Preparation method of nanocellulose titanium dioxide photocatalytic self-cleaning film

Abstract

The application relates to the field of photocatalytic film preparation, in particular to a preparation method of a nanocellulose titanium dioxide photocatalytic self-cleaning film. Through in-situ covalent polymerization growth of titanium dioxide on nanocellulose and treatment of a low-eutectic solvent, the prepared composite film material has strong interface combination and high photocatalytic efficiency.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic thin film preparation, specifically to a method for preparing a nano-cellulose titanium dioxide photocatalytic self-cleaning thin film. Background Technology

[0002] With the increasing severity of environmental pollution, photocatalytic self-cleaning materials, due to their green and sustainable characteristics, have shown great application potential in fields such as wastewater treatment, air purification, and building facades. Titanium dioxide, as a typical photocatalytic material, has become a core material for developing self-cleaning functions due to its high chemical stability, non-toxicity, and excellent photocatalytic activity. However, traditional TiO2-based materials still have significant drawbacks in practical applications: high photogenerated carrier recombination rates, weak interfacial bonding, and limited photoresponse range, making it difficult to meet practical requirements in terms of catalytic efficiency and material stability.

[0003] In existing technologies, TiO2 thin films are mostly prepared using physical spraying or sol-gel methods. For example, patent CN102560325A proposes to melt-deposit TiO2 onto the substrate surface using plasma spraying technology. Although this can form a nanostructured coating, the adhesion between the coating and the substrate is mainly physical adsorption, resulting in weak interfacial bonding. This makes the coating prone to peeling due to mechanical stress or differences in thermal expansion, especially under high humidity or dynamic conditions where durability significantly decreases. Similarly, patent CN113699612A uses electrospinning to load TiO2 onto the fiber surface, but the TiO2 particles are only bonded to the fiber substrate through van der Waals forces. After long-term use, the particles are prone to detachment, and the photocatalytic activity decreases significantly.

[0004] The photocatalytic performance of TiO2 is highly dependent on its crystal structure and surface defects. While anatase TiO2 exhibits high photocatalytic activity, its band gap only responds to ultraviolet light, which accounts for only 5% of the solar spectrum, resulting in low energy utilization in practical applications. Existing technologies attempt to extend the photoresponse range by doping with metals or non-metals. For example, patent CN114835936A describes doping TiO2 with Fe³⁺ and Mo. 5 ⁺ Plasma can redshift the absorption edge to the visible light region, but the doping process requires high-temperature calcination, which can easily damage the structure of organic substrates such as cellulose, limiting its application in flexible films.

[0005] Cellulose nanofibers (CNFs) are considered ideal TiO2 supports due to their high specific surface area, biodegradability, and surface modifiability. However, the composite of CNFs and TiO2 often faces the problem of poor interfacial compatibility. Patent CN103934036A utilizes a low-temperature preparation of a mixed solution of titanium tetrachloride and water, followed by the addition of cellulose as a template and heating treatment to obtain a composite material with titanium dioxide nanocrystals supported on cellulose. However, no further treatment is applied to the composite material, resulting in a still low photocatalytic efficiency.

[0006] In summary, existing cellulose-titanium dioxide composite thin film materials suffer from weak interfacial bonding, demanding preparation conditions, and insufficient photocatalytic efficiency. There is an urgent need to develop a composite thin film material with stable interfacial bonding, mild preparation conditions, and high photocatalytic efficiency. Summary of the Invention

[0007] Based on the problems summarized above, this invention provides a method for preparing a nano-cellulose titanium dioxide photocatalytic self-cleaning film. Its main feature is that the composite film material prepared by in-situ covalent polymerization growth of titanium dioxide on nano-cellulose, combined with the treatment of eutectic solvent, has strong interfacial bonding and high photocatalytic efficiency.

[0008] The specific technical solution is as follows:

[0009] A method for preparing a nanocellulose titanium dioxide photocatalytic self-cleaning film includes a method for growing titanium dioxide by in-situ covalent polymerization of titanium oxysulfate on nanocellulose to prepare a nanocellulose titanium dioxide composite material.

