Preparation method of 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue

Abstract

The invention discloses a preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue, which comprises the following steps: adding nickel nitrate hexahydrate and terephthalic acid into N, N-dimethylformamide, adding deionized water containing NaOH, and stirring; transferring to a reaction kettle, centrifugally collecting light green precipitate, washing and drying; the preparation method comprises the following steps: adding Ni-MOLs, CdCl2, InCl3. 4H2O, TAA and PVP (Polyvinyl Pyrrolidone) into a mixed solution, and stirring; and transferring into a reaction kettle, centrifugally collecting dark green precipitate, washing and drying to obtain CdIn2S4 / Ni-MOLs. According to the preparation method, photocatalytic degradation of methylene blue is promoted, the preparation process is simple, the degradation effect is excellent, the light absorption capacity of Ni-MOLs and the separation efficiency of a photo-generated carrier are improved, the stability of the composite material is enhanced, the degradation efficiency of the catalyst is greatly improved, and the application design of a photocatalytic coupling catalytic system is greatly facilitated.

Description

Technical Field

[0001] The present invention relates to the field of preparation of 3D / 2D CdIn2S4 / Ni-MOLs heterojunctions, and particularly to a method for preparing a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue. Background Art

[0002] The discharge of wastewater containing industrial toxic dyes into the ecosystem will cause increasingly serious pollution.

[0003] Among them, azo dyes are a class of synthetic dyes most widely used in the printing and dyeing process of textiles and clothing, used for the dyeing and printing of a variety of natural and synthetic fibers, and also for the coloring of paints, plastics, rubbers, etc. However, since human enzymes and microbiomes can cleave azo dyes, and the long-term absorption of such dyes by the human body may lead to mutant or carcinogenic metabolites, causing human health problems. Therefore, it is urgent to develop effective methods for removing azo dyes from wastewater.

[0004] Nowadays, various strategies have been adopted to solve the problem of dye wastewater. Currently, the methods for removing dyes from wastewater mainly include: (a) Biological removal method: Utilize the biodegradability of bacteria and fungi, and through their metabolic actions, convert the organic pollutants in the wastewater into stable and harmless substances. However, it has a large floor area, complex management, poor decolorization effect, and low COD removal rate, seriously affecting its wide application;

[0005] (b) Adsorption method: Utilize the physical and chemical adsorption properties of solid adsorbents to adsorb pollutants into the pores or surfaces, thereby removing pollutants from the wastewater. However, the amount of adsorbent required is large, resulting in high costs;

[0006] (c) Membrane separation method: Use a selective permeable membrane as the separation medium. Under the action of a certain driving force (such as concentration difference, pressure difference, potential difference, etc.), the membrane can selectively permeate certain substances while retaining other components in the solution to achieve the purpose of separating pollutants. However, it has strict requirements for equipment, high prices of membrane materials, easy blockage and pollution of the thin film, and high requirements for the acid-base resistance and corrosion resistance of the membrane material, resulting in obstacles to its application;

[0007] (d) Flocculation method: Add a flocculant to the wastewater. Through chemical action, the pollutants that were originally dissolved in the wastewater or in a fine suspended state and were not easy to settle and filter are aggregated into larger particles for separation from the water, so as to separate and remove the pollutants enriched in the wastewater. However, some flocculants may generate by-products during the treatment process. If these by-products cannot be properly treated, they will cause environmental pollution.

[0008] Therefore, it is necessary to find an efficient, green and simple-process method for treating methylene blue wastewater, which is of great significance for both environmental protection and human health. The environmentally friendly, economical and efficient photocatalytic technology for degrading dyes has received wide attention. By exciting the generation of electron-hole pairs (e - and h + ) through sunlight illumination, the e - on the conduction band CB will react with O2 on the semiconductor surface, and generate ·O2 - radicals through the reduction process. Then these radicals combine with the captured electrons and generate hydrogen peroxide H2O2 and hydroxide radicals ·OH. Both ·O2 - and ·OH radicals are strong oxidants, which are the main active substances of oxygen (ROS) for the photocatalytic degradation of organic pollutants, and can mineralize dyes and antibiotics into small molecules (such as H2O, CO2, etc.).

