Zirconium-modified nitrogen-doped biochar based on chemical oxidation and preparation method and application thereof

Abstract

This invention relates to the field of water pollution catalytic treatment technology, and particularly to a zirconium-modified nitrogen-doped biochar based on chemical oxidation, its preparation method, and its application. By nitrogen doping, zirconium modification, and hydrogen peroxide oxidation of the biochar, and by controlling the carbonization temperature, nitrogen source doping ratio, and hydrogen peroxide oxidation treatment conditions, a structurally stable modified biochar material with sufficient nitrogen doping and good zirconium species dispersion is obtained. This material can achieve a near 100% removal rate of high-concentration phosphorus, solving the problems of low phosphorus adsorption efficiency and complex preparation processes of existing biochars, and providing a new solution for achieving green and efficient phosphorus removal.

Description

Technical Field

[0001] This invention relates to the field of water pollution catalytic treatment technology, and in particular to a zirconium-modified nitrogen-doped biochar based on chemical oxidation, its preparation method, and its application. Background Technology

[0002] With the rapid development of industrial and agricultural production and the acceleration of urbanization, water pollution has become one of the global environmental problems, among which eutrophication of water bodies is becoming increasingly prominent. Phosphorus, as one of the key pollutants in eutrophic waters, will lead to algal blooms, water quality deterioration, and ecosystem imbalance if it accumulates excessively. Therefore, there is an urgent need for a green and efficient phosphorus removal technology for water bodies.

[0003] Traditional phosphorus removal technologies (such as chemical precipitation, biological methods, and membrane separation) suffer from high costs, secondary pollution, and poor stability. Adsorption methods, on the other hand, are widely used for phosphorus removal from water bodies due to their low cost, ease of operation, minimal byproducts, and readily available resources. Common adsorbents include activated carbon, zeolite, ceramics, and chitosan. Currently, various adsorbents are available for removing phosphorus from water, such as activated carbon, zeolite, modified biochar, chitosan, and fly ash.

[0004] Biochar (BC), a porous material derived from biomass pyrolysis, is widely used for adsorbing pollutants in water bodies due to its abundant and renewable raw materials and diverse surface functional groups. Corn stalks, as agricultural waste, are widely available and produced in large quantities. Biochar obtained from high-temperature pyrolysis possesses a porous structure and certain adsorption properties, making it an ideal substrate for environmental functional materials. However, raw biochar has a limited range of surface functional groups and weak specific adsorption capacity for phosphorus. Phosphorus fixation performance is often improved through metal loading or non-metal doping, but single modification methods often fail to achieve efficient adsorption, and there is a lack of systematic solutions for optimizing process parameters under the influence of multiple factors. Summary of the Invention

[0005] In view of this, the present invention proposes a zirconium-modified nitrogen-doped biochar based on chemical oxidation, its preparation method and application. It mainly obtains a modified biochar material with stable structure, sufficient nitrogen doping and good zirconium species dispersion by nitrogen doping, high modification and hydrogen peroxide oxidation, as well as by controlling carbonization temperature, nitrogen source doping ratio and hydrogen peroxide oxidation treatment conditions. This solves the problems of low phosphorus adsorption efficiency and complex preparation process of existing biochar, and provides a new solution for achieving green and efficient phosphorus removal.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation, comprising the following steps: S1, uniformly mix biomass raw material powder with nitrogen source and pyrolyze to obtain nitrogen-doped biochar; S2, nitrogen-doped biochar is mixed evenly with zirconium source solution, shaken, aged, filtered, washed and dried to obtain zirconium-modified nitrogen-doped biochar; S3, zirconium-modified nitrogen-doped biochar is mixed with hydrogen peroxide solution, heated, filtered, centrifuged, washed and dried to obtain chemically oxidized zirconium-modified nitrogen-doped biochar.

[0007] Based on the above technical solutions, preferably, in step S1, the mass ratio of the biomass raw material to the nitrogen source is 4:(1~16).

[0008] Based on the above technical solution, a further preferred embodiment is that the mass ratio of the biomass raw material to the nitrogen source is 1:1.

[0009] Based on the above technical solutions, preferably, the biomass raw material is selected from natural plant materials.

[0010] Based on the above technical solutions, a further preferred embodiment is that the biomass raw material includes corn stalks; and the nitrogen source includes urea.

