A defect-regulated ultra-thin molybdenum disulfide-loaded organic manganese complex heterostructure catalyst and its preparation method and application

Abstract

The present invention discloses a heterogeneous structure catalyst of defect-regulated ultrathin molybdenum disulfide supported with an organic manganese complex, and a preparation method and application thereof. The preparation is as follows: first, flaky molybdenum sulfide is prepared; then it is exfoliated to form monolayer MoS2 with rich defects, which is added to a dispersion solution of the organic manganese complex, and the catalyst is obtained through centrifugation, washing, drying, and calcination. The present invention adopts a simple method of mixing and loading to form a heterogeneous structure by compounding two two-dimensional semiconductors, effectively solving the activation problems of CO2 and H2O. By regulating the amount of defects on the surface of ultrathin MoS2, the contact with MnBO is regulated, forming new defect energy levels, which is beneficial to the progress of the reduction reaction, and effectively inhibits the problem of carrier recombination. Finally, a methanol selectivity of 90% is obtained, providing a feasible research strategy for the high-value conversion of photocatalytic CO2.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic materials, and in particular to a defect-controlled ultra-thin molybdenum disulfide-loaded organic manganese complex heterostructure catalyst, and a preparation method and application thereof. Background Art

[0002] Excessive use of fossil fuels has led to a continuous increase in carbon dioxide emissions, which has had many negative impacts on the global environment and greatly hindered the sustainable development of human society. 2 Converting it into valuable green and clean fuels (methanol and ethanol) not only helps reduce greenhouse gas emissions, but also creates a carbon-neutral energy utilization model, which is of great significance for achieving sustainable development. However, efficient photocatalysts require fast charge transfer and low electron-hole recombination rate to promote redox reactions, which is an obstacle to CO 2 The key bottleneck for the widespread application of photoreduction to methanol.

[0003] Two-dimensional ultrathin photocatalysts are rich in defects, have suitable band gap potentials and tunable optical properties, and have been shown to be a material that accelerates vertical charge separation and planar proton transfer. However, due to surface stress, ultrathin catalysts rich in defects often have structural instability. During the catalytic process, strong interactions can lead to their aggregation and dissociation, affecting CO 2 Catalytic activity and stability. In addition, the problem of electron-hole recombination is easy and fast, which also limits the improvement of the photoactivity efficiency of a single two-dimensional material.

[0004] In recent years, people have conducted extensive research on defect-rich two-dimensional heterojunction photocatalysts. CN118287111A discloses a method for preparing a bismuth / molybdenum / zinc vacancy-rich bismuth molybdate / zinc selenide heterojunction photocatalyst, wherein a molybdenum source, a surfactant and a bismuth source are hydrothermally synthesized to produce defect-rich bismuth molybdate, which is then ground and ion-dialyzed with hydrothermally synthesized zinc selenide to produce bismuth / molybdenum / zinc vacancy-rich bismuth molybdate / zinc selenide. This photocatalytic material has high purity, stable strength, low surface charge transfer resistance, high photocurrent density and excellent catalytic performance.

[0005] CN118237053A discloses a method for preparing a molybdenum selenide / oxygen-deficient bismuth oxybromide@gold three-phase Z-type heterojunction photocatalyst, wherein oxygen-deficient BiOBr nanospheres are prepared by a solvent thermal method, and then tetrachloroauric acid is directly reacted with oleylamine in toluene to prepare monodisperse Au nanoparticles, which are then composited with oxygen-deficient BiOBr to prepare BiOBr@Au nanosphere core-shell structure; finally, MoSe is prepared by a hydrothermal reaction. 2 / oxygen defect BiOBr@Au three-phase composite material. It solves the problems of low photogenerated electron-hole separation rate, narrow full-spectrum response range and poor stability in existing bismuth-based photocatalysts. However, the synthesis methods used in these heterogeneous structure catalysts are relatively complicated, involving a large number of synthetic materials, including highly toxic organic substances, which is contrary to the concept of green material synthesis; and their reaction activity has not reached the ideal level.

