Bio-based degradable photocatalytic film and preparation method thereof

Abstract

The invention relates to the field of forming preparation of plastic state materials, in particular to a bio-based degradable photocatalytic film and a preparation method thereof. The invention provides a ternary composite system taking bacterial cellulose as a framework, chitosan as an interface adhesive and doped titanium dioxide as a photocatalytic active component, and continuous production of the film is realized by adopting an extrusion blow molding process for molding a plastic state material. The degradable photocatalytic film prepared by the method is high in mechanical property, high in photocatalytic capacity and rapid and thorough in degradation under natural conditions.

Description

Technical Field

[0001] The present invention relates to the field of forming and preparing materials in a plastic state, and particularly to a bio-based degradable photocatalytic film and a preparation method thereof. Background Art

[0002] Due to the non-degradability of traditional petroleum-based plastics, the problem of "white pollution" has been deteriorating continuously. Photocatalytic materials have shown great potential in environmental protection fields such as sewage treatment and air purification. However, existing photocatalytic materials (such as titanium dioxide) generally have problems such as difficult recovery, low visible light utilization rate, and secondary pollution generated during the degradation process, which severely limit their large-scale application. Therefore, there is an urgent need to develop a new composite system with high photocatalytic activity, biodegradability, and mechanical stability.

[0003] Bacterial cellulose (BC) is a natural polymer polysaccharide synthesized by microorganisms (such as Acetobacter xylinum), and has an ultra-fine three-dimensional network structure, high crystallinity, high water retention, and excellent biocompatibility. Compared with plant cellulose, BC does not need to remove lignin and hemicellulose, and its nanofiber network can be used as an ideal carrier platform to provide a high specific surface area and stable dispersion sites for inorganic photocatalysts. However, BC itself lacks photocatalytic activity and needs to be functionally modified to achieve the multifunctionality of the composite material.

[0004] As a typical photocatalytic material, titanium dioxide is widely used in the fields of pollutant degradation and hydrogen production due to its high chemical stability, non-toxicity, low cost, etc. However, its band gap is relatively wide, and it can only respond to ultraviolet light. Moreover, the nanoparticles are prone to agglomeration and difficult to recover, resulting in low photoquantum efficiency. Existing technologies have tried to reduce the band gap by doping, but traditional doping processes require high-temperature calcination or complex chemical modification, which are likely to damage the nanostructure of the carrier, and the binding force between the dopant and the carrier interface is weak, and the activity decreases significantly after repeated use.

[0005] The current preparation methods of cellulose-based photocatalytic materials have significant defects: for example, Patent CN103908979A uses a hydrothermal reaction (>150°C) to load titanium dioxide, resulting in the collapse of the BC network structure and the weak binding between titanium dioxide particles and BC; Patent CN101745430B uses regenerated cellulose, but it lacks the three-dimensional pore structure of BC and has low photocatalytic efficiency.

[0006] To address the above problems, the present invention proposes to use bacterial cellulose (BC) as the skeleton, chitosan (CS) as the interfacial adhesive, and nitrogen / cerium co-doping A ternary composite system is used as the photocatalytic active component. The in-situ loading of TiO2 is achieved by the low-temperature sol-gel method, the interfacial bonding between BC and CS is strengthened by ultraviolet crosslinking, and finally the continuous production of the film is realized by the extrusion blow molding process. This design not only solves the problems of high energy consumption and poor interfacial compatibility in the traditional process, but also provides a new solution for the industrial application of bio-based photocatalytic films through the synergy of multiple functions. Summary of the Invention

[0007] Based on the problems summarized above, the present invention provides a bio-based degradable photocatalytic film and its preparation method. The main feature is to form a composite ternary system through bacterial cellulose, chitosan, and doped titanium dioxide, and to realize the continuous preparation of the bio-based photocatalytic film through the forming method of plastic state materials. The specific technical solutions are as follows: The bio-based degradable photocatalytic film comprises the following components: bacterial cellulose, chitosan, and doped titanium dioxide, with a mass ratio of 20-40:50-70:10-30.

[0008] Further, the bacterial cellulose has undergone citric acid modification treatment and nano-cellulose whisker reinforcement treatment.

[0009] Further, the doped titanium dioxide has preparation raw materials including a precursor solution, a dopant solution, and a reinforcing agent solution.

[0010] Further, the precursor solution is a solution formed by mixing tetrabutyl titanate and absolute ethanol at a volume ratio of 1:10; The dopant solution is a solution formed by dissolving urea in deionized water; The reinforcing agent solution is a solution formed by dissolving ammonium cerium nitrate in absolute ethanol.

[0011] The present invention also provides a preparation method for the bio-based degradable photocatalytic film, which includes the following steps: S1: Prepare the bacterial cellulose and perform modification and reinforcement treatment on the bacterial cellulose; S2: Prepare the doped titanium dioxide, perform reinforcement treatment on the doped titanium dioxide, and then let it stand, age, and calcine; S3: Melt-blend the pretreated chitosan and doped titanium dioxide to obtain a composite masterbatch; S4: Blow-mold the composite masterbatch and the bacterial cellulose completed in S1 into a composite film at a mass ratio of 7:3, and then irradiate the composite film with light to obtain the bio-based degradable photocatalytic film.

