A heavy metal wastewater treatment agent and its preparation method and application

Abstract

The present invention provides a heavy metal wastewater treatment agent and its preparation method and application. The heavy metal wastewater treatment agent is composed of Ce / MnO2 and Co / carbon nanosheets in a mass ratio of 3-5:1, wherein Ce / MnO2 is hydrothermally synthesized into rod-shaped Ce / MnO2, which has a higher surface area than spherical or irregular particles and has more active adsorption sites, thereby achieving effective removal of heavy metal ions. The Co / carbon nanosheets are ion-exchanged with fulvic acid to form a core-shell structure wrapped around the rod-shaped Ce / MnO2, thereby increasing the stability of the wastewater treatment agent and improving its reusability. The Ce / MnO2 and Co / carbon nanosheets of the present invention are combined to enhance synergy, thereby improving the effect of the wastewater treatment agent in removing heavy metal ions and achieving the effect of removing multiple heavy metal ions simultaneously.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a heavy metal wastewater treatment agent and a preparation method and application thereof. Background Art

[0002] Heavy metal ion wastewater is a major form of pollution caused by the migration of heavy metal ions. To date, a variety of heavy metal wastewater treatment methods have been developed both domestically and internationally, including chemical methods, ferrite methods, adsorption methods, ion exchange methods, membrane filtration methods, flotation methods, and electrochemical methods. These methods have achieved good results to a certain extent, but they also generally suffer from secondary pollution, high costs, and less-than-ideal treatment results. Compared with other methods, adsorption methods utilize porous solid materials to adsorb heavy metal ions in wastewater and remove them. It is suitable for a variety of heavy metal wastewaters, especially the deep treatment of low-concentration wastewater. It is also simple to operate and relatively low in cost. Therefore, it is a cost-effective and application-worthy method for heavy metal ion wastewater treatment.

[0003] However, the current traditional adsorbents are not ideal for simultaneously adsorbing multiple heavy metal ions, and it is difficult to completely remove them, which can easily cause secondary pollution. At the same time, because the adsorbents are unstable and cannot be reused, their costs are relatively high and their scope of use is also subject to certain restrictions. Therefore, current research focuses on developing a low-cost, efficient, and reusable adsorbent to remove heavy metal ions from wastewater. Summary of the Invention

[0004] In view of this, the present invention provides a heavy metal wastewater treatment agent and a preparation method and application thereof.

[0005] The technical solution of the present invention is achieved as follows:

[0006] A heavy metal wastewater treatment agent is composed of Ce / MnO2 and Co / carbon nanosheets in a mass ratio of 3-5:1.

[0007] Furthermore, the preparation method of Ce / MnO2 comprises:

[0008] (1) Potassium permanganate and manganese sulfate are added to water and stirred, and the solution is placed in a high-pressure reactor for hydrothermal reaction, washed, dried, and calcined to obtain rod-shaped MnO2;

[0009] (2) Dissolve cerium nitrate hexahydrate in water to prepare a solution, add rod-shaped MnO2, stir with ultrasound, filter and dry, and calcine to obtain Ce / MnO2.

[0010] Furthermore, in step (1), the molar ratio of potassium permanganate to manganese sulfate is 2-4:1; the solid-liquid ratio of potassium permanganate and manganese sulfate to water is 1:60-80 g / mL; the stirring time is 30-60 min; the temperature of the hydrothermal reaction is 135-145° C., and the time is 8-12 h; the temperature of the calcination is 450-550° C., and the time is 2-4 h; in step (2), the solid-liquid ratio of cerium nitrate hexahydrate to water is 1:100-120 g / mL; the ultrasonic stirring time is 1-3 h, and the rotation speed is 600-800 rpm; the calcination temperature is 450-550° C., and the time is 2-4 h.

[0011] Furthermore, the preparation method of the Co / carbon nanosheets includes:

[0012] (1) adding fulvic acid to a sodium hydroxide solution, removing excess inorganic salts, and filtering to obtain pretreated fulvic acid;

[0013] (2) Pretreated fulvic acid and cobalt nitrate hexahydrate were added to water, ultrasonically treated, filtered, freeze-dried, and calcined under an inert atmosphere to obtain Co / carbon nanosheets.

