Preparation method and application of polypyrrole graphene oxide cellulose hydrogel

Abstract

The invention provides a preparation method and application of polypyrrole graphene oxide hydrogel with an anisotropic structure. The preparation method comprises the following steps: adding sodium hydroxide and urea into water according to a certain proportion, adding microcrystalline cellulose into an alkali urea solution, uniformly stirring, and repeatedly freezing and thawing to obtain a cellulose solution; adding graphene oxide into water for cell disruption and dispersion to obtain a uniform graphene oxide solution; adding the graphene oxide solution into the cellulose solution, then adding an epichlorohydrin cross-linking agent, and carrying out stirring treatment, centrifugation and low-temperature standing to form gel; and pre-stretching the hydrogel to a certain length, immersing the hydrogel into a dilute sulphuric acid solution, taking out the hydrogel, adding pyrrole, carrying out polymerization growth in a closed environment, taking out the hydrogel, soaking the hydrogel in water, and washing the hydrogel to obtain the anisotropic polypyrrole graphene oxide hydrogel. The anisotropic polypyrrole graphene oxide cellulose hydrogel disclosed by the invention has excellent solar photo-thermal water evaporation performance and also has excellent thermal management performance.

Description

Technical Field

[0001] The present invention relates to the field of water treatment, and relates to a preparation method and application of an anisotropic structure poly (pyrrole-graphene oxide-cellulose) hydrogel. Background Art

[0002] Water resources are an important and indispensable part of the development of human society. However, the uneven distribution of global fresh water resources has led to water shortage problems in many places. Solar steam generation is a basic part of the natural water cycle. Therefore, the solar-thermal interfacial evaporation technology has received extensive attention due to its low cost, environmental friendliness, and no need for additional energy input.

[0003] Cellulose-based solar evaporators, with three-dimensional water channels and hierarchical porous structures, have been proven to have fast water transport characteristics driven by strong capillary forces. However, the relatively large pore sizes and randomly arranged microchannel structures in cellulose-based solar evaporators result in inefficient coupling of water transport and heat diffusion. For the solar-thermal interfacial evaporation process, it mainly involves heat management and water delivery, and adjusting the water path is the most common and effective strategy to improve solar evaporation performance. Water delivery mainly involves the direction and flux of microfluids, which depend on the size and framework of the evaporator microchannels. Heat diffusion involves the arrangement direction of microchannels and the properties of the material itself, etc. For cellulose-based solar evaporators, it is easier to regulate the arrangement and size of microchannels to adjust water transport and heat diffusion. Therefore, how to construct anisotropic microchannels without affecting the flux of the evaporator is the key to achieving excellent solar-thermal interfacial evaporation performance. Summary of the Invention

[0004] The present invention provides a preparation method and application of an anisotropic structure poly (pyrrole-graphene oxide-cellulose) hydrogel. By adding graphene oxide two-dimensional nanosheets to assist in constructing oriented channels. And the poly (pyrrole-graphene oxide) hydrogel obtained by stretching is an anisotropic structure and has excellent photothermal conversion performance.

[0005] The technical solution of the present invention:

[0006] The specific steps include:

[0007] S1. Add urea and sodium hydroxide to pure water to obtain an alkaline urea solution;

[0008] S2. Add microcrystalline cellulose to the alkaline urea solution prepared in step S1, stir it, and then repeatedly perform freeze-thaw treatment to obtain a cellulose solution;

[0009] S3. Add graphene oxide to water and perform cell disruption dispersion to obtain a uniform graphene oxide solution;

[0010] S4. Add the graphene oxide solution to the cellulose solution in S3 and perform stirring treatment;

[0011] S5. Add epichlorohydrin to the graphene oxide / cellulose solution in S4, perform stirring treatment, centrifuge, and let it stand at low temperature to form a gel to obtain a pre-loosely cross-linked graphene oxide cellulose hydrogel;

[0012] S6. Stretch the pre-loosely cross-linked graphene oxide cellulose hydrogel in S5. After the stretching length ratio ranges from 0% to 160%, immerse it in a dilute sulfuric acid solution for an acid-base neutralization reaction to fix the length of the graphene oxide cellulose hydrogel, thereby forming hydrogels with different lengths;

[0013] S7. Immerse the anisotropic graphene oxide cellulose hydrogel in S6 in an ammonium persulfate solution. After taking it out, add pyrrole and place it in a sealed environment for polymerization growth. After taking it out, wash it repeatedly with water to obtain an anisotropic polypyrrole graphene oxide cellulose hydrogel.

