Full-biomass-based nitrogen and phosphorus co-doped biochar as well as preparation method and application thereof

Abstract

The invention provides full-biomass-based nitrogen-phosphorus co-doped biochar as well as a preparation method and application thereof, aiming at the problems that the adsorption performance is limited due to the fact that a pore structure of traditional biochar is disordered and a surface functional group is single, and environmental pollution is caused by a traditional chemical modification reagent. According to the method, natural cork is used as a carbon substrate, chitin from shrimp shells is used as a nitrogen source, phytic acid extracted from cereal bran is used as a phosphorus source, and efficient modification is realized through a two-step sequential doping process. Firstly, in-situ doping of a nitrogen element is completed in a low-temperature pyrolysis stage, and then precise modification of phosphorus species is achieved in a high-temperature activation stage. According to the method, harmful chemical reagents used in the traditional biochar preparation process are avoided, and the produced biochar has a uniform honeycomb structure, a high specific surface area (1059.17 m < 2 > / g), a large pore volume (1.16 cm < 3 > / g), a good hierarchical porous structure and rich nitrogen-containing, oxygen-containing and phosphorus-containing groups. The TC adsorption capacity and the SMX adsorption capacity can reach 350.72 mg / g and 290.45 mg / g respectively after reaction contact is carried out for 5 min, the TC adsorption capacity and the SMX adsorption capacity are improved by 40 times and 41 times respectively compared with original biochar, and excellent adsorption performance is shown.

Description

Technical Field

[0001] This application relates to the field of biochar materials technology, and in particular to a fully biomass-based nitrogen and phosphorus co-doped biochar, its preparation method, and its application. Background Technology

[0002] With the rapid development of aquaculture and the pharmaceutical industry, the problem of antibiotic residues in the environment has become increasingly prominent. Antibiotics have stable molecular structures, strong chemical stability, and resistance to biodegradation, making them difficult to remove effectively using traditional water treatment methods. Long-term accumulation of antibiotics in the environment not only leads to the spread of antibiotic resistance genes but also poses a potential threat to aquatic ecosystems and human health. Therefore, the development of efficient and sustainable antibiotic pollution control technologies is urgently needed.

[0003] Porous char materials derived from natural biomass are considered a promising environmental remediation material due to their abundant resources, green renewability, and low cost. However, the adsorption performance of traditional biochar is limited by the disordered distribution of its pore structure and the heterogeneity of its chemical composition. Cork, a biomass material with a unique porous structure, is collected from the outer bark of oak trees. Its cellular structure exhibits hollow, thin-walled polyhedral morphology, with uniform cell size and an ordered honeycomb structure. Compared with conventional biomass, cork-derived porous char materials have a more regular pore structure and more abundant surface active sites, providing an ideal structural basis for pollutant adsorption. However, the adsorption performance of unmodified cork biochar for antibiotics is still limited by insufficient surface functional groups and limited adsorption affinity, requiring targeted modification to regulate its surface chemical properties.

[0004] Heteroatom doping technology can significantly enhance the adsorption performance of biochar for antibiotics in water by adjusting its surface chemistry and electronic structure. Cheng et al. prepared nitrogen-doped biochar using a mixture of Chlorella and corn stalks through synergistic pyrolysis activation, achieving an adsorption capacity of 1159.7 mg / g for tetracycline (TC). Analysis showed that pyrrole nitrogen, as an electrophilic active site, specifically binds to the electron-rich region of TC. Wang et al. successfully prepared phosphorus-doped biochar using corn stalks and phosphoric acid via in-situ activation. Their research indicated that the C3-PO configuration on the biochar dominated the efficient adsorption (148.62 mg / g) of sulfamethoxazole (SMX) through hydrogen bonding, while electrostatic interactions and π-π interactions contributed synergistically. However, existing studies mostly employ single pyrolysis processes to achieve individual nitrogen or phosphorus doping. Research on the synergistic effect of nitrogen-phosphorus co-doping through stepwise pyrolysis remains lacking, providing a new research direction for developing highly efficient antibiotic adsorbent materials.

