Preparation method of ZIF / LDH loaded biochar composite adsorbent and application thereof

Abstract

The application discloses a preparation method of a ZIF / LDH loaded biochar composite adsorbent and application thereof, and comprises the following steps: (1) mixing, calcining and washing and drying pretreated corn stalks and alkali to obtain biochar BC; (2) mixing, washing, drying and calcining a certain proportion of the biochar BC and acetate, then mixing with 2-methyl imidazole, aging, and washing and drying to obtain BC / ZIF; and (3) immersing a certain amount of BC / ZIF in a nitrate solution, stirring, standing, washing and drying to obtain a BC / ZIF8 / LDH composite adsorbent. The composite adsorbent has a layered and open structure, a large specific surface area, a large number of adsorption sites, and a nitrosamine precursor removal rate of more than 95%; has a good binding capacity and selective adsorption on small-molecule amine, histidine, protein and other nitrogen disinfection by-product N-DBPs precursors; has good dispersing performance, high utilization rate of LDH metal, stable structure, good reaction activity and good repeated use effect; and has a wide source of raw materials, low price, low production cost and high economic benefit.

Description

Technical Field

[0001] This invention relates to a method for preparing an adsorbent and its application, and more particularly to a method for preparing a ZIF / LDH-loaded biochar composite adsorbent and its application. Background Technology

[0002] Disinfection treatment of drinking water and wastewater leads to the generation of numerous byproducts. Among these, nitrogen-containing disinfection byproducts (N-DBPs), represented by halogenated acetonitrile, N-nitrosamines, and their halonitromethanes, are highly toxic and carcinogenic, endangering drinking water safety and ecosystem health. Research on N-DBPs has become a hot topic of interest for many scholars. Adsorption methods utilize the interaction forces between adsorbents and target pollutants in water to adsorb pollutants onto the surface of solid adsorbents, thereby separating pollutants from water. Due to their high adsorption efficiency, simple operation, and low cost, they are widely used in water treatment. Commonly used adsorbents include zeolites, activated carbon, and metal-organic frameworks (MOFs). Biochar, in particular, is an activated carbon that is produced by directly pyrolyzing various biomass raw materials under limited oxygen conditions, causing its internal structure to react and generate active groups and adsorption sites to effectively adsorb inorganic or organic pollutants. However, for highly mobile water bodies, especially for pollutants with high concentrations and low molecular weights, such as secondary or tertiary amines in nitrosamine precursors, biochar has few functional groups and low activity, resulting in limited adsorption capacity and inability to effectively adsorb nitrogen-containing disinfection byproducts (N-DBPs) in water treatment. Layered bimetallic hydroxides (LDHs) are composed of overlapping main layers and interlayer anions and water molecules. Their advantages include easy adjustment of the types and proportions of metal ions on the main layers and the types of interlayer anions, easy structural customization, and ease of functionalization through combination with other materials, giving them broad application potential in water treatment. Traditionally prepared LDH materials exhibit poor dispersion, tend to aggregate into lumps, and cannot effectively control their morphology, particle size, and surface area, thus failing to selectively, efficiently, and stably adsorb pollutants. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for preparing a ZIF / LDH-loaded biochar composite adsorbent that can improve the activity and increase the adsorption selectivity of biochar; another purpose of this invention is to provide the application of this biochar composite adsorbent.

[0004] Technical solution: The preparation method of the ZIF / LDH-loaded biochar composite adsorbent of the present invention includes the following steps:

[0005] (1) Pretreated corn stalks were mixed with alkali, calcined, washed and dried to obtain biochar BC;

[0006] (2) The above biochar BC and acetate were mixed in a mass ratio of 1:0.37-0.74, washed, dried and calcined, then mixed with 2-methylimidazole, aged and then washed and dried to obtain BC / ZIF. The mass ratio of biochar material BC to 2-methylimidazole was 1:3.83-5.47.

