Preparation method and application of transition metal cobalt loaded graphene aerogel

Abstract

The invention discloses a preparation method and application of transition metal cobalt loaded graphene aerogel, and belongs to the technical field of catalysts. Transition metal cobalt is stably combined to a graphene sheet layer through interaction of coordination bonding and the like in the form of cobaltosic oxide nanoclusters, stability is high, good strength is provided for a graphene base, and leaching of cobalt metal is reduced. In the preparation process, graphene oxide is used as an aerogel precursor, transition metal cobalt is used as a modified metal precursor, thiourea is added, heating reduction is performed, supercritical drying is performed after cooling, and finally high-temperature reduction is performed to obtain the transition metal cobalt loaded graphene aerogel. When being used as a catalyst to catalyze peracetic acid to degrade organic pollutants such as antibiotics, the catalyst has relatively high stability, catalytic activity and recyclability.

Description

Technical Field

[0001] This application belongs to the technical field of industrial catalysts, and particularly relates to a preparation method and application of a transition metal cobalt supported graphene aerogel. Background Art

[0002] In recent years, with the application of antibiotics in human beings and livestock breeding, the refractory antibiotics produced flow into water bodies, becoming an important problem of water environmental pollution and water resource shortage. Among them, the toxicity brought by the exposure of tetracycline antibiotics to organisms and the water problems brought by their persistence in the aquatic environment are one of the prominent problems. During the production and use of tetracycline antibiotics, a large amount of inorganic salt ions are usually contained, which will inevitably affect the degradation pathway of antibiotics and the purification effect of wastewater.

[0003] The peracetic acid radical generated by the peracetic acid ((Peracetic Acid, PAA)) advanced oxidation technology shows unique catalytic performance in antibiotic degradation, and it is also another green and efficient degradation system after the birth of the persulfate degradation system. In some cases, peracetic acid can be directly used to decompose and generate free radicals under specific conditions to treat sewage. However, the decomposition rate of peracetic acid in this system is relatively slow, and the amount of free radicals generated is limited. The treatment effect on high-concentration and refractory organic pollutants may not be good. To improve the decomposition efficiency of peracetic acid and the amount of free radicals generated, catalysts are often added. Common catalysts include transition metal ions (such as Fe 2+ 、Co 2+ etc.) and metal oxides (such as MnO 2 、Fe 3 O 4 etc.). How to improve the catalytic activity, stability and recyclability of catalysts is a key concern in the field of catalysts.

[0004] In the related art, for example, a method for activating persulfate by a cathode carbon material loaded with cobalt tetroxide to enhance the photocatalytic degradation of organic matter is disclosed in a Chinese invention patent application with the publication number CN108147507A. In this patent application, sodium hydroxide and cobalt nitrate are added to water at a molar ratio of 4:1 and transferred to a reaction kettle, and a carbon substrate material is added thereto. The reaction is carried out at 150 °C for 5 hours, and after washing and drying multiple times, a carbon material electrode loaded with cobalt tetroxide is obtained. Using this as the cathode, a photoelectrode with visible light catalytic activity is used as the anode, visible light with a wavelength greater than 420 nm is used as the photocatalytic light source, 1.0 - 10.0 mM of electrolyte is added, 0.2 - 20.0 mM of persulfate is added, and an external bias voltage of 0.1 - 2.0 V is applied through a potentiostat or a DC power supply, and the treatment time is 30 - 120 minutes. However, unfortunately, the specific carbon material is not disclosed in this patent. At the same time, when using it as the cathode, a relatively complex treatment system is still required, such as constructing the cathode and anode, visible light irradiation, etc. Summary of the Invention

[0005] 1. Object of the Invention

[0006] The object of the present invention is to provide a preparation method and application of a transition metal cobalt loaded graphene aerogel. In this transition metal cobalt loaded graphene aerogel, the transition metal cobalt is mainly in the form of Co 3 O 4 nanoclusters loaded in the graphene sheets. Using it as a catalyst to catalyze the degradation of organic pollutants such as antibiotics by peracetic acid shows excellent degradation performance.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solutions adopted in the present application are as follows:

[0009] The present application provides a transition metal cobalt loaded graphene aerogel, which includes a graphene substrate with a sheet structure and Co 3 O 4 nanoclusters loaded on the graphene sheets. The particle size of the above Co 3 O 4 nanoclusters is 30 - 60 nm.

[0010] Further, for the above transition metal cobalt loaded graphene aerogel, the particle size of Co 3 O 4 nanoclusters is 30 - 35 nm.

[0011] Further, for the above transition metal cobalt loaded graphene aerogel, the pore size of the aerogel includes 200 - 250 μm.

[0012] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the pore size of the aerogel is 205 - 230 μm.

[0013] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the peak pore size of the aerogel is 227 μm.

[0014] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the cobalt loading is 1 - 10 wt%.

[0015] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the cobalt loading is 3 - 10 wt%.

[0016] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the cobalt loading is 5 - 10 wt%.

[0017] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the cobalt loading is 8 - 10 wt%.

[0018] Further, for the above-mentioned transition metal cobalt-loaded graphene aerogel, the cobalt loading is 8 wt%.

[0019] This application also provides a preparation method of the above-mentioned transition metal cobalt-loaded graphene aerogel. The method includes using graphene oxide as the aerogel precursor, using transition metal cobalt as the modified metal precursor, adding thiourea and then performing heat reduction, performing supercritical drying after cooling, and finally performing high-temperature reduction to obtain the transition metal cobalt-loaded graphene aerogel.

[0020] Further, the preparation method of the above-mentioned transition metal cobalt-loaded graphene aerogel includes the following steps:

[0021] Mix the graphene oxide solution with the transition metal cobalt precursor solution, add thiourea after stirring, continue stirring for 20 - 30 h and then heat at 80 - 90 °C for 3 - 5 h; perform supercritical drying for 20 - 30 h after cooling; raise the temperature to 400 - 800 °C at a heating rate of 4 - 6 °C / min in a nitrogen atmosphere and calcine for 2 - 3 h to obtain the Co 3 O 4 nanocluster-loaded graphene aerogel.

[0022] Further, the above-mentioned metal cobalt precursor solution is cobalt acetate tetrahydrate solution.

[0023] Further, in the above-mentioned preparation method, continue stirring for 24 h and then heat at 85 °C for 4 h; perform supercritical drying for 24 h after cooling; raise the temperature to 700 °C at a heating rate of 5 °C / min in a nitrogen atmosphere and calcine for 2 h.

[0024] Further, in the above preparation method, relative to a 10 mL system, the concentration of graphene oxide is 2 - 4 mg / mL; the mass ratio of thiourea to graphene oxide is 4% - 10%.

[0025] Further, in the above preparation method, relative to a 10 mL system, the concentration of graphene oxide is 3 mg / mL; the mass ratio of thiourea to graphene oxide is 8%.

[0026] The present application also provides an application of the above-mentioned transition metal cobalt-loaded graphene aerogel in catalyzing the degradation of antibiotics in a target solution by peracetic acid.

[0027] Further, in the above application, the pH of the target solution is 5 - 11.

[0028] Further, in the above application, the pH of the target solution is 7 - 11.

[0029] Further, in the above application, the pH of the target solution is 9 - 11.

[0030] 3. Beneficial effects

[0031] Compared with the prior art, the beneficial effects of the present application are as follows:

[0032] (1) For the transition metal cobalt-loaded graphene aerogel provided by the present application, the transition metal cobalt is stably bonded to the graphene sheets in the form of cobalt tetroxide nanoclusters through coordination bonding and Π-Π interactions, etc. The graphene matrix provides good strength and reduces the leaching of cobalt metal; the cobalt tetroxide nanoclusters serve as active sites and can accelerate the formation of peracetic acid free radicals from peracetic acid. This transition metal cobalt-loaded graphene aerogel has a relatively large pore size (200 - 250 μm). During the application process, when the reaction medium is adsorbed into the pores and on the surface of the aerogel, the mass transfer rate can be increased, thereby improving the overall reaction kinetics.

[0033] (2) The preparation method of the transition metal cobalt-loaded graphene aerogel provided by this application uses graphene oxide as the aerogel precursor and transition metal cobalt as the modified metal precursor. After adding thiourea, heating reduction is carried out, followed by supercritical drying after cooling, and finally high-temperature reduction to obtain the transition metal cobalt-loaded graphene aerogel. The addition of thiourea not only provides strong reducibility but also sufficient N atoms to form coordination with transition metal cobalt. There is a strong attraction between the negatively charged nitrogen atoms and metal cobalt, and metal cobalt ions can easily enter the structure of the graphene sheet layer; the carbon defects generated on the graphene aerogel sheet layer after high-temperature calcination can coordinate and covalently bond with cobalt ions. The obtained transition metal cobalt-loaded graphene aerogel, such as Co8GAT, exhibits uniformly and densely loaded metal active sites, and the size of the cobalt tetroxide nanoclusters is small, significantly improving its surface activity and catalytic performance. The graphene aerogel promotes the electron conduction and catalytic reaction of cobalt tetroxide through its unique porous structure and excellent conductivity.

[0034] (3) The application of the transition metal cobalt-loaded graphene aerogel provided by this application has high stability, catalytic activity, and recyclability. The degradation rate of tetracycline antibiotics remains as high as over 90% after 5 cycles. The stability is due to the fact that after adding cobalt ions to graphene oxide, N atoms are introduced through hydrothermal reduction with the addition of thiourea, providing an N source for better contact between Co ions and the graphene sheet layer. Subsequently, intermolecular water is removed through supercritical drying technology, resulting in the formation of a graphene aerogel with macropores. Then, through high-temperature calcination, Co ions are bonded to the vacancies of the graphene sheet layer, further improving the cobalt loading stability. Coupled with the certain strength of the graphene aerogel itself, in the degradation of flowing water devices, it not only remains intact and has a high degradation rate but also does not produce heavy metal pollution; the catalytic activity benefits from the presence of cobalt tetroxide nanoclusters on the surface. The exposure of cobalt ions provides more abundant active sites for the catalytic reaction, and can instantaneously generate peracetic acid radicals when in contact with peracetic acid. At the same time, the rich pore structure and the local "space confinement effect" formed by the conductivity significantly promote the mass transfer rate between the antibiotic and the active species; combined with the fact that the aerogel is a three-dimensional block solid with strong compressive and anti-deformation properties, it is more conducive to recycling compared to the powder state catalyst and can still be reused after one degradation. Description of the Drawings

[0035] Figure 1 are the SEM, TEM, and HRTEM images of Co8GAT and GAT, where: a-c are the SEM images of GAT at different magnifications; d-f are the SEM images of Co8GAT at different magnifications; g is the HRTEM image of Co8GAT; h-i are the EDS mapping images and element mappings of Co8GAT.

[0036] Figure 2 Raman spectra of Co8GAT, Co8GOT and GAT.

[0037] Figure 3 Fourier transform infrared spectra of Co8GAT, Co8GOT and GAT.

[0038] Figure 4 XPS spectra of C, N, and S elements of Co8GAT, Co5GAT, Co3GAT, Co1GAT, and Co8GOT, where: (a) C 1s; (b) N 1s; (c) S2p.

[0039] Figure 5 XPS spectra of Co and O elements of Co8GAT, Co5GAT, Co3GAT, Co1GAT, and Co8GOT: where: (a) Co 2p; (b) O 1s.

[0040] Figure 6 Electrochemical performance test diagrams of Co8GAT and GAT, where: (a) Current-time curve; (b) Nyquist impedance diagram.

[0041] Figure 7 BET data diagrams of Co8GAT, Co8GOT and GAT.

[0042] Figure 8 Results of the degradation kinetics analysis of tetracycline hydrochloride in different reaction systems, where: (a) Degradation curves of TCH in different systems, (b) Fitting of the degradation rate constants of TCH in different systems, (c) Histogram of the first-stage reaction rates in different systems.

[0043] Figure 9 Degradation curves of different tetracycline antibiotics in the Co8GAT / PAA system.

[0044] Figure 10 Fitting of the degradation rates of different tetracycline antibiotics in the Co8GAT / PAA degradation system.

[0045] Figure 11 Effect of different calcination temperatures on the degradation performance during high-temperature reduction, where: (a) Degradation effect diagram; (b) Fitting of the degradation rate constant; (c) Reaction rate histogram; (d) Dissolution concentration of Co ions.

[0046] Figure 12 Effect of different Co doping ratios on the degradation performance, where: (a) Degradation effect diagram; (b) Fitting of the degradation rate constant; (c) Reaction rate histogram; (d) Dissolution concentration of Co ions.

[0047] Figure 13are the TCH degradation kinetics at different pH values, where: (a) degradation effect diagram; (b) fitting of degradation rate constant; (c) reaction rate histogram.

[0048] Figure 14 is the histogram of the degradation effect of TCH under the condition of different anions in the Co8GAT / PAA system.

[0049] Figure 15 are the kinetic fittings of the degradation effect of TCH under the condition of different anions in the Co8GAT / PAA system, where: (a) fitting of degradation rate constant; (b) reaction rate constant.

[0050] Figure 16 is the intermediate product path diagram of TCH degradation under the Co8GAT / PAA system.

[0051] Figure 17 is the toxicity heat map of the acute toxicity of the intermediate product to three aquatic organisms under the Co8GAT / PAA system.

[0052] Figure 18 is the degradation effect diagram of TCH when the Co8GAT / PAA system is reused 5 times.

[0053] Figure 19 is the degradation effect diagram of TCH in the Co8GAT / PAA system in different real water bodies. Detailed implementation manners

[0054] The following further describes the present application in combination with specific embodiments.

[0055] It should be noted that the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the convenience of narration and are not used to limit the scope of implementation. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art belonging to the technical field of the present application; the term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0057] For those not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0058] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. Those skilled in the art can easily determine the degree of flexibility of a specific variable.

[0059] As used herein, the term "at least one of..." is intended to be synonymous with "one or more of...". For example, "at least one of A, B, and C" expressly includes only A, only B, only C, and their respective combinations.

[0060] Concentrations, amounts, and other numerical data may be presented herein in a range format. It should be understood that such range formats are used merely for convenience and brevity and should be interpreted flexibly as including not only the numerical values explicitly recited as the limits of the range, but also all individual numerical values or sub-ranges subsumed within that range, as if each numerical value and sub-range were explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted as including not only the explicitly recited limits of 1 to about 4.5, but also the individual numbers (such as 2, 3, 4) and sub-ranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges reciting only one numerical value, such as "less than about 4.5", which should be interpreted as including all of the above values and ranges. In addition, this interpretation should apply regardless of the breadth of the range or feature being described.

[0061] In this application, unless otherwise specified, the solvent in the solution involved is ultrapure water.

[0062] In this application, unless otherwise specified, as in Example 10, Co8GAT refers to Co8GAT prepared in Example 1.

[0063] In this application, graphene oxide (GO) can be obtained by purchasing commercially or prepared by oneself. As an example, this application provides a method for preparing graphene oxide using natural graphite powder according to the modified Hummers method, including the following steps:

[0064] (1) Graphite pre-oxidation: Add 120 mL of concentrated sulfuric acid to a conical flask, heat it in a water bath to 80 °C, then add 25 g of K 2 S 2 O 8 , 30 g of graphite powder, and 25 g of P 2 O 5 , and stir magnetically at 80 °C until evenly mixed, and keep the reaction for 4.5 hours; after the sample in the mixed solution is cooled to room temperature, add 4 L of ultrapure water in 3 portions for suction filtration and washing, stop washing until the supernatant is neutral, and put the solid sample in an oven at 60 °C to dry;

[0065] (2) Preparation of graphene oxide: First, add 10 g of NaNO 320 g of pre-oxidized graphite was added to 460 mL of concentrated sulfuric acid that had been pre-cooled to 4 °C. The mixture was magnetically stirred in an ice bath for 30 min (the temperature was maintained below 4 °C). Subsequently, 60 g of KMnO 4 powder was slowly added to the mixture. The temperature of the water bath was adjusted to 35 °C and maintained for 2 h. After 2 h, 920 mL of ultrapure water was slowly added to the reaction solution, and the temperature was adjusted to 98 °C and maintained for 15 min. Subsequently, another 920 mL of ultrapure water was added for dilution. After the reaction solution cooled to room temperature, 54 mL of H 2 O 2 was added, and the mixture was stirred evenly and left to stand overnight. The supernatant of the sample left standing overnight was removed, and then the water was vacuum-filtered to dryness. The sample was continuously suction-filtered and washed 5 - 6 times with 10% HCl (about 8 L) until the lower-layer filtrate was detected to have no SO 2 present by 0.1 M BaCl 4 2- . Then, it was washed with ultrapure water until it was about neutral to remove the excess acid. Subsequently, it was centrifuged at 8000 - 10000 rpm for 20 min to remove the supernatant. The collected sample was sonicated for 30 min under the condition of 250 HZ (80%). Subsequently, the sample was collected into a dialysis bag and dialyzed for two weeks to obtain the original graphene oxide solution. Subsequently, the original solution was diluted with ultrapure water, and its concentration was measured to obtain the original graphene oxide solution (GO) (concentration: 6.32 mg / mL).

[0066] In this application, unless otherwise specified, the antibiotic degradation kinetics experiments were all carried out under simulation in the laboratory. The degradation reaction was carried out in a 100 mL glass beaker at room temperature (25 °C ± 1 °C). Taking TCH as an example, Co8GAT was placed in 50 mL of a TCH solution with a concentration of 10 mg / L, and a magnetic rotor was placed in the reaction beaker to make the reaction proceed under stirring at a constant rotation speed (250 r / min). The purpose of this operation was to simulate water body flow and verify the strength of the aerogel at the same time. First, it was adsorbed for 30 minutes to ensure that the pollutant solution and the aerogel reached the adsorption / desorption equilibrium at room temperature. Then, 0.5 mM PAA was added as the starting point for the catalytic degradation reaction. During the degradation process, at certain time intervals (-30 min, 0 min, 0.5 min, 3 min, 5 min, 7 min, 10 min, 15 min, 20 min, 30 min), 1 mL of the reaction solution was sampled with a pipette and 1 mL of methanol was added for quenching. Finally, the mixed sample was filtered through a 0.22 μm filter membrane and loaded into a liquid-phase vial for high-performance liquid chromatography (HPLC) analysis. The dissolution of Co ions during the reaction of the aerogel was tested by an atomic absorption spectrophotometer.

[0067] In this application, unless otherwise specified, the reuse experiments were also carried out by simulation in the laboratory. First, the reuse performance of a single aerogel was verified. Under room temperature conditions, a 50 mL degradation system was used as a group, and each group was equipped with a pollutant solution containing 10 mg / L TCH. The aerogel was placed into the first group of pollutant solutions, and the adsorption time was 30 min to ensure that the pollutant solution and the aerogel reached the adsorption / desorption equilibrium at room temperature. Then, 0.5 mM PAA solution was added as the zero point of the catalytic reaction. Subsequently, at certain intervals (-30 min, 0 min, 0.5 min, 3 min, 5 min, 7 min, 10 min, 15 min, 20 min, 30 min), 1 mL of the reaction solution was sampled with a pipette, and 1 mL of methanol was added for quenching. The mixed samples were filtered through a 0.22 μm filter membrane and loaded into liquid-phase vials for high-performance liquid chromatography (HPLC) analysis. The dissolution concentration of Co ions was detected using an atomic absorption spectrophotometer. This operation was one cycle. After the first cycle ended, the aerogel was taken out and directly placed into the second group of systems for degradation with PAA. A total of 5 cycles were carried out. The reuse experiment can evaluate the reuse effect and anti-interference ability of the aerogel, and at the same time evaluate the degradation effect of TCH during 5 cycles of reuse and the dissolution of Co ions during the entire cycle process.

[0068] In this application, unless otherwise specified, a scanning electron microscope (SEM, ZEISS Sigma 300, Germany) and a transmission electron microscope (TEM, JEOL JEM-F200, Japan) were used to observe the microstructure and morphology of the aerogel; X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, USA), Raman spectroscopy (Raman, HoribaLabRAM HR Evolution, Japan), and Fourier transform infrared spectroscopy (FT-IR, USA) were used to analyze the chemical composition and structure of the aerogel samples; an automatic surface area and pore size analyzer (BET, Micromeritics ASAP 2460, USA) was used to analyze the specific surface area and pore size distribution of the samples; a high-performance liquid chromatograph (UPLC, Waters e2695, USA) was used to quantitatively analyze the concentration of pollutants during the entire degradation reaction process; an LC-QTOF-MS system (AB Sciex, CAN) was used to detect degradation intermediates; the ECOSAR software (version 2.2) was used to predict the acute and chronic toxicity of TCH and the degradation intermediates found in fish, daphnia, and algae. As an example:

[0069] Scanning Electron Microscope (SEM): The sample to be measured was precisely fixed on the nano-carbon glue substrate by means of cutting and pasting. After gold spraying treatment, precise tests were carried out at 100 nm, 200 nm, 500 nm, 1 μm, 2 μm, 5 μm, 10 μm, 50 μm and 100 μm to deeply observe the surface morphology and internal pore structure of the aerogel;

[0070] Transmission Electron Microscope: Before the detection, the Co8GAT sample was first ground and dispersed evenly to enable it to be stably suspended in the alcohol solution; after the treatment, the dispersion showed an almost colorless and transparent state; then the dispersion was dropped onto the carbon film of the microgrid and dried under infrared irradiation, and finally the microscope test was carried out; the lattice fringes and EDS diffraction rings of the Co metal nanoparticles were observed respectively at the electron microscope resolutions of 1.05MxCamera and 660mm Camera, and the crystal structure of the cobalt oxide could be further analyzed; in addition, by performing an EDS energy spectrum scan (81000x SI) on the Co8GAT material, the existence of elements such as carbon (C), oxygen (O), nitrogen (N) and cobalt (Co) in the material was verified and established;

[0071] Fourier Transform Infrared Spectroscopy: High-purity potassium bromide was selected, and Co8GAT, Co8GOT and GAT were mixed with potassium bromide in a mass ratio of 1:100 and ground, and then pressed into tablets; the whole experimental process was carried out under the illumination of a fluorescent lamp to avoid the absorption of moisture by potassium bromide; finally, the treated sample was put into the FT-IR instrument for testing.

[0072] In this application, unless otherwise specified, high performance liquid chromatography was used to detect the target pollutants. As an example: The instrument was equipped with an XDB-C18 chromatographic column (250 mm × 4.6 mm, 5 μm) and an E2695 ultraviolet detector, and the HPLC analysis methods for different pollutants are shown in the following table ×

[0073]

[0074] In this application, unless otherwise specified, the intermediate products generated during the degradation of TCH in the Co8GAT / PAA system were analyzed by LC-QTOF-MS. Based on the peak data at specific time points, the Tic detection products at each time point were inferred. As an example, reversed-phase chromatographic columns (Acquity UPLC HSS T3 column, 2.1 mm × 100 mm, particle size 1.8 μm; Acquity UPLC BEH C18 column, 2.1 mm × 100 mm, particle size 1.8 μm) were used for chromatographic analysis; data collection was carried out by electrospray ionization (ESI) technology in both positive and negative modes, with a total collection cycle of 1.25 seconds, covering IDA and TOF scans; the parameter settings for full TOF scans were: mass range m / z 50 - 1000, collision energy (CE) of -10 eV, focusing voltage (DP) set at -60 eV, and accumulation time of 150 ms; IDA scans were performed in high-sensitivity mode, with the set parameters: mass range m / z 50 - 1000, CE of -35 eV, CE spread (CES) of 25 eV, DP of -60 eV, and accumulation time of 70 ms; the specific elution program, mobile phase scheme, and ion source information are shown in the following table:

[0075]

[0076] In this application, unless otherwise specified, the quantitative structure-activity relationship (QSAR) model in ECOSAR (version 2.2) was used to predict the acute and chronic toxicity of TCH and its degradation intermediate products. As an example: Based on the LC50 and EC50 concentration values of the intermediate products for three aquatic organisms, namely fish, green algae, and water fleas, the acute and chronic toxicity of the intermediate products were evaluated. Given that some complex chemical substances may contain multiple functional groups, resulting in certain differences in their LC50, EC50, and ChV values, the lowest estimated value was selected as the basis for toxicity assessment in this study. According to the Globally Harmonized System of Classification and Labelling of Chemicals, toxicity is classified into four grades: highly toxic (K ≤ 1 mg / L), toxic (1 mg / L < K ≤ 10 mg / L), harmful (10 mg / L < K ≤ 100 mg / L), and non-harmful (K > 100 mg / L), where K represents the concentration.

[0077] Example 1

[0078] This example provides a preparation method of Co 3 O 4 nanocluster-loaded graphene aerogel and the prepared Co 3 O 4 nanocluster-loaded graphene aerogel.

[0079] Co 3 O 4Preparation method of nano-cluster loaded graphene aerogel, and its preparation schematic diagram is as shown in Figure 1 Taking a 10 mL system as an example, where: the concentration of GO is 3 mg / mL, Co ions are added according to the doping ratio, and the mass ratio of thiourea (TU) to GO is 8%. The specific steps are as follows:

[0080] Mix 4.75 mL of graphene oxide stock solution (6.32 mg / mL) with 4.25 mL of cobalt acetate tetrahydrate (Co(CH 3 CO 2 )) 2 ·4H 2 O) (2.28 mg / mL) precursor solution, stir magnetically for 2 h, then add 1 mL of the prepared thiourea (TU) (2.4 mg / mL) solution, and continue to stir for 24 h;

[0081] After stirring, take 1 mL each and put it into a digestion tube with a volume of 10 mL; heat it in a water bath at 85 °C for 4 h; after natural cooling to room temperature, wash it with ultrapure water for 20 h, changing the water 3 times in the middle; after washing, put it in the refrigerator at -4 °C for pre-freezing for 3 h, and then put it into a freeze dryer, and perform supercritical drying at a sublimation temperature of -40 °C and a vacuum of 0.1 Torr for 24 h; at this time, the aerogel that has not been thermally reduced is named Co8GOT;

[0082] After freeze-drying, heat it in a nitrogen (N 2 ) atmosphere at a heating rate of 5 °C / min to 700 °C and calcine for 2 h to obtain Co 3 O 4 nano-cluster loaded graphene aerogel, with a mass of about 1.8 - 2.0 mg / each, the doping amount of Co is 8 wt%, and the existing form of cobalt is Co 3 O 4 nano-clusters (Co 3 O 4 NCs), named Co8GAT.

[0083] Example 2

[0084] This example provides a preparation method of Co 3 O 4 nano-cluster loaded graphene aerogel and the prepared Co 3 O 4 nano-cluster loaded graphene aerogel.

[0085] The preparation method refers to Example 1, the difference is that the concentration of cobalt acetate tetrahydrate is 0.285 mg / mL, and the doping amount of Co in the prepared Co 3 O 4 nano-cluster loaded graphene aerogel is 1 wt%, named Co8GAT. Correspondingly, the aerogel that has not been thermally reduced is named Co1GOT.

[0086] Example 3

[0087] This example provides Co 3 O 4 A preparation method of cobalt nanocluster-loaded graphene aerogel and the prepared Co 3 O 4 Cobalt nanocluster-loaded graphene aerogel.

[0088] The preparation method refers to Example 1, except that the concentration of cobalt acetate tetrahydrate is 0.855 mg / mL, and the doping amount of Co in the prepared Co 3 O 4 Cobalt nanocluster-loaded graphene aerogel is 3 wt%, named Co3GAT. Correspondingly, the aerogel without high-temperature reduction is named Co3GOT.

[0089] Example 4

[0090] This example provides Co 3 O 4 A preparation method of cobalt nanocluster-loaded graphene aerogel and the prepared Co 3 O 4 Cobalt nanocluster-loaded graphene aerogel.

[0091] The preparation method refers to Example 1, except that the concentration of cobalt acetate tetrahydrate is 1.425 mg / mL, and the doping amount of Co in the prepared Co 3 O 4 Cobalt nanocluster-loaded graphene aerogel is 5 wt%, named Co5GAT. Correspondingly, the aerogel without high-temperature reduction is named Co5GOT.

[0092] Example 5

[0093] This example provides Co 3 O 4 A preparation method of cobalt nanocluster-loaded graphene aerogel and the prepared Co 3 O 4 Cobalt nanocluster-loaded graphene aerogel.

[0094] The preparation method refers to Example 1, except that the concentration of cobalt acetate tetrahydrate is 2.85 mg / mL, and the doping amount of Co in the prepared Co 3 O 4 Cobalt nanocluster-loaded graphene aerogel is 3 wt%, named Co10GAT. Correspondingly, the aerogel without high-temperature reduction is named Co10GOT.

[0095] Comparative Example 1

[0096] This example provides the preparation of graphene aerogel without loading transition metal cobalt.

[0097] Referring to Example 1, the difference is that in the preparation process, cobalt acetate tetrahydrate precursor solution is not added, and graphene aerogel without loading transition metal cobalt is prepared and named GAT.

[0098] Example 7

[0099] This example provides the characterization of graphene aerogel loaded with Co 3 O 4 nanoclusters.

[0100] In this example, characterization methods such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical tests were used to evaluate the surface composition, structural characteristics, and chemical properties of the materials.

[0101] (1) Microscopic morphology analysis

[0102] The microscopic morphology and structure of the materials were studied by SEM and TEM, as Figure 1 shown.

[0103] First, SEM characterization analysis was performed on Co8GAT and GAT. By observing the material surface at different magnifications, the structural differences between GAT and Co8GAT can be compared and analyzed. GAT was observed at SEM magnifications of (100 nm, 2 μm, and 50 μm) ( Figure 1 a-c in). The surface structure of the GAT sample at the nanoscale can be seen, with a relatively smooth surface and fewer details, which is in line with the characteristics of materials without adding transition metal Co. At a larger scale, the microstructure of GAT is more obvious, showing a more fibrous structure, but without the typical cobalt oxide nanocluster characteristics in Co8GAT ( Figure 1 d in). At an even larger scale, GAT shows relatively uniform pores or large-scale structures, with a pore size of approximately 120.4 μm and a relatively smooth overall structure, in contrast to the complex structure of Co8GAT. The Co8GAT sample shows more obvious nanoparticle characteristics compared to GAT. Figure 1 The 33.6 nm and 32.7 nm marked in d in indicate the presence of cobalt oxide nanoclusters, proving that the Co ions provided by the cobalt acetate tetrahydrate precursor were initially loaded onto the graphene sheets through hydrothermal reduction at 85 °C and supercritical drying treatment, and then successfully loaded into the sheet structure of the graphene aerogel through high-temperature thermal reduction, forming Co 3 O 4Nanoclusters. At the same time, Co8GAT exhibits a relatively complex fibrous structure at the microscale, and the introduction of cobalt may have affected the morphology of the material ( Figure 1 in e). At a larger scale, Co8GAT still shows a relatively complex pore structure. Compared with the GAT sample, the surface is more irregular, and the pore diameter of the aerogel becomes larger, with most pore diameters above 200 μm, further proving the existence of cobalt oxide clusters ( Figure 1 in f). Moreover, during the application process, the ultra-large pore diameter in the graphene aerogel significantly promotes the mass transfer rate between antibiotics and reactive species and interacts with the cobalt tetroxide nanoclusters.

[0104] Secondly, the HRTEM image shows the lattice fringes of cobalt oxide nanoclusters (Co 3 O 4 NCs) ( Figure 1 in g), with a width of 0.22 nm. By comparing the fringe spacing with the PDF card information of cobalt tetroxide, it is obtained that this lattice fringe belongs to the (222) diffraction plane of cobalt tetroxide, proving the crystal structure of these clusters. This figure also further confirms the existence of cobalt oxide clusters in Co8GAT.

[0105] To verify the formation of Co 3 O 4 NCs again, EDS mapping and elemental mapping were performed on Co8GAT ( Figure 1 in h and i). Through the EDS image, three diffraction rings in Co8GAT can be seen. According to the PDF card information, they respectively correspond to the three diffraction rings ((311), (220), and (111)) of Co 3 O 4 NCs, which is consistent with the reported situation in the literature. The elemental mapping diagram shows the elemental distributions of C (red), O (yellow), N (green), and Co (blue). Especially in the region where Co and O overlap, the formation of cobalt oxide clusters can be seen. The distribution of cobalt (Co) and oxygen (O), and the coincidence of their signals verify the formation of Co 3 O 4 NCs.

[0106] In summary, without cobalt, GAT presents a relatively simple morphology, while Co8GAT shows a more complex structure with nanoclusters, especially at the nanoscale and microscale. This is also the main difference in their microtopographies. The addition of cobalt changes the structure and elemental composition of the material, and cobalt oxide clusters are formed on the surface of Co8GAT, namely Co 3 O 4When used as a catalyst for antibiotic degradation, NCs provide sufficient active sites for the formation of active free radicals by the oxidant.

[0107] (2) Raman spectroscopy

[0108] The Raman spectra of Co8GAT, Co8GOT, and GAT are as Figure 2 shown, showing the Raman spectral curves of the three samples in the Raman shift (800 - 2000 cm -1 ) region. By comparing their peak characteristics, especially the intensity ratio between the D peak and the G peak (I D / I G ), the respective defect conditions can be revealed.

[0109] Co8GAT (blue curve) shows a lower intensity ratio of the D peak to the G peak (I D / I G = 0.878), indicating fewer defects in the material. The lower I D / I G ratio usually means that the structure of the material is relatively complete, with fewer lattice defects in the carbon-based material, or the defects are modified by the presence of cobalt. The D peak and G peak in the Raman spectrum are clear and of moderate intensity, indicating that the structure of Co8GAT has a good degree of graphitization. The introduction of cobalt may help reduce the defect density in the material while enhancing the graphitized structure, thus improving its electrical conductivity and mechanical properties. Since Co8GAT is obtained after high-temperature thermal reduction of Co8GOT (red curve), the high-temperature thermal reduction in the N 2 gas atmosphere during this process promotes the further graphitization of the material structure and reduces the number of defects.

[0110] The I D / I G ratio of Co8GOT is higher than that of Co8GAT, indicating more defects in its material. Compared with Co8GAT, Co8GOT contains more oxides or other irregular structures. And the high defect density of Co8GOT leads to a decrease in the electrical conductivity of the material.

[0111] GAT (black curve) is a control aerogel without the addition of cobalt, and its I D / I G = 0.882 ratio is between Co8GAT and Co8GOT, indicating that GAT has relatively fewer defects but still more than Co8GAT. In the Raman spectrum, the graphitization degree of GAT is not as good as that of Co8GAT but still higher than that of Co8GOT, indicating that the GAT material is relatively more complete with fewer defects but lacks the modification of cobalt elements.

[0112] In summary, Co8GAT has the best structural stability and lower defect density compared to GAT and Co8GOT, indicating that the introduction of cobalt and the high-temperature thermal reduction process promoted the graphitization of the carbon-based material, thereby improving its structural stability. After the hydrothermal reduction of thiourea and the reaction of cobalt at high temperature, Co was better combined onto the graphene sheets, reducing the defects. The role of cobalt helped to eliminate some amorphous carbon structures and promoted a more ordered graphite structure, resulting in a lower I D / I G ratio. Therefore, Co8GAT shows obvious advantages in electrical conductivity, mechanical properties, and thermal stability, etc.

[0113] (3) Fourier transform infrared spectroscopy

[0114] The characteristic peaks of Fourier transform infrared spectroscopy ( FTIR) can be used for qualitative and semi-quantitative analysis, helping to identify the functional groups, chemical structures of unknown substances in the material, as well as the chemical reaction process, and can also evaluate the purity of the analyte.

[0115] The Fourier transform infrared spectra of Co8GAT, Co8GOT, and GAT are as shown in Figure 3 Figure [X], and the three materials all show similar characteristic peaks. First, a broad peak appears at Figure [X], which is usually related to the presence of water molecules or hydroxyl groups, indicating that the material surface contains a certain amount of adsorbed water or oxides. Second, the peaks at 2925 cm -1 and 2855 cm -1 are small peaks generated by the asymmetric and symmetric stretching vibrations of C-H, which are related to the C functional groups introduced during the graphene reduction process. Among them, the intensity of the C-H absorption peak of Co8GAT is relatively obvious, indicating that the material contains more organic functional groups or hydrocarbon structures, and the presence of cobalt affects the distribution and intensity of these organic functional groups. Third, the peak at 1630 cm -1 is generated by the C═C stretching vibration on the graphene surface, which is the C═C stretching deformation vibration caused by the water molecules adsorbed between the graphene sheets. The stretching vibration peak of C═C reflects the presence of certain graphitized or organic carbon in the material, indicating that Co8GAT has a certain ordered carbon structure, which corresponds to its lower I D / I G ratio in the Raman spectrum, showing its relatively ordered structure. Finally, the small peaks that appear at 400 - 500 cm -1 for Co8GAT and Co8GOT indicate the vibration of the Co-O bond, indicating that Co is successfully loaded onto the graphene sheets in the form of Co 3 O 4 .

[0116] In summary, the excellent performance of Co8GAT in the FTIR spectrum, especially the appearance of the Co-O absorption peak, indicates that the introduction of cobalt not only promotes the formation of cobalt oxides but also improves their structural stability and graphitization degree. This endows Co8GAT with remarkable advantages in terms of electrical conductivity, mechanical strength, and thermal stability. In contrast, due to incomplete reduction of cobalt and a higher defect density, Co8GOT exhibits inferior performance compared to Co8GAT, and the loading of Co is extremely unstable and prone to shedding, causing heavy metal pollution to the water environment. GAT, on the other hand, shows a relatively simple structure and low catalytic efficiency as a control material.

[0117] (4) X-ray photoelectron spectroscopy

[0118] To detect the differences in the functional groups of different elements in the materials and the influence of high-temperature thermal reduction on material preparation, XPS photoelectron spectroscopy analysis was performed on Co8GAT, Co5GAT, Co3GAT, Co1GAT, and Co8GOT. The existing forms of the functional groups of C, N, and S in the five materials were analyzed, and the results are as Figure 4 shown.

[0119] First of all, the XPS spectra of the C element in all five materials show typical peaks of carbon ( Figure 4 a in it). The characteristic peak appearing at 284.6 eV belongs to C═C, which represents the carbon-carbon double bond in the graphene substrate. C-O-C (286.0 eV) represents the carbon-oxygen bond present in graphene oxide. As the addition amount of Co increases (from Co1GAT to Co8GAT), the intensity of C-O-C gradually weakens, indicating a decrease in the oxidation degree of the graphene substrate, while the intensity of C═C gradually increases, indicating a more complete and ordered structure of graphene. In Co8GOT, C═O (about 288.0 eV) is mainly the carbon atom of oxygen-containing functional groups such as ketones or aldehydes, and O-C═O (about 289.0 eV) usually comes from carboxyl groups (-COOH) or other oxygen-containing functional groups. This also proves that the oxygen-containing functional groups in Co8GOT are reduced during high-temperature calcination, and at the same time, the stability and integrity of the material are increased. Especially in Co8GAT, due to the process of high-temperature thermal reduction, the oxygen groups in the graphene oxide substrate are removed, so the peak intensity of C═C is the strongest.

[0120] Secondly, the XPS spectra of the N element and S element were analyzed ( Figure 4In b and c), three different forms of nitrogen can be seen, corresponding to different functional groups respectively. The characteristic peak signal of pyridine nitrogen appears at 398.0 eV. Pyridine nitrogen is usually located at the edge of graphene. Pyrrole nitrogen (about 399.5 eV) is usually related to the cyclic structure. Graphitic nitrogen (about 401.0 eV) is usually the nitrogen atom connected to carbon in graphene, forming an N-C bond. In different materials, the proportions of the three types of nitrogen will vary, and with the increase of the Co addition amount, the contents of these nitrogens will change. In Co1GAT, the proportion of pyridine nitrogen is relatively low, the proportion of pyrrole nitrogen is relatively high, and the proportion of graphitic nitrogen is at a medium level. In Co5GAT and Co3GAT, the proportion of pyridine nitrogen will gradually increase, and the proportion of graphitic nitrogen will also increase, indicating that the addition of cobalt improves the nitrogen incorporation and forms more pyridine nitrogen and graphitic nitrogen. In Co8GAT, the proportions of pyridine nitrogen and pyrrole nitrogen decrease, and the proportion of graphitic nitrogen is relatively high. It may be that with the increase of the Co addition amount, the graphitization degree of the material by high-temperature reduction treatment is enhanced, which indicates that the structure of graphene is more stable, and the nitrogen incorporation helps to enhance the electrochemical performance of the material; the appearance of the S element is because thiourea was added during the material preparation process for the hydrothermal reaction to preliminarily reduce graphene oxide, so the S element in the material comes from thiourea. The formation of the S-C bond (about 163.0 eV) indicates that S is also successfully doped into the graphene aerogel. Also because of the addition of Co, an S-Co bond appears in all 5 materials, and there is also the possibility of formation under hydrothermal reaction conditions, so that Co can better adhere to the graphene sheet layer during the subsequent high-temperature thermal reduction step to form Co 3 O 4 NCs provides tensile force. The peak of sulfate or sulfite appearing at about 168.0 eV is the sulfur-containing oxide functional group formed during the high-temperature thermal reduction process. Co8GAT shows the richest sulfur-containing functional groups, especially the presence of S-Co, indicating that its surface has the closest interaction with cobalt, which helps to improve its catalytic performance.

[0121] To further verify the existence of Co 3 O 4 NCs in the aerogel material and analyze other possible existing functional groups, the XPS spectra of Co and O elements in the 5 materials are analyzed, as Figure 5 shown.

[0122] First, the XPS spectra of Co elements in the 5 materials are analyzed ([[]] Figure 5 in a). The XPS spectrum of Co usually shows two main peaks centered at Co 2+ (about 780.0 eV) and Co 3+ (about 795.0 eV). Their signal sources are related to Co in NCs 2+ and Co3+ Secondly, the XPS spectra analysis of the O element ( Figure 5 b) in. The peak appearing at about 532.0 eV belongs to the C-O bond (or O-C=O) of the oxidized carboxyl group or other oxygen-containing functional groups. At the same time, the peak signal of C=O (about 533.0 eV) appears corresponding to the spectrum of the C element, representing oxygen-containing functional groups such as ketones or aldehydes. The peak of Co-O (about 530.0 eV) represents the Co 3 O 4 -O bond in Co 2+ and Co 3+ NCs. As the addition amount of Co increases, the peak intensities of Co 2+ and Co 3+ will gradually increase, indicating an increase in the content of cobalt and the formation of cobalt oxides. In Co8GAT, the content of Co is the highest, so the signals of Co 3 O 4 are the strongest. As the addition amount of Co increases, from Co1GAT to Co8GAT, the peaks of O-C and C=O will gradually weaken, and the peak of Co-O will gradually increase, indicating that the oxygen groups of graphene oxide in the material gradually decrease, while the formation of Co oxides increases. Especially in Co8GAT, the O element mainly shows the form of Co-O, which indicates that after high-temperature reduction treatment, the formation of Co

[0123] NCs is an important feature of Co8GAT.

[0123] In summary, the high-temperature thermal reduction treatment significantly improves the ordered structure of graphene and enhances the electrical conductivity of graphene by reducing oxygen groups. The high-temperature treatment also promotes the formation of Co 3 O 4 , which provides better active sites for catalytic reactions. Co8GAT has a high Co content and the formation of Co oxides, which gives it obvious advantages in catalytic performance and electrochemical performance. The incorporation method and proportion of nitrogen in Co8GAT are also more conducive to improving the electrochemical performance of the material. Especially the proportion of graphitic nitrogen is relatively high, which helps to enhance the electrical conductivity and catalytic activity. Through these analyses, Co8GAT is superior to other materials in terms of structural stability, electrochemical performance, and catalytic activity. Especially the Co 3 O 4 NCs formed during the high-temperature thermal reduction process provide enhanced support for its performance.

[0124] (5) Electrochemical characterization

[0125] This application also conducts electrochemical tests on Co8GAT and GAT to explore the influence of the addition of Co on the performance of the aerogel material. The results are as Figure 6 shown.

[0126] First, chronoamperometry tests were conducted on Co8GAT and GAT. Figure 6 As shown in a), the chronoamperometry curves (i-t curves) of Co8GAT and GAT show the current changes of the two materials at different times. Tetracycline hydrochloride (TCH) was added at 100 s, and peracetic acid (PAA) was added at 200 s to simulate the current changes in the PAA catalytic degradation system. As can be seen from the figure, the initial current of Co8GAT is higher and it maintains high stability during the response process. Especially in the later stage of the reaction, the current remains at a high level. After 200 s, the current rebounds rapidly. Compared with Co8GAT, the current change of GAT is relatively slow, and during the reaction process, the current fails to maintain at a high level, showing lower catalytic activity. Thus, it can be seen that the current response of Co8GAT is faster and more stable, indicating that it has better activity and stability in the catalytic reaction. This is because the Co 3 O 4 NCs loaded in Co8GAT can effectively promote the electrochemical reaction, while GAT lacks the active sites of cobalt oxide.

[0127] Subsequently, the electrochemical impedance of Co8GAT and GAT was also tested to examine the charge transfer resistance and diffusion characteristics of the materials ( Figure 6 as shown in b). The horizontal axis of the electrochemical impedance spectroscopy (EIS) diagram is the real part impedance, and the vertical axis is the imaginary part impedance. As can be seen from the figure, the impedance of Co8GAT in the low-frequency band is significantly higher than that of GAT. This is because the introduction of Co 3 O 4 NCs increases the diffusion resistance of the system, but the charge transfer resistance (related to the width of the approximate semicircle) in the high-frequency band is smaller than that of GAT, indicating faster charge transfer. The impedance curve of GAT shows lower impedance values throughout the frequency range, indicating lower electron and ion diffusion resistance, but its charge transfer resistance is slightly higher than that of Co8GAT.

[0128] In summary, the presence of Co 3 O 4 NCs in Co8GAT provides rich active sites for the catalytic reaction, promoting the reaction rate and efficiency. Co8GAT shows a higher current response in the current-time curve, indicating that its catalytic reaction is more active. Moreover, Co8GAT has a lower charge transfer impedance, indicating better conductivity and a more efficient charge transfer process. Co8GAT shows high stability in the electrochemical test and can maintain a high current level, indicating good stability during long-term use, which gives it an advantage in practical catalytic applications.

[0129] (6) Specific surface area and pore size analysis

[0130] Specific surface area analysis can determine the adsorption characteristics and specific surface area of materials. In this application, BET tests were conducted on Co8GAT, Co8GOT, and GAT, and the results are as Figure 7 shown.

[0131] First, from the data in the figure, it can be seen that the adsorption capacity of Co8GAT (red curve) increases rapidly with the increase of relative pressure. Especially when approaching P / P 0 = 1, it shows a large specific surface area and pore volume. At a relatively low relative pressure (P / P 0 <0.2), the adsorption capacity of Co8GAT is relatively stable, indicating that it has a large microporous structure; as the pressure increases, the adsorption capacity increases rapidly, which indicates that this material has a large macroporous structure at higher pressures and can adsorb more gas. The adsorption capacities of Co8GOT (blue curve) and GAT (green curve) are less than that of Co8GAT. Although Co8GOT also shows a certain adsorption capacity, its pore structure and specific surface area are much lower than those of Co8GAT, which limits its performance in catalytic reactions.

[0132] Secondly, Co8GAT shows a significant specific surface area, which can provide more reaction sites. Especially the increase in adsorption capacity under high pressure is obvious, indicating that it has a good pore structure (both micropores and macropores). This structure provides more surface areas for catalytic reactions, thereby enhancing its catalytic activity. Compared with Co8GOT and GAT, Co8GAT has more excellent adsorption performance and pore structure, especially showing better gas adsorption capacity under high pressure. This characteristic enables Co8GAT to more effectively provide reaction sites and adsorb substances in catalytic reactions, improving catalytic performance.

[0133] In summary, due to its large specific surface area, rich pore structure, and better gas adsorption performance, Co8GAT demonstrates obvious advantages in catalytic reactions.

[0134] Example 8

[0135] This example provides an analysis of the catalytic performance of Co 3 O 4 nanocluster-loaded graphene aerogel.

[0136] In this example, TCH was used as a probe chemical substance, and multiple different reaction systems were compared. A two-stage calculation method was adopted, and through pseudo-first-order reaction kinetics, the degradation rate constant k of each reaction system was calculated and fitted. By comparing the reaction rate magnitudes in the first stage, the degradation effects of all systems were explored, and the results are as Figure 8 shown.

[0137] In this example, the reaction system was 50 mL, the TCH concentration was 10 mg / L, the PAA concentration was 0.5 mM, the pH was 9, and the Co8GAT / GAT was 36 mg / L.

[0138] The results showed that in the Co8GAT / PAA / TCH system, 81% of TCH was degraded within the first 5 minutes of the degradation start at a reaction rate of 2.99 min -1 . During the subsequent 25-minute degradation time, the overall degradation rate reached 91%; while in the GAT / PAA / TCH system, the degradation efficiency of TCH only reached 61%, and the reaction rate in the first stage was 1.23 min -1 ; meanwhile, it could be observed that TCH hardly had self-degradation properties in the natural state. In the Co8GAT / TCH system, the adsorption removal rate in 60 minutes was approximately 20.5%, and only 9% in the first thirty minutes, which indicated that catalytic degradation was the main mechanism for removing TCH, and the doping of transition metal Co could indeed improve the catalytic effect. The reason was that the activation ability of graphene aerogel without metal loading for PAA was limited, while the incorporation of metal Co could significantly improve the utilization rate of PAA. In particular, the formation of Co 3 O 4 NCs in the graphene sheets of Co8GAT provided surface active sites and a large specific surface area, thus significantly improving the degradation effect on TCH. In contrast, in the commercially available cobalt ferrite (Co 3 O 4 -C) / PAA / TCH system, the catalytic degradation effect of TCH only reached 79% within 30 minutes, which also indicated that graphene aerogel as a substrate provided attachment sites for Co 3 O 4 NCs, and at the same time further provided a large specific surface area and pore size for activating PAA, and the two complemented each other. Further compared with the PAA / TCH system, in this system, the degradation rate of TCH was only 52%, and the reaction rate was also only half of that in the Co8GAT / PAA / TCH system. This could fully illustrate the advantages of Co-loaded graphene aerogel in terms of degradation rate and reaction rate. The reason was that Co8GAT had a high specific surface area and pore structure, and Co 3 O 4 NCs in the graphene sheets could effectively promote the mass transfer rate and activate PAA, and the reaction effect was significantly better than that of the homogeneous solution.

[0139] Example 9

[0140] This example provides an analysis of the degradation performance of Co 3 O 4 nanocluster-loaded graphene aerogel on different tetracycline antibiotics.

[0141] To evaluate the catalytic degradation effect of Co8GAT on different tetracycline pollutants ( Figure 9 ), a reaction system of Co8GAT / PAA and different pollutants was constructed. The selected pollutants included doxycycline (DOC), tetracycline (TC), oxytetracycline (OTC), minocycline (MCH), oxytetracycline hydrochloride (OHCL), and TCH. In this example, the reaction system was 50 mL, the concentrations of DOC, TC, OTC, MCH, OHCL, and TCH were all 10 mg / L, the PAA concentration was 0.5 mM, the pH was 9, and the Co8GAT was 36 mg / L.

[0142] The degradation curves of different tetracycline antibiotics in the Co8GAT / PAA system are as Figure 9 shown. From the results in the figure combined with the piecewise pseudo-first-order kinetic fitting ( Figure 10 ), it can be seen that in the Co8GAT / PAA system, the first-stage degradation rate constants of DOC and MCH were 5.62 min -1 and 6.78 min -1 respectively, and both could be completely degraded within 30 minutes. TC (3.79 min -1 ), OTC (2.97 min -1 ), and TCH (2.99 min -1 ) were all degraded by nearly 90%, and OHCL (3.02 min -1 ) was also degraded by 82%. This result indicates that the Co8GAT / PAA system exhibits good degradation effect, greatly promotes the degradation process of tetracycline antibiotic pollutants, and shows excellent catalytic oxidation and selective pollutant removal capabilities.

[0143] It can also be seen from the piecewise kinetic fitting image that the degradation reaction rate is extremely fast. Free radicals are generated immediately when the Co 3 O 4 nanocluster-loaded graphene aerogel contacts with PAA to degrade pollutants, which can reflect the advantages of the Co8GAT / PAA system.

[0144] Example 10

[0145] This example provides a study on the effect of the temperature of high-temperature reduction on the catalytic performance of Co 3 O 4 nanocluster-loaded graphene aerogel.

[0146] Referring to Example 1, the temperatures of high-temperature reduction were adjusted to 300, 400, 500, 600, and 700 °C respectively to prepare Co 3 O 4 nanocluster-loaded graphene aerogel.

[0147] In this example, the reaction system is 50 mL, the TCH concentration is 10 mg / L, the PAA concentration is 0.5 mM, the pH is 9, and the Co8GAT is 36 mg / L.

[0148] Co prepared at different temperatures 3 O 4 The degradation results of the nanocluster-loaded graphene aerogel are as Figure 11 shown.

[0149] From Figure 11 a in, it can be obtained that as the calcination temperature increases, the degradation effect of the system shows a trend of first decreasing and then increasing. Co8GAT calcined at 300 °C fails to achieve complete loading of Co due to the low temperature. From the dissolution data ([[]] Figure 11 d in), although the reaction rate of the first stage (3.75 min -1 ) is faster than that at 700 °C, the concentration of dissolved Co ions exceeds 1 mg / L, causing secondary pollution to the water environment. In contrast, Co8GAT calcined at 700 °C shows the best degradation effect and a safe Co ion dissolution concentration, indicating that Co 3 O 4 nanoclusters are successfully formed on the graphene sheets of Co8GAT under this condition, with excellent catalytic performance. The reaction rate constants of Co8GAT calcined at 400 °C to 600 °C ([[]] Figure 11 b and c in) are lower than those of Co8GAT calcined at 700 °C, probably because the temperature is not high enough and Co ions on the graphene sheets are still not completely reduced and polymerized to form Co 3 O 4 nanoclusters, and the reaction sites are wrapped by other functional groups, affecting the degradation effect.

[0150] Example 11

[0151] This example provides a study on the effect of Co loading in Co 3 O 4 nanocluster-loaded graphene aerogel on its catalytic performance.

[0152] In this example, the reaction system is 50 mL, the TCH concentration is 10 mg / L, the PAA concentration is 0.5 mM, the pH is 9, and the Co8GAT is 36 mg / L.

[0153] The results of the effect of different Co doping ratios on the degradation performance are as Figure 12 shown. As the core active component of Co8GAT, the doping amount of the transition metal Co has a significant effect on its catalytic degradation performance. As Figure 12As shown in a), with the increase of the doping ratio of transition metal Co, the catalytic degradation activity of the CoXGAT / PAA (X = 1, 3, 5, 8, 10) system continuously improves. When the added mass ratio of transition metal Co reaches 8.0 wt%, the best degradation effect of TCH is achieved within 30 min. At this time, the degradation reaction rate is the highest ( Figure 12 in b and c), reaching 2.99 min-1, which is significantly higher than other doping ratios. However, when the doping amount is further increased to 10.0%, the degradation efficiency decreases due to the saturation of active sites. At the same time, the Co ion dissolution of the materials with 5 doping ratios was monitored ( Figure 12 in d), and all reached the safety standards (Discharge Standard of Pollutants for Copper, Nickel and Cobalt Industries GB25467-2010).

[0154] Example 12

[0155] This example provides a study on the effect of the initial pH of the solution on the catalytic performance of Co 3 O 4 nanocluster-loaded graphene aerogel.

[0156] In this example, the reaction system was 50 mL, the TCH concentration was 10 mg / L, the PAA concentration was 0.5 mM, the pH was 3, 5, 7, 9, 11, and the Co8GAT was 36 mg / L.

[0157] By adjusting the initial pH value of the reaction solution to 3, 5, 7, 9, 11, it was found that with the increase of the pH value, the degradation effect of the Co8GAT / PAA system on TCH gradually increased ( Figure 13 in a). When the pH value was 11, the highest reaction rate in the first stage could reach 4.15 min-1 ( Figure 13 in b and c). Compared with the degradation rate at pH = 3, the catalytic effect under alkaline conditions was significantly increased. The results show that the catalytic performance of the reaction was relatively stable in the pH range of 5.0 - 11.0. It should be noted that the best TCH degradation effect was observed at pH = 11, and degradation was inhibited at pH = 3. The reason for this phenomenon may be that metal oxides such as Co 3 O 4 NCs are prone to protonation (-OH 2 + ) of surface hydroxyl groups (-OH) at low pH, resulting in a positively charged surface. And THC (pKa1≈3.3, pKa2≈7.7) exists in the form of cations (THC + ) under acidic conditions, generating electrostatic repulsion with the positive charge on the catalyst surface, inhibiting adsorption and interfacial reactions. Moreover, the passivation of the catalyst or the ineffective decomposition of PAA caused by strong acidic conditions reduces the degradation efficiency. At high pH, Co 3 O 4The surface of NCs is deprotonated (-O - ), becoming negatively charged, while THC is deprotonated into a neutral or anionic form (THC 0 / THC - ), enhancing the electrostatic attraction and promoting the adsorption and catalytic reaction.

[0158] Secondly, PAA (pKa≈8.2) exists in a protonated form under acidic conditions with relatively high stability, but the efficiency of activating to generate free radicals (such as ·OH, CH 3 C(O)O · ) is relatively low. In addition, Co 3+ is easily reduced to Co 2+ in an acidic environment, but the rate of regenerating to Co 3+ is slow, resulting in the obstruction of the catalytic cycle. At high pH, PAA is deprotonated to CH 3 COOO - , which is more easily activated by Co 3 O 4 NCs to generate reactive oxygen species (ROS), including ·OH, O 2 - and 1 O 2 , thereby accelerating the degradation of THC. The alkaline environment can also promote the oxidation of Co 2+ to Co 3+ , maintaining the catalytic activity. Moreover, THC is prone to form cations at low pH, and some structures (such as phenolic hydroxyl groups) are protonated, reducing its reactivity. In addition, acidic conditions trigger the hydrolysis side reaction of THC, generating more difficult-to-degrade intermediate products. However, after deprotonation at high pH, it is more easily attacked by ROS, especially the oxidative ring-opening reactions of aromatic rings and amino groups are more efficient. Finally, Co 3 O 4 is structurally stable in an alkaline medium, and a Co-OOH active layer is formed on the surface, enhancing the catalytic activity.

[0159] Example 13

[0160] This example provides a study on the influence of inorganic ions in solution on the catalytic performance of Co 3 O 4 nanocluster-loaded graphene aerogel.

[0161] In this example, the reaction system is 50 mL, the TCH concentration is 10 mg / L, the PAA concentration is 0.5 mM, the pH is 9, the Co8GAT is 36 mg / L, humic acid (HA), SO 4 2- , H 2 PO 4 - , HCO 3- , Cl - , NO 3 - The concentrations are all 0.5 mM.

[0162] The bar chart of the degradation effect of TCH under the presence of different anions or humic acid in the Co8GAT / PAA system is as Figure 14 shown. It can be seen from the figure that, compared with the control group, first of all, humic acid has a certain inhibitory effect. This may be because HA competes with pollutants for reaction sites and also competes with active species, thus reducing the removal effect on pollutants. In addition, studies have shown that humic acid aggregates will deposit in the macroporous structure of graphene aerogel, resulting in a decrease in adsorption performance and further affecting the catalytic degradation effect. Secondly, the inhibition of SO 4 2- is due to its influence on the reduction potential of O 2 ·- , thus inhibiting the degradation of TCH.

[0163] The remaining H 2 PO 4 - , HCO 3 - , Cl - and NO 3 - have a promoting effect on degradation when present. By fitting the two-stage degradation rate constants of the degradation data ( Figure 15 a)), comparing the reaction rate constants of the first stage, it can be seen that the instantaneous reaction rates of H 2 PO 4 - and HCO 3 - are twice as high as that of the control group. This is because H 2 PO 4 - can form a coordination complex with the Co active site (such as Co-O-PO 3 ), change the surface electronic structure of the catalyst, enhance the polarization breaking efficiency of the O-O bond in the PAA molecule, and thus increase the generation rate of CH 3 C(O)O · . At the same time, phosphate stabilizes CH 3 C(O)O · in the solution through hydrogen bonding or electrostatic interaction, delays its self-quenching, and prolongs the reaction life, so it has a promoting effect on the degradation of TCH. The catalytic promoting effect of HCO 3 - may be that HCO 3 - can react with O 2·- The reaction generates CO with a higher oxidation potential 3 ·- (E 0 = 1.78 V), and it has a selective attacking ability especially for the aromatic ring of tetracycline. As Figure 15 shown in b of - Figure - also has a certain promoting effect, probably because 3 is oxidized by CH · C(O)O · to generate active chlorine species such as Cl · 、ClO 2 ·- and so on, which form a synergistic oxidation network with the original free radicals, expanding the pollutant attack sites.

[0164] In summary, the Co8GAT / PAA system still has an efficient TCH degradation effect in an environment with complex anions, and for some anions, it has a promoting effect on the reaction rate. This also proves the stability of the system and its high selective catalytic ability.

[0165] Example 14

[0166] This example provides a study on the toxicity of the intermediate products during the degradation of TCH under the Co8GAT / PAA system.

[0167] In this example, the reaction system was 50 mL, the TCH concentration was 10 mg / L, the PAA concentration was 0.5 mM, the pH was 9, and the Co8GAT was 36 mg / L.

[0168] By using LC-QTOF-MS to detect the intermediate products during the degradation of TCH in the Co8GAT / PAA system, the degradation path of the intermediate products during the degradation of TCH in this system was obtained, as Figure 16 shown. According to the TIC peak data at different time points, the product types corresponding to each time point can be judged. The structural analysis of the products mainly depends on the high-precision mass measurement results provided by the TOF analyzer. The mass spectrometry analysis results showed that a total of 12 intermediate products of TCH degradation were detected.

[0169] During the degradation process, TCH experienced the following three paths: (1) In Path 1, first, free radicals such as CH 3 C(O)O · remove the amino group (-NH 2) The group is then further attacked by active free radicals to generate P1 (m / z = 403), which then further decomposes to generate P4 (m / z = 387), and finally P7 (m / z = 318) is obtained by C-C bond cleavage; (2) Path two is to form P2 (m / z = 416) through a demethylation reaction. Subsequently, a hydrogenation reaction occurs at the C-C site in P2, and the C=C double bond in P2 is attacked by free radicals such as CH 3 C(O)O · etc., resulting in the cleavage of the benzene ring and finally generating the product P8 (m / z = 215); (3) TCH is attacked by free radicals such as CH 3 C(O)O · etc., and a ring-opening reaction with deamination occurs to generate P3 (m / z = 391). Through the oxidative cleavage of the benzene ring, P6 (m / z = 272) and P9 (m / z = 218) are formed, and finally further reaction gives P10 (m / z = 218). The intermediate products obtained in the above three steps are further oxidized and decomposed to obtain small molecule products such as P11 (m / z = 130) and P12 (m / z = 173), and finally decomposed into H 2 O, CO 2 etc.

[0170] Subsequently, the ECOSAR software (version 2.2) was used to analyze the toxicity of the intermediate products in the Co8GAT / PAA reaction system, and the results are as Figure 17 shown. Through the existing data of quantitative structure-activity relationship (QSAR), the acute and chronic toxicities of the intermediate products were analyzed (Table 1). According to the Globally Harmonized System of Classification and Labelling of Chemicals, toxicity is divided into four grades: highly toxic (K ≤ 1 mg / L), toxic (1 mg / L < K ≤ 10 mg / L), harmful (10 mg / L < K ≤ 100 mg / L), and harmless (K > 100 mg / L), where K represents the concentration. TCH has a certain chronic harmfulness (10 mg / L < K ≤ 100 mg / L) in the water environment. During the degradation process, the toxic intermediate products generated will be rapidly oxidized and destroyed, thus reducing the overall toxicity. Generally speaking, the Co8GAT / PAA reaction system reduces the ecological toxicity of TCH, and the toxicity is reduced by about 100 times. Through Figure 17 the toxicity scatter plot and heat map in, it can be seen that product P12 is non-toxic, and multiple products are harmless.

[0171] Table 1 Summary of toxicity prediction of TCH and its degradation intermediate products

[0172]

[0173]

[0174] Example 15

[0175] This example provides a study on the reusability of Co8GAT.

[0176] In this example, the reaction system is 50 mL, the TCH concentration is 10 mg / L, the PAA concentration is 0.5 mM, the pH is 9, and the Co8GAT is 36 mg / L.

[0177] To evaluate the reusability and stability of Co8GAT to realize its practical application value, 5 cyclic degradation experiments of TCH were carried out, and the results are as Figure 18 shown. Without changing the conditions, the 5 degradation data show that the Co8GAT / PAA system still maintains a high degradation effect after 5 cycles. During the 30-min degradation time, the degradation rate of TCH remains above 90%. This also proves that the use of TU-reduced graphene oxide and supercritical drying provides sufficient mechanical strength for the preparation of Co8GAT, and also provides a solid base for the loading of Co 3 O 4 NCs, making the material have good stability and reusability, and providing support for its practical application.

[0178] Example 16

[0179] This example provides a study on the degradation of TCH by the Co8GAT / PAA system in different real waters.

[0180] In this example, the real waters include tap water, river water and industrial wastewater; the reaction system is 50 mL, the TCH concentration is 10 mg / L, the PAA concentration is 0.5 mM, the pH is 9, and the Co8GAT is 36 mg / L.

[0181] The degradation effect of the Co8GAT / PAA system on TCH in different real waters is as Figure 19 shown. It can be seen from the figure that the Co8GAT / PAA system shows excellent degradation effects in all three different waters. Among them, in the tap water and river water environments, the instantaneous degradation rate does not decrease but increases, which is consistent with what is mentioned in the above text of this application that there are complex coexisting ions in the water, and many of these ions have a promoting effect on the degradation of the system. Comparing the degradation effects in industrial wastewater, there are certain inhibitions in both the adsorption and degradation effects, but the overall degradation effect also reaches 79%. The reason may be that some organic acids contained in industrial wastewater can block the pore structure of the graphene aerogel, reduce the adsorption of PAA, and inhibit the generation of active free radicals. In summary, the Co8GAT / PAA system can still show excellent catalytic degradation effects under various complex water quality conditions.

Claims

1. A transition metal cobalt-loaded graphene aerogel, characterized in that: The aerogel comprises a graphene substrate and Co3O4 nanoclusters supported on graphene sheets, and the particle size of the Co3O4 nanoclusters is 30-60nm.

2. The transition metal cobalt-loaded graphene aerogel according to claim 1, characterized in that: The particle size of the Co3O4 nano clusters is 30-35 nm.

3. A transition metal cobalt-loaded graphene aerogel according to claim 1 or 2, characterized in that: The pore size of the aerogel is 200-250 μm.

4. The transition metal cobalt-loaded graphene aerogel according to claim 3, characterized in that: The cobalt loading amount comprises 1 to 10 wt %.

5. A method for preparing transition metal cobalt-loaded graphene aerogel, characterized in that: The method comprises the steps of using graphene oxide as an aerogel precursor, using transition metal cobalt as a modified metal precursor, adding thiourea, performing heating reduction, cooling, performing supercritical drying, and finally performing high-temperature reduction to obtain transition metal cobalt-loaded graphene aerogel.

6. The preparation method according to claim 5, characterized in that: The preparation method comprises the following steps: The graphene oxide solution is mixed with the transition metal cobalt precursor solution, thiourea is added after stirring, and the stirring is continued for 20 to 30 hours, and then heated at 80 to 90°C for 3 to 5 hours; after cooling, supercritical drying is performed for 20 to 30 hours; the temperature is increased to 400 to 800°C at a heating rate of 4 to 6°C / min in a nitrogen atmosphere, and fired for 2 to 3 hours to obtain Co3O4 nanocluster-loaded graphene aerogel.

7. The preparation method according to claim 6, characterized in that: In the preparation method, the concentration of graphene oxide is 2-4 mg / mL relative to 10 mL of the system; and the mass ratio of thiourea to graphene oxide is 4%-10%.

8. The preparation method according to claim 6 or 7, characterized in that: In the preparation method, the metal cobalt precursor solution is a cobalt acetate tetrahydrate solution.

9. Use of the transition metal cobalt-loaded graphene aerogel according to any one of claims 1 to 4 in catalyzing the degradation of antibiotics in a target solution by peracetic acid.

10. The use according to claim 9, characterized in that: The pH of the target solution is 5-11.

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