Bio-based degradable photocatalytic film and preparation method thereof

Abstract

The present invention relates to the field of forming and preparing plastic materials, specifically to a bio-based degradable photocatalytic film and its preparation method. The present invention proposes a ternary composite system using bacterial cellulose as a skeleton, chitosan as an interfacial adhesive, and doped titanium dioxide as a photocatalytically active component. The film is continuously produced using an extrusion blow molding process for forming the plastic material. The degradable photocatalytic film produced by the present invention exhibits high mechanical properties, strong photocatalytic activity, and rapid and complete degradation under natural conditions.

Description

Technical Field

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

[0002] Traditional petroleum-based plastics, due to their non-degradability, continue to worsen the problem of "white pollution." Photocatalytic materials, however, show great potential in environmental protection areas such as wastewater treatment and air purification. However, existing photocatalytic materials (such as titanium dioxide) generally suffer from difficulties in recycling, low visible light utilization, and secondary pollution generated during degradation, severely limiting their large-scale application. Therefore, there is an urgent need to develop novel composite systems that combine high photocatalytic activity, biodegradability, and mechanical stability.

[0003] Bacterial cellulose (BC) is a natural high-molecular-weight polysaccharide synthesized by microorganisms such as Acetobacter xylinum. It possesses an ultrafine three-dimensional network structure, high crystallinity, high water-holding capacity, and excellent biocompatibility. Compared to plant cellulose, BC does not require the removal of lignin and hemicellulose, and its nanofiber network serves as an ideal carrier platform, providing a high surface area and stable dispersion sites for inorganic photocatalysts. However, BC itself lacks photocatalytic activity, necessitating functional modification to achieve multifunctionalization in composite materials.

[0004] Titanium dioxide, a typical photocatalytic material, is widely used in pollutant degradation and hydrogen production due to its high chemical stability, non-toxicity, and low cost. However, its bandgap is relatively wide, and it only responds to ultraviolet light. Furthermore, nanoparticles easily agglomerate and are difficult to recycle, resulting in low photon quantum efficiency. Existing technologies attempt to reduce the bandgap through doping, but traditional doping processes require high-temperature calcination or complex chemical modification, which can easily destroy the nanostructure of the carrier. Furthermore, the interfacial bonding between the dopant and the carrier is weak, leading to a significant decrease in activity after recycling.

[0005] Current methods for preparing cellulose-based photocatalytic materials have significant defects: for example, patent CN103908979A uses a hydrothermal reaction (>150°C) to load titanium dioxide, which causes the BC network structure to collapse and the titanium dioxide particles to be loosely bound to the BC; patent CN101745430B uses regenerated cellulose, but it lacks the three-dimensional pore structure of BC and has low photocatalytic efficiency.

[0006] In order to solve the above problems, the present invention proposes to use bacterial cellulose (BC) as the skeleton, chitosan (CS) as the interface adhesive, nitrogen / cerium co-doping This ternary composite system of photocatalytically active components achieves in-situ TiO2 loading through a low-temperature sol-gel method, combined with UV crosslinking to strengthen the interfacial bonding between BC and CS, and ultimately achieves continuous film production using an extrusion blow molding process. This design not only addresses the high energy consumption and poor interfacial compatibility of traditional processes, but also provides a novel solution for the industrial application of bio-based photocatalytic films through the synergistic integration of multiple functions. Summary of the Invention

[0007] Based on the above-mentioned problems, the present invention provides a bio-based degradable photocatalytic film and a preparation method thereof. The main features of the present invention are that a composite ternary system is formed by bacterial cellulose, chitosan and doped titanium dioxide, and a plastic state material molding method is used to achieve continuous preparation of the bio-based photocatalytic film. The specific technical solution is as follows:

[0008] 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.

[0009] Furthermore, the bacterial cellulose has been subjected to citric acid modification and nanocellulose whisker reinforcement treatment.

