Multistage composite structure carbon-based adsorption material and preparation method and application thereof

Abstract

The application discloses a kind of multistage composite structure carbon-based adsorption material and its preparation method and application, comprising: under inert gas atmosphere, biomass is carbonized, then activated treatment is carried out, and porous activated carbon is obtained;Porous activated carbon is immersed in precursor aqueous solution, room temperature is kept for 12~24 hours, filtration, drying, again heat treatment, and modified activated carbon is obtained;Carbon nanotube is mixed with modified activated carbon, and mixed material is obtained, then dispersing agent is added and ball milled to be uniform, under inert atmosphere, heat treatment is carried out at 400~600 DEG C for 1~3 hours, and carbon-based composite is obtained;Carbon-based composite, inorganic clay and water are mixed, and suspension is obtained, the pH of the suspension is adjusted to 8~10, constant-temperature stirring reaction is carried out at 30~60 DEG C for 2~6 hours, centrifugation is carried out, drying is carried out, and enhanced composite material is obtained;Enhanced composite material is mixed with binder, granulation is carried out, calcination is carried out at 300~500 DEG C for 1~3 hours, and multistage composite structure carbon-based adsorption material is obtained.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment materials technology, specifically relating to a multi-level composite carbon-based adsorbent material, its preparation method, and its application in deep purification treatment. Background Technology

[0002] At present, water pollution problems are characterized by a wide variety of pollutants, complex composition, and great difficulty in treatment. In particular, the coexistence of heavy metal ions and recalcitrant organic pollutants has become a key factor restricting the development of the wastewater treatment industry.

[0003] Currently, most existing adsorption materials are based on single carbon materials. Among them, powdered activated carbon has a large specific surface area, but it is easy to disperse and be lost in water, making solid-liquid separation difficult and its long-term operational stability insufficient. Granular activated carbon is easy to pack and recover, but its pore structure is mainly micropores, resulting in insufficient mass transfer efficiency for macromolecular pollutants (such as dyes and aromatic amines), and its adsorption site utilization is limited in complex water quality.

[0004] Although carbon nanotubes, graphene and other nanomaterials have good adsorption potential and structural enhancement effects, they are prone to agglomeration when used directly in wastewater treatment, are costly and difficult to recycle. Although inorganic clay materials such as bentonite, kaolin and montmorillonite have layered structures and certain ion exchange capabilities, their adsorption capacity and structural stability are still insufficient when used alone.

[0005] Therefore, there is an urgent need to provide a composite carbon-based wastewater adsorption carrier that can take into account high specific surface area, multi-level pore structure, rich surface functional groups and good particle mechanical stability, so that it can meet the treatment needs of long-term stable operation under the condition of multiple pollutants coexisting in industrial wastewater and domestic sewage. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a multi-level composite carbon-based adsorbent material. This method involves modifying biomass to obtain modified activated carbon, which is then combined with carbon nanotubes and inorganic clay to successfully construct a multi-level porous structure possessing micropores, mesopores, and macropores. This simultaneously improves the number of adsorption sites, particle mechanical strength, and stability of the water treatment process.

[0007] Another object of the present invention is to provide a multi-level composite carbon-based adsorbent material obtained by the above preparation method.

[0008] Another objective of this invention is to provide the application of the above-mentioned multi-level composite carbon-based adsorbent material in the treatment of wastewater under conditions where multiple pollutants coexist.

[0009] The objective of this invention is achieved through the following technical solutions.

[0010] A method for preparing a multi-level composite carbon-based adsorbent material includes the following steps:

[0011] Step 1: Under a nitrogen or inert gas atmosphere, the biomass is carbonized at 500~800℃ for 1~3 hours, and then activated to obtain porous activated carbon. The biomass is one or more of straw, sawdust, coconut shell, camellia shell and rice husk.

[0012] In step 1, the particle size of the biomass is less than 5 mm, preferably 3-5 mm.

[0013] In step 1, the activation treatment conditions include: maintaining the temperature at 800~950℃ for 1~2 hours in a carbon dioxide or water vapor atmosphere.

[0014] In step 1, the temperature is increased to 500-800°C at a heating rate of 3-8°C / min.

[0015] In the above technical solution, the temperature is increased to 800-950℃ at a heating rate of 3-8℃ / min.

[0016] Step 2: Immerse porous activated carbon in a precursor aqueous solution, maintain at room temperature for 12-24 hours, filter, dry, and then heat-treat at 200-400℃ for 2-5 hours to obtain modified activated carbon. The precursor in the precursor aqueous solution is urea, NH3, hydrogen peroxide, HNO3, or KMnO4, and the concentration of the precursor in the precursor aqueous solution is 3-20 wt%.

