CN115193410B

CN115193410B - Modified activated carbon and preparation method and application thereof

Info

Publication number: CN115193410B
Application number: CN202211039912.0A
Authority: CN
Inventors: 梁鼎成; 于凤芹; 刘缘; 解强; 刘金昌
Original assignee: China University of Mining and Technology Beijing CUMTB
Current assignee: China University of Mining and Technology Beijing CUMTB
Priority date: 2021-11-30
Filing date: 2022-08-29
Publication date: 2023-09-22
Anticipated expiration: 2042-08-29
Also published as: CN115193410A

Abstract

The application provides modified activated carbon, a preparation method and application thereof. In the application, the quaternary ammonium salt carrying positive electricity is combined with the activated carbon with the surface being negative electricity in a targeted manner through coulomb attraction, then the carbon-carbon double bond or carbon-carbon triple bond carried by the quaternary ammonium salt can be opened to be combined with the surface of the activated carbon, and the quaternary ammonium salt is firmly combined with the surface of the activated carbon, so that the change of the charge distribution of the surface of the activated carbon is realized, the phenomenon of pore blocking caused by adsorption of the quaternary ammonium salt by the activated carbon is effectively prevented, and in addition, the ammonium ions which are easy to dissolve in water obviously improve the hydrophilicity of the surface of the activated carbon.

Description

Modified activated carbon and preparation method and application thereof

Technical Field

The application relates to the field of activated carbon modification, in particular to modified activated carbon, and a preparation method and application thereof.

Background

With the development of human society, the variety of pollutants in water body is more and more, and particularly the occurrence of some anionic pollutants, which can pose a great threat to human health, such as F ^- 、ClO ₄ ^- Etc. If the fluorine content of the water is higher than 1.0-1.5 mg/L after long-term drinking, the water is liable to be affected by plaque and odontopathy, and if the fluorine content of the water is higher than 4mg/L, diseases such as fluoritis can be caused. Perchlorate not only can affect thyroid, but also can have certain effects on growth and development of organisms, reproductive behaviors, development of nervous systems and the like.

For removing pollutants in a water body, an activated carbon adsorption mode is generally adopted. More than half of the wastewater treatment plants in the united states use powdered or granular activated carbon to treat wastewater. Activated carbon is a porous adsorption material with high porosity and large specific surface area, and is a broad-spectrum adsorbent, however, the isoelectric point (pH _IEP ) Typically low, resulting in activated carbon that is typically negatively charged in neutral solution. Therefore, the anion effect of treating the water body with activated carbon is not ideal. In addition, activated carbon is often used as a support for composite materials by incorporating a material having certain specific properties on the activated carbon, but often because both the support and the incorporated material are negatively charged in solution, it is difficult to form the composite material by means of electrostatic self-assembly.

Aiming at the phenomenon, the problem of regulating and controlling the surface charge distribution of the activated carbon in the solution is to be solved urgently, the main treatment mode at present is to modify the surface chemistry of the activated carbon by adopting a cationic active agent, but because the pores of the activated carbon are developed, most cationic active agents are adopted to change the surface charge distribution of the activated carbon, and meanwhile, more cationic active agents are adsorbed into the pores by the activated carbon, so that the phenomenon of serious pore blocking is caused. Therefore, how to target the surface charge distribution of the modified activated carbon and alleviate the blocking of the activated carbon channels has not been developed.

Disclosure of Invention

In order to solve the problems, the application prepares the modified activated carbon by a method of chemically modifying the activated carbon by quaternary ammonium salt. The quaternary ammonium salt carrying positive electricity is combined with the activated carbon with the surface being negative electricity in a targeted manner through coulomb attraction, then the carbon-carbon double bond or carbon-carbon triple bond carried by the quaternary ammonium salt can be opened to be combined with the surface of the activated carbon, the quaternary ammonium salt is firmly combined with the surface of the activated carbon, the change of the charge distribution on the surface of the activated carbon is realized, the phenomenon of blocking holes caused by adsorption of the quaternary ammonium salt by the activated carbon is effectively prevented, and in addition, the ammonium ions which are easy to dissolve in water obviously improve the hydrophilicity of the surface of the activated carbon.

According to one aspect of the application, a preparation method of modified activated carbon is provided, wherein quaternary ammonium salt solution is mixed with activated carbon for reaction to obtain modified activated carbon; the quaternary ammonium salt is at least one selected from compounds with a structure of formula I,

wherein M is ^n- Is negatively charged ion, n is the charge number of M; r is R ₁ 、R ₂ 、R ₃ 、R ₄ Independently selected from substituent-containing or substituent-free C ₁ ～C ₅ Any one of alkane, alkene or alkyne, and R ₁ 、 R ₂ 、R ₃ 、R ₄ At least one of which contains a carbon-carbon unsaturated bond; the mass ratio of the quaternary ammonium salt to the activated carbon is (0.5-10): 1.

Optionally, the activated carbon is carbon subjected to high-temperature carbonization and high-temperature activation; the high temperature is 600 ℃ or higher.

The active carbon is obtained by carbonizing solid carbonaceous matters (such as coal, timber, hard fruit shell, fruit core, resin and the like) at a high temperature of 600-900 ℃ under the condition of air isolation, and then performing oxidation activation by using carbon dioxide, water vapor or mixed gas of the three under the condition of 900-1500 ℃.

The carbonization volatilizes substances except carbon, and the oxidation activation can further remove residual volatile substances to generate new and enlarged original pores, improve the micropore structure and increase the activity.

Optionally, the activated carbon is coal-based activated carbon.

Distinction of coal-based activated carbon and biomass activated carbon: the essential difference is that raw materials are different, coal-based activated carbon is produced by taking coal as a raw material, biomass activated carbon is produced by taking biomass as a raw material, so that the main difference of the raw materials is that the two raw materials are prepared by different production raw materials, for example, the macromolecular structure of coal is more in a polycyclic aromatic hydrocarbon structure, the biomass is mainly in a molecular structure of cellulose-like and hemicellulose, so that the surface of the activated carbon prepared by cellulose-like and hemicellulose contains more oxygen-containing functional groups, such as-O H, COOH and other groups, and the oxygen-containing functional groups in the coal-based activated carbon are less, and only a small amount of-OH exists. In addition, the coal-based activated carbon mainly comprises micropores, and the pore structure in the biomass activated carbon mainly comprises mesopores and macropores.

Optionally, the coal-based activated carbon contains phenolic hydroxyl groups.

Optionally, the coal-based activated carbon containing phenolic hydroxyl groups is prepared by steam.

