A porous mn-cds / cerium dioxide heterojunction photocatalyst and a preparation method thereof

Abstract

The present application relates to a kind of porous MnCdS / CeO2 heterojunction photocatalyst and its preparation method, belong to composite photocatalytic material technical field.To solve the problem of low photocatalytic hydrogen production efficiency of existing MnCdS / CeO2 composite system, the present application provides a kind of porous MnCdS / CeO2 heterojunction photocatalyst, by nanosheet CeO2 carrier and the granular MnCdS solid solution in situ growth on its surface composition.The CeO2 nanosheet surface prepared by calcination method is rich in defect structure, when MnCdS is in situ grown on the CeO2 surface by solvothermal method, MnCdS particle is stacked to form abundant intergranular pore, and MnCdS / CeO2 hierarchical porous heterostructure is constructed, which synergistically promotes the separation of photo-generated carriers, so that hydrogen production rate reaches about 20.26mmol·g ‑1 ·h ‑1 , significantly enhance the photocatalytic hydrogen production performance under full spectrum.

Description

Technical Field

[0001] This invention belongs to the field of composite photocatalytic materials technology, and particularly relates to a porous MnCdS / CeO2 heterojunction photocatalyst and its preparation method. Background Technology

[0002] Solar energy and hydrogen energy, with their abundant resources and clean, efficient operation, have become ideal alternative energy sources. Photocatalytic hydrogen production technology, which combines the advantages of both, is considered one of the key pathways to address the energy and environmental dilemmas.

[0003] MnCdS solid solution, as a visible light-responsive photocatalytic material, possesses a tunable bandgap structure and excellent light absorption capacity, showing great promise in the field of photocatalytic water splitting for hydrogen production. However, the practical application of pure MnCdS solid solution is limited by the following problems: (1) the high recombination rate of photogenerated electron-hole pairs leads to low quantum efficiency; (2) nanoparticles are prone to agglomeration, reducing the effective reaction area; and (3) insufficient surface active sites restrict hydrogen production performance.

[0004] CeO2, as a typical representative of lanthanide rare earth oxides, is characterized by its unique 4f electron configuration, abundant oxygen vacancies, and Cee content. 4+ / Ce 3+ The high oxygen storage / release capacity imparted by reversible pairs has attracted much attention in the field of photocatalysis and co-catalysis. However, pure CeO2 also has significant drawbacks in practical applications: its photoresponse range is mainly limited to the ultraviolet region, resulting in low solar energy utilization; at the same time, the recombination rate of photogenerated carriers is fast, making it difficult to achieve efficient photocatalytic hydrogen production independently.

[0005] To address the aforementioned shortcomings, constructing a heterojunction composite structure of CeO2 and MnCdS solid solution is considered an effective strategy for synergistic enhancement. This strategy utilizes the charge separation effect of the heterojunction to promote the spatial separation of photogenerated carriers and suppress their recombination, thereby improving photocatalytic hydrogen production performance. However, even with this heterojunction strategy, the hydrogen production efficiency of existing MnCdS / CeO2 composite photocatalytic materials remains low. For example, the MnCdS / CeO2 composite photocatalytic material reported by Xu et al. (Applied Surface Science, Vol. 669, 2024) has shown limited efficiency. 0.2 Cd 0.8 The hydrogen production of the S / CeO2 heterojunction under simulated sunlight is only 291.8 μmol, which is far from meeting the needs of practical applications. Therefore, how to further and significantly improve the photocatalytic hydrogen production efficiency of the MnCdS / CeO2 composite system based on the charge separation effect of the heterojunction remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the problem that existing MnCdS / CeO2 composite systems have low photocatalytic hydrogen production efficiency and cannot meet the needs of practical applications, this invention provides a porous MnCdS / CeO2 heterojunction photocatalyst and its preparation method.

[0007] The technical solution of this invention:

[0008] A method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst includes the following steps:

[0009] Step 1: Preparation of CeO2 precursor:

[0010] An aqueous solution of ammonium bicarbonate was poured into an aqueous solution of cerium nitrate and allowed to stand for 3-5 hours to obtain a white precipitate. The precipitate was washed with deionized water and ethanol respectively and then dried to obtain the CeO2 precursor.

[0011] Step 2: Calcination to prepare nanosheet CeO2:

[0012] The CeO2 precursor obtained in step one was calcined at 300~500℃ for 2~5h to obtain nano-sheet CeO2;

[0013] Step 3: Prepare the MnCdS solid solution precursor solution:

[0014] Manganese acetate, cadmium acetate and L-cysteine ​​were added to triethylene glycol solvent, stirred and sonicated until completely dissolved to obtain MnCdS solid solution precursor solution.

