Biochar-based adsorbent activated by polyphenol hydroxyl organic acid potassium salt and preparation method thereof

Abstract

The invention relates to a polyphenol hydroxyl organic acid potassium salt activated charcoal-based adsorbent and a preparation method thereof. The method comprises the following steps: pre-carbonizing a biomass material to obtain biochar; the preparation method comprises the following steps: stirring and dipping charcoal in a polyphenol hydroxyl organic acid hot solution to obtain a dipping solution, and then filtering the dipping solution to obtain charcoal coated with a polyphenol hydroxyl organic acid layer; stirring and dipping the charcoal coated with the polyphenol hydroxyl organic acid layer in a potassium hydroxide solution, and then drying to obtain a slurry mixture; and performing high-temperature pyrolysis on the slurry mixture to prepare the polyphenol hydroxyl organic acid potassium salt activated charcoal-based adsorbent. The biochar-based adsorbent obtained by the invention has a high specific surface area, a developed pore structure and excellent adsorption performance, and can be used for efficiently adsorbing and removing organic pollutants such as dyes, antibiotics and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorbent materials, in particular to a kind of polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent and preparation method thereof. BACKGROUND

[0002] With the development of industrialization, the problem of organic pollutant pollution in China is becoming increasingly serious, and the treatment of dyes, antibiotics and other organic pollutants is urgent. The conventional treatment method for wastewater containing organic pollutants at home and abroad is biochemical pond treatment, that is, after pretreatment to improve the biodegradability, the wastewater is introduced into the biochemical pond, and the organic pollutants are degraded under the action of microorganisms. The effluent still contains low concentration of pollutants, which still has potential harm to the environment and needs to be treated deeply. In the deep treatment method, adsorption is a more economical and practical method. Activated carbon material has excellent adsorption performance and is one of the most suitable adsorbents for organic pollutant treatment. Biochar is easy to obtain, cheap, has high yield and certain adsorption capacity, and can be used as a cheap substitute for activated carbon to achieve the effect of waste treatment. China is rich in biomass resources, but the development of biomass materials such as agricultural and forestry waste resources, grass leaves and / or wood materials is not sufficient, and the added value of biomass-related products is not high, which needs to be developed deeply. The main component of agricultural and forestry waste is lignocellulose, which is the main raw material of biochar. However, the existing prepared biochar material has poor adsorption and removal effect on dyes and antibiotics and other organic pollutants.

[0003] In view of the above, it is necessary to provide a kind of polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent and preparation method thereof. SUMMARY

[0004] In order to solve one or more technical problems in the prior art, the present application provides a kind of polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent and preparation method thereof.

[0005] The present application provides a kind of polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent and preparation method thereof in the first aspect, the method comprises the following steps:

[0006] (1) the biomass material is pre-carbonized, and biochar is obtained;

[0007] (2) the biochar is stirred and immersed in a polyphenol hydroxyl organic acid hot solution, an immersion solution is obtained, then the immersion solution is filtered, and the biochar coated with a polyphenol hydroxyl organic acid layer is obtained;

[0008] (3) the biochar coated with a polyphenol hydroxyl organic acid layer is stirred and immersed in a potassium hydroxide solution, and then dried to obtain a slurry mixture;

[0009] (4) high-temperature pyrolysis of the slurry-like mixture to obtain a polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent.

[0010] Preferably, in step (1): the biomass material is a lignocellulosic biomass material, preferably, the lignocellulosic biomass material is one or more of agricultural and forestry wastes, grass leaves and wood materials, more preferably, the lignocellulosic biomass material is one or more of straw, grass leaves, fruit shells and wood materials, further preferably, the fruit shells are acorn shells; and / or the biomass material is pretreated before pre-carbonization to obtain biomass material with particle size less than 18 mesh.

[0011] Preferably, in step (1): the pre-carbonization is carried out under inert gas protection, preferably in a nitrogen atmosphere, or the pre-carbonization is carried out in a closed space by pre-removing oxygen through limited combustion; and / or the temperature of the pre-carbonization is 300-600℃, and the time is 1-3h.

[0012] Preferably, in step (2): the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is one or more of gallic acid, tannic acid, other aromatic organic acids containing multiple phenolic hydroxyl groups or biomass extracts containing more of the above components, preferably, the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is gallic acid and / or tannic acid.

[0013] Preferably, in step (2): when the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is gallic acid, the concentration of gallic acid in the polyphenol hydroxyl organic acid hot solution is 50-150g / L, and the temperature of the polyphenol hydroxyl organic acid hot solution is 70-90℃, preferably 80-90℃; when the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is tannic acid, the concentration of tannic acid in the polyphenol hydroxyl organic acid hot solution is 200-300g / L, and the temperature of the polyphenol hydroxyl organic acid hot solution is 50-60℃; the ratio of the use amount of the biochar to the polyphenol hydroxyl organic acid hot solution is (25-115)g:1L; the mass ratio of the biochar to the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is 1:(1-3); and / or the time of the stirring and impregnation is 12-24h.

[0014] Preferably, in step (2), when the polyphenol hydroxyl organic acid in the hot solution of polyphenol hydroxyl organic acid is gallic acid, the temperature of the impregnation solution before filtration is not less than 70℃, the filtration time is not more than 5 min, preferably, the filtrate after filtration is recycled and reused until no solid is precipitated when cooled to 40℃; or when the polyphenol hydroxyl organic acid in the hot solution of polyphenol hydroxyl organic acid is tannic acid, the temperature of the impregnation solution before filtration is not less than 50℃, the filtration time is not more than 5 min, preferably, the filtrate after filtration is recycled and reused until no solid is precipitated when cooled to 30℃.

[0015] Preferably, in step (3), the temperature of the potassium hydroxide solution is not more than 30℃, preferably not more than 20℃; the concentration of the potassium hydroxide solution is 200-300 g / L; the time of stirring impregnation is 1-2 h; and / or the mass ratio of potassium hydroxide in the potassium hydroxide solution to the biochar in step (2) is (1-3) : 1.

[0016] Preferably, in step (3), the temperature of the potassium hydroxide solution is not more than 30℃, preferably not more than 20℃; the concentration of the potassium hydroxide solution is 200-300 g / L; the time of stirring impregnation is 1-2 h; and / or the mass ratio of potassium hydroxide in the potassium hydroxide solution to the biochar in step (2) is (1-3) : 1.

[0017] Preferably, in step (4), the high-temperature pyrolysis is carried out under the protection of inert gas, preferably in a nitrogen atmosphere, or the high-temperature pyrolysis is carried out in a closed space by pre-removing oxygen through limited combustion; and / or the temperature of the high-temperature pyrolysis is 800-1000℃, the time is 1-3 h, and the heating rate to the temperature of high-temperature pyrolysis is 2-5℃ / min.

[0018] The present application provides, in a second aspect, a polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent prepared by the preparation method described in the first aspect of the present application.

