AU2020100229A4 - Activated carbon prepared from biomass waste, preparation method thereof, and use thereof in treatment of nitrophenol compounds in wastewater - Google Patents

Abstract

The present invention discloses a preparation method of activated carbon from a biomass waste. The preparation method includes the following steps: (a) grafting 2-acrylamido-2-methylpropane sulfonic acid onto the surface of a biomass waste; and (b) conducting carbonization on the biomass waste treated by step (a) to obtain activated carbon. Compared with the prior art, the biomass-based activated carbon prepared by the method has a good adsorption capacity to p-nitrophenol, which can reach above 480 mg/g. Moreover, it can almost completely remove lead ions, chromium ions, nickel ions, and arsenic ions from water. The biomass-based activated carbon has good cycle stability. After more than five cycles, its adsorption capacity still remains above 98%. Therefore, the biomass-based activated carbon is a multifunctional comprehensive wastewater adsorbent.

Description

ACTIVATED CARBON PREPARED FROM BIOMASS WASTE, PREPARATION METHOD THEREOF, AND USE THEREOF IN TREATMENT OF NITROPHENOL COMPOUNDS IN WASTEWATER

TECHNICAL FIELD

The present invention belongs to the field of activated carbon, and specifically relates to activated carbon that is prepared by using a biomass waste and has an excellent adsorption effect on nitrophenol compounds.

BACKGROUND

Biomass wastes mainly include organic substances derived from organisms, such as microorganisms, plants, and animals, their excreta, garbage, and organic wastewater. A biomass waste is usually generated in the production and consumption using biomass. It still belongs to the macro category of biomass, but energy density, availability, etc. thereof have been significantly reduced.

Currently, there are a large quantity of biomass wastes in rural areas of China, for example, various plant straws, corncobs, potato starch residues, wine residues, animal wastes, etc. Using only plant straws as an example, a total of 1 trillion kg of biomass wastes are produced every year in China, which includes 700 billion kg of agricultural straws and 300 billion kg of wood wastes. These wastes are either discarded or burned. Waste discarding will cause environmental pollution and waste much land due to waste stockpiling; while waste burning is more serious and will greatly affect the earth's climate due to burning of a huge quantity of wastes. This causes serious environmental pollution to vast areas and is also a main cause of the haze formation in winter.

In recent years, because of state subsidies and the supervision of laws and regulations, more

2020100229 17 Feb 2020 attention has been paid to the recycling of biomass wastes. For example, plant straws are used to prepare various activated carbon, feeds, wood-plastic plates, fuels, biomass ethanol, etc. Many studies have been conducted on the preparation of activated carbon by using biomass straws, but there still exist the following problems: First, the preparation of activated carbon by using biomass straws has an excessively low carbon yield. In literatures that have been currently reported, rare preparation methods of activated carbon by using biomass straws have a carbon yield higher than 40%. Second, activated carbon prepared by using biomass straws has lower quality than that prepared by using coconut shells or other wood materials. Therefore, the activated carbon has a lower adsorption capacity. Third, the biomass straws have excessively high ash content, which is also a main factor that affects the quality of activated carbon prepared by using biomass straws.

In numerous biomass straws, corn straws are the most productive biomass straw waste. In 2017, the yield of com straws in China was 259.2 million tons. A vast quantity of com straws were produced, but the really effective utilization of com straws was not greater than 50%. Among reported literatures, the preparation of water-absorbent resin and activated carbon by using com straws are most studied. The patent CN110342510A discloses a preparation method of activated carbon by using corn straws. In this method, com straws are used as a raw material, and a sodium bicarbonate solution is added to raw material granules. Based on a characteristic that sodium bicarbonate is decomposed to carbon dioxide gas and water vapor when being heated, a pore structure of activated carbon is changed. Specific steps include: (1) crushing corn straws; (2) preparing a sodium bicarbonate aqueous solution; (3) soaking com straw granules in the sodium bicarbonate aqueous solution, and conducting dehydration and drying; (4) conducting extrusion and granulation by a pan granulator; (5) carbonizing straw granules by a continuous charcoal making machine; and (6) conducting classified screening on carbon granules obtained after carbonization, and outputting the carbon granules to a drum-type steam activating oven for

