Magnetic biomass activated carbon as well as preparation method and application thereof

Abstract

The invention relates to the field of adsorption materials, in particular to magnetic biomass activated carbon and a preparation method and application thereof. Comprising the following steps: (1) pretreatment: drying agricultural wastes in a drying oven, then crushing and sieving the agricultural wastes, repeatedly washing the agricultural wastes with deionized water, drying the agricultural wastes, and fully grinding the agricultural wastes to obtain a pretreated biomass raw material; (2) loading the biomass raw material pretreated in the step (1) into a crucible, and carbonizing to obtain a carbonized material; (3) magnetizing the carbonized material, and adding the carbonized material in the step (2) in the process of preparing a magnetic material by a coprecipitation method; and (4) loading the magnetic biomass carbonized material magnetized in the step (3) into a crucible, and activating to obtain the magnetic biomass activated carbon. The method for adsorbing the low-concentration PFAS in the tap water by using the magnetic biomass activated carbon is simple to operate, low in cost, good in adsorption removal effect, good in magnetic separation performance and convenient to recycle and regenerate an adsorption material.

Description

Technical Field

[0001] The present invention relates to the field of adsorption materials, and in particular to a magnetic biomass activated carbon and a preparation method and application thereof. Background Art

[0002] Perfluorinated compounds (PFAS) are novel organic compounds formed by the complete replacement of hydrogen atoms in C-H chains with fluorine atoms. Thousands of PFAS exist, depending on the functional group and carbon chain length. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), with their C8 structure, are the oldest and most frequently detected PFAS. Their half-lives in the human body range from 2.3 to 5.4 years. PFAS are toxic to organisms, including reproductive, hepatotoxic, cardiotoxic, immunotoxic, and neurotoxic. Given the potential harms of PFAS to the environment and human health, global regulation of PFAS is being strengthened annually. The U.S. Environmental Protection Agency (USEPA) included perfluorinated compounds on its Fourth Contaminant Candidate List, issued at the end of 2016. Subsequently, the EPA established a drinking water health advisory level of 70 ng / L for the two most common perfluorinated compounds, PFOA and PFOS. Health Canada has also issued relevant drinking water guidelines, which set the maximum allowable concentration of PFOA at 0.2 μg / L and the maximum allowable concentration of PFOS at 0.6 μg / L. A study by a research team from Tsinghua University showed that PFAS has been detected in drinking water in many cities in China, including 502.9 ng / L in Zigong, 332.6 ng / L in Lianyungang, 119.4 ng / L in Chengdu, 93.6 ng / L in Wuxi, and 74.1 ng / L in Hangzhou. On December 29, 2022, my country announced the "List of New Pollutants Under Key Control (2023 Edition)", which included three new pollutants related to perfluorinated compounds, and the list will take effect on March 1, 2023. To this end, GB / T5749-2022, the "Standard for Drinking Water Quality," has added indicators for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), stipulating that PFOA levels should be less than 80 ppt and PFOS levels should be less than 40 ppt. This standard will be implemented on April 1, 2023. The aquatic environment is the primary environmental destination for PFAS, and the control and removal of PFAS from water bodies has become a global research hotspot. The development of an economically viable PFAS treatment technology is urgently needed.

[0003] In recent years, universities have conducted extensive research on this topic. Methods for treating PFAS in water can be categorized into chemical, physical, and biological methods. Adsorption, with its relatively low technical and operational costs and favorable economical practicality, has demonstrated significant advantages. Activated carbon is one of the most commonly used adsorbents in water treatment. Due to its large surface area, well-developed pore structure, low cost, excellent adsorption efficiency, simple preparation, and wide availability, it is used to remove a wide range of pollutants. However, current research focuses primarily on the adsorption performance of activated carbon on PFAS solutions, while its adsorption performance on PFAS in actual tap water has been less studied. Coal-based activated carbon may be contaminated with heavy metal impurities, potentially causing secondary contamination of water. Therefore, biomass-based activated carbon is often used for pollutant removal in tap water. Powdered activated carbon (PAC) has more adsorption sites than granular activated carbon (GAC) of the same weight, but the difficulty of PAC recovery limits its usefulness. Summary of the Invention

