Ternary heterostructure composite photocatalyst, preparation method thereof and application of ternary heterostructure composite photocatalyst in photocatalytic hydrogen production and organic pollutant degradation

Abstract

The invention belongs to the field of photocatalysts, and particularly discloses a ternary heterostructure composite photocatalyst, a preparation method of the ternary heterostructure composite photocatalyst and application of the ternary heterostructure composite photocatalyst in photocatalytic hydrogen production and organic pollutant degradation. A petal-shaped CZS / ZIS / Ni-MOF composite material is successfully prepared by adopting a hydrothermal method and an electrostatic self-assembly method, a noble metal cocatalyst is abandoned, and the cost is reduced. The economic cost and resource dependence are reduced; the efficient charge separation is realized by constructing double heterojunctions of a type II heterojunction (ZIS / Ni-MOF) and a type Z heterojunction (Ni-MOF / CZS), and efficient photocatalytic hydrogen production and organic pollutant degradation are realized through a double-heterojunction synergistic mechanism.

Description

Technical Field

[0001] The present invention relates to the field of photocatalysts, in particular to a ternary heterostructure composite photocatalyst, a preparation method thereof, and applications in photocatalytic hydrogen production and degradation of organic pollutants. Background Art

[0002] In the prior art, the photocatalytic hydrogen evolution technology relies on noble metals (such as Pt) as co-catalysts, which has problems of high cost and scarce resources. Single semiconductor materials (such as CZS, ZIS) have limited efficiency due to narrow light response range and high carrier recombination rate. For example, CZS (Cd 0.5 Zn 0.5 S) has good visible light response but poor stability, and ZIS (ZnIn2S4) has a wide band gap resulting in low light utilization rate. Although traditional binary composites can partially improve the situation, they still cannot optimize light absorption, charge separation, and redox ability simultaneously. Therefore, developing noble metal-free, highly efficient and stable ternary composites has become a key requirement. Summary of the Invention

[0003] In order to solve the problems of traditional photocatalysts relying on noble metal co-catalysts (high cost, poor stability), low visible light utilization rate, and high carrier recombination rate, the present invention provides a ternary heterostructure composite photocatalyst, a preparation method thereof, and applications in photocatalytic hydrogen production and degradation of organic pollutants, and realizes efficient photocatalytic hydrogen production and degradation of organic pollutants through a double heterojunction synergistic mechanism.

[0004] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0005] The first technical solution provided by the present invention is a preparation method of a ternary heterostructure composite photocatalyst, including the following steps:

[0006] S1. Prepare Ni-MOF material;

[0007] S2. Prepare Cd 0.5 Zn 0.5 S nanoparticles;

[0008] S3. Prepare ZnIn2S4 nanosheets;

[0009] S4. Prepare the ternary heterostructure composite photocatalyst: Disperse 20 mg of Ni-MOF material, 10 - 50 mg of ZnIn2S4 nanosheets, and 50 - 90 mg of Cd 0.5 Zn 0.5 S nanoparticles in 30 mL of methanol solution, magnetically stir for 24 h, achieve uniform loading through electrostatic self-assembly, and then evaporate and dry in an oil bath at 65°C for 2 h to obtain the ternary heterostructure composite photocatalyst, denoted as CZS / ZIS / Ni-MOF.

[0010] Further, in the step S1, the specific process of preparing the Ni-MOF material is as follows:

[0011] S1-1. Mix 35 mL of N,N-dimethylformamide and 35 mL of deionized water to obtain solution A;

[0012] S1-2. Weigh 4.4 g of Ni(NO3)2·6H2O, 1.2 g of terephthalic acid and 6 g of polyvinylpyrrolidone, add them into solution A, and after stirring for 2 h, obtain solution B;

[0013] S1-3. Transfer solution B to a polytetrafluoroethylene autoclave, react at 150 °C for 10 h, centrifuge to collect the product, wash it three times with deionized water and anhydrous ethanol respectively, then dry it overnight in an oven at 70 °C, and grind it into powder to obtain the light green petal-shaped Ni-MOF material.