2020100229 17 Feb 2020 activation. Modified activated carbon with higher activity and adsorbability can be prepared by using the method in the invention, so as to increase an additional valve of a product. Except for the conventional performance test, no adsorption study on other pollutants is conducted. The patent CN109850889A discloses a method for preparing activated carbon from com straws by a microwave method, in which microwave heating is conducted for chemical activation to transform com straws to high-quality activated carbon. In the patent, the influence of main operating conditions (an impregnation ratio between an activating agent to a raw material, a concentration of the activating agent, the impregnation time of the activating agent, microwave power, and the irradiation time) on an adsorption capacity of activated carbon is studied; an optimal process condition of activated carbon production is obtained by an orthogonal experiment method; and an experiment product is used for adsorption of effluent obtained after secondary biochemical treatment. However, a sewage treatment capacity of the activated carbon is not mentioned in the invention. Li Zhe et al. have disclosed a literature titled Preparation of Activated Carbon from Corn Straws by Microwave Method and Effect thereof on Adsorption of Malachite Green. Activated carbon is prepared from corn straws with zinc chloride as an activating agent by using a microwave method; the adsorption performance of the activated carbon on malachite green is studied; an optimal adsorption condition, adsorption thermodynamics, and kinetic characteristics of malachite green on the activated carbon are also studied; and the prepared activated carbon has relatively low adsorption capacity to organic matters. In Suo Fengyue's paper titled Preparation of Biochar from Corn Straws and Study on Adsorption Mechanisms of Pesticides in Water on Biochar, a composite prepared from a biomass waste from corn straws and graphene oxide has the best adsorption effect on pesticides. However, high-price graphene oxide is used for the adsorbent preparation, which is not conducive to promotion. The patent numbered CN108383119Adiscloses a method for preparing a hierarchical pore activated carbon material from com straws by a microbiological method. The

2020100229 17 Feb 2020 activated carbon material is prepared from corn straws according to steps such as crushing, mixing with an inorganic culture solution, sterilization, inoculated culture, high-temperature carbonization, grinding with compound alkali and mixing, high-temperature activation, washing, and drying. The preparation method uses corn straws as a raw material that is simple and easy to get, thereby turning waste into treasure. The invention can not only resolve a waste treatment problem of corn straws, but also provide an activated carbon material with a high adsorption capacity to Rhodamine B. The adsorption capacity of the activated carbon material to Rhodamine B is 1333.32 mg/g, which is approximately six times that of commercial activated carbon powder and twice that of a straw carbon material prepared in a conventional KOH activation mode. The prepared activated carbon material has good adsorption performance and material stability. When placed at normal temperature for one year, the adsorption performance of the activated carbon material on Rhodamine B is unchanged. The preparation method is simple and easy for implementation, and is worthy of market promotion and application. Rhodamine B is a material that can be relatively easily adsorbed and removed. However, in the patent, an adsorption effect of the activated carbon material on nitrophenol compounds that are difficult to be treated is not mentioned. The patent CN106276891A discloses a method for preparing activated carbon from Camellia oleifera shells. This method includes the following steps: step 1. crushing camellia oleifera shells to obtain shell granules; step 2. placing the shell granules in a water vapor activation device for carbonization, and introducing water vapor for heating and activation to obtain a crude activated carbon product; and step 3. mixing (by weight) 10 parts of the crude activated carbon product with 20 parts of an acetic acid solution, 3 parts of mannitol, 0.5 parts of soya bean lecithin, 0.1 parts of 2-acrylamido-2-methylpropane sulfonic acid, and 0.4 parts of phenolic resin, conducting impregnation at 40°C for 6 h, and drying to obtain a modified crude product; and step 4. mixing (by weight) 10 parts of the modified crude product with 0.5 parts of sodium bicarbonate, heating to 600°C under the protection of nitrogen gas, conducting activation

