Photocatalytic porous composite material for sewage treatment as well as preparation method and application thereof

Abstract

The invention provides a photocatalytic porous composite material for sewage treatment and a preparation method and application thereof, and the preparation method comprises the following steps: dropwise adding an organic ligand solution into a precursor solution composed of a nano cellulose solution and a cobalt source solution, mixing a reaction solution with polyvinyl alcohol, injecting the mixture into a mold, and carrying out directional freezing to obtain an aerogel matrix; carrying out hydrophobic modification on the aerogel matrix to obtain a modified aerogel matrix; the preparation method comprises the following steps: dissolving tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethyl alcohol, stirring and heating to obtain precursor sol, adding a ferric nitrate solution into the precursor sol for hydrothermal reaction, and filtering and calcining after the reaction is finished to obtain doped titanium dioxide particles; and dispersing the doped titanium dioxide particles in deionized water to obtain a dispersion liquid, and dipping the modified aerogel matrix. According to the invention, a composite material composed of a nanocellulose / ZIF-67 composite aerogel matrix and doped titanium dioxide particles is constructed, and efficient sewage treatment of adsorption-catalysis-regeneration cycle is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and relates to a photocatalytic porous composite material for sewage treatment, a preparation method thereof, and uses thereof. Background Art

[0002] With the acceleration of industrialization and urbanization, the types and concentrations of harmful substances such as refractory organic pollutants, heavy metal ions, and microorganisms in water bodies are increasing day by day. Traditional physical adsorption, chemical precipitation, and biological treatment technologies face problems such as low efficiency, high cost, and easy generation of secondary pollution when treating complex sewage systems. Photocatalytic technology has attracted much attention because it can use solar energy to drive the degradation of pollutants. However, conventional photocatalytic materials have bottlenecks such as a narrow visible light response range, low quantum efficiency, easy deactivation of the catalyst, and difficult recovery, which restrict practical applications. Especially in sewage systems with high turbidity or containing suspended solids, problems such as a high recombination rate of photo-generated carriers and limited mass transfer of pollutants further reduce the degradation efficiency. There is an urgent need to develop new materials with both efficient adsorption and photocatalytic synergy functions.

[0003] Porous materials exhibit unique advantages in pollutant enrichment and interfacial reactions due to their high specific surface area and adjustable pore structure. However, single porous materials usually only have adsorption functions and are difficult to achieve the complete decomposition of pollutants. In recent years, researchers have tried to combine photocatalytic components with porous carriers, but there are often problems in the prior art such as uneven loading of active components, blockage of pore structures, and difficulty in synergistically optimizing light absorption and mass transfer efficiency. For example, some composite materials have the photocatalyst being overly embedded due to preparation process limitations, weakening the light energy utilization efficiency; some other materials are prone to shedding of active components or collapse of pore structures during the recycling process, affecting long-term stability. In addition, the design of pore size distribution and interfacial charge transport paths of hierarchically porous materials prepared by traditional methods still has deficiencies, restricting the separation efficiency of photo-generated electron-hole pairs. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a photocatalytic porous composite material for sewage treatment, a preparation method thereof, and uses thereof, and construct a composite material composed of a nanocellulose / ZIF-67 composite aerogel matrix and doped titanium dioxide particles, combining a hierarchically porous structure with a heterojunction photocatalytic function to achieve efficient sewage treatment.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect, a preparation method of a photocatalytic porous composite material for sewage treatment, the preparation method includes:

[0007] (I) Drop the organic ligand solution into the precursor solution composed of the nanocellulose solution and the cobalt source solution to obtain a reaction solution; mix the reaction solution with polyvinyl alcohol and then inject it into a mold for directional freezing to obtain an aerogel matrix; perform hydrophobic modification on the aerogel matrix to obtain a modified aerogel matrix.

[0008] (II) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol, stir and heat to obtain a precursor sol, add a ferric nitrate solution to the precursor sol for hydrothermal reaction, and after the reaction is completed, perform filtration and calcination to obtain doped titanium dioxide particles.

[0009] (III) Disperse the doped titanium dioxide particles in deionized water to obtain a dispersion, immerse the modified aerogel matrix in the dispersion, take it out and dry it to obtain the photocatalytic porous composite material.

[0010] The present invention constructs a composite material composed of a nanocellulose / ZIF-67 composite aerogel matrix and doped titanium dioxide particles, combines the hierarchical pore structure with the heterojunction photocatalytic function, and realizes efficient sewage treatment. The vertically through pores of the aerogel matrix and the ZIF-67 mesoporous network form a rapid mass transfer channel for pollutants, and selective adsorption of pollutants is achieved through hydrophobic modification; the doped titanium dioxide particles generate stable electron-hole pairs under visible light excitation, and the heterojunction structure formed with ZIF-67 significantly improves the carrier separation efficiency. At the same time, the cobalt nodes act as electron transport bridges to strengthen the free radical generation ability.

[0011] The present invention uses nanocellulose as a biomass skeleton material and utilizes the rich hydroxyl functional groups on its surface to coordinate with cobalt ions. When the cobalt nitrate solution is mixed with nanocellulose, cobalt ions are preferentially adsorbed around the oxygen-containing groups of the cellulose molecular chain to form a uniform metal ion distribution network. Subsequently, the introduced 2-methylimidazole organic ligand undergoes a self-assembly reaction with cobalt ions to generate the metal-organic framework material ZIF-67 in the gaps of the nanocellulose network. The excessive organic ligand not only ensures the complete progress of the reaction but also inhibits the excessive growth of crystals through steric hindrance effects, and finally forms regular dodecahedral crystals. These ZIF-67 crystals are tightly bound to the nanocellulose network through hydrogen bonding, retaining both the three-dimensional pore structure of the aerogel matrix and endowing it with catalytic active sites, which can quickly capture heavy metal ions (such as Pb 2+ 、Cd 2 + ), organic dye molecules and oil pollutants in wastewater; at the same time, its Lewis acidic sites (Co 2+ nodes) can also bind to specific pollutants (such as sulfur- or nitrogen-containing compounds) through coordination to enhance selective adsorption.

[0012] In the process of preparing doped titanium dioxide particles, the present invention first forms a uniform titanium dioxide nanostructure through the step-by-step hydrolysis of tetrabutyl titanate in an acidic environment. Cetyltrimethylammonium bromide (CTAB) is used as a template agent to adjust the morphology and structure of titanium dioxide through molecular self-assembly. Its cationic head adsorbs on the negatively charged colloid surface generated by the hydrolysis of tetrabutyl titanate through electrostatic interaction, forming an oriented monolayer. The steric hindrance generated by the long alkyl chains effectively inhibits the aggregation of titanium dioxide particles generated by hydrolysis, and promotes the orderly hydrolysis of tetrabutyl titanate to generate titanium dioxide nanoparticles with uniform size. Subsequently, the present invention realizes the doping of iron element through the hydrothermal reaction of iron nitrate solution, so that Fe 3+ partially replaces Ti 4+ sites in the titanium dioxide lattice, triggering lattice distortion to generate oxygen vacancy defects. These defects, as electron traps, significantly extend the lifetime of photo-generated carriers, and at the same time change the energy band structure of the material. The 3d orbit of Fe 3+ forms an intermediate energy level in the forbidden band, shifting the light absorption red to the visible light region of 550 nm.

[0013] The present invention realizes the enhanced composite of the modified aerogel matrix and the doped titanium dioxide particles by the negative pressure-atmospheric pressure alternating impregnation method, forming a multi-level synergistic photocatalytic porous composite material. In the process of sewage treatment, pollutants are first captured by the hydrophobic surface of the modified aerogel matrix, and the oil droplets quickly spread under the action of surface tension to form an adsorption layer, and then penetrate into the material through the capillary action of the pores. Under the irradiation of visible light, the doped titanium dioxide particles are activated to generate electron-hole pairs. After the electrons jump from the valence band to the conduction band, they are transferred to the material surface through the cobalt nodes of ZIF-67 and react with adsorbed oxygen to generate superoxide radicals (·O2 - ), and the holes directly oxidize pollutants or react with water to generate hydroxyl radicals (·OH). A heterojunction structure is formed between ZIF-67 and the doped titanium dioxide particles. The relatively narrow band gap of ZIF-67 promotes the transfer of photo-generated electrons as an electron acceptor, while the wide band gap characteristic of the doped titanium dioxide particles maintains a strong oxidation potential, and the energy level matching of the two forms an electron transport channel.

[0014] As a preferred technical solution of the present invention, in step (Ⅰ), the organic ligand solution is composed of 2-methylimidazole and methanol.

