CN115228437B - A surface modification method to make the surface of activated carbon positively charged - Google Patents

Abstract

The invention discloses a surface modification method for making active carbon positive in aqueous solution, which synthesizes chloridized-1-methylquinoline on the surface of the active carbon pretreated by hydrochloric acid in situ. The invention utilizes the alkalinity of quinoline to enable the quinoline to be adsorbed on an acidic adsorption site on the activated carbon treated by hydrochloric acid, then reacts with methanol on the surface of the activated carbon under the catalysis of concentrated hydrochloric acid to synthesize the chloridized-1-methylquinoline in situ, so that the activated carbon has positive electricity on the surface of an aqueous solution, thereby improving the adsorption rate and adsorption capacity of the activated carbon on perfluorooctanoic acid.

Description

A surface modification method to make the surface of activated carbon positively charged

Technical field

The present invention relates to the technical field of adsorbent materials, and in particular to a surface modification method for making the surface of activated carbon positively charged.

Background technique

Perfluorooctanoic acid (PFOA) has unique thermal stability, chemical stability and high surface activity, and is widely used in the production of many daily and industrial products. Because the C–F bond of PFOA has extremely high bond energy, it is difficult for PFOA molecules to be photolyzed, hydrolyzed, and biodegraded. Studies have shown that PFOA can enter the human body through the respiratory tract, esophagus, etc., causing serious damage to people's reproductive system, liver and kidneys, and may even cause cancer. Therefore, exploring fast, efficient, and low-cost PFOA removal methods is of great significance to ecological environment protection and human health.

Activated carbon is the most common carbon adsorption material. PFOA has a large molecular size, has certain hydrophobic properties, and exists in the form of perfluorooctanoate anion in the solution. Therefore, using the hydrophobic effect and electrostatic adsorption of adsorbents to remove PFOA from aqueous solutions is the most effective method. However, the surface of ordinary activated carbon contains a large number of oxygen-containing functional groups. These functional groups make the surface of activated carbon electronegative in aqueous solution, and perfluorooctanoate ions are also electronegative in aqueous solution. The two are easily repulsive, resulting in the activated carbon's rejection of perfluorooctanoate ions. Adsorption performance is reduced. Existing technology also considers grafting or loading other compounds that make activated carbon positively charged on the surface of activated carbon, such as loading metal cations, or grafting 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc., to achieve the purpose of improving the adsorption effect. , but the loaded metal ions are easy to fall off from the surface of activated carbon, causing secondary pollution. The long carbon chain of the epoxy-grafted quaternary ammonium salt will increase the steric hindrance of PFOA adsorption (atom electron cloud overlap, manifested as repulsion), thus affecting its Improvement of PFOA adsorption performance.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for modifying the surface of activated carbon to be positively charged in an aqueous solution, so as to solve the problem of poor adsorption effect of activated carbon on perfluorooctanoic acid in water and loading on the surface of activated carbon. The compound easily falls off.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

A surface modification method to make the surface of activated carbon electropositive, specifically including the following steps:

Step 1: Screen the activated carbon, wash it with deionized water, and then heat and dry it for later use;

Step 2: Add the activated carbon obtained in step 1 to soak in hydrochloric acid with a concentration of 1 mol/L, then wash it and dry it to constant weight;

Step 3: Add quinoline to the activated carbon obtained in step 2; the ratio of activated carbon to quinoline is 1g: (0.5~3.5) mL, and stir slightly for 0.5~1 h to allow the activated carbon to fully adsorb quinoline;

Step 4: Slowly add concentrated hydrochloric acid to the mixture in step 3. The number of moles of concentrated hydrochloric acid added is 3-5 times the number of moles of quinoline. After the dropwise addition of concentrated hydrochloric acid is completed, stir slightly for 0.5-1 h to allow the activated carbon to fully adsorb. Concentrated hydrochloric acid;

Step 5: Distill the mixture obtained in Step 4 under reduced pressure at 45°C;

Step 6: Transfer the product obtained in step 5 to the hydrothermal reaction kettle, add methanol, mix evenly, seal it, and react at 145-180°C for 6-12 hours; where the number of moles of methanol added is the number of moles of quinoline 2-3 times;

Step 7: After the reaction kettle is cooled, take out the product in the reaction kettle and distill it under reduced pressure at 70°C to remove unreacted methanol;

Step 8: Wash the activated carbon treated in step 7 repeatedly with absolute ethanol and then with deionized water, and then dry it to obtain activated carbon modified with 1-methylquinoline chloride.