[0011] The preparation of the biochar raw material powder includes the following steps: using corn stalks as raw material, washing with deionized water, drying in an 80℃ oven to constant weight, crushing with a crusher, grinding, and passing through a 100-mesh stainless steel sieve to obtain biochar raw material powder.

[0012] Based on the above technical solutions, a further preferred embodiment is that the corn stalks are sourced from agricultural waste from Kuiwen District, Weifang City, Shandong Province.

[0013] Based on the above technical solutions, preferably, in step S1, the pyrolysis temperature is 300~500℃.

[0014] Based on the above technical solution, it is further preferred that the pyrolysis temperature is 300℃; even more preferably, the pyrolysis is performed in an oxygen-free pyrolysis in a muffle furnace under N2 atmosphere, with the temperature increased to 300℃ at a rate of 10℃ / min.

[0015] Nitrogen doping significantly alters the electronic structure and surface charge distribution of biochar, affecting the loading morphology, dispersion, and chemical valence state of subsequent zirconium sources on the carbon substrate. The nitrogen-containing functional groups introduced by nitrogen doping (such as -NH2, -C=N-) can serve as additional coordination sites, more firmly binding zirconium ions (Zr). 4+This prevents agglomeration or loss during subsequent washing, drying, or use. Further zirconium modification on top of nitrogen doping results in a more uniform dispersion and higher stability of zirconium active sites, an effect that single zirconium modification may not achieve. Nitrogen doping alters the electron-donating ability of biochar, potentially giving the supported zirconium oxide (Zr-O) stronger Lewis acidity or more abundant surface hydroxyl groups (-OH). These hydroxyl groups are key active sites for ligand exchange chemisorption with phosphate groups. Therefore, the introduction of nitrogen enhances the inherent reactivity of the zirconium active sites, rather than simply increasing the number of sites.

[0016] Based on the above technical solution, preferably, in step S2, the mass-to-volume ratio of the nitrogen-doped biochar to the zirconium source solution is 1 g: (45~55) mL, and the concentration of the zirconium source solution is 0.1~0.3 mol / L.

[0017] Based on the above technical solution, a further preferred embodiment is that the mass-to-volume ratio of the nitrogen-doped biochar to the zirconium source solution is 1g:50mL, and the concentration of the zirconium source solution is 0.2mol / L.

[0018] Based on the above technical solutions, preferably, the zirconium source solution includes a zirconium oxychloride solution.

[0019] Based on the above technical solution, a further preferred method is to dissolve ZrOCl2·8H2O (99% purity) in ultrapure water and use magnetic stirring until ZrOCl2·8H2O is completely dissolved to obtain a ZrOCl2·8H2O solution. The magnetic stirring is performed at 25℃ and 450 rpm for 10 min. The nitrogen-doped biochar and ZrOCl2·8H2O solution are mixed evenly in the above ratio and kept at 25℃ and 180 rpm for 12 h. 1 mol / L NaOH solution is added to adjust the pH to 10, and the mixture is kept at 25℃ and 180 rpm for another 12 h. Then, it is aged for 10 h, filtered, and repeatedly washed with deionized water until the supernatant is neutral. It is then dried in an 80℃ oven for 12 h and passed through a 200-mesh stainless steel sieve to obtain zirconium-modified nitrogen-doped biochar.

[0020] Based on the above technical solutions, preferably, in step S3, the concentration of the hydrogen peroxide solution is 5~30wt%, the heating temperature is 30~80℃, and the heating time is 2~4h.

[0021] Based on the above technical solution, a further preferred embodiment is that the concentration of the hydrogen peroxide solution is 15 wt%, and the heating temperature is 80°C for 4 hours.

[0022] Based on the above technical solutions, preferably, in step S3, the mass-to-volume ratio of the zirconium-modified nitrogen-doped biochar to the hydrogen peroxide solution is 1g:(25~35)mL; more preferably, the mass-to-volume ratio of the zirconium-modified nitrogen-doped biochar to the hydrogen peroxide solution is 1g:30mL.