[0014] Furthermore, in step (1), the concentration of the sodium hydroxide solution is 0.05-0.15 mol / L; the solid-liquid ratio of the fulvic acid to the sodium hydroxide solution is 1:10-20 g / mL; in step (2), the mass ratio of the cobalt nitrate hexahydrate to the pretreated fulvic acid is 1:1-3; the ultrasonic treatment time is 30-60 min, and the rotation speed is 400-600 rpm; the inert atmosphere is nitrogen or helium; the calcination temperature is 500-600°C, and the time is 2-4 h.

[0015] A preparation method of a heavy metal wastewater treatment agent comprises the following specific steps: adding Ce / MnO2 to anhydrous ethanol, ultrasonically treating, sequentially adding Co / carbon nanosheets and sodium dodecyl sulfate, continuing stirring, standing overnight, centrifuging, washing the precipitate, and drying to obtain a wastewater treatment agent with a core-shell structure.

[0016] Furthermore, the solid-liquid ratio of Ce / MnO2 to anhydrous ethanol is 1:50-60 g / mL; the ultrasonic treatment time is 30-60 min, and the rotation speed is 400-600 rpm; the mass of the sodium dodecyl sulfate is 3%-5% of the Co / carbon nanosheets; and the stirring time is 1-3 h.

[0017] The invention discloses an application of a heavy metal wastewater treatment agent in heavy metal wastewater treatment.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The rod-shaped Ce / MnO2 of the present invention has a higher surface area than spherical or irregular particles and has more active adsorption sites. Ce has a higher surface area than spherical or irregular particles and has more active adsorption sites for heavy metal ions (Pb 2+ 、Cd 2+ and Cu 2+ ) has high affinity and can effectively remove heavy metal ions. MnO2 forms stable complexes with high-valent heavy metal ions, thereby achieving effective removal of heavy metal ions.

[0020] 2. The carboxyl group, alkyl ring of hydroxyl, carbon group and methoxy group of fulvic acid in the Co / carbon nanosheets of the present invention are complexed with Co to form stable Co / carbon nanosheets with uniform distribution, providing more active sites, improving selectivity, and achieving good removal of heavy metal ions.

[0021] 3. The present invention wraps Co / carbon nanosheets around the rod-shaped Ce / MnO2 to form a core-shell structure, which increases the stability of the wastewater treatment agent and improves its reusability. At the same time, the Ce / MnO2 and Co / carbon nanosheets are combined to enhance their synergy, thereby improving the effect of the wastewater treatment agent in removing heavy metal ions and achieving the effect of removing multiple heavy metal ions at the same time. DETAILED DESCRIPTION

[0022] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0023] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0024] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0025] Example 1

[0026] A heavy metal wastewater treatment agent is composed of Ce / MnO2 and Co / carbon nanosheets in a mass ratio of 4:1.

[0027] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0028] (1) Preparation of Ce / MnO2: Weigh 3.16 g of potassium permanganate and 1.51 g of manganese sulfate and add them to 327 mL of water, stir for 45 min, place the solution in an autoclave, react at 140°C for 10 h, wash, dry, place the product in a muffle furnace, adjust the temperature to 500°C, and calcine for 3 h to obtain rod-shaped MnO2. Weigh 1.3 g of cerium nitrate hexahydrate and dissolve it in 143 mL of water to prepare a solution, add rod-shaped MnO2, ultrasonically stir at 700 rpm for 2 h, filter and dry, place the product in a muffle furnace, adjust the temperature to 500°C and calcine for 3 h to obtain Ce / MnO2;

[0029] (2) Preparation of Co / carbon nanosheets: 5 g of fulvic acid was added to 75 mL of 0.1 mol / L sodium hydroxide solution, excess inorganic salts were removed, and the mixture was filtered to obtain pretreated fulvic acid. 2 g of pretreated fulvic acid and 1 g of cobalt nitrate hexahydrate were added to water, and ultrasonically treated at 500 rpm for 45 min. The mixture was filtered and freeze-dried. The temperature was raised to 550°C under a nitrogen atmosphere and calcined for 3 h to obtain Co / carbon nanosheets.

[0030] (3) Weigh 4 g of Ce / MnO2 and add it to 220 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 500 rpm for 45 min. 1 g of Co / carbon nanosheets and 0.04 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 2 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0031] Example 2

[0032] A heavy metal wastewater treatment agent is composed of Ce / MnO2 and Co / carbon nanosheets in a mass ratio of 3:1.

