A TEMPO oxidized bacterial cellulose / hydroxyapatite super-long nanowire composite membrane, and a preparation method and application thereof

Abstract

The application discloses a TEMPO oxidized bacterial cellulose / hydroxyapatite super-long nanowire composite membrane and a preparation method and application thereof. The preparation of the composite membrane comprises the following steps: preparation of TEMPO oxidized bacterial cellulose nanofiber, preparation of a hydroxyapatite super-long nanowire aqueous solution, and preparation of a TEMPO oxidized bacterial cellulose / hydroxyapatite super-long nanowire composite membrane; and the prepared composite membrane is applied as a filter membrane. The preparation method is simple and mild, the preparation process is environment-friendly, the cost is low, the prepared composite membrane presents a reticular porous surface and a layered cross-section structure, and the fiber bundle diameter is uniform; the composite membrane can efficiently separate various pollutants and can be used for multiple times and for a long time, and solves problems of poor mechanical property, low filtration efficiency and short service life of the filter membrane material, and has a wide application prospect in the fields of environmental protection, especially water pollution treatment.

Description

TECHNICAL FIELD

[0001] The present application mainly relates to the technical field of biological materials, and particularly relates to a TEMPO oxidized bacterial cellulose / hydroxyapatite ultra-long nanowire composite film and a preparation method and application thereof. BACKGROUND

[0002] Bacterial cellulose (BC) is a natural polymer synthesized by some microorganisms in Acetobacter, etc. Compared with plant cellulose, BC has many unique physical and chemical properties, such as high purity (without lignin and other cell wall components), high crystallinity (up to 95%), high polymerization degree (up to 8000), three-dimensional ultra-fine network structure formed by nanofiber bundles interweaving with each other, high elastic modulus and tensile strength, ultra-high water holding capacity, good biocompatibility and biodegradability, etc. In addition, due to the “nanometer effect”, the BC film also has high water absorption and water retention, good liquid and gas permeability, and strong in-situ plasticity in the wet state. Therefore, in recent years, BC has become a new type of nanobiomaterial that is widely studied. TEMPO oxidation system is an effective selective oxidation system for cellulose, which can selectively oxidize the primary alcohol hydroxyl group of cellulose to carboxyl group in aqueous solution, and the reaction conditions are mild and the energy consumption is low. After TEMPO oxidation of cellulose and homogenization treatment, high beating degree nanocellulose with uniform size, large aspect ratio and good dispersibility can be prepared, and more hydroxyl groups are exposed on the surface of the fibers and the fibers have negative charge, which has become the main method for alcohol selective oxidation and nanocellulose preparation under mild conditions.

[0003] Hydroxyapatite ([Ca 10 PO4)6(OH)2], HAP) is a natural inorganic mineral formed by natural mineralization in vivo, and is the main inorganic component of hard tissues such as teeth and bones of vertebrates. Due to its excellent biocompatibility and ion exchange properties, HAP has been widely used in the fields of biological medicine and environmental remediation. According to the existing literature reports, the morphology and size of HAP synthesized by different methods have a great influence on its performance and application. Traditional HAP materials have high brittleness, poor stability and easy dissolution, while one-dimensional HAP nanowire materials in the form of fibers are easy to form a three-dimensional network structure, which realizes self-supporting and also makes the assembled material have better flexibility and enhanced mechanical properties.

[0004] Membrane separation technology, as a highly efficient, energy-saving, and environmentally friendly innovative technology, has become an important way to solve water scarcity and water pollution. As the core of membrane separation technology, the preparation of membrane materials is receiving increasing attention, and selecting suitable membrane materials is a key factor determining the efficient separation process of the filter membrane. Currently, the most researched and applied filter membrane materials mainly include cellulose-based membranes, polyamide-based membranes, polyethersulfone-based membranes, polyacrylonitrile membranes, and inorganic ceramic membranes. Polymer membranes are generally widely available, low in cost, have good toughness, and simple membrane fabrication processes, but they suffer from drawbacks such as poor heat resistance, short service life, susceptibility to fouling, and difficulty in restoring performance after cleaning. Ceramic membranes, on the other hand, are temperature and pressure resistant, have high mechanical strength, long service life, and their performance is easily restored after cleaning, but their manufacturing cost is high, the process is complex, and they are brittle. Therefore, preparing organic-inorganic nanocomposites can not only combine the advantages of both organic and inorganic components, but also, based on the nanoscale interaction between the two components assembled in a nanostructure, can produce additional performance enhancements, resulting in filter membranes with ideal properties such as environmental friendliness, multifunctionality, high permeability, and rapid filtration.

