Chitin two-dimensional ultrathin porous nanosheet and preparation method thereof
Patent Information
- Application Number
- CN202410206202.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-02-26
- Publication Date
- 2026-09-29
- Estimated Expiration
- 2044-02-26
AI Technical Summary
[0005]本发明的目的在于提供一种甲壳素二维超薄多孔纳米片及其制备方法，解决现有技术对于甲壳素纳米片难以剥离的问题
[0025]本发明首先对甲壳素进行浓碱脱乙酰处理或者季铵化改性，修饰正电荷，增加静电斥力、削弱氢键作用，然后将处理后的甲壳素在酸蒸汽环境下酸解，得到一种类手风琴状的甲壳素，相比于甲壳素原料，片层之间得到极大的疏松，最后只经1～4min的超声波处理，就可以剥离出大比表面积、面内含丰富纳米孔(～34nm)的甲壳素二维超薄(1～5nm)多孔纳米片，其将在离子传输、力学增强、纳米固载等应用领域展现性能优势。另外该方法过程操作简易、化学试剂浓度低、超声波能耗低，制造成本低，符合低碳发展目标。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of biomass nanomaterials technology, and in particular to a chitin two-dimensional ultrathin porous nanosheet and its preparation method. Background Technology
[0002] In recent years, two-dimensional (2D) materials have been widely studied and applied in fields such as nanofluidics, optoelectronics, energy storage, sensing, and catalyst supports due to their high surface area and unique two-dimensional nanostructure properties. Currently, the preparation methods of commonly used two-dimensional (2D) materials such as graphene, graphene oxide (GO), transition metal carbide / nitride (Mxenes), and boron nitride (h-BN) are relatively complex. The preparation process often uses toxic and environmentally harmful chemical reagents (such as N-methylpyrrolidone or highly corrosive chlorosulfonic acid for exfoliating graphene, and hydrofluoric acid for exfoliating mexenes), and the raw materials used for exfoliation are expensive.
[0003] Chitin, a natural polysaccharide widely found in the shells of many organisms (such as shrimp, crabs, squid, shellfish, and various arthropods), is abundant in nature. It is estimated that up to 10 billion tons of chitin are synthesized annually, the vast majority of which is considered marine waste and wasted. Therefore, the high-value utilization of chitin is of great significance for sustainable and healthy development. Chitin possesses a natural "twisted plywood-like layered structure," which holds promise for exfoliating chitin nanosheets composed of chitin nanofibers. Due to the natural environmental friendliness, biocompatibility, and low cost of biomass, it is expected to find applications in the field of traditional two-dimensional materials. However, the hydroxyl groups at C3 and C6 and the acetylamino group at C2 of the chitin molecule can form numerous hydrogen bonds, making chitin nanosheets difficult to exfoliate.
[0004] Therefore, how to exfoliate chitin to form chitin nanosheets is of great significance to the development of two-dimensional materials. Summary of the Invention
[0005] The purpose of this invention is to provide a two-dimensional ultrathin porous chitin nanosheet and its preparation method, thereby solving the problem of the difficulty in peeling off chitin nanosheets in the prior art.
[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:
[0007] This invention provides a method for preparing two-dimensional ultrathin porous nanosheets of chitin, comprising the following steps:
[0008] (1) The shells of crustaceans are crushed, and then subjected to alternating acid and alkali treatment and bleaching to obtain purified chitin;
[0009] (2) The purified chitin was surface treated to obtain positively charged chitin powder;
[0010] (3) Spray the acid solution onto the surface of positively charged chitin powder at a certain solid-liquid ratio, perform acid hydrolysis in a sealed container, wash until neutral and then dry to obtain chitin-based accordion-like three-dimensional porous material.
[0011] (4) A suspension of chitin-based accordion-like three-dimensional porous material mixed with water was subjected to ultrasonic treatment, followed by centrifugation and freeze-drying to obtain chitin two-dimensional ultrathin porous nanosheets.
[0012] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the bleaching solution in step (1) is a mixed solution of NaClO2 and CH3COONa; the concentration of NaClO2 in the mixed solution is 1-2 wt%; and the concentration of CH3COONa in the mixed solution is 0.1-1 mol / L.