2020100229 17 Feb 2020 for 90 min, cooling to room temperature, washing with boiling water, and drying. The patent CN105148844A discloses a preparation method of an activated carbon filter element material with a bactericidal effect. The preparation method includes the following steps: step 1. adding 500 g of activated carbon with a particle size of 100 pm and 125 g of polypropylene fiber into 1250 g of deionized water, adding 50 g of 2-acrylamido-2-methylpropane sulfonic acid, and heating to boiling and evaporating water to dryness to obtain a solid mixture; step 2. dissolving p-hydroxybenzoate ester in ethanol to obtain a solution 1, where a mass concentration of p-hydroxybenzoate ester in ethanol is 20%; and step 3. adding 500 g of the solid mixture to 500 g of the solution 1, mixing them uniformly, heating to 40°C in a vacuum condition of 0.02 MPa and holding at 40°C for 30 min, conducting heating under the protection of nitrogen gas, conducting sintering at 280°C, and cooling to room temperature for cooling forming, to obtain an activated carbon filter element material with a bactericidal effect. Neither of the two patent applications mentioned above has disclosed a function of 2-acrylamido-2-methylpropane sulfonic acid and an adsorption effect of activated carbon on nitrophenol compounds.

In literatures that have been reported in public, there is no study on the adsorption of picric acid or p-nitrophenol on activated carbon prepared from corn straws. Through long-term studies, inventors of the present invention have found that, a main reason of the foregoing situation is that com straws cannot be effectively bonded with nitrophenol compounds due to few functional groups on their surfaces.

Nitrophenol compounds are main components of metallurgical wastewater, which can cause great harm and is difficult to be treated. Therefore, the metallurgical wastewater has become one of sewages that are most concerned in current wastewater treatment in China. Phenolic wastewater is harmful to human bodies, aquatic creatures, and the agriculture. Drinking phenol-polluted water for a long time will cause dizziness, anemia, and various neurological diseases.

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At present, phenolic wastewater is mainly treated by catalytic oxidation. This method cannot completely eliminate phenol pollution. Moreover, it is very difficult for treatment of comprehensive wastewater using this method.

SUMMARY

Based on the problem that the existing activated carbon mentioned above has limited adsorption effects on nitrophenol compounds, the present invention provides a preparation method of activated carbon from a biomass waste. The activated carbon prepared by the method has a significantly improved adsorption effect on nitrophenol compounds.

To achieve the above objective, the technical solution adopted by the present invention is as follows.

A preparation method of activated carbon from a biomass waste is provided, including the following steps:

(a) grafting 2-acrylamido-2-methylpropane sulfonic acid onto the surface of a biomass waste; and (b) conducting carbonization on the biomass waste treated by step (a) to obtain activated carbon.

Preferably, the step of grafting 2-acrylamido-2-methylpropane sulfonic acid onto the surface of a biomass waste includes:

(al) mixing the biomass waste with water, and conducting thermal activation at 100-170°C for 10-20 h;

(a2) after thermal activation, adding an initiator and the 2-acrylamido-2-methylpropane

2020100229 17 Feb 2020 sulfonic acid, and conducting pre-reaction at 70-90°C for 0.5-1.5 h; and (a3) after pre-reaction, adding a cross-linking agent, and conducting reaction at 50-80°C for 8-15 h

Preferably, a mass ratio of the biomass waste to the 2-acrylamido-2-methylpropane sulfonic acid is 1:(0.5-2.5).

Preferably, the initiator is potassium persulfate, and the cross-linking agent is

N, N'-methylenebisacrylamide.

More preferably, a dosage of the potassium persulfate is 0.1-1% of the mass of the biomass waste, and a dosage of the Ν,Ν'-methylenebisacrylamide is 0.01-0.1% of the mass of the biomass waste.

Preferably, step (a2) and step (a3) are conducted under the protection of nitrogen gas.

Preferably, the step of conducting carbonization on the biomass waste treated by step (a) to obtain activated carbon includes:

(bl) impregnating the biomass waste treated by step (a) with a sodium bicarbonate solution, and (b2) conducting carbonization on the biomass waste treated by step (bl) at 450-750°C for

O. 5-2 h in a carbon dioxide atmosphere, to obtain the activated carbon.

More preferably, a concentration of the sodium bicarbonate solution is 5-20wt%, and the impregnation time is 15-30 h. In the present invention, sodium bicarbonate is used as a pore-forming agent and an activating agent, and carbon dioxide is used as a carbonization reinforcing agent.