[0005] Reference 1 (Bacterial cellulose membranes for environmental waterremediation and industrial wastewater treatment, AA Alves et al. International Journal of Environmental Science and Technology 17 (2020) 3997-4008) reports the use of bacterial cellulose membranes as filters for actual water remediation, testing the membrane's filtration efficiency for E. coli suspension and industrial wastewater from dairy and textile mills. The results show that these membranes can effectively intercept E. coli and dyes and have good reusability. However, for separation membranes, water flux and particle rejection rate are the standards for evaluating the basic performance of membrane materials. This paper does not present relevant test data such as water flux for bacterial cellulose membranes, and the rejection rate for dyes is slightly low, indicating a single function and unsuitability for filtering multiple pollutants in complex aquatic environments.

[0006] Reference 2 (Tuning the synthetic conditions of graphene oxide / magnetite / hydroxyapatite / cellulose acetate nanofibrous membranes for removing Cr(VI), Se(IV) and methylene blue from aqueous solutions, Reem Al-Waf et al. Journal of Water Process Engineering 38 (2020) 101543) reported the removal performance of electrospun cellulose acetate nanofiber membranes (GO / MNPs / HAP@CA) using graphene oxide, nanomagnetite, and hydroxyapatite as fillers for representative pollutants Cr(VI), Se(IV), and methylene blue. However, the preparation process is cumbersome and the manufacturing cost is high. Furthermore, characterization results show that the electrospun fibers have varying diameters and agglomerate, while the composite membrane has low mechanical strength.

[0007] In summary, existing filter membrane materials suffer from technical problems such as poor mechanical properties and low filtration efficiency. Summary of the Invention

[0008] The present invention addresses the problem of overly simplistic solutions in existing technologies by providing a significantly different approach. It primarily offers a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite membrane, its preparation method, and its applications, thereby resolving the technical problems mentioned in the background section, such as poor mechanical properties and low filtration efficiency of existing filter membrane materials.

[0009] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: Traditional hydroxyapatite materials are brittle, have poor stability and are easily dissolved during the adsorption of pollutants, and have a small adsorption capacity. However, TEMPO-oxidized bacterial cellulose, after homogenization, can produce high-freezing-degree nanocellulose with uniform size, large aspect ratio, and good dispersibility. Simultaneously, the fiber surface exposes more hydroxyl groups and carries a negative charge. Therefore, the network structure formed by the interweaving of nanofibers not only provides numerous channels for water transport but also enables physical interception or chemical adsorption of particles or pollutant molecules, thereby effectively improving the material's filtration and adsorption performance for impurities and dyes in water.

[0010] This invention provides a method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film, comprising the following steps:

[0011] (1) The bacterial cellulose membrane was oxidized by the 4-acetamide-TEMPO / NaClO / NaClO2 system and then homogenized into a slurry by an ultra-high speed universal homogenizer to obtain TEMPO oxidized bacterial cellulose nanofibers.

[0012] (2) Using sodium oleate as a precursor, calcium chloride as a calcium source and phosphate as a phosphorus source, the mixture was stirred to form a milky white suspension. The milky white suspension was transferred to a stainless steel high-pressure reactor. After the reaction was completed, the mixture was cooled to room temperature. The product hydroxyapatite ultra-long nanowires were washed and centrifuged multiple times with ethanol and deionized water to obtain an aqueous solution of hydroxyapatite ultra-long nanowires.

[0013] (3) The TEMPO oxidizing bacteria cellulose nanofibers obtained in step (1) are mixed with the aqueous solution of hydroxyapatite ultralong nanowires obtained in step (2), and then the mixture is mixed at high speed using a vortex oscillator. The mixed slurry is then poured into a sand core filter device for vacuum filtration and finally placed in a vacuum drying oven to dry, thus obtaining a TEMPO oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane.

[0014] Furthermore, in step (1), the reaction temperature for bacterial cellulose membrane oxidation is 60 °C, and the oxidation time is 12–36 h.

[0015] Furthermore, in step (1), the speed of the ultra-high-speed general homogenizer is 3000-8000 rpm, and the homogenization time is 3-8 min, preferably 5 min.

[0016] Furthermore, in step (2), the reaction time in the stainless steel high-pressure reactor is 24-36 h, and the reaction temperature is 180-200 ℃, preferably 200 ℃.

[0017] Furthermore, in step (2), the number of times the rinsing and centrifugation with ethanol and deionized water is performed is 1 to 3 times, preferably 3 times.

[0018] Further, in step (3), the mass ratio of the aqueous solution of TEMPO-oxidizing bacterial cellulose nanofibers to hydroxyapatite ultralong nanowires is (0.66-4):1, preferably 3:2.

