Titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane, preparation method and application thereof

Abstract

The application discloses a titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel film, a preparation method and application thereof. The method comprises the following steps: firstly, a titanium dioxide nanotube / graphene / polyvinyl alcohol hydrogel precursor solution is prepared by using a one-pot method; secondly, graphene oxide is reduced by using an ultraviolet lamp during the synthesis process; and finally, the precursor solution is prepared into a hydrogel by means of repeated freezing and thawing. The hydrogel film has excellent mechanical properties, catalytic properties and self-repairing capacity, and can adapt to complex application environments.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic membranes, and relates to a flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol, its preparation method and its application. Background Technology

[0002] Currently, water and air pollution are serious environmental problems worldwide. Industrial wastewater, in particular, contains various harmful substances and chemicals, such as heavy metals, organic matter, and toxic substances. These substances accumulate in water bodies, posing a potential threat to aquatic ecosystems and human health. Eliminating the harm of pollutants and developing green, economical, and efficient pollutant degradation technologies and related materials is of significant research importance. Among these, the use of semiconductor photocatalysis technology to achieve renewable energy and degrade organic pollution has attracted considerable attention.

[0003] Titanium dioxide (TiO2) is a commonly used photocatalytic material, characterized by high photocatalytic activity, hydrophilicity, and low cost. However, TiO2 nanoparticles have a narrow light absorption range and limited selective adsorption capacity. Although researchers have made many efforts to improve its photocatalytic activity, problems such as agglomeration leading to decreased photocatalytic efficiency and difficulty in recycling still exist.

[0004] Compared to directly using TiO2 nanoparticles, TiO2-based thin films exhibit better photocatalytic reaction stability, lower preparation costs, and longer lifespan. Currently, there are three main methods for preparing TiO2-based thin films: (1) depositing TiO2 on hard conductive glass, which results in films lacking flexibility and prone to catalyst detachment; (2) growing TiO2 particles on a flexible substrate, which relies on the interaction between the two and carries the risk of TiO2 leakage during use; and (3) forming a hybrid film by covering TiO2 with other layers, which may hinder the contact between reactant molecules and TiO2. Therefore, how to maintain or further enhance the photocatalytic performance of TiO2 while achieving optimal synergy with the film-forming substrate material remains to be explored.

[0005] Graphene, as an excellent electron acceptor, possesses superior mechanical, electronic, and thermal properties, and is widely used in catalysis, energy storage devices, and environmental applications. Zhang et al. synthesized a TiO2 / PVA / RGO / Au composite material with a hierarchical network structure via a wet chemical method, reducing agglomeration and improving the photoresponse range and photodegradation efficiency. However, the use of the precious metal gold increased the manufacturing cost, and the composite material lacks self-healing capabilities (Liang Zhang, 2019, Applied Surface Science). Wang et al. prepared polyvinyl alcohol nanofibers of graphene oxide using electrospinning, which can serve as templates to assist TiO2 growth and thus be applied in various fields. However, its preparation process is relatively complex, and there is a potential problem of TiO2 shedding during use (Bo Wang, 2014, Colloids and Surfaces A: Physicochemical and Engineering Aspects). Summary of the Invention

[0006] The present invention aims to provide a flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol, its preparation method, and its applications. This method involves composite titanium dioxide with graphene and polyvinyl alcohol to obtain a flexible hydrogel membrane with self-healing, adhesive, and high photocatalytic activity.

[0007] The technical solution for achieving the objective of this invention is as follows:

[0008] A method for preparing a flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol involves first preparing a titanium dioxide nanotube / graphene / polyvinyl alcohol hydrogel precursor solution using a one-pot method, then reducing the graphene oxide using ultraviolet light during the synthesis process, and finally preparing the hydrogel from the precursor solution through repeated freeze-thaw cycles. The specific steps include:

[0009] (1) Add TiO2 nanotubes to an aqueous dispersion of graphene oxide, mix evenly, add polyvinyl alcohol, and place in an oil bath at 90±5℃ and under ultraviolet light irradiation to completely dissolve the polyvinyl alcohol and partially reduce the graphene oxide. The mass ratio of graphene oxide, TiO2 nanotubes and polyvinyl alcohol is 0.03~0.05:1:10.

