Fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation and preparation method thereof
A high specific surface area and hydrophobic fruit peel carbon aerogel was prepared by low-temperature plasma synergistic micro-metal activation. This method solves the problems of lengthy process, poor pore structure and hydrophilicity in the preparation of traditional fruit peel carbon aerogels, and achieves efficient and environmentally friendly VOCs adsorption effect, which is suitable for industrial waste gas treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-13
- Publication Date
- 2026-04-03
AI Technical Summary
Existing technologies for preparing fruit peel-based carbon aerogels suffer from problems such as lengthy process flow, reliance on high-pressure equipment, poor pore structure, and limited adsorption capacity due to hydrophilicity. Furthermore, traditional chemical activation methods cause environmental pollution and equipment corrosion.
A low-temperature plasma-assisted trace metal activation method was adopted to prepare a fruit peel carbon aerogel adsorbent with high specific surface area, well-developed microporous structure and hydrophobicity by mixing fruit peel particles with transition metal nitrate solution, followed by low-temperature plasma modification, freeze drying, high-temperature carbonization and acid washing.
This method enables the large-scale production of fruit peel carbon aerogel, improves the ability to capture volatile organic compounds, solves the problems of poor pore structure and hydrophilicity in traditional methods, reduces production costs, and has good reusability and industrial application prospects.
Smart Images
Figure CN121775823A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of VOCs adsorbent technology, and in particular to a fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation and its preparation method. Background Technology
[0002] Volatile organic compounds (VOCs), as a typical class of air pollutants, pose a serious threat to the ecological environment and public health due to their widespread toxicity and carcinogenicity. Among numerous end-of-pipe treatment technologies, adsorption is considered one of the most promising technical routes for achieving deep purification of VOCs due to its high efficiency, relatively low energy consumption, and ease of operation.
[0003] Among various adsorbents, carbon aerogels, with their unique physical structural advantages—including low density, high specific surface area, tunable morphology, and well-developed pore structure—exhibit enormous application potential and have become an ideal choice for VOCs adsorption materials. Currently, utilizing widely available, low-cost, and renewable environmentally friendly biomass waste as precursors for the targeted conversion into high-performance carbon materials is an important research direction for realizing the resource utilization of solid waste and reducing the production cost of adsorbents. Among numerous biomass raw materials, waste fruit peels have attracted much attention due to their large annual yield, high carbon content, and natural pectin content, making them an ideal raw material for preparing carbon aerogels.
[0004] However, most existing studies employ a hydrothermal method combined with freeze-drying to process fruit peels to prepare three-dimensional fruit peel-based carbon aerogels. This process suffers from several problems: the entire process is time-consuming and heavily reliant on complex high-pressure heating equipment, significantly hindering its large-scale production and widespread application. Furthermore, fruit peel-based carbon aerogels prepared using this traditional process typically exhibit hydrophilic properties and have poor pore structure, particularly a low proportion of micropores crucial for VOC adsorption, resulting in limited ability to capture small gaseous pollutants.
[0005] While traditional chemical activation methods (such as using corrosive reagents like KOH and H3PO4) can effectively increase the specific surface area and porosity of materials, the harsh activation conditions and subsequent cleaning processes also bring environmental burdens and equipment corrosion problems. Therefore, developing a green, efficient, and mild novel modification technology to prepare fruit peel-based carbon aerogels with high specific surface area, well-developed microporous structure, and excellent hydrophobicity is of great significance. Summary of the Invention
[0006] In view of this, the present invention provides a fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation and its preparation method. This invention combines low-temperature plasma technology with trace metal activators to achieve a synergistic effect. The process is simple, eliminates the need for high-pressure heating equipment required by traditional hydrothermal methods, and utilizes widely available and inexpensive raw materials, realizing the resource utilization of agricultural waste and showing good prospects for industrial application.
[0007] The first aspect of this invention is to provide a fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation. It is prepared by fruit peel particles through transition metal nitrate activation, low-temperature plasma modification, freeze drying, high-temperature carbonization and acid washing. The surface of the adsorbent contains oxygen-containing functional groups such as hydroxyl, carboxyl and aldehyde groups. After acid washing, the metal oxides are removed, while the pore structure formed by the metal oxides is retained. The fruit peel is at least one of grapefruit peel, passion fruit peel, and banana peel, and the transition metal is at least one of manganese, iron, cobalt, nickel, copper, and zinc. The adsorbent is spherical with a BET specific surface area of 647.82-897.64 m². 2 / g, the pore volume of the adsorbent is 0.32-0.49 cm³. 3 / g, with an average pore size of 1.64-1.89 nm and a microporous specific surface area of 567.40-804.20 m². 2 / g, micropore volume is 0.28-0.40 cm³. 3 / g, with a micropore content of 87.6%-90.6% and a water contact angle of 134.9°-147.6°.
[0008] The second aspect of this invention is to provide a method for preparing the above-mentioned fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation, comprising the following steps: S1. Dry and crush the fruit peel to produce uniform fruit peel granules; S2. Mix the fruit peel particles with a transition metal nitrate solution and stir for 5-30 minutes until a gel is formed. The fruit peel particles are directly mixed with deionized water and stirred at room temperature to form a self-forming gel. The gelation driving force of the self-forming gel depends on the pectin component in the fruit peel particles and the interaction between the powder particles and the solvent droplets. S3. Place the gel-like fruit peel in an air dielectric barrier discharge low-temperature plasma modification device. In an air environment, the discharge voltage is 30-60 V, the discharge current is 2.0-2.3 A, and the discharge time is 5-20 min. S4. Fill the low-temperature plasma-treated material into a spherical silicone mold, freeze-dry it in a refrigerator for 0.5-2 hours, and then freeze-dry it in a vacuum freeze dryer for 24-48 hours. S5. Place the freeze-dried material in a tube furnace and carbonize it at high temperature under N2 atmosphere to obtain lightweight carbon aerogel balls. S6. Place the carbonized carbon aerogel balls in an HCl solution, and evacuate the solution to fully immerse the lightweight carbon aerogel balls in the HCl solution. After washing with deionized water until neutral, place them in a forced-air drying oven to dry, and finally obtain the fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation.
