CN116726879B

CN116726879B - Zeolite activated carbon composite material and preparation method and application thereof

Info

Publication number: CN116726879B
Application number: CN202310884213.4A
Authority: CN
Inventors: 梁鼎成; 解强; 于凤芹; 刘缘; 张蕊聪; 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: 2023-07-18
Filing date: 2023-07-18
Publication date: 2025-03-07
Anticipated expiration: 2043-07-18
Also published as: CN116726879A

Abstract

The present application provides a zeolite activated carbon composite material and a preparation method and application thereof. The zeolite activated carbon composite material includes modified activated carbon and zeolite; the modified activated carbon includes quaternary ammonium salt and activated carbon; the quaternary ammonium salt is located on the surface of the activated carbon; the zeolite is located on the surface of the modified activated carbon. The present application modifies the surface of the activated carbon with quaternary ammonium salt to change the charge on the surface of the activated carbon; when the surface of the modified activated carbon is positively charged, it can generate electrostatic attraction with the zeolite and thus combine with each other to generate a zeolite activated carbon composite material with broad-spectrum adsorption characteristics.

Description

Zeolite activated carbon composite material and preparation method and application thereof

Technical Field

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

Background

Volatile Organic Compounds (VOCs) emission control and effective remediation have become key tasks in the current world for the control of atmospheric pollution. In VOCs treatment technology, the adsorption method has the advantages of mature technology, high purification efficiency, wide application range, small energy consumption and the like, or is used independently or combined with other technologies, and has been widely applied. The core of the adsorption purification technology is an adsorbent, and activated carbon and zeolite are used as common adsorbents in VOCs adsorption purification, and have unique advantages and have the defect of difficulty in overcoming. VOCs are widely available and various, and have nonpolar or weak polar hydrocarbon and aromatic hydrocarbon compounds, polar alcohols, aldehydes/ketones, fatty acids and halogenated hydrocarbon compounds, and the actual industrial source VOCs waste gas is often a mixture of various polar/nonpolar organic matters. The zeolite and active carbon sectional filling or sectional purifying technology is adopted, and although the difficult problem of the adsorption and purification of the polar/nonpolar mixed waste gas can be solved to a certain extent, the technology is long and the equipment is complex. If the active carbon-zeolite molecular sieve composite adsorption material for purifying VOCs can be prepared, the problem of difficult adsorption of industrial source VOCs waste gas can be effectively solved.

The preparation of activated carbon and zeolite composites has been studied for a long time. From the early days, the activated carbon, zeolite were mechanically mixed by a binder and then shaped to obtain their composites. In recent years, agricultural and forestry waste is used for preparing zeolite/active carbon composite materials, for example, fly ash, coal gangue, wood fiber and the like are used as raw materials, organic matters are carbonized and activated and then are converted into porous carbon, and inorganic matters are synthesized into zeolite through a hydrothermal method. The problems of the methods are that the prepared composite material has low mechanical strength and is easy to break, or the preparation process is complex, and the carbonization, activation and crystallization are affected by different factors in each stage, so that the structure control of the composite material is difficult to realize. Rostami et al propose a preparation method of a composite material, namely, active carbon is taken as a carrier, mixed with water glass solution, and then subjected to hydrothermal reaction to obtain the zeolite active carbon composite material. The preparation process, while simple and rapid, was characterized by the fact that the zeolite and activated carbon did not combine to form a composite material having both characteristics. In addition, zeolite is of various types, and the zeolite molecular sieve is matched with the activated carbon, so that the zeolite activated carbon composite material for purifying VOCs has the basis of broad spectrum and high efficiency.

Disclosure of Invention

Aiming at the limitations, the application provides a zeolite activated carbon composite material, which is characterized in that quaternary ammonium salt is used for modifying the surface of activated carbon to change the charge of the surface of the activated carbon to be neutral or positively charged, so that electrostatic repulsion with negatively charged zeolite can be avoided, and when the surface of the modified activated carbon is positively charged, electrostatic attraction with zeolite can be generated to be mutually combined to generate the zeolite activated carbon composite material, so that the defects and the defects in the background art are overcome.

In order to achieve the above purpose, the present application adopts the following technical scheme:

The application provides a zeolite activated carbon composite material which comprises modified activated carbon and zeolite, wherein the modified activated carbon comprises quaternary ammonium salt and activated carbon, the quaternary ammonium salt is positioned on the surface of the activated carbon, and the zeolite is positioned on the surface of the modified activated carbon.

Optionally, the mass content of the zeolite in the zeolite activated carbon composite material is more than or equal to 15 percent.

Optionally, the silicon-aluminum ratio of the zeolite is less than or equal to 30.

Optionally, the isoelectric point of the modified activated carbon is more than or equal to 7, and the mass content of the quaternary ammonium salt in the modified activated carbon is 1% -5%.

Another aspect of the present application is to provide a method for preparing the zeolite activated carbon composite material as described above.

Optionally, the preparation method comprises (1) obtaining modified activated carbon, (2) mixing the modified activated carbon with zeolite synthetic liquid, crystallizing to obtain the zeolite activated carbon composite material, wherein the zeolite synthetic liquid comprises strong alkaline hydroxide or alkali metal oxide, a silicon source, an aluminum source and water.

Optionally, the step (1) comprises mixing the quaternary ammonium salt solution with activated carbon, and reacting to obtain the modified activated carbon. Optionally, the addition amount of the modified activated carbon is 10-50wt% of the zeolite synthetic liquid, and the crystallization condition is that the temperature is 80-200 ℃ and the time is more than or equal to 4 hours.

Optionally, step (2) comprises mixing the modified activated carbon with the zeolite synthesis liquid in the presence of zeolite seeds.

Optionally, dispersing zeolite seed crystal in solvent, adding modified active carbon to obtain mixture I, and mixing the mixture I with zeolite synthetic liquid.

Another aspect of the present application is to provide a use of the zeolite activated carbon composite as described above in a process for adsorbing exhaust gas and waste water, preferably in the adsorption of VOCs.

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

(1) In the zeolite activated carbon composite material, the modified activated carbon and the zeolite are tightly combined, the strength is higher, the zeolite content is higher, most of the zeolite is positioned on the surface of the modified activated carbon, the adsorption effect can be remarkably improved, and the adsorption performance is far greater than that of the activated carbon and the zeolite when the activated carbon and the zeolite are independently used. And the ignition point of the composite material is similar to that of the activated carbon, i.e. the thermal stability of the composite material is not reduced.

