A single-atom nickel catalyst composite single-walled carbon nanotube, its preparation method and application

Abstract

This invention relates to a single-atom nickel catalyst composite with single-walled carbon nanotubes, its preparation method, and its applications. The materials include a single-atom nickel catalyst and single-walled carbon nanotubes; the single-atom nickel catalyst is an ultrathin two-dimensional carbon nitride matrix doped with single-atom nickel. This invention also provides a method for combining a single-atom nickel catalyst with single-walled carbon nanotubes and its application in the electrochemical degradation of organochlorine pollutants. The single-atom nickel catalytic electrode combined with single-walled carbon nanotubes provided by this invention can efficiently electrocatalyze the degradation of chlorine-containing pollutants. The design of this multifunctional electrocatalyst provides a new degradation pathway for the efficient electrocatalytic degradation of chlorine-containing pollutants, and it has promising applications in wastewater remediation.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a single-atom nickel catalyst composite single-walled carbon nanotube, its preparation method, and its application. Background Technology

[0002] Chlorinated pollutants (COPs) are commonly used as pesticides, industrial raw materials, and chemically synthesized products. Electrochemical treatment has shown high efficiency in their detoxification and degradation. Hydrogen reduction dechlorination (HRD) and electrofentonation (EF) are the main research methods for COP degradation. Studies on the combined use of HRD and EF for COP removal are limited, and the mechanisms are still unclear.

[0003] Currently, single-atom metals are widely studied in heterogeneous catalysis due to their high dispersibility and catalytic activity. However, few studies have focused on the selective role of single atoms in dechlorination and electron emission (EF), lacking support for material selection. This study presents the design of a novel multifunctional electrocatalyst, along with the electron transfer pathway and H2O2 activation mechanism. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a single-atom nickel catalyst composite single-walled carbon nanotube, its preparation method, and its application.

[0005] According to this invention, metallic Ni and Cu undergo different reductive dechlorination processes, with surface adsorption of COPs playing a crucial role. This invention selects Ni atoms to complex with SWCNTs as a reductive-oxidative complex on the cathode catalyst. In this process, COPs are completely dechlorinated and mineralized via HRD-mediated reduction and oxidation-mediated EF. This is the first explanation of the three key steps in the degradation of single-atom Ni and SWCNTs, including adsorption, dechlorination, and ·OH radical EF. H2O2 needs to be generated in situ through O2 reduction, and then effectively activated to generate ·OH radicals. This invention enhances COP degradation by using SWCNTs to disperse Ni-NCs. Pi-pi adsorption occurs between the benzene rings on the COPs and SWCNTs, and then the adjacent Ni-NCs complete the COP degradation via HRD and EF. A cathode with synergistic functions of adsorption, HRD, and EF is constructed using Ni-NCs and SWCNTs. This invention compares the differences between Ni-NCs and Cu-NCs, as well as between aliphatic and aromatic COPs. The key active sites for the three functions (adsorption, HRD, and EF) were verified through electrochemical and EPR experiments. The novel multifunctional electrocatalyst design, electron transfer pathway, and H2O2 activation mechanism provided by this invention have excellent potential applications in wastewater remediation.

[0006] The first aspect of this invention provides a single-atom nickel catalyst composite with single-walled carbon nanotubes, comprising a single-atom nickel catalyst and single-walled carbon nanotube materials; the single-atom nickel catalyst is a single-atom nickel-doped ultrathin nitride two-dimensional carbon matrix. This invention, through the rational design and synthesis of single-atom nickel anchored on an ultrathin nitride two-dimensional carbon matrix (Ni-NC), combines it with single-walled carbon nanotube (SWCNTs) materials to form (Ni-NC / SWCNTs), which can effectively degrade aromatic COPs. The single-atom nickel catalyst composite with single-walled carbon nanotubes provided by this invention can efficiently electrocatalyze the degradation of chlorine-containing pollutants, providing a new degradation pathway for the efficient electrocatalytic degradation of chlorine-containing pollutants. Only aromatic COPs containing benzene rings can be degraded; chloroacetic acid cannot be degraded. This invention provides a novel design of a multifunctional electrocatalyst, as well as an electron transfer pathway and H2O2 activation mechanism, which has potential application prospects in wastewater remediation.

[0007] Preferably, the mass ratio of the single-atom nickel catalyst to the single-walled carbon nanotube material is (0.5:1) to (2:1), and more preferably 1:1.

[0008] Further preferably, the single-atom nickel is anchored on the ultrathin two-dimensional carbon nitride matrix; and / or, the mass ratio of the single-atom nickel to the ultrathin two-dimensional carbon nitride matrix is ​​(0.5:100) to (4:100), preferably 1:100.