[0014] Further, in the step S2, the specific process of preparing the Cd 0.5 Zn 0.5 S nanoparticles is as follows:

[0015] S2-1. Add 6 mmol of Cd(CH3COO)2·2H2O and 6 mmol of Zn(CH3COO)2·2H2O into a mixed solvent composed of 12.5 mL of distilled water and 17.5 mL of diethylenetriamine to obtain solution C. After stirring for 15 min, add 50 mmol of L-cysteine into solution C; further stir solution C for 30 min to form a stable L-cysteine-Cd 2+ / Zn 2+ complex to obtain solution D;

[0016] S2-2. Transfer solution D to a Teflon autoclave and heat it to 160 °C for 24 h;

[0017] S2-3. Naturally cool the product to room temperature, then centrifuge and wash it three times with double-distilled water and ethanol; dry the obtained product in a vacuum oven at 60 °C for 12 h to obtain Cd 0.5 Zn 0.5 S nanoparticles, denoted as CZS.

[0018] Further, in the step S3, the specific process of preparing the ZnIn2S4 nanosheets is as follows:

[0019] S3-1. Dissolve 68 mg of ZnCl2, 293 mg of InCl3·4H2O and 300 mg of trisodium citrate in 25 mL of deionized water and 5 mL of ethylene glycol, and after vigorously stirring at room temperature for 30 min, obtain solution E;

[0020] S3-2: Add 150 mg of thioacetamide to solution E, stir for another 30 min, then transfer it to a 50 mL Teflon-lined stainless-steel autoclave and keep it in an oven at 120 °C for 12 h. After natural cooling, collect the product by centrifugation, rinse it twice with ethanol and distilled water, and then freeze-dry to obtain ZnIn2S4 nanosheets, denoted as ZIS.

[0021] The second technical solution provided by the present invention is a ternary heterostructure composite photocatalyst prepared by the above method.

[0022] The third technical solution provided by the present invention is an application of a ternary heterostructure composite photocatalyst in photocatalytic hydrogen production and degradation of organic pollutants.

[0023] Furthermore, the organic pollutant is Rhodamine B.

[0024] Compared with the prior art, the present invention successfully prepares a petal-shaped CZS / ZIS / Ni-MOF composite material by a hydrothermal method and an electrostatic self-assembly method, abandons noble metal cocatalysts, and reduces economic costs and resource dependence; by constructing a type-II heterojunction (ZIS / Ni-MOF) + type-Z heterojunction (Ni-MOF / CZS) double heterojunction, efficient charge separation is achieved, specifically manifested as follows:

[0025] (1) Type-Z heterojunction (Ni-MOF / CZS):

[0026] The conduction band of CZS (-1.255 eV) is higher than the valence band of Ni-MOF (0.954 eV), forming a thermodynamically allowed electron transfer path (e - →h + recombination of Ni-MOF), retaining the highly reducing electrons (-1.266 eV) in the conduction band of Ni-MOF;

[0027] This mechanism is verified by XPS analysis: the Cd 3d binding energy of CZS shifts positively (electron density decreases), while the Ni 2p binding energy of Ni-MOF shifts negatively (electron density increases);

[0028] (2) Type-II heterojunction (ZIS / Ni-MOF):

[0029] The conduction band of ZIS (-1.911 eV) is significantly lower than the conduction band of Ni-MOF (-1.266 eV), driving the migration of e- from ZIS to Ni-MOF, forming a stepped energy level arrangement;

[0030] (3) Ternary synergistic enhancement mechanism:

[0031] Under the coupling effect of the Z-scheme (CZS / Ni-MOF) and type-II (ZIS / Ni-MOF) heterojunctions, Ni-MOF serves as an electron transport mediator to construct a cascade electron channel of "ZIS→Ni-MOF→CZS".