(2) According to the application, the quaternary ammonium salt is used for modifying the surface of the activated carbon, the electrostatic interaction of quaternary ammonium salt electropositivity and activated carbon electronegativity is used for changing the charge distribution on the surface of the activated carbon in a targeted manner, meanwhile, the carried carbon-carbon double bond or triple bond is opened and is bonded with the carbon on the surface of the activated carbon to form stable modified activated carbon, N ⁺ ions are positioned outside the modified activated carbon, the charge property of the charge on the surface of the activated carbon is finally changed to enable the activated carbon to be neutral or positively charged, the zeolite is synthesized under alkaline condition, the activated carbon is negatively charged under alkaline condition, the activated carbon modified by the quaternary ammonium salt is positively charged under alkaline condition, the negatively charged zeolite crystal nucleus can be attracted under the electrostatic effect, so that the crystal nucleus is loaded on the surface of the activated carbon for further crystallization, when the surface of the modified activated carbon is positively charged, the modified activated carbon can be mutually combined with the zeolite, and a large amount of the crystal nucleus is attracted to the activated carbon under the electrostatic attraction effect, so that the loading capacity and loading uniformity of the zeolite are improved, and the zeolite activated carbon composite material is generated, and the broad-spectrum characteristic of adsorbing the VOCs is achieved.

Drawings

Fig. 1 is a graph showing the release of dimethyldiallylammonium chloride (DDA) in water, plotted on the abscissa as h and on the ordinate as mass concentration as ppm, in modified activated carbon according to an embodiment of the present application. FIG. 2 shows microstructure diagrams of LTA zeolite and zeolite activated carbon composite material (LTA/D-AC) according to an embodiment of the present application, (a-c) zeolite activated carbon composite material (LTA/D-AC) prepared in test example 1, (D) XRD pattern of LTA zeolite generated by seed induction method, horizontal axis is 2θ, unit is degree, vertical axis is strength, no unit, (e-f) SEM pattern and TEM pattern of LTA zeolite generated by seed induction method, and (g-i) SEM pattern of different angles of zeolite activated carbon composite material (LTA/D-AC) prepared in test example 2.

Fig. 3 is an SEM image of a zeolite activated carbon composite (LTA/D-AC) prepared by various methods according to an embodiment of the present application, in which (a) and (b) are zeolite seeds dispersed in ethanol, then activated carbon is added to the synthesis solution, (c) and (D) are zeolite seeds added to the synthesis solution before the activated carbon is modified, and (e) and (f) are modified activated carbon added to the synthesis solution before the zeolite seeds.

Fig. 4 is an analysis chart of a zeolite activated carbon composite material (LTA/D-AC) according to an embodiment of the present application, wherein (a) and (b) are microscopic morphology charts of the composite material, and (c) and (D) are element distribution charts of the composite material.

Fig. 5 is an analysis chart of the zeolite activated carbon composite material provided in test example 6 of the present application, (a) is an XRD chart of the zeolite activated carbon composite material, the abscissa is 2θ, the unit is degree, the ordinate is strength, and no unit is found, and (b) is an SEM chart of the zeolite activated carbon composite material.

FIG. 6 shows an analysis chart of ZSM-5 zeolite and zeolite activated carbon composite material (ZSM-5/D-AC) according to an embodiment of the application, wherein (a) is XRD of ZSM-5 zeolite, the abscissa is 2θ, the unit is degree, the ordinate is strength, and no unit is present, (b) is SEM of ZSM-5 zeolite, (c) is TEM of ZSM-5 zeolite, and (D-f) is SEM of ZSM-5/D-AC at different angles.

Fig. 7 (a) is a simulated process diagram of LTA zeolite and modified activated carbon (D-AC) combination provided in an embodiment of the application, and fig. 7 (b) is an SEM image of the different angles of the Activated Carbon (AC) and LTA zeolite reaction products. FIG. 8 (a) is a graph of adsorption performance of a zeolite activated carbon composite (LTA/D-AC) to methylene dichloride, time in min on the abscissa, C _t/C₀ in no units on the ordinate, adsorption amount of the zeolite activated carbon composite (LTA/D-AC), LTA zeolite and activated carbon in FIG. 8 (b), relative pressure P/P0 in no units on the abscissa, adsorption amount in cm ³/g on the ordinate.

FIG. 9 is a graph of weight loss of activated carbon (a) and zeolite activated carbon composite LTA/D-AC (b), plotted on the abscissa as temperature in degrees Celsius and on the ordinate as mass in percent.

FIG. 10 is a TEM image of the composite material 1 of example 4, (a) 50 μm, (b) 20 μm, (c) 10 μm, and (d) 2. Mu.m.

FIG. 11 is a TEM image of the composite material 2 of example 4, (a) 50 μm, (b) 20 μm, (c) 10 μm, and (d) 2. Mu.m.

FIG. 12 is a graph of nitrogen adsorption and desorption test of columnar carbon, composite 1 and composite 2 in example 4, with the abscissa representing columnar carbon, composite 1 and composite 2, and the ordinate representing surface area in m ²/g.

Detailed Description

The present application will be described in further detail below in order to make the objects, technical solutions and advantages of the present application more apparent. It is to be understood that the description is only intended to illustrate the application and is not intended to limit the scope of the application.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs, and the terms used herein in this description of the application are for the purpose of describing particular embodiments only and are not intended to be limiting of the application. Reagents and instruments used herein are commercially available, and reference to characterization means is made to the relevant description of the prior art and will not be repeated herein.

For a further understanding of the present application, the present application will be described in further detail with reference to the following preferred embodiments.

Example 1

The embodiment provides a zeolite activated carbon composite material, which comprises modified activated carbon and zeolite, wherein the modified activated carbon comprises quaternary ammonium salt and activated carbon, the quaternary ammonium salt is positioned on the surface of the activated carbon, and the zeolite is positioned on the surface of the modified activated carbon.

When the quaternary ammonium salt is loaded on the surface of the activated carbon through chemical bond combination of the quaternary ammonium salt and the activated carbon, the surface of the activated carbon is targeted through electrostatic interaction of the positive electricity of the quaternary ammonium salt and the electronegativity of the activated carbon, and simultaneously the carried carbon-carbon double bond or triple bond is opened to bond with the carbon on the surface of the activated carbon, so that stable modified activated carbon is formed, and N ⁺ ions are positioned outside the modified activated carbon.

For the modified activated carbon with the modified activated carbon surface, the surface of the modified activated carbon carries positive charges, and zeolite crystal nuclei with negative charges are attracted under the action of electrostatic attraction, so that the crystal nuclei are loaded on the surface of the activated carbon for further crystallization, and a large amount of zeolite is finally obtained and attached to the activated carbon, so that the loading capacity and loading uniformity of the activated carbon on the zeolite are improved.

The mass content of zeolite in the zeolite active carbon composite material is more than or equal to 15 percent.