[0004] The present invention provides a method for preparing magnetic biomass activated carbon to solve the technical problems of secondary pollution of water quality by heavy metal impurities in coal-based activated carbon and difficulty in recovering powdered activated carbon.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing magnetic biomass activated carbon, comprising the following steps: (1) Preprocessing The agricultural waste is placed in an oven to dry, free moisture in the biomass raw material is removed, and then the raw material is crushed, sieved to 80-200 mesh, repeatedly washed with deionized water, dried and fully ground to obtain the pretreated biomass raw material; (2) Carbonization The biomass raw material pretreated in step (1) is placed in a crucible for carbonization, and then taken out to obtain the carbonized material; (3) Magnetization of carbonized materials In the process of preparing the magnetic material by the coprecipitation method, the carbonized material of step (2) is added, FeCl2·4H2O and FeCl3·6H2O are added to a conical flask filled with deionized water and fully dissolved, and then the carbonized material of step (2) is added and stirred at 80°C for 30 min under N2 protection. After being mixed evenly, NH3·H2O is added dropwise until the pH is 9-10, and finally dried in a vacuum drying oven. The dried magnetic carbonized material is washed with deionized water until neutral, and then dried and ground for use; (4) Activation The magnetic biomass carbonized material after magnetization in step (3) is placed in a crucible for activation, and then taken out to obtain magnetic biomass activated carbon.

[0006] As a further limitation of the technical solution of the present invention, the first oven drying in step (1) is carried out at a temperature of 110°C for 24 hours, and the drying temperature after washing with deionized water is 105°C.

[0007] As a further limitation of the technical solution of the present invention, the carbonization condition in step (2) is carbonization at 50-500°C for 2h.

[0008] As a further limitation of the technical solution of the present invention, in step (3), Fe 2+ :Fe 3+ The molar ratio is 1:2, and the mass volume ratio of carbonized material, FeCl2·4H2O and deionized water is 15g:1g:20mL.

[0009] As a further limitation of the technical solution of the present invention, the drying condition in the vacuum drying oven in step (3) is drying at 80° C. for 12 h.

[0010] As a further limitation of the technical solution of the present invention, the activation condition in step (4) is activation at 200-600°C for 2 h.

[0011] The present invention also provides magnetic biomass activated carbon obtained by the above preparation method.

[0012] In addition, the present invention also provides the use of the above-mentioned magnetic biomass activated carbon in removing PFAS from tap water.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces biomass carbonized material into the process of preparing magnetic material by co-precipitation method to prepare magnetic biomass activated carbon, thereby improving the stability of the magnetic material in the activated carbon.

[0014] The present invention provides a method for adsorbing low-concentration PFAS in tap water using magnetic biomass activated carbon. The method has the advantages of simple operation, low cost, good adsorption and removal effect, good magnetic separation performance, convenient recovery and regeneration of adsorption materials, and avoids secondary pollution of water quality by heavy metal impurities in coal-based activated carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Transmission electron micrograph of the magnetic walnut shell activated carbon prepared in Example 1.

[0016] Figure 2 Schematic diagram of magnetic recovery of walnut shell activated carbon prepared in Example 1.

[0017] Figure 3 This is the adsorption kinetics curve of the walnut shell activated carbon prepared in Example 1. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to specific embodiments. Example 1

[0019] A method for preparing magnetic walnut shell activated carbon comprises the following steps: (1) Preprocessing The walnut shells were dried in an oven at 110°C for 24 hours to remove free moisture from the biomass raw material. The raw material was then crushed and sieved to 80-200 mesh. The shells were repeatedly washed with deionized water, dried at 105°C, and thoroughly ground to obtain the pretreated biomass raw material.

[0020] (2) Carbonization The biomass raw material pretreated in step (1) is placed in a crucible and carbonized at 50-500°C for 2 h, and then taken out to obtain the carbonized material.

[0021] (3) Magnetization of carbonized materials In the process of preparing magnetic materials by coprecipitation, the carbonized material of step (2) was added, and 2 g FeCl2·4H2O and 4 g FeCl3·6H2O (Fe 2+ :Fe 3+ =1:2) was added into a conical flask filled with 40 mL of deionized water to fully dissolve, followed by the addition of 30 g of biomass carbonized material and stirring at 80°C for 30 min under N2 protection. After uniform mixing, NH3·H2O was added dropwise and finally dried in a vacuum drying oven at 80°C for 12 h. The dried magnetic walnut shell carbonized material was washed with deionized water until neutral, dried and ground for later use.

[0022] (4) Activation The magnetic walnut shell carbonized material after magnetization in step (3) is placed in a crucible, activated at 200-600 °C for 2h, and then taken out to obtain magnetic walnut shell activated carbon.

[0023] The adsorption evaluation of perfluorinated compounds by the magnetic walnut shell activated carbon material prepared in Example 1 was conducted in the following steps: Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), two representative perfluorochemicals, were selected to prepare a 50 mg / L solution. 0.05 g of the magnetic walnut shell activated carbon material prepared in Experimental Example 1 was mechanically mixed with 100 mL of the above-mentioned solutions at room temperature for 60 min. Samples were taken at 5, 10, 20, 30, 45, and 60 min, respectively. The magnetic material was separated by an external magnetic field and the perfluorochemical content was quantitatively tested using LC-MS / MS. The adsorption amount (mg) of the magnetic walnut shell activated carbon material for each compound per unit mass (g) at this concentration was calculated, and the adsorption kinetic curve ( Figure 3 ).from Figure 3As can be seen, the material exhibits high adsorption capacity for both perfluorinated compounds, with adsorption equilibrium of the perfluorinated compounds reached within 20 minutes. Perfluorinated compound molecules act as mass transfer vehicles from the solution to the adsorbent surface. Once they reach the adsorbent surface, they gradually occupy the abundant high-energy adsorption sites on the adsorbent surface. As adsorption time increases, the number of available adsorption sites on the adsorbent surface decreases, and the adsorption rate gradually slows. Ultimately, the change in adsorption capacity is minimal, and the adsorbent surface approaches a state of adsorption equilibrium.

[0024] Depend on Figure 1 Transmission electron microscopy shows that the morphology of each magnetic nanoparticle is clearly visible, the particle size is between 10 and 20 nm, there is little or no overlap between particles, and the dispersion is relatively uniform. Therefore, this loading method effectively avoids the disadvantage of easy agglomeration of nanoparticles. Figure 2 It can be seen that the magnetic walnut shell activated carbon material has good magnetic recovery performance. Example 2

[0025] A method for preparing magnetic peach shell activated carbon comprises the following steps: (1) Preprocessing The peach shells were dried in an oven at 110°C for 24 hours to remove free moisture from the biomass raw material. The raw material was then pulverized and sieved to 80-200 mesh. The raw material was washed repeatedly with deionized water, dried at 105°C, and fully ground to obtain the pretreated biomass raw material.

[0026] (2) Carbonization The biomass raw material pretreated in step (1) is placed in a crucible and carbonized at 50-500°C for 2 h, and then taken out to obtain the carbonized material.

[0027] (3) Magnetization of carbonized materials In the process of preparing magnetic materials by coprecipitation, the carbonized material of step (2) was added, and 1 g FeCl2·4H2O and 2 g FeCl3·6H2O (Fe 2+ :Fe 3+ =1:2) was added into a conical flask filled with 20 mL of deionized water to fully dissolve, followed by the addition of 15 g of biomass carbonized material and stirring at 80°C for 30 min under N2 protection. After mixing evenly, NH3·H2O was added dropwise and finally dried in a vacuum drying oven at 80°C for 12 h. The dried magnetic peach shell carbonized material was washed with deionized water until neutral, dried and ground for later use.