[0009] A second aspect of this invention provides a method for preparing the single-atom nickel catalyst composite single-walled carbon nanotube, comprising:

[0010] 1) Mix Ni-MOF and curing agent, and then carbonize to obtain electrode modified material (Ni-NC);

[0011] 2) The electrode modifier, SWCNTs, and solvent are mixed and ultrasonicated to obtain the modified solution;

[0012] 3) Apply the modification solution to the conductive carbon material or electrode material and dry it.

[0013] Preferably, in step 1), the mass ratio of the Ni-MOF to the curing agent is 5-15:80-120, and the curing agent is preferably dicyandiamine; and / or, the carbonization temperature is 600-1100℃, and the carbonization time is 1-3h; and / or, the process further includes leaching in a sulfuric acid solution after carbonization.

[0014] In this invention, the degradation of typical organochlorine compounds can be better achieved by optimizing the electrode material ratio and electrochemical method parameters.

[0015] Further preferred, step 1) further includes: dissolving Ni(NO3)2 and terephthalic acid in DMF, adding NaOH aqueous solution, sonicating and heating; cooling and filtering to separate, adding DMF and ethanol in sequence, drying to obtain Ni-MOF.

[0016] Further preferably, in step 2), the mass ratio of the electrode modifier to the SWCNTs is (0.5:1) to (2:1), preferably 1:1; and / or, the solvent preferably includes ethanol, water, and a Nafion solution; preferably, the concentration of the Nafion solution is 3% to 7%, and the ratio of the electrode modifier, Nafion solution, ethanol, and water is 1 to 5 mg: 20 to 40 μL: 0.5 mL: 0.5 mL; the ultrasonic time is preferably 30 to 50 min.

[0017] Further preferably, in step 3), the conductive carbon material is conductive carbon paper; and / or, the electrode material is a GCE electrode; and / or, the drying is performed using infrared drying.

[0018] A third aspect of the present invention provides a working electrode sheet comprising the above-described single-atom nickel catalyst composite single-walled carbon nanotubes or the single-atom nickel catalyst composite single-walled carbon nanotubes prepared by the above-described single-atom nickel catalyst composite single-walled carbon nanotubes preparation method.

[0019] The fourth aspect of the present invention provides the application of the above-described working electrode sheet in the electrocatalytic degradation of pollutants; preferably, a three-electrode system is used for electrochemical degradation, the electrolyte being a 0.04-0.06 mol / L Na2SO4 solution with pH = 4-6; and / or, the working electrode is the aforementioned working electrode sheet, the reference electrode is a saturated calomel electrode, and the anode is a platinum sheet electrode; and / or, the pollutants include a variety of COPs, preferably selected from one or more of 4-chlorophenol, 2,4-dichlorophenol, and phenol.

[0020] The beneficial effects of this invention are at least as follows: This invention fixes single-atom Ni onto N-doped carbon and composites it with SWCNTs to form an electrochemical cathode, serving as a trifunctional electrode. COPs are removed through adsorption, hydrogen reduction dechlorination, and EF processes. The effective degradation is due to the adsorption of H* on Ni-NC and COPs on SWCNTs, as well as the presence of ·OH free radicals. TOC is significantly reduced, and biotoxicity is decreased. This invention is the first to design a single-atom metal electrode with three functional effects for COPs degradation. This invention provides a new approach for preparing highly efficient, multifunctional electrocatalysts to treat COPs in water. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The following are examples of 4-CP degradation in this invention: (a) degradation time curve; (b) first-order reaction rate constant Kobs value; (c) degradation curves (wt%) of materials with different proportions; (d) comparison of Kobs values ​​of GP / SWCNTs / Ni-NC degradation reaction (at different temperatures), pH=7, 0.05M Na2SO4, -0.8V.

[0023] Figure 2 In the embodiment of the present invention, (a) I-scan rate 0.5 Curve, pH=7, 0.05M [(Fe(CN6)] 3- / 4- (a) -0.8V; (b) Polarization curves of electrodes containing hydrogen evolution and oxygen evolution; (c) Impedance spectra of different catalysts;

