A nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring, preparation method and application thereof

Abstract

The present invention discloses a nitrogen-doped MXene electrocatalytic membrane anchored by single-atom chromium, a preparation method, and its application, relating to the field of electrocatalysis technology. The invention utilizes hexadecyltrimethylammonium bromide to nitrogen-dope MXene, then adds K₂Cr₂Oₐ to anchor the single-atom chromium. After calcination, the resulting solid powder catalyst is dispersed in water, coated, and dried to form a CrN₄ / MXene electrocatalytic membrane. The CrN₄ / MXene electrocatalytic membrane can efficiently degrade organic pollutants in water.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis technology, and specifically relates to a nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring, a preparation method and applications thereof. Background Art

[0002] Advanced oxidation processes (AOPs) can generate reactive oxygen species (hydroxyl radicals (·OH), singlet oxygen ( 1 O2) and superoxide radicals (O2· - )) Achieve deep mineralization removal of organic micropollutants. Compared with short life and poor selectivity · Compared with OH, the metastable state with unoccupied π* orbitals 1 O2 can achieve highly selective degradation of electron-rich organic micropollutants through electrophilic addition reactions. 1 The method of using O2 to purify organic wastewater is highly dependent on environmental pH and chemical input, which seriously hinders its further development in practical applications. 1 O2 has become a potential alternative strategy. In particular, it can be highly automated and industrially produced. 1 The electrocatalytic method of O2 has broad research and application prospects.

[0003] Generally speaking, O2 can inhibit the cleavage of the OO bond through the Pauling adsorption configuration on the metal site, promote the cleavage of the MO bond, and be conducive to the formation of -OO- intermediates (generating 1 The most important intermediate of O2); Griffiths and Yeager adsorption configurations easily promote the cleavage of OO bonds to form H2O. Single-atom catalysts (SACs) have independent active sites and can selectively generate H2O by adjusting the catalytic center and coordination environment. 1 In addition, heteroatom doping can be used to regulate the electronic structure of the metal catalytic center, thereby regulating the binding energy and adsorption configuration of O2 on the catalytic site to improve the electrocatalytic activity and selectivity. For example, Lou et al. can selectively generate Fe2N nanocrystals by nitrogen doping. · OOH intermediates can promote the electrocatalytic activity of the oxygen reduction reaction (ORR). However, the construction of heteroatom-coordinated single-atom electrocatalysts is usually in the form of powders, which are prone to agglomeration and difficult to separate and regenerate during water treatment, seriously hindering their engineering application in water treatment technology.

[0004] Therefore, how to provide a single-atom chromium-anchored nitrogen-doped MXene electrocatalytic membrane with a simple preparation method is of great significance to the development of water treatment technology. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring and a preparation method thereof.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for preparing a nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring comprises the following steps:

[0008] Step 1: Disperse MXene in water to prepare a MXene aqueous dispersion, then add cetyltrimethylammonium bromide, wherein the mass ratio of MXene to cetyltrimethylammonium bromide is 80-120:320-480, and stir and mix to obtain a nitrogen-doped MXene solution; the MXene of the present invention is Ti3C2T x , 400 mesh, purchased from Jilin Yiyi Technology Co., Ltd.;

[0009] Step 2: adding a K2Cr2O7 aqueous solution dropwise to the nitrogen-doped MXene solution and mixing them uniformly by ultrasonication to obtain a mixed solution, wherein the mass ratio of the added amount of K2Cr2O7 to the MXene is 2-8:80-120;

[0010] Step 3: The mixed solution obtained in step 2 was centrifuged and washed with deionized water, then freeze-dried, and finally calcined in an Ar atmosphere to obtain a solid CrN4 / MXene powder catalyst;

[0011] Step 4: The solid CrN4 / MXene powder catalyst obtained in step 3 is placed in deionized water and ultrasonically dispersed to obtain a dispersion;

[0012] Step 5: The dispersion obtained in step 4 is vacuum filtered onto a polytetrafluoroethylene support membrane to prepare a CrN4 / MXene electrocatalytic membrane.

[0013] Preferably, the concentration of the MXene aqueous dispersion in step 1 of the present invention is 1 to 3 mg / mL.

[0014] Preferably, the stirring speed in step 1 of the present invention is 600-800 rpm, the stirring temperature is 30-50° C., and the stirring time is 35-55 h.

[0015] Preferably, in step 2, the ultrasonic power is 100-300 W, and the ultrasonic time is 30-60 min.

[0016] Preferably, in step 3, the centrifugal speed is 6000-8000 rpm, the centrifugal time is 10-30 min, the freeze-drying temperature is -40°C to -50°C, the freeze-drying time is 8-12 h; the calcination temperature is 350-450°C; and the calcination time is 2-5 h.

[0017] Preferably, in step 4, the ratio of the solid powder catalyst to deionized water is 20-30 mg:40-50 mL, the ultrasonic power is 200-400 W, and the ultrasonic time is 70-100 min.