[0013] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the surface treatment method in step (2) is: mixing purified chitin with NaOH solution and then reacting;
[0014] Alternatively, purified chitin, 2,3-epoxypropyltrimethylammonium chloride, and NaOH solution can be mixed and reacted.
[0015] Alternatively, purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution, and NaOH solution can be mixed and reacted.
[0016] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, in the reaction of mixing purified chitin with NaOH solution, the concentration of NaOH solution is 30-50 wt%, the reaction temperature is 70-80℃, and the reaction time is 1-5 h;
[0017] In the reaction of purified chitin, 2,3-epoxypropyltrimethylammonium chloride with NaOH solution, and the reaction of purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution with NaOH solution, the concentration of NaOH solution is independently 1-5 wt%, the reaction temperature is independently 50-70℃, and the reaction time is independently 10-12 h.
[0018] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the concentration of the acid solution in step (3) is 0.5-5 mol / L; the solid-liquid ratio of the positively charged chitin and the acid solution is 0.1-1 g: 1-5 mL; and the acid solution in step (3) is hydrochloric acid, acetic acid, nitric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, hydrosulfuric acid, or formic acid.
[0019] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the acid hydrolysis temperature in step (3) is 70-120°C; and the acid hydrolysis time is 0.5-8h.
[0020] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the mass content of chitin-based accordion-like three-dimensional porous material in the suspension in step (4) is 1-5 wt%.
[0021] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the power of the ultrasonic treatment in step (4) is 200-300W; and the ultrasonic treatment time is 1-4min.
[0022] Preferably, in the above-mentioned method for preparing chitin two-dimensional ultrathin porous nanosheets, the centrifugation speed in step (4) is 4000-7000 rpm; the centrifugation time is 5-20 min.
[0023] The present invention also provides a method for preparing chitin two-dimensional ultrathin porous nanosheets to obtain chitin two-dimensional ultrathin porous nanosheets.
[0024] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:
[0025] This invention first involves deacetylation of chitin with concentrated alkali or quaternization modification to alter its positive charge, increase electrostatic repulsion, and weaken hydrogen bonding. The treated chitin is then acid-hydrolyzed in an acid vapor environment to obtain an accordion-like chitin with significantly more porous layers compared to the raw chitin. Finally, after only 1–4 minutes of ultrasonic treatment, two-dimensional ultrathin (1–5 nm) porous chitin nanosheets with a large specific surface area and abundant in-plane nanopores (~34 nm) can be exfoliated. These nanosheets will exhibit performance advantages in applications such as ion transport, mechanical reinforcement, and nanofiber immobilization. Furthermore, this method is simple to operate, requires low chemical reagent concentrations, consumes low ultrasonic energy, and has low manufacturing costs, aligning with low-carbon development goals. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.
[0027] Figure 1 This is a schematic diagram illustrating the preparation of chitin two-dimensional ultrathin porous nanosheets in Example 1;
[0028] Figure 2 SEM image of purified chitin prepared in step (1) of Example 1;
[0029] Figure 3 The chitin-based accordion-like three-dimensional porous material prepared in step (3) of Example 1 is shown in an SEM image with a scale bar of 200 μm.
[0030] Figure 4 The chitin-based accordion-like three-dimensional porous material prepared in step (3) of Example 1 is shown in an SEM image with a scale bar of 10 μm.
[0031] Figure 5 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 1 are shown in an SEM image with a scale bar of 10 μm.
[0032] Figure 6 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 1 are shown in an SEM image with a scale bar of 1 μm.
[0033] Figure 7 AFM image at low magnification of the two-dimensional ultrathin porous chitin nanosheets prepared in step (4) of Example 1;
[0034] Figure 8 A high-magnification AFM image of the two-dimensional ultrathin porous chitin nanosheets prepared in step (4) of Example 1; where the inset is a nanopore size distribution map;
[0035] Figure 9 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 1 are shown in a TEM image with a scale bar of 2 μm.
[0036] Figure 10 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 1 are TEM images with a scale bar of 500 nm.
[0037] Figure 11 Nitrogen adsorption-desorption curves of chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 1 (the inset is a pore size distribution diagram of chitin two-dimensional ultrathin porous nanosheets).
[0038] Figure 12 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 2 are shown in an SEM image with a scale bar of 2 μm.