[0032] The petal-shaped Ni-MOF / CZS / ZIS composite material prepared in this invention has dual advantages:

[0033] 1) High reduction ability: Electrons from the conduction bands of CZS (-1.255 eV) and Ni-MOF (-1.266 eV) jointly participate in H + reduction; under the condition of no noble metal cocatalyst, its average hydrogen evolution rate is as high as 19775.1116 μmol·g -1 ·h -1 , which are 6.398 times that of undoped CZS and 5.30 times that of ZIS respectively;

[0034] 2) Strong oxidation ability: The holes of the valence bands of ZIS (0.099 eV) and Ni-MOF (0.954 eV) synergistically oxidize pollutants (RhB), and the degradation efficiency of RhB is the highest (99.37%) under light illumination conditions, which is significantly better than that of Ni-MOF, CZS, ZIS and other heterojunction samples with different ratios. This result verifies the effectiveness of the synergistic construction strategy of Z-scheme and type-II heterojunctions in improving photocatalytic activity and has an excellent degradation effect on rhodamine B. Description of the Drawings

[0035] Figure 1 It is the scanning electron microscope image of CZS-70 / ZIS-30 / Ni-MOF-20.

[0036] Figure 2 It is the transmission electron microscope (TEM) image of CZS-70 / ZIS-30 / Ni-MOF-20.

[0037] Figure 3 It is the X-ray diffraction (XRD) pattern of CZS-70 / ZIS-30 / Ni-MOF-20.

[0038] Figure 4 It is the XPS measurement spectra of Cd, In, Ni, O, S and Zn in CZS-70 / ZIS-30 / Ni-MOF-20: (a) Cd; (b) In; (c) Ni; (d) O; (e) S; (f) Zn.

[0039] Figure 5 It is the photocatalytic hydrogen production rate diagram of different photocatalysts.

[0040] Figure 6Schematic diagram of the mechanism of Ni-MOF / CZS / ZIS photocatalytic hydrogen production.

[0041] Figure 7 PL spectra and transient fluorescence spectra (TRPL) of Ni-MOF, CZS, ZIS, and CZS-70 / ZIS-30 / Ni-MOF-20: (a) PL spectra; (b) transient fluorescence spectra (TRPL).

[0042] Figure 8 Degradation effects of different photocatalysts on Rhodamine B: (a) Degradation efficiency spectra of different samples on 20 mg / L Rhodamine B; (b) UV-visible absorption spectra of Rhodamine B with a concentration of 20 mg / L degraded at different time points; (c) UV-visible absorption spectra of Rhodamine B with a concentration of 60 mg / L degraded at different time points; (d) UV-visible absorption spectra of Rhodamine B with a concentration of 100 mg / L degraded at different time points; (e) UV-visible absorption spectra of methyl orange degraded at different time points; (f) Degradation rate of Rhodamine B after adding different radical scavengers. Detailed implementation manners

[0043] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the present invention in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0044] The raw materials and reagents used in the following embodiments are all commercially available unless otherwise specified, where:

[0045] Absolute ethanol (EtOH, purity > 99.5%), cadmium acetate dihydrate (Cd(CH3COO)2·H2O, purity > 99.9%), zinc acetate dihydrate (Zn(CH3COO)2·H2O, purity > 99.9%), diethylenetriamine (DETA, purity > 99%), L-cysteine (C3H7NO2S, purity > 99%), zinc chloride (ZnCl2, purity > 99%), indium chloride tetrahydrate (InCl3·4H2O, purity > 98%), ethylene glycol (C2H6O2, purity > 99%), thioacetamide (C2H5NS, purity > 99%), trisodium citrate (C6H5O7Na3, purity > 98%), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, purity > 99.9%), terephthalic acid (PTA, purity > 99%), polyvinylpyrrolidone (PVP, purity > 99.9%), N,N-dimethylformamide (DMF, purity > 99.9%), lactic acid (C3H6O3, purity > 90%), sodium sulfide nonahydrate (Na2S·9H2O, purity > 98%), sodium sulfite (Na2SO3, purity > 98%) were all purchased from Shanghai Macklin Biochemical Technology Co., Ltd. or Shanghai Aladdin Reagent or Tianjin Damao or Guangzhou Chemical Reagent Factory. All chemical reagents were used directly without secondary purification.

