Carbon-coated tungsten sulfide / MXene composite material as well as preparation method and application thereof

Abstract

The invention relates to preparation of a carbon-coated tungsten sulfide / MXene composite material (WS2 (at) C / Ti3C2Tx). The obtained composite material is used for synthesizing ammonia through electro-catalysis nitrate radical reduction at normal temperature and normal pressure. The preparation method comprises the following steps: stirring phosphotungstic acid PW12 at normal temperature and normal pressure to grow on porous Ti < 3 > C < 2 > T < x > in situ to obtain a PW12 / Ti < 3 > C < 2 > T < x > composite material, and further performing a high-temperature vulcanization process to obtain the WS < 2 > C / Ti < 3 > C < 2 > T < x > composite material. The composite electrode material has the advantages of high structural uniformity, firm interface bonding, efficient conductive network, controllable process and enhanced structural stability. The advantages directly promote the performance improvement in the field of electro-catalysis, so that the material becomes a composite electrode material with great application potential. The yield of the electrocatalyst prepared by the method for synthesizing ammonia by reducing nitrate radicals is 7.49 mg h <-1 > mgcat <-1 >. The preparation process is simple and easy to operate, the cost is low, and the obtained material has good electrocatalytic synthesis ammonia performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalytic nitrate reduction synthesis ammonia catalyst material, and is a carbon-coated tungsten sulfide / MXene composite material and a preparation method and application thereof. BACKGROUND

[0002] Electrocatalytic nitrate reduction (NO3RR) is a green chemical process that reduces excess nitrate (NO3 - ) in water bodies into other nitrogen-containing products through electrocatalysis, and has dual values of environmental governance and resource recycling. The electrocatalytic reduction of nitrate is a complex process of multiple electrons and multiple steps, which is essentially that nitrate (NO3 - ) is gradually converted into nitrogen-containing intermediates by accepting electrons (combining protons) on the surface of a catalyst under the driving of an electric field, and finally generates different products. As the core of the NO3RR reaction, the electrocatalyst has a crucial influence on the reaction performance. By adjusting the applied potential value of different electrocatalysts, efficient production of ammonia and optimization of energy consumption can be achieved.

[0003] MXene is a kind of extremely potential two-dimensional nanomaterial, which is a two-dimensional inorganic compound composed of several atomic layer thick transition metal carbide, nitride or carbonitride. MXene has a typical two-dimensional layered structure, like a stack of thin sheets, each layer is only a few atomic layers thick, and this structure gives it a large specific surface area. The larger specific surface area provides more active sites for the adsorption of substances, catalytic reactions, etc., and can be used for adsorbing pollutants, catalyzing chemical reactions, etc. MXene has excellent metal conductivity, which makes it have broad application prospects in the fields of electronic devices, electrode materials, etc. WS2 has a typical layered structure, each layer is composed of a tungsten atom layer sandwiched between two sulfur atom layers, and the layers interact with each other through weak van der Waals forces. This structure makes WS2 easy to slide between layers, exhibiting unique electrical properties. MXene has high conductivity like a metal, while WS2, as a typical layered sulfide semiconductor, has weak intrinsic conductivity and limited electron transport efficiency. When combined, MXene can act as an "electron transport channel" to effectively improve the conductivity of WS2 and reduce the charge transfer resistance of the composite material. The combination of MXene and WS2 through structure complementation, electron synergy and performance optimization exhibits application potential far beyond single materials in the field of electrocatalysis, and is a promising composite nanomaterial. SUMMARY

[0004] The purpose of the present application is to bond the porous structure Ti3C2T x with layered tungsten sulfide to synthesize PW 12 / Ti3C2T xA composite material, further prepared by high-temperature calcination in a tube furnace WS2@C / Ti3C2T x A composite material. Both MXene and WS2 are layered structures (MXene is a transition metal carbon / nitride layer, and WS2 is a "S-W-S" sandwich layer), and they can form a tightly bound heterojunction through van der Waals forces or chemical bonds (such as the interaction between the -O, -OH functional groups on the surface of MXene and the S atoms on the edge of WS2). The interlayer stacking structure can inhibit the interlayer aggregation of a single material (such as WS2 which is prone to stacking due to van der Waals forces, and MXene layers may also aggregate due to electrostatic interaction), and significantly increase the specific surface area of the composite material. Using this material as a catalyst, the performance of electrocatalytic reduction of nitrate to synthesize ammonia can be improved.