[0019] Compared with the prior art, the present application has at least the following beneficial effects:

[0020] (1) The present application develops a method for activating biochar by polyphenol hydroxyl organic acid potassium, thereby obtaining an activated biochar-based adsorbent material with high specific surface area and developed pore structure, for rapid and efficient removal of pollutants such as dyes and antibiotics in wastewater. The method of the present application uses biochar as raw material, takes advantage of the different solubility of polyphenol hydroxyl organic acid in hot water and cold water, coats a thin layer of polyphenol hydroxyl organic acid on the surface of biochar, and then converts it to polyphenol hydroxyl organic acid potassium through the reaction of polyphenol hydroxyl organic acid and potassium hydroxide. Subsequently, at high temperature, the reaction of polyphenol hydroxyl organic acid salt carbonization at high temperature can form microspheres, and the chemical activation of polyphenol hydroxyl organic acid potassium on the surface of biochar at high temperature, finally obtains an activated biochar-based adsorbent material with extremely high specific surface area, which can quickly remove organic pollutants such as dyes and antibiotics in water.

[0021] (2) Compared with using only potassium hydroxide for activation, the present application coats a layer of polyphenol hydroxyl organic acid on the surface of biochar in advance, thereby improving the dispersibility of potassium hydroxide on the surface of biochar during impregnation, improving the activation effect of biochar, and making the surface pore distribution more uniform. The utilization rate of potassium hydroxide in the activation process is improved, and the adsorption performance of the material is also improved.

[0022] (3) Because polyphenol hydroxyl organic acid can carbonize to form microspheres at high temperature, these microspheres can construct more three-dimensional and hierarchical pore structures after being fixed on the surface of biochar, thereby improving the diffusion rate of organic pollutants in the pores and facilitating the rapid and efficient removal of organic pollutants. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a comparison chart of scanning electron microscope photos of biochar-based adsorbents prepared in Examples 1-2 and Comparative Examples 1-2 of the present application;

[0024] Figure 2 is a SEM photo of the sample obtained before the final high-temperature pyrolysis in Example 1 and Comparative Example 1 of the present application, and the corresponding SEM-EDS mapping photo of K element;

[0025] Figure 3 is a comparison chart of methylene blue adsorption curves of biochar-based adsorbents prepared in Examples 1-2 and Comparative Examples 1-2 of the present application. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present application.

[0027] The present application provides, in a first aspect, a method for preparing a polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent, the method comprising the following steps:

[0028] (1) pre-carbonizing a biomass material to obtain biochar; in the present application, the biochar is also referred to as the original biomass carbon material; in the present application, for example, the pretreated biomass material is pre-carbonized under a limited oxygen condition (for example, under a nitrogen atmosphere) to obtain the original biomass carbon material;

[0029] (2) stirring and impregnating the biochar in a hot solution of polyphenol hydroxyl organic acid to obtain an impregnation solution, and then filtering the impregnation solution to obtain biochar coated with a layer (thin layer) of polyphenol hydroxyl organic acid; in the present application, a hot solution impregnation method is used to coat a layer (also referred to as a thin layer) of polyphenol hydroxyl organic acid on the surface of the biochar, for example, the biochar is stirred and impregnated in a hot solution of polyphenol hydroxyl organic acid with a certain concentration for a certain time, and then filtered in a room temperature environment (for example, in a room temperature environment with a temperature not higher than 30℃); by virtue of the different solubility of the polyphenol hydroxyl organic acid in hot water and cold water, the polyphenol hydroxyl organic acid is precipitated on the surface of the biochar during the filtering process, achieving a uniform and dense coating effect; in step (2), the filtering is performed using a filtering device, and the pore size of the filter membrane, filter paper, filter cloth or filter screen used by the filtering device needs to ensure that the biochar particles can be intercepted; in the present application, the hot solution of polyphenol hydroxyl organic acid uses water as the solvent and polyphenol hydroxyl organic acid as the solute;

[0030] (3) stirring and impregnating the biochar coated with the layer of polyphenol hydroxyl organic acid in a potassium hydroxide solution (cold potassium hydroxide solution), and then drying, for example, drying at an appropriate temperature, to obtain a slurry-like mixture; in the present application, the biochar is coated with a layer of polyphenol hydroxyl organic acid, and then impregnated with potassium hydroxide, so that the biochar surface is coated with polyphenol hydroxyl organic acid potassium, and the biochar surface of the slurry-like mixture obtained is coated with polyphenol hydroxyl organic acid potassium; the present application does not specifically limit the stirring and impregnation speed in steps (2) and / or (3), which can be routinely selected by those skilled in the art, for example, it can be 200-1000 r / min; in the present application, the potassium hydroxide solution uses water as the solvent and potassium hydroxide as the solute;

[0031] (4) the slurry-like mixture is pyrolyzed at high temperature to obtain a biochar-based adsorbent activated by polyphenol hydroxyl organic acid potassium salt; in the present application, the slurry-like mixture is pyrolyzed at high temperature in a limited oxygen environment (for example, a nitrogen atmosphere), and after the product is subjected to acid washing, water washing and drying (baking), a biochar-based adsorbent activated by polyphenol hydroxyl organic acid potassium salt with a high specific surface area is obtained; in the present application, the biochar-based adsorbent activated by polyphenol hydroxyl organic acid potassium salt utilizes polyphenol hydroxyl organic acid potassium salt (i.e., bio-organic acid salt) to activate biochar, thereby obtaining active biochar with a high specific surface area and a developed pore structure, which has excellent adsorption performance as a biochar-based adsorbent and can be used for efficient and rapid removal of organic pollutants such as dyes and antibiotics; the biochar-based adsorbent obtained in the present application has a specific surface area of 1950-2250 m 2 / g.

[0032] The present application first utilizes the different solubilities of polyphenol hydroxyl organic acid in hot water and cold water to uniformly coat the surface of biochar material, so that a uniform polyphenol hydroxyl organic acid layer is formed on the surface of the biochar, and then the polyphenol hydroxyl organic acid is converted into polyphenol hydroxyl organic acid potassium by reaction with potassium hydroxide. Since it has an improving effect on the dispersibility of potassium hydroxide on the surface of biochar, and in addition to the activation of polyphenol hydroxyl organic acid potassium salt to biochar, and the tendency of polyphenol hydroxyl organic acid to form microspheres under high temperature, an active biochar material (biochar-based adsorbent) with a multi-level three-dimensional surface pore structure is constructed.

[0033] The present application utilizes the difference in solubility of polyphenol hydroxyl organic acid in hot water and cold water, dissolves polyphenol hydroxyl organic acid in hot water, then adds biochar to the system, and then cools to precipitate polyphenol hydroxyl organic acid on the surface of biochar, thereby forming a uniform layer of polyphenol hydroxyl organic acid on the surface of biochar. Compared with the traditional method of not controlling the temperature of impregnation and loading, but directly coating the surface of biochar with organic acid by stirring, the present application can significantly improve the uniformity and compactness of the coating by using the precipitation process formed by the difference in hot and cold solubility, avoiding the problem of uneven deposition of polyphenol hydroxyl organic acid on the surface of carbon. The polyphenol hydroxyl organic acid with high solubility in hot water can penetrate into the surface of the biochar pore, and then precipitate on the surface of the biochar by cooling to form a uniform and compact layer. In addition, the present application induces precipitation by alternating hot and cold, which promotes polyphenol hydroxyl organic acid to preferentially deposit on the surface of biochar rather than remaining in the solution, which can improve the utilization rate of polyphenol hydroxyl organic acid, effectively reduce the waste of raw materials, and the layer formed by cooling after hot water dissolution usually has better crystallinity or agglomeration structure, which enhances its adhesion to the surface of biochar. The combination of the polyphenol hydroxyl organic acid layer and the surface of biochar is more firm, which gives it better stability and wash-off resistance, and ultimately can significantly improve its adsorption performance, etc.