[0005] Traditional nitrogen and phosphorus dopants typically rely on industrial chemicals such as melamine, urea, and phosphates. These chemical modifiers often bring high environmental burdens and uncontrollable pollution risks. In contrast, using chitin and phytic acid as green dopants has significant advantages. Chitin, derived from the exoskeleton of crustaceans, is a renewable, low-cost natural biopolymer. Its abundant acetylamino groups can be converted into active sites such as pyrrole nitrogen and pyridine nitrogen during pyrolysis. Phytic acid, a naturally occurring organophosphorus compound in plant seeds, provides a rich phosphorus source with its six phosphate groups. Simultaneously, it releases in-situ pore-forming gases such as CO2 and H2O during pyrolysis, avoiding the pollution risks associated with external activators. Therefore, using modifiers derived from green biomass becomes an environmentally friendly, efficient, and sustainable alternative.

[0006] Compared to the traditional one-pot doping method, the two-step pyrolysis doping strategy can first achieve the pyrolysis transformation of chitin at a lower temperature, avoiding nitrogen loss caused by high-temperature pyrolysis. Subsequently, phytic acid is introduced at a high temperature stage to promote the uniform distribution of phosphorus species on the pre-formed nitrogen-doped carbon framework. This sequential doping method not only precisely controls the bonding morphology and spatial distribution of heteroatoms, but also constructs abundant surface active sites through the synergistic effect of nitrogen and phosphorus elements, while optimizing the surface functional groups and pore structure of the material.

[0007] In summary, this invention uses natural cork with ordered pore structure, uniform chemical composition, and renewable properties as a precursor, employs chitin from crustacean exoskeletons as a nitrogen source, and phytic acid extracted from grain bran as a phosphorus source, to prepare nitrogen-phosphorus co-doped biochar with high antibiotic adsorption performance through a two-step pyrolysis sequential doping process. Summary of the Invention

[0008] This invention addresses the limitations of traditional biochar materials, such as disordered pore structure and limited surface functional groups leading to poor adsorption performance, as well as the environmental pollution caused by traditional chemical modification reagents. It proposes a fully biomass-based nitrogen-phosphorus co-doped biochar, its preparation method, and its applications, as detailed in the appendix. Figure 1 As shown. This invention avoids the use of traditional chemical modification reagents, and the nitrogen-phosphorus co-doped cork-based biochar prepared by two-step pyrolysis sequential doping has excellent internal pore structure and abundant surface functional groups.

[0009] The manufacturing method includes the following steps: Step 1: Mix cork and chitin in a certain proportion, then place them in a tube furnace under an inert atmosphere and pyrolyze them at a certain temperature. After pyrolysis, cool to room temperature, take out the solid product, wash it with deionized water until neutral, and dry it in a drying oven to obtain nitrogen-doped cork-based biochar intermediate. Step 2: The nitrogen-doped cork-based biochar intermediate obtained in Step 1 is placed in a phytic acid solution and stirred and mixed evenly at room temperature. The mixture is then dried to constant weight and placed in a tube furnace under an inert atmosphere for pyrolysis at a certain temperature. After pyrolysis, the mixture is cooled to room temperature, the solid product is removed, washed with deionized water until neutral, and dried in a drying oven to obtain nitrogen and phosphorus co-doped cork-based biochar.

[0010] Furthermore, in step one, the cork size is 10-200 mesh; the inert atmosphere is nitrogen; the ratio of cork to chitin is 1:1-5; the pyrolysis temperature is 400-700℃, which ensures stable doping of nitrogen while avoiding the loss of surface functional groups of biochar at excessively high temperatures; the heating rate is 2-10℃ / min; and the holding time is 0.5-2h.

[0011] Furthermore, in step one, the BET specific surface area of ​​the nitrogen-doped biochar after the first stage of pyrolysis is ≥300 m². 2 / g, and the nitrogen-containing functional groups on the surface are mainly pyrrole nitrogen, accounting for ≥40%.

[0012] Furthermore, in step two, the inert atmosphere is nitrogen; the mass fraction of the phytic acid solution is 10-50%, which can effectively promote stable phosphorus doping and ensure the synergistic effect between nitrogen and phosphorus elements is maximized; the pyrolysis temperature is 700-900℃; the heating rate is 2-10℃ / min; and the holding time is 0.5-2h.

