Porous charcoal / cellulose / polyvinyl alcohol aerogel as well as preparation method and application thereof

Abstract

The invention provides a porous charcoal / cellulose / polyvinyl alcohol aerogel, a preparation method and application thereof, the preparation method comprises the following steps: (1) pretreating traditional Chinese medicine residues with alkali, and calcining the traditional Chinese medicine residues and cysteine in a tubular furnace to obtain nitrogen and sulfur doped porous charcoal; (2) dissolving carboxymethyl cellulose and polyvinyl alcohol in deionized water to form a uniform solution; (3) mixing the two solutions obtained in the step (2) to form a mixed solution; and carrying out ultrasonic treatment on the mixed solution for 10-60 minutes, heating at 30-70 DEG C for 10-60 minutes, freezing, slicing, and soaking slices in an acid solution with the pH value of 3-5 for 0.5-1 hour to obtain the porous aerogel. The preparation method of the porous aerogel is simple, green, environment-friendly and excellent in effect, and can be used for pollutant removal and seawater desalination at the same time.

Description

Technical Field

[0001] This application relates to the field of aerogel materials technology, and in particular to a porous biochar / cellulose / polyvinyl alcohol aerogel, its preparation method, and its application. Background Technology

[0002] With increasing population and continuous economic development, water scarcity has become one of the most pressing problems facing humanity. Studies have found that seawater accounts for approximately 97.5% of the global water volume, making seawater desalination an effective solution to alleviate water shortages. Furthermore, the large-scale discharge of heavy metal wastewater from industries such as smelting, chemicals, electroplating, and electronics also contributes to water scarcity. During wastewater discharge, heavy metal wastewater causes serious harm to the ecological environment. Once it enters the human body, it can damage the nervous and immune systems and even induce cancer, seriously threatening human health. Therefore, removing heavy metals from wastewater not only reduces ongoing environmental damage but is also an effective way to alleviate water scarcity. Aerogels, as materials with a three-dimensional network structure, are widely used in wastewater pollutant removal and seawater desalination due to their excellent specific surface area, abundant porous structure, various functional groups, and excellent thermal insulation properties.

[0003] In the process of developing this application, the applicant discovered that the relevant technology has at least the following problems:

[0004] Existing aerogel synthesis processes are complex and costly. Currently, the synthesis and application of aerogels are mostly focused on single-function research, and they are difficult to play a role in complex environments during actual use. Summary of the Invention

[0005] In view of this, this application provides a porous biochar / cellulose / polyvinyl alcohol aerogel, its preparation method and its application, aiming to solve the problems of complex and costly aerogel preparation process and limited application of aerogel.

[0006] To achieve the above objectives, this application provides a method for preparing porous aerogels, comprising the following steps: (1) Using alkali pretreatment of Chinese medicine residue, the Chinese medicine residue and cysteine ​​are calcined in a tube furnace to obtain nitrogen and sulfur doped porous biochar. (2) Dissolve carboxymethyl cellulose and polyvinyl alcohol in deionized water to form a homogeneous solution; (3) Mix the two solutions obtained in step (2), add 0.2-2 wt% of the nitrogen- and sulfur-doped porous biochar and 0.01-0.1 wt% of nano-calcium carbonate to form a mixed solution; sonicate the mixed solution for 10-60 min, and then react it at 30-70℃ for 10-60 min to form a hydrogel; freeze and thaw the hydrogel, and then slice it; soak the slice in an acid solution, wash it, and freeze-dry it to obtain a porous aerogel.

[0007] In some embodiments, in step (1), the Chinese herbal medicine residue is licorice residue and astragalus residue, and the mass ratio of the Chinese herbal medicine residue to the cysteine ​​is (14-16):1.

[0008] In some embodiments, in step (1), the alkali is NaOH, KOH, Na2CO3, or K2CO3, with a concentration of 0.5-1.0 mol / L, and the alkali treatment time is 9-11 h.