[0010] Furthermore, the nano-cellulose titanium dioxide composite material needs to be optimized by eutectic solvent treatment, wherein the eutectic solvent is prepared by choline chloride, lactic acid and oxalic acid in a molar ratio of 1:2:1.

[0011] Furthermore, it includes the following steps:

[0012] S1: Natural cellulose raw materials are pretreated by swelling, and then subjected to mechanical peeling and oxidation treatment with 2,2,6,6-tetramethylpiperidine oxide. After treatment, the raw materials are centrifuged at 8000 rpm for 20 minutes, and finally dialyzed and the concentration is adjusted to obtain a 1.5 wt% homogeneous nanocellulose fiber solution.

[0013] S2: The homogeneous nanocellulose fiber liquid obtained in S1 was heated to 45°C and kept at that temperature for 20 minutes. 15wt% titanium oxysulfate solution was added dropwise. After the solution was added to a fixed volume ratio, it was kept at 45°C and stirred for 45 minutes. After cooling to room temperature, it was dialyzed until the specified conditions were met to obtain the in-situ covalently polymerized composite material.

[0014] S3: The in-situ covalent polymer composite material obtained in S2 was mixed with a eutectic solvent in a certain proportion, ultrasonically dispersed for 30 minutes, then treated at high temperature, naturally cooled to room temperature, and then centrifuged in segments. It was then washed three times alternately with ethanol and deionized water, and vacuum dried at 60°C for 12 hours to obtain the composite powder.

[0015] S4: The composite powder obtained in S4 was dispersed in a 1:1 volume ratio acetic acid / acetone mixed solvent. After dispersion, it was magnetically stirred at 800 rpm for 4 hours, then ultrasonically treated at 40 kHz for 30 minutes, and finally obtained by electrospinning to obtain a nano-cellulose titanium dioxide photocatalytic self-cleaning film.

[0016] Furthermore, the swelling pretreatment described in S1 specifically includes immersing the natural cellulose raw material in a mixed solution of 6 wt% LiOH and 10 wt% urea, and then freezing it at -10°C for 18 hours.

[0017] The mechanical stripping process described in S1 specifically includes 3 to 5 cycles of treatment using a high-pressure homogenizer at a pressure of 100 MPa under a controlled temperature of ≤40℃.

[0018] Furthermore, the 2,2,6,6-tetramethylpiperidine oxide oxidation treatment described in S1 comprises a treatment reagent combination including 2,2,6,6-tetramethylpiperidine oxide, sodium bromide, and sodium hypochlorite.

[0019] Furthermore, the addition to a fixed volume ratio described in S2 means that the volume ratio of the uniform nanocellulose fiber solution to the titanium oxysulfate solution reaches 100-150:1.

[0020] Furthermore, the dialysis described in S2 until the specified conditions are met specifically includes: dialysis until the conductivity is less than 30 μS / cm. 3 Add sodium hydroxide to adjust the pH to 6, and perform dialysis again until the conductivity is <30 μS / cm. 3 .

[0021] Furthermore, the proportional mixing mentioned in S3 refers to mixing the in-situ covalent polymer composite material with the eutectic solvent at a mass ratio of 1:10.

[0022] Furthermore, the high-temperature treatment described in S3 involves heating to 180°C at a rate of 3°C / min and maintaining the temperature for 4–8 hours;

[0023] The segmented centrifugation process described in S3 involves first centrifuging at 3000 rpm for 5 minutes, and then centrifuging at 12000 rpm for 15 minutes.

[0024] Furthermore, the electrospinning process described in S4 includes the following process parameters: a voltage of 20kV, a feed speed of 0.3mL / min, a receiving distance of 15cm, a temperature of 23-27℃, and a relative humidity of 40-50%.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention achieves the close bonding of nanocellulose and titanium dioxide through in-situ covalent polymerization growth of titanium dioxide. Nanocellulose provides a stable growth attachment point for titanium dioxide and does not cause the agglomeration of titanium dioxide particles, thus achieving good dispersion and improving the overall performance of the composite material.