[0019] Further, in step (3), the mixed slurry is first placed in a vacuum drying oven to remove air bubbles from the solution, and then poured into a sand core filter device for vacuum filtration. After drying and forming, it is placed in a glass plate and compacted for further dehydration treatment for 30 min. Finally, it is placed in a vacuum drying oven for drying at a temperature of 60 ℃ for 24 h.

[0020] The present invention also provides a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite membrane, which is prepared by any of the above preparation methods.

[0021] The present invention also provides the application of the above-mentioned TEMPO oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane, wherein the composite membrane is used as a filter membrane.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention achieves uniform mixing of TEMPO-oxidized bacterial cellulose and hydroxyapatite ultralong nanowires by controlling the mass ratio of the two raw materials. Macroscopically, the composite membrane surface is highly uniform. Microscopically, there are no clear boundaries between the TEMPO-oxidized bacterial cellulose nanofiber clusters and the hydroxyapatite ultralong nanowire clusters, and their diameters are significantly increased due to the intertwining of the two types of fibers. Simultaneously, during filtration, the two fibers further assemble into a network-like porous structure and a unique layered structure, with uniform fiber bundle diameters, enabling the assembled composite membrane to achieve self-support. Furthermore, its ultra-high aspect ratio gives it excellent flexibility. Experiments also show that this composite membrane exhibits good hydrophilicity.

[0024] This invention tested the mechanical properties of the composite membranes from the examples and comparative examples. The results showed that the addition of a small amount of HAPNW significantly improved the mechanical properties of the composite membrane. With further increases in the specific gravity of HAPNW, the elongation at break and tensile strength of the composite material gradually decreased. This is due to the relatively rigid nature of HAPNW, resulting in weaker bonding between nanowires and nanofibers compared to cellulose. However, due to hydrogen bonds and van der Waals forces, HAPNW can tightly interweave with TEMPO-BC to form a network structure and a densely ordered layered structure between the networks, further enhancing the interaction between nanowires and nanofibers. This resulted in an improvement in the Young's modulus of the composite membrane compared to pure TEMPO-BC.

[0025] (3) In the filtration experiment of TiO2 nanoparticles, the composite membrane of the present invention not only showed long-term stability, but also maintained a high water flux (greater than 800 L·m) while achieving high retention efficiency (greater than 99%). -2 ·h -1 Due to steric hindrance and electrostatic interaction, this composite membrane can also filter and adsorb the cationic dye methylene blue, and still has a high rejection efficiency after multiple cycles of regeneration (the rejection rate of methylene blue can still be maintained above 85% after 5 cycles of filtration). It also has good stability and is expected to be applied in fields such as water shortage and wastewater purification.

[0026] (4) The preparation method of the present invention is mainly carried out in three steps. The equipment required mainly includes a homogenizer, a stainless steel high-pressure reactor, a vortex shaker, a sand core filter device, and a vacuum drying oven. The reaction temperature is up to 200 ℃. The method is simple, mild, environmentally friendly, and low in cost.

[0027] In summary, the TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite membrane provided by this invention has high flexibility, high mechanical strength, high water flux, and excellent membrane separation performance. It is also easy to produce and can be used as a novel biomass filter membrane.

[0028] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0029] Figure 1 (A) is a photograph of the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite film prepared in Example 2. Figure 1 (B) is for Figure 1 (A) shows the results of the surface wettability test of the composite film. Figure 1 (C)- Figure 1 (F) is for Figure 1 (A) is a digital photograph of the composite film shown in the image, after being folded, bent, rolled, and subjected to other complex mechanical processes.

[0030] Figure 2 (A) From left to right, these are photographs of the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite films prepared in Comparative Example 1, Example 1, Example 2, Example 3, and Comparative Example 2. Figure 2 (B) is correct. Figure 2 (A) shows the results of mechanical property testing of the composite membrane, including stress-strain curve, elongation at break bar graph, tensile strength bar graph, and Young's modulus bar graph;

[0031] Figure 3 (A) is a surface and cross-sectional SEM image of the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite film prepared in Example 2; Figure 3 (B) are SEM images of the surface and cross-section of the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite film prepared in Comparative Example 2. Figure 3 (C) is the composite membrane in Comparative Example 2 at 20 mg·L⁻¹ -1 Images showing the effects of methylene blue solution adsorption before and after adsorption.

[0032] Figure 4 (A) is a line graph showing the permeation flux and rejection rate of the composite membrane for TiO2 nanoparticles of different concentrations in Example 2; Figure 4(B) is a line graph showing the water flux and the rejection rate of TiO2 nanoparticles at a concentration of 100 ppm in the composite membrane during the long-term filtration test in Example 2.

