. This new phase has a different crystal structure, no longer produces a diffraction peak at 27.5°, and due to its unique physicochemical properties, the performance of the composite material is enhanced.

[0119] Similarly, it can be observed that the diffraction peak at 22.22° initially increases and then decreases with the formation of ZIS. As the reaction proceeds, ZIS begins to grow, and its crystal structure begins to form and gradually improve, leading to an increase in the intensity of its corresponding XRD diffraction peak. This is because as the crystal grows, the grain size increases and the crystallinity improves, making the diffraction peak sharper and more pronounced. However, when the ZIS phase continues to grow and reaches a certain thickness, its crystal structure gradually changes, forming lattice distortions and defects. These changes affect the position and intensity of the XRD diffraction peak, causing the intensity of the diffraction peak at 22.22° to decrease.

[0120] like Figure 5 As shown, in Example 2, after in-situ loading of CQDs onto the 2-ZIS / CdS binary composite material, the XRD diffraction peaks remained essentially unchanged. CQDs are nanoscale carbon materials, typically possessing small size and low crystallinity. When CQDs are loaded onto the surface of the composite material, due to their small size and high dispersion, they are loaded in an amorphous form on the surface, making it difficult to form sufficient lattice matching or generate obvious diffraction signals. Therefore, their characteristic peaks are not easily observed in the XRD pattern.

[0121] (III) BET Analysis

[0122] Figure 6 The nitrogen adsorption-desorption isotherms are shown for CdS, ZIS, and the 2-ZIS / CdS binary composite material in Example 2. Figure 7Nitrogen adsorption-desorption isotherms for 2-ZIS / CdS binary composite material and 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst. Figure 6 and Figure 7 The nitrogen adsorption-desorption isotherm shown is a typical type IV isotherm. This indicates that the two prepared composite materials have a significant mesoporous structure, and the adsorption hysteresis loop is generated due to the capillary condensation effect.

[0123] Aperture distribution curve ( Figure 8 and Figure 9 Further analysis confirmed that the material is mainly composed of abundant mesopores, due to the stacking and accumulation of nanoparticles. Precise surface area and pore volume values ​​obtained through Brunauer-Emmett-Teller testing (see Table 1) show that the construction of heterojunction nanocomposites significantly affects the porosity of the material. After the formation of the 2-ZIS / CdS binary composite material, the specific surface area increased compared to CdS and ZIS alone. Because the main morphology of ZIS is a nanoflower-like spherical structure, and CdS is composed of stacked nanospheres, the combination of the two, due to the synergistic effect of the multi-level structure, allows the CdS nanospheres to embed within the ZIS micro-flower layered structure, significantly increasing the total surface area. Furthermore, the insertion of nanospheres into the micro-flower layered structure prevents the tight stacking of the micro-flower plates, maintaining their openness and avoiding the loss of specific surface area due to agglomeration. In addition, the combination of ZIS micro-flowers (negatively charged) and CdS (with different surface charges) introduces electrostatic repulsion and steric hindrance effects, reducing the agglomeration tendency of individual components and maintaining a more uniform dispersion.

[0124] Figure 7 In-situ loading of CQDs onto the surface of the 2-ZIS / CdS binary composite material further increases the specific surface area of ​​the 2-ZIS / CdS / CQDs-2 composite photocatalyst. This is because the uniform loading of CQDs onto the surface of the binary composite material modifies its surface morphology, forming a nanoscale rough surface (similar to a "nanoparticle-base" composite structure). This increase in roughness leads to an increase in specific surface area. Simultaneously, when CQDs are combined with the composite material, their inherent functional groups can interact with the composite material, forming new active sites and further enhancing the material's reactivity.