[0005] In order to achieve the above-mentioned purpose of the application, the application provides the following technical solutions:

[0006] I. Cu 2+ -Ti3C2T x Preparation of solution: take single-layer Ti3C2T x dispersed in deionized water, dissolve copper nitrate trihydrate (Cu(NO3)2·3H2O) in deionized water, and quickly mix the two to form a porous three-dimensional network structure of Cu 2+ -Ti3C2T x solution.

[0007] II. PW 12 / Ti3C2T x Preparation: Solution A, dissolve H3PW 12 O 40 ·NH2O in water and adjust the pH with NaOH; Solution B, prepared Cu 2+ -Ti3C2T x solution. Slowly add solution B to solution A, stir well at room temperature and atmospheric pressure, wash, centrifuge, freeze-dry, and collect the product PW 12 / Ti3C2T x composite material.

[0008] III. WS2@C / Ti3C2T x composite material: take a certain amount of PW 12 / Ti3C2T x composite material and thiourea in a mass ratio of 1:20, mix and grind thoroughly, put into a reaction porcelain boat, and calcine in a tube furnace at high temperature, cool down, and collect the product.

[0009] 1. The Cu 2+ -Ti3C2T x solution of the first step, wherein the mass of Ti3C2T x is 58-62 mg,

[0010] Cu(NO3)2·3H2O is 58-62 mg;

[0011] 2, H3PW in step two 12 O 40 ·NH2O is 0.45-0.55 g, and the solvent is deionized water;

[0012] 3, PW in step two 12 is 0.3-0.4 g;

[0013] 4, the stirring time in step two is 30 min, and the washing is carried out with anhydrous ethanol and deionized water respectively, and the washing is carried out several times;

[0014] 5, PW in step three 12 / Ti3C2T x composite material is 0.15-0.25 g;

[0015] 6, the thiourea in step three is 3.5-4.5 g;

[0016] 7, the temperature of the tubular furnace in step three is 800 DEG C, the heating rate is 7 DEG C / min, the holding time is 2 h, and the cooling rate is the same as the heating rate.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] The present application successfully prepares a WS2@C / Ti3C2T x composite electrode material by high-temperature calcination technology. In the synthesis process, the layered structure of Ti3C2T x serves as a "base skeleton" to provide anchoring sites for WS2 precursors. The introduction of the carbon layer can serve as a "bridge" to enhance the interfacial bonding strength of WS2 and Ti3C2T x , avoiding the problem of component shedding caused by weak interfacial action in traditional composites. On this basis, WS2 itself has poor conductivity (semiconductor properties), while Ti3C2T x (electrical conductivity of 10 4 S / m or more) and carbon (graphitized carbon electrical conductivity can reach 10 3 S / m) are both excellent conductors. The introduction of the carbon layer can form a "protective effect" on Ti3C2T x and WS2, reducing the structural degradation in synthesis and subsequent application. These advantages directly promote the performance improvement in the field of electrocatalysis, making it a composite electrode material with great application potential. Therefore, using phosphotungstate as a precursor, tungsten sulfide is modified on three-dimensional porous Ti3C2T xThe surface of the catalyst is stable and the catalyst has high efficiency in the reduction of nitrate to synthesize ammonia. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 WS2@C / Ti3C2T x Scanning electron microscope image of the composite material.

[0020] Figure 2 WS2@C / Ti3C2T x Scanning electron microscope image of the composite material.

[0021] Figure 3 WS2@C / Ti3C2T x Transmission electron microscope image of the composite material.

[0022] Figure 4 WS2@C / Ti3C2T x Raman spectrum of the composite material.

[0023] Figure 5 WS2@C / Ti3C2T x Electrochemical linear sweep voltammogram of the composite material in the presence or absence of NO3 – in the electrolyte.

[0024] Figure 6 WS2@C / Ti3C2T x Powder X-ray diffraction pattern of the composite material.

[0025] Figure 7 WS2@C / Ti3C2T x The composite material prepared in the embodiment 1 of the present application was used to carry out the reduction of nitrate to synthesize ammonia in a neutral electrolyte (0.1 mol / L Na2SO4 and 0.1 mol / L NaNO3), and after potentiostatic electrolysis for 1 h under different voltages, the obtained ultraviolet-visible light absorption spectrum (UV-vis) of the electrolyte was determined.