[0033] Figure 5 The filtration and adsorption performance of the composite membrane for methylene blue solution in Example 2 is as follows: Figure 5 (A) is a fitted graph of the Langmuir adsorption isotherm, and the inset shows photographs of the methylene blue solution before and after adsorption. Figure 5 (B) is the fitted plot of the Freundlich adsorption isotherm. Figure 5 (C) shows the UV absorption spectra of methylene blue in the feed liquid and filtrate, as well as digital photographs before and after filtration through the composite membrane. Figure 5 (D) is a bar graph showing the retention efficiency of methylene blue in each experiment of the composite membrane cycling experiment. Detailed Implementation

[0034] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0035] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] Hydroxyapatite ultralong nanowires were prepared based on existing literature [Li H, Zhu Y, Jiang Y, Yu Y, Chen F, Dong L, Wu J. Hierarchical assembly of monodisperse hydroxyapatite nanowires and construction of high-strength fire-resistant inorganic paper with high-temperature flexibility[J]. ChemNanoMat, 2017, 3: 259-268.].

[0038] Membrane flux and TiO2 rejection experiments: First, TiO2 nanoparticle suspensions (average particle size 100 nm) with concentrations of 50, 100, 200, and 300 ppm were prepared for membrane permeate flux and rejection rate testing. Then, a long-term filtration performance test was conducted using a 100 ppm TiO2 nanoparticle suspension. To stabilize membrane performance, the sample membrane was pre-pressurized for 30 min before each flux test, and then different test solutions were passed through it. The permeate flux of the sample over time was recorded. The concentration of nanoparticles in the filtrate was determined using UV-Vis absorption spectroscopy.

[0039] Dye filtration and adsorption experiment: The filtration and adsorption performance of the membrane was tested using a low-concentration methylene blue solution. For the dye adsorption experiment, 10 mg of the sample membrane was added to 10 mL of 20 mg·L⁻¹ solution. -1 The solution was placed in a methylene blue solution and shaken at 37 °C for 12 h, and the supernatant was collected. For the dye filtration experiment, 20 mL of 20 mg·L⁻¹ solution was introduced. -1 The methylene blue solution was filtered, and the filtrate was collected. The filtered sample membrane was washed with ethanol and deionized water and then used in the next cycle of testing. The concentration of methylene blue in the solution was also determined by UV-Vis spectroscopy. Example 1

[0040] Preparation of TEMPO-oxidized bacterial cellulose nanofibers (TEMPO-BC fibers): 36.5 g of BC hydrogel was weighed and immersed in 220 mL of 0.05 M NaH2PO4-Na2HPO4 buffer solution (pH = 6) to prepare the BC hydrogel reaction solution. Separately, 50 mL of NaH2PO4-Na2HPO4 buffer solution was added and 4 mL of NaClO was added, and the mixture was stirred thoroughly to prepare a NaClO solution. Then, 0.08 g of 4-acetamido-TEMPO, the aforementioned NaClO solution, and 5 g of NaClO2 were added sequentially to the BC hydrogel reaction solution. The mixture was stirred for 12 h in a 60 ℃ water bath, and finally, 5 mL of ethanol solution was added to terminate the reaction. The TEMPO-oxidized BC hydrogel was washed with a large amount of deionized water until neutral, and then homogenized into a slurry using an ultra-high-speed general-purpose homogenizer at 3000 rpm for 8 min.

[0041] Preparation of hydroxyapatite ultralong nanowire aqueous solution (HAPNW aqueous solution): 10 g of sodium oleate was dissolved in 100 mL of deionized water. Under continuous stirring, 37.5 mL of CaCl2 (1.1 g) aqueous solution and NaH2PO4·2H2O (1.4 g) aqueous solution were added sequentially to form a milky white suspension. The suspension was then transferred to a 300 mL stainless steel high-pressure reactor, sealed, and placed in a 200 ℃ oven for 24 h. After the reaction was complete, the mixture was cooled to room temperature, and the product HAPNW was washed three times with ethanol and deionized water, followed by centrifugation.