When the mass content of zeolite is less than 15%, it is considered that the zeolite and the activated carbon do not form a composite material, and the mass content is preferably not less than 20%. The zeolite content in the zeolite active carbon composite material prepared by the application is more than 15 percent. The silicon-aluminum ratio of the zeolite is less than or equal to 30.

Zeolites are tetrahedral structures consisting of silica and alumina. Wherein, the outermost layer of the silicon atoms has 4 electrons, 1 silicon atom forms bond with 4 oxygen atoms, the charge balance of the system, and the outermost layer of the aluminum atoms has 3 electrons, and 1 aluminum atom forms bond with 4 oxygen atoms to form tetrahedron, so that the system has negative charge, therefore, the higher the content of the aluminum atoms in the zeolite is, the stronger the negative charge of the zeolite is. Conversely, the lower the aluminum content of the zeolite, the weaker the negative electrical properties exhibited by the zeolite. Therefore, when the silicon content in the zeolite is too high, namely when the silicon-aluminum ratio is large, the electronegativity of the zeolite is weakened, even neutral, and the zeolite is difficult to combine with the positively charged modified activated carbon through electrostatic force, and when the silicon-aluminum ratio is small, the zeolite is electronegative and can be loaded on the surface of the modified activated carbon through electrostatic force interaction. Therefore, the silicon to aluminum ratio is not more than 30, preferably not more than 20, preferably not more than 15, more preferably not more than 10, still more preferably not more than 5.

The zeolite can be natural or artificial zeolite with low silicon-aluminum ratio, or the zeolite is dealuminated after being loaded with the low silicon zeolite to improve the silicon-aluminum ratio of the loaded zeolite.

The isoelectric point of the modified activated carbon is more than or equal to 7, and the mass content of the quaternary ammonium salt in the modified activated carbon is 1% -5%.

Only when the isoelectric point of the modified activated carbon is more than or equal to 7, the change of the charge distribution on the surface of the activated carbon is changed from negative charge to neutral charge or positive charge.

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

Wherein X ^- is an ion with a negative charge, R ₁、R₂、R₃、R₄ is independently selected from any one of alkane, alkene or alkyne of C ₁～C₅ containing substituent or not, and at least one of R ₁、R₂、R₃、R₄ contains a carbon-carbon double bond or a carbon-carbon triple bond.

X is halogen and is any one selected from F, cl, br, I, at.

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

Wherein R ₁、R₂、R₃、R₄ is independently selected from any one of alkane, alkene or alkyne of C ₁～C₅ containing substituent or not, and at least one of R ₁、R₂、R₃、R₄ contains carbon-carbon double bond or carbon-carbon triple bond.

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

Wherein X ^- is an ion with a negative charge, and R ₁₁、R₂₁ is independently selected from any one of alkane, alkene or alkyne of C ₁～C₄ containing substituent or not containing substituent.

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

Wherein R ₁₁、R₂₁ is independently selected from any one of alkane, alkene or alkyne of C ₁～C₄ containing substituent or not containing substituent.

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

the carbon-carbon double bond or carbon-carbon triple bond in the quaternary ammonium salt is combined with the carbon on the surface of the activated carbon.

The mass content of the quaternary ammonium salt in the modified activated carbon is 1% -5%.

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 surface of the active carbon is covered with a large part of quaternary ammonium salt, the surface is difficult to react again due to steric hindrance, and excessive quaternary ammonium salt can enter into the pore channel to react with the carbon in the pore channel, so that the pore channel 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.

Example 2

The present embodiment provides a method for preparing a zeolite activated carbon composite material, which is the same as the zeolite activated carbon composite material of embodiment 1, and is not described herein.

The preparation method comprises (1) obtaining modified activated carbon, (2) mixing the modified activated carbon with zeolite synthetic liquid, crystallizing to obtain the zeolite activated carbon composite material, wherein the zeolite synthetic liquid comprises strong alkaline hydroxide or mixed alkali, a silicon source, an aluminum source and water.

The step (1) comprises the steps of mixing quaternary ammonium salt solution with active carbon, and reacting to obtain modified active carbon.

Preparing a dimethyldiallylammonium chloride solution (water is used as a solvent) with the mass fraction of 5wt%, taking a certain amount of the dimethyldiallylammonium chloride solution and the dimethyldiallylammonium chloride solution into a conical flask according to the solid-to-liquid ratio of 1g (active carbon sample), putting the conical flask into a room temperature (25 ℃) for water bath oscillation (160 rpm/min), oscillating for 3 hours, 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 active carbon. The addition amount of the modified activated carbon is 10-50wt% of the zeolite synthetic liquid, and for example, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% or 50wt%.

The crystallization condition is that the temperature is 80-200 ℃ and the time is more than or equal to 4 hours.

The temperature of crystallization may be 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃, or 200 ℃.

The crystallization time may be 4h, 5h, 6h, 7h, 8h, 9h, 10h or more.

When zeolite is synthesized relatively simply, the modified active carbon may be mixed directly with zeolite synthesizing liquid for crystallization, or when crystal seed or template is needed for synthesis of zeolite, the modified active carbon may be mixed with zeolite synthesizing liquid in the presence of zeolite crystal seed. When both methods are available, the selection can be made according to the actual situation.

The mass ratio of the zeolite synthesis liquid to the zeolite seed crystal is 100 (0.1-2).

Dispersing zeolite seed crystal in solvent, adding modified active carbon to obtain mixture I, and mixing the mixture I with zeolite synthetic liquid.

Adding seed crystal into ethanol, uniformly dispersing in ethanol by ultrasonic wave, and adding modified active carbon to effectively combine with seed crystal. Drying to remove ethanol after a period of time to obtain modified activity combined with seed crystal, and adding into synthetic solution to prepare zeolite active carbon composite material.

As the seed crystal is generally smaller in size and the activated carbon is also smaller in size, the seed crystal is directly added into the synthetic liquid to be easy to agglomerate and agglomerate, and the combination of the seed crystal and the synthetic liquid is influenced, so that the zeolite on the surface of the activated carbon is unevenly loaded. And the bonding process of the seed crystal and the activated carbon takes time. When they are added simultaneously to the synthesis liquid, seeds surrounded by a silicon source and an aluminum source may crystallize preferentially, which also affects their combination. Therefore, the seed crystal can be dispersed in the solvent, and then the modified activated carbon is added to be dispersed on the surface of the modified activated carbon, so that the agglomeration between the seed crystal and the activated carbon is reduced, the seed crystal and the activated carbon are mutually combined through electrostatic interaction, a good foundation is laid for subsequent crystallization, and the problems of uneven load and the like can be avoided.