[0024] Figure 3 The following diagrams illustrate the relationship between 4-CP electrode degradation products in this invention: (ab) Concentration changes of 4-CP degradation products by CP / SWCNTs / Ni-NC; (c) Degradation of CP / SWCNTs / Ni-NC at different pH values; (de) Concentration changes of 4-CP degradation products by CP / SWCNTs / Cu-NC at pH = 5, 0.05M Na2SO4, -1.4V; (f) Degradation of CP / SWCNTs / Cu-NC at different pH values; (g) Degradation of 30ppm phenol by CP / SWCNTs / Ni-NC and CP / SWCNTs / Cu-NC at pH = 5, -0.8V, 0.05M Na2SO4; (h) Degradation of 2,4-dichlorophenol by CP / SWCNTs / Ni-NC, (i) dichloroacetic acid, (j) monochloroacetic acid, pH = 5, 0.05M Na2SO4, -0.8V;

[0025] Figure 4 The following are examples from the present invention: (a) Degradation curves of 4-CP by CP / SWCNTs / Ni-NC under different conditions; (b)-(d) Effects of different media on the degradation of 4-CP electrode, pH=5, 0.05M Na2SO4, -0.8V; (e) ESR spectrum of DMPO—OH and (f) Comparison of ·OH and H2O2 concentrations; (g) Degradation curves of 10 batches of 4-CP treated by CP / SWCNTs / Ni-NC. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] Unless otherwise specified, specific techniques or conditions in the embodiments of this invention shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Devices, instruments, reagents, etc., whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. All raw materials used in this invention are readily available in the domestic market.

[0028] In this embodiment of the invention, single-atom Ni (Ni-NC), single-atom Cu (Cu-NC), and NC were all self-made; ultra-high purity carboxylated single-walled carbon nanotubes (SWCNTs, purity >95%, diameter 1-2 nm) were purchased from Sigma-Aldrich, USA; anhydrous ethanol (EtOH), p-chlorophenol (4-CP), 2-chlorobenzene (2-CP), 2,4-dichlorophenol (2,4-DCP), chloroacetic acid (HAAs), and 1,2-dichloroacetic acid (DCA) were all purchased from Shanghai E.A. Chemical Technology Co., Ltd.; 5% DuPont membrane solution and Nafion... 117 ion-exchange membranes were purchased from Shanghai Sanshe Co., Ltd.; potassium ferricyanide (K3[Fe(CN)6]), potassium chloride (KCl), 98% sulfuric acid (H2SO4), and sodium hydroxide (NaOH) were purchased from Beijing Chemical Plant; phenol (PH) and anhydrous sodium sulfate (Na2SO4) were from Xilong Chemical Co., Ltd.; methanol (MeOH), tert-butanol (TBA), p-benzoquinone (PBQ), and potassium thiocyanate (KSCN) were from Macklin Ltd.; all reagents were analytical grade and could be used without additional purification. Unless otherwise specified, all solutions were prepared using deionized water (DD), and all experiments were performed at room temperature.

[0029] Example 1

[0030] 1) Synthesis of electrode modifiers (Ni-NC, Cu-NC and NC)

[0031] 1g of Cu(NO3)2 or Ni(NO3)2 and terephthalic acid are dissolved in DMF, and then 0.2mol·L⁻¹ NaOH aqueous solution is added. -150 mL of the mixture was then continuously sonicated for 1 h. Afterwards, the mixture was added to a 100 mL autoclave and maintained at 1000 MPa and 100 °C for 10 h. After cooling to room temperature, the precipitate was separated by filtration, and DMF and ethanol (50 mL) were added sequentially. The mixture was dried at 40 °C to obtain Ni-MOF or Cu-MOF. Cu-MOF or Ni-MOF (10 mg) was mixed with dicyandiamine (100 mg) in a mortar and ground. Then, under Ar protection, it was carbonized at different temperatures (600, 700, 800, 900, 1000, and 1100 °C) for 2 h at a heating rate of 5 °C·min. -1 After cooling to room temperature, these materials were subjected to 3 mol·L⁻¹ -1 Leaching in H2SO4 for 24 h to remove metal particles and unstable substances. Finally, Cu-NCx or Ni-NCx (x is the pyrolysis temperature, °C) catalyst was obtained as a black powder. PTA (10 mg) and dicyandiamide (100 mg) were ground and mixed and annealed at 800 °C, denoted as NC-800.