[0023] H2O2, as a strong oxidant, while oxidizing the biochar framework and increasing oxygen-containing functional groups, also strongly affects the zirconium (Zr) already loaded on the surface, which serves as a key phosphorus-fixing active center. If conventional oxidation conditions (such as high concentration, long duration, or high temperature) are used, the zirconium oxide (Zr-O) can be over-oxidized or even partially dissolved, reducing the number of core phosphorus-fixing sites or destroying the carbon framework that facilitates zirconium anchoring, thus decreasing the adsorption efficiency. Therefore, it is necessary to achieve oxidation of the biochar framework in the complex and sensitive ternary (CN-Zr) system of zirconium-modified nitrogen-doped biochar to increase beneficial oxygen-containing functional groups (-COOH, -OH) to provide additional adsorption sites and hydrophilicity, while protecting the pre-constructed highly active nitrogen-zirconium synergistic activation centers from destruction. Based on these core requirements, a near 100% removal rate was ultimately achieved through systematic optimization of the H2O2 oxidation process.

[0024] Secondly, a zirconium-modified nitrogen-doped biochar based on chemical oxidation is provided, which is prepared by the method described above for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation.

[0025] Thirdly, the application of chemically oxidized zirconium-modified nitrogen-doped biochar in phosphorus removal from water is provided, as described above.

[0026] The zirconium-modified nitrogen-doped biochar based on chemical oxidation, its preparation method, and its application, as described in this invention, have the following advantages over existing technologies: 1. This invention significantly improves the phosphorus fixation performance of biochar through synergistic modification of nitrogen doping and zirconium loading, combined with optimization via hydrogen peroxide chemical oxidation. The optimal modification process was established through orthogonal experiments. This process effectively increases the specific surface area of ​​the material, enriches surface functional groups, and forms highly dispersed active sites, thereby greatly enhancing its coordination and complexation capacity for phosphates. The resulting material exhibits high adsorption capacity and removal rate for medium-to-high concentration phosphorus-containing wastewater, making it suitable for the deep treatment and resource utilization of high-load phosphorus-containing wastewater.

[0027] 2. Using waste corn stalks as the main raw material, this method achieves the resource utilization of agricultural waste; the preparation process requires no precious metals or high-energy-consuming equipment, resulting in low cost and environmental friendliness. The obtained product can not only be used for deep phosphorus removal in wastewater treatment plants, but also shows great application potential in the control of endogenous phosphorus pollution and eutrophication treatment in lakes, reservoirs, and other water bodies. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0029] Figure 1 This is a schematic diagram of the preparation method of the present invention; Figure 2 This is a comparison chart of the adsorption efficiencies of ZrNBC300, ZrNBC400 and ZrNBC500 on a 50 mg / L phosphorus solution according to embodiments of the present invention. Figure 3 This is a comparison chart of the adsorption efficiencies of ZrNBC300-4:1, ZrNBC300-1:1, and ZrNBC300-1:4 on a 50 mg / L phosphorus solution according to embodiments of the present invention. Figure 4 A comparison of the adsorption efficiencies of BC300, NBC300, ZrBC300, ZrNBC300, and O-ZrNBC prepared for embodiments of the present invention in a 50 mg / L phosphorus solution; Figure 5 SEM comparison images of BC300, NBC300, ZrNBC300 and O-ZrNBC300 prepared for embodiments of the present invention, wherein (a) represents BC300, (b) represents NBC300, (c) represents ZrNBC300 and (d) represents O-ZrNBC300; Figure 6 This is a kinetic fitting diagram of phosphorus adsorption by O-ZrNBC300 according to the present invention; Figure 7 This is the isothermal adsorption fitting diagram of O-ZrNBC300 of the present invention; Figure 8 The Fourier transform infrared (FTIR) spectra of O-ZrNBC300 before and after phosphorus adsorption in this invention are shown below. Figure 9 This is a mapping diagram of the O-ZrNBC300 before and after phosphorus adsorption according to the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] The method for testing the phosphorus adsorption performance of the adsorbent in this invention is as follows: 50 mL of 50 mg / L phosphate standard solution is added to a beaker, and then 0.1 g of each example or comparative example adsorbent is added. The adsorption is carried out at 25 °C and a rotation speed of 180 r / min for 38 h. After centrifugation, the adsorption is filtered through a 0.45 μm hydrophilic polytetrafluoroethylene (PTFE) membrane. Finally, the absorbance of the solution is measured by ultraviolet-visible spectrophotometry (UV-Vis method), the data is recorded, and the adsorption amount and adsorption efficiency are calculated according to formulas (1) and (2).

