Composite aerogel, preparation thereof and application of composite aerogel in adsorption-degradation of dye wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to composite aerogel as well as preparation and application thereof in adsorption-degradation of dye wastewater. The composite aerogel comprises cellulose aerogel and metal organic framework compound crystals doped with copper, the metal organic framework compound crystals doped with copper are loaded in through holes of the cellulose aerogel, and the composite aerogel is applied to adsorption and degradation of dye wastewater. The composite aerogel is prepared through chemical bonding among the components, the structural stability among the components can be optimized by adjusting the Cu content, enrichment of dye molecules is facilitated, the recycling capacity of Cu / ZIF-67 is improved, secondary pollution is avoided, and the adsorption-degradation performance on dye is extremely good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to a composite aerogel and preparation and application thereof in adsorption-degradation of dye wastewater. BACKGROUND

[0002] Traditional pollutants such as heavy metals, dyes and oils in industrial wastewater, as well as emerging pollutants such as pharmaceuticals, have caused serious damage to the ecological environment due to their persistence and high hazard. The most typical pollutant in industrial wastewater is high water-soluble organic dye, which can cause an increase in water color, reduce the penetration of incident light, and further disrupt the balance of the water ecosystem. Therefore, it is urgent to address the pollution problem caused by dye wastewater. Currently, the methods applied to the purification of industrial dye wastewater mainly include physical, chemical and biological methods, and specific technologies include extraction, adsorption, electrochemistry, photocatalytic degradation and aerobic-anaerobic biological combination method, etc.

[0003] Physical method is one of the commonly used methods for treating dye wastewater, which can promote the recovery of dye molecules in wastewater and reduce the content of salt and metal ions. It mainly includes flocculation, extraction, adsorption and membrane filtration technologies. Flocculation method is applied to the decolorization field of dyeing and printing wastewater; extraction method can realize the reuse of dyes after enrichment; membrane filtration method filters through membrane micropores to reduce water waste; adsorption process does not produce harmful substances during water purification, which is beneficial to the purification treatment of dye wastewater. However, the existing physical method for treating dye wastewater has the disadvantages of single treatment effect, incomplete removal effect and secondary pollution.

[0004] Chemical method mainly includes electrochemistry, ozone oxidation and photocatalytic degradation technologies. Electrochemical method has the disadvantages of high energy consumption, high cost and difficulty in storing electrodes. Ozone oxidation method can achieve efficient decolorization of organic dyes by reducing the concentration of organic pollutants, but high cost limits its large-scale application. Photocatalytic degradation technology refers to the use of photocatalysts to generate free radicals with strong oxidizing properties to decompose difficult-to-degrade macromolecular organic pollutants into small molecular substances, and ultimately convert them into H2O and CO2. Due to its biocompatibility, photocatalytic efficiency and other advantages, it has been widely studied and applied in water pollution control. However, the existing photocatalytic degradation technology needs to consume a large amount of energy and has high cost.

[0005] Biological method is to use the metabolic capacity of microorganisms to adsorb or biodegrade organic pollutants, which has the advantages of large treatment capacity, high efficiency and no secondary pollution. Biological method mainly includes anaerobic biological method, aerobic biological method and aerobic-anaerobic combined method. Anaerobic treatment method can effectively degrade complex macromolecular organic matter in wastewater, but the removal rate is low when used alone; aerobic treatment method has good removal effect on easily degradable organic matter, but the degradation capacity for complex macromolecular organic matter is limited. In addition, the composition of wastewater is complex, the survival of microorganisms is difficult, and the treatment device occupies a large area, which is difficult to be applied on a large scale.

[0006] At the same time, the current dye wastewater treatment materials are often difficult to degrade, and the raw material cost is relatively high. Therefore, it is necessary to develop a biodegradable, relatively low-cost adsorption-degradation material with synergistic effect of adsorption and degradation for dye wastewater treatment. SUMMARY

[0007] The purpose of the present application is to solve the problems existing in the prior art, and to provide a composite aerogel and its preparation and application in adsorption-degradation of dye wastewater.

[0008] A composite aerogel comprises: a cellulose aerogel and a copper-doped metal organic framework compound crystal, and the copper-doped metal organic framework compound crystal is loaded in the through hole of the cellulose aerogel.