[0046] Example 1

[0047] S1. Prepare Ni-MOF material;

[0048] S1-1. Mix 35 mL of N,N-dimethylformamide and 35 mL of deionized water to obtain solution A;

[0049] S1-2. Weigh 4.4 g of Ni(NO3)2·6H2O, 1.2 g of PTA and 6 g of PVP, add them to solution A, and stir for 2 h to obtain solution B;

[0050] S1-3. Transfer solution B to a polytetrafluoroethylene autoclave, react at 150 °C for 10 h, centrifuge to collect the product, wash it three times with deionized water and absolute ethanol respectively, then dry it overnight in an oven at 70 °C, and grind it into powder to obtain a light green petal-shaped Ni-MOF material;

[0051] S2. Prepare Cd 0.5 Zn 0.5 S nanoparticles;

[0052] S2-1. Add 6 mmol of Cd(CH3COO)2·2H2O and 6 mmol of Zn(CH3COO)2·2H2O to a mixed solvent composed of 12.5 mL of distilled water and 17.5 mL of DETA to obtain solution C. After stirring for 15 min, add 50 mmol of L-cysteine to solution C; further stir solution C for 30 min to form a stable L-cysteine-Cd 2+ / Zn 2+ complex, obtaining solution D;

[0053] S2-2. Transfer solution D to a Teflon autoclave and heat it to 160 °C for 24 h;

[0054] S2-3. Naturally cool the product to room temperature, then centrifuge and wash it three times with double-distilled water and ethanol; dry the obtained product in a vacuum oven at 60 °C for 12 h to obtain Cd 0.5 Zn 0.5 S nanoparticles, denoted as CZS;

[0055] S3. Prepare ZnIn2S4 nanosheets;

[0056] S3-1. Dissolve 68 mg of ZnCl2, 293 mg of InCl3·4H2O, and 300 mg of trisodium citrate in 25 mL of deionized water and 5 mL of ethylene glycol. After vigorously stirring at room temperature for 30 min, obtain solution E;

[0057] S3-2. Add 150 mg of thioacetamide to solution E, stir for another 30 min, then transfer it to a 50 mL Teflon-lined stainless steel autoclave and keep it in an oven at 120 °C for 12 h. After natural cooling, collect the product by centrifugation, wash it twice with ethanol and distilled water, and then freeze-dry to obtain ZnIn2S4 nanosheets, denoted as ZIS;

[0058] S4. Prepare a ternary heterostructure composite photocatalyst: Disperse 20 mg of Ni-MOF material, 10 mg of ZIS, and 90 mg of ZIS in 30 mL of methanol solution, stir magnetically for 24 h, achieve uniform loading through electrostatic self-assembly, and then evaporate and dry it in an oil bath at 65 °C for 2 h to obtain a ternary heterostructure composite photocatalyst, denoted as CZS-90 / ZIS-10 / Ni-MOF-20.

[0059] Example 2

[0060] The difference from Example 1 is only that: in step S4, the addition amount of CZS is 80 mg, and the addition amount of ZIS is 20 mg, and the obtained ternary heterostructure composite photocatalyst is CZS-80 / ZIS-20 / Ni-MOF-20.

[0061] Example 3

[0062] The difference from Example 1 is only that: in step S4, the addition amount of CZS is 70 mg, and the addition amount of ZIS is 30 mg, and the obtained ternary heterostructure composite photocatalyst is CZS-70 / ZIS-30 / Ni-MOF-20.