[0010] Furthermore, the raw materials for preparing the doped titanium dioxide include a precursor solution, a dopant solution and an enhancer solution.

[0011] Furthermore, the precursor solution is a solution formed by mixing tetrabutyl titanate and anhydrous ethanol in a volume ratio of 1:10;

[0012] The dopant solution is a solution formed by dissolving urea in deionized water;

[0013] The enhancer solution is a solution formed by dissolving ammonium cerium nitrate in anhydrous ethanol.

[0014] The present invention also provides a method for preparing a biodegradable photocatalytic film, comprising the following steps:

[0015] S1: preparing the bacterial cellulose, and performing modification and enhancement treatment on the bacterial cellulose;

[0016] S2: preparing the doped titanium dioxide, performing a strengthening treatment on the doped titanium dioxide, and then allowing the doped titanium dioxide to stand, age, and calcine;

[0017] S3: melt-blending the pretreated chitosan and doped titanium dioxide to prepare a composite masterbatch;

[0018] S4: blowing the composite masterbatch and the bacterial cellulose processed in S1 into a composite film at a mass ratio of 7:3, and then subjecting the composite film to light-enhanced irradiation to obtain a bio-based degradable photocatalytic film.

[0019] Furthermore, the bacterial cellulose prepared in S1 is prepared by static fermentation of Acetobacter xylinum;

[0020] The modification described in S1 specifically includes: immersing in a 5% citric acid solution and reacting at 60°C for 2 hours;

[0021] The enhancement treatment described in S1 specifically includes: immersing in a 1% nanocellulose whisker dispersion, with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1, and then vacuum filtering for 30 minutes.

[0022] Furthermore, the preparation of the doped titanium dioxide described in S2 specifically includes: adding urea dissolved in deionized water dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed at a volume ratio of 1:10, while stirring at 800 rpm in an ice water bath;

[0023] The enhancement treatment described in S2 specifically includes: adding ammonium cerium nitrate-ethanol solution and stirring for 30 minutes;

[0024] The standing, aging, and calcining described in S2 specifically include: standing for 12 hours, aging at 60° C. for 24 hours, grinding the powder into powder, and then calcining the powder at 500° C.

[0025] Furthermore, the pretreatment described in S3 specifically includes: drying the chitosan, ultrafine grinding the chitosan, and passing the chitosan through a 200-mesh sieve, and immersing the doped titanium dioxide in a 3% KH-550 ethanol solution for optimization and modification;

[0026] The melt blending described in S3 specifically includes: adding a plasticizer and a compatibilizer into a twin-screw extruder for melt blending, with the temperature set at 150-170° C. and the rotation speed at 200 rpm.

[0027] Furthermore, the plasticizer is glycerol with a purity of ≥99% and a moisture content of ≤0.5%;

[0028] The phase solvent is polyethylene glycol with a molecular weight of 4000 Da.

[0029] Furthermore, the blow molding into a composite film in S4 has the following specific parameters: setting the barrel temperature to 160-180°C, the die head temperature to 170°C, and the blow-up ratio to 2.5:1;

[0030] The specific parameters of the light-enhanced irradiation described in S4 include: setting a passing speed of 0.5 m / min and a single-side cumulative irradiation dose of 1800 mJ / cm².

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The modified bacterial cellulose is then reinforced by filling the pores of the BC network with cellulose nanowhiskers (CNWs), and the composite film has high mechanical properties through cross-linking with chitosan;

[0033] (2) By co-doping titanium dioxide with nitrogen / cerium, the band gap is reduced and the visible light absorption rate is improved, so that the degradation rate of pollutants in the film is also higher and the photocatalytic activity is easy to maintain;

[0034] (3) The film is made of bio-based materials, which are easy to degrade under natural conditions and degrade more thoroughly;

[0035] (4) The product is prepared by using related processes for forming plastic materials, which can achieve continuous production;