[0009] Preferably, the metal organic framework compound is ZIF-67.

[0010] Preferably, the raw materials include: cobalt salt, copper salt, 2-methyl imidazole and cellulose aerogel.

[0011] Preferably, the cobalt salt includes cobalt nitrate, cobalt acetate, cobalt chloride or a hydrate of any of the above cobalt salts.

[0012] Preferably, the copper salt is copper nitrate, copper acetate, copper sulfate or a hydrate of any of the above copper salts.

[0013] Preferably, the molar ratio of copper ions to cobalt ions is 0-5:5-10, and the molar ratio of copper ions to cobalt ions is not 0:10.

[0014] Preferably, the ratio of the total molar amount of cobalt salt and copper salt to the mass of cellulose aerogel is 5mmol:1g.

[0015] Preferably, the cellulose aerogel is prepared by the following steps: freeze-drying treatment of forestry material rich in pore structure, then vacuum heating and dissolving in a lignocellulose dissolving solvent, repeatedly soaking in deionized water, and freeze-drying.

[0016] More preferably, the specific operation of freeze-drying treatment of the forestry material rich in pore structure is as follows: the forestry material rich in pore structure without defects such as holes, cracks, insect damage, etc. is selected, cut into a sample with a length of 2 cm, a width of 0.5 cm and a height of 0.5 cm, and placed in a 60°C deionized water bath for 1 h to remove water-soluble impurities in the sample; after being taken out after being frozen at -20°C for 12 h, freeze-drying treatment is performed in a freeze dryer for 24 h.

[0017] More preferably, the forestry material rich in pore structure is at least one of redwood, balsa wood, cork oak and Paulownia.

[0018] More preferably, the specific operation of vacuum heating and dissolving in the lignocellulose dissolving solvent is as follows: the material after freeze-drying treatment and the lignocellulose dissolving solvent are placed in a reaction tube, vacuum is drawn, and oil bath heating is performed; wherein the solid-liquid ratio of the material after freeze-drying treatment and the lignocellulose dissolving solvent is 1:50, the oil bath heating temperature is 70°C, and the oil bath heating time is 24 h.

[0019] More preferably, the lignocellulose dissolving solvent is a choline chloride-based deep eutectic solvent or an ionic liquid.

[0020] Specifically, the choline chloride-based deep eutectic solvent is obtained by stirring and heating choline chloride and oxalic acid.

[0021] More specifically, the choline chloride-based deep eutectic solvent is obtained by mixing choline chloride and oxalic acid in a molar ratio of 1-2:1-2 at 88-92°C to obtain a clear and transparent liquid.

[0022] More specifically, the choline chloride-based deep eutectic solvent is obtained by stirring choline chloride and oxalic acid in a molar ratio of 1-2:1-2 at 88-92°C for 1 h at a stirring speed of 500 rpm to obtain a clear and transparent liquid.

[0023] Specifically, the ionic liquid is any one of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ionic liquid, 1-butyl-3-methylimidazolium chloride ionic liquid, 1-allyl-3-methylimidazolium chloride ionic liquid, 1-(2-hydroxyethyl)-3-methylimidazolium chloride ionic liquid and 1-ethyl-3-methylimidazolium chloride ionic liquid.

[0024] More preferably, in the process of repeatedly immersing in deionized water, the wet gel obtained by oil bath heating is repeatedly immersed in deionized water, and the deionized water is replaced regularly until a white and transparent hydrogel is formed.

[0025] More preferably, the specific operation of freeze-drying after repeated immersion is as follows: the hydrogel obtained by repeated immersion is placed in a freeze dryer after being frozen at -20°C for 12 h, and freeze-drying treatment is performed for 48 h.

[0026] The preparation method of the composite aerogel comprises the following steps: dissolving a cobalt salt and a copper salt in a solvent to obtain solution A; dissolving 2-methyl imidazole in a solvent to obtain solution B; immersing cellulose aerogel in solution A, then adding solution B, immersing again, washing and drying.

[0027] Preferably, the specific operation of immersing cellulose aerogel in solution A is as follows: immersing the system in a 0.01 MPa environment for 30 min, then standing for 30 min under ambient pressure, and repeating the process twice.