[0015] In some alternative examples, the concentration of 2-methylimidazole in the organic ligand solution is 0.9 - 1 mol / L. For example, it can be 0.9 mol / L, 0.91 mol / L, 0.92 mol / L, 0.93 mol / L, 0.94 mol / L, 0.95 mol / L, 0.96 mol / L, 0.97 mol / L, 0.98 mol / L, 0.99 mol / L or 1 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0016] In some alternative examples, the mass fraction of the nanocellulose solution is 1 - 2 wt%. For example, it can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt% or 2.0 wt%. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0017] In some alternative examples, the cobalt source solution is composed of cobalt nitrate and deionized water.

[0018] In some alternative examples, the concentration of cobalt nitrate in the cobalt source solution is 0.15 - 0.25 mol / L. For example, it can be 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, 0.2 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L or 0.25 mol / L. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0019] In some alternative examples, the volume ratio of the nanocellulose solution to the cobalt source solution is (2 - 3):1. For example, it can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0020] The present invention specifically defines that the volume ratio of the nanocellulose solution to the cobalt source solution is (2 - 3):1. As the core component of the aerogel framework, the dosage of nanocellulose directly affects the crosslinking density of the fiber network and the coordination efficiency of cobalt ions. When the volume ratio of the nanocellulose solution to the cobalt source solution is within the range defined by the present invention, the hydroxyl groups on the nanocellulose chains can form an appropriate coordination interaction with cobalt ions, ensuring that sufficient metal ions are anchored on the surface of the nanocellulose network and avoiding the destruction of the hydrogen bond crosslinking structure of nanocellulose by excessive cobalt salts. This enables the subsequent added 2-methylimidazole organic ligand to be evenly distributed in the gaps of the cellulose network and combine with cobalt ions to form ZIF-67 crystals with uniform size, constructing a stable hierarchical pore structure for the aerogel matrix.

[0021] When the addition amount of the nanocellulose solution is too low, the concentration of cobalt ions is too high, causing the coordination reaction to concentrate in local areas and the ZIF-67 crystals to grow excessively to form large-size aggregates. This not only blocks the pores of the aerogel matrix and reduces its porosity but also weakens the mechanical strength of the nanocellulose network. At the same time, the unreacted free cobalt ions will crystallize out during the directional freezing process, destroying the regularity of the pore structure of the aerogel matrix.

[0022] When the addition amount of the nanocellulose solution is too high, the excessive nanocellulose chains hinder the uniform distribution of cobalt ions due to steric hindrance effects, resulting in insufficient nucleation sites for ZIF-67 crystals. Eventually, the formed ZIF-67 crystals have poor dispersibility and a reduced density of catalytic active sites. At the same time, the dense network formed by excessive crosslinking of nanocellulose will compress the pore space, significantly reducing the specific surface area of the aerogel matrix.

[0023] It should be noted that the present invention does not make specific requirements or special limitations on the dropping rate of the organic ligand solution. Exemplarily, the dropping rate of the organic ligand solution is 1.5 - 2.5 mL / min. For example, it can be 1.5 mL / min, 1.6 mL / min, 1.7 mL / min, 1.8 mL / min, 1.9 mL / min, 2.0 mL / min, 2.1 mL / min, 2.2 mL / min, 2.3 mL / min, 2.4 mL / min, or 2.5 mL / min, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0024] In some alternative examples, the molar ratio of 2-methylimidazole in the organic ligand solution to cobalt ions in the cobalt source solution is (5 - 6):1. For example, it can be 5.0:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1, or 6.0:1, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0025] In some alternative examples, under stirring and heating conditions, the organic ligand solution is dropped into the precursor solution.

[0026] In some alternative examples, the heating temperature when the organic ligand solution is dropped is 60 - 70 °C, for example, it can be 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C or 70 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] In some alternative examples, after the organic ligand solution is completely dropped, stirring and mixing continue under heating conditions for 4 - 5 h to obtain the reaction solution, for example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] As a preferred technical solution of the present invention, in step (Ⅰ), the addition amount of the polyvinyl alcohol is 7 - 9 wt% of the mass of the reaction solution, for example, it can be 7.0 wt%, 7.2 wt%, 7.4 wt%, 7.6 wt%, 7.8 wt%, 8.0 wt%, 8.2 wt%, 8.4 wt%, 8.6 wt%, 8.8 wt% or 9.0 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] In some alternative examples, the stirring and mixing time of the reaction solution and the polyvinyl alcohol is 2 - 4 h, for example, it can be 2.0 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3.0 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h or 4.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In some alternative examples, the directional freezing process includes:

[0031] Cooling to a first freezing temperature at a first cooling rate and holding, and then continuing to cool to a second freezing temperature at a second cooling rate and holding.

[0032] In the present invention, in the first cooling stage, the temperature is rapidly decreased to -15~-20°C at a rate of -1~-2°C / min, which promotes the formation of a large number of tiny ice crystal nuclei in the solution. During the heat preservation process, the ice crystals initially extend and grow along the temperature gradient direction to form an initial pore framework with a diameter of about 50~150μm. In the second cooling stage, the temperature is slowly decreased to -30~-40°C at a rate of -0.5~-1°C / min. At this time, the solution viscosity increases significantly, and a secondary microporous structure is induced to form on the wall surface of the already formed initial pores. During the heat preservation process, the solvent molecules in the remaining unfrozen liquid phase are fully crystallized, avoiding stress concentration caused by rapid deep cooling, and finally forming a hierarchical pore structure in which vertically arranged through pores and wall surface micropores are intertwined. This hierarchical pore structure directly affects the sewage treatment effect of the material. The through large-diameter channels greatly improve the pollutant adsorption rate, and the secondary microporous structure formed on the wall surface of the large-diameter channels provides a high-density anchoring site for the loading of ZIF-67 crystals.

[0033] In some optional examples, the first cooling rate is -1~-2°C / min. For example, it can be -1°C / min, -1.1°C / min, -1.2°C / min, -1.3°C / min, -1.4°C / min, -1.5°C / min, -1.6°C / min, -1.7°C / min, -1.8°C / min, -1.9°C / min or -2°C / min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] In some optional examples, the first freezing temperature is -15~-20°C. For example, it can be -15°C, -15.5°C, -16°C, -16.5°C, -17°C, -17.5°C, -18°C, -18.5°C, -19°C, -19.5°C or -20°C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] In some optional examples, the heat preservation time at the first freezing temperature is 0.5~1.5h. For example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h or 1.5h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] In some alternative examples, the second cooling rate is -0.5 to -1 °C / min. For example, it can be -0.5 °C / min, -0.55 °C / min, -0.6 °C / min, -0.65 °C / min, -0.7 °C / min, -0.75 °C / min, -0.8 °C / min, -0.85 °C / min, -0.9 °C / min, -0.95 °C / min, or -1 °C / min. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0037] In some alternative examples, the second freezing temperature is -30 to -40 °C. For example, it can be -30 °C, -31 °C, -32 °C, -33 °C, -34 °C, -35 °C, -36 °C, -37 °C, -38 °C, -39 °C, or -40 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0038] In some alternative examples, the holding time at the second freezing temperature is 3 to 4 h. For example, it can be 3.0 h, 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h, or 4.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0039] As a preferred technical solution of the present invention, in step (I), the hydrophobic modification treatment includes:

[0040] Soak the aerogel matrix in a silane coupling agent solution, oscillate and heat it, then take out the aerogel matrix, wash and dry it to obtain the modified aerogel matrix.

[0041] During the modification process, the silanol groups generated by the hydrolysis of the silane coupling agent undergo a condensation reaction with the hydroxyl groups on the surface of the aerogel matrix to form a dense Si-O-Si covalent bond network. The directional arrangement of the long-chain alkyl groups makes the surface contact angle of the modified aerogel matrix reach more than 145°. This chemical modification endows the aerogel matrix with superhydrophobic properties on the one hand, which can effectively block the penetration of water molecules and prevent the hydrolysis reaction of ZIF-67 crystals in the water environment, resulting in the dissolution of cobalt ions, so that the modified aerogel matrix maintains its structural integrity in a wide range of pH = 3 to 11. On the other hand, the silane layer grafted on the surface of the aerogel matrix can also reinforce the nodal connection of cellulose fibers through intermolecular forces, significantly improving the anti-swelling ability of the modified aerogel matrix in the aqueous phase environment.

[0042] In some alternative examples, the silane coupling agent solution is composed of a silane coupling agent and an ethanol aqueous solution.