[0028] (4) Activation The magnetic peach shell carbonized material after magnetization in step (3) is placed in a crucible, activated at 200-600 °C for 2 h, and then taken out to obtain magnetic peach shell activated carbon. Example 3

[0029] A method for preparing magnetic apricot shell activated carbon comprises the following steps: (1) Preprocessing Apricot shells were dried in an oven at 110°C for 24 hours to remove free moisture from the biomass raw material. The raw material was then pulverized and sieved to 80-200 mesh. The raw material was washed repeatedly with deionized water, dried at 105°C, and thoroughly ground to obtain the pretreated biomass raw material.

[0030] (2) Carbonization The biomass raw material pretreated in step (1) is placed in a crucible and carbonized at 50-500°C for 2 h, and then taken out to obtain the carbonized material.

[0031] (3) Magnetization of carbonized materials In the process of preparing magnetic materials by coprecipitation, the carbonized material of step (2) was added, and 2.5 g FeCl2·4H2O and 5 g FeCl3·6H2O (Fe 2+ :Fe 3+ =1:2) was added into a conical flask filled with 50 mL of deionized water to fully dissolve, followed by the addition of 37.5 g of biomass carbonized material and stirring at 80°C for 30 min under N2 protection. After uniform mixing, NH3·H2O was added dropwise and finally dried in a vacuum drying oven at 80°C for 12 h. The dried magnetic apricot shell carbonized material was washed with deionized water until neutral, dried and ground for later use.

[0032] (4) Activation The magnetic apricot shell carbonized material after magnetization in step (3) is placed in a crucible, activated at 200-600 °C for 2 h, and then taken out to obtain magnetic apricot shell activated carbon.

Claims

1. A method for preparing magnetic biomass activated carbon, characterized in that: The following steps are involved: (1) Preprocessing The agricultural waste is placed in an oven to dry, free moisture in the biomass raw material is removed, and then the raw material is crushed, sieved to 80-200 mesh, repeatedly washed with deionized water, dried and fully ground to obtain the pretreated biomass raw material; (2) Carbonization The biomass raw material pretreated in step (1) is placed in a crucible for carbonization, and then taken out to obtain the carbonized material; (3) Magnetization of carbonized materials In the process of preparing the magnetic material by the coprecipitation method, the carbonized material of step (2) is added, FeCl2·4H2O and FeCl3·6H2O are added to a conical flask filled with deionized water and fully dissolved, and then the carbonized material of step (2) is added and stirred at 80°C for 30 min under N2 protection. After being mixed evenly, NH3·H2O is added dropwise until the pH is 9-10, and finally dried in a vacuum drying oven. The dried magnetic carbonized material is washed with deionized water until neutral, and then dried and ground for use; (4) Activation The magnetic biomass carbonized material after magnetization in step (3) is placed in a crucible for activation, and then taken out to obtain magnetic biomass activated carbon.

2. The method for preparing magnetic biomass activated carbon according to claim 1, wherein: The first oven drying condition in step (1) is drying at a temperature of 110°C for 24 h, and the drying temperature after washing with deionized water is 105°C.

3. The method for preparing magnetic biomass activated carbon according to claim 1, wherein: The carbonization condition in step (2) is 50-500°C for 2 h.

4. The method for preparing magnetic biomass activated carbon according to claim 1, wherein: Fe in step (3) 2+ :Fe 3+ The molar ratio is 1:2, and the mass volume ratio of carbonized material, FeCl2·4H2O and deionized water is 15g:1g:20mL.

5. The method for preparing magnetic biomass activated carbon according to claim 1, wherein: The drying condition in the vacuum drying oven in step (3) is 80° C. for 12 h.

6. The method for preparing magnetic biomass activated carbon according to claim 1, wherein: The activation condition in step (4) is activation at 200-600 °C for 2 h.

7. A magnetic biomass activated carbon obtained according to the preparation method according to any one of claims 1 to 6.

8. Use of the magnetic biomass activated carbon according to claim 7 in removing PFAS from tap water.

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