Modified pomelo peel-based carbon aerogel, and preparation method and application thereof

Abstract

This invention discloses a modified grapefruit peel-based carbon aerogel, its preparation method, and its applications, belonging to the field of adsorbent preparation technology. The preparation method involves placing the grapefruit peel-based carbon aerogel in a potassium hydroxide solution and stirring at 75–85°C for 2.5–3.5 hours. After stirring, the mixture is filtered and dried, then calcined at 850–950°C for 1–1.5 hours in a nitrogen atmosphere. This invention solves the problems of low adsorption capacity and poor selectivity in current adsorbent materials. The modified grapefruit peel-based carbon aerogel electrode exhibits preferential selectivity for nitrates and phosphates. The invention utilizes capacitive deionization technology, resulting in low energy consumption and cost savings. The electroadsorption system electrode uses grapefruit peel as a raw material, which is widely available, convenient, and inexpensive. The resulting biomass-based carbon aerogel has the advantages of being renewable, biodegradable, and rich in carbon sources. It also enables the recycling of waste grapefruit peels, making it an environmentally friendly renewable material.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent preparation technology, specifically relating to a modified grapefruit peel-based carbon aerogel, its preparation method, and its application. Background Technology

[0002] Nitrates are positively charged, electrophilic inorganic compounds that are not hydrolyzed and precipitated by cations in aqueous solutions. Phosphorus plays a vital role in human metabolism and plant growth, and is widely used in industry, agriculture, and daily life. Currently, methods for treating nitrogen and phosphorus-containing wastewater include biological, physical, and chemical methods. Biological methods suffer from drawbacks such as long treatment cycles and unsatisfactory treatment results; physical methods may cause secondary pollution and are too costly. Capacitive deionization technology achieves high removal efficiency in treating nitrates and phosphates, with simple subsequent treatment processes and no secondary pollution, making it an environmentally friendly new technology.

[0003] Electro-sorption technology (EST), also known as capacitive deionization (CDI), is a novel water treatment technology that utilizes the adsorption of ions and charged particles from water onto the surface of charged electrodes. This concentrates dissolved salts and other charged substances on the electrode surface, achieving water purification / desalination. The principle of electro-sorption technology is to create an electrostatic field between the electrodes using an applied voltage. Charged particles are forced to move towards the oppositely charged electrode plate due to electrostatic force, forming an electric double layer on the electrode plate surface. The charged particles are adsorbed and temporarily stored in the double layer. When the adsorption process reaches equilibrium, the electric field is removed or the power supply is reversed, and the ions adsorbed on the electrode return to the solution, achieving desorption. In electro-sorption, the storage / release of charge is achieved through ion adsorption / desorption rather than chemical reactions, allowing for rapid charging and discharging. Furthermore, since only ion adsorption / desorption occurs during charging and discharging, the electrode structure remains unchanged, so the number of charge / discharge cycles is theoretically unlimited. When the electrode surface potential reaches a certain value, the concentration of ions in the double layer can be hundreds or thousands of times that of the bulk solution. Under the action of a DC electric field, the ions are stored in the double layer on the electrode surface until the electrode reaches saturation. At this point, the DC power supply is removed and the positive and negative electrodes are short-circuited. Due to the disappearance of the DC electric field, the ions stored in the double layer return to the channel and are discharged with the water flow, thus regenerating the electrode.

[0004] Electrodes, as the most important component of electroadsorption devices, are key to electroadsorption technology. The performance of electrodes directly determines the adsorption rate, adsorption capacity, and selectivity. High-performance adsorption electrodes have the characteristics of good conductivity, high stability, large specific surface area, suitable pore volume, large adsorption capacity, and high selectivity. The requirements for electrodes determine that the raw materials for preparing electrodes should have the following characteristics: (1) Large specific surface area. The larger the specific surface area, the larger the contact area between the electrode and the solution, and the faster the adsorption rate; (2) Suitable pore size. Studies have shown that the adsorption effect is best when the pore size is in the mesoporous range; (3) Large pore volume. The larger the pore volume, the larger the space for adsorbing and storing ions, and the better the adsorption effect; (4) Wide availability, environmentally friendly, stable performance, and easy to form. Therefore, seeking new electrode adsorption materials is the key to electroadsorption technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a new electrode adsorption material modified grapefruit peel-based carbon aerogel.