[0039] Figure 13 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 2 are SEM images with a scale bar of 200 nm.
[0040] Figure 14 The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 3 are shown in an SEM image with a scale bar of 1 μm.
[0041] Figure 15The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) of Example 3 are SEM images with a scale bar of 200 nm.
[0042] Figure 16 SEM image of acid-hydrolyzed chitin prepared in step (2) of Comparative Example 1;
[0043] Figure 17 SEM image of chitin nanosheets prepared in step (3) of Comparative Example 1 with a scale bar of 20 μm;
[0044] Figure 18 SEM image of chitin nanosheets prepared in step (3) of Comparative Example 1 with a scale bar of 10 μm;
[0045] Figure 19 AFM image of chitin nanosheets prepared in step (3) of Comparative Example 1 at low magnification;
[0046] Figure 20 AFM image of chitin nanosheets prepared in step (3) of Comparative Example 1 at high magnification;
[0047] Figure 21 Nitrogen adsorption-desorption curves of chitin nanosheets prepared in step (3) of Comparative Example 1 (inset shows the pore size distribution of chitin nanosheets). Detailed Implementation
[0048] This invention provides a method for preparing two-dimensional ultrathin porous nanosheets of chitin, comprising the following steps:
[0049] (1) The shells of crustaceans are crushed, and then subjected to alternating acid and alkali treatment and bleaching to obtain purified chitin;
[0050] (2) The purified chitin was surface treated to obtain positively charged chitin powder;
[0051] (3) Spray the acid solution onto the surface of positively charged chitin powder at a certain solid-liquid ratio, perform acid hydrolysis in a sealed container, wash until neutral and then dry to obtain chitin-based accordion-like three-dimensional porous material.
[0052] (4) A suspension of chitin-based accordion-like three-dimensional porous material mixed with water was subjected to ultrasonic treatment, followed by centrifugation and freeze-drying to obtain chitin two-dimensional ultrathin porous nanosheets.
[0053] In this invention, the crustacean shell in step (1) is preferably a shrimp shell and / or a crab shell.
[0054] In this invention, the pulverization process in step (1) further includes sieving; the preferred mesh size of the sieve is 60 mesh.
[0055] In this invention, the acid-base alternation treatment method in step (1) is as follows: 400g of crustacean carcass is crushed, treated with 5L of 5wt% NaOH solution at room temperature for 6h with stirring at 800rpm, washed with distilled water until neutral and filtered, and then treated with 5L of 7wt% HCl solution at room temperature for 36h with stirring at 800rpm, washed with distilled water until neutral and filtered. The NaOH solution treatment and HCl solution treatment are repeated twice alternately.
[0056] In this invention, the bleaching solution in step (1) is preferably a mixed solution of NaClO2 and CH3COONa; the concentration of NaClO2 in the mixed solution is preferably 1-2 wt%, more preferably 1.2-1.8 wt%, and more preferably 1.7 wt%; the concentration of CH3COONa in the mixed solution is preferably 0.1-1 mol / L, more preferably 0.2-0.5 mol / L, and more preferably 0.3 mol / L.
[0057] In this invention, the preferred ratio of crustacean carcass to bleaching solution in step (1) is 400g:5L.
[0058] In this invention, the bleaching temperature in step (1) is preferably 80°C; the bleaching time is preferably 6 hours.
[0059] In this invention, the bleaching process in step (1) further includes washing with water until neutral, filtering, and drying.
[0060] In this invention, the surface treatment method in step (2) is: mixing purified chitin with NaOH solution and then reacting;
[0061] Alternatively, purified chitin, 2,3-epoxypropyltrimethylammonium chloride, and NaOH solution can be mixed and reacted.
[0062] Alternatively, purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution, and NaOH solution can be mixed and reacted.
[0063] In this invention, during the reaction of purified chitin with NaOH solution, the concentration of NaOH solution is preferably 30-50 wt%, more preferably 34-47 wt%, and even more preferably 40 wt%; the reaction temperature is preferably 70-80°C, more preferably 75-80°C, and even more preferably 80°C; the reaction time is preferably 1-5 h, more preferably 1.2-2 h, and even more preferably 2 h; the ratio of purified chitin to NaOH solution is preferably 15-25 g: 150-300 mL, more preferably 16-22 g: 170-260 mL, and even more preferably 20 g: 200 mL.