[0028] Preferably, the specific operation of immersing again by adding solution B is as follows: immersing the system in a 0.01 MPa environment for 30 min, then standing for 30 min under ambient pressure, and repeating the process twice, and then oscillating for 12 h under ambient pressure.

[0029] Preferably, the specific operation of washing is as follows: washing with methanol and deionized water for several times to remove unreacted chemicals and unloaded nanocrystals on the sample.

[0030] Preferably, the specific operation of drying is as follows: after washing, the sample is frozen at -20 DEG C for 24 h, and then subjected to freeze-drying treatment in a freeze dryer for 48 h.

[0031] The application of the composite aerogel in adsorption-degradation of dye wastewater.

[0032] A method for degrading dye wastewater, comprising the following steps: placing the composite aerogel in dye wastewater, stirring, adding hydrogen peroxide solution, and performing ultraviolet irradiation.

[0033] The present application has the following advantages: ①the adsorption and degradation reactions can be carried out simultaneously, achieving the effect of adsorption-degradation synergy, and the operation is simple, easy to realize and low in cost; ②the forestry wastes (such as balsa wood, light wood, cork oak and paulownia) are reasonably utilized to improve their added value, and the raw materials used are green and degradable, meeting the needs of sustainable development; ③the wood cellulose aerogel prepared by the "top-down" strategy not only saves time and energy, but also retains the honeycomb network structure and natural skeleton structure of the forestry material itself rich in pore structure, realizing effective compounding of nanoscale functional materials and biomass aerogel, and providing a new idea for developing green and efficient adsorption-degradation materials. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The figure is a schematic diagram for preparing the composite aerogel of the present application.

[0035] Figure 2Scanning electron microscope image of the sample obtained after freeze-drying of the tuber of Pothos scandens for Example 1, magnified 300 times.

[0036] Figure 3 Scanning electron microscope image of the sample obtained after freeze-drying of the tuber of Pothos scandens for Example 1, magnified 3000 times.

[0037] Figure 4 SEM images of Cu / ZIF-67@D-MT-1, Cu / ZIF-67@D-MT-2, Cu / ZIF-67@D-MT-3, ZIF-67@D-MT obtained in Examples 1-3 and Comparative Examples; wherein, a and b are ZIF-67@D-MT obtained in Comparative Examples, c and d are Cu / ZIF-67@D-MT-1 obtained in Example 1, e and f are Cu / ZIF-67@D-MT-2 obtained in Example 2, g and h are Cu / ZIF-67@D-MT-3 obtained in Example 3.

[0038] Figure 5 Compression stress-strain (σ-ε) curves of Cu / ZIF-67@D-MT-1, Cu / ZIF-67@D-MT-2, Cu / ZIF-67@D-MT-3, ZIF-67@D-MT obtained in Examples 1-3 and Comparative Examples at 70% strain and their corresponding compression strength and compression modulus; wherein, (a) is the compression stress-strain curve, (b) is the compression strength and compression modulus column chart.

[0039] Figure 6 Adsorption / degradation performance of methylene blue of Cu / ZIF-67@D-MT-1, Cu / ZIF-67@D-MT-2, Cu / ZIF-67@D-MT-3, ZIF-67@D-MT obtained in Examples 1-3 and Comparative Examples; wherein, (a) is the adsorption performance of methylene blue of each group of samples, (b) is the adsorption-degradation performance of methylene blue of each group of samples.

[0040] Figure 7 Degradation performance of methylene blue of Cu / ZIF-67@D-MT-2 obtained in Example 2 under different H2O2 dosages.

[0041] Figure 8 Adsorption-degradation performance of methylene blue of Cu / ZIF-67@D-MT-2 obtained in Example 2 under different dosages; wherein, (a) is the dosage of Cu / ZIF-67@D-MT-2 obtained in Example 2 and the adsorption-degradation performance curve, (b) is the reaction constant k.

[0042] Figure 9The adsorption-degradation performance of Cu / ZIF-67@D-MT-2 obtained in Example 2 for methylene blue at different initial concentrations; wherein, (a) is the initial concentration of methylene blue and the adsorption-degradation performance curve, and (b) is the reaction constant k.