[0009] In some embodiments, in step (1), the calcination temperature is 300-800℃ and the time is 0.5-2h.

[0010] In some embodiments, in step (2), the concentration of carboxymethyl cellulose is 2-5 wt%, and the concentration of polyvinyl alcohol is 5-15 wt%.

[0011] In some embodiments, in step (3), the hydrogel undergoes at least one cycle of freezing, thawing and refreezing to crosslink the functional groups such as carboxyl and hydroxyl groups between cellulose, biochar and polyvinyl alcohol; the thickness of the slice is 1.5-2.5 cm.

[0012] In some embodiments, in step (3), the acid solution is acetic acid or hydrochloric acid solution, the pH of the acid solution is 3-5, and the soaking time of the acid solution is 0.5-1h.

[0013] In some embodiments, the porous aerogel prepared by any of the methods described above is a porous biochar / cellulose / polyvinyl alcohol aerogel.

[0014] In some embodiments, the application of the porous aerogel in water treatment includes the following steps: (1) Removal of multi-metal ions: The aerogel was placed in an aqueous solution of multi-metal ions and stirred for 2-4 hours for adsorption. After adsorption was completed, the supernatant was filtered and the concentration of the remaining metal ions in the aqueous solution was determined by atomic absorption fluorescence spectroscopy. (2) Water treatment: The aerogel is placed in pure water or seawater and temperature and water evaporation tests are performed.

[0015] In some embodiments, the aqueous solution of the multi-metal ions includes Cu, Pb, Zn, Ni, and Cr metal ions, with a concentration of 10-200 mg / L.

[0016] Compared with existing technologies, the porous biochar / cellulose / polyvinyl alcohol aerogel, its preparation method, and its application described in this application have the following beneficial effects: (1) This application uses inexpensive and readily available biomass as raw material to synthesize porous biochar / cellulose / polyvinyl alcohol aerogel. The synthesized aerogel is non-toxic and harmless, and can be naturally degraded after use, without causing secondary pollution to the environment. At the same time, it provides a sustainable development path for the resource recycling of biomass and achieves the purpose of treating waste with waste.

[0017] (2) The synthesis of porous aerogels is achieved by ultrasonic-heating-freezing, forming a physical-chemical-physical alternating crosslinking method to synthesize hydrogels, which significantly enhances the mechanical strength of the gel, ensures that the synthesized aerogels can be reused multiple times, avoids the use of crosslinking agents and initiators, and reduces the potential environmental risks and production costs of raw materials.

[0018] (3) The porous biochar / cellulose / polyvinyl alcohol aerogel in this application can simultaneously achieve the adsorption of heavy metals in wastewater and seawater desalination. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a flowchart illustrating the preparation process of the porous biochar / cellulose / polyvinyl alcohol aerogel of this application; Figure 2 This is the experimental result of using porous biochar / cellulose / polyvinyl alcohol aerogel in seawater desalination. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0021] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] like Figure 1 As shown, one embodiment of this application provides a method for preparing porous biochar / cellulose / polyvinyl alcohol aerogel, comprising the following steps: (1) Using alkali pretreatment of Chinese medicine residue, the Chinese medicine residue and cysteine ​​are calcined in a tube furnace to obtain nitrogen and sulfur doped porous biochar. The method of treating medicinal herb residue with alkali increases its carbon content by dissolving impurities, lignin, and hemicellulose. The medicinal herb residue used is either licorice residue or astragalus residue. The mass ratio of medicinal herb residue to cysteine ​​is (14-16):1. The alkali used is NaOH, KOH, Na₂CO₃, or K₂CO₃ at a concentration of 0.5-1.0 mol / L, and the alkali treatment time is 9-11 hours. The medicinal herb residue and cysteine ​​are calcined in a tubular furnace at a temperature of 300-800℃ for 0.5-2 hours to obtain nitrogen- and sulfur-doped porous biochar.