[0015] Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method:

[0016] The nanosheet CeO2 obtained in step 2 was added to the MnCdS solid solution precursor solution obtained in step 3. After mixing evenly, the mixture was reacted at 150~250℃ for 15~30 h. After cooling, the mixture was washed, centrifuged and dried to obtain a porous MnCdS / CeO2 heterojunction photocatalyst.

[0017] Furthermore, the concentration of cerium nitrate in the cerium nitrate aqueous solution in step one is 5.45~10.00 g / L, and the concentration of ammonium bicarbonate in the ammonium bicarbonate aqueous solution is 3.75 g / L.

[0018] Furthermore, the drying process described in step one involves drying at 60-90°C for 18-24 hours.

[0019] Furthermore, in step three, the concentration of manganese acetate in the MnCdS solid solution precursor solution is 5.00~15.00 g / L, the concentration of cadmium acetate is 5.00~15.00 g / L, and the concentration of L-cysteine ​​is 15.00~37.50 g / L.

[0020] Furthermore, in step four, the volume-to-mass ratio of nanosheet CeO2 to MnCdS solid solution precursor solution is 0.375~1.5g:100mL.

[0021] Furthermore, the centrifugation speed in step four is 8000~10000 r / min; the washing process involves first washing with deionized water 3~5 times, and then washing with anhydrous ethanol 3~5 times.

[0022] Furthermore, the drying process described in step four involves drying in a vacuum drying oven at 60-90°C for 12-24 hours.

[0023] A porous MnCdS / CeO2 heterojunction photocatalyst prepared by a preparation method provided by the present invention.

[0024] Furthermore, it includes a nanosheet-like CeO2 support and a particulate MnCdS solid solution. The particulate MnCdS solid solution is grown in situ on the surface of the nanosheet-like CeO2 support and forms a heterojunction structure at the interface. The particulate MnCdS solid solution is stacked on the surface of the nanosheet-like CeO2 support to form intergranular pores, thus constituting a porous structure.

[0025] The beneficial effects of this invention are:

[0026] This invention is the first to discover that CeO2 nanosheets prepared by calcination exhibit a defect-rich surface structure. This defect-rich structure provides a high density of nucleation sites, enabling MnCdS to grow uniformly and densely in situ on the CeO2 surface. A heterojunction structure is formed at the interface, which not only effectively alleviates MnCdS aggregation but also naturally forms intergranular pores between adjacent MnCdS particles, thus constructing a hierarchical porous heterostructure of MnCdS / CeO2. This structure, in synergy with the heterojunction, significantly promotes the separation and transfer of photogenerated carriers, effectively suppresses carrier recombination, and provides more reactive sites and facilitates mass transfer, thereby significantly improving the utilization rate of solar energy in the photocatalytic process.

[0027] The results of the photocatalytic hydrogen production experiment show that the porous MnCdS / CeO2 composite photocatalyst material prepared in this invention achieved a total hydrogen production of approximately 81.06 mmol and a hydrogen yield of approximately 20.26 mmol·g under simulated sunlight for four hours. -1 ·h -1 The efficiency is approximately 5 times that of pure MnCdS and 241 times that of pure CeO2, respectively, demonstrating significant advantages.

[0028] The preparation process of this invention requires no additional template agents or complex post-processing steps. It involves preparing defect-rich CeO2 nanosheets via calcination, followed by in-situ growth of MnCdS using a solvothermal method to form a hierarchical porous structure. This simple and low-cost process is suitable for industrial production. The porous MnCdS / CeO2 heterojunction photocatalyst provided by this invention exhibits excellent photocatalytic hydrogen production performance across the entire spectrum, offering an effective solution to the low hydrogen production efficiency of existing MnCdS / CeO2 composite systems. It has broad application prospects in the field of photocatalytic water splitting for hydrogen production. Attached Figure Description

[0029] Figure 1 The images show the XRD patterns of the porous MnCdS / CeO2 composite photocatalyst material obtained in Example 2, the nanosheet CeO2 photocatalyst material of Comparative Example 1, and the MnCdS solid solution photocatalyst material of Comparative Example 2.

[0030] Figure 2 The images show TEM images of the nanosheet CeO2 and porous MnCdS / CeO2 heterojunction photocatalysts prepared in Example 2. (a) is the HAADF-STEM image of the nanosheet CeO2, and (b) is the HAADF-STEM image of the porous MnCdS / CeO2 composite photocatalyst.

[0031] Figure 3 SEM images of the porous MnCdS / CeO2 composite photocatalyst material obtained in Example 2, the nanosheet CeO2 photocatalyst material of Comparative Example 1, and the MnCdS solid solution photocatalyst material of Comparative Example 2 are shown. (a) shows MnCdS nanoparticles, (b) shows nanosheet CeO2, and (c) shows the porous MnCdS / CeO2 composite photocatalyst material.