[0042] Preparation of TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane: High-beaten TEMPO-BC fiber and HAPNW aqueous solution were mixed at a ratio of 4:1, and then mixed at high speed using a vortex shaker at 1000 rpm. After vacuuming to remove air bubbles from the solution in a vacuum drying oven, 5 mL of the mixed slurry was poured into a sand core filter for vacuum filtration. After drying and shaping, it was placed in a glass plate and compacted for further dehydration for 30 min. Finally, it was placed in a vacuum drying oven and dried at 60 ℃ for 24 h to obtain the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane. Example 2

[0043] Preparation of TEMPO-oxidized bacterial cellulose nanofibers (TEMPO-BC fibers): 36.5 g of BC hydrogel was weighed and immersed in 220 mL of 0.05 M NaH2PO4-Na2HPO4 buffer solution (pH = 6) to prepare the BC hydrogel reaction solution. Separately, 50 mL of NaH2PO4-Na2HPO4 buffer solution was added and 4 mL of NaClO was added, and the mixture was stirred thoroughly to prepare a NaClO solution. Then, 0.08 g of 4-acetamido-TEMPO, the aforementioned NaClO solution, and 5 g of NaClO2 were added sequentially to the BC hydrogel reaction solution. The mixture was stirred for 24 h in a 60 ℃ water bath, and finally, 5 mL of ethanol solution was added to terminate the reaction. The TEMPO-oxidized BC hydrogel was washed with a large amount of deionized water until neutral, and then homogenized into a slurry using an ultra-high-speed general-purpose homogenizer at 5000 rpm for 5 min.

[0044] Preparation of hydroxyapatite ultralong nanowire aqueous solution (HAPNW aqueous solution): 10 g of sodium oleate was dissolved in 100 mL of deionized water. Under continuous stirring, 37.5 mL of CaCl2 (1.1 g) aqueous solution and NaH2PO4·2H2O (1.4 g) aqueous solution were added to form a milky white suspension. The suspension was then transferred to a 300 mL stainless steel high-pressure reactor, sealed, and placed in a 200 ℃ oven for 30 h. After the reaction was complete, the mixture was cooled to room temperature, and the product HAPNW was washed three times with ethanol and deionized water, followed by centrifugation.

[0045] Preparation of TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane: High-beaten TEMPO-BC fiber and HAPNW aqueous solution were mixed at a ratio of 3:2, and then mixed at high speed using a vortex oscillator at 1000 rpm. After vacuuming to remove air bubbles from the solution, an appropriate amount of the mixed slurry was poured into a sand core filter device for vacuum filtration. After drying and shaping, it was placed in a glass plate and compacted for further dehydration for 30 min. Finally, it was placed in a vacuum drying oven and dried at 60 ℃ for 24 h to obtain the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane. Example 3

[0046] Preparation of TEMPO-oxidized bacterial cellulose nanofibers (TEMPO-BC fibers): 36.5 g of BC hydrogel was weighed and immersed in 220 mL of 0.05 M NaH2PO4-Na2HPO4 buffer solution (pH = 6) to prepare the BC hydrogel reaction solution. Separately, 50 mL of NaH2PO4-Na2HPO4 buffer solution was added and 4 mL of NaClO was added, and the mixture was stirred thoroughly to prepare a NaClO solution. Then, 0.08 g of 4-acetamido-TEMPO, the aforementioned NaClO solution, and 5 g of NaClO2 were added sequentially to the BC hydrogel reaction solution. The mixture was stirred for 36 h in a 60 ℃ water bath, and finally, 5 mL of ethanol solution was added to terminate the reaction. The TEMPO-oxidized BC hydrogel was washed with a large amount of deionized water until neutral, and then homogenized into a slurry using an ultra-high-speed universal homogenizer at 8000 rpm for 3 min.

[0047] Preparation of hydroxyapatite ultralong nanowire aqueous solution (HAPNW aqueous solution): 10 g of sodium oleate was dissolved in 100 mL of deionized water. Under continuous stirring, 37.5 mL of CaCl2 (1.1 g) aqueous solution and NaH2PO4·2H2O (1.4 g) aqueous solution were added to form a milky white suspension. The suspension was then transferred to a 300 mL stainless steel high-pressure reactor, sealed, and placed in a 200 ℃ oven for 36 h. After the reaction was complete, the mixture was cooled to room temperature, and the product HAPNW was washed three times with ethanol and deionized water, followed by centrifugation.

[0048] Preparation of TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane: High-beaten TEMPO-BC fiber and HAPNW aqueous solution were mixed at a ratio of 2:3, and then mixed at high speed using a vortex oscillator at 1000 rpm. After vacuuming to remove air bubbles from the solution in a vacuum drying oven, an appropriate amount of the mixed slurry was poured into a sand core filter device for vacuum filtration. After drying and shaping, it was placed in a glass plate and compacted for further dehydration for 30 min. Finally, it was dried in a vacuum drying oven at 60℃ for 24 h to obtain the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane.