[0023] (2) Dissolve 2-5 wt% sodium carboxymethyl cellulose and 5-15 wt% polyvinyl alcohol in 25 mL of deionized water to form a homogeneous solution.

[0024] (3) The two solutions obtained in step (2) are mixed, and 0.2-2 wt% of the nitrogen- and sulfur-doped porous biochar and 0.01-0.1 wt% of nano-calcium carbonate are added to form a mixed solution. The mixed solution is ultrasonically reacted for 10-60 min, and then reacted at 30-70℃ for 10-60 min to form a hydrogel. The hydrogel is frozen and then thawed, and then sliced. The slices are soaked in an acid solution for 0.5-1 h, washed, and freeze-dried to obtain a porous bifunctional aerogel. Cellulose, biochar and polyvinyl alcohol are physically crosslinked by ultrasound, and then chemically crosslinked by heating. Then, the functional groups such as carboxyl and hydroxyl groups of cellulose, biochar and polyvinyl alcohol are entangled and crosslinked by hydrogen bonds by freezing, thawing and freezing again, so as to achieve physical crosslinking. The gel is prepared by a variety of alternating crosslinking methods. Furthermore, the acid solution mentioned in step (3) is acetic acid or hydrochloric acid solution with a pH value of 3-5. The soaking time of the acid solution is 20-40 minutes to prevent the solution from being too acidic and the time from being too long, which would cause the pores to collapse. At the same time, the aerogel is cut into slices with a thickness of 1-3 cm so that it can fully contact the acid solution and ensure the formation of pores.

[0025] This application provides an application of porous biochar / cellulose / polyvinyl alcohol aerogel in water treatment. Furthermore, the application of the aerogel in wastewater heavy metal adsorption and seawater desalination includes the following steps: (1) Removal of multiple metal ions: The synthetic cellulose / biochar / polyvinyl alcohol bifunctional porous aerogel was placed in an aqueous solution of multiple metal ions and stirred for 2-4 hours for adsorption. After adsorption was completed, the supernatant was filtered and the concentration of the remaining metal ions in the aqueous solution was determined by atomic absorption fluorescence spectroscopy. Further, the aqueous solution of multiple metal ions was a mixture of Cu, Pb, Zn, Ni, Cr and other metal ions with a concentration of 10-200 mg / L.

[0026] (2) Seawater desalination: The synthetic aerogel was placed in pure water or seawater and subjected to temperature and water evaporation tests under sunlight. Further, the seawater consisted of simulated seawater and actual seawater, with the simulated seawater being a 3.5 wt% NaCl solution.

[0027] The specific implementation of this application will be described in detail below with reference to specific embodiments: Example 1 A method for preparing porous biochar / cellulose / polyvinyl alcohol aerogel includes the following steps: (1) Dissolve 2 wt% sodium carboxymethyl cellulose and 5 wt% polyvinyl alcohol in 25 mL of deionized water, then mix the above solutions, and then add 0.2 wt% nitrogen and sulfur doped porous biochar and 0.01 wt% nano calcium carbonate to form a uniform mixture. Sonicate for 10 min.

[0028] (2) Then react at 30°C for 60 min. After the reaction is complete, the hydrogel formed will be frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0029] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in an acetic acid solution with a pH of 4 for 0.5 h. After washing, place the hydrogel into a freeze dryer to obtain porous biochar / cellulose / polyvinyl alcohol aerogel.

[0030] Example 2 A method for preparing porous biochar / cellulose / polyvinyl alcohol aerogel includes the following steps: (1) Dissolve 2 wt% sodium carboxymethyl cellulose and 5 wt% polyvinyl alcohol in 25 mL of deionized water, then mix the above solutions, and then add 0.5 wt% nitrogen and sulfur doped porous biochar and 0.01 wt% nano calcium carbonate to form a uniform mixture. Sonicate for 10 min.