[0036] (5) Chitosan has a high antibacterial rate, and the dense network of bacterial cellulose reduces the water vapor permeability. The film prepared by the present invention has strong comprehensive performance and has a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart of the preparation method of the bio-based degradable photocatalytic film of the present invention;

[0038] Figure 2 The figure is a Fourier transform infrared spectrum test result diagram of modified and unmodified bacterial cellulose of the present invention;

[0039] Figure 3 This is a comparison chart of the transmittance results of the doped titanium dioxide of the present invention measured by ultraviolet-visible diffuse reflectance spectroscopy;

[0040] Figure 4 This is a comparison chart of the calculation results of the band gap of the doped titanium dioxide of the present invention. DETAILED DESCRIPTION

[0041] The following examples further illustrate and describe the technical solutions of the present invention. It is particularly noted that each specific embodiment is intended to be a concretization and explanation of the technical solutions and should not be construed as limiting the scope of protection of the present invention. Persons of ordinary skill in the art are entitled to modify the technical solutions of these embodiments and to substitute equivalent features for some or all of the technical features. Such modifications or substitutions do not alter the essence of the corresponding technical solutions and do not deviate from the scope of the technical solutions described in the present invention.

[0042] The present invention proposes a bio-based degradable photocatalytic film and a preparation method thereof, wherein the film composition comprises bacterial cellulose (BC), chitosan (CS) and doped titanium dioxide (doped titanium dioxide), with a mass ratio of 20-40:50-70:10-30, as shown in the attached Figure 1 The preparation method flow shown in FIG. 1 includes the following detailed preparation steps:

[0043] 1. Bacterial cellulose pretreatment and functional modification

[0044] 1.1 Raw material preparation and carboxylation modification

[0045] —Biosynthesis of bacterial cellulose (BC)

[0046] Bacteria activation: Acetobacter xylinum ( Acetobacter xylinum CGMCC 1.1812) was inoculated into 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 h;

[0047] Static fermentation: Transfer the activated bacterial solution to a sterilized polyethylene culture dish at a 5% inoculum size. Adjust the culture medium to the above-mentioned basic formula by adding 0.1% sodium citrate to inhibit bacteria. Incubate at 28°C for 7 days, supplementing with 1% glucose every 24 hours to maintain the carbon source.

[0048] Membrane stripping: After the incubation period, the BC was mechanically stripped from the liquid surface and rinsed with deionized water, 1% NaOH solution (treated at 80°C for 1 hour), and deionized water until neutral to obtain transparent BC.

[0049] —Carboxylation modification treatment

[0050] Citric acid esterification reaction: BC is immersed in 5% citric acid In aqueous solution, set the liquid-to-solid ratio to 20:1 and place in a constant temperature water bath shaker at 60°C and 50 rpm for 2 hours;

[0051] Reaction control: Real-time monitoring of the solution pH value ensures the stability of the carboxylation degree;

[0052] Post-treatment: After the reaction, the BC was rinsed with deionized water until the conductivity of the eluate was less than 5 μS / cm, and then dried in a vacuum drying oven at 50°C to constant weight, with the moisture content controlled at ≤5%.

[0053] 1.2 Enhancement treatment: infiltration of cellulose nanowhiskers (CNWs) dispersion

[0054] —Preparation of CNWs dispersion

[0055] Microcrystalline cellulose (MCC) was added to 64% sulfuric acid solution with a solid-liquid ratio of 1:20 and hydrolyzed at 45°C with stirring for 45 minutes;

[0056] The reaction was quickly terminated with 10 volumes of cold water, and the acid was removed by centrifugation at 8000 rpm for 15 minutes. The solution was dialyzed to neutrality and then ultrasonically disrupted (power 300 W, 30 minutes) to obtain a 1% CNWs aqueous dispersion with cellulose length of 200-500 nm, diameter of 10-20 nm, and aspect ratio >20.

