Application of an S-type heterojunction ZnCo2S4 / MOF-199 composite material

Abstract

In this invention, ZnCo2S4 (ZCS) nanoparticles are coupled onto the surface of MOF-199 by a simple ultrasonic impregnation method to form an S-scheme heterojunction. Compared with ZCS and MOF-199, the photocatalytic performance of ZCS / MOF under simulated sunlight is significantly improved, with the hydrogen evolution efficiency reaching 11.62 mmol g ‑1 h ‑1 , and the AQY reaches 12.6% at 420 nm, which are 83 times and 48.41 times that of ZCS and MOF-199 respectively. In addition, ZCS / MOF-199 also has good performance in the photocatalytic degradation of tetracycline (TC). The improvement of the photocatalytic performance of ZCS / MOF-199 is mainly due to the S-scheme heterojunction. On the one hand, the S-scheme electron transfer path not only improves the electron-hole separation efficiency but also the charge transfer efficiency. On the other hand, ZCS significantly improves the visible light absorption of ZCS / MOF.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanocomposite materials, and particularly relates to the application of an S-type heterojunction ZnCo2S4 / MOF-199 composite material, especially its application in photocatalytic hydrogen evolution and degradation and removal of tetracycline in water. Background Art

[0002] The demand of mankind for clean energy, such as hydrogen energy, is becoming increasingly urgent. Sunlight is a renewable energy source. Hydrogen obtained from water through light irradiation returns to the form of water after being used as an energy source, which is a completely sustainable development and utilization with broad application prospects. Photocatalysts are one of the key factors determining the practical application of the photocatalytic process. Although great progress has been made in the research of visible-light semiconductor photocatalysts, there is still a considerable gap from practical applications. On the other hand, with the development of human society, a large number of antibiotics flow into the environment, and among them, tetracycline (TC) is the most typical. TC returns to the human body through the cycle of the food chain and threatens human health. Finding effective methods to remove TC has become a challenge.

[0003] Metal sulfides are widely used in the field of photocatalytic hydrogen evolution. Compared with traditional catalytic materials such as CdS, PbS, and TaS2, the structure of bimetallic sulfides introduces additional metal atoms, enriches the connection modes between atoms, further leads to structural diversification, and endows the materials with excellent electrical, optical and other properties. However, two prominent characteristics limit the photocatalytic activity of ZnCo2S4. First, photo-generated electron-hole pairs will quickly recombine, which limits the photocatalytic activity. On the other hand, the property of easy aggregation limits the absorption of visible light and reduces the exposure of active sites. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides the application of an S-type heterojunction ZnCo2S4 / MOF-199 composite material. In the present invention, MOF-199 is first synthesized by a solvothermal method, ZnCo2S4 quantum dots are synthesized, and then ZnCo2S4 is uniformly loaded on the surface of MOF-199 by a simple ultrasonic impregnation method to prepare a ZnCo2S4 / MOF-199 composite photocatalyst; the ZnCo2S4 / MOF-199 composite photocatalyst is used for photocatalytic water decomposition to produce hydrogen and degrade tetracycline.

[0005] According to the present invention, there is provided the application of an S-type heterojunction ZnCo2S4 / MOF-199 composite material. The prepared ZnCo2S4 / MOF-199 composite material used as a photocatalyst effectively inhibits the recombination of photo-generated electron-hole pairs, has good visible-light photocatalytic activity, and also has a large specific surface area and hydrophilicity.

[0006] The preparation method of the ZnCo2S4 / MOF-199 composite material comprises the following steps:

[0007] Completely dissolve MOF-199 in a mixed solution of water and ethanol, denoted as solution E;

[0008] Ultrasonically dissolve ZnCo2S4 quantum dots in a mixed solution of water and ethanol, denoted as solution F;

[0009] Drop the solution F into the solution E, and continuously stir at a temperature of 60-70 °C until the solvent is completely evaporated. The obtained solid is the ZnCo2S4 / MOF-199 composite material.