[0007] (3) The above BC / ZIF was immersed in a nitrate solution with a mass ratio of BC / ZIF to nitrate of 1:20-50. After stirring and standing, it was washed and dried to obtain the BC / ZIF8 / LDH composite adsorbent.

[0008] Furthermore, step (1) includes the following steps:

[0009] (11) After washing and crushing the corn stalks with deionized water at room temperature, screen them into 200-250 mesh particles.

[0010] (12) Mix the corn stalks with alkali;

[0011] (13) Calcine the above mixture in a muffle furnace at 300-500℃;

[0012] (14) Immerse the calcined product in hydrochloric acid solution, stir, separate, and wash until the pH of the supernatant is neutral.

[0013] (15) After drying the powder, place it in a zinc chloride solution, stir, separate, wash until the pH of the supernatant is neutral, and then dry.

[0014] (16) Calcination at 500-900℃ under nitrogen protection;

[0015] (17) The biochar BC was obtained by washing with ethanol and deionized water 3-5 times and freeze-drying.

[0016] Furthermore, the base in step (1) is sodium bicarbonate.

[0017] Furthermore, step (2) includes the following steps:

[0018] (21) Mix biochar BC and acetate in a mass ratio of 1:0.37-0.74, stir in a water bath at 60°C, and age at 40°C;

[0019] (22) Separate, wash 3-5 times and then dry;

[0020] (23) Calcination at 300℃ for 20-30 min under nitrogen protection;

[0021] (24) Wash 3-5 times, then freeze dry;

[0022] (25) The above freeze-dried powder was immersed in a certain concentration of 2-methylimidazole and stirred for 10 min. The mass ratio of the dry powder to 2-methylimidazole was 1:3.83-5.47. The powder was aged for 12-24 h and the solid powder was separated by filtration.

[0023] (26) Wash with deionized water 3-5 times and dry to obtain BC / ZIF8.

[0024] Furthermore, the acetate in step (2) is cobalt acetate or zinc acetate.

[0025] Furthermore, step (2) also includes immersing the dried powder of biochar BC and acetate after calcination in zinc nitrate hexahydrate Zn(NO3)2·6(H2O) and hexamethylenetetramine (C6H2O). 12 In a mixed solution of N4, zinc ions are loaded onto biochar material BC by heating. The mass ratio of lyophilized powder to zinc nitrate and hexamethylenetetramine is 1:4.26:2. The secondary loading allows more zinc ions to be loaded on the surface of biochar BC, which can form more bimetallic organic framework materials, provide more active adsorption centers, and thus improve the adsorption and removal efficiency of nitrogen-containing disinfection byproducts N-DBPs precursors.

[0026] Furthermore, the solvent for the acetate in step (2) is 50% (v / v) ethanol or deionized water.

[0027] Furthermore, in step (3), the nitrate is one of cobalt nitrate Co(NO3)2·6H2O, zinc nitrate Zn(NO3)2·6H2O, nickel nitrate Ni(NO3)2·6H2O, magnesium nitrate Mg(NO3)2·6H2O, iron nitrate Fe(NO3)3·9H2O, and aluminum nitrate Al(NO3)3·9H2O. Different bimetallic organic frameworks have certain adsorption and removal effects on nitrogen-containing disinfection byproducts N-DBPs precursors, among which ZnNi bimetallic organic framework material has the best removal effect.

[0028] Furthermore, the solvent for the nitrate in step (3) is 33% (v / v) ethanol.

[0029] This invention also provides an application of ZIF / LDH biochar composite adsorbent in removing nitrogen-containing disinfection byproducts N-DBPs precursors from water.