[0009] However, the existing photocatalysts face the following problems:

[0010] (1) There is recombination between photo-generated electron-hole pairs. When the recombination is too fast, the photo-generated electrons will not be able to complete the degradation;

[0011] (2) The utilization efficiency of the photocatalyst for sunlight is not high, resulting in only a part of the energy being absorbed, which greatly reduces the degradation rate.

[0012] Among them, when comparing the degradation of the azo dye methyl orange in the literature (Ceramics International, 2019, 45, 15942-15953), the degradation efficiency of CdIn2S4 / TiO2 for methyl orange reached 85.9% within 180 min. And the degradation efficiency of the present invention within the same degradation time is much higher than that of the comparative literature.

[0013] In the comparative literature (Applied Catalysis B: Environment and Energy, 2025, 361, 124657), a novel binary heterojunction photocatalyst constructed by ZnIn2S4 nanoflowers and Ni-MOLs nanosheets exhibited an excellent hydrogen evolution rate of 4.75 mmol·g -1 ·h -1 under visible light irradiation. CdIn2S4 and Ni-MOLs are mostly used for hydrogen production. And the present invention modifies CdIn2S4 on two-dimensional sheet-like Ni-MOLs through a simple one-pot hydrothermal reaction and applies it to the degradation of methylene blue dye. There is innovation in the application of materials, and the CIS / NM photocatalyst prepared by the present invention has better catalytic activity and environmental friendliness.

[0014] Therefore, in view of the disadvantages of the existing technology, the present invention uses the semiconductor coupling method to modify CdIn2S4 on Ni-MOLs to form a heterojunction for degrading methylene blue, which can not only improve the light absorption ability of Ni-MOLs and the separation efficiency of photo-generated carriers, but also enhance the adsorption of dyes, thereby improving the degradation efficiency of methylene blue. Moreover, the photocatalyst is simple to prepare, has low cost and is conducive to recycling. Summary of the Invention

[0015] In view of this, the present invention provides a preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue.

[0016] To solve the above technical problems, the present invention adopts the following technical solutions:

[0017] A preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue, comprising the following steps:

[0018] Step 1: Preparation of Ni-MOLs

[0019] Step 1.1: Add nickel nitrate hexahydrate and terephthalic acid to N,N-dimethylformamide, slowly add deionized water containing NaOH, and stir magnetically until dissolved;

[0020] Step 1.2: Transfer to a reaction kettle, centrifuge to collect the light green precipitate, wash and dry;

[0021] Step 2: Preparation of CdIn2S4 / Ni-MOLs

[0022] Step 2.1: Add Ni-MOLs, CdCl2, InCl3·4H2O, TAA, and PVP to a mixed solution and stir magnetically;

[0023] Step 2.2: Transfer to a reaction kettle, centrifuge to collect the dark green precipitate, wash and dry to obtain CdIn2S4 / Ni-MOLs.

[0024] Preferably, in Step 1.1, the concentration of nickel nitrate hexahydrate is 6 mmol, the concentration of terephthalic acid is 4 mmol, the addition amount of N,N-dimethylformamide is 150 mL, and 10 mL of deionized water containing 0.32 mmol of NaOH is added.

[0025] Preferably, in Step 1.2, the reaction temperature in the reaction kettle is 120 °C and the reaction time is 10 h.

[0026] Preferably, in Step 1.2 and Step 2.2, the centrifugation speed is 8000 rpm;

[0027] Preferably, in the steps 1.2 and 2.2, the washing is carried out three times respectively with deionized water and absolute ethanol.

[0028] Preferably, in the steps 1.2 and 2.2, the drying temperature is 60 °C and the drying time is 12 h.

[0029] Preferably, in the step 2.1, the addition amount of Ni-MOLs is 0.1 g, the addition amount of CdCl2 is 0.0389 g, the addition amount of InCl3·4H2O is 0.1243 g, the addition amount of TAA is 0.1272 g, and the addition amount of PVP is 0.1060 g.

[0030] Preferably, in the step 2.1, the mixed solution is a solution prepared by mixing deionized water and absolute ethanol at a volume ratio of 1:1, the addition amount is 40 mL, and the magnetic stirring time is 30 min.

[0031] Preferably, in the step 2.2, the reaction temperature in the autoclave is 180 °C and the reaction time is 24 h.