[0043] In some alternative examples, the mass fraction of the silane coupling agent in the silane coupling agent solution is 1.8 - 2.2 wt%, for example, it can be 1.8 wt%, 1.85 wt%, 1.9 wt%, 1.95 wt%, 2.0 wt%, 2.05 wt%, 2.1 wt%, 2.15 wt% or 2.2 wt%, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative examples, when the aerogel matrix is soaked in the silane coupling agent solution, the heating temperature is 35 - 45 °C, for example, it can be 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, 40 °C, 41 °C, 42 °C, 43 °C, 44 °C or 45 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative examples, the soaking time of the aerogel matrix in the silane coupling agent solution is 12 - 24 h, for example, it can be 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0046] It should be noted that after the soaking of the aerogel matrix is completed, it is taken out, washed with absolute ethanol, and then vacuum dried. The present invention does not make specific requirements and special limitations on the temperature and time of vacuum drying. Exemplarily, the temperature of vacuum drying is 45 - 55 °C, for example, it can be 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 51 °C, 52 °C, 53 °C, 54 °C or 55 °C; the time of vacuum drying is 10 - 12 h, for example, it can be 10 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0047] As a preferred technical solution of the present invention, in step (II), tetrabutyl titanate and cetyltrimethylammonium bromide are dissolved in absolute ethanol, and after mixing evenly, a precursor solution is obtained. A nitric acid solution is added dropwise to the precursor solution to adjust its pH value to 4 - 5, and then the precursor solution is stirred and heated to obtain the precursor sol, for example, it can be 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0048] In some alternative embodiments, the molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:(0.5 - 1). For example, it can be 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95 or 1:1. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0049] The present invention specifically defines that the molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide (CTAB) is 1:(0.5 - 1). Within this molar ratio range, the cationic head of CTAB is adsorbed on the negatively charged colloid surface generated by the hydrolysis of tetrabutyl titanate through electrostatic interaction, forming a monolayer coverage. The steric hindrance generated by its long alkyl chain can effectively inhibit the excessive condensation of titanium species, contributing to the formation of titanium dioxide nanoparticles with uniform particle size. In addition, the appropriate addition of CTAB also significantly improves the doping efficiency of iron ions. CTAB molecules stabilize Fe 3+ , enabling it to be uniformly dispersed in the titanium dioxide lattice, forming an appropriate amount of oxygen vacancy defects to capture photo-generated electrons, and at the same time extending the light response to the visible light region.

[0050] If the addition amount of CTAB is lower than the lower limit of the range defined in the present invention, the CTAB concentration is insufficient to form an effective micelle template, and the hydrolysis rate of tetrabutyl titanate increases, resulting in non-uniform sizes of the hydrolyzed titanium dioxide nanoparticles. Moreover, when the addition amount of CTAB is too low, the steric hindrance effect is insufficient, triggering the aggregation of titanium dioxide nanoparticles and forming a dense blocky structure, leading to a reduction in the specific surface area of the material. In addition, during the iron ion doping process, due to the lack of the dispersion effect of CTAB, Fe 3+ enriches on the outer surface of the crystal lattice rather than uniformly replacing Ti 4+ sites, forming an unstable doping structure and increasing the recombination rate of photo-generated carriers.

[0051] If the addition amount of CTAB exceeds the upper limit of the range defined in the present invention, the excessive CTAB forms high-density micelles, overly inhibiting the hydrolysis reaction of tetrabutyl titanate, resulting in the formation of ultra-fine nanoparticles with low crystallinity. These nanoparticles exhibit the quantum confinement effect due to the size effect, with an increased bandgap width and loss of visible light response ability. At the same time, the carbon layer remaining after high-temperature calcination of the excessive CTAB molecules is too thick, wrapping the surface of the titanium dioxide particles and hindering the exposure of active sites, leading to a reduction in the photocatalytic degradation efficiency. In addition, during the iron ion doping process, due to the overly strong complexation effect of the excessive CTAB on Fe 3+ , Fe 3+ cannot effectively enter the lattice, not only unable to form a stable charge transfer channel, but also covering the active sites of TiO2 and reducing the effective contact area for photocatalytic reactions.

[0052] In some optional examples, the mass fraction of tetrabutyl titanate in the precursor solution is 10 - 12 wt%, for example, it can be 10 wt%, 10.2 wt%, 10.4 wt%, 10.6 wt%, 10.8 wt%, 11 wt%, 11.2 wt%, 11.4 wt%, 11.6 wt%, 11.8 wt% or 12 wt%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0053] It should be noted that the present invention does not make specific requirements and special limitations on the concentration of the nitric acid solution. Exemplarily, the concentration of the nitric acid solution is 0.5 - 1.5 mol / L, for example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0054] In some optional examples, the mixing and stirring time of the precursor solution is 3 - 5 h, for example, it can be 3.0 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h, 4.0 h, 4.2 h, 4.4 h, 4.6 h, 4.8 h or 5.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0055] In some optional examples, the heating temperature during the mixing and stirring of the precursor solution is 55 - 65 °C, for example, it can be 55 °C, 56 °C, 57 °C, 58 °C, 59 °C, 60 °C, 61 °C, 62 °C, 63 °C, 64 °C or 65 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0056] As a preferred technical solution of the present invention, in step (II), the molar ratio of Fe:Ti of the ferric nitrate solution to the precursor sol is (0.02 - 0.03):1, for example, it can be 0.02:1, 0.021:1, 0.022:1, 0.023:1, 0.024:1, 0.025:1, 0.026:1, 0.027:1, 0.028:1, 0.029:1 or 0.03:1, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0057] The present invention specifically limits the molar ratio of Fe:Ti of the ferric nitrate solution to the precursor sol to be (0.02 - 0.03):1. Within this range, Fe 3+ partially replaces Ti in the titanium dioxide lattice through hydrothermal reaction4+ sites, forming moderate lattice distortion and generating oxygen vacancy defects. These defects act as electron trapping centers, effectively suppressing the recombination of photo-generated electron-hole pairs and prolonging the carrier lifetime. At the same time, the 3d orbitals of Fe 3+ introduce intermediate energy levels in the TiO2 bandgap, shifting the light absorption red to about 550 nm and endowing the material with significant visible light response ability. During the iron ion doping process, Fe in iron nitrate 3+ forms a coordination bond with the titanium hydroxyl groups generated by the hydrolysis of tetrabutyl titanate. The surfactant effect of CTAB further guides the uniform distribution of Fe 3+ in the lattice, avoiding phase separation caused by local enrichment.

[0058] When the addition amount of the iron nitrate solution is lower than the lower limit of the range defined in the present invention, the insufficient doping concentration of iron ions results in too low lattice defect density, and the number of oxygen vacancies is not enough to form an effective electron transport channel. The recombination rate of photo-generated carriers increases, the quantum efficiency decreases, and the intermediate energy level bandgap is too narrow, resulting in a decrease in visible light absorption effect. The photocatalytic effect of the finally obtained photocatalytic porous composite material still depends on ultraviolet light excitation, and the pollutant degradation efficiency under natural light conditions is poor.

[0059] When the addition amount of the iron nitrate solution is higher than the upper limit of the range defined in the present invention, excessive Fe 3+ triggers excessive lattice distortion, and Fe2O3 heterophase is formed in some regions due to charge imbalance. These heterophases act as recombination centers of electron-hole pairs, shortening the carrier lifetime. In addition, the surface of titanium dioxide particles is covered by iron oxides, reducing the effective contact area of active sites and decreasing the pollutant adsorption capacity.

[0060] In some alternative examples, the mass fraction of the iron nitrate solution is 10-12 wt%, for example, it can be 10 wt%, 10.2 wt%, 10.4 wt%, 10.6 wt%, 10.8 wt%, 11 wt%, 11.2 wt%, 11.4 wt%, 11.6 wt%, 11.8 wt% or 12 wt%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0061] It should be noted that preferably before the hydrothermal reaction, the mixed solution composed of the precursor sol and the iron nitrate solution is ultrasonically dispersed. The present invention does not make specific requirements and special limitations on the power and time of ultrasonic dispersion. Exemplarily, the ultrasonic power of the ultrasonic dispersion of the precursor sol and the iron nitrate solution is 300 - 400 W, for example, it can be 300 W, 310 W, 320 W, 330 W, 340 W, 350 W, 360 W, 370 W, 380 W, 390 W or 400 W; the time of the ultrasonic dispersion of the precursor sol and the iron nitrate solution is 1 - 2 h, for example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0062] In some alternative examples, the temperature of the hydrothermal reaction is 160 - 180 °C, for example, it can be 160 °C, 162 °C, 164 °C, 166 °C, 168 °C, 170 °C, 172 °C, 174 °C, 176 °C, 178 °C or 180 °C, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0063] In some alternative examples, the time of the hydrothermal reaction is 12 - 24 h, for example, it can be 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h or 24 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0064] As a preferred technical solution of the present invention, in step (II), the calcination process includes:

[0065] First, heat to the first calcination temperature at the first heating rate and hold the temperature.

[0066] Subsequently, continue to heat to the second calcination temperature at the second heating rate and hold the temperature.

