A sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material and its preparation method and application

Abstract

The present invention discloses a sulfur-vacancies-rich nickel sulfide nanosheet array structure catalyst material and a preparation method and application thereof. The present invention adopts a hydrothermal method to directly in-situ grow a Ni3S2 ultra-thin nanosheet precursor on a nickel foam substrate, and then introduces sulfur vacancies by high-temperature calcination in an inert atmosphere to obtain V s ‑Ni3S2 nanosheet array structure material. The preparation method has the advantages of simple process, low cost and environmental friendliness. The introduction of sulfur vacancies effectively regulates the electronic structure and carrier concentration of the material, improves the intrinsic conductivity of the material and the diversity of redox reactions and the adsorption performance of reactants; the defective catalyst can be used for the electrocatalytic oxidation of benzyl alcohol to prepare benzoic acid, with a conversion rate of up to 99% and a selectivity of up to 99%.

Description

Technical Field

[0001] The invention belongs to the field of catalytic preparation technology and organic electrocatalysis, and specifically relates to a sulfur vacancy-rich nickel sulfide nanosheet array structure catalyst material and a preparation method thereof, as well as an application in the electrocatalytic oxidation reaction of benzyl alcohol. Background Art

[0002] At present, the industrial-scale production of benzoic acid is almost entirely dependent on the resource- and energy-intensive toluene oxidation process, which usually requires high temperature (150℃~170℃), high pressure (1MPa) and the use of toxic chemical oxidants. The reaction conditions are harsh, the cost is high and there are serious environmental pollution problems. Therefore, the development of sustainable and environmentally friendly new methods for the production of benzoic acid is of great significance to alleviate the increasingly prominent energy problems and increasingly severe environmental problems. The electrocatalytic oxidation of benzyl alcohol in water has the advantages of mild reaction conditions, low thermodynamic barriers, and green energy saving. Its main competing reaction is the anodic oxygen evolution reaction (OER) of water splitting. How to effectively improve the selectivity of the reaction and increase the yield of the target product benzoic acid is a key problem that needs to be solved urgently. Based on this, the rational design of electrocatalysts is crucial.

[0003] Transition metal sulfides are considered to be the most promising candidates for replacing noble metal-based catalysts due to their low cost, rich phase structure and good stability. Among them, nickel sulfide Ni3S2 materials are favored due to their excellent electrical conductivity, low cost and good intrinsic catalytic activity. In order to further improve the catalytic activity of Ni3S2 materials, the electronic structure of Ni3S2 can be changed by creating vacancy defects to achieve the regulation of the adsorption energy of organic substrates on the catalyst surface, and finally promote the efficient conduct of the catalytic reaction. For the regulation of sulfur vacancies in nickel sulfide, it has been reported (patent CN 108677207A) that the concentration of sulfur vacancies in Ni3S2 is achieved by regulating the oxygen vacancies of the precursor oxide. Considering the instability of oxygen vacancy defects, the vacancy concentration is very easy to change in the subsequent process of preparing sulfide by sulfurization treatment. In addition, the content of oxygen vacancies cannot represent the concentration of sulfur vacancies.

[0004] In view of this, the present invention prepares a Ni3S2 nanosheet array structure precursor by directly in-situ growth on a nickel foam substrate, and then directly obtains a sulfur-vacancy-rich Ni3S2 catalyst (V s -Ni3S2). The method is simple in process and highly operable. The nickel foam serves as both a supporting substrate material and a nickel source to participate in the reaction, thus saving costs. The obtained defective catalyst material can realize the efficient electro-oxidation of benzyl alcohol to produce benzoic acid at a relatively low potential, with a yield of up to 99.99% and a Faraday efficiency of 99.99%. Summary of the invention

[0005] The invention provides a sulfur vacancy-rich Ni3S2 nanosheet array structure catalyst and a preparation method thereof, and applies the catalyst to an organic synthesis reaction of producing benzoic acid by electro-oxidation of benzyl alcohol.