[0032] Preferably, in the step 2.2, by changing the mass ratio mMOLS:mCdIn2S4 = 2:1, 2:2, 2:3, 2:4, 0.5CdIn2S4 / Ni-MOLs, CdIn2S4 / Ni-MOLs, 1.5CdIn2S4 / Ni-MOLs, and 2.0CdIn2S4 / Ni-MOLs are obtained.

[0033] The present invention has achieved the following technical effects compared with the prior art:

[0034] (1) In the present invention, 3D bulk CdIn2S4 is modified on two-dimensional sheet-like Ni-MOLs by a one-pot hydrothermal method, and finally 3D / 2D CdIn2S4 / Ni-MOLs heterojunction is synthesized.

[0035] (2) In the present invention, through structural design, Ni-MOF is designed as a two-dimensional sheet-like structure, which not only increases the contact area between the two monomers, but also reduces the photogenerated electron conduction path, thereby promoting the photocatalytic degradation of methylene blue.

[0036] (3) The preparation process of the present invention is simple and the degradation effect is excellent. After optimization of the initial concentration and pH, finally 99.83% of the methylene blue solution with an initial concentration of 10 mg L -1 is degraded within 180 min.

[0037] (4) In the present invention, CdIn2S4 is modified on two-dimensional sheet-like Ni-MOLs and coupled into a heterojunction, which improves the light absorption ability of Ni-MOLs and the separation efficiency of photo-generated carriers, enhances the stability of the composite material, and greatly improves the degradation efficiency of the catalyst. It is very helpful for the application design of the photocatalytic coupling catalytic system. Description of the Drawings

[0038] Figure 1 It is the X-ray diffraction (XRD) pattern of the composite sample of the present invention;

[0039] Figure 2 (a)-2(c) are the SEM images of Ni-MOLs, CdIn2S4 and CIS / NM of the present invention;

[0040] Figure 2 (d)-2(e) are the TEM and HR-TEM images of CIS / NM of the present invention;

[0041] Figure 2 (f)-2(m) are the EDS images of CIS / NM of the present invention;

[0042] Figure 3 (a) is the degradation curve of methylene blue at 10 mg L -1 of the present invention;

[0043] Figure 3 (b) is the first-order kinetic curve of methylene blue degradation at 10 mg L -1 of the present invention;

[0044] Figure 3 (c) is the distribution diagram of the kinetic constant of methylene blue degradation at 10 mg L -1 of the present invention;

[0045] Figure 3 (d) is the experimental distribution diagram of cyclic degradation of methylene blue of the present invention;

[0046] Figure 4 (a) is the curve of methylene blue degradation with different initial concentrations of the present invention;

[0047] Figure 4 (b) is the first-order kinetic curve of methylene blue degradation with different initial concentrations of the present invention;

[0048] Figure 4 (c) is the distribution diagram of the kinetic constant of methylene blue degradation with different initial concentrations of the present invention;

[0049] Figure 5 (a) is the curve of MB degradation at different solution pH values of the present invention;

[0050] Figure 5(b) is the first-order kinetic curve of MB degradation at different solution pH values of the present invention;

[0051] Figure 5 (c) is the distribution diagram of kinetic constants of MB degradation at different solution pH values of the present invention;

[0052] Figure 6 (a) is the degradation curve of the scavenger experiment of the present invention;

[0053] Figure 6 (b) is the first-order kinetic curve of the scavenger experiment degradation of the present invention;

[0054] Figure 6 (c) is the distribution diagram of kinetic constants of the scavenger experiment degradation of the present invention. Detailed implementation manners

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] A preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue, characterized by comprising the following steps:

[0057] Step 1: Preparation of Ni-MOLs

[0058] Step 1.1: Add 6 mmol of nickel nitrate hexahydrate and 4 mmol of terephthalic acid to 150 mL of N,N-dimethylformamide, slowly add 10 mL of deionized water containing 0.32 mmol of NaOH, and stir magnetically until dissolved;

[0059] Step 1.2: Transfer to a reaction kettle, react at 120 °C for 10 h, collect the light green precipitate by centrifugation at 8000 rpm, wash it three times with deionized water and anhydrous ethanol respectively, and dry it at 60 °C for 12 h;

[0060] Step 2: Preparation of CdIn2S4 / Ni-MOLs

[0061] Step 2.1: Add 0.1 g of Ni-MOLs, 0.0389 g of CdCl2, 0.1243 g of InCl3·4H2O, 0.1272 g of TAA, and 0.1060 g of PVP to a mixed solution prepared by mixing deionized water and anhydrous ethanol according to a volume ratio of 1:1, and stir magnetically for 30 min;

[0062] Step 2.2: Transfer it to a reaction kettle, react at 180 °C for 24 h, centrifuge to collect the dark green precipitate at 8000 rpm, wash it three times with deionized water and absolute ethanol respectively, and dry it at 60 °C for 12 h to obtain CdIn2S4 / Ni-MOLs.