[0009] The fruit peel mentioned in step S1 is at least one of grapefruit peel, passion fruit peel, and banana peel, the particle size of the fruit peel is 0.10-0.25 mm, and the transition metal nitrate is at least one of manganese nitrate tetrahydrate, ferric nitrate hexahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate hexahydrate, and zinc nitrate hexahydrate.
[0010] The concentration of the transition metal nitrate in step S2 is 2.50 × 10⁻⁶. -3 -8.50×10 -3 The mass ratio of fruit peel particles to transition metal nitrate solution is 1:(5-8).
[0011] The working atmosphere of the low-temperature plasma in step S3 is air, with a relative humidity range of 0-100%, the discharge voltage is 30-60 V, the processing time is 5-20 min, and the mass of material modified by the low-temperature plasma each time is 5-10 g.
[0012] In step S5, the temperature is increased to the carbonization temperature at a rate of 5 °C / min under a N2 atmosphere. The carbonization temperature is 800-900 °C, the carbonization time is 60 min, the HCl solution concentration is 0.1-2.0 mol / L, the hydrochloric acid soaking time is 6-12 h, and the drying temperature is 50-100 °C for 6-48 h.
[0013] A third aspect of this invention is to provide the application of the above-mentioned fruit peel carbon aerogel in VOCs adsorption, wherein the volatile organic compound is at least one of p-xylene, dimethyl disulfide, ethyl acetate, acetone, and toluene. The fruit peel carbon aerogel VOCs adsorbent adsorbs volatile organic compounds in a high humidity environment, and after multiple cycles of use, the adsorption amount remains basically unchanged, demonstrating good reusability.
[0014] This invention involves directly mixing fruit peel particles—namely, grapefruit peel (PP), passion fruit peel (PFP), and banana peel (BP)—with deionized water until homogeneous. Stirring at room temperature for 2-10 minutes allows for the formation of a self-forming gel. The driving force behind this gelation relies on the abundant pectin content in the fruit peel particles and the interaction between the powder particles and solvent droplets. In particular, the fruit peel carbon aerogel obtained by directly mixing fruit peel particles with water, followed by vacuum freeze-drying and direct pyrolysis, retains the shape of the freeze-dried fruit peel. This method is simple to operate and saves time in preparing fruit peel carbon aerogels.
[0015] Low-temperature plasma (NTP) technology can generate high-energy electrons, ultraviolet photons, and various active particles (such as ·OH, O·, and ·O2) during atmospheric pressure gas discharge. - Non-equilibrium plasmas (such as O3, etc.). Grapefruit peel contains a large amount of cellulose. Many studies have shown that NTPs have a good bond-breaking effect on the C-C and CH bonds of organic compounds, and in the presence of active O·, they help to generate oxygen-containing functional groups such as hydroxyl, carboxyl, and aldehyde groups.
[0016] The high-energy active particles generated during NTP treatment can effectively break the C-C and CH bonds of cellulose in the pericarp, introducing a large number of oxygen-containing functional groups such as hydroxyl, carboxyl, and aldehyde groups onto the material surface. This invention uses a gel-state pericarp for NTP treatment, where the abundant H2O molecules generate rich active H·, O·, N·, and e· particles under high-energy bombardment. These active particles attack the chemical bonds in the fruit peel, forming more oxygen-containing functional groups. During the subsequent high-temperature carbonization process, these oxygen-containing functional groups undergo thermal decomposition, producing a large number of CO, CO2 and other gas molecules as gasifying agents. These molecules then etch and create pores within the carbon matrix, thereby significantly increasing the specific surface area and porosity of the material.
[0017] Transition metal nitrates play a dual role in this invention. First, during carbonization, the transition metal nitrates decompose to form corresponding metal oxides (such as MnO, Mn2O3, MnO2, or cobalt oxides), while simultaneously releasing NO. x The rapid escape of gases etches numerous micropores and mesoporous structures into the carbon matrix. Secondly, the resulting metal oxide nanoparticles, dispersed within the carbon matrix, act as a supporting framework, effectively preventing the carbon framework from shrinking and stacking at high temperatures, thus maintaining and strengthening the porous structure of the aerogel. In subsequent acid washing, these metal oxides are removed, leaving abundant pores in situ, further increasing the specific surface area and pore volume of the material.
[0018] The synergistic effect of NTP modification and metal activators is key to this invention. Transition metal elements possess excellent conductivity, promoting uniform current transfer during NTP treatment, resulting in a more uniform and intense modification of the metal-containing fruit peel gel in the plasma field. Experimental data show that after doping with Mn(NO3)2·4H2O, the effective output power significantly increased from 47.20 W to 57.99 W during NTP treatment, and after doping with Co(NO3)2·6H2O, it increased to 54.30 W. The enhanced energy input excites more active particles, generating richer oxygen-containing functional groups on the fruit peel surface. These functional groups play a stronger role as pore-forming agents in the subsequent carbonization process. Furthermore, the process sequence of first doping with metal and then performing NTP modification is crucial, ensuring uniform distribution of metal ions in the fruit peel matrix and guaranteeing the formation of a uniform and well-developed pore structure during subsequent carbonization and acid washing processes.
[0019] Different transition metals have varying effects on material properties. Among manganese-based adsorbents, MnO2 possesses multiple crystal structures, including α, β, γ, and δ forms. Its unique hierarchical structure facilitates the adsorption of aromatic VOC molecules with conjugated structures, such as p-xylene. Cobalt-based adsorbents exhibit superior adsorption performance after acid washing, primarily due to the larger atomic radius of Co compared to Mn. Acid washing removes cobalt oxides, leaving larger pores on the material surface, thus providing a greater adsorption capacity.
