Activated carbon material, method for preparing the same, and use thereof

Abstract

The application discloses an activated carbon material and a preparation method and application thereof, and belongs to the technical field of water pollution control and aquaculture environmental protection. The preparation method of the activated carbon material comprises the following steps: mixing biomass and a nitrogen-containing precursor, and then performing a hydrothermal reaction to obtain a hydrothermal carbon precursor; mixing the hydrothermal carbon precursor and an activating agent, and carbonizing the mixture under an inert atmosphere to obtain a carbonized product; and performing acid pickling on the carbonized product to obtain the activated carbon material. The activated carbon material prepared by the application has a large specific surface area, rich pores and a surface rich in active functional groups, and exhibits high capacity and fast speed adsorption characteristics for organic matters such as diazepam.

Description

Technical Field

[0001] This invention relates to the fields of water pollution control and environmental protection technology in aquaculture, and in particular to an activated carbon material, its preparation method, and its application. Background Technology

[0002] Diazepam is a common benzodiazepine sedative-tranquilizer. It is structurally stable and difficult to biodegrade, and is considered one of the persistent organic pollutants (POPs). Its environmental residues have received widespread attention in recent years. Studies have found residues of diazepam and its metabolites in fish and water bodies in aquaculture environments. Reports indicate that diazepam concentrations in fishponds in aquaculture farms can reach 5.56–391 ng·L⁻¹. -1 Adding diazepam to feed is considered a major cause of drug residues in aquatic products. Once diazepam enters aquaculture water, it is ingested by fish, potentially altering their behavior and physiology (e.g., making them more active or inhibiting reproduction), and can also be transmitted through the food chain, posing ecological risks.

[0003] Currently, there is a lack of effective treatment methods for such drug pollution in static water bodies such as aquaculture ponds. Conventional biodegradation and natural dilution are not very effective for treating persistent organic pollutants like diazepam, with removal rates ranging from only 16% to 83%. In practical engineering, advanced treatment processes such as advanced oxidation and activated carbon adsorption are usually required to achieve higher removal efficiency. Studies have shown that combining biological treatment, photochemical oxidation, and activated carbon adsorption can increase the diazepam removal rate to 99.99%. However, in non-circulating aquaculture pond environments, it is difficult to deploy complex water treatment systems. Generally, water is changed periodically or the pond water is discharged into a sewage treatment system, which easily leads to water waste and pollution transfer. Moreover, diazepam may accumulate in the sediment at the bottom of the pond, leaving long-term environmental hazards. Although commercially available powdered or granular activated carbon can be used to remove organic pollutants in water treatment, its raw materials are mostly coal or coconut shells, which are costly and difficult to recover after being added to the water body. Resin adsorbents (such as macroporous adsorption resins) have a certain removal effect on some drugs, but they suffer from problems such as insufficient selectivity, high cost, and slow diffusion rate in static water. C is commonly used in laboratories. 18 Hydrophobic materials such as silica gel can be used to enrich and extract diazepam, but they are not suitable for direct addition to large volumes of water. Therefore, there is an urgent need for a low-cost, high-efficiency, and easily recyclable adsorbent material specifically designed for the removal of trace drug residues such as diazepam in static aquaculture environments. Summary of the Invention

[0004] The purpose of this invention is to provide an activated carbon material (environmentally functional material), its preparation method, and its application, in order to solve the problems existing in the prior art. The activated carbon material of this invention (i.e., nitrogen-doped activated carbon adsorbent material) can be used to efficiently remove diazepam residues from aquaculture water bodies (especially non-circulating static water bodies such as recreational fishing ponds).

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention: a method for preparing activated carbon material, comprising the following steps: Biomass is mixed with nitrogen-containing precursors and then subjected to a hydrothermal reaction to obtain hydrothermal carbon precursors. The hydrothermal carbon precursor was mixed with an activator and carbonized under an inert atmosphere to obtain the carbonized product. The activated carbon material is obtained by acid washing of the carbonization product.

[0006] Preferably, the biomass includes shrimp shells (crayfish shells) with an ash content of <1 wt.%.

[0007] Crayfish shells are a waste product from aquatic product processing, rich in bio-polysaccharides (mainly chitin) and proteins, as well as approximately 5 wt.% calcium. Chitin molecules contain a large number of amino and amide groups (containing nitrogen), which can be partially retained as nitrogen heteroatoms in the carbon material after high-temperature carbonization. Therefore, preparing activated carbon from crayfish shells not only achieves waste resource utilization, but the resulting carbon material also naturally possesses certain nitrogen-doped characteristics, exhibiting excellent adsorption performance for polar organic pollutants.

[0008] Preferably, the mass ratio of biomass to nitrogen-containing precursor is 1:0.5 to 1:1.

[0009] Preferably, the hydrothermal reaction is carried out at a temperature of 180°C for 8 to 12 hours.

[0010] Preferably, the nitrogen-containing precursor includes melamine or urea.