[0013] Furthermore, in step two, the specific surface area of ​​the nitrogen-phosphorus co-doped cork-based biochar prepared is ≥1000 m². 2 / g, total pore volume ≥1cm³ 3 / g; the area of ​​PN bond peaks in the XPS spectrum is ≥30%.

[0014] Furthermore, in step two, the nitrogen-phosphorus co-doped cork-based biochar is used as an adsorbent to remove antibiotics from water. The tetracycline antibiotics include at least one of tetracycline and chlortetracycline, and the sulfonamide antibiotics include at least one of sulfamethoxazole and sulfadiazine.

[0015] Compared with the existing technology, the beneficial effects of the present invention are as follows: 1. This invention employs a two-step sequential doping method, combining three materials entirely derived from renewable biomass—cork, chitin, and phytic acid—to prepare nitrogen-phosphorus co-doped biochar. Compared to traditional single-doping methods, sequential doping allows for precise control over the introduction order and synergistic effects of nitrogen and phosphorus elements, maximizing the advantages of nitrogen-phosphorus doping. Furthermore, all raw materials used are green biomass resources, avoiding the harmful chemical reagents used in traditional preparation processes, aligning with the sustainable development principles of green chemistry, significantly improving environmental friendliness, and possessing higher social and economic value. 2. The nitrogen-phosphorus co-doped cork biochar prepared in this invention possesses a uniform honeycomb structure, high specific surface area, excellent hierarchical porous structure, and abundant nitrogen and phosphorus functional groups. This unique physicochemical structure endows it with superior adsorption performance for various antibiotics (tetracyclines, sulfonamides, etc.) far exceeding that of conventional biochar. It exhibits high adsorption capacity, fast adsorption rate, good selectivity, and excellent resistance to interference in complex aquatic environments. Therefore, the all-biomass-based nitrogen-phosphorus co-doped cork biochar prepared in this invention shows great potential for industrial application in treating antibiotic pollution in water bodies. Attached Figure Description

[0016] Appendix Figure 1 This is a process flow diagram for preparing nitrogen and phosphorus co-doped cork biochar according to the present invention;

[0017] Appendix Figure 2 This is the N2 adsorption curve of the implementation case;

[0018] Appendix Figure 3 This is a DFT aperture distribution diagram of an implementation case;

[0019] Appendix Figure 4 This is an example of the adsorption capacity of tetracycline and sulfamethoxazole;

[0020] Appendix Figure 5 This refers to the adsorption capacity of nitrogen-phosphorus co-doped biochar for tetracycline and sulfamethoxazole in the presence of coexisting ions in the example case.

[0021] Table 1 shows the specific surface area, pore characteristics, and adsorption capacity of tetracycline and sulfamethoxazole for the implementation cases. Table 1. Specific surface area, pore characteristics, and adsorption capacity of tetracycline and sulfamethoxazole for the implementation cases. Detailed Implementation

[0022] The present invention will be further described below with reference to specific preferred embodiments and the accompanying drawings, but this does not limit the scope of protection of the present invention.

[0023] Implementation Case 1: A fully biomass-based nitrogen and phosphorus co-doped biochar, its preparation method, and its application, comprising the following steps: Step 1: Cork pretreatment: Wash the cork particles thoroughly with distilled water, dry them in a forced-air drying oven at 103℃ for 12 hours, then crush them using a high-speed pulverizer, and sieve them to obtain 40-60 mesh cork powder for later use. Step 2: Preparation of nitrogen-doped cork-based biochar: 2g of cork powder treated in Step 1 was uniformly mixed with 6g of chitin powder and placed in a quartz boat, which was then placed in the middle of the heating zone of a vacuum tube pyrolysis furnace. Before heating, nitrogen was purged for 30 minutes to remove all air. The temperature was increased from room temperature to 550℃ at a rate of 10℃ / min and held for 30 minutes. After cooling, the solid product was removed and washed with distilled water until neutral. It was then dried to obtain nitrogen-doped cork-based biochar. The control group consisted of raw cork biochar prepared without the addition of chitin. Step 3: Preparation of nitrogen-phosphorus co-doped cork-based biochar: 1g of nitrogen-doped cork biochar prepared in Step 2 was placed in 20ml of a 50% (w / w) phytic acid solution and stirred until homogeneous at room temperature. The mixture was then transferred to a forced-air drying oven and dried for 12h. The dried sample was placed in an 800℃ vacuum tube pyrolysis furnace and activated under a nitrogen atmosphere for 2h. After cooling, the solid product was removed and washed with distilled water until neutral. It was then dried to obtain nitrogen-phosphorus co-doped cork-based biochar. The control group consisted of phosphorus-doped cork biochar prepared by adding only phosphoric acid.