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Preferably, the biomass waste is plant straws; preferably, the plant straws are corn straws; and more preferably, a particle size D90 of the corn straws is greater than 2500 meshes.

Preferably, in step (b2), the temperature rises to 450-750°C at l-10°C/min.

The activated carbon prepared according to the above method can be used for treatment of nitrophenol compounds and/or heavy metal ions in wastewater, for example, p-nitrophenol, lead ions, chromium ions, nickel ions, and arsenic ions.

Beneficial Effects:

In the present invention, 2-acrylamido-2-methylpropane sulfonic acid is grafted onto the surface of a biomass waste by a chemical reaction method; and carbonization is conducted on the biomass waste to prepare biomass-based activated carbon with a surface containing amino groups and sulfonic groups. When used to adsorb p-nitrophenol, the active carbon granules have a super adsorption capacity to p-nitrophenol. Compared with existing activated carbon, the biomass-based activated carbon prepared by the method in the present invention has the following advantages:

1. The biomass-based activated carbon prepared by the method has a good adsorption capacity to p-nitrophenol compounds, which can reach above 480 mg/g. Moreover, it can almost completely remove lead ions, chromium ions, nickel ions, and arsenic ions from water. Therefore, the biomass-based activated carbon is a multifunctional comprehensive wastewater adsorbent.

2. The biomass-based activated carbon has stable performance, and can be recycled for many times. After activated carbon-containing sludge having adsorbed p-nitrophenol is calcined, its adsorption capacity is improved when it is used to adsorb p-nitrophenol again. After more than five cycles, its adsorption capacity still remains above 98%.

2020100229 17 Feb 2020

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an infrared spectrogram of a porous activated carbon according to Embodiment 1;

FIG. 2 is a scanning electron micrograph of activated carbon prepared from pure com straws;

FIG. 3 is a scanning electron micrograph of polymer carbon prepared from pure 2-acrylamido-2-methylpropane sulfonic acid;

FIG. 4 is a scanning electron micrograph of the porous activated carbon according to Embodiment 1; and

FIG. 5 shows surface elemental analysis of the porous activated carbon according to Embodiment 1.

DETAILED DESCRIPTION

The present invention is further described in detail below with reference to embodiments.

Embodiment 1

Preparation of a porous activated carbon material: Com straws were subject to superfine crushing to a particle size D90 greater than 2500 meshes; 100 g of corn straw powder was weighed and placed in a 500 mL flask, 300 g of distilled water was added, and thermal activation was conducted at 150°C for 15 h; a solution obtained after thermal activation was cooled to room temperature, and 0.5 g of potassium persulfate as an initiator and 125 g of 2-acrylamido-2-methylpropane sulfonic acid were successively added, and pre-reaction was conducted at 80°C for 1 h in a nitrogen gas atmosphere; a reaction mixture was frozen by liquid nitrogen; then 0.05 g of Ν,Ν'-methylenebisacrylamide was added as a cross-linking agent, degassing was conducted for more than ten times, and the reaction mixture was slowly heated to

2020100229 17 Feb 2020

70°C under the protection of nitrogen gas; and the reaction was conducted at 70°C for more than 10 h. After the reaction, an obtained polymer sample was crushed to granules with a particle size of 2-3 mm and dried. 100 g of the dried sample was placed in 500 mL of a 10% sodium bicarbonate solution, and stood for more than 24 h; an obtained product was filtered and dried in air; the dried sample treated by sodium bicarbonate was placed in a rotary tube furnace, heated to 550°C at 5°C/min at 50 r/min in a carbon dioxide atmosphere, and then held at 550°C for 1 h; and then an obtained product was slowly cooled to room temperature under the protection of nitrogen gas, so as to obtain the porous activated carbon material with a particle size of 0.5-1 mm (a carbon yield is 67%). An infrared spectrogram of the porous activated carbon material is shown in FIG. 1; its scanning electron micrograph is shown in FIG. 4; its elemental analysis is shown in FIG. 5; and its test result of a specific surface area is shown in Table 1.