[0032] 2) Preparation of working electrode

[0033] Weigh 3 mg of electrode modifiers (Ni-NC, Cu-NC, NC) prepared under different temperature conditions. Depending on the research requirements, add SWCNTs in different mass ratios (0.5:1, 1:1, 2:1) and dissolve them in 30 μL of Nafion solution (5%, DuPont), 1 mL of ethanol and water (1:1). Sonicate for 30-50 min until a uniform ink pattern is achieved. Cut commercially available conductive carbon paper into 1 cm × 2 cm pieces (carbon paper, CP). Rinse the paper with ethanol and water (1:1) and bake it under an infrared lamp until dry. After the conductive carbon paper cools to room temperature, evenly drop 1 mL of the modification solution onto both sides of the conductive carbon paper. After drying under an infrared lamp, cool it to room temperature and let it stand overnight to obtain a series of electrodes, including CP / SWCNTs, CP / NC, CP / SWCNTs / Ni, CP / SWCNTs / Cu, and other working electrode sheets. In addition, 3 μL of the above-mentioned series of modification solutions were drop-coated onto the polished GCE electrode. After infrared drying, a series of electrodes, namely GCE / SWCNTs, GCE / Cu, GCE / Ni, GCE / SWCNTs / Ni, and GCE / SWCNTs / Cu, were obtained for use in impedance ESI characterization experiments. Ni-NC-800℃ and Cu-NC-800℃ are abbreviated as Ni-NC and Cu-NC in the description of the modified electrodes.

[0034] Experimental Example 1

[0035] 1) Degradation experiment

[0036] Electrochemical degradation experiments were conducted in a 50 mL single-chamber electrolytic cell using 30 mL of 0.05 mol / L Na₂SO₄ solution at pH 5 as the electrolyte. A three-electrode system was employed, with the modified electrode as the working electrode, a saturated calomel electrode as the reference electrode, and a 1 cm × 1 cm platinum sheet electrode as the anode. Power was supplied by a Shanghai Chenhua Chi660e electrochemical workstation, and the iterative method was used at a potential of -0.8 V. The concentration of the pollutants to be degraded (4-CP, 2-CP, 2,4-DCP, phenol, and chloroacetic acid derivatives) was 30 ppm. The apparatus was placed on a magnetic stirrer for stirring during the experiment, with air pumped in during the reaction (N₂ protection was used for control experiments). At predetermined time points, 1 mL samples were taken, filtered through a 0.22 μm organic filter membrane, and injected into a 1.5 mL sample vial for HPLC analysis. Optimization was performed on parameters such as the selection of carbon-based materials, the ratio of carbon-based materials to single-atom metals, the single-atom metals at different temperatures, and the pH of the electrolyte.

[0037] 2) Analytical Methods

[0038] The concentrations of 4-CP, 2-CP, 2,4-DCP, and phenol were determined by high-performance liquid chromatography (HPLC, Agilent 1260). An Agilent Venusil XBP C18 column (250 × 4.6 mm, 5 μm) was used. The mobile phase was ultrapure water (A) and chromatographic methanol (B), with a volume ratio of 3:7. The flow rate was 1 mL / min, the injection volume was 20 μL, and the detection wavelength was 220 nm. Cl- was determined by ion chromatography (Dionex Aquion RFIC, Thermo). - Ni 2+ With Cu 2+Concentration; Total organic carbon (TOC) was measured using an N / C 2001s analyzer; GC-MS (Agilent 7890A-7000C) was used to detect and analyze 4-CP degradation products. The chromatographic column was HP-5 (30m × 0.25mm, 0.25μm), the injection port temperature was 150℃, the initial column temperature was 50℃, held for 4 min, increased to 80℃ at a rate of 5℃ / min, and then increased to 220℃ at a rate of 40℃ / min, held for 5 min. The detector temperature was 220℃, the carrier gas was high-purity nitrogen, the column flow rate was 1 mL / min, and the injection volume was 1 μL. The electron impact source (EI source) had an electron energy of 70 eV; the ion source temperature was 230℃. The quadrupole temperature was 150℃, and the auxiliary heater was 280℃. The mass scan was performed in full scan mode, with a mass scan range of 10–300 amu; the solvent delay time was 3 min; hydrogen peroxide molecules were detected using a spectrophotometer (UV1800PC). Under acidic conditions, hydrogen peroxide reacts with titanium ions to form an orange complex. Hydrogen peroxide standard solutions with concentrations of 0, 5, 10, 20, 50, 100, 150, and 200 μM were prepared in 25 mL cuvettes, 5 mL of titanium solution was added, and the volume was adjusted to 25 mL with water. The absorbance was measured at a wavelength of 430 nm, and a standard curve was plotted. The same method was used to detect actual samples, and the hydrogen peroxide concentration was obtained from the absorbance. The concentration of hydroxyl radicals (·OH) was detected using HPLC with salicylic acid to capture hydroxyl radicals (·OH). Salicylic acid (o-hydroxybenzoic acid) combines with hydroxyl radicals to produce 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). The yield of ·OH is equivalent to the amount of 2,3-DHBA and 2,5-DHBA, and can be determined by HPLC. The concentration of salicylic acid was 0.01 mol / L, the mobile phase of HPLC was 0.5% acetic acid and methanol (v / v, 50 / 50), the flow rate was 1 mL / min, and the detector wavelength was 320 nm. Genetic toxicity was assessed by SOSumu test, and the test strain was Salmonella Typhimurium TA1535 / pSK1002. Each test was repeated three times on 96-well microplates (Costar, USA). The results were invalid when the growth factor (G) was below 0.5 (Formula (1)). Bacterial growth and density were determined by turbidimeter. 4-Nitroquinoline-1-oxide (0.5 mg / mL⁻¹) was used as a positive control for the standard test strain TA1535 / pSK1002 in parallel tests. If a substance is positive in three independent replicate tests (Ir > 2), it is considered to have significant genotoxicity (Equation (2)). The results of the SOS / umu test follow two equations:

[0039] G = (A 600,T - A 600,B ) / (A 600,N - A 600,B(1)

[0040] IR = (A 420,T - A 420,B ) / (A 420N - A 420B ) X 1 / G (2)

[0041] Among them, A 600,T A 600,B A 600N A 420,T A 420,B A 420N The absorbance values ​​at wavelengths of 600 nm and 420 nm represent the absorbance of the treated sample, blank control, and negative control, respectively.

[0042] Results and analysis of COPs degradation by metal-NC cathode: In this embodiment of the invention, 4-chlorophenol (4-CP) degradation was carried out in a single-chamber electrolytic cell with continuous air flow. Different cathode catalyst compositions affected the degradation of 4-CP. Figure 1 a shows the 4-CP degradation curves as a function of reaction time for CP, CP / NC, CP / SWCNTs, CP / SWCNTs / Ni-NC, and CP / SWCNTs / Cu-NC (where the mass ratio of SWCNTs to Ni-NC or Cu-NC is 1:1). Among these, CP / SWCNTs / Ni-NC showed the highest removal rate, reaching 95% within 60 minutes. Figure 1 b shows the first-order reaction kinetic parameters (Ki) of CP / SWCNTs / Ni-NC. obs The duration is 2.66h. -1 It was significantly higher than CP (0.40h). -1 ), CP / NC (0.70h -1 ), CP / SWCNTs (1.02h) -1 ), CP / SWCNTs / Cu-NC (1.5h -1 To eliminate the influence of adsorption and anodizing, adsorption (without applied potential) and anodizing experiments (with Nafion 117 ion exchange membranes added to the anode and cathode electrolytic cells) were conducted. After 120 min of treatment, no 4-CP was removed during either adsorption or anodizing. The results indicate that the degradation of 4-CP is mainly caused by the cathode reaction process.

[0043] K obs Comparative analysis shows that CP / SWCNTs / Ni-NC can effectively degrade 4-CP. The SWCNTs to Ni-NC mass ratio of 2:1 shows the strongest effect. Figure 1c) This indicates that the two materials have a synergistic effect in the degradation of 4-CP. Comparing the dechlorination degradation effect of Ni-NC at different temperatures, from 600℃ to 1100℃, the Kc of Ni-NC at 800℃... obs Optimal value ( Figure 1 d). Therefore, the present invention characterizes Ni-NC at 800℃ and performs subsequent degradation experiments, and Ni-NC-800 is abbreviated as Ni-NC.

[0044] To further investigate the degradation mechanism of CP / SWCNTs / Ni-NC (SWCNTs to Ni-NC mass ratio 2:1), these electrodes were electrochemically characterized. The effective surface area of ​​the four modified electrodes was calculated based on the potassium ferrocyanide detection results according to equation (3).

[0045]

[0046] In the formula: n represents the number of electrons present in the redox half-reaction, [Fe(CN6)] 3- / 4- n is 1; v is the voltage scan rate, V·s -1 A is the effective area of ​​the electrode, in cm². 2 D is the diffusion coefficient, typically 6.057 × 10⁻⁶. -6 cm 2 ·s -1 (25℃); C is [Fe(CN6)] 3- / 4- The concentration, mmol·L -1 Ip is the peak current value of the redox reaction, in A. Simplifying the formula, we get Ip = 3.310 × 10⁻⁶. -2 Av 1 / 2 By plotting and fitting the peak current at different scan rates, a linear regression equation was obtained ( Figure 2 a) The slope of the regression equation shows that the effective surface areas of the four electrodes are 3, 81, 112, and 139 cm², respectively. 2 Due to the modification with SWCNTs and metal-NC, the effective surface area of ​​the electrode increases sequentially.