[0014] Further, in step S1, the mass ratio of sodium hydroxide to urea is 1:1.4 - 2; the solid-liquid mass ratio of urea to water is 1:6 - 10.

[0015] Further, in step S2, the mass ratio of microcrystalline cellulose to the alkali-urea solution is 1:15 - 20. The stirring speed is 200 - 500 rpm.

[0016] Further, in step S2, the freeze-thaw steps are: freeze at -20°C for 16 - 18 h, take it out and stir in an ice bath condition for 1 h - 2 h, and repeat the steps 3 - 4 times.

[0017] Further, in step S3, the cell disruption is specifically: first use a cell disruption instrument and ultrasonicate for 10 min.

[0018] Further, in step S4, the liquid ratio of the graphene oxide solution to the cellulose solution is 1 mL:20 - 25 mL

[0019] Further, in step S5, the mass ratio of the epichlorohydrin cross-linking agent to the graphene oxide cellulose solution is 1:25 - 30. The stirring temperature is 0°C - 5°C, the rotation speed is 1200 - 1500 rpm. The time is 2 - 3 h. The time for low-temperature gel formation is 5 - 8 h.

[0020] Further, in step S6, the concentration of the dilute sulfuric acid solution is 2 - 5 wt%. The reaction time is 1 - 3 min.

[0021] Further, in step S7, the concentration of the ammonium persulfate solution is 1 - 3 wt%; soak for 1 - 4 h. The polypyrrole growth time is 12 - 24 h. Wash with water for 1 - 3 days. Freeze at -20°C for 8 - 12 h.

[0022] Another object of the present invention is to obtain a polypyrrole-reduced graphene oxide-cellulose hydrogel with an anisotropic structure obtained by the above preparation method.

[0023] Another object of the present invention is the application of the polypyrrole-reduced graphene oxide-cellulose hydrogel with an anisotropic structure prepared by the above preparation method in solar desalination.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] The present invention prepares an anisotropic cellulose hydrogel by graphene oxide and microcrystalline cellulose and by stretching means. In the pre-loose state of the hydrogel, the directional orientation structure of graphene oxide two-dimensional nanosheets and cellulose molecular chains is controlled by means of orientation. Subsequently, polypyrrole is grown on the surface of anisotropic graphene oxide by means of chemical vapor deposition and has good photothermal conversion ability. Driven by water and heat, the polypyrrole-reduced graphene oxide-cellulose hydrogel with an anisotropic structure has excellent water evaporation performance. It provides a good strategy for obtaining fresh water resources. Description of the Drawings

[0026] Figure 1 It is the electron microscope image of the MCC@PPy / GO-160% anisotropic polypyrrole-reduced graphene oxide hydrogel of Examples 1-3.

[0027] Figure 2 It is the infrared spectrum of the MCC@PPy / GO-160% of Examples 1-3.

[0028] Figure 3 It is the XRD pattern of the anisotropic polypyrrole-reduced graphene oxide-cellulose hydrogel of Examples 1-3.

[0029] Figure 4 It is the heating rate graph of Examples 1-3.

[0030] Figure 5 It is the infrared thermal imaging of Examples 1-3.

[0031] Figure 6 It is the contact angle graph of Examples 1-3.

[0032] Figure 7 It is the water evaporation mass change graph of Examples 1-3.

[0033] Figure 8 It is the water evaporation mass change graph of the comparative example.

[0034] Figure 9 It is the example concentration graph of Example 3. Detailed Embodiments

[0035] The materials and reagents used in the present invention can all be purchased through commercial channels.

[0036] The stretching lengths in the present invention are 0%, 80%, and 160%, named MCC@PPy / GO-0%, MCC@PPy / GO-80%, and MCC@PPy / GO-160% respectively.

[0037] The maximum stretching length of the present invention is 160%. It will break if it exceeds 160%, and the present invention does not study the situation exceeding 160%.

[0038] Example 1

[0039] The pre-stretching length is 0%;

[0040] S1: Weigh 7 g of sodium hydroxide and 12 g of urea, add them to 81 mL of pure water to prepare an alkali-urea solution;

[0041] S2: Weigh 6 g of microcrystalline cellulose and add it to 94 mL of the alkali-urea solution. Stir at 400 rpm for 30 min. Freeze it at -20 °C for 18 h, take it out and stir it in an ice bath for 1 h, and repeat this step 4 times;

[0042] S3: Add 0.2 g of graphene oxide to 20 mL of water and perform cell disruption and dispersion for 10 min to obtain a uniform graphene oxide solution;

[0043] S4: Add 5 mL of the graphene oxide solution to 100 mL of the cellulose solution and perform stirring treatment;