[0057] —Vacuum filtration enhancement

[0058] The carboxylated BC was spread evenly on a Buchner funnel with a built-in filter membrane with a pore size of 0.45 μm, and the CNWs dispersion was poured in with a mass ratio of BC to CNWs of 1:0.1. The vacuum pump (pressure -0.08 MPa) was started and filtered for 30 minutes to allow the CNWs to evenly penetrate the BC fiber network.

[0059] In the above steps, bacterial cellulose (BC) is composed of β-1,4-glucose chains, rich in hydroxyl groups (-OH) on its surface. BC is immersed in a 5% citric acid solution at 60°C. The carboxyl groups (-COOH) of the citric acid react with the hydroxyl groups of the BC to form a stable ester bond (RO-CO-R'), thereby introducing carboxyl functional groups onto the BC surface. The introduction of carboxyl groups enhances the subsequent interfacial bonding between BC and chitosan (CS). The amino groups (-NH2) on the chitosan molecular chains can bind to the carboxyl groups through hydrogen or ionic bonds, forming a dense three-dimensional network structure, which improves the mechanical properties and interfacial compatibility of the composite material.

[0060] The modified BC was immersed in a 1% cellulose nanowhisker (CNWs) dispersion, and the CNWs were infiltrated into the BC fiber network by vacuum filtration. Due to the high modulus and specific surface area of CNWs, they can fill the pores between BC fibers; CNWs and BC fibers form a rigid network through hydrogen bonding and mechanical interlocking.

[0061] 2. Preparation of doped titanium dioxide

[0062] 2.1 Raw material preparation and proportion

[0063] Precursor solution: Tetrabutyl titanate Mix with anhydrous ethanol at a volume ratio of 1:10 and stir magnetically until completely dissolved to form a transparent solution A.

[0064] Dopant solution: Nitrogen source - urea Dissolve in 10 mL of deionized water and stir until clear;

[0065] Cerium source - ammonium cerium nitrate Dissolve in 5 mL of anhydrous ethanol and disperse by ultrasonic for 10 minutes.

[0066] 2.2 Sol preparation and hydrolysis and condensation

[0067] Slowly add the urea aqueous solution to solution A at a rate of 1 mL / min while maintaining stirring (800 rpm) and an ice-water bath (0-5°C) to inhibit the rapid hydrolysis of tetrabutyl titanate;

[0068] After the addition was complete, the cerium source ethanol solution was added and stirred for 30 minutes to form a light yellow transparent sol;

[0069] The sol was allowed to stand at room temperature for 12 hours, and a wet gel with a three-dimensional network structure was gradually formed.

[0070] 2.3 Aging and drying

[0071] The wet gel was transferred to a constant temperature drying oven and aged at 60°C for 24 hours to remove residual solvent and promote the densification of the network structure;

[0072] The dried gel was ground to a particle size of ≤100 μm to obtain a light blue precursor powder.

[0073] 2.4 Calcination

[0074] The precursor powder was placed in a muffle furnace, heated to 500°C at a rate of 5°C / min, calcined in air atmosphere for 2 hours, and then naturally cooled to room temperature.

[0075] In the above steps, tetrabutyl titanate Hydrolyze in anhydrous ethanol to form titanium oxyhydroxide Network; Urea As a nitrogen source, it decomposes to generate NH3 during the calcination process, and the nitrogen atoms replace Oxygen atoms in the lattice form bond, nitrogen doping introduces intermediate energy levels, making The band gap width is reduced and the visible light absorption edge is red-shifted; adding ethanol solution, Enter Lattice gaps act as electron traps to suppress the recombination of photogenerated electron-hole pairs and improve quantum efficiency.

[0076] 3. Preparation of chitosan-titanium dioxide composite masterbatch

[0077] 3.1 Raw material pretreatment and ratio optimization

[0078] —Chitosan (CS) pretreatment

[0079] The chitosan was dried in a vacuum drying oven at 60°C for 12 hours, and then pulverized with an ultrafine grinder (rotation speed 20000 rpm) to a particle size of ≤50 μm, and passed through a 200-mesh sieve for later use.