[0047] The potential window of an electrode plays a crucial role in its electrochemical performance, such as... Figure 2 As shown in b, the hydrogen evolution and oxygen evolution capabilities of the four electrodes are, in descending order:

[0048] CP / SWCNTs / Ni-NC>CP / SWCNTs / Cu-NC>CP / SWCNTs>CP.

[0049] The electrode impedance value is ( Figure 2 c)

[0050] GCE > GCE / Cu-NC > GCE / Ni-NC > GCE / SWCNTs / Cu-NC > GCE / SWCNTs / Ni-NC > GCE / SWCNTs. This invention infers that the effects of SWCNTs and metal-NC on 4-CP are not merely simple electrocatalytic effects, but also involve a more complex synergistic mechanism.

[0051] like Figure 3 As shown in Figure 4, the degradation results of Ni-NC and Cu-NC modified CP differ at near-neutral pH (pH=5). The degradation products of CP / SWCNTs / Cu-NC for 4-CP are almost conserved as phenol, with the total carbon (phenol and remaining 4-CP) maintaining a constant concentration. Chloride ions also increase with decreasing 4-CP concentration, keeping the total concentration (Cl and remaining 4-CP) constant. This indicates that under near-neutral conditions, the Cu-NC modified electrode exhibits a typical hydrogen dechlorination mechanism, while the Ni-NC modified electrode does not. Although Cl... - The amount of phenol and the remaining 4-CP are constant, but the total carbon (phenol and the remaining 4-CP) is not in balance, indicating that phenol continues to degrade. At pH 5, Ni-NC exhibits a different oxidation mechanism than Cu-NC, continuing oxidation after dechlorination. To further investigate the differences between the two metal-NCs, experiments were conducted with varying pH values. Figure 3 c, f). It can be seen that CP / SWCNTs / Ni-NC and CP / SWCNTs / Cu-NC exhibit different pH dependencies. The optimal pH for CP / SWCNTs / Ni-NC degradation is 3, while the degradation rate of CP / SWCNTs / Cu-NC increases continuously with decreasing pH. This result confirms the hypothesis that the hydrodechlorination process of Ni-NC is accompanied by the adsorption of chlorophenol. Simultaneously, the CP / SWCNTs / Ni-NC electrode can also degrade pure phenol at pH 3. Figure 3 g). EF is the main mechanism of phenol degradation on the electrode. Cu-NC modified electrodes have a weak activation ability for active hydrogen, and therefore are more pH dependent; decreasing pH leads to increased degradation. Figure 3 This demonstrates that CP / SWCNTs / Ni-NC is a combined reaction of adsorption, hydrogen reduction dechlorination, and EF oxidative degradation.

[0052] Degradation of 2,4-dichlorophenol (2,4-dcp) and benzene-free COPs (monochloroacetic acid and dichloroacetic acid) using CP / SWCNTs / Ni-NC revealed that the initial degradation product of 2,4-dcp was 2-chlorophenol (2-cp), which continued to degrade. The concentration showed a trend of first increasing and then decreasing. Neither monochloroacetic acid nor dichloroacetic acid underwent dechlorination. Figure 3This means that pi-pi adsorption is important for HRD. In the degradation of CP / SWCNTs / Ni-NC, adsorption, reduction (HRD), and oxidation (EF) cause the degradation of COPs.

[0053] To determine the mechanism of EF, the degradation differences were compared by varying the oxygen content of the reaction system. Comparing the degradation under nitrogen protection and oxygenation, nitrogen protection reduced the degradation rate of the CP / SWCNTs / Ni-NC system from 100% to 20% (reaction time 2 h), and the degradation rate of the CP / SWCNTs / Cu-NC system from 76% to 23%. Figure 4 a) Oxygen is crucial to the reaction system, therefore EF is one of the important means of cathodic degradation of 4-CP.

[0054] TBA has the effect of eliminating active hydrogen. With different concentrations added, the degradation rate significantly decreased. In Cu-NC modified electrodes, the degradation rate decreased from 55% to 40% after the addition of TBA, while in Ni-NC modified electrodes, the degradation rate decreased from 90% to 45%. Figure 4 b) Using p-benzoquinone (BQ) as a ·OH trap yielded similar results. The metal-NC modified electrode reduced the degradation of 4-CP, but significantly affected the degradation of Ni-NC. The results indicate that ·OH plays a crucial role in the removal of 4-CP on CP / SWCNTs / Ni-NC, and Ni-NC has a stronger ability to form ·OH than Cu-NC. Therefore, as... Figure 3 As shown in d, the main degradation component of CP / SWCNTs / Cu-NC is phenol, while the degradation mechanisms of Ni-NC and Cu-NC modified electrodes are different.