The synthetic liquid is the synthetic liquid required by the conventional zeolite, and generally comprises strong alkaline hydroxide or mixed alkali, a silicon source, an aluminum source and water, and can be used for synthesizing the zeolite. The alkali may be a strong alkali hydroxide or a mixed alkali, a silicon source, or an aluminum source, which are commonly used in the market, and the alkali is not limited thereto. The molar ratio relation among the strong alkaline hydroxide or the mixed alkali, the silicon source, the aluminum source and the water is also selected according to the conventional method.

Example 3

In accordance with the teachings of the present application, the zeolite activated carbon composite of example 1 and the method of preparation of example 2 are specifically described as follows:

Diallyl dimethyl ammonium chloride (DDA, 60 wt%), silica sol (29-31 wt%), sodium aluminate (AR grade), aluminum sulfate (AR grade), tetrapropylammonium hydroxide (TPAOH, AR grade), tetraethylorthosilicate (TEOS, 25 wt%), sodium hydroxide (AR grade) were purchased from shanghai microphone Lin Shenghua, inc.

LTA zeolite powder was purchased from shanghai ala Ding Shenghua technologies, inc.

The active carbon is commercial columnar active carbon produced by Ningxia Wangda coal industry Co., ltd, is ground to a particle size smaller than 74 mu m in a pulverizer, and then is air-dried to constant weight.

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

preparing a dimethyldiallylammonium chloride solution (water as a solvent) with the mass fraction of 5wt%, taking a certain amount of an activated carbon sample and the dimethyldiallylammonium chloride solution into a conical flask according to the solid-to-liquid ratio of 1g (activated carbon, AC), putting the conical flask into a room temperature (25 ℃) for water bath oscillation (160 rpm/min), oscillating for 3 hours, carrying out suction filtration on the mixed solution, and drying the solid sample obtained by suction filtration in an oven at 80 ℃ for 12 hours to obtain the modified activated carbon (the mass content of the quaternary ammonium salt in the modified activated carbon is 10 wt%). The modified activated carbon is positively charged in alkaline solution (pH is more than 7), namely the isoelectric point of the modified activated carbon is more than or equal to 7.

Since it takes a long time to synthesize zeolite, it is necessary to verify whether dimethyl diallyl ammonium chloride (DDA) can be tightly combined with activated carbon for a long period of time to ensure that zeolite is effectively attracted to the modified activated carbon surface during the synthesis.

The combination of dimethyldiallylammonium chloride (DDA) and Activated Carbon (AC) was verified by mixing modified activated carbon (D-AC) with deionized water in a solid to liquid ratio of 1:500g/mL in a conical flask, placing the conical flask in a water bath shaker at a frequency of 150r/min at 25℃for 24 hours, stopping shaking, collecting samples every 2 hours, and determining the concentration of dimethyldiallylammonium chloride (DDA) in the filtrate. The determination of dimethyl diallyl ammonium chloride (DDA) in water is relatively complex because it cannot be determined by uv-vis spectrophotometry. The content of dimethyl diallyl ammonium chloride (DDA) in water was determined by an indirect capillary electrophoresis (Beckman Coulter, P/ACETM MDQ CE) working curve method, the detector was a 200nm UV, the buffer solution was an acetic acid-imidazole system, and the separation voltage was 20kV.

Considering that zeolite synthesis takes a long time, dimethyl diallyl ammonium chloride (DDA) molecules are separated from the surface of Activated Carbon (AC), resulting in weaker attraction to zeolite loading. Therefore, it is necessary to verify the bonding strength of dimethyl diallyl ammonium chloride (DDA) and Activated Carbon (AC) in the solution for a long period of time, and the results of the shake flask experiment are shown in FIG. 1.

As shown in FIG. 1, in shake flask experiment 2h, dimethyldiallylammonium chloride (DDA) molecules were easily separated from the surface of the modified activated carbon (D-AC) and released into water, resulting in a concentration of dimethyldiallylammonium chloride (DDA) in the water of more than 300ppm. But as the experiment continued, the content of dimethyldiallylammonium chloride (DDA) in the water decreased significantly, less than 100ppm after 24 hours. Previous work indicated that the c=c bond in dimethyldiallylammonium chloride (DDA) reacted with the phenolic hydroxyl group on Activated Carbon (AC), and it was concluded that these released dimethyldiallylammonium chloride (DDA) molecules reacted with the phenolic hydroxyl group on Activated Carbon (AC) and then immobilized on AC over time. In addition, activated Carbon (AC) with developed pore structure has adsorption force to dimethyl diallyl ammonium chloride (DDA) molecules, and part of released dimethyl diallyl ammonium chloride (DDA) molecules are adsorbed into the pores. The results show that the content of dimethyl diallyl ammonium chloride (DDA) released by the modified activated carbon (D-AC) into water is smaller and smaller with the extension of the experimental time. It can be concluded that the long time required for zeolite synthesis does not lead to a large release of dimethyldiallylammonium chloride (DDA) in the modified activated carbon (D-AC) but promotes their better binding.

Quaternary ammonium salts are often used as cationic surfactants to modify porous materials to increase the adsorption capacity of the porous materials for anionic contaminants in water. From the modification effect, the Zeta potential of the material can be effectively improved by modification. There is sufficient evidence that pH _IEP can reflect the external electrical characteristics of the modified material in different aqueous environments at a point where the pH value of the external isoelectric point (pH _IEP) is zero. It was found that dimethyl diallyl ammonium chloride (DDA) significantly increased the pH _IEP of Activated Carbon (AC) to above 12, indicating that modified activated carbon (D-AC) has a positive charge in alkaline solution. This means that dimethyl diallyl ammonium chloride (DDA) adheres to the surface of Activated Carbon (AC), changing the charge distribution on the surface of Activated Carbon (AC). Meanwhile, the charge distribution of the modified activated carbon (D-AC) modified by dimethyl diallyl ammonium chloride (DDA) has little negative influence on the original pore structure, and is far lower than that of other quaternary ammonium salts such as benzalkonium chloride, QUAB series and the like used in various reports.

Test example 1

Adding the modified activated carbon into zeolite synthetic solution (the molar ratio of Na ₂O:Al₂O₃:SiO₂:H₂ O is 3.165:1:1.926:128), aging at room temperature for 24 hours, transferring into a hydrothermal reaction kettle, placing into an oven for heating and crystallizing, wherein the crystallization temperature is 100 ℃, the crystallization time is 4 hours, and washing, filtering and drying to obtain the zeolite activated carbon composite material (LTA/D-AC). Wherein, the addition amount of the modified activated carbon is 10wt% of the zeolite synthetic liquid. The silicon-aluminum ratio of the zeolite is 2:1.926, and the mass content of the zeolite in the zeolite active carbon composite material is 37.16%.