A large number of coal-based commercial activated carbons in the market are mainly prepared by a physical activation method (carbonization is performed before activation), the used activating agent is water vapor, when the activated carbon is prepared by water vapor and activated carbonized materials, hydroxyl groups are on the activated carbon, and the molecular structure of the coal mainly takes polycyclic aromatic hydrocarbon as a main part, so that more hydroxyl groups are phenolic hydroxyl groups.

Optionally, the carbon-carbon unsaturation comprises a carbon-carbon double bond and/or a carbon-carbon triple bond.

Alternatively, the quaternary ammonium salt side chain has too many carbon molecules, which can lead to high steric hindrance and change of hydrophilicity and hydrophobicityAnd (5) melting. Specifically, the carbon chain is long, the steric hindrance is large, the quaternary ammonium salt cannot be well combined with the surface of the activated carbon, and the long-chain alkyl is hydrophobic, so that the surface of the activated carbon presents hydrophobicity, and therefore, C ₁ ～C ₅ Alkane, alkene or alkyne.

Optionally, the mass ratio of the quaternary ammonium salt to the activated carbon is 0.5: 1. 0.6: 1. 0.7: 1. 0.8: 1. 0.9: 1. 1: 1. 2: 1. 3: 1. 4: 1. 5: 1. 6: 1. 7: 1. 8: 1. 9: 1. 1 0:1 or any ratio between any two ratios.

If the mass ratio of the quaternary ammonium salt to the activated carbon is less than 0.5, less quaternary ammonium salt combined with the surface of the activated carbon is caused, so that N on the surface of the activated carbon ⁺ The ions are less, the change of the charge on the surface of the activated carbon is less, and the effect of effectively modifying the charge distribution on the surface of the activated carbon cannot be achieved; if the mass ratio of the quaternary ammonium salt to the activated carbon is more than 10, although the surface charge distribution of the activated carbon can be effectively modified, excessive quaternary ammonium salt can be continuously combined with the activated carbon, and when the carbon on the surface is completely combined, the quaternary ammonium salt can carry out activated carbon pore channels, so that the activated carbon pore channels are easily blocked.

Preferably, the mass ratio of the quaternary ammonium salt to the activated carbon is (5-10): 1.

preferably, the mass ratio of the quaternary ammonium salt to the activated carbon is (2-10): 1.

optionally, the quaternary ammonium salt is selected from at least one of the compounds having the structure of formula II,

wherein X is ^- Is an ion with a negative charge; r is R ₁ 、R ₂ 、R ₃ 、R ₄ Independently selected from substituent-containing or substituent-free C ₁ ～C ₅ Any one of an alkane, alkene, or alkyne; r is R ₁ 、R ₂ 、R ₃ 、R ₄ Containing a carbon-carbon double bond or a carbon-carbon triple bond.

Optionally, the X is halogen.

Optionally, the halogen is selected from any one of F, cl, br, I, at.

Optionally, the quaternary ammonium salt is selected from at least one of the compounds having the structure of formula III,

wherein R is ₁ 、R ₂ 、R ₃ 、R ₄ Independently selected from substituent-containing or substituent-free C ₁ ～C ₅ Any one of an alkane, alkene, or alkyne; r is R ₁ 、R ₂ 、R ₃ 、R ₄ Containing a carbon-carbon double bond or a carbon-carbon triple bond.

Optionally, the quaternary ammonium salt is selected from at least one of the compounds having the structure of formula IV,

wherein X is ^- Is an ion with a negative charge; r is R ₁₁ 、R ₂₁ Independently selected from substituent-containing or substituent-free C ₁ ～C ₄ Any one of alkanes, alkenes, or alkynes.

Optionally, the quaternary ammonium salt is selected from at least one of the compounds having the structure of formula V,

wherein R is ₁₁ 、R ₂₁ Independently selected from substituent-containing or substituent-free C ₁ ～C ₄ Any one of alkanes, alkenes, or alkynes.

Optionally, the quaternary ammonium salt is dimethyl diallyl ammonium chloride, and the structural formula is as follows:

alternatively, the reaction is carbon-carbon double bonds or carbon-carbon triple bonds in the quaternary ammonium salt with carbon on the surface of the activated carbon.

Alternatively, the conditions of the reaction are: the reaction temperature is 15-30 ℃ and the reaction time is 3-24 h.

Alternatively, the reaction temperature is 15 ℃, 16 ℃, 17 ℃, 18 ℃, 19 ℃, 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃, 29 ℃, 30 ℃, or any value between any two values.

Alternatively, the reaction time is 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h or any value between any two values.

Optionally, the modified activated carbon has an isoelectric point4。

The initial isoelectric point of the activated carbon is less than or equal to 3, and after the activated carbon is modified by the quaternary ammonium salt, the quaternary ammonium salt can change the electric charge on the surface of the activated carbon, namely the isoelectric point of the modified activated carbon can be increased.

Optionally, the isoelectric point of the modified activated carbon is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or any value between any two values.

Optionally, the modified activated carbon has an isoelectric point ∈ 7.

Optionally, the modified activated carbon has an isoelectric point ∈ 10.

Only when the isoelectric point of the modified activated carbon is not less than 7, the property of the original activated carbon with negative electricity can be changed, so that the adsorption capacity of the activated carbon is changed. When the isoelectric point of the modified activated carbon is not less than 10, anions in water can be effectively adsorbed, so that the modified activated carbon can be used as an adsorption carrier to adsorb anion pollutants under alkaline conditions.

Optionally, the modified activated carbon has a contact angle with water of less than 60 °.

Due to this applicationThe contact angle between the activated carbon and water is about 70 degrees, and the activated carbon has certain hydrophilicity, so that the activated carbon with stronger hydrophilicity is needed for increasing the adsorption of pollutants in the water body. In the application, the quaternary ammonium salt is used for modifying the activated carbon, so that the surface of the activated carbon is provided with N ⁺ The group has good hydrophilicity. With the increase of the modification time and the quaternary ammonium salt amount, the contact angle between the modified activated carbon and water gradually decreases, and finally the activated carbon can be completely dissolved in water, namely, the contact angle is 0 degrees.

Optionally, the mass content of the quaternary ammonium salt in the modified activated carbon is 3% -15%.

In the application, the quaternary ammonium salt firstly reacts with carbon on the surface of the active carbon to generate stable carbon-carbon single bond, but with the increase of the quaternary ammonium salt amount, after the surface of the active carbon is fully reacted with the quaternary ammonium salt, namely when the quaternary ammonium salt covers most of the surface of the active carbon, the surface is difficult to react due to steric hindrance, and excessive quaternary ammonium salt can enter the pore canal to react with the carbon in the pore canal, so that the pore canal is blocked. The application can avoid the blockage of the pore canal to a certain extent by controlling the proportion of the quaternary ammonium salt in the whole modified activated carbon, thereby achieving the effect of only changing the surface charge of the activated carbon.

