Preparation method and application of multi-stage activated bioporous carbon from waste fruit and vegetable peels

Abstract

The present invention belongs to the technical field of bioporous carbon preparation, and discloses a method for preparing multi-stage activated waste fruit and vegetable peel bioporous carbon and its application. Through the multi-stage steps of ultrasonic impregnation of waste fruit and vegetable peels with metal salts, initial carbonization activation, ultrasonic impregnation mixing, and co-pyrolysis activation of etchants and phosphides, a bioporous carbon with an ultra-high specific surface area (3149 m 2 / g), macropore volume (1.76cm 3 / g) of PBC. This represents 102.7% of the currently patented maximum specific surface area. Furthermore, the PBC significantly improves its adsorption performance for VOCs (represented by acetone and n-hexane vapor), reaching 1046 mg / g and 760 mg / g, respectively, representing increases of 138% and 132%, and exhibits excellent recyclability. This invention truly transforms waste into treasure, improving energy efficiency and possessing significant economic and social benefits.

Description

Technical Field

[0001] The invention relates to a preparation method of high-performance multi-stage activated waste fruit and vegetable peel bioporous carbon and application thereof, belonging to the technical field of bioporous carbon preparation. Background Art

[0002] With the continuous advancement of industrialization and urbanization in my country, the demand for energy is increasing. Fossil fuels such as coal and oil, as the primary energy source in my country, also generate large amounts of volatile organic compounds (VOCs) while promoting economic development. These organic compounds are released into the atmosphere, reducing air quality indicators and impacting people's quality of life. Among the numerous VOC treatment technologies, adsorption technology has few restrictions and is applicable to VOC treatment under various conditions. It also offers high adsorption capacity and efficiency, and can be reused with simple process steps. It is recognized as an efficient and economical VOC control strategy. Adsorption materials are the core of adsorption technology. Activated carbon has great potential due to its wide range of raw materials, high adsorption capacity, low cost, and high efficiency. Among them, bioporous carbon stands out due to its wide and environmentally friendly raw material supply, large specific surface area, and low pyrolysis product content.

[0003] At present, bioporous carbon is mainly prepared by high-temperature carbonization of single biomass, KOH activation, hydrothermal carbonization, etc., and is applied to CO2 adsorption, wastewater treatment and soil remediation. For example, patent CN114130361A uses poplar sawdust as carbon source, microalgae as nitrogen source, and sesbania powder as binder, and obtains porous carbon granules through high-temperature carbonization, KOH activation and extrusion granulation, with a specific surface area of ​​up to 1553m 2 / g, used for CO2 adsorption. Patent CN116618018A discloses a phosphorus-modified chestnut shell biochar and its preparation method and application. The chestnut shell biochar is first obtained by high-temperature pyrolysis under oxygen-limited conditions. Then, the chestnut shell biochar is evenly mixed with sodium dihydrogen phosphate powder and subjected to hydrothermal reaction to obtain phosphorus-modified chestnut shell biochar with a specific surface area of ​​179m 2 / g, micropore volume is 0.103cm 3 / g, with an average pore size of 8.61nm, which can achieve efficient removal of cadmium in water. Patent CN106010601B crushes banana peels, mixes them with an aqueous solution of an activator, and then dries them. The mixture is then mixed with an acid solution and subjected to a hydrothermal carbonization reaction to prepare biochar with a specific surface area of ​​550 to 1200m 2 / g, the maximum reaches 1189m 2 / g, can effectively adsorb heavy metals such as Zn, Cd, Pb or Cu. Patent CN116618018A obtained phosphorus-modified chestnut shell biochar with a specific surface area of ​​179m2 / g, micropore volume is 0.103cm 3 / g.

[0004] The above method has a single biomass source, the raw materials are difficult to obtain, and the preparation cost is high; the specific surface area of ​​the prepared porous carbon is not significantly improved compared with the activated carbon, the pore size distribution is narrow, and the application area is single. Therefore, using low-cost biomass as raw material, a new type of biomass porous carbon material with superior performance is developed and applied to the adsorption of VOCs, which can not only achieve the goal of improving atmospheric governance, but also achieve the purpose of carbon fixation and emission reduction, and contribute to the vision of "dual carbon". At present, the activated carbon prepared from biomass as raw material is mainly composed of micropores. Although micropores are conducive to the adsorption of small molecules, it lacks mesopores, which affects the mass transfer rate and the adsorption capacity of large molecular VOCs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the limitations of the existing technology and provide a method for preparing multi-stage activated waste fruit and vegetable peels bioporous carbon with ultra-high specific surface area and its application for super strong adsorption of VOCs. Bioporous carbon with ultra-micro-micro-meso-spanning pores and ultra-high specific surface area is obtained by multi-stage activation such as carbonization activation of waste fruit and vegetable peels, ultrasonic impregnation mixing, and co-pyrolysis activation of etchants and phosphides. The finally prepared bioporous carbon has an ultra-high specific surface area of ​​2000-4000m 2 / g, it can strongly adsorb VOCs, with an adsorption capacity of 500-2000mg / g.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing multi-stage activated bioporous carbon from discarded fruit and vegetable peels, comprising the following steps:

[0008] (1) After removing the pulp from the discarded fruit and vegetable peels, the peels were washed, dried, and crushed for pretreatment. The peels were ultrasonically immersed in a 0.1-0.5M iron salt solution for 4-10 hours. The peels were then placed in a vacuum sintering furnace. In an N2 atmosphere, the temperature was raised to 400-500°C at a rate of 5-10°C / min and maintained for 1-3 hours. The sample was taken out when the temperature dropped to room temperature to obtain the carbonized and activated fruit and vegetable peel carbonized material PC.

[0009] (2) The fruit and vegetable peel carbonized material PC and the etchant are fully mixed and dried in a mass ratio of 1: (1-5) to obtain PC-OH; PC-OH and phosphide are fully mixed and dried to obtain PC-OH-P; PC and phosphide are weighed in a mass ratio of 1: (0.1-0.4).

[0010] (3) PC-OH-P was placed in a vacuum atmosphere sintering furnace for co-pyrolysis activation. When the sample temperature dropped to room temperature, it was taken out to obtain fruit and vegetable peel activated carbon PAC.

[0011] (4) The PAC was washed with a 1-3 mol / L hydrochloric acid solution to fully dissolve and remove the residual etchant and other impurities, and then washed with deionized water until the pH value of the washing water became neutral. It was then vacuum dried at 100-120 ° C until a constant weight was maintained to prepare a multi-stage activated waste fruit and vegetable peel bioporous carbon PBC with an ultra-high specific surface area.

[0012] Furthermore, the fruits and vegetables include at least one of watermelon, banana, pitaya, durian, cantaloupe, and potato that can produce waste peels. Fruit and vegetable peels are used as raw materials. This is a widely available and often overlooked waste biomass with specific types of cellulose, hemicellulose, lignin, and natural sugars. In an inert atmosphere at around 400°C, hemicellulose decomposition occurs first, producing raw carbon, water vapor, and some small-molecule organic compounds, including acidic substances, aldehydes, and ketones. Secondly, cellulose decomposition occurs, and the main product is charcoal. Subsequently, lignin and natural sugars decompose, and the main products are phenolic compounds, small-molecule organic compounds, and charcoal. Different biomass raw materials will produce different carbon structures and functional groups during the carbonization or activation process.

[0013] The iron salt includes at least one of ferrous sulfate and ferric nitrate. The iron salt undergoes physical or chemical adsorption on the surface of the PC structure at high temperature to form a stable metal-carboxylate bond or other type of bond to produce a modification effect.

[0014] In the present invention, iron salt is added and processed together with the carbon source precursor so that the metal elements are evenly distributed throughout the material, including the surface and the interior. The iron salt solution fully attached to the surface and the interior of the PC will generate different forms of iron (such as Fe 0 , Fe2O3, Fe3O4), but mainly produces lower valence Fe and Fe 0 During the initial carbonization, these iron elements are physically adsorbed on the surface or in the pores of the PC structure, and then react with the abundant hydroxyl and carboxyl groups in the fruit and vegetable peels at high temperatures to form stable metal-carboxylate bonds. On the other hand, the iron elements can chemically bond with the decomposition products of PC - phenolic compounds, stably anchoring them on the PC surface and in the pores, improving the performance of the material.

[0015] Then, in the mixture of PC, KOH and phosphide, the lower valence Fe and Fe 0It will be oxidized to generate Fe2O3 and Fe3O4. On the one hand, Fe2O3 and Fe3O will give PC catalytic performance, improve the redox reaction in the secondary activation process, and promote the subsequent full mixing and reaction of PC with KOH and phosphide; on the other hand, it will form new adsorption sites on the PBC surface, promoting the adsorption capacity of PBC for n-hexane and acetone.

[0016] Furthermore, the etchant includes at least one of potassium hydroxide, sodium hydroxide, phosphoric acid, potassium carbonate, and zinc chloride.