[0067] In the present invention, through the low-temperature treatment in the first stage, the organic template CTAB is removed and the anatase phase structure is stabilized. Through the high-temperature calcination in the second stage, the uniform distribution and lattice reconstruction of Fe 3+ are promoted, and finally doped titanium dioxide particles with high crystallinity and good stability are obtained.

[0068] In some alternative examples, the first heating rate is 2 to 3 °C / min. For example, it can be 2.0 °C / min, 2.1 °C / min, 2.2 °C / min, 2.3 °C / min, 2.4 °C / min, 2.5 °C / min, 2.6 °C / min, 2.7 °C / min, 2.8 °C / min, 2.9 °C / min or 3.0 °C / min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0069] In some alternative examples, the first calcination temperature is 250 to 300 °C. For example, it can be 250 °C, 255 °C, 260 °C, 265 °C, 270 °C, 275 °C, 280 °C, 285 °C, 290 °C, 295 °C or 300 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0070] In some alternative examples, it is held at the first calcination temperature for 2 to 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0071] In some alternative examples, the second heating rate is 4 to 5 °C / min. For example, it can be 4.0 °C / min, 4.1 °C / min, 4.2 °C / min, 4.3 °C / min, 4.4 °C / min, 4.5 °C / min, 4.6 °C / min, 4.7 °C / min, 4.8 °C / min, 4.9 °C / min or 5.0 °C / min. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0072] In some alternative examples, the second calcination temperature is 350 to 400 °C. For example, it can be 350 °C, 355 °C, 360 °C, 365 °C, 370 °C, 375 °C, 380 °C, 385 °C, 390 °C, 395 °C or 400 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0073] The present invention specifically defines that the second calcination temperature is 350 to 400 °C. Within this temperature range, the residual CTAB template agent is carbonized to form a thin layer of graphitized carbon, and this carbon layer generates electron coupling with the iron-doped sites through π-π interaction to form an electron transport channel.

[0074] When the second calcination temperature is lower than 350 °C, the anatase phase crystallization is incomplete, and the remaining amorphous regions become carrier recombination centers, resulting in a decrease in quantum efficiency. In addition, when the calcination temperature is too low, the long-chain alkyl residues generated by incomplete pyrolysis of CTAB wrap the particle surface, hindering the contact between pollutant molecules and active sites, leading to a reduction in catalytic effect. At the same time, when the calcination temperature is too low, iron doping mainly occurs through surface adsorption and fails to effectively enter the lattice to form stable defect pairs, making it prone to ion dissolution under light illumination or water flow impact.

[0075] When the second calcination temperature exceeds 400 °C, the anatase phase transforms into the rutile phase. The relatively wide bandgap of the rutile phase weakens the visible light response ability, and its high carrier recombination rate reduces the photocatalytic efficiency. In addition, CTAB is overly graphitized at high temperatures to form an overly thick graphite layer, and its shielding effect makes it difficult for photo-generated electrons to migrate to the surface to participate in the oxidation reaction. At the same time, the thermal stress induced by high temperature generates microcracks on the material surface, making it prone to structural collapse in dynamic water flow and significantly shortening the service life.

[0076] In some alternative examples, keep the temperature for 3 - 4 h at the second calcination temperature. For example, it can be 3.0 h, 3.1 h, 3.2 h, 3.3 h, 3.4 h, 3.5 h, 3.6 h, 3.7 h, 3.8 h, 3.9 h or 4.0 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0077] As a preferred technical solution of the present invention, in step (III), the mass fraction of the doped titanium dioxide particles in the dispersion liquid is 2 - 3 wt%. For example, it can be 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt% or 3.0 wt%, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0078] In some alternative examples, the impregnation process includes:

[0079] Add the modified aerogel matrix and the dispersion liquid into a reaction kettle, completely immerse the modified aerogel matrix in the dispersion liquid, evacuate the reaction kettle, and then restore it to normal pressure. Stir the dispersion liquid under normal pressure; then continue to evacuate; repeat the evacuation and restoration to normal pressure of the reaction kettle 3 - 5 times.

[0080] The negative-pressure - normal-pressure alternating impregnation process adopted by the present invention realizes the deep penetration and uniform loading of doped titanium dioxide particles in the multi-level pores of the modified aerogel matrix. In the first vacuum pumping stage, the gas in the pores of the modified aerogel matrix is discharged, and a stable low-pressure environment is formed inside, prompting the dispersion liquid to gradually infiltrate the main pores in the modified aerogel matrix under capillary action. In the negative-pressure holding stage, the dispersion liquid can overcome the wetting resistance of the micro-nano pores inside the modified aerogel matrix and penetrate to the deep layer of the modified aerogel matrix. When nitrogen is introduced to restore normal pressure, the external air pressure increases, prompting the secondary distribution of the dispersion liquid in the pores of the modified aerogel matrix, and the doped titanium dioxide particles gradually settle on the pore wall under the action of gravity and van der Waals force. Stir the dispersion liquid in the normal-pressure stage to break the particle aggregates in the dispersion liquid.

[0081] In some optional examples, the mass ratio of the modified aerogel matrix to the doped titanium dioxide particles in the dispersion liquid is 1:(0.5 - 0.7). For example, it can be 1:0.5, 1:0.52, 1:0.54, 1:0.56, 1:0.58, 1:0.6, 1:0.62, 1:0.64, 1:0.66, 1:0.68 or 1:0.7, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0082] The present invention specifically defines that the mass ratio of the modified aerogel matrix to the doped titanium dioxide particles in the dispersion liquid is 1:(0.5 - 0.7). Within this mass ratio range, the doped titanium dioxide particles are evenly distributed on the pore walls of the modified aerogel matrix, forming both a continuous catalytic active layer and retaining sufficient pore space for pollutant diffusion. An appropriate amount of doped titanium dioxide particles enables the pore structure of the modified aerogel matrix to be maintained, and pollutants quickly enter the interior of the pores under capillary action and are gradually captured and degraded by the catalytic active layer on the wall.

[0083] When the addition amount of the doped titanium dioxide particles is lower than the lower limit of the range defined by the present invention, the doped titanium dioxide particles are sparsely distributed and it is difficult to form a continuous catalytic active layer. Although the modified aerogel matrix maintains a highly open pore structure, the catalytic active sites are dispersed, and the photo-generated carriers cannot be transferred through a continuous path, resulting in a large amount of recombination of electron-hole pairs during migration, leading to insufficient local catalytic ability and inability to completely degrade pollutants.

[0084] When the addition amount of the doped titanium dioxide particles is higher than the lower limit of the range defined by the present invention, the excessive doped titanium dioxide particles accumulate in the pores to form a dense catalytic active layer, resulting in a significant reduction in the pore diameter of the modified aerogel matrix, blocking the diffusion path of pollutants, and a significant decrease in the adsorption rate. In addition, although the dense-packed catalytic active layer can increase the density of surface catalytic sites, the aggregation effect between the doped titanium dioxide particles weakens the light energy absorption efficiency, resulting in a narrow visible light response range.

[0085] In some alternative examples, the reactor is evacuated to -80 to -90 kPa. For example, it can be -80 kPa, -81 kPa, -82 kPa, -83 kPa, -84 kPa, -85 kPa, -86 kPa, -87 kPa, -88 kPa, -89 kPa, or -90 kPa. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0086] In some alternative examples, the time for which the reactor maintains the vacuum is 20 to 30 min. For example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min, or 30 min. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0087] In some alternative examples, during the atmospheric pressure stage, the dispersion is stirred for 30 to 40 min. For example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, or 40 min. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0088] It should be noted that after the impregnation is completed, the impregnated modified aerogel matrix is taken out and dried. The present invention does not make specific requirements or special limitations on the drying temperature and time. Exemplarily, the drying temperature is 50 to 60 °C. For example, it can be 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C, or 60 °C, and the drying time is 10 to 12 h. For example, it can be 10 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h, or 12 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0089] In a second aspect, the present invention provides a photocatalytic porous composite material for sewage treatment prepared by using the preparation method described in the first aspect.

[0090] In a third aspect, the present invention provides a use of the photocatalytic porous composite material for sewage treatment described in the second aspect, and the photocatalytic porous composite material is used for sewage treatment.