[0012] Further, the preparation of the bacterial cellulose in S1 is obtained by static fermentation of Acetobacter xylinum; The modification described in S1 specifically includes: impregnating in a 5% citric acid solution and reacting at 60°C for 2 hours; The strengthening treatment described in S1 specifically includes: immersing in a 1% nano-cellulose whisker dispersion solution, with the mass ratio of bacterial cellulose to nano-cellulose whiskers being 1:0.1, and then performing vacuum filtration for 30 minutes.

[0013] Further, the preparation of the doped titanium dioxide described in S2 specifically includes: dropping urea dissolved in deionized water into a tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10, while dropping and maintaining stirring at 800 rpm in an ice-water bath; The strengthening treatment described in S2 specifically includes: adding ammonium cerium nitrate - ethanol solution and stirring for 30 minutes; The standing, aging, and calcination described in S2 specifically include: standing for 12 hours, then aging at 60°C for 24 hours and grinding into powder, and then calcining the powder at 500°C.

[0014] Further, the pretreatment described in S3 specifically includes: drying chitosan, then ultrafinely pulverizing and passing through a 200-mesh sieve, and immersing the doped titanium dioxide in a 3% KH-550 ethanol solution for optimized modification; The melt blending described in S3 specifically includes: adding a plasticizer and a compatibilizer and placing them in a twin-screw extruder for melt blending, with the temperature set at 150 - 170°C and the rotation speed at 200 rpm.

[0015] Further, the plasticizer is glycerol, with a purity ≥ 99% and a moisture content ≤ 0.5%; The compatibilizer is polyethylene glycol with a molecular weight of 4000 Da.

[0016] Further, the blow molding into a composite film described in S4 specifically includes the following parameters: setting the barrel temperature at 160 - 180°C, the die head temperature at 170°C, and the blow-up ratio at 2.5:1; The light-enhanced irradiation described in S4 specifically includes the following parameters: setting the passing speed at 0.5 m / min and the single-sided cumulative irradiation dose at 1800 mJ / cm².

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The modified bacterial cellulose is further strengthened by filling the pores of the BC network with nano-cellulose whiskers (CNWs), and through cross-linking with chitosan, the composite film has high mechanical properties; (2) Through nitrogen / cerium co-doped titanium dioxide, the band gap is reduced and the visible light absorption rate is increased, so that the degradation rate of the film for pollutants is also high and the photocatalytic activity is easily maintained; (3) The film is prepared using bio-based materials, which are easily degraded under natural conditions and the degradation is relatively complete; (4)The preparation is carried out by adopting relevant processes of forming materials in a plastic state, and continuous production can be achieved; (5)Chitosan has a high antibacterial rate. The dense network of bacterial cellulose makes the water vapor transmission rate small. The prepared film of the present invention with strong comprehensive performance has a wide range of application scenarios. Description of the Drawings

[0018] Figure 1 It is a flowchart of the preparation method of the bio-based degradable photocatalytic film of the present invention; Figure 2 It is a test result diagram of Fourier transform infrared spectroscopy of modified and unmodified bacterial cellulose of the present invention; Figure 3 It is a comparison diagram of the measured light transmittance results of the doped titanium dioxide ultraviolet-visible diffuse reflection spectrum of the present invention; Figure 4 It is a comparison diagram of the calculated results of the band gap fitting of the doped titanium dioxide of the present invention. Detailed Embodiments

[0019] The following embodiments further explain and illustrate the technical solutions of the present invention. It is specifically pointed out that each specific embodiment is a specific implementation and explanation of the technical solution, and should not be regarded as a limitation of the protection scope of the present invention. Those of ordinary skill in the art still have the right to modify the technical solutions of these embodiments and perform equivalent replacements on some or all of the technical features, and these modifications or replacements do not change the essence of the corresponding technical solutions and do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0020] The present invention provides a bio-based degradable photocatalytic film and its preparation method. The film composition includes: bacterial cellulose (BC), chitosan (CS) and doped titanium dioxide (doped titanium dioxide), and the mass ratio is 20-40:50-70:10-30. As shown in the preparation method process Figure 1 shown, its detailed preparation steps include: 1. Pretreatment and functional modification of bacterial cellulose 1.1 Raw material preparation and carboxylation modification — Biosynthesis of bacterial cellulose (BC) Strain activation: Acetobacter xylinum ( Acetobacter xylinum CGMCC 1.1812) was inoculated into a culture medium (containing 2% glucose, 0.5% yeast extract, 0.5% peptone, pH 6.0), and pre-cultured in a shaker at 30 °C and 150 rpm for 24 hours; Static fermentation: The activated bacterial liquid was transferred to a sterilized polyethylene culture dish at an inoculation amount of 5%. The culture medium was adjusted to add 0.1% sodium citrate in the original basic formula to inhibit miscellaneous bacteria, and cultured statically at 28 °C for 7 days. During this period, 1% glucose was supplemented every 24 hours to maintain the carbon source; Film layer peeling: After the culture was completed, BC was mechanically peeled from the liquid surface and rinsed successively with deionized water, 1% NaOH solution (treated at 80 °C for 1 hour), and deionized water until neutral to obtain transparent BC.