[0033] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0034] (1) Preparation of Ce / MnO2: Weigh 1.58 g of potassium permanganate and 1.51 g of manganese sulfate and add them to 186 mL of water, stir for 30 min, place the solution in an autoclave, react at 135°C for 8 h, wash, dry, place the product in a muffle furnace, adjust the temperature to 450°C, and calcine for 2 h to obtain rod-shaped MnO2. Weigh 1.3 g of cerium nitrate hexahydrate and dissolve it in 130 mL of water to prepare a solution, add rod-shaped MnO2, ultrasonically stir at 600 rpm for 1 h, filter and dry, place the product in a muffle furnace, adjust the temperature to 450°C, and calcine for 2 h to obtain Ce / MnO2;

[0035] (2) Preparation of Co / carbon nanosheets: 5 g of fulvic acid was added to 50 mL of 0.05 mol / L sodium hydroxide solution, excess inorganic salts were removed, and the mixture was filtered to obtain pretreated fulvic acid. 1 g of pretreated fulvic acid and 1 g of cobalt nitrate hexahydrate were added to water, and ultrasonically treated at 400 rpm for 30 min. The mixture was filtered and freeze-dried. The temperature was raised to 500°C under a nitrogen atmosphere and calcined for 2 h to obtain Co / carbon nanosheets.

[0036] (3) Weigh 3 g of Ce / MnO2 and add it to 150 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 400 rpm for 30 min. 1 g of Co / carbon nanosheets and 0.03 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 1 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0037] Example 3

[0038] A heavy metal wastewater treatment agent is composed of Ce / MnO2 and Co / carbon nanosheets in a mass ratio of 5:1.

[0039] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0040] (1) Preparation of Ce / MnO2: Weigh 4.74 g of potassium permanganate and 1.51 g of manganese sulfate and add them to 500 mL of water, stir for 60 min, place the solution in an autoclave, react at 145°C for 12 h, wash, dry, place the product in a muffle furnace, adjust the temperature to 550°C, and calcine for 4 h to obtain rod-shaped MnO2. Weigh 1.3 g of cerium nitrate hexahydrate and dissolve it in 156 mL of water to prepare a solution, add rod-shaped MnO2, ultrasonically stir at 800 rpm for 3 h, filter and dry, place the product in a muffle furnace, adjust the temperature to 550°C, and calcine for 4 h to obtain Ce / MnO2;

[0041] (2) Preparation of Co / carbon nanosheets: 5 g of fulvic acid was added to 100 mL of 0.15 mol / L sodium hydroxide solution, excess inorganic salts were removed, and the mixture was filtered to obtain pretreated fulvic acid. 3 g of pretreated fulvic acid and 1 g of cobalt nitrate hexahydrate were added to water, and ultrasonically treated at 600 rpm for 60 min. The mixture was filtered and freeze-dried. The temperature was raised to 600 °C under a nitrogen atmosphere and calcined for 4 h to obtain Co / carbon nanosheets.

[0042] (3) Weigh 5 g of Ce / MnO2 and add it to 300 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 600 rpm for 60 min. 1 g of Co / carbon nanosheets and 0.05 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 3 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0043] Comparative Example 1

[0044] The difference from Example 1 is that the mass ratio of Ce / MnO2 and Co / carbon nanosheets is 1:1; the others are consistent with Example 1.

[0045] A heavy metal wastewater treatment agent is composed of Ce / MnO2 and Co / carbon nanosheets in a mass ratio of 1:1.

[0046] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0047] (1) Preparation of Ce / MnO2: Weigh 3.16 g of potassium permanganate and 1.51 g of manganese sulfate and add them to 327 mL of water, stir for 45 min, place the solution in an autoclave, react at 140°C for 10 h, wash, dry, place the product in a muffle furnace, adjust the temperature to 500°C, and calcine for 3 h to obtain rod-shaped MnO2. Weigh 1.3 g of cerium nitrate hexahydrate and dissolve it in 143 mL of water to prepare a solution, add rod-shaped MnO2, ultrasonically stir at 700 rpm for 2 h, filter and dry, place the product in a muffle furnace, adjust the temperature to 500°C and calcine for 3 h to obtain Ce / MnO2;

[0048] (2) Preparation of Co / carbon nanosheets: 5 g of fulvic acid was added to 75 mL of 0.1 mol / L sodium hydroxide solution, excess inorganic salts were removed, and the mixture was filtered to obtain pretreated fulvic acid. 2 g of pretreated fulvic acid and 1 g of cobalt nitrate hexahydrate were added to water, and ultrasonically treated at 500 rpm for 45 min. The mixture was filtered and freeze-dried. The temperature was raised to 550°C under a nitrogen atmosphere and calcined for 3 h to obtain Co / carbon nanosheets.