[0017] Furthermore, the method of fully mixing and drying is ultrasonic immersion mixing, and the specific steps are as follows:

[0018] First, dissolve a certain amount of etchant or phosphide in deionized water at a ratio of 1:(5-10), then slowly add PC into the KOH solution until it is fully soaked, and move it to an ultrasonic container for 10-30 minutes to ensure thorough mixing;

[0019] After mixing evenly, vacuum dry at 100-120°C until constant weight is maintained. When the sample temperature drops to room temperature, take it out and grind it evenly.

[0020] Furthermore, the phosphide should have a high nitrogen and phosphorus content, with a nitrogen content of 30%-50% and a phosphorus content of 10%-30%, and should be capable of generating gas at high temperatures. The phosphide may include one of melamine phosphate, ammonium phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and sodium hydrogen phosphate. Melamine phosphate is more preferred.

[0021] Furthermore, the pyrolysis activation conditions of the vacuum atmosphere sintering furnace are: in an N2 atmosphere, heating to 700-1000°C at a rate of 5-10°C / min and maintaining for 1-3 hours.

[0022] Furthermore, the bioporous carbon is used for the adsorption of VOCs; and further used for the adsorption of acetone and / or n-hexane.

[0023] Beneficial effects:

[0024] (1) The present invention uses widely available and environmentally friendly waste fruit and vegetable peels as raw materials and a phosphide rich in N and P as a modifier. A multi-stage activation method, including ultrasonic impregnation of metal salts, initial carbonization activation, and co-pyrolysis activation of the etchant and phosphide, is used to prepare a bioporous carbon with both ultra-high specific surface area and pore volume. This preparation method is simple, uses environmentally friendly raw materials, and fully utilizes fruit and vegetable peel waste during the preparation process, avoiding secondary pollution to the environment and waste of resources, thus truly "turning waste into treasure."

[0025] (2) The average specific surface area of ​​activated carbon currently on the market is about 1500m2 / g, and the average pore volume is about 0.5cm 3 / g. Compared with the activated carbon on the market, the current patent has not significantly improved the specific surface area. The bioporous carbon prepared by the above process has an ultra-micro-micro-meso-crossing pore structure and an ultra-high specific surface area. The specific surface area and pore volume are 3149m 2 / g and 1.76cm 3 / g, which is 109.9% and 252% of the activated carbon on the market, and 102.7% of the current patented maximum specific surface area, with great economic and social benefits.

[0026] (3) The ultra-micro-micro-meso-macroporous spanning pore structure and ultra-high specific surface area of ​​the bioporous carbon prepared by the present invention provide more adsorption sites for VOCs adsorbents, reduce the diffusion resistance of VOCs, and enable rapid diffusion and desorption of VOCs. Among them, the introduced metal elements such as iron give biochar catalytic ability and adsorption sites; the quadrupole effect of the introduced rich non-metallic elements such as N and P promotes PBC to have a higher affinity for VOCs. The synergistic effect of metals and non-metals enables biochar to have a higher adsorption capacity for VOCs represented by acetone and n-hexane vapor, reaching 1046 mg / g and 760 mg / g respectively, and the adsorption performance is improved by nearly 138% and 132%. In addition, the present invention can use a simple and low-cost desorption operation for repeated adsorption. After 5 adsorption-desorption cycles, the PBC adsorption capacity retains 97% of its initial adsorption capacity, with better recyclability. The bioporous carbon prepared by the present invention has excellent performance, helps to solve the dilemma of poor adsorption capacity, low efficiency, high energy consumption and short life of traditional activated carbon, is conducive to improving energy utilization, and has extremely strong economic benefits and sustainability.

[0027] (4) Compared with traditional single mixing methods such as physical grinding mixing, impregnation mixing, and stirring mixing, the ultrasonic impregnation mixing in the preparation method of the present invention can make the biochar, the etchant and the phosphide mix more fully and more efficiently. Compared with traditional activation methods such as KOH pyrolysis activation and hydrothermal activation, the co-pyrolysis activation of the KOH etchant and the phosphide in the preparation method of the present invention has higher preparation efficiency and more thorough activation. This patent makes full use of biochar prepared from green waste to achieve the purpose of carbon fixation and emission reduction, contribute to the vision of "dual carbon", and meet the current national situation and demand for carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Attachment Figure 1 SEM images of PBC and PBC-0.3;

[0029] Attachment Figure 2 The infrared spectra of PBC and PBC-0.3;

[0030] Attachment Figure 3 is the adsorption capacity of (a) acetone and (b) n-hexane vapor by PBC and PBC-X at 30 °C;

[0031] Attachment Figure 4 These are five consecutive adsorption and desorption cycles of n-hexane on PBC and PBC-0.3 at 30°C.