As shown in fig. 2 (a) -2 (c), a certain amount of LTA zeolite was supported on the modified activated carbon. However, LTA zeolite is not uniformly supported on the surface of modified activated carbon, and particularly zeolite supported on the smooth surface of modified activated carbon is sparsely distributed. It is speculated that low-silicon zeolites have a higher negative charge and can bind to positively charged modified activated carbon in solution, but zeolite crystal growth is the primary reaction occurring in the system, and the process of binding the zeolite to the modified activated carbon is weaker and needs to be further enhanced.

Test example 2

The seed induction method is adopted, and the loading of the LTA zeolite on the activated carbon is optimized by artificially enhancing the combination process between the LTA zeolite and the activated carbon.

It was first verified whether LTA zeolite could be produced by seed induction.

The specific procedure of the test is as follows:

Preparing synthetic solution (molar ratio of Na ₂O:Al₂O₃:SiO₂:H₂ O is 3.165:1:1.926:128), fully mixing the synthetic solution with the zeolite seed crystal, aging at room temperature for 24 hours, transferring to a hydrothermal reaction kettle, heating and crystallizing in an oven at 100 ℃ for 6 hours, washing, filtering and drying to obtain the LTA zeolite. Wherein the mass ratio of the zeolite synthetic liquid to the zeolite seed crystal is 100:0.6.

The product was tested to verify whether the process was able to synthesize LTA zeolite. As shown in FIGS. 2 (d) -2 (f), the product has characteristic diffraction peaks and cubic morphology of LTA zeolite, indicating that the seed induction method is also suitable for preparing LTA zeolite.

On the basis, the seeds and the modified activated carbon are added into the synthetic liquid at the same time to prepare the composite material, and the specific process is as follows:

Preparing synthetic solution (molar ratio of Na ₂O:Al₂O₃:SiO₂:H₂ O is 3.165:1:1.926:128), fully mixing the synthetic solution, the zeolite seed crystal and modified active carbon, adding the mixture into a stainless steel autoclave, aging for 24 hours at room temperature, putting the mixture into a baking oven, crystallizing at 100 ℃ for 4 hours, washing, filtering and drying to obtain the zeolite active carbon composite material (LTA/D-AC). Wherein the mass ratio of the zeolite synthetic solution to the zeolite seed crystal is 100:0.6, and the addition amount of the modified activated carbon is 10wt% of the zeolite synthetic solution. The silicon-aluminum ratio of the zeolite is 1:1, and the mass content of the zeolite in the zeolite active carbon composite material is 46.51%.

The product is measured, and the result is shown in fig. 2 (g) -fig. 2 (i), and the composite material prepared by the method further improves the load of zeolite on the surface of the modified activated carbon. In addition, most of the zeolite is cubic compared with zeolite synthesized directly by the seed induction method. After the modified activated carbon is added, the quantity of the cubic zeolite loaded on the surface of the modified activated carbon is obviously reduced, which indicates that the modified activated carbon influences the growth process of the LTA zeolite.

Test example 3

Using LTA zeolite powder as zeolite seeds;

adding zeolite seed crystal into ethanol, dispersing in ethanol uniformly by ultrasonic wave, adding modified active carbon, drying to remove ethanol after a period of time to obtain modified active carbon combined with seed crystal;

Adding the modified activated carbon combined with the seed crystal into zeolite synthetic solution (the molar ratio of Na ₂O:Al₂O₃:SiO₂:H₂ O is 3.165:1:1.926:128), then aging for 24 hours at room temperature, transferring into a hydrothermal reaction kettle, placing into an oven for heating and crystallizing, wherein the crystallization temperature is 100 ℃, the crystallization time is 4 hours, and washing, filtering and drying to obtain the zeolite activated carbon composite material (LTA/D-AC). Wherein the mass ratio of the zeolite synthetic solution to the zeolite seed crystal is 100:0.6, and the addition amount of the modified activated carbon is 10wt% of the zeolite synthetic solution.

The low-silicon zeolite with high aluminum content has stronger negative electricity performance, the LTA zeolite in the test example has high aluminum content and aluminum-silicon ratio close to 1:1, has better electronegativity, and can be combined with positively charged modified activated carbon to form a composite material. The mass content of zeolite in the zeolite activated carbon composite material is 58.20%.

As shown in the graph of FIG. 3, it can be seen from the graphs of FIG. 3 (a) and FIG. 3 (b) that the agglomeration of the seeds and the modified activated carbon is solved by adopting an ethanol solution and ultrasonic dispersion method, the seeds are fully combined through electrostatic attraction, the seeds are uniformly distributed on the surface of the modified activated carbon, and a satisfactory zeolite activated carbon composite material (LTA/D-AC) is obtained after crystallization, namely a large amount of LTA zeolite is loaded on the modified activated carbon.

Test example 4

The procedure is closer to that of test example 3, except that the order of addition was changed, i.e., the modified activated carbon was added to the synthesis liquid first and then the zeolite seed crystal was added, or the zeolite seed crystal was added to the synthesis liquid first and then the modified activated carbon was added. As shown in fig. 3 (c) -3 (f), no matter seeds or AC are added into the synthetic liquid in sequence, the load of LTA zeolite on the modified activated carbon in the prepared composite material is obviously weaker, and the mass content of zeolite in the zeolite activated carbon composite material is 47.2% and 47.38%, respectively.

Test example 5

Closer to test example 3, the crystallization time was changed to 12 hours. The zeolite activated carbon composite material was obtained in the same manner as in test example 3, wherein the mass content of zeolite in the zeolite activated carbon composite material was 62.46%.

As a result of growth in the composite material, as shown in fig. 4 (a) and 4 (b), the amount of zeolite having a regular shape increases as the crystallization time increases and the zeolite supported on the surface of the modified activated carbon becomes denser.

To verify that the prepared sample was LTA/D-AC composite, EDS analysis was performed on the elemental distribution of the sample surface in FIG. 4 (b), as shown in FIG. 4 (c) and FIG. 4 (D). The results show that a large amount of silicon element and aluminum element exist on the surface of the sample, the ratio is close to 1:1, similar to LTA zeolite. In addition, there is a large amount of carbon under the silicon and aluminum, demonstrating that LTA zeolite is supported on the surface of the modified activated carbon. In summary, ethanol and ultrasonic dispersion can be used to eliminate the agglomeration of the seed and the modified activated carbon powder, so that they are combined with each other by electrostatic attraction, and then the low-silicon zeolite composite material loaded on the surface of the modified activated carbon is successfully prepared by prolonging the crystallization time.

Test example 6

Using 13X zeolite powder as zeolite seeds;

adding zeolite seed crystal into ethanol, dispersing in ethanol with ultrasonic wave, adding modified active carbon, drying for a period of time, and removing ethanol to obtain modified active carbon combined with seed crystal.