[0010] (2) Pour the mixed solution obtained in step (1) into a mold and repeatedly freeze and thaw to obtain a flexible composite hydrogel film of titanium dioxide nanotubes / graphene / polyvinyl alcohol.

[0011] Preferably, in step (1), the concentration of the aqueous dispersion of graphene oxide is 0.3 to 0.5 mg / mL.

[0012] Preferably, in step (1), the power of the ultraviolet lamp is 300W.

[0013] Preferably, in step (2), the freezing and thawing times are 2 to 3 times, and the freezing temperature is -37°C.

[0014] The present invention also provides a flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol prepared by the above preparation method.

[0015] Furthermore, the present invention provides the application of the above-mentioned titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane in photocatalytic degradation of organic pollutants.

[0016] Furthermore, the organic pollutants include methyl orange, rhodamine B, and methylene blue.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) In this invention, titanium dioxide nanotubes are used as photocatalysts. Compared with titanium dioxide particles, titanium dioxide nanotubes can be intertwined, so that reduced graphene oxide is wrapped on the nanotubes to form a three-dimensional network structure.

[0019] (2) The present invention uses ultraviolet light to reduce graphene oxide in the titanium dioxide nanotube / graphene / polyvinyl alcohol hydrogel precursor solution, avoiding the problem that the reduced hydrophilicity of graphene oxide makes it difficult to disperse in the solution. At the same time, it improves the mechanical properties of the composite hydrogel film, giving it excellent mechanical properties, enabling it to withstand a weight of nearly 300g without breaking, and retaining the excellent photocatalytic activity of titanium dioxide, which can rapidly degrade a certain concentration of dye molecules within 15 minutes.

[0020] (3) The hydrogel membrane prepared by this invention possesses a certain degree of self-healing properties due to the hydrogen bonds in polyvinyl alcohol. Using it as a substrate can prevent catalyst leakage after the membrane is damaged, thereby extending the service life of the hydrogel membrane. Furthermore, the hydrogel membrane has certain adhesion and plasticity, enabling it to adapt to more complex application environments. Attached Figure Description

[0021] Figure 1 The flowchart for preparing the flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol according to the present invention is shown below.

[0022] Figure 2 This is a physical image of a flexible composite hydrogel membrane made of titanium dioxide nanotubes / graphene / polyvinyl alcohol.

[0023] Figure 3 This is a scanning electron microscope image of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane obtained in Example 2.

[0024] Figure 4 The image shows a scanning electron microscope image of the titanium dioxide nanoparticle / graphene / polyvinyl alcohol flexible composite hydrogel film obtained in Comparative Example 4.

[0025] Figure 5 The UV absorption spectra of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel films obtained in Example 2 and Comparative Example 5 are shown.

[0026] Figure 6 The image shows the XRD pattern of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel film obtained in Example 2.

[0027] Figure 7 The image shows the color change of methyl orange during photocatalytic degradation of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel film obtained in Example 2.

[0028] Figure 8 The image shows the test results of the self-healing performance of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane obtained in Example 2.

[0029] Figure 9 The bending performance test diagram of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel film obtained in Example 2 is shown.

[0030] Figure 10 The plasticity (a) and adhesion test results (b) of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel film obtained in Example 2 are shown.

[0031] Figure 11 The stress-strain curves are those of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel film obtained in Example 2. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0033] Example 1

[0034] (1) Add 1g of TiO2 nanotubes to 100mL of 0.3mg / mL of graphene oxide aqueous dispersion, mix thoroughly, add 10g of polyvinyl alcohol, then transfer to a 250mL round bottom flask, heat in an oil bath at 90℃, and irradiate with a 300W xenon lamp until the polyvinyl alcohol is completely dissolved to obtain a mixed solution.