[0021] —Carboxylation modification treatment Citric acid esterification reaction: BC was immersed in 5% citric acid aqueous solution, with the liquid-solid ratio set at 20:1, and reacted in a constant temperature water bath oscillator at 60 °C and 50 rpm for 2 hours; Reaction control: By monitoring the pH value of the solution in real time, ensure the stability of the degree of carboxylation; Post-treatment: After the reaction, BC was rinsed with deionized water until the conductivity of the eluate was <5 μS / cm, and then dried to a constant weight in a vacuum drying oven at 50 °C, controlling the moisture content ≤5%.

[0022] 1.2 Reinforcement treatment: Penetration of nanocellulose whisker (CNWs) dispersion —Preparation of CNWs dispersion Microcrystalline cellulose (MCC) was added to 64% sulfuric acid solution, with the solid-liquid ratio set at 1:20, and stirred and hydrolyzed at 45 °C for 45 minutes; The reaction was terminated rapidly with 10 times the volume of cold water, centrifuged at 8000 rpm for 15 minutes to remove the acid solution, dialyzed to neutrality and then ultrasonically broken (power 300 W, 30 minutes) to obtain 1% CNWs aqueous dispersion, with the cellulose length of 200 - 500 nm, diameter of 10 - 20 nm, and aspect ratio >20.

[0023] —Vacuum filtration strengthening The carboxylated BC was laid flat on a Buchner funnel with a 0.45 μm pore size filter membrane inside, the CNWs dispersion was poured in, and the mass ratio of BC to CNWs was 1:0.1. The vacuum pump (pressure -0.08 MPa) was started to filter for 30 minutes to make CNWs uniformly penetrate into the BC fiber network.

[0024] In the above steps, bacterial cellulose (BC) is composed of β-1,4-glucose chains and is rich in hydroxyl groups (-OH) on its surface. When BC is impregnated in 5% citric acid solution, at 60 °C, the carboxyl group (-COOH) of citric acid reacts with the hydroxyl group of BC to form a stable ester bond (R-O-CO-R'), thereby introducing carboxyl functional groups on the surface of BC. The introduction of carboxyl groups can enhance the interfacial binding force between subsequent BC and chitosan (CS). The amino group (-NH2) on the chitosan molecular chain can bind to the carboxyl group through hydrogen bonds or ionic bonds to form a dense three-dimensional network structure, improving the mechanical properties and interfacial compatibility of the composite material.

[0025] The modified BC was immersed in a 1% nanofibrillated cellulose whisker (CNWs) dispersion, and CNWs were infiltrated into the BC fiber network by vacuum filtration. Due to the high modulus and specific surface area of CNWs, the pores between BC fibers could be filled; a rigid network was formed between CNWs and BC fibers through hydrogen bonding and mechanical interlocking.

[0026] 2. Preparation of doped titanium dioxide 2.1 Raw material preparation and ratio Precursor solution: Tetrabutyl titanate was mixed with absolute ethanol at a volume ratio of 1:10 and magnetically stirred until completely dissolved to form a transparent solution A.

[0027] Dopant solution: Nitrogen source - Urea was dissolved in 10 mL of deionized water and stirred until clear; Cerium source - Ammonium cerium nitrate was dissolved in 5 mL of absolute ethanol and ultrasonically dispersed for 10 minutes.

[0028] 2.2 Sol preparation and hydrolysis polycondensation The urea aqueous solution was slowly added dropwise to solution A at a dropping rate of 1 mL / min, while stirring (800 rpm) and ice-water bath (0 - 5 °C) were maintained to inhibit the rapid hydrolysis of tetrabutyl titanate; After the addition was completed, the cerium source ethanol solution was added, and stirring was continued for 30 minutes to form a pale yellow transparent sol; The sol was left standing at room temperature for 12 hours to gradually form a wet gel with a three-dimensional network structure.

[0029] 2.3 Aging and drying The wet gel was transferred to a constant temperature drying oven and aged at 60 °C for 24 hours to remove residual solvents and promote the densification of the network structure; The dried gel was ground to a particle size ≤100 μm to obtain a pale blue precursor powder.

[0030] 2.4 Calcination The precursor powder was placed in a muffle furnace, heated to 500 °C at a rate of 5 °C / min, calcined in an air atmosphere for 2 hours, and then naturally cooled to room temperature.

[0031] In the above steps, tetrabutyl titanate hydrolyzes in absolute ethanol to form titanium hydroxy oxide network; Urea as a nitrogen source decomposes to generate NH3 during calcination, and nitrogen atoms replace oxygen atoms in the lattice to form bonds, and nitrogen doping introduces intermediate energy levels, making the band gap decrease and the visible light absorption edge redshift; Addition ethanol solution enter the lattice interstitial sites to suppress the recombination of photo-generated electron-hole pairs as electron traps, thereby enhancing the quantum efficiency.

[0032] 3. Preparation of Chitosan-Titanium Dioxide Composite Masterbatch 3.1 Pretreatment of Raw Materials and Optimization of Proportion - Pretreatment of Chitosan (CS) Place chitosan in a vacuum drying oven at 60 °C for 12 hours, then crush it with an ultrafine grinder (rotation speed 20000 rpm) to a particle size ≤50 μm, and sieve it through a 200-mesh sieve for later use.

[0033] - Surface Modification of Doped Titanium Dioxide Immerse the doped titanium dioxide powder in a 3% KH-550 ethanol solution, set the ultrasonic dispersion at 40 kHz for 30 minutes, and then dry it at 60 °C. The silane coupling agent forms groups on the surface to enhance the interfacial bonding with chitosan.

[0034] - Selection of Plasticizer and Phase Solvent Plasticizer: Glycerol, purity ≥99%, moisture content ≤0.5%; Phase Solvent: Polyethylene Glycol (PEG), molecular weight 4000 Da, melting point 50 - 55 °C, to ensure a matching melting temperature with chitosan.

[0035] 3.2 Twin-Screw Melting and Blending - Equipment Parameter Setting Twin-Screw Extruder: Select a co-rotating intermeshing twin-screw, L / D = 40, screw diameter 35 mm, and set the partition temperatures as follows: feeding zone 150 °C, melting zone 160 °C, mixing zone 170 °C, extrusion zone 165 °C; Screw Rotation Speed: 200 rpm, shear rate .

[0036] Vacuum Degassing: Set a vacuum pump in the extrusion zone to remove the melt bubbles.

[0037] - Feeding and Blending Main Feeding Port: Add the premix of chitosan, doped titanium dioxide, and PEG, and set the premixing time to 10 minutes; Side Feeding Port: Inject liquid glycerol into the melting zone to avoid premature volatilization.

[0038] - Pelletizing and Post-treatment Extrusion granulation: After the melt is extruded through the die head (aperture 3 mm), it is cut into cylindrical masterbatch particles with a diameter of 3 mm and a length of 5 mm by a water-cooled strand pelletizer at 15°C. Drying: The particles are treated in a hot air circulation drying oven at 50°C for 6 hours, and the moisture content ≤ 0.3%.

[0039] In the above steps, glycerol is inserted between the chitosan molecular chains as a plasticizer, breaking the intramolecular hydrogen bonds, reducing the glass transition temperature, and enhancing the melt fluidity; the ether bond of polyethylene glycol forms hydrogen bonds with the surface hydroxyl groups of the doped titanium dioxide, and at the same time its long-chain structure wraps the particles to prevent agglomeration; the twin-screw extruder evenly disperses in the chitosan matrix through high shear force to form a "sea-island structure", ensuring that the photocatalytic active sites are fully exposed.

[0040] 4. Plastic forming and post-treatment 4.1 Extrusion blow molding — Raw material pretreatment and blending Composite masterbatch drying: The chitosan / titanium dioxide composite masterbatch particles and the pretreated BC fibers are mixed at a mass ratio of 7:3, placed in a hot air drying oven at 50°C for 4 hours of pretreatment to ensure that the moisture content ≤ 0.1%; Premixing process: Use a high-speed mixer to evenly disperse the composite masterbatch and BC fibers, set the rotation speed at 1000 rpm, and the time at 10 minutes.

[0041] — Single-screw extrusion blow molding process Temperature zone control: Feeding zone 160°C, compression zone 170°C, metering zone 180°C, die head 170°C; Screw design: Select a gradually changing screw, L / D = 25, compression ratio 3:1, to ensure full plasticization of the melt; Blow molding process: The melt is extruded from the annular gap of the die head (gap 0.8 mm) to form a tubular film blank. At the same time, compressed air is injected into the film blank, the pressure is set at 0.3 MPa, and the blow-up ratio is set at 2.5:1 to stretch the film tube horizontally to 2.5 times the original diameter; It is quickly cooled and shaped by the traction roller (speed 10 m / min) and the cooling air ring (wind speed 5 m / s, temperature 15°C) to obtain a composite film with a thickness of 20 - 50 μm.

[0042] 4.2 Photo-crosslinking strengthening Light source parameters: Low-pressure mercury lamp, main wavelength 254 nm, intensity 30 mW / cm², irradiation distance 10 cm, spot uniformity > 90%.

[0043] Conveyor belt speed: The prepared film passes through the irradiation area at a speed of 0.5 m / min to ensure a single-sided cumulative irradiation dose of 1800 mJ / cm².

[0044] In the above steps, the composite masterbatch and the pretreated BC fibers are melted in a single-screw extruder, and the BC fibers form a "fiber-matrix" interpenetrating network as the reinforcing phase; ultraviolet light excites the amino group of chitosan to react with the carboxyl group of BC to form a Schiff base reaction, forming a covalent crosslinking network; ultraviolet light simultaneously excites Hydroxyl radicals are generated, the surface hydroxyl density increases, and the photocatalytic activity is enhanced.

[0045] Example 1

[0046] A bio-based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan, and doped titanium dioxide, with a mass ratio of 30:55:15.

[0047] The preparation process includes: S1: Bacterial cellulose is prepared by static fermentation of Acetobacter xylinum, impregnated in a 5% citric acid solution, reacted at 60°C for 2 hours, and then the modified bacterial cellulose is immersed in a 1% nanocellulose whisker dispersion. The mass ratio of bacterial cellulose to nanocellulose whiskers is 1:0.1, and vacuum filtration is carried out for 30 minutes to obtain pretreated bacterial cellulose; S2: Urea dissolved in deionized water is dropped into a tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10, while dropping, stirring is maintained at 800 rpm in an ice-water bath. After dropping, an ammonium cerium nitrate - ethanol solution is added and stirring is continued for 30 minutes. After standing for 12 hours, it is aged at 60°C for 24 hours and then ground into a powder. The powder is calcined at 500°C to obtain doped titanium dioxide; S3: Chitosan is dried, ultrafinely pulverized, and passed through a 200-mesh sieve. The doped titanium dioxide is immersed in a 3% KH-550 ethanol solution for optimization and modification. The pretreated chitosan, doped titanium dioxide, glycerol, and polyethylene glycol are placed in a twin-screw extruder for melt blending. The temperature is set at 150 - 170°C and the rotation speed is 200 rpm to obtain a composite masterbatch; S4: The composite masterbatch and the pretreated bacterial cellulose are added to a single-screw blown film unit at a mass ratio of 7:3. The barrel temperature is set at 160 - 180°C, the die head temperature is 170°C, and the blow-up ratio is 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then the composite film is irradiated by light intensification at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0048] Example 2

[0049] A bio-based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan, and doped titanium dioxide, with a mass ratio of 20:50:30.

[0050] The preparation process includes: S1: Bacterial cellulose is prepared by static fermentation of Acetobacter xylinum, impregnated in a 5% citric acid solution, reacted at 60 °C for 2 hours, and then the modified bacterial cellulose is immersed in a 1% nanocellulose whisker dispersion. The mass ratio of bacterial cellulose to nanocellulose whiskers is 1:0.1, and vacuum filtration is carried out for 30 minutes to obtain pretreated bacterial cellulose; S2: Urea dissolved in deionized water is dropped into a tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10, while dropping, stirring is maintained at 800 rpm in an ice - water bath. After dropping, ammonium cerium nitrate - ethanol solution is added and stirring continues for 30 minutes. After standing for 12 hours, it is aged at 60 °C for 24 hours and ground into a powder, and the powder is calcined at 500 °C to obtain doped titanium dioxide; S3: Chitosan is dried, ultrafinely pulverized, and passed through a 200 - mesh sieve. The doped titanium dioxide is immersed in a 3% KH - 550 ethanol solution for optimization modification. The pretreated chitosan, doped titanium dioxide, glycerol, and polyethylene glycol are placed in a twin - screw extruder for melt blending. The temperature is set at 150 - 170 °C and the rotation speed is 200 rpm to obtain a composite masterbatch; S4: The composite masterbatch and the pretreated bacterial cellulose are added to a single - screw blown - film unit at a mass ratio of 7:3. The barrel temperature is set at 160 - 180 °C, the die head temperature is 170 °C, and the blow - up ratio is 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then the composite film is passed through light - enhanced irradiation at a speed of 0.5 m / min to obtain a bio - based degradable photocatalytic film.

[0051] Example 3 A bio - based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan, and doped titanium dioxide, with a mass ratio of 20:70:10.

[0052] The preparation process includes: S1: Bacterial cellulose is prepared by static fermentation of Acetobacter xylinum, impregnated in a 5% citric acid solution, reacted at 60 °C for 2 hours, and then the modified bacterial cellulose is immersed in a 1% nanocellulose whisker dispersion. The mass ratio of bacterial cellulose to nanocellulose whiskers is 1:0.1, and vacuum filtration is carried out for 30 minutes to obtain pretreated bacterial cellulose; S2: Drop the urea dissolved in deionized water into the tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10. While dropping, keep stirring at 800 rpm in an ice-water bath. After dropping, add the ammonium cerium nitrate - ethanol solution and continue stirring for 30 minutes. After standing for 12 hours, age at 60 °C for 24 hours and grind into powder. Calcinate the powder at 500 °C to obtain doped titanium dioxide; S3: Dry the chitosan, then ultrafinely pulverize it and sieve it through a 200-mesh sieve. Immerse the doped titanium dioxide in a 3% KH-550 ethanol solution for optimization and modification. Put the pretreated chitosan, doped titanium dioxide, glycerol and polyethylene glycol into a twin-screw extruder for melt blending. Set the temperature to 150 - 170 °C and the rotation speed to 200 rpm to obtain a composite masterbatch; S4: Add the composite masterbatch and the pretreated bacterial cellulose to a single-screw blown film unit at a mass ratio of 7:3. Set the barrel temperature to 160 - 180 °C, the die head temperature to 170 °C, and the blow-up ratio to 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then pass the composite film through light enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0053] Example 4 A bio-based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 40:50:10.