Optionally, the specific surface area of the modified activated carbon is 50% -90% of that of the activated carbon.

As the quaternary ammonium salt reacts with the surface of the activated carbon, the specific surface area of the surface of the activated carbon is preferentially reduced, namely, the specific surface area is reduced by about 10-50 percent. When the specific surface area is reduced by less than 10%, the amount of the quaternary ammonium salt for modifying the surface of the activated carbon is small, and the surface charge of the activated carbon cannot be effectively changed; when the content is more than 50%, the quaternary ammonium salt enters the activated carbon pore canal, and once the quaternary ammonium salt enters the pore canal, the specific surface area of the activated carbon is seriously reduced, so that the activated carbon pore canal is blocked.

Optionally, stirring or shaking is included in the reaction.

The stirring or shaking is used for uniformly mixing the quaternary ammonium salt and the activated carbon, and the reaction is more sufficient.

Optionally, the preparation method further comprises filtering and drying.

Optionally, unreacted quaternary ammonium salt and other impurities are filtered to obtain a product with higher purity in the subsequent operation.

Specifically, the mixture after the reaction is dried.

Optionally, the drying conditions are: the drying time is 10-20 h at 70-100 ℃.

Preferably, drying is carried out at 80℃for 12 hours.

According to another aspect of the present application, there is provided a modified activated carbon prepared according to any one of the methods described above.

Optionally, the modified activated carbon has an isoelectric point4。

The initial isoelectric point of the activated carbon is less than or equal to 3, and after the quaternary ammonium salt is modified, the quaternary ammonium salt can modify the electric charge on the surface of the activated carbon, so that the surface of the activated carbon is positively charged, namely the isoelectric point of the modified activated carbon can be increased.

Optionally, the charge points of the modified activated carbon are 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or any value between any two values.

Optionally, the modified activated carbon has an isoelectric point7。

Optionally, the modified activated carbon has an isoelectric point10。

The contact angle between the activated carbon and water used in the application is about 70 degrees, and the activated carbon has certain hydrophilicity, so that the activated carbon with stronger hydrophilicity is needed for increasing the adsorption of pollutants in water. In the application, the quaternary ammonium salt is used for modifying the activated carbon, so that the surface of the activated carbon is provided with N ⁺ The group has good hydrophilicity. Along with modificationThe contact angle between the modified activated carbon and water is gradually reduced due to the increase of the amount of the meta-ammonium salt and the quaternary ammonium salt, and finally the activated carbon can be completely dissolved in the water, namely, the contact angle is 0 degrees.

According to a further aspect of the present application there is provided the use of a modified activated carbon selected from at least one of the modified activated carbons prepared according to any of the methods described above for removing anions from water.

Alternatively, the anion is selected from F ^- 、ClO ₄ ^- 、Cl ^- 、NO ₂ ^- 、Br ^- 、NO ₃ ^- 、PO ₄ ^3- 、SO ₃ ^2- 、 SO ₄ ^2- 、ClO ₃ ^- 、ClO ₂ ^- At least one of (a)。

Compared with the prior art, the application has the following beneficial effects:

(1) The application provides a modified activated carbon, wherein quaternary ammonium salt and carbon on the surface of the activated carbon are combined and coated on the surface of the activated carbon, and the quaternary ammonium salt contains N ⁺ Ions with positive charges can change the charge property of the surface of the activated carbon, so that the activated carbon is changed from electronegativity to electropositivity, negative anions in a water body can be adsorbed, and the anions cannot be adsorbed by the pores of the activated carbon in a large amount, thereby effectively relieving the phenomenon that the pore channels of the activated carbon are blocked; in addition, due to N ⁺ The ion has better hydrophilicity, the hydrophilicity of the activated carbon can be changed, the contact angle of the modified activated carbon is obviously reduced, and the modified activated carbon is shown to have better dissolution in water, so that the dispersion of the activated carbon in water is more facilitated, and the adsorption and removal of anions in water are promoted.

(2) The application adopts the method of combining the quaternary ammonium salt and the active carbon chemical bond, when the quaternary ammonium salt is loaded on the surface of the active carbon, the surface of the active carbon is targeted through the electrostatic interaction of the quaternary ammonium salt positive electricity and the active carbon negative electricity, and simultaneously the carried carbon-carbon double bond or triple bond is opened to bond with the carbon on the surface of the active carbon, thus forming stable modified active carbon, N ⁺ The ions are located outside the modified activated carbon. The modification method can greatly improve the charge distribution on the surface of the activated carbon under a milder condition; the required reaction conditions are simple, a small amount of quaternary ammonium salt can reach the modification effect, the cost can be obviously reduced, and the large-scale application is realized.

Drawings

FIG. 1 is a Zeta potential diagram of modified activated carbon and unmodified activated carbon prepared in comparative example 1 of the present application; (a) a potential map of different modification times; the abscissa is pH, no unit; the ordinate is Zeta potential, and the unit is mV; (b) potential diagrams of different modification concentrations; the abscissa is pH, no unit; the ordinate is the Zeta potential in mV.

FIG. 2 is a Zeta potential diagram of modified activated carbon and unmodified activated carbon prepared in example 3 of the present application; the abscissa is pH, no unit; the ordinate is the Zeta potential in mV.

FIG. 3 is a Zeta potential diagram of the modified activated carbon and the unmodified activated carbon prepared in example 1 and example 2 of the present application; the abscissa is pH, no unit; the ordinate is the Zeta potential in mV.

FIG. 4 is a Zeta potential diagram of the modified activated carbon and the unmodified activated carbon prepared in comparative example 2 and comparative example 3 according to the present application; the abscissa is pH, no unit; the ordinate is the Zeta potential in mV.

FIG. 5 is a graph showing the analysis of specific surface areas of modified activated carbon and unmodified activated carbon prepared in examples 1 to 3 and comparative example 1 according to the present application; (a) A specific surface area analysis chart of the BAC modified activated carbon prepared in comparative example 1; the abscissa is the number of the modified activated carbon without units; the ordinate is the specific surface area, the unit is m ² ·g ^-1 The method comprises the steps of carrying out a first treatment on the surface of the (b) Specific surface area analysis diagrams of the DDA modified activated carbon prepared in examples 1 to 3; the abscissa is the number of the modified activated carbon without units; the ordinate is the specific surface area, the unit is m ² ·g ^-1 。

FIG. 6 is a drawing showing nitrogen adsorption and desorption of modified activated carbon and unmodified activated carbon prepared in examples 1 to 3 and comparative example 1 of the present application; the abscissa is relative pressure, without units; the ordinate is the adsorption quantity, and the unit is 3-1

cm·g。

FIG. 7 is a thermogravimetric analysis of the modified activated carbon and the unmodified activated carbon prepared in examples 1 to 3 and comparative example 1 of the present application; the abscissa is temperature in degrees celsius; the ordinate is mass, the unit is; the ordinate is differential weight loss rate in%. Min ^-1 The method comprises the steps of carrying out a first treatment on the surface of the (a) Thermogravimetric analysis of BAC modified activated carbon prepared in comparative example 1; (b) Thermogravimetric analysis diagrams of the DDA modified activated carbon prepared in examples 1 to 3; (c) thermogravimetric analysis of BAC and DDA.