[0125] Table 1

[0126]

[0127] (iv) SEM and TEM analysis

[0128] The morphology of pure ZIS, CdS, X-ZIS / CdS binary composite materials, and X-ZIS / CdS / CQDs-X ternary composite photocatalysts was further measured using SEM and TEM, such as... Figure 10 As shown. Figure 10 The results indicate that the ZIS micro-flowers exhibit a multi-level flower-like structure, composed of numerous stacked nanosheets. These nanosheets interconnect, forming a flower-like overall morphology, consistent with previous studies. Figure 10 In b, individual CdS mainly exhibits an irregular nanoparticle structure with obvious aggregation, which is consistent with... Figure 10 The X-ZIS / CdS binary composite material in section c has the same main morphology as ZIS, but the difference lies in the dense aggregation of CdS nanoparticles on the ZIS sheets. Compared with the SEM images of ZIS alone, the X-ZIS / CdS binary composite material exhibits a more unique layered structure and significantly reduced porosity. Because CdS is loaded on the surface of the ZIS nanosheets, the unique structure of the ZIS microflowers and nanoparticles increases the specific surface area of ​​the material, causing multiple reflections and scatterings of light on the surface, thereby improving light absorption efficiency. This means that more light energy is absorbed by the catalyst and converted into chemical energy, thus improving the efficiency of the photocatalytic reaction. Figure 10 c~f are SEM images of binary composite materials with different ZIS ratios. As the ZIS ratio increases, the micron flower structure gradually decreases. Figure 10 As observed by g~h, after in-situ loading of CQDs on the surface of the composite material, the diameter of the micron-flowers significantly decreased, from 3 μm to 1 μm. In photocatalytic reactions, the separation efficiency of photogenerated electrons and holes has a significant impact on catalytic activity. When the size of the micron-flowers decreases, the distance that photogenerated electrons and holes travel from the catalyst interior to the surface is significantly reduced, thereby decreasing their recombination probability during migration. This improves the separation efficiency of photogenerated electrons and holes, allowing more electrons and holes to participate in redox reactions, thus enhancing photocatalytic activity.

[0129] Figure 11 The image shows a TEM image (left) of the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst and an elemental distribution map (right) of the region obtained by EDS energy dispersive spectroscopy. Figure 11 (b~f) shows that various elements are uniformly distributed on the surface of the photocatalyst. Based on the above analysis, the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst has been successfully prepared. Figure 11 EDS mapping revealed a uniform distribution of In, Zn, Cd, S, and C components in the 2-ZIS / CdS / CQDs ternary composite photocatalyst, providing excellent interfacial contact between ZIS and CdS / CQDs. This contact facilitates the movement of electron-hole pairs during photocatalysis and improves the overall performance of the composite photocatalyst.

[0130] (V) XPS Analysis

[0131] The surface chemical state of the material was determined using X-ray photoelectron spectroscopy (XPS) (all peak positions were calibrated to the C1s peak at 284.80 eV). The full-range XPS spectrum is shown below. Figure 12 The results show that C, Zn, Cd, O, In, and S coexist in the 2-ZIS / CdS binary composite material, further proving that the 2-ZIS / CdS binary composite material contains ZIS and CdS. The S 2p spectrum of CdS and the Cd 3d... Figure 13 and Figure 16 The results showed that charge transfer at the interface caused negative shifts in Cd 3d and S 2p in CdS. This is because during the contact process between ZIS and CdS at the phase interface, electrons flow from ZIS to CdS, increasing the electron cloud density around CdS, which corresponds to the reduction process. To further investigate the charge transfer between the 2-ZIS / CdS binary composites, we compared the Zn 2p and In 3d spectra in ZIS. Figure 14 and Figure 15 It was found that the binding energies of Zn 2p and In 3d in the 2-ZIS / CdS binary composite material underwent a positive shift compared to ZIS. This is because ZIS loses electrons during the contact process at the ZIS-CdS interface, resulting in a decrease in the electron cloud density around it, which corresponds to the oxidation process. Since the binding energy in XPS is negatively correlated with the surface electron density, and this study showed a negative shift in Cd 3d and a positive shift in Zn 2p and In 3d, it was concluded that an S-shaped heterostructure was formed between the ZIS and CdS interfaces.

[0132] (vi) In-situ XPS

[0133] To further verify the type of heterojunction generated when ZIS and CdS come into contact at the interface, the 2-ZIS / CdS binary composite material was characterized in situ by XPS. Figure 17-20 It is clearly shown that a stepped heterojunction is formed between ZIS and CdS. This unique charge transfer path can effectively separate photogenerated carriers and retain high redox capacity charges, thereby improving the efficiency of photocatalytic hydrogen production. Since the work function of CdS is higher than that of ZIS, electrons spontaneously flow from ZIS to CdS, forming a built-in electric field (IEF) at the interface pointing from ZIS to CdS. The direction of the built-in electric field is from ZIS to CdS. Figure 9 After illumination, the Cd binding energy decreased, indicating an increase in the electron density of the Cd region; while the increase in the Zn binding energy indicated a decrease in the electron density of the ZIS region, because ZIS electrons had transferred to CdS.