[0032]

[0033] In the formula, q e The adsorption capacity of the material for phosphate at adsorption equilibrium is expressed in mg / g. C 0 The initial concentration of the phosphorus solution is in mg / L. C e Let be the concentration of the phosphorus solution at adsorption equilibrium at time e, in mg / L; V ρ is the volume of the reaction solution, in L; m is the mass of the adsorbent added, in g.

[0034]

[0035] In the formula, η The percentage of phosphate removal is indicated. C 0 The initial concentration of the phosphorus solution is in mg / L. C e Let be the concentration of the phosphorus solution at adsorption equilibrium at time e, in mg / L.

[0036] Example 1 Preparation of zirconium-modified nitrogen-doped biochar based on chemical oxidation.

[0037] 1. Raw material preparation: Corn stalks are used as raw materials. After being washed with deionized water, they are dried in an oven at 80℃ until constant weight. Then, they are crushed and ground by a crusher and sieved through a 100-mesh stainless steel sieve to obtain corn stalk powder.

[0038] 2. Preparation of nitrogen-doped biochar: The sieved corn stalk powder and urea were mixed evenly in a 1:1 mass ratio and placed in a crucible. Under a N2 atmosphere, the mixture was placed in a muffle furnace and heated to 300℃ at 10℃ / min for anaerobic pyrolysis to obtain nitrogen-doped biochar. The obtained nitrogen-doped biochar was ground and passed through a 200-mesh stainless steel sieve again for later use.

[0039] 3. Preparation of zirconium-modified nitrogen-doped biochar: Prepare 0.2 mol / L ZrOCl2·8H2O, dissolve ZrOCl2·8H2O in 200 ml of ultrapure water, and stir with a magnetic stirrer at 450 rpm for 10 min until ZrOCl2·8H2O is completely dissolved to obtain a ZrOCl2·8H2O solution; take 4 g of the above nitrogen-doped biochar and mix it evenly with the ZrOCl2·8H2O solution at a solid-liquid ratio of 1:50, shake at a constant temperature for 12 h, add 1 mol / L NaOH solution to adjust the pH to 10, continue shaking at a constant temperature for 12 h, then age for 10 h, filter and centrifuge, and wash repeatedly with deionized water until the supernatant is neutral, and then dry in an oven at 80℃ to obtain zirconium-modified nitrogen-doped biochar.

[0040] 4. Chemical oxidation modification: Prepare a 15wt% hydrogen peroxide solution, take 1g of zirconium-modified nitrogen-doped biochar from step 3 and mix it with 30mL of hydrogen peroxide solution, place it in a constant temperature water bath and heat it at 80℃ for 4h, filter and centrifuge, and wash it repeatedly with deionized water until the supernatant is neutral, and then place it in an oven to dry, to obtain chemically oxidized zirconium-modified nitrogen-doped biochar, denoted as O-ZrNBC300.

[0041] The preparation process of zirconium-modified nitrogen-doped biochar based on chemical oxidation is as follows: Figure 1 As shown.

[0042] Example 2 Optimization of carbonization temperature in the preparation of nitrogen-doped biochar.

[0043] 1. Raw material preparation: Same as in Example 1.

[0044] 2. Preparation of nitrogen-doped biochar: The sieved corn stalk powder and urea were mixed evenly in a 1:1 mass ratio and placed in a crucible. Under a N2 atmosphere, the mixture was placed in a muffle furnace and heated to 300℃, 400℃ and 500℃ respectively for anaerobic pyrolysis. The subsequent steps were the same as step 2 in Example 1. The nitrogen-doped biochar obtained was designated as NBC300, NBC400 and NBC500 respectively.

[0045] 3. Preparation of zirconium-modified nitrogen-doped biochar: Similar to step S3 in Example 1, the nitrogen-doped biochars NBC300, NBC400, and NBC500 obtained in the above steps were modified with zirconium, and the resulting zirconium-modified nitrogen-doped biochars were denoted as ZrNBC300, ZrNBC400, and ZrNBC500, respectively.