[0017] In step 2, when the precursor aqueous solution is urea aqueous solution, the urea content in the precursor aqueous solution is 5~15wt%; when the precursor aqueous solution is hydrogen peroxide aqueous solution, the hydrogen peroxide content in the precursor aqueous solution is 3~10wt%; when the precursor aqueous solution is nitric acid, the HNO3 content in the precursor aqueous solution is 3~12wt%; when the precursor aqueous solution is KMnO4 aqueous solution, the KMnO4 content in the precursor aqueous solution is 3~8wt%; and when the precursor aqueous solution is ammonia, the NH3 content in the precursor aqueous solution is 8~20wt%.

[0018] In step 2, the ratio of the porous activated carbon to the precursor in the precursor aqueous solution is 1:(0.5~2) by mass.

[0019] In step 2, the drying temperature is 80~100℃ and the drying time is 12~24 hours.

[0020] In step 2, the room temperature is 20~30℃.

[0021] Step 3: Mix the oxidized and purified carbon nanotubes with modified activated carbon to obtain a mixture, then add a dispersant and ball mill until uniform. Heat treat at 400~600℃ for 1~3 hours under an inert atmosphere to obtain a carbon-based composite. The ratio of the oxidized and purified carbon nanotubes to the modified activated carbon is 1:(5~20) by mass. The dispersant is polyvinylpyrrolidone, sodium dodecylbenzenesulfonate or Tween-80.

[0022] In step 3, the ratio of the dispersant to the mixture is (0.005~0.02):1 by mass.

[0023] In step 3, the rate of heating to 400~600℃ is 5~10℃ / min.

[0024] In step 3, the inert atmosphere includes nitrogen or argon.

[0025] In step 3, the ball milling speed is 300~500 r / min, and the ball milling time is 2~6 hours.

[0026] In step 3, the method for obtaining oxidized and purified carbon nanotubes includes: placing carbon nanotubes in a mixed acid solution, sonicating at 60-90°C for 2-4 hours, centrifuging to obtain a first solid, washing the first solid with water until the pH value is 6.5-7.0, and then drying at 60-80°C for 12-24 hours to obtain oxidized and purified carbon nanotubes. The ratio of the mass fraction of carbon nanotubes to the volume fraction of the mixed acid solution is 100:(100-150), where the mass fraction is in mg and the volume fraction is in mL. The mixed acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1.

[0027] Step 4: Mix the carbon-based composite, inorganic clay and water to obtain a suspension. Adjust the pH of the suspension to 8-10, stir and react at a constant temperature of 30-60℃ for 2-6 hours, centrifuge and dry to obtain the reinforced composite material. The ratio of the carbon-based composite to the inorganic clay is 1:(1-3) by mass. The inorganic clay is one or a mixture of bentonite, kaolin and montmorillonite.

[0028] In step 4, the content of inorganic clay in the suspension is 10~20wt%.

[0029] In step 4, the drying temperature is 60~100℃ and the drying time is 6~12 hours.

[0030] Step 5: Mix the reinforced composite material with the binder, granulate, and calcine at 300~500℃ for 1~3 hours to set the shape, thereby obtaining a multi-level composite structure carbon-based adsorbent material.

[0031] In step 5, the adhesive includes a solid, which is polyvinyl alcohol, sodium carboxymethyl cellulose, silica sol or phenolic resin, wherein the ratio of the reinforced composite material to the solid is (7~9):(1~3) by mass parts.

[0032] In step 5, the granulation method includes: extrusion granulation or spray granulation.

[0033] In step 5, the temperature is increased to 300-500°C at a heating rate of 1-3°C / min.

[0034] The multi-level composite carbon-based adsorbent material obtained by the above preparation method.

[0035] In the above technical solution, the particle size of the multi-level composite carbon-based adsorbent material is 1~5mm.

[0036] In the above technical solution, the multi-level composite carbon-based adsorbent material has a multi-level pore structure in which micropores, mesopores, and macropores coexist, and its specific surface area is not less than 800 m². 2 / g.

[0037] The above-mentioned multi-level composite carbon-based adsorbent materials are used in wastewater treatment under conditions where multiple pollutants coexist.

[0038] In the above technical solution, the pollutants include: heavy metal ions and organic pollutants, wherein the heavy metal ions are ions containing chromium, lead or cadmium, and the organic pollutants are rhodamine B, methyl orange, aniline or phenol.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) This invention uses agricultural and forestry biomass waste as a carbon source to prepare porous activated carbon. The raw materials are widely available and the cost is low, which is conducive to realizing the resource utilization of waste biomass. The preparation method of this invention is controllable, and the resulting multi-level composite carbon-based adsorbent material has stable performance and good adsorption performance under the condition of coexistence of multiple pollutants.