Table 1 The test on a specific surface area of porous activated carbon

Sample	Specific surface area (m2-g_1)	Total pore volume (cm3-g_1)	Average pore diameter (nm)
Porous activated carbon	1587	1.095	2.46

It can be seen from FIG. 1 that, 3429 cm^-1 indicates stretching vibration peaks of N-H and O-H; 2920 cm^-1 and 2850 cm^-1 indicate stretching vibration peaks of methyl and methylene; 1776 cm^-1, 1438 cm^-1, and 1141 cm^-1 indicate stretching vibration peaks of-COOH, C=O, and -OH; 1604 cm^-1 indicates a stretching vibration peak of C=O; 1438 cm^-1 indicates a bending vibration peak of C-H; 1334 cm^-1, 1274 cm^-1, and 1141 cm^-1 indicate stretching vibration peaks of-SOs; 993 cm^-1, 879 cm^-1, and 628 cm^-1 indicate that C-H is in out-of-plane bending vibration. FIG. 1 can prove that 2-acrylamido-2-methylpropane sulfonic acid is successfully grafted onto the surface of com straws in the present invention, and the prepared porous carbon material is a composite of these two substances.

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Comparative Example 1

Preparation of activated carbon from pure com straws: Corn straws were subject to superfine crushing to a particle size D90 greater than 2500 meshes; 100 g of com straw powder was weighed and placed in a 500 mL flask, 300 g of distilled water was added, and thermal activation was conducted at 150°C for 15 h; and an product is filtered and dried in air. 100 g of the dried sample was placed in 500 mL of a 10% sodium bicarbonate solution, and stood for more than 24 h; an obtained product was filtered and dried in air; the dried sample treated by sodium bicarbonate was placed in a rotary tube furnace, heated to 550°C at 5°C/min at 50 r/min in a carbon dioxide atmosphere, and then held at 550°C for 1 h; and then an obtained product was slowly cooled to room temperature under the protection of nitrogen gas, so as to obtain activated carbon prepared from pure com straws and with a particle size of 0.5-1 mm. A scanning electron micrograph of the activated carbon is shown in FIG. 2.

Comparative Example 2

Preparation of polymer carbon from pure 2-acrylamido-2-methylpropane sulfonic acid: 300 g of distilled water, 0.5 g of potassium persulfate as an initiator, and 125 g of 2-acrylamido-2-methylpropane sulfonic acid were successively added to a 500 mL flask, and pre-reaction was conducted at 80°C for 1 h in a nitrogen gas atmosphere; a reaction mixture was cooled by liquid nitrogen; then 0.05 g of Ν,Ν'-methylenebisacrylamide was added as a cross-linking agent, degassing was conducted for more than ten times, and the reaction mixture was slowly heated to 70°C under the protection of nitrogen gas; and the reaction was conducted at 70°C for more than 10 h. After the reaction, an obtained polymer sample was crushed to granules with a particle size of 2-3 mm and dried. 100 g of the dried sample was placed in 500 mL of a 10% sodium bicarbonate solution, and stood for more than 24 h; an obtained product was filtered and dried in air; the dried sample treated by sodium bicarbonate was placed in a rotary

2020100229 17 Feb 2020 tube furnace, heated to 550°C at 5°C/min at 50 r/min in a carbon dioxide atmosphere, and then held at 550°C for 1 h; and then an obtained product was slowly cooled to room temperature under the protection of nitrogen gas, so as to obtain polymer carbon with a particle size of 0.5-1 mm. A scanning electron micrograph of the polymer carbon is shown in FIG. 3.

It can be seen from FIG. 2, FIG. 3, FIG. 4, and FIG. 5, morphologies of the activated carbon prepared from pure corn straws, the polymer carbon, and the porous activated carbon in Embodiment 1 are completely different. This indicates that a new substance is successfully prepared. It can also be seen through surface element analysis that 2-acrylamido-2-methylpropane sulfonic acid is successfully grafted onto the surface of com straws in the present invention.