[0063] Among them, by changing the mass ratio mMOLS:mCdIn2S4 = 2:1, 2:2, 2:3, 2:4, 0.5CdIn2S4 / Ni-MOLs, CdIn2S4 / Ni-MOLs, 1.5CdIn2S4 / Ni-MOLs, and 2.0CdIn2S4 / Ni-MOLs are obtained.

[0064] Example 1: Structure and Morphology Characterization of MNM Composite

[0065] First, the microscopic crystal structure of the CIS / NM composite was analyzed by XRD. As Figure 1 shown, the diffraction peaks of the composite at 2θ = 12.8°, 26.8°, 28.3°, 44.1°, and 47.3° correspond to the crystal planes (111), (311), (222), (511), and (440) of CdIn2S4 respectively. In addition, the diffraction peak at 2θ = 8.5° corresponds to the (100) crystal plane of Ni-MOLs.

[0066] With the increase in the content of CdIn2S4, the characteristic diffraction peaks of CdIn2S4 gradually become stronger, confirming the successful synthesis of the CIS / NM heterojunction, and the characteristic diffraction peaks of CdIn2S4 and Ni-MOLs are observed in the diffraction peaks of the composite, indicating that the crystal structure of Ni-MOLs is retained during the in-situ loading of CdIn2S4 on Ni-MOLs.

[0067] The morphologies and microstructures of the monomers and composites were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM of Ni-MOLs is as Figure 2 (a) shown. It can be seen that Ni-MOLs change from 3D to a 2D sheet structure with a relatively smooth surface, and then assemble into a unique three-dimensional flower-like structure with a size of about 5 μm.

[0068] The SEM of CdIn2S4 is as Figure 2 (b) shown. CdIn2S4 is a three-dimensional block structure of Ni-MOLs.

[0069] The SEM of the composite shows as Figure 2As shown in (c), the bulk-structured CdIn2S4 is dispersed on the sheet-assembled microflowers Ni-MOLs, demonstrating the successful synthesis of the composite. The transformation from a 3D / 3D heterojunction to a 3D / 2D heterojunction greatly reduces the transfer path of photo-generated carriers, thus accelerating the separation of photo-generated carriers and also providing a larger contact area for more effective degradation of pollutants.

[0070] The TEM and HR-TEM of the composite are as Figure 2 shown in (d)-2(e). The measured lattice spacing of Ni-MOLs is 0.31 nm, corresponding to the (100) crystal plane of Ni-MOLs, and the measured lattice spacing of CdIn2S4 is 0.38 nm, corresponding to the (220) crystal plane of CdIn2S4. This indicates that the composite has been successfully prepared.

[0071] Energy-dispersive spectroscopy (EDS) is as Figure 2 shown in (f)-2(m), showing the presence of C, O, S, Ni, Cd, and In elements in the composite CIS / NM, and the loading of CdIn2S4 on the surface of Ni-MOLs sheets, further confirming the successful synthesis of the binary heterojunction CIS / NM.

[0072] Example 2: Performance of the CIS / NM composite in degrading methylene blue

[0073] The performance of the CdIn2S4 / Ni-MOLs photocatalyst was evaluated by degrading methylene blue using a 300 W xenon lamp with a cut-off filter (λ≥420 nm) as the visible light source.

[0074] A simulated dye wastewater of methylene blue with a concentration of 10 mg / L and a pH of 7.0 was prepared. 100 mL of the simulated wastewater was added to a 200 mL reactor, and 30 mg of the photocatalyst was used to degrade methylene blue at room temperature. The solution was stirred in the dark for 60 min to achieve adsorption equilibrium, and then a photocatalytic reaction was carried out under a 300 W xenon lamp and a 420 nm cut-off filter for 3 hours. The absorbance was measured every 30 min. The remaining pollutants in the filtered methylene blue degradation solution were analyzed by a UV-visible spectrophotometer (λ = 664 nm). (Before measuring the absorbance, the sample was filtered through a 0.45 μm syringe filter).