[0020] The fruit peel carbon aerogel adsorbent prepared in this invention exhibits excellent hydrophobic properties, with a water contact angle reaching 134.9°-147.6°. This highly hydrophobic surface characteristic allows the material to maintain excellent adsorption performance even in high humidity environments, as water molecules struggle to compete for hydrophobic adsorption sites. The well-developed microporous structure of the material provides numerous adsorption sites for VOCs molecules, and the hydrophobic nature of the micropores further enhances the selective adsorption capacity for organic pollutants. Adsorption experiments on different types of VOCs show that the material has the highest adsorption capacity for sulfur-containing VOCs (dimethyl disulfide), because sulfur atoms can generate stronger dipole interactions, coordination bonds, and hydrogen bonds with the adsorbent surface. For oxygen-containing VOCs (acetone), its active oxygen atoms also generate strong interactions with the material surface. For aromatic VOCs (toluene, para-xylene), adsorption is mainly achieved through van der Waals forces and π-π interactions. This broad-spectrum adsorption capacity for different types of VOCs makes the adsorbent prepared in this invention a promising candidate for practical industrial waste gas treatment.
[0021] Cyclic performance tests demonstrate that the adsorbent of this invention exhibits excellent structural stability and reusability. This superior cycling performance is attributed to the material's high degree of carbonization and stable microporous structure, preventing significant collapse or blockage of the pore structure during desorption and regeneration. Furthermore, the material's hydrophobic properties help reduce the impact of moisture on the pore structure, maintaining the stability of its adsorption performance.
[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention allows for the direct mixing of fruit peel particles with deionized water, followed by stirring at room temperature to form a self-forming gel. This eliminates the need for high-pressure heating equipment required by traditional hydrothermal methods, avoiding the problems of lengthy processes and high equipment investment. It significantly shortens preparation time, reduces production costs, and facilitates large-scale production and industrial application.
[0023] This invention uses low-temperature plasma technology to modify fruit peel gel, which can be completed under normal pressure. This avoids the environmental pollution and equipment corrosion problems caused by the use of highly corrosive reagents such as KOH and H3PO4 in traditional chemical activation methods. It achieves green, efficient and mild material modification, which is in line with the development direction of environmentally friendly processes.
[0024] This invention effectively introduces a large number of oxygen-containing functional groups into the surface of fruit peel through low-temperature plasma modification. These functional groups decompose during the subsequent carbonization process to produce gases such as CO and CO2, which act as gasifying agents to etch and create pores inside the carbon matrix. This effectively solves the problems of poor pore structure and low micropore ratio in traditional fruit peel carbon aerogels, significantly improves the specific surface area and porosity of the material, and significantly enhances the ability to capture gaseous small molecule VOCs pollutants.
[0025] This invention combines low-temperature plasma technology with trace metal activators to achieve a synergistic effect. The conductivity of transition metal elements promotes the uniform transmission of current in the plasma field, enhancing the modification effect; the metal oxides produced by the decomposition of metal nitrates during carbonization serve as a supporting framework, preventing the carbon framework from shrinking and stacking, while the gases released during decomposition etch numerous micropores and mesopores in the carbon matrix; after acid washing removes the metal oxides, abundant pores are left in situ, further increasing the specific surface area and pore volume, solving the problem that using metal activators alone requires high concentrations and harsh conditions.
[0026] The fruit peel carbon aerogel adsorbent prepared by this invention exhibits excellent hydrophobic properties, effectively solving the problem that traditional fruit peel carbon aerogels exhibit hydrophilic characteristics and their adsorption performance decreases significantly under high humidity environments. The highly hydrophobic surface of the material makes it difficult for water molecules to compete for adsorption sites, ensuring stable VOCs adsorption performance under different relative humidity conditions.
[0027] The adsorbent prepared by this invention has a well-developed microporous structure, providing a large number of adsorption sites for VOCs molecules. The material exhibits good adsorption performance for different types of VOCs (sulfur-containing VOCs, oxygen-containing VOCs, aromatic VOCs, etc.), and has broad application prospects.
[0028] The process sequence of this invention, which involves first doping with metal and then modifying with low-temperature plasma, achieves a uniform distribution of metal ions in the fruit peel matrix. This ensures that the subsequent carbonization and pickling processes form a uniform and well-developed pore structure, solving the problem of unstable material properties caused by uneven distribution of activators in traditional processes and improving the consistency of product quality.
[0029] The adsorbent prepared by this invention exhibits excellent structural stability and reusability. The high degree of carbonization and stable microporous structure of the material prevent significant collapse or blockage of the pore structure during multiple adsorption-desorption cycles, solving the problems of poor recyclability and frequent replacement required by traditional adsorbents, thus reducing operating costs and improving economic efficiency.
[0030] This invention uses waste fruit peels as raw materials to realize the resource utilization of solid waste, transforming agricultural waste into high-value-added functional materials. It not only solves the problem of fruit peel waste disposal but also reduces the production cost of adsorbents, which is in line with the concept of sustainable development. Attached Figure Description
[0031] The present invention will be further described below with reference to the accompanying drawings.