FIG. 8 is a thermogravimetric analysis of the modified carbon prepared in comparative example 4 of the present application; the abscissa is temperature in degrees celsius; the ordinate is mass, the unit is; the ordinate is differential weight loss rate in%. Min ^-1 。

FIG. 9 is a schematic diagram of contact angle; (a) activated carbon before modification; (b) the modified activated carbon prepared in comparative example 1; (c) modified activated carbon prepared in examples 1 to 3.

FIG. 10 is a schematic diagram of molecular structures of BAC and DDA; (a) BAC; (b) DDA.

FIG. 11 is XPS C1s spectra of the activated carbon of the present application and the partially modified activated carbon and the unmodified activated carbon prepared in examples 1 to 3 and comparative example 1; the abscissa is binding energy in eV; the ordinate is bond strength, no units.

FIG. 12 is a flow chart of static adsorption of anions by the modified activated carbon of the present application.

FIG. 13 is a graph of isothermal adsorption of fluoride ions by unmodified activated carbon according to the present application; the abscissa is the equilibrium concentration C of fluoride ions _e The unit is mg/L; the ordinate is the saturated adsorption quantity Q of fluorine ions _e The unit is mg/g.

FIG. 14 is an isothermal adsorption graph of fluorine ions of the modified activated carbon prepared in comparative example 1 of the present application; the abscissa is the equilibrium concentration C of fluoride ions _e The unit is mg/L; the ordinate is the saturated adsorption quantity Q of fluorine ions _e The unit is mg/g.

FIG. 15 is a graph showing isothermal adsorption of fluorine ions in the modified activated carbon prepared in example 2 of the present application; the abscissa is the equilibrium concentration C of fluoride ions _e The unit is mg/L; the ordinate is the saturated adsorption quantity Q of fluorine ions _e The unit is mg/g.

Detailed Description

The following describes specific embodiments of the present application with reference to the drawings.

In the present application, unless otherwise indicated, scientific and technical terms used herein have the meanings commonly understood by one of ordinary skill in the art. Also, reagents, materials, and procedures used herein are reagents, materials, and conventional procedures widely used in the corresponding field.

It should be noted that the application modes shown in the following examples are only preferred application modes for materials, and the examples described below are only illustrative of the present application and are not to be construed as limiting the present application. In addition, all reagents employed in the examples below are commercially available or may be synthesized according to methods herein or known, and are readily available to those skilled in the art for reaction conditions not listed, if not explicitly stated. The methods of operation, under which specific conditions are not noted in the examples below, are generally in accordance with conventional conditions, or in accordance with the conditions recommended by the manufacturer.

The quaternary ammonium salt used in this study was an ionic solution, so a 6-31+G (d) group was used, which was based on a 6-31G valent layer split 3zeta group with the addition of d-orbital polarization function and dispersion function. The energy calculated by the base group is similar to the energy calculated by the 6-31++ G (d, p) base group, has p orbit polarization function and more chromatic dispersion function, and ensures the high precision of the 6-31+G (d) base group calculation. Thus, molecular modeling of quaternary ammonium salts was performed with the 6-31+G (d) group. Then, the Surface Electrostatic Potentials (SEPs) of the different quaternary ammonium salts are calculated by using a wave function analysis program Multiwfn, and the results are visualized by using a molecular model visualization program VMD, so that the analysis is facilitated.

Activated carbon: ningxia Wangdaka coal industry Co., ltd, uses Ningxia anthracite as raw material to prepare columnar active carbon;

quaternary ammonium salt solutions of benzalkonium chloride (BAC, 80 wt%), 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA, 65 wt%) and diallyldimethylammonium chloride (DDA, 60 wt%) were all purchased from shanghai mike Lin Shenghua, inc.

Water bath constant temperature oscillator: SHZ-B, beijing Yi Decheng trade company, inc;

circulating water type multipurpose vacuum pump: SHB-III type, shanghai vibration laboratory equipment Co., ltd.

Example 1

Quaternary ammonium salt: dimethyl diallyl ammonium chloride C ₈ H ₁₆ ClN (abbreviated as DDA) having the structural formula:

the preparation method of the modified activated carbon comprises the following steps:

preparing 2wt% dimethyl diallyl ammonium chloride solution (water as solvent) according to a solid-to-liquid ratio of 1g (active carbon sample) of 50ml (dimethyl diallyl ammonium chloride solution), adding a certain amount of active carbon sample and dimethyl diallyl ammonium chloride solution into a conical flask, putting the conical flask at room temperature (25 ℃) for water bath oscillation (160 rpm/min), and oscillating for 3h; and (3) carrying out suction filtration on the mixed solution, and drying a solid sample obtained by suction filtration in an oven at 80 ℃ for 12 hours to obtain the modified activated carbon A C-DDA-2-3.

Example 2

As in example 1, only the amount fraction of the dimethyldiallylammonium chloride solution in example 1 was changed to 1%, 5% and 10% to obtain modified activated carbons AC-DDA-1-3, AC-DDA-5-3 and AC-DD A-10-3, respectively.

Example 3

As in example 1, the amount fraction of the dimethyldiallylammonium chloride solution in example 1 was changed to 0.5% to obtain AC-DDA-0.5-3; and changing the reaction time into 12h and 24h to respectively obtain modified active carbon AC-DDA-0.5-12 and AC-DDA-0.5-24.

Example 4

As in example 1, only the quaternary ammonium salts in example 1 were changed to:

modified activated carbon AC-a, AC-b, AC-c, AC-d are obtained respectively. The same properties as those of the modified activated carbon obtained in example 1. ( The cas numbers of the quaternary ammonium salts are respectively: 29443-23-0, 3004-51-1, 1516-27-4, 7505-53-5 )

Comparative example 1

As in example 3, only the quaternary ammonium salt in example 3 was changed to benzalkonium chloride (BAC) to obtain modified activated carbon AC-BAC-0.5-3, AC-BAC-0.5-12 and AC-BAC-0.5-24.

As in example 1 and example 2, the quaternary ammonium salt in example 3 was changed to benzalkonium chloride (BAC), and the reaction time 3h was changed to 24h. Obtaining the modified active carbon AC-BAC-1-24, AC-BAC-2-24, AC-BAC-5-24 and AC-BAC-10-24.