[0041] (2) This invention improves the surface affinity of the resulting multi-level composite carbon-based adsorbent material for heavy metal ions and polar organic pollutants by modifying porous activated carbon with nitrogen- or oxygen-containing functional groups. The oxidized and purified carbon nanotubes are then combined with the modified activated carbon, distributing the carbon nanotubes between the activated carbon particles to form a bridging framework and mesoporous channels, thus improving the mass transfer limitation problem caused by the predominantly microporous structure of traditional activated carbon. The layered structure and bonding reinforcement of inorganic clay are utilized to improve the compressive strength and water treatment operation stability of the granular multi-level composite carbon-based adsorbent material.

[0042] (3) The multi-level composite carbon-based adsorbent material obtained in this invention has high specific surface area, high compressive strength and high unit adsorption capacity, and is suitable for deep purification treatment of industrial wastewater and domestic sewage. Attached Figure Description

[0043] Figure 1 A scanning electron microscope (SEM) image of the multi-level composite carbon-based adsorbent material obtained in Example 3;

[0044] Figure 2 The nitrogen isothermal adsorption-desorption curve of the multi-level composite carbon-based adsorbent material obtained in Example 3 is shown. Detailed Implementation

[0045] This invention uses agricultural and forestry biomass waste as a carbon source to prepare porous activated carbon, which is beneficial for realizing the resource utilization of waste biomass. The resulting multi-level composite carbon-based adsorbent material has stable performance and good adsorption performance under conditions where multiple pollutants coexist. The technical solution of this invention will be further described below with reference to embodiments and accompanying drawings.

[0046] Unless otherwise specified, the water used in the following embodiments is deionized water; drying is carried out in a vacuum drying oven.

[0047] The raw materials used in the following embodiments are from the following sources:

[0048] Coconut shells, straw, sawdust, camellia shells and rice husks (agricultural and forestry biomass waste) are all taken from agricultural and sideline product processing enterprises in Laosongzhuang Village, Houjiaying Town, Jizhou District, Tianjin. They are used after being crushed and screened, and their particle size ranges from 3 to 5 mm.

[0049] Urea, hydrogen peroxide, nitric acid, sodium hydroxide, phenol, rhodamine B, aniline, methyl orange, polyvinylpyrrolidone, sodium carboxymethyl cellulose, sodium dodecylbenzene sulfonate, and polyvinyl alcohol were all purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd., and were of analytical grade.

[0050] Bentonite, kaolin, and montmorillonite were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and were of analytical grade.

[0051] Cr(VI), Pb 2+ and Cd 2+ The standard solution was purchased from Tianjin Kemeo Chemical Reagent Co., Ltd.; analytical standard.

[0052] In this invention, if the carbon nanotubes are self-made, they can be prepared by chemical vapor deposition. The carbon source gas is one of methane, acetylene, or propylene, and the catalyst is a single-metal nanoparticle of iron, cobalt, or nickel, or a bimetallic alloy nanoparticle of iron-cobalt or iron-nickel, with a catalyst particle size of 5-20 nm. This method of preparing carbon nanotubes is an optional method for obtaining carbon nanotubes and is not the sole core difference between this invention and existing technologies. In the following examples, the carbon nanotubes were purchased from Shenzhen Suiheng Technology Co., Ltd., and were multi-walled carbon nanotubes with an inner diameter of 3-5 nm, a length of 8-15 μm, and a purity of 99%.

[0053] In the following embodiments, the method for obtaining oxidized and purified carbon nanotubes includes: placing carbon nanotubes in a mixed acid solution, ultrasonically treating them at 60°C (ultrasonic frequency of 50Hz) for 2 hours, centrifuging to obtain a first solid, washing the first solid with water until the pH of the washing solution is 6.5, and then drying it at 80°C for 12 hours to obtain oxidized and purified carbon nanotubes, wherein the mass fraction of carbon nanotubes and the volume fraction of the mixed acid solution are 100:100, the mass fraction is in mg and the volume fraction is in mL; the mixed acid solution is a mixture of concentrated sulfuric acid (98%) and concentrated nitric acid (65%) in a volume ratio of 3:1.

[0054] The water vapor (pure water) atmosphere involved in the following examples is a water vapor flow rate of 500 ml / min.

[0055] Example 1

[0056] A method for preparing a multi-level composite carbon-based adsorbent material includes the following steps:

[0057] Step 1: Place biomass (particle size 3~5mm) in a tubular atmosphere furnace (model OTF-1200X, purchased from Hefei Kejing Materials Technology Co., Ltd.), heat it to 650℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and carbonize it at 650℃ for 2 hours. Then, under a steam (pure water) atmosphere, heat it to 850℃ at a heating rate of 5℃ / min and hold it at 850℃ for 1.5 hours for activation treatment to obtain porous activated carbon. The biomass is coconut shell.

[0058] Step 2: Immerse porous activated carbon in a precursor aqueous solution and maintain at room temperature (25°C) for 18 hours to allow the porous activated carbon to recombine with the nitrogen-containing functional groups in the precursor aqueous solution. Filter to obtain a second solid, dry the second solid at 80°C for 12 hours, and then heat-treat at 300°C for 3 hours to obtain modified activated carbon. The precursor aqueous solution is a 10wt% urea aqueous solution (i.e., the precursor is urea). By mass fraction, the ratio of porous activated carbon to the precursor in the precursor aqueous solution is 1:1.5.

