A method for preparing a highly efficient hierarchical micro / nano Cd-Ni-MOF / CdS / NiS photocatalyst

Abstract

The invention aims to provide a method for preparing an efficient hierarchical micro / nano Cd‑Ni‑MOF / CdS / NiS photocatalyst, which belongs to the technical field of photocatalytic hydrogen production. The nickel ions in a pre-prepared Ni‑MOF‑74 structure are partially replaced with cadmium ions, and a solvothermal reaction is carried out in DMF and ethanol in different volume ratios to prepare a series of hierarchical Cd‑Ni‑MOF micro / nano structures assembled from nanosheets or nanorods. After further sulfurization, a hierarchical Cd‑Ni‑MOF / CdS / NiS composite photocatalytic material can be obtained. The material preparation process of the invention is simple, the product morphology is controllable, and the catalyst exhibits good photocatalytic hydrogen production activity and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic hydrogen production, and specifically relates to a method for preparing a high-efficiency hierarchical micro / nano Cd-Ni-MOF / CdS / NiS photocatalyst. Background Art

[0002] The photocatalytic decomposition of water to produce hydrogen using semiconductor materials with light response has mild reaction conditions and a wide range of applications, and has broad application prospects. However, problems such as insufficient light utilization, low quantum efficiency, and poor catalytic activity have hindered the further development of this technology. Cadmium sulfide has a band gap of about 2.4 eV and has excellent visible light response ability, and is widely used in the field of photocatalysis. When used in photocatalytic hydrogen production, CdS alone has disadvantages such as high recombination efficiency of photogenerated carriers and poor stability. Some measures such as regulating morphology, loading co-catalysts, forming solid solutions with other semiconductors, and constructing heterojunctions can improve the photocatalytic hydrogen production activity of CdS. Nickel sulfide (NiS) has almost zero binding energy with hydrogen and is an ideal material for forming heterojunctions with CdS. In addition, morphology has an important influence on the photocatalytic performance of NiS / CdS heterojunctions. For example, the p–n junction of CdS nanorods loaded with NiS nanoparticles showed 1.131 mmol·g -1 ·h -1 The hydrogen production rate of CdS / NiS spherical nanoparticles synthesized by a simple one-pot hydrothermal method was 24.37 mmol·g -1 ·h -1 High efficiency hydrogen evolution rate 《International Journal of Hydrogen Energy, 2017, 42, 16: 11199-11205》. The hydrogen evolution rate of the hierarchical CdS nanoflower heterostructure modified with β-NiS film reached 30.1 mmol·g -1 ·h -1 "Applied Catalysis B-Environmental, 2018,224, 1000-1008".

[0003] MOF has unique application value in the fields of luminescence, separation, catalysis and biochemistry due to its adjustable pore size and surface properties. MOF-derived CdS / NiS materials have shown excellent photocatalytic activity. For example, the hydrogen production rate of CdS@NiS photocatalyst synthesized with bimetallic Cd / Ni-MOF as precursor reached 42.7 mmol·g -1 ·h -1《Industrial & Engineering Chemistry Research, 2021, 30, 60, 11439-11449》. Solvents usually have a very important influence on the formation and regulation of MOFs with different forms and shapes. The hierarchical micro / nanostructure self-assembled by low-dimensional nanounits not only retains the advantages of small nanoparticle size, high specific surface area, and strong catalytic activity, but also effectively overcomes the disadvantages of nanoparticles being difficult to recycle after use, showing a more excellent overall structural effect. For MOF materials with hierarchical structures, they can be designed by adjusting the proportion of different solvents. However, there has been no obvious report on Cd-Ni-MOF hierarchical micro-nanostructure materials. Summary of the invention

[0004] The purpose of the present invention is to provide a hierarchical Cd-Ni-MOF micro / nano structure assembled from nanosheets or nanorods, and to obtain a composite hierarchical Cd-Ni-MOF / CdS / NiS photocatalytic material after further sulfurization, which shows important application prospects in photocatalytic decomposition of water to produce hydrogen.