[0063] Example 4

[0064] The difference from Example 1 is only that: in step S4, the addition amount of CZS is 60 mg, and the addition amount of ZIS is 40 mg, and the obtained ternary heterostructure composite photocatalyst is CZS-60 / ZIS-40 / Ni-MOF-20.

[0065] Example 5

[0066] The difference from Example 1 is only that: in step S4, the addition amount of CZS is 50 mg, and the addition amount of ZIS is 50 mg, and the obtained ternary heterostructure composite photocatalyst is CZS-50 / ZIS-50 / Ni-MOF-20.

[0067] Taking the ternary heterostructure composite photocatalyst CZS-70 / ZIS-30 / Ni-MOF-20 prepared in Example 5 as an example, its scanning electron microscope image is as Figure 1 shown, and its transmission electron microscope (TEM) image is as Figure 2 shown, and its x-ray diffraction (XRD) image is as Figure 3 shown.

[0068] From Figure 1 it can be seen that CZS-70 / ZIS-30 / Ni-MOF-20 as a whole presents a petal shape, where the whole of the petal is Ni-MOF, and CZS and ZIS are inlaid on the petal. From Figure 2 it can be seen that there are differences in the different color depths and lattice spacings of the composite material. It shows that CZS and ZIS are inlaid on Ni-MOF, and the lattice spacing also represents the presence of characteristic peaks. From Figure 3 it can be seen that in the diffraction spectrum of the Ni-MOF / CZS / ZIS ternary composite, the characteristic peaks of Ni-MOF, CZS, and ZIS are all contained, indicating that the three substances of Ni-MOF, CZS, and ZIS are successfully compounded together.

[0069] The XPS measurement spectra of Cd, In, Ni, O, S, and Zn in CZS-70 / ZIS-30 / Ni-MOF-20 are as Figure 4 shown, and from Figure 4 it can be seen that the binding energies of the Ni 2p spectrum at 856.36 eV and 874.25 eV can be attributed to nickel oxide (Ni 2+) of Ni 2p 3 / 2 and Ni2p 1 / 2 , while the binding energy peaks at 861.82 eV and 879.38 eV correspond to Ni 2p 3 / 2 and Ni 2p 1 / 2 . In the Cd fine spectrum of Ni, there are two peaks at 404.79 eV and 411.67 eV ] , corresponding to Cd 3d 5 / 2 and Cd 3d 3 / 2 respectively. In Ni-MOF / CZS, Cd 3d 5 / 2 and Cd 3d 3 / 2 are shifted to 406.40 eV and 413.20 eV respectively, showing a positive shift, indicating that the electrons on Cd have been transferred to Ni-MOF. In the Ni-MOF / CZS / ZIS composite, the binding energies of Cd 3d 5 / 2 and Cd 3d 3 / 2 are 405.46 eV and 412.28 eV respectively. This negative shift means that electrons are injected from ZIS into Ni-MOF, and CZS subsequently obtains a part of these electrons. In addition, the XPS analysis of the three-dimensional spectrum shows that there is a positive binding energy shift in Ni-MOF / CZS / ZIS relative to the original ZIS, further confirming the transfer of electrons to Ni-MOF. The observed negative shift of Ni-MOF / CZS / ZIS indicates that part of the electrons migrate from ZIS to CZS through Ni-MOF as a mediator. These mutually corroborating results consistently demonstrate the directional redistribution of electrons within the heterostructure: ZIS→Ni-MOF→CZS, highlighting the synergistic electron interaction between the components.

[0070] The PL spectra and transient fluorescence spectra TRPL of Ni-MOF, CZS, ZIS, and CZS-70 / ZIS-30 / Ni-MOF-20 are as Figure 7 shown, and as can be seen from Figure 7 , this design of the ternary heterostructure not only broadens the visible light response range but also suppresses carrier recombination through the band bending effect (the PL intensity is reduced by 83.28%).