Comparative Example 3

A difference from Embodiment 1 lies in that, during carbonization, the carbon dioxide atmosphere is replaced by a nitrogen gas atmosphere, and a carbon yield of porous activated carbon is only 31%.

Embodiment 2

Preparation of a porous activated carbon material: Corn straws were subject to superfine crushing to a particle size D90 greater than 2500 meshes; 100 g of corn straw powder was weighed and placed in a 500 mL flask, 300 g of distilled water was added, and thermal activation was conducted at 100°C for 20 h; a solution obtained after thermal activation was cooled to room temperature, and 0.1 g of potassium persulfate as an initiator and 50 g of 2-acrylamido-2-methylpropane sulfonic acid were successively added, and pre-reaction was conducted at 70°C for 1.5 h in a nitrogen gas atmosphere; a reaction mixture was frozen by liquid nitrogen; then 0.01 g of Ν,Ν'-methylenebisacrylamide was added as a cross-linking agent, degassing was conducted for more than ten times, and the reaction mixture was slowly heated to

2020100229 17 Feb 2020

80°C under the protection of nitrogen gas; and the reaction was conducted at 80°C for 15 h. After the reaction, an obtained polymer sample was crushed to granules with a particle size of 2-3 mm and dried. 100 g of the dried sample was placed in 500 mL of a 5% sodium bicarbonate solution, and stood for 30 h; an obtained product was filtered and dried in air; the dried sample treated by sodium bicarbonate was placed in a rotary tube furnace, heated to 750°C at 10°C/min at 50 r/min in a carbon dioxide atmosphere, and then held at 750°C for 0.5 h; and then an obtained product was slowly cooled to room temperature under the protection of nitrogen gas, so as to obtain the porous activated carbon material.

Embodiment 3

Preparation of a porous activated carbon material: Corn straws were subject to superfine crushing to a particle size D90 greater than 2500 meshes; 100 g of corn straw powder was weighed and placed in a 500 mL flask, 300 g of distilled water was added, and thermal activation was conducted at 170°C for 10 h; a solution obtained after thermal activation was cooled to room temperature, and 1 g of potassium persulfate as an initiator and 250 g of 2-acrylamido-2-methylpropane sulfonic acid were successively added, and pre-reaction was conducted at 90°C for 0.5 h in a nitrogen gas atmosphere; a reaction mixture was frozen by liquid nitrogen; then 0.1 g of Ν,Ν'-methylenebisacrylamide was added as a cross-linking agent, degassing was conducted for more than ten times, and the reaction mixture was slowly heated to 50°C under the protection of nitrogen gas; and the reaction was conducted at 50°C for 8 h. After the reaction, an obtained polymer sample was crushed to granules with a particle size of 2-3 mm and dried. 100 g of the dried sample was placed in 500 mL of a 20% sodium bicarbonate solution, and stood for 15 h; an obtained product was filtered and dried in air; the dried sample treated by sodium bicarbonate was placed in a rotary tube furnace, heated to 450°C at l°C/min at 50 r/min in a carbon dioxide atmosphere, and then held at 450°C for 2 h; and then an obtained product was slowly cooled to room temperature under the protection of nitrogen gas, so as to obtain the

2020100229 17 Feb 2020 porous activated carbon material.

Embodiment 4

Adsorption experiments of activated carbon:

mg of the porous activated carbon prepared in the present invention was placed in each 50 mL iodine flask; then a 15 mL solution (pH=5) was added; and these iodine flasks were placed in a water bath constant temperature oscillator at 30°C at 160 rpm. In a solution in a flask 1, an initial concentration of p-nitrophenol was 500 mg/L and a concentration of lead ions was 100 mg/L; in a solution in a flask 2, an initial concentration of p-nitrophenol was 500 mg/L and a concentration of chromium ions was 100 mg/L; in a solution in a flask 3, an initial concentration of p-nitrophenol in solution was 500 mg/L and a concentration of nickel ions was 100 mg/L; and in a solution in a flask 4, an initial concentration of p-nitrophenol in solution was 500 mg/L and a concentration of arsenic ions was 100 mg/L.