[0010] Optionally, the MOF-199 is obtained by the following method:

[0011] Mix DMF, ethanol and deionized water according to a volume ratio of 1:(0.9-1.1):(0.9-1.1), and divide it into two equal parts, solution C and solution D;

[0012] Add Cu(NO3)2·3H2O and 1,3,5-benzenetricarboxylic acid to the solution C and the solution D respectively, ultrasonically treat and stir until completely dispersed, and then slowly drop the solution D into the solution C to obtain solution H;

[0013] Pour the solution H into a reaction kettle, react in an oven at 85-100 °C for 10-12 hours to obtain product Ι; then centrifuge and wash the product Ι several times and dry it for several hours to obtain MOF-199.

[0014] Optionally, the ZnCo2S4 quantum dots are obtained by the following method:

[0015] Dissolve Co(NO3)2·6H2O and Zn(NO3)2·6H2O in deionized water, ultrasonically treat and stir to form an aqueous solution, and then add 5 times the molar amount of solid NaOH of Co(NO3)2·6H2O, and stir to form solution A;

[0016] Add 4 times the molar amount of thioacetamide of Co(NO3)2·6H2O to the solution A, and stir at room temperature until the solution turns black, denoted as solution B;

[0017] Transfer the solution B to a high-pressure reaction kettle, react in an oven at 170-185 °C for 12-15 hours, take it out and ultrasonically treat it to form a suspension, and then centrifuge to separate the ZnCo2S4 quantum dots from the ZnCo2S4 nanoparticles. Take the suspension, that is, the suspension of ZnCo2S4 quantum dots, and dry it for later use.

[0018] Optionally, the mass of the ZnCo2S4 accounts for 5% to 25% of the total mass of the ZnCo2S4 and the MOF-199.

[0019] Optionally, the MOF-199 is completely dissolved in a mixed solution of water and ethanol, wherein the volume ratio of water to ethanol is 1:(3.5 to 4.5).

[0020] Optionally, the molar ratio of Cu(NO3)2·3H2O to 1,3,5-benzenetricarboxylic acid is 2:1.

[0021] Optionally, the product Ι is centrifuged and washed several times and dried for several hours to obtain MOF-199, wherein the drying temperature is 60 to 70 °C and the drying time is 10 to 24 hours.

[0022] Optionally, the molar ratio of Co(NO3)2·6H2O to Zn(NO3)2·6H2O is 2:1.

[0023] The application of the S-type heterojunction ZnCo2S4 / MOF-199 composite material provided by the present invention is used for photocatalytic hydrogen evolution or degradation and removal of tetracycline in water.

[0024] According to the present invention, a simple ultrasonic impregnation method was successfully used to prepare an S-type heterojunction ZnCo2S4 / MOF-199 composite material and apply it to photocatalytic hydrogen evolution and removal of tetracycline residues in a visible light environment. Black ZnCo2S4 quantum dots are uniformly distributed on the surface of octahedral MOF-199, improving the absorption of visible light by MOF-199. In addition, the introduction of ZnCo2S4 significantly improves the separation of photogenerated electrons of the carrier MOF-199, inhibits the recombination of electron-hole pairs, thereby improving the photocatalytic activity of the composite material, and also has a large specific surface area and hydrophilicity. The photocatalytic experimental results show that ZnCo2S4 / MOF-199 has higher photocatalytic hydrogen evolution ability and TC degradation activity than MOF-199 and ZnCo2S4. In addition, the existence of an S-type heterojunction between MOF-199 and ZnCo2S4 was confirmed by experiments and characterization, and a feasible photocatalytic reaction mechanism was proposed. Description of the Drawings

[0025] Figure 1 (a) XRD patterns of ZnCo2S4, MOF-199 and X-ZCS / MOF of an exemplary embodiment of the present invention;

[0026] Figure 1 (b) FT-IR spectra of ZnCo2S4, MOF-199 and X-ZCS / MOF of an exemplary embodiment of the present invention;

[0027] Figure 2 (a-c) are SEM images of ZCS / MOF of the exemplary embodiments of the present invention;

[0028] Figure 2 (d-f) are TEM images of ZCS / MOF of the exemplary embodiments of the present invention;

[0029] Figure 2 (g-h) are EDS images of ZCS / MOF of the exemplary embodiments of the present invention;

[0030] Figure 3 is the XPS spectrum of ZCS / MOF of the exemplary embodiments of the present invention, including Figure 3 (a) survey spectrum; Figure 3 (b) Zn 2p; Figure 3 (c) Co 2p; Figure 3 (d) S 2p; Figure 3 (e) Cu 2p and Figure 3 (f) O 1s;