[0043] Figure 10 The degradation performance of Cu / ZIF-67@D-MT-2 obtained in Example 2 on methylene blue under different light sources.

[0044] Figure 11 UV-visible absorption spectra of methylene blue after degradation by different degradation systems.

[0045] Figure 12 The cyclic degradation performance of Cu / ZIF-67@D-MT-2 obtained in Example 2 for methylene blue. DETAILED DESCRIPTION

[0046] The present invention will be further explained below with reference to specific embodiments.

[0047] The following examples take chlorinated wood and choline chloride-based deep eutectic solvents as examples, and other materials can also be used to prepare composite aerogels. Example 1

[0048] Parts of MT wood without holes, cracks, insect damage, or other defects were selected and cut into several rectangular specimens with a length of 2 cm, a width of 0.5 cm, and a height of 0.5 cm. The specimens were placed in a water bath heated at 60°C in deionized water for 1 hour to remove water-soluble impurities in the specimens. The specimens were then placed in a low-temperature freezer for 12 hours. Finally, they were freeze-dried for 24 hours and stored in sealed bags for later use.

[0049] The freeze-dried samples of the tongdel wood were scanned by electron microscope. Figure 2 and Figure 3 shown.

[0050] Choline chloride and oxalic acid in a molar ratio of 1:1 were magnetically stirred at 90°C and 500 rpm until the solution became clear and transparent, thereby preparing ChCl-DES, which was then stored in a dry place for later use.

[0051] ChCl-DES and pretreated MT were placed in a 250 mL flask with a side arm at a liquid to solid ratio of 50:1, and heated in a 70 °C oil bath for 24 h after being evacuated. ChCl-DES solution entered the natural pore structure of MT by infiltration and diffusion, and dissolved to different degrees, obtaining MT wet gel. Then, the MT wet gel was repeatedly soaked in deionized water, and the deionized water was replaced regularly, obtaining a white and transparent hydrogel. Finally, the hydrogel was frozen at -4 °C for 12 h and then placed in a freeze dryer for 48 h, and D-MT was successfully prepared.

[0052] 0.72 g of cobalt nitrate hexahydrate and 0.149 g of copper nitrate trihydrate (Co 2+ / Cu 2+ molar ratio = 8:2) were dissolved in 30 mL of methanol to obtain solution A; 12 mmol of 2-methylimidazole was dissolved in 30 mL of methanol to obtain solution B. Then, 0.6 g of D-MT was immersed in solution A, and the system was immersed in a 0.01 MPa environment for 30 min to promote more copper ions and cobalt ions to enter the interior of D-MT, and then was placed under ambient pressure for 30 min, and the process was repeated twice. Then, solution B was added, and the same immersion method was used to promote better coordination of the 2-methylimidazole organic ligand with the metal ions. Then, the sample was taken out of the solution after being shaken under ambient pressure for 12 h, and was washed with methanol and deionized water in sequence to remove unreacted chemicals and unloaded nanocrystals on the sample. Finally, the washed sample was placed in a freezer at -20 °C for 24 h, and then was taken out and freeze-dried in a freeze dryer for 48 h. The product was labeled as Cu / ZIF-67@D-MT-1. Example 2

[0053] The difference from Example 1 is that the amount of cobalt nitrate hexahydrate used is 0.54 g, and the amount of copper nitrate trihydrate used is 0.299 g (Co 2+ / Cu 2+ molar ratio = 6:4). The product is labeled as Cu / ZIF-67@D-MT-2. Example 3

[0054] The difference from Example 1 is that the amount of cobalt nitrate hexahydrate used is 0.45 g, and the amount of copper nitrate trihydrate used is 0.374 g (Co 2+ / Cu 2+ molar ratio = 5:5). The product is labeled as Cu / ZIF-67@D-MT-3.

[0055] Comparative Example The difference from Example 1 is that the amount of cobalt nitrate hexahydrate used is 0.9 g, and the amount of copper nitrate trihydrate used is 0 g (Co 2+ / Cu2+ Molar ratio = 10:0). The product was labeled as ZIF-67@D-MT.