[0011] Preferably, the mass ratio of the activator to the hydrothermal carbon precursor is 1:0.5 to 1:2; The activator includes potassium hydroxide; The carbonization heating rate is 3-20℃ / min, the temperature is 700-800℃, and the time is 1-2 hours; The pickling process involves soaking in a dilute hydrochloric acid solution with a concentration of 0.1–1 M for 6–48 hours.

[0012] Traditional activated carbon preparation often employs a single-step physical or chemical activation process. However, this invention combines hydrothermal reaction with high-temperature carbonization. The hydrothermal reaction promotes the reaction between biomass and nitrogen-containing precursors, increasing the doping amount of nitrogen and other heteroatoms. The high-temperature carbonization utilizes the dual effects of a small amount of CaCO3 template (<1 wt.%) naturally present in shrimp shells and the chemical activation of KOH to construct a pore system that combines micropores and mesopores. This results in activated carbon materials with both hierarchical pore structure and high heteroatom content, significantly improving the adsorption kinetics and capacity utilization of the material.

[0013] The second technical solution of the present invention: an activated carbon material prepared by the above preparation method.

[0014] The third technical solution of the present invention: an application of the above-mentioned activated carbon material as an adsorbent for recalcitrant organic pollutants.

[0015] Preferably, the recalcitrant organic pollutant includes diazepam.

[0016] The fourth technical solution of the present invention: a method for removing recalcitrant organic pollutants from pond water, comprising the following steps: The activated carbon material was made into granules, filled into porous containers, and added to pond water to adsorb recalcitrant organic pollutants.

[0017] Preferably, the pond water body includes either a circulating dynamic water body or a non-circulating static water body.

[0018] Preferably, the porous container includes a porous fiber bag (mesh bag), a suspended six-cylinder, or a floating basket.

[0019] Unlike traditional water treatment methods that require water pumps for circulation, this invention achieves purification of static water bodies without the need for pumps, using activated carbon materials prepared according to this invention. Specifically, water purification is carried out in situ through methods such as hanging mesh bags. This method balances adsorption efficiency and ease of operation for pollutant removal, solving the problem of difficult adsorbent addition and recovery, and has strong practical value and scalability.

[0020] The activated carbon material prepared by this invention has the following advantages: (1) Highly efficient removal of diazepam residue: The activated carbon material prepared by this invention has a rapid and efficient adsorption and removal capacity for trace diazepam in water, with a removal rate of over 90%, which can reduce the concentration of diazepam in water to a safe level (below the detection limit or ecological risk threshold), thus solving the defect of existing technologies that make it difficult to efficiently remove diazepam residue.

[0021] (2) Utilizing waste resources and reducing costs: The activated carbon material of this invention uses shrimp shells, aquatic waste, as a carbon source, turning waste into treasure; and shrimp shells are rich in natural nitrogen sources, which are not only cheaper and easier to obtain than traditional coal / coconut shell carbon sources, but also have nitrogen doping characteristics after carbonization; this waste resource utilization method has dual significance of environmental protection and economy (can reduce material preparation costs), achieving the "two benefits in one" of material preparation and waste reduction, and is suitable for large-scale water treatment.

[0022] (3) Excellent material performance: In the preparation of activated carbon materials, nitrogen-containing precursors are incorporated into the process to achieve nitrogen doping. The use of hydrothermal reaction + carbonization technology can endow the material with a hierarchical porous structure. Under the synergistic effect of nitrogen doping and hierarchical porous structure, the activated carbon material can be endowed with a higher specific surface area and more polar surface functional groups, thus making it superior to commercially available activated carbon and macroporous resins in terms of adsorption capacity and rate. Furthermore, the activated carbon material prepared by this invention can maintain good adsorption performance under conventional aquaculture water conditions.

[0023] (4) Easy to use and recyclable: The activated carbon material of the present invention is easy to use. It can be directly put into fish ponds for in-situ purification and can be easily recycled from the water. The recycled saturated adsorbent can be directly burned for harmless treatment or buried for natural degradation without causing secondary pollution.

[0024] The method of this invention is technically feasible, economically reasonable, and environmentally friendly. While effectively solving the problem of diazepam residue pollution in aquaculture water environments, it can also ensure the quality of aquatic products and ecological safety.

[0025] The present invention discloses the following technical effects: (1) The activated carbon material prepared by the present invention has a large specific surface area, abundant pores and surface rich in active functional groups, and exhibits high capacity and fast adsorption characteristics for organic substances such as diazepam.

[0026] (2) The activated carbon material prepared by this invention has significantly higher adsorption capacity, removal rate, and removal speed for diazepam than existing similar materials; the Qmax of commercially available activated carbon is approximately 10 mg·g. -1 The activated carbon material prepared by this invention can reach approximately 16 mg·g. -1 The activated carbon material of this invention exhibits an extremely high removal rate (removal rate >95%) for trace amounts (10 ppb) of diazepam, significantly higher than the 80-90% of commercially available activated carbon. Using the activated carbon material of this invention, the concentration of diazepam in water can be reduced to ng·L⁻¹. -1 This significantly reduces its potential risks to aquatic organisms and human health.