[0005] The present invention adopts the following technical solution:

[0006] The present invention partially replaces nickel ions in a pre-prepared Ni-MOF-74 structure with cadmium ions, performs a solvothermal reaction in DMF and ethanol at different volume ratios, and prepares a series of hierarchical Cd-Ni-MOF micro / nano structures assembled from nanosheets or nanorods. After further sulfurization, a hierarchical Cd-Ni-MOF / CdS / NiS composite photocatalytic material can be obtained, thereby greatly improving the hydrogen production activity.

[0007] The composite photocatalyst synthesized by the present invention is derived from hierarchical micro-nano Cd-Ni-MOF self-assembled from nanorods or nanosheets, and has a large specific surface area and excellent photogenerated charge separation capability.

[0008] Hierarchical micro-nano Cd-Ni-MOF was prepared by a two-step solvothermal method to regulate the volume of the synthetic solvents dimethylformamide (DMF) and ethanol.

[0009] The Cd-Ni-MOF / CdS / NiS photocatalyst is prepared by room temperature sulfurization reaction of hierarchical micro-nano Cd-Ni-MOF and Na2S aqueous solution, and the original micro-nano structure morphology of Cd-Ni-MOF is maintained. The pn junction between CdS and NiS is conducive to the migration of photogenerated electrons from the conduction band of NiS to the conduction band of CdS, and the heterojunction of CdS and Cd-Ni-MOF-T further promotes the transfer of electrons from the conduction band of CdS to the conduction band of Cd-Ni-COF-T. The photocatalyst shows excellent photogenerated electron and hole separation ability.

[0010] The specific steps are as follows:

[0011] Step 1, preparation of Ni-MOF-74: NiCl2·6H2O, terephthalic acid and polyvinyl pyrrolidone were added to a mixed solution A of dimethylformamide, ethanol and water in a volume ratio of 1:1:1. After stirring for 1 hour, the above solution was poured into a 100 mL autoclave with an internal polytetrafluoroethylene liner and kept in an oven at 150-180°C for 10 hours. When the mixture was cooled to room temperature, it was centrifuged at 8000 rpm for 10 minutes, then rinsed with distilled water and ethanol several times, and finally dried in an oven at 60°C for 12 hours to obtain a light green powder Ni-MOF-74.

[0012] Step 2: Preparation of hierarchical micro-nano Cd-Ni-MOF: Cd(CH3COO)2·2H2O was dissolved in a mixed solution B of ethanol and DMF in different volume ratios. Then, Ni-MOF-74 was dispersed in the above solution and stirred for 1 h to obtain a uniformly mixed suspension, which was kept in an autoclave at 150 °C for 5-10 h. Then, the mixed product was cooled to room temperature, centrifuged, washed and dried at 60 °C overnight to obtain Cd-Ni-MOF.

[0013] The third step is the preparation of hierarchical micro-nano Cd-Ni-MOF / CdS / NiS composite photocatalyst: the Cd-Ni-MOF sample prepared in the second step and Na2S are added to deionized water and stirred continuously at room temperature for 2 h. After the reaction, the precipitation is centrifuged, washed with deionized water and alcohol several times, soaked in alcohol, and dried in an oven at 60°C for 12 h. Finally, a dark yellow powder sample is obtained.

[0014] Furthermore, as described in the first step, the ratio of NiCl2·6H2O, terephthalic acid, polyvinyl pyrrolidone, and mixed solution A is 500-1000 mg: 100-500 mg: 50-200 mg: 60-100 mL.

[0015] Furthermore, as described in the second step, the ratio of Cd(CH3COO)2·2H2O, mixed solution B, and Ni-MOF-74 is 500-1000 mg:40 mL:100-500 mg.

[0016] Furthermore, as described in the third step, the ratio of Cd-Ni-MOF, Na2S, and deionized water is 100 mg: 2000 mg: 40 mL.

[0017] The beneficial effects of the present invention are as follows:

[0018] The Cd-Ni-MOF / CdS / NiS composite photocatalyst prepared by the present invention has good cyclic hydrogen production performance and visible light response performance, and has important application prospects in photocatalytic hydrogen production.

[0019] The invention has the characteristics of simple preparation process, no precious metal catalyst and controllable product morphology. The photocatalyst prepared by the invention has excellent photocatalytic water splitting hydrogen production activity and stability. The most active catalyst has a hydrogen production activity of 40.08 mmol h under simulated sunlight and visible light, respectively. -1 g -1 (Test conditions: 10 mg catalyst, 50 mL water, 5 mL lactic acid). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of the composite sulfide obtained based on Cd-Ni-MOF;

[0021] Figure 2 a is the XRD pattern of the composite sulfide obtained based on Cd-Ni-MOF;

[0022] Figure 3 b is the XRD pattern of the composite sulfide obtained based on Cd-Ni-MOF;

[0023] Figure 4 c is the XRD pattern of the composite sulfide obtained based on Cd-Ni-MOF;

[0024] Figure 5 d is the XRD pattern of the composite sulfide obtained based on Cd-Ni-MOF;

[0025] Figure 6 Figure a shows the photocatalytic decomposition of water to produce hydrogen based on the composite sulfide obtained based on Cd-Ni-MOF;

[0026] Figure 7 Figure b is the photocatalytic decomposition of water to produce hydrogen based on the composite sulfide obtained based on Cd-Ni-MOF;

[0027] Figure 8 Figure c is the photocatalytic decomposition of water to produce hydrogen by the composite sulfide obtained based on Cd-Ni-MOF;

[0028] Fig. 9 Figure d shows the photocatalytic decomposition of water to produce hydrogen based on the composite sulfide obtained based on Cd-Ni-MOF. DETAILED DESCRIPTION

[0029] A method for preparing a highly efficient hierarchical micro / nano Cd-Ni-MOF / CdS / NiS photocatalyst comprises the following steps:

[0030] Step 1, preparation of Ni-MOF-74: NiCl2·6H2O, terephthalic acid and polyvinyl pyrrolidone were added to a mixed solution A of dimethylformamide, ethanol and water in a volume ratio of 1:1:1. After stirring for 1 hour, the above solution was poured into a 100 mL autoclave with an internal polytetrafluoroethylene liner and kept in an oven at 150-180°C for 10 hours. When the mixture was cooled to room temperature, it was centrifuged at 8000 rpm for 10 minutes, then rinsed with distilled water and ethanol several times, and finally dried in an oven at 60°C for 12 hours to obtain a light green powder Ni-MOF-74.

[0031] Step 2: Preparation of hierarchical micro-nano Cd-Ni-MOF: Cd(CH3COO)2·2H2O was dissolved in a mixed solution B of ethanol and DMF in different volume ratios. Then, Ni-MOF-74 was dispersed in the above solution and stirred for 1 h to obtain a uniformly mixed suspension, which was kept in an autoclave at 150 °C for 5-10 h. Then, the mixed product was cooled to room temperature, centrifuged, washed and dried at 60 °C overnight to obtain Cd-Ni-MOF.

[0032] The third step is the preparation of hierarchical micro-nano Cd-Ni-MOF / CdS / NiS composite photocatalyst: the Cd-Ni-MOF sample prepared in the second step and Na2S are added to deionized water and stirred continuously at room temperature for 2 h. After the reaction, the precipitation is centrifuged, washed with deionized water and alcohol several times, soaked in alcohol, and dried in an oven at 60°C for 12 h. Finally, a dark yellow powder sample is obtained.

[0033] Example 1

[0034] Preparation of Ni-MOF: 880 mg NiCl2·6H2O, 240 mg terephthalic acid, and 100 mg polyvinylpyrrolidone were added to 60 mL of a 1:1:1 (v / v / v) solution of dimethylformamide (DMF), ethanol, and water. After stirring for 1 hour, the above solution was poured into a 100 mL autoclave with an internal polytetrafluoroethylene liner and kept at 150 °C for 10 hours. The mixture was then cooled to room temperature, centrifuged at 8000 rpm for 10 minutes, and washed several times with distilled water and ethanol. Finally, a light green powder was obtained by drying at 60 °C for 12 hours.

[0035] Example 2

[0036] Preparation of hierarchical micro-nano Cd-Ni-MOF: 550 mg Cd(CH3COO)2·2H2O was dissolved in 40 mL solution containing ethanol and DMF with different volume ratios (ethanol:DMF were 0:40, 10:30, 20:20, 30:10, 40:0, respectively). Then, 100 mg Ni-MOF-74 was dispersed in the above solution, stirred for 1 hour to obtain a uniformly mixed suspension, and kept in an autoclave at 150 °C for 10 hours. Then, the mixed product was cooled to room temperature, centrifuged, washed, and dried at 60 °C overnight.

[0037] Example 3

[0038] Preparation of Cd-Ni-MOF / CdS / NiS composite photocatalyst: 100 mg Cd-Ni-MOF and 2000 mg Na2S were added to 40 mL deionized water and stirred continuously at room temperature for 2 h. After the reaction, the precipitate was centrifuged and washed several times with deionized water and ethanol. The precipitate was then soaked in ethanol and dried in an oven at 60 °C for 12 h. Finally, a dark yellow powder was obtained.

Claims

1. A method for preparing a highly efficient hierarchical micro / nano Cd-Ni-MOF / CdS / NiS photocatalyst, characterized by: The steps include: Step 1, preparation of Ni-MOF-74: NiCl2·6H2O, terephthalic acid and polyvinyl pyrrolidone were added to a mixed solution A of dimethylformamide, ethanol and water in a volume ratio of 1:1:

1. After stirring for 1 h, the solution was poured into a 100 mL autoclave with an internal polytetrafluoroethylene liner and kept in an oven at 150-180 °C for 10 h. When the mixture was cooled to room temperature, it was centrifuged at 8000 rpm for 10 min, then rinsed with distilled water and ethanol several times, and finally dried in an oven at 60 °C for 12 h to obtain a light green powder Ni-MOF-74. The second step is the preparation of hierarchical micro-nano Cd-Ni-MOF: Cd(CH3COO)2·2H2O is dissolved in a mixed solution B of ethanol and DMF in a certain volume ratio, then Ni-MOF-74 is dispersed in the solution and stirred for 1 h to obtain a uniformly mixed suspension, which is kept in an autoclave at 150°C for 5-10 h, then the mixed product is cooled to room temperature, centrifuged, washed and dried at 60°C overnight to obtain Cd-Ni-MOF; Step 3: Preparation of hierarchical micro-nano Cd-Ni-MOF / CdS / NiS composite photocatalyst: Add the Cd-Ni-MOF sample prepared in the second step and Na2S to deionized water and stir continuously at room temperature for 2 h. After the reaction, centrifuge and precipitate, wash with deionized water and alcohol several times, soak in alcohol, and dry in an oven at 60 °C for 12 h. Finally, a dark yellow powder sample is obtained. In the second step, the ratio of Cd(CH3COO)2·2H2O, mixed solution B, and Ni-MOF-74 is 500-1000 mg: 40 mL: 100-500 mg; The ratio of Cd-Ni-MOF, Na2S, and deionized water in the third step is 100 mg: 2000 mg: 40 mL.

2. The method for preparing a highly efficient hierarchical micro / nano Cd-Ni-MOF / CdS / NiS photocatalyst according to claim 1, characterized in that: The ratio of NiCl2·6H2O, terephthalic acid, polyvinyl pyrrolidone and mixed solution A in the first step is 500-1000 mg: 100-500 mg: 50-200 mg: 60-100 mL.

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