[0031] Figure 4 (a-b) are hydrogen evolution efficiency spectra of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention;

[0032] Figure 4 (c) is the cycling experiment of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention;

[0033] Figure 4 (d) is the TC degradation efficiency graph of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention;

[0034] Figure 5 (a) is the fluorescence emission spectrum of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention

[0035] Figure 5 (b) is the UV-Vis diffuse reflectance spectrum of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention;

[0036] Figure 5 (c-d) are band gap spectra of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention

[0037] Figure 5 (e-f) are valence band spectra of ZnCo2S4, MOF-199 and X-ZCS / MOF of the exemplary embodiments of the present invention;

[0038] Figure 6 (a) Photocurrent response diagrams of ZnCo2S4, MOF-199, and X-ZCS / MOF according to exemplary embodiments of the present invention;

[0039] Figure 6 (b) EIS impedance of ZnCo2S4, MOF-199, and X-ZCS / MOF according to exemplary embodiments of the present invention;

[0040] Figure 6 (c) LSV of ZnCo2S4, MOF-199, and X-ZCS / MOF according to exemplary embodiments of the present invention;

[0041] Figure 6 (d) Tafel curves of ZnCo2S4, MOF-199, and X-ZCS / MOF according to exemplary embodiments of the present invention;

[0042] Figure 6 (e-f) Mott-Schottky curves of ZnCo2S4, MOF-199, and X-ZCS / MOF according to exemplary embodiments of the present invention.

[0043] Figure 7 Schematic diagram of the separation of photo-generated electron-hole pairs of ZnCo2S4, MOF-199, and X-ZCS / MOF according to exemplary embodiments of the present invention. Detailed implementation manners

[0044] In the specific implementation manners of the present invention, MOF-199 is composed of 1,3,5-benzenetricarboxylic acid (BTC) organic linkers, which are combined by tetra-carboxylic acid double copper paddle-wheel SBUs. Each SBU contains two Cu ions that are combined with four tricarboxylic acid linkers. These strategies, including constructing heterojunctions, co-catalyst modification, and element doping, can effectively accelerate the photocatalytic activity. Among them, the reasonable design of heterojunctions is very helpful for promoting charge separation and photocatalytic activity.

[0045] X-ZCS / MOF refers to a composite photocatalyst obtained by uniformly loading ZnCo2S4 with a mass percentage of X on the surface of MOF-199, where X represents the mass ratio of ZCS in ZCS / MOF.

[0046] Please refer to Figure 7, heterojunctions can be classified into type I, type II, type Z, and type S according to the electron migration path. Among them, the unique internal electric field (IEF) in type S heterojunctions can effectively separate photo-generated electron-hole pairs, which endows the material with excellent redox ability and charge utilization efficiency. Metal-organic frameworks (MOFs) are porous hybrid materials composed of organic ligands and metal ions, with advantages such as large specific surface area, high porosity, diverse structures, and stable chemical properties. Among them, MOF-199 (HKUST-1) is composed of Cu ions and 1,3,5-benzenetricarboxylate (BTC), and exhibits excellent performance in photocatalysis and adsorption separation. Therefore, it is feasible to use MOF-199 as the carrier material of ZCS for photocatalytic hydrogen evolution research. On the one hand, ZCS and MOF-199 have appropriate energy band structures, which are conducive to the formation of type S heterostructures, thereby promoting the separation of photo-generated electron-hole pairs. On the other hand, the uniform and ordered structure of MOF-199 provides a good growth environment, and ZCS nanoparticles can be anchored through organic ligands, thus exposing more active sites.