[0006] The applicant's early research CN 116273180 A disclosed a catalyst of heterostructure of organic zinc complex and molybdenum sulfide, preparation method and application, the preparation comprising the following steps: step 1, preparing flaky molybdenum sulfide; step 2, preparing layered organic zinc complex; step 3, dispersing molybdenum sulfide and organic zinc complex in solvents respectively, adding dropwise a solution containing organic zinc complex to a solution containing molybdenum sulfide for reaction, and obtaining the catalyst by centrifugation, washing, drying and calcining. The catalyst photocatalyzes CO 2 Nearly 90% methanol selectivity was achieved. But creating a more efficient catalyst is still a research direction for researchers. Summary of the invention

[0007] The present invention is directed to photocatalytic CO 2 and H 2 The efficient preparation of methanol by O reaction has the problems of insufficient catalytic efficiency and poor stability, as well as the problem of high-speed carrier recombination caused by the unstable structure of the catalyst itself. This paper provides a defect-regulated ultra-thin molybdenum disulfide-loaded organic manganese complex heterostructure catalyst, which can achieve high photocatalytic selectivity and high stability for the reduction of carbon dioxide, and has higher methanol selectivity and yield.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a defect-controlled ultra-thin molybdenum disulfide-loaded organic manganese complex heterostructure catalyst comprises the following steps:

[0010] Step 1, stirring and mixing molybdate and an organic sulfur-containing compound in a solvent, crystallizing and washing to obtain flaky molybdenum sulfide;

[0011] Step 2, dispersing the flaky molybdenum sulfide in a solvent and performing ultrasonic exfoliation, and obtaining defect-rich ultrathin molybdenum sulfide after centrifugation;

[0012] Step 3, mixing manganese salt, bipyridine and oxalic acid in a solvent, dispersing and washing to obtain a layered organic manganese complex;

[0013] Step 4, stirring and mixing the ultra-thin molybdenum sulfide and the layered organic manganese complex solution for reaction, and obtaining the heterogeneous structure catalyst through centrifugation, washing, drying and calcination.

[0014] After trying a variety of transition metal elements, the present invention found that the catalyst loaded with an organic manganese complex and formed a heterogeneous interface with defective ultra-thin molybdenum sulfide can greatly improve the CO 2 The adsorption and activation of H 2 O efficiently reduces CO 2 The catalytic effect is much higher than that of the catalyst reported in the prior art, and the catalyst has suitable light absorption characteristics, can generate sufficient electron-hole pairs, improve the efficiency of separation and transfer of photogenerated electrons and holes, and effectively inhibit the rapid recombination of carriers, thereby efficiently participating in the redox process and effectively improving the yield of the target product methanol.

[0015] The molybdate includes one or a combination of two or more of sodium molybdate, potassium molybdate and ammonium molybdate;

[0016] The organic sulfur-containing compound includes one or a combination of two or more of mercaptan, thiophenol, thiourea, and disulfide;

[0017] The solvent in step 2 includes one or a combination of two or more of ethanol, isopropanol, water, N-methylpyrrolidone, and ethylene glycol.

[0018] The manganese salt includes one or a combination of two or more of manganese nitrate, manganese carbonate, manganese acetate and manganese sulfate; the bipyridine includes 2,2-bipyridine and / or 4,4-bipyridine. The manganese salt and bipyridine react easily to form an organic manganese complex.

[0019] The molar ratio of the organic sulfur-containing compound to the molybdate is 0.5-50:0.5-30, preferably 0.5-30:0.5-15, and more preferably 5-15:0.5-5. The stirring and mixing are carried out at room temperature for 2-50 hours, preferably 4-24 hours, 6-35 hours at room temperature; the crystallization temperature is 100-400°C, and the time is 6-30 hours; for example, 120°C, 160°C, 200°C, 240°C, 280°C, and the crystallization is carried out for 8 hours, 12 hours, 16 hours, 20 hours, 24 hours, 28 hours; preferably, the crystallization temperature is 140-200°C, and the crystallization time is 15-25 hours.

[0020] In step 2, the mass concentration of flaky molybdenum sulfide in the solvent is 0.01-50 mg / ml, the ultrasonic time is 1-50 h, and the ultrasonic temperature is room temperature. Preferably, the mass concentration of flaky molybdenum sulfide in the solvent is 0.1-30 mg / ml, and the time is 5-18 h. A further preferred mass concentration is 0.1-25 mg / ml, and a further preferred mass concentration is 0.1-2 mg / ml. The ultrasonic time is preferably 5-15 h, and more preferably 10-15 h.

[0021] Effect of stripping concentration and stripping time on MoS 2The construction of defect-rich thin-layer structures has an important impact. When the solvent concentration is low, the layers are easier to separate, resulting in more defect sites; under high concentration conditions, solvent molecules may occupy some potential defect sites, thereby limiting the generation of defects. On the other hand, the longer the ultrasonic time, the better the MoS 2 The greater the mechanical stress and shear force on the layer, the more opportunities for defects to form; too short an ultrasonic time will inhibit the dispersion of the material.

[0022] In step 3, the molar ratio of manganese salt, bipyridine and oxalic acid is 0.5-50:0.5-50:0.1-80; preferably, the molar ratio of manganese salt, bipyridine and oxalic acid is 0.5-20:0.5-20:0.5-20, and further preferably, the molar ratio of manganese salt, bipyridine and oxalic acid is 0.5-8:0.5-5:0.5-5.

[0023] The dispersion temperature in step 3 is 10-60°C and the time is 1-36h. Preferably, the dispersion temperature is 20-40°C and the time is 2-6h;

[0024] Preferably, the manganese salt, bipyridine and oxalic acid can be separately dispersed in a solvent in advance, and then the three solutions are mixed and dispersed to prepare the layered organic manganese complex. Dispersing in advance helps to disperse the substances evenly and improve the reaction efficiency.

[0025] In step 4, the mass ratio of the organic manganese complex to the ultrathin molybdenum sulfide is 5-150:50-500; preferably, the mass ratio of the organic manganese complex to the ultrathin molybdenum sulfide is 5-100:50-200, and further preferably, the mass ratio of the organic manganese complex to the ultrathin molybdenum sulfide is 5-70:100-200.

[0026] In step 4, the reaction temperature is 5-60°C and the reaction time is 5-48h; preferably the temperature is 10-40°C and the reaction time is 10-24h; the solvent includes water and / or alcohols; the alcohols include methanol, ethanol, ethylene glycol, n-butanol, benzyl alcohol, etc., preferably methanol, ethanol, and ethylene glycol.

[0027] The calcination temperature is 50-450°C, and the calcination time is 2-20h; preferably, the calcination temperature is 50-400°C, more preferably 100-300°C, and more preferably 200-300°C; the calcination time is preferably 4-20h. Calcination is particularly important in the synthesis process, which is a key step in forming a heterostructure.

[0028] The product washing in each step is done by co-washing with a specific solvent, and drying is done at 60-80° C. for 1-6 hours, or 1-10 hours.

[0029] The present invention also provides a defect-controlled ultra-thin molybdenum disulfide loaded with an organic manganese complex heterostructure catalyst prepared by the preparation method, wherein the catalyst is composed of a layered organic manganese complex and an ultra-thin molybdenum sulfide, wherein the thickness of the ultra-thin molybdenum sulfide is 0.1-20nm, the thickness of the layered organic manganese complex is 0.5-10nm, and the total thickness of the catalyst is 0.6-30nm; the mass proportion of the Mn element in the catalyst is less than 50wt%. The manganese content is preferably 0.1-10wt%; the manganese content is further preferably 0.5-10wt%, and the manganese content is further preferably 2-8wt%.

[0030] The present invention also provides application of the heterogeneous structure catalyst in photocatalytic preparation of methanol.

[0031] The photocatalytic reaction is carried out at 10-100°C, 0.05-10MPa, and the light source is a 100-600W xenon lamp. The methanol yield is 538μmol·g cat -1 ·h -1 The methanol selectivity is above 80%. Preferably, the methanol yield is 613 μmol·g cat -1 ·h -1 The methanol selectivity is above 82%; the methanol yield is further preferably 652 μmol·g cat -1 ·h -1 Above, methanol selectivity is more than 85%;

[0032] In order to achieve photocatalytic CO 2 The catalyst designed needs to have high catalytic performance and stability in reducing to methanol, and has high photogenerated carrier transfer ability and utilization rate, and can improve the metastable properties of thin-layer material defects. 2 The defects on the surface of MoS are used as the positioning sites, which are combined with the MnBO organic ligand to form an ultra-thin two-dimensional heterostructure, which effectively inhibits the recombination of electrons and holes and improves the defect-rich MoS 2 The structural instability of 2 The obtained catalyst can promote the reduction of H under light, at low temperature and low pressure without any reaction aid or sacrificial agent. 2 O reduces CO 2 , high-value chemicals such as methanol are obtained, and the methanol selectivity and yield are greatly improved.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention adopts a simple mixed loading method, uses defects as positioning points, and combines two ultra-thin two-dimensional semiconductors to form a heterostructure, effectively solving the CO 2 and H 2 O activation problem; at the same time, by regulating the ultrathin MoS 2 The amount of surface defects regulates its contact with MnBO, forming new defect energy levels, which is conducive to the generation of high-energy electrons that promote the reduction reaction, thereby effectively improving the reaction activity and obtaining nearly 90% methanol selectivity, which is a promising target for photocatalytic CO 2 High-value transformation provides a practical research strategy.

[0035] (2) The catalyst prepared by the present invention has light absorption characteristics, so it can generate sufficient electron-hole pairs under light conditions, improve the efficiency of separation and transfer of photogenerated carriers, and effectively inhibit the rapid recombination of electrons and holes, thereby efficiently participating in the H 2 The oxidation process of O and CO 2 The reduction process can promote H 2 O reduces CO 2 , methanol selectivity and yield were greatly improved, with methanol yield at 652μmol·gcat -1 ·h -1 Above, the methanol selectivity is above 85%.

[0036] (3) Compared with conventional catalysts, the preparation process of the heterostructured catalyst of organic manganese complex and molybdenum sulfide is simple, easy to operate, and the raw materials are simple and easy to obtain. It has the potential for industrial application and is suitable for popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Preparation of heterogeneous structure catalyst, organic manganese complex and MoS for Example 1 2 (1) X-ray diffraction spectrum.

[0038] Figure 2 TEM image (a), EDX mapping image and EDX mapping image (b) of each element in the catalyst prepared in Example 1.

[0039] Figure 3 Preparation of heterogeneous structure catalyst for CO catalysis in Example 1-3 2 and H 2 O performance comparison chart for preparing methanol.

[0040] Figure 4 Heterogeneous structure catalysts prepared for Example 1 and Example 4-5 to catalyze CO 2 and H 2 O methanol preparation performance comparison chart.

[0041] Figure 5 The heterogeneous structure catalyst prepared in Example 1 catalyzes CO 2 and H 2 O prepared methanol stability diagram.

[0042] Figure 6 The heterogeneous structure catalyst prepared in Example 1 and Comparative Example 6 catalyzes CO under the reaction conditions of 6 MPa. 2 and H 2 O preparation of methanol performance diagram. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0044] The raw materials used in the following specific embodiments were purchased from Aladdin or Sinopharm Reagent and used directly without treatment.

[0045] Example 1

[0046] Step 1, 891 mg of ammonium molybdate and 1745 mg of thiourea (the molar ratio of the two is 0.7:10.7) are placed in 30 ml of deionized water, stirred at room temperature for 3 hours, then placed in a 100 ml stainless steel autoclave, crystallized in an oven at 170° C. for 20 hours, washed with water and alcohol, and dried in a vacuum oven at 80° C. overnight to obtain petal-shaped flaky molybdenum sulfide;

[0047] Step 2: 200 mg of molybdenum sulfide was placed in 500 ml of N-methylpyrrolidone (mass concentration of molybdenum sulfide was 0.4 mg / ml), ultrasonicated at room temperature for 15 h, centrifuged, and vacuum dried at 70 ° C to obtain a defect-rich monolayer molybdenum sulfide, denoted as MoS 2 (1);

[0048] Step 3, respectively prepare three solutions, A: 822 mg of manganese nitrate hydrate is ultrasonically dispersed in 30 ml of deionized water; B: 358 mg of 2,2'-bipyridine is ultrasonically dispersed in 15 ml of methanol; C: 150 mg of oxalic acid is ultrasonically dispersed in 20 ml of deionized water, after the three solutions are evenly dispersed, the B solution and the C solution are respectively added dropwise to the A solution (the molar ratio of manganese nitrate, 2,2'-bipyridine and oxalic acid is 2.6:1.4:1.0), stirred at 30° C. for 5 hours, and then centrifuged, washed, and dried to obtain a layered organic manganese complex;

[0049] Step 4: ultrasonically disperse 48 mg of the organic manganese complex in 30 ml of deionized water, and after being evenly dispersed, add 200 mg of monolayer molybdenum sulfide into the solution, stir at 30°C for 18 h, wash, centrifuge, and dry. Finally, place the obtained product in a muffle furnace, and calcine the temperature from 50°C to 300°C, and keep calcining at 300°C for 15 h to obtain an organic manganese complex and molybdenum sulfide heterostructure catalyst, recorded as Mn / MoS 2 (1).

[0050] Mn / MoS 2 (1) The catalyst is composed of a layered organic manganese complex and ultrathin molybdenum sulfide, wherein the thickness of the ultrathin molybdenum sulfide is 0.9 nm, the thickness of the layered organic manganese complex is 2.3 nm, and the total thickness of the catalyst is 3.5 nm; the manganese content in the heterogeneous structure catalyst prepared by calculating the input ratio of the raw materials is 5 wt%.

[0051] Figure 1 The prepared organic manganese complex and ultrathin molybdenum sulfide heterostructure catalyst Mn / MoS 2 (1) and the precursor MoS 2 (1) and the X-ray diffraction spectrum of the organic manganese complex. Figure 1 It can be seen that after the organic manganese complex is loaded on molybdenum sulfide, the crystal structure of molybdenum sulfide remains intact, but compared with unloaded molybdenum sulfide, Mn / MoS 2 The characteristic diffraction peaks of the organic manganese complex appeared in the XRD spectrum of (1).

[0052] Figure 2 a is the TEM image of the prepared 5wt% organic manganese complex and ultra-thin molybdenum sulfide heterostructure catalyst. Figure 2 a It can be seen that the organic manganese complex shows a more obvious MnBO encapsulated MoS 2 The thin layer structure is closely connected with the two surfaces of molybdenum sulfide, showing heterogeneous structural characteristics. 2 (1) It is also proved in the EDX mapping of heterogeneous catalysts (such as Figure 2 b).

[0053] Example 2-3

[0054] According to the preparation process of Example 1, only the amount of solvent in step 2 was changed, that is, step 2 was: 200 mg of molybdenum sulfide was placed in 100 ml and 10 ml of N-methylpyrrolidone, respectively, and the corresponding molybdenum sulfide mass concentrations were 2 mg / ml and 20 mg / ml, respectively. After ultrasonication for 15 h, MoS with different defect contents were obtained. 2 200 mg of MoS with different defect amounts were added 2They were compounded with 48 mg of MnBO to obtain Mn / MoS 2 (3) and Mn / MoS 2 (6).

[0055] Embodiment 4-5

[0056] According to the preparation process of Example 1, the ultrasonic time in step 2 was changed to 5 h and 10 h respectively, that is, step 2 was: 200 mg of molybdenum sulfide was placed in 500 ml of N-methylpyrrolidone (mass concentration of molybdenum sulfide was 0.4 mg / ml), ultrasonicated for 5 h and 10 h respectively at room temperature, centrifuged, and vacuum dried at 70 ° C to obtain Mn / MoS with different synthesis times. 2 (1)-5h, Mn / MoS 2 (1)-10h.

[0057] Comparative Example 1

[0058] According to the preparation process of Example 1, the calcination step in step 4 is not performed. Step 4 is: 48 mg of the organic manganese complex is ultrasonically dispersed in 30 ml of deionized water, and after being evenly dispersed, 200 mg of monolayer molybdenum sulfide is added to the solution, and stirred at 30° C. for 18 h. The catalyst obtained by washing, centrifugation and drying is recorded as Mn-MoS 2 .

[0059] Comparative Example 2

[0060] According to the preparation process of Example 1, the carrier MoS 2 Without performing the stripping step, i.e. omitting step 2, flake molybdenum sulfide is directly used in step 4 to prepare Mn / MoS 2 .

[0061] Comparative Examples 3-5

[0062] According to the preparation process of Example 1, without changing step 1 and step 2, the type of metal nitrate in step 3 and the molar ratio thereof to bipyridine and oxalic acid are changed, that is, step 3 is: three solutions are prepared respectively, A: 745 mg of cobalt nitrate hydrate is ultrasonically dispersed in 30 ml of deionized water; B: 400 mg of 2,2'-bipyridine is ultrasonically dispersed in 15 ml of methanol; C: 150 mg of oxalic acid is ultrasonically dispersed in 20 ml of deionized water, after the three solutions are evenly dispersed, solution B and solution C are respectively added dropwise to solution A (the molar ratio of cobalt nitrate, 2,2'-bipyridine and oxalic acid is 2.1:2.1:1.0), stirred at 30°C for 5 hours, centrifuged, washed and dried to obtain a layered organic cobalt complex;

[0063] Repeat the above operation to prepare three solutions: A: 1489 mg of copper nitrate hydrate is ultrasonically dispersed in 30 ml of deionized water; B: 385 mg of 2,2'-bipyridine is ultrasonically dispersed in 15 ml of methanol; C: 170 mg of oxalic acid is ultrasonically dispersed in 20 ml of deionized water. After the three solutions are evenly dispersed, solution B and solution C are added dropwise to solution A (the molar ratio of copper nitrate, 2,2'-bipyridine and oxalic acid is 2.6:2.7:1.0), stirred at 30°C for 5 hours, and then centrifuged, washed and dried to obtain a layered organic copper complex.

[0064] Repeat the above operation to prepare three solutions: A: 909 mg of nickel nitrate hydrate ultrasonically dispersed in 30 ml of deionized water; B: 500 mg of 2,2'-bipyridine ultrasonically dispersed in 15 ml of methanol; C: 150 mg of oxalic acid ultrasonically dispersed in 20 ml of deionized water. After the three solutions are evenly dispersed, solution B and solution C are added dropwise to solution A (the molar ratio of nickel nitrate, 2,2'-bipyridine and oxalic acid is 2.4:1.81:1.0), stirred at 30°C for 5 hours, and then centrifuged, washed, and dried to obtain a layered organic nickel complex.

[0065] At the same time, the type of organic complex in step 4 is changed, that is, step 4 is: 48 mg of organic cobalt complex or organic copper complex or organic nickel complex is ultrasonically dispersed in 30 ml of deionized water, and after being evenly dispersed, 200 mg of monolayer molybdenum sulfide is added to the solution, stirred at 30° C. for 18 h, washed, centrifuged, and dried, and finally the obtained product is placed in a muffle furnace, the calcination temperature is increased from 50° C. to 300° C., and kept at 300° C. for 15 h to obtain an organic metal complex and molybdenum sulfide heterostructure catalyst, recorded as Co / MoS 2 (1) Cu / MoS 2 (1) Ni / MoS 2 (1).

[0066] Comparative Example 6

[0067] According to the preparation process of Example 1, without changing step 1 and step 2, three solutions were prepared respectively: A: 714 mg of zinc nitrate was ultrasonically dispersed in 30 ml of deionized water; B: 348 mg of 2,2'-bipyridine was ultrasonically dispersed in 15 ml of methanol; C: 120 mg of oxalic acid was ultrasonically dispersed in 20 ml of deionized water. After the three solutions were evenly dispersed, solution B and solution C were added dropwise to solution A (the molar ratio of zinc nitrate, 2,2'-bipyridine and oxalic acid was 2.4:2.2:1.0), stirred at 30°C for 3 hours, and then centrifuged, washed, and dried to obtain a layered organic zinc complex;

[0068] Step 4 is: 48 mg of the organic zinc complex is ultrasonically dispersed in 30 ml of deionized water, and after being evenly dispersed, 200 mg of monolayer molybdenum sulfide is added to the solution, stirred at 30°C for 18 hours, washed, centrifuged, and dried, and finally the obtained product is placed in a muffle furnace, and the calcination temperature is increased from 50°C to 300°C, and maintained at 300°C for 15 hours to obtain an organic metal complex and molybdenum sulfide heterostructure catalyst, recorded as Zn / MoS 2 (1).

[0069] Catalyst performance evaluation

[0070] The photocatalytic performance of the catalysts prepared in Examples 1-5 and the catalysts prepared in Comparative Examples 1-4 was evaluated. The photocatalytic reaction was carried out in a specially made quartz closed high-pressure reaction device, and photocatalysis was achieved by simulating solar radiation with a xenon lamp.

[0071] Reaction conditions: Before the photocatalytic reaction, 40 mg of the catalyst was dispersed in the above quartz reactor, and 15 ml of deionized water was injected, followed by 6 MPa of CO 2 The air in the reactor was exhausted and then CO 2 The pressure was increased to 0.5 MPa. A 500W xenon lamp was used for illumination, the reaction temperature was 28°C, and a cut-off filter (<420nm) was used to filter out ultraviolet light in the illumination. After controlling the reaction time, the relevant products were quantitatively analyzed by gas chromatography and nuclear magnetic resonance.

[0072] Table 1 Methanol yield and selectivity of catalysts of Examples and Comparative Examples

[0073]

[0074] Table 1 and Figure 3 Different MoS synthesized with different ultrasonic concentrations prepared in Examples 1-3 2 Methanol yield graph of heterostructured catalyst with organomanganese complex. The lower the concentration, the lower the reaction activity.

[0075] Table 1 and Figure 4 The following is a comparison of the reaction performance of the heterogeneous structure catalysts of molybdenum sulfide and organic manganese complex synthesized at different ultrasonic times. By comparison, 15h is the best ultrasonic time, under which the methanol yield is the highest. On this basis, if the ultrasonic time is further extended, MoS 2 The reaction activity is still similar to that of 15h, but its energy consumption is significantly increased.

[0076] Figure 5 It can be seen that the heterostructure catalyst of molybdenum sulfide and organic manganese complex has good stability and can maintain a high methanol yield for 50 hours.

[0077] It can be seen from Comparative Example 1 that at a calcination temperature of 300°C, the manganese organic complex is beneficial to the reaction with MoS 2 A relatively stable heterostructure is formed, which effectively promotes the transfer of electrons between the two two-dimensional materials, avoids the recombination of holes and electrons, and thus increases the production of methanol.

[0078] From Comparative Example 2, we can see that the defect-rich MoS formed after ultrasound 2 It can better combine with the precursor Mn complex to promote electron transfer and ultimately obtain better photocatalytic activity.

[0079] The applicant's early research found that the catalyst combined with zinc coordination and molybdenum sulfide has good photocatalytic carbon dioxide performance. Further research found that after the molybdenum sulfide is stripped, it can not only combine with the Zn organic complex to form a defect-rich heterostructure catalyst, but also reach 570μmol·gcat under near-normal pressure reaction conditions. -1 ·h -1 The methanol yield and selectivity of the single layer defect-rich MoS 2 It can also be combined with organic complexes corresponding to various transition metal elements (Mn, Co, Cu, Ni) to obtain considerable CO 2 The photoreduction activity of Mn is much better than that of Zn. 2 (1) can reach 843 μmol·gcat -1 ·h -1 The methanol yield and selectivity of 94% are due to Zn / MoS 2 (1) The activity is 1.7 times higher. This indicates that Mn and defect-rich MoS 2 After binding, due to the unsaturated electron coordination, it provides more active sites to catalyze CO 2 conversion, and finally achieved better catalytic activity.

[0080] In addition, in order to compare with previous studies, photocatalytic CO 2 The restored test results are as follows Figure 6 As shown, by comparison, Mn and MoS 2 The combination indeed more effectively promoted electron transfer, inhibited the recombination of photogenerated carriers, and ultimately achieved the efficient production of methanol.

[0081] The catalyst Mn / MoS prepared in Example 1 2 (1) The performance of photocatalytic carbon dioxide reduction was compared with that of some catalysts reported in the literature. The results are shown in Table 2. It can be seen that under photocatalytic conditions, Mn / MoS2 (1) The heterogeneous structure catalyst has a strong ability to selectively reduce carbon dioxide by photocatalysis, and can highly selectively produce high value-added chemicals such as methanol and oxygen, which proves that the catalyst has a highly efficient photocatalytic effect, which can alleviate the problem of high-speed recombination of electron-hole pairs to a certain extent, and can effectively improve the reaction activity and stability of photocatalytic carbon dioxide reduction.

[0082] Table 2 Comparison of the performance of the catalyst of Example 1 and the catalyst of the literature for photocatalytic carbon dioxide reduction

[0083]

[0084]

Claims

1. A method for preparing a defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst, characterized in that: Includes steps: Step 1, stirring and mixing molybdate and an organic sulfur-containing compound in a solvent, crystallizing and washing to obtain flaky molybdenum sulfide; Step 2, dispersing the flaky molybdenum sulfide in a solvent for ultrasonic exfoliation, and obtaining defect-rich ultrathin molybdenum sulfide after centrifugation; in step 2, the mass concentration of the flaky molybdenum sulfide in the solvent is 0.01-2 mg / ml; Step 3, mixing manganese salt, bipyridine and oxalic acid in a solvent, dispersing and washing to obtain a layered organic manganese complex; Step 4, stirring and mixing the solution of ultrathin molybdenum sulfide and layered organic manganese complex for reaction, and obtaining the heterogeneous structure catalyst through centrifugation, washing, drying and calcination, wherein the mass ratio of the organic manganese complex to the ultrathin molybdenum sulfide is 5-150:50-500.

2. The method for preparing the defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst according to claim 1, characterized in that: The molybdate includes one or a combination of two or more of sodium molybdate, potassium molybdate and ammonium molybdate; And / or, the organic sulfur-containing compound includes one or a combination of two or more of mercaptans, thiophenols, thioureas, and disulfides; And / or, the solvent in step 2 includes one or a combination of two or more of ethanol, isopropanol, water, N-methylpyrrolidone, and ethylene glycol.

3. The method for preparing the defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst according to claim 1, characterized in that: The manganese salt includes one or a combination of two or more of manganese nitrate, manganese carbonate, manganese acetate and manganese sulfate; And / or, the bipyridine includes 2,2-bipyridine and / or 4,4-bipyridine.

4. The method for preparing the defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst according to claim 1, characterized in that: The molar ratio of the organic sulfur-containing compound to the molybdate is 0.5-50:0.5-30; the stirring and mixing are carried out at room temperature for 2-50 hours; the crystallization temperature is 100-400° C., and the time is 6-30 hours.

5. The method for preparing the defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst according to claim 1, characterized in that: In step 2, the ultrasonic time is 1-50h, and the ultrasonic temperature is room temperature.

6. The method for preparing the defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst according to claim 1, characterized in that: In step 3, the molar ratio of the manganese salt, bipyridine and oxalic acid is 0.5-50:0.5-50:0.1-80; the dispersion temperature is 10-60°C, and the dispersion time is 1-36h.

7. The method for preparing the defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst according to claim 1, characterized in that: In step 4, the reaction temperature is 5-60° C., the reaction time is 5-48 hours, and the solvent includes water and / or alcohols; the calcination temperature is 50-450° C., and the calcination time is 2-20 hours.

8. The defect-controlled ultra-thin molybdenum disulfide-supported organic manganese complex heterostructure catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The catalyst consists of a layered organic manganese complex and ultrathin molybdenum sulfide, wherein the ultrathin molybdenum sulfide has a thickness of 0.1-20 nm, the layered organic manganese complex has a thickness of 0.5-10 nm, and the total thickness of the catalyst is 0.6-30 nm; the mass proportion of the Mn element in the catalyst is less than 50 wt%.

9. Use of the heterogeneous structure catalyst according to claim 8 in photocatalytic preparation of methanol.

10. Use of the heterogeneous structure catalyst according to claim 9 in photocatalytic preparation of methanol, characterized in that: The photocatalytic reaction was carried out at 10-100℃, 0.05-10MPa, and the light source was a 100-600W xenon lamp. The methanol yield was 538μmol·g cat -1 ·h -1 Above, the methanol selectivity is above 80%.

Images