[0056] The Cu / ZIF-67@D-MT-1, Cu / ZIF-67@D-MT-2, Cu / ZIF-67@D-MT-3, ZIF-67@D-MT obtained from Example 1-3 and Comparative Example were subjected to electron microscopy scanning, as shown in Figure 4

[0057] As can be seen from Figure 4 a, c, e, g, the Cu / ZIF-67@D-MTs exhibit a honeycomb-like porous structure similar to that of ZIF-67@D-MT, and Cu / ZIF-67 nanoparticles are densely arranged in the channel surface of the aerogel. As can be seen from Figure 4 b, d, f, h, pure ZIF-67 nanoparticles exhibit a polyhedral shape and a smooth surface, however, as the Cu doping amount increases, the average particle size of Cu / ZIF-67 crystals gradually decreases, and the morphology changes from a regular polyhedron to an irregular flower structure; as the Cu doping amount continues to increase, the crystal structure gradually disappears and is embedded in the cellulose matrix. The generation of this morphological change is likely due to the atomic radius of Cu (0.128 nm) being larger than that of Co (0.125 nm), and this size difference will cause lattice defects when Cu atoms replace Co atoms. These lattice defects will extend to the entire composite aerogel framework, and the increased lattice defects can provide more active sites, improve the electron transport capacity, and be beneficial to improve the catalytic degradation performance.

[0058] The Cu / ZIF-67@D-MT-1, Cu / ZIF-67@D-MT-2, Cu / ZIF-67@D-MT-3, ZIF-67@D-MT obtained from Example 1-3 and Comparative Example were subjected to mechanical property testing.

[0059] As shown in Figure 5 , the Cu / ZIF-67@D-MTs continue the excellent mechanical properties of ZIF-67@D-MT. However, as the Cu content increases, the compression modulus and compression strength of the composite aerogel both show a trend of first increasing and then decreasing. This is likely due to the excessive Cu doping amount leading to a decrease in the stability of the ZIF-67 framework. The results show that appropriate doping of Cu helps to improve or maintain the mechanical properties of ZIF-67@D-MT.

[0060] ​With methylene blue (MB) as the test dye, 20 ± 0.02 mg of Cu / ZIF-67@D-MT-1, Cu / ZIF-67@D-MT-2, Cu / ZIF-67@D-MT-3 and ZIF-67@D-MT obtained in Examples 1-3 and Comparative Examples were respectively put into 100 mL of MB solution with a concentration of 50 mg / L, and magnetically stirred under light shielding conditions for 30 min; then 3 mmol / L H2O2 aqueous solution was added, and immediately placed under ultraviolet light irradiation for degradation reaction. Every 10 min, 1 mL of supernatant was extracted, and its absorbance was measured by ultraviolet-visible spectrophotometry to calculate the concentration. The photocatalytic degradation efficiency was calculated according to the following formula.

[0061] In the formula, Co and C x respectively represent the initial concentration and the final concentration of MB (mg / L).

[0062] As shown in Figure 6 As shown in Fig. (a), under light shielding conditions, only relying on adsorption, the removal rate of ZIF-67@D-MT for MB was 38.23% within 180 min. With Cu doping, the removal rate of Cu / ZIF-67@D-MTs for MB first increased and then decreased, in which the removal rates of Cu / ZIF-67@D-MT-1 and Cu / ZIF-67@D-MT-2 for MB were 44.52% and 40.93% respectively, both of which were higher than that of ZIF-67@D-MT; but the removal rate of Cu / ZIF-67@D-MT-3 for MB (31.45%) was lower than that of ZIF-67@D-MT. The reason might be that the Cu / ZIF-67 crystal was embedded in the cellulose matrix, resulting in a decrease in porosity, which hindered the dye molecules from entering the composite aerogel inside, thereby reducing the adsorption amount. The SEM observation results could prove this conclusion, indicating that doping an appropriate amount of Cu could help to improve the adsorption performance.