Detailed adsorption results are shown in Table 2. All removal rates of p-nitrophenol are 96% or higher, and removal rates of various metal ions are 99.5% or higher. To prove that the porous activated carbon prepared in the present invention has better performance than activated carbon prepared from pure corn straws (referred to as pure carbon for short below) and polymer carbon prepared from pure 2-acrylamido-2-methylpropane sulfonic acid (referred to as polymer carbon for short), the pure carbon and polymer carbon were also prepared by using the same method, and they were applied to wastewater treatment described above. Results are shown in Table 2.

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Table 2 Adsorption performance of different carbon materials

	Flask 1	Flask 2	Flask 3	Flask 4
p-Nitrophenol	Lead ions	p-Nitrophenol	Chromium ions	p-Nitrophenol	Nickel ions	p-Nitrophenol	Arsenic ions
Porous
activated	96.0%	99.7%	98.7	99.5%	98.9%	99.9%	99.1%	99.6%
carbon
Pure carbon	2.1%	68%	2.4%	48%	2.0%	31%	2.4%	39%
Polymer carbon	19.6%	14%	18.9%	19%	19.8%	9.7%	21.4%	11%

Embodiment 5

Recycling of porous activated carbon: 100 g of porous activated carbon-containing sludge having adsorbed p-nitrophenol was dried in air at 80-100°C for 2-5 h; then the sludge was placed in a rotary tube furnace, heated to 550°C at 5°C/min at 50 r/min in a carbon dioxide atmosphere, and then held at 550°C for 1 h; and then an obtained product was slowly cooled to room temperature under the protection of nitrogen gas. After more than five cycles, an adsorption capacity of the sludge still remains above 98%.

Finally, it should be noted that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present

2020100229 17 Feb 2020 invention is described in detail with reference to the foregoing embodiments, a person skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments, or make equivalent replacement to some technical characteristics. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should fall within the protection scope of the present invention.

Claims (5)

1. What is claimed is:

   1. A preparation method of activated carbon from a biomass waste, comprising the following steps:

   (a) grafting 2-acrylamido-2-methylpropane sulfonic acid onto the surface of a biomass waste; and (b) conducting carbonization on the biomass waste treated by step (a) to obtain activated carbon.
2. 2. The preparation method according to claim 1, wherein the step of grafting 2-acrylamido-2-methylpropane sulfonic acid onto the surface of a biomass waste comprises:

   (al) mixing the biomass waste with water, and conducting thermal activation at 100-170°C for 10-20 h;

   (a2) after thermal activation, adding an initiator and the 2-acrylamido-2-methylpropane sulfonic acid, and conducting pre-reaction at 70-90°C for 0.5-1.5 h; and (a3) after pre-reaction, adding a cross-linking agent, and conducting reaction at 50-80°C for 8-15 h;

   preferably, wherein a mass ratio of the biomass waste to the 2-acrylamido-2-methylpropane sulfonic acid is 1:(0.5-2.5);

   preferably, wherein the initiator is potassium persulfate, and the cross-linking agent is Ν,Ν'-methylenebisacrylamide, further preferably, wherein a dosage of the potassium persulfate is 0.1-1% of the mass of the biomass waste, and a dosage of the Ν,Ν'-methylenebisacrylamide is

   0.01-0.1% of the mass of the biomass waste.

   2020100229 17 Feb 2020
3. 3. The preparation method according to claim 1, wherein the step of conducting carbonization on the biomass waste treated by step (a) to obtain activated carbon comprises:

   (bl) impregnating the biomass waste treated by step (a) with a sodium bicarbonate solution, and (b2) conducting carbonization on the biomass waste treated by step (bl) at 450-750°C for 0.5-2 h in a carbon dioxide atmosphere, to obtain the activated carbon, preferably, wherein a concentration of the sodium bicarbonate solution is 5-20wt%, and the impregnation time is 15-30 h.
4. 4. The preparation method according to claim 1, wherein the biomass waste is plant straws; preferably, the plant straws are corn straws; and more preferably, a particle size D90 of the corn straws is greater than 2500 meshes.
5. 5. Activated carbon prepared according to the preparation method according to any one of claims 1 to 4.