[0049] (3) Weigh 1 g of Ce / MnO2 and add it to 55 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 500 rpm for 45 min. 1 g of Co / carbon nanosheets and 0.04 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 2 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0050] Comparative Example 2

[0051] The difference from Example 1 is that Ce / MnO2 is replaced by Co / MnO2, and Co / carbon nanosheets are replaced by Ce / carbon nanosheets; the rest are the same as Example 1.

[0052] A heavy metal wastewater treatment agent is composed of Co / MnO2 and Ce / carbon nanosheets in a mass ratio of 4:1.

[0053] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0054] (1) Preparation of Co / MnO2: Weigh 3.16 g of potassium permanganate and 1.51 g of manganese sulfate and add them to 327 mL of water, stir for 45 min, place the solution in an autoclave, react at 140°C for 10 h, wash, dry, place the product in a muffle furnace, adjust the temperature to 500°C, and calcine for 3 h to obtain rod-shaped MnO2. Weigh 1.3 g of cobalt nitrate hexahydrate and dissolve it in 143 mL of water to prepare a solution, add rod-shaped MnO2, and ultrasonically stir at 700 rpm for 2 h. Filter and dry, place the product in a muffle furnace, adjust the temperature to 500°C, and calcine for 3 h to obtain Co / MnO2.

[0055] (2) Preparation of Ce / carbon nanosheets: 5 g of fulvic acid was added to 75 mL of 0.1 mol / L sodium hydroxide solution, excess inorganic salts were removed, and the mixture was filtered to obtain pretreated fulvic acid. 2 g of pretreated fulvic acid and 1 g of cerium nitrate hexahydrate were added to water, and ultrasonically treated at 500 rpm for 45 min. The mixture was filtered and freeze-dried. The temperature was raised to 550°C under a nitrogen atmosphere and calcined for 3 h to obtain Ce / carbon nanosheets.

[0056] (3) Weigh 4 g of Co / MnO2 and add it to 220 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 500 rpm for 45 min. 1 g of Ce / carbon nanosheets and 0.04 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 2 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0057] Comparative Example 3

[0058] The difference from Example 1 is that Ce / MnO2 is replaced by MnO2; the rest is the same as Example 1.

[0059] A heavy metal wastewater treatment agent is composed of MnO2 and Co / carbon nanosheets in a mass ratio of 4:1.

[0060] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0061] (1) Preparation of MnO2: 3.16 g of potassium permanganate and 1.51 g of manganese sulfate were weighed and added to 327 mL of water. The mixture was stirred for 45 min. The solution was placed in an autoclave and reacted at 140°C for 10 h. The mixture was washed and dried. The product was placed in a muffle furnace at 500°C and calcined for 3 h to obtain rod-shaped MnO2.

[0062] (2) Preparation of Co / carbon nanosheets: 5 g of fulvic acid was added to 75 mL of 0.1 mol / L sodium hydroxide solution, excess inorganic salts were removed, and the mixture was filtered to obtain pretreated fulvic acid. 2 g of pretreated fulvic acid and 1 g of cobalt nitrate hexahydrate were added to water, and ultrasonically treated at 500 rpm for 45 min. The mixture was filtered and freeze-dried. The temperature was raised to 550°C under a nitrogen atmosphere and calcined for 3 h to obtain Co / carbon nanosheets.

[0063] (3) Weigh 4 g of MnO2 and add it to 220 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 500 rpm for 45 min. 1 g of Co / carbon nanosheets and 0.04 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 2 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0064] Comparative Example 4

[0065] The difference from Example 1 is that Co / carbon nanosheets are replaced by carbon nanosheets; the rest are the same as Example 1.

[0066] A heavy metal wastewater treatment agent is composed of Ce / MnO2 and carbon nanosheets in a mass ratio of 4:1.