[0080] —Surface modification of doped titanium dioxide

[0081] The doped titanium dioxide powder was immersed in 3% KH-550 ethanol solution, and ultrasonic dispersion was set at 40 kHz for 30 minutes, and then dried at 60 ° C. The silane coupling agent was added at 40 ° C. Surface formation groups, enhancing the interfacial bonding with chitosan.

[0082] —Plasticizer and solvent selection

[0083] Plasticizer: glycerol, purity ≥99%, moisture content ≤0.5%;

[0084] Phase solvent: polyethylene glycol (PEG), molecular weight 4000 Da, melting point 50-55 °C, to ensure matching with the melting temperature of chitosan.

[0085] 3.2 Twin-screw melt blending

[0086] —Device parameter settings

[0087] Twin-screw extruder: Use a co-rotating intermeshing twin-screw with an L / D ratio of 40 and a screw diameter of 35 mm. The zone temperatures are set as follows: feeding zone 150°C, melting zone 160°C, mixing zone 170°C, and extrusion zone 165°C.

[0088] Screw speed: 200 rpm, shear rate .

[0089] Vacuum degassing: set up a vacuum pump in the extrusion area , remove melt bubbles.

[0090] —Adding and blending

[0091] Main feeding port: add the premix of chitosan, doped titanium dioxide and PEG, and set the premixing time to 10 minutes;

[0092] Side feed port: Inject liquid glycerin into the melting zone to avoid premature volatilization.

[0093] —Granulation and post-processing

[0094] Extrusion granulation: After the melt is extruded through a die (aperture 3 mm), it is cut into cylindrical masterbatch pellets with a diameter of 3 mm and a length of 5 mm by a 15°C water-cooled strand pelletizer;

[0095] Drying: The particles are dried in a hot air circulation drying oven at 50℃ for 6 hours, with a moisture content of ≤0.3%.

[0096] In the above steps, glycerol is inserted into the chitosan molecular chain as a plasticizer, destroying its intramolecular hydrogen bonds, lowering the glass transition temperature, and improving melt fluidity; the ether bond of polyethylene glycol forms a hydrogen bond with the hydroxyl group on the surface of doped titanium dioxide, and its long chain structure wraps Particles to prevent agglomeration; twin-screw extruder uses high shear force to It is evenly dispersed in the chitosan matrix to form an "island structure" to ensure that the photocatalytic active sites are fully exposed.

[0097] 4. Plastic forming and post-processing

[0098] 4.1 Extrusion blow molding

[0099] —Raw material pretreatment and blending

[0100] Drying of composite masterbatch: Mix chitosan / titanium dioxide composite masterbatch particles with pretreated BC fibers in a mass ratio of 7:3 and place in a hot air drying oven at 50°C for 4 hours to ensure that the moisture content is ≤0.1%;

[0101] Premixing process: Use a high-speed mixer to evenly disperse the composite masterbatch and BC fiber, set the speed to 1000 rpm, and the time to 10 minutes.

[0102] —Single screw extrusion blow molding process

[0103] Temperature zone control: feeding zone 160℃, compression zone 170℃, metering zone 180℃, die head 170℃;

[0104] Screw design: Use a gradual screw with L / D=25 and a compression ratio of 3:1 to ensure that the melt is fully plasticized;

[0105] 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 with a pressure of 0.3 MPa and a blow-up ratio of 2.5:1, so that the film tube is transversely stretched to 2.5 times its original diameter.

[0106] The film was quickly cooled and shaped by a pulling roller (speed 10 m / min) and a cooling air ring (wind speed 5 m / s, temperature 15°C) to obtain a composite film with a thickness of 20 to 50 μm.

[0107] 4.2 Photocrosslinking

[0108] Light source parameters: low-pressure mercury lamp, dominant wavelength 254 nm, intensity 30 mW / cm², irradiation distance 10 cm, spot uniformity >90%.