Adding the modified activated carbon combined with the seed crystal into zeolite synthetic solution (the molar ratio of Na ₂O:K₂O：Al₂O₃:SiO₂:H₂ O is 5.5:1.65:1:2.2:122), pouring the reaction solution into a polytetrafluoroethylene lining, aging for 3 hours at 70 ℃, transferring the reaction solution into a hydrothermal reaction kettle, placing the reaction kettle into an oven for heating and crystallizing, wherein the crystallization temperature is 100 ℃, the crystallization time is 2 hours, and finally washing, filtering and drying to obtain the zeolite activated carbon composite material (13X/D-AC). Wherein the mass ratio of the zeolite synthetic solution to the zeolite seed crystal is 100:0.6, and the addition amount of the modified activated carbon is 10wt% of the zeolite synthetic solution. The silicon-aluminum ratio of the zeolite is 1.1:1, and the mass content of the zeolite in the zeolite active carbon composite material is 50.51%.

The results of the measurement of the product are shown in FIG. 5, and it can be seen from FIG. 5 (a) that the product has a characteristic diffraction peak of 13X zeolite, indicating that the seed induction method is also applicable to 13X zeolite. Fig. 5 (b) shows that the 13X zeolite can be successfully supported on the surface of the modified activated carbon.

Comparative example 1

Preparing zeolite seed crystal, namely transferring zeolite precursor suspension with the molar ratio of TEOS to TPAOH to H ₂ O of 1:0.36:19.2 into a hydrothermal reaction kettle, crystallizing for 24 hours in a 100 ℃ oven, centrifugally drying, and roasting for 6 hours at 550 ℃ to obtain zeolite seed crystal;

Preparing a synthetic solution (the molar ratio of Na ₂O:Al₂O₃:SiO₂:H₂ O is 12:2:100:2500), fully mixing the synthetic solution and zeolite seeds in a mass ratio of 100:1, then adding the mixture into a stainless steel autoclave, aging for 24 hours at room temperature, then placing the mixture into a baking oven, crystallizing for 24 hours at 180 ℃, and washing, filtering and drying to obtain ZSM-5 zeolite;

Preparing a synthetic solution (the molar ratio of Na ₂O:Al₂O₃:SiO₂:H₂ O is 12:2:100:2500), fully mixing the synthetic solution, zeolite seed crystals and modified activated carbon in a mass ratio of 100:0.6:10, then adding the mixture into a stainless steel autoclave, aging for 24 hours at room temperature, putting the mixture into a baking oven, crystallizing for 24 hours at 180 ℃, and washing, filtering and drying to obtain the zeolite activated carbon composite material (ZSM-5/D-AC).

The high-silicon zeolite has good hydrophobicity, strong dispersibility and electrostatic force, and has good adsorption capacity for strong polar molecules. Therefore, the introduction of high-silicon zeolite on D-AC is beneficial to improving the adsorption effect of the composite material on polar VOCs. Meanwhile, the flame retardance of the composite material can be effectively improved by increasing the silicon content in the composite material. ZSM-5 zeolite is used as typical high-silicon MFI zeolite and has wide application in the fields of adsorption, catalysis and the like. The ZSM-5 zeolite and zeolite activated carbon composite material (ZSM-5/D-AC) obtained by the preparation method are characterized, and the result is shown in figure 6.

The product has obvious diffraction peaks of ZSM-5 zeolite as seen in FIG. 6 (a), and the microscopic morphology of the product is coffin-shaped as seen in FIG. 6 (b) and FIG. 6 (c), which both confirm that the method can successfully synthesize ZSM-5 zeolite.

SEM results of the zeolite activated carbon composite (ZSM-5/D-AC) are shown in FIG. 6 (D-f). The result shows that the surface of the AC is only loaded with a small amount of ZSM-5 zeolite, and the mass content of the zeolite in the zeolite activated carbon composite material is only about 12.51%, which is consistent with the previous research result, namely, the AC and the zeolite are mutually independent and do not form an integral structure, which shows that the ZSM-5 zeolite and the modified AC can not be combined under the induction of electrostatic attraction.

Simulation calculation experiments the above experiments demonstrate that modifying the surface charge of AC with quaternary ammonium salt makes it positively charged in a strong alkaline solution, self-assembling with negatively charged low-silicon zeolite by electrostatic attraction. To verify this corollary of the improvement of quaternary ammonium salts on activated carbon surfaces, it is necessary to accurately evaluate the effect of quaternary ammonium salts on the bond strength of AC and low-silicon zeolite. However, it is difficult to quantify the binding strength by conventional experimental methods. The mode of action between them is thus calculated by means of molecular dynamics simulation, and the interaction energy and radial distribution function are calculated.

Model describing the binding process of modified activated carbon to LTA zeolite:

Since this process occurs primarily at the interface between the modified activated carbon and the LTA zeolite, some simplification is made during the model building process. For example, graphene is used for simulating the surface of the activated carbon, and certain specific functional groups are introduced into the graphene according to the component characteristics of the activated carbon, so that the chemical properties of the surface of the activated carbon are as close as possible. Simultaneously carrying out (110) planarization on the LTA zeolite by MATERIALS STUDIO software, filling sodium ions in the LTA zeolite framework to balance charges, and matching the LTA zeolite (110) plane with graphite by cell expansion to construct an active carbon and zeolite system. Dimethyl diallyl ammonium chloride (DDA) molecules are added between graphene and zeolite to simulate the interface condition between modification and zeolite.

On this basis, molecular dynamics simulation was performed on the above model using LAMMPS software. The simulation is performed using a reactive force field (ReaxFF) that can describe the interactions of all atoms in the system. Firstly, respectively carrying out structure relaxation optimization on Active Carbon (AC), dimethyl diallyl ammonium chloride (DDA), LTA zeolite, modified active carbon (D-AC) system, active carbon-LTA zeolite (LTA/AC) system and modified active carbon-zeolite (LTA/D-AC) system under the condition of 0K, and then calculating to obtain the formation energy and the binding energy of the active carbon and the modified active carbon respectively combined with the LTA zeolite through a formula (1) and a formula (2). Then, the molecular dynamics of the modified activated carbon-LTA zeolite (LTA/D-AC) system after structural relaxation in the NPT ensemble was simulated with a step size of 300K,1atm,0.25fs. The system firstly runs 25ps to balance, then runs 200ps, and samples every 1000 steps to obtain the phase space motion trail of the system. The calculation formulas of the formation energy and the binding energy in the above experimental process are shown in table 2.

E_f＝E_AB-E_A-E_B (1)

E_b＝-E_f (2)

Wherein E _f is the formation energy of A and B to form AB and E _b is the binding energy of A and B in AB.