[0047] Application of the type S heterojunction ZnCo2S4 / MOF-199 composite material in the specific implementation manner of the present invention. The ZnCo2S4 / MOF-199 composite material is obtained by the following method:

[0048] Completely dissolve MOF-199 in a mixed solution of water and ethanol, denoted as solution E. In the specific embodiments of the present invention, the volume ratio of water to ethanol is 1:(3.5 - 4.5); among them, MOF-199 is obtained by the following method:

[0049] Mix DMF, ethanol, and deionized water according to a volume ratio of 1:(0.9 - 1.1):(0.9 - 1.1), and divide it into two equal parts, solution C and solution D;

[0050] Add Cu(NO3)2·3H2O and 1,3,5-benzenetricarboxylic acid to the solution C and the solution D respectively, ultrasonically treat and stir until completely dispersed, and then slowly drop the solution D into the solution C to obtain solution H;

[0051] Pour the solution H into a reaction kettle, react in an oven at 85 - 100 °C for 10 - 12 hours to obtain product Ι; then centrifuge and wash the product Ι several times and dry it for several hours to obtain MOF-199.

[0052] Ultrasonically dissolve ZnCo2S4 quantum dots in a mixed solution of water and ethanol, denoted as solution F; among them, the ZnCo2S4 quantum dots are obtained by the following method:

[0053] Dissolve Co(NO3)2·6H2O and Zn(NO3)2·6H2O in deionized water, ultrasonically treat and stir to form an aqueous solution, then add 5 times the molar amount of solid NaOH of the Co(NO3)2·6H2O, and stir to form solution A;

[0054] Add 4 times the molar amount of thioacetamide of the Co(NO3)2·6H2O to the solution A, and stir at room temperature until the solution turns black, denoted as solution B;

[0055] Transfer the solution B to a high-pressure reactor, react in an oven at 170 - 185 °C for 12 - 15 hours, then take it out and ultrasonicate to form a suspension, and then centrifuge to separate the ZnCo2S4 quantum dots from the ZnCo2S4 nanoparticles. Take the suspension, that is, the suspension of ZnCo2S4 quantum dots, and dry it for later use.

[0056] Drop the solution F into the solution E, and continuously stir at a temperature of 60 - 70 °C until the solvent completely evaporates. The obtained solid is the ZnCo2S4 / MOF-199 composite material. In the specific embodiments of the present invention, the mass of ZnCo2S4 accounts for 5% - 25% of the total mass of ZnCo2S4 and MOF-199.

[0057] The type II heterojunction ZnCo2S4 / MOF-199 composite material in the specific embodiments of the present invention is applied to photocatalytic hydrogen evolution and the removal of tetracycline residues in a visible light environment. The black ZnCo2S4 quantum dots are evenly distributed on the surface of the octahedral MOF-199, improving the absorption of visible light by MOF-199. In addition, the introduction of ZnCo2S4 significantly improves the separation of photo-generated electrons of the carrier MOF-199, inhibits the recombination of electron-hole pairs, thereby improving the photocatalytic activity of the composite material, and also has a large specific surface area and hydrophilicity. The photocatalytic experiment results show that ZnCo2S4 / MOF-199 has higher photocatalytic hydrogen evolution ability and TC degradation activity than MOF-199 and ZnCo2S4. In addition, the existence of the S-type heterojunction between MOF-199 and ZnCo2S4 is confirmed by experiments and characterizations, and a feasible photocatalytic reaction mechanism is proposed.

[0058] The following further illustrates the present invention in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0059] Example 1

[0060] 1. MOF-199 is prepared by a hydrothermal method. The specific steps are as follows:

[0061] 1.1 Put 1 mmol of Cu(NO3)2·3H2O into a solution containing 15 ml of DMF, 15 ml of ethanol and 15 ml of deionized water, and disperse it by ultrasonic treatment, denoted as solution A;

[0062] 1.2 Put 0.5 mmol of 1,3,5-benzenetricarboxylic acid (BTC) into the mixed solution containing 15 ml of DMF, 15 ml of ethanol and 15 ml of deionized water, and disperse it by ultrasonic treatment, denoted as solution B;

[0063] 1.3 Slowly drop solution A into solution B and stir for 30 min;

[0064] 1.4 Pour the solution into a 100 ml polytetrafluoroethylene liner and react in an oven at 85 - 100 °C for 10 - 12 hours.

[0065] 1.5 Collect MOF-199 by centrifugation and wash it several times with distilled water, and dry the product at 60 - 70 °C for 10 - 24 h.