[0027] Compared with commercially available activated carbon, the activated carbon material of this invention has a saturated adsorption capacity increased by more than 50%, and an adsorption equilibrium time shortened by more than half. Compared with high-priced resins, it also exhibits higher removal rates and faster kinetic performance. For an initial concentration of 1 mg·L⁻¹... -1 In polluted water samples, the activated carbon material of this invention can adsorb more (commercially available activated carbon, macroporous resin, C) per unit mass (per gram) than the control. 18 The dosage of tens of milligrams of diazepam demonstrates its superior performance.

[0028] (2) When using the activated carbon material prepared by the present invention to purify non-circulating static water bodies, there is no need to use a water pump for circulation. In-situ water purification can be achieved by means of hanging net bags, which not only greatly simplifies the operation process, but also solves the problem of difficult adsorbent addition and recovery.

[0029] (3) The activated carbon material of the present invention uses shrimp shells, which are widely available and inexpensive (available from a large amount of aquaculture and catering waste), as raw materials. This not only reduces production costs (the cost per ton of activated carbon is much lower than that of traditional coal or coconut shell activated carbon), but also realizes the high-value utilization of agricultural by-products. It has obvious economic feasibility and is suitable for large-scale preparation and promotion.

[0030] (4) Compared with complicated water treatment systems (such as membrane filtration, ozone oxidation, etc.), the application of the activated carbon material of the present invention only requires placing it in the water body, without the need for electrical equipment or complicated pipelines. Therefore, it can be conveniently used in remote aquaculture areas and scattered small fish ponds.

[0031] The activated carbon material of this invention, packaged in a net bag and then released into the water, will not affect the normal activity of fish or the aquatic landscape; maintenance only requires periodic replacement of the net bag, making it a low-tech process. Furthermore, the activated carbon material prepared by this invention exhibits good stability, does not release harmful components in water, does not decompose itself, has no side effects on the water body, and is safe and reliable.

[0032] (5) The activated carbon material of the present invention effectively solves the hidden risks caused by the application of diazepam, improves the safety of water use in recreational fisheries and the quality of aquatic products, and has significant social and ecological benefits. Its successful application can serve as a demonstration to promote the development of more waste-based functional materials in agricultural environmental governance. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram illustrating the application of activated carbon materials in fishponds. Figure 2 This is a schematic diagram of the preparation process of the activated carbon material in Example 1; Figure 3 The adsorption-desorption isotherm of the activated carbon material prepared in Example 1; Figure 4 The pore size distribution curve of the activated carbon material prepared in Example 1; Figure 5 The Fourier transform infrared (FTIR) spectrum of the activated carbon material prepared in Example 1 is shown below. Figure 6 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the activated carbon material prepared in Example 1, where A is the high-resolution 1s spectrum of C, B is the high-resolution 1s spectrum of N, C is the high-resolution 1s spectrum of O, and D is the total elemental spectrum. Figure 7 The zero-charge point (pHpzc) curve on the surface of the activated carbon material prepared in Example 1 is shown. Figure 8 The graph shows the adsorption rate curves for different adsorbents, where A represents the activated carbon material (NC) prepared in Example 1, B represents commercially available activated carbon (C), C represents macroporous resin, and D represents C... 18 ; Figure 9 The figures show isothermal adsorption curves for different adsorbents, where A represents the activated carbon material (NC) prepared in Example 1, B represents commercially available activated carbon (C), C represents macroporous resin, and D represents C... 18 ; Figure 10 The figures show the adsorption kinetics curves for different adsorbents, where A is the activated carbon material (NC) prepared in Example 1, B is commercially available activated carbon (C), C is macroporous resin, and D is C... 18 . Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0038] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0041] In a first aspect, the present invention provides a method for preparing activated carbon material, comprising the following steps: (1) Raw material pretreatment: Fresh or dried crayfish shells are selected as biomass. The shells are thoroughly washed with distilled water to remove residual organic impurities (such as attached meat). Then, they are soaked in a dilute hydrochloric acid solution (5-10 wt.% HCl solution) for 2-3 hours for demineralization. The shells are washed with water until neutral and dried at 60-80℃ to obtain pretreated biomass.

[0042] The pretreated shrimp shells are clean, light-colored solids, mainly composed of organic matter (chitin and protein), with an inorganic salt content (as ash) of less than 1 wt.%, which can provide uniform raw materials for subsequent preparation.

[0043] (2) Preparation of precursors by hydrothermal reaction: The pretreated biomass is pulverized (particle size 20-60 mesh) to obtain pretreated biomass powder; Pretreated biomass powder was mixed with nitrogen-containing precursors, and deionized water was added (the liquid-solid ratio was controlled at 10 mL: 1 g). After mixing evenly, the mixture was placed in a stainless steel high-pressure reactor, sealed, and subjected to hydrothermal reaction. This caused partial hydrolysis and carbonization of the organic matter, which then reacted with the nitrogen-containing precursors. After the hydrothermal reaction, the mixture was cooled, filtered, washed, and dried at 80–100 °C to obtain the hydrothermal carbon precursor.