[0024] The effect of this implementation case is that the nitrogen-phosphorus co-doped biochar produced has a uniform honeycomb structure and a high specific surface area (1059.17 m²) compared to other control groups. 2 / g), with a relatively large pore volume (1.16cm). 3 The biochar, with its well-developed hierarchical porous structure and abundant nitrogen-, oxygen-, and phosphorus-containing groups, exhibits unique structural and surface chemical properties. Within 5 minutes, it achieves adsorption capacities of 350.72 mg / g and 290.45 mg / g for TC and SMX, respectively, significantly superior to pristine biochar (8.7 mg / g and 7.1 mg / g), nitrogen-doped biochar (41.76 mg / g and 31.45 mg / g), and phosphorus-doped biochar (284.49 mg / g and 256.7 mg / g). This significantly improved adsorption performance stems from the optimized doping sequence achieved through a two-step pyrolysis method, precisely controlling the synergistic effect of nitrogen and phosphorus elements and the distribution of surface active sites. Furthermore, it exhibits strong adsorption capacity in the presence of various competing cations (Na+, Na+, SMX, and SMX). + K + Ca 2+ Mg 2+ Under coexisting conditions, the material still exhibits excellent anti-interference adsorption performance, with removal rates of TC and SMX remaining above 85.3% and 89.6%, respectively.

[0025] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the inventive concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principle of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A fully biomass-based nitrogen and phosphorus co-doped biochar, its preparation method, and its application, characterized in that, Includes the following steps: Step 1: Mix cork and chitin in a certain proportion, then place them in a tube furnace under an inert atmosphere and pyrolyze them at a certain temperature. After pyrolysis, cool to room temperature, take out the solid product, wash it with deionized water until neutral, and dry it in a drying oven to obtain nitrogen-doped cork-based biochar intermediate. Step 2: The nitrogen-doped cork-based biochar intermediate obtained in Step 1 is placed in a phytic acid solution and stirred and mixed evenly at room temperature. The mixture is then dried to constant weight and placed in a tube furnace under an inert atmosphere for pyrolysis at a certain temperature. After pyrolysis, the mixture is cooled to room temperature, the solid product is removed, washed with deionized water until neutral, and dried in a drying oven to obtain nitrogen and phosphorus co-doped cork-based biochar.

2. The preparation method according to claim 1, characterized in that, In step one, the cork size is 10-200 mesh; the inert atmosphere is nitrogen; the ratio of cork to chitin is 1:1-5; the pyrolysis temperature is 400-700℃; the heating rate is 2-10℃ / min; and the holding time is 0.5-2h.

3. The preparation method according to claim 1, characterized in that: In step one, the BET specific surface area of ​​the nitrogen-doped biochar after the first stage of pyrolysis is ≥300 m². 2 / g, and the nitrogen-containing functional groups on the surface are mainly pyrrole nitrogen, accounting for ≥40%.

4. The preparation method according to claim 1, characterized in that: In step two, the pyrolysis atmosphere is nitrogen; the mass fraction of the phytic acid solution is 10-50%; the pyrolysis temperature is 700-900℃; the heating rate is 2-10℃ / min; and the holding time is 0.5-2h.

5. The preparation method according to claim 1, characterized in that: In step two, the specific surface area of ​​the nitrogen-phosphorus co-doped cork-based biochar prepared is ≥1000 m². 2 / g, total pore volume ≥1cm³ 3 / g; NP bond peak area ratio in XPS spectra ≥30%.

6. The preparation method according to claim 1, characterized in that: In step two, the nitrogen-phosphorus co-doped cork-based biochar is used as an adsorbent to remove antibiotics from water. The tetracycline antibiotics include at least one of tetracycline and chlortetracycline, and the sulfonamide antibiotics include at least one of sulfamethoxazole and sulfadiazine.

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