[0030] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: 1. The ZIF / LDH biochar composite adsorbent has a layered and open structure, which greatly increases the specific surface area and the adsorption sites of the material, effectively adsorbing and separating pollutants, and achieving a removal rate of over 95% for nitrosamine precursors in water; 2. The ZIF / LDH biochar composite adsorbent has good binding capacity and selective adsorption for nitrogen-containing disinfection byproducts (N-DBPs) such as small molecule amines, histidine, and proteins; 3. It has good dispersion performance, avoiding agglomeration, improving the utilization rate of LDH metal, and the doped metal can improve the stability of the adsorbent structure and its reactivity with pollutants, resulting in good repeated use; 4. The raw materials are widely available, inexpensive, and have low production costs, resulting in high economic benefits. Attached Figure Description

[0031] Figure 1 The XRD pattern of the adsorbent prepared in this invention;

[0032] Figure 2 Here is a SEM image of the adsorbent prepared in this invention;

[0033] Figure 3 Pore ​​size distribution diagrams of BC / ZIF8 and BC / ZIF8 / LDH prepared according to the present invention;

[0034] Figure 4 The adsorption performance of the adsorbent prepared in Example 2 of this invention for dimethylamine DMA, diethylamine DEA and pyrrolidine PYR at different pH values ​​is shown in the figure.

[0035] Figure 5 The Raman spectrum of the adsorbent prepared in Example 2 of this invention;

[0036] Figure 6 This is a diagram showing the anti-interference performance of the adsorbent prepared in Example 2 of the present invention;

[0037] Figure 7 This is a diagram showing the recycling effect of the adsorbent prepared in Example 2 of the present invention. Detailed Implementation

[0038] 1. Preparation of amorphous biochar BC, including the following steps:

[0039] (1) Corn stalks were washed with deionized water at room temperature for 30 minutes and then finely crushed and screened into 200-250 mesh particles.

[0040] (2) Mix corn stalks with sodium bicarbonate at a mass ratio of 1:2;

[0041] (3) Calcine the above mixture in a muffle furnace at 300°C for 3 hours;

[0042] (4) Immerse the calcined product in a 10% hydrochloric acid solution, stir magnetically for 2 hours, filter to separate the solid powder, and wash with deionized water until the pH of the supernatant is neutral.

[0043] (5) After drying the powder, place it in a 1.34% zinc chloride solution, stir magnetically for 2 hours, wash with deionized water until the pH of the supernatant reaches neutral, and then dry.

[0044] (6) Calcination at 500℃ for 2 hours under nitrogen protection;

[0045] (7) The biochar BC was obtained by washing with ethanol and deionized water three times and freeze-drying.

[0046] 2. Utilize the above-mentioned biochar BC to synthesize a ZIF / LDH-loaded biochar composite adsorbent.

[0047] Example 1

[0048] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0049] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0050] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0051] (4) Wash three times with deionized water and freeze-dry;

[0052] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0053] (6) Wash with deionized water 3 times and dry to obtain BC / ZIF8-2;

[0054] (7) Immerse 0.25g of BC / ZIF8-2 in 100mL of nickel nitrate Ni(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min;

[0055] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-2.

[0056] Example 2

[0057] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0058] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0059] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0060] (4) Wash three times with deionized water and freeze-dry;

[0061] (5) Immerse 0.35g of the above freeze-dried powder in 50ml of 0.1mol / L zinc nitrate hexahydrate Zn(NO3)2·6(H2O) and hexamethylenetetramine (C6H2O). 12 The mixture of N4) was heated at 90°C for 4 hours;

[0062] (6) Wash with deionized water and ethanol three times, and dry at 60°C;

[0063] (7) Immerse 0.3g of the above dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0064] (8) Wash with deionized water 3 times and dry to obtain BC / ZIF8-3;

[0065] (9) Immerse 0.25g of the dried BC / ZIF8-3 above into 100mL of nickel nitrate Ni(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min.

[0066] (10) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-7.