[0026] Figure 8 WS2@C / Ti3C2T x The composite material prepared in the embodiment 1 of the present application was used to carry out the reduction of nitrate to synthesize ammonia in a neutral electrolyte (0.1 mol / L Na2SO4 and 0.1 mol / L NaNO3), and after 1 h current-time test under different voltages, the ammonia production and Faraday efficiency diagram were obtained. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to implementation, comparative cases and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0028] Implementation Case 1

[0029] This embodiment provides a WS2@C / Ti3C2T x The composite electrocatalyst is prepared according to the following method:

[0030] Cu 2+ -Ti3C2T x Solution preparation: Take a monolayer of Ti3C2T x Copper nitrate trihydrate (Cu(NO3)2·3H2O) is dissolved in deionized water and the two are rapidly mixed to form Cu 2+ -Ti3C2T x Solution.

[0031] PW 12 / Ti3C2T x Preparation: Solution A, H3PW 12 O 40 NH₂O dissolves in water, and the pH is adjusted with NaOH; Solution B contains the prepared Cu. 2+ -Ti3C2T x Solution. Slowly add solution B to solution A, stir thoroughly at room temperature and pressure, wash, centrifuge, freeze dry, and collect product PW. 12 / Ti3C2T x Composite materials.

[0032] WS2@C / Ti3C2T x Preparation of composite materials: Take a certain amount of PW 12 / Ti3C2T x The composite material and thiourea were mixed at a mass ratio of 1:20 and thoroughly ground. The mixture was then placed in a reaction ceramic boat and calcined at high temperature in a tube furnace. After cooling, the product was collected.

[0033] The invention will be further described below with reference to the accompanying drawings:

[0034] Figure 1 WS2@C / Ti3C2T prepared for Embodiment 1 of the present invention x Scanning electron microscope image of the composite material. (e.g.) Figure 1 As shown, the substrate is Ti3C2T x Its surface is rough and has a three-dimensional porous structure.

[0035] Figure 2 WS2@C / Ti3C2T prepared for Embodiment 1 of the present invention xScanning electron microscope image of the composite material. As shown in the figure, it can be observed that the nanoparticles are uniformly dispersed on the surface of the substrate Ti3C2T Figure 2 x , indicating the successful loading of MXene and WS2.

[0036] Figure 3 Transmission electron microscope image of the WS2@C / Ti3C2T x composite material prepared in the embodiment 1 of the present application. As shown in the figure, the lattice spacing of 0.218 nm coincides with the crystal plane of WS2(103), indicating the successful loading of WS2; there are curved fingerprint-like stripes on the periphery of the WS2 particles, indicating the formation of a carbon layer after high-temperature calcination. Figure 3

[0037] Figure 4 Raman spectrum of the WS2@C / Ti3C2T x composite material prepared in the embodiment 1 of the present application. As shown in the figure, there are strong absorption peaks at 1366 cm -1 (D peak) and 1580 cm -1 (G peak), which are the typical characteristic peaks of carbon materials, and the I D / I G value is 1.05, indicating that the material contains a partially graphitized carbon layer, which is more conducive to improving the electron mobility and catalytic stability. Figure 4

[0038] Figure 5 Electrochemical linear sweep voltammogram of the WS2@C / Ti3C2T x composite material in the electrolyte containing or not containing NO3 - . As can be seen from the figure, the reduction current density value of the composite material in the electrolyte containing NO3 – is significantly increased compared with that in the electrolyte without NO3 – , indicating that the WS2@C / Ti3C2T x composite material has the ability of electrocatalytic reduction of nitrate.

[0039] Figure 6 Powder X-ray diffraction pattern of the WS2@C / Ti3C2T x composite material prepared in the embodiment 1 of the present application. As shown in the figure, the diffraction peaks located at 14.36°, 28.96°, 33.59°, 35.94°, 39.60° and 58.49° correspond to the (002), (004), (101), (102), (103) and (110) crystal planes of WS2 (JCPDS NO. 84-1398); and the diffraction peaks of the composite material WS2@C / Ti3C2T x ​​​characteristic peaks of Ti3C2T x x , which proves that the structure of Ti3C2T x is not destroyed, WS2 is successfully loaded on Ti3C2T x , and WS2@C / Ti3C2T x composite material is successfully synthesized.