[0032] Figure 4 The graph shows a comparison of hydrogen production from the porous MnCdS / CeO2 composite photocatalyst material obtained in Examples 1-5, the nanosheet CeO2 photocatalyst material of Comparative Example 1, and the MnCdS solid solution photocatalyst material of Comparative Example 2. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0034] Example 1

[0035] This embodiment provides a method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst, comprising the following steps:

[0036] Step 1: Preparation of CeO2 precursor

[0037] Add 1.39g of cerium nitrate to 200mL of deionized water and stir magnetically to dissolve the cerium nitrate completely until the solution is transparent and free of powder particles, thus obtaining solution A;

[0038] Dissolve 0.75 g of ammonium bicarbonate in 200 mL of deionized water and stir until completely dissolved to obtain solution B;

[0039] Solution B was quickly poured into solution A to allow cerium nitrate to react with ammonium bicarbonate. The mixture was then allowed to stand at room temperature for 4 hours to allow the reaction to proceed fully, resulting in a white precipitate.

[0040] The mixed solution after the reaction was centrifuged at 8000 r / min. After removing the supernatant, it was washed three times with deionized water and then twice with ethanol to remove impurities from the precipitate. Deionized water was chosen for washing because it does not react with the reaction products and does not introduce new impurities.

[0041] The washed precipitate was placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a white powdery CeO2 precursor.

[0042] Step 2: Calcination to prepare nanosheet CeO2

[0043] The dried CeO2 precursor powder was transferred to a muffle furnace and calcined at 400°C for 4 hours to fully oxidize the precursor, resulting in a light yellow powder-like nanosheet CeO2 material. The nanosheet CeO2 surface exhibits a defect-rich structure, providing a high density of nucleation sites.

[0044] Step 3: Prepare MnCdS solid solution precursor solution

[0045] 0.245 g manganese acetate, 0.2664 g cadmium acetate and 0.726 g L-cysteine ​​were added to 35 mL of triethylene glycol solvent, and stirred and sonicated until completely dissolved to obtain a MnCdS solid solution precursor solution.

[0046] Triethylene glycol can dissolve both organic and inorganic substances. Choosing triethylene glycol as a solvent allows for the good dissolution of manganese acetate, cadmium acetate, and L-cysteine, thus ensuring that the reactants react fully in the mixed solution.

[0047] Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method

[0048] Take 0.1892g of the nanosheet CeO2 material obtained in step two and add it to the MnCdS solid solution precursor solution obtained in step three while stirring, so that the nanosheet CeO2 material is evenly dispersed and avoids accumulation, and a reaction solution is obtained.

[0049] The reaction solution was transferred to a polytetrafluoroethylene-lined reactor and kept at 180°C for 24 hours. During the reaction, manganese acetate, cadmium acetate, and L-cysteine ​​reacted to generate MnCdS solid solution. The MnCdS solid solution grew uniformly and densely on the CeO2 surface, forming a heterojunction structure at the interface. The particulate MnCdS solid solution also formed interparticle pores by stacking on the nanosheet CeO2 support, thus constructing a hierarchical porous heterostructure of MnCdS / CeO2.

[0050] After the reaction is complete, allow the mixture to cool naturally to room temperature. Wash the resulting precipitate 3 to 5 times with deionized water, and then wash it 3 to 5 times with anhydrous ethanol. After each washing, centrifuge at 8000 r / min.

[0051] The washed product was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain a porous MnCdS / CeO2 heterojunction photocatalyst, denoted as MnCdS / CeO2-1.1.

[0052] Example 2

[0053] This embodiment provides a method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst, comprising the following steps:

[0054] Step 1: Preparation of CeO2 precursor

[0055] Add 1.39g of cerium nitrate to 200mL of deionized water and stir magnetically to dissolve the cerium nitrate completely until the solution is transparent and free of powder particles, thus obtaining solution A;

[0056] Dissolve 0.75 g of ammonium bicarbonate in 200 mL of deionized water and stir until completely dissolved to obtain solution B;

[0057] Solution B was quickly poured into solution A to allow cerium nitrate to react with ammonium bicarbonate. The mixture was then allowed to stand at room temperature for 4 hours to allow the reaction to proceed fully, resulting in a white precipitate.

[0058] The mixed solution after the reaction was centrifuged at 8000 r / min. After removing the supernatant, it was washed three times with deionized water and then twice with ethanol to remove impurities from the precipitate. Deionized water was chosen for washing because it does not react with the reaction products and does not introduce new impurities.

[0059] The washed precipitate was placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a white powdery CeO2 precursor.

[0060] Step 2: Calcination to prepare nanosheet CeO2

[0061] The dried CeO2 precursor powder was transferred to a muffle furnace and calcined at 400°C for 4 hours to fully oxidize the precursor, resulting in a light yellow powder-like nanosheet CeO2 material. The nanosheet CeO2 surface exhibits a defect-rich structure, providing a high density of nucleation sites.