[0006] The present invention uses in-situ grown nickel sulfide nanosheet material as a precursor, introduces sulfur vacancies by calcining in an inert gas atmosphere, and prepares a sulfur-vacancy-rich Ni3S2 nanosheet array structure catalyst V s -Ni3S2; The introduction of sulfur vacancies can effectively regulate the electronic structure and carrier concentration of metal sulfide materials, improve the intrinsic conductivity and the diversity of redox reactions, thereby improving the adsorption capacity of organic reactants and promoting the efficient catalytic reaction.

[0007] The preparation method proposed by the invention has the advantages of simple process, short time consumption, low cost, etc. The material is used as an organic small molecule electrocatalyst to show excellent benzyl alcohol electrocatalytic performance and catalytic stability.

[0008] The technical solution of the present invention is as follows:

[0009] A sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material, which is composed of a nickel foam substrate and a Ni3S2 nanosheet array structure with sulfur vacancies in situ grown on the nickel foam substrate;

[0010] The Ni3S2 nanosheet array structure with sulfur vacancies is formed by using thiourea as a sulfur source, deionized water as a solvent, and nickel foam as a current collector substrate and a nickel source. The Ni3S2 precursor material is in situ grown on the nickel foam substrate by a hydrothermal method, and sulfur vacancies are introduced by calcination under inert atmosphere protection.

[0011] The preparation method of the sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material of the present invention is:

[0012] (1) dissolving thiourea in deionized water, adding a nickel foam (NF) substrate, and hydrothermally reacting at 100-160° C. for 1-10 h, then taking out, washing, and drying, to obtain a Ni3S2 precursor material (denoted as Ni3S2) on the nickel foam substrate;

[0013] The nickel foam substrate needs to be cleaned before use, specifically: ultrasonically cleaned with acetone, deionized water, 3M HCl solution, deionized water and ethanol for 15 minutes in sequence, and vacuum dried for use;

[0014] The concentration of the solution obtained by dissolving the thiourea in deionized water is 1 to 5 mmol / L;

[0015] (2) placing the nickel foam loaded with Ni3S2 precursor material into a tube furnace, heating it to 250-450°C under inert gas protection and calcining it for 0.5-4.5h to obtain the sulfur-rich vacancy nickel sulfide nanosheet array structure catalyst material (denoted as V s -Ni3S2);

[0016] The inert gas is nitrogen, argon or helium;

[0017] The heating rate of the calcination is 5 to 15°C / min.

[0018] Particularly preferably, the preparation method of the sulfur-rich vacancy nickel sulfide nanosheet array structure catalyst material is:

[0019] Weigh thiourea and add it to deionized water to form a reaction solution. The thiourea concentration in the reaction solution is 1.445 mM. Then, stir magnetically for 30 min at a speed of 600 rpm to obtain a uniform solution, which is then transferred to a hydrothermal reactor. Then, add dry and clean nickel foam (the area of ​​the nickel foam is 1×3 cm 2 ), heated to 150 ° C for reaction for 5 hours, wait for the hydrothermal autoclave to cool naturally to room temperature, take out the nickel foam, rinse with deionized water and ethanol, and then put it into a vacuum drying oven to dry, so as to obtain the nickel foam loaded with Ni3S2 precursor material, put it into a tubular furnace, heat to 300 ° C under argon protection and calcine for 0.5 h to obtain the sulfur-rich vacancy nickel sulfide nanosheet array structure catalyst material.

[0020] The sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material of the present invention can be applied to the reaction of electrooxidation of benzyl alcohol to generate benzoic acid, and the conversion rate of benzyl alcohol reaches 100%, and the yield of benzoic acid reaches 99%.

[0021] In the reaction, the sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material can be directly used as an electrode material or as a catalyst.