[0044] S5: Add 3.426 epoxy chloropropane to 100 mL of the graphene oxide / cellulose solution, perform stirring treatment at 1500 rpm, centrifuge at 6000 rpm for 20 min, and let it stand in a 5 °C environment for 8 h to form a gel, obtaining a pre-loosely crosslinked graphene oxide cellulose hydrogel;

[0045] S6: Stretch the pre-loosely crosslinked graphene oxide cellulose hydrogel with a stretching length ratio of 0%, then immerse it in a 5 wt% dilute sulfuric acid solution for 2 min for acid-base neutralization reaction to fix the length of the graphene oxide cellulose hydrogel, thereby forming a cellulose gel with a length ratio of 0%;

[0046] S7: Immerse the poly-pyrrole graphene oxide cellulose hydrogel in a 0.1 mol / L ammonium persulfate solution for 4 h. After taking it out, add pyrrole and place it in a closed environment for polymerization growth for 24 h. After taking it out, wash it repeatedly with water for 2 days, changing the water every 1 day, to obtain the MCC@PPy / GO-0% cellulose hydrogel;

[0047] Example 2

[0048] The pre-stretching length is 80%;

[0049] S1 Weigh 7 g of sodium hydroxide and 12 g of urea, add them to 81 mL of pure water, and prepare an alkali-urea solution;

[0050] S2 Weigh 6 g of microcrystalline cellulose and add it to 94 mL of the alkali-urea solution. Stir at 400 rpm for 30 min. Freeze it at -20 °C for 18 h, take it out and stir it under ice bath conditions for 1 h, and repeat this step 4 times;

[0051] S3 Add 0.2 g of graphene oxide to 20 mL of water and perform cell disruption and dispersion for 10 min to obtain a uniform graphene oxide solution;

[0052] S4 Add 5 mL of the graphene oxide solution to 100 mL of the cellulose solution and perform stirring treatment;

[0053] S5 Add 3.426 epoxy chloropropane to 100 mL of the graphene oxide / cellulose solution, perform stirring treatment at 1500 rpm, centrifuge at 6000 rpm for 20 min, and let it stand in a 5 °C environment for 8 h to form a gel, obtaining a pre-loosely crosslinked graphene oxide cellulose hydrogel;

[0054] S6 Stretch the pre-loosely crosslinked graphene oxide cellulose hydrogel, with a stretching length ratio of 80%, and then immerse it in a 5 wt% dilute sulfuric acid solution for 2 min for an acid-base neutralization reaction to fix the length of the graphene oxide cellulose hydrogel, thereby forming a cellulose gel with a length ratio of 80%;

[0055] S7 Immerse the polypyrrole graphene oxide cellulose hydrogel in a 0.1 mol / L ammonium persulfate solution for 4 h. After taking it out, add pyrrole and place it in a closed environment for polymerization growth for 24 h. After taking it out, wash it repeatedly with water for 2 days, changing the water every 1 day, to obtain MCC@PPy / GO-80% cellulose hydrogel;

[0056] Example 3

[0057] The pre-stretched length is 160%;

[0058] S1 Weigh 7 g of sodium hydroxide and 12 g of urea, add them to 81 mL of pure water, and prepare an alkali-urea solution;

[0059] S2 Weigh 6 g of microcrystalline cellulose and add it to 94 mL of the alkali-urea solution. Stir at 400 rpm for 30 min. Freeze it at -20 °C for 18 h, take it out and stir it under ice bath conditions for 1 h, and repeat this step 4 times;

[0060] S3 Add 0.2 g of graphene oxide to 20 mL of water and perform cell disruption and dispersion for 10 min to obtain a uniform graphene oxide solution;

[0061] S4. Add 5 mL of graphene oxide solution to 100 mL of cellulose solution and perform stirring treatment.

[0062] S5. Add 3.426 of epichlorohydrin to 100 mL of graphene oxide / cellulose solution, perform stirring treatment at 1500 rpm, centrifuge at 6000 rpm for 20 min, and let it stand in a 5°C environment for 8 h to form a gel, obtaining a pre-loosely cross-linked graphene oxide cellulose hydrogel.

[0063] S6. Stretch the pre-loosely cross-linked graphene oxide cellulose hydrogel with a stretching length ratio of 160%, then immerse it in a 5 wt% dilute sulfuric acid solution for 2 min for acid-base neutralization reaction to fix the length of the graphene oxide cellulose hydrogel, thereby forming a cellulose hydrogel with a length ratio of 160%.