The interaction energy of the activated carbon and the modified activated carbon with the LTA zeolite, respectively, is shown in Table 3, and it can be seen that the formation energy of both the activated carbon-LTA zeolite (LTA/AC) system and the modified activated carbon-zeolite (LTA/D-AC) system is negative, and the formation energy of the activated carbon and the LTA zeolite is-324.97 kcal mol-1, indicating that the activated carbon and the LTA zeolite can be combined with each other. After adding dimethyl diallyl ammonium chloride (DDA), the formation can be obviously reduced from-324.97 kcal mol < -1 > to-1076.46 kcal mol < -1 >, which shows that the modified activated carbon is easier to combine with the LTA zeolite. The binding energy is opposite to the formation energy, and the binding energy of the modified activated carbon-LTA zeolite system is much higher than that of the AC-LTA zeolite system. The result shows that the LTA zeolite and the modified activated carbon are combined strongly, and the composite material is more stable in application.

TABLE 3 interaction energy of activated carbon and modified activated carbon with LTA zeolite, respectively

On this basis, equilibrium Molecular Dynamics (EMD) simulation was performed on modified activated carbon-zeolite (LTA/D-AC) after structure relaxation, which describes the binding process of modified activated carbon and LTA zeolite in the presence of dimethyl diallyl ammonium chloride (DDA), and then the average distance between modified graphene and LTA zeolite in different stages was calculated, and the result is shown in FIG. 7.

As shown in FIG. 7 (a), a significant displacement of the LTA zeolite to the modified graphene can be observed, the distance between them being fromShortened toThe combination of LTA zeolite, dimethyl diallyl ammonium chloride (DDA) and modified activated carbon (D-AC) became compact, and the simulation results were substantially consistent with the experiments.

But also differs from previous analyses in that it is pointed out in the analysis that LTA zeolite and Activated Carbon (AC) are difficult to bind due to both negative charges. During the simulation, LTA zeolite and Activated Carbon (AC) can combine themselves because their formation energy is negative.

To verify this, the crystallization was performed by adding unmodified AC and seed crystals to the synthesis liquid in the same manner as in test example 1 except that the modified activated carbon was replaced with activated carbon to obtain zeolite activated carbon composite (LTA/AC).

The microstructure of the product is shown in FIG. 7 (b). It is evident that a small amount of zeolite is loaded on the unmodified Activated Carbon (AC), which is consistent with the simulation conclusion, but contradictory with the conclusion that they have the same negative charge and are difficult to bind due to electrostatic repulsion. The main reason for this discrepancy is to ignore the adsorption capacity of Activated Carbon (AC). Because the seed induction method is adopted to prepare the composite material, the adsorption force of part of zeolite spar is larger than the electrostatic repulsive force, so that the zeolite spar is combined with Activated Carbon (AC), and then the composite material is formed by crystallization. Also, because of the electroneutrality of zeolite spar, the attraction of Activated Carbon (AC) to zeolite activated carbon (ZSM-5/AC) in the preparation of the composite depends on the adsorption force, and furthermore, these zeolite spar sizes are nano-sized and mostly adsorbed by AC into the pores, which causes the prepared composite to be loaded with a small amount of ZSM-5 zeolite. It is difficult to improve the problem of poor loading of high and pure silicalite on Activated Carbon (AC) because the process described above cannot be enhanced. In a word, a small amount of low-silicon zeolite can be loaded on the activated carbon by a seed induction method, but the surface charge modification of the activated carbon and the strengthening of the combination process of seeds and modified activated carbon are effective methods for greatly increasing the zeolite loading, and the modified activated carbon and the zeolite in the prepared composite material are tightly combined and have strong binding force.

Performance testing

(1) Adsorption performance

The adsorption performance of the composite material is evaluated by adopting dichloromethane with stronger polarity as an adsorbent, specifically, a fixed bed adsorption device is adopted, the adsorption performance of a sample on the dichloromethane is evaluated through the steps of gas mixing, adsorption, analysis and the like, and the influence of the loaded zeolite on the adsorption capacity of the activated carbon is examined.

The composite material and activated carbon were placed in a vacuum oven at 150℃for 4 hours, respectively, and 100mg was weighed and charged into a tubular fixed bed glass reactor (id 10 mm).

The raw material gas is methylene dichloride standard gas (8.314 g/m ³) produced by Beijing Huayuan gas chemical industry Co., ltd, and the gas flow is 50ml/min. The methylene chloride content of the outlet gas was determined by means of an Agilent 7980A on-line gas chromatograph GC-flame ionization detector FID.

As a result, as shown in FIG. 8 (a), the activated carbon adsorbed dichloroethane, the permeation time of the activated carbon bed was 20 minutes, and the permeation time of the LTA/D-AC composite bed was nearly 40 minutes. This indicates that the LTA/D-AC composite material can effectively enhance its adsorption to methylene chloride.

Meanwhile, in order to understand in depth the evolution of the pore structure of the D-AC and LTA zeolites during the combination process, the main cause of the variation of the adsorption performance of the zeolite activated carbon (LTA/D-AC) composite material is clearly defined, and the pore structure is characterized as shown in fig. 8 (b).

FIG. 8 (b) shows that the specific surface area of AC is 846.9m ²/g and that of LTA zeolite is 466.0m2/g. The specific surface area of the zeolite activated carbon (LTA/D-AC) composite material is 519.3m ²/g, which is between the two. The specific surface area of the composite material is significantly reduced compared to AC, mainly due to the plugging of part of the pores with DDA modified AC and the loading of large amounts of LTA zeolite on the D-AC surface. In general, when the pore structure is negatively affected, the adsorption capacity of the composite material is reduced, and the adsorption curve also demonstrates this point. However, the adsorption capacity of the composite material to methylene dichloride is better than that of AC, and the result proves that the method of loading zeolite on D-AC to improve the adsorption effect of polar organic matters is feasible.

(2) Thermal stability

The thermal stability of the activated carbon and LTA/D-AC composite material in an air atmosphere was evaluated using a thermogravimetric analyzer, and the results are shown in fig. 9.

From the TG curve, it can be seen that at temperatures above 650 ℃, the mass of activated carbon is only 7.8% and the mass loss is 92.2%, mainly due to oxidation of the carbon matrix in the activated carbon. Under the same conditions, the residual mass of the composite material is 39.4%, the mass loss is 60.6%, and the mass loss is far lower than that of the activated carbon, and according to approximate analysis, the composite material shows that more than 30% of zeolite is loaded on the activated carbon, which is consistent with the result that a large amount of zeolite is loaded on the surface of the activated carbon observed by SEM. Meanwhile, the mass loss rate of the activated carbon is higher than that of the composite material from the DTG curve.