[0032] Figure 1 This is a schematic diagram of the morphology of the fruit peel carbon aerogel product in Example 1 of the present invention, wherein: (A) a photo of PP@Mn-NTP-CA-H before carbonization; (B) a photo of PP@Mn-NTP-CA-H after carbonization; and (C) a picture of PP@Mn-NTP-CA-H placed on grass. Figure 2 The following are performance characterization diagrams of different adsorbents of the present invention, wherein: (A) represents the performance of different samples at relative humidity (RH). air (A) is a comparison of the adsorption kinetics curves of para-xylene (PX) at 100% concentration; (B) is the adsorption curve of PX by PP@Mn-NTP-CA-H in Example 1 of the present invention under different relative humidity conditions (0%, 20%, 40%, 60%, 80%, 100%); (C) is a cycle performance graph of PP@Mn-NTP-CA-H in Example 1 of the present invention, showing the change in adsorption amount after five adsorption-desorption cycles; (D) is a bar chart comparing the adsorption amounts of five different types of VOCs by PP@Mn-NTP-CA-H in Example 1 of the present invention. Figure 3This is a comparison chart of the effects of pectinase treatment in Test Example 1 of the present invention, where: (A1-A3) are the grapefruit peel before reaction, after reaction, and after reaction (horizontal and inverted) under pectinase concentrations of 0, 1.5, 3, and 4.5 μ / mL, respectively; (B1-B3) are the passion fruit peel under the same conditions; (C1-C3) are the banana peel under the same conditions, used to verify that the pectin component in the peel helps the peel to self-form; Figure 4 This is a comparative bar chart showing the effect of the non-adsorbent of this invention on the PX removal rate; Figure 5 This is a comparison chart of the PX removal rates of adsorbents prepared from different fruit peel raw materials according to the present invention. Figure 6 This is a test diagram of the water contact angle of different fruit peel carbon aerogels of the present invention; Figure 7 This is a bar chart comparing the effects of different preparation processes using cobalt as a transition metal activator on PX removal rate in this invention. Detailed Implementation
[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0034] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.
[0035] Example 1: Preparation method of grapefruit peel carbon aerogel adsorbent (PP@Mn-NTP-CA-H), the steps are as follows: S1. Crush the dried grapefruit peel to obtain grapefruit peel powder with a particle size of 0.180 mm; S2. Mix 10 g of grapefruit peel powder with 65 mL of a solution containing 5.36 × 10⁻⁶ g of grapefruit peel powder. -3 Mixing with mol / L Mn(NO3)2·4H2O solution and stirring at room temperature for 10 min results in a uniform gel. During this process, the fruit peel particles can form a self-forming gel simply by mixing with the manganese nitrate solution. The gelation driving force depends on the large amount of pectin in the fruit peel particles. The large amount of soluble fiber generates viscosity after dissolving in water, which helps the interaction between the fruit peel particles and the water solvent droplets, thereby achieving the self-forming effect. S3. The gel-like manganese-containing grapefruit peel was subjected to NTP modification under the conditions of 100% relative humidity, discharge voltage of 40 V, discharge current of 2.0 A, and discharge time of 10 min. Through NTP treatment, the material surface was etched, and a large number of oxygen-containing functional groups were introduced into the material surface. S4. The NTP-treated manganese-containing grapefruit peel gel was filled into a spherical silicone mold and placed in the freezing layer of a -20 ℃ freezer for 1 h. After being removed, it was placed in a vacuum freeze dryer at -60 ℃ for 24 h to obtain a spherical freeze-dried sample with a diameter of 9 mm. S5. Place the dried material in a tube furnace and heat it to 900℃ at a rate of 5℃ / min under a N2 atmosphere, then maintain the temperature at 900℃ for 60 min for carbonization. During the high-temperature calcination process, the oxygen-containing functional groups anchored on the material surface decompose with the material components, generating CO2, CO, etc., which expand the pores inside the material. At the same time, manganese nitrate decomposes to generate manganese oxides such as MnO, Mn2O3, or MnO2, releasing NO. x Gases are released, and the escape of these gases etches numerous micropores and mesopores in the carbon matrix; after naturally cooling to room temperature, spherical carbon aerogels with a diameter of 6 mm are obtained. S6. The carbonized carbon aerogel balls were placed in a 1 mol / L HCl solution and vacuum-soaked for 12 h to fully remove the manganese oxides contained in the carbon aerogel balls. They were then washed with deionized water until neutral and dried with a blower at a temperature of 80 ℃ for 12 h to obtain PP@Mn-NTP-CA-H.
[0036] The PP@Mn-NTP-CA-H adsorbent obtained in this embodiment is spherical, lightweight, and has excellent hydrophobic properties.
[0037] Example 2 The preparation method of grapefruit peel carbon aerogel adsorbent (PP@Co-NTP-CA-H) differs from that of Example 1 in that: S2: the transition metal nitrate is replaced by Co(NO3)2·6H2O instead of Mn(NO3)2·4H2O.
[0038] The PP@Co-NTP-CA-H adsorbent obtained in this embodiment is spherical, lightweight, and has excellent hydrophobic properties.
[0039] Example 3 The preparation method of passion fruit peel carbon aerogel adsorbent (PFP@Mn-NTP-CA-H) differs from that of Example 1 in that: S1: Passion fruit peel is used instead of grapefruit peel as the fruit peel raw material.
[0040] The PFP@Mn-NTP-CA-H adsorbent obtained in this embodiment is spherical, lightweight, and has excellent hydrophobic properties.
[0041] Example 4: The preparation method of a banana peel carbon aerogel adsorbent (BP@Mn-NTP-CA-H) differs from that of Example 1 in that: S1: Banana peel is used instead of grapefruit peel as the fruit peel raw material.
[0042] In this embodiment, the BP@Mn-NTP-CA-H adsorbent is spherical, lightweight, and exhibits excellent hydrophobic properties.
[0043] Comparative Example 1: The preparation method of a grapefruit peel carbon aerogel adsorbent (PP-CA) differs from that of Example 1 in that: S2: Grapefruit peel powder is directly mixed with deionized water without adding transition metal nitrates; S3: The NTP modification step is omitted; S4, S5, S6: After omitting step S3, freeze-drying (S4 corresponds to the original S4) and carbonization (S5 corresponds to the original S5) are carried out directly, and the acid washing step (original S6) is omitted. The product is simply soaked in deionized water for 6 hours and then dried.