[0091] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0092] The present invention constructs a composite material composed of a nanocellulose / ZIF-67 composite aerogel matrix and doped titanium dioxide particles, combines the hierarchical pore structure with the heterojunction photocatalytic function, and realizes efficient sewage treatment. The vertically penetrating pores of the aerogel matrix and the mesoporous network of ZIF-67 form a rapid mass transfer channel for pollutants, and selective adsorption of pollutants is achieved through hydrophobic modification; the doped titanium dioxide particles generate stable electron-hole pairs under visible light excitation, and the heterojunction structure formed with ZIF-67 significantly improves the carrier separation efficiency. At the same time, the cobalt nodes strengthen the free radical generation ability as an electron transport bridge. Description of the Drawings

[0093] Figure 1 It is a process flow chart for the preparation of the photocatalytic porous composite material provided in Examples 1-15 of the present invention;

[0094] Figure 2 It is an infrared spectrum diagram of nanocellulose, ZIF-67 and the aerogel matrix prepared in Example 1 of the present invention;

[0095] Figure 3 It is an XRD spectrum diagram of nanocellulose, ZIF-67 and the aerogel matrix prepared in Example 1 of the present invention;

[0096] Figure 4 It is a test curve graph of the water contact angle and oil contact angle of the modified aerogel matrix prepared in Example 1 of the present invention;

[0097] Figure 5 It is an ultraviolet-visible light spectrum diagram of the doped titanium dioxide particles prepared in Example 1 of the present invention;

[0098] Figure 6 It is an XRD spectrum diagram of the doped titanium dioxide particles prepared in Example 1 of the present invention;

[0099] Figure 7 It is a scanning electron microscope image of the doped titanium dioxide particles prepared in Example 1 of the present invention. Detailed Embodiments

[0100] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims of this application and its specification, and these technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0101] Example 1

[0102] This embodiment provides a preparation method of a photocatalytic porous composite material for sewage treatment, as Figure 1 shown. The specific preparation method includes the following steps:

[0103] (1) Disperse cobalt nitrate in deionized water. After mixing evenly, a cobalt source solution with a concentration of 0.15 mol / L is obtained. Mix a nanocellulose solution with a mass fraction of 1 wt% and the cobalt source solution in a volume ratio of 3:1 to obtain a precursor solution. Disperse 2-methylimidazole in methanol. After mixing evenly, an organic ligand solution with a concentration of 0.9 mol / L is obtained. Under stirring and heating at 60 °C, the organic ligand solution is dropped into the precursor solution at a rate of 1.5 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5:1. After all the organic ligand solution is dropped, continue to stir the obtained mixture at 60 °C for 5 h to obtain a reaction solution;

[0104] Mix the reaction solution and polyvinyl alcohol and stir for 2 h. The addition amount of polyvinyl alcohol is 7 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool down at a rate of -1 °C / min to -15 °C and keep warm for 1.5 h, and then continue to cool down at a rate of -0.5 °C / min to -30 °C and keep warm for 4 h to obtain an aerogel matrix;

[0105] Add silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 1.8 wt% is obtained. Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 35 °C for 24 h. Then take out the aerogel matrix, wash it with ethanol and place it in a vacuum dryer at 45 °C for 12 h to obtain a modified aerogel matrix;

[0106] (2) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol. The molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:0.5. After mixing evenly, a precursor solution is obtained. The mass fraction of tetrabutyl titanate in the precursor solution is 10 wt%. Drop a nitric acid solution with a concentration of 0.5 mol / L into the precursor solution to adjust its pH value to 5. Mix and stir the precursor solution at 55 °C for 5 h to obtain a precursor sol;

[0107] Add a nitric acid iron solution with a mass fraction of 10 wt% to the precursor sol. The molar ratio of Fe:Ti in the nitric acid iron solution to the precursor solution is 0.02:1. Ultrasonically disperse it at an ultrasonic power of 300 W for 2 h, and then carry out a hydrothermal reaction at 160 °C for 24 h. After the reaction is completed, filter to obtain a reaction product;

[0108] The reaction product was heated to 250 °C at a heating rate of 2 °C / min and held for 3 h, and then continued to be heated to 350 °C at a heating rate of 4 °C / min and held for 4 h to obtain doped titanium dioxide particles;

[0109] (3)The doped titanium dioxide particles obtained in step (2) were dispersed in deionized water, and after mixing evenly, a dispersion was obtained. The mass fraction of the doped titanium dioxide particles in the dispersion was 2 wt%; the modified aerogel matrix obtained in step (1) and the dispersion were added to a reaction kettle. The mass ratio of the modified aerogel matrix to the doped titanium dioxide particles was 1:0.5 to ensure that the modified aerogel matrix was completely immersed in the dispersion. The reaction kettle was evacuated to -80 kPa and maintained for 30 min; then nitrogen was introduced into the reaction kettle to return to normal pressure, and the dispersion was stirred for 30 min; then the reaction kettle was continuously evacuated to -80 kPa and maintained for 30 min; the reaction kettle was repeatedly evacuated and returned to normal pressure 5 times, and then taken out and vacuum dried at 50 °C for 12 h to obtain the photocatalytic porous composite material.

[0110] Figure 2 are the infrared spectra of nanocellulose, ZIF-67, and the aerogel matrix prepared in this example. It can be seen from the figure that in the infrared spectrum of nanocellulose, the characteristic peaks at 3460 cm -1 and 1735 cm -1 are attributed to the C-H stretching of cellulose hydroxyl and the C=O stretching vibration of carboxyl, respectively. In the infrared spectrum of the aerogel matrix obtained by in-situ growth of ZIF-67 nanoparticles, the absorption band appearing at 422 cm -1 is attributed to the Co-N stretching vibration of ZIF-67, and the vibration peaks at 1382 cm -1 , 1417 cm -1 and 1453 cm -1 are attributed to the C-N bond stretching vibration of 2-methylimidazole, and the characteristic peaks at 689 cm -1 , 753 cm -1 and 1306 cm -1 are attributed to the bending vibration of 2-methylimidazole. The above results indicate that ZIF-67 nanoparticles are successfully loaded on the aerogel matrix.

[0111] Figure 3XRD patterns of nanocellulose, ZIF-67 and the aerogel matrix prepared in this example. As can be seen from the figure, the main diffraction peaks at 2θ = 7.4°, 10.4°, 12.7°, 18.1° and 26.7° correspond to the (011), (002), (112), (222) and (134) crystal planes of ZIF-67 respectively. In addition, in the XRD pattern of the aerogel matrix, the weak characteristic peak at 22.6° belongs to the (002) crystal plane of nanocellulose. The above results indicate that ZIF-67 is successfully loaded on the aerogel matrix.

[0112] Figure 4 Test curve graphs of the water contact angle and oil contact angle of the modified aerogel matrix prepared in this example. As can be seen from the figure, with the extension of the test time, the surface water contact angle of the modified aerogel matrix decreases slightly, but its average value is 145°, still belonging to a superhydrophobic surface; similarly, with the extension of the test time, the surface oil contact angle of the modified aerogel matrix also decreases slightly, but its average value is 10°, belonging to a superoleophilic surface, which indicates that the modified aerogel matrix obtained after modification with silane coupling agent has hydrophobic and oleophilic properties.

[0113] Figure 5 UV-visible light spectrum of the doped titanium dioxide particles prepared in this example. As can be seen from the figure, when doped with Fe 3+ After that, the absorption wavelength of the doped titanium dioxide particles redshifts towards visible light, and the absorption of visible light increases.

[0114] Figure 6 XRD pattern of the doped titanium dioxide particles prepared in this example. As can be seen from the figure, the doped titanium dioxide particles prepared in this example have characteristic peaks of anatase type, corresponding to the (101), (004), (200), (105), (211) crystal planes of anatase phase at 2θ = 25.28°, 38.12°, 48.22°, 54.24°, 62.84° respectively.

[0115] Figure 7 Scanning electron micrograph of the doped titanium dioxide particles prepared in this example. As can be seen from the figure, the doped titanium dioxide particles present a spherical structure with regular structure and uniform particle size, and their particle size is in the range of 20 - 50 nm.