In the prior art, in order to improve the PFOA adsorption performance of activated carbon, metal ions are often directly loaded on the surface of activated carbon or compounds such as 3-chloro-2-hydroxypropyltrimethylammonium chloride are grafted. However, metal ions are easy to fall off, and the long-chain structure of 3-chloro-2-hydroxypropyltrimethylammonium chloride will increase the steric hindrance of pollutant adsorption and block the micropores of activated carbon, which will affect the improvement of the adsorption performance of activated carbon. have adverse effects. By in-situ synthesizing the quaternary ammonium salt with a non-long-chain structure, 1-methylquinoline chloride, on the surface of activated carbon, the present invention can not only increase the adsorption capacity of perfluorooctanoate ions by activated carbon, but also improve the adsorption capacity of perfluorooctanoate ions by activated carbon. The adsorption speed of activated carbon improves the adsorption effect of perfluorooctanoate ions on activated carbon.

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

1. The method of the present invention adopts the method of first pretreating activated carbon with acid. First, the inorganic salts and ash left during the preparation process of activated carbon are washed away, creating new pores and increasing the specific surface area of activated carbon; second, making the activated carbon The acidic oxygen-containing functional groups are increased, and the alkalinity of quinoline is used to not only make quinoline adsorbed on the surface of activated carbon and not easily fall off from the surface of activated carbon, but also improve the adsorption effect of activated carbon on perfluorooctanoic acid.

2. In the method of the present invention, concentrated hydrochloric acid is used as a catalyst instead of HCl gas, and water is removed through vacuum distillation to avoid environmental pollution caused by HCl gas and inconvenient transportation and storage problems.

Description of the drawings

Figure 1 shows the SEM image of unmodified activated carbon.

Figure 2 is a diagram of activated carbon modified with 1-methylquinoline chloride obtained in Example 2.

Figure 3 is an evaluation chart of the performance evaluation of activated carbon adsorption of PFOA.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples.

1. Example

Example 1

(1) Sieve the activated carbon with a standard sieve to screen out activated carbon with a particle size of 20-60 mesh, wash it with deionized water 3-6 times to remove impurities and dust on the surface of the activated carbon, and then place it in a blast drying oven at 110°C Dry to constant weight, cool to room temperature and then put into sample bag;

(2) Place 5 g of activated carbon obtained in step (1) into a beaker, add 400 mL of hydrochloric acid with a concentration of 1 mol/L, and soak at room temperature for 24 hours. Then wash with deionized water and suction filter 3-6 times, and dry to constant weight;

(3) Weigh 2.5g of the activated carbon obtained in step (2) and add it to the three-necked flask. Place the three-necked flask in an ice water bath and control the temperature in the three-necked flask to not exceed 50°C; then add 2 mL of quinoline dropwise. .

(4) After the activated carbon adsorbs quinoline for 0.5 h, slowly add 4.2 mL of concentrated hydrochloric acid dropwise to the three-neck flask through the dropping funnel;

(5) After adding concentrated hydrochloric acid dropwise for 0.5 h, place the three-neck flask in a 45°C constant temperature water bath and perform vacuum distillation;

(6) After the vacuum distillation is completed, transfer all the activated carbon and solution in the three-neck flask to the hydrothermal synthesis reaction kettle, then add 1.37 mL of methanol respectively, stir slightly with a glass rod, seal it, and place it at 145 React in oven at ℃ for 6 hours;

(7) Take out the reaction kettle, cool it naturally to room temperature, transfer the activated carbon and liquid to a three-neck flask, and distill under reduced pressure at 70°C to remove unreacted methanol;

(8) First filter and wash the activated carbon with absolute ethanol 3-6 times, then use deionized water to filter and wash it 3-6 times, and then put the obtained activated carbon into a 70°C oven to dry to constant weight to obtain chlorination -1-Methylquinoline modified activated carbon.

Among them, the structural formula of 1-methylquinoline chloride is:

Example 2

(1) Sieve the activated carbon with a standard sieve to screen out activated carbon with a particle size of 20-60 mesh, wash it with deionized water 3-6 times to remove impurities and dust on the surface of the activated carbon, and then place it in a blast drying oven at 110°C Dry to constant weight, cool to room temperature and then put into sample bag;

(2) Place 5 g of activated carbon obtained in step (1) into a beaker, add 400 mL of hydrochloric acid with a concentration of 1 mol/L, and soak at room temperature for 24 hours. Then wash with deionized water and suction filter 3-6 times, and dry to constant weight;

(3) Weigh 2.5 g of the activated carbon obtained in step (2) and add it to the three-neck flask. Place the three-neck flask in an ice water bath. The ice water bath controls the temperature in the three-neck flask to not exceed 50°C; then add 6.5 mL dropwise quinoline.