[0034] Compared with the traditional alkali activation method, the distribution of the basic activator on the surface of the biochar can be improved by preferentially coating the polyphenol hydroxyl organic acid in the application, so that the polyphenol hydroxyl organic acid potassium and the potassium hydroxide not reacted with the polyphenol hydroxyl organic acid can fully coat the surface of the biochar, the surface of the biochar is more fully and uniformly activated, the distribution state of the effective adsorption site of the prepared activated biochar (biochar-based adsorbent) is improved, the surface participating in the adsorption reaction is increased, and thus the adsorption capacity and the adsorption rate are effectively improved; meanwhile, the polyphenol hydroxyl organic acid potassium can generate microspheres under high temperature carbonization, the microspheres are fixed on the surface of the biochar, the surface activity and the pore level of the biochar are further increased, the diffusion rate of the organic pollutants in the pore channel is effectively improved, and the purpose of rapid adsorption is achieved. The method for loading and coating the biochar with the polyphenol hydroxyl organic acid and then activating the biochar in the application can effectively improve the specific surface area and the adsorption performance of the biochar compared with the method for pre-treating and then activating the biochar by using common organic acids such as formic acid, oxalic acid, citric acid, ethanedioic acid and acrylic acid. The polyphenol hydroxyl organic acid molecule structure contains multiple phenolic hydroxyl groups and carboxyl functional groups, can form a more stable combination with the surface of the biochar, enhances the carbon skeleton stability in the process, and is more prone to forming a regular aromatic carbon skeleton, so that the KOH activation reaction is more uniform and controllable. Under high temperature, the polyphenol hydroxyl structure helps to induce the formation of a more developed pore structure in the carbon material, significantly improves the specific surface area and the porosity of the biochar, and thus improves the adsorption performance of the biochar on the organic pollutants such as dyes and antibiotics.

[0035] According to some preferred embodiments, in step (1), the biomass material is a lignocellulosic biomass material, preferably, the lignocellulosic biomass material is one or more of agricultural and forestry wastes, grass leaves and wood materials, more preferably, the lignocellulosic biomass material is one or more of straw, grass leaves, fruit shells and wood materials; further preferably, the fruit shell is an acorn shell; and / or the biomass material is pretreated to obtain a biomass material with a particle size of not more than 18 mesh before pre-carbonization; in the application, the pretreatment of the biomass material is, for example, cleaning the biomass material, drying, crushing and screening to obtain a biomass material with a particle size of not more than 18 mesh; in some specific embodiments, the cleaned biomass material can be cut into blocks before drying according to needs; specifically, the pretreatment can be, for example, first cleaning the biomass material to remove excess surface dirt and the like; then cutting the biomass material into small pieces, drying to remove most of the water, crushing with a crusher, and screening to select a biomass material with a size (particle size) of not more than 18 mesh, and then naturally air-drying for use.

[0036] According to some preferred embodiments, in step (1): the pre-carbonization is carried out under inert gas protection, preferably in a nitrogen atmosphere, or the oxygen can also be removed in advance by limited combustion in a closed space; and / or the pre-carbonization temperature is 300-600℃ (for example 300℃, 400℃, 500℃ or 600℃), and the time is 1-3h, preferably 1-2h, preferably the pre-carbonization temperature is 400℃ and the time is 2h.

[0037] According to some specific embodiments, step (1) is: the biomass material (such as fruit shells such as Korean pine nut shells, hazel nut shells, acorn shells, etc. and straw such as corn cobs, corn stalks, straw, etc.) is washed, dried, crushed and then sieved to retain the powder that can pass through an 18-mesh sieve, and these materials are pre-carbonized at 300-600℃ (for example 300℃, 400℃, 500℃ or 600℃) for 1-3 hours under limited oxygen conditions to obtain the original biomass carbon material (biochar); in the present application, the limited oxygen conditions can be obtained by passing inert gases such as nitrogen into a tubular furnace or a high-temperature reaction furnace, or pyrolysis is carried out in a closed environment, and the limited oxygen effect is achieved by the consumption of a limited amount of oxygen by an excess amount of biomass raw material; the biochar prepared under these different limited oxygen pre-carbonization conditions does not have significant differences in properties and does not have a significant impact on the performance of the subsequent activated biochar.

[0038] According to some preferred embodiments, in step (2): the polyphenol hydroxyl organic acid (bioorganic acid) in the hot solution of polyphenol hydroxyl organic acid is one or more of gallic acid, tannic acid, other aromatic organic acids containing multiple phenolic hydroxyl groups, or a biomass extract containing a large amount of the above components, preferably the polyphenol hydroxyl organic acid in the hot solution of polyphenol hydroxyl organic acid is gallic acid and / or tannic acid; in the present application, a biomass extract containing a large amount of the above components refers to a biomass extract containing a high content of polyphenol hydroxyl organic acids, such as tannic acid and / or gallic acid, etc. A variety of agricultural crop wastes such as gallnut, grape, pomegranate, tea, tomato and hawthorn also contain a high content of polyphenol hydroxyl organic acids, including tannic acid and gallic acid, etc. The present application uses biomass materials as raw materials to obtain biochar, and uses polyphenol hydroxyl organic acid potassium (bioorganic acid salt) to activate the biochar to prepare high specific surface area active biochar (active adsorbent) for adsorbing organic pollutants in water bodies, which is an effective method for increasing the added value of biomass materials such as agricultural and forestry waste, grass leaves and / or wood materials, etc.

[0039] In the present application, the concentration and temperature of the hot solution of polyphenol hydroxyl organic acid need to be adjusted according to the type of organic acid. The present application has obtained suitable concentrations and temperatures of the hot solution through a large number of creative experiments.

[0040] According to some preferred embodiments, in step (2): when the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is gallic acid, the concentration of gallic acid in the polyphenol hydroxyl organic acid hot solution is 50-150 g / L (e.g. 50, 60, 70, 80, 90, 100, 110, 120, 130, 140 or 150 g / L), and the temperature of the polyphenol hydroxyl organic acid hot solution is 70-90℃ (e.g. 70℃, 75℃, 80℃, 85℃ or 90℃), preferably 80-90℃ (e.g. 80℃, 85℃ or 90℃); it is found in the present application that during the stirring and soaking process in the hot solution of gallic acid, the temperature of the hot solution is 70-90℃, and if the temperature is too high, it is easy to affect the coating effect due to boiling of the hot solution, and if the temperature is too low, it is easy to cause excessive precipitation of gallic acid, which will ultimately affect the subsequent activation process; when the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is tannic acid, the concentration of tannic acid in the polyphenol hydroxyl organic acid hot solution is 200-300 g / L (e.g. 200, 210, 220, 230, 240, 250, 260, 270, 280, 290 or 300 g / L), preferably 270-300 g / L, and the temperature of the polyphenol hydroxyl organic acid hot solution is 50-60℃ (e.g. 50℃, 55℃ or 60℃); the ratio of the amount of use of the biochar to the polyphenol hydroxyl organic acid hot solution is (25-115) g: 1 L (e.g. 25 g: 1 L, 30 g: 1 L, 35 g: 1 L, 40 g: 1 L, 45 g: 1 L, 50 g: 1 L, 55 g: 1 L, 60 g: 1 L, 65 g: 1 L, 70 g: 1 L, 75 g: 1 L, 80 g: 1 L, 85 g: 1 L, 90 g: 1 L, 95 g: 1 L, 100 g: 1 L, 105 g: 1 L, 110 g: 1 L or 115 g: 1 L), when it is gallic acid, the ratio is preferably (25-75) g: 1 L, and when it is tannic acid, the ratio is preferably (90-115) g: 1 L; the mass ratio of the biochar to the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is 1:(1-3) (e.g. 1:1, 1:1.5, 1:2, 1:2.5 or 1:3), and in the present application, it is preferred that the mass ratio of the biochar to the polyphenol hydroxyl organic acid is 1:(1-3), if the polyphenol hydroxyl organic acid is too much, it is easy to precipitate on the surface of the biochar, and if it is too little, it cannot achieve sufficient effect; and / or the time of stirring and soaking is 12-24 h (e.g. 12, 14, 16, 18, 20, 22 or 24 h).