[0134] (vii) Optical properties and band structure

[0135] The light absorption properties of the material were evaluated using ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). Figure 21 and 22 ).like Figure 21 As shown, the absorption edges of ZIS and CdS monomers appear at 550 nm and 620 nm, respectively. The absorption edges of the X-ZIS / CdS binary composite material exhibit a redshift compared to both ZIS and CdS monomers. This indicates that the incorporation of ZIS can increase the light absorption intensity of the binary composite material and lower the potential barrier. Among them, the 2-ZIS / CdS binary composite material shows the most significant redshift trend, exhibiting stronger light absorption capacity, meaning it can generate more visible electron-hole pairs. This result further proves that the coupling of ZIS and CdS can significantly improve the photocatalytic performance of the composite catalyst. Therefore, the 2-ZIS / CdS binary composite material was selected as the subject of further research to construct a ternary composite photocatalyst with CQDs.

[0136] according to Figure 22 and Figure 24 The Tauc equation (Equation 1) shown is used to calculate the corresponding Tauc curve of the composite photocatalyst. Figure 22 As shown, since the particle size of CdS in the binary composite material is on the order of nm, the quantum confinement effect increases the band gap of the formed composite material, resulting in a blue shift of the band gap of the X-ZIS / CdS binary composite material. Figure 23 and Figure 24 In the process of introducing CQDs into the 2-ZIS / CdS binary composite material, the absorption edge of the ternary composite photocatalyst shifts to the visible light region and the band gap width changes through surface defects, band structure adjustment, quantum confinement effect and charge transfer.

[0137] To further elucidate the mechanism of the enhanced performance of photocatalytic hydrogen production, Mot-Schottky (MS) curves of ZIS and CdS were plotted under dark conditions using an AC signal at a frequency of 1 kHz and an electrolyte of 0.1 mol / L Na2SO4. Figure 25 and Figure 26As can be seen, the slopes of the MS curves for both ZIS and CdS are positive, indicating that ZIS and CdS are n-type semiconductors. The MS curves show that the potentials of ZIS and CdS relative to the Ag / AgCl electrode are -0.49V and -0.86V (vs. Ag / AgCl), respectively. According to Equation 2, the potentials of the Ag / AgCl electrode can be converted to the potentials of the standard hydrogen electrode. Therefore, the potentials of ZIS and CdS relative to the standard hydrogen electrode are -0.29V and -0.66V (vs. NHE), respectively. Since the conduction band potential (ECB) of an n-type semiconductor is -0.1V smaller than that of Ag / AgCl, the ECBs of ZIS and CdS are -0.39V and -0.76V (vs. NHE), respectively. The valence band potentials EVB (vs. NHE) of ZIS and CdS can be calculated according to Equation 3 (e.g., ...). Figure 27 (As shown).

[0138] (αhν) n = A(hν - Eg) Equation 1

[0139] E(NHE) = E(Ag / AgCl) + 0.197 Equation 2

[0140] Eg = E VB - E CB Formula 3

[0141] In the formula, α is the absorption coefficient, A is a constant, h is Planck's constant, ν is the incident photon frequency, Eg is the semiconductor band gap, E(NHE) is the hydrogen standard electrode potential, E(Ag / AgCl) is the Ag / AgCl standard electrode potential, and E... VB E is the valence band potential. CB This is the conduction band potential.

[0142] (viii) Photoelectrochemical properties

[0143] This invention tested the transient photocurrent of ZIS, CdS, X-ZIS / CdS binary composite materials, and 2-ZIS / CdS / CQDs-X ternary composite photocatalysts under 300W (wavelength >420nm) xenon lamp irradiation to evaluate the photoelectrochemical performance of the photocatalysts. Transient photocurrent is commonly used to assess the separation efficiency of photogenerated electrons and holes; the higher the photocurrent intensity, the higher the electron-hole separation efficiency. Figure 29It is evident that the current density of the ZIS, CdS, and 2-ZIS / CdS binary composite photoelectrodes is almost zero in the absence of light. When illuminated, the photoresponse of ZIS and CdS remains weak, indicating that ZIS and CdS have poor conductivity. However, the current of the X-ZIS / CdS binary composite material increases instantaneously, indicating that the formation of the heterojunction in the binary composite material effectively improves the separation efficiency of electrons and holes, with the 2-ZIS / CdS binary composite material exhibiting the strongest photocurrent response.