[0071] Application Example 1

[0072] The photocatalytic hydrogen production performance of the ternary heterostructure composite photocatalysts prepared in Examples 1-5 was tested respectively, with CZS, ZIS, and Ni-MOF as the controls. The specific test process is as follows:

[0073] In the photocatalytic hydrogen evolution experiment, 10 mg of CZS-90 / ZIS-10 / Ni-MOF-20, CZS-80 / ZIS-20 / Ni-MOF-20, CZS-70 / ZIS-30 / Ni-MOF-20, CZS-60 / ZIS-40 / Ni-MOF-20, CZS-50 / ZIS-50 / Ni-MOF-20, CZS, ZIS, and Ni-MOF were respectively dispersed in 100 mL of deionized water containing 10% TEOA (sacrificial agent). Then, the suspension was transferred to a sealable quartz reactor, and nitrogen gas was introduced into the sealable system for 0.5 h to ensure that all oxygen in the reaction system was depleted. The H2 concentration in the gas was collected once every hour for a total of 4 hours. During the experiment, the visible light source was a 300 W xenon lamp equipped with a 420 nm cut-off filter. The hydrogen content was detected using a gas chromatograph equipped with a TCD detector with N2 as the carrier gas. Briefly, the H2 concentration in the gas was sampled every hour, and the photocatalytic hydrogen production rate of the samples was evaluated.

[0074] The photocatalytic hydrogen production rate diagrams of different photocatalysts are as Figure 5 shown. It can be seen from Figure 5 that the photocatalytic hydrogen production rates of CZS-90 / ZIS-10 / Ni-MOF-20, CZS-80 / ZIS-20 / Ni-MOF-20, CZS-70 / ZIS-30 / Ni-MOF-20, CZS-60 / ZIS-40 / Ni-MOF-20, and CZS-50 / ZIS-50 / Ni-MOF-20 are all higher than those of CZS and ZIS. Among them, the photocatalytic hydrogen production rate of CZS-70 / ZIS-30 / Ni-MOF-20 is the highest, up to 19775.112 μmol·g -1 ·h -1 . The hydrogen production rate of pure Ni-MOF is 0. The schematic diagram of the photocatalytic hydrogen production mechanism of Ni-MOF / CZS / ZIS is as Figure 6 shown. It can be seen from Figure 6It is known that under light irradiation, electrons belonging to CZS and Ni-MOF will absorb sufficient energy to be excited and transfer from the VB to the CB, leaving photo-induced holes on the VB. Compared with CZS, the CB of Ni-MOF has more negative charges. Due to the potential difference, the photoelectrons on the CB of CZS will recombine with the holes on the VB of Ni-MOF. At the same time, the CB of ZIS is lower than that of Ni-MOF, and electrons will flow from ZIS to the higher material. Similarly, if the top of the VB of Ni-MOF is higher than that of ZIS, holes will flow from Ni-MOF to ZIS. Thus, a hybrid heterojunction structure of Z-scheme (CZS / Ni-MOF) and type-II (ZIS / Ni-MOF) heterojunctions is established. The hybrid heterojunction significantly improves the separation efficiency of photoelectrons and holes. Ni-MOF acts as an electron transport mediator, constructing a cascade electron channel of "ZIS→Ni-MOF→CZS", delaying the recombination rate of electron-hole pairs, and prolonging the lifetime of photoelectrons.