[0044] (3) High-temperature carbonization and activation: After the hydrothermal carbon precursor and activator are mixed evenly, they are placed in a ceramic boat in a tube furnace and carbonized under an inert atmosphere (high-purity nitrogen). The mixture is then naturally cooled to room temperature to obtain a black carbonized product.

[0045] (4) Rinsing and drying: The carbonized product is soaked in a dilute hydrochloric acid solution to dissolve the inorganic salts (such as K2CO3, CaO / CaCO3, etc.) generated during the reaction. Then, it is repeatedly washed with distilled water until the pH of the washing solution is close to neutral. Finally, it is filtered and dried at 105°C to constant weight to obtain a black powdery activated carbon material (i.e., adsorbent).

[0046] Preferably, in step (2), the nitrogen-containing precursor is a compound that can provide nitrogen, including melamine or urea; among which melamine is inexpensive, abundant, and has a nitrogen content as high as 67%, which is conducive to the incorporation of nitrogen atoms into the carbon skeleton; The mass ratio of pretreated biomass powder to nitrogen-containing precursor is 1:0.5 to 1:1; The hydrothermal reaction was carried out at a temperature of 180℃ for 8–12 hours.

[0047] Through hydrothermal reaction, a brownish-black hydrothermal carbon precursor can be obtained, in which the biomass components of the shrimp shell have been partially carbonized and nitrogen-containing functional groups have been introduced. For example, under hydrothermal conditions, melamine can decompose to generate active substances such as ammonia, which can combine with carbon groups on the surface of the carbon precursor, helping to initially introduce nitrogen heteroatoms and form nitrogen-containing functional groups.

[0048] Preferably, in step (3), the mass ratio of the activator to the hydrothermal carbon precursor is 1:0.5 to 1:2; the activator includes potassium hydroxide (KOH). The carbonization heating rate is 3–20℃ / min, the temperature is 700–800℃, and the time is 1–2 hours.

[0049] Using potassium hydroxide as an activator can effectively increase the specific surface area and porosity of carbon materials.

[0050] At high temperatures, the organic matter in the hydrothermal carbon precursor prepared from shrimp shells undergoes pyrolysis and carbonization, forming a carbonaceous framework. Simultaneously, KOH reacts with carbon to produce products such as potassium carbonate, creating abundant micropores within the carbon framework. The residual CaCO3 partially decomposes into CaO at high temperatures, also acting as a hard template to support the pore structure.

[0051] Preferably, in step (4), the soaking time is 6 to 48 hours and the concentration of the dilute hydrochloric acid solution is 0.1 to 1 M.

[0052] Preferably, step (4) further includes grinding and sieving the activated carbon material to a particle size of 20-80 mesh to facilitate subsequent packaging and use.

[0053] This invention employs a dual process of "high-pressure hydrothermal synthesis + high-temperature carbonization" to introduce nitrogen heteroatoms into carbon materials and construct a hierarchical porous structure. This two-step method utilizes a hydrothermal reaction to promote heteroatom incorporation, followed by high-temperature activation to generate abundant pores. Compared to traditional single-step preparation, this method achieves higher doping content and a more developed pore structure. For the specific preparation route, see [link to details]. Figure 2 .

[0054] In a second aspect, the present invention provides an activated carbon material prepared by the above-described preparation method.

[0055] In a third aspect, the present invention provides an application of the above-mentioned activated carbon material as an adsorbent for recalcitrant organic pollutants.

[0056] Preferred recalcitrant organic pollutants include diazepam.

[0057] In a fourth aspect, this invention provides a method for removing recalcitrant organic pollutants from aquaculture water, comprising the following steps: The activated carbon material was made into granules, filled into porous containers, and added to aquaculture water to adsorb recalcitrant organic pollutants.

[0058] Preferred recalcitrant organic pollutants include diazepam.

[0059] Preferably, activated carbon materials are mainly used in non-circulating aquaculture ponds, especially in static water bodies such as recreational fishing ponds where frequent water changes are not advisable. To ensure the optimal performance of activated carbon materials in practical scenarios, a reasonable usage process needs to be designed, including the application method, action cycle, and recycling / replacement methods (e.g., ...). Figure 1 (The illustration shows an application diagram of a fishpond). Specific steps include: (1) Placement method: The above activated carbon material is made into granules with a particle size of 0.5 to 2 mm to obtain granular carbon; the granular carbon is filled into a porous container made of water-resistant material. The filling amount is determined according to the pond water volume and pollution level, such as adding 50 to 100 g of granular carbon per cubic meter of water; then the porous container containing granular carbon is placed in the pond and suspended at an appropriate depth below the water surface (such as 0.5 m from the water surface), or fixed at a location with more water flow, such as the pond inlet or the outlet of the aerator pump, to increase the contact with water.

[0060] Making activated carbon materials into granules with a particle size of 0.5–2 mm facilitates their use and recycling. Compared to directly sprinkling activated carbon material powder, using porous containers for filling can prevent the activated carbon material from being lost, facilitate recycling, and does not affect water transparency or fish activity.

[0061] (2) Action cycle: After being put into use, the granular carbon made of activated carbon material will immediately begin to adsorb recalcitrant organic pollutants (such as diazepam molecules) in the water.