[0054] The preparation process includes: S1: Obtain bacterial cellulose by static fermentation of Acetobacter xylinum, immerse it in a 5% citric acid solution and react at 60 °C for 2 hours. Then immerse the modified bacterial cellulose in a 1% nanocellulose whisker dispersion. The mass ratio of bacterial cellulose to nanocellulose whiskers is 1:0.1. Perform vacuum filtration for 30 minutes to obtain pretreated bacterial cellulose; S2: Drop the urea dissolved in deionized water into the tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10. While dropping, keep stirring at 800 rpm in an ice-water bath. After dropping, add the ammonium cerium nitrate - ethanol solution and continue stirring for 30 minutes. After standing for 12 hours, age at 60 °C for 24 hours and grind into powder. Calcinate the powder at 500 °C to obtain doped titanium dioxide; S3: Dry the chitosan, then ultrafinely pulverize it and sieve it through a 200-mesh sieve. Immerse the doped titanium dioxide in a 3% KH-550 ethanol solution for optimization and modification. Put the pretreated chitosan, doped titanium dioxide, glycerol and polyethylene glycol into a twin-screw extruder for melt blending. Set the temperature to 150 - 170 °C and the rotation speed to 200 rpm to obtain a composite masterbatch; S4: Add the composite masterbatch and pretreated bacterial cellulose into a single-screw blown film unit at a mass ratio of 7:3. Set the barrel temperature at 160 - 180 °C, the die head temperature at 170 °C, and the blow-up ratio at 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then pass the composite film through light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0055] Example 5 A bio-based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan, and doped titanium dioxide, with a mass ratio of 30:60:10.

[0056] The preparation process includes: S1: Prepare bacterial cellulose by static fermentation of Acetobacter xylinum, immerse it in a 5% citric acid solution, react at 60 °C for 2 hours, then immerse the modified bacterial cellulose in a 1% nanofibrillated cellulose whisker dispersion. The mass ratio of bacterial cellulose to nanofibrillated cellulose whiskers is 1:0.1, and vacuum filtration is carried out for 30 minutes to obtain pretreated bacterial cellulose; S2: Drop urea dissolved in deionized water into a tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10, while dropping, maintain stirring at 800 rpm in an ice-water bath. After dropping, add ammonium cerium nitrate - ethanol solution and continue stirring for 30 minutes. After standing for 12 hours, age at 60 °C for 24 hours and grind into a powder. The powder is calcined at 500 °C to obtain doped titanium dioxide; S3: Dry chitosan, then ultrafinely pulverize it and pass it through a 200-mesh sieve. Immerse the doped titanium dioxide in a 3% KH-550 ethanol solution for optimization modification. Place the pretreated chitosan, doped titanium dioxide, glycerol, and polyethylene glycol into a twin-screw extruder for melt blending. Set the temperature at 150 - 170 °C and the rotation speed at 200 rpm to obtain a composite masterbatch; S4: Add the composite masterbatch and pretreated bacterial cellulose into a single-screw blown film unit at a mass ratio of 7:3. Set the barrel temperature at 160 - 180 °C, the die head temperature at 170 °C, and the blow-up ratio at 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then pass the composite film through light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0057] Example 6 A bio-based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan, and doped titanium dioxide, with a mass ratio of 30:50:20.

[0058] The preparation process includes: S1: Prepare bacterial cellulose by static fermentation of Acetobacter xylinum, immerse it in a 5% citric acid solution, react at 60 °C for 2 hours, then immerse the modified bacterial cellulose in a 1% nanocellulose whisker dispersion. The mass ratio of bacterial cellulose to nanocellulose whiskers is 1:0.1, and vacuum filtration is carried out for 30 minutes to obtain pretreated bacterial cellulose; S2: Drop urea dissolved in deionized water into a tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10, while dropping, maintain stirring at 800 rpm in an ice - water bath. After dropping, add ammonium cerium nitrate - ethanol solution and continue stirring for 30 minutes. After standing for 12 hours, age at 60 °C for 24 hours and grind into powder, then calcine the powder at 500 °C to obtain doped titanium dioxide; S3: Dry chitosan, then ultrafinely pulverize it and pass through a 200 - mesh sieve. Immerse the doped titanium dioxide in a 3% KH - 550 ethanol solution for optimization and modification. Put the pretreated chitosan, doped titanium dioxide, glycerol and polyethylene glycol into a twin - screw extruder for melt blending. Set the temperature to 150 - 170 °C and the rotation speed to 200 rpm to obtain a composite masterbatch; S4: Add the composite masterbatch and pretreated bacterial cellulose to a single - screw blown - film unit at a mass ratio of 7:3. Set the barrel temperature to 160 - 180 °C, the die head temperature to 170 °C, and the blow - up ratio to 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then pass the composite film through light - enhanced irradiation at a speed of 0.5 m / min to obtain a bio - based degradable photocatalytic film.

[0059] Example 7 A bio - based degradable photocatalytic film and its preparation method are as follows: The film composition includes: bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 20:60:20.