[0067] Example 3

[0068] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0069] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0070] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0071] (4) Wash three times with deionized water and freeze-dry;

[0072] (5) Immerse 0.35g of lyophilized powder in 50ml of 0.1mol / L zinc nitrate hexahydrate Zn(NO3)2·6(H2O) and 50ml of 0.1mol / L hexamethylenetetramine (C6H2O). 12 The mixture of N4) was heated at 90°C for 4 hours;

[0073] (6) Wash with deionized water and ethanol three times, and dry at 60°C;

[0074] (7) Immerse 0.3g of the above dry powder in 100mL of 2-methylimidazole (0.07mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0075] (8) Wash with deionized water 3-5 times and dry to obtain BC / ZIF8-5;

[0076] (9) Immerse 0.25g of the dried BC / ZIF8-5 above into 100mL of nickel nitrate Ni(NO3)2·6H2O (0.018mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min.

[0077] (10) Wash with deionized water 3-5 times and dry for 12 hours to obtain BC / ZIF8 / LDH-9.

[0078] Comparative Example 1

[0079] (1) Mix 0.5g of biochar BC and 100ml of cobalt acetate (0.02mol / L) containing 50% (v / v) ethanol, stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H.

[0080] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0081] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0082] (4) Wash three times with deionized water and freeze-dry;

[0083] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0084] (6) Wash with deionized water three times and dry to obtain BC / ZIF67;

[0085] (7) Immerse 0.25g of BC / ZIF67 in 100mL of nickel nitrate Ni(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min;

[0086] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF67 / LDH.

[0087] Comparative Example 2

[0088] (1) Mix 0.5g of biochar BC and 100ml of zinc acetate (0.01mol / L) containing 50% (v / v) ethanol, stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H.

[0089] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0090] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0091] (4) Wash three times with deionized water and freeze-dry;

[0092] (5) Immerse 0.3g of freeze-dried powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0093] (6) Wash with deionized water 3 times and dry to obtain BC / ZIF8-1;

[0094] (7) Immerse 0.25g of the dried BC / ZIF8-1 above into 100mL of nickel nitrate Ni(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min, and let stand for 20min.

[0095] The BC / ZIF8 / LDH-1 was prepared by washing three times with deionized water and drying for 12 hours.

[0096] Comparative Example 3

[0097] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0098] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0099] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0100] (4) Wash three times with deionized water and freeze-dry;

[0101] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0102] (6) Wash with deionized water 3 times and dry to obtain BC / ZIF8-2;

[0103] (7) Immerse 0.25g of BC / ZIF8-2 in 100g of cobalt nitrate Co(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min;

[0104] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-3.

[0105] Comparative Example 4

[0106] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0107] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0108] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0109] (4) Wash three times with deionized water and freeze-dry;

[0110] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0111] (6) Wash with deionized water 3 times and dry to obtain BC / ZIF8-2;

[0112] (7) Immerse 0.25g of BC / ZIF8-2 in 100mL of ferric nitrate Fe(NO3)3·9H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min;

[0113] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-4.

[0114] Comparative Example 5

[0115] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0116] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0117] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0118] (4) Wash three times with deionized water and freeze-dry;

[0119] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0120] (6) Wash with deionized water 3 times and dry to obtain BC / ZIF8-2;

[0121] (7) Immerse 0.25g of BC / ZIF8-2 in 100mL of aluminum nitrate Al(NO3)3·9H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min;

[0122] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-5.

[0123] Comparative Example 6

[0124] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L), stir in a water bath at 60℃ for 6H, and age at 40℃ for 4H;

[0125] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0126] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0127] (4) Wash three times with deionized water and freeze-dry;

[0128] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0129] (6) Wash with deionized water 3 times and dry to obtain BC / ZIF8-2;

[0130] (7) Immerse 0.25g of BC / ZIF8-2 in 100mL of magnesium nitrate Mg(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min.

[0131] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-6.

[0132] Comparative Example 7

[0133] (1) Mix 0.5g of biochar BC with 100ml of zinc acetate aqueous solution (0.02mol / L) and soak for 1 hour;

[0134] (2) The solid powder was separated by vacuum filtration, washed three times with deionized water and then dried.