[0116] Example 2

[0117] This example provides a preparation method of a photocatalytic porous composite material for sewage treatment. As Figure 1 shown, the preparation method specifically includes the following steps:

[0118] (1) Disperse cobalt nitrate in deionized water. After mixing evenly, a cobalt source solution with a concentration of 0.18 mol / L is obtained. Mix a nanocellulose solution with a mass fraction of 1.2 wt% and the cobalt source solution evenly according to a volume ratio of 2.8:1 to obtain a precursor solution. Disperse 2-methylimidazole in methanol. After mixing evenly, an organic ligand solution with a concentration of 0.92 mol / L is obtained. Under stirring and heating at 62 °C, the organic ligand solution is dropped into the precursor solution at a rate of 1.8 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5.2:1. After all the organic ligand solution is dropped, continue to stir the obtained mixture at 62 °C for 4.8 h to obtain a reaction solution;

[0119] Mix the reaction solution and polyvinyl alcohol and stir for 2.5 h. The addition amount of polyvinyl alcohol is 7.5 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool down to -16 °C at a cooling rate of -1.2 °C / min and keep warm for 1.2 h. Then continue to cool down to -32 °C at a cooling rate of -0.6 °C / min and keep warm for 3.8 h to obtain an aerogel matrix;

[0120] Add silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 1.9 wt% is obtained. Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 38 °C for 21 h. Then take out the aerogel matrix, wash it with ethanol and place it in a vacuum dryer at 48 °C for 11.5 h to obtain a modified aerogel matrix;

[0121] (2) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol. The molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:0.6. After mixing evenly, a precursor solution is obtained. The mass fraction of tetrabutyl titanate in the precursor solution is 10.5 wt%. Add a nitric acid solution with a concentration of 0.8 mol / L to the precursor solution to adjust its pH value to 4.8. Mix and stir the precursor solution at 58 °C for 4.5 h to obtain a precursor sol;

[0122] Add a ferric nitrate solution with a mass fraction of 10.5 wt% to the precursor sol. The molar ratio of Fe:Ti in the ferric nitrate solution to the precursor solution is 0.022:1. Ultrasonically disperse it at an ultrasonic power of 320 W for 1.8 h. Then carry out a hydrothermal reaction at 165 °C for 21 h. After the reaction is completed, filter to obtain a reaction product;

[0123] The reaction product was heated to 260 °C at a heating rate of 2.2 °C / min and held for 2.8 h, and then continued to be heated to 360 °C at a heating rate of 4.2 °C / min and held for 3.8 h to obtain doped titanium dioxide particles;

[0124] (3) The doped titanium dioxide particles obtained in step (2) were dispersed in deionized water, and after mixing evenly, a dispersion was obtained. The mass fraction of the doped titanium dioxide particles in the dispersion was 2.2 wt%; the modified aerogel matrix obtained in step (1) and the dispersion were added to a reaction kettle. The mass ratio of the modified aerogel matrix to the doped titanium dioxide particles was 1:0.55, ensuring that the modified aerogel matrix was completely immersed in the dispersion. The reaction kettle was evacuated to -82 kPa and maintained for 28 min; then nitrogen was introduced into the reaction kettle to return to atmospheric pressure, and the dispersion was stirred for 32 min; then the reaction kettle was evacuated to -82 kPa again and maintained for 28 min; the reaction kettle was evacuated and restored to atmospheric pressure 4 times, and then taken out and vacuum dried at 52 °C for 11.5 h to obtain the photocatalytic porous composite material.

[0125] Example 3

[0126] This example provides a preparation method of a photocatalytic porous composite material for sewage treatment, as Figure 1 shown. The preparation method specifically includes the following steps:

[0127] (1) Cobalt nitrate was dispersed in deionized water, and after mixing evenly, a cobalt source solution with a concentration of 0.2 mol / L was obtained. A nanocellulose solution with a mass fraction of 1.5 wt% and the cobalt source solution were mixed evenly according to a volume ratio of 2.5:1 to obtain a precursor solution; 2-methylimidazole was dispersed in methanol, and after mixing evenly, an organic ligand solution with a concentration of 0.95 mol / L was obtained. Under stirring and heating conditions at 65 °C, the organic ligand solution was dropped into the precursor solution at a rate of 2 mL / min. The molar ratio of 2-methylimidazole to cobalt ions was 5.5:1. After all the organic ligand solution was dropped, the resulting mixture was continuously stirred at 65 °C for 4.5 h to obtain a reaction solution;

[0128] The reaction solution was mixed and stirred with polyvinyl alcohol for 3 h. The addition amount of polyvinyl alcohol was 8 wt% of the mass of the reaction solution. The mixed solution was injected into a mold for directional freezing. First, it was cooled to -17 °C at a cooling rate of -1.5 °C / min and held for 1 h, and then continued to be cooled to -35 °C at a cooling rate of -0.7 °C / min and held for 3.5 h to obtain an aerogel matrix;

[0129] Add silane coupling agent KH550 into the ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 2wt% is obtained. Immerse the aerogel matrix in the silane coupling agent solution, oscillate at 40 °C for 18 h, then take out the aerogel matrix, wash it with ethanol, and place it in a vacuum dryer at 50 °C for 11 h to obtain a modified aerogel matrix;

[0130] (2) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol. The molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:0.7. After mixing evenly, a precursor solution is obtained, and the mass fraction of tetrabutyl titanate in the precursor solution is 11wt%. Add a nitric acid solution with a concentration of 1 mol / L to the precursor solution to adjust its pH value to 4.5, and mix and stir the precursor solution at 60 °C for 4 h to obtain a precursor sol;

[0131] Add a ferric nitrate solution with a mass fraction of 11wt% to the precursor sol. The molar ratio of Fe:Ti in the ferric nitrate solution to the precursor solution is 0.025:1. Ultrasonically disperse it at an ultrasonic power of 350 W for 1.5 h, and then carry out a hydrothermal reaction at 170 °C for 18 h. After the reaction is completed, filter to obtain a reaction product;

[0132] Heat the reaction product to 270 °C at a heating rate of 2.5 °C / min and keep it warm for 2.5 h, and then continue to heat it to 370 °C at a heating rate of 4.5 °C / min and keep it warm for 3.5 h to obtain doped titanium dioxide particles;

[0133] (3) Disperse the doped titanium dioxide particles obtained in step (2) in deionized water. After mixing evenly, a dispersion is obtained, and the mass fraction of the doped titanium dioxide particles in the dispersion is 2.5wt%. Add the modified aerogel matrix obtained in step (1) and the dispersion into a reaction kettle. The mass ratio of the modified aerogel matrix to the doped titanium dioxide particles is 1:0.6, ensuring that the modified aerogel matrix is completely immersed in the dispersion. Vacuum the reaction kettle to -85 kPa and maintain it for 25 min; then introduce nitrogen into the reaction kettle to restore to normal pressure, and stir the dispersion for 35 min; then continue to vacuum the reaction kettle to -85 kPa and maintain it for 25 min; repeat the vacuuming and restoring to normal pressure of the reaction kettle 4 times, then take it out and vacuum dry it at 55 °C for 11 h to obtain the photocatalytic porous composite material.

[0134] Example 4

[0135] This example provides a preparation method of a photocatalytic porous composite material for sewage treatment, as Figure 1 shown. The specific preparation method includes the following steps:

[0136] (1) Disperse cobalt nitrate in deionized water. After mixing evenly, a cobalt source solution with a concentration of 0.22 mol / L is obtained. Mix a nanocellulose solution with a mass fraction of 1.8 wt% and the cobalt source solution according to a volume ratio of 2.2:1 to obtain a precursor solution. Disperse 2-methylimidazole in methanol. After mixing evenly, an organic ligand solution with a concentration of 0.98 mol / L is obtained. Under stirring and heating at 68 °C, the organic ligand solution is dropped into the precursor solution at a rate of 2.2 mL / min. The molar ratio of 2-methylimidazole to cobalt ions is 5.8:1. After all the organic ligand solution is dropped, continue to stir the obtained mixture at 68 °C for 4.2 h to obtain a reaction solution.

[0137] Mix the reaction solution and polyvinyl alcohol and stir for 3.5 h. The addition amount of polyvinyl alcohol is 8.5 wt% of the mass of the reaction solution. Inject the mixed solution into a mold for directional freezing. First, cool down to -18 °C at a cooling rate of -1.8 °C / min and keep warm for 0.8 h. Then continue to cool down to -38 °C at a cooling rate of -0.8 °C / min and keep warm for 3.2 h to obtain an aerogel matrix.

[0138] Add silane coupling agent KH550 to an ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 2.1 wt% is obtained. Immerse the aerogel matrix in the silane coupling agent solution and oscillate at 42 °C for 15 h. Then take out the aerogel matrix, wash it with ethanol, and place it in a vacuum dryer at 52 °C for 10.5 h to obtain a modified aerogel matrix.

[0139] (2) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol. The molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:0.8. After mixing evenly, a precursor solution is obtained. The mass fraction of tetrabutyl titanate in the precursor solution is 11.5 wt%. Drop a nitric acid solution with a concentration of 1.2 mol / L into the precursor solution to adjust its pH value to 4.2. Mix and stir the precursor solution at 62 °C for 3.5 h to obtain a precursor sol.

[0140] Add a ferric nitrate solution with a mass fraction of 11.5 wt% to the precursor sol. The molar ratio of Fe:Ti in the ferric nitrate solution to the precursor solution is 0.028:1. Ultrasonically disperse it at an ultrasonic power of 380 W for 1.2 h. Then carry out a hydrothermal reaction at 175 °C for 15 h. After the reaction is completed, filter to obtain a reaction product.