[0066] 2. Synthesis of ZnCo2S4 is carried out specifically according to the following steps:

[0067] 2.1 Dissolve 1 mmol of Co(NO3)2·6H2O and 0.5 mmol of Zn(NO3)2·6H2O in deionized water, ultrasonically treat for 30 minutes, and stir to form a uniformly dispersed solution, then add 5 mmol of NaOH and continue to stir, denoted as solution A;

[0068] 2.2 Add 4 mmol of thioacetamide solution to solution A in step 2.1 and continue to stir at room temperature for 1 hour until the solution turns black;

[0069] 2.3 Pour the solution into a 100 ml polytetrafluoroethylene liner and react in an oven at 180 °C for 12 hours.

[0070] 2.4 Separate ZnCo2S4 quantum dots from nanoparticles by ultrasonic treatment and centrifugation, take its suspension (quantum dots) and dry it to obtain ZnCo2S4 quantum dots for standby.

[0071] Preparation of 5-ZnCo2S4 / MOF-199 composite material:

[0072] 3.1 Dissolve 0.95 g of MOF-199 in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as solution A;

[0073] 3.2 Ultrasonically dissolve 0.05 g of ZnCo2S4 quantum dots in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as solution B;

[0074] 3.3 Slowly and dropwise add Solution B into Solution A and continuously stir at 65 °C until the solvent is completely evaporated, and finally obtain the 5-ZnCo2S4 / MOF-199 composite material.

[0075] Example 2

[0076] 1. Preparation of MOF-199:

[0077] Obtain MOF-199 using the same preparation method as in Example 1.

[0078] 2. Synthesis of ZnCo2S4:

[0079] Obtain ZnCo2S4 quantum dots using the same preparation method as in Example 1.

[0080] 10-ZnCo2S4 / MOF-199 composite material preparation:

[0081] 3.1 Dissolve 0.9 g of MOF-199 in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as Solution A;

[0082] 3.2 Also ultrasonically dissolve 0.1 g of ZnCo2S4 quantum dots in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as Solution B;

[0083] 3.3 Slowly and dropwise add Solution B into Solution A and continuously stir at 65 °C until the solvent is completely evaporated, and finally obtain the 10-ZnCo2S4 / MOF-199 composite material.

[0084] Example 3

[0085] 1. Preparation of MOF-199:

[0086] Obtain MOF-199 using the same preparation method as in Example 1.

[0087] 2. Synthesis of ZnCo2S4:

[0088] Obtain ZnCo2S4 quantum dots using the same preparation method as in Example 1.

[0089] 15-ZnCo2S4 / MOF-199 composite material preparation:

[0090] 3.1 Dissolve 0.85 g of MOF-199 in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as Solution A;

[0091] 3.2 Also ultrasonically dissolve 0.15 g of ZnCo2S4 quantum dots in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as Solution B;

[0092] 3.3 Slowly and dropwise add Solution B into Solution A and continuously stir at 65 °C until the solvent is completely evaporated, and finally obtain the 15-ZnCo2S4 / MOF-199 composite material.

[0093] Example 4

[0094] 1. Preparation of MOF-199:

[0095] Obtain MOF-199 by using the same preparation method as in Example 1.

[0096] 2. Synthesis of ZnCo2S4:

[0097] Obtain ZnCo2S4 quantum dots by using the same preparation method as in Example 1.

[0098] 3. Preparation of 25-ZnCo2S4 / MOF-199 composite material:

[0099] 3.1 Dissolve 0.75 g of MOF-199 in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as Solution A;

[0100] 3.2 Also ultrasonically dissolve 0.25 g of ZnCo2S4 quantum dots in a solution of 50 ml of water and ethanol (volume ratio 1:4), denoted as Solution B;

[0101] 3.3 Slowly and dropwise add Solution B into Solution A and continuously stir at 65 °C until the solvent is completely evaporated, and finally obtain the 25-ZnCo2S4 / MOF-199 composite material.