[0067] The preparation method of the heavy metal wastewater treatment agent comprises the following specific steps:

[0068] (1) Preparation of Ce / MnO2: Weigh 3.16 g of potassium permanganate and 1.51 g of manganese sulfate and add them to 327 mL of water, stir for 30-60 min, place the solution in an autoclave, react at 140°C for 10 h, wash, dry, place the product in a muffle furnace, adjust the temperature to 500°C, and calcine for 3 h to obtain rod-shaped MnO2. Weigh 1.3 g of cerium nitrate hexahydrate and dissolve it in 143 mL of water to prepare a solution, add rod-shaped MnO2, ultrasonically stir at 700 rpm for 2 h, filter and dry, place the product in a muffle furnace, adjust the temperature to 500°C and calcine for 3 h to obtain Ce / MnO2;

[0069] (2) Preparation of carbon nanosheets: 5 g of fulvic acid was weighed and added to 75 mL of 0.1 mol / L sodium hydroxide solution. Excess inorganic salts were removed and filtered to obtain pretreated fulvic acid. The temperature was raised to 550°C under a nitrogen atmosphere and calcined for 3 h to obtain carbon nanosheets.

[0070] (3) Weigh 4 g of Ce / MnO2 and add it to 220 mL of anhydrous ethanol. Ultrasonic treatment is performed at a speed of 500 rpm for 45 min. 1 g of carbon nanosheets and 0.04 g of sodium dodecyl sulfate are added in sequence. Stirring is continued for 2 h. The mixture is allowed to stand overnight, centrifuged, the precipitate is washed, and dried to obtain a core-shell structured wastewater treatment agent.

[0071] Comparative Example 5

[0072] The difference from Example 1 is that Co / carbon nanosheets are missing, that is, Ce / MnO2 is 5g.

[0073] A heavy metal wastewater treatment agent is composed of 5g of Ce / MnO2 and carbon nanosheets.

[0074] The preparation method of the above-mentioned heavy metal wastewater treatment agent specifically includes the following steps: weighing 3.16g of potassium permanganate and 1.51g of manganese sulfate, adding them to 327mL of water, stirring for 45min, placing the solution in a high-pressure reactor, reacting at 140°C for 10h, washing, drying, placing the product in a muffle furnace, adjusting the temperature to 500°C, and calcining for 3h to obtain rod-shaped MnO2, weighing 1.3g of cerium nitrate hexahydrate and dissolving it in 143mL of water to prepare a solution, adding rod-shaped MnO2, ultrasonically stirring at a speed of 700rpm for 2h, filtering and drying, placing the product in a muffle furnace, adjusting the temperature to 500°C and calcining for 3h to obtain Ce / MnO2.

[0075] Comparative Example 6

[0076] The difference from Example 1 is that Ce / MnO2 is missing, that is, the Co / carbon nanosheets are 5 g.

[0077] A heavy metal wastewater treatment agent is composed of 5g of Co / carbon nanosheets.

[0078] The preparation method of the above-mentioned heavy metal wastewater treatment agent specifically includes the following steps: weighing 10g of fulvic acid, adding it to 150mL of 0.1mol / L sodium hydroxide solution, removing excess inorganic salts, filtering to obtain pretreated fulvic acid, weighing 5g of pretreated fulvic acid and 2.5g of cobalt nitrate hexahydrate, adding them to water, ultrasonically treating at a speed of 500rpm for 45min, filtering, freeze-drying, raising the temperature to 550°C under a nitrogen atmosphere, and calcining for 3h to obtain Co / carbon nanosheets.