[0032] Attachment Figure 5 This is the process flow chart for the preparation of PBC-0.3. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0034] Example 1

[0035] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; watermelon peel carbonized material PC: potassium hydroxide: melamine phosphate are weighed in a mass ratio of 1:3:0.1, potassium hydroxide is dissolved in deionized water in a mass ratio of 1:10, PC is soaked and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until constant weight is maintained, and PC-OH is taken out and ground evenly; melamine phosphate is dissolved in deionized water in a mass ratio of 1:10 The PC-OH was infiltrated and mixed, and ultrasonicated for 30 minutes. After being taken out, it was vacuum dried at 105°C until it maintained a constant weight, and then taken out and ground evenly to obtain PC-OH-P-0.1; PC-OH-P-0.1 was placed in a vacuum atmosphere sintering furnace for pyrolysis activation, and heated to 800°C at a heating rate of 5°C / min in a high-purity nitrogen atmosphere for activation for 1 hour. When the sample temperature dropped to room temperature, it was taken out to obtain watermelon peel activated carbon PAC-0.1; PAC-0.1 was washed with 2 mol / L hydrochloric acid solution with a pH of 4 to fully dissolve and remove residual potassium hydroxide and other impurities, and then washed with deionized water until the pH value of the washing water became neutral, and then vacuum dried at 105°C until it maintained a constant weight to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBC-0.1.

[0036] Example 2

[0037] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; PC: potassium hydroxide: melamine phosphate are weighed in a mass ratio of 1:3:0.2, potassium hydroxide is dissolved in deionized water in a mass ratio of 1:10, PC is soaked and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until constant weight is maintained, and PC-OH is taken out and ground evenly; melamine phosphate is dissolved in deionized water in a mass ratio of 1:10, The PC-OH was infiltrated and mixed, and ultrasonicated for 30 minutes. After being taken out, it was vacuum dried at 105°C until it maintained a constant weight, and then taken out and ground evenly to obtain PC-OH-P-0.2; PC-OH-P-0.2 was placed in a vacuum atmosphere sintering furnace for pyrolysis activation, heated to 800°C at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and activated for 1 hour. When the sample temperature dropped to room temperature, it was taken out to obtain watermelon peel activated carbon PAC-0.2; PAC-0.2 was washed with 2 mol / L hydrochloric acid solution with a pH of 4 to fully dissolve and remove residual potassium hydroxide and other impurities, and then washed with deionized water until the pH value of the washing water became neutral, and then vacuum dried at 105°C until it maintained a constant weight to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBC-0.2.

[0038] Example 3

[0039] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; PC: potassium hydroxide: melamine phosphate are weighed in a mass ratio of 1:3:0.3, potassium hydroxide is dissolved in deionized water in a mass ratio of 1:10, PC is soaked and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until constant weight is maintained, and PC-OH is taken out and ground evenly; melamine phosphate is dissolved in deionized water in a mass ratio of 1:10, The PC-OH was infiltrated and mixed, and ultrasonicated for 30 minutes. After being taken out, it was vacuum dried at 105°C until it maintained a constant weight, and then taken out and ground evenly to obtain PC-OH-P-0.3; PC-OH-P-0.3 was placed in a vacuum atmosphere sintering furnace for pyrolysis activation, heated to 800°C at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and activated for 1 hour. When the sample temperature dropped to room temperature, it was taken out to obtain watermelon peel activated carbon PAC-0.3; PAC-0.3 was washed with 2 mol / L hydrochloric acid solution with a pH of 4 to fully dissolve and remove residual potassium hydroxide and other impurities, and then washed with deionized water until the pH value of the washing water became neutral, and then vacuum dried at 105°C until it maintained a constant weight to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBC-0.3.

[0040] Example 4

[0041] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; PC: potassium hydroxide: melamine phosphate are weighed in a mass ratio of 1:3:0.4, potassium hydroxide is dissolved in deionized water in a mass ratio of 1:10, PC is soaked and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until constant weight is maintained, and PC-OH is taken out and ground evenly; melamine phosphate is dissolved in deionized water in a mass ratio of 1:10, The PC-OH was infiltrated and mixed, and ultrasonicated for 30 minutes. After being taken out, it was vacuum dried at 105°C until it maintained a constant weight, and then taken out and ground evenly to obtain PC-OH-P-0.4; PC-OH-P-0.4 was placed in a vacuum atmosphere sintering furnace for pyrolysis activation, heated to 800°C at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and activated for 1 hour. When the sample temperature dropped to room temperature, it was taken out to obtain watermelon peel activated carbon PAC-0.4; PAC-0.4 was washed with 2 mol / L hydrochloric acid solution with a pH of 4 to fully dissolve and remove residual potassium hydroxide and other impurities, and then washed with deionized water until the pH value of the washing water became neutral, and then vacuum dried at 105°C until it maintained a constant weight to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBC-0.4.

[0042] Comparative Example 1 (direct carbonization of watermelon rind, unmodified)

[0043] Preparation method: First, the discarded peel of commercially available watermelon is removed from the pulp, washed, dried, and crushed for pretreatment, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 800°C for activation for 1 hour. When the sample temperature drops to room temperature, it is taken out to obtain watermelon peel activated carbon PAC.

[0044] Comparative Example 2 (no phosphide added)

[0045] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; PC: potassium hydroxide are weighed in a mass ratio of 1:3, potassium hydroxide is dissolved in deionized water in a ratio of 1:10, PC is soaked and mixed, and ultrasonicated for 30 minutes. After being taken out, it is vacuum dried at 105°C until Maintain constant weight, take out and grind evenly to obtain PC-OH; place PC-OH in a vacuum atmosphere sintering furnace for pyrolysis activation, heat to 800℃ at a heating rate of 5℃ / min in a high-purity nitrogen atmosphere for activation for 1h, and take out when the sample temperature drops to room temperature to obtain watermelon peel activated carbon PAC; wash PAC with 2mol / L hydrochloric acid solution with a pH of 4 to fully dissolve and remove residual potassium hydroxide and other impurities, then wash with deionized water until the pH value of the washing water becomes neutral, and then vacuum dry at 105℃ until constant weight is maintained to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBC.

[0046] Comparative Example 3 (without addition of phosphide and potassium hydroxide)

[0047] Preparation method: First, the discarded peel of commercially available watermelon is removed from the pulp, washed, dried, and crushed for pretreatment, ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 800°C for activation for 1 hour. When the sample temperature drops to room temperature, it is taken out to obtain watermelon peel activated carbon PACP.

[0048] Comparative Example 4 (no metal salt added)

[0049] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing, and then placed in a vacuum atmosphere sintering furnace for carbonization activation, and heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PCP; PCP: potassium hydroxide: melamine phosphate are weighed in a mass ratio of 1:3:0.3, potassium hydroxide is dissolved in deionized water in a ratio of 1:10, PCP is infiltrated and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until constant weight is maintained, and PCP-OH is taken out and ground evenly; melamine phosphate is dissolved in deionized water in a ratio of 1:10, PCP-OH is infiltrated and mixed , and ultrasonicated for 30 minutes, then taken out and vacuum dried at 105°C until constant weight was maintained, taken out and ground evenly to obtain PCP-OH-P-0.3; PCP-OH-P-0.3 was placed in a vacuum atmosphere sintering furnace for pyrolysis activation, heated to 800°C at a heating rate of 5°C / min in a high-purity nitrogen atmosphere and activated for 1 hour, and taken out when the sample temperature dropped to room temperature to obtain watermelon peel activated carbon PACP-0.3; PACP-0.3 was washed with 2 mol / L hydrochloric acid solution to fully dissolve and remove residual potassium hydroxide and other impurities, and then washed with deionized water until the pH value of the washing water became neutral, and then vacuum dried at 105°C until constant weight was maintained to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBCP-0.3.

[0050] Comparative Example 5 (Changing the Phosphide to Sodium Hydrogen Phosphate)

[0051] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is ultrasonically immersed in a 0.3M ferric nitrate solution for 5 hours, and then placed in a vacuum atmosphere sintering furnace for carbonization activation. It is heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; PC: potassium hydroxide: sodium hydrogen phosphate are weighed in a mass ratio of 1:3:0.3, potassium hydroxide is dissolved in deionized water in a mass ratio of 1:10, PC is soaked and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until constant weight is maintained, and PC-OH is taken out and ground evenly; sodium hydrogen phosphate is dissolved in deionized water in a mass ratio of 1:10, PC-OH is soaked and mixed, and ultrasonicated for 30 minutes. The watermelon peel activated carbon PACN-0.4 was obtained by mixing the watermelon peel and ultrasonicating the watermelon peel for 30 minutes. The watermelon peel activated carbon PACN-0.4 was obtained by vacuum drying at 105°C until the weight was constant. The watermelon peel activated carbon PACN-0.4 was obtained by vacuum drying at 105°C until the weight was constant. The watermelon peel activated carbon PACN-0.4 was obtained by heating the watermelon peel to 800°C at a heating rate of 5°C / min in a high-purity nitrogen atmosphere. The activated carbon PACN-0.4 was obtained by washing the PACN-0.3 with a 2 mol / L hydrochloric acid solution with a pH of 4 to fully dissolve and remove residual potassium hydroxide and other impurities. The activated carbon PACN-0.4 was obtained by vacuum drying the watermelon peel at 105°C until the weight was constant. The activated carbon PACN-0.4 was obtained by vacuum drying the watermelon peel at 105°C until the weight was constant.