[0006] A second objective of this invention is to provide a method for preparing modified grapefruit peel-based carbon aerogel.

[0007] A third objective of this invention is to provide the application of modified grapefruit peel-based carbon aerogel as an electrode adsorption material in water treatment.

[0008] The objective of this invention is achieved through the following technical solution: a method for preparing modified grapefruit peel-based carbon aerogel, wherein grapefruit peel-based carbon aerogel is placed in a potassium hydroxide solution and stirred at 75-85°C for 2.5-3.5 hours, after stirring, it is filtered and dried, and then calcined at 850-950°C for 1-1.5 hours in a nitrogen atmosphere to obtain modified grapefruit peel-based carbon aerogel.

[0009] Furthermore, the grapefruit peel-based carbon aerogel is prepared using the following method:

[0010] S1. Sol-gel: Add deionized water to dried grapefruit peel and react at a constant temperature of 170-190℃ for 10-14 hours;

[0011] S2. Solvent replacement: After the reaction is completed, cool to room temperature to obtain grapefruit peel hydrogel. Soak and wash the grapefruit peel hydrogel with 50% ethanol aqueous solution.

[0012] S3. Freeze-drying: Place the cleaned grapefruit peel hydrogel in a refrigerator at -18℃ for 10-14 hours; immediately freeze-dry the frozen grapefruit peel under vacuum for 45-55 hours to obtain grapefruit peel-based aerogel.

[0013] S4. Carbonization: The grapefruit peel-based aerogel is calcined at 850–950°C for 50–70 min in a nitrogen atmosphere, and after cooling, it becomes grapefruit peel-based carbon aerogel.

[0014] Furthermore, the conditions for vacuum freeze drying in step S3 are: pressure of 0.01 Pa and temperature of -80 °C.

[0015] Furthermore, the carbonization described in step S4 is carried out in a tube furnace, and the heating conditions of the tube furnace are set as follows: from 60°C to 850-950°C at a rate of 4-6°C per minute for 150-180 minutes.

[0016] Furthermore, the concentration of the potassium hydroxide solution is 0.6–1.0 mol / L.

[0017] Furthermore, the filtration is performed using a filter membrane with a pore size of 45 μm.

[0018] Furthermore, the drying temperature is 75–85°C, and the drying time is 5–7 hours.

[0019] The grapefruit peel-based carbon aerogel prepared by the above method.

[0020] The above-mentioned grapefruit peel-based carbon aerogel is used as an electrode adsorption material in water treatment.

[0021] Furthermore, the water treatment involves removing nitrogen and phosphorus from the water.

[0022] 1) This invention has the following advantages: This invention utilizes KOH-modified biomass-based carbon aerogel, solving the problems of low adsorption capacity and poor selectivity in current adsorption materials. The optimal modified material has a specific surface area of ​​653.9 m². 2 / g, micropore volume 0.299cm³ 3 With a microporosity of 53.39%, the adsorption capacity for nitrate and phosphate reached 0.9935 mmol / g and 0.6246 mmol / g, respectively. The selectivity coefficients of nitrate for sulfate and chloride ions and phosphate for chloride ions were both greater than 1, indicating that the grapefruit peel-based carbon aerogel electrode has preferential selectivity for nitrate and phosphate.

[0023] 2) This invention employs a novel water desalination electrotreatment technology—capacitor deionization technology—which has low energy consumption and saves costs. Using the grapefruit peel-based carbon aerogel of this invention, the energy consumption per unit volume of simulated wastewater with an initial nitrate and phosphate concentration of 0.3 mmol / L is 0.1175 kWh / m³. 3The cost of treating total phosphorus is only 7,010 yuan / ton of phosphorus, while other phosphorus removal methods, such as biological phosphorus removal, chemical phosphorus removal, and crystallization treatment, all have a cost of over 30,000 yuan / ton of phosphorus. Compared to other treatment methods, this invention requires less energy.