[0102] Further, in combination with the accompanying drawings, it is described how each embodiment of the present invention reflects the object of the present invention and realizes the beneficial effects of the present invention:

[0103] Please refer to Figure 1 , and the crystal phases of ZCS, MOF-199 and X-ZCS / M of Examples 1-5 of the present invention were measured by X-ray diffraction spectroscopy (XRD). As Figure 1 (a) shows, the diffraction peaks of the prepared MOF-199 are located at 6.67°, 9.39°, 11.58°, 13.39°, 18.99° and 25.88° respectively, which are in good agreement with MOF-199 in the literature. The four obvious diffraction peaks of ZCS located at 28.64°, 47.64° and 56.54° correspond to the (111), (220) and (311) planes of ZnCo2S4 (JCPDS No. 47-1656), respectively. Most significantly, the characteristic peaks of MOF-199 and ZCS appear in all X-ZCS / M samples, and the characteristic peaks of ZCS are significantly enhanced with the increase of the ZCS content in the samples, indicating that the material is successfully prepared.

[0104] Please refer to Figure 1 (b) The chemical bonds and functional groups of the samples were studied by Fourier transform infrared (FTIR) spectroscopy. The sharp peak at 730 cm-1 in MOF-199 is caused by the stretching vibration of Cu-O, while the peak at 758 cm–1 is assigned to the out-of-plane bending mode of C-C rings. The absorption peaks located at 1373, 1447, and 1640 cm-1 are assigned to the stretching vibrations of O-H, C-O, and C=O bonds, respectively, demonstrating the presence of carboxyl functional groups. Compared with the spectrum of ZCS, these characteristic peaks belonging to MOF-199 are retained in the spectrum of the X-ZCS / M sample, further proving the existence of MOF-199 in the X-ZCS / M sample.

[0105] Please refer to Figure 2 (a-c), the morphologies of ZCS, MOF-199, and 15-ZCS / M (d) were studied by scanning electron microscopy (SEM). As Figure 2 (a) shows, the prepared ZCS exhibits irregular nanoparticles with diameters less than 100 nm. Figure 2 (b) shows, the prepared MOF-199 has an octahedral morphology with clear boundaries, and the particle size is between 10 and 20 μm. In Figure 2 (c), ZCS is uniformly distributed on the surface of MOF-199 with an irregular nanoparticle morphology. The microstructure of the catalyst was further studied by high-resolution transmission electron microscopy (HRTEM). As Figure 2 (d-f) shows, a lattice with a spacing of 0.27 nm can be clearly observed, belonging to ZCS(200). In addition, the EDS mapping of 15-ZCS / M Figure 2 (g-h) shows that Zn, Co, and S are uniformly distributed on the surface of MOF-199.

[0106] Please refer to Figure 3 , the elements and surface electronic states of the samples were studied by X-ray photoelectron spectroscopy (XPS). As Figure 3 (a) shows, the survey XPS spectrum shows that the characteristic peaks of ZCS and MOF-199 coexist on the surface of ZCS / M, including Cu, C, O, S, Co, and Zn. The two peaks in the figure. Figure 3 (b) The two characteristic peaks located at 1021.9 and 1044.9 eV are attributed to Zn 2p3 / 2 and Zn 2p1 / 2. Figure 3 (c) The two peaks of Co 2p correspond to two spin-orbit doublets, and the signals at 781.2 and 797.3 eV prove the existence of Co3+ and Co2+. Figure 3 (d) In, the two S 2p peaks located at 161.2 and 162.4 eV are attributed to S 2p3 / 2 and S 2p1 / 2, which confirms the existence of S2- species.Figure 3 (e) At 934.6 and 954.4 eV, attributed to Cu 2p3 / 2 and Cu 2p1 / 2, the binding energy peaks at 932.6 and 934.6 eV represent Cu+ and Cu2+ respectively. However, after introducing ZCS, the amount of Cu+ increased significantly, indicating that ZCS became an electron donor for Cu2+. Figure 3 (f) The two O1s peaks at 531.58 and 533.18 eV are attributed to the C=O and -OH groups. Additionally, for ZCS / M, compared with MOF-199, the peaks of Cu 2p and O1s shifted 0.3 eV to lower binding energies, while the peaks of Zn 2p, Co 2p, and S 2p shifted 0.2 eV to higher binding energy (BE) values, which represents electron migration due to different work functions. This electron migration formed an internal electric field (IEF) at the interface pointing from ZCS to MOF-199, facilitating the construction of the S-type ZCS / M heterojunction without any redox mediators.