[0060] The preparation process includes: S1: Prepare bacterial cellulose by static fermentation of Acetobacter xylinum, immerse it in a 5% citric acid solution, react at 60 °C for 2 hours, then immerse the modified bacterial cellulose in a 1% nanocellulose whisker dispersion. The mass ratio of bacterial cellulose to nanocellulose whiskers is 1:0.1, and vacuum filtration is carried out for 30 minutes to obtain pretreated bacterial cellulose; S2: Drop urea dissolved in deionized water into a tetrabutyl titanate - absolute ethanol solution mixed at a volume ratio of 1:10, while dropping, maintain stirring at 800 rpm in an ice - water bath. After dropping, add ammonium cerium nitrate - ethanol solution and continue stirring for 30 minutes. After standing for 12 hours, age at 60 °C for 24 hours and grind into powder, then calcine the powder at 500 °C to obtain doped titanium dioxide; S3: Dry the chitosan, then ultrafinely pulverize it and sieve it through a 200-mesh sieve. Immerse the doped titanium dioxide in a 3% KH-550 ethanol solution for optimized modification. Place the pretreated chitosan, doped titanium dioxide, glycerol, and polyethylene glycol into a twin-screw extruder for melt blending. Set the temperature to 150 - 170 °C and the rotation speed to 200 rpm to obtain a composite masterbatch. S4: Add the composite masterbatch and pretreated bacterial cellulose to a single-screw blown film unit at a mass ratio of 7:3. Set the barrel temperature to 160 - 180 °C, the die head temperature to 170 °C, and the blow-up ratio to 2.5:1 to obtain a composite film with a thickness of 20 - 50 μm. Then pass the composite film through light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0061] Comparative Example 1 A bio-based degradable photocatalytic film and its preparation method are as follows: Refer to the material ratio and preparation steps of Example 1, except that in step S1, the bacterial cellulose is not modified with a citric acid solution.

[0062] Comparative Example 2 A bio-based degradable photocatalytic film and its preparation method are as follows: Refer to the material ratio and preparation steps of Example 1, except that in step S1, nano-crystalline cellulose whiskers are not added to reinforce the bacterial cellulose.

[0063] Comparative Example 3 A bio-based degradable photocatalytic film and its preparation method are as follows: Refer to the material ratio and preparation steps of Example 1, except that in step S2, ammonium cerium nitrate - ethanol solution is not added to reinforce the titanium dioxide.

[0064] Experimental Example 1 Perform Fourier transform infrared spectroscopy (FTIR) analysis on the citric acid solution-modified bacterial cellulose prepared in step S1 of Example 1 and the unmodified bacterial cellulose. The experimental method refers to GB / T 32199-2015: General Rules for Qualitative Analysis of Infrared Spectroscopy. The results are as shown in the appendix Figure 2 , which is a comparative diagram of the Fourier transform infrared spectroscopy results of the bacterial cellulose modified with citric acid solution and the unmodified bacterial cellulose in step S1. The ester bond appears at the marked position on the graph for the modified bacterial cellulose, confirming the successful introduction of carboxyl groups.

[0065] Experimental Example 2 Respectively mix the doped titanium dioxide prepared in step S2 of Example 1 and the undoped titanium dioxide powder with barium sulfate Mix and grind according to a mass ratio of 1:10, and press into a uniform test piece; Refer to the test standard of ASTM E903-20 "Standard Test Method for Solar Absorptance of Materials Using an Integrating Sphere", and use a UV-visible diffuse reflectance spectroscopy test instrument (equipped with an integrating sphere attachment) to test the sample; — Instrument parameter settings: Wavelength range: 0 - 1100 nm; Scanning mode: Reflection mode, the integrating sphere collects diffuse reflected light; Reference substance: (Reflectivity > 99%); Scanning speed: Medium speed, 200 nm / min, data interval 1 nm.

[0066] — Baseline correction: Using the blank piece as a reference, perform a baseline scan to eliminate the instrument background noise.

[0067] — Data processing: Convert the reflectivity data to the Kubelka-Munk function (F(R)): ; Band gap calculation, fit versus the photon energy The intersection point of the extrapolated straight line part to the horizontal axis of the relationship curve is the band gap.

[0068] The results are as shown in Appendix Figure 3 and Appendix Figure 4 It can be seen that compared with the untreated titanium dioxide, the doped titanium dioxide obtained in step S2 has a significantly reduced light transmittance, and conversely, its absorbance is significantly increased, and its band gap is significantly reduced, thus improving the utilization rate of visible light.

[0069] Experimental Example 3 Test the thickness, mechanical properties, photocatalytic efficiency and degradation performance of the finally prepared bio-based degradable photocatalytic films in Examples 1 - 7 and Comparative Examples 1 - 3, and compare the test results. Thickness test: Measure using a thickness gauge with a precision of 1 μm. Randomly select 5 points on each different film to measure the thickness and record the average value; Mechanical properties: Refer to the national standard GB / T 13022 "Test Method for Tensile Properties of Plastic Films", and mainly test and compare the tensile properties of the films; Photocatalytic efficiency: Test according to the national standard GB / T 23762-2020 "Test Method for Aqueous Solution Purification Performance of Photocatalytic Materials", using methylene blue and tetracycline hydrochloride as target pollutants; Degradation performance: The test was carried out with reference to the national standard GB / T 19277.1-2011 Determination of the Ultimate Aerobic Biodegradability of Materials under Controlled Composting Conditions.