[0052] Comparative Example 6 (changing the order of carbon source modification: adding metal salt first and then adding phosphide and potassium hydroxide)

[0053] Preparation method: First, the commercially available watermelon discarded peel is cleaned of the pulp, and then pre-treated by washing, drying, and crushing. It is then placed in a vacuum atmosphere sintering furnace for carbonization activation, and heated at a heating rate of 5°C / min in a high-purity nitrogen atmosphere, and the temperature is maintained at 400°C for 1 hour. After cooling to room temperature, it is taken out to obtain watermelon peel carbonized material PC; PC: potassium hydroxide: melamine phosphate are weighed in a mass ratio of 1:3:0.3, potassium hydroxide is dissolved in deionized water in a ratio of 1:10, PC is infiltrated and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until a constant weight is maintained, and then taken out and ground evenly to obtain PC-OH; melamine phosphate is dissolved in deionized water in a ratio of 1:10, PC-OH is infiltrated and mixed, and ultrasonicated for 30 minutes, and then taken out and vacuum dried at 105°C until a constant weight is maintained, and then taken out and ground evenly to obtain PC-OH-P-0.3; PC-OH-P -0.3 was placed in a vacuum atmosphere sintering furnace for pyrolysis activation, and heated to 800℃ at a heating rate of 5℃ / min for activation for 1h in a high-purity nitrogen atmosphere. The sample was taken out when the temperature dropped to room temperature to obtain watermelon peel activated carbon PAC-0.3; PC-OH-P-0.3 was placed in a 0.3M ferric nitrate solution for ultrasonic immersion for 5h, and then placed in a vacuum atmosphere sintering furnace for pyrolysis activation, and heated to 400℃ at a heating rate of 5℃ / min for activation for 1h in a high-purity nitrogen atmosphere. The sample was taken out when the temperature dropped to room temperature to obtain watermelon peel activated carbon PAC-0.3-Fe; PAC-0.3-Fe was washed with 2mol / L hydrochloric acid solution to fully dissolve and remove residual potassium hydroxide and other impurities, and then washed with deionized water until the pH value of the washing water became neutral, and then vacuum dried at 105℃ until constant weight was maintained to prepare multi-stage activated waste watermelon peel bioporous carbon, named PBC-0.3-Fe.

[0054] The SEM morphology of Example 3 and Comparative Examples 1-6 was observed. Figure 1 SEM images of Example 3 and Comparative Examples 1-6 are shown.

[0055] By the attached Figure 1 The results show that PAC and PBC are mainly composed of large irregular blocky particles with rough and uneven surfaces and rich pore structures. PBC has richer pore structures. PBCP-0.3 is mainly composed of some rough blocky particles and some smooth flakes, while PBCP-0.3 has more smooth flakes. This difference is attributed to the following reasons: ① The iron salt solution fully attached to the surface and inside of PC will generate different forms of iron (such as Fe 0 , Fe2O3, Fe3O4), but mainly produces lower valence Fe and Fe 0During the initial carbonization, these iron elements are physically adsorbed on the surface or pores of the PC structure, and then react with the abundant hydroxyl and carboxyl groups of fruit and vegetable peels at high temperature to form stable metal-carboxylate bonds; moreover, the iron elements can chemically bond with the decomposition products of PC - phenolic compounds, and stably anchored on the surface and pores of PC. Subsequently, in the mixture of PC, KOH and phosphide, the lower valence Fe and Fe 0 Oxidation produces Fe2O3 and Fe3O4, which impart catalytic properties to PC, enhance redox reactions during secondary activation, and form new adsorption sites on the PBC surface, promoting its adsorption capacity for n-hexane and acetone. ② KOH activation causes severe etching and modification of the surface. ③ The pyrolysis of melamine phosphate produces some H3PO4 and releases a large amount of gas, further activating and modifying the PBC-0.3 morphology and optimizing its pore structure.

