Activated carbon for reducing the content of chlorate in water and a method for preparing the same

Abstract

The application discloses activated carbon for reducing content of chlorate in water and a preparation method thereof, and belongs to the technical field of wastewater treatment. The application sequentially constructs a chlorinated glycidyl trimethyl ammonium cation layer for electrostatic adsorption of chlorate and a nano zero-valent iron functional layer for chemical reduction of the chlorate on the coconut shell activated carbon through bridging action and chemical grafting of polydopamine, forms a unique 'adsorption-degradation' integrated structure, greatly improves the treatment efficiency, ensures stability of functional components through chemical bonding, avoids secondary pollution, and has remarkable social, economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to activated carbon for reducing chlorate content in water and its preparation method. Background Technology

[0002] Chlorate is a common persistent inorganic contaminant in drinking water and food. It is extremely stable under normal temperature and pressure, but highly mobile and water-soluble, easily causing persistent and widespread pollution. It mainly originates from water treatment processes or food processing using chlorine-containing disinfectants (such as sodium hypochlorite). Studies have shown that excessive chlorate intake may pose health risks, especially to infants and young children and those with hypothyroidism. Therefore, health organizations and regulatory agencies in many countries have set strict limits on chlorate levels in drinking water and food.

[0003] Currently, methods for removing chlorate from water include activated carbon adsorption, reverse osmosis, ion exchange, and chemical reduction. Among these, activated carbon adsorption has attracted much attention due to its relatively low cost and ease of operation. However, ordinary activated carbon has limited adsorption capacity for small-molecule inorganic anions like chlorate, exhibiting poor selectivity and low adsorption capacity, making it difficult to meet increasingly stringent regulatory requirements. Therefore, there is an urgent need to develop a novel modified activated carbon material and its preparation method that possesses high selectivity, high adsorption capacity, and stable and reliable adsorption for chlorate.

[0004] Chinese patent document CN102424448A discloses a method for removing perchlorate from water, the method comprising the following steps: (1) in a solution containing ClO4 - (1) Add an adsorbent to the polluted water; (2) Add a stirring device or carry out the adsorption reaction in a shaker; (3) After the adsorption is completed, retain and separate the adsorbent in the water. The calcined layered bimetallic oxide can quickly and efficiently remove perchlorate ions from deionized water and tap water, thereby meeting the drinking water quality standards. The calcined layered compound after adsorption can be regenerated. The adsorbent used in this invention is magnesium-aluminum bimetallic composite oxide Mg6Al2O9. However, if the regeneration process of the adsorbent used in this invention is not handled properly, or a high concentration of desorption waste liquid is generated, it is very easy to cause secondary pollution. Summary of the Invention

[0005] The main objective of this invention is to propose an activated carbon for reducing chlorate content in water and its preparation method. By grafting glycidyltrimethylammonium chloride onto coconut shell activated carbon and generating highly reducing nano-zero valent iron in situ, a unique "adsorption-degradation" integrated structure is formed. This not only greatly improves the treatment efficiency, but also ensures the stability of functional components through chemical bonding, thus avoiding secondary pollution.

[0006] The technical solution of this invention is implemented as follows:

[0007] In a first aspect, the present invention proposes a method for preparing activated carbon to reduce the chlorate content in water, comprising the following steps:

[0008] S1. The coconut shell activated carbon is pretreated by acidification, and then the pretreated coconut shell activated carbon and dopamine are added to Tris-HCl buffer solution and mixed. The mixture is stirred at room temperature to obtain coated modified coconut shell activated carbon.

[0009] S2. Dissolve glycidyltrimethylammonium chloride in water, add coated and modified coconut shell activated carbon, heat to react, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon.

[0010] S3. Under a nitrogen atmosphere, cationic coconut shell activated carbon is ultrasonically dispersed in water, and FeSO₄ is added. 4· Mix 7H2O with water to ensure complete chelation, then add sodium borohydride aqueous solution dropwise, stir, filter, collect the solids, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0011] Preferably, the specific steps of the acidification pretreatment in step S1 are as follows: the coconut shell activated carbon is crushed, sieved, and then immersed in dilute nitric acid for heating treatment. After filtration, washing, and drying, pretreated coconut shell activated carbon is obtained.

[0012] More preferably, in step S1, the heating temperature in the acidification pretreatment step is 50-80℃, and the heating time is 5-8h; the concentration of the dilute nitric acid is 3-5mol / L.