[0018] The nitrogen-doped MXene electrocatalytic membrane based on single-atom chromium anchoring prepared by the above method has a high specific surface area and porosity, improves the utilization rate of active sites, and solves the current situation that granular catalysts are difficult to recycle and reuse.

[0019] Another object of the present invention is to use the above-mentioned nitrogen-doped MXene electrocatalytic membrane to make an electrocatalytic reactor and treat water containing organic pollutants to achieve the purpose of degrading organic pollutants in water.

[0020] The organic pollutants described in the present invention include but are not limited to sulfamethoxazole, bisphenol A, tetracycline, carbamazepine and 4-nitrophenol.

[0021] Preferably, the structure of the electrocatalytic reactor of the present invention is as follows Figure 1 As shown, it includes a shell 7, the upper end of the shell 7 is provided with a water inlet 5, and the lower end is provided with a water outlet 6; a cathode 2 and an anode 4 are provided in the shell 7, the cathode 2 is the nitrogen-doped MXene electrocatalytic membrane prepared by the present invention, and the anode 4 is a porous titanium sheet (purchased from Inokai Co., Ltd., with a thickness of 0.127 mm and a purity of 99%); the anode 4 and the cathode 2 are provided with a number of insulating silicone blocks 3.

[0022] Under different external voltages, water containing organic pollutants is drawn into the housing 7 from the water inlet 5 by a peristaltic pump, and flows out from the water outlet 6 after being electrocatalytically treated.

[0023] The present invention adopts the doping / calcination method to prepare nitrogen-doped MXene electrocatalytic membrane (CrN4 / MXene electrocatalytic membrane). The flow-through operation coupled with membrane separation and electrochemical technology can significantly improve the mass transfer and electron transfer efficiency within the membrane. Under the action of the auxiliary electric field, the CrN4 / MXene electrocatalytic membrane reduces O2 in situ at the cathode to selectively generate · OOH intermediate, and then generate 1 O2. 1 O2 can selectively degrade aromatic electron-rich organic matter, has a high redox potential (2.2V vs NHE), and has high tolerance to complex systems (pH, inorganic salts).

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention uses a nitrogen-doped MXene electrocatalytic membrane anchored by single-atom chromium (CrN4 / MXene electrocatalytic membrane), which increases the specific surface area and porosity compared to granular catalysts, improves the utilization rate of active sites, and solves the current situation that granular catalysts are difficult to recycle and reuse;

[0026] 2. The present invention adopts an improved method combining membrane separation and electrochemical technology and operates in a flow-through mode to enhance mass transfer during the reaction process and accelerate the degradation kinetics of organic pollutants;

[0027] 3. The oxygen active species that plays a leading role in the system of the present invention is 1 O2, has high tolerance to complex water bodies;

[0028] 4. The system of the present invention can selectively treat electron-rich organic pollutants and has a wide pH application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of an electrocatalytic reactor made using the nitrogen-doped MXene electrocatalytic membrane of the present invention;

[0030] Figure 2 This is the HAADF-STEM image of CrN4 / MXene prepared in Example 1 of the present invention;

[0031] Figure 3 Electron paramagnetic resonance spectra of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) (upper) and 2,2,6,6-tetramethylpiperidine (TEMP) (lower) as reactive oxygen species scavengers;

[0032] Figure 4 To demonstrate the treatment effect of the electrocatalytic system of the present invention on five kinds of organic pollutants;

[0033] Figure 5 To investigate the treatment effect of sulfamethoxazole using the electrocatalytic system of the present invention under different pH conditions;

[0034] Figure 6 To investigate the treatment effect of sulfamethoxazole using the electrocatalytic system of the present invention under different voltage conditions;

[0035] Figure 7 The treatment effects of sulfamethoxazole using the electrocatalytic system of the present invention and the electrocatalytic system of Comparative Example 1 under different voltage conditions are shown. DETAILED DESCRIPTION

[0036] To make the objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described below in detail. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0037] Example 1

[0038] A method for preparing a nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring, comprising the following steps:

[0039] (1) 400 mg of hexadecyltrimethylammonium bromide was dissolved in 50 mL of 2 mg / mL MXene aqueous dispersion and stirred to disperse it evenly. The stirring conditions were: stirring speed 700 rpm, stirring temperature 40 °C, stirring time 48 h to obtain a mixed solution.

[0040] (2) Add 5.0 mL of 1.0 mg / mL K2Cr2O7 aqueous solution to the above mixed solution and disperse it by ultrasonication. The ultrasonication conditions are as follows: ultrasonic power of 200 W and ultrasonication time of 40 min to obtain a precursor;

[0041] (3) The precursor was centrifuged at 7000 rpm for 20 min and then freeze-dried at -45 °C for 10 h to obtain solid CrN4 / MXene powder;

[0042] (4) calcining the solid powder in a tube furnace under Ar atmosphere at a temperature of 400 °C for 3 h to obtain solid CrN4 / MXene powder;

[0043] (5) Dissolve 25 mg of the calcined solid powder in 30 mL of deionized water and disperse it evenly by ultrasonication at a power of 300 W for 90 min to obtain a dispersion.