[0024] 3) The electrodes of the electroadsorption system use grapefruit peel as raw material, which is widely available, convenient, and inexpensive. The resulting biomass-based carbon aerogel has the advantages of being renewable, biodegradable, and rich in carbon sources. It also enables the recycling of waste grapefruit peel, making it an environmentally friendly renewable material. Attached Figure Description

[0025] Figure 1 The images show the FTIR spectra of the carbon aerogel before and after modification.

[0026] Figure 2 This is the KCA nitrogen adsorption-desorption isotherm diagram.

[0027] Figure 3 Figure 1 shows the changes in sulfate nitrogen concentration over time for KCA competitive adsorption (a) and the changes in adsorption capacity over time (b).

[0028] Figure 4 Figure 1 shows the changes in nitrate concentration over time (a) and adsorption capacity over time (b) for KCA competitive adsorption.

[0029] Figure 5 Figure 1 shows the changes in phosphate concentration over time for KCA competitive adsorption (a) and the changes in adsorption capacity over time (b).

[0030] Figure 6 Figure 1 shows the changes in KCA competitive adsorption chloride ion concentration over time (a) and adsorption capacity over time (b). Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments. The scope of protection of the present invention is not limited to the following: Embodiment 1: Grapefruit peel-based carbon aerogel was prepared by the following method:

[0032] S1. Sol-gel: Add deionized water to dried grapefruit peel and react at a constant temperature of 170℃ for 14 hours;

[0033] S2. Solvent replacement: After the reaction is completed, cool to room temperature to obtain grapefruit peel hydrogel. Soak and wash the grapefruit peel hydrogel with 50% ethanol aqueous solution.

[0034] S3. Freeze-drying: The cleaned grapefruit peel hydrogel was placed in a refrigerator at -18°C for 10 hours; the frozen grapefruit peel was immediately vacuum freeze-dried for 45 hours. The vacuum freeze-drying conditions were: pressure of 0.01 Pa and temperature of -80°C, to obtain grapefruit peel-based aerogel.

[0035] S4. Carbonization: The carbonization of grapefruit peel-based aerogel is carried out in a tube furnace. The tube furnace heating conditions are set in a nitrogen environment as follows: from 60°C to 950°C at a rate of 4°C per minute for 180 minutes, calcined for 70 minutes, and then cooled to obtain grapefruit peel-based carbon aerogel.

[0036] Example 2: Grapefruit peel-based carbon aerogel was prepared using the following method:

[0037] S1. Sol-gel: Add deionized water to dried grapefruit peel and react at a constant temperature of 190℃ for 10 hours;

[0038] S2. Solvent replacement: After the reaction is completed, cool to room temperature to obtain grapefruit peel hydrogel. Soak and wash the grapefruit peel hydrogel with 50% ethanol aqueous solution.

[0039] S3. Freeze-drying: The cleaned grapefruit peel hydrogel was placed in a refrigerator at -18°C for 14 hours; the frozen grapefruit peel was immediately vacuum freeze-dried for 55 hours. The vacuum freeze-drying conditions were: pressure of 0.01 Pa and temperature of -80°C, to obtain grapefruit peel-based aerogel.

[0040] S4. Carbonization: The carbonization of grapefruit peel-based aerogel is carried out in a tube furnace. The heating conditions of the tube furnace in a nitrogen atmosphere are set as follows: from 60°C to 850°C at a rate of 6°C per minute for 150 minutes, calcined for 50 minutes, and then cooled to obtain grapefruit peel-based carbon aerogel.

[0041] Example 3: Grapefruit peel-based carbon aerogel was prepared using the following method:

[0042] S1. Sol-gel: Add deionized water to dried grapefruit peel and react at a constant temperature of 180℃ for 12 hours;

[0043] S2. Solvent replacement: After the reaction is completed, cool to room temperature to obtain grapefruit peel hydrogel. Soak and wash the grapefruit peel hydrogel with 50% ethanol aqueous solution.

[0044] S3. Freeze-drying: The cleaned grapefruit peel hydrogel was placed in a refrigerator at -18°C for 12 hours; the frozen grapefruit peel was immediately vacuum freeze-dried for 50 hours. The vacuum freeze-drying conditions were: pressure of 0.01 Pa and temperature of -80°C, to obtain grapefruit peel-based aerogel.