[0056] Fourier infrared test was carried out on Example 3 and Comparative Example 1. Figure 2 The infrared spectra of PBC and PBC-0.3 are shown.

[0057] By the attached Figure 2 The spectral trends of PBC and PBC-0.3 are similar, with 3441 cm -1 The peak at 1510 cm is caused by OH stretching vibration, while the peak at 1510 cm -1 The peak at 1100 cm is caused by C=N, which is attributed to the pyrolysis and cross-linking reaction between the rich N content of FR-MP and activated carbon. -1 A sharp and intense peak was observed at 1100 cm-1, which is attributed to the peak of CC stretching vibration. It is worth noting that PBC-0.3 shows stronger group characteristics than PBC. This is because for PBC-0.3, the peak at 1100 cm-1 is -1 In addition to the C—C stretching vibration, there is also the PO bond stretching vibration generated by FR-MP during the pyrolysis of porous carbon. FTIR spectroscopy results show that FR-MP is successfully incorporated into the carbon skeleton of activated carbon.

[0058] The specific surface area, total pore volume, micropore area, and n-hexane adsorption capacity of the bioporous carbons produced in Examples 1-4 were measured and compared with those of Comparative Examples 1-6. Before the adsorption test, the test samples were heated to 100-150°C for 30-60 minutes to remove residual gas in the pores. After cooling to room temperature, n-hexane adsorption was achieved by bubbling. The results are shown in Table 1.

[0059] Table 1. Performance test results of the composite materials prepared in Examples 1-4 and Comparative Examples

[0060]

[0061] As shown in Table 1, the bioporous carbons prepared in Examples 1-4 all have a large number of micropores. The specific surface area of ​​PBC-X (X = 0.1, 0.2, 0.3, 0.4) shows a trend of first increasing and then decreasing with the increase of the mass ratio of melamine phosphate. Among them, PBC-0.3 shows the best physical structure properties, with a specific surface area and pore volume of 3149 m 2 / g and 1.76cm 3 / g. However, when the mass ratio reaches 0.4, the specific surface area of ​​PBC-0.4 begins to decline (2381m 2 / g). Comparing PBC-0.1 and PBC-0.4, it is found that the two samples have similar specific surface areas, but the total pore volume of PBC-0.4 is much larger than that of PBC-0.1 (1.60 cm 3 / g>1.38cm 3 / g), which is attributed to the further etching and conversion of the micropores induced by the addition of excessive melamine phosphate into mesopores. The results show that the addition of melamine phosphate helps to further optimize the pore structure of activated carbon.

[0062] The adsorption of acetone and n-hexane vapor by the bioporous carbon prepared in Examples 1-4 was tested at 30°C and compared with Comparative Examples 1-6. Figure 3 Shown are the adsorption capacities of (a) acetone and (b) n-hexane vapor by PBC and PBC-X at 30 °C.

[0063] Table 2. Adsorption capacity of (a) acetone and (b) n-hexane vapor of the composite materials prepared in Examples 1-4 and Comparative Example at 30°C

[0064] serial number Sample name Acetone adsorption capacity mg / g n-Hexane adsorption capacity mg / g Example 1 PBC-0.1 649 482 Example 2 PBC-0.2 807 674 Example 3 PBC-0.3 1046 760 Example 4 PBC-0.4 723 498 Comparative Example 1 PAC 336 129 Comparative Example 2 PBC 440 327 Comparative Example 3 PACP 597 463 Comparative Example 4 PBCP-0.3 786 597 Comparative Example 5 PBCN-0.3 942 751 Comparative Example 6 PBC-0.3-Fe 866 683

[0065] By the attached Figure 3The results show that the adsorption capacities of acetone and n-hexane vapors on PBC are relatively low, at 440 mg / g for acetone and 327 mg / g for n-hexane vapor, respectively. However, after modification with melamine phosphate, the adsorption capacities of both acetone and n-hexane vapors on the porous carbon were significantly increased. PBC-0.3 reached its maximum adsorption capacities for both adsorbates, reaching 1046 mg / g and 760 mg / g, respectively, representing increases of nearly 138% and 132% in adsorption performance. These results indicate that the large surface area of ​​PBC-0.3 provides more adsorption sites for the adsorbate, enhancing the adsorption performance of the porous carbon for VOCs. Comparing the adsorption curves of PBC-X for acetone and n-hexane vapors, the prepared PBC-X exhibits a higher adsorption capacity for acetone and reaches adsorption saturation more rapidly. This is partly because acetone molecules have a smaller molecular dynamic diameter than n-hexane molecules, allowing for the adsorption of more acetone molecules within the same pore size. On the other hand, smaller acetone molecules have less diffusion resistance and can quickly pass through the mesopores of the porous carbon and enter the pores for adsorption. PBC-X modified with melamine phosphate shows potential as an excellent adsorbent.