[0107] Photocatalytic hydrogen evolution and tetracycline degradation activity

[0108] Using triethanolamine (TEOA) as a hole scavenger, the hydrogen evolution rate of the samples was studied through photocatalytic experiments. A 300 W xenon lamp with a 420 nm filter was used as the light source. Before the experiment, it was determined that no H2 would be obtained without a catalyst, light, or water. Figure 4 The amount of H2 evolved by the sample in (a) increased steadily within 5 h. For the H2 evolution rate of the sample, see Figure 4 (a - b), the photocatalytic activities of ZCS (140 μmol·g-1·h-1) and MOF-199 (240 μmol·g-1·h-1) were poor, probably due to the rapid recombination of photo-generated electron-hole pairs. Notably, compared with ZCS and MOF-199, the composite material ZCS / M exhibited excellent hydrogen evolution performance, which should be due to the construction of the S-type heterojunction promoting the separation of space charges. Among them, the H2 evolution rate of 15-ZCS / M reached 11.6 mmol·g-1·h-1, which was 83.3 times that of ZCS and 48.4 times that of MOF respectively.

[0109] After 5 cycle experiments, see Figure 4 (c), the photocatalytic hydrogen evolution activity of 15-ZCS / M remained stable.

[0110] In addition, Figure 4(d) is the photocatalytic degradation efficiency of the sample for tetracycline, where 10-ZCS / M exhibits the highest photocatalytic degradation efficiency (98.4%), significantly higher than that of MOF-199 (58%) and ZCS (56%). In summary, the ZCS / M composite shows excellent activity in both photocatalytic hydrogen evolution and TC degradation.

[0111] Please refer to Figure 5 (a), photoluminescence (PL) spectroscopy characterization was carried out to gain a deeper understanding of charge transfer. The higher the fluorescence emission peak means the higher the recombination rate of electron-hole pairs. The PL emission intensities of ZCS and MOF-199 indicate the rapid recombination of photo-generated electron-hole pairs, which is not conducive to the evolution of photocatalytic H2. However, the PL emission intensity of 15-ZCS / M is significantly lower than that of ZCS and MOF-199, indicating that the construction of the heterojunction alleviates the recombination of photo-generated carriers.

[0112] Please refer to Figure 5 (b) The light-harvesting ability of the samples was measured by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). ZCS / M has a stronger visible light absorption ability compared to MOF-199, and the light absorption edge of X-ZCS / M is close to 470 nm. In addition, as Figure 5 (c-d) shown, the band gaps (Eg) of ZCS and MOF-199 were obtained as 2.8 and 2.65 eV through the Kubelka-Munk function. As Figure 5 (e-f) From the XPS valence band spectra, the valence band maxima (EVB) of ZCS and MOF-199 are 1.1 and 1.85 eV, respectively. The maximum conduction bands (ECB) of ZCS and MOF-199 are -1.7 and -0.8 eV, respectively (ECB = EVB - Eg).

[0113] To study the interfacial charge separation, photoelectrochemical (PEC) measurements were carried out. The transient photocurrent response was detected to study the photopotential under a 300 W Xe lamp with a 420 nm filter. Please see Figure 6 (a) shown, the photocurrent density of 15-ZCS / M in the sample is the highest, which is due to the improved interfacial interaction between ZCS and MOF-199 due to the uniform dispersion of the structure. Please see Figure 6 (b) The electrochemical impedance spectroscopy (EIS) analysis shows that the Nyquist arc radius of 15-ZCS / M in the sample is significantly the smallest, which is attributed to the excellent conductivity of ZCS, which improves the interfacial charge transfer rate. Figure 6Analysis of the linear sweep voltammetry (LSV) curves in (c) shows that when the current density is -1 mA / cm2, the onset potentials of ZCS, MOF-199, and 15-ZCS / M are -1.029, -1.057, and -0.941 V, respectively, indicating that the formation of the heterostructure promotes the interfacial charge transfer. In addition, as Figure 6 shown in (d), the Tafel slope can reflect the H2 evolution activity of the samples. The Tafel slopes of ZCS, MOF-199, and 15-ZCS / M are 20.9, 20.7, and 18.2 mV / dec, respectively. Combining Figure 6 (c) the LSV curves and Figure 6 (d) the Tafel curve analysis shows that the improvement of the hydrogen evolution reaction (HER) activity is due to the reduction of the energy required for bond breaking. The semiconductor type and flat band potential of the samples can be confirmed by the M-S curve analysis in the figure. As Figure 6 shown in (e-f), according to the slope of the Mott-Schottky curve, ZCS and MOF-199 are typical n-type semiconductors. In addition, the flat band potentials (Efb) of ZCS and MOF-199 are -1.78 and -0.75 V (vs. Ag / AgCl), respectively. Since the ECB of n-type semiconductors is 0.1 - 0.2 V higher than the negative value of Efb, the ECBs of ZCS and MOF-199 are -1.98 and -0.95 V, respectively. By calculation (ENHE = EAg / AgCl + 0.197 eV), the ECBs of ZCS and MOF-199 are -1.783 and -0.753 eV (vs. the standard hydrogen electrode), which are consistent with the ECBs calculated from EVB and Eg (-1.7 and -0.8 eV, vs. the standard hydrogen electrode).