[0027] (2) The present invention optimizes the eutectic solvent to control the ratio of titanium dioxide anatase to rutile phase within a suitable range and introduces oxygen vacancy defects, which causes the light absorption edge of the membrane material to red-shift and improves the photocatalytic performance of the membrane material. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation method of the nano-cellulose titanium dioxide photocatalytic self-cleaning film of the present invention.

[0029] Figure 2 This is a comparison chart of the Fourier transform infrared spectral results of Experiment Example 1 of the present invention;

[0030] Figure 3 This is a comparison chart of the solid ultraviolet-visible diffuse reflectance spectra of Experimental Example 2 of the present invention. Detailed Implementation

[0031] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0032] This invention proposes a method for preparing a nano-cellulose titanium dioxide photocatalytic self-cleaning film, as shown in the appendix. Figure 1 The diagram shown is a flowchart of the preparation method for nano-cellulose titanium dioxide photocatalytic self-cleaning film. The detailed preparation steps are as follows:

[0033] 1. Pretreatment and surface functionalization of nanocellulose:

[0034] 1.1 Raw material swelling treatment

[0035] Natural cellulose raw materials, such as wood pulp, cotton fiber, or bacterial cellulose, are selected and pretreated with an alkali / urea system for swelling. The specific procedures are as follows:

[0036] Cellulose raw materials were immersed in a mixed solution of 6 wt% LiOH and 10 wt% urea, and then frozen at -10°C for 18 hours to disrupt the hydrogen bonds between cellulose molecules and promote fiber bundle swelling. After swelling, the crystallinity of cellulose fibers decreased from 60-80% of natural cellulose to 40-50%, significantly improving subsequent peeling efficiency.

[0037] 1.2 Synergistic treatment of mechanical peeling and TEMPO oxidation

[0038] Mechanical exfoliation: The swollen cellulose suspension is diluted to 2 wt% and then circulated 3–5 times using a high-pressure homogenizer at 100 MPa. Shear force is used to exfoliate the fiber bundles into cellulose nanofibers (CNF) with diameters of 3–20 nm and lengths of several micrometers. This process requires temperature control at ≤40℃ to prevent thermal degradation of the cellulose.

[0039] TEMPO (2,2,6,6-tetramethylpiperidine oxide) oxidation treatment: The mechanically exfoliated solution was further treated using a TEMPO / NaClO / NaBr oxidation system. 0.2 mmol / g TEMPO and an equimolar amount of NaBr were added to the CNF suspension, followed by dropwise addition of a 10% NaClO solution as the oxidant. The reaction was carried out under nitrogen protection to avoid side reactions such as the formation of carboxylic anhydrides or over-oxidation. Specific conditions: pH = 10–11, temperature 5–10℃, NaClO to cellulose mass ratio 0.5:1, reaction time 3 hours. TEMPO catalyzes the selective oxidation of the C6 hydroxyl group of cellulose to a carboxyl group (-COOH), accompanied by the formation of a small amount of aldehyde group (-CHO), increasing the surface charge density of CNF and achieving a zeta potential of over -40 mV in the suspension, significantly enhancing dispersion stability.

[0040] 1.3 Dispersion and Purification

[0041] The CNF suspension after treatment was centrifuged at 8000 rpm for 20 minutes to remove undissociated coarse fibers, and then dialyzed to remove residual alkali and small molecule byproducts. Finally, it was adjusted to a uniform dispersion system of 1.5 wt% for later use.

[0042] In the above steps, the supramolecular structure of cellulose is destroyed by low-temperature swelling, which reduces the energy consumption of mechanical peeling, while preserving the high aspect ratio and crystallinity of CNF, providing a structural basis for subsequent functionalization; the TEMPO oxidation system is used to efficiently introduce carboxyl groups into the cellulose surface, while controlling the concentration and reaction conditions to avoid fiber breakage caused by excessive oxidation, thus ensuring the mechanical properties of CNF.