[0109] Conveyor speed: The prepared film passes through the irradiation zone at a speed of 0.5 m / min, ensuring a cumulative irradiation dose of 1800 mJ / cm² on a single side.

[0110] In the above steps, the composite masterbatch and pre-treated BC fiber are melted in a single-screw extruder, and the BC fiber is used as a reinforcement phase to form a "fiber-matrix" interpenetrating network; ultraviolet light excites the amino groups of chitosan and the carboxyl groups of BC to react with Schiff bases to form a covalent cross-linked network; ultraviolet light also excites Hydroxyl radicals are generated, the surface hydroxyl density increases, and the photocatalytic activity is improved.

[0111] Example 1

[0112] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0113] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 30:55:15.

[0114] The preparation process includes:

[0115] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0116] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0117] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0118] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0119] Example 2

[0120] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0121] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide in a mass ratio of 20:50:30.

[0122] The preparation process includes:

[0123] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0124] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0125] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0126] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0127] Example 3

[0128] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0129] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 20:70:10.

[0130] The preparation process includes:

[0131] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0132] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0133] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0134] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0135] Example 4

[0136] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0137] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 40:50:10.

[0138] The preparation process includes:

[0139] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0140] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0141] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0142] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0143] Example 5

[0144] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0145] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 30:60:10.

[0146] The preparation process includes:

[0147] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0148] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0149] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0150] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0151] Example 6

[0152] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0153] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 30:50:20.

[0154] The preparation process includes:

[0155] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0156] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0157] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0158] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0159] Example 7

[0160] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0161] The film composition includes bacterial cellulose, chitosan and doped titanium dioxide in a mass ratio of 20:60:20.

[0162] The preparation process includes:

[0163] S1: Bacterial cellulose was prepared by static fermentation of Acetobacter xylinum, immersed in 5% citric acid solution, reacted at 60°C for 2 hours, and then immersed in 1% nanocellulose whisker dispersion with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1. The pretreated bacterial cellulose was obtained by vacuum filtration for 30 minutes.

[0164] S2: Urea dissolved in deionized water was added dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed in a volume ratio of 1:10, while stirring at 800 rpm in an ice-water bath. After the addition was complete, ammonium cerium nitrate-ethanol solution was added and stirring was continued for 30 minutes. After standing for 12 hours, the mixture was aged at 60°C for 24 hours and ground into powder. The powder was calcined at 500°C to obtain doped titanium dioxide.

[0165] S3: After drying, chitosan is ultrafinely ground 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 melt-blended in a twin-screw extruder at a temperature of 150-170°C and a speed of 200 rpm to obtain a composite masterbatch.

[0166] S4: The composite masterbatch and pretreated bacterial cellulose were added into a single-screw film blowing unit in a mass ratio of 7:3. The barrel temperature was set at 160-180°C, the die temperature was 170°C, and the blowing ratio was 2.5:1 to obtain a composite film with a thickness of 20-50 μm. The composite film was then subjected to light-enhanced irradiation at a speed of 0.5 m / min to obtain a bio-based degradable photocatalytic film.

[0167] Comparative Example 1

[0168] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0169] The material ratios and preparation steps of Reference Example 1 are the same, except that in step S1, no citric acid solution is used to modify the bacterial cellulose.

[0170] Comparative Example 2

[0171] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0172] The material ratio and preparation steps of Reference Example 1 are the same, except that in step S1, no nanocellulose whiskers are added to enhance the bacterial cellulose.

[0173] Comparative Example 3

[0174] Bio-based degradable photocatalytic film and preparation method thereof are as follows:

[0175] The material ratio and preparation steps of Reference Example 1 are the same, except that in step S2, no cerium ammonium nitrate-ethanol solution is added to strengthen the titanium dioxide.