[0022] Compared with the existing anodized electrode materials, the beneficial effects of the present invention are as follows:

[0023] (1) Nickel foam not only serves as a supporting material to ensure the excellent conductivity of the overall material, but also as a nickel source precursor to participate in the reaction to prepare nickel sulfide catalyst, avoiding the use of conductive agents and binders, effectively reducing material costs, and improving the stability of catalyst materials.

[0024] (2) Directly calcining the sulfide to produce sulfur vacancies, and directly adjusting the vacancy concentration by controlling the calcination temperature and time, thereby optimizing the catalytic activity.

[0025] (3) The calcination treatment method under inert atmosphere changes the exposed crystal surface of Ni3S2 material. The optimized crystal surface enhances the adsorption capacity of the material for organic small molecule substrates, thereby greatly improving the benzyl alcohol oxidation performance of the material.

[0026] (4) The nickel sulfide material prepared by the present invention is a three-dimensional hierarchical structure of two-dimensional nanosheet stacking. The increased specific surface area is conducive to exposing more active sites, effectively reducing the interfacial contact resistance between the electrolyte and the catalytic material.

[0027] (5) The preparation method of the present invention has the advantages of simple operation, good reproducibility, low cost and environmental friendliness. s -Ni3S2 catalyst material is used for the electro-oxidation reaction of benzyl alcohol, and exhibits low overpotential, high yield, selectivity and Faraday efficiency in 20 mM benzyl alcohol solution, and has a broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 (a, b) Ni3S2-5h and (c, d) V obtained in Example 1 s -Scanning electron microscopy (SEM) image of Ni3S2 electrode material.

[0029] Figure 2 (a) Ni3S2-5h and (b) V obtained in Example 1 s -X-ray diffraction pattern (XRD) of Ni3S2 electrode material.

[0030] Figure 3 The Ni3S2-5h and V obtained in Example 1 s -Raman graph of Ni3S2 material.

[0031] Figure 4 The Ni3S2-5h and V obtained in Example 1 s -X-ray photoelectron spectroscopy (XPS) of Ni3S2 materials.

[0032] Figure 5 This is the electron paramagnetic resonance spectrum (EPR) of the Ni3S2-5h and Vs-Ni3S2 materials obtained in Example 1.

[0033] Figure 6 The linear voltammetric scanning graphs (LSV) and Tafel graphs of (a, c) Ni3S2-5h and (b, d) Vs-Ni3S2 materials obtained in Example 1 are shown.

[0034] Figure 7 Ni3S2-5h and V obtained in Example 1 s-BA conversion rate of Ni3S2 material at different potentials, and the yield of oxidation products benzaldehyde and benzoic acid.

[0035] Figure 8 is the V obtained in Example 1 s -Stability diagram of the electrochemical oxidation of benzyl alcohol by Ni3S2 electrode material.

[0036] Fig. 9 (a, b) Ni3S2-8h and (c, d) V obtained in Example 3 s -SEM images of Ni3S2-8h material at different magnifications.

[0037] Fig.10 The (a) Ni3S2-8h and (b) V obtained in Example 3 s -Linear voltammetry (LSV) and Tafel plot of Ni3S2-8h material.

[0038] Fig.11 The Ni3S2-8h and Vs-Ni3S2-8h materials obtained in Example 3 consumed 95C (a) and 137C (b) of electricity respectively after electrolysis at 1.35V vs. RHE for 120 minutes; (c) BA conversion rate of Ni3S2-8h and (d) Vs-Ni3S2-8h materials at 1.35V vs. RHE potential, and the yield of oxidation products benzaldehyde and benzoic acid. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with specific embodiments, which are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0040] The nickel foam used in the following examples was purchased from Tianjin Avixin Chemical Technology Co., Ltd. The nickel foam had a thickness of 1.5 mm and a porosity of 98%.