[0064] S7. Immerse the poly(3,4-ethylenedioxythiophene) / graphene oxide cellulose hydrogel in 0.1 mol / L ammonium persulfate solution for 4 h. After taking it out, add pyrrole and place it in a closed environment for polymerization growth for 24 h. After taking it out, wash it repeatedly with water for 2 days, changing the water every 1 day, obtaining MCC@PPy / GO-160% cellulose hydrogel.

[0065] 1. Observe the morphological structure of the anisotropic poly(3,4-ethylenedioxythiophene) / graphene oxide cellulose hydrogels of Examples 1-3 through scanning electron microscopy images. As Figure 1 , from Figure 1 it can be seen that the axial cross-section of MCC@PPy / GO-160% shows a regularly arranged lamellar pore distribution. This regularly arranged pore structure is an anisotropic structure, providing a more efficient channel for the transport of water molecules during the evaporation process and ensuring an adequate supply of water.

[0066] 2. Perform Fourier transform infrared spectroscopy analysis on the anisotropic poly(3,4-ethylenedioxythiophene) / cellulose gels prepared in Examples 1-3. As Figure 2 , from Figure 2 it can be seen that obvious poly(3,4-ethylenedioxythiophene) functional groups and graphene oxide functional groups appear in MCC@PPy / GO-160%, proving that graphene oxide and poly(3,4-ethylenedioxythiophene) have been successfully loaded.

[0067] 3. Perform XRD tests on the anisotropic poly(3,4-ethylenedioxythiophene) / cellulose gels prepared in Examples 1-3. As Figure 3 , from Figure 3 it can be seen that in the XRD patterns of the three samples of MCC@PPy / GO-0%, MCC@PPy / GO-80%, and MCC@PPy / GO-160%, characteristic peaks appear at the same positions for all samples. This result indicates that the introduction of GO does not affect the crystal structure of cellulose.

[0068] 4. Infrared thermal imaging analysis was performed on the anisotropic polypyrrole / cellulose gels prepared in Examples 1-3. As Figure 4 shown, it can be seen from Figure 4 that as time increases, the surface temperature of MCC@PPy / GO-160% has a higher heating rate within 200 s of light irradiation than that of MCC@PPy / GO-0% and MCC@PPy / GO-80%. This indicates that MCC@PPy / GO-160% has good photothermal conversion ability.

[0069] 5. The heating rate test was carried out on the anisotropic polypyrrole / cellulose gels prepared in Examples 1-3. As Figure 5 shown, it can be seen from Figure 5 that the higher the degree of orientation, the faster the heating rate, and the temperature of MCC@PPy / GO-160% can reach 69.29 °C in 30 min. It is proved that it has good photothermal conversion ability in photothermal interfacial evaporation.

[0070] 6. Infrared thermal imaging analysis was performed on the anisotropic polypyrrole / cellulose gels prepared in Examples 1-3. As Figure 6 shown, it can be seen from Figure 6 that the MCC@PPy / GO-0% sample before stretching can completely absorb the droplet within 0.08 s. While the absorption times of the stretched MCC@PPy / GO-80% and MCC@PPy / GO-160% samples for the droplet are 0.12 s and 0.08 s respectively. The results show that the hydrophilicity of the sample does not change much before and after stretching. The reason for this phenomenon is that the sample itself contains a large amount of cellulose and GO, which contain rich hydrophilic functional groups, and these functional groups endow the material with extremely high hydrophilicity.

[0071] 7. Infrared thermal imaging analysis was performed on the anisotropic polypyrrole / cellulose gels prepared in Examples 1-3. As Figure 7 shown, it can be seen from Figure 7 that as the degree of orientation increases, the water evaporation rate increases, that is, the evaporation rate of MCC@PPy-160% in Example 3 reached 2.71 kg·m-2 at 1 h.

[0072] Comparative Example

[0073] The difference from Example 3 is that: polypyrrole is not loaded, and the others are the same as Example 3.

[0074] That is, the preparation method of the anisotropic cellulose gel in this comparative example specifically includes the steps of:

[0075] The pre-stretched length is 160%;

[0076] S1 Weigh 7 g of sodium hydroxide and 12 g of urea, add them to 81 mL of pure water, and prepare an alkali-urea solution;

[0077] S2 Weigh 6 g of microcrystalline cellulose and add it to 94 mL of the alkali-urea solution. Stir at 400 rpm for 30 min. Freeze it at -20 °C for 18 h. After taking it out, stir it under ice bath conditions for 1 h, and repeat this step 4 times;

[0078] S3 Add 0.2 g of graphene oxide to 20 mL of water and perform cell disruption and dispersion for 10 min to obtain a uniform graphene oxide solution;