[0079] Experimental situation

[0080] Preparation containing Cd 2+ , Pb 2+ 、Cu 2+300 ml of a 70 mg / L heavy metal-contaminated wastewater solution was prepared using 5 g of each of the wastewater treatment agents prepared in Examples 1-3 and Comparative Examples 1-6 of the present invention to perform adsorption treatment on the heavy metal-contaminated wastewater. The concentration of heavy metal ions in the heavy metal-contaminated wastewater before and after adsorption was determined using a plasma inductively coupled optical emission spectrometer (ICP-OES). The adsorption rate of the heavy metal ions by the wastewater adsorbent was calculated using the following formula: adsorption rate = (heavy metal ion concentration before adsorption - heavy metal ion concentration after adsorption) / heavy metal ion concentration before adsorption × 100%. The test results are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] As shown in Table 1, the wastewater treatment agents prepared in Examples 1-3 of the present invention can adsorb heavy metal ions (Cd 2+ , Pb 2+ 、Cu 2+ ), the adsorption efficiency is higher than 98%. Compared with Example 1, the mass ratio of Ce / MnO2 and Co / carbon nanosheets in Comparative Example 1 is different. The Ce / MnO2 in Comparative Example 2 is replaced by Co / MnO2, and the Co / carbon nanosheets are Ce / carbon nanosheets. The Ce / MnO2 in Comparative Example 3 is replaced by MnO2, and the Co / carbon nanosheets in Comparative Example 4 are replaced by carbon nanosheets, which all lead to a decrease in the efficiency of adsorbing heavy metal ions in wastewater. Comparative Examples 5-6 lack one of Ce / MnO2 and Co / carbon nanosheets, and the efficiency of adsorbing heavy metal ions in wastewater is significantly reduced, indicating that the Ce / MnO2 and Co / carbon nanosheets of the present invention synergistically enhance efficiency and jointly remove heavy metal ions.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A heavy metal wastewater treatment agent, characterized in that It is composed of Ce / MnO2 and Co / carbon nanosheets with a mass ratio of 3-5:1; The preparation method of Ce / MnO2 comprises: (1) Potassium permanganate and manganese sulfate are added to water and stirred, the solution is placed in a high-pressure reactor, and a hydrothermal reaction is carried out at 135-145°C for 8-12 hours, followed by washing and drying, and calcination at 450-550°C for 2-4 hours to obtain rod-shaped MnO2; (2) dissolving cerium nitrate hexahydrate in water to prepare a solution, adding rod-shaped MnO2, ultrasonically stirring, filtering and drying, and calcining at 450-550°C for 2-4h to obtain Ce / MnO2; The preparation method of the Co / carbon nanosheets comprises: (1) adding fulvic acid to a sodium hydroxide solution, removing excess inorganic salts, and filtering to obtain pretreated fulvic acid; (2) Pretreated fulvic acid and cobalt nitrate hexahydrate were added to water, ultrasonically treated, filtered, freeze-dried, and calcined under an inert atmosphere to obtain Co / carbon nanosheets.

2. A heavy metal wastewater treatment agent according to claim 1, characterized in that: In the preparation method of Ce / MnO2, in step (1), the molar ratio of potassium permanganate to manganese sulfate is 2-4:1; the solid-liquid ratio of potassium permanganate and manganese sulfate to water is 1:60-80 g / mL; and the stirring time is 30-60 min; in step (2), the solid-liquid ratio of cerium nitrate hexahydrate to water is 1:100-120 g / mL; the ultrasonic stirring time is 1-3 h, and the rotation speed is 600-800 rpm.

3. A heavy metal wastewater treatment agent according to claim 1, characterized in that: In the preparation method of Co / carbon nanosheets, in step (1), the concentration of the sodium hydroxide solution is 0.05-0.15 mol / L; the solid-liquid ratio of the fulvic acid to the sodium hydroxide solution is 1:10-20 g / mL; in step (2), the mass ratio of the cobalt nitrate hexahydrate to the pretreated fulvic acid is 1:1-3; the ultrasonic treatment time is 30-60 min, and the rotation speed is 400-600 rpm; the inert atmosphere is nitrogen or helium; the calcination temperature is 500-600°C, and the time is 2-4 h.

4. The method for preparing a heavy metal wastewater treatment agent according to claim 1, wherein: The specific steps include: adding Ce / MnO2 to anhydrous ethanol, ultrasonic treatment, adding Co / carbon nanosheets and sodium dodecyl sulfate in sequence, continuing stirring, standing overnight, centrifuging, washing the precipitate, and drying to obtain a core-shell structured wastewater treatment agent.

5. The method for preparing a heavy metal wastewater treatment agent according to claim 4, characterized in that: The solid-liquid ratio of Ce / MnO2 to anhydrous ethanol is 1:50-60g / mL; the ultrasonic treatment time is 30-60min, and the rotation speed is 400-600rpm; the mass of the sodium dodecyl sulfate is 3%-5% of the Co / carbon nanosheets; and the stirring time is 1-3h.

6. Use of the wastewater treatment agent according to any one of claims 1 to 3 in the treatment of heavy metal wastewater.

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