[0144] Figure 30 The current density response of the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst is significantly enhanced compared to that of the 2-ZIS / CdS binary composite material, indicating higher efficiency in photogenerated electron and hole separation. This performance improvement is attributed to the presence of more surface reduction active sites in the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst. Furthermore, the CQDs anchored on the surface of the 2-ZIS / CdS binary composite material extend the electron lifetime by enhancing charge separation, significantly improving the current response intensity. These results suggest that 2-ZIS / CdS / CQDs-2 can serve as a highly efficient ternary composite photocatalyst for the photocatalytic water splitting to H2 production process.

[0145] (ix) Electrochemical impedance spectroscopy (EIS)

[0146] Electrochemical impedance spectroscopy (EIS) can detect the separation and transport characteristics of photogenerated electrons and holes in more detail. EIS Nyquist plots of ZIS, CdS, and 2-ZCS / CdS-X (X=1, 2, 3) binary composites are shown below. Figure 31 and 32 As shown. Generally, the radius of curvature of the EIS plot is proportional to the impedance of the working electrode and the resistance of the charge carriers. Therefore, the smaller the radius of curvature, the lower the impedance, and the lower the resistance of charge carrier transport, meaning that charge carrier transport between electrodes is easier and faster. This usually implies that the working electrode has better electrochemical activity and higher electron transport efficiency. Compared with CdS and ZIS, the 2-ZIS / CdS binary composite material has the smallest radius of curvature and the lowest resistance to electron migration. The micron-like flower structure of ZIS combined with the nanoparticles of CdS forms a continuous electron transport channel, shortening the charge carrier migration path and reducing interface scattering. When CQDs are combined with the binary composite material, a defect passivation mechanism is generated. CQDs are anchored to the surface of the heterojunction through chemical bonds (such as CS bonds), reducing the capture of charge carriers by surface defect states and extending the charge carrier lifetime.

[0147] Figure 33The photoluminescence (PL) emission spectra of ZIS and CdS, and 2-ZIS / CdS binary composites are shown. At excitation at 315 nm, the fluorescence peak height of the 2-ZIS / CdS binary composite is significantly lower than that of ZIS and CdS, reflecting reduced electron-hole recombination. After the formation of the S-type heterojunction, there are fewer interface defects, and carriers mainly transfer through band paths. The carriers are rapidly separated and participate in hydrogen production reactions, shortening the excited-state lifetime and leading to fluorescence quenching. Therefore, non-radiative recombination is reduced, resulting in a lower PL intensity. Notably, after doping with CQDs, the PL peak position undergoes a blue shift, which is attributed to quantum size effects (such as...). Figure 33 (As shown).

[0148] (x) Evaluation of hydrogen production performance

[0149] The photocatalytic water splitting performance of the catalysts under visible light (420 nm < λ < 800 nm) was compared. Figure 34 and 35 As shown, under visible light irradiation, the H2 production amounts of ZIS and CdS within 5 h were 30.83 mmol and 4 mmol, respectively. The catalytic activity of ZIS and CdS alone was limited by their wide band gaps, especially the low H2 production of CdS under visible light irradiation. However, after adding different proportions of ZIS to CdS, the H2 production rate of the X-ZIS / CdS binary composite material showed a trend of first increasing and then decreasing with increasing ZIS content. When X=2, the H2 production effect was optimal, reaching 153.5 mmol in 5 h, which was 4.78 times and 38.38 times that of ZIS and CdS alone, respectively. When X in the X-ZIS / CdS binary composite material was greater than 2, the ZIS content increased, but the hydrogen production effect gradually decreased. This indicates that although the ZIS content increased, it also led to the covering of the hydrogen production active potential, hindering H2 production. + The adsorption-reduction reaction of the X-ZIS / CdS binary composite material. The photocatalytic hydrogen production rate of the X-ZIS / CdS binary composite material is as follows: Figure 36 As shown, as expected, the H2 evolution capacity is greatly enhanced when an appropriate amount of ZIS combines with CdS to form a heterojunction. The comparative results clearly demonstrate that the heterojunction combination strategy of the ZIS / CdS binary composite material effectively improves the H2 evolution efficiency, with hydrogen production rates being 5.90 times and 39.75 times that of ZIS and CdS, respectively.