[0045] S4. Carbonization: The carbonization of grapefruit peel-based aerogel is carried out in a tube furnace. The tube furnace heating conditions are set in a nitrogen environment as follows: from 60°C to 900°C at a rate of 5°C per minute for 165 minutes, calcined for 60 minutes, and then cooled to obtain grapefruit peel-based carbon aerogel.

[0046] Example 4: A method for preparing modified grapefruit peel-based carbon aerogel

[0047] The grapefruit peel-based carbon aerogel prepared in Example 1 was placed in a 0.6 mol / L potassium hydroxide solution and stirred at 75°C for 2.5 h. After stirring, it was filtered and dried. The filtration was carried out using a filter membrane with a pore size of 45 μm, and the drying temperature was 75°C for 7 h. Then, it was calcined at 850°C for 1 h in a nitrogen atmosphere to obtain the modified grapefruit peel-based carbon aerogel.

[0048] Example 5: A method for preparing a modified grapefruit peel-based carbon aerogel

[0049] The grapefruit peel-based carbon aerogel prepared in Example 2 was placed in a 1.0 mol / L potassium hydroxide solution and stirred at 85°C for 3.5 h. After stirring, it was filtered and dried. The filtration was carried out using a filter membrane with a pore size of 45 μm, and the drying temperature was 85°C for 5 h. Then, it was calcined at 950°C for 1.5 h in a nitrogen atmosphere to obtain the modified grapefruit peel-based carbon aerogel.

[0050] Example 6: A method for preparing a modified grapefruit peel-based carbon aerogel

[0051] The grapefruit peel-based carbon aerogel prepared in Example 3 was placed in a 0.8 mol / L potassium hydroxide solution and stirred at 80°C for 3 h. After stirring, it was filtered and dried. The filtration was carried out using a filter membrane with a pore size of 45 μm, and the drying temperature was 80°C for 6 h. Then, it was calcined at 900°C for 1.2 h in a nitrogen atmosphere to obtain the modified grapefruit peel-based carbon aerogel.

[0052] The following experiments illustrate the beneficial effects of this invention:

[0053] 1. Preparation of grapefruit peel-based carbon aerogel

[0054] A grapefruit peel-based carbon aerogel was obtained by combining a hydrothermal method with freeze-drying and finally carbonizing at high temperature. The specific steps are as follows:

[0055] (1) Sol-gel: Wash and dry the grapefruit peel for 48 hours until the moisture is roughly evaporated, then put it into a polytetrafluoroethylene lined tank, add a certain amount of deionized water, and ensure that the volume of the contents of the tank does not exceed 50% of the total capacity. After placing the liner in the reaction vessel, place it in a constant temperature electric blast drying oven at 180°C for 12 hours.

[0056] (2) Solvent replacement: The reaction vessel was removed and allowed to cool naturally to room temperature before being opened to obtain grapefruit peel hydrogel. The hydrogel was washed with 50% ethanol and soaked for 12 hours, with the water changed every 3 hours during this period, to wash away the inorganic components and impurities, so that the solution changed from turbid to clear;

[0057] (3) Freeze-drying: The prepared material was frozen in a freezer at -18℃ for 12 hours and then placed in a vacuum freeze dryer at a pressure of 0.01Pa and -80℃ for 50 hours to obtain grapefruit peel-based carbon aerogel.

[0058] (4) Carbonization: The frozen material was placed in a tube furnace for carbonization, while N2 gas was introduced for protection. The heating conditions of the tube furnace were set as follows: from 60°C to 900°C at a rate of 5°C per minute for 168 minutes, and finally the carbon aerogel was calcined at a constant temperature for 1 hour, while nitrogen gas was introduced. After natural cooling, the carbonized material was taken out and ground in a mortar to obtain carbonized grapefruit peel-based carbon aerogel (PCA), which was then sealed and stored in a desiccator.