[0040] Figure 7 The WS2@C / Ti3C2T x composite material prepared in the embodiment 1 of the application is used for nitrate reduction to synthesize ammonia in a neutral electrolyte (0.1 mol / L Na2SO4 and 0.1 mol / L NaNO3), and the ultraviolet-visible light absorption spectrum (UV-vis) of the electrolyte obtained after potentiostatic electrolysis for 1 h under different voltages is determined. As shown in the figure, with the gradual increase of the applied voltage, the absorbance of the electrolyte after the electrocatalytic test for color development also gradually increases.

[0041] Figure 8 The WS2@C / Ti3C2T -1 composite material prepared in the embodiment 1 of the application is used for nitrate reduction to synthesize ammonia in a neutral electrolyte (0.1 mol / L Na2SO4 and 0.1 mol / L NaNO3), and the ammonia yield and Faraday efficiency diagram after current-time test for 1 h under different voltages are shown in the figure. As shown in the figure, the highest Faraday efficiency of 56.9% is reached at the potential of-0.5 V vs. RHE, and the corresponding NH3 yield is 7.49 mg h cat. mg -1 . Therefore, the WS2@C / Ti3C2T x composite material can be used as an efficient catalyst for electrocatalytic reduction of nitrate to synthesize ammonia.

[0042] In summary, the WS2@C / Ti3C2T x composite material of the embodiment 1 is successfully prepared by using the synthesis method of stirring at room temperature and normal pressure and high-temperature calcination, and is successfully applied to electrocatalytic reduction of nitrate to synthesize ammonia. The combination of WS2 and Ti3C2T x has the following advantages: high structural uniformity, firm interface bonding, efficient conductive network, controllable process and enhanced stability. These synthesis advantages directly promote the performance improvement of the composite electrode material in the fields of electrocatalysis, lithium ion batteries, supercapacitors and the like, so that the composite electrode material has great application potential. The preparation process of the application is simple and easy to operate, and the cost is low. The obtained material has good electrocatalytic ammonia synthesis performance.

Claims

1. A carbon-coated tungsten sulfide / Mxene composite material and its preparation method, characterized in that: (1)Cu 2+ -Ti3C2T x Solution preparation: Take a monolayer of Ti3C2T x Copper nitrate trihydrate (Cu(NO3)2·3H2O) is dissolved in deionized water and the two are rapidly mixed to form Cu 2+ -Ti3C2T x Solution; (2)PW 12 / Ti3C2T x Preparation: Solution A, H3PW 12 O 40 NH₂O dissolves in water, and the pH is adjusted with NaOH; Solution B contains the prepared Cu. 2+ -Ti3C2T x Solution. Slowly add solution B to solution A, stir thoroughly at room temperature and pressure, wash, centrifuge, freeze dry, and collect product PW. 12 / Ti3C2T x Composite materials; (3)WS2@C / Ti3C2T x Preparation of composite materials: Take a certain amount of PW 12 / Ti3C2T x The composite material and thiourea were mixed at a mass ratio of 1:20 and thoroughly ground. The mixture was placed in a reaction ceramic boat and calcined at high temperature in a tube furnace. After cooling, the product was collected. (4) Cu according to step (1) of claim 1 2+ -Ti3C2T x Solution containing Ti3C2T x The mass is 58–62 mg, and the mass of Cu(NO3)2·3H2O is 58–62 mg; (5) H3PW according to step (2) of claim 1 12 O 40 ·NH2O, with a mass of 0.45–0.55 g, and deionized water as the solvent; (6) The PW according to step (2) of claim 1 12 Its mass is 0.3–0.4 g; (7) The stirring time in step (2) of claim 1 is 30 min, and the washing is performed several times with anhydrous ethanol and deionized water respectively; (8) The PW according to step (3) of claim 1 12 / Ti3C2T x Composite material, with a mass of 0.15–0.25 g; (9) The thiourea described in step (3) of claim 1, wherein the mass is 3.5 to 4.5 g; (10) The temperature of the tubular furnace described in step (3) of claim 1 is 800°C, the heating rate is 7°C / min, the temperature is maintained for 2 hours, and the cooling rate is the same as the heating rate.

2. The WS2@C / Ti3C2T composite material prepared according to the method of claim 1. x The composite material is used in the electrocatalytic reduction of nitrate to ammonia synthesis under normal temperature and pressure.

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