[0044] Comparative Example 2: The preparation method of a microporous grapefruit peel carbon aerogel adsorbent (PP-NTP-CA) differs from that of Example 1 in that: S2: grapefruit peel powder is directly mixed with deionized water without adding transition metal nitrates; S6: the acid washing step is omitted, and the product is simply soaked in deionized water for 6 hours and then dried.
[0045] Comparative Example 3: The preparation method of a manganese-doped grapefruit peel carbon aerogel adsorbent (PP@Mn-CA) differs from that of Example 1 in that: S3: the NTP modification step is omitted; S4, S5, S6: after omitting step S3, freeze drying (S4 corresponds to the original S4) and carbonization (S5 corresponds to the original S5) are performed directly, the acid washing step (original S6) is omitted, and the product is simply soaked in deionized water for 6 h and then dried.
[0046] Comparative Example 4: The preparation method of a manganese-doped grapefruit peel carbon aerogel adsorbent (PP@Mn-NTP-CA) differs from that of Example 1 in that: S6: the acid washing step is omitted, and the product is simply soaked in deionized water for 6 hours and then dried. This comparative example retains the metal oxide and is not acid-washed.
[0047] Comparative Example 5: A method for preparing a grapefruit peel carbon aerogel adsorbent (PP-NTP@Mn-CA), the steps of which are as follows: S1. Crush the dried grapefruit peel to obtain grapefruit peel powder with a particle size of 0.180 mm; S2. Mix 10 g of grapefruit peel powder with 65 mL of deionized water and stir at room temperature for 10 min until a uniform gel is formed. S3. NTP modification was carried out on the gel-like grapefruit peel under the conditions of 100% relative humidity, discharge voltage of 40 V, discharge current of 2.0 A, and discharge time of 10 min. S4. Mix the NTP-treated grapefruit peel gel with 65 mL of a solution containing 5.36 × 10⁻⁶ NTP. -3 Mix with mol / L Mn(NO3)2·4H2O solution and stir at room temperature for 10 min until homogeneous; S5. Fill the well-stirred manganese-containing grapefruit peel gel into a spherical silicone mold, place it in the freezer at -20 ℃ for 1 h, and then place it in a vacuum freeze dryer at -60 ℃ for 24 h. S6. The dried material was placed in a tube furnace and heated to 900℃ at a rate of 5℃ / min under N2 atmosphere, and carbonized at 900℃ for 60 min. After naturally cooling to room temperature, it was soaked in deionized water for 6 h, and dried with a blower at 80℃ for 12 h to obtain PP-NTP@Mn-CA (NTP added first, then manganese added, without acid washing).
[0048] This comparative example is used to verify the difference in effectiveness between "adding metal first and then NTP" and "adding metal first and then NTP".
[0049] Comparative Example 6: A method for preparing a grapefruit peel carbon aerogel adsorbent (PP-NTP@Mn-CA-H), the steps of which are as follows: S1. Crush the dried grapefruit peel to obtain grapefruit peel powder with a particle size of 0.180 mm; S2. Mix 10 g of grapefruit peel powder with 65 mL of deionized water and stir at room temperature for 10 min until a uniform gel is formed. S3. NTP modification was carried out on the gel-like grapefruit peel under the conditions of 100% relative humidity, discharge voltage of 40 V, discharge current of 2.0 A, and discharge time of 10 min. S4. Mix the NTP-treated grapefruit peel gel with 65 mL of a solution containing 5.36 × 10⁻⁶ NTP. -3 Mix with mol / L Mn(NO3)2·4H2O solution and stir at room temperature for 10 min until homogeneous; S5. Fill the well-stirred manganese-containing grapefruit peel gel into a spherical silicone mold, place it in the freezer at -20 ℃ for 1 h, and then place it in a vacuum freeze dryer at -60 ℃ for 24 h. S6. The dried material was placed in a tube furnace and heated to 900℃ at a rate of 5℃ / min under a N2 atmosphere, and carbonized at 900℃ for 60 min. After naturally cooling to room temperature, the carbonized carbon aerogel balls were placed in a 1mol / L HCl solution and vacuum-soaked for 12 h to fully remove the manganese oxides contained in the carbon aerogel balls. The balls were washed with deionized water until neutral and dried with a blower at a temperature of 80℃ for 12 h to obtain PP-NTP@Mn-CA-H (NTP added first, then manganese added, and acid washed).
[0050] Comparative Example 7: The preparation method of a cobalt-doped grapefruit peel carbon aerogel adsorbent (PP@Co-CA) differs from that of Example 1 in that: S2: Co(NO3)2·6H2O is used instead of Mn(NO3)2·4H2O for the transition metal nitrate; S3: The NTP modification step is omitted. S4, S5, S6: After omitting step S3, directly perform freeze drying (S4 corresponds to the original S4) and carbonization (S5 corresponds to the original S5), omit the acid washing step (original S6), and simply soak in deionized water for 6 hours before drying.
[0051] Comparative Example 8: The preparation method of a cobalt-doped grapefruit peel carbon aerogel adsorbent (PP@Co-NTP-CA) differs from that of Example 1 in that: S2: Co(NO3)2·6H2O is used instead of Mn(NO3)2·4H2O for the transition metal nitrate; S6: the acid washing step is omitted, and the product is simply soaked in deionized water for 6 h and then dried.