[0059] 2. Preparation and characterization of modified grapefruit peel-based carbon aerogel

[0060] KOH alkali modification was performed on grapefruit peel-based carbon aerogel. 1.0 g of the prepared grapefruit peel-based carbon aerogel material was weighed out. 400 mL of 0.6 mol / L, 0.8 mol / L, and 1 mol / L KOH solutions were prepared in beakers. 1.0 g of the material was placed in the alkaline solution and stirred for 3 h using a magnetic stirrer under constant temperature water bath conditions at 80℃. After stirring, the mixture was filtered, and the pH of the filtrate was washed to neutral with deionized water. The filter residue was dried in an oven at 80℃ for 6 h until completely dry to obtain the KOH-modified material. The prepared KOH-modified material was then placed back into a tube furnace and calcined at 900℃ in a nitrogen atmosphere, followed by cooling to obtain the final modified grapefruit peel-based carbon aerogel materials with KCA values ​​of 0.6 KCA, 0.8 KCA, and 1.0 KCA. FTIR, specific surface area, and pore structure characterization results are shown below. Figure 1 , Figure 2 As shown.

[0061] 3. Capacitive deionization nitrogen and phosphorus removal experimental apparatus and method

[0062] 1. Experimental Methods

[0063] 1.1 Electrode preparation and device assembly

[0064] (1) Electrode material plate preparation: Dissolve 0.125g of PVDF binder in 3.125ml of dimethylacetamide, and dissolve it thoroughly using an ultrasonic machine. Then weigh 0.125g of carbon black and add it to the dimethylacetamide solution, stirring thoroughly. Add 1g of modified grapefruit peel-based carbon aerogel material to the above mixed solution, setting the ratio of carbon aerogel powder: carbon black: PVDF = 8g: 1g: 1g. Seal the beaker containing the above materials with plastic wrap and stir for at least 10 hours. After stirring, a paste-like material will form. Take a current collector titanium plate, weigh it and record the data. Place the paste-like material on it and use a 400mm graduated scale to spread it into a material plate with a thickness of 400mm, and mark it. Place the titanium plate coated with electrode material in a vacuum drying oven and dry it at 60℃ for 10 hours. After drying, cool it and weigh it, then place it in a desiccator for later use.

[0065] (2) Assembly: Place the 0.5cm thick rigid acrylic shell with inlet and outlet ports on the outer layer, place the silicone pad on top, and then place the silicone pad and the partition in sequence. Set the spacing between the two electrode materials to 0.3cm. Then place the diaphragm, and then place the silicone pad, electrode materials, silicone pad, and shell. Secure the device with screws.

[0066] 1.2 Nitrogen and Phosphorus Removal Experiment

[0067] 1.2.1 Experimental Procedure

[0068] The specific experimental steps are as follows:

[0069] (1) Preparation of influent: Prepare a 50 mg / L nitrogen (KNO3) / phosphorus (KH2PO4) standard stock solution for later use. Prepare and use immediately.

[0070] (2) Powering on: Connect the two ends of the current collector of the assembled CDI processing device to the power supply, connect the two electrode plates to the positive and negative terminals respectively, and set the constant voltage to 1.2V.

[0071] (3) Inlet and outlet water settings: Dilute the standard stock solution 10 times to prepare the inlet water. Take 500ml of the prepared water sample into a beaker. Set the inlet water flow rate to 25ml / min using a circulation pump. Connect both ends of the device to the inlet and outlet water ports respectively. Set the operating conditions to a circulation treatment device, i.e., both the inlet and outlet water are in the 500ml beaker. Run stably for 6 hours, and set the sampling time to 0, 0.5h, 1h, 2h, 3h, 4h, 5h, and 6h respectively.

[0072] (4) Water sample determination: The experiment was divided into a phosphate / nitrate adsorption capacity experiment and a phosphate / nitrate competitive adsorption experiment. Total phosphorus and Cl in the water were determined by ammonium molybdate spectrophotometry and ion chromatography, respectively. - NO3 - SO4 2- .