[0062] Step 3: Prepare MnCdS solid solution precursor solution

[0063] 0.245 g manganese acetate, 0.2664 g cadmium acetate and 0.726 g L-cysteine ​​were added to 35 mL of triethylene glycol solvent, and stirred and sonicated until completely dissolved to obtain a MnCdS solid solution precursor solution.

[0064] Triethylene glycol can dissolve both organic and inorganic substances. Choosing triethylene glycol as a solvent allows for the good dissolution of manganese acetate, cadmium acetate, and L-cysteine, thus ensuring that the reactants react fully in the mixed solution.

[0065] Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method

[0066] Take 0.2064g of the nanosheet CeO2 material obtained in step two and add it to the MnCdS solid solution precursor solution obtained in step three while stirring, so that the nanosheet CeO2 material is evenly dispersed and avoids accumulation, and a reaction solution is obtained.

[0067] The reaction solution was transferred to a polytetrafluoroethylene-lined reactor and kept at 180°C for 24 hours. During the reaction, manganese acetate, cadmium acetate, and L-cysteine ​​reacted to generate MnCdS solid solution. The MnCdS solid solution grew uniformly and densely on the CeO2 surface, forming a heterojunction structure at the interface. The particulate MnCdS solid solution also formed interparticle pores by stacking on the nanosheet CeO2 support, thus constructing a hierarchical porous heterostructure of MnCdS / CeO2.

[0068] After the reaction is complete, allow the mixture to cool naturally to room temperature. Wash the resulting precipitate 3 to 5 times with deionized water, and then wash it 3 to 5 times with anhydrous ethanol. After each washing, centrifuge at 8000 r / min.

[0069] The washed product was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain a porous MnCdS / CeO2 heterojunction photocatalyst, denoted as MnCdS / CeO2-1.2.

[0070] Example 3

[0071] This embodiment provides a method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst, comprising the following steps:

[0072] Step 1: Preparation of CeO2 precursor

[0073] Add 1.39g of cerium nitrate to 200mL of deionized water and stir magnetically to dissolve the cerium nitrate completely until the solution is transparent and free of powder particles, thus obtaining solution A;

[0074] Dissolve 0.75 g of ammonium bicarbonate in 200 mL of deionized water and stir until completely dissolved to obtain solution B;

[0075] Solution B was quickly poured into solution A to allow cerium nitrate to react with ammonium bicarbonate. The mixture was then allowed to stand at room temperature for 4 hours to allow the reaction to proceed fully, resulting in a white precipitate.

[0076] The mixed solution after the reaction was centrifuged at 8000 r / min. After removing the supernatant, it was washed three times with deionized water and then twice with ethanol to remove impurities from the precipitate. Deionized water was chosen for washing because it does not react with the reaction products and does not introduce new impurities.

[0077] The washed precipitate was placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a white powdery CeO2 precursor.

[0078] Step 2: Calcination to prepare nanosheet CeO2

[0079] The dried CeO2 precursor powder was transferred to a muffle furnace and calcined at 400°C for 4 hours to fully oxidize the precursor, resulting in a light yellow powder-like nanosheet CeO2 material. The nanosheet CeO2 surface exhibits a defect-rich structure, providing a high density of nucleation sites.

[0080] Step 3: Prepare MnCdS solid solution precursor solution

[0081] 0.245 g manganese acetate, 0.2664 g cadmium acetate and 0.726 g L-cysteine ​​were added to 35 mL of triethylene glycol solvent, and stirred and sonicated until completely dissolved to obtain a MnCdS solid solution precursor solution.

[0082] Triethylene glycol can dissolve both organic and inorganic substances. Choosing triethylene glycol as a solvent allows for the good dissolution of manganese acetate, cadmium acetate, and L-cysteine, thus ensuring that the reactants react fully in the mixed solution.

[0083] Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method

[0084] Take 0.2236g of the nanosheet CeO2 material obtained in step two and add it to the MnCdS solid solution precursor solution obtained in step three while stirring, so that the nanosheet CeO2 material is evenly dispersed and avoids accumulation, and a reaction solution is obtained.

[0085] The reaction solution was transferred to a polytetrafluoroethylene-lined reactor and kept at 180°C for 24 hours. During the reaction, manganese acetate, cadmium acetate, and L-cysteine ​​reacted to generate MnCdS solid solution. The MnCdS solid solution grew uniformly and densely on the CeO2 surface, forming a heterojunction structure at the interface. The particulate MnCdS solid solution also formed interparticle pores by stacking on the nanosheet CeO2 support, thus constructing a hierarchical porous heterostructure of MnCdS / CeO2.

[0086] After the reaction is complete, allow the mixture to cool naturally to room temperature. Wash the resulting precipitate 3 to 5 times with deionized water, and then wash it 3 to 5 times with anhydrous ethanol. After each washing, centrifuge at 8000 r / min.

[0087] The washed product was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain a porous MnCdS / CeO2 heterojunction photocatalyst, denoted as MnCdS / CeO2-1.3.