Comparative example 2

Adding coal-based activated carbon AC into a solution of (3-chloro-2-hydroxypropyl) dodecyl dimethyl ammonium chloride (CTA, mass content is 65%) with a solid-to-liquid ratio of 1g:10mL; then adding 1mol/L NaOH solution, adjusting the pH value to 8.5, reacting for 48 hours to obtain ER by epoxidation of CTA, and reacting the epoxidized CTA with activated carbon AC to generate modified activated carbon AC-ER.

Comparative example 3

The procedure was the same as in comparative example 2 except that the activated carbon was changed to 5mol/L nitric acid solution and the activated carbon was stirred at 9 0 ℃for 12 hours to obtain a nitrated activated carbon, nitric acid oxidation was performed to increase the content of oxygen-containing functional groups on the AC surface, and the remaining steps were the same as in comparative example 2 to obtain a modified activated carbon N-AC-ER.

Comparative example 4

As with CAC-BAC-1-24 of comparative example 1, activated Carbon (AC) was changed to a carbonized material (C) before activation, which was the same as the preparation method of CAC-BAC-1-24, to give C-BAC-1-24.

Performance analysis

1. The modified activated carbon prepared in examples and comparative examples was subjected to Zeta potential test, specifically as follows: preparing 50mL of 0.1mol/L NaCl solution, and regulating the pH value of the NaCl solution (from 2 to 12) by 0.1mol/L HCl or NaOH to obtain a series of NaCl solutions with different pH values; then 0.1g of the sample is added into NaCl solution with different pH values and stirred for 24 hours at room temperature; finally the Zeta potential of the NaCl solution added to the sample was measured by means of a Zeta potential analyzer (Anton Paar, litesizer 500). Isoelectric point pH _IEP Refers to the pH at which the potential (ZP) is zero. If at this pH, when the solution pH is lower than the pH _IEP When the sample is negatively charged in solution and vice versa.

As shown in FIG. 1 (a), the modification time has a significant effect on the BAC result, i.e., the pH of the sample _IEP As the modification time increased, the action time of AC with BAC was determined to be 24h in the subsequent modification experiment. From FIG. 2, it can be seen that the time versus pH during the DDA modification of the activated carbon _IEP Influence of (2)Is not obvious; when the DDA and AC reaction times were 12 and 24 hours, respectively, the pH of the modified AC was _IEP The values are substantially the same. The time of DDA modification of AC was set to 3 hours in consideration of cost and efficiency of modification in practical application.

Although the pH of the modified activated carbon _IEP Increasing from 2.51 to 6.03 or 3.89, but still not to the extent of the application; that is, the modified activated carbon is used to adsorb anions in water, but due to pH _IEP Less than 7, the modified activated carbon has negative charge in neutral solution, and the adsorption capacity for anions is not improved. Thus, the pH of the AC is significantly increased _IEP Is very important. Increasing the pH of AC by increasing the concentration of BAC and DDA in solution _IEP As a result, as shown in FIG. 1 (b) and FIG. 3, when the BAC concentration in the solution was increased to 1wt%, the pH of the modified AC was increased _IEP Reaching 10.38. While modifying the pH of the AC _IEP The DDA concentration increases substantially with increasing DDA concentration, and when the DDA concentration exceeds 5wt%, the modified AC is always positively charged in the solution. When modifying the pH of the activated carbon _IEP When the value exceeds 10, anions in water can be effectively adsorbed, and the anion can be adsorbed as an adsorption carrier under alkaline conditions. From this, it is clear that the manner of DDA modified AC is significantly different from that of BAC modified AC.

Based on previous studies, AC was modified with a quaternary ammonium salt containing 3-chloro-2-hydroxypropyl. Since the epoxidized CTA reacts with the oxygen-containing functional groups of the AC, and the number of the oxygen-containing functional groups on the AC surface prepared by anthracite is small, the AC is oxidized by nitric acid, so that the content of the oxygen-containing functional groups on the AC surface is increased. The results are shown in FIG. 4, pH of AC-ER _IEP The improvement is limited, namely, only 0.92, and the pH of the N-AC after the nitration is limited _IEP Significantly reduced. Therefore, the 3-chloro-2-hydroxypropyl quaternary ammonium salt has an unsatisfactory modifying effect on the coal-based activated carbon, the equivalent charge point of the 3-chloro-2-hydroxypropyl quaternary ammonium salt is only slightly changed, and the charge of the activated carbon is not converted.

2. The specific surface area test is carried out on the activated carbon modified by BAC and DDA, and the specific surface area test is as follows: the pore structure parameters of the AC and its modified samples were determined using a gas adsorption analyzer (microtracbl, belsorp max) and the samples were degassed at 100 ℃ until the pressure was less than 0.01T and then analyzed. Free space analysis data was obtained by DFT analysis of helium adsorption and then used to measure pore volume distribution and BET specific surface area. The specific surface area of the modified sample is divided by the original specific surface area of the activated carbon to obtain the specific surface area ratio of the modified activated carbon to the activated carbon, and the test results are shown in fig. 5, wherein the specific surface area ratio is 89.63%, 78.31%, 60.98%, 38.22% and 27.15%, respectively.

As can be seen from fig. 5 (a), BACs severely block the pore structure of AC, resulting in an order of magnitude decrease in the specific surface area of AC. And as the concentration of BAC increases, the specific surface area of the modified AC is reduced greatly, but the length of the BAC modification time has no obvious influence on the modified AC. Fig. 5 (b) shows that as DDA concentration increases, the surface area of the modified activated carbon also decreases, but the surface area of AC decreases far less than BAC. For example, the surface area of AC-DDA-0.5-3 is 759.1, while AC-BAC-0.5-3 is reduced to 98.8. The significant decrease in specific surface area of the modified activated carbon indicates that the pores of the AC are blocked by the BAC, and the more the decrease in specific surface area, the more serious the pore blocking problem. BAC is more easily adsorbed into the pores of AC than DDA, and it can be presumed that BAC is adsorbed into the pores of activated carbon, and it is seen that BAC is first carried on the pores of activated carbon, thereby causing blocking of the pores of activated carbon.

3. The adsorption amount of nitrogen was measured for the activated carbon modified with BAC and DDA, and the measurement results are shown in fig. 6.

The pore structure parameters of AC and its modified samples were determined using a gas adsorption analyzer (microtracbl, belsorp max) and these samples were first degassed at 100 ℃ until the pressure was less than 0.01 torr prior to analysis. Free space analysis data of the sample was obtained by DFT analysis of helium adsorption for measuring specific surface area of the sample.