[0031] (2) Then react at 30°C for 60 min. After the reaction is complete, the hydrogel formed will be frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0032] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in an acetic acid solution with a pH of 4 for 0.5 h. After washing, place the hydrogel into a freeze dryer to obtain porous biochar / cellulose / polyvinyl alcohol aerogel.

[0033] Example 3 A method for preparing porous biochar / cellulose / polyvinyl alcohol aerogel includes the following steps: (1) Dissolve 3.5wt% sodium carboxymethyl cellulose and 10wt% polyvinyl alcohol in 25mL of deionized water, then mix the above solutions, and then add 1wt% nitrogen and sulfur doped porous biochar and 0.05wt% nano calcium carbonate to form a uniform mixture. Sonicate for 30min.

[0034] (2) Then react at 50°C for 10 min. After the reaction is complete, the hydrogel is frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0035] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in a hydrochloric acid solution with a pH of 4 for 0.5 h. After washing, place the hydrogel in a freeze dryer to obtain porous biochar / cellulose / polyvinyl alcohol aerogel.

[0036] Example 4 A method for preparing porous biochar / cellulose / polyvinyl alcohol aerogel includes the following steps: (1) Dissolve 2wt% sodium carboxymethyl cellulose and 10wt% polyvinyl alcohol in 25mL of deionized water, then mix the above solutions, and then add 2wt% nitrogen and sulfur doped porous biochar and 0.05wt% nano calcium carbonate to form a uniform mixture. Sonicate for 30min.

[0037] (2) Then react at 50°C for 10 min. After the reaction is complete, the hydrogel is frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0038] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in a hydrochloric acid solution with a pH of 4 for 0.5 h. Place the cleaned hydrogel in a freeze dryer to obtain porous biochar / cellulose / polyvinyl alcohol aerogel.

[0039] Example 5 A method for preparing porous biochar / cellulose / polyvinyl alcohol aerogel includes the following steps: (1) Dissolve 5 wt% sodium carboxymethyl cellulose and 15 wt% polyvinyl alcohol in 25 mL of deionized water, then add 2 wt% nitrogen and sulfur doped porous biochar and 0.1 wt% nano calcium carbonate to form a uniform mixture and sonicate for 60 min.

[0040] (2) Then react at 70°C for 30 min. After the reaction is complete, the hydrogel is frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0041] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in a hydrochloric acid solution with a pH of 4 for 0.5 h. Place the washed hydrogel into a freeze dryer to obtain porous biochar / cellulose / polyvinyl alcohol aerogel.

[0042] Comparative Example 1 The preparation method of porous cellulose / polyvinyl alcohol aerogel includes the following steps: (1) Dissolve 5 wt% sodium carboxymethyl cellulose and 15 wt% polyvinyl alcohol in 25 mL of deionized water, then add 0.1 wt% nano calcium carbonate to form a uniform mixture and sonicate for 60 min.

[0043] (2) Then react at 70°C for 30 min. After the reaction is complete, the hydrogel is frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0044] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in a hydrochloric acid solution with a pH of 4 for 0.5 h. Place the washed hydrogel into a freeze dryer to obtain a porous cellulose / polyvinyl alcohol aerogel.

[0045] Comparative Example 2 A method for preparing a cellulose / biochar / polyvinyl alcohol bifunctional porous aerogel includes the following steps: (1) Dissolve 5 wt% sodium carboxymethyl cellulose and 15 wt% polyvinyl alcohol in 25 mL of deionized water, then add 2 wt% nitrogen and sulfur doped porous biochar to form a uniform mixture and sonicate for 60 min.

[0046] (2) Then react at 70°C for 30 min. After the reaction is complete, the hydrogel is frozen in the freezer for 8 h, thawed and then frozen for another 8 h.