[0059] Step 3: Mix the oxidized and purified carbon nanotubes with modified activated carbon to obtain a mixture. Then add a dispersant and grinding balls (made of zirconium oxide). Ball mill at 400 r / min for 4 hours until homogeneous. Heat treat at 500℃ (heating rate to 500℃ is 5℃ / min) for 2 hours under an inert (nitrogen) atmosphere to obtain a carbon-based composite. The mass ratio of oxidized and purified carbon nanotubes to modified activated carbon is 1:10, the dispersant is polyvinylpyrrolidone, the mass ratio of dispersant to mixture is 0.01:1, and the mass ratio of grinding balls to mixture is 15:1.

[0060] Step 4: Add the carbon-based composite and inorganic clay to deionized water to obtain a suspension. Adjust the pH of the suspension to 9 with a sodium hydroxide aqueous solution (sodium hydroxide concentration of 1 mol / L). Stir and react at 45℃ for 4 hours. Centrifuge to obtain a third solid. Dry the third solid at 80℃ for 12 hours to obtain the reinforced composite material. The ratio of carbon-based composite to inorganic clay is 1:2 by mass, and the inorganic clay is bentonite. The inorganic clay content in the suspension is 10 wt%.

[0061] Step 5: Mix the reinforced composite material with the binder, and prepare particles with a particle size of about 3 mm by extrusion granulation. Then, place the particles in a tube furnace and heat them to 400 °C at a heating rate of 2 °C / min and calcine them at 400 °C for 2 hours to solidify the particles and obtain a multi-level composite carbon-based adsorbent material (particles with an average particle size of 3 mm). The binder is an aqueous solution of sodium carboxymethyl cellulose (the concentration of sodium carboxymethyl cellulose in the aqueous solution is 5 wt%). By mass, the ratio of the reinforced composite material to sodium carboxymethyl cellulose is 8:2.

[0062] Example 2

[0063] A method for preparing a multi-level composite carbon-based adsorbent material includes the following steps:

[0064] Step 1: Place biomass (particle size 3~5mm) in a tubular atmosphere furnace, heat it to 600℃ at a heating rate of 4℃ / min under a nitrogen atmosphere, and carbonize it at 600℃ for 2 hours. Then, heat it to 820℃ at a heating rate of 4℃ / min under a carbon dioxide (pure carbon dioxide) atmosphere and hold it at 820℃ for 1 hour to obtain porous activated carbon. The biomass is a mixture of straw and wood chips in a mass ratio of 1:1.

[0065] Step 2: Immerse porous activated carbon in a precursor aqueous solution and maintain at room temperature for 12 hours to allow the porous activated carbon to recombine with the oxygen-containing functional groups in the precursor aqueous solution. Filter to obtain a second solid, dry the second solid at 80°C for 12 hours, and then heat-treat at 250°C for 3 hours to obtain modified activated carbon. The ratio of porous activated carbon to precursor in the precursor aqueous solution is 1:0.6 by mass, and the precursor aqueous solution is a 5wt% hydrogen peroxide aqueous solution (the precursor is hydrogen peroxide).

[0066] Step 3: Mix the oxidized and purified carbon nanotubes with modified activated carbon to obtain a mixture. Then add a dispersant and grinding balls, and ball mill at 350 r / min for 3 hours until homogeneous. Heat treat at 450℃ (heating rate to 450℃ is 5℃ / min) for 2 hours under an inert (nitrogen) atmosphere to obtain a carbon-based composite. The mass ratio of oxidized and purified carbon nanotubes to modified activated carbon is 1:8, the dispersant is sodium dodecylbenzenesulfonate, the mass ratio of dispersant to mixture is 0.008:1, and the mass ratio of grinding balls to mixture is 10:1.

[0067] Step 4: Add the carbon-based composite and inorganic clay to deionized water to obtain a suspension. Adjust the pH of the suspension to 8.5 with a sodium hydroxide aqueous solution (sodium hydroxide concentration of 1 mol / L). Stir and react at 40℃ for 3 hours. Centrifuge to obtain a third solid. Dry the third solid at 70℃ for 12 hours to obtain the reinforced composite material. The ratio of carbon-based composite to inorganic clay is 1:1 by mass, and the inorganic clay is kaolin. The inorganic clay content in the suspension is 10 wt%.

[0068] Step 5: Mix the reinforced composite material with the binder, and prepare particles with a particle size of about 2 mm by spray granulation. Then, place the particles in a tube furnace and heat them to 350 °C at a heating rate of 2 °C / min and calcine them at 350 °C for 2 hours to solidify the particles and obtain a multi-level composite carbon-based adsorbent material (particles with an average particle size of 2 mm). The binder is a polyvinyl alcohol aqueous solution (the concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 5 wt%). By mass, the ratio of the reinforced composite material to polyvinyl alcohol is 9:1.