[0049] Comparative Example 1

[0050] Preparation of TEMPO-oxidized bacterial cellulose nanofibers (TEMPO-BC fibers): 36.5 g of BC hydrogel was weighed and immersed in 220 mL of 0.05 M NaH2PO4-Na2HPO4 buffer solution (pH = 6) to prepare the BC hydrogel reaction solution. Separately, 50 mL of NaH2PO4-Na2HPO4 buffer solution was added and 4 mL of NaClO was added, and the mixture was stirred thoroughly to prepare a NaClO solution. Then, 0.08 g of 4-acetamido-TEMPO, the aforementioned NaClO solution, and 5 g of NaClO2 were added sequentially to the BC hydrogel reaction solution. The mixture was stirred for 24 h in a 60 ℃ water bath, and finally, 5 mL of ethanol solution was added to terminate the reaction. The TEMPO-oxidized BC hydrogel was washed with a large amount of deionized water until neutral, and then homogenized into a slurry using an ultra-high-speed general-purpose homogenizer at 5000 rpm for 5 min.

[0051] Membrane preparation: High-beatenness TEMPO-BC fibers were mixed at high speed using a vortex oscillator at 1000 rpm. After being placed in a vacuum drying oven to remove air bubbles from the solution, an appropriate amount of the mixed slurry was poured into a sand core filter device for vacuum filtration. After drying and forming, it was placed in a glass plate and compacted for further dehydration treatment for 30 min. Finally, it was placed in a vacuum drying oven and dried at 60 ℃ for 24 h to obtain a TEMPO oxidized bacterial cellulose membrane.

[0052] Comparative Example 2

[0053] Preparation of TEMPO-oxidized bacterial cellulose nanofibers (TEMPO-BC fibers): 36.5 g of BC hydrogel was weighed and immersed in 220 mL of 0.05 M NaH2PO4-Na2HPO4 buffer solution (pH = 6) to prepare the BC hydrogel reaction solution. Separately, 50 mL of NaH2PO4-Na2HPO4 buffer solution was added and 4 mL of NaClO was added, and the mixture was stirred thoroughly to prepare a NaClO solution. Then, 0.08 g of 4-acetamido-TEMPO, the aforementioned NaClO solution, and 5 g of NaClO2 were added sequentially to the BC hydrogel reaction solution. The mixture was stirred for 24 h in a 60 ℃ water bath, and finally, 5 mL of ethanol solution was added to terminate the reaction. The TEMPO-oxidized BC hydrogel was washed with a large amount of deionized water until neutral, and then homogenized into a slurry using an ultra-high-speed general-purpose homogenizer at 5000 rpm for 5 min.

[0054] Preparation of hydroxyapatite ultralong nanowire aqueous solution (HAPNW aqueous solution): 10 g of sodium oleate was dissolved in 100 mL of deionized water. Under continuous stirring, 37.5 mL of CaCl2 (1.1 g) aqueous solution and NaH2PO4·2H2O (1.4 g) aqueous solution were added to form a milky white suspension. The suspension was then transferred to a 300 mL stainless steel high-pressure reactor, sealed, and placed in a 200 ℃ oven for 30 h. After the reaction was complete, the mixture was cooled to room temperature, and the product HAPNW was washed three times with ethanol and deionized water, followed by centrifugation.

[0055] Preparation of TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane: High-beaten TEMPO-BC fiber and HAPNW aqueous solution were mixed at a ratio of 1:4, and then mixed at high speed using a vortex oscillator at 1000 rpm. After vacuuming to remove air bubbles from the solution in a vacuum drying oven, an appropriate amount of the mixed slurry was poured into a sand core filter device for vacuum filtration. After drying and shaping, it was placed in a glass plate and compacted for further dehydration treatment for 30 min. Finally, it was placed in a vacuum drying oven and dried at 60 ℃ for 24 h to obtain the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane.

[0056] The experimental methods for performance testing of the above embodiments and comparative examples are as follows:

[0057] Take the composite membrane prepared in Example 2, such as Figure 1 As shown in (A), the composite membrane has a thickness of 112 μm, a diameter of 37 mm, and a white color;

[0058] The surface wettability of the composite film was tested, and the results are shown in the figure. Figure 1 (B) The results showed that the water contact angle at the moment of contact was 21.5 ± 0.3°, while the water contact angle of the pure TEMPO-BC surface was ≈ 0°. This is because there are still a small number of oleic acid groups in the composite material that have a strong interaction with the calcium ions of HAPNW. Subsequently, water droplets (stained with methylene blue for easy observation) gradually and completely wetted the composite film, indicating that the composite film has good hydrophilicity.

[0059] The composite film is subjected to folding, bending, rolling, and other complex mechanical processes, such as... Figure 1 (C)- Figure 1 As shown in (F), the treated composite membranes can maintain their intact shape without any cracks, indicating that the composite membrane has extremely high flexibility.