In order to further evaluate the safety of activated carbon and composite materials, the thermogravimetric results were subjected to an in-depth analysis, resulting in their ignition points, 571 ℃ and 564 ℃, respectively, which are not very different. Clearly, the loading of zeolite did not lower the ignition point of the AC, but still had a higher ignition point.

Example 4

In the field of purifying VOCs on an industrial scale, activated carbon is generally formed into a column or honeycomb shape for adsorption and purification of gas, and in particular, column-shaped activated carbon is widely used in printing, painting, and the like. In order to embody the application value of the application, the commercial columnar activated carbon (non-powder) is modified and then loaded with zeolite, and the specific steps are as follows:

Test example 1

(1) The modification of the activated carbon, namely weighing 4g of columnar activated carbon and 200ml of dimethyl diallyl ammonium chloride solution (the concentration is 5wt percent), mixing and oscillating for 3 hours in a water bath shaking table, rotating at 160rpm/min, reacting at 25 ℃, filtering, and drying for 12 hours in an 80 ℃ oven;

(2) Wet mixing, namely weighing 2.73g of modified columnar active carbon, 0.16g of commercial 5A molecular sieve, 3.85g of silica sol (SiO ₂ solid content is 30%), 1.64g of sodium metaaluminate, 1.73g of sodium hydroxide and 19.95g of deionized water in the step (1), mixing and oscillating for 1h in a water bath shaking table at the rotating speed of 160rpm/min and the reaction temperature of 25 ℃;

(3) Aging, namely placing a polytetrafluoroethylene lining on the wet material after mixing, and standing and aging for 24 hours at normal temperature and normal pressure;

(4) And (5) drying, namely washing the wet material after crystallization to pH less than 8 by water, then drying at 80 ℃ for 24 hours, and cooling to obtain the zeolite activated carbon composite material (LTA/modified columnar activated carbon, composite material 1).

Test example 2

The order of addition in step (2) was changed by dispersing the commercial LTA zeolite molecular sieve first in ethanol, then adding the modified activated carbon, drying and mixing with the zeolite synthesis solution. The zeolite activated carbon composite (LTA/modified columnar activated carbon, composite 2) was obtained in the same manner as described above.

Performance analysis

(1) And (3) carrying out apparent morphology analysis on the prepared zeolite active carbon composite materials (composite material 1 and composite material 2), and observing the load of the zeolite molecular sieve on the surface of the active carbon through a scanning electron microscope.

The method comprises the following steps of analyzing the apparent morphology of the composite material by using a Gemini 30 thermal field emission scanning electron microscope of Zeiss company in England, wherein the accelerating voltage is 2kV, and the probe is SE2. The sample is pre-treated before testing, the sample is dispersed in ethanol solution for 30min, then a drop of sample suspension is dripped on the copper sheet, the copper sheet is dried in a 105 ℃ oven for 5min, and then the copper sheet is placed on a workbench for observation in a transmission electron microscope. The test results are shown in fig. 10 and 11.

As shown in fig. 10 and 11, two prepared composite materials can be seen, the zeolite molecular sieve has a good surface loading effect on the activated carbon, and the obtained zeolite molecular sieve crystal grains have a good morphology and are in a regular cubic block shape. (2) And carrying out nitrogen adsorption and desorption tests on the original columnar activated carbon and the zeolite activated carbon composite materials (composite material 1 and composite material 2) prepared by the two methods.

The pore structure parameters of AC and its modified samples were determined using a gas adsorption analyzer (ASAP 2020 Plus, american microphone), these samples were first degassed at 200 ℃ prior to analysis, and the total specific surface area of the samples was calculated using the BET model by measuring the amount of adsorbed and desorbed gas. The test results are shown in FIG. 12.

As shown in fig. 12, the surface area of the composite material is slightly reduced compared with the original activated carbon, mainly because some pores are blocked when the activated carbon is modified by using dimethyl diallyl ammonium chloride, and a large amount of LTA zeolite is loaded on the surface of the activated carbon, but the specific surface areas of the original activated carbon and the composite material are not greatly different, which means that LTA zeolite loaded on the surface of the activated carbon cannot block the pore channels of the activated carbon, and the two have no "coated" core-shell structure, which accords with the results observed in fig. 10 and 11.

The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, or alternatives falling within the spirit and principles of the application.

Claims

1. A preparation method of a zeolite activated carbon composite material is characterized in that the zeolite activated carbon composite material comprises modified activated carbon and zeolite;

The preparation method comprises the specific steps of (1) obtaining modified activated carbon, (2) mixing the modified activated carbon with zeolite synthetic liquid, crystallizing to obtain the zeolite activated carbon composite material, wherein the addition amount of the modified activated carbon is 10-50wt% of the zeolite synthetic liquid, and the crystallization condition is that the temperature is 80-200 ℃ and the time is more than or equal to 4 hours, and mixing the modified activated carbon with the zeolite synthetic liquid in the presence of zeolite seed crystals;

The modified activated carbon comprises quaternary ammonium salt and activated carbon, wherein the quaternary ammonium salt is positioned on the surface of the activated carbon;

The zeolite is positioned on the surface of the modified activated carbon;

IV (IV)

Wherein X ^- is an ion with a negative charge, R ₁₁、R₂₁ is independently selected from any one of alkane, alkene or alkyne of C ₁~C₄ containing substituent or not containing substituent;

the mass content of the zeolite in the zeolite activated carbon composite material is more than or equal to 20%;

the silicon-aluminum ratio of the zeolite is less than or equal to 15.

2. The preparation method of the modified activated carbon according to claim 1, wherein the isoelectric point of the modified activated carbon is more than or equal to 7, and the mass content of the quaternary ammonium salt in the modified activated carbon is 10%.

3. The method according to claim 1, wherein the quaternary ammonium salt is dimethyldiallylammonium chloride.

4. A method according to claims 1-3, characterized in that the zeolite synthesis liquid comprises a strong alkali hydroxide or alkali metal oxide, a silicon source, an aluminium source, water.

5. The method of preparing the modified activated carbon according to claim 1-3, wherein the step (1) comprises mixing the quaternary ammonium salt solution with the activated carbon, and reacting to obtain the modified activated carbon.

6. A process according to any one of claims 1 to 3, wherein zeolite seeds are dispersed in a solvent and modified activated carbon is added to obtain a mixture I, and the mixture I is mixed with a zeolite synthesis solution.

7. The zeolite activated carbon composite material prepared by the preparation method of the zeolite activated carbon composite material according to any one of claims 1-6, and the application of the zeolite activated carbon composite material in a waste gas and waste water adsorption process.

8. The use according to claim 7, wherein the use is in the adsorption of VOCs.