[0075] The degradation rate formula of methylene blue is as follows:

[0076] D(%) = [(C0 - C t ) / C0] × 100%

[0077] where C0 is the initial concentration of methylene blue, and C t is the concentration of methylene blue after degradation.

[0078] Next, to evaluate the photocatalytic activity of the composite material CIS / NM, 30 mg of the catalyst was added to 100 mL of a 10 mg / L -1 methylene blue solution.

[0079] As Figure 3 (a) shows, after 60 min of adsorption equilibrium, the adsorption rate of 1.5 CIS / NM reached the highest at 62.27%. After 180 min of visible light irradiation, the degradation rates of methylene blue for CdIn2S4, Ni-MOLs, 0.5 CIS / NM, CIS / NM, 1.5 CIS / NM, and 2.0 CIS / NM were 81.93%, 72.65%, 93.20%, 98.51%, 98.54%, and 95.67%, respectively. Among them, the adsorption-photocatalytic synergistic removal effect of CIS / NM was the best, because too much CdIn2S4 would block the adsorption sites and photocatalytic active sites on Ni-MOLs, and too little CdIn2S4 would greatly weaken the separation of photogenerated carriers. Next, the degradation kinetics was studied, and a first-order degradation kinetic straight line was obtained.

[0080] As Figure 3 (b) shows, in order to more intuitively observe the slope change, a bar chart of kinetic constants was made.

[0081] As Figure 3 (c) shows, the slope of the first-order kinetic straight line of CIS / NM was the largest, at 0.02196 min -1 , which was 2.59 times and 3.20 times that of CdIn2S4 (k1 = 0.00849 min -1 ) and Ni-MOLs (k1 = 0.00687 min -1 ), indicating that its reaction kinetics was the fastest. In summary, the combination of CdIn2S4 and Ni-MOLs will greatly improve the photocatalytic efficiency. In addition, the stability of the composite material CIS / NM was also tested.

[0082] As Figure 3 (d) shows, it can be seen that after five cycles of the MNM composite material, the degradation rate only decreased by 4.72%, indicating that CIS / NM has good stability.

[0083] Next, the effect of MB solutions with different initial concentrations on the adsorption-photocatalytic synergistic removal performance of the composite catalyst CIS / NM was studied.

[0084] As Figure 4(As shown in (a)), it can be seen that as the initial concentration of MB increases, the MB removal rate decreases from 98.54% to 64.37%, and the adsorption efficiency also decreases. This may be because excessive MB will block the adsorption sites and active sites of the composite material, and excessive MB will form a shielding effect, making it difficult for visible light to penetrate, reducing the utilization rate of visible light by the catalyst, and resulting in a decrease in photocatalytic efficiency. Then, kinetic studies were carried out;

[0085] As Figure 4 (b - c) shows that the degradation of the composite material conforms to the first-order kinetic curve, and the kinetic constant is the largest when the initial concentration is 10 mg L -1 , k1 = 0.01843 min -1 , which are 2.11 times, 3.57 times, 4.58 times, and 4.05 times that of 15 mg L -1 (0.00873 min -1 ), 20 mg L -1 (0.00516 min -1 ), 25 mg L -1 (0.00402 min -1 ), and 30 mg L -1 (0.00455 min -1 ) respectively.

[0086] Next, the solution pH was further optimized. Since the pH in the solution affects the charged nature and stability of the material surface, thereby affecting the adsorption performance of the material. 30 mg of the catalyst was added to 100 mL of 10 mg L -1 methylene blue solution, and the pH value of the solution was adjusted to 3.0, 5.0, 7.0, 9.0, and 11.0 with HCl and NaOH solutions.

[0087] As Figure 5 (a) shows that as the pH value increases, the degradation effect shows a gradually increasing trend. The degradation effect of CIS / NM under alkaline conditions is significantly better than that under acidic and neutral conditions. When pH = 3, 5, 7, 9, 11, the degradation rates of CIS / NM for 10 mg L -1 MB solution are 83.96%, 91.03%, 98.54%, 99.62%, and 99.83% respectively. It can be seen that the degradation rate is the highest when pH = 11. Next, the degradation curve was fitted with pseudo-first-order linear fitting for kinetic studies.