[0041] According to some preferred embodiments, in step (2): when the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is gallic acid, the temperature of the impregnation solution should not be lower than 70℃ before the impregnation solution is filtered, i.e. when the impregnation solution contacts the filter layer of the filtering device, and the filtering time should not be longer than 5 min; preferably, the filtrate after filtering is recycled and reused until no solid is precipitated when cooled to 40℃; and / or when the polyphenol hydroxyl organic acid in the polyphenol hydroxyl organic acid hot solution is tannic acid, the temperature of the impregnation solution should not be lower than 50℃ before the impregnation solution is filtered, i.e. when the impregnation solution contacts the filter layer of the filtering device, and the filtering time should not be longer than 5 min; preferably, the filtrate after filtering is recycled and reused until no solid is precipitated when cooled to 30℃. In the present application, during the process of separating the biochar coated with the polyphenol hydroxyl organic acid layer from the impregnation solution by filtering, the filtering device is used to filter at room temperature not higher than 30℃, and the time for the impregnation solution to pass through the filtering device should be controlled within 5 min to control the amount of polyphenol hydroxyl organic acid precipitated on the surface of the biochar and ensure the appropriate thickness of the coating layer; in the present application, if the impregnation solution is cooled to room temperature of 25℃ before filtering, a large amount of polyphenol hydroxyl organic acid will be precipitated, and the effective precipitation of polyphenol hydroxyl organic acid on the surface of the biochar cannot be controlled.

[0042] In order to ensure the activation effect of the biochar, the polyphenol hydroxyl organic acid coating needs to be carried out under the above appropriate conditions and process parameters, so that the biochar surface is uniformly coated with an organic acid layer with appropriate thickness, thereby making the subsequent distribution of potassium organic acid and potassium hydroxide on the surface of the biochar more uniform. It is found that both too low or too high loading (thickness) of the polyphenol hydroxyl organic acid (layer) can easily lead to a decrease in surface activation effect, thereby resulting in a decrease in adsorption capacity; if the loading is too low, it cannot ensure that enough surface is fully activated, thereby resulting in a decrease in adsorption capacity, and if the loading is too high, potassium polyphenol hydroxyl organic acid is easily separated from the surface of the biochar during the potassium hydroxide impregnation process, thereby also leading to a decrease in activation effect and a decrease in adsorption capacity. In order to ensure the coating effect of the polyphenol hydroxyl organic acid, the temperature of the impregnation solution, the concentration of the organic acid, the dosage of the biochar, the impregnation time, the filtering time and the filtering temperature during the coating process need to be controlled, so that the biochar surface can be uniformly coated with an organic acid layer with appropriate thickness.

[0043] According to some specific embodiments, a certain amount of polyphenol hydroxyl organic acid is added to hot water (when the organic acid is tannic acid, the temperature is 50-60°C; when the organic acid is gallic acid, the temperature is 70-90°C), to obtain a hot solution thereof (when the organic acid is tannic acid, the concentration is 200-300 g / L; when the organic acid is gallic acid, the concentration is 50-150 g / L), then biochar is added under stirring, the addition amount is 25-115 g per liter of solution, and the mass ratio of biochar to polyphenol hydroxyl organic acid is maintained at 1:1-1:3, and stirring is continued for 12-24 hours (for example, 100 g of gallic acid is dissolved in 1 L of hot water with a temperature of 85°C, then 40 g of biochar is added, and stirring is continued for 18 hours). Then, at room temperature not higher than 30°C, using a filtering device (such as a filter membrane, filter screen, filter paper or filter cloth), the biochar is separated from the solution within 5 minutes, so that the polyphenol hydroxyl organic acid is precipitated on the surface of the biochar during the filtering process, achieving the coating effect; the solution needs to be kept at a certain temperature before filtering (for gallic acid, the temperature is not lower than 70°C; for tannic acid, the temperature is not lower than 50°C), and the filtering time is not more than 5 min; the filtrate after filtering can be reused after recovery, and preferably, when the filtrate after filtering is cooled to a certain temperature without solid precipitation (for example, for gallic acid, the temperature is 40°C; for tannic acid, the temperature is 30°C), the polyphenol hydroxyl organic acid needs to be supplemented to the solution after filtering, the supplementing amount is the initial addition amount, and water is supplemented to maintain the volume of the solution; in some specific examples, a small amount of filtrate can be cooled to a certain temperature (for gallic acid, the temperature is 40°C; for tannic acid, the temperature is 30°C) to analyze and determine whether there is solid precipitation.

[0044] According to some preferred embodiments, in step (3): the temperature of the potassium hydroxide solution is no more than 30°C, preferably no more than 20°C; the concentration of the potassium hydroxide solution is 200-300 g / L (e.g. 200, 210, 220, 230, 240, 250, 260, 270, 280, 290 or 300 g / L); the time for stirring and soaking is 1-2 h (e.g. 1, 1.5 or 2 h); it is preferred in the present application that the temperature of the potassium hydroxide solution is no more than 30°C, the concentration of the potassium hydroxide solution is 200-300 g / L, and the time for stirring and soaking in the potassium hydroxide solution is 1-2 h. It is found in the present application that too high a temperature of the potassium hydroxide solution tends to cause the polyphenol hydroxyl organic acid to dissolve and separate from the surface of the biochar, too low a concentration of the potassium hydroxide solution corresponds to a large solution volume, which also tends to cause the polyphenol hydroxyl organic acid to dissolve and separate from the surface of the biochar and increase the time for subsequent drying, and too high a concentration of the potassium hydroxide solution corresponds to a small solution volume, which tends to cause the biochar to be insufficiently dispersed in the solution and cause the polyphenol hydroxyl organic acid and the potassium hydroxide to be insufficiently reacted. In addition, too long a stirring time also tends to cause the polyphenol hydroxyl organic acid to dissolve and separate from the surface of the biochar, and too short a stirring time tends to cause the polyphenol hydroxyl organic acid and the potassium hydroxide to be insufficiently reacted.

[0045] According to some preferred embodiments, the mass ratio of the potassium hydroxide in the potassium hydroxide solution to the biochar in step (2) is (1-3): 1 (e.g. 1:1, 1.5:1, 2:1, 2.5:1 or 3:1); it is preferred in the present application that the mass ratio of the potassium hydroxide to the biochar is (1-3): 1. It is found in the present application that if the amount of potassium hydroxide is too low, the amount of the alkaline activator is insufficient to sufficiently activate the surface of the biochar, and if the amount of potassium hydroxide is too high, the alkaline activator is excessive, which also tends to cause the specific surface area and the adsorption performance to be insufficiently improved and cause the yield to be greatly reduced. In some specific embodiments, for example, the mass ratio of the biochar to the potassium hydroxide used is 1:3, and the concentration of the potassium hydroxide solution is 300 g / L during stirring and soaking.