[0013] In this step, dilute nitric acid is used to pretreat the coconut shell activated carbon. This can remove ash, inorganic salts, and some impurities that may be adsorbed during the production and storage of the coconut shell activated carbon, and clear the pores. In addition, it can increase active oxygen-containing functional groups such as carboxyl and hydroxyl groups on the surface of the coconut shell activated carbon. This not only improves its hydrophilicity, but also provides more active sites for subsequent experimental steps.

[0014] Preferably, the mass ratio of pretreated coconut shell activated carbon to dopamine in step S1 is 1:2-4.

[0015] This step generates polydopamine through in-situ polymerization on the surface and pores of pretreated coconut shell activated carbon. The polydopamine molecule contains a large number of catechol groups, amino groups, and imino groups, which are excellent metal ion chelating agents and chemical reaction sites, which are beneficial to the grafting of quaternary ammonium salts and uniform iron loading in subsequent steps.

[0016] Preferably, in step S2, the mass ratio of glycidyltrimethylammonium chloride to coated modified coconut shell activated carbon is 1:0.8-1; the heating reaction temperature is 40-60℃, and the heating time is 3-5h.

[0017] In this step, the epoxy groups in the glycidyltrimethylammonium chloride molecule undergo a ring-opening reaction with the amino or phenolic hydroxyl groups on the polydopamine layer, thereby firmly grafting glycidyltrimethylammonium chloride onto the polydopamine coating layer. Through the mutual attraction of positive and negative charges, it can directionally and efficiently adsorb and enrich negatively charged chlorate in the water. By grafting glycidyltrimethylammonium chloride onto activated carbon, its ultra-high stability and functional durability under water flow and complex environments are ensured. This avoids the fatal defect of rapid detachment and failure of glycidyltrimethylammonium chloride and secondary pollution caused by ordinary physical mixing, and greatly improves the capture efficiency of chlorate.

[0018] Preferably, in step S3, the cationic coconut shell activated carbon and FeSO₄ 4· The mass ratio of 7H2O is 10:5-8; the concentration of the sodium borohydride aqueous solution is 0.1-0.5 mol / L.

[0019] In this step, the excess active groups on the surface of polydopamine are used to react with Fe. 2+ Chelation is performed to fix it onto the surface of the already positively charged activated carbon, and then sodium borohydride is used to fix these Fe... 2+ In-situ reduction produces nano-zero valent iron with higher reducing activity. Nano-zero valent iron can reduce chlorate to non-toxic chloride ions, thereby reducing the chlorate content in water. Compared with physical mixing of nano-zero valent iron, nano-zero valent iron generated by in-situ reduction can be more dispersed and implanted into the surface and pores of cationic coconut shell activated carbon, avoiding the problem of easy agglomeration of nano-zero valent iron. It also has a stronger bond with activated carbon and greater stability, ultimately improving the removal efficiency of chlorate and the service life of the material.

[0020] When activated carbon that reduces chlorate content in water is placed in water, negatively charged chlorate ions are first rapidly captured and enriched on the surface of activated carbon by positively charged glycidyltrimethylammonium chloride. Then, these captured chlorate ions can be efficiently reduced to harmless chloride ions by adjacent nano-zero-valent iron particles. The synergistic effect of glycidyltrimethylammonium chloride and nano-zero-valent iron significantly improves the removal effect of chlorate.

[0021] Secondly, the present invention also provides a method for preparing activated carbon that reduces the chlorate content in water, resulting in coconut shell activated carbon that reduces the chlorate content in water.

[0022] Thirdly, the present invention also provides the application of the activated carbon described above for reducing chlorate content in water in water treatment.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention proposes an activated carbon for reducing chlorate content in water and its preparation method. Through the bridging effect of polydopamine and chemical grafting, a glycidyltrimethylammonium chloride cationic layer for electrostatic adsorption of chlorate and a nano-zero-valent iron functional layer for chemical reduction are sequentially constructed on coconut shell activated carbon, forming a unique integrated "adsorption-degradation" structure. This not only greatly improves the treatment efficiency but also ensures the stability of the functional components through chemical bonding, avoiding secondary pollution. It has significant socio-economic and environmental benefits. At the same time, this invention uses inexpensive and readily available coconut shell activated carbon as a substrate, and the preparation process is mild and easy to scale up, significantly reducing the treatment cost of high-concentration chlorate wastewater. It can efficiently and stably remove chlorate from water bodies, effectively ensuring drinking water safety and protecting aquatic ecosystems. It has significant practical significance and broad application prospects for solving the environmental pollution problems caused by specific industrial wastewater and promoting sustainable development. Detailed Implementation

[0025] To avoid unnecessary details, unless otherwise specified, all items used in the following examples are commercially available products, and all methods used are conventional methods unless otherwise specified.