[0176] Experimental Example 1

[0177] The citric acid solution-modified bacterial cellulose prepared in step S1 of Example 1 and the unmodified bacterial cellulose were subjected to Fourier transform infrared spectroscopy (FTIR) analysis. The experimental method was based on GB / T 32199-2015: "General Rules for Qualitative Analysis Techniques by Infrared Spectroscopy";

[0178] The results are as attached Figure 2 The figure shows the comparison of the Fourier transform infrared spectra of bacterial cellulose modified with citric acid solution in step S1 and unmodified bacterial cellulose. The figure shows the modified bacterial cellulose in Ester bond Characteristic peaks confirmed the successful introduction of carboxyl groups.

[0179] Experimental Example 2

[0180] The doped titanium dioxide powder and the undoped titanium dioxide powder prepared in step S2 of Example 1 were mixed with barium sulfate. Mix and grind in a mass ratio of 1:10 and press into uniform test pieces; refer to the test standard ASTM E903-20 "Standard Method for Determination of Solar Absorbance of Materials Using an Integrating Sphere" and use a UV-Vis diffuse reflectance spectrometer (equipped with an integrating sphere accessory) to test the samples;

[0181] —Instrument parameter settings:

[0182] Wavelength range: 0-1100 nm;

[0183] Scanning mode: Reflection mode, the integrating sphere collects diffuse reflected light;

[0184] Reference material: (Reflectivity>99%);

[0185] Scan speed: medium, 200 nm / min, data interval 1 nm.

[0186] —Baseline correction:

[0187] by The blank piece was used as a reference to perform a baseline scan and eliminate the instrument background noise.

[0188] —Data processing:

[0189] Convert reflectance data to Kubelka-Munk function (F(R)): ;

[0190] Bandgap calculation and fitting and photon energy The extrapolated straight line part to the intersection of the horizontal axis is the band gap width.

[0191] The results are as attached Figure 3 and attached Figure 4 As shown, the transmittance of the doped titanium dioxide obtained in step S2 is greatly reduced compared with the untreated titanium dioxide, while its absorbance is greatly increased and its band gap is significantly reduced, which can improve the utilization rate of visible light.

[0192] Experimental Example 3

[0193] The bio-based degradable photocatalytic films finally prepared in Examples 1-7 and Comparative Examples 1-3 were tested for thickness, mechanical properties, photocatalytic efficiency and degradation performance, and the test results were compared.

[0194] Thickness test: Use a thickness gauge with an accuracy of 1 μm. Measure the thickness at 5 randomly selected points on each film and record the average value.

[0195] Mechanical properties: Refer to the national standard GB / T 13022 "Test method for tensile properties of plastic films", mainly focusing on the tensile properties of the film for testing and comparison;

[0196] Photocatalytic efficiency: Tested in accordance with the national standard GB / T 23762-2020 "Test method for purification performance of aqueous solutions of photocatalytic materials", with methylene blue and tetracycline hydrochloride as target pollutants;

[0197] Degradability: Tested with reference to the national standard GB / T 19277.1-2011 “Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions”.

[0198] The test comparison results are shown in Table 1

[0199] Table 1 Comparison of experimental results of Experimental Example 3 for Examples 1-7 and Comparative Examples 1-3

[0200]

[0201] From the above comparison results, it can be seen that in Comparative Example 1, the bacterial cellulose was not modified with citric acid solution, which weakened the subsequent interfacial bonding force with chitosan and affected the mechanical properties of the final film; in Comparative Example 2, the bacterial cellulose was not reinforced by adding nanocellulose whiskers, and a rigid network could not be formed with the help of nanocellulose whiskers and bacterial biocellulose, which had a greater impact on the mechanical properties of the final film; in Comparative Example 3, the doped titanium dioxide was not reinforced by adding ammonium cerium nitrate-ethanol solution, resulting in no Enter The lattice gaps act as electron traps to suppress the recombination of photogenerated electron-hole pairs, improve quantum efficiency, and ultimately affect the photocatalytic efficiency of the final film. Since bio-based substrates are used to prepare the film, the degradation performance is good.

Claims

1. Bio-based degradable photocatalytic film, characterized in that: The invention comprises the following components: bacterial cellulose, chitosan and doped titanium dioxide, with a mass ratio of 20-40:50-70:10-30; the bacterial cellulose has been modified with citric acid and reinforced with nanocellulose whiskers; the raw materials for preparing the doped titanium dioxide include a precursor solution, a dopant solution and a reinforcing agent solution; the doped titanium dioxide needs to be pre-treated by immersing in a 3% KH-550 ethanol solution for optimization and modification; The precursor solution is a solution formed by mixing tetrabutyl titanate and anhydrous ethanol in a volume ratio of 1:10; the dopant solution is a solution formed by dissolving urea in deionized water; and the enhancer solution is a solution formed by dissolving ammonium cerium nitrate in anhydrous ethanol.

2. The method for preparing a biodegradable photocatalytic film according to claim 1, wherein: The steps include: S1: preparing the bacterial cellulose, and performing modification and enhancement treatment on the bacterial cellulose; S2: preparing the doped titanium dioxide, performing a strengthening treatment on the doped titanium dioxide, and then allowing the doped titanium dioxide to stand, age, and calcine; S3: melt-blending the pretreated chitosan and the pretreated doped titanium dioxide to prepare a composite masterbatch; S4: blowing the composite masterbatch and the bacterial cellulose processed in S1 into a composite film at a mass ratio of 7:3, and then subjecting the composite film to light-enhanced irradiation to obtain a bio-based degradable photocatalytic film.

3. The method for preparing a biodegradable photocatalytic film according to claim 2, wherein: The bacterial cellulose described in S1 is prepared by static fermentation of Acetobacter xylinum; The modification described in S1 specifically includes: immersing in a 5% citric acid solution and reacting at 60°C for 2 hours; The enhancement treatment described in S1 specifically includes: immersing in a 1% nanocellulose whisker dispersion, with a mass ratio of bacterial cellulose to nanocellulose whiskers of 1:0.1, and then vacuum filtering for 30 minutes.

4. The method for preparing a biodegradable photocatalytic film according to claim 2, wherein: The preparation of the doped titanium dioxide described in S2 specifically comprises: adding urea dissolved in deionized water dropwise to a tetrabutyl titanate-anhydrous ethanol solution mixed at a volume ratio of 1:10, while stirring at 800 rpm in an ice water bath; The enhancement treatment described in S2 specifically includes: adding ammonium cerium nitrate-ethanol solution and stirring for 30 minutes; The standing, aging, and calcining described in S2 specifically include: standing for 12 hours, aging at 60° C. for 24 hours, grinding the powder into powder, and then calcining the powder at 500° C.

5. The method for preparing a bio-based degradable photocatalytic film according to claim 2, wherein: The pre-treated chitosan described in S3 specifically comprises: drying the chitosan, ultrafinely grinding the chitosan, and passing the mixture through a 200-mesh sieve; The melt blending described in S3 specifically includes: adding a plasticizer and a compatibilizer into a twin-screw extruder for melt blending, with the temperature set at 150-170° C. and the rotation speed at 200 rpm.

6. The method for preparing a biodegradable photocatalytic film according to claim 5, wherein: The plasticizer is glycerol with a purity of ≥99% and a moisture content of ≤0.5%; The phase solvent is polyethylene glycol with a molecular weight of 4000 Da.

7. The method for preparing a biodegradable photocatalytic film according to claim 2, wherein: The blow molding into a composite film as described in S4 includes the following specific parameters: setting the barrel temperature to 160-180°C, the die temperature to 170°C, and the blow-up ratio to 2.5:1; The specific parameters of the light-enhanced irradiation described in S4 include: setting a passing speed of 0.5 m / min and a single-side cumulative irradiation dose of 1800 mJ / cm².

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