[0069] Example 3

[0070] A method for preparing a multi-level composite carbon-based adsorbent material includes the following steps:

[0071] Step 1: Place biomass (particle size 3~5mm) in a tubular atmosphere furnace, heat it to 700℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and carbonize it at 700℃ for 2 hours. Then, activate it by heating it to 900℃ at a heating rate of 5℃ / min under a steam atmosphere and holding it at 900℃ for 1.5 hours to obtain porous activated carbon. The biomass is a mixture of camellia oleifera shells and rice husks in a mass ratio of 2:1.

[0072] Step 2: Immerse porous activated carbon in a precursor aqueous solution and maintain at room temperature for 18 hours to allow the porous activated carbon to recombine with the oxygen-containing functional groups in the precursor aqueous solution. Filter to obtain a second solid, dry the second solid at 80°C for 12 hours, and then heat-treat at 300°C for 3 hours to obtain modified activated carbon. The ratio of porous activated carbon to precursor in the precursor aqueous solution is 1:1.2 by mass, and the precursor aqueous solution is 8 wt% nitric acid (the precursor is HNO3).

[0073] Step 3: Mix the oxidized and purified carbon nanotubes with modified activated carbon to obtain a mixture. Then add a dispersant and grinding balls, and ball mill at 400 r / min for 4 hours until homogeneous. Heat treat at 500℃ (heating rate to 500℃ is 5℃ / min) for 2 hours under an inert (nitrogen) atmosphere to obtain a carbon-based composite. The mass ratio of oxidized and purified carbon nanotubes to modified activated carbon is 1:15, the dispersant is polyvinylpyrrolidone, the mass ratio of dispersant to mixture is 0.01:1, and the mass ratio of grinding balls to mixture is 15:1.

[0074] Step 4: Add the carbon-based composite and inorganic clay to deionized water to obtain a suspension. Adjust the pH of the suspension to 9 with a sodium hydroxide aqueous solution (sodium hydroxide concentration of 1 mol / L). Stir and react at 45℃ for 4 hours. Centrifuge to obtain a third solid. Dry the third solid at 80℃ for 12 hours to obtain the reinforced composite material. The ratio of carbon-based composite to inorganic clay is 1:3 by mass, and the inorganic clay is a mixture of montmorillonite and bentonite in a mass ratio of 1:1. The inorganic clay content in the suspension is 10 wt%.

[0075] Step 5: Mix the reinforced composite material with the binder, and prepare particles with a particle size of about 4 mm by extrusion granulation. Then, place the particles in a tube furnace and heat them to 400 °C at a heating rate of 2 °C / min and calcine them at 400 °C for 2 hours to solidify the particles and obtain a multi-level composite carbon-based adsorbent material (particles with an average particle size of 4 mm). The binder is an aqueous solution of sodium carboxymethyl cellulose (the concentration of sodium carboxymethyl cellulose in the aqueous solution is 5 wt%). By mass, the ratio of the reinforced composite material to sodium carboxymethyl cellulose is 8:2.

[0076] The multi-level composite carbon-based adsorbent material obtained in Example 3 was subjected to SEM testing using a scanning electron microscope (Quanta FEG, purchased from FEI, USA). Its surface morphology is shown in the figure below. Figure 1 As shown. By Figure 1 As can be seen, the multi-level composite carbon-based adsorbent material obtained in Example 3 exhibits a rough, porous surface structure, with obvious lamellar and channel structures. This indicates that the inorganic clay and carbon-based composite form a composite hierarchical structure, which is beneficial for providing a larger specific surface area and more pollutant mass transfer channels.

[0077] Comparative Example 1

[0078] A method for preparing a carbon-based adsorbent material includes the following steps:

[0079] Step 1: Place the biomass (coconut shell, particle size less than 5mm) in a tube furnace, heat it to 650℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and carbonize it at 650℃ for 2 hours. Then, heat it to 850℃ at a heating rate of 5℃ / min under a steam atmosphere and hold it at 850℃ for 1.5 hours to activate it, thereby obtaining porous activated carbon. The biomass is coconut shell.

[0080] Step 2: The porous activated carbon is mixed with a binder and granulated by extrusion to prepare particles with a diameter of about 3 mm. The particles are then placed in a tube furnace and heated to 400 °C at a heating rate of 2 °C / min and calcined at 400 °C for 2 hours to solidify the particles and obtain carbon-based adsorbent material (particles with an average particle size of 3 mm). The binder is an aqueous solution of sodium carboxymethyl cellulose (the concentration of sodium carboxymethyl cellulose in the aqueous solution is 5 wt%). The ratio of porous activated carbon to sodium carboxymethyl cellulose is 8:2 by mass.