[0043] 2. In-situ covalent polymerization growth of titanium dioxide

[0044] The prepared uniformly dispersed CNF suspension was heated to 45°C in a water bath and kept at this temperature for 20 minutes. Then, a 15 wt% titanium oxysulfate (TiOSO4) solution was added dropwise, with a CNF suspension to titanium oxysulfate solution volume ratio of 100–150:1. After the addition was complete, the mixture was kept at this temperature and stirred for 45 minutes to form a white gel. After cooling to room temperature, the gel was poured into a dialysis bag for dialyzing. When the conductivity was less than 30 μS / cm... 3 Add an appropriate amount of NaOH to adjust the pH to 6, and perform dialysis again until the conductivity is <30 μS / cm. 3 CNF and titanium dioxide composite material was obtained.

[0045] In the above steps, CNF is an excellent biological template that provides growth attachment sites for TiO2. This is mainly because CNF itself has a certain continuity in space and good mechanical stability, which can provide certain structural support and form an effective scaffold that can be used to fix TiO2. Secondly, the treated surface contains abundant hydroxyl groups, which can be used to guide the in-situ growth of TiO2 and prevent nanoparticle aggregation.

[0046] 3. Optimized performance of eutectic solvent (DES) treatment

[0047] 3.1 Construction of DES

[0048] Choline chloride (ChCl, purity ≥ 98%) was selected as the hydrogen bond acceptor, and lactic acid (LA, purity ≥ 90%) and oxalic acid (OA, purity ≥ 99%) were selected as the hydrogen bond donors. The molar ratio of ChCl, lactic acid and oxalic acid was 1:2:1.

[0049] First, choline chloride and lactic acid are magnetically stirred at 60°C for 30 minutes to form a premix. Then, oxalic acid powder is slowly added to avoid local over-concentration that could lead to crystal precipitation. After mixing evenly, the mixture is continuously stirred in a 60°C constant temperature oil bath for 3 hours under nitrogen protection until a homogeneous and transparent liquid is formed.

[0050] 3.2 DES-induced heterojunction

[0051] The obtained CNF / TiO2 composite material was mixed with DES at a mass ratio of 1:10 and ultrasonically dispersed for 30 minutes to form a homogeneous slurry. The slurry was then transferred to a high-pressure reactor and heated to 180°C at a rate of 1–5°C / min, maintained for 4–8 hours, and then allowed to cool naturally to room temperature. During this process, DES simultaneously acts as a solvent, structure directing agent, and defect inducing agent.

[0052] 3.3 Optimization of Centrifugal Separation and Washing

[0053] First, the mixed slurry was centrifuged at 3000 rpm for 5 minutes to remove large particulate impurities, and then centrifuged at 12000 rpm for 15 minutes to collect the CNF / TiO2 complex. The mixture was washed three times with alternating ethanol and deionized water to effectively remove DES residue.

[0054] 3.4 Vacuum drying and structural stabilization

[0055] The washed CNF / TiO2 composite was placed in a vacuum drying oven and dried at 60°C for 12 hours. The vacuum degree was set to ≤0.1MPa to avoid CNF fiber collapse or TiO2 crystal transformation caused by high temperature, thus obtaining CNF / TiO2 composite powder.

[0056] In the above steps, Cl⁻ and oxalate ions (C₂O₄²⁻) in DES preferentially adsorb onto the TiO₂ crystal face, reducing the surface energy of the anatase (001) face through selective dissolution and promoting the directional growth of the rutile phase (110) face; by adjusting the hydrothermal time, the ratio of anatase to rutile phase can be controlled between 7:3 and 5:5, optimizing the carrier separation efficiency; lactic acid decomposes at high temperature to produce reducing intermediates, partially reducing Ti 4 ⁺ is Ti³⁺, which forms oxygen vacancy defects. Oxygen vacancies introduce defect energy levels in the band gap of TiO2, causing a redshift in the light absorption edge.