[0035] (2) Take a certain amount of the mixed solution and put it into the mold. Repeat the freezing and thawing process at -37℃ three times to obtain a flexible composite hydrogel film of titanium dioxide nanotubes / graphene / polyvinyl alcohol.

[0036] Example 2

[0037] Similar to Example 1, except that the concentration of the aqueous dispersion of graphene oxide was changed to 0.5 mg / mL, while other conditions remained the same.

[0038] Figure 2 This is a photograph of a flexible composite hydrogel membrane made of titanium dioxide nanotubes, graphene, and polyvinyl alcohol. Figure 3 The image shown is a scanning electron microscope image of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane obtained in Example 2. It can be seen that the titanium dioxide nanotubes and reduced graphene oxide inside the hydrogel membrane form a three-dimensional network structure, which is conducive to the transfer of photogenerated electrons. In addition, there are a large number of micropores in the gel, which helps the dye molecules to contact the catalyst and promote the photocatalytic reaction.

[0039] Comparative Example 1

[0040] Similar to Example 1, except that the concentration of the aqueous dispersion of graphene oxide was changed to 0.1 mg / mL, while other conditions remained the same.

[0041] Comparative Example 2

[0042] Similar to Example 1, except that the concentration of the aqueous dispersion of graphene oxide was changed to 1 mg / mL, while other conditions remained the same.

[0043] Comparative Example 3

[0044] Similar to Example 1, except that the concentration of the aqueous dispersion of graphene oxide was changed to 0 mg / mL, while other conditions remained the same.

[0045] Comparative Example 4

[0046] Similar to Example 1, the difference is that titanium dioxide nanotubes are replaced with titanium dioxide nanoparticles, the graphene oxide concentration is changed to 0.5 mg / mL, and other conditions remain the same.

[0047] like Figure 4 As shown, in the hydrogel film prepared in Comparative Example 4, the titanium dioxide nanoparticles agglomerate together and are encapsulated by reduced graphene oxide, making the titanium dioxide particles less susceptible to light radiation and reducing photocatalytic efficiency.

[0048] Comparative Example 5

[0049] Similar to Example 1, except that ultraviolet light irradiation is not performed.

[0050] The hydrogel membranes prepared in Example 2 and Comparative Example 5 were tested using a UV spectrophotometer, and the results are as follows: Figure 5As shown, the hydrogel film prepared by reduced graphene oxide has higher light absorption intensity and wider light absorption range, where GO represents graphene oxide and rGO represents reduced graphene oxide.

[0051] Meanwhile, the degree of reduction of graphene oxide in the hydrogel film prepared in Example 2 was characterized by XRD, and the results are as follows: Figure 6 As shown, GO exhibits a strong diffraction peak at 11°, corresponding to the (200) crystal plane. However, after 3 hours of UV irradiation for reduction, this peak shifted significantly to the right and its intensity weakened, demonstrating that the π-conjugated structure of graphene was restored to some extent during the reduction process. Furthermore, the interplanar spacing of rGO decreased from 0.841 nm to 0.736 nm, proving the removal of oxygen-containing functional groups.

[0052] Application Example 1

[0053] The photocatalytic performance of each hydrogel membrane was evaluated by degrading methyl orange, specifically including the following steps:

[0054] (1) Prepare a 0.02 mg / ml methyl orange solution and put 10 ml into a 50 ml quartz jacketed beaker and circulate cooling water through it.

[0055] (2) Add the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane prepared in Examples 1-2 and Comparative Examples 1-4, and irradiate it with a 300W high-pressure mercury lamp, taking the solution every 5 minutes.

[0056] Figure 7 The image shows the color change of methyl orange during photocatalytic degradation of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane obtained in Example 2. It can be seen that the methyl orange solution gradually turns colorless under light. Furthermore, after degradation, the hydrogel membrane can be easily removed with tweezers, washed with water, and stored, which is very convenient, shortens the experimental time, and is easy to use.