[0081] Nitrogen adsorption-desorption tests were performed on the samples using a fully automated specific surface area and microporous physical and chemical adsorption analyzer (model ASAP2020M+C, purchased from Micromeritics, USA). The samples were one of the multi-stage composite carbon-based adsorbent materials obtained in Examples 1-3 and the carbon-based adsorbent material obtained in Comparative Example 1. The nitrogen adsorption-desorption test temperature was 77 K, and the samples were degassed under vacuum at 120 °C for 6 hours before the test. The specific surface areas of the samples obtained by fitting the BET model are shown in Table 1. Table 1 shows that the specific surface areas of the multi-stage composite carbon-based adsorbent materials obtained in Examples 1-3 and the carbon-based adsorbent material obtained in Comparative Example 1 were 926, 889, 965, and 425 m², respectively. 2 / g.

[0082] Figure 2 The isothermal adsorption-desorption curves of the multi-level composite carbon-based adsorbent material obtained in Example 3 are shown below. Figure 2 It can be seen that the micropore adsorption capacity of the multi-level composite carbon-based adsorbent material obtained in Example 3 is as high as 200 cm³. 3 The adsorption capacity is / g, and a hysteresis loop is present. This exhibits typical adsorption characteristics of mesoporous materials, and the accompanying hysteresis loop indicates the presence of a mesoporous structure. Specifically, the isothermal adsorption-desorption curve shows a rapid increase in adsorption capacity in the low-pressure range, indicating that the multi-level composite carbon-based adsorbent material contains certain micropores, while the increase in adsorption capacity in the high-pressure range indicates the presence of macropores or interparticle packing pores. This demonstrates that the multi-level composite carbon-based adsorbent material obtained in this invention possesses a multi-level pore structure with synergistic micropores, mesopores, and macropores.

[0083] Table 1

[0084]

[0085] Compressive strength test: The compressive strength of the samples was tested using an electronic universal testing machine (model INSTRON 5967, purchased from Instrand Corporation, USA). The samples were one of the multi-level composite carbon-based adsorbent materials obtained in Examples 1-3 and the carbon-based adsorbent material obtained in Comparative Example 1. Ten particles of similar particle size were selected from each sample for testing to obtain the compressive strength. The average compressive strength of the ten particles was recorded as the sample's compressive strength, and the results are shown in Table 1. Table 1 shows that the compressive strengths of the multi-level composite carbon-based adsorbent materials obtained in Examples 1 and 2 were 88.3 N and 76.2 N, respectively; the compressive strength of the multi-level composite carbon-based adsorbent material obtained in Example 3 was as high as 92.5 N, which is 2.64 times that of the carbon-based adsorbent material obtained in Comparative Example 1. This indicates that the multi-level composite carbon-based adsorbent material obtained in this invention has high compressive strength and good mechanical stability.

[0086] Single-system adsorption test: Accurately weigh 0.1g of the sample to be tested and add it to a conical flask containing 200mL of phenol solution (the phenol solution is a mixture of phenol and deionized water, with a phenol concentration of 1g / L (i.e., C0 is 1g / L), pH≈5). Place the conical flask at 25℃ and 150r / min and shake for 3 hours until adsorption equilibrium is reached. Take 50mL of the supernatant from the equilibrium system and filter it through a 0.45μm microporous membrane to obtain the test solution. Measure the concentration of the test solution at 270nm wavelength using a UV-Vis spectrophotometer to obtain the phenol concentration (C) in the test solution. Calculate the unit adsorption capacity according to the formula: q=(C0-C)V / m, where q is the unit adsorption capacity (mg / g), V is the volume of the test solution (mL), and m is the mass of the sample (g). The sample to be tested is one of the multi-level composite carbon-based adsorbent materials obtained in Examples 1-3 and the carbon-based adsorbent material obtained in Comparative Example 1.

[0087] The adsorption capacities per unit area of ​​the multi-level composite carbon-based adsorbent materials obtained in Examples 1-3 and the carbon-based adsorbent obtained in Comparative Example 1 are shown in Table 2. Table 2 shows that the multi-level composite carbon-based adsorbent material obtained in Example 3 exhibits the best adsorption performance for phenol, with a per unit adsorption capacity as high as 1056 mg / g. The adsorption performance of the multi-level composite carbon-based adsorbent material obtained in Example 3 is far superior to that of Comparative Example 1, which relies solely on a single activated carbon site.