[0070] The test comparison results are shown in Table 1 Table 1 Comparison table of experimental results of Experimental Example 3 of Examples 1-7 and Comparative Examples 1-3

[0071] From the above comparison results, it can be seen that in Comparative Example 1, the bacterial cellulose was not modified with a citric acid solution, which weakened the subsequent interfacial binding force with chitosan and affected the mechanical properties of the final film; in Comparative Example 2, nano-cellulose whiskers were not added to reinforce the bacterial cellulose, and a rigid network could not be formed by means of nano-cellulose whiskers and bacterial bio-cellulose, which had a greater impact on the mechanical properties of the final film; in Comparative Example 3, ammonium cerium nitrate-ethanol solution was not added to reinforce the doped titanium dioxide, resulting in no entering the lattice gap to act as an electron trap to inhibit the recombination of photo-generated electron-hole pairs and improve the quantum efficiency, ultimately affecting the photocatalytic efficiency of the final film; due to the use of bio-based substrates to prepare the film, good performance was shown in terms of degradation performance.

Claims

1. A bio-based degradable photocatalytic thin film, characterized in that, It contains the following components: bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 20-40:50-70:10-30.

2. The bio-based degradable photocatalytic film according to claim 1, wherein The bacterial cellulose has undergone citric acid modification treatment and nano-cellulose whisker reinforcement treatment.

3. The bio-based degradable photocatalytic film according to claim 1, wherein For the doped titanium dioxide, its preparation raw materials include a precursor solution, a dopant solution and a reinforcing agent solution.

4. The bio-based degradable photocatalytic film according to claim 3, wherein The precursor solution is a solution formed by mixing tetrabutyl titanate and absolute ethanol at a volume ratio of 1:10; The dopant solution is a solution formed by dissolving urea in deionized water; The reinforcing agent solution is a solution formed by dissolving ammonium cerium nitrate in absolute ethanol.

5. The preparation method of the bio-based degradable photocatalytic film according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1: Prepare the bacterial cellulose and conduct modification and reinforcement treatment on the bacterial cellulose; S2: Prepare the doped titanium dioxide, conduct reinforcement treatment on the doped titanium dioxide, and then let it stand, age and calcine; S3: Conduct melt blending of the pretreated chitosan and doped titanium dioxide to obtain a composite masterbatch; S4: Blow-mold the composite masterbatch and the bacterial cellulose completed in S1 at a mass ratio of 7:3 into a composite film, and then subject the composite film to light-intensified irradiation to obtain a bio-based degradable photocatalytic film.

6. The preparation method of the bio-based degradable photocatalytic film according to claim 5, wherein The preparation of the bacterial cellulose in S1 is obtained by static fermentation of Acetobacter xylinum; The modification in S1 specifically includes: impregnating in a 5% citric acid solution and reacting at 60°C for 2 hours; The reinforcement treatment in S1 specifically includes: immersing in a 1% nano-cellulose whisker dispersion liquid, with a mass ratio of bacterial cellulose to nano-cellulose whiskers of 1:0.1, and then vacuum filtering for 30 minutes.

7. The preparation method of the bio-based degradable photocatalytic film according to claim 5, wherein The preparation of the doped titanium dioxide in S2 specifically includes: dropping urea dissolved in deionized water into a tetrabutyl titanate-absolute ethanol solution mixed at a volume ratio of 1:10, and stirring at 800 rpm in an ice-water bath while dropping; The reinforcement treatment in S2 specifically includes: adding an ammonium cerium nitrate-ethanol solution and stirring for 30 minutes; The standing, aging and calcining in S2 specifically include: standing for 12 hours, then aging at 60°C for 24 hours and grinding into a powder, and then calcining the powder at 500°C.

8. The preparation method of the bio-based degradable photocatalytic film according to claim 5, wherein The pretreatment in S3 specifically includes: drying chitosan, then ultra-finely pulverizing and passing through a 200-mesh sieve, and immersing the doped titanium dioxide in a 3% KH-550 ethanol solution for optimization modification; The melt blending in S3 specifically includes: adding a plasticizer and a phase solvent and placing them in a twin-screw extruder for melt blending, with the temperature set at 150-170°C and the rotation speed at 200 rpm.

9. The preparation method of the bio-based degradable photocatalytic film according to claim 8, wherein The plasticizer is glycerol, with a purity ≥ 99% and a moisture content ≤ 0.5%; The phase solvent is polyethylene glycol with a molecular weight of 4000 Da.

10. The method for preparing the bio-based degradable photocatalytic thin film according to claim 5, characterized in that For the blow molding into a composite film in S4, the specific parameters include: setting the barrel temperature at 160 - 180 °C, the die head temperature at 170 °C, and the blow-up ratio at 2.5:1; For the light-enhanced irradiation in S4, the specific parameters include: setting the passing speed at 0.5 m / min and the single-sided cumulative irradiation dose at 1800 mJ / cm².

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