[0026] The sources of some of the raw materials used in this invention are as follows:

[0027] Coconut shell activated carbon, purchased from Dongguan Hongsheng Activated Carbon Co., Ltd.

[0028] Example 1

[0029] A method for preparing activated carbon to reduce chlorate content in water includes the following steps:

[0030] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 4 mol / L dilute nitric acid and heated for 6 hours at 60°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 30 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0031] S2. Dissolve 10g of glycidyltrimethylammonium chloride in 150mL of water, add 9g of coated modified coconut shell activated carbon, heat at 50℃ for 4h, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon.

[0032] S3. Under a nitrogen atmosphere, ultrasonically disperse 10g of cationic coconut shell activated carbon in 200mL of water, and add 6.8g of FeSO₄. 4· Mix and stir with 7H2O for 1 hour, then add 200 mL of 0.3 mol / L sodium borohydride aqueous solution dropwise, stir for 2 hours, filter, collect the solid, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0033] Example 2

[0034] A method for preparing activated carbon to reduce chlorate content in water includes the following steps:

[0035] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 3 mol / L dilute nitric acid and heated for 5 hours at 80°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 20 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0036] S2. Dissolve 10g of glycidyltrimethylammonium chloride in 150mL of water, add 8g of coated modified coconut shell activated carbon, heat and react at 40℃ for 5h, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon.

[0037] S3. Under a nitrogen atmosphere, ultrasonically disperse 10g of cationic coconut shell activated carbon in 200mL of water, and add 5g of FeSO₄. 4· Mix and stir with 7H2O for 1 hour, then add 400 mL of 0.1 mol / L sodium borohydride aqueous solution dropwise, stir for 2 hours, filter, collect the solid, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0038] Example 3

[0039] A method for preparing activated carbon to reduce chlorate content in water includes the following steps:

[0040] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 5 mol / L dilute nitric acid and heated and impregnated at 50°C for 8 hours. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. Then, 10 g of pretreated coconut shell activated carbon and 40 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred and reacted at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0041] S2. Dissolve 10g of glycidyltrimethylammonium chloride in 150mL of water, add 10g of coated modified coconut shell activated carbon, heat and react at 60℃ for 3h, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon.

[0042] S3. Under a nitrogen atmosphere, ultrasonically disperse 10g of cationic coconut shell activated carbon in 200mL of water, and add 8g of FeSO₄. 4· Mix and stir with 7H2O for 1 hour, then add 150 mL of 0.5 mol / L sodium borohydride aqueous solution dropwise, stir for 2 hours, filter, collect the solid, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0043] Comparative Example 1

[0044] A method for preparing activated carbon to reduce chlorate content in water is similar to that in Example 1, except that nano-zero valent iron is not generated in situ. The method specifically includes the following steps:

[0045] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 4 mol / L dilute nitric acid and heated for 6 hours at 60°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 30 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0046] S2. Dissolve 10g of glycidyltrimethylammonium chloride in 150mL of water, add 9g of coated modified coconut shell activated carbon, heat and react at 50℃ for 4h, filter, collect the solid, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0047] Comparative Example 2

[0048] A method for preparing activated carbon to reduce chlorate content in water is similar to that in Example 1, except that glycidyltrimethylammonium chloride and coated modified coconut shell activated carbon are physically mixed, specifically including the following steps:

[0049] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 4 mol / L dilute nitric acid and heated for 6 hours at 60°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 30 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0050] S2. Mix 10g of glycidyltrimethylammonium chloride and 9g of coated modified coconut shell activated carbon evenly to obtain activated carbon that reduces the chlorate content in water.

[0051] Comparative Example 3

[0052] A method for preparing activated carbon to reduce chlorate content in water is similar to that in Example 1, except that glycidyltrimethylammonium chloride is not added. The method specifically includes the following steps:

[0053] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 4 mol / L dilute nitric acid and heated for 6 hours at 60°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 30 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0054] S2. Under a nitrogen atmosphere, ultrasonically disperse 10g of coated modified coconut shell activated carbon in 200mL of water, and add 6.8g of FeSO₄. 4· Mix and stir with 7H2O for 1 hour, then add 200 mL of 0.3 mol / L sodium borohydride aqueous solution dropwise, stir for 2 hours, filter, collect the solid, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0055] Comparative Example 4

[0056] A method for preparing activated carbon to reduce chlorate content in water is similar to that in Example 1, except that FeSO₄ is not used. 4· The in-situ reduction of 7H2O to nano-zero valent iron involves the following steps:

[0057] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 4 mol / L dilute nitric acid and heated for 6 hours at 60°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 30 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0058] S2. Dissolve 10g of glycidyltrimethylammonium chloride in 150mL of water, add 9g of coated modified coconut shell activated carbon, heat at 50℃ for 4h, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon.