[0135] (3) Calcination at 300℃ for 20 min under nitrogen protection;

[0136] (4) Wash three times with deionized water and freeze-dry;

[0137] (5) Soak 0.3g of dry powder in 20ml of 2-methylimidazole (0.1mol / L) and stir for 10min. Let it age for 24h and filter to separate the solid powder.

[0138] (6) Wash with deionized water three times and dry to obtain BC / ZIF8-4;

[0139] (7) Immerse 0.25g of BC / ZIF8-4 in 100mL of nickel nitrate Ni(NO3)2·6H2O (0.043mol / L) containing 33% (v / v) ethanol, stir magnetically for 10min and let stand for 20min;

[0140] (8) Wash with deionized water 3 times and dry for 12 hours to obtain BC / ZIF8 / LDH-8.

[0141] The ZIF8 / LDH-loaded biochar composite adsorbents prepared in the above examples and comparative examples were tested as follows:

[0142] 1. Testing of removal rates of dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR):

[0143] 100 mL solutions of dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR) with a concentration of 100 mg / L and pH values ​​of 3, 5, 7, 9, and 11 were pre-prepared. 50 mg of the ZIF8 / LDH biochar composite adsorbent prepared in Example 2 was added, and the solutions were placed in a shaker at room temperature and 150 rpm for adsorption experiments. After 12 hours of adsorption, samples were taken to determine the adsorption capacity of the composite material. The results showed that the removal rate was highest at pH 11 and lowest at pH 3. The material exhibited good removal effects in solutions with pH values ​​of 7-11, with removal rates exceeding 80%. The removal effect at pH 10 and 11 tended to be relatively stable, while the removal effect was optimal at pH 11, reaching 97%, 93.7%, and 96%, respectively. This is mainly related to the electrostatic interaction between the aliphatic secondary amine and the surface of the charged substance.

[0144] The removal rates of dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR) of the ZIF8 / LDH biochar composite adsorbents prepared in the above examples and comparative examples were tested using the above test methods, and the results are shown in Table 1.

[0145] Table 1 Removal rates of dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR)

[0146]

[0147] 2. Testing of resistance to interference from pollutants

[0148] Prepare solutions of 100 mg / L dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR), each containing a certain amount of Cl. - NO3 - HCO3 - SO4 2- and PO4 3- 50 mg of the adsorbent prepared in Example 2 was placed in a shaker at 150 rpm for adsorption. After 12 hours of adsorption, a sample was taken to determine the adsorption capacity of the composite material. The results are as follows. Figure 6 As shown.

[0149] 3. Reusability test of ZIF8 / LDH biochar composite adsorbent

[0150] 50 mg of the adsorbent prepared in Example 2 was added to 100 mL of the above solutions to prepare 100 mg / L concentrations of dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR, respectively. The solutions were then placed in a shaker at 150 rpm for adsorption experiments. The solutions were circulated to remove dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR. The results are as follows: Figure 7 The removal rate still reached over 90% after 5 cycles, indicating that the prepared ZIF8 / LDH biochar composite adsorbent has high stability and good reusability.

[0151] Analysis of Examples 1-3: Loading the first ion Zn onto biochar BC 2+ In comparison, the ZIF8 / LDH biochar composite adsorbents prepared by secondary loading in Examples 2 and 3 showed better removal effects on dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR) than those prepared by primary loading in Example 1. As shown in Table 1, the BC / ZIF8 / LDH-7 prepared in Example 2 exhibited the best removal effects on dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR), with removal rates of 96% for dimethylamine (DMA), 93% for diethylamine (DEA), and 91% for pyrrolidine (PYR). By loading nano-zinc ions onto biochar and derivatizing them into ZIF / BC, and then synthesizing LDH / ZIF / BC based on the synthesized ZIF / BC, in-situ synthesis of LDH was ensured. The adsorbent was not a mixture of LDH, ZIF, and LDH / BC, possessing a specific surface area and micropore size not found in LDH / BC, enabling selective adsorption of small molecule pollutants. Furthermore, the material's surface defects, abundant active sites, and good chemical stability improved its adsorption performance. Comparing Examples 2 and 3, the secondary loading of Zn... 2+ Increasing the dosage of nitrate and 2-methylimidazole did not improve the Zn loading.2+ The amount is insufficient to form effective composite sites for Ni on biochar BC. 3+ The formation of effective metal-organic framework materials (MOFs) allows for more effective adsorption of nitrogen-containing disinfection byproducts in wastewater.