[0052] Comparative Example 9: A method for preparing a grapefruit peel carbon aerogel adsorbent (PP-NTP@Co-CA), the steps of which are as follows: S1. Crush the dried grapefruit peel to obtain grapefruit peel powder with a particle size of 0.180 mm; S2. Mix 10 g of grapefruit peel powder with 65 mL of deionized water and stir at room temperature for 10 min until a uniform gel is formed. S3. NTP modification was carried out on the gel-like grapefruit peel under the conditions of 100% relative humidity, discharge voltage of 40 V, discharge current of 2.0 A, and discharge time of 10 min. S4. Mix the NTP-treated grapefruit peel gel with 65 mL of a solution containing 5.36 × 10⁻⁶ NTP. -3 Mix with mol / L Co(NO3)2·6H2O solution and stir at room temperature for 10 min until homogeneous; S5. Fill the well-stirred cobalt-containing grapefruit peel gel into a spherical silicone mold, place it in the freezer at -20 ℃ for 1 h, and then place it in a vacuum freeze dryer at -60 ℃ for 24 h. S6. The dried material is placed in a tube furnace and heated to 900℃ at a rate of 5℃ / min under N2 atmosphere, and carbonized at 900℃ for 60 min. After naturally cooling to room temperature, it is soaked in deionized water for 6 h, and dried by blower at 80℃ for 12 h to obtain PP-NTP@Co-CA (NTP added first, then cobalt added, without acid washing).
[0053] Comparative Example 10: A method for preparing a grapefruit peel carbon aerogel adsorbent (PP-NTP@Co-CA-H), the steps of which are as follows: S1. Crush the dried grapefruit peel to obtain grapefruit peel powder with a particle size of 0.180 mm; S2. Mix 10 g of grapefruit peel powder with 65 mL of deionized water and stir at room temperature for 10 min until a uniform gel is formed. S3. NTP modification was carried out on the gel-like grapefruit peel under the conditions of 100% relative humidity, discharge voltage of 40 V, discharge current of 2.0 A, and discharge time of 10 min. S4. Mix the NTP-treated grapefruit peel gel with 65 mL of a solution containing 5.36 × 10⁻⁶ NTP. -3 Mix with mol / L Co(NO3)2·6H2O solution and stir at room temperature for 10 min until homogeneous; S5. Fill the well-stirred cobalt-containing grapefruit peel gel into a spherical silicone mold, place it in the freezer at -20 ℃ for 1 h, and then place it in a vacuum freeze dryer at -60 ℃ for 24 h. S6. The dried material was placed in a tube furnace and heated to 900℃ at a rate of 5℃ / min under a N2 atmosphere, and carbonized at 900℃ for 60 min. After naturally cooling to room temperature, the carbonized carbon aerogel balls were placed in a 1mol / L HCl solution and vacuum-soaked for 12 h to fully remove the cobalt oxides contained in the carbon aerogel balls. The balls were washed with deionized water until neutral and dried with a blower at a temperature of 80℃ for 12 h to obtain PP-NTP@Co-CA-H (NTP added first, then cobalt added, and acid-washed).
[0054] Test Example 1: Verification Experiment of the Self-Forming Gelatinization Mechanism of Fruit Peel To verify that the self-forming of the peel at room temperature depends on the pectin component in the peel particles, an experiment was conducted to treat the peel with pectinase.
[0055] Experimental steps: S1. Prepare a citric acid / sodium citrate buffer solution with a pH of 4 and a concentration of 0.1 mol / L; S2, Grapefruit Peel Treatment: Using a 36 mL buffer solution, pectinases with different activities (0, 1.5, 3, and 4.5 u / mL) were placed in four 250 mL Erlenmeyer flasks, simultaneously treating 4 g of PP. The Erlenmeyer flasks were sealed and placed in an air shaker at 40 ℃ and 150 r / min for 2 h. After the reaction, the temperature was raised to 80 ℃ and held for 10 min to inactivate the enzyme. S3. Passion fruit peel treatment: 4 g PFP was used with a buffer solution volume of 48 mL, and the other conditions were the same as those for grapefruit peel. S4. Banana peel treatment: 4 g BP was treated with a buffer solution of 40 mL, and the other conditions were the same as for grapefruit peel.
[0056] Experimental results: Before the pectinase reaction, the substances in the four conical flasks were in the same state. After the pectinase reaction, the peels without pectinase formed. When the conical flask was inverted, the PP (208.16 g / kg) and PFP (233.45 g / kg) peels with higher pectin content were concentrated at the bottom and did not flow down, while the BP (121.67 g / kg) peel with lower pectin content was a viscous gel, partially flowing down but sticking to the walls. The peels with pectinase did not form, and all of them flowed down after the conical flask was inverted. This proves that the self-forming of peels at room temperature depends on the large amount of pectin in the peel particles.
[0057] Test Example 2: Low-Temperature Plasma Modification Effect Test Table 1. Discharge parameters of NTP treatment for pure grapefruit peel and metal-doped grapefruit peel.
[0058] Note: f a The frequency of the input power; V pp b Peak-to-peak voltage; P out c To output effective power; A d Let be the area of the Lissajous figure.
[0059] Table 1 shows that, under humid air with a relative humidity of 100%, and with an input voltage of 40 V and a discharge current of 2.0 A, pure grapefruit peel, after NTP treatment for 10 min, outputs an effective power of 47.20 W. After pure grapefruit peel is doped with the metal salt Mn(NO3)2·4H2O, under the same NTP treatment conditions, the effective power increases to 57.99 W; after doping with Co(NO3)2·6H2O, the effective power output is 54.30 W. This is because the metal itself is conductive, which facilitates current transfer during NTP treatment, allowing the grapefruit peel to receive more energy and resulting in more uniform material modification. This allows the grapefruit peel powder to uniformly incorporate oxygen-containing functional groups, and the increased number of oxygen-containing functional groups acts as a pore-forming agent during subsequent calcination.
[0060] Test Example 3: Physical Property Characterization Table 2 Physical parameters of different samples
[0061] As shown in Table 2, after NTP modification, the BET specific surface area of PP-NTP-CA increased from 22.99 m² / g. 2 / g increased to 768.02m 2 / g, and the pore volume also increased from 0.02 cm³. 3 / g increased to 0.41 cm 3 / g, the average pore size decreased significantly from 3.02 nm to 1.85 nm. After doping with Mn(NO3)2·4H2O and then modifying with NTP, the specific surface area of PP@Mn-NTP-CA continued to increase to 831.62 m² / g. 2 / g, pore volume 0.32 cm³ 3 / g, with an average pore size of 1.77 nm. After acid washing, the specific surface area of PP@Mn-NTP-CA-H continued to increase to 865.01 m² / g. 2 / g, the pore volume continued to increase to 0.46 cm³. 3 The average pore size is 1.87 nm. The micropore content of PP@Mn-NTP-CA-H is approximately 87.6%-90.6%. Modification with Mn(NO3)2·4H2O followed by NTP helps to obtain microporous grapefruit peel-based carbon aerogels. After doping with Co(NO3)2·6H2O followed by NTP modification, the specific surface area of PP@Co-NTP-CA further increases to 812.97 m² / g. 2 / g, pore volume 0.35 cm³ 3 / g, with an average pore size of 1.72 nm. After acid washing, the specific surface area of PP@Co-NTP-CA-H continued to increase to 897.64 m². 2 / g, the pore volume continued to increase to 0.49 cm³.3 The average pore size was 1.89 nm. The micropore content of PP@Co-NTP-CA-H was approximately 89.6%. However, the specific surface area of PP-NTP@Mn-CA obtained by first modifying grapefruit peel with NTP and then doping it with Mn(NO3)2·4H2O was 567.38 m² / g. 2 / g, the specific surface area of PP-NTP@Mn-CA-H obtained after acid washing is 612.42m². 2 / g; The specific surface area of PP-NTP@Co-CA obtained by first modifying grapefruit peel with NTP and then doping it with Co(NO3)2·6H2O is 376.78m². 2 / g, the specific surface area of PP-NTP@Co-CA-H obtained after acid washing is 689.35 m² / g. 2 / g. This indicates that the modification method of NTP modification after doping with metal salts helps to obtain microporous grapefruit peel-based carbon aerogels. However, NTP doping followed by metal salt doping at room temperature results in uneven metal salt doping, which clogs the pore structure of the grapefruit peel after NTP modification, leading to a lower specific surface area of the carbon aerogel obtained by calcination. Furthermore, the specific surface areas of PFP@Mn-NTP-CA-H and BP@Mn-NTP-CA-H obtained by replacing grapefruit peel with passion fruit peel and banana peel, respectively, after doping with Mn(NO3)2·4H2O, followed by NTP modification and acid washing, are 647.82 m², respectively. 2 / g and 870.74 m 2 / g, proving that the method of NTP modification after doping with metal salts is applicable to the preparation of carbon aerogels with different fruit peels.
[0062] Test Example 4: VOCs Adsorption Performance Test To further illustrate the effect of the present invention in improving adsorption performance, the adsorption performance of the fruit peel carbon aerogel adsorbents prepared in Examples 1-4 and Comparative Examples 1-10 was characterized in a 635 mL headspace vial at an ambient temperature of 30 °C and a relative humidity of 100%, with p-xylene (PX) at a concentration of 26.227 mg / L as the target pollutant. The amount of adsorbent used each time was 0.05 g, and the adsorption time for gaseous PX was 100 min.
[0063] Table 3. Removal rate of PX by different samples (adsorption for 100 min)
[0064] Table 3 shows that the carbon aerogel PP-CA prepared directly from grapefruit peel has almost no adsorption effect, with an adsorption efficiency of 2.96%. The adsorption efficiency of the carbon aerogel PP-NTP-CA prepared from grapefruit peel after NTP treatment under 100% relative humidity is significantly improved, reaching 75.19%. This proves that NTP modification can effectively improve the adsorption performance of fruit peel carbon aerogels. The carbon aerogel PP@Mn-CA prepared directly from grapefruit peel doped with the metal salt Mn(NO3)2·4H2O has poor adsorption effect, with an adsorption efficiency of 12.48%, indicating that the effect of simply doping with metal without NTP modification is limited. The adsorption efficiency of the carbon aerogel PP@Mn-NTP-CA prepared by uniformly mixing grapefruit peel with the metal salt Mn(NO3)2·4H2O and then treating it with NTP under 100% relative humidity increases to 85.52%. After acid washing to remove metal oxides, the adsorption efficiency of PP@Mn-NTP-CA-H was further improved to 96.69%, demonstrating that hydrochloric acid post-treatment is beneficial for removing metals and their oxides from grapefruit peel carbon aerogel, increasing the specific surface area and pore volume of the carbon aerogel, and improving its adsorption performance. Comparative Example 5 had an adsorption efficiency of only 17.07%, while Example 1 achieved 96.69%, demonstrating the importance of the modification sequence; doping with metal first followed by NTP modification yields better synergistic effects. Comparative Example 6, after acid washing, had an adsorption efficiency of 24.83%, which was improved compared to Comparative Example 5 (17.07%) without acid washing, but still significantly lower than Example 1 (96.69%), further demonstrating the superiority of the technical route of doping with metal first followed by NTP modification. After changing the metal to cobalt, Example 2 achieved an adsorption efficiency of 99.38%, higher than Example 1's 96.69%, indicating that the method of this invention has universality for different transition metals. The cobalt-doped sample showed better adsorption after acid washing, possibly because Co has a larger atomic radius than Mn. After acid washing removes the metal, the pore volume left on the material surface is larger, thus increasing its adsorption capacity. When the fruit peel raw materials were changed to passion fruit peel (Example 3) and banana peel (Example 4), the adsorption effects were 30% and 95%, respectively, demonstrating that the technology of this invention is universally applicable to different fruit peel raw materials and can prepare microporous, highly hydrophobic carbon aerogel adsorbents.
[0065] Test Example 5: Adsorption Performance at Different Relative Humidities At an ambient temperature of 30 °C, the adsorption of PX by PP@Mn-NTP-CA-H prepared in Example 1 was investigated under varying relative humidity conditions. air The adsorption effect was observed under the following conditions: the adsorbent dosage was 0.05 g, the PX concentration was 26.227 mg / L, and the adsorption time was 100 min.