[0057] During the DES treatment, the carboxyl groups formed on the CNF surface in the previous treatment interact with the DES components through hydrogen bonds to form a protective layer, which inhibits the excessive growth of TiO2 particles at high temperatures. The three-dimensional network structure of CNF provides spatial confinement for the heterogeneous TiO2 phase junction, preventing particle agglomeration.

[0058] 4. Composite film molding

[0059] 4.1 Preparation of Composite Spinning Solution

[0060] The DES-treated CNF / TiO2 composite material was dispersed in a mixed solvent of acetic acid / acetone (1:1 volume ratio). The selection of the mixed solvent was based on the following criteria:

[0061] Acetic acid: provides moderate polarity to promote uniform dispersion of CNF and TiO2, while adjusting solution viscosity;

[0062] Acetone: Its low boiling point (56°C) can accelerate solvent evaporation and prevent fiber sticking.

[0063] After dispersion, the mixture was magnetically stirred at 800 rpm for 4 hours, followed by ultrasonic treatment at 40 kHz for 30 minutes to achieve full dispersion of the composite material. The final solid content was controlled at 8-10 wt%, and the solution conductivity was adjusted to 50-80 μS / cm to match the requirements of electrospinning.

[0064] 4.2 Electrospinning

[0065] The key parameters of the multi-needle electrospinning equipment are designed as follows:

[0066] Voltage: 20kV, ensuring that the electric field force is sufficient to overcome the surface tension of the solution and form a stable Taylor cone;

[0067] Propulsion speed: 0.3 mL / min. Low-speed propulsion can reduce the problem of discontinuous droplet spray and ensure the uniformity of fiber diameter.

[0068] Receiving distance: 15cm, to balance solvent evaporation time and fiber stretching, and avoid fiber breakage or excessive adhesion;

[0069] Environmental control: Temperature 25±2℃, relative humidity 40~50%, to suppress fiber surface defects caused by excessive solvent evaporation.

[0070] Nanocellulose titanium dioxide photocatalytic self-cleaning films were obtained through electrospinning.

[0071] In the above steps, the composite spinning solution jet undergoes three stages in a high-voltage electrostatic field: Taylor cone formation, where the electric field increases the surface charge density of the droplets, overcoming surface tension to form a cone-shaped jet; jet instability stretching, where the jet experiences whipping instability in the electric field, reducing its diameter from the millimeter to the nanometer scale; and solvent evaporation and solidification, where the rapid evaporation of acetone / acetic acid promotes the directional alignment of the TiO2 / CNF composite structure within the fiber, forming a "fiber core-photocatalytic shell" structure. During solvent evaporation, CNF undergoes liquid-liquid phase separation with acetic acid / acetone, forming an interpenetrating network structure. The hydrogen bond network remaining from DES acts as a soft template, guiding TiO2 nanoparticles to form ordered mesopores on the fiber surface.

[0072] Example 1

[0073] The preparation method of nano-cellulose titanium dioxide photocatalytic self-cleaning film is as follows:

[0074] S1: Natural cellulose raw material was soaked in a mixed solution of 6wt% LiOH and 10wt% urea and frozen at -10℃ for 18 hours. The treated cellulose suspension was diluted to 2wt% and circulated 3-5 times under high pressure homogenization at 100MPa while maintaining a temperature ≤40℃. After treatment, 0.2mmol / g TEMPO and an equimolar amount of NaBr were added to the CNF suspension under nitrogen protection, and then 10% NaClO solution was added dropwise as an oxidant. The temperature was maintained at 5-10℃ during the addition, the mass ratio of NaClO to cellulose was 0.5:1, and the reaction time was 3 hours. After the reaction, the solution was centrifuged at 8000rpm for 20 minutes, dialyzed, and adjusted to 1.5wt% to obtain a homogeneous CNF solution.

[0075] S2: Heat the homogenized CNF solution to 45°C in a water bath and maintain the temperature for 20 minutes. Then, add 15 wt% TiOSO4 solution dropwise, with a volume ratio of homogenized CNF solution to TiOSO4 solution of 125:1. After the addition is complete, maintain the temperature at 45°C with stirring for 45 minutes. After cooling to room temperature, pour the solution into a dialysis bag for dialysis. When the conductivity is less than 30 μS / cm... 3 Then, add NaOH to adjust the pH to 6, and dialyze again until the conductivity is <30 μS / cm. 3 CNF / TiO2 composite material was obtained.