[0150] like Figure 35As shown, after loading different proportions of CQDs onto the 2-ZIS / CdS binary composite material, the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst exhibited the best hydrogen production capacity, achieving an H2 production of 185.21 mmol within 5 hours. This is because CQDs provide more active sites, effectively capturing photogenerated carriers and reducing the hole recombination probability, thus further enhancing the photocatalytic activity of the binary composite material. Similarly, from Figure 37 It can be seen that after loading CQDs onto the surface of the binary composite material to construct a ternary composite photocatalyst, the H2 production rate was improved to a certain extent, reaching 37.04 mmol / g•h, which is 1.29 times that of the 2-ZIS / CdS binary composite material. Figure 38 The relationship between hydrogen production and time after 5 cycles of the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst is shown. The results indicate that the photocatalytic hydrogen evolution activity of the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst did not decrease after 5 H2 production cycles, and the hydrogen production in the 5th cycle still reached 184.41 mmol. This fully demonstrates that the ternary composite photocatalyst can maintain its original activity and possess good catalytic stability after 25 h of reaction. This is because the CdS particles and CQDs attached to the ZIS surface jointly inhibit the photocorrosion of ZIS. Simultaneously, the amino groups (-NH2) on the CQDs surface can passivate defects on the surface of the 2-ZIS / CdS binary composite material, reducing carrier recombination. Furthermore, the XRD patterns of the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst before and after the reaction after 5 cycles of stability testing are shown (…). Figure 39 The results showed that after five cycles of reaction, the characteristic diffraction peaks of the 2-ZIS / CdS / CQDs-2 ternary composite photocatalyst did not shift, indicating no new phase formation and good sample stability. Similarly, scanning electron microscopy images before and after the reaction (…) Figure 40 and 41 It can be observed that its structure remains intact after 5 cycles of reaction.

Claims

1. A method for preparing a ZIS / CdS / CQDs ternary composite photocatalyst, characterized in that, The method includes the following steps:

1. Add CdS to a methanol solution, then add Zn(CH3COO)2•2H2O, InCl3•4H2O and thioacetamide in sequence, sonicate and stir; then add Na2CO3 to obtain a mixed solution.

2. The obtained mixture is transferred to a reaction vessel and kept at 160~200℃ for 10~14h. After naturally cooling to room temperature, the obtained product is washed and dried to obtain ZIS / CdS binary composite material.

3. Mix the ZIS / CdS binary composite material from step 2 with the freeze-dried CQDs powder, put it into a reaction vessel, keep it at 160~200℃ for 10~14h, cool it naturally to room temperature, wash it, and dry it to obtain the ZIS / CdS / CQDs ternary composite photocatalyst.

2. The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst according to claim 1, characterized in that, In step one, the volume concentration of the methanol solution is 40% to 60%.

3. The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst according to claim 1 or 2, characterized in that, In step one, the mass ratio of CdS to the volume ratio of methanol solution is (0.05~0.06) g: 70 mL.

4. The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst according to claim 3, characterized in that, In step one, the molar ratio of CdS to Zn(CH3COO)2•2H2O, InCl3•4H2O and thioacetamide is 1: (4~4.2): (6.5~7): (3~3.2).

5. The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst according to claim 4, characterized in that, In step one, the mass ratio of CdS to Na2CO3 is 1:(2~2.2).

6. The preparation method of the ZIS / CdS / CQDs ternary composite photocatalyst according to claim 5, characterized in that, In step three, the mass ratio of ZIS / CdS binary composite material to freeze-dried CQDs powder is 247.6: (11~15).

7. The application of the ZIS / CdS / CQDs ternary composite photocatalyst as described in claim 1 in photocatalytic hydrogen production.

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