[0047] (3) Thaw the hydrogel from step (2) and cut it into gel slices with a thickness of 2 cm. Soak the slices in a hydrochloric acid solution with a pH of 4 for 0.5 h. Place the washed hydrogel into a freeze dryer to obtain porous biochar / cellulose / polyvinyl alcohol aerogel.

[0048] Example 1 Adsorption experiments of multiple heavy metals were conducted on the synthesized samples of Examples 1-5 and Comparative Examples 1-2. First, 0.1 g of the bifunctional aerogels synthesized in Examples 1-5 and Comparative Examples 1-2 were weighed and placed in 100 mL of Cu, Pb, Zn, Ni, and Cd solutions, respectively, and shaken for 3 h for adsorption. After adsorption, the supernatant was collected, filtered, and the concentration of remaining heavy metal ions in the aqueous solution was measured. The adsorption efficiency was calculated and is shown in Table 1.

[0049] Table 1. Removal efficiency of heavy metal ions (%)

[0050] As shown in Table 1, the adsorption efficiency of Cu, Pb, Zn, Ni, and Cd ions in Examples 1-5 gradually increased, indicating that biochar plays a crucial role in the adsorption of metal ions. Meanwhile, the adsorption efficiency of the five metal ions in Comparative Example 1 was significantly lower than that in Example 5, further demonstrating that the addition of biochar can provide more porous structures and functional groups containing sulfur, nitrogen, and hydroxyl groups for heavy metals, enhancing the adsorption of cationic heavy metals through physical adsorption, electrostatic adsorption, and chemical complexation. Simultaneously, it can also enhance the adsorption of cationic heavy metals through surface K... + Ca² + It undergoes ion exchange with metal ions, thereby increasing the removal performance of pollutants. The adsorption efficiency of Comparative Example 2 was also lower than that of Example 5. This phenomenon also indicates that by creating pores with calcium carbonate, the aerogel can have a richer pore structure and a better specific surface area, which can improve the removal efficiency of pollutants.

[0051] Example 2 Water evaporation experiments were conducted on the synthesized samples from Examples 1-5 and Comparative Examples 1-2. A 1L beaker was prepared and filled with 800mL of deionized water. A 3×3cm perforated foam of the same shape was then placed on top of the beaker, and the synthetic aerogel was placed on top of the perforated foam. The experimental setup was then wrapped with aluminum foil and placed on an electronic balance under simulated sunlight, and the change in water volume was recorded. Simultaneously, the water evaporation rate was tested in the absence of the sample, serving as a control group. The calculated water evaporation rates are shown in Table 2.

[0052] Table 2 Results of water evaporation rate test

[0053] As shown in Table 2, the calculation results indicate that under one solar radiation, the water evaporation rate in Examples 1-5 is 1.51-1.93 kg·m³. -2 ·h -1 All of these rates were significantly higher than the water evaporation rate of the control group (0.38 kg·m³).-2 ·h -1 The low water evaporation rates in Examples 1 and 2 indicate that lower cellulose content results in lower gel strength, and the gel dissolves with prolonged evaporation time, thus affecting water transport. The water evaporation rate in Comparative Example 1 was 1.23 kg·m³. -2 ·h -1 The water evaporation rate was lower than that of Examples 1-5. These results indicate that the addition of biochar can effectively increase the water evaporation rate of the samples. When biochar is added, its high blackness, porous structure, and wide light absorption range facilitate endothermic reactions in the samples, reduce light reflection loss, and thus promote water evaporation. However, due to the limited water transport rate, the water evaporation rate did not significantly increase even with high biochar content. The water evaporation rate of Comparative Example 2 was 1.77 kg·m³. -2 ·h -1 The water evaporation rate was lower than that of Example 5. This result indicates that the addition of the pore-forming agent, nano-calcium carbonate, can make the internal pore structure of the gel interconnected, which can help improve water transport and water evaporation.