[0088] As Figure 5 (b - c) shows that the kinetic constant is the largest when pH = 11, k1 = 0.02239 min -1 , which are pH = 3 (k1 = 0.00799 min -1)、pH = 5 (k1 = 0.01063 min -1 )、pH = 7 (k1 = 0.01843 min -1 ) and pH = 9 (k1 = 0.02053 min -1 ) are 2.80 times, 2.11 times, 1.21 times and 1.09 times respectively. When the solution is alkaline, the photocatalytic degradation performance of MB is greatly improved. This may be because MB exists in the form of positive ions in the solution. When the solution is acidic, H + in water will be adsorbed on the surface of the catalyst, - thus making it positively charged. At this time, the positive ions of MB will be repelled. Due to the electrostatic repulsion, it is not conducive to the adsorption of pollutants by the catalyst, thus reducing the degradation efficiency; when the solution is alkaline, the surface of the catalyst is negatively charged. Due to the electrostatic adsorption, the adsorption of the catalyst is enhanced. And since the ·OH active free radicals are generated by the oxidation of OH - , the more the number of OH

[0089] Next, by adding p-benzoquinone (BQ), isopropyl alcohol (IPA) and disodium ethylenediaminetetraacetate (EDTA-2Na) as free radical scavengers to capture ·O2 - , ·OH and h + respectively, the main active free radicals in the photocatalytic reaction are determined, so as to further explain the reaction degradation mechanism.

[0090] As Figure 6 (a - c) shows that after adding BQ and IPA, the degradation efficiency of MB by CIS / NM is greatly inhibited, and the degradation rate of MB drops to 79.62% and 77.62% respectively. This indicates that ·O2 - , ·OH are the dominant active groups in the CIS / NM photocatalytic system.

[0091] The above is only a preferred embodiment of the present invention, and does not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue, characterized in that, It includes the following steps: Step 1: Preparation of Ni-MOLs Step 1.1: Add nickel nitrate hexahydrate and terephthalic acid into N,N-dimethylformamide, slowly add deionized water containing NaOH, and stir magnetically until dissolved; Step 1.2: Transfer it to a reaction kettle, centrifuge to collect the light green precipitate, wash it, and dry it; Step 2: Preparation of CdIn2S4 / Ni-MOLs Step 2.1: Add Ni-MOLs, CdCl2, InCl3·4H2O, TAA, and PVP into the mixed solution, and stir magnetically; Step 2.2: Transfer it to a reaction kettle, centrifuge to collect the dark green precipitate, wash it, and dry it to obtain CdIn2S4 / Ni-MOLs.

2. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, wherein, In the said Step 1.1, the concentration of nickel nitrate hexahydrate is 6 mmol, the concentration of terephthalic acid is 4 mmol, the addition amount of N,N-dimethylformamide is 150 mL, and 10 mL of deionized water containing 0.32 mmol of NaOH is added.

3. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 1.2, the reaction temperature in the reaction kettle is 120 °C, and the reaction time is 10 h.

4. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 1.2 and Step 2.2, the centrifugation speed is 8000 rpm.

5. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 1.2 and Step 2.2, the washing is to wash three times with deionized water and absolute ethanol respectively.

6. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, wherein In the said Step 1.2 and Step 2.2, the drying temperature is 60 °C, and the drying time is 12 h.

7. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 2.1, the addition amount of Ni-MOLs is 0.1 g, the addition amount of CdCl2 is 0.0389 g, the addition amount of InCl3·4H2O is 0.1243 g, the addition amount of TAA is 0.1272 g, and the addition amount of PVP is 0.1060 g.

8. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 2.1, the mixed solution is a solution prepared by mixing deionized water and absolute ethanol at a volume ratio of 1:1, the addition amount is 40 mL, and the magnetic stirring time is 30 min.

9. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 2.2, the reaction temperature in the reaction kettle is 180 °C, and the reaction time is 24 h.

10. The preparation method of a 3D / 2D CdIn2S4 / Ni-MOLs heterojunction for removing methylene blue according to claim 1, characterized in that, In the said Step 2.2, by changing the mass ratio mMOLS:mCdIn2S4 = 2:1, 2:2, 2:3, 2:4, 0.5CdIn2S4 / Ni-MOLs, CdIn2S4 / Ni-MOLs, 1.5CdIn2S4 / Ni-MOLs, and 2.0CdIn2S4 / Ni-MOLs are obtained.

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