[0063] As shown in Figure 6As shown in (b), the dye molecules were first enriched in the composite aerogels by adsorption for 30 min in the dark to increase their contact with the catalyst surface, followed by photocatalytic degradation experiments. Compared with ZIF-67@D-MT, Cu / ZIF-67@D-MTs exhibited faster degradation rates, which could be attributed to the Cu doping, which reduced the band gap of ZIF-67 and inhibited the recombination of charge carriers as electron trapping centers, thereby accelerating the photocatalytic reaction. Cu / ZIF-67@D-MTs exhibited significant degradation efficiency, with a degradation rate of methylene blue (MB) of more than 98% within 20 min. Among them, Cu / ZIF-67@D-MT-2 had the fastest degradation rate, while Cu / ZIF-67@D-MT-3 had a lower degradation efficiency, possibly due to its poor adsorption effect and weak ability to enrich dye molecules. Considering both the adsorption / degradation degree and the degradation rate, Cu / ZIF-67@D-MT-2 catalyst was used for the next adsorption-degradation experiment.

[0064] Methylene blue (MB) was used as the test dye, and Cu / ZIF-67@D-MT-2 obtained in Example 2 was used as the catalyst to analyze the effects of H2O2 input amount, catalyst input amount, test dye initial concentration, and light source on the degradation performance.

[0065] (1) H2O2 input amount 20±0.02 mg of Cu / ZIF-67@D-MT-2 was added to 100 mL of MB solution with a concentration of 50 mg / L, and magnetically stirred for 30 min in the dark; then 0.5, 1, 2, 3, 4, and 5 mM of H2O2 were added for degradation experiments.

[0066] As shown in Figure 7 When the H2O2 dosage increased from 0.5 mM to 5 mM, the degradation rate of MB within 20 min increased from 76.91% to 98.57%. The increase in degradation rate may be due to the increase in H2O2 dosage, which generates more hydroxyl radicals (•OH) that can attack organic pollutants and trigger a free radical chain reaction, thereby effectively degrading the pollutants.

[0067] However, when the H2O2 dosage increased from 2 mM to 5 mM, the degradation rate remained almost unchanged, but the degradation rate significantly increased from 18 min to 10 min, which may be due to the reaction of excess H2O2 with •OH, which inhibits the decomposition of H2O2. Considering both the degradation degree and the degradation rate, the H2O2 dosage should be 3 mM.

[0068] (2) Catalyst input amount The adsorption-degradation performance experiment was carried out by adding 10 mg, 15 mg, 20 mg, 40 mg and 60 mg of catalyst into 100 mL MB solution with a concentration of 50 mg / L, respectively.

[0069] As shown in Figure 8 As shown in Fig. 2 (a), with the increase of the dosage of Cu / ZIF-67@D-MT-2, the adsorbed dye molecules increased in the dark reaction process, so the relative dye concentration was lower at the end of the dark reaction. When the dosage of Cu / ZIF-67@D-MT-2 increased from 0.1 g / L to 0.2 g / L, the photocatalytic degradation rate increased from 93.01% to 98.71%. This is mainly because during the adsorption process in the dark reaction, the more the dosage, the more the enriched MB molecules, which is more conducive to the catalytic degradation reaction; on the other hand, the increase of the catalyst is conducive to enhancing the interaction between the catalyst and H2O2, generating a large number of active sites to promote the progress of the photo-Fenton reaction.

[0070] When the dosage of Cu / ZIF-67@D-MT increased from 0.2 g / L to 0.6 g / L, the photocatalytic degradation rate remained basically unchanged, but the degradation time decreased from 18 min to 12 min. Figure 8 Fig. 2 (b) is the corresponding pseudo-first-order kinetic constant k, which increased from 0.1366 min -1 to 0.3085 min -1 . The results show that increasing the dosage of Cu / ZIF-67@D-MT-2 can significantly improve its adsorption-degradation performance on MB, and considering the application cost and degradation rate, the optimal dosage of Cu / ZIF-67@D-MT is 0.2 g / L.

[0071] (3) Test the initial concentration of dye The adsorption-degradation performance experiment was carried out by adding 20±0.02 mg of catalyst into 100 mL MB solution with a concentration of 10, 30, 50, 70, 90 and 110 mg / L, respectively.