[0066] Five cycles of adsorption and desorption experiments on n-hexane vapor were conducted on Example 3 and Comparative Example 1 at 30°C. Figure 4 Five consecutive adsorption and desorption cycles of n-hexane on PBC and PBC-0.3 at 30 °C are shown.

[0067] By the attached Figure 4 The results show that after five adsorption-desorption cycles, the adsorption capacities of both PBC and PBC-0.3 decreased slightly. However, PBC-0.3 retained 97% of its initial adsorption capacity after the fifth adsorption cycle, while PBC retained only 94% and required a longer desorption time. This is because the micropores of PBC-0.3 allow the adsorbate to easily desorb from the adsorption sites and be released from the pores after absorbing the escape heat energy. This demonstrates that the prepared bioporous carbon has superior recyclability.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing multi-stage activated bioporous carbon from discarded fruit and vegetable peels, characterized in that: The preparation method comprises the following steps: (1) After removing the pulp from the discarded fruit and vegetable peels, they were pre-treated by washing, drying, and crushing, and ultrasonically immersed in a 0.1-0.5M iron salt solution for 4-10 hours. The samples were then placed in a vacuum atmosphere sintering furnace and heated to 400-500°C at a rate of 5-10°C / min in an N2 atmosphere and maintained for 1-3 hours. The samples were taken out when the temperature dropped to room temperature to obtain the carbonized and activated fruit and vegetable peel carbonized material PC. (2) PC and an etchant are fully mixed in a mass ratio of 1:(1-5), and dried to obtain PC-OH; (3) fully mixing PC-OH and phosphide, and drying to obtain PC-OH-P; (4) PC-OH-P was placed in a vacuum atmosphere sintering furnace for co-pyrolysis activation, and the sample was taken out when the temperature dropped to room temperature to obtain fruit and vegetable peel activated carbon PAC; (5) The PAC was washed with hydrochloric acid solution, and then washed with deionized water until the pH value of the washing water became neutral, and then dried to prepare a multi-stage activated waste fruit and vegetable peel bioporous carbon PBC with an ultra-high specific surface area; the specific surface area of ​​the porous carbon PBC was 2000-4000m 2 / g, pore volume of 1.3~1.8cm 3 / g -1 .

2. The preparation method according to claim 1, characterized in that The fruits and vegetables include at least one of watermelon, banana, dragon fruit, durian, cantaloupe and potato that can produce waste peels.

3. The preparation method according to claim 1, characterized in that The iron salt includes at least one of ferrous sulfate and ferric nitrate.

4. The preparation method according to claim 1, characterized in that The etchant includes at least one of potassium hydroxide, sodium hydroxide, phosphoric acid, potassium carbonate, and zinc chloride.

5. The preparation method according to claim 1, characterized in that The specific steps of fully mixing and drying are as follows: First, dissolve the etchant or phosphide in deionized water, then slowly add PC to the etchant solution or PC-OH to the phosphide solution until fully soaked, then transfer to an ultrasonic container and perform ultrasonication for 10-30 minutes to ensure thorough mixing. After mixing evenly, vacuum dry at 100-120°C until constant weight is maintained. When the sample temperature drops to room temperature, take it out and grind it evenly.

6. The preparation method according to claim 1, characterized in that The phosphide includes one of melamine phosphate, ammonium phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and sodium hydrogen phosphate; the mass ratio of PC to the phosphide is 1:(0.1-0.4).

7. The preparation method according to claim 1, characterized in that The pyrolysis activation conditions of the vacuum atmosphere sintering furnace in step (4) are: in an N2 atmosphere, heating to 700-1000°C at a rate of 5-10°C / min and maintaining for 1-3 hours.

8. Application of multi-stage activated waste fruit and vegetable peel bioporous carbon prepared by the method according to any one of claims 1 to 7, characterized in that: The bioporous carbon is used for adsorption of VOCs.

9. Application of multi-stage activated waste fruit and vegetable peel bioporous carbon prepared by the method according to any one of claims 1 to 7, characterized in that: The bioporous carbon is used for adsorption of acetone and / or n-hexane.

Images