(4) After the activated carbon adsorbs quinoline for 0.5 h, slowly add 13.65 mL of concentrated hydrochloric acid dropwise to the three-neck flask through the dropping funnel;

(5) After adding concentrated hydrochloric acid dropwise for 0.5 h, place the three-neck flask in a 45°C constant temperature water bath and perform vacuum distillation;

(6) After the vacuum distillation is completed, transfer all the activated carbon and solution in the three-neck flask to the hydrothermal synthesis reaction kettle, then add 4.45mL of methanol respectively, stir slightly with a glass rod, seal it, and place it at 145 React in oven for 6 hours;

(7) Take out the reaction kettle, cool it naturally to room temperature, transfer the activated carbon and liquid to a three-neck flask, and distill under reduced pressure at 70°C to remove unreacted methanol;

(8) Wash the activated carbon with absolute ethanol and suction filtration 3-6 times, then wash it with deionized water and suction filtration 3-6 times, and then dry the obtained activated carbon in a 70°C oven to a constant weight to obtain Activated carbon modified with 1-methylquinoline chloride.

Comparative example: 3-chloro-2-hydroxypropyltrimethylammonium chloride modified activated carbon

(1) Sieve the activated carbon with a standard sieve to screen out activated carbon with a particle size of 20-60 mesh, wash it with deionized water 3-6 times to remove impurities and dust on the surface of the activated carbon, and then place it in a blast drying oven at 110°C Dry to constant weight, cool to room temperature and then put into sample bag;

(2) Place 5 g of activated carbon obtained in step (1) into a beaker, add 400 mL of hydrochloric acid with a concentration of 1 mol/L, and soak at room temperature for 24 hours. Then wash with deionized water and suction filter 3-6 times, and dry to constant weight;

(3) Place 2.0 g of activated carbon obtained in step (2) into a 250 mL Erlenmeyer flask. Add 20 mL of 3-chloro-2-hydroxypropyltrimethylammonium chloride solution to the Erlenmeyer flask, and then seal the Erlenmeyer flask;

(4) Place the Erlenmeyer flask from step (3) into a constant-temperature water bath shaker and shake at room temperature for 24 hours to allow 3-chloro-2-hydroxypropyltrimethylammonium chloride to evenly adhere to the surface of the activated carbon;

(5) Place the Erlenmeyer flask in step (4) into a 50°C water bath, then add 5 mol/L NaOH solution dropwise into the Erlenmeyer flask, and adjust the pH of the solution to 11-12.5 to meet the requirements for the epoxy reaction pH, seal the Erlenmeyer flask and react for 8 hours;

(6) Take out the Erlenmeyer flask in step (5) and cool it to room temperature. Add 5 mol/L HCl solution dropwise into the Erlenmeyer flask to adjust the pH to less than 7 to terminate the cationization reaction;

(7) Filter the mixture obtained in step (6), wash the modified activated carbon with absolute ethanol several times, and then wash with deionized water until the pH of the washing water becomes neutral to remove unreacted 3-chlorine. -2-Hydroxypropyltrimethylammonium chloride;

(8) Dry the modified activated carbon obtained in step (7) in an oven at 60°C for 24 h, then take it out and cool it to room temperature to obtain 3-chloro-2-hydroxypropyltrimethylammonium chloride modified activated carbon, labeled QAC- 1:10.

2. Performance research

The unmodified activated carbon and the activated carbon modified with 1-methylquinoline chloride obtained in Example 2 were subjected to SEM characterization, and the obtained SEM characterization images are shown in Figure 1 and Figure 2 respectively.

As can be seen from Figure 1, the surface of unmodified activated carbon is loose, uneven and has many fragments. As can be seen from Figure 2, many fluffy spherical particles are attached to the surface of activated carbon modified with 1-methylquinoline chloride, which are the generated 1-methylquinoline chloride. It can also be seen from Figure 2 that these synthesized substances have not fallen off from the surface of activated carbon even after repeated washings with anhydrous ethanol and deionized water, indicating that the binding force between 1-methylquinoline chloride and the surface of activated carbon is strong. , not easy to fall off from the surface of activated carbon and cause secondary pollution.

