A Z-type heterojunction Mn3O4@CdIn2S4 composite material, a preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic hydrogen production, and particularly relates to a Z-type heterojunction Mn3O4@CdIn2S4 composite material and a preparation method and application thereof. The application synthesizes Mn3O4 microspheres by taking Mn-MOF as a precursor, in-situ grows a CdIn2S4 (CIS) shell, and prepares core-shell type Mn3O4@CdIn2S4 microspheres, and simultaneously forms a Z-type heterojunction. Compared with CdIn2S4 and Mn3O4, the photocatalytic performance of Mn3O4@CdIn2S4 under simulated sunlight is significantly improved. On one hand, the Z-type electron transfer path not only improves the electron-hole separation efficiency, but also improves the charge transfer efficiency. On the other hand, the existence of the core-shell heterojunction increases the light absorption range.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic hydrogen production, and particularly relates to a Z-type heterojunction Mn3O4@CdIn2S4 composite material and a preparation method and application thereof. BACKGROUND

[0002] Environmental pollution and energy shortage have become a hot topic. Using sustainable, pollution-free and low-cost new energy to replace fossil energy has become a way to solve the current environmental deterioration problem. Hydrogen energy is considered to be one of the environmentally friendly and effective clean energy, which is effectively converted from renewable solar energy. Since Fujishima and Honda first successfully used a TiO2 single crystal electrode to decompose water into hydrogen and oxygen under ultraviolet light, the photocatalytic water splitting technology has become the most environmentally friendly, safest and most effective method to solve the energy crisis. However, for most semiconductor materials, it is not easy to achieve high photocatalytic activity by itself. Therefore, it is a great challenge for this technology to prepare photocatalysts with excellent performance, low price and high quantum efficiency.

[0003] In recent years, photocatalysts for generating H2 have been explored, and metal chalcogenides are widely favored due to their suitable band gap and band position. Among them, three-dimensional flower-like microspheres CdIn2S4 belonging to the ternary compound AB2X4 family have been applied to the field of hydrogen production due to their appropriate band edge position, narrow band gap and excellent charge mobility. However, there are many urgent problems in the process of hydrogen production reaction, such as rapid recombination of electron-hole pairs and serious photo corrosion.

[0004] In addition, manganese oxides have been widely studied due to their novel structure and excellent physical and chemical applications. Among these manganese oxides, Mn3O4 is an interesting material because of its extraordinary surface area and unique nano-electronic structure, which is suitable for wide application, and secondly, Mn3O4 is a stable oxide with spinel structure, which also has catalytic performance and electrochemical properties.

[0005] By constructing a heterojunction, modifying a cocatalyst and doping an element, the photocatalytic activity can be effectively accelerated. Among them, the reasonable design of the heterojunction is of great help to promote charge separation and photocatalytic activity. The heterojunction can be divided into type I, type II and type Z according to the electron transfer path. Among them, the unique internal electric field (IEF) in the Z-type heterojunction can effectively separate the electron-hole pairs, reduce the recombination probability, retain strong oxidation-reduction active sites, expand the light response range and improve the photocatalytic activity. SUMMARY

[0006] In view of the deficiencies in the prior art, the application provides a Z-type heterojunction Mn3O4@CdIn2S4 composite material with a core-shell heterostructure and a preparation method and application thereof.

[0007] The technical scheme adopted by the present application is: a Z-type heterojunction Mn3O4@CdIn2S4 core-shell heterostructure composite material is synthesized by taking Mn-MOF as a precursor to synthesize Mn3O4 microspheres, and growing a CdIn2S4 (CIS) shell in situ to form a Z-type heterojunction.

[0008] The preparation method of the Z-type heterojunction Mn3O4@CdIn2S4 composite material specifically includes the following steps:

[0009] (1) 1,3,5-benzenetricarboxylic acid (C6H3(CO2H)3) and MnCl2 are dissolved in N,N-dimethylformamide (DMF), ultrasonic treatment and stirring are performed until complete dissolution, and then the mixture is transferred to a high-pressure reaction kettle, and after reaction at 160±10℃ for 46-48 hours, the mixture is taken out, centrifuged, and dried to obtain a solid product of Mn-MOF. The solid product Mn-MOF is placed in a tube furnace, and after oxidation calcination at 500℃±20℃ for 0.5-1.5 hours, the solid Mn3O4 is obtained.