[0064] In this invention, during the reaction of purified chitin, 2,3-epoxypropyltrimethylammonium chloride, and NaOH solution, the concentration of NaOH solution is preferably 1-5 wt%, more preferably 2-3 wt%, and even more preferably 2 wt%; the reaction temperature is preferably 50-70°C, more preferably 55-65°C, and even more preferably 60°C; the reaction time is preferably 10-12 h, more preferably 11-12 h, and even more preferably 12 h; the ratio of purified chitin, 2,3-epoxypropyltrimethylammonium chloride, and NaOH solution is preferably 1-2 g: 7-8 g: 100-150 mL, more preferably 1.2-1.8 g: 7.2-7.5 g: 110-140 mL, and even more preferably 1.5 g: 7.3 g: 120 mL.
[0065] In this invention, in the reaction of purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution, and NaOH solution, the concentration of NaOH solution is preferably 1-5 wt%, more preferably 2-4 wt%, and even more preferably 3 wt%; the reaction temperature is preferably 50-70°C, more preferably 55-65°C, and even more preferably 60°C; the reaction time is preferably 10-12 h, more preferably 11-12 h, and even more preferably 12 h; the concentration of (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution is preferably 60-70 wt%, more preferably 63-67 wt%, and even more preferably 65 wt%; the ratio of purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution, and NaOH solution is preferably 1-2 g: 10-15 g: 100-200 mL, more preferably 1.3-1.9 g: 12-15 g: 130-170 mL, and even more preferably 1.7 g: 14 g: 150 mL.
[0066] In this invention, after the surface treatment in step (2) is completed, the process further includes washing with water until neutral, filtering, and drying.
[0067] In this invention, the concentration of the acid solution in step (3) is preferably 0.5 to 5 mol / L, and more preferably 1 to 4 mol / L.
[0068] In this invention, the acid solution in step (3) is preferably hydrochloric acid, acetic acid, nitric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, hydrosulfuric acid or formic acid, more preferably hydrochloric acid, nitric acid, hydrosulfuric acid or formic acid, and even more preferably hydrochloric acid.
[0069] In this invention, the solid-liquid ratio of the positively charged chitin and acid solution in step (3) is preferably 0.1-1g:1-5mL, and more preferably 0.2-0.6g:1-2mL.
[0070] In this invention, the sealed container in step (3) is preferably a high-density polyethylene plastic bottle or a hydrothermal reactor, and more preferably a hydrothermal reactor.
[0071] In this invention, the acid hydrolysis temperature in step (3) is preferably 70-120°C, more preferably 75-85°C; the acid hydrolysis time is preferably 0.5-8h, more preferably 5-7h.
[0072] In this invention, after the acid hydrolysis in step (3) is completed, sieving is also included; the mesh size of the sieve is preferably 100 to 500 mesh, and more preferably 200 to 300 mesh.
[0073] In this invention, the freeze-drying in step (3) is preferably liquid nitrogen freeze-drying, supercritical drying or acetone displacement drying.
[0074] In this invention, the mass content of chitin-based accordion-like three-dimensional porous material in the suspension in step (4) is preferably 1-5 wt%, more preferably 1-3 wt%, and even more preferably 1 wt%.
[0075] In this invention, the power of the ultrasonic treatment in step (4) is preferably 200-300W, more preferably 220-270W; the time of the ultrasonic treatment is preferably 1-4min, more preferably 2-3min, and more preferably 2min.
[0076] In this invention, the instrument for ultrasonic treatment in step (4) is preferably a cell disruptor; the working process of the cell disruptor is preferably 2 seconds of ultrasonic treatment followed by 2 seconds of rest.
[0077] In this invention, the centrifugation speed in step (4) is preferably 4000–7000 rpm, more preferably 4500–5000 rpm; the centrifugation time is preferably 5–20 min, more preferably 15–20 min. After centrifugation, the supernatant is removed, and the sediment is freeze-dried.
[0078] The present invention also provides a method for preparing chitin two-dimensional ultrathin porous nanosheets to obtain chitin two-dimensional ultrathin porous nanosheets.