[0062] The activated carbon material of this invention can reach adsorption equilibrium for trace amounts of diazepam within several hours, for example, with an initial concentration of over 100 ng·L⁻¹. -1 At that time, the removal rate can exceed 90% within 1-2 days, and the residue in the water is reduced to several ng·L. -1 Even below the detection limit; if the initial contamination is higher (μg·L -1 (The magnitude of the substance will be slightly longer, but it can generally be basically achieved within 24 to 48 hours, i.e., less than 10 ng·L). -1 This demonstrates that continuous application for 1-2 weeks in actual ponds (such as fishponds) can significantly reduce the concentration of diazepam in the water. Porous containers filled with granular activated carbon made from the activated carbon material of this invention can be placed in water for extended periods to continuously purify the water. When new diazepam enters (e.g., through external injection or release by fish metabolism), the adsorbent can immediately capture it, thus stabilizing and controlling water quality. For recreational fishing ponds, porous containers filled with granular activated carbon can be continuously placed to purify the water after the pond closes or on non-fishing days, and removed when fishermen are fishing to avoid disturbance.

[0063] (3) Recycling and replacement method: When the active sites of granular carbon made of activated carbon material gradually become saturated, the adsorption efficiency decreases, and it is necessary to replace it.

[0064] Depending on the pollution level, the effective lifespan of a batch of materials can range from several weeks to several months. In practical applications, the need for replacement can be determined by monitoring the concentration of residual recalcitrant organic pollutants (such as diazepam) in the water: if the concentration of diazepam in the water begins to rebound and increase, it indicates that the adsorbent is approaching saturation and should be replaced promptly. During use, it is necessary to prevent the adsorbent from scattering to the bottom of the pond or being ingested by fish. Therefore, it is recommended to fix the position of the porous container and choose a sufficiently small pore size to prevent granular carbon leakage. The recycled and replaced waste activated carbon material should be properly disposed of to avoid direct disposal and secondary pollution; if it is not intended to be reused, it can be handed over to a qualified unit for harmless disposal (such as high-temperature incineration) to destroy the adsorbed diazepam and other pollutants.

[0065] Preferred porous containers made of water-resistant materials include porous fiber bags (mesh bags), suspended six-cylinder containers, or floating baskets.

[0066] Through the above process design, the activated carbon material of this invention can be safely and efficiently applied to actual aquaculture ponds to achieve on-site water purification. Moreover, this method of use is simple and easy to implement, requires no complex equipment, and is inexpensive, making it very suitable for aquaculture farmers and recreational fishery practitioners.

[0067] Example 1 A method for preparing activated carbon (NC) material: (1) Raw material pretreatment: Fresh crayfish shells were selected as biomass. The shells were thoroughly washed with distilled water to remove residual organic impurities (such as attached meat). Then, they were soaked in dilute hydrochloric acid solution (10 wt.% HCl solution) for 2 h for demineralization. The shells were washed with water until neutral and dried at 80℃ for 12 h to constant weight to obtain pretreated biomass (ash content <1 wt.%).

[0068] (2) Preparation of precursors by hydrothermal reaction: The pretreated biomass is pulverized (particle size 20-60 mesh) to obtain pretreated biomass powder; Pretreated biomass powder and nitrogen-containing precursor (melamine) were mixed at a mass ratio of 1:1, and deionized water was added (the liquid-solid ratio was controlled at 10 mL: 1 g). After mixing evenly, the mixture was placed in a stainless steel high-pressure reactor, sealed, and subjected to hydrothermal reaction (temperature 180℃, time 12 hours). After hydrothermal reaction, the mixture was cooled, filtered, washed, and dried at 100℃ to obtain hydrothermal carbon precursor.

[0069] (3) High-temperature carbonization and activation: The hydrothermal carbon precursor and potassium hydroxide were mixed evenly at a mass ratio of 1:2 and placed in a ceramic boat in a tube furnace. The mixture was then carbonized under an inert atmosphere (high-purity nitrogen) (heating rate of 5℃ / min, temperature of 800℃, time of 1 hour) and allowed to cool naturally to room temperature to obtain a black carbonized product.

[0070] (4) Rinsing and drying: The carbonized product was soaked in a 0.2M dilute hydrochloric acid solution for 24 hours, then repeatedly washed with distilled water until the pH of the wash solution was close to neutral. Finally, it was filtered and dried at 105℃ to constant weight to obtain a black powdery activated carbon material.

[0071] Comparative Example 1 Same as Example 1, except that the shrimp shells are replaced with crab shells.

[0072] The adsorption effect decreased significantly after replacement. This is because the microstructure and proportion of chitin, protein, and inorganic salts in shrimp and crab shells differ, resulting in different pore sizes and distributions in the final carbon material even under the same activation process. Diazepam, with a molecular size of approximately 0.8 nm, is a typical small-to-medium molecule organic compound. Activated carbon's physical adsorption of diazepam relies primarily on its well-developed microporous structure (pore size < 2 nm). The large specific surface area provided by the micropores and the superimposed forces of the pore walls are key to efficient adsorption; a reduction in the proportion of micropores will hinder adsorption.