[0076] S3: First, choline chloride and lactic acid were magnetically stirred at 60℃ for 30 minutes to form a premix. Then, oxalic acid powder was slowly added. The molar ratio of ChCl, lactic acid, and oxalic acid was 1:2:1. After mixing evenly, the mixture was continuously stirred in a constant temperature oil bath at 60℃ for 3 hours under nitrogen protection to form DES. CNF / TiO2 composite material and DES were mixed at a mass ratio of 1:10 and ultrasonically dispersed for 30 minutes. The mixture was then transferred to a high-pressure reactor and heated to 180℃ at a rate of 3℃ / min and maintained for 6 hours. After cooling, the mixture was centrifuged at 3000 rpm for 5 minutes and then centrifuged at 12000 rpm for 15 minutes. The mixture was then washed three times with alternating ethanol and deionized water and placed in a vacuum drying oven at 60℃ for 12 hours with a vacuum degree ≤0.1MPa to obtain CNF / TiO2 composite powder.

[0077] S4: CNF / TiO2 composite powder was dispersed in a 1:1 volume ratio acetic acid / acetone mixed solvent. After dispersion, it was magnetically stirred at 800 rpm for 4 hours and then ultrasonically treated at 40 kHz for 30 minutes. Nanocellulose titanium dioxide photocatalytic self-cleaning film was obtained by electrospinning process with a voltage of 20 kV, a feed rate of 0.3 mL / min, a receiving distance of 15 cm, a temperature of 23-27℃, and a relative humidity of 40-50%.

[0078] Example 2

[0079] The preparation method is the same as in Example 1, except that:

[0080] In step S2, the volume ratio of homogenized CNF solution to TiOSO4 solution is 100:1.

[0081] In step S3, the temperature is increased to 180°C at a rate of 1°C / min and maintained for 4 hours.

[0082] All other specific steps are the same.

[0083] Example 3

[0084] The preparation method is the same as in Example 1, except that:

[0085] In step S2, the volume ratio of homogenized CNF solution to TiOSO4 solution is 150:1.

[0086] In step S3, the temperature is increased to 180°C at a rate of 5°C / min and maintained for 8 hours.

[0087] All other specific steps are the same.

[0088] Example 4

[0089] The preparation method is the same as in Example 1, except that:

[0090] In step S2, the volume ratio of homogenized CNF solution to TiOSO4 solution is 118:1.

[0091] In step S3, the temperature is increased to 180°C at a rate of 2°C / min and maintained for 5 hours.

[0092] All other specific steps are the same.

[0093] Example 5

[0094] The preparation method is the same as in Example 1, except that:

[0095] In step S2, the volume ratio of homogenized CNF solution to TiOSO4 solution is 136:1.

[0096] In step S3, the temperature is increased to 180°C at a rate of 4°C / min and maintained for 7 hours.

[0097] All other specific steps are the same.

[0098] Comparative Example 1

[0099] Referring to the preparation steps of Example 1, the difference lies in the use of a blending method to prepare the CNF / TiO2 composite material in step S2. This step includes dispersing TiO2 powder in distilled water, then adding it dropwise to a homogeneous CNF solution, stirring, ultrasonically dispersing, and centrifuging to obtain the CNF / TiO2 composite material prepared by the blending method. All other steps are the same.

[0100] Comparative Example 2

[0101] The preparation steps are the same as in Example 1, except that step S3 is omitted.