[0088] Example 4

[0089] This embodiment provides a method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst, comprising the following steps:

[0090] Step 1: Preparation of CeO2 precursor

[0091] Add 1.39g of cerium nitrate to 200mL of deionized water and stir magnetically to dissolve the cerium nitrate completely until the solution is transparent and free of powder particles, thus obtaining solution A;

[0092] Dissolve 0.75 g of ammonium bicarbonate in 200 mL of deionized water and stir until completely dissolved to obtain solution B;

[0093] Solution B was quickly poured into solution A to allow cerium nitrate to react with ammonium bicarbonate. The mixture was then allowed to stand at room temperature for 4 hours to allow the reaction to proceed fully, resulting in a white precipitate.

[0094] The mixed solution after the reaction was centrifuged at 8000 r / min. After removing the supernatant, it was washed three times with deionized water and then twice with ethanol to remove impurities from the precipitate. Deionized water was chosen for washing because it does not react with the reaction products and does not introduce new impurities.

[0095] The washed precipitate was placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a white powdery CeO2 precursor.

[0096] Step 2: Calcination to prepare nanosheet CeO2

[0097] The dried CeO2 precursor powder was transferred to a muffle furnace and calcined at 400°C for 4 hours to fully oxidize the precursor, resulting in a light yellow powder-like nanosheet CeO2 material. The nanosheet CeO2 surface exhibits a defect-rich structure, providing a high density of nucleation sites.

[0098] Step 3: Prepare MnCdS solid solution precursor solution

[0099] 0.245 g manganese acetate, 0.2664 g cadmium acetate and 0.726 g L-cysteine ​​were added to 35 mL of triethylene glycol solvent, and stirred and sonicated until completely dissolved to obtain a MnCdS solid solution precursor solution.

[0100] Triethylene glycol can dissolve both organic and inorganic substances. Choosing triethylene glycol as a solvent allows for the good dissolution of manganese acetate, cadmium acetate, and L-cysteine, thus ensuring that the reactants react fully in the mixed solution.

[0101] Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method

[0102] Take 0.2408g of the nanosheet CeO2 material obtained in step two and add it to the MnCdS solid solution precursor solution obtained in step three while stirring, so that the nanosheet CeO2 material is evenly dispersed and avoids accumulation, and a reaction solution is obtained.

[0103] The reaction solution was transferred to a polytetrafluoroethylene-lined reactor and kept at 180°C for 24 hours. During the reaction, manganese acetate, cadmium acetate, and L-cysteine ​​reacted to generate MnCdS solid solution. The MnCdS solid solution grew uniformly and densely on the CeO2 surface, forming a heterojunction structure at the interface. The particulate MnCdS solid solution also formed interparticle pores by stacking on the nanosheet CeO2 support, thus constructing a hierarchical porous heterostructure of MnCdS / CeO2.

[0104] After the reaction is complete, allow the mixture to cool naturally to room temperature. Wash the resulting precipitate 3 to 5 times with deionized water, and then wash it 3 to 5 times with anhydrous ethanol. After each washing, centrifuge at 8000 r / min.

[0105] The washed product was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain a porous MnCdS / CeO2 heterojunction photocatalyst, denoted as MnCdS / CeO2-1.4.

[0106] Example 5

[0107] This embodiment provides a method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst, comprising the following steps:

[0108] Step 1: Preparation of CeO2 precursor

[0109] Add 1.39g of cerium nitrate to 200mL of deionized water and stir magnetically to dissolve the cerium nitrate completely until the solution is transparent and free of powder particles, thus obtaining solution A;

[0110] Dissolve 0.75 g of ammonium bicarbonate in 200 mL of deionized water and stir until completely dissolved to obtain solution B;

[0111] Solution B was quickly poured into solution A to allow cerium nitrate to react with ammonium bicarbonate. The mixture was then allowed to stand at room temperature for 4 hours to allow the reaction to proceed fully, resulting in a white precipitate.

[0112] The mixed solution after the reaction was centrifuged at 8000 r / min. After removing the supernatant, it was washed three times with deionized water and then twice with ethanol to remove impurities from the precipitate. Deionized water was chosen for washing because it does not react with the reaction products and does not introduce new impurities.

[0113] The washed precipitate was placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a white powdery CeO2 precursor.

[0114] Step 2: Calcination to prepare nanosheet CeO2

[0115] The dried CeO2 precursor powder was transferred to a muffle furnace and calcined at 400°C for 4 hours to fully oxidize the precursor, resulting in a light yellow powder-like nanosheet CeO2 material. The nanosheet CeO2 surface exhibits a defect-rich structure, providing a high density of nucleation sites.