[0073] Meanwhile, the difference in biopolymer composition between crab and shrimp shells leads to differences in the type and quantity of heteroatoms (such as N and O) doping on the surface of the final carbon material. This change is unfavorable for generating specific electron-donating and electron-accepting interactions with diazepam molecules, thus resulting in a decrease in adsorption capacity.

[0074] Comparative Example 2 Same as Example 1, except that step (4) dilute hydrochloric acid soaking step is omitted. This operation significantly reduces the adsorption effect of activated carbon on diazepam.

[0075] After the acid washing step, residual carbonates and other salts, as well as metal oxide particles, physically clog micropores and mesopores, reducing the specific surface area and pore volume, preventing diazepam molecules from entering the pores. At the same time, the active sites on the activated carbon surface are shielded, reducing the π-π interaction and hydrogen bonding capacity, and weakening both the non-polar and polar interactions between diazepam molecules and the carbon skeleton. Impurities remaining on the surface of un-acid-washed activated carbon powder may dissolve during actual application, causing secondary pollution and interfering with the stability of the adsorption process.

[0076] Comparative Example 3 Similar to Example 1, the only difference is that the high-temperature carbonization temperature in step (3) is reduced to 400°C. The adsorption effect of the activated carbon material prepared is far less than that of the activated carbon material prepared in Example 1.

[0077] This is because the high temperature of 700-800℃ is necessary for the potassium hydroxide to react with carbon and violently etch the carbon framework, forming numerous micropores during the activation process. At 400℃, the activation reaction is extremely inefficient, failing to form a well-developed pore structure. Studies have confirmed that higher carbonization temperatures typically produce a richer pore structure. Therefore, materials obtained under these conditions will have a very low specific surface area, fundamentally losing their strong adsorption capacity.

[0078] Furthermore, low-temperature carbonization alters surface functional groups: materials carbonized at lower temperatures may retain more complex oxygen- and nitrogen-containing functional groups from the precursor. If these functional groups are too complex or hydrophilic, they may repel the more hydrophobic diazepam molecules or preferentially adsorb water molecules, thereby weakening the affinity for diazepam.

[0079] Example 1 (1) The adsorption-desorption isotherms and corresponding pore size distribution curves of the activated carbon material prepared in Example 1 are shown in the figure. Figure 3 and Figure 4 .

[0080] from Figure 3 As can be seen, the isotherms exhibit a mixture of Type II and Type IV characteristics, accompanied by a significant hysteresis loop. From... Figure 4As can be seen, the activated carbon material prepared in Example 1 contains both micropores and mesopores.

[0081] (2) The Fourier transform infrared (FTIR) spectrum of the activated carbon material prepared in Example 1 is shown in Figure 1. Figure 5 See Table 1.

[0082] Table 1. Functional groups and annotations corresponding to the Fourier transform infrared spectra of activated carbon materials. (3) The X-ray photoelectron spectroscopy (XPS) spectrum of the activated carbon material prepared in Example 1 is shown in Figure 1. Figure 6 , Figure 6 In the diagram, A is the 1s high-resolution spectrum of C, B is the 1s high-resolution spectrum of N, C is the 1s high-resolution spectrum of O, and D is the total elemental spectrum.

[0083] from Figure 6 As can be seen from the above, the activated carbon material prepared by this invention contains nitrogen element, and the nitrogen has different valence states, indicating the presence of pyridine nitrogen, pyrrole nitrogen, etc.

[0084] (4) The zero charge point (pHpzc) measurement curve of the activated carbon material surface prepared in Example 1 is shown in the figure. Figure 7 The horizontal axis represents the initial pH, and the vertical axis represents the Zeta potential.

[0085] from Figure 7 As can be seen, when the pH is between 5 and 10, the zeta points of the activated carbon material are all negative, while diazepam exists in the form of neutral molecules within this pH range. This indicates that the adsorption does not mainly rely on electrostatic adsorption. Therefore, it shows that the adsorption effect of this material on diazepam is not affected by the pH of the environmental water body, and it has good adaptability and can reliably play a role within the actual water quality range.

[0086] Example 2 (1) Adsorbent: a. Commercially available activated carbon (C) (damads-beta, Aladdin): This refers to conventional commercially available powdered activated carbon (made from coconut shells or coal), representing traditional adsorbents.

[0087] b. Macroporous resin (Resin) (purchased from Tianjin Yunkai Resin Technology Co., Ltd.): Commonly used water treatment adsorption resins (such as Amberlite XAD series macroporous resins or activated carbon fibers) are selected, representing high molecular adsorption materials.

[0088] cC 18 Hydrophobic materials (C) 18 (Agela Technologies): Utilizing silicone bonding C 18Packing material (commonly used in laboratory solid-phase extraction of drugs such as diazepam) represents hydrophobic adsorbents.

[0089] d. Activated carbon material (NC) prepared in Example 1.