[0057] The degradation rate of methyl orange by photocatalytic degradation of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membranes prepared in each example and comparative example was calculated by UV-Vis measurement. The results are shown in Table 1. It can be seen that the hydrogel membranes prepared in Examples 1 to 2 have good photocatalytic activity, which is close to 100%.

[0058] Table 1

[0059] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Degradation rate (%) 83 98 42 44 41 58

[0060] Application Example 2

[0061] The hydrogel membrane prepared in Example 2 was subjected to five photocatalytic degradation experiments under the same conditions as in Application Example 1.

[0062] As a gel material, the stability of the gel is an important criterion. The results are shown in Table 2. The degradation efficiency of the hydrogel membrane prepared in Example 2 did not decrease with the increase of the number of experiments and remained close to 100%, indicating that the hydrogel membrane has good stability.

[0063] Table 2

[0064] Example 2 First cycle Second cycle 3rd cycle 4th cycle 5th cycle Degradation rate (%) 95 94 95 94 94

[0065] Application Example 3

[0066] The hydrogel membrane prepared in Example 2 was subjected to a self-healing test.

[0067] The self-healing property of hydrogels is a key advantage, enabling them to repair themselves after damage in the application environment and thus extend their service life. To test the self-healing performance of the hydrogel film, a 2mm deep and nearly 10mm long "wound" was created on its surface. It was then placed in a 50℃ oven for 6 hours and wrapped in a plastic bag to maintain humidity. After 6 hours of healing, the results were as follows... Figure 8 As shown, the wound has healed, leaving only a shallow mark, indicating that the hydrogel membrane prepared in Example 2 has excellent self-healing properties.

[0068] Application Example 4

[0069] The hydrogel membrane prepared in Example 2 was bent several times at angles exceeding 180°. The results are as follows: Figure 9 As shown, the hydrogel membrane has good bending properties.

[0070] Application Example 5

[0071] To ensure the material can adapt to various applications, it should possess strong plasticity. Therefore, hydrogels of various shapes were prepared using simple English letter molds, such as... Figure 10 As shown in Figure a, this demonstrates that the prepared hydrogel can handle complex applications such as pipes and meshes. Furthermore, the hydrogel exhibits certain adhesive properties, such as... Figure 10 As shown in Figure b, it can adhere firmly to the glass plate without falling off, which helps to fix it on the light source or glass substrate, thereby more effectively contacting the light source and improving the degradation efficiency in the photocatalytic process.

[0072] Application Example 6

[0073] The hydrogel membrane prepared in Example 2 was subjected to tensile strength testing.

[0074] Based on the stress-strain curve obtained from the universal testing machine, such as Figure 11 As shown, the tensile strength of the hydrogel membrane is 32 MPa.

Claims

1. A method for preparing a flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol, characterized in that, Specifically, the following steps are included: (1) Add TiO2 nanotubes to the aqueous dispersion of graphene oxide, mix evenly, add polyvinyl alcohol, and place in an oil bath at 90±5℃ and under ultraviolet light irradiation to completely dissolve the polyvinyl alcohol and partially reduce the graphene oxide. The mass ratio of graphene oxide, TiO2 nanotubes and polyvinyl alcohol is 0.03~0.05:1:

10. (2) Pour the mixed solution obtained in step (1) into a mold and freeze and thaw repeatedly to obtain a flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the aqueous dispersion of graphene oxide is 0.3~0.5 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the power of the ultraviolet lamp is 300W.

4. The preparation method according to claim 1, characterized in that, In step (2), the freezing and thawing process is repeated 2 to 3 times, and the freezing temperature is -37℃.

5. A flexible composite hydrogel membrane of titanium dioxide nanotubes / graphene / polyvinyl alcohol prepared by any one of the preparation methods according to claims 1 to 4.

6. The application of the titanium dioxide nanotube / graphene / polyvinyl alcohol flexible composite hydrogel membrane according to claim 5 in the photocatalytic degradation of organic pollutants.

7. The application according to claim 6, characterized in that, The organic pollutants are methyl orange, rhodamine B, or methylene blue.

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