[0152] Analysis of Examples 1-3 and Comparative Example 1 shows that metal-organic framework (MOF) materials BC / ZIF8 and BC / ZIF67 were selected for in-situ conversion to LDH, respectively. Figure 1 As shown, the ZIF8 characteristic peaks in the BC / ZIF8 / LDH prepared in Examples 1-3 are clearly visible, indicating high crystallinity. Furthermore, the diffraction peaks at 12°, 24°, 34°, and 60° are clearly visible, corresponding to the (003), (006), (012), and (110) crystal planes of a typical hydrotalcite phase, indicating that ZIF8 was partially converted into LDH. The XRD pattern of the BC / ZIF67 / LDH prepared in Comparative Example 1 shows a carbon diffraction peak at 21.5°, while the ZIF67 diffraction peak is incomplete, indicating an indistinct crystal structure. This demonstrates that under the same conditions, ZIF8 loading and in-situ conversion are more effective, resulting in better removal rates of dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR in Examples 1-3 compared to Comparative Example 1, as shown in Table 1.

[0153] The analysis of Examples 1 and Comparative Examples 3-6, which varied the type of nitrate during LDH conversion to investigate the influence of different bimetallic materials on the adsorption performance of nitrogen-containing disinfection byproducts, is shown in Table 1. The best removal efficiency for dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR) was observed when ZnNi was used as the bimetallic material. This is because ZnNi bimetallic materials, compared to ZnCo, ZnFe, ZnAl, and ZnMg bimetallic materials, have a higher specific surface area and a microporous structure, making them more effective at adsorbing small-molecule disinfection byproducts and their precursors, such as dimethylamine (DMA) and diethylamine (DEA). Compared to other materials containing large molecules, ZnNi bimetallic materials achieve better selective adsorption. Nitrosamine precursors are mainly adsorbed through electrostatic attraction, hydrogen bonding, and complexation. Ni... 2+ The complexation of N with nitrogen on the nitrogen-containing pollutant framework plays a major role, therefore ZnNi bimetallic material is selected as the best composite material.

[0154] To investigate the synthesis conditions of BC / ZIF8 and BC / ZIF8 / LDH, Examples 1-3 and Comparative Examples 2 and 7 were analyzed. The effects of BC-ZIF8-2 prepared in Example 1, BC-ZIF8-3 prepared in Example 2, BC-ZIF8-5 prepared in Example 3, BC-ZIF8-1 prepared in Comparative Example 2, and BC-ZIF8-4 prepared in Comparative Example 7 on Zn were characterized. 2+The loading amounts are shown in Table 2, where the amount of zinc acetate was doubled, and the heating condition of the mixture with zinc nitrate and hexamethylenetetramine was increased to 4 hours to make it more fully loaded with zinc ions. This is the case for the BC-ZIF8-3 Zn-loaded preparation prepared in Example 2. 2+ The amount reached a maximum of 28.853%, therefore there were many metal sites, resulting in a greater amount of LDH being converted in situ. After synthesizing ZIF / LDH, as... Figure 2 The SEM images show that the surface morphology of biochar BC is relatively irregular. The ZIF8 crystals exhibit a characteristic rhombic dodecahedral structure with uniform size distribution. LDH has an ultrathin nanosheet crystalline porous silver ear-like structure, with ZIF8 crystals uniformly inserted into the silver ear-like nanosheets of LDH. Furthermore, LDH has a higher conversion rate, a larger specific surface area, and a microporous structure. Figure 5 As shown in the Raman spectroscopy analysis, the D band signal represents disordered carbon, and the G band represents graphitized carbon. The D band can be attributed to defects or partially chaotic (D-band) properties of carbon. The intensities of the G and D bands are often used as quantitative values ​​to understand defect barriers; larger values ​​indicate more internal defects and a greater degree of disorder in the sample. The I band of BC / ZIF8 / LDH-7 prepared in Example 2... D / I G =1.09, demonstrating that the material has abundant surface defects and active sites, enhancing its removal efficiency for dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR; Figure 3 The BC / ZIF8-3 prepared in Example 2 showed an uneven pore size distribution, with 2-3 nm pores dominating. Further conversion to BC / ZIF8 / LDH-7 resulted in a significant decrease in pore size, a significant increase in the proportion of 2-3 nm pores, and a more uniform pore size distribution, thus enhancing the selectivity for dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR. Figure 6 As shown in Cl - NO3 - HCO3 - SO4 2- and PO4 3- Even in the presence of these substances, the removal rates of dimethylamine (DMA), diethylamine (DEA), and pyrrolidine (PYR) remained around 90%. Therefore, the ZIF8 / LDH-loaded biochar composite adsorbent prepared in Example 2 showed the best removal efficiency for these substances. Example 3 reduced the amounts of dimethylimidazole and nickel nitrate. Figure 1 The BC / ZIF8 / LDH-9 prepared in Example 3 shows a reduction in dimethylimidazole and nickel nitrate, and the diffraction peak of LDH is basically not visible, indicating a low conversion amount.

[0155] Table 2. BC-ZIF8 synthesized under different conditions for Zn 2+ load

[0156] Material Znwt% BC / ZIF8-1 8.40％ BC / ZIF8-2 9.08％ BC / ZIF8-3 28.85％ BC / ZIF8-4 9.20％ BC / ZIF8-5 8.63％

[0157] Example 1 lacks further loading of Zn through soaking and heating. 2+ ,like Figure 2 SEM images show that the ZIF8 and LDH nanosheets of BC / ZIF8 / LDH-2 are unevenly formed, with few surface defects and active centers, resulting in poor selectivity and removal of dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR.

[0158] Changing the solvent for the BC-ZIF8-1 zinc acetate prepared in Comparative Example 2 to a solvent containing 50% (v / v) ethanol had little effect on the results, but changing the amount of zinc acetate to 0.01 mmol and Zn 2+ With low load, ZIF8 formation is uneven and limited, such as... Figure 2 SEM images show that the ZIF8 and LDH nanosheets in the composite material BC / ZIF8 / LDH-1 are unevenly formed, with few surface defects and active centers, resulting in poor selectivity and removal of dimethylamine DMA, diethylamine DEA, and pyrrolidine PYR.

[0159] Comparative Example 7 changed the conditions of 60°C water bath stirring and 40°C aging, and only soaked in zinc acetate solution for 1 hour, such as Figure 2 SEM images show that the layered LDH and the dodecahedral ZIF8 in BC / ZIF8 / LDH-8 exist independently. ZIF8 does not insert into the layered structure of LDH, resulting in a reduction in specific surface area and active sites. Therefore, the selectivity and removal effect on dimethylamine DMA, diethylamine DEA and pyrrolidine PYR are generally poor.

Claims

1. An application of a ZIF / LDH biochar composite adsorbent in removing nitrogen-containing disinfection byproducts (N-DBPs) precursors from water, characterized in that, The preparation method of the ZIF / LDH-loaded biochar composite adsorbent includes the following steps: (1) The corn stalks were mixed with alkali, calcined, washed and dried to obtain biochar BC; (2) The above biochar BC and acetate were mixed in a mass ratio of 1:0.37-0.74, washed, dried and calcined, then mixed with 2-methylimidazole, aged and then washed and dried to obtain BC / ZIF. The mass ratio of biochar BC to 2-methylimidazole was 1:3.83-5.