[0090] (2) Experimental medium: Prepare simulated polluted water samples, and use pure water to prepare diazepam standard solutions with concentrations set within the typical pollution range (mg·L). -1 The sample size is used for isothermal adsorption and kinetic testing; a low concentration group (μg·L⁻¹) is also included. -1 The magnitude of the sample was used to investigate the removal rate. All experiments were conducted at room temperature (25°C), with the initial pH of the solution at approximately 7.0 under baseline conditions. To investigate the effect of pH, parallel experiments were performed by adjusting the initial pH of the solution to 5.0, 7.0, and 9.0 using buffer solutions, respectively.

[0091] (3) Comparison of isothermal adsorption curves Add 100 mL of diazepam solution (initial concentration 0.1–20 mg / L) to a 250 mL Erlenmeyer flask. -1 Different gradients were selected, and then 0.1 g of different adsorbents were added to each. The mixture was then sealed and shaken to equilibrate for 8 hours. The supernatant was taken and the equilibrium concentration was determined by high performance liquid chromatography (HPLC). The adsorption capacity was calculated, and isothermal adsorption curves for each adsorbent material were plotted (the vertical axis represents the equilibrium adsorption capacity Qc (mg·g)). -1 The horizontal axis represents the equilibrium concentration Ce (mg·L). -1 The maximum adsorption capacity Qmax and adsorption constant K were obtained by fitting the data using the Langmuir model. L Alternatively, the Freundlich model can be used to assess adsorption strength and susceptibility; results are shown in [link to results]. Figure 9 And Table 2, Figure 9 In the diagram, A represents the activated carbon material (NC) prepared in Example 1, B represents commercially available activated carbon (C), C represents macroporous resin, and D represents C... 18 .

[0092] Table 2 NC, Activated Carbon, Macroporous Resin and C 18 Isothermal model fitting parameters for diazepam adsorption from Figure 9 As can be seen from Table 2, the isotherm of NC prepared in Example 1 of this invention is higher than that of each comparative material (C, macroporous resin, C) throughout the entire concentration range. 18 NC exhibits the highest adsorption capacity. The Qmax for diazepam is close to 20 mg / g. -1 Commercially available activated carbon (C) lacks surface heteroatom functional sites, resulting in a Qmax of only 15 mg·g. -1 Left and right; macroporous resin and C 18The material has a lower capacity. And NC's K L The highest value indicates that it has the strongest binding ability to diazepam.

[0093] (4) Adsorption kinetics and adsorption rate comparison: 100 mL of adsorption kinetics was used to adsorb 1 mg·L⁻¹ of adsorption kinetics and adsorption rate comparison. -1 Aqueous solutions of diazepam were mixed with 0.1 g of different adsorbents and stirred in a constant-temperature shaker. Samples were taken at 0.5, 1, 2, 4, and 8 hours after addition, and the residual concentration of diazepam in the solution was determined by rapid filtration. Removal rate (i.e., adsorption rate) versus adsorption capacity curves over time were plotted. The results are shown in [Figure number missing]. Figure 8 and Figure 10 ; Figure 8 In the diagram, A represents the activated carbon material (NC) prepared in Example 1, B represents commercially available activated carbon (C), C represents macroporous resin, and D represents C... 18 ; Figure 10 In the diagram, A represents the activated carbon material (NC) prepared in Example 1, B represents commercially available activated carbon (C), C represents macroporous resin, and D represents C... 18 .

[0094] from Figure 8 and Figure 10 As can be seen, NC can remove most of the diazepam within the first hour, and reaches a removal rate of >95% in about 2 hours; while commercially available activated carbon (C) takes more than 4 hours to approach a similar removal rate; macroporous resin reaches equilibrium more slowly due to diffusion limitations within the pores (requiring more than 12 hours for the removal rate to approach 90%).

[0095] In the initial 0.5–2 hours, the adsorption rate of NC was significantly higher than that of the control material. By fitting the kinetic data to pseudo-first-order and pseudo-second-order models, the rate constants K1 and K2 for each material were obtained, and the results are shown in Table 3.

[0096] Table 3 NC, commercially available activated carbon, macroporous resin and C 18 Quasi-first-order and quasi-second-order dynamic fitting parameters As can be seen from Table 3, NC exhibits the highest pseudo-second-order rate constant K2, indicating its fastest chemisorption rate. This is mainly attributed to the high specific surface area of ​​NC, reaching 598.7887 m². 2 ·g -1 It is significantly larger than that of macroporous resins (480-520 μm). 2 ·g -1 C 18 (400 m) 2 ·g -1 ) and commercially available activated carbon (500 m 2 ·g -1Furthermore, the NC surface is rich in active sites, which can rapidly adsorb and bind diazepam molecules; in contrast, commercially available activated carbon (C) and macroporous resins have weaker interactions with diazepam and smaller adsorption driving forces, resulting in lower rate constants.

[0097] (5) pH adaptability test: The adsorption performance of NC prepared in Example 1 was compared and examined under three conditions: pH=5.0, 7.0, and 9.0. The specific method was to pre-adjust the initial solution pH of the above isothermal or kinetic experiments to the target value, and then conduct the experiments in parallel. The removal rate and adsorption capacity of diazepam at different pH values ​​were measured to evaluate the stability of the material performance.