[0046] 4. Screening of the optimal carbonization temperature for modified biochar: 0.1g of each of the above-mentioned ZrNBC300, ZrNBC400, and ZrNBC500 were taken and their phosphorus adsorption performance was tested. Phosphorus removal rate curves were plotted, and the results are shown below. Figure 2 As shown.

[0047] according to Figure 2 The phosphorus removal rates of three materials were compared: ZrNBC300, ZrNBC400, and ZrNBC500 achieved phosphorus removal rates of 95.54%, 84.08%, and 71.10% for 50 mL and 50 mg / L phosphate standard solutions, respectively; the corresponding adsorption capacities were 23.89 mg / g, 21.02 mg / g, and 17.78 mg / g, respectively. ZrNBC300 exhibited a faster adsorption rate and higher adsorption capacity under the same conditions, indicating that the carbon framework obtained at 300 °C is more conducive to the exposure and utilization of active sites after nitrogen doping and zirconium loading.

[0048] Accordingly, the present invention selects ZrNBC300 prepared at 300℃ as the target for subsequent optimization of nitrogen doping ratio and oxidation modification.

[0049] Example 3 Optimization of the ratio of nitrogen source to biochar in the preparation of nitrogen-doped biochar.

[0050] 1. Raw material preparation: Same as in Example 1.

[0051] 2. Preparation of nitrogen-doped biochar: The sieved corn stalk powder and urea were mixed evenly at mass ratios of 1:1, 1:4 and 4:1, respectively. The mixture was placed in a crucible and subjected to anaerobic pyrolysis in a muffle furnace under N2 atmosphere, with the temperature increased to 300℃ at 10℃ / min. The other steps were the same as step 2 in Example 1. The nitrogen-doped biochar obtained was denoted as NBC300-1:1, NBC300-1:4 and NBC300-4:1, respectively.

[0052] 3. Preparation of zirconium-modified nitrogen-doped biochar: Similar to step S3 in Example 1, the nitrogen-doped biochars NBC300-1:1, NBC300-1:4, and NBC300-4:1 obtained in the above steps were modified with zirconium, and the resulting zirconium-modified nitrogen-doped biochars were denoted as ZrNBC300-1:1, ZrNBC300-1:4, and ZrNBC300-4:1, respectively.

[0053] 4. Screening of the optimal nitrogen source dosage for modified biochar: 0.1g of each of the above ZrNBC300-1:1, ZrNBC300-1:4, and ZrNBC300-4:1 were taken and their phosphorus adsorption performance was tested. Phosphorus removal rate curves were plotted, and the results are shown below. Figure 3 As shown.

[0054] The phosphorus removal rates of three materials were compared: ZrNBC300-1:1, ZrNBC300-1:4, and ZrNBC300-4:1 achieved phosphorus removal rates of 95.54%, 76.4%, and 84.88% for 50 mL and 50 mg / L phosphate standard solutions, respectively; the corresponding adsorption capacities were 23.89 mg / g, 19.1 mg / g, and 21.22 mg / g, respectively. When the nitrogen source to straw raw material mass ratio was 1:1, the material could ensure a high nitrogen doping level without structural collapse or pore blockage due to excessive nitrogen source. ZrNBC300-1:1 prepared at this ratio showed comprehensive advantages in adsorption capacity and rate; therefore, ZrNBC300-1:1 was identified as the base material for subsequent hydrogen peroxide oxidation modification.

[0055] Example 4 Optimization of the chemical oxidation modification process.

[0056] 1. Raw material preparation: Same as the steps in Example 1.

[0057] 2. Preparation of nitrogen-doped biochar: The steps are the same as in Example 1.

[0058] 3. Preparation of zirconium-modified nitrogen-doped biochar: The steps are the same as in Example 1.

[0059] 4. Using zirconium-modified nitrogen-doped biochar from S3 as the substrate, hydrogen peroxide was used for oxidative modification. A three-factor, four-level orthogonal experiment was designed (factors: hydrogen peroxide concentration, water bath temperature, and time). The removal rate was obtained through phosphorus adsorption performance testing, and the optimal conditions were determined through range analysis to obtain the final material. The orthogonal experimental factors and levels are shown in Table 1, and the orthogonal experimental design and results are shown in Table 2.

[0060] Table 1

[0061] Table 2 Orthogonal Experimental Design L 16 (4 5 ) and test results

[0062] Based on the results of the orthogonal experiