Low-coordination Mn monatomic doped ZnS catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalytic CO2 reduction, and discloses a low-coordination Mn monatomic doped ZnS catalyst as well as a preparation method and application thereof. The method comprises the following steps: (1) in the presence of ethylene glycol, contacting and mixing zinc salt, manganese salt and a sulfur source to obtain a mixed solution I; (2) carrying out first microwave treatment on the mixed solution I in an inert atmosphere to obtain an intermediate I; and (3) in an inert atmosphere, carrying out second microwave treatment on the intermediate I and a hydrogen peroxide solution to obtain the low-coordination Mn monatomic doped ZnS catalyst. The catalyst prepared by the method provided by the invention can significantly improve the selectivity of C2H4 in the photocatalytic CO2 reduction process.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of photocatalytic CO2 reduction, and particularly relates to a low-coordination Mn single-atom doped ZnS catalyst and a preparation method and application thereof. BACKGROUND

[0002] Solar-driven conversion of carbon dioxide (CO2) into multi-carbon (C 2+ ) solar fuels, as a green approach to address global energy demand and mitigate the impact of climate change, has attracted extensive attention in the industry.

[0003] Although recent studies have demonstrated the potential of photocatalytic systems in the conversion of carbon dioxide to C 2+ , achieving high selectivity remains a key challenge, as the formation of C 2+ products is heavily dependent on the stability of carbon-based intermediates at catalytically active sites.

[0004] Among various developed photocatalysts for CO2 reduction reaction (CO2RR), transition metal sulfides such as CdS, Bi2S3, CulnSnS4, etc., have attracted particular interest due to their tunable d-orbitals.

[0005] However, the above-mentioned materials often exhibit weak adsorption of C1 intermediates (such as *CO), leading to premature desorption and preferential formation of C1 products such as CO, CH4 and HCOOH, rather than the target C 2+ compounds.

[0006] To address this limitation, researchers have explored several effective strategies, including heterostructure construction, crystal plane engineering, doping and defect engineering, aiming to improve the selectivity of C 2+ by stabilizing carbon-based intermediates.

[0007] For example, in the MoS x / Fe2O3 system, the d-p orbital hybridization of Mo-Fe sites reduces the electrostatic repulsion between *CO and *COH intermediates, promoting the formation of C2H4; the Co-O-Fe triatomic site in partially oxidized FeCoS2 increases the local charge density, enriches the C1 intermediates, and directs the reaction path to C2 products.

[0008] The addition of Co in NiS2 adjusts the coordination number and oxidation state of Ni sites, promoting asymmetric C-C coupling between *CO intermediates in top and bridge adsorption configurations, with a selectivity of 75% for C2H4.

[0009] Although the above-mentioned studies have made some progress, the diverse coordination environments in these systems complicate the establishment of clear structure-activity relationships, which hinders the optimization of C 2+The rational design of catalyst production presents a major challenge.

[0010] Single atom catalysts (SACs) have atomically dispersed metal centers and well-defined coordination environments, and are a promising alternative material. Its unique structure allows it to make full use of metal atoms and allows precise modulation of the electronic structure to fine-tune the adsorption of reaction intermediates, thereby improving the activity and selectivity of CO2RR.

[0011] CN110449176A discloses a preparation method of a non-noble metal single atom catalyst. The method is to mix a photoactive carrier, a metal source and an electron donor reagent, and react under light in a low concentration oxygen or oxygen-free system to obtain a single atom catalyst. The photoactive carrier can be any one or more of the following: TiO2, BiOX (wherein X = Cl, Br, I), CdX (wherein X = S, Se, Te), BiWO6, BiVO4, Cu2O, C3N4, ZnO, ZnS, ZnSe, zinc oxide-ruthenium oxide, sulfide copper gallium, gallium phosphide, gallium arsenide. The metal in the metal source is selected from non-noble metals, including iron, cobalt, nickel, copper, manganese, zinc, aluminum, chromium, molybdenum, tungsten; the metal source is selected from a salt of the metal, and the salt includes a chloride salt, a bromide salt, a nitrate salt, a nitrite salt, a sulfate salt, a sulfite salt or an acetate salt. The electron providing reagent includes one or more of methanol, ethanol, isopropanol, thiourea, triethanolamine, etc. However, the prior art research on SACs is concentrated in the traditional single atom saturated symmetrical coordination environment, and the inherent electronic structure is not conducive to the adsorption of CO intermediates for the next carbon-carbon coupling, thereby affecting the selectivity of C2H4. SUMMARY

[0012] The purpose of the present application is to overcome the problem of poor selectivity of C2H4 product in the photocatalytic reduction of CO2 in the prior art.

[0013] To achieve the above-mentioned purpose, the first aspect of the present application provides a method for preparing a low coordination Mn single atom doped ZnS catalyst, which comprises: (1) contacting and mixing a zinc salt, a manganese salt and a sulfur source in the presence of ethylene glycol to obtain a mixed solution I; The molar ratio of the zinc salt calculated based on zinc element, the manganese salt calculated based on manganese element and the sulfur source calculated based on sulfur element is 1:0.003-0.020:1-3; (2) under an inert atmosphere, the mixed solution I is subjected to first microwave treatment to obtain an intermediate I; (3) under an inert atmosphere, the intermediate I and a hydrogen peroxide solution are subjected to second microwave treatment to obtain the low coordination Mn single atom doped ZnS catalyst; The second microwave treatment has a power < the power of the first microwave treatment.

[0014] The second aspect of the present application provides a low-coordination Mn single-atom doped ZnS catalyst prepared by the method of the aforementioned first aspect.

[0015] The third aspect of the present application provides an application of the low-coordination Mn single-atom doped ZnS catalyst of the aforementioned second aspect in the field of photocatalytic CO2 reduction.

[0016] The method for preparing the low-coordination Mn single-atom doped ZnS catalyst provided by the present application is simple, short in time consumption, and strong in operability, and is suitable for industrial production.

[0017] The active component Mn single atom in the low-coordination Mn single-atom doped ZnS catalyst prepared by the method provided by the present application is highly dispersed in ZnS, and the catalyst has a uniform size distribution, with an average particle size of about 41.3 nm; the catalyst also has an asymmetric charge distribution, which greatly improves the catalytic activity and selectivity of the catalyst in the system of photocatalytic CO2 reduction to C2 products. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a TEM image of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1 of the present application; Figure 2 is an XRD spectrum of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1, Comparative Example 5, and Comparative Example 6 of the present application; Figure 3 is a STEM-EDX mapping image of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1 of the present application; Figure 4 is an EPR spectrum of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1 and Comparative Example 5 of the present application; Figure 5 is a structural model diagram of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1, Comparative Example 5, and Comparative Example 6 of the present application; Figure 6 is an activity evaluation diagram of photocatalytic CO2 reduction of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1, Comparative Example 5, and Comparative Example 6 of the present application; Figure 7 is a catalytic stability result diagram of the low-coordination Mn single-atom doped ZnS catalyst prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the purposes of the application. The endpoints of the ranges and any values are provided as approximations only and are understood to encompass a range of values which are near the recited values. For values which are less than one, multiple, small values are intended to be encompassed.

[0020] In the present application, the room temperature represents a temperature of 23±2℃.

[0021] As previously described, the first aspect of the present application provides a method for preparing a low-coordination Mn single-atom doped ZnS catalyst, the method comprising: (1) contacting and mixing a zinc salt, a manganese salt and a sulfur source in the presence of ethylene glycol to obtain a mixed solution I; The molar ratio of the zinc salt calculated by the element zinc, the manganese salt calculated by the element manganese and the sulfur source calculated by the element sulfur is 1:0.003-0.020:1-3; (2) under an inert atmosphere, subjecting the mixed solution I to a first microwave treatment to obtain an intermediate I; (3) under an inert atmosphere, subjecting the intermediate I and a hydrogen peroxide solution to a second microwave treatment to obtain the low-coordination Mn single-atom doped ZnS catalyst; The power of the second microwave treatment is lower than the power of the first microwave treatment.

[0022] Preferably, in step (1), the zinc salt is zinc acetate.

[0023] Preferably, in step (1), the manganese salt is manganese acetate.

[0024] According to a preferred embodiment, in step (1), the sulfur source is thiourea. The inventors of the present application have found that, in this preferred case, it is beneficial to control the nucleation and growth rate of ZnS, reduce agglomeration and have a better morphology.

[0025] Preferably, in step (1), the amount of ethylene glycol is 15-18 mL per 1 mmol of the zinc salt.

[0026] Preferably, in step (1), the contacting and mixing is performed under the conditions of a rotation speed of 500-700 rpm and a time of 30-50 min.

[0027] Preferably, in step (2), the power of the first microwave treatment is 240-280 W.

[0028] Preferably, in step (2), the conditions of the first microwave treatment further comprise: heating at a rate of 30-50℃ / min to T1, and maintaining at T1 for 8-12 min, wherein T1=140-160℃.

[0029] According to one preferred embodiment, in step (2), the material after the first microwave treatment is cooled to room temperature, and then sequentially washed with water and anhydrous ethanol for 3-5 times, and finally the washed material is subjected to drying treatment I to obtain the intermediate I.

[0030] According to another preferred embodiment, in step (3), the material after the second microwave treatment is filtered, and then sequentially washed with water and anhydrous ethanol for 3-5 times, and finally the washed material is subjected to drying treatment II to obtain the low-coordination Mn single-atom doped ZnS catalyst.

[0031] The present application does not have special requirements for the type of water, and those skilled in the art can select according to the needs. Illustratively, the water can be ultrapure water, deionized water.

[0032] Preferably, the drying treatment I and the drying treatment II are both carried out by vacuum drying.

[0033] Preferably, the conditions of the drying treatment I comprise: temperature of 70-90℃, and time of 8-10h.

[0034] Preferably, the conditions of the drying treatment II comprise: temperature of 50-70℃, and time of 5-7h.

[0035] Preferably, the first microwave treatment and the second microwave treatment are both carried out in a microwave reactor with a reflux device.

[0036] Preferably, in step (3), the concentration of the hydrogen peroxide solution is 0.05-0.10 mol / L.

[0037] Preferably, in step (3), the amount of the hydrogen peroxide solution is 3-5 mL per 100 mg of the intermediate I.

[0038] Preferably, in step (3), the power of the second microwave treatment is 80-120W.

[0039] Preferably, the conditions of the second microwave treatment further comprise: temperature of 80-100℃, and holding time of 5-20s.

[0040] Preferably, the inert atmosphere is argon or nitrogen.

[0041] As described above, the second aspect of the present application provides a low-coordination Mn single-atom doped ZnS catalyst prepared by the method of the aforementioned first aspect.

[0042] As described above, the third aspect of the present application provides an application of the low-coordination Mn single-atom doped ZnS catalyst of the aforementioned second aspect in the field of photocatalytic CO2 reduction.

[0043] The present application will be described in detail below by way of examples. In the following examples, if not specifically stated, the instruments, reagents, materials and the like involved are conventional instruments, reagents, materials and the like, which can be obtained through regular commercial channels. Among them, if there is no contrary statement, the reagents used are commercially available analytical pure products.

[0044] Zinc salt: zinc acetate, Zn(OAc)2.

[0045] Manganese salt: manganese acetate, Mn(OAc)2.

[0046] Sulfur source: Sulfur source I: thiourea, CH4N2S.

[0047] Sulfur source II: sodium sulfide, NaS.

[0048] Hydrogen peroxide solution: concentration is 0.05 mol / L.

[0049] Inert atmosphere: argon.

[0050] Example 1 This example is used to illustrate the preparation of a low-coordination Mn single-atom doped ZnS catalyst by referring to the raw material formula in Table 1 and following the method of the following steps: (1) In the presence of ethylene glycol, the zinc salt, manganese salt and sulfur source are contacted and mixed to obtain a mixed solution I; (2) Under an inert atmosphere, the mixed solution I is subjected to first microwave treatment, and the material after the first microwave treatment is cooled to room temperature, then sequentially subjected to deionized water washing, anhydrous ethanol washing 3 times, and finally the washed material is subjected to drying treatment I to obtain an intermediate I; (3) Under an inert atmosphere, the intermediate I and the hydrogen peroxide solution are subjected to second microwave treatment, and the material after the second microwave treatment is filtered, then sequentially subjected to deionized water washing, anhydrous ethanol washing 5 times, and finally the washed material is subjected to drying treatment II to obtain the low-coordination Mn single-atom doped ZnS catalyst; Contact mixing: rotation speed is 600 rpm, time is 30 min; Drying treatment I: vacuum drying, temperature is 80℃, time is 8h; Drying treatment II: vacuum drying, temperature 60℃, time 6h; Example 2 This example is carried out in a similar way to Example 1, except that the raw material formula and process parameters are different. As shown in Table 1, the parts not listed are the same as Example 1, and a low-coordination Mn single-atom doped ZnS catalyst is prepared.

[0051] Example 3 This example is carried out in a similar way to Example 1, except that the sulfur source in Example 1 is adjusted to an equimolar amount of sodium sulfide. The parts not listed are the same as Example 1, and a low-coordination Mn single-atom doped ZnS catalyst is prepared.

[0052] Example 4 This example is carried out in a similar way to Example 1, except that the time of the second microwave treatment in this example is 30s. The parts not listed are the same as Example 1, and a low-coordination Mn single-atom doped ZnS catalyst is prepared.

[0053] Comparative Example 1 This comparative example is carried out in a similar way to Example 1, except that the raw material formula and process parameters are different. As shown in Table 1, the parts not listed are the same as Example 1, and a Mn atom doped ZnS catalyst is prepared.

[0054] Table 1

[0055] Comparative Example 2 (1) The same as step (1) in Example 1; (2) The mixed solution I is transferred to a polytetrafluoroethylene lining and a stainless steel reaction kettle, heated at 180℃ for 8h to obtain intermediate I; (3) The same as step (3) in Example 1; The parts not listed are the same as Example 1, and a Mn atom doped ZnS catalyst is prepared.

[0056] Comparative Example 3 This comparative example is carried out in a similar way to Example 1, except that the ethylene glycol in Example 1 is replaced with an equal volume of N,N-dimethylformamide (DMF); The parts not listed are the same as Example 1, and a low-coordination Mn single-atom doped ZnS catalyst is prepared.

[0057] Comparative Example 4 This comparative example is carried out using a method similar to that of Example 1, except that the power of the second microwave processing is adjusted to 240W in this comparative example. For the parts not listed, the same as in Example 1 was used to prepare a low-coordinate Mn single-atom doped ZnS catalyst.

[0058] Comparative Example 5 (1) In the presence of ethylene glycol, zinc salt, manganese salt and sulfur source are contacted and mixed to obtain mixture I; (2) Under an inert atmosphere, the mixture I is subjected to a first microwave treatment, the material after the first microwave treatment is cooled to room temperature, and then washed with deionized water and anhydrous ethanol three times in sequence. Finally, the washed material is dried to obtain Mn single atom doped ZnS catalyst. The raw materials and dosages involved in steps (1) and (2), as well as the process parameters, are the same as in Example 1.

[0059] Comparative Example 6 In this comparative example, ZnS was used directly as a catalyst.

[0060] Test case 1. The microstructure of the low-coordinated Mn single-atom doped ZnS catalyst prepared in Example 1 was tested using transmission electron microscopy. The results are as follows: Figure 1 As shown: pass Figure 1 It can be seen that the ZnS polycrystalline nanoparticles in the catalyst are uniformly distributed, with an average size of about 41.3 nm.

[0061] 2. The low-coordinate Mn single-atom doped ZnS catalysts prepared in Examples 1, 5, and 6 were analyzed using X-ray diffraction. The results are as follows: Figure 2 As shown: pass Figure 2 It can be seen that the diffraction peaks of the low-coordinated Mn single-atom doped ZnS catalyst correspond to the cubic phase of wurtzite ZnS (PDF#05-0566).

[0062] 3. The elemental distribution of the low-coordinated Mn single-atom doped ZnS catalyst prepared in Example 1 was studied by scanning transmission microscopy (STEM-EDX mapping). The results are as follows: Figure 3 As shown: pass Figure 3 It can be seen that the low-coordinated Mn single-atom doped ZnS catalyst has a nanoparticle structure, with Zn, Mn and S elements uniformly distributed, Mn atoms penetrating into the Zn element region, and Mn species exhibiting high dispersion on the catalyst surface.

[0063] 4. The electron paramagnetic resonance (EPR) spectra of the low-coordinated Mn single-atom doped ZnS catalysts prepared in Example 1 and Comparative Example 5 were analyzed, and the results are as follows: Figure 4 As shown: pass Figure 4 It can be seen that at g=2.005, a clear signal confirms the presence of sulfur vacancies in the low-coordinated Mn single-atom doped ZnS catalyst of Example 1.

[0064] 5. Using density functional theory (DFT) combined with HRTEM results, the catalysts prepared in Example 1, Comparative Example 5, and Comparative Example 6 were structurally modeled, and the results are as follows: Figure 5 As shown: pass Figure 5 It can be seen that each Mn atom is coordinated by two S atoms, confirming that the preparation method provided by this invention yields an unsaturated, low-coordinated Mn single-atom-doped ZnS catalyst.

[0065] 6. Photocatalytic CO2 reduction performance test, the specific operation is as follows: a. Take 0.02g of the catalyst prepared in the above example and 1.5mL of deionized water respectively and place them in a reaction dish. Disperse them by ultrasonication for 5min to obtain uniformly dispersed samples. b. Place each sample in the photocatalytic Labsolar6A quartz reactor, seal the device, and perform a three-cycle vacuum treatment on the reaction system. Slowly and uniformly introduce CO2 gas into the reactor until the pressure reaches 80.0 kPa. Set the chromatographic cycle interval to 30 min and perform a 4-hour test. The yield (μmol g) of reduction products during photocatalytic CO2 reduction. -1 h -1 The selectivity of C2H4 products and reduction products are used as parameters to evaluate catalytic performance; quantum efficiency (AQE) is an important indicator for measuring the efficiency of photocatalytic reactions in converting light energy; the selectivity of C2H4 products is denoted as S. C2H4 (%) S C2H4 (%) = 12 n (C2H4) / [12 n (C2H4)+ n (CO)+ n (CH4)+2 n [(CHOOH)]×100%; ; The performance of the catalysts in the above examples is shown in Table 2: Table 2

[0066] Note: " / " means not measured.

[0067] The photocatalytic CO2 reduction activity of the catalysts obtained in Example 1, Comparative Example 5, and Comparative Example 6 was evaluated as shown in Figure 6 (Fig. left ordinate for each of the reduced carbon products, right ordinate for C2H4 product selectivity): By Figure 6 It can be seen that the rate of CO production in Comparative Example 6 is 64.6 μmol g -1 h -1 , and the selectivity of C2H4 is only 5.6%. After adding the saturated coordinated Mn monatomic (Comparative Example 5), both the activity and the selectivity are significantly improved, the formation rate of C2H4 is 47.5 μmol g -1 h -1 , and the selectivity is 74.5%. Notably, the low-coordinated Mn monatomic doped ZnS catalyst (Example 1) significantly improves the formation rate of C2H4 (76.6 μmol g -1 h -1 ), which is 58.9 times higher than that of Comparative Example 6, and the selectivity of C2H4 reaches a record high of 99.1%, indicating that the low-coordinated Mn monatomic plays a key role in guiding the reaction pathway to selectively generate C 2+ products.

[0068] 7. Photocatalytic CO2 recycling stability test, the specific operation is as follows: (i) 0.02 g of the catalyst prepared in Example 1 above and 1.5 mL of deionized water were placed in a reaction dish and ultrasonically dispersed for 5 min to obtain uniformly dispersed samples; (ii) Each sample was placed in a photocatalytic Labsolar 6A quartz reactor, and after sealing the device, the reaction system was subjected to three cycles of vacuum pumping, and CO2 gas was slowly and uniformly injected into the reactor until the pressure reached 80.0 kPa; the chromatographic cycle interval was set to 30 min, and the test was performed for 4 h; the test was continuously performed for 200 h, and 1.5 mL of deionized water was injected into the quartz reactor every 8 h, a total of 50 cycles; the results are shown in Figure 7 By Figure 7 It can be seen that after 50 cycles of CO2 photoreduction experiments, the yield and selectivity of C2H4 are close to those of the fresh sample, indicating that the low-coordinated Mn monatomic doped ZnS catalyst prepared by the method of the present application has excellent catalytic stability.

[0069] ​It can be seen from the above results that the low coordination Mn single atom doped ZnS catalyst prepared by the preparation method provided by the application greatly improves the catalytic activity and selectivity in the photocatalytic CO2 reduction to C2 product system.

[0070] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A method of preparing a low-coordinated Mn single atom-doped ZnS catalyst, characterized by, The method comprises: (1) contacting and mixing a zinc salt, a manganese salt and a sulfur source in the presence of ethylene glycol to obtain a mixed solution I; the molar ratio of the zinc salt calculated by zinc element, the manganese salt calculated by manganese element and the sulfur source calculated by sulfur element is 1:0.003-0.020:1-3; (2) under an inert atmosphere, the mixed solution I is subjected to first microwave treatment to obtain intermediate I; (3) under an inert atmosphere, the intermediate I and a hydrogen peroxide solution are subjected to second microwave treatment to obtain the low-coordination Mn monatomic-doped ZnS catalyst; the power of the second microwave treatment is lower than that of the first microwave treatment.

2. The method of claim 1, wherein, In step (1), the zinc salt is zinc acetate; and / or, in step (1), the manganese salt is manganese acetate; and / or, in step (1), the sulfur source is thiourea.

3. The method according to claim 1 or 2, characterized in that, In step (1), the amount of the ethylene glycol is 15-18 mL per 1 mmol of the zinc salt.

4. The method according to claim 1 or 2, characterized in that, In step (2), the power of the first microwave treatment is 240-280 W.

5. The method of claim 4, wherein, In step (2), the first microwave treatment further comprises: heating at a rate of 30-50 ℃ / min to T1, and incubating at T1 for 8-12 min, wherein T1=140-160 ℃.

6. The method of claim 1 or 2, wherein, In step (3), the concentration of the hydrogen peroxide solution is 0.05-0.10 mol / L; and / or, in step (3), the amount of the hydrogen peroxide solution is 3-5 mL per 100 mg of the intermediate I.

7. The method according to claim 1 or 2, characterized in that, In step (3), the power of the second microwave treatment is 80-120 W.

8. The method of claim 7, wherein, The second microwave treatment further comprises: a temperature of 80-100 ℃, and an incubation time of 5-20 s.

9. A low-coordination Mn monatomic-doped ZnS catalyst prepared by the method of any one of claims 1-8.

10. Use of the low-coordination Mn monatomic-doped ZnS catalyst of claim 9 in the field of photocatalytic reduction of CO2.

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