[0055] When the TBA concentration was further increased to 500 mM, the degradation efficiency of 4-CP remained almost unchanged. Figure 4 (b) This phenomenon indicates that even if all the ·OH generated in the system is captured by TBA, there is still a 45%-50% 4-CP removal rate. The results show that in addition to ·OH oxidation, 4-CP undergoes other degradation processes, confirming the existence of the HRD reaction.

[0056] The degradation intermediates of 4-CP were determined by gas chromatography-mass spectrometry and high-performance liquid chromatography. Phenol appeared on both metal-NC electrodes, indicating that the HRD reaction occurred on both electrodes. The addition of NaSCN to the reaction reduced the degradation of 4-CP, indicating that the metal-NC electrode is the major active site. Figure 4c). Based on the above inference, it can be speculated that the entire degradation process of 4-CP on CP / SWCNTs / Ni-N-C is as follows: 4-CP is adsorbed on SWCNTs, and then dechlorinated by H* on Ni-N-C. Nitrogen-doped graphene (N-C) promotes the reduction of O2 to H2O2, which is decomposed by Ni-N-C to generate hydroxyl radical (·OH). The dechlorinated product is further oxidized and mineralized by ·OH.

[0057] The oxygen evolution process of CP / SWCNTs / Ni-N-C was carried out through LSV experiment ( Figure 2 b). At a current density of -0.01 A, it can be seen that CP / SWCNTs / Ni-N-C has the minimum hydrogen and oxygen evolution potential at +1.0 V. The potentials of carbon paper, CP / SWCNTs and CP / SWCNTs / Cu-N-C are +1.2 V, +1.3 V and +1.5 V respectively. Meanwhile, CP / SWCNTs / Ni-N-C has the highest hydrogen evolution current at -1.6 V and exhibits good oxygen reduction activity (ORR), but this result is inconsistent with the concentration of in-situ generated H2O2.

[0058] Using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a probe, reactive oxygen species (ROS) generated during 4-CP degradation were determined by EPR spectroscopy ( Figure 4 e). A characteristic 1:2:2:1 quadruple peak related to DMPO-·OH was observed on four electrodes. The ·OH concentration obtained with CP / SWCNTs / Ni-N-C was the highest, while the H2O2 concentration obtained with CP / SWCNTs was the highest ( Figure 4 f), this abnormal result indicates that Ni-N-C has an activation effect on H2O2, decomposing it into ·OH, and promoting the forward progression of the ORR reaction.

[0059] SWCNTs can promote the generation of H2O2 but cannot effectively promote the decomposition of H2O2, while Ni-N-C or Cu-N-C can promote the generation and decomposition of ·OH. Therefore, the ·OH concentration formed by the four electrodes increases in sequence: CP / N-C < CP / SWCNTs < CP / SWCNTs / Cu-N-C < CP / SWCNTs / Ni-N-C. The result is consistent with Figure 1 the 4-CP dechlorination process in b, the degradation rate constant K of 4-CP by CP / SWCNTs / Ni-N-C obs is higher than that of CP / SWCNTs.

[0060] The degradation experiment of 4-CP by CP / SWCNTs / Ni-NC was conducted for 2 hours, and the degradation rate of 4-CP reached over 90%. 4-Chlorophenol was completely dechlorinated and degraded. Simultaneously, SOS / umu experiments of 30 ppm 4-CP and its degradation solution showed that the IR values ​​of the degradation solution were both lower than the positive reference value. After 2 and 5 hours of degradation, the IR values ​​of the degradation solution decreased from the initial 1.43 to 1.11 and 1.02, respectively. The toxicity value showed a decreasing trend during the reaction. The degradation products posed no toxic risk. Therefore, the CP / SWCNTs / Ni-NC electrode combined with EF and HRD is recommended for the degradation of 4-CP.

[0061] The stability and reusability of CP / SWCNTs / Ni-NC were evaluated through 20-hour electrolysis experiments at -0.8V and an initial pH of 3, and 10 successful 4-CP batch treatments. It exhibited a stable electrolysis current with negligible decay, indicating that the Ni-NC complex with SWCNTs possesses excellent stability during long-term operation, and the degradation of 4-CP remained almost constant in each cycle.

[0062] This invention fixes single-atom Ni onto N-doped carbon and combines it with SWCNTs to form an electrochemical cathode, serving as a trifunctional electrode to remove COPs through adsorption, hydrogen reduction dechlorination, and EF processes. NC promotes 2e- ... - ORR improves performance, Ni-NC via 1e - The process activates H₂O₂ into ·OH. The CP / SWCNTs / Ni-NC electrocatalytic system completely dechlorinates 4-CP within 2 hours, with a significant reduction in TOC and biotoxicity. Thanks to the synergistic effect of Ni-NC and SWCNTs, the kinetic constant of the 4-CP degradation electrode reaches 2.66 h. -1 This invention is the first to design a single-atom metal electrode with three functional effects to degrade COPs. This invention provides a new approach for preparing highly efficient, multifunctional electrocatalysts for treating COPs in water.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single-atom nickel catalyst composite single-walled carbon nanotube, characterized in that, It includes a single-atom nickel catalyst and a single-walled carbon nanotube material; the single-atom nickel catalyst is an ultrathin two-dimensional carbon nitride matrix doped with single-atom nickel; The mass ratio of the single-atom nickel catalyst to the single-walled carbon nanotube material is (0.5:1) to (2:1). The single-atom nickel catalyst is prepared by a method comprising the following steps: Ni(NO3)2 and terephthalic acid were dissolved in DMF, and then NaOH aqueous solution was added. The mixture was ultrasonically treated and then heated. After cooling, the mixture was filtered and separated. DMF and ethanol were added in sequence, and the mixture was dried to obtain Ni-MOF. Ni-MOF was then mixed with a curing agent and carbonized to obtain the final product.

2. The single-atom nickel catalyst composite single-walled carbon nanotube according to claim 1, characterized in that, The single-atom nickel is anchored on the ultrathin nitrided two-dimensional carbon matrix; and / or, the mass ratio of the single-atom nickel to the ultrathin nitrided two-dimensional carbon matrix is ​​(0.5:100) to (4:100).

3. The method for preparing the single-atom nickel catalyst composite single-walled carbon nanotube as described in claim 1 or 2, characterized in that, include: 1) Mix Ni-MOF and curing agent and carbonize to obtain electrode modified material (Ni-NC); 2) The electrode modifier, SWCNTs, and solvent are mixed and ultrasonicated to obtain the modified solution; 3) Apply the modification solution to the conductive carbon material or electrode material and dry it.

4. The method for preparing single-atom nickel catalyst composite single-walled carbon nanotubes according to claim 3, characterized in that, In step 1), the mass ratio of Ni-MOF to curing agent is 5~15:80~120, and the curing agent is dicyandiamine; and / or, the carbonization temperature is 600~1100℃, and the carbonization time is 1~3h; and / or, it also includes leaching in sulfuric acid solution after carbonization.

5. The method for preparing single-atom nickel catalyst composite single-walled carbon nanotubes according to claim 3 or 4, characterized in that, Step 1) further includes: dissolving Ni(NO3)2 and terephthalic acid in DMF, adding NaOH aqueous solution, sonicating and heating; cooling and filtering to separate, adding DMF and ethanol in sequence, drying to obtain Ni-MOF.

6. The method for preparing single-atom nickel catalyst composite single-walled carbon nanotubes according to claim 3, characterized in that, In step 2), the mass ratio of the electrode modifier to the SWCNTs is (0.5:1) to (2:1).

7. The method for preparing single-atom nickel catalyst composite single-walled carbon nanotubes according to claim 6, characterized in that, In step 2), the solvent includes ethanol, water, and Nafion solution; the concentration of the Nafion solution is 3% to 7%, and the ratio of the electrode modifier, Nafion solution, ethanol, and water is 1 to 5 mg: 20 to 40 μL: 0.5 mL: 0.5 mL; the sonication time is 30 to 50 min.

8. The method for preparing single-atom nickel catalyst composite single-walled carbon nanotubes according to claim 3, characterized in that, In step 3), the conductive carbon material is conductive carbon paper; and / or, the electrode material is a GCE electrode; and / or, the drying is performed using infrared drying.

9. A working electrode sheet, characterized in that, The single-atom nickel catalyst composite single-walled carbon nanotubes obtained by the preparation method of the single-atom nickel catalyst composite single-walled carbon nanotubes according to claim 1 or 2 or any one of claims 3-8.

10. The application of the working electrode sheet according to claim 9 in the electrocatalytic degradation of pollutants.

11. The application according to claim 10, characterized in that, Electrochemical degradation is carried out using a three-electrode system, with the electrolyte being a 0.04-0.06 mol / L Na2SO4 solution at pH 4-6; and / or, the working electrode is the aforementioned working electrode sheet, the reference electrode is a saturated calomel electrode, and the anode is a platinum sheet electrode.

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