[0114] The above are only the preferred or exemplary embodiments of the present invention. It should be noted that: for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements or refinements can be made, and these improvements or refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of an S-type heterojunction ZnCo2S4 / MOF-199 composite material, characterized in that, The ZnCo2S4 / MOF-199 composite material is applied to photocatalytic hydrogen evolution or degradation and removal of tetracycline in water, and is obtained by an ultrasonic impregnation method: Completely dissolve MOF-199 in a mixed solution of water and ethanol, denoted as solution E; Ultrasonically dissolve ZnCo2S4 quantum dots in a mixed solution of water and ethanol, denoted as solution F; Drop the solution F into the solution E, and continuously stir at a temperature of 60 - 70 °C until the solvent is completely evaporated. The obtained solid is the S-type heterojunction ZnCo2S4 / MOF-199 composite material.

2. Application of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 1, characterized in that, The MOF-199 is obtained by the following method: Mix DMF, ethanol and deionized water in a volume ratio of 1:(0.9 - 1.1):(0.9 - 1.1), and divide it into two equal parts, solution C and solution D; Add Cu(NO3)2·3H2O and 1,3,5-benzenetricarboxylic acid to the solution C and the solution D respectively, ultrasonically treat and stir until completely dispersed, and then slowly drop the solution D into the solution C to obtain solution H; Pour the solution H into a reaction kettle, react in an oven at 85 - 100 °C for 10 - 12 hours to obtain product Ι; then centrifuge and wash the product Ι several times and dry it for several hours to obtain MOF-199.

3. Use of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 1, characterized in that, The ZnCo2S4 quantum dots are obtained by the following method: Dissolve Co(NO3)2·6H2O and Zn(NO3)2·6H2O in deionized water, ultrasonically treat and stir to form an aqueous solution, and then add solid NaOH with a molar amount 5 times that of Co(NO3)2·6H2O, and stir to form solution A; Add thioacetamide with a molar amount 4 times that of Co(NO3)2·6H2O to the solution A, and stir at room temperature until the solution turns black, denoted as solution B; Transfer the solution B to a high-pressure reaction kettle, react in an oven at 170 - 185 °C for 12 - 15 hours, take it out and ultrasonicate to form a suspension, and then centrifuge to separate the ZnCo2S4 quantum dots from the ZnCo2S4 nanoparticles. Take the suspension, that is, the suspension of ZnCo2S4 quantum dots, and dry it for standby.

4. Use of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 1, characterized in that, The mass of ZnCo2S4 accounts for 5% - 25% of the total mass of ZnCo2S4 and MOF-199.

5. Application of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 1, characterized in that, Completely dissolve MOF-199 in a mixed solution of water and ethanol, wherein the volume ratio of water to ethanol is 1:(3.5 - 4.5).

6. Use of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 2, characterized in that, The molar ratio of Cu(NO3)2·3H2O to 1,3,5-benzenetricarboxylic acid is 2:

1.

7. Use of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 2, characterized in that, Then centrifuge and wash the product Ι several times and dry it for several hours to obtain MOF-199, wherein the drying temperature is 60 - 70 °C and the drying time is 10 - 24 hours.

8. Use of the S-type heterojunction ZnCo2S4 / MOF-199 composite material according to claim 3, characterized in that, The molar ratio of Co(NO3)2·6H2O to Zn(NO3)2·6H2O is 2:1.

Images