[0072] As shown in Figure 9As shown, the degradation rate of MB by Cu / ZIF-67@D-MT-2 can reach more than 96% within 20 min when the initial concentration of MB solution is within 90 mg / L. With the increase of the initial concentration of MB solution, the degradation rate of MB by Cu / ZIF-67@D-MT-2 first increases and then decreases. The main reason is that a higher initial concentration can provide a greater driving force for the diffusion of MB, increase the collision frequency of MB with active sites on Cu / ZIF-67@D-MT-2, and thus improve the degradation efficiency. However, since the number of active sites on the surface of Cu / ZIF-67@D-MT-2 is limited, the further increase of the initial concentration of MB will lead to a decrease in degradation efficiency. Even so, the degradation rate of MB by Cu / ZIF-67@D-MT-2 can still reach 80.44% when the initial concentration is 110 mg / L, further confirming the excellent degradation performance of Cu / ZIF-67@D-MT-2 for MB.

[0073] (4) Light source 20 ± 0.02 mg of catalyst was added to 100 mL of MB solution with a concentration of 50 mg / L, and the mixture was magnetically stirred in the dark for 10 min, and then immediately placed under ultraviolet light, sunlight, LED, indoor, and dark conditions for degradation experiment. The photocatalytic degradation efficiency was calculated after the reaction was completed.

[0074] As shown in Figure 10 , the catalysts all showed good photocatalytic degradation performance under different light sources. Under ultraviolet light irradiation, the degradation rate of MB by the composite aerogel reached 98.15% within 20 min, which indicated that the composite aerogel could efficiently generate photo-generated carriers under the excitation of high-energy ultraviolet light, and thus drive the degradation of MB. In addition, the degradation rate of MB by the catalyst under sunlight reached 53.87%, which indicated that Cu / ZIF-67@D-MT-2 could effectively degrade MB under natural light conditions, and had certain practical application potential. Under indoor and LED light, the degradation rate was more than 30%, which further confirmed the adaptability and degradation capacity of the catalyst under different light conditions. This characteristic of achieving high degradation efficiency under multiple light sources makes Cu / ZIF-67@D-MT-2 have broad application prospects in practical applications.

[0075] (5) Different degradation systems Different degradation systems were used to degrade 100 mL of MB solution with an initial concentration of 50 mg / L, in which the amount of H2O2 was 3 mM, the amount of Cu / ZIF-67@D-MT-2 was 0.2 g / L, and the light source was ultraviolet light.

[0076] As shown in Figure 11As shown, in the system only with Cu / ZIF-67@D-MT, the absorbance of MB slightly decreases, which is due to the adsorption of the composite aerogel itself, which is consistent with the previous experimental results; for the H2O2+UV light system, the absorbance of the dye changes little, indicating that neither H2O2 nor ultraviolet light can degrade the dye molecule; in the Cu / ZIF-67@D-MT+UV light system, the absorbance of the dye decreases obviously, indicating that Cu / ZIF-67@D-MT has a significant degradation effect on MB under ultraviolet light excitation; for the Cu / ZIF-67@D-MT+H2O2+UV light system, the absorbance peak of MB almost disappears, indicating that the system can efficiently degrade dye wastewater.

[0077] In addition, after the degradation of MB by Cu / ZIF-67@D-MT+UV light and Cu / ZIF-67@D-MT+H2O2+UV light systems, the peak at 664 nm produces a blue shift, indicating that the dye may be decomposed.

[0078] Reusability is an important parameter for evaluating catalysts. In order to study the reusability of Cu / ZIF-67@D-MT, the used Cu / ZIF-67@D-MT was washed with deionized water for several times, and after drying, the adsorption-degradation experiment was carried out again. In the regeneration experiment, the adsorption-degradation efficiency of Cu / ZIF-67@D-MT on MB was calculated for the first 5 cycles.

[0079] As shown in Figure 12 , the removal rate of MB decreases with the increase of cycle number, and a small amount of pollutants may occupy part of the active sites in the cycle, thereby limiting the subsequent photocatalytic degradation. However, Cu / ZIF-67@D-MT still maintains a removal rate of 77.87% after 5 cycles, indicating that Cu / ZIF-67@D-MT catalyst has good stability and great application potential in wastewater treatment.