[0098] The results showed that since diazepam exists mainly in a neutral molecular form within the pH range of 5-9, the adsorption effect of the NC material prepared in Example 1 of this invention did not differ significantly. Under slightly alkaline conditions (pH=9), the NC surface is negatively charged, and the solubility of diazepam decreases, resulting in a slight increase in adsorption capacity. Under acidic conditions (pH=5), the NC surface is positively charged, and some diazepam is protonated into positively charged ions, which generates electrostatic repulsion, slightly reducing the adsorption capacity. However, the overall removal rate still remains high (slightly decreasing from 95% to 90%). Therefore, the NC material prepared in this invention has good adaptability to the pH of environmental water bodies and can reliably function within the actual water quality range. In comparison, the performance of commercially available activated carbon (C) does not change much under different pH conditions (its adsorption mainly relies on hydrophobic interactions), and macroporous resins and C... 18 It is extremely insensitive to pH changes (mainly due to hydrophobic adsorption mechanism), and pH changes have little effect on the adsorption effect. Its adsorption effect is consistently worse than that of NC.

[0099] The comparative experiments above demonstrate that the activated carbon material prepared in Example 1 of this invention significantly outperforms existing materials in key indicators such as diazepam removal rate, adsorption capacity, and adsorption rate. At the same initial concentration, the activated carbon material (NC) prepared in Example 1 can reduce diazepam residues to below the detection limit, while ordinary activated carbon can only reduce them to tens of ng·L⁻¹. -1 In terms of adsorption capacity, NC can reach nearly 20 mg·g. -1 While macroporous resins, etc., only require a few mg / g. -1 In terms of kinetics, NC only needs 2 hours to achieve an adsorption rate close to 100%, completing the purification, while the adsorption rate of the control material only reaches 80%~90%. The above results fully demonstrate that the activated carbon material prepared by this invention can be effectively used for the removal of diazepam residues in aquaculture environments, and these results also provide strong data support for its promotion and application.

[0100] Application Example 1 In-situ application of crayfish shell-based activated carbon in still water ponds for carp (1) Application scheme The "activated carbon filter media hanging bag" method was adopted. Activated carbon granules were filled into water-permeable nylon mesh bags (5 kg per bag), secured with ropes, and then evenly suspended in the water body (approximately 200 cubic meters) around the aerator or near the feeding area in the aquaculture pond. The activated carbon granules were prepared by combining the activated carbon material prepared in Example 1, commercially available activated carbon, macroporous resin, and C... 18 They were made into particles with a diameter of 0.5 to 2 mm.

[0101] The density of activated carbon particles is 0.1 kg / m³. 3 The water body relies on the natural flow of the pond water and the water flow generated by the aerator (one 1.5 kW impeller type, with an oxygenation efficiency of 2 kg O2 / h) to ensure continuous contact between the water and activated carbon particles. Pollutants are adsorbed and removed by the activated carbon particles, and the biofilm formed on the surface of the activated carbon particles also assists in biodegradation.

[0102] Table 4. Performance Data and Description In summary, among the four materials, NC exhibits the highest removal rate, and its raw materials are inexpensive and its preparation process is controllable, making it more suitable for large-scale pond water treatment. It can ensure efficient adsorption while also possessing good economic and environmental friendliness.

[0103] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing an activated carbon material, characterized in that, Includes the following steps: Biomass is mixed with nitrogen-containing precursors and then subjected to a hydrothermal reaction to obtain hydrothermal carbon precursors. The hydrothermal carbon precursor was mixed with an activator and carbonized under an inert atmosphere to obtain the carbonized product. The activated carbon material is obtained by acid washing of the carbonization product.

2. The preparation method according to claim 1, characterized in that, The biomass includes shrimp shells with an ash content of <1 wt.%.

3. The preparation method according to claim 1, characterized in that, The mass ratio of biomass to nitrogen-containing precursor is 1:0.5 to 1:

1.

4. The preparation method according to claim 1, characterized in that, The hydrothermal reaction was carried out at a temperature of 180°C for 8–12 hours.

5. The preparation method according to claim 1, characterized in that, The nitrogen-containing precursors include melamine or urea.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the activator to the hydrothermal carbon precursor is 1:0.5 to 1:2; And / or, the activator includes potassium hydroxide; And / or, the carbonization heating rate is 3-20℃ / min, the temperature is 700-800℃, and the time is 1-2 hours; And / or, the pickling includes soaking in a dilute hydrochloric acid solution with a concentration of 0.1 to 1 M for 6 to 48 hours with stirring.

7. An activated carbon material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the activated carbon material according to claim 7 as an adsorbent for recalcitrant organic pollutants.

9. The application according to claim 8, characterized in that, The recalcitrant organic pollutants include diazepam.

10. A method for removing recalcitrant organic pollutants from aquaculture water, characterized in that, Includes the following steps: The activated carbon material described in any one of claims 1 to 6 is made into granules, filled into a porous container, and added to aquaculture water to adsorb recalcitrant organic pollutants.

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