[0060] (2) Take the composite membranes prepared in Examples 1-3 and Comparative Examples 1-2, such as Figure 2As shown in (A), from left to right, are physical images of the TEMPO oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite films prepared by Comparative Example 1, Example 1, Example 2, Example 3, and Comparative Example 2.

[0061] The mechanical properties of the above composite films were tested, and stress-strain curves, elongation at break histograms, tensile strength histograms, and Young's modulus histograms were plotted. The results are shown in [the table below]. Figure 2 (B) Figure 2 The stress-strain curves in (B) reflect the effect of different HAPNW proportions on the mechanical properties of the composite membrane. It can be seen that the addition of a small amount of HAPNW significantly improves the mechanical properties of the composite membrane. With further increases in the HAPNW proportion, the elongation at break and tensile strength of the composite material gradually decrease. This is due to the relatively rigid nature of HAPNW, resulting in weaker bonding between nanowires and nanofibers compared to cellulose. However, due to hydrogen bonds and van der Waals forces, HAPNW can tightly interweave with TEMPO-BC to form a network structure and a densely ordered layered structure between the networks, further enhancing the interaction between nanowires and nanofibers. This results in an improvement in the Young's modulus of the composite membrane compared to pure TEMPO-BC.

[0062] (3) The composite film prepared in Example 2 was used to observe its surface and cross-sectional morphology using a scanning electron microscope (SEM). The results are as follows: Figure 3 As shown in (A), the two types of fibers are intertwined and further assembled into a network structure with uniform fiber diameter. The cross-section of the composite membrane has a distinct layered structure, and its highly ordered and regular interlayer channels can provide pathways for the lateral diffusion and longitudinal transport of water molecules, which indirectly confirms the potential value of this composite membrane in applications as a composite membrane.

[0063] The composite film prepared in Comparative Example 2 was used to observe its surface and cross-sectional morphology using scanning electron microscopy (SEM). The results are as follows: Figure 3 As shown in (B), combine it with Figure 3 (A) Comparison shows that the increased specific gravity of TEMPO-BC helps promote the interweaving of the two fibers, forming fiber bundles of uniform thickness, and the large number of interwoven nanofibers is conducive to the formation of numerous pores and a high specific surface area. Meanwhile, the test results of this composite membrane at 20 mg·L⁻¹... -1 The adsorption effect of methylene blue solution is determined by Figure 3 (C) It can be seen that the methylene blue solution only faded slightly, and the adsorption effect was generally poor.

[0064] (4) The composite membrane prepared in Example 2 was used to conduct membrane flux and TiO2 rejection experiments. The permeation flux and rejection rate of the composite membrane for TiO2 nanoparticles of different concentrations were detected. The results are shown in the figure. Figure 4 (A), byFigure 4 (A) It can be seen that when the initial concentration is 50 ppm, the permeation flux of the composite membrane to TiO2 nanoparticles is 474.3 L·m. -2 ·h -1 The rejection rate is 98.5%. The good permeability is mainly attributed to the large number of micro and nano interconnected channels inside the composite membrane and the hydrophilicity of the material itself. The high rejection efficiency is due to the fact that the tightly interwoven network structure inside the composite membrane can effectively intercept impurity particles.

[0065] Long-term filtration tests were conducted on the composite membrane to detect its water flux and retention rate of TiO2 nanoparticles at a concentration of 100 ppm. The results are as follows: Figure 4 As shown in (B), by Figure 4 (B) It can be seen that during the continuous operation for 6 hours, the water flux and TiO2 rejection rate remained relatively stable, maintaining at 800 L·m -2 ·h -1 With a filtration efficiency of over 99%, it is evident that the composite membrane not only possesses long-term stability but also maintains a high water flux while achieving excellent filtration results.

[0066] (5) The composite membrane prepared in Example 2 was used to conduct a dye filtration and adsorption experiment. The filtration and adsorption performance of the membrane was tested using a low-concentration methylene blue solution. For the dye adsorption experiment, 10 mg of the sample membrane was added to 10 mL of 20 mg·L⁻¹ solution. -1 The solution was placed in a methylene blue solution and shaken in a constant temperature shaker at 37 °C for 12 h. The supernatant was collected, and the Langmuir adsorption isotherm fitting diagram was obtained, as shown in the figure. Figure 5 As shown in (A), and the inset in the figure is a photograph of the methylene blue solution before and after adsorption, it can be seen that the initial concentration is 20 mg·L. -1 After adsorption, the methylene blue solution changed from blue to colorless, confirming that the prepared composite membrane has a certain adsorption capacity; the filtration and adsorption performance of the membrane was tested, and the Freundlich adsorption isotherm fitting diagram was obtained, as shown in the figure. Figure 5 As shown in (B), from the fitted plot (including Figure 5 (A) and Figure 5 (B) and the correlation coefficient table in the figure show that the adsorption of methylene blue by the composite membrane is more consistent with the Langmuir model, indicating that the active adsorption sites on the surface of the composite membrane are evenly distributed, the adsorption process is monolayer adsorption, and the theoretical equilibrium adsorption capacity calculated by this model is 73.2 mg·g. -1 .