[0046] According to some preferred embodiments, in step (3): the drying temperature is 60-70℃; and / or the drying is performed to obtain a slurry-like mixture with a water content (relative water content) of 20-40%; in some specific embodiments, for example, the drying temperature is 60℃, and the drying is performed to obtain a slurry-like mixture with a water content (relative water content) of 25%; in the present application, it is preferred that the drying temperature is 60-70℃, and the drying is performed to obtain a slurry-like mixture with a water content (relative water content) of 20-40%, it is found in the present application that a too high drying temperature is easy to cause excessive dissolution of the polyphenol hydroxyl organic acid potassium, leading to its separation from the surface of the biochar, and a too low drying temperature is easy to cause a too long drying time, which also leads to excessive dissolution of the polyphenol hydroxyl organic acid potassium, leading to its separation from the surface of the biochar, and a too low water content after drying is easy to cause the mixture to be too dense during the pyrolysis process, affecting the pore-forming process during the pyrolysis activation process, and a too high water content is easy to cause the water to not be removed in time during the pyrolysis process, leading to the separation of the activator from the surface of the biochar, resulting in insufficient activation.

[0047] According to some specific embodiments, step (3) is: the biochar coated with the polyphenol hydroxyl organic acid layer separated in step (2) is immersed in a cold solution (temperature not higher than 30℃) of potassium hydroxide, the amount of potassium hydroxide used is 1-3 times the amount of the biochar added in step (2), the concentration of potassium hydroxide is 200-300g / L, after stirring immersion for 1-2 hours, the solution is removed by drying at a temperature of 60-70℃ to obtain a slurry-like mixture with a water content of 20-40%.

[0048] According to some preferred embodiments, in step (4): the high-temperature pyrolysis is performed under the protection of an inert gas, preferably in a nitrogen atmosphere, or the high-temperature pyrolysis is performed in a closed space after pre-removal of oxygen by limited combustion; and / or the temperature of the high-temperature pyrolysis is 800-1000℃, preferably 850℃, the time is 1-3h, preferably 2h, and the heating rate for heating to the temperature of the high-temperature pyrolysis is 2-5℃ / min, preferably 3℃ / min; in the present application, the high-temperature pyrolysis is performed in a limited oxygen environment under the protection of an inert gas, heated to 800-1000℃ at a heating rate of 2-5℃ / min, and pyrolyzed at this temperature for 1-3 hours; it is preferred that the temperature of the high-temperature pyrolysis is 800-1000℃, and the time is 1-3h, it is found in the present application that a too low pyrolysis temperature will lead to insufficient activation reaction, reducing the adsorption capacity of the adsorbent, and a too high pyrolysis temperature is easy to cause the collapse of the formed pores, leading to a decrease in the specific surface area, also reducing the adsorption capacity of the adsorbent, a too short pyrolysis time leads to insufficient activation reaction, reducing the adsorption capacity of the adsorbent, and an extended pyrolysis time does not improve the activation effect.

[0049] According to some specific embodiments, step (4) is: placing the slurry-like mixture in an oxygen-limited environment, high-temperature pyrolysis at a temperature of 800-1000℃ for 1-3 hours, the temperature rising speed being 2-5℃ / min, then washing the obtained product with a dilute acid of about 1 mol / L to remove excessive alkaline substances, washing with clean water, and finally drying to obtain the activated biochar-based adsorbent with high specific surface area, i.e. the polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent.

[0050] The present application provides, in a second aspect, a polyphenol hydroxyl organic acid potassium salt activated biochar-based adsorbent prepared by the preparation method described in the first aspect of the present application.

[0051] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application. In the absence of specific description, each raw material used in the embodiments and comparative examples of the present application can be commercially purchased or synthesized by existing methods.

[0052] Embodiment 1

[0053] ①The acorn shell was cleaned, dried and then crushed by a crusher, and the powder with a size (particle size) less than 18 mesh was selected by sieving to obtain the pretreated biomass material, which was naturally air-dried for use. The pretreated biomass material was placed in a nitrogen atmosphere (the flow rate of the inlet was 8 L / h), and the temperature was raised to 400℃. After 2 hours of pre-carbonization treatment, biochar (acorn shell biochar) was obtained.

[0054] ②The biochar obtained in step ① was added to a hot gallic acid solution (polyphenol hydroxyl organic acid hot solution) with a temperature of 80℃ and a concentration of 150 g / L. The solution was stirred and soaked for 24 hours under the condition that the solution temperature was maintained at 80℃ to obtain an impregnation solution. The ratio of the use amount of biochar to the hot gallic acid solution was 50 g: 1 L, i.e. the addition amount of biochar was 50 g per liter of hot gallic acid solution.

[0055] ③The impregnation solution obtained in step ② (the temperature was 80℃ before filtration) was poured into a filtration device (suction filtration device) containing a water filter membrane (pore size 0.45 μm) while hot, and was filtered at room temperature of 25℃. The filtration time was controlled to be not more than 5 min, and the solid was separated to obtain biochar coated with a polyphenol hydroxyl organic acid layer.

[0056] ④The biochar coated with the polyphenol hydroxyl organic acid layer obtained in step ③ is stirred and immersed in a cold potassium hydroxide solution (temperature is 20℃) for 1h, and then is dried at 60℃ to obtain a slurry-like mixture with a water content of 25%; wherein the concentration of the cold potassium hydroxide solution is 250g / L, and the amount of potassium hydroxide used is 3 times the mass of the biochar added in step ②.

[0057] ⑤The slurry-like mixture obtained in step ④ is placed in a corundum crucible, and is pyrolyzed in a tube furnace at a high temperature of 850℃ for 2 hours at a rate of 3℃ / min with nitrogen as the protective gas (inlet flow rate is 8L / h). After cooling, the sample is washed in 1mol / L hydrochloric acid, then is washed with clean water until neutral, and then is dried at 60℃ to constant weight to obtain a biochar-based adsorbent activated by polyphenol hydroxyl organic acid potassium salt.

[0058] Example 2

[0059] Example 2 is basically the same as Example 1, except that:

[0060] The biomass material used in step ① is red pine seed shell.

[0061] Example 3

[0062] Example 3 is basically the same as Example 1, except that:

[0063] ②The biochar obtained in step ① is added to a hot tannic acid solution (polyphenol hydroxyl organic acid hot solution) with a temperature of 60℃ and a concentration of 270g / L, and is stirred and immersed for 24 hours under the condition that the temperature of the solution is maintained at 60℃ to obtain an immersion solution; wherein the ratio of the amount of biochar to the tannic acid hot solution is 90g:1L, that is, the addition amount of biochar is 90g per liter of tannic acid hot solution.

[0064] ③The immersion solution obtained in step ② (temperature is 60℃ before filtration) is poured into a filtration device (suction filtration device) containing a water filter membrane (pore size is 0.45μm) while hot, and is filtered at room temperature of 25℃, and the filtration time is controlled to be not more than 5min, and the solid is separated to obtain biochar coated with a polyphenol hydroxyl organic acid layer.

[0065] Example 4

[0066] ①The corn cob is washed, cut into small pieces, then is dried and crushed by a crusher, and the powder with a size (particle size) of less than 18μm is selected by sieving to obtain pretreated biomass material, which is air dried for use. The pretreated biomass material is placed in a nitrogen atmosphere (inlet flow rate is 8L / h), and the temperature is raised to 400℃, and is subjected to a pre-carbonization treatment for 2 hours to obtain biochar (corn cob biochar).