[0066] Figure 2(B) indicates that the adsorption of PX by PP@Mn-NTP-CA-H is largely unaffected by air humidity, maintaining good adsorption performance under different relative humidity conditions. This is attributed to the material's excellent hydrophobic properties, making it difficult for water molecules to compete for adsorption sites.
[0067] Test Example 6: Reuse Performance Test The cyclic adsorption performance of PP@Mn-NTP-CA-H for PX prepared in Example 1 was tested under ambient temperature of 30 ℃ and relative humidity of 100%. After each adsorption for 100 min, regeneration was performed by heating desorption, and a total of 5 cycles were carried out.
[0068] Figure 2 (C) indicates that PP@Mn-NTP-CA-H has good reusability.
[0069] Test Example 7: Adsorption Performance of Different VOCs To further investigate the adsorption effect of PP@Mn-NTP-CA-H prepared in Example 1 on other VOCs, the adsorption effects of PP@Mn-NTP-CA-H on common sulfur-containing VOCs in industrial emissions (represented by dimethyl disulfide, ethyl acetate, acetone, and toluene) were tested under the conditions of an ambient temperature of 30 ℃ and a relative humidity of 100%. The adsorbent dosage was 0.05 g, the VOC concentration was 26.227 mg / L, and the adsorption time was 100 min.
[0070] Figure 2(D) indicates that PP@Mn-NTP-CA-H exhibits the highest adsorption capacity for dimethyl disulfide (341.579 mg / g). This is because the sulfur atom in the dimethyl disulfide molecule allows for stronger and more diverse interactions (such as dipole interactions, coordinate bonds, and hydrogen bonds) with the PP@Mn-NTP-CA-H surface. The adsorption capacity of acetone (336.646 mg / g) is slightly lower than that of dimethyl disulfide, because the oxygen atom in acetone is more reactive and can generate stronger interactions with the PP@Mn-NTP-CA-H surface. The adsorption capacities of toluene (299.307 mg / g) and p-xylene (249.677 mg / g) are greater than those of ethyl acetate (207.631 mg / g), mainly because toluene and p-xylene, as nonpolar molecules, can generate stronger van der Waals forces and π-π interactions with the PP@Mn-NTP-CA-H surface through their large benzene ring structures. Ethyl acetate, being a polar molecule with relatively stable ester groups, is more susceptible to interference from environmental humidity (competitive adsorption by water molecules), resulting in a weaker affinity for PP@Mn-NTP-CA-H. PP@Mn-NTP-CA-H exhibits excellent adsorption performance for different types of VOCs, demonstrating the broad applicability of the fruit peel carbon aerogel adsorbent prepared in this invention to VOCs.
[0071] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation, characterized in that, It is prepared by activating fruit peel particles with transition metal nitrates, modifying them with low-temperature plasma, freeze-drying, carbonizing them with high temperature and acid washing. The fruit peel is at least one of grapefruit peel, passion fruit peel, and banana peel; the transition metal is at least one of manganese, iron, cobalt, nickel, copper, and zinc; and the adsorbent is spherical. The surface of the adsorbent includes oxygen-containing functional groups. After acid washing, the metal oxides are removed, but the porous structure formed by the metal oxides is retained.
2. The preparation method of the fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation as described in claim 1, characterized in that, Includes the following steps: S1. Dry and crush the fruit peel to produce uniform fruit peel granules; S2. Mix the fruit peel particles with the transition metal nitrate solution and stir until it becomes a gel. S3. Place the gel-like fruit peel in a dielectric barrier discharge low-temperature plasma modification device and perform low-temperature plasma treatment in an air environment with a discharge voltage of 30-60 V, a discharge current of 2.0-2.3 A, and a discharge time of 5-20 min. S4. Fill the low-temperature plasma-treated material into a spherical silicone mold and freeze-dry it. S5. Place the cooled material in a tube furnace and carbonize it at high temperature in a nitrogen atmosphere to obtain lightweight carbon aerogel balls. S6. The carbonized carbon aerogel balls are placed in HCl solution, vacuum soaked, washed with deionized water until neutral, and dried to obtain a fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation.
3. The preparation method according to claim 2, characterized in that, The peel mentioned in step S1 is at least one of grapefruit peel, passion fruit peel, and banana peel.
4. The preparation method according to claim 2, characterized in that, The transition metal nitrate is at least one of manganese nitrate tetrahydrate, ferric nitrate hexahydrate, cobalt nitrate hexahydrate, nickel nitrate hexahydrate, copper nitrate hexahydrate, and zinc nitrate hexahydrate.
5. The preparation method according to claim 4, characterized in that, The concentration of the transition metal nitrate in step S2 is 2.50 × 10⁻⁶. -3 -8.50×10 -3 The mass ratio of fruit peel particles to transition metal nitrate solution is 1:(5-8).
6. The preparation method according to claim 2, characterized in that, The low-temperature plasma working atmosphere described in step S3 is air, with a relative humidity range of 0-100%.
7. The preparation method according to claim 2, characterized in that, In step S5, the temperature is increased to the carbonization temperature at a rate of 5 °C / min under a N2 atmosphere. The carbonization temperature is 800-900 °C, and the carbonization time is 60 min.
8. The preparation method according to claim 2, characterized in that, The concentration of the HCl solution is 0.1-2.0 mol / L, the hydrochloric acid soaking time is 6-12 h, and the drying temperature is 50-100 ℃ for 6-48 h.
9. The application of a fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation in the preparation of VOCs adsorbent materials, wherein the fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation is the fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation as described in claim 1 or the fruit peel carbon aerogel VOCs adsorbent based on low-temperature plasma synergistic trace metal activation prepared by any one of claims 2-8.
10. The application according to claim 9, characterized in that, The VOCs are at least one of p-xylene, dimethyl disulfide, ethyl acetate, acetone, and toluene.