[0059] S3. Under a nitrogen atmosphere, ultrasonically disperse 10g of cationic coconut shell activated carbon in 200mL of water, and add 6.8g of FeSO₄. 4· Mix and stir with 7H2O for 1 hour, filter, collect the solids, wash and dry to obtain activated carbon that reduces the chlorate content in water.

[0060] Comparative Example 5

[0061] A method for preparing activated carbon to reduce chlorate content in water is similar to that in Example 1, except that the nano-zero valent iron is physically mixed, and specifically includes the following steps:

[0062] S1. After crushing and passing the coconut shell activated carbon through a 50-mesh sieve, it was added to 4 mol / L dilute nitric acid and heated for 6 hours at 60°C. After cooling, the mixture was filtered, and the solid was collected and washed until the filtrate was neutral. The solid was then dried to obtain pretreated coconut shell activated carbon. 10 g of pretreated coconut shell activated carbon and 30 g of dopamine were added to 200 mL of Tris-HCl buffer solution with a pH of 8 and mixed. The mixture was stirred at room temperature for 3 hours. After filtration, the solid product was collected, washed, and dried to obtain coated modified coconut shell activated carbon.

[0063] S2. Dissolve 10g of glycidyltrimethylammonium chloride in 150mL of water, add 9g of coated modified coconut shell activated carbon, heat at 50℃ for 4h, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon.

[0064] S3. Under a nitrogen atmosphere, 10g of cationic coconut shell activated carbon and 6.8g of nano-zero valent iron are mixed evenly to obtain activated carbon that reduces the chlorate content in water.

[0065] Simulated adsorption test of chlorate:

[0066] 200g of activated carbon prepared in Examples 1-3 and Comparative Examples 1-5 for reducing chlorate content in water was uniformly packed into 500mL glass adsorption columns using a wet method, and rinsed and vented with deionized water. Then, simulated wastewater with a pre-prepared chlorate content of 5mg / L and a pH of 6 was continuously pumped into the activated carbon column at a constant flow rate of 10mL / min using a peristaltic pump. Three hours after the start of the experiment, precise samples were taken from the outlet of the adsorption column, and the chlorate concentration of the effluent samples was determined. The chlorate removal rate was calculated, and the test results are shown in Table 1.

[0067] Table 1 Results of chlorate simulated adsorption experiments

[0068]

[0069] As can be seen from the experimental results in Table 1, the activated carbon prepared by this invention for reducing chlorate content in water has a good chlorate removal capacity.

[0070] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for producing activated carbon for reducing the content of chlorate in water, characterized by, Includes the following steps: S1. The coconut shell activated carbon is pretreated by acidification, and then the pretreated coconut shell activated carbon and dopamine are added to Tris-HCl buffer solution and mixed. The mixture is stirred at room temperature to obtain coated modified coconut shell activated carbon. S2. Dissolve glycidyltrimethylammonium chloride in water, add coated and modified coconut shell activated carbon, heat to react, filter, collect the solid, wash and dry to obtain cationic coconut shell activated carbon. S3. Under a nitrogen atmosphere, cationic coconut shell activated carbon is ultrasonically dispersed in water, FeSO4·7H2O is added and stirred to fully chelate it, then sodium borohydride aqueous solution is added dropwise, stirred, filtered, and the solids are collected, washed and dried to obtain activated carbon that reduces the chlorate content in water. In step S1, the mass ratio of pretreated coconut shell activated carbon to dopamine is 1:2-4. In step S2, the mass ratio of glycidyltrimethylammonium chloride and coated modified coconut shell activated carbon is 1:0.8-1. In step S2, the heating reaction temperature is 40-60℃, and the heating time is 3-5 hours. In step S3, the mass ratio of cationic coconut shell activated carbon to FeSO4·7H2O is 10:5-8.

2. The production method according to claim 1, characterized by, The specific steps of the acidification pretreatment in step S1 are as follows: after crushing and sieving the coconut shell activated carbon, it is immersed in dilute nitric acid and heated, and then filtered, washed and dried to obtain pretreated coconut shell activated carbon.

3. The method of claim 2, wherein: In step S1, the acidification pretreatment step involves heating at a temperature of 50-80°C for 5-8 hours.

4. The method of claim 2, wherein: The concentration of the dilute nitric acid is 3-5 mol / L.

5. An activated carbon for reducing the content of chlorate in water, characterized by: It is prepared by the preparation method described in any one of claims 1-4.

6. Use of the activated carbon of claim 5 for reducing the content of chlorate in water, characterized in that: It is applied to the field of water treatment.

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