[0067] ②The biochar obtained in step 1 is added to a hot gallic acid solution (polyphenol hydroxyl organic acid hot solution) with a temperature of 90 DEG C and a concentration of 50 g / L, and is stirred and immersed for 12 hours under the condition that the temperature of the solution is kept at 90 DEG C to obtain an impregnation solution; wherein the ratio of the use amount of the biochar to the hot gallic acid solution is 50 g:1 L, that is, the addition amount of the biochar is 50 g per liter of the hot gallic acid solution.

[0068] ③The impregnation solution obtained in step 2 is poured into a filtering device (suction filtering device) provided with a water filter membrane (pore size 0.45 μm) while hot (temperature 90 DEG C before filtration), and is filtered at room temperature of 25 DEG C, and the filtering time is controlled to be not more than 5 minutes, and the solid is separated to obtain biochar coated with a polyphenol hydroxyl organic acid layer.

[0069] ④The biochar coated with the polyphenol hydroxyl organic acid layer obtained in step 3 is stirred and immersed in a cold potassium hydroxide solution (temperature 20 DEG C) for 1 hour, and is dried at a temperature of 70 DEG C to obtain a slurry-like mixture with a water content of 20%; wherein the concentration of the cold potassium hydroxide solution is 200 g / L, and the use amount of potassium hydroxide is 1 times the mass of the biochar added in step 2.

[0070] ⑤The slurry-like mixture obtained in step 4 is placed in a corundum crucible, and is pyrolyzed in a tube furnace at a high temperature of 1000 DEG C at a rate of 3 DEG C / min for 1 hour under the protection of nitrogen gas (inlet flow rate 8 L / h), and after cooling, the sample is washed in 1 mol / L hydrochloric acid, then is washed with clean water until neutral, and is dried at 70 DEG C to constant weight to obtain a biochar-based adsorbent activated by a polyphenol hydroxyl organic acid potassium salt.

[0071] Example 5

[0072] ①The wheat straw is washed, cut into small pieces, dried, and then crushed by a pulverizer, and the powder with a size (particle size) less than 18 mesh is selected by sieving to obtain pretreated biomass material, which is air dried for use; the pretreated biomass material is placed in a nitrogen atmosphere (inlet flow rate 8 L / h), and the temperature is raised to 400 DEG C for 2 hours of pre-carbonization treatment to obtain biochar (wheat straw biochar).

[0073] ②The biochar obtained in step 1 is added to a hot gallic acid solution (polyphenol hydroxyl organic acid hot solution) with a temperature of 90 DEG C and a concentration of 50 g / L, and is stirred and immersed for 12 hours under the condition that the temperature of the solution is kept at 90 DEG C to obtain an impregnation solution; wherein the ratio of the use amount of the biochar to the hot gallic acid solution is 50 g:1 L, that is, the addition amount of the biochar is 50 g per liter of the hot gallic acid solution.

[0074] ③ While hot, pour the impregnation solution obtained in step ② (temperature is 50℃ before filtration) into a filtering device (suction filtering device) equipped with a water filter membrane (pore size is 0.45 μm), filter at room temperature of 25℃, control the filtering time to be no more than 5 min, separate the solid to obtain the biochar coated with polyphenol hydroxyl organic acid layer.

[0075] ④ Stir and immerse the biochar coated with polyphenol hydroxyl organic acid layer obtained in step ③ in a cold potassium hydroxide solution (temperature is 20℃) for 2 h, and then dry at 60℃ to obtain a slurry-like mixture with a water content of 40%; wherein the concentration of the cold potassium hydroxide solution is 250 g / L, and the amount of potassium hydroxide used is 2 times the mass of the biochar added in step ②.

[0076] ⑤ Place the slurry-like mixture obtained in step ④ in a corundum crucible, and pyrolyze in a tube furnace at a temperature of 800℃ for 3 h with nitrogen as the protective gas (inlet flow rate is 8 L / h) at a rate of 2℃ / min. After cooling, wash the sample in 1 mol / L hydrochloric acid, then wash with clean water until neutral, and then dry at 60℃ to constant weight to obtain the biochar-based adsorbent activated by polyphenol hydroxyl organic acid potassium salt.

[0077] Comparative Example 1

[0078] ① The same as step ① of Example 1.

[0079] ② Stir and immerse the biochar obtained in step ① in a potassium hydroxide solution (temperature is 20℃) for 1 h, and then dry at 60℃ to obtain a slurry-like mixture with a water content of 25%; wherein the concentration of the potassium hydroxide solution is 250 g / L, and the amount of potassium hydroxide used is 3 times the mass of the biochar added.

[0080] ③ Place the slurry-like mixture obtained in step ② in a corundum crucible, and pyrolyze in a tube furnace at a temperature of 850℃ for 2 h with nitrogen as the protective gas (inlet flow rate is 8 L / h) at a rate of 3℃ / min. After cooling, wash the sample in 1 mol / L hydrochloric acid, then wash with clean water until neutral, and then dry at 60℃ to constant weight to obtain the biochar-based adsorbent activated by potassium hydroxide.

[0081] Comparative Example 2

[0082] Comparative Example 2 is basically the same as Comparative Example 1, except that:

[0083] The biomass material used in step ① is red pine seed shell.

[0084] Comparative Example 3

[0085] ① The same as step ① of Example 1.

[0086] ②The biochar obtained in step 1 is added to a hot gallic acid solution (polyphenol hydroxyl organic acid hot solution) with a temperature of 80 DEG C and a concentration of 150 g / L, and is stirred and immersed for 24 hours under the condition that the temperature of the solution is kept at 80 DEG C, to obtain an impregnation solution; wherein the ratio of the amount of biochar to the amount of hot gallic acid solution is 50 g: 1 L, that is, the dosage of biochar is 50 g per liter of hot gallic acid solution.

[0087] ③The impregnation solution obtained in step 2 (temperature is 80 DEG C before filtration) is poured into a filtering device (suction filtering device) containing a water filter membrane (pore size is 0.45 μm) while hot, and is filtered at room temperature of 25 DEG C, and the filtering time is controlled to be no more than 5 minutes, and the solid is separated to obtain biochar coated with a polyphenol hydroxyl organic acid layer.

[0088] ④The biochar coated with a polyphenol hydroxyl organic acid layer obtained in step 3 is placed in a corundum crucible, and is pyrolyzed in a tube furnace at a high temperature of 850 DEG C for 2 hours at a rate of 3 DEG C / min with nitrogen as the protective gas (inflow rate is 8 L / h), to obtain a biochar-based adsorbent coated with a polyphenol hydroxyl organic acid.

[0089] Comparative Example 4

[0090] Comparative Example 4 is basically the same as Example 1, except that:

[0091] In step 2, a hot gallic acid solution with a concentration of 25 g / L is used.

[0092] Comparative Example 5

[0093] Comparative Example 5 is basically the same as Example 1, except that:

[0094] In step 2, a hot gallic acid solution with a concentration of 200 g / L is used.

[0095] Comparative Example 6

[0096] Comparative Example 6 is basically the same as Example 1, except that:

[0097] In step 3, the filtering device is preheated to 55 DEG C before filtering, and the filtering is performed at an environment of 55 DEG C.