[0075] Application Example 2

[0076] Degradation tests of Rhodamine B were carried out using CZS-90 / ZIS-10 / Ni-MOF-20, CZS-70 / ZIS-30 / Ni-MOF-20, and CZS-50 / ZIS-50 / Ni-MOF-20 respectively. At the same time, CZS, ZIS, and Ni-MOF were used as controls. The specific test process is as follows:

[0077] The experimental design for photocatalytic degradation of Rhodamine B (RhB) is as follows: The light source is a 300W xenon lamp with a 420nm cut-off filter. 20mg of CZS-90 / ZIS-10 / Ni-MOF-20, CZS-70 / ZIS-30 / Ni-MOF-20, CZS-50 / ZIS-50 / Ni-MOF-20, CZS, ZIS, and Ni-MOF were respectively added to 50mL of RhB solution (20mg / L). Then, the solution was stirred in the dark for 30min to reach the adsorption equilibrium. After the illumination started, 2mL of the suspension was taken every 20min, and the remaining content of the Rhodamine B solution was evaluated using a UV-visible spectrophotometer. The total illumination time was 80min. The formula for the degradation rate is as follows:

[0078] Degradation rate = (a0 - a t ) / a0 × 100%;

[0079] where: α0 is the characteristic absorbance of the original Rhodamine B solution, and α t is the characteristic peak absorbance of the remaining concentration of the Rhodamine B solution at different illumination times.

[0080] The degradation results of Rhodamine B by different photocatalysts are as Figure 8 shown. From Figure 8As can be seen from (a) in [reference], the degradation effects of CZS-90 / ZIS-10 / Ni-MOF-20, CZS-70 / ZIS-30 / Ni-MOF-20, and CZS-50 / ZIS-50 / Ni-MOF-20 on Rhodamine B are far better than those of CZS and ZIS on Rhodamine B; among them, Ni-MOF / CZS-70 / ZIS-30, as shown in Figure 8 (b) in [reference], the degradation rate reaches 83.53% at 20 min of visible light irradiation, increases to 98.08% at 60 min, and reaches 99.37% at 80 min. The experiment shows that the Ni-MOF / CZS-70 / ZIS-30 composite material has the highest degradation efficiency (99.37%) for RhB under light irradiation conditions, significantly better than Ni-MOF, CZS, ZIS, and other heterojunction samples with different ratios. This result verifies the effectiveness of the synergistic construction strategy of Z-scheme and type-II heterojunctions in improving photocatalytic activity. Through the structural design of the Ni-MOF / CZS-70 / ZIS-30 heterojunction, the efficient degradation mechanism of RhB is realized from physical adsorption to chemical conversion, indicating that heterojunction interface engineering can significantly enhance the chemical treatment ability in catalytic reactions. The concentration of Rhodamine B is increased to 60 mg / L and 100 mg / L for photocatalytic degradation experiments. As shown in Figure 8 (c) in [reference], for pollutants with a concentration of 60 mg / L, the degradation rate reaches 71.65% at 40 min of visible light irradiation, increases to 82.65% at 60 min, and the degradation effect reaches 87.74% at 80 min. While in Figure 8 (d) in [reference], it is obtained that for pollutants with a concentration of 100 mg / L, the degradation rate is as high as 93.93% at 60 min of visible light irradiation, and Rhodamine B is degraded up to 97.98% at 80 min.

[0081] The ternary heterostructure composite photocatalyst prepared in the above examples has a good effect on the degradation of Rhodamine B. The excellent performance of the ternary system (the mixed heterojunction structure of Z-scheme (CZS / Ni-MOF) and type-II (ZIS / Ni-MOF) heterojunctions +, with Ni-MOF as the electron transport mediator) stems from the multi-dimensional synergistic mechanism: (1) The porous structure of Ni-MOF provides abundant adsorption sites; (2) The type-II heterojunction formed by Ni-MOF and ZnIn2S4 (ZIS) promotes the migration of the conduction band electrons of ZIS (E CB =-1.91 eV) to the conduction band of Ni-MOF (E CB =-1.26 eV), enabling the surface of Ni-MOF to be enriched with a high concentration of photo-generated electrons, significantly enhancing its generation of superoxide radicals (O2 / ·O2) with dissolved oxygen. –, -0.33 eV); (3) CZS through the Z-scheme mechanism formed with Ni-MOF; ZIS through the type-II heterojunction formed with Ni-MOF, both respectively retain more photo-generated holes (h + ) that synergistically oxidize pollutants (RhB).