[0041] Example 1: Preparation of a sulfur-vacancy-rich Ni3S2 nanosheet array structure catalyst

[0042] Dissolve 1.1 mg of thiourea in 10 mL of deionized water, stir evenly, and transfer the solution to a 25 mL hydrothermal kettle; add the pretreated 1×3 cm 2The nickel foam substrate was reacted at 150°C for 5 hours. After the reaction was completed, it was naturally cooled to room temperature, the nickel foam substrate was taken out, rinsed with deionized water and anhydrous ethanol several times, and dried at 60°C in vacuum overnight to obtain Ni3S2-5h. The obtained nickel foam loaded with the precursor material Ni3S2-5h was placed in a tubular furnace, heated to 300°C under Ar gas protection and calcined for 0.5h to finally obtain V s -Ni3S2 electrocatalyst samples.

[0043] from Figure 1 (a, b) SEM clearly shows that the Ni3S2-5h sample exhibits a three-dimensional hierarchical structure of two-dimensional nanosheet stacking. s -The nanosheet array morphology of the Ni3S2 material remains basically intact. Figure 2 The XRD patterns of Ni3S2-5h and V s -The diffraction peaks of Ni3S2 material correspond to the PDF card JCPDS no.44-1418. Nickel sulfide is a hexagonal system. For Ni3S2-5h sample, the diffraction peaks at 2θ values ​​of 31.1°, 38.3°, 50.1° and 54.6° correspond to the (110), (021), (211) and (104) crystal planes of Ni3S2. s The diffraction peaks of the Ni3S2 material at 2θ values ​​of 31.1°, 37.7°, 38.3°, 50.1° and 54.6° correspond to the (110), (003), (021), (211) and (104) crystal planes of Ni3S2. Comparing the two figures, it can be found that calcination causes changes in the exposed crystal planes of nickel sulfide: the (110) crystal plane peak becomes stronger and the (003) crystal plane peak becomes more obvious.

[0044] Figure 3 The Ni3S2-5h and V obtained in Example 1 s -Raman pattern of Ni3S2 material. ~200, 220, 274, 322, and 355 cm -1 These characteristic peaks indicate that hexagonal nickel sulfide materials have been successfully prepared, which is consistent with the results of XRD. Comparing the two materials, it is found that these characteristic peaks are shifted to the low wave number direction and the peak shape becomes wider, indicating that there is V s -The increase in short-range disorder in Ni3S2 indicates the generation of defects.

[0045] Figure 4 The Ni3S2-5h and V obtained in Example 1 s -S 2p XPS graph of Ni3S2 material. It can be seen from the figure that S2p 1 / 2 and 2p 3 / 2The bond energy shifts toward the lower bond energy, indicating that the concentration of S vacancies increases. Figure 5 The EPR graphs of Ni3S2-5h and Vs-Ni3S2 materials obtained in Example 1. The increase in the intensity of the characteristic peak at g = 0.2003 indicates that more sulfur vacancies are generated.

[0046] Example 2: Application of sulfur-vacancy-rich Ni3S2 nanosheet catalyst in electrooxidation of benzyl alcohol to produce benzoic acid