[0079] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0080] Example 1
[0081] This embodiment provides a method for preparing two-dimensional ultrathin porous nanosheets of chitin, as shown in the schematic diagram below. Figure 1 As shown, the specific steps include:
[0082] (1) 400g of crab shells were crushed and passed through a 60-mesh sieve. They were then treated with 5L of 5wt% NaOH solution at room temperature for 6h with stirring at 800rpm. After the treatment, the shells were washed with distilled water until neutral and filtered. Then, they were treated with 5L of 7wt% HCl solution at room temperature for 36h with stirring at 800rpm. After the treatment, the shells were washed with distilled water until neutral and filtered. The treatment with NaOH solution and HCl solution was repeated twice. Then, the shells were bleached with a mixed solution of 5L of 1.7wt% NaClO2 and 0.3mol / L CH3COONa at 80℃ for 6h with stirring at 800rpm. After the treatment, the shells were washed with distilled water until neutral and filtered. Finally, the shells were dried at 60℃ to obtain purified chitin.
[0083] (2) 20g of purified chitin was placed in 200mL of 40wt% NaOH solution and reacted at 80℃ for 2h with stirring at 800rpm. After the reaction was completed, the chitin was washed with distilled water until neutral and filtered. It was then dried at 60℃ to obtain positively charged chitin.
[0084] (3) Place 1g of positively charged chitin into a 40mL hydrothermal reactor. Spray 1mL of 3mol / L HCl solution evenly onto the surface of the positively charged chitin using a small plastic spray bottle. Seal the hydrothermal reactor and place it in a forced-air drying oven at 70℃ for 4h. Shake the hydrothermal reactor every 1h during the reaction to make the reaction more uniform. After the reaction is complete, wash with distilled water until neutral and filter. Then pass through a 300-mesh sieve to remove the micro-nano chitin fibers (undersize material) generated by excessive acid hydrolysis. Freeze-dry the sieve material with liquid nitrogen to obtain chitin-based accordion-like three-dimensional porous material.
[0085] (4) Mix the chitin-based accordion-like three-dimensional porous material with deionized water to prepare a 40 mL 1 wt% suspension. Use a cell disruptor to sonicate the suspension at 200 W power for 2 min, followed by 2 s of sonication and 2 s rest. After sonication, centrifuge at 6000 rpm for 20 min to separate the supernatant and sediment. Freeze-dry the sediment with liquid nitrogen to obtain chitin two-dimensional ultrathin porous nanosheets.
[0086] The purified chitin prepared in step (1), the chitin-based accordion-like three-dimensional porous material prepared in step (3), and the chitin two-dimensional ultrathin porous nanosheets prepared in step (4) were characterized by SEM, and the results are as follows: Figures 2-6 As shown. The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) were characterized by AFM and TEM, respectively, and the results are as follows. Figures 7-10As shown. The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) were characterized by nitrogen adsorption-desorption, and the results are as follows. Figure 11 As shown.
[0087] Depend on Figure 2 It can be seen that purified chitin has a compact, thick, sheet-like structure with no obvious pores on its surface. Figures 3-4 It can be seen that accordion-like chitin structures were obtained by purifying chitin through positively charged surface treatment (deacetylation) followed by acid vapor treatment. Deacetylation reduced the hydrogen bonding between chitin molecules and decreased the crystallinity of chitin. In addition, the protonation of amino groups (-NH3) under acid vapor conditions... + The static repulsion between the chitin layers, working together, facilitates the separation of the chitin sheets. Figures 5-10 It is known that the two-dimensional ultrathin porous chitin nanosheets are formed by the disordered stacking of chitin nanofibers on a plane, with micron and nanopores existing between the fibers. The sheet thickness is approximately 1.75 nm, and the average pore size of the nanopores is approximately 34 nm. Figure 11 It can be seen that the specific surface area of the chitin two-dimensional ultrathin porous nanosheets is 64.2 m². 2 / g.
[0088] Example 2
[0089] This embodiment provides a method for preparing two-dimensional ultrathin porous nanosheets of chitin, including the following steps:
[0090] (1) For details on the preparation of purified chitin, please refer to Example 1;
[0091] (2) 1g of purified chitin was placed in 100mL of 2wt% NaOH solution, and 7.8g of 2,3-epoxypropyltrimethylammonium chloride was added. The mixture was reacted at 65℃ for 12h with stirring at 800rpm. After the reaction was completed, the mixture was washed with distilled water until neutral and filtered. The mixture was dried at 60℃ to obtain positively charged chitin.