[0141] The reaction product was heated to 280 °C at a heating rate of 2.8 °C / min and held for 2.2 h, and then continued to be heated to 380 °C at a heating rate of 4.8 °C / min and held for 3.2 h to obtain doped titanium dioxide particles;

[0142] (3) The doped titanium dioxide particles obtained in step (2) were dispersed in deionized water, and after mixing evenly, a dispersion was obtained. The mass fraction of the doped titanium dioxide particles in the dispersion was 2.8 wt%; the modified aerogel matrix obtained in step (1) and the dispersion were added to a reaction kettle. The mass ratio of the modified aerogel matrix to the doped titanium dioxide particles was 1:0.65, ensuring that the modified aerogel matrix was completely immersed in the dispersion. The reaction kettle was evacuated to -88 kPa and maintained for 22 min; then nitrogen was introduced into the reaction kettle to restore to atmospheric pressure, and the dispersion was stirred for 38 min; then the reaction kettle was evacuated to -88 kPa again and maintained for 22 min; the reaction kettle was evacuated and restored to atmospheric pressure 3 times, and then taken out and vacuum dried at 58 °C for 10.5 h to obtain the photocatalytic porous composite material.

[0143] Example 5

[0144] This example provides a preparation method of a photocatalytic porous composite material for sewage treatment, as Figure 1 shown. The specific preparation method includes the following steps:

[0145] (1) Cobalt nitrate was dispersed in deionized water, and after mixing evenly, a cobalt source solution with a concentration of 0.25 mol / L was obtained. A nanocellulose solution with a mass fraction of 2 wt% and the cobalt source solution were mixed evenly according to a volume ratio of 2:1 to obtain a precursor solution; 2-methylimidazole was dispersed in methanol, and after mixing evenly, an organic ligand solution with a concentration of 1 mol / L was obtained. Under stirring and heating conditions at 70 °C, the organic ligand solution was dropped into the precursor solution at a rate of 2.5 mL / min. The molar ratio of 2-methylimidazole to cobalt ions was 6:1. After all the organic ligand solution was dropped, the obtained mixture was continuously stirred at 70 °C for 4 h to obtain a reaction solution;

[0146] The reaction solution and polyvinyl alcohol were mixed and stirred for 4 h. The addition amount of polyvinyl alcohol was 9 wt% of the mass of the reaction solution. The mixed solution was injected into a mold for directional freezing. First, it was cooled to -20 °C at a cooling rate of -2 °C / min and held for 0.5 h, and then continued to be cooled to -40 °C at a cooling rate of -1 °C / min and held for 3 h to obtain an aerogel matrix;

[0147] Add silane coupling agent KH550 into the ethanol aqueous solution (the volume ratio of absolute ethanol to deionized water in the ethanol aqueous solution is 9:1). After mixing evenly, a silane coupling agent solution with a mass fraction of 2.2 wt% is obtained. Immerse the aerogel matrix in the silane coupling agent solution, oscillate it at 45 °C for 12 h, then take out the aerogel matrix, wash it with ethanol, and place it in a vacuum dryer at 55 °C for 10 h to obtain a modified aerogel matrix;

[0148] (2) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol. The molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:1. After mixing evenly, a precursor solution is obtained. The mass fraction of tetrabutyl titanate in the precursor solution is 12 wt%. Dropwise add a nitric acid solution with a concentration of 1.5 mol / L to the precursor solution to adjust its pH value to 4, and mix and stir the precursor solution at 65 °C for 3 h to obtain a precursor sol;

[0149] Add a ferric nitrate solution with a mass fraction of 12 wt% to the precursor sol. The molar ratio of Fe:Ti in the ferric nitrate solution to the precursor solution is 0.03:1. Ultrasonically disperse it at an ultrasonic power of 400 W for 1 h, and then carry out a hydrothermal reaction at 180 °C for 12 h. After the reaction is completed, filter it to obtain a reaction product;

[0150] Heat the reaction product to 300 °C at a heating rate of 3 °C / min and hold for 2 h, and then continue to heat it to 400 °C at a heating rate of 5 °C / min and hold for 3 h to obtain doped titanium dioxide particles;

[0151] (3) Disperse the doped titanium dioxide particles obtained in step (2) in deionized water. After mixing evenly, a dispersion is obtained. The mass fraction of the doped titanium dioxide particles in the dispersion is 3 wt%. Add the modified aerogel matrix obtained in step (1) and the dispersion into a reaction kettle. The mass ratio of the modified aerogel matrix to the doped titanium dioxide particles is 1:0.7, ensuring that the modified aerogel matrix is completely immersed in the dispersion. Vacuum the reaction kettle to -90 kPa and maintain it for 20 min; then introduce nitrogen into the reaction kettle to restore it to normal pressure, and stir the dispersion for 40 min; then continue to vacuum the reaction kettle to -90 kPa and maintain it for 20 min; repeat the vacuuming and restoring to normal pressure of the reaction kettle 3 times, then take it out and vacuum dry it at 60 °C for 10 h to obtain the photocatalytic porous composite material.

[0152] Example 6

[0153] This example provides a preparation method of a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (1), the volume ratio of the nanocellulose solution to the cobalt source solution is adjusted to 1:1, and other operation steps and process parameters are exactly the same as those in Example 1.

[0154] Example 7

[0155] This example provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (1), the volume ratio of the nanocellulose solution to the cobalt source solution is adjusted to 4:1, and other operating steps and process parameters are exactly the same as those in Example 1.

[0156] Example 8

[0157] This example provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is adjusted to 1:0.1, and other operating steps and process parameters are exactly the same as those in Example 1.

[0158] Example 9

[0159] This example provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is adjusted to 1:1.5, and other operating steps and process parameters are exactly the same as those in Example 1.

[0160] Example 10

[0161] This example provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the Fe:Ti molar ratio of the iron nitrate solution to the precursor solution is adjusted to 0.01:1, and other operating steps and process parameters are exactly the same as those in Example 1.

[0162] Example 11

[0163] This example provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the Fe:Ti molar ratio of the iron nitrate solution to the precursor solution is adjusted to 0.05:1, and other operating steps and process parameters are exactly the same as those in Example 1.

[0164] Example 12

[0165] This example provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Example 1 is that in step (2), the second calcination temperature is adjusted to 330 °C, and other operating steps and process parameters are exactly the same as those in Example 1.

[0166] Example 13

[0167] This embodiment provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Embodiment 1 is that in step (2), the second calcination temperature is adjusted to 450 °C, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0168] Embodiment 14

[0169] This embodiment provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Embodiment 1 is that in step (3), the mass ratio of the modified aerogel matrix to the doped titanium dioxide particles in the dispersion liquid is adjusted to 1:0.3, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0170] Embodiment 15

[0171] This embodiment provides a method for preparing a photocatalytic porous composite material for sewage treatment. The difference from Embodiment 1 is that in step (3), the mass ratio of the modified aerogel matrix to the doped titanium dioxide particles in the dispersion liquid is adjusted to 1:1, and other operation steps and process parameters are exactly the same as those in Embodiment 1.

[0172] The photocatalytic porous composite materials prepared by using Embodiments 1-15 of the present invention are used to treat printing and dyeing wastewater and petrochemical wastewater, specifically including:

[0173] The photocatalytic porous composite materials prepared by using Embodiments 1-15 of the present invention are put into the printing and dyeing wastewater. The COD value in the printing and dyeing wastewater is 824 mg / L, the NH3-N value is 18.3 mg / L, the suspended solid content is 255 mg / L, and the chromaticity value is 580 times (dilution multiple method). The dosage is 2.5 kg / m 3 , and after 10 days, the concentrations of various pollutants in the treated printing and dyeing wastewater are tested. The concentrations of various pollutants in the treated printing and dyeing wastewater are shown in Table 1.

[0174] The photocatalytic porous composite materials prepared by using Embodiments 1-15 of the present invention are put into the petrochemical wastewater. The COD value in the petrochemical wastewater is 2820 mg / L, the NH3-N value is 58.6 mg / L, the suspended solid content is 236 mg / L, and the petroleum content is 125.3 mg / L. The dosage is 5 kg / m 3 , and after 10 days, the concentrations of various pollutants in the treated petrochemical wastewater are tested. The concentrations of various pollutants in the treated petrochemical wastewater are shown in Table 2.

[0175] Table 1

[0176]

[0177] Table 2

[0178]

[0179] It can be seen from the test data provided in Table 1 and Table 2 that the effluent water quality of Examples 1-5 is comprehensively better than the national standard requirements of printing and dyeing wastewater (GB 4287-2012 "Discharge Standard of Water Pollutants for the Textile Dyeing and Finishing Industry") and petrochemical wastewater (GB 31571-2015 "Discharge Standard of Pollutants for the Petrochemical Industry"). This technology combines a multi-level pore structure with iron-doped titanium dioxide photocatalysis to achieve efficient and stable sewage treatment performance, especially suitable for the advanced treatment of high-difficulty printing and dyeing wastewater and petrochemical wastewater.