[0088] Table 2

[0089]

[0090] Composite System Adsorption Test: The multi-stage composite carbon-based adsorbent material obtained in Example 3 was used as the adsorbent to investigate its removal capacity in systems with multiple coexisting pollutants. The adsorbent (the multi-stage composite carbon-based adsorbent material obtained in Example 3) was added to simulated wastewater in different systems to obtain adsorption systems. The concentration of the adsorbent in the adsorption system was 0.5 g / L. The systems were shaken at 25℃ and 150 r / min for 3 hours until adsorption equilibrium was reached, resulting in a mixed equilibrium system. 50 mL of the supernatant was filtered through a 0.45 μm microporous membrane to obtain the test sample. The simulated wastewater was a mixture of deionized water and pollutants. The different pollutants and their initial concentrations (C0, mg / L) in the simulated wastewater of systems 1 to 9 are shown in Table 3.

[0091] In the test samples of different systems, heavy metal ions (Cr(VI), Pb) 2+ and Cd 2+ The concentrations (C, mg / L) of phenyl benzoate (PURCHEP) were determined using an atomic absorption spectrophotometer (PURCHEP TAS-990, purchased from Beijing PURCHEP General Instrument Co., Ltd.); the concentrations (C) of rhodamine B and methyl orange were determined using a UV-Vis spectrophotometer (PURCHEP T6, purchased from Beijing PURCHEP General Instrument Co., Ltd.); and the concentrations (C) of aniline and phenol were determined using a high-performance liquid chromatograph (Themal UltiMate 3000 HPLC, purchased from Thermo Fisher Scientific, USA). When using the UV-Vis spectrophotometer, the concentration of rhodamine B was measured at a wavelength of 554 nm, and the concentration of methyl orange was measured at a wavelength of 465 nm.

[0092] The pollutant removal rate is calculated using the following formula: η=(C0-C) / C0, where η is the removal rate (%).

[0093] Table 3

[0094]

[0095] The removal rates of the multi-level composite carbon-based adsorbent obtained in Example 3 as an adsorbent in a system with multiple coexisting pollutants are shown in Table 3. Table 3 shows that in System 1, the removal rates of 20 mg / L Cr(VI), 20 mg / L Rhodamine B, and 30 mg / L aniline by the multi-level composite carbon-based adsorbent obtained in Example 3 were all higher than 95.8%. This indicates that the multi-level porous structure and surface functional groups synergistically improved the adsorption performance of low-concentration pollutants. In System 2, the removal rates of 50 mg / L Cr(VI), 20 mg / L Rhodamine B, and 30 mg / L aniline by the multi-level composite carbon-based adsorbent obtained in Example 3 were all above 93.2%. Comparing the removal rates of Cr(VI) in System 1 and System 2, it can be seen that the removal rate slightly decreased with increasing Cr(VI) concentration, but still remained at a high level. In System 3, the multi-level composite carbon-based adsorbent obtained in Example 3 achieved removal rates of over 90.8% for 80 mg / L Cr(VI), 20 mg / L Rhodamine B, and 30 mg / L aniline. This indicates that the multi-level composite carbon-based adsorbent maintains good adsorption stability even at high Cr(VI) concentrations.

[0096] In systems 4-6, the multi-level composite carbon-based adsorbent obtained in Example 3 is effective against Pb. 2+ Methyl orange and aniline all showed high removal rates. This indicates that modified activated carbon, carbon nanotube bridging structures, and clay-reinforced frameworks can collectively improve the removal efficiency of heavy metal ions, azo dyes (methyl orange), and aromatic amine pollutants.

[0097] In systems 7-9, the multi-level composite carbon-based adsorbent material obtained in Example 3 is effective for Cd. 2+ Phenol and aniline all have good removal effects. When Cd 2+ As the concentration increased, the removal rate decreased somewhat, but remained at a high level. This indicates that the multi-level composite carbon-based adsorbent material can adapt to different heavy metal concentrations and exhibits good adsorption stability in practical applications.

[0098] Adsorption test of the mixed system of carbon-based adsorbent material obtained in Comparative Example 1: This is basically the same as the "composite system adsorption test," except for the concentrations of the adsorbent and pollutants in the simulated wastewater. The adsorbent is the carbon-based adsorbent material obtained in Comparative Example 1. The initial concentrations of different pollutants in the simulated wastewater of systems 10 to 12 are shown in Table 4.

[0099] Table 4

[0100]

[0101] The removal rates of Cr(VI), Rhodamine B, and aniline by the carbon-based adsorbent material obtained in Comparative Example 1 in different systems are shown in Table 4. As can be seen from Table 4, the removal rates of Cr(VI) and Rhodamine B by the carbon-based adsorbent material obtained in Comparative Example 1 in different systems are all below 70%. This indicates that conventional physical adsorption relying solely on activated carbon is ineffective, making it difficult to achieve the high removal efficiency of the multi-stage composite structure carbon-based adsorbent material of this invention.