[0082] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A preparation method of a ternary heterostructure composite photocatalyst, characterized in that, It includes the following steps: S1. Prepare Ni-MOF material; S2. Preparation of Cd 0.5 Zn 0.5 S nanoparticles; S3. Prepare ZnIn2S4 nanosheets; S4. Preparation of ternary heterostructure composite photocatalyst: Disperse 20 mg of Ni-MOF material, 10 - 50 mg of ZnIn2S4 nanosheets and 50 - 90 mg of Cd 0.5 Zn 0.5 S nanoparticles in 30 mL of methanol solution, stir magnetically for 24 h, achieve uniform loading through electrostatic self-assembly, and then evaporate and dry in an oil bath at 65 °C for 2 h to obtain the ternary heterostructure composite photocatalyst.

2. The preparation method of the ternary heterostructure composite photocatalyst according to claim 1, characterized in that, In the step S1, the specific process of preparing Ni-MOF material is as follows: S1-1. Mix 35 mL of N,N-dimethylformamide and 35 mL of deionized water to obtain solution A; S1-2. Weigh 4.4 g of Ni(NO3)2·6H2O, 1.2 g of terephthalic acid and 6 g of polyvinylpyrrolidone, add them into solution A, and stir for 2 h to obtain solution B; S1-3. Transfer solution B to a polytetrafluoroethylene autoclave, react at 150 °C for 10 h, collect the product by centrifugation, wash it three times with deionized water and absolute ethanol respectively, then dry it overnight in an oven at 70 °C, and grind it into powder to obtain a light green petal-shaped Ni-MOF material.

3. The preparation method of the ternary heterostructure composite photocatalyst according to claim 1, characterized in that, In the step S2, the specific process of preparing Cd0.5Zn0.5S nanoparticles is as follows: S2-1. Add 6 mmol of Cd(CH3COO)2·2H2O and 6 mmol of Zn(CH3COO)2·2H2O to a mixed solvent composed of 12.5 mL of distilled water and 17.5 mL of diethylenetriamine to obtain solution C. After stirring for 15 min, add 50 mmol of L-cysteine to solution C; further stir solution C for 30 min to form a stable L-cysteine-Cd 2+ / Zn 2+ complex to obtain solution D; S2-2. Transfer solution D to a Teflon autoclave and heat it to 160 °C for 24 h; S2-3. Naturally cool the product to room temperature, then centrifuge and wash it three times with double-distilled water and ethanol; dry the obtained product in a vacuum oven at 60 °C for 12 h to obtain Cd 0.5 Zn 0.5 S nanoparticles.

4. The preparation method of the ternary heterostructure composite photocatalyst according to claim 1, characterized in that, In the step S3, the specific process of preparing ZnIn2S4 nanosheets is as follows: S3-1. Dissolve 68 mg of ZnCl2, 293 mg of InCl3·4H2O and 300 mg of trisodium citrate in 25 mL of deionized water and 5 mL of ethylene glycol, and stir vigorously at room temperature for 30 min to obtain solution E; S3-2. Add 150 mg of thioacetamide to solution E, stir for another 30 min, then transfer it to a 50 mL stainless steel autoclave lined with Teflon, and keep it in an oven at 120 °C for 12 h. After natural cooling, collect the product by centrifugation, wash it twice with ethanol and distilled water, and then freeze-dry it to obtain ZnIn2S4 nanosheets.

5. A ternary heterostructure composite photocatalyst prepared by the method according to any one of claims 1-4.

6. An application of the ternary heterostructure composite photocatalyst according to claim 5 in photocatalytic hydrogen production and degradation of organic pollutants.

7. The application according to claim 6, wherein The organic pollutant is Rhodamine B.

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