[0098] Comparative Example 7

[0099] Comparative Example 7 is basically the same as Example 1, except that:

[0100] In step 4, the mass of potassium hydroxide is 5 times the mass of the biochar added in step 2.

[0101] Comparative Example 8

[0102] Comparative Example 8 is substantially the same as Example 1, except that:

[0103] In step IV, the mass of potassium hydroxide is 0.5 times the mass of the biochar added in step II.

[0104] Comparative Example 9

[0105] Comparative Example 9 is substantially the same as Example 1, except that:

[0106] In step IV, the concentration of the cold potassium hydroxide solution is 100 g / L.

[0107] Comparative Example 10

[0108] Comparative Example 10 is substantially the same as Example 1, except that:

[0109] In step IV, the concentration of the cold potassium hydroxide solution is 400 g / L.

[0110] Comparative Example 11

[0111] Comparative Example 11 is substantially the same as Example 1, except that:

[0112] In step IV, the mixture is dried to obtain a slurry with a water content of 5%.

[0113] Comparative Example 12

[0114] Comparative Example 12 is substantially the same as Example 1, except that:

[0115] In step IV, the mixture is dried to obtain a slurry with a water content of 50%.

[0116] Comparative Example 13

[0117] Comparative Example 13 is substantially the same as Example 1, except that:

[0118] In step V, the temperature of the high-temperature pyrolysis is 700°C.

[0119] Comparative Example 14

[0120] Comparative Example 14 is substantially the same as Example 1, except that:

[0121] In step V, the temperature of the high-temperature pyrolysis is 1100°C.

[0122] Comparative Example 15

[0123] Comparative Example 15 is substantially the same as Example 1, except that:

[0124] IV. The biochar coated with the polyphenol hydroxyl organic acid layer obtained in step III is stirred and immersed in a potassium hydroxide solution (temperature 60°C) for 1 h, and then dried at 60°C to obtain a slurry-like mixture with a water content of 25%; wherein the concentration of the potassium hydroxide solution is 250 g / L, and the amount of potassium hydroxide used is 3 times the mass of the biochar added in step II.

[0125] Comparative Example 16

[0126] Comparative Example 16 is basically the same as Example 1, except that:

[0127] III. The impregnation solution obtained in step II is cooled to 25°C, poured into a filtering device (suction filtering device) equipped with a water filter membrane (pore size 0.45 μm), filtered at room temperature of 25°C, and the filtering time is controlled to be no more than 5 min, and the solid is separated to obtain the biochar coated with the polyphenol hydroxyl organic acid.

[0128] Comparative Example 17

[0129] Comparative Example 17 is basically the same as Example 3, except that:

[0130] II. The biochar obtained in step I is added into a tannic acid solution with a concentration of 5 g / L (the temperature of the tannic acid solution is room temperature 25°C), and stirred and immersed at room temperature 25°C for 18 hours to obtain an impregnation solution; wherein the ratio of the amount of biochar to the amount of tannic acid solution is 10 g: 1 L, that is, the amount of biochar added is 10 g per liter of tannic acid solution.

[0131] III. The impregnation solution (temperature 25°C) obtained in step II is poured into a filtering device (suction filtering device) equipped with a water filter membrane (pore size 0.45 μm), filtered at room temperature of 25°C, and the filtering time is controlled to be no more than 5 min, and the solid is separated to obtain the biochar coated with the polyphenol hydroxyl organic acid.

[0132] IV. The biochar coated with the polyphenol hydroxyl organic acid obtained in step III is stirred and immersed in a potassium hydroxide solution (room temperature 25°C) for 1 h, and then dried at 60°C to obtain a slurry-like mixture with a water content of 25%; wherein the concentration of the potassium hydroxide solution is 250 g / L, and the amount of potassium hydroxide used is 3 times the mass of the biochar added in step II.

[0133] Comparative Example 18

[0134] Comparative Example 18 is basically the same as Example 1, except that:

[0135] ②The biochar obtained in step 1 is added into a 150 g / L formic acid aqueous solution (the temperature of the formic acid aqueous solution is room temperature 25℃), and stirred and immersed at room temperature 25℃ for 24 hours to obtain an impregnation solution; wherein the ratio of the use amount of biochar to the formic acid aqueous solution is 50 g: 1 L, that is, the addition amount of biochar is 50 g per liter of formic acid aqueous solution.

[0136] ③The impregnation solution obtained in step 2 is poured into a filtering device (suction filtering device) provided with a water filter membrane (pore size 0.45 μm), and filtered at room temperature 25℃, and the filtering time is controlled to be not more than 5 min, and the solid is separated to obtain acidified biochar.

[0137] ④The acidified biochar obtained in step 3 is stirred and immersed in a potassium hydroxide solution (temperature 25℃) for 1 h, and then dried at 60℃ to obtain a slurry-like mixture with a water content of 25%; wherein the concentration of the potassium hydroxide solution is 250 g / L, and the use amount of potassium hydroxide is 3 times the mass of the biochar added in step 2.

[0138] Comparative Example 19

[0139] The acorn shell is washed, dried, and then crushed by a crusher, and the powder with a size (particle size) less than 18 mesh is selected by sieving to obtain pretreated biomass material, which is air dried for use. The pretreated biomass material is placed in a nitrogen atmosphere (inlet flow rate 8 L / h), and the temperature is raised to 400℃, and then pre-carbonized for 2 hours to obtain biochar (acorn shell biochar). 1 g of biochar is added into 75 mL of 5 mol / L formic acid aqueous solution, and after ultrasonic treatment until the biochar is completely immersed, it is transferred into a 100 mL hydrothermal reactor, and kept at 100℃ for 24 h, and then naturally cooled to room temperature, and then suction filtered and dried to obtain acidified biochar. Then the acidified biochar and potassium hydroxide are weighed according to the mass ratio of 1:4, and then poured into a crucible, and a small amount of water is added to completely dissolve the potassium hydroxide and mix well, and then the mixture is placed in a tube furnace, and heated to 900℃ at a rate of 5℃ / min under N2 atmosphere (inlet flow rate 8 L / h), and kept at 900℃ for 180 min, and then washed with hydrochloric acid and water until neutral, and then dried at 60℃ to constant weight to obtain a biochar-based adsorbent.

[0140] Comparative Example 20

[0141] ①The same as step 1 of Example 1.

[0142] ②The biochar and tannic acid obtained in step 1 are added into a potassium hydroxide solution (temperature 25℃) for stirring and immersion for 2 h, and then dried at 60℃ to obtain a slurry-like mixture with a water content of 25%; wherein the concentration of the potassium hydroxide solution is 250 g / L, and the use amount of potassium hydroxide is 3 times the mass of the biochar added; and the use amount of tannic acid is 0.05 times the mass of the biochar.

[0143] ③ The slurry mixture obtained in step ② was placed in a corundum crucible, and the temperature was raised to 850°C at a rate of 3°C / min in a tubular furnace with nitrogen as the protective gas (the flow rate was 8 L / h) for high-temperature pyrolysis for 2 hours. After cooling, the sample was washed in hydrochloric acid, washed with clean water until neutral, and then dried at 60°C to constant weight to obtain a potassium hydroxide-activated biochar-based adsorbent.

[0144] The present invention tested the adsorption performance of the biochar-based adsorbents finally prepared in each embodiment and each comparative example. The test method is as follows: 10 mg of the biochar-based adsorbent was placed in 500 mL of a solution containing 50 mg / L of different organic pollutants, and adsorbed at an oscillation rate of 150 rpm for 24 hours. The adsorption results are shown in Table 1. The present invention also measured the specific surface area and yield of the biochar-based adsorbents finally prepared in each embodiment and each comparative example. The results are shown in Table 1.