[0102] This invention prepares porous activated carbon using agricultural and forestry biomass waste as a carbon source. By modifying the porous activated carbon with nitrogen- or oxygen-containing functional groups, the surface affinity of the resulting hierarchical composite carbon-based adsorbent material for heavy metal ions and polar organic pollutants is improved. Oxidized and purified carbon nanotubes are composited with the modified activated carbon, allowing the carbon nanotubes to distribute between the activated carbon particles, forming a bridging framework and mesoporous channels, thus improving the mass transfer limitation problem caused by the predominantly microporous nature of traditional activated carbon. The layered structure and bonding reinforcement effect of inorganic clay are utilized to improve the compressive strength and water treatment operation stability of the granular hierarchical composite carbon-based adsorbent material.

[0103] The multi-level composite carbon-based adsorbent material obtained by this invention has high specific surface area, high compressive strength and high adsorption capacity per unit area, making it suitable for the deep purification treatment of industrial wastewater and domestic sewage.

[0104] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a multi-level composite carbon-based adsorbent material, characterized in that, Includes the following steps: Step 1: Under a nitrogen or inert gas atmosphere, the biomass is carbonized at 500~800℃ for 1~3 hours, and then activated to obtain porous activated carbon. The biomass is one or more of straw, sawdust, coconut shell, camellia shell and rice husk. Step 2: Immerse porous activated carbon in a precursor aqueous solution, maintain at room temperature for 12-24 hours, filter, dry, and then heat-treat at 200-400℃ for 2-5 hours to obtain modified activated carbon. The precursor in the precursor aqueous solution is urea, NH3, hydrogen peroxide, HNO3, or KMnO4, and the concentration of the precursor in the precursor aqueous solution is 3-20 wt%. Step 3: Mix the oxidized and purified carbon nanotubes with modified activated carbon to obtain a mixture, then add a dispersant and ball mill until uniform. Heat treat at 400~600℃ for 1~3 hours under an inert atmosphere to obtain a carbon-based composite. The ratio of the oxidized and purified carbon nanotubes to the modified activated carbon is 1:(5~20) by mass. The dispersant is polyvinylpyrrolidone, sodium dodecylbenzenesulfonate or Tween-80. Step 4: Mix the carbon-based composite, inorganic clay and water to obtain a suspension. Adjust the pH of the suspension to 8-10, stir and react at a constant temperature of 30-60℃ for 2-6 hours, centrifuge and dry to obtain the reinforced composite material. The ratio of the carbon-based composite to the inorganic clay is 1:(1-3) by mass. The inorganic clay is one or a mixture of bentonite, kaolin and montmorillonite. Step 5: Mix the reinforced composite material with the binder, granulate, and calcine at 300~500℃ for 1~3 hours to set the shape, thereby obtaining a multi-level composite structure carbon-based adsorbent material.

2. The preparation method according to claim 1, characterized in that, In step 5, the adhesive includes a solid, which is polyvinyl alcohol, sodium carboxymethyl cellulose, silica sol or phenolic resin, wherein the ratio of the reinforced composite material to the solid is (7~9):(1~3) by mass parts.

3. The preparation method according to claim 1, characterized in that, In step 5, the granulation method includes: extrusion granulation or spray granulation.

4. The preparation method according to claim 1, characterized in that, In step 1, the biomass particle size is less than 5 mm.

5. The preparation method according to claim 1, characterized in that, In step 1, the activation treatment conditions include: maintaining the temperature at 800~950℃ for 1~2 hours in a carbon dioxide or water vapor atmosphere.

6. The preparation method according to claim 1, characterized in that, In step 4, the content of inorganic clay in the suspension is 10~20wt%.

7. The preparation method according to claim 1, characterized in that, In step 2, when the precursor aqueous solution is urea aqueous solution, the urea content in the precursor aqueous solution is 5~15wt%; when the precursor aqueous solution is hydrogen peroxide aqueous solution, the hydrogen peroxide content in the precursor aqueous solution is 3~10wt%; when the precursor aqueous solution is nitric acid, the HNO3 content in the precursor aqueous solution is 3~12wt%; when the precursor aqueous solution is KMnO4 aqueous solution, the KMnO4 content in the precursor aqueous solution is 3~8wt%; and when the precursor aqueous solution is ammonia, the NH3 content in the precursor aqueous solution is 8~20wt%.

8. The preparation method according to claim 1, characterized in that, In step 3, the method for obtaining oxidized and purified carbon nanotubes includes: placing carbon nanotubes in a mixed acid solution, sonicating at 60-90°C for 2-4 hours, centrifuging to obtain a first solid, washing the first solid with water until the pH value is 6.5-7.0, and then drying at 60-80°C for 12-24 hours to obtain oxidized and purified carbon nanotubes. The ratio of the mass fraction of carbon nanotubes to the volume fraction of the mixed acid solution is 100:(100-150), where the mass fraction is in mg and the volume fraction is in mL. The mixed acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1.

9. The multi-level composite carbon-based adsorbent material obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the multi-level composite carbon-based adsorbent material as described in claim 9 in the treatment of wastewater under conditions of multiple pollutant coexistence.

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