[0092] (3) Place 0.2g of positively charged chitin into a 30mL hydrothermal reactor. Spray 2mL of 2mol / L HCl solution evenly onto the surface of the positively charged chitin using a small plastic spray bottle. Seal the hydrothermal reactor and place it in a forced-air drying oven at 80℃ for 7h. Shake the hydrothermal reactor every 2h during the reaction to make the reaction more uniform. After the reaction is complete, wash with distilled water until neutral and filter. Then pass through a 300-mesh sieve to remove the micro-nano chitin fibers (undersize material) generated by excessive acid hydrolysis. Freeze-dry the sieve material with liquid nitrogen to obtain a chitin-based accordion-like three-dimensional porous material.
[0093] (4) Mix the chitin-based accordion-like three-dimensional porous material with deionized water to prepare a 40 mL 1 wt% suspension. Use a cell disruptor to sonicate the suspension at 200 W power for 2 min, followed by 2 s of sonication and a 2 s rest period. After sonication, centrifuge at 6000 rpm for 20 min to separate the supernatant and sediment. Freeze-dry the sediment with liquid nitrogen to obtain chitin two-dimensional ultrathin porous nanosheets.
[0094] The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) were characterized by SEM, and the results are as follows: Figures 12-13 As shown. By Figures 12-13 It can be seen that the chitin nanosheets were successfully exfoliated and have micron and nanopores.
[0095] Example 3
[0096] This embodiment provides a method for preparing two-dimensional ultrathin porous nanosheets of chitin, including the following steps:
[0097] (1) For details on the preparation of purified chitin, please refer to Example 1;
[0098] (2) 1g of purified chitin was placed in 100mL of 2wt% NaOH solution, and then 12g of 65wt% (3-chloro-2-hydroxypropyl)trimethylammonium chloride aqueous solution was added. The mixture was reacted at 65℃ for 12h with stirring at 800rpm. After the reaction was completed, the mixture was washed with distilled water until neutral and filtered. The mixture was dried at 60℃ to obtain positively charged chitin.
[0099] (3) Place 0.5g of positively charged chitin into a 30mL hydrothermal reactor. Spray 1mL of 3mol / L HCl solution evenly onto the surface of the positively charged chitin using a small plastic spray bottle. Seal the hydrothermal reactor and place it in a forced-air drying oven at 85℃ for 7h. Shake the hydrothermal reactor every 1h during the reaction to make the reaction more uniform. After the reaction is complete, wash with distilled water until neutral and filter. Then pass through a 300-mesh sieve to remove the micro-nano chitin fibers (undersize material) generated by excessive acid hydrolysis. Freeze-dry the sieve material with liquid nitrogen to obtain chitin-based accordion-like three-dimensional porous material.
[0100] (4) Mix the chitin-based accordion-like three-dimensional porous material with deionized water to prepare a 25 mL 1 wt% suspension. Use a cell disruptor to sonicate the suspension at 300 W for 3 min, followed by 2 s of sonication and a 2 s rest period. After sonication, centrifuge at 7000 rpm for 15 min to separate the supernatant and sediment. Freeze-dry the sediment with liquid nitrogen to obtain chitin two-dimensional ultrathin porous nanosheets.
[0101] The chitin two-dimensional ultrathin porous nanosheets prepared in step (4) were characterized by SEM, and the results are as follows: Figures 14-15 As shown. By Figures 14-15 It can be seen that the chitin nanosheets were successfully exfoliated and have micron and nanopores.
[0102] Comparative Example 1
[0103] This comparative example provides a method for preparing chitin nanosheets, including the following steps:
[0104] (1) For details on the preparation of purified chitin, please refer to Example 1;
[0105] (2) Place 1g of purified chitin into a 40mL hydrothermal reactor. Spray 2mL of 2mol / L HCl solution evenly onto the surface of the purified chitin using a small plastic spray bottle. Seal the hydrothermal reactor and place it in a forced-air drying oven at 70℃ for 4h. Shake the hydrothermal reactor every 1h during the reaction to make the reaction more uniform. After the reaction is complete, wash with distilled water until neutral and filter. Then pass through a 300-mesh sieve to remove the sieve material. Freeze-dry the sieve material with liquid nitrogen to obtain acid-hydrolyzed chitin.