[0116] Step 3: Prepare MnCdS solid solution precursor solution

[0117] 0.245 g manganese acetate, 0.2664 g cadmium acetate and 0.726 g L-cysteine ​​were added to 35 mL of triethylene glycol solvent, and stirred and sonicated until completely dissolved to obtain a MnCdS solid solution precursor solution.

[0118] Triethylene glycol can dissolve both organic and inorganic substances. Choosing triethylene glycol as a solvent allows for the good dissolution of manganese acetate, cadmium acetate, and L-cysteine, thus ensuring that the reactants react fully in the mixed solution.

[0119] Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method

[0120] Take 0.258g of the nanosheet CeO2 material obtained in step two and add it to the MnCdS solid solution precursor solution obtained in step three while stirring, so that the nanosheet CeO2 material is evenly dispersed and avoids accumulation, and a reaction solution is obtained.

[0121] The reaction solution was transferred to a polytetrafluoroethylene-lined reactor and kept at 180°C for 24 hours. During the reaction, manganese acetate, cadmium acetate, and L-cysteine ​​reacted to generate MnCdS solid solution. The MnCdS solid solution grew uniformly and densely on the CeO2 surface, forming a heterojunction structure at the interface. The particulate MnCdS solid solution also formed interparticle pores by stacking on the nanosheet CeO2 support, thus constructing a hierarchical porous heterostructure of MnCdS / CeO2.

[0122] After the reaction is complete, allow the mixture to cool naturally to room temperature. Wash the resulting precipitate 3 to 5 times with deionized water, and then wash it 3 to 5 times with anhydrous ethanol. After each washing, centrifuge at 8000 r / min.

[0123] The washed product was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain a porous MnCdS / CeO2 heterojunction photocatalyst, denoted as MnCdS / CeO2-1.5.

[0124] Comparative Example 1

[0125] This comparative example provides a method for preparing nanosheet-like CeO2, including the following steps:

[0126] Step 1: Preparation of CeO2 precursor

[0127] Add 1.39g of cerium nitrate to 200mL of deionized water and stir magnetically to dissolve the cerium nitrate completely until the solution is transparent and free of powder particles, thus obtaining solution A;

[0128] Dissolve 0.75 g of ammonium bicarbonate in 200 mL of deionized water and stir until completely dissolved to obtain solution B;

[0129] Solution B was quickly poured into solution A to allow cerium nitrate to react with ammonium bicarbonate. The mixture was then allowed to stand at room temperature for 4 hours to allow the reaction to proceed fully, resulting in a white precipitate.

[0130] The mixed solution after the reaction was centrifuged at 8000 r / min. After removing the supernatant, it was washed three times with deionized water and then twice with ethanol to remove impurities from the precipitate.

[0131] The washed precipitate was placed in a vacuum drying oven and dried at 60°C for 24 h to obtain a white powdery CeO2 precursor.

[0132] Step 2: Calcination to prepare nanosheet CeO2

[0133] The dried CeO2 precursor powder was transferred to a muffle furnace and calcined at 400°C for 4 hours to fully oxidize the precursor, resulting in a light yellow powder-like nanosheet CeO2 material.

[0134] Comparative Example 2

[0135] This comparative example provides a method for preparing a MnCdS solid solution photocatalytic material, including the following steps:

[0136] 0.245 g of manganese acetate, 0.2664 g of cadmium acetate, and 0.726 g of L-cysteine ​​were added to 35 mL of triethylene glycol solvent, and the mixture was stirred and sonicated until completely dissolved to obtain a MnCdS solid solution precursor solution. The MnCdS solid solution precursor solution was transferred to a reaction vessel and reacted at 180 °C for 24 h. Then, it was centrifuged at 8000 r / min, and the precipitate obtained by centrifugation was washed four times with deionized water and anhydrous ethanol. The precipitate was then dried at 80 °C for 12 h to obtain the MnCdS solid solution photocatalytic material.

[0137] Experimental Example 1

[0138] The porous MnCdS / CeO2 composite photocatalyst material obtained in Example 2, the nanosheet CeO2 photocatalyst material of Comparative Example 1, and the MnCdS solid solution photocatalyst material of Comparative Example 2 were detected using an X'Pert PRO Cu-Kα diffractometer from Panalytical Analytical Instrument Company. The scanning angle 2θ during the diffraction process ranged from 20° to 80°.

[0139] The results are as follows Figure 1 As shown, Figure 1 The horizontal axis represents the scanning angle, and the vertical axis represents the peak intensity. Figure 1 The three curves in the middle, from top to bottom, represent CeO2 photocatalytic material, porous MnCdS / CeO2 composite photocatalytic material, and MnCdS solid solution photocatalytic material, respectively.