47. (3) Immerse the above BC / ZIF in nitrate solution, the mass ratio of BC / ZIF to nitrate is 1:20-50, stir and let stand, then wash and dry to obtain BC / ZIF8 / LDH composite adsorbent; The acetate in step (2) is cobalt acetate or zinc acetate; In step (3), the nitrate is one of the following: cobalt nitrate Co(NO3)2·6H2O, zinc nitrate Zn(NO3)2·6H2O, nickel nitrate Ni(NO3)2·6H2O, magnesium nitrate Mg(NO3)2·6H2O, iron nitrate Fe(NO3)3·9H2O, and aluminum nitrate Al(NO3)3·9H2O.

2. The application of the ZIF / LDH biochar composite adsorbent according to claim 1 in removing nitrogen-containing disinfection byproducts (N-DBPs) precursors from water, characterized in that, Step (1) includes the following steps: (11) After washing and crushing the corn stalks with deionized water at room temperature, screen them into 200-250 mesh particles; (12) Mix the corn stalks with alkali to obtain a mixture; (13) Calcine the above mixture in a muffle furnace at 300-500℃; (14) Immerse the calcined product in hydrochloric acid solution, stir, separate, and wash until the pH of the supernatant is neutral; (15) After drying the powder, place it in a zinc chloride solution, stir, separate, wash until the pH of the supernatant is neutral, and then dry. (16) Calcination at 500-900℃ under nitrogen protection; (17) The biochar BC was obtained by washing with ethanol and deionized water 3-5 times and freeze-drying.

3. The application of the ZIF / LDH biochar composite adsorbent according to claim 1 or 2 in removing nitrogen-containing disinfection byproducts (N-DBPs) precursors from water, characterized in that... The alkali used in step (1) is sodium bicarbonate.

4. The application of the ZIF / LDH biochar composite adsorbent according to claim 1 in removing nitrogen-containing disinfection byproducts N-DBPs precursors from water, characterized in that, Step (2) includes the following steps: (21) Mix biochar BC and acetate in a mass ratio of 1:0.37-0.74, stir in a water bath at 60°C, and age at 40°C; (22) Separate, wash 3-5 times and then dry; (23) Calcination at 300℃ for 20-30 min under nitrogen protection; (24) Wash 3-5 times, freeze dry to obtain freeze-dried powder; (25) The above freeze-dried powder was immersed in a certain concentration of 2-methylimidazole and stirred. The mass ratio of the freeze-dried powder to 2-methylimidazole was 1:3.83-5.

47. The powder was aged for 12-24 hours and then separated. (26) Wash 3-5 times and dry to obtain BC / ZIF8.

5. The application of the ZIF / LDH biochar composite adsorbent according to claim 1 or 4 in removing nitrogen-containing disinfection byproducts N-DBPs precursors from water, characterized in that, Step (2) further includes immersing the dried powder of calcined biochar BC and acetate mixture in zinc nitrate hexahydrate Zn(NO3)2·6(H2O) and hexamethylenetetramine C6H2O. 12 The reaction was carried out by heating in a mixed solution of N4 to secondary loading of zinc ions on biochar BC, and the mass ratio of lyophilized powder to zinc nitrate and hexamethylenetetramine was 1:4.26:

2.

6. The application of the ZIF / LDH biochar composite adsorbent according to claim 1 or 4 in removing nitrogen-containing disinfection byproducts (N-DBPs) precursors from water, characterized in that, The solvent for the acetate in step (2) is 50 vol% ethanol or deionized water.

7. The application of the ZIF / LDH biochar composite adsorbent according to claim 1 in removing nitrogen-containing disinfection byproducts N-DBPs precursors from water, characterized in that, In step (3), the solvent for nitrate is 33% ethanol.

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