[0145] Table 1

[0146]

[0147]

[0148] The surface activation degree of the biochar activated by the potassium salt of polyphenolic hydroxy organic acid prepared in Examples 1 and 2 of the present invention is significantly higher than that of Comparative Examples 1 and 2 which are not coated with polyphenolic hydroxy organic acid. Figure 1 As shown, the surfaces of Examples 1 and 2 still have a large number of relatively flat surfaces, and the surfaces of the biochar-based adsorbents of Examples 1 and 2 are fully activated and form a hierarchical multi-level pore structure. Therefore, they can fully contact with the adsorbate during the adsorption process, and the diffusion rate of the adsorbate in the pores is faster during the adsorption process, thereby accelerating the adsorption rate and improving the adsorption performance. SEM photos of the samples obtained before the final high-temperature pyrolysis in Example 1 of the present invention and Comparative Example 1 and the corresponding SEM-EDS mapping photos of the K element are shown, as shown in FIG. Figure 2 As shown in the figure, after the potassium hydroxide impregnation, the coating of the polyphenolic hydroxy organic acid is conducive to the attachment of potassium to the surface of the biochar, so that the components with activating effects (potassium hydroxide and polyphenolic hydroxy organic acid potassium) are fully coated on the surface of the biochar, thereby improving the activation effect and facilitating the uniform distribution of pores on the surface of the activated biochar material and the construction of a multi-level pore structure. The adsorption curve comparison of the biochar-based adsorbents prepared in Examples 1-2 of the present invention and Comparative Examples 1-2 for methylene blue is shown in the figure. Figure 3As shown, due to the increase of adsorbate diffusion rate caused by the formation of multi-level pore structure and the optimization of pore distribution state of the adsorbent surface, the adsorption capacity and adsorption rate of Examples 1 and 2 are significantly improved compared with Comparative Examples 1 and 2. Taking methylene blue as an example, the adsorption capacity of Example 1 is increased by 180% compared with Comparative Example 1, and the adsorption equilibrium time is shortened to 1 / 6 of Comparative Example 1; the adsorption capacity of Example 2 is increased by 27.6% compared with Comparative Example 2, and the adsorption equilibrium time is shortened to 1 / 12 of Comparative Example 1.

[0149] The part of the present application not described in detail is the technology known to those skilled in the art.

[0150] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a biochar-based adsorbent activated by potassium salt of polyphenolic hydroxy organic acid, characterized in that: The method comprises the following steps: (1) Pre-carbonizing the biomass material to obtain biochar; (2) stirring and impregnating the biochar in a hot solution of a polyphenol hydroxyl organic acid to obtain an impregnation solution, and then filtering the impregnation solution to obtain a biochar coated with a polyphenol hydroxyl organic acid layer; (3) stirring and immersing the biochar coated with the polyphenol hydroxy organic acid layer in a potassium hydroxide solution, and then drying the solution to obtain a slurry mixture; (4) The slurry mixture is subjected to high-temperature pyrolysis to obtain a biochar-based adsorbent activated by potassium salt of polyphenolic hydroxy organic acid.

2. The preparation method according to claim 1, characterized in that In step (1): The biomass material is a lignocellulosic biomass material. Preferably, the lignocellulosic biomass material is one or more of agricultural and forestry waste, grass leaves, and wood materials. More preferably, the lignocellulosic biomass material is one or more of straw, grass leaves, fruit shells, and wood materials. Further preferably, the fruit shells are acorn shells; and / or Before pre-carbonization, the biomass material is pretreated to obtain a biomass material with a particle size less than 18 meshes.

3. The preparation method according to claim 1, characterized in that In step (1): The pre-carbonization is carried out under the protection of an inert gas, preferably in a nitrogen atmosphere, or the pre-carbonization is carried out in a closed space after pre-removal of oxygen by limited combustion; and / or The pre-carbonization temperature is 300-600° C., and the time is 1-3 hours.

4. The preparation method according to claim 1, characterized in that In step (2): The polyphenolic hydroxy organic acid in the polyphenolic hydroxy organic acid hot solution is one or more of gallic acid, tannic acid, and other aromatic organic acids containing multiple phenolic hydroxyl groups, or a biomass extract containing more of the above components. Preferably, the polyphenolic hydroxy organic acid in the polyphenolic hydroxy organic acid hot solution is gallic acid and / or tannic acid.

5. The preparation method according to claim 1, characterized in that In step (2): When the polyphenol hydroxy organic acid in the hot solution of polyphenol hydroxy organic acid is gallic acid, the gallic acid concentration of the hot solution of polyphenol hydroxy organic acid is 50-150 g / L, and the temperature of the hot solution of polyphenol hydroxy organic acid is 70-90° C., preferably 80-90° C.; when the polyphenol hydroxy organic acid in the hot solution of polyphenol hydroxy organic acid is tannic acid, the tannic acid concentration of the hot solution of polyphenol hydroxy organic acid is 200-300 g / L, and the temperature of the hot solution of polyphenol hydroxy organic acid is 50-60° C.; The ratio of the biochar to the polyphenol hydroxy organic acid hot solution is (25-115) g: 1 L; The mass ratio of the biochar to the polyphenolic hydroxy organic acid in the polyphenolic hydroxy organic acid hot solution is 1:(1-3); and / or The stirring and soaking time is 12 to 24 hours.

6. The preparation method according to claim 1, characterized in that In step (2): When the polyphenolic hydroxy organic acid in the hot polyphenolic hydroxy organic acid solution is gallic acid, the temperature of the impregnation solution before filtering is not lower than 70° C., and the filtration time is not more than 5 minutes. Preferably, the filtrate after filtration is recovered and reused until no solid is precipitated when cooled to 40° C.; or When the polyphenol hydroxy organic acid in the hot polyphenol hydroxy organic acid solution is tannic acid, the temperature of the impregnation solution is not lower than 50°C before filtering, and the filtration time is not more than 5 minutes. Preferably, the filtrate after filtration is recovered and reused until no solid is precipitated when it is cooled to 30°C.

7. The preparation method according to claim 1, characterized in that In step (3): The temperature of the potassium hydroxide solution does not exceed 30°C, preferably does not exceed 20°C; The concentration of the potassium hydroxide solution is 200-300 g / L; The stirring and soaking time is 1 to 2 hours; and / or The mass ratio of potassium hydroxide in the potassium hydroxide solution to the biochar in step (2) is (1-3):

1.

8. The preparation method according to claim 1, characterized in that In step (3): The drying temperature is 60-70°C; and / or Drying is performed to obtain a slurry mixture having a moisture content of 20 to 40%.

9. The preparation method according to claim 1, characterized in that In step (4): The high-temperature pyrolysis is carried out under the protection of an inert gas, preferably in a nitrogen atmosphere, or the high-temperature pyrolysis is carried out in a closed space after pre-removal of oxygen by limited combustion; and / or The temperature of the high-temperature pyrolysis is 800-1000° C., the time is 1-3 hours, and the heating rate to the high-temperature pyrolysis temperature is 2-5° C. / min.

10. A biochar-based adsorbent activated by the potassium salt of a polyphenolic hydroxy organic acid prepared by the preparation method according to any one of claims 1 to 9.

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