As shown in fig. 6, the adsorption of nitrogen by DDA-modified activated carbon and unmodified activated carbon is not much different, but is far greater than that of BAC-modified activated carbon, and in combination with fig. 7, DDA hardly blocks the pore channel, and thus is almost indistinguishable from unmodified activated carbon; however, BAC enters the pore channel preferentially, so that the pore channel is blocked, and the specific surface area and the adsorption of nitrogen are reduced seriously.

4. Thermogravimetric analysis

Performing thermogravimetric analysis on the BAC modified activated carbon, analyzing the AC and the modified sample by a thermogravimetric method, and exploring the decomposition behavior of the quaternary ammonium salt on the AC so as to determine the combination position of the quaternary ammonium salt and the AC, wherein the specific operation is as follows: performing thermogravimetric experiments on the AC and modified samples thereof using a thermogravimetric analyzer (setam, labsys Evo); about 20mg of the sample was uniformly coated on an alumina crucible and heated from room temperature to 600℃at a temperature of 5℃per minute under a continuous nitrogen flow of 100ml/min to obtain information on decomposition of these quaternary ammonium salts in the modified sample. In addition, the decomposition behavior of the purchased BAC and DDA solutions at high temperature was also determined by thermogravimetry, under unchanged conditions. In addition, byThe thermal weight data is calculated by the formula, the weight loss value of the activated carbon sample is subtracted from the modified sample, so that the mass content of the quaternary ammonium salt in the activated carbon is obtained, and the test result is shown in fig. 7 and 8, wherein the mass content of the quaternary ammonium salt in the activated carbon is 3-15%.

In FIG. 7 (a), the BAC-modified activated carbon has a plurality of weight loss peaks from room temperature to 600℃with a temperature span of 100 to 500 ℃; as can be seen in FIG. 7 (b), the DDA modified AC has only one loss in weight peak, with a temperature span of 100-250 ℃. As shown in fig. 7 (c), the single BAC and DDA were decomposed before 250 ℃ and only one weight loss peak was present, indicating that the modification modes of BAC and DDA for activated carbon were completely different, and also indicating that BAC was simultaneously loaded on the surface, mesopores and pore channels of activated carbon from the side, thereby causing the existence of multiple weight loss peaks.

During heating, a temperature gradient exists between the AC pores and the surface, and the pore structure can be roughly divided into macropores, mesopores and micropores. As the temperature increases, BAC-modified activated carbon preferentially decomposes the surface BAC, forming a weight loss peak I. The macropores are usually connected with the outer surface, and the decomposition of BAC in the macropores forms a weightlessness peak II; similarly, BAC is decomposed in mesopores and micropores to form weight loss peaks III and IV respectively, and the peak intensity of the weight loss peak III is weaker than that of other peaks, which indicates that the BAC content in the mesopores is lower, and the characteristics of the coal-based activated carbon pore structure with micropores as the main and fewer mesopores are consistent. The decomposition behavior of DDA-modified activated carbon was similar to that of DDA solution, and there were no multiple weight loss peaks in fig. 7 (b), indicating that DDA was mainly supported on the AC surface and not in the pores of the activated carbon.

The carbonized material is void free prior to activation. To demonstrate the above reasoning, we performed BAC modification on the carbonized material before activation, and examined the decomposition behavior of BAC on the modified carbonized material, as shown in fig. 8. It can be seen from the graph that at 150-250 ℃, only one weightlessness peak appears in the decomposition of BAC on the carbonized material with less pore structure, which is relatively similar to the decomposition behavior of BAC solution. After removing the influence of the pore structure, BACs can only bind to the surface of the carbonized material, and these BACs decompose at high temperature, producing weight loss peaks. The result shows that in the pyrolysis process of the activated carbon modified activated carbon, four weight loss peaks are generated because the activated carbon is adsorbed into the pores of the activated carbon.

5. Contact angle analysis

The hydrophilicity and the hydrophobicity of different quaternary ammonium salt modified ACs are measured through the contact angle, so that the combination modes of different quaternary ammonium salts and ACs can be effectively distinguished. AC and its modified sample were tested for surface wettability using a contact angle meter (Dataphysics, OCA 20). The powder sample was pressed onto a tape to make a smooth square block 1 cm in length. Deionized water was injected into the syringe and the drop volume was typically 3 μl. Each sample was measured at five different places and the contact angle was the average of five results.

As shown in fig. 9 (a), coal-based commercial activated carbon is prepared by a steam activation method, and generally has a certain hydrophilicity. The BAC modified AC changed from hydrophilic to hydrophobic, but as the BAC concentration increased, the hydrophobicity of the modified AC decreased, as shown in fig. 9 (b). In contrast, the hydrophilicity of the DDA-modified AC was enhanced, and the degree of hydrophilicity enhancement was proportional to the DDA concentration, as shown in fig. 9 (c). Furthermore, BAC concentration has a much weaker effect on the properties of the modified AC than DDA, and the change in hydrophilicity and hydrophobicity of the modified AC and the change in surface charge distribution are the same. These phenomena also demonstrate the above reasoning that BAC is more readily adsorbed into the pores by AC than DDA. Therefore, even if BAC content is increased, these BACs adsorb into the pores of AC without significant effect on the surface properties of AC. BAC and DDA are both easily soluble in water, but the hydrophilicity and hydrophobicity of the activated carbon modified by BAC and DDA are opposite. Because the modified objects are all the same activated carbon, the hydrophilic and hydrophobic properties are different due to the quaternary ammonium salt used to modify the activated carbon and the manner in which the quaternary ammonium salt is combined with the activated carbon.

In order to investigate the modification modes of BAC and DDA on activated carbon differently, the molecular structure of the quaternary ammonium salt was simulated using a molecular simulation method, and simultaneously the surface electrostatic potential of the quaternary ammonium salt was calculated as shown in fig. 10 (a) and 10 (b). As can be seen from the figure, the molecular size of BAC is indeed larger than DDA, but BAC takes on a chain-like structure, and the surface electrostatic potential of BAC is much smaller than DDA. Based on the above study, activated carbon was negatively charged in aqueous solution, while the surface electrostatic potential of DDA molecules was positively charged and strong (maximum potential 115.15kcal/mol, more than 108.83kcal/mol of BAC). Thus, when AC is modified with a DDA solution, DDA molecules diffuse to the surface of activated carbon in the solution and bind to negatively charged activated carbon. In addition, because of the relatively low molecular mass of DDA, the electrostatic force between DDA and activated carbon is strong enough that few DDA molecules are adsorbed into the pores of the activated carbon. As the DDA concentration increases, DDA bound to the activated carbon surface approaches saturation, and the remaining DDA that cannot be bound to the activated carbon surface is eventually adsorbed into the pores, resulting in a decrease in the specific surface area of AC. The binding mode of BAC and active carbon is different from DDA. Since the surface electrostatic potential of BAC is weak, the relative molecular mass is high, the binding force between BAC and AC is weak, resulting in adsorption of most of BAC having a chain structure into the pores of AC. As the BAC content in the activated carbon pores increases, hydrophobic alkyl chains in the BAC will bind together to form a coagulated micelle, resulting in the activated carbon pores being blocked and the surface area being reduced.