[0073] 1.2.2 Calculation of Adsorption Capacity and Selectivity:

[0074]

[0075] Where q is the adsorption capacity (mg / g); m1 is the mass of total phosphorus adsorbed (mg); m2 is the amount of adsorbent added (g); the selectivity coefficient is calculated using the following formula:

[0076]

[0077] [RA] represents the molar concentration (mmol / L) of the target ion in the adsorbent;

[0078] [RB] represents the molar concentration (mmol / L) of competing ions in the adsorbent;

[0079] [A - [This represents the molar concentration (mmol / L) of the target ion in the solution.]

[0080] [B - [Icon] represents the molar concentration (mmol / L) of competing ions in the solution.

[0081] 2. Experimental Results

[0082] The experimental results are shown in Table 1. Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown:

[0083] Table 1: Overview of Selective Adsorption Data

[0084]

[0085] As shown in the charts, the modified carbon aerogel exhibits significantly improved adsorption performance for nitrates compared to the raw material. The raw material showed low adsorption capacity for nitrogen and phosphorus, while the modified material with 0.8 kcal / g showed the highest adsorption capacity for nitrates and phosphates (0.9935 mol / g and 0.6246 mmol / g, respectively), representing increases of 73.2% and 59.3% for nitrogen and phosphorus, respectively, compared to the raw material. The selectivity coefficients for nitrogen and phosphorus were also improved compared to 0.6 kcal / g and 1.0 kcal / g. The selectivity for nitrates relative to other coexisting ions was greater than 1, indicating that the grapefruit peel-based carbon aerogel electrode has preferential selectivity for nitrates. Comparison experiments with coexisting ions revealed that the presence or absence of coexisting ions had little effect on the adsorption capacity of the alkali-modified material for nitrates, indicating that the modified material with 0.8 kcal / g possesses good selective adsorption and a large adsorption capacity for nitrates.

[0086] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, are covered within the scope of protection of the present invention.

Claims

1. The application of a modified grapefruit peel-based carbon aerogel as an electrode adsorbent in water treatment, characterized in that, The modified grapefruit peel-based carbon aerogel exhibits adsorption capacities of 0.9935 mmol / g for nitrates and 0.6246 mmol / g for phosphates; the grapefruit peel-based carbon aerogel is prepared using the following method: S1. Sol-gel: Add deionized water to dried grapefruit peel and react at a constant temperature of 170-190℃ for 10-14 hours; S2. Solvent replacement: After the reaction is completed, cool to room temperature to obtain grapefruit peel hydrogel. Soak and wash the grapefruit peel hydrogel with 50% ethanol aqueous solution. S3. Freeze-drying: Place the cleaned grapefruit peel hydrogel in a refrigerator at -18°C for 10-14 hours; immediately freeze-dry the frozen grapefruit peel under vacuum for 45-55 hours to obtain grapefruit peel-based aerogel; S4. Carbonization: The grapefruit peel-based aerogel is calcined at 850–950°C for 50–70 min in a nitrogen atmosphere, and after cooling, it becomes grapefruit peel-based carbon aerogel. The modified grapefruit peel-based carbon aerogel was obtained by placing grapefruit peel-based carbon aerogel into a 0.8 mol / L potassium hydroxide solution, stirring at 80°C for 3 hours, filtering and drying after stirring, and then calcining at 900°C for 1.2 hours in a nitrogen atmosphere.

2. The application according to claim 1, characterized in that, The conditions for vacuum freeze drying in step S3 are: pressure of 0.01 Pa and temperature of -80℃.

3. The application according to claim 1, characterized in that, The carbonization described in step S4 is carried out in a tube furnace. The heating conditions of the tube furnace are set as follows: from 60°C, the temperature is increased at a rate of 4 to 6°C per minute for 150 to 180 minutes, and then increased to 850 to 950°C.

4. The application according to claim 1, characterized in that, The filtration is performed using a filter membrane with a pore size of 45 μm.

5. The application according to claim 1, characterized in that, The drying temperature is 75~85℃, and the drying time is 5~7h.

6. The application according to claim 1, characterized in that, The modified grapefruit peel-based carbon aerogel has an adsorption capacity of greater than 0.85 mmol / g for nitrates and greater than 0.60 mmol / g for phosphates; and the selectivity coefficients of nitrates relative to sulfates and chloride ions, as well as the selectivity coefficients of phosphates relative to chloride ions, are all greater than 1.

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