[0047] In 1M KOH solution, the catalyst material prepared in Example 1 was used as the working electrode, the platinum sheet was used as the counter electrode, and the Hg / HgO electrode was used as the reference electrode. The electro-oxidation catalytic performance of the catalyst material for benzyl alcohol (BA) was systematically studied in an H-type electrolyzer. Figure 6 Figures a and b show Ni3S2-5h and V s Linear sweep voltammetry (LSV) curves of BA oxidation and water oxygen evolution reaction (OER) catalyzed by Ni3S2 in 1.0 M KOH. In the absence of BA, obvious anodic peaks were observed for both catalysts, and strong oxygen bubbles were released at positive potentials exceeding 1.4 V vs. RHE. Ni3S2-5h and V s -Ni3S2 at 10mA·cm -2 The overpotentials of Ni3S2-5h and Ni3S2-5h were 1.448 and 1.436 V vs. RHE, indicating that they all have good water oxidation ability. The anodic peak current increased sharply after adding 30 mMBA. The peak current of Ni3S2-5h reached 74.8 mA cm at 1.343 V vs. RHE. -2 , V s -Ni3S2 reaches 94.2 mA·cm at 1.336 V vs. RHE -2 , which means that defective nickel sulfide materials have a promoting effect on the oxidation ability of BA. That is, abundant sulfur vacancies are conducive to promoting the electrooxidation reaction of organic small molecule alcohols. This electrochemical process is also confirmed by the Tafel slope ( Figure 6 (c, d) V s The Tafel slopes of BAOR of -Ni3S2 and Ni3S2-5h are 33.45 mV·dec, respectively. -1 and 57.52mV·dec -1 , which is lower than the OER of 106.21 mV·dec -1 and 114.83mV·dec -1 . V s -Ni3S2 exhibits a smaller Tafel slope for BA electrooxidation, which also indicates that V s -Ni3S2 has excellent electrooxidation kinetics for benzyl alcohol.

[0048] Figure 7 Ni3S2-5h and V s -BA conversion rate of Ni3S2 material at different potentials, and yields of oxidation products benzaldehyde and benzoic acid (30mM BA added to 1M KOH in the initial reaction system). By comparison, it can be seen that at 1.325V vs. RHE, V s -Ni3S2 exhibits a better BA electrooxidation reaction: after 100 minutes of constant potential electrolysis, the electrolysis results on Ni3S2-5h material are 83.8% BA conversion, 67.8% benzoic acid yield, and 88.5% Faraday efficiency ( Figure 7 In a), V s -The electrolysis results on Ni3S2 material showed that the conversion rate of BA was 100%, the yield of benzoic acid was 97.8%, and the Faraday efficiency was close to 100% ( Figure 7 b). When the electrolysis potential is increased to 1.35Vvs.RHE, Ni3S2-5h( Figure 7 c) and V s -Ni3S2( Figure 7 In both cases, nearly 100% conversion of BA into benzoic acid can be achieved. Figure 8 Yes V s -Stability diagram of cyclic electrolysis of Ni3S2 material at 1.35V vs. RHE. As can be seen from the figure, after 5 cycles, it still has good BAOR performance (conversion rate, yield, selectivity and Faraday efficiency are all close to 99%). This shows that the catalyst can be reused many times.

[0049] Example 3: Preparation and application of a sulfur-vacancy-rich Ni3S2 nanosheet array structure catalyst

[0050] Dissolve 1.1 mg of thiourea in 10 mL of deionized water, stir evenly, and transfer the solution to a 25 mL hydrothermal kettle; add the pretreated 1×3 cm 2 The nickel foam substrate was reacted at 150°C for 8 hours. After the reaction was completed, it was naturally cooled to room temperature, the nickel foam substrate was taken out, rinsed with deionized water and anhydrous ethanol several times, and dried at 60°C in vacuum overnight to obtain Ni3S2-8h. The obtained nickel foam loaded with the precursor material Ni3S2-8h was placed in a tube furnace, heated to 300°C under argon protection and calcined for 0.5h to finally obtain V s -Ni3S2-8h electrocatalyst sample.

[0051] Fig. 9 The Ni3S2-8h and V obtained in Example 3 s-SEM images of Ni3S2-8h materials at different magnifications. From the SEM, it can be clearly seen that the nanosheet arrays in the Ni3S2-8h sample have double sheet stacking ( Fig. 9 a, b), after argon calcination, V s -The surface of the nanosheets in the Ni3S2-8h material becomes rough and thick ( Fig. 9 (c, d).