[0054] Example 3 Seawater desalination experiments were conducted on the aerogel synthesized in Example 5 to analyze its desalination effect. The experimental procedures were basically the same as in Example 2, with the main difference being that 800 mL of deionized water in the beaker was replaced with actual seawater. After the photothermal treatment, the Na+ content in the water sample was determined by ICP-MS. + K + Ca 2+ and Mg 2+ The ion concentration.

[0055] Experimental results are as follows Figure 2 As shown, Example 5 synthesizes aerogels for Na... + K + Ca 2+ and Mg 2+ The removal rates can all reach over 95%, and the residual concentration is significantly lower than that of the original water sample, and far below the WHO standard limit. This further demonstrates that the porous biochar / cellulose / polyvinyl alcohol aerogel synthesized in this invention can be well applied to wastewater treatment and seawater desalination.

[0056] The above description is only a partial embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing porous aerogel, characterized in that, Includes the following steps: (1) Using alkali pretreatment of Chinese medicine residue, the Chinese medicine residue and cysteine ​​are calcined in a tube furnace to obtain nitrogen and sulfur doped porous biochar. (2) Dissolve carboxymethyl cellulose and polyvinyl alcohol in deionized water to form a homogeneous solution; (3) Mix the two solutions obtained in step (2), add 0.2-2 wt% of the nitrogen- and sulfur-doped porous biochar and 0.01-0.1 wt% of nano-calcium carbonate to form a mixed solution; sonicate the mixed solution for 10-60 min, then heat it at 30-70℃ for 10-60 min to form a hydrogel; freeze and thaw the hydrogel, then slice it; soak the slices in an acid solution, wash them, and freeze-dry them to obtain a porous aerogel.

2. The method for preparing a porous aerogel according to claim 1, characterized in that, In step (1), the Chinese medicine residue is licorice residue and astragalus residue, and the mass ratio of the Chinese medicine residue to the cysteine ​​is (14-16):

1.

3. The method for preparing a porous aerogel according to claim 1, characterized in that, In step (1), the alkali is NaOH, KOH, Na2CO3, or K2CO3, with a concentration of 0.5-1.0 mol / L, and the alkali treatment time is 9-11 h.

4. The method for preparing a porous aerogel according to claim 1, characterized in that, In step (1), the calcination temperature is 300-800℃ and the time is 0.5-2h.

5. The method for preparing a porous aerogel according to claim 1, characterized in that, In step (2), the concentration of carboxymethyl cellulose is 2-5 wt%, and the concentration of polyvinyl alcohol is 5-15 wt%.

6. The method for preparing a porous aerogel according to claim 1, characterized in that, In step (3), the hydrogel undergoes at least one cycle of freezing, thawing and refreezing to crosslink the functional groups such as carboxyl and hydroxyl groups between cellulose, biochar and polyvinyl alcohol; the thickness of the slice is 1.5-2.5 cm.

7. The method for preparing a porous aerogel according to claim 1, characterized in that, In step (3), the acid solution is acetic acid or hydrochloric acid solution, the pH of the acid solution is 3-5, and the soaking time of the acid solution is 0.5-1h.

8. The porous aerogel prepared by the method according to any one of claims 1-7, characterized in that, It is a porous biochar / cellulose / polyvinyl alcohol aerogel.

9. The application of the porous aerogel according to claim 8 in water treatment, characterized in that, Includes the following steps: (1) Removal of multi-metal ions: The aerogel was placed in an aqueous solution of multi-metal ions and stirred for 2-4 hours for adsorption. After adsorption was completed, the supernatant was filtered and the concentration of the remaining metal ions in the aqueous solution was determined by atomic absorption fluorescence spectroscopy. (2) Water treatment: The aerogel is placed in pure water or seawater and temperature and water evaporation tests are performed.

10. The application according to claim 9, characterized in that, In step (1), the aqueous solution of multi-metal ions includes Cu, Pb, Zn, Ni, and Cr metal ions with a concentration of 10-200 mg / L.

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