[0180] It can be seen from the test data of Example 1, Example 6 and Example 7 that the effluent water quality of Example 6 and Example 7 is inferior to that of Example 1. This is because the dosage of the nanocellulose solution in Example 6 is too small, resulting in the aggregation of ZIF-67 crystals, blocking the pores and reducing the adsorption and catalytic efficiency. In Example 7, the dosage of the nanocellulose solution is too large, affecting the structural stability, resulting in the collapse of the pores and the decline of the interception efficiency of pollutants.

[0181] It can be seen from the test data of Example 1, Example 8 and Example 9 that the effluent water quality of Example 8 and Example 9 is inferior to that of Example 1. This is because the dosage of cetyltrimethylammonium bromide in Example 8 is too small, resulting in the aggregation of the generated titanium dioxide nanoparticles, the reduction of the specific surface area and the deterioration of the catalytic effect. In Example 9, the dosage of cetyltrimethylammonium bromide is too large, forming too many mesoporous structures, but the particles are too small to cause inactivation and the catalytic effect becomes poor.

[0182] It can be seen from the test data of Example 1, Example 10 and Example 11 that the effluent water quality of Example 10 and Example 11 is inferior to that of Example 1. This is because the dosage of the iron nitrate solution in Example 10 is too small, resulting in poor visible light response of the doped titanium dioxide particles and reduced catalytic efficiency. In Example 11, the dosage of the iron nitrate solution is too large, generating Fe2O3 heterophase, resulting in the reduction of the catalytic activity of the doped titanium dioxide particles and the deterioration of the catalytic effect.

[0183] It can be seen from the test data of Example 1, Example 12 and Example 13 that the effluent water quality of Example 12 and Example 13 is inferior to that of Example 1. This is because the second calcination temperature in Example 12 is too low, resulting in insufficient crystallinity of the doped titanium dioxide particles and reduced catalytic efficiency. In Example 13, the second calcination temperature is too high, and the phase change leads to a wider band gap and weaker visible light response, resulting in reduced catalytic efficiency.

[0184] It can be seen from the test data of Example 1, Example 14, and Example 15 that the effluent water quality of Example 14 and Example 15 is inferior to that of Example 1. This is because the dosage of doped titanium dioxide particles in Example 14 is too small, resulting in insufficient catalytic sites in the photocatalytic porous composite and a decrease in catalytic efficiency. In Example 15, the dosage of doped titanium dioxide particles is too large, resulting in the blockage of the pores of the modified aerogel matrix and a decrease in the interception and adsorption efficiency of pollutants.

[0185] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a photocatalytic porous composite material for sewage treatment, characterized in that, The preparation method includes: (I) Drop the organic ligand solution into the precursor solution composed of the nanocellulose solution and the cobalt source solution to obtain a reaction solution; mix the reaction solution with polyvinyl alcohol and then inject it into a mold for directional freezing to obtain an aerogel matrix; perform hydrophobic modification on the aerogel matrix to obtain a modified aerogel matrix; (II) Dissolve tetrabutyl titanate and cetyltrimethylammonium bromide in absolute ethanol, stir and heat to obtain a precursor sol, add a ferric nitrate solution to the precursor sol for hydrothermal reaction, and after the reaction is completed, perform filtration and calcination to obtain doped titanium dioxide particles; (III) Disperse the doped titanium dioxide particles in deionized water to obtain a dispersion, immerse the modified aerogel matrix in the dispersion, take it out and dry it to obtain the photocatalytic porous composite material.

2. The preparation method according to claim 1, characterized in that, In step (I), the organic ligand solution is composed of 2-methylimidazole and methanol; The concentration of 2-methylimidazole in the organic ligand solution is 0.9 - 1 mol / L; The mass fraction of the nanocellulose solution is 1 - 2 wt%; The cobalt source solution is composed of cobalt nitrate and deionized water; The concentration of cobalt nitrate in the cobalt source solution is 0.15 - 0.25 mol / L; The volume ratio of the nanocellulose solution to the cobalt source solution is (2 - 3):1; The molar ratio of 2-methylimidazole in the organic ligand solution to cobalt ions in the cobalt source solution is (5 - 6):1; Under stirring and heating conditions, drop the organic ligand solution into the precursor solution; The heating temperature when the organic ligand solution is dropped is 60 - 70 °C; After all the organic ligand solution is dropped, continue to mix and stir under heating conditions for 4 - 5 h to obtain the reaction solution.

3. The preparation method according to claim 1, characterized in that, In step (I), the addition amount of polyvinyl alcohol is 7 - 9 wt% of the mass of the reaction solution; The mixing and stirring time of the reaction solution and polyvinyl alcohol is 2 - 4 h; The directional freezing process includes: Cool down to the first freezing temperature at the first cooling rate and keep warm, and then continue to cool down to the second freezing temperature at the second cooling rate and keep warm; The first cooling rate is -1 - -2 °C / min; The first freezing temperature is -15 - -20 °C; The heat preservation time at the first freezing temperature is 0.5 - 1.5 h; The second cooling rate is -0.5 - -1 °C / min; The second freezing temperature is -30 - -40 °C; The heat preservation time at the second freezing temperature is 3 - 4 h.

4. The preparation method according to claim 1, wherein, In step (I), the hydrophobic modification treatment includes: Immerse the aerogel matrix in the silane coupling agent solution, oscillate and heat, then take out the aerogel matrix, wash and dry it to obtain the modified aerogel matrix; The silane coupling agent solution is composed of a silane coupling agent and an ethanol aqueous solution; The mass fraction of the silane coupling agent in the silane coupling agent solution is 1.8 - 2.2 wt%; The heating temperature when the aerogel matrix is immersed in the silane coupling agent solution is 35 - 45 °C; The immersion time of the aerogel matrix in the silane coupling agent solution is 12 - 24 h.

5. The preparation method according to claim 1, characterized in that, In step (II), tetrabutyl titanate and cetyltrimethylammonium bromide are dissolved in absolute ethanol. After mixing evenly, a precursor solution is obtained. A nitric acid solution is added dropwise to the precursor solution to adjust its pH value to 4 - 5. Subsequently, the precursor solution is stirred and heated to obtain the precursor sol; The molar ratio of tetrabutyl titanate to cetyltrimethylammonium bromide is 1:(0.5 - 1); The mass fraction of tetrabutyl titanate in the precursor solution is 10 - 12 wt%; The mixing and stirring time of the precursor solution is 3 - 5 h; The heating temperature during the mixing and stirring of the precursor solution is 55 - 65 °C.

6. The preparation method according to claim 1, characterized in that, In step (II), the molar ratio of Fe:Ti of the iron nitrate solution to the precursor sol is (0.02 - 0.03):1; The mass fraction of the iron nitrate solution is 10 - 12 wt%; The temperature of the hydrothermal reaction is 160 - 180 °C; The time of the hydrothermal reaction is 12 - 24 h.

7. The preparation method according to claim 1, wherein, In step (II), the calcination process includes: First, heat to the first calcination temperature at the first heating rate and hold for a certain time; Subsequently, continue to heat to the second calcination temperature at the second heating rate and hold for a certain time; The first heating rate is 2 - 3 °C / min; The first calcination temperature is 250 - 300 °C; Hold for 2 - 3 h at the first calcination temperature; The second heating rate is 4 - 5 °C / min; The second calcination temperature is 350 - 400 °C; Hold for 3 - 4 h at the second calcination temperature.

8. The preparation method according to claim 1, wherein In step (III), the mass fraction of the doped titanium dioxide particles in the dispersion liquid is 2 - 3 wt%; The impregnation process includes: Add the modified aerogel matrix and the dispersion liquid into a reaction kettle. The modified aerogel matrix is completely immersed in the dispersion liquid. The reaction kettle is evacuated and then restored to normal pressure. The dispersion liquid is stirred under normal pressure; then continue to evacuate; repeat the evacuation and restoration to normal pressure of the reaction kettle 3 - 5 times; The mass ratio of the modified aerogel matrix to the doped titanium dioxide particles in the dispersion liquid is 1:(0.5 - 0.7); The reaction kettle is evacuated to - 80 - - 90 kPa; The time for the reaction kettle to maintain vacuum is 20 - 30 min; During the normal pressure stage, the dispersion liquid is stirred for 30 - 40 min.

9. A photocatalytic porous composite material for sewage treatment prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the photocatalytic porous composite material for sewage treatment according to claim 9, characterized in that, The photocatalytic porous composite material is used for sewage treatment.

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