[0052] In 1M KOH solution, the prepared catalyst material was used as the working electrode, platinum sheet as the counter electrode, and Hg / HgO electrode as the reference electrode. The electro-oxidation catalytic performance of the catalyst material for benzyl alcohol (BA) was systematically studied in an H-type electrolyzer. Fig.10 Figures a and b show Ni3S2-8h and V s Linear sweep voltammetry (LSV) curves of BA oxidation and water oxygen evolution reaction (OER) catalyzed by -Ni3S2-8h in 1.0 M KOH. In the absence of BA, obvious anodic peaks were observed for both catalysts, and strong oxygen bubbles were released at positive potentials exceeding 1.4 V vs. RHE. The anodic peak current increased sharply after adding 30 mM BA. Ni3S2-8h reached 68.8 mA cm at 1.327 V vs. RHE. -2 , V s -Ni3S2 reaches 74.6 mA cm at 1.322 V vs. RHE -2 , which means that defective nickel sulfide materials have better BA electro-oxidation ability.

[0053] Fig.11 The Ni3S2-8h and V obtained in Example 3 s -It graph of Ni3S2-8h material electrolysis at 1.35V vs.RHE and BA conversion rate, and yield graph of oxidation products benzaldehyde and benzoic acid (30mM BA was added to the initial reaction system 1M KOH). s -Ni3S2-8h materials consume 95C of electricity ( Fig.11 a) and 137C( Fig.11 In b), the Faradaic efficiency (FE) is 78.78% and 96.14% respectively. s -Ni3S2-8h material showed higher catalytic activity: the conversion of BA was 69.9%, the yield was 65.89%, and the selectivity was 94.26% ( Fig.11 d), which is higher than 61.54%, 38.69% and 62.87% of Ni3S2-8h ( Fig.11 (c).

Claims

1. A method for preparing a sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material, characterized in that: The preparation method is: (1) dissolving thiourea in deionized water, adding the nickel foam substrate, and hydrothermally reacting at 100-160° C. for 1-10 h, then taking out, washing, and drying, to obtain a Ni3S2 precursor material on the nickel foam substrate; (2) placing the nickel foam loaded with Ni3S2 precursor material into a tubular furnace, heating it to 250-450°C under inert gas protection and calcining it for 0.5-4.5h to obtain the sulfur-rich vacancy nickel sulfide nanosheet array structure catalyst material.

2. The method for preparing the sulfur-vacancies-rich nickel sulfide nanosheet array structure catalyst material according to claim 1, characterized in that: In step (1), the concentration of the solution obtained by dissolving the thiourea in deionized water is 1 to 5 mmol / L.

3. The method for preparing the sulfur-vacancies-rich nickel sulfide nanosheet array structure catalyst material according to claim 1, characterized in that: In step (2), the heating rate of the calcination is 5 to 15°C / min.

4. The method for preparing the sulfur-vacancies-rich nickel sulfide nanosheet array structure catalyst material according to claim 1, characterized in that: The preparation method is: Weigh thiourea and add it to deionized water to form a reaction solution with a thiourea concentration of 1.445 mM. Then, magnetic stirring is performed for 30 minutes at a rotation speed of 600 rpm to obtain a uniform solution, which is transferred to a hydrothermal kettle. Then, dry and clean nickel foam is added, the temperature is raised to 150°C and the reaction is performed for 5 hours. After the hydrothermal kettle is naturally cooled to room temperature, the nickel foam is taken out, rinsed with deionized water and ethanol, and then dried in a vacuum drying oven to obtain nickel foam loaded with Ni3S2 precursor material. The nickel foam is placed in a tubular furnace, the temperature is raised to 300°C under argon protection and calcined for 0.5 hours to obtain the sulfur-rich vacancy nickel sulfide nanosheet array structure catalyst material.

5. Use of the sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material obtained by the preparation method according to claim 1 in the reaction of electro-oxidation of benzyl alcohol to produce benzoic acid.

6. The use according to claim 5, characterized in that The sulfur-vacancy-rich nickel sulfide nanosheet array structure catalyst material is directly used as an electrode material or as a catalyst.

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