Adsorption kinetics experiments were used to conduct adsorption performance of activated carbon, activated carbon modified with 1-methylquinoline chloride prepared in Examples 1 and 2, and activated carbon modified with 3-chloro-2-hydroxypropyltrimethylammonium chloride in the control example. evaluate. Specific steps are as follows,

(1) Use a volumetric flask to prepare a 50 mg/L perfluorooctanoic acid solution and put it into a plastic bottle for later use;

(2) Use an analytical balance to accurately weigh 50 mg of activated carbon under different modification conditions into a 100 mL ground-mouth Erlenmeyer flask, use a pipette to accurately draw 50 mL of PFOA solution and seal it in the Erlenmeyer flask;

(3) Place the Erlenmeyer flask in a water bath constant-temperature oscillator and react at room temperature; every 12 hours, take 1 mL of the supernatant into a 15 mL plastic tube, add excess ammonia, and allow the perfluorooctanoic acid to completely react into ammonium perfluorooctanoate;

(4) Use UV spectrophotometry to measure the concentration of perfluorooctanoate, and then obtain the concentration of PFOA.

As can be seen from Figure 3, when the activated carbon is modified with a positive surface charge, its adsorption capacity and adsorption rate of PFOA are better than those of the original activated carbon. The 1-methylquinoline chloride modified activated carbon obtained in Example 2 was due to the addition of more quinoline than in Example 1, that is, more 1-methylquinoline chloride was synthesized than in Example 1, resulting in the activated carbon obtained in Example 2. Some micropores are blocked, resulting in the adsorption performance of the activated carbon obtained in Example 2 for PFOA being lower than that of the activated carbon obtained in Example 1. The adsorption performance of the activated carbon modified with chloro-2-hydroxypropyltrimethylammonium chloride in Comparative Example 3 is lower than that of the activated carbon obtained in Examples 1 and 2 due to the steric hindrance effect caused by the long carbon chain of the quaternary ammonium salt.

Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those of ordinary skill in the art should understand that those technical solutions of the present invention can be modified or equivalently substituted without departing from the technical solutions. The purpose and scope of the present invention shall be covered by the claims of the present invention.

Claims (6)

1. A surface modification method to make the surface of activated carbon electropositive, characterized in that it specifically includes the following steps: Step 1: Screen the activated carbon, wash it with deionized water, and then dry it for later use; Step 2: Soak the activated carbon obtained in step 1 in hydrochloric acid with a concentration of 1 mol/L, then wash with deionized water until neutral and dry to constant weight; Step 3: Add quinoline to the activated carbon obtained in step 2; the ratio of activated carbon to quinoline is 1g: (0.5~3.5)mL, and stir slightly for 0.5~1h to fully adsorb quinoline on the activated carbon; Step 4: Slowly add concentrated hydrochloric acid to the mixture in step 3. The number of moles of concentrated hydrochloric acid added is 3-5 times the number of moles of quinoline. After the dropwise addition of concentrated hydrochloric acid is completed, stir slightly for 0.5 to 1 hour to fully adsorb the activated carbon. Concentrated hydrochloric acid; Step 5: Distill the activated carbon obtained in Step 4 that has adsorbed quinoline and concentrated hydrochloric acid under reduced pressure at 45°C; Step 6: Transfer the pasty activated carbon obtained in step 5 to the hydrothermal reaction kettle, add methanol, mix evenly, seal it, and react at 145-180°C for 6-12 hours; the number of moles of methanol added is the mole of quinoline. 2-3 times the number; Step 7: After the reaction kettle is cooled, take out the product in the reaction kettle and distill it under reduced pressure at 70°C to remove unreacted methanol; Step 8: Wash the activated carbon treated in step 7 repeatedly with anhydrous ethanol and deionized water, and dry it at 70°C to obtain activated carbon modified with 1-methylquinoline chloride; The structural formula of 1-methylquinoline chloride is as follows: 2. The surface modification method for making the surface of activated carbon electropositive according to claim 1, characterized in that in step 1, activated carbon with a particle size of 20 to 60 mesh is screened out. 3. The surface modification method for making the surface of activated carbon electropositive according to claim 1, characterized in that, in step 2, the soaking time is at least 24 hours. 4. The surface modification method for making the surface of activated carbon electropositive according to claim 1, characterized in that in step 3, the temperature when the activated carbon adsorbs quinoline does not exceed 50°C. 5. The surface modification method for making the surface of activated carbon electropositive according to claim 1, characterized in that, in step 4, the adding speed of concentrated hydrochloric acid is 3 mL/min to 9 mL/min. 6. The surface modification method for making the surface of activated carbon electropositive according to claim 5, characterized in that in step 7, vacuum distillation is performed until the white substance is completely precipitated.