According to contact angle analysis, although BAC can change the surface charge of the active carbon, the BAC firstly enters the pore canal of the active carbon to cause the blocking of the pore canal of the active carbon, and has opposite effects on the hydrophilicity of the active carbon, while DDA can change the surface charge of the active carbon without blocking the pore canal, and can change the hydrophilicity of the active carbon to a great extent, so that the BAC has good effects on subsequent adsorption.

6. XPS analysis

The surface functional groups of AC and its modified samples were identified using x-ray photoelectron spectroscopy (XPS, thermo Scientific, esclab 250 Xi) and monochromatic alkαx-rays. To exclude the effect of sample variation on binding energy during XPS, the binding energy was calibrated with contaminating carbon (c1s=284.8ev). XPS is commonly used to characterize the surface chemistry of solids, and to explore the binding patterns of different quaternary ammonium salts and ACs, activated carbon and modified activated carbon were analyzed by XPS and XPS C1 spectra, which were curve fitted using avant software.

As shown in fig. 1, the C1 deconvolution spectrum can be divided into four peaks: the binding energy of peak 1 was about 284.4eV, which was sp ² A hybrid carbon; peak 2 is sp ³ Hybrid carbon having a binding energy from 285.0eV to 285.2eV; peak 3 is a c—o bond in phenol, alcohol, ether, binding energy is about 285.4 eV; peak 4 is pi-pi, its binding energy is from 291.2eV to 292.1eV. That is, the activated carbon used in the present application contains a c—o bond, but does not contain a c=o bond, indicating that c—o is a hydroxyl group.

FIG. 11 is fitted to give deconvolution results shown in Table 1, sp in activated carbon ² The peak area of the hybridized carbon and the C-O group is larger than that of the C-C, which is consistent with the structural characteristics of the smokeless coal-based active carbon. Anthracite coal has high deterioration degree and contains a large amount of polycyclic aromatic hydrocarbon. In addition, steam is used as a catalyst in the preparation of activated carbon, and thus, a large amount of hydroxyl groups form phenolic hydroxyl groups with edges or defects of polycyclic aromatic hydrocarbons. When BAC is modified with active carbon, sp ² Peak area of hybridized carbon decreases and sp ³ The increase of the hybridized carbon shows that the content of C-C bonds on the surface of the modified activated carbon is increased, and the content of C=C bonds is reduced.

TABLE 1 XPS C1s analysis of activated carbon and modified activated carbon

XPS can only show a thickness of 1-10 nmChemical properties of solid surfaces, molecular modeling showed that BAC chain structure and only a small amount of BAC was bound to the surface of activated carbon. At BAC pass N ⁺ When the electrostatic attraction is combined with the surface of the activated carbon, the alkyl chain and the phenyl are outwards caused by steric hindrance of BAC molecules; since the alkyl chain of BAC has carbon chain with more than 12 carbons, the carbon-carbon bond content is high, and thus, the surface sp of the activated carbon is modified with the increase of BAC concentration ³ The peak area of the hybridized carbon also increases. In addition, since the activated carbon surface before modification contains a large amount of polycyclic aromatic hydrocarbons (sp ² Hybrid carbon), only one benzene ring is present in BAC molecule, so BAC-modified activated carbon surface sp ² The content of hybridized carbon is reduced.

Since these hydrophobic groups are located at the periphery of the surface of the activated carbon, in particular, long carbon chains of not less than 12 carbons, the surface of the modified activated carbon is changed from hydrophilic to hydrophobic. When the concentration of BAC in the solution further increases, some of the hydrophobic groups on the modified activated carbon combine with the hydrophobic groups of BAC in the solution to form aggregates similar to a bilayer. Outside of these aggregates are hydrophilic ammonium ions, which reduces the hydrophobicity of the modified AC, which is substantially consistent with the change in surface hydrophilicity and hydrophobicity of BAC-modified activated carbon.

As is clear from the above table, the surface sp of the modified activated carbon was increased with the increase of the DDA concentration ² The peak area of the hybridized carbon is obviously reduced, sp ³ The peak area of the hybridized carbon increases. The above shows that DDA molecules have a strong electrostatic potential and a low relative molecular weight. After DDA modification, the surface of the active carbon is loaded with a plurality of DDA molecules, but due to limited XPS detection depth, the XPS deconvolution result of the DDA modified AC is consistent with the property of the DDA molecules, such as sp ² Less hybridized carbon, sp ³ Many hybridized carbons, and the like. Since DDA molecules have no hydrophobic long chain alkyl groups, the hydrophilicity of the modified activated carbon increases with increasing DDA concentration, regardless of whether DDA and activated carbon form hydrophilic ether linkages or double electric layers.

Because the unmodified activated carbon contains C-O groups, the C-O groups can react with double bonds of the quaternary ammonium salt to a certain extent, but the content is low and the influence on the combination of the quaternary ammonium salt and the activated carbon surface carbon is low, and the method is not in the scope of the application.

Adsorption effect: static adsorption of anions

The experiment was carried out by using the above-mentioned activated carbon (AC, columnar activated carbon prepared from anthracite in Ningxia), 5 wt% DDA modified AC (modified activated carbon in test example 2: AC-DDA-5-3) and 2

Modified AC (modified activated carbon in comparative example 1: AC-BAC-5-24) produced by BAC in wt% was used as a main raw material. Before the experiment, sodium fluoride was dried at 100℃for 2 hours, and then 0.221g of NaF (0.1 mol F) was weighed ^- ) Dissolved in a 100mL volumetric flask, and diluted to give 5ppm, 10ppm, 20ppm, 40ppm, 60ppm, 80ppm, 100ppm solutions, respectively. Respectively transferring 25mL of the solution into a 25mL conical flask to obtain three groups of parallel samples (21 samples), and dividing the parallel samples into three groups, wherein each group contains 25mL of 5ppm, 10ppm, 20ppm, 40ppm, 60ppm, 80ppm and 100ppm of solution, and the total number of the solutions is 7;

50mg of unmodified AC was added to the first group, and 50mg of DDA-modified AC (modified activated carbon: AC-DDA-5-3 in test example 2) and BAC-modified AC (modified activated carbon: AC-BAC-5-24 in comparative example 1) were added to the second and third groups, respectively; the above samples were subjected to a static adsorption test (oscillation frequency 150 rpm/min) at room temperature, and the oscillation time was set for 24 hours. Filtering the sample after shaking with filter paper under normal pressure, filtering with 0.45 μm filter membrane, and detecting anion equilibrium concentration C with ion chromatography _e (mg/L) and the specific experimental procedure is shown in FIG. 12. The adsorption capacity Q (mg/g) was calculated as follows.