[0140] from Figure 1 As can be seen, the crystal phase composition of the MnCdS / CeO2 sample was studied using X-ray powder diffraction. A mixed phase structure of MnCdS and CeO2 was observed. The sample exhibited obvious characteristic peaks at 2θ = 28.55°, 33.08°, 47.49°, 56.35°, 76.71°, and 88.44°. These peaks were well aligned with the (111), (200), (220), (311), and (331) crystal planes of pure CeO2. The diffraction peaks at 2θ = 25.2°, 27°, 28.7°, 37.3°, 44.5°, 48.8°, and 52.8° matched well with those of MnCdS. The XRD results indicate that the porous MnCdS / CeO2 composite photocatalytic material was successfully prepared. It is worth noting that the strong XRD diffraction peak at 2θ = 28.5 ° indicates that the characteristic peaks of the MnCdS solid solution sample and the CeO2 sample are similar, and that CeO2 and MnCdS solid solution are combined in the porous MnCdS / CeO2 composite photocatalytic material.

[0141] Experimental Example 2

[0142] The porous MnCdS / CeO2 composite photocatalyst material obtained in Example 2 was characterized and observed using transmission electron microscopy (TEM, JEOL JEM-2100F). The results are as follows: Figure 2 As shown, Figure (a) is a HAADF-STEM image of nanosheet CeO2, and Figure (b) is a HAADF-STEM image of porous MnCdS / CeO2 composite material.

[0143] As can be seen from Figure (a), the surface of the nanosheet CeO2 exhibits a distinct defect-rich structure. As can be seen from Figure (b), in the porous MnCdS / CeO2 composite photocatalytic material, a large number of nanoscale particles are uniformly distributed and loaded on the surface of the nanosheet CeO2. Moreover, the nanoscale particles stacked on the composite CeO2 nanosheets have a distinct porous / mesoporous structure, and the pore characteristics between the particles are clearly visible.

[0144] The porous MnCdS / CeO2 composite photocatalyst material obtained in Example 2, the nanosheet CeO2 photocatalyst material of Comparative Example 1, and the MnCdS solid solution photocatalyst material of Comparative Example 2 were characterized and observed using field emission scanning electron microscopy (FE-SEM, Sirion200, Philips).

[0145] The results are as follows Figure 3 As shown, where Figure 3 (a) is a SEM image of the MnCdS solid solution photocatalytic material, (b) is a SEM image of the nanosheet CeO2 photocatalytic material, and (c) is a SEM image of the porous MnCdS / CeO2 composite photocatalytic material.

[0146] from Figure 3 As can be seen in (a), the MnCdS solid solution photocatalytic material obtained in Comparative Example 2 is granular; from Figure 3 As can be seen in (b), the CeO2 photocatalytic material obtained in Comparative Example 1 has a nanosheet structure; from Figure 3 As can be seen in (c), the obtained porous MnCdS / CeO2 composite photocatalyst material consists of particulate MnCdS solid solution composite nanosheet CeO2 and... Figure 3 In (c), it can be clearly seen that there is a hierarchical porous structure between the stacked nanoscale particles on the CeO2 nanosheets.

[0147] Experimental Example 3

[0148] Photocatalytic water splitting to produce hydrogen was conducted using a porous MnCdS / CeO2 composite photocatalytic material obtained in Examples 1-5, a nanosheet CeO2 photocatalytic material obtained in Comparative Example 1, and a MnCdS solid solution photocatalytic material obtained in Comparative Example 2, respectively, to verify the performance of the pure samples and the composite materials.

[0149] The specific experimental method was as follows: A 300W xenon lamp was used as the reaction instrument and light source in a top-irradiated reaction apparatus. 10mg of MnCdS / CeO2 composite photocatalyst, nanosheet CeO2 photocatalyst, and MnCdS solid solution photocatalyst were uniformly dispersed in 50mL of water. Sodium sulfide and sodium sulfite were used as sacrificial agents. The photocatalytic hydrogen experiment was carried out at a temperature of 5℃. Every hour, the volume of hydrogen generated was quantitatively analyzed and detected by gas chromatography, and the hydrogen production efficiency was calculated.

[0150] The results are as follows Figure 4 As shown, Figure 4 The horizontal axis represents catalytic time, and the vertical axis represents hydrogen production. MnCdS / CeO2 represents porous MnCdS / CeO2 composite photocatalytic material, CeO2 represents nanosheet CeO2 material photocatalytic material, and MnCdS represents particulate MnCdS solid solution photocatalytic material.

[0151] from Figure 4 As can be seen, after 4 hours of catalysis, the H2 yield produced by the porous MnCdS / CeO2 composite photocatalyst is approximately 81.06 mmol, far exceeding the catalytic yields of the nanosheet CeO2 photocatalyst (approximately 0.336 mmol) and the MnCdS solid solution photocatalyst (approximately 16 mmol). This indicates that the porous MnCdS / CeO2 composite photocatalyst prepared by the method of this invention can improve the photocatalytic hydrogen production performance. This is mainly because MnCdS / CeO2 has a large specific surface area, which not only improves the light absorption rate but also facilitates the exposure of more edge positions. When MnCdS solid solution particles grow in situ on the surface of nanosheet CeO2 to form a composite heterojunction interface, the composite of the two materials leads to defects and pores on the CeO2 surface, effectively promoting the separation and transfer of photogenerated carriers, thereby greatly improving the photocatalytic hydrogen production activity.