[0079] S4 Add 5 mL of the graphene oxide solution to 100 mL of the cellulose solution and perform stirring treatment;

[0080] S5 Add 3.426 epoxy chloropropane to 100 mL of the graphene oxide / cellulose solution, perform stirring treatment at 1500 rpm, centrifuge at 6000 rpm for 20 min, and let it stand in a 5 °C environment for 8 h to form a gel, obtaining a pre-loosely cross-linked graphene oxide cellulose hydrogel;

[0081] S6 Stretch the pre-loosely cross-linked graphene oxide cellulose hydrogel, with a stretching length ratio of 160%, and then immerse it in a 5 wt% dilute sulfuric acid solution for 2 min for acid-base neutralization reaction to fix the length of the graphene oxide cellulose hydrogel, thereby forming an MCC@GO-160% cellulose gel with a length ratio of 160%;

[0082] See Figure 8 , from Figure 8 it can be seen that the evaporation rate of the MCC@GO-160% without loaded PPy is much lower than that of the sample loaded with polypyrrole in Example 3 (MCC@PPy / GO-160%).

[0083] Application Example

[0084] The photothermal interfacial evaporation performance of the MCC@PPy / GO-160% sample was evaluated through a desalination experiment. See Figure 9 , as Figure 9 shown, compared with natural seawater, the ion concentration in the condensate water generated by MCC@PPy / GO-160% is significantly reduced, and the desalination efficiency is as high as 99.95%. It meets the WHO drinking water standard.

[0085] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing anisotropic polypyrrole graphene oxide cellulose hydrogel, characterized in that: The specific steps include: S1, adding urea and sodium hydroxide into pure water to obtain an alkaline urea solution; S2, adding microcrystalline cellulose to the alkaline urea solution prepared in step S1, stirring, and then repeatedly performing freeze-thaw treatment to obtain a cellulose solution; S3, adding graphene oxide to water to crush and disperse the cells to obtain a uniform graphene oxide solution; S4, adding the graphene oxide solution to the cellulose solution in S2, and stirring the mixture; S5, adding epichlorohydrin to the graphene oxide / cellulose solution in S4, stirring, centrifuging, and standing at low temperature to form a gel, to obtain a pre-loosely cross-linked graphene oxide cellulose hydrogel; S6, stretching the pre-loosely cross-linked graphene oxide cellulose hydrogel in S5, and then immersing it in a dilute sulfuric acid solution for acid-base neutralization reaction to fix the length of the graphene oxide cellulose hydrogel, thereby forming hydrogels of different lengths; S7. Immerse the anisotropic graphene oxide cellulose hydrogel of S6 in an ammonium persulfate solution, take it out, add pyrrole and place it in a closed environment for polymerization growth, take it out and wash it repeatedly with water to obtain anisotropic polypyrrole graphene oxide cellulose hydrogel.

2. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S1, the mass ratio of sodium hydroxide to urea is 1:1.4-2; the solid-liquid mass ratio of urea to water is 1:6-10.

3. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S2, the mass ratio of microcrystalline cellulose to alkaline urea solution is 1:15-20; the stirring speed is 200-500 rpm; the freeze-thaw step is: freeze at -20°C for 16-18h, take out and stir in an ice bath for 1h-2h, and repeat the step 3-4 times.

4. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S3, the cell disruption is specifically as follows: first, a cell disruption instrument is used and ultrasonicated for 10 minutes.

5. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S4, the volume ratio of the graphene oxide solution to the cellulose solution is 1:20-25.

6. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S5, the mass ratio of epichlorohydrin crosslinking agent to graphene oxide cellulose solution is 1:25-30; the stirring temperature is 0-5°C, the rotation speed is 1200-1500rpm; the time is 2-3h; and the low-temperature gelation time is 5-8h.

7. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S6, the concentration of the dilute sulfuric acid solution is 2-5wt%, and the reaction time is 1-3min.

8. The method for preparing an anisotropic polypyrrole graphene oxide cellulose gel according to claim 1, characterized in that: In step S7, the concentration of the ammonium persulfate solution is 1-3 wt %; the immersion is 1-4 hours; the polypyrrole growth time is 12-24 hours; the water washing is 1-3 days; and the freezing is carried out at -20°C for 8-12 hours.

9. A polypyrrole graphene oxide cellulose hydrogel with an anisotropic structure, prepared by the preparation method according to any one of claims 1 to 8.

10. Application of the anisotropic polypyrrole graphene oxide cellulose hydrogel according to claim 9 in solar seawater desalination.

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