Wherein C is ₀ Adsorption of initial concentration (mg/L) for fluoride ions; m is the added mass (mg) of the AC; v is the volume (L) of the water sample.

Analysis of results

The method for detecting F-by using ion chromatography (Thermo Scientific, dionex Aquion Rfic) in GB 8538-2016 national safety Standard for food safety is characterized in that different anion species have great difference on affinity of ion exchange resin in ion chromatography separation columns, so that different anion movement speeds are caused, the purpose of separation is achieved, signal peaks of different ions are sequentially output through elements such as a conductivity detector, and F-concentration is obtained through comparison with a standard working curve. On this basis, the adsorption capacity was calculated using the above formula.

In contrast, the introduction of electrostatic forces may allow the adsorbate to more effectively adsorb the anisotropically charged ions. In order to verify the positive modification effect of the surface of the activated carbon, the adsorption capacity of the activated carbon to fluoride ions is used as one of judging standards. The dynamic equilibrium relationship between the adsorbents is generally described by adsorption isotherms, and a common isothermal adsorption model is a Langmuir adsorption model based on monolayer adsorption, and the adsorption isotherm is represented by the following formula.

In which Q _e Saturated adsorption amount (mg/g) of fluorine ions; q (Q) _max Maximum adsorption capacity (mg/g) for fluoride ions; k is the adsorption equilibrium constant.

As shown in fig. 13 to 15, the data were fitted according to Langmuir adsorption isotherms, and thus, it was considered that the adsorption of F-on AC satisfied Langmuir isothermal adsorption model, and the maximum adsorption capacity Qmax of unmodified AC was calculated to be 1.18mg/g, the BAC-modified AC adsorption capacity was 3.31mg/g, and the DDA-modified AC adsorption capacity Qmax was 54.98mg/g, which was approximately 46-fold improvement in adsorption effect over unmodified AC. The unmodified activated carbon has negative electricity on the surface of the water body, has electrostatic shielding effect on anions in the water body, and has poor adsorption effect of only 1.18mg/g; the surface of the modified activated carbon is not successfully modified by BAC, most of the modifier enters an AC pore structure, and the porous structure of the AC is destroyed, so that the adsorption effect on anions is not satisfactory, and the maximum adsorption capacity is only 3.31mg/L. The DDA modification can achieve the effect of two best, the positive charge on the surface of the AC is effectively loaded, and the influence on the pore structure of the active carbon is small, so that the modified active carbon has high adsorption level on anions F-and can be applied in the next step.

In conclusion, the modified activated carbon prepared by the method has the advantages that quaternary ammonium salt is loaded on the surface, so that the charge property of the surface of the activated carbon is changed, meanwhile, the pore canal of the activated carbon is not blocked, the hydrophilicity of the activated carbon is increased, and the modified activated carbon has a good adsorption effect on anions in a water body.

In the present application, only a part of structures are selected as representative examples in the experimental examples to illustrate the preparation method, effect, etc. of the present application, and other structures not listed have similar effects.

The monomers used in the experimental examples can be purchased or simply prepared, and the preparation process is also the prior art, so the details are not described in the specification.

It should be noted that the present inventors have made a large number of experiments on the series of structures, and sometimes, for better comparison with the existing system, there are cases where the same structure and system are used for more than one experiment, and thus, there may be some errors in different experiments.

Finally, it should be noted that: the embodiments described above are only for illustrating the technical solution of the present application, and are not limiting; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced with equivalents; such modifications and substitutions do not depart from the spirit of the application.

While the preferred embodiments and examples of the present application have been described in detail with reference to the accompanying drawings, the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A preparation method of modified activated carbon is characterized in that quaternary ammonium salt solution is mixed with activated carbon to react to obtain modified activated carbon; wherein the activated carbon is coal-based activated carbon;

the quaternary ammonium salt is at least one selected from compounds with a structure of formula I,

i is a kind of

Wherein M is ^n- Is negatively charged ion, n is the charge number of M; r is R ₁ 、R ₂ 、R ₃ 、R ₄ Independently selected from substituent-containing or substituent-free C ₁ ~C ₅ Any one of alkane, alkene or alkyne, and R ₁ 、R ₂ 、R ₃ 、R ₄ Containing a carbon-carbon double bond or a carbon-carbon triple bond;

the reaction is that carbon-carbon double bonds or carbon-carbon triple bonds in the quaternary ammonium salt are combined with carbon on the surface of the activated carbon; the mass ratio of the quaternary ammonium salt to the activated carbon is (0.5-10): 1, a step of; the reaction conditions are as follows: the reaction temperature is 15-30 ℃ and the reaction time is 3-24 h.

2. The method of claim 1, wherein the mass ratio of the quaternary ammonium salt to the activated carbon is (2-10): 1.

3. The method according to claim 1, wherein the quaternary ammonium salt is at least one selected from the group consisting of compounds having the structure of formula II,

II (II)

Wherein X is ^- Is an ion with a negative charge; r is R ₁ 、R ₂ 、R ₃ 、R ₄ Independently selected from substituent-containing or substituent-free C ₁ ~C ₅ Any one of an alkane, alkene, or alkyne; r is R ₁ 、R ₂ 、R ₃ 、R ₄ At least one of them contains a carbon-carbon double bond or a carbon-carbon triple bond。

4. The method of claim 1, wherein the quaternary ammonium salt is selected from at least one of the compounds having the structure of formula IV,

IV (IV)

Wherein X is ^- Is an ion with a negative charge; r is R ₁₁ 、R ₂₁ Independently selected from substituent-containing or substituent-free C ₁ ~C ₄ Any one of alkanes, alkenes, or alkynes.

5. The method of claim 1, wherein the modified activated carbon has an isoelectric point ∈ 7;

the contact angle of the modified activated carbon and water is smaller than 60 degrees.

6. The method according to claim 1, wherein the mass content of the quaternary ammonium salt in the modified activated carbon is 3% -15%;

the specific surface area of the modified activated carbon is 50% -90% of that of the activated carbon.

7. A modified activated carbon prepared according to the method of any one of claims 1-6.

8. The use of modified activated carbon for removing anions from water, wherein the modified activated carbon is selected from at least one of the modified activated carbon prepared by the method according to any one of claims 1 to 6.