[0152] In summary, the embodiments of this invention provide a porous MnCdS / CeO2 heterojunction photocatalyst and its preparation method. The prepared porous MnCdS / CeO2 composite photocatalyst is a binary composite material composed of nanosheet CeO2 and particulate MnCdS solid solution. The particulate MnCdS solid solution is grown in situ on the surface of the nanosheet CeO2, and the two materials form a heterojunction structure at the interface. The nanosheet CeO2 has a large specific surface area, thus exposing more active sites, while the MnCdS solid solution has a suitable band structure (-1.06-1.38 eV) and a good conduction band potential, making it easier to absorb visible light and form photogenerated carriers. Furthermore, its conduction band potential is beneficial for the decomposition and reduction of water to produce hydrogen. In addition, CeO2, as a cocatalyst, has a specific 4f electronic structure, which can enable the photogenerated electrons formed after the MnCdS solid solution is irradiated to transfer rapidly through the heterojunction, thereby reducing the recombination rate of photogenerated carriers and improving photocatalytic efficiency.

Claims

1. A method for preparing a porous MnCdS / CeO2 heterojunction photocatalyst, characterized in that, Includes the following steps: Step 1: Preparation of CeO2 precursor: An aqueous solution of ammonium bicarbonate was poured into an aqueous solution of cerium nitrate and allowed to stand for 3-5 hours to obtain a white precipitate. The precipitate was washed with deionized water and ethanol respectively and then dried to obtain the CeO2 precursor. Step 2: Calcination to prepare nanosheet CeO2: The CeO2 precursor obtained in step one was calcined at 300~500℃ for 2~5h to obtain nano-sheet CeO2; Step 3: Prepare the MnCdS solid solution precursor solution: Manganese acetate, cadmium acetate and L-cysteine ​​were added to triethylene glycol solvent, stirred and sonicated until completely dissolved to obtain MnCdS solid solution precursor solution. Step 4: Preparation of porous MnCdS / CeO2 composite material by solvothermal method: The nanosheet CeO2 obtained in step 2 was added to the MnCdS solid solution precursor solution obtained in step 3. After mixing evenly, the mixture was reacted at 150~250℃ for 15~30 h. After cooling, the mixture was washed, centrifuged and dried to obtain a porous MnCdS / CeO2 heterojunction photocatalyst.

2. The method for preparing the porous MnCdS / CeO2 heterojunction photocatalyst according to claim 1, characterized in that, In step one, the concentration of cerium nitrate in the cerium nitrate aqueous solution is 5.45~10.00 g / L, and the concentration of ammonium bicarbonate in the ammonium bicarbonate aqueous solution is 3.75 g / L.

3. The method for preparing the porous MnCdS / CeO2 heterojunction photocatalyst according to claim 1 or 2, characterized in that, The drying process described in step one involves drying at 60-90℃ for 18-24 hours.

4. The method for preparing the porous MnCdS / CeO2 heterojunction photocatalyst according to claim 3, characterized in that, In step three, the concentration of manganese acetate in the MnCdS solid solution precursor solution is 5.00~15.00 g / L, the concentration of cadmium acetate is 5.00~15.00 g / L, and the concentration of L-cysteine ​​is 15.00~37.50 g / L.

5. The preparation method of the porous MnCdS / CeO2 heterojunction photocatalyst according to claim 4, characterized in that, In step four, the volume-to-mass ratio of nanosheet CeO2 to MnCdS solid solution precursor solution is 0.375~1.5g:100mL.

6. The method for preparing the porous MnCdS / CeO2 heterojunction photocatalyst according to claim 5, characterized in that, The centrifugation speed in step four is 8000~10000 r / min; the washing process involves washing with deionized water 3~5 times, followed by washing with anhydrous ethanol 3~5 times.

7. The method for preparing the porous MnCdS / CeO2 heterojunction photocatalyst according to claim 6, characterized in that, The drying process described in step four involves drying in a vacuum drying oven at 60-90°C for 12-24 hours.

8. A porous MnCdS / CeO2 heterojunction photocatalyst prepared by any one of the preparation methods described in claims 1-7.

9. The porous MnCdS / CeO2 heterojunction photocatalyst according to claim 8, characterized in that, It includes a nanosheet-like CeO2 support and a particulate MnCdS solid solution. The particulate MnCdS solid solution is grown in situ on the surface of the nanosheet-like CeO2 support and forms a heterojunction structure at the interface. The particulate MnCdS solid solution is stacked on the surface of the nanosheet-like CeO2 support to form intergranular pores, thus constituting a porous structure.

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