[0102] Experimental Example 1

[0103] Samples were taken from the homogeneous CNF liquid prepared in step S1 of Example 1, the CNF / TiO2 composite material prepared in step S2 of Comparative Example 1, and the CNF / TiO2 composite material prepared in step S2 of Comparative Example 1. Fourier transform infrared spectroscopy (FTIR) analysis was performed on the samples, following the experimental methods outlined in national standard GB / T 32199-2015: "General Rules for Qualitative Analysis by Infrared Spectroscopy". The experimental results are attached. Figure 2 As shown, at 1500 cm -1 Up to 1700 cm -1 The absorption peaks at this location showed significant differences. These absorption peaks correspond to the stretching vibrations of carboxylate on the surface of nanocellulose. The experimental groups of CNF alone and CNF blended with TiO2 both showed obvious and strong vibrations. However, in the experimental group of CNF and TiO2 covalently polymerized in situ, Ti atoms replaced the original functional groups, and the peak positions changed significantly, proving the change of functional groups.

[0104] Experiment Example 2

[0105] The TiO2, the nano-cellulose titanium dioxide photocatalytic self-cleaning film prepared in Example 1, and the film finally prepared in Comparative Example 2 were used as samples for solid-state ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis). The specific steps are as follows: Measurements were performed using a UV-Vis diffuse reflectance spectrometer with barium sulfate (BaSO4) as the blank background. The scanning range was set to 200–800 nm, and the scanning interval was 1 nm. The test results are attached. Figure 3 As shown, the absorption edge of the film material formed by in-situ covalent polymerization in Comparative Example 2 is red-shifted, and the absorption range is wider than that of TiO2 alone. More excited-state electrons are generated in the visible light region, which indicates that in-situ covalent polymerization of TiO2 and CNF is conducive to absorption. Compared with Comparative Example 2, the composite material of Example 1, after being treated with DES, shows a further red-shifted absorption edge in the figure and a wider absorption range in the visible light region, indicating that the DES treatment can further enhance the light absorption of the film material.

[0106] Experimental Example 3

[0107] The membrane materials prepared according to the methods in Examples 1-5 and Comparative Examples 1-2 were used to prepare samples. The samples were then tested for their pollutant separation, purification, and photodegradation self-cleaning performance. Tests were conducted according to the national standard GB / T 23762-2020 "Test Method for Purification Performance of Photocatalytic Materials in Aqueous Solutions," using methylene blue and tetracycline hydrochloride as target pollutants. The test results are shown in Table 1.

[0108] Table 1. Comparison of experimental results of Examples 1-5 and Comparative Examples 1-2, Example 3

[0109] Example group Degradation rate of methylene blue after 4 hours (%) Degradation rate of tetracycline hydrochloride in 2 hours (%) Example 1 96.8 81.7 Example 2 90.7 74.1 Example 3 91.1 74.6 Example 4 93.1 77.7 Example 5 94.4 78.3 Comparative Example 1 82.7 64.4 Comparative Example 2 72.1 52.1

[0110] As can be seen from the above comparison results, Comparative Example 1 uses a blending method to prepare CNF / TiO2 composite material. Compared with the in-situ covalent polymerization method, it cannot better guide the distribution of TiO2 during composite formation and cannot achieve a uniform compatibility state of the composite material during in-situ growth, resulting in poorer performance after film formation. Comparative Example 2 does not use DES to treat the composite material, so it is impossible to adjust the ratio of TiO2 anatase to rutile phase through the action of DES, nor can oxygen vacancy defects be introduced, which ultimately affects the light absorption performance after film formation.