[0106] (3) Mix acid-hydrolyzed chitin with deionized water to prepare a 40 mL 1 wt% suspension. Use a cell disruptor to sonicate the suspension at 200 W for 2 min, followed by 2 s of sonication and a 2 s rest period. After sonication, centrifuge at 6000 rpm for 20 min to separate the supernatant and precipitate. Freeze-dry the precipitate with liquid nitrogen to obtain chitin nanosheets.
[0107] The acid-hydrolyzed chitin prepared in step (2) and the chitin nanosheets prepared in step (3) were characterized by SEM, and the results are as follows: Figures 16-18 As shown. The chitin nanosheets prepared in step (3) were characterized by AFM, and the results are as follows. Figures 19-20 As shown. The chitin nanosheets prepared in step (3) were characterized by nitrogen adsorption-desorption, and the results are as follows. Figure 21 As shown.
[0108] Depend on Figure 16 It is known that without positively charged treatment, acid hydrolysis of chitin using only acid vapor does not result in an accordion-like structure; only preliminary separation between the layers occurs. Figures 17-20 It can be seen that after ultrasonic exfoliation, the surface of the chitin nanosheets is virtually pore-free, and the sheet thickness is also greater (~124.7 nm). Different nanosheet structures can be obtained by whether or not a positive charge treatment is performed. Figure 21 It can be seen that the specific surface area of chitin nanosheets is 36.6 m². 2 / g.
[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing two-dimensional ultrathin porous nanosheets of chitin, characterized in that, Includes the following steps: (1) The shells of crustaceans are crushed and then subjected to alternating acid and alkali treatment and bleaching to obtain purified chitin; (2) The purified chitin was surface treated to obtain positively charged chitin powder; (3) Spray the acid solution onto the surface of positively charged chitin powder at a certain solid-liquid ratio, perform acid hydrolysis in a sealed container, wash until neutral and then dry to obtain chitin-based accordion-like three-dimensional porous material. (4) A suspension of chitin-based accordion-like three-dimensional porous material mixed with water was subjected to ultrasonic treatment, then centrifuged and freeze-dried to obtain chitin two-dimensional ultrathin porous nanosheets. The surface treatment method in step (2) is as follows: reacting purified chitin with NaOH solution; or reacting purified chitin, 2,3-epoxypropyltrimethylammonium chloride with NaOH solution; or reacting purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution with NaOH solution. The acid solution in step (3) is hydrochloric acid or acetic acid.
2. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, The bleaching solution in step (1) is a mixed solution of NaClO2 and CH3COONa; the concentration of NaClO2 in the mixed solution is 1~2wt%; the concentration of CH3COONa in the mixed solution is 0.1~1mol / L.
3. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, In the reaction of purified chitin with NaOH solution, the concentration of NaOH solution is 30-50 wt%, the reaction temperature is 70-80℃, and the reaction time is 1-5 h. In the reaction of purified chitin, 2,3-epoxypropyltrimethylammonium chloride with NaOH solution, and the reaction of purified chitin, (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution with NaOH solution, the concentration of NaOH solution is independently 1~5wt%, the reaction temperature is independently 50~70℃, and the reaction time is independently 10~12h.
4. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, The concentration of the acid solution in step (3) is 0.5~5 mol / L; the solid-liquid ratio of the positively charged chitin and the acid solution is 0.1~1 g: 1~5 mL.
5. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, The acid hydrolysis temperature in step (3) is 70~120℃; the acid hydrolysis time is 0.5~8h.
6. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, The mass content of the chitin-based accordion-like three-dimensional porous material in the suspension in step (4) is 1~5wt%.
7. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, The ultrasonic power in step (4) is 200~300W; the ultrasonic treatment time is 1~4min.
8. The method for preparing chitin two-dimensional ultrathin porous nanosheets according to claim 1, characterized in that, In step (4), the centrifugation speed is 4000~7000 rpm; the centrifugation time is 5~20 min.
9. A chitin two-dimensional ultrathin porous nanosheet prepared by the method of any one of claims 1 to 8.