[0044] (6) The above dispersion was vacuum filtered onto a polytetrafluoroethylene support membrane with a diameter of 47 mm to prepare a CrN4 / MXene electrocatalytic membrane, the HAADF-STEM image of which is shown in FIG. Figure 2 shown.

[0045] Example 2

[0046] An electrocatalytic reactor having a structure as follows Figure 1 As shown, the cathode is the CrN4 / MXene electrocatalytic membrane prepared in Example 1.

[0047] Under different applied voltages, 50 mL of O2 saturated deionized water solution was pumped from the water inlet 5 along the Figure 2Enter the shell 7 in the direction of the solid arrow, pass through the CrN4 / MXene membrane and the porous titanium sheet, and follow Figure 2 The direction of the hollow arrow is from the water outlet 6;

[0048] like Figure 3 As shown, when DMPO and TEMP are used as active oxygen scavengers, 1 O2 and · The electron paramagnetic resonance spectrum of OH. As can be seen from the figure, 1 The characteristic signal peak of O2 is significantly higher than · The characteristic signal peak of OH, based on which, it is confirmed that the electrocatalytic filtration system can selectively generate 1 O2 electrochemical system.

[0049] Example 3

[0050] The electrocatalytic reactor prepared in Example 2 was used to treat water containing organic pollutants. The specific treatment method is as follows:

[0051] The water bodies to be treated are O2-saturated deionized water solutions to which sulfamethoxazole, bisphenol A, ciprofloxacin, carbamazepine and 4-nitrophenol have been added, and the concentrations of the above organic pollutants in the water bodies are all 10 mg / L.

[0052] Under the condition of an external voltage of 2.5V, the typical water to be treated was passed through the electrocatalytic reactor of Example 2 at a flow rate of 6mL / min by a peristaltic pump. Figure 4 As shown, the electrocatalytic reactor of the present invention can effectively degrade different types of electron-rich organic pollutants (>95%) and has specific selectivity.

[0053] Example 4

[0054] Taking sulfamethoxazole as a model organic pollutant, the degradation efficiency of the water containing sulfamethoxazole in Example 3 was investigated using the electrocatalytic reactor of Example 2 under different applied voltage conditions. Figure 5 When the applied voltage is 2.5V, the electrocatalytic membrane 1 O2 is generated efficiently and quickly, thereby improving the degradation rate of organic pollutants.

[0055] Example 5

[0056] Taking sulfamethoxazole as a model organic pollutant, the degradation efficiency of the water containing sulfamethoxazole in Example 3 was investigated using the electrocatalytic reactor of Example 2 under different solution pH conditions. Figure 6The electrocatalytic reactor of the present invention has an efficiency of removing sulfamethoxazole greater than 93% under acidic, neutral, and alkaline conditions. This indicates that the electrocatalytic effect of the CrN4 / MXene membrane prepared by the present invention is not affected by the pH value of the solution and has strong anti-interference ability.

[0057] Comparative Example 1

[0058] An electrocatalytic reactor, which differs from Example 2 in that a MXene electrocatalytic membrane is used instead of the CrN4 / MXene electrocatalytic membrane.

[0059] The preparation method of MXene electrocatalytic film is as follows:

[0060] 50 mL of 2 mg / mL MXene aqueous dispersion was vacuum filtered onto a polytetrafluoroethylene support membrane with a diameter of 47 mm to prepare a MXene electrocatalytic membrane.

[0061] The experimental data of Comparative Example 1 are as follows Figure 7 As shown by Figure 7 It can be seen that the electrocatalytic membrane containing CrN4 active sites of the present invention can electrocatalyze O2 to generate 1 O2, promotes the efficient degradation of sulfamethoxazole.

[0062] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring, characterized in that: Here are the steps: (1) 400 mg of hexadecyltrimethylammonium bromide was dissolved in 50 mL of 2 mg / mL MXene aqueous dispersion and stirred to disperse it evenly. The stirring conditions were: stirring speed 700 rpm, stirring temperature 40 °C, stirring time 48 h to obtain a mixed solution. (2) Add 5.0 mL of 1.0 mg / mL K2Cr2O7 aqueous solution to the above mixed solution and disperse it by ultrasonication. The ultrasonication conditions are as follows: ultrasonic power of 200 W and ultrasonication time of 40 min to obtain a precursor; (3) The precursor was centrifuged at 7000 rpm for 20 min and then freeze-dried at -45 °C for 10 h to obtain solid CrN4 / MXene powder; (4) calcining the solid powder in a tube furnace under Ar atmosphere at a temperature of 400 °C for 3 h to obtain solid CrN4 / MXene powder; (5) Dissolve 25 mg of the calcined solid powder in 30 mL of deionized water and disperse it evenly by ultrasonication at a power of 300 W for 90 min to obtain a dispersion. (6) The above dispersion was vacuum filtered onto a polytetrafluoroethylene support membrane with a diameter of 47 mm to prepare a CrN4 / MXene electrocatalytic membrane.

2. A nitrogen-doped MXene electrocatalytic film based on single-atom chromium anchoring, characterized in that: Prepared by the method of claim 1.

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