[0067] For the dye filtration experiment, 20 mL of 20 mg·L⁻¹ dye was introduced. -1The methylene blue solution was filtered, and the filtrate was collected. The filtered sample membrane was washed with ethanol and deionized water and then used in the next cycle of testing. The concentration of methylene blue in the solution was also determined by UV-Vis spectroscopy. The UV absorption spectra of methylene blue in the feed solution and filtrate, as well as digital photographs of the composite membrane before and after filtration, are shown below. Figure 5 As shown in (C), the dye rejection experiment results show that the composite membrane has a rejection efficiency of 97.4% for methylene blue. From the UV-Vis spectra of the feed liquid and permeate before and after filtration, it can be seen that the absorption intensity of the filtrate at 664 nm is significantly reduced after filtration, the surface of the composite membrane is deep blue, and it remains intact without damage. The sample membrane underwent 5 cycles of experimentation, and the rejection efficiency of the composite membrane for methylene blue was recorded each time, and a bar graph was plotted, as shown below. Figure 5 As shown in (D), it can be seen that the rejection rate of the composite membrane decreases slowly with the increase of the number of cycles, and the rejection rate of methylene blue can still be maintained above 85% after 5 cycles of filtration, indicating that the composite membrane has good reusability.

[0068] The present invention has been described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvement made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, shall be within the protection scope of the present invention.

Claims

1. A method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film, characterized in that: Includes the following steps: (1) The bacterial cellulose membrane was oxidized by the 4-acetamide-TEMPO / NaClO / NaClO2 system and then homogenized into a slurry by an ultra-high speed universal homogenizer to obtain TEMPO oxidized bacterial cellulose nanofibers. (2) Using sodium oleate as a precursor, calcium chloride as a calcium source and phosphate as a phosphorus source, the mixture was stirred to form a milky white suspension. The milky white suspension was transferred to a stainless steel high-pressure reactor. After the reaction was completed, the mixture was cooled to room temperature. The product hydroxyapatite ultra-long nanowires were washed and centrifuged multiple times with ethanol and deionized water to obtain an aqueous solution of hydroxyapatite ultra-long nanowires. (3) The TEMPO oxidizing bacteria cellulose nanofibers obtained in step (1) are mixed with the aqueous solution of hydroxyapatite ultralong nanowires obtained in step (2), and then the mixture is mixed at high speed using a vortex oscillator. The mixed slurry is then poured into a sand core filter device for vacuum filtration and finally placed in a vacuum drying oven to dry, thus obtaining a TEMPO oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane.

2. The method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film according to claim 1, characterized in that: In step (1), the reaction temperature for bacterial cellulose membrane oxidation is 60 °C, and the oxidation time is 12–36 h.

3. The method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film according to claim 1, characterized in that: In step (1), the speed of the ultra-high-speed general homogenizer is 3000-8000 rpm, and the homogenization time is 3-8 min.

4. The method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film according to claim 1, characterized in that: In step (2), the reaction time in the stainless steel high-pressure reactor is 24-36 h and the reaction temperature is 180-200 ℃.

5. The method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film according to claim 1, characterized in that: In step (2), the number of times to rinse and centrifuge with ethanol and deionized water is 1 to 3.

6. The method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film according to claim 1, characterized in that: The mass ratio of the aqueous solution of TEMPO-oxidizing bacterial cellulose nanofibers to hydroxyapatite ultralong nanowires in step (3) is (0.66-4):

1.

7. The method for preparing a TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite film according to claim 1, characterized in that: In step (3), the mixed slurry is first placed in a vacuum drying oven to remove air bubbles from the solution, and then poured into a sand core filter device for vacuum filtration. After drying and forming, it is placed in a glass plate and compacted for further dehydration treatment for 30 min. Finally, it is placed in a vacuum drying oven for drying at a temperature of 60 ℃ for 24 h.

8. A TEMPO-oxidizing bacterial cellulose / hydroxyapatite ultralong nanowire composite membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. An application of the TEMPO-oxidizing bacteria cellulose / hydroxyapatite ultralong nanowire composite membrane according to claim 8, wherein the composite membrane is used as a filter membrane.

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