Claims

1. A method for preparing a nanocellulose titania photocatalytic self-cleaning film, characterized by, The application relates to a method for preparing a nanocellulose-titanium dioxide composite material by in-situ covalent polymerization growth of titanium dioxide on nanocellulose by using titanyl sulfate, and the preparation method comprises the following specific steps: S1: the natural cellulose raw material is subjected to swelling pretreatment, and after the pretreatment, mechanical peeling treatment and 2,2,6,6-tetramethylpiperidine oxide oxidation treatment are carried out, the treatment is completed, and then the nanocellulose fiber liquid with a concentration of 1.5wt% is obtained by centrifugation under the condition of 8000rpm for 20 minutes, dialysis and concentration adjustment; S2: the nanocellulose fiber liquid obtained in S1 is heated to 45 DEG C and kept for 20 minutes, 15wt% titanyl sulfate solution is added drop by drop, and after the dropwise addition is completed, the mixture is kept at 45 DEG C and stirred for 45 minutes; after cooling at room temperature, dialysis is carried out until the specified conditions are met, and an in-situ covalent polymerization composite material is obtained; S3: the in-situ covalent polymerization composite material obtained in S2 is mixed with a deep eutectic solvent in a certain proportion, ultrasonic dispersion is carried out for 30 minutes, high-temperature treatment is carried out, natural cooling is carried out to room temperature, and then step-by-step centrifugal treatment is carried out; the composite powder is obtained by washing three times with ethanol and deionized water alternately and vacuum drying at 60 DEG C for 12 hours; the deep eutectic solvent is prepared by using choline chloride, lactic acid and oxalic acid in a molar ratio of 1:2:1; S4: the composite powder obtained in S4 is dispersed in a mixed solvent of acetic acid / acetone with a volume ratio of 1:1, magnetic stirring is carried out at 800rpm for 4 hours after dispersion, ultrasonic treatment is carried out at 40kHz for 30 minutes, and a nanocellulose-titanium dioxide photocatalytic self-cleaning film is obtained through an electrospinning process. The electrospinning process has the following process parameters: the voltage is set to 20kV, the propelling speed is 0.3mL / min, the receiving distance is 15cm, the temperature is 23-27 DEG C, and the relative humidity is 40-50%; through the electrospinning process, the nanocellulose-titanium dioxide photocatalytic self-cleaning film forms a "fiber core-photocatalytic shell" structure, the nanocellulose forms an interpenetrating network structure, and the titanium dioxide forms ordered mesopores on the fiber surface.

2. The preparation method of the nanocellulose-titanium dioxide photocatalytic self-cleaning film according to claim 1, wherein the swelling pretreatment in S1 comprises the following steps: the natural cellulose raw material is soaked in a mixed solution of LiOH and 10wt% urea with a concentration of 6wt%, and the soaking is carried out under the condition of-10 DEG C freezing treatment for 18 hours; the mechanical peeling treatment in S1 comprises the following steps: the temperature is controlled to be less than or equal to 40 DEG C, and the high-pressure homogenizer is used for cyclic treatment for 3-5 times under the condition of a pressure of 100MPa; the 2,2,6,6-tetramethylpiperidine oxide oxidation treatment in S1 uses a reagent combination comprising 2,2,6,6-tetramethylpiperidine oxide, sodium bromide and sodium hypochlorite; 3. The method for preparing the nano-cellulose titanium dioxide photocatalytic self-cleaning film as described in claim 1, characterized in that, the dropwise addition to a fixed volume ratio in S2 is that the volume ratio of the nanocellulose fiber liquid and the titanyl sulfate solution reaches 100-150:1; 4. The method for preparing the nano-cellulose titanium dioxide photocatalytic self-cleaning film as described in claim 1, characterized in that, the proportional mixing in S3 is that the in-situ covalent polymerization composite material is mixed with the deep eutectic solvent in a mass ratio of 1:

10.

5. The method for preparing the nano-cellulose titanium dioxide photocatalytic self-cleaning film as described in claim 1, characterized in that, S2 said dialysis to specified conditions are completed, specifically including: dialysis to conductivity less than 30 μS / cm 3 , add sodium hydroxide to adjust the pH to 6, dialysis again until the conductivity <30 μS / cm 3 .

6. The method for preparing the nano-cellulose titanium dioxide photocatalytic self-cleaning film as described in claim 1, characterized in that, ​ 7. The method according to claim 1, wherein the high-temperature treatment of S3 is performed by heating at a rate of 3°C / min to 180°C and maintaining for 4-8 hours. The high-temperature treatment of S3 is performed by heating at a rate of 3°C / min to 180°C and maintaining for 4-8 hours. The stepwise centrifugation treatment of S3 is performed by centrifugation at 3000 rpm for 5 min and then at 12000 rpm for 15 min.

Images