[0010] Optionally, the molar ratio of the 1,3,5-benzenetricarboxylic acid (C6H3(CO2H)3) to the MnCl2 is 1:1~2; preferably 1:2.

[0011] Optionally, the vacuum drying temperature of the Mn-MOF is 60~70℃, and the drying time is 10~24 hours.

[0012] (2) Thiourea is dissolved in deionized water, ultrasonic treatment and stirring are performed until complete dissolution to obtain a thiourea solution; a soluble cadmium salt and a soluble indium salt are dissolved in deionized water, ultrasonic treatment and stirring are performed until complete dissolution, the thiourea solution is added, and stirring is performed until the mixture is uniform; the Mn3O4 obtained in step (1) is ultrasonic dispersed and stirred at room temperature until the mixture is uniform to obtain a mixed solution; the mixed solution is hydrothermally reacted at 170~190℃ for 18~20 hours, centrifuged, washed, and dried to obtain the Z-type heterojunction Mn3O4@CdIn2S4 composite material.

[0013] Optionally, the molar ratio of the soluble cadmium salt, the soluble indium salt, and the thiourea is 1:1~3:1~4; preferably 1:2:4.

[0014] Optionally, the mass ratio of the Mn3O4 to the generated CdIn2S4 is 4:6; 3:7; 2:8; 1:9; preferably 3:7. The mass of the Mn3O4 in the Mn3O4@CdIn2S4 composite material accounts for 10%~40%.

[0015] Optionally, the soluble cadmium salt is CdCl2 or CdCl2·2.5H2O; and the soluble indium salt is InCl3 or InCl3·4H2O.

[0016] Optionally, the product Mn3O4@CdIn2S4 has a drying temperature of 60-70 DEG C and a drying time of 10-24 hours.

[0017] The application provides the Z-type heterojunction Mn3O4@CdIn2S4 composite material prepared by the preparation method.

[0018] The application also provides application of the Z-type heterojunction Mn3O4@CdIn2S4 core-shell heterostructure composite material, and the Z-type heterojunction Mn3O4@CdIn2S4 core-shell heterostructure composite material is used for photocatalytic hydrogen evolution, and is particularly used for visible light catalytic hydrogen evolution.

[0019] The application successfully prepares a Z-type heterojunction Mn3O4@CdIn2S4 composite material by using a simple in-situ growth method, and the material is applied to photocatalytic hydrogen evolution. Mn3O4 microspheres are synthesized by taking Mn-MOF as a precursor, and a CdIn2S4 (CIS) shell is in-situ grown, and the existence of the core-shell heterostructure is favorable to increasing the light absorption range, thereby improving the photocatalytic activity. In addition, the introduction of Mn3O4 significantly improves the separation of the CdIn2S4 carrier, inhibits the recombination of the electron-hole pairs, and thereby improves the photocatalytic activity of the composite material. The photocatalytic experiment results show that the Mn3O4@CdIn2S4 has higher photocatalytic hydrogen evolution capacity than Mn3O4 and CdIn2S4. In addition, the existence of the Z-type heterojunction between Mn3O4 and CdIn2S4 is verified through experiments and characterization, and a possible photocatalytic reaction mechanism is proposed.

[0020] Therefore, it is feasible to study the photocatalytic hydrogen evolution of CdIn2S4 coupled with Mn3O4. On one hand, CdIn2S4 and Mn3O4 have appropriate energy band structures, which are favorable to the formation of the Z-type heterostructure, thereby promoting the separation of the photo-generated electron-hole pairs. On the other hand, the core-shell heterostructure is formed, the light absorption range is greatly increased, and the hydrogen production activity is enhanced. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 XRD patterns of Mn3O4, CdIn2S4 and 30% Mn3O4@CdIn2S4;

[0022] Figure 2 SEM patterns (a-c) of Mn3O4, CdIn2S4 and 30% Mn3O4@CdIn2S4;

[0023] Figure 3 TEM patterns (a-f) of 30% Mn3O4@CdIn2S4;

[0024] Figure 4XPS spectra of 30% Mn3O4@CdIn2S4; (a) total spectrum; (b) S 2p; (c) In 3d; (d) Cd 3d; (e) O 1s; (f) Mn 2p;

[0025] Figure 5 Hydrogen evolution efficiency spectra of Mn-MOF, Mn3O4, CdIn2S4, Mn3O4@CdIn2S4 (a-b);

[0026] Figure 6 Cycle experiment chart of 30% Mn3O4@CdIn2S4;

[0027] Figure 7 Fluorescence emission spectra of Mn3O4, CdIn2S4, Mn3O4@CdIn2S4 prepared in Example 3;

[0028] Figure 8 UV-Vis diffuse reflectance spectra of Mn3O4, CdIn2S4, Mn3O4@CdIn2S4 prepared in Example 3;

[0029] Figure 9 Photoelectric current response chart of Mn3O4, CdIn2S4, Mn3O4@CdIn2S4 prepared in Example 3;

[0030] Figure 10 EIS impedance chart of Mn3O4, CdIn2S4, Mn3O4@CdIn2S4 prepared in Example 3. DETAILED DESCRIPTION

[0031] The application will be further described below in conjunction with the accompanying drawings and specific embodiments, but the scope of protection of the application is not limited thereto. Example 1

[0032] Preparation of Mn3O4@CdIn2S4 composite material with mass ratio of 1:9:

[0033] (1) Mn3O4 was prepared by oxidation calcination, and the specific steps were as follows:

[0034] 0.21g 1,3,5-benzene tricarboxylic acid C6H3(CO2H)3 and 0.252g MnCl2 were dissolved in 10ml DMF, ultrasonic and stirred until completely dissolved, transferred to a high-pressure reaction kettle, reacted in an oven at 160℃ for 48 hours, collected by centrifugation and washed with ethanol and ionized water for several times, and the product was dried at 60℃ for 10 hours to obtain solid product Mn-MOF. The solid product Mn-MOF was placed in a tube furnace, calcined at 500℃ for 1 hour, and then taken out to obtain solid Mn3O4.

[0035] (2) 0.2284 g CdCl2·2.5H2O and 0.587 g InCl3·4H2O were dissolved in 30 ml deionized water, ultrasonic and stirring until completely dissolved. 0.304 g thiourea (CH4N2S) was dissolved in 20 ml deionized water, ultrasonic and stirring until completely dissolved. The solution containing CH4N2S was poured into the solution containing CdCl2·2.5H2O and InCl3·4H2O and stirred for 1 hour. 0.1244 g Mn3O4 was added and ultrasonic dispersed, noted as mixed solution; the mixed solution was poured into the reaction kettle and reacted in the oven at 180℃ for 18 hours. The product was collected by centrifugation and washed with ethanol and ionized water for several times, and dried at 60℃ for 10 hours. The obtained solid product was Mn3O4@CdIn2S4 composite material with mass ratio of 1:9, noted as 10% Mn3O4@CdIn2S4.

[0036] As a comparison, CdIn2S4 pure sample was also prepared, i.e. according to the preparation method of Mn3O4@CdIn2S4, without adding Mn3O4, and the obtained solid product was CdIn2S4, with mass of 1.1196 g. Example 2

[0037] Preparation of Mn3O4@CdIn2S4 composite material with mass ratio of 2:8:

[0038] The difference between this example and Example 1 is that 0.27985 g Mn3O4 was added in step (2), and the obtained solid product was Mn3O4@CdIn2S4 composite material with mass ratio of 2:8, noted as 20% Mn3O4@CdIn2S4. Example 3

[0039] Preparation of Mn3O4@CdIn2S4 composite material with mass ratio of 3:7:

[0040] The difference between this example and Example 1 is that 0.4797 g Mn3O4 was added in step (2), and the obtained solid product was Mn3O4@CdIn2S4 composite material with mass ratio of 3:7, noted as 30% Mn3O4@CdIn2S4. Example 4

[0041] The difference between this example and Example 1 is that 0.7463 g Mn3O4 was added in step (2), and the obtained solid product was Mn3O4@CdIn2S4 composite material with mass ratio of 4:6, noted as 40% Mn3O4@CdIn2S4.

[0042] The embodiments of the present application will be further described in conjunction with the accompanying drawings to illustrate how the embodiments embody the purpose of the present application and achieve the beneficial effects of the present application:

[0043] Please refer toFigure 1 The XRD patterns of Mn304, CdIn2S4, and 30% Mn304@CdIn2S4 were measured by X-ray diffraction spectroscopy (XRD). As shown in FIG. 8, Figure 1 the diffraction peaks of the prepared Mn304 were located at 18.00°, 28.88°, 31.02°, 32.32°, 36.08°, 37.98°, 44.44°, 50.70°, 58.51°, 59.84°, and 64.65°, all of which were in good agreement with the plane (PDF #24-0734). The nine obvious diffraction peaks of CdIn2S4 at 14.1°, 23.2°, 27.2°, 28.4°, 29.1°, 33.0°, 40.6°, 43.3°, and 47.4° were all in accordance with the plane (PDF #27-0060). Most significantly, the characteristic peaks of Mn304 and CdIn2S4 appeared in the Mn304@CdIn2S4 sample, indicating that the material was successfully prepared.

[0044] Referring to Figure 2 (a-c), the morphology of Mn304, CdIn2S4, and 30% Mn304@CdIn2S4 was studied by scanning electron microscopy (SEM). As shown in FIG. 9, Figure 2 (a), the prepared CdIn2S4 was composed of irregular nanoparticles. Figure 2 (b), the prepared Mn304 had a clear layered structure. In Figure 2 (c), the prepared Mn304@CdIn2S4 was clearly composed of nanoparticles and a layered structure, further indicating that the material was successfully prepared.

[0045] Referring to Figure 3 , TEM analysis showed that the elements S, In, and Cd were dispersed on the periphery of the core-shell structure, and the elements Mn and O were inside the core-shell structure, indicating that the core-shell heterostructure was successfully prepared.

[0046] Referring to Figure 4 , the elements and surface electronic states of the samples were studied by X-ray photoelectron spectroscopy (XPS). As shown in FIG. 10, Figure 4 (a), the survey XPS spectrum showed that the characteristic peaks of Mn304 and CdIn2S4 were present on the surface of Mn304@CdIn2S4, including S, In, Cd, O, and Mn. Figure 4 (b), two characteristic peaks at 161.14 and 162.37 eV were attributed to S 2p 3 / 2 and S 2p 1 / 2 . Figure 4 (c), signals at 451.95 and 444.35 eV proved In 3d 3 / 2 and In 3d 5 / 2presence of Cd 3d Figure 4 (d) two characteristic peaks located at 411.5 and 404.74 eV, attributed to Cd 3d 3 / 2 and Cd 3d 5 / 2 presence of Cd 3d Figure 4 (e) two characteristic peaks located at 531.36 and 529.8 eV, attributed to O 1s Figure 4 (f) two characteristic peaks located at 641.46 and 653.22 eV, attributed to Mn 2p 3 / 2 and Mn 2p 1 / 2 In addition, S, In and Cd peaks move to higher binding energy, and Mn and O peaks move to lower binding energy. This represents the migration of electrons due to the difference in binding energy, and the internal electric field is closely bound together, which again proves that Mn304@CdIn2S4 forms a tight heterojunction.

[0047] Photocatalytic hydrogen evolution

[0048] The photocatalytic experiments were carried out in a photoreactor, xenon lamp irradiation, 50 mL of deionized water and 50 mL of sacrificial agent (0.35 M Na2S and 0.25 M Na2SO3) were added to the reactor, then 0.01 g of catalyst was added to Na2S and Na2SO3 as hole scavenger, and the hydrogen evolution rate of the sample was studied by photocatalytic experiment. A 300 W xenon lamp with a 420 nm filter was used as the light source, and the reaction was carried out for 5 h. Before the experiment, it was determined that no H2 could be obtained without catalyst, light or water. Figure 5 The amount of H2 evolution of the sample in a is steadily increasing within 5 h. The H2 evolution rate of the sample, see Figure 5 (a-b), the photocatalytic activity of Mn304(1.654 mmol·g −1 ·h −1 ) and CdIn2S4(1.447 mmol·g −1 ·h −1 ) is poor, which may be due to the rapid recombination of photo-generated electron-hole pairs. It is worth noting that compared with Mn304 and CdIn2S4, the composite Mn304@CdIn2S4 exhibits excellent hydrogen evolution performance, which should be due to the construction of Z-type heterojunction promoting the spatial charge separation. Among them, the H2 evolution rate of 30% Mn304@CdIn2S4 reaches 17.866 mmol·g −1 ·h −1 , which is 10.80 times that of Mn304 and 12.35 times that of CdIn2S4, respectively.

[0049] See Figure 6After 5 cycles, the photocatalytic hydrogen evolution activity of 30Mn3O4@CdIn2S4 still maintained 95% of the initial catalytic activity, indicating that the catalyst had good stability.

[0050] See Figure 7 Photoluminescence (PL) spectra were measured to further understand the charge transfer. Higher fluorescence emission peaks mean higher recombination rates of electron-hole pairs. The PL emission intensity of Mn3O4 and CdIn2S4 indicated the fast recombination of photo-generated electron-hole pairs, which was not conducive to the photocatalytic H2 evolution. However, the PL emission intensity of Mn3O4@CdIn2S4 was significantly lower than that of Mn3O4 and CdIn2S4, which indicated that the construction of heterojunctions alleviated the recombination of photo-generated carriers.

[0051] See Figure 8 The light capture ability of the samples was measured by ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). Mn3O4@CdIn2S4 had a stronger visible light absorption ability, with a light absorption edge close to 680 nm.

[0052] See Figure 9 In order to study the interface charge separation, photoelectrochemical (PEC) measurements were performed. The transient photocurrent response was detected to study the light-induced potential under a 300 W Xe lamp with a 420 nm filter. Mn3O4@CdIn2S4 had the highest photocurrent density, which was due to the interface interaction between Mn3O4 and CdIn2S4, which improved the uniform dispersion of the structure.

[0053] See Figure 10 Electrochemical impedance spectroscopy (EIS) analysis in the Nyquist plot showed that the Nyquist arc radius of Mn3O4@CdIn2S4 was significantly the smallest, which was attributed to the construction of heterojunctions, which improved the conductivity and thus accelerated the interface charge transfer rate.

[0054] The above only describes the preferred or exemplary embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements or refinements can also be made, which should be considered as the protection scope of the present application.

Claims

1. A method for preparing a Z-type heterojunction Mn3O4@CdIn2S4 composite material, characterized in that, Specifically, the steps include the following: (1) Preparation of Mn-MOF-derived Mn3O4: 1,3,5-benzenetricarboxylic acid and MnCl2 were dissolved in N,N-dimethylformamide, sonicated and stirred until completely dissolved, transferred to a high-pressure reactor, reacted at 150~170℃ for 46~48 hours, removed, centrifuged and dried to obtain Mn-MOF; Mn-MOF was oxidized and calcined at 480~520℃ for 0.5~1.5 hours and removed to obtain Mn-MOF-derived Mn3O4; (2) Dissolve thiourea in deionized water, sonicate and stir until completely dissolved to obtain a thiourea solution; dissolve soluble cadmium salt and soluble indium salt in deionized water, sonicate and stir until completely dissolved, add thiourea solution and stir until mixed evenly; add Mn-MOF-derived Mn3O4 and sonicate to disperse, and stir at room temperature until mixed evenly to obtain a mixed solution; hydrothermally react the mixed solution at 170~190℃ for 18~20 hours, centrifuge, wash and dry to obtain Z-type heterojunction Mn3O4@CdIn2S4 composite material.

2. The method for preparing the Z-type heterojunction Mn3O4@CdIn2S4 composite material according to claim 1, characterized in that, The molar ratio of 1,3,5-benzenetricarboxylic acid and MnCl2 in step (1) is 1:1~2.

3. The method for preparing the Z-type heterojunction Mn3O4@CdIn2S4 composite material according to claim 1, characterized in that, The molar ratio of the soluble cadmium salt, soluble indium salt and thiourea in step (2) is 1:1~3:1~4.

4. The method for preparing the Z-type heterojunction Mn3O4@CdIn2S4 composite material according to claim 1, characterized in that, The soluble cadmium salt in step (2) is cadmium chloride or its hydrate; the soluble indium salt is indium chloride or its hydrate.

5. The method for preparing the Z-type heterojunction Mn3O4@CdIn2S4 composite material according to claim 1, characterized in that, In step (2), the mass percentage of Mn3O4 derived from Mn-MOF in the Mn3O4@CdIn2S4 composite material is 10%~40%.

6. A Z-type heterojunction Mn3O4@CdIn2S4 composite material prepared by the method according to any one of claims 1-5.

7. The application of the Z-type heterojunction Mn3O4@CdIn2S4 composite material as described in claim 6 in photocatalytic hydrogen evolution.

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