[0080] In summary, the Cu / ZIF-67@D-MT composite aerogel obtained by the present application has a chemical bond effect between the components, and the structure stability between the components can be optimized by adjusting the Cu content. Moreover, Cu / ZIF-67@D-MT not only helps to enrich the dye molecules, but also improves the recycling ability of Cu / ZIF-67, avoiding secondary pollution.

[0081] The results of the dye adsorption-degradation test by Cu / ZIF-67@D-MT show that the effect of Cu / ZIF-67@D-MT-2 is the best, and the removal rate of MB is 40.93% within 180 min only by adsorption; the degradation rate of MB can reach 98.71% within 20 min by the synergistic effect of adsorption and degradation. The results of the cyclic degradation experiment show that Cu / ZIF-67@D-MT-2 still maintains a removal rate of 77.87% after 5 cycles, indicating that it has good stability and great application potential in dye wastewater treatment.

[0082] The doping of Cu not only accelerates the decomposition of H2O2, but also promotes the redox cycle of Co 3+ / Co 2+ by accelerating electron transfer to achieve rapid separation of electrons and holes. This makes Cu / ZIF-67@D-MT have better activation performance and higher electron mobility, thereby improving the photocatalytic degradation efficiency.

[0083] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A composite aerogel, characterized in that: include: Cellulose aerogel and copper-doped metal organic framework compound crystals, wherein the copper-doped metal organic framework compound crystals are loaded in the through-pores of the cellulose aerogel; Cellulose aerogel is prepared by freeze-drying a porous forest material, then dissolving it in a cellulose dissolving solvent by vacuum heating, repeatedly soaking it in deionized water, and freeze-drying it. The specific operation of vacuum heating and dissolving in a cellulose dissolving solvent is as follows: the freeze-dried material and the cellulose dissolving solvent are placed in a branched reaction tube, evacuated to a vacuum state, and then heated in an oil bath; wherein, the solid-liquid ratio of the freeze-dried material to the cellulose dissolving solvent is 1:50, the oil bath heating temperature is 70°C, and the oil bath heating time is 24 hours.

2. The composite aerogel according to claim 1, characterized in that The metal organic framework compound is ZIF-67.

3. The composite aerogel according to claim 1, characterized in that Its raw materials include: cobalt salt, copper salt, 2-methylimidazole and cellulose aerogel.

4. The composite aerogel according to claim 3, characterized in that Cobalt salts include cobalt nitrate, cobalt acetate, cobalt chloride or hydrates of any of the above cobalt salts; The copper salt is copper nitrate, copper acetate, copper sulfate or a hydrate of any of the above copper salts.

5. The composite aerogel according to claim 3, characterized in that: The molar ratio of copper ions to cobalt ions is 0-5:5-10, and the molar ratio of copper ions to cobalt ions is not 0:10; The ratio of the total molar amount of cobalt salt and copper salt to the mass of cellulose aerogel is 5 mmol:1 g.

6. The composite aerogel according to claim 1, characterized in that The forestry material rich in pore structure is at least one of tung wood, balsa wood, cork oak and paulownia.

7. The composite aerogel according to claim 1, characterized in that: The lignocellulose dissolving solvent is a choline chloride-based deep eutectic solvent or an ionic liquid; The choline chloride-based deep eutectic solvent is prepared by stirring and heating choline chloride and oxalic acid; The ionic liquid is any one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ionic liquid, 1-butyl-3-methylimidazolium chloride salt ionic liquid, 1-allyl-3-methylimidazolium chloride salt ionic liquid, 1-(2-hydroxyethyl)-3-methylimidazolium chloride salt ionic liquid, and 1-ethyl-3-methylimidazolium chloride salt ionic liquid.

8. A method for preparing the composite aerogel according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: dissolving cobalt salt and copper salt in a solvent to obtain solution A; dissolving 2-methylimidazole in a solvent to obtain solution B; immersing cellulose aerogel in solution A, adding solution B, immersing again, washing, and drying.

9. Use of the composite aerogel according to any one of claims 1 to 7 in adsorption-degradation of dye wastewater.

10. A method for degrading dye wastewater, characterized in that: The method comprises the following steps: placing the composite aerogel according to any one of claims 1 to 7 in dye wastewater, stirring the mixture, adding hydrogen peroxide solution, and irradiating the mixture with ultraviolet light.

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