A thermal annealing tetragonal metal nanocomposite and its preparation method and application

Abstract

The present invention provides a thermally annealed tetragonal metal nanocomposite and its preparation method and application. Using dimethylformamide (DMF) as a ligand, the tetragonal metal nanocomposite qMNC is synthesized by a solvothermal method, and then the thermally annealed tetragonal metal nanocomposite qMNC@600 is obtained by calcining the tetragonal metal nanocomposite qMNC. The thermally annealed tetragonal metal nanocomposite has an irregular spherical structure with pores on the spherical outer surface. The thermally annealed tetragonal metal nanocomposite has a particle size of 300 - 350 nm, a surface area of 40 - 45 m<supgt;2< / supgt> / g, an average pore diameter of 20 - 25 nm, and a pore volume of 0.30 - 0.35 cm<supgt;3 / g. The qMNC@600 has excellent effects on treating dyes with a concentration of 10 - 100 mg / L, the decolorization rate can reach more than 94%, and the colority can be reduced to 60 - 90 times, having good industrial practicability.

Description

Technical Field

[0001] The present invention belongs to the technical fields of material preparation and environmental protection, and particularly relates to a thermally annealed tetragonal metal nanocomposite material, a preparation method thereof, and an application thereof. Background Art

[0002] Industrialization helps to improve productivity and facilitate access to basic goods and services, but the processing of raw materials into finished products generates a large amount of waste, including some toxic waste. If the toxic waste is not pretreated, it will have an impact on the environment, especially water bodies. It is estimated that more than 900 new pollutants from the petrochemical, agro-industrial, textile, pharmaceutical, and personal care product industries have been detected in aquatic ecosystems. Among them, the textile and dye industries are considered the main sources of water pollution because of the abundance and broad spectrum of dyes required for textile and paper processing. Synthetic dyes have problems such as being difficult to biodegrade, having the ability to bioaccumulate, and having a carcinogenic effect on organisms, which have a greater impact on human health and the environment. Therefore, dyes need to be treated.

[0003] Currently, the main methods for treating wastewater include photolysis, biodegradation, chemical precipitation, precipitation, filtration, adsorption, catalysis, electrochemical reduction, and ion exchange, etc. Through the above methods, dyes are chelated or mineralized into oxidation end products. Due to the complexity and structural diversity of dyes, the existing dye wastewater treatment methods all have certain limitations. For example, the treatment efficiency of the biological method with lower cost is limited to a certain extent, and it has certain requirements for the environment; the separation efficiency of the membrane separation method is high, but the operating cost is high, and there are problems of membrane fouling and replacement; the oxidation method has a high conversion rate, but its cost is high and the operation is complex; the electrochemical method has controllable and high treatment efficiency, but there are problems of high energy consumption and equipment maintenance. Catalytic treatment is considered an effective, reliable, and cost-effective tool for completely removing and mineralizing organic and inorganic pollutants, especially for removing and mineralizing from wastewater. It is based on the in-situ generation of free electrons or strong oxidative free radicals with dominant and non-selective capabilities to convert toxic substances into non-toxic or low-toxic substances, thereby eliminating pollutants in wastewater. However, the current catalysts have a long catalytic consumption time, low catalytic efficiency, and a single type of dye for catalytic degradation. Therefore, there is a need to provide a catalyst that can efficiently, quickly, and promote the color change of various dyes after catalysis under stable conditions. Summary of the Invention

[0004] In view of some deficiencies in the existing technology, the present invention provides a thermally annealed tetragonal metal nanocomposite and its preparation method and application; in the present invention, dimethylformamide (DMF) is used as a ligand, and a tetragonal metal nanocomposite qMNC is synthesized by a solvothermal method, and then the tetragonal metal nanocomposite qMNC is calcined to obtain a thermally annealed tetragonal metal nanocomposite qMNC@600; the qMNC@600 has an irregular spherical structure with pores on the outer surface of the sphere; the particle size of the thermally annealed tetragonal metal nanocomposite is 300-350 nm, the surface area is 40-45 m 2 / g, the average pore diameter is 20-25 nm, and the pore volume is 0.30-0.35 cm 3 / g; the qMNC@600 has excellent effects on treating dyes with a concentration of 10-100 mg / L, the decolorization rate can reach more than 94%, and the color degree can be reduced to 60-90 times, having good industrial practicability.

[0005] In order to solve the above technical problems, the present invention adopts the following technical means:

[0006] The present invention first provides a thermally annealed tetragonal metal nanocomposite, which has an irregular spherical structure with pores on the outer surface of the sphere; the particle size of the thermally annealed tetragonal metal nanocomposite is 300-350 nm, the surface area is 40-45 m 2 / g, the average pore diameter is 20-25 nm, and the pore volume is 0.30-0.35 cm 3 / g.

[0007] The present invention also provides a preparation method of the above thermally annealed tetragonal metal nanocomposite, which specifically includes the following steps:

[0008] (1) Preparation of the tetragonal metal nanocomposite qMNC;

[0009] Dissolve cobalt, chromium, iron, and nickel sources in a metal-organic ligand solvent to obtain solution A containing four metal solutions; dissolve benzene-1,3,5-tricarboxylic acid in a metal-organic ligand solvent to obtain solution B; mix solution A and solution B evenly and then carry out a solvothermal reaction, and after the reaction is completed, wash, centrifuge, and dry to obtain the tetragonal metal nanocomposite qMNC;

[0010] (2) Thermally annealed tetragonal metal nanocomposite:

[0011] Calcine the tetragonal metal nanocomposite qMNC at a high temperature, and after the calcination is completed, obtain the thermally annealed tetragonal metal nanocomposite qMNC@600.

[0012] Preferably, in step (1), the cobalt source includes cobalt nitrate and its hexahydrate (cobalt nitrate and Co(NO3)2·6H2O);

[0013] the chromium source includes chromium chloride and its hexahydrate (CrCl3 and CrCl3·6H2O);

[0014] the iron source includes iron chloride and its trihydrate (FeCl3 and FeCl3·6H2O);

[0015] the nickel source includes nickel acetate and its tetrahydrate (Ni(CH3COO)2 and Ni(CH3COO)2·4H2O).

[0016] Preferably, in solution A of step (1), the molar ratio of the cobalt source, chromium source, iron source, and nickel source is 1:1:1:1; the concentrations of the cobalt source, chromium source, iron source, and nickel source are 5 - 10 mM;

[0017] in solution B, the final concentration of benzene - 1,3,5 - tricarboxylic acid is 100 - 200 mM.

[0018] Preferably, in step (1), in the metal - organic ligand solvent, the metal - organic ligand includes dimethylformamide.

[0019] Preferably, in step (1), the volume ratio of solution A to solution B is 2:1.

[0020] Preferably, in step (1), the conditions of the solvothermal reaction are: high - pressure steam reaction at 180°C for 15 - 20 hours.

[0021] Preferably, in step (2), the tetragonal metal nanocomposite qMNC is gradually heated to 300°C at a stable rate of 2°C / minute, and then heated to 600°C at a rate of 5°C / minute, with a heating time of 5 hours.

[0022] The present invention also provides the application of the above - mentioned thermally annealed tetragonal metal nanocomposite in adsorbing dyes.

[0023] Preferably, the dyes include one or more of Coomassie Brilliant Blue (CBB), Methyl Orange (MO), Allura Red (AR), Crystal Violet (CV), and Malachite Green (MG).

[0024] Preferably, after the thermally annealed tetragonal metal nanocomposite adsorbs the dye, it is centrifuged or magnetically adsorbed, dried at 40 - 60°C for 1 - 2 hours, washed with ethanol, then rinsed with distilled water, dried at 70°C for 1 hour, and renewed for the next catalytic cycle.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The thermally annealed tetragonal metal nanocomposite prepared by the present invention is an ordered coordination material synthesized conjugately with nickel as the node and dimethylformamide as the linker. In the thermally annealed tetragonal metal nanocomposite, there are first-row transition metals (Cr, Fe, Ni, Co), which have different coordination chemical properties and can tolerate a variety of organic connectors. The thermally annealed tetragonal metal nanocomposite has variable oxidation states, high abundance, low cost, low toxicity, and is easy to prepare.

[0027] (2) In the thermally annealed tetragonal metal nanocomposite of the present invention, Cr, as an element in the synthesis of the multi-metal nanocomposite, reduces sintering during the annealing process while improving the corrosion stability and catalytic performance of the nanocomposite. Cr has variability in oxidation states and interacts with certain metals such as cerium (Ce) to increase the proportion of lattice oxygen and improve its catalytic performance. In the hybrid nanocomposite, the interaction between Cr and cationic metals with similar oxidation properties can significantly improve the catalytic performance by accelerating the redox cycle of the material, thereby increasing the catalytic rate. Cobalt (Co), like Fe, exhibits reliable catalytic performance through a Fenton-like redox system or a photocatalytic system, can change oxidation states and decompose oxidants to generate reactive species, and has the ability to degrade pollutants. Nickel (Ni) metal is doped into the mixed metal nanocomposite as an electron-trapping co-catalyst to limit the possibility of electron-hole recombination, generate additional reaction sites to enhance material function. Ni, as a dopant, creates surface defects in the mixed nanocomposite, promotes the separation and transport of charges in the MMNC lattice, resulting in higher sensitivity. In addition, Ni also acts as a catalytic center to promote oxidation reactions by increasing the oxygen content on the catalyst surface, which is the key to forming alkoxides in the pseudo-Fenton reaction. qMNC@600 allows for functional diversity and the ability to act on different substrates, as well as the ability to generate different forms of free radicals for different targets, due to the differences in active sites within the same complex.

[0028] (3) In the thermally annealed tetragonal metal nanocomposite of the present invention, the organic ligand does not widely participate in the catalytic process but limits the quantity and availability of active sites. Therefore, the catalytic performance of the synthesized nanocomposite is fine-tuned by post-synthesis thermal annealing. In qMNC@600, the ligand is decomposed, leaving only the target metal, thereby improving the accessibility of the oxidant (H2O2) to the active sites to enhance the generation of free radicals. Therefore, qMNC@600 has high catalytic performance. This catalyst has a uniform distribution of catalytic sites and improved porosity, and at the same time has higher selectivity for the oxidant (H2O2).

[0029] (4) The qMNC@600 material used in the present invention has excellent effects on treating single or mixed dyes of Maxilon Brilliant Blue (CBB), methyl orange (MO), allura red (AR), crystal violet (CV) and malachite green (MG) with a concentration of 10 - 100 mg / L. For the dyes treated by the present invention, the concentration and color degree of the filtrate are significantly reduced, and the decolorization rate can reach more than 94%, and the color degree can be reduced to 60 - 90 times.

[0030] The qMNC@600 material described in the present invention can be reused multiple times with good repeatability. The qMNC@600 adsorbing dyes can be updated after each cycle by washing with ethanol and then drying at 60 - 100 °C before use, and can be reused, belonging to a green and environmentally friendly sewage treatment material.

[0031] (5) The qMNC@600 material described in the present invention has the abilities of rapidity, high removal rate, strong removal ability and removing multiple dyes. Compared with traditional materials, the qMNC@600 material can be directly used for catalytic decolorization of dyes without activation and pretreatment, solving the cumbersome pretreatment section of traditional adsorbents and reducing the operation cost of wastewater treatment. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the process preparation and catalytic principle of qMNC@600 described in the present invention.

[0033] Figure 2 It is a thermogravimetric analysis (A) of the synthesized qMNC, crystal structures (B), FIIR (C), BET surface area (D) and pore size (E) diagrams of qMNC and qMNC@600.

[0034] Figure 3 It is a scanning electron microscope diagram of qMNC (A1 - A3) and qMNC@600 (B1 - B3).

[0035] Figure 4 It is a diagram of the effects of pH (A), amount of hydrogen peroxide (H2O2) (B), amount of qMNC@600 (C) and dye concentration (D) on the catalytic efficiency of qMNC@600 for dyes.

[0036] Figure 5 It is a zero charge diagram of qMNC@600.

[0037] Figure 6 It is a diagram of the effects of temperature and time on the catalytic efficiency of qMNC@600 for dyes AR (A), CBB (B), CV (C), MG (D), MO (E).

[0038] Figure 7Efficiency diagrams of AR (A), CBB (B), CV (C), MG (D), and MO (E) dyes catalyzed by different catalytic combinations respectively.

[0039] Figure 8 Diagram of the color change rate of different mixed dyes at different times under the optimal pH; in the figure, A1 - D1 are AR + MG, and A2 - D2 are CB + CV + MO.

[0040] Figure 9 Diagram of the catalytic effect of mixed dyes at different initial concentrations (10, 30, 50, 70, and 100 mg / L); in the figure, A is CBB + CV + MO (pH 2), and B is AR + MG (pH 7).

[0041] Figure 10 Diagram of the reuse of qMNC@600 for dye catalysis.

[0042] Figure 11 Diagram of the reuse cycle of free radicals generated in dye - containing water without a catalyst; A1 - B1 are dye - containing waters of AR, CBB, CV, MG, and MO at 20 mg / L respectively; A2 - E2 are dye - containing waters of AR, CBB, CV, MG, and MO at 20 mg / L respectively.

[0043] Figure 12 Diagram of the effect of free radical scavengers (quenchers) on the inhibition of the catalytic color - change performance of qMNC@600.

[0044] Figure 13 Diagram of the generation and mechanism of intermediate alkoxy and hydrogen peroxide radical species mediated by the decomposition of H2O2 by qMNC@600. Detailed implementation mode

[0045] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0046] Example 1:

[0047] Figure 1 Schematic diagram of the preparation process of the tetragonal metal nanocomposite qMNC@600 according to the present invention. According to Figure 1 the steps, in this example, cobalt hexahydrate nitrate was used as the cobalt source, chromium hexahydrate chloride was used as the chromium source, iron(III) chloride trihydrate was used as the iron source, and nickel(II) acetate tetrahydrate was used as the nickel source to prepare the tetragonal metal nanocomposite qMNC@600. The specific preparation steps are as follows:

[0048] (1) Preparation of the tetragonal metal nanocomposite qMNC:

[0049] Dissolve 0.9 g of Co(NO3)2·6H2O, 0.8 g of CrCl3·6H2O, 0.82 g of FeCl3·6H2O, and 0.75 g of Ni(CH3COO-)2·4H2O in 40 mL of dimethylformamide to obtain solution A; dissolve 0.88 g of benzene-1,3,5-tricarboxylic acid in 20 mL of dimethylformamide to obtain solution B.

[0050] Mix solution A and solution B together and stir for 10 minutes, then transfer to a stainless steel with a polytetrafluoroethylene lining, and carry out a high-pressure reaction at 180 °C for 15 - 20 hours to synthesize a tetragonal metal nanocomposite (qMNC). Then wash with ethanol and distilled water until the detergent becomes colorless, and then carefully dry in a non-vacuum oven at 70 °C.

[0051] (2) Preparation of calcined tetragonal metal nanocomposite qMNC@600:

[0052] Gradually heat qMNC from room temperature to 300 °C at a stable rate of 2 °C / minute, and then heat to 600 °C at a rate of 5 °C / minute for annealing and calcining qMNC for 5 hours to obtain the final product qMNC@600.

[0053] Use a NETZSCH STA449 C thermogravimetric analyzer to perform thermogravimetric analysis (TGA) from 20 °C to 800 °C at a flow rate of 2 mL / min in a nitrogen atmosphere. The analysis results are as Figure 2 shown in A. In the detected temperature range, the mass loss is divided into 4 steps: in the first step, from 21 °C to 118 °C, the weight drops by about 11.44%, which is attributed to the loss of physically or chemically adsorbed water molecules; the second step is from 118 °C to 400 °C, the weight gradually drops, with a loss of about 12.86%, which is attributed to the start of the decomposition of organic ligands; the third step involves a weight loss of about 26.73% from 400 °C to 530 °C, which is due to the combustion and decomposition of metal ions and carboxylic acid residues, resulting in the release of gases such as H2O, CO2, and N2; the fourth step is that the weight gradually and steadily drops from 530 °C to 800 °C, with a weight loss of about 6.83%. It can be seen that the decomposition mode of qMNC is similar to that of MIL series MOFs. Since it is stable at 600 °C and above during calcination, annealing at 600 °C for 5 hours ensures the significant decomposition of organic ligands, increasing the number and availability of active sites for active metal ions and hydrogen peroxide to generate free radicals.

[0054] Use an X-ray diffractometer XRD-6100 to detect the 2θ angle from 10° to 80° of the prepared material. The detection results are as Figure 2As shown in Figure B. It can be seen from the figure that the XRD pattern of the synthesized qMNC shows sharp and intense peaks, confirming the formation of a highly crystalline material. The qMNC and qMNC@600 correspond to (111), (200), and (222), which are the presence of metals Cr (JCPDS No.: 01-1250), Fe (JCPDS NO: 01-1252), Ni (JCPDS No.: 01-1258), and Co (JCPDS No: 01-1255), as well as the possible presence of Ni-Cr-Fe (JCPDS NO.: 33-0945) and Ni-Fe (JCPD No.: 38-0419) complexes. After annealing, additional peaks were observed at 18.4°, 30.19°, 35.56°, 37.26°, 43.24°, 53.49°, 57.02°, 62.6°, and 74.42°, corresponding to (111), (220), (311), (222), (400), (422), (511), (440), and (253). These diffraction patterns are closely related to magnetite Fe3O4 (JCPDS No.: 01-1111), NiFe2O4 (JCPDSNo.: 44-1485), and CoCr2O4 (JCPDS No.: 78-0711), indicating that all metal elements are completely incorporated into the crystal structure of the synthesized and heat-treated metal nanocomposites.

[0055] The Fourier transform infrared (FT-IR) spectra of the materials were detected using a Nicolet Nexus 470 spectrometer (Nicola Corporation, USA), and the detection results are as Figure 2 shown in Figure C. It can be seen from the figure that the infrared spectrum of qMNC shows stretching vibrations with peaks at 3406 cm -1 , which is characteristic of the presence of the O-H group. The frequency vibration bands with peaks at 1630 cm -1 and 1564 cm -1 belong to the C-O bending of the carboxylic acid group, while the characteristic peaks at 1444 cm -1 and 1375 cm -1 are attributed to the symmetric and asymmetric vibrations of the carboxylic acid (COO-) group, respectively. The stretching vibration at 1044 cm -1 is also attributed to the benzene ring of the BTC linker. The vibration bands with peaks at 761 and 718 cm -1 are widely related to the bending vibration of the C-H bond of the benzene ring in the linker. The vibration at 463 cm -1 can indicate the presence of metal oxide vibrations. The observed IR spectrum of qMNC is the same as that of MOFs in the MIL series 36. In addition, the annealed nanocomposites show peaks at 609 and 480 cm -1A unique peak spectrum is shown at the frequency, which is characteristic of the formation and presence of metal oxide vibrations.

[0056] The nitrogen adsorption - desorption isotherms were measured using a NDVA - 2000e from Canta Instruments Inc (USA). The BET model and BJH model were used to calculate the surface area and pore size distribution of the materials respectively, and the results are as Figure 2 shown in Figures D and E. It can be seen from the figures that the surface areas of qMNC and qMNC@600 are 923.30 m 2 / g and 44.93 m 2 / g respectively, while the average pore diameters and pore volumes are 5.22 nm, 21.19 nm and 1.4 cm 3 / g, 0.301 cm 3 / g respectively. Compared with the specific surface area of qMNC, although the specific surface area of qMNC@600 is significantly reduced, the pore diameter increases, which is crucial for enhancing the easy diffusion and accessibility of the oxidant to the catalytic metal center.

[0057] The structural morphologies of qMNC and qMNC@600 were detected using a cold field emission scanning electron microscope. The microstructural and morphological results of qMNC and qMNC@600 are as Figure 3 shown. It can be seen from the figures that the prepared qMNC ( Figure 3 A1 - A3) and annealed qMNC@600 ( Figure 3 B1 - B3) exhibit a particulate structure with a grain size of approximately 340 nm. Except for the protrusion of the particles in the annealed material qMNC@600, no distinguishable morphological differences were observed from the SEM.

[0058] Example 2:

[0059] In this example, taking Allura Red (AR), Coomassie Brilliant Blue (CBB), Crystal Violet (CV), Malachite Green (MG) and Methyl Orange (MO) as examples, the effects of different pH values, amounts of H2O2, amounts of qMNC@600 and dye concentrations on the catalysis of dyes by qMNC@600 were investigated by adjustment, so as to optimize the best conditions for qMNC@600 to catalyze dyes. The specific investigation steps are as follows.

[0060] (1) Effect of different pH values on the adsorption of dyes by qMNC@600:

[0061] Under the conditions of a pH range of 2 - 9, a catalyst dosage of 10 mg, an initial dye concentration of 100 mg / L (50 mL) and 0.12% H2O2, the reaction pH for achieving the best degradation was studied, and the reaction time was 12 hours. The results are as Figure 4As shown in A, it can be seen from the figure that the catalyst requires different pH values to achieve the best dye color change. Complete color change of dyes such as CBB, CV, and MO was observed at pH 2, while pH 6 - 9 was effective for the color change of AR, CV, and MG. Therefore, pH 2 (CBB, CV - MO) and pH 7 or 8 (AR, MG) were used as the optimization conditions and applied to all subsequent catalytic color change studies.

[0062] The pH difference can determine the point of zero charge of the catalyst (pH pzc ), as its oxidation ability may be affected by pH changes. In a sodium nitrate (NaNO3, 0.1 M) buffer medium, nitric acid (HNO3, 0.1 M) and sodium hydroxide (NaOH, 0.1 M) were used to prepare pH values from 2 - 10 to adjust to the desired pH. qMNC@600 (20 mg) was added to each container (50 mL), and the mixture was shaken and incubated at 35 °C for 24 hours, and then the final pH was recorded. The change in pH value is as Figure 5 shown.

[0063] As can be seen from Figure 5 , the point of zero charge of qMNC@600 (pH pzc ) was determined to be approximately 7.45, at which point qMNC@600 has a net neutral charge. Therefore, it can be concluded that when pH > pHpzc, the catalyst exhibits a net positive charge that makes it easy to attract negatively charged dyes, while when pH < pH pzc , it exhibits a net negative charge, making it easy to adsorb positively charged dyes. However, within the detected pH range, the color change efficiency of the catalyst was observed to be significantly low at pH 4 and 5, indicating that there may be electrostatic repulsion between the weak positive charge of the catalyst and the dyes. At lower pH (2), the degradation of CBB, CV, and MO increased, while at pH 7, the catalysis of AR and MG increased. This may be because within these two pH ranges, van der Waals interactions may dominate the electrostatic repulsion, forcing the dyes to contact the catalyst surface, thereby enhancing the catalysis.

[0064] (2) Effect of different H2O2 dosages on the adsorption of dyes by qMNC@600:

[0065] At pH 2 (CBB, CV, MO) or pH 7 (AR, MG), with a catalytic time of 12 hours, at H2O2 dosages of 0.05%, 0.1%, 0.15%, and 0.2%, under the conditions of 10 mg of qMNC@600 and an initial dye concentration of 100 mg / L, the optimal amount of H2O2 required to change the color of the dyes in the Fenton oxidation reaction was detected. Figure 4Figure B shows the variation of the dye discoloration efficiency at different H2O2 concentrations. At all H2O2 concentrations, the discoloration efficiencies of CBB, CV, MG, and MO were >98%, while at doses above 0.1%, the discoloration rate of AR was complete discoloration. At 0.05% and 0.1%, the fading rates of AR were 78.17% and 94.16%, respectively. Increasing the H2O2 dose directly corresponded to enhanced attachment to the active sites of the catalyst and improved free radical generation. Since 100% discoloration was observed at H2O2 doses above 0.1% for all dyes, the optimized H2O2 concentration was adjusted to 0.12% and used for all subsequent dye catalytic studies.

[0066] (3) Effect of different amounts of qMNC@600 on the adsorption of dyes by qMNC@600:

[0067] In a heterogeneous catalytic system, an active solid catalyst is essential for activating the oxidant to generate active free radicals. Although the discoloration of some dyes may occur only in the presence of an oxidant, most dyes discolor by generating a series of free radicals that are crucial for breaking the bonds in the dye structure. Therefore, in terms of reducing operating costs, it is crucial to evaluate the minimum catalyst dose of the catalyst.

[0068] At pH 2 (CBB, CV, MO), 7 (AR, MG), an initial dye dose of 100 mg / L, an H2O2 dose of 0.12%, and a catalytic time of 12 hours, the amount of qMNC@600 required for the catalytic discoloration of dyes was studied. The measurement results are as Figure 4 shown in Figure C. It can be seen from the figure that the amount of qMNC@600 required for the catalytic discoloration of dyes was 1 - 20 mg, and the greater the catalyst dosage, the higher the degradation rate. Although 1 mg was sufficient for the complete catalytic degradation of MG, AR, CBB, CV, and MO required 10 mg or more to achieve 100% dye removal. No substantial change in catalysis was observed after 10 mg of qMNC@600, indicating that 10 - 15 mg of qMNC@600 was sufficient to catalyze the generation of free radicals crucial for dye discoloration under optimal conditions. Therefore, 10 mg of qMNC@600 was selected as the optimized amount to further study the effect of qMNC@600 on other parameters.

[0069] (4) Effect of different dye concentrations on the adsorption of dyes by qMNC@600:

[0070] In the Fenton oxidation reaction, under the conditions of pH 2 (CBB, CV, MO) or 7 (AR, MG), a qMNC@600 dose of 10 mg, and an H2O2 dose of 0.12%, the optimal dye concentration for the catalytic discoloration of qMNC@600 was detected in the range of dye amounts of 10, 30, 50, 80, 100, 150, and 200 mg / L.Figure 4 D shows the change in the degradation efficiency with different dye concentrations. 100% degradation of MG was observed at all concentrations, while complete discoloration of AR, CBB, CV, and MO was observed at 100 mg / L. At 150 and 200 mg / L, the discoloration rates of AR were 96.73% and 94.52% respectively, those of CBB were 88.31% and 73.36%, those of CV were 98.97% and 98.31% in sequence, and those of MO were 98.93% and 90.36% respectively. Since >99% discoloration was observed at a dye dose of 100 mg / L, 100 mg / L was selected as the optimal dose for further dye catalytic studies.

[0071] (5) Effects of temperature and time on the adsorption of dyes by qMNC@600:

[0072] Temperature plays a key role in the catalytic process, which increases the kinetic energy of the reactants and enables the reaction to proceed rapidly to form products. In this step, based on the optimized pH, H2O2, catalyst dosage, and dye dosage in steps (1) to (4), the change in the dye color over time was investigated under different temperatures (25, 35, 40, 50 °C) catalysis, and the change is as Figure 6 shown.

[0073] It can be seen from Figure 6 that the catalytic times of AR, CBB, CR, and MO are 180, 120, 180, and 120 minutes respectively; the catalytic time of MG is 10 minutes. The catalytic discoloration of MG is independent of temperature because the dye is catalytically completely discolored within 10 minutes at all temperature points, while the catalytic discoloration rates of AR, CBB, CV, and MO increase with the increase in temperature. Moreover, at 35 °C, 40 °C, and 50 °C, the catalytic discoloration efficiencies of AR, CBB, and MO exceed 92%, while similar catalytic discoloration efficiencies of CV are observed at 40 °C and 50 °C. This is because higher temperatures increase the rate of oxidant decomposition and the kinetic energy of the generated radical species, increasing the contact rate between dye particles and radical species, thereby leading to faster and more effective discoloration.

[0074] In summary, when the adsorbed dyes are CBB, CV, and MO, the optimal conditions for the reaction system are: qMNC@600 10 mg, H2O2 0.12 wt%, dye amount 100 mg / L, pH = 2; when the adsorbed dyes are AR and MG, the optimal conditions for the reaction system are: qMNC@600 10 mg, H2O2 0.12 wt%, dye amount 100 mg / L, pH = 7. In addition, the catalytic discoloration of MG is independent of temperature, while the catalytic discoloration rates of AR, CBB, CV, and MO increase with the increase in temperature; the catalytic time of AR, CBB, CR, and MO is preferably 3 hours, and the catalytic time of MG is 10 minutes.

[0075] Example 3:

[0076] To better understand the catalytic efficiency of the materials, in this example, the synthesized qMNC and qMNC@600 were used as catalysts to study the effects of H2O2, qMNC@600, qMNC + H2O2, and qMNC@600 + H2O2 on the color change of catalytic dyes, respectively.

[0077] The results are as Figure 7 shown. For all treatments using H2O2, complete color change of MG was observed within the first 1 hour ( Figure 7 D), while the treatment without H2O2 (qMNC@600) showed a slow color change rate. It can be assumed that MG may be a dye that is prone to color change even without a catalyst and only requires a strong oxidant at pH 7. In the absence of an oxidant, qMNC@600 failed to catalyze the color change of AR ( Figure 7 A), CBB ( Figure 7 B), CV ( Figure 7 C), and MO ( Figure 7 E), and neither H2O2 alone could cause the color change of AR, CV, and MO, but the color change efficiency of CBB was 35% at 24 hours. After 24 hours, the color change of qMNC + H2O2 reached 89.3% (AR), 61% (CBB), 20.25% (CV), 100% (MG), and 71.23% (MO).

[0078] Although BET analysis revealed a high surface area of qMNC, the slow and inefficient catalytic ability of qMNC + H2O2 may be related to most of the unavailable active metal centers (due to ligand binding), which are necessary for reacting with the oxidant to generate active species. At the same time, after 6 hours of treatment with qMNC@600 + H2O2, the color change rates of CBB, CV, MG, and MO dyes could reach over 90%, and the color change of AR reached 85.56% within 6 hours. After 12 hours, qMNC@600 + H2O2 caused the color change rates of all 5 dyes to exceed 95%, confirming its efficiency in catalyzing the color change of dyes.

[0079] In summary, qMNC@600 can be used as a catalyst to catalyze H2O2 to generate oxygen free radicals for dye degradation.

[0080] Example 4:

[0081] Since the dye - contaminated wastewater from industrial sources may contain more than one dye, this example simulates the color change of qMNC@600 for multiple dyes. Since the main limitation encountered is the difference in pH conditions required for effective catalysis, based on the pH requirements of the dyes, AR and MG are used in one group, and CBB, CV, and MO are used in another group to catalyze the dyes. The specific steps are as follows: In a 50 - mL beaker containing 10 mg of catalyst and distilled water with adjusted pH, dyes are added at doses of 10, 30, 50, 70, and 100 mg / L, then 0.12% H2O2 is added, stirred and mixed. Aliquots are taken after 1, 3, and 6 hours, and the residual dyes are measured according to the absorption spectrum.

[0082] The analysis results are as Figure 8 and 9 shown. It can be seen from the figure that at all doses, the dyes in both groups (pH 2 and 7) are completely discolored at 6 hours. Although trace amounts of MG could not be detected after 1 hour at all concentrations, the spectrum shows that AR could not be detected after 6 hours ( Figure 8 A1 - D1). The color change of the mixture of CBB, CV, and MO is equally effective, and complete catalysis occurs within 6 hours ( Figure 8 A2 - D2). In addition, different from AR, MG, and MO, the catalysis of CBB and CV results in the formation of precipitates, which precipitate from the catalytic medium over time ( Figure 9 ). When CBB, CV, and MO are mixed together, the coalescence rate increases, resulting in faster color change. The broken structures of CBB and CV may interact through π - π bond interactions, which may be the reason for the increased polymerization rate (occurring within 3 hours) and the precipitation of catalytic intermediates from the liquid medium.

[0083] In summary, the qMNC@600 described in the present invention is an effective catalyst, which is not only used for the color change of single dyes, but also can discolor multiple dyes at an optimized pH in the presence of H2O2 as an oxidant.

[0084] Example 5:

[0085] The adsorption efficiency and reusability of the adsorption material are two important parameters to consider when selecting materials for pollutant removal, which can reduce costs and limit secondary pollution generated during treatment. This example examines the reusability of qMNC@600, and the specific steps are as follows:

[0086] In this example, the reusability and stability of the qMNC@600 catalyst were first studied through a recyclability experiment of 10 cycles for the degradation of each dye. Secondly, the ability of free radicals generated by Fenton oxidation in the already decolorized water to decolorize fresh dyes was studied for 3 cycles. After each catalytic experiment, since the qMNC@600 catalyst contains iron, a magnet was used to separate the catalyst, which was washed with 5 mL of ethanol and rinsed with distilled water, and then dried at 70 °C for 1 hour before being used in the next catalytic cycle. In addition, the recycling of the catalytically dyed water containing free radical species was studied by introducing 20 or 50 mg / L of fresh dye after each cycle.

[0087] The research results are as Figure 10 shown. As can be seen from the figure, under the optimal conditions after each run, the catalyst maintained almost 100% catalytic efficiency for MG and 94% efficiency for AR, indicating that qMNC@600 exhibited good catalytic activity even after repeated runs. However, qMNC@600 lost almost all of its catalytic performance after three cycles for CBB, CV, and MO, suggesting that although low pH (2) is crucial for the generation of free radicals, compared with qMNC@600 used at neutral pH, low pH (2) may have a negative impact on the catalytic performance of qMNC@600, and qMNC@600 at neutral pH maintained 90% catalytic performance after 10 cycles. In addition, the degradation efficiency of the dye using the previously catalytic aqueous solution showed a mixed catalytic efficiency, with 100% degradation of MG through 3 cycles, while the catalysis for AR, CBB, CV, and MO decreased slightly after 3 cycles ( Figure 11 ). This indicates that the free radical species required to initiate dye discoloration still exist in the aqueous medium after catalysis and can be reused at least once more depending on the dose of fresh dye.

[0088] In summary, qMNC@600 can be reused 10 times or more as a catalyst for the degradation of MG and AR; it can be reused 3 times for CBB, CV, and MO.

[0089] Example 6:

[0090] Fenton oxidation is based on the premise of the dissociation of H2O2 mediated by a catalyst to generate active free radicals. Research has shown the importance of the hydroxyl radical (*OH) as the most fundamental element for initiating and maintaining catalysis in the Fenton oxidation system. And the active components include *O2 - , h + , eˉ, RO˙2, RO2H, RO˙ can also be generated through pathways other than the Fenton process, and these active components can also play a role in initiating and maintaining catalysis due to their high redox potential.

[0091] To identify the radical species required to initiate and promote the color change process, in this example, each dye was color-changed for 12 hours. Under optimal conditions, different radical scavengers were introduced into the color-changing water, including isopropyl alcohol (IPA, 0.4%) for hydroxyl scavenging, tert-butanol (tert-B, 0.4%) for OH scavenging, EDTA, oxalic acid (OA), + quenched citric acid (CA, 1 mM), superoxide dismutase (SOD, 0.1 mg / mL), 2- 1,4-benzoquinone (BZQ, 1 mM) for O Figure 12 ion scavenging. The solution was reacted for 1 hour, then 100 mg / L dye was added and left for 12 hours. Then, the ability of the scavenger to inhibit color change was determined by the percentage of catalytic efficiency, and the measurement results are as

[0092] shown. Figure 12 It can be seen that adding IPA, Tert-B, and SOD cannot inhibit the color change of all dyes, indicating that the radicals generated by Fenton oxidation are neither hydroxyl nor superoxide. EDTA can inhibit the color change of AR (1.17%), CBB (15.84%), CV (26.68%), and MO (6.02%), but cannot inhibit the color change of MG (99.36%). Citric acid cannot inhibit the color change of CBB (89.0%), CV (88.67%), and MO (99.31%), but affects the color change of AR (6.68%) and MG (46.65%). Although EDTA, CA, and OA are known to scavenge + , holes are not generated in the Fenton reaction, indicating that the radicals must be of other types. The inhibitory properties of EDTA, CA, and OA are due to their ability to sequester metal ions, chelating metal ions and thus preventing catalysis with the oxidant. Therefore, due to the oxidation of high-valent metal ions (such as Cr, Fe, and Co), the alkoxy and / or H2O2-derived reactive radical intermediates generated from organic dyes must be responsible for mediating the color change process. Figure 13 Furthermore, the generation and mechanism of intermediate alkoxy and H2O2 radical species mediated by qMNC@600 through H2O2 decomposition were concluded.

[0093] In summary, the solvent thermal method for synthesizing and annealing the tetragonal metal nanocomposite of the present invention can catalyze one or more dyes such as AR, CBB, CV, MG, and MO in water. The qMNC@600 has excellent effects on treating dyes with a concentration of 10-100 mg / L, and the decolorization rate can reach more than 94%, and the color degree can be reduced to 60-90 times. Moreover, the qMNC@600 of the present invention has the advantages of simple process, high porosity, fast speed, high removal rate, strong removal ability, and can be reused multiple times. The qMNC@600 of the present invention can greatly reduce the treatment cost and has important social significance.

[0094] The described embodiments are the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the substantial content of the present invention, any obvious improvements, substitutions, or variations that those skilled in the art can make all belong to the protection scope of the present invention.

Claims

1. A method for preparing a thermally annealed tetragonal metal nanocomposite material, characterized in that, It includes the following steps: (1) Preparation of tetragonal metal nanocomposite qMNC; Dissolve cobalt, chromium, iron, and nickel sources in a metal-organic ligand solvent to obtain solution A containing a solution of four metals; dissolve benzene-1,3,5-tricarboxylic acid in the metal-organic ligand solvent to obtain solution B; mix solution A and solution B evenly and then carry out a solvothermal reaction. After the reaction is completed, wash, centrifuge, and dry to obtain the tetragonal metal nanocomposite qMNC; In solution A, the molar ratio of the cobalt source, chromium source, iron source, and nickel source is 1:1:1:1; the concentrations of the cobalt source, chromium source, iron source, and nickel source are 5-10 mM; In the metal-organic ligand solvent, the metal-organic ligand includes dimethylformamide; The volume ratio of solution A and solution B is 2:1; (2) Thermal annealing of the tetragonal metal nanocomposite: Calcine the tetragonal metal nanocomposite qMNC at a high temperature. After the calcination is completed, obtain the thermally annealed tetragonal metal nanocomposite qMNC@600; The thermally annealed tetragonal metal nanocomposite has an irregular spherical structure with pores on the outer surface of the sphere; the thermally annealed tetragonal metal nanocomposite has a particle size of 300 - 350 nm, a surface area of 40 - 45 m² / g, an average pore diameter of 20 - 25 nm, and a pore volume of 0.30 - 0.35 cm 3 / g.

2. The method for preparing a thermally annealed tetragonal metal nanocomposite according to claim 1, wherein In step (1), the cobalt source includes cobalt nitrate and its hexahydrate; The chromium source includes chromium chloride and its hexahydrate; The iron source includes ferric chloride and its trihydrate; The nickel source includes nickel acetate and its tetrahydrate.

3. The preparation method of the thermally annealed tetragonal metal nanocomposite according to claim 1, wherein, In step (1), the conditions of the solvothermal reaction are: carry out a high-pressure steam reaction at 180 °C for 15-20 hours.

4. The method for preparing a thermally annealed tetragonal metal nanocomposite according to claim 1, characterized in that, In step (2), the tetragonal metal nanocomposite qMNC is gradually heated to 300 °C at a stable rate of 2 °C / minute, and then heated to 600 °C at a rate of 5 °C / minute, with a heating time of 5 hours.

5. The thermally annealed tetragonal metal nanocomposite according to any one of claims 1 to 4.

6. Application of the thermally annealed tetragonal metal nanocomposite according to claim 5 in adsorbing dyes.

7. The application according to claim 6, wherein The dyes include one or more of Coomassie Brilliant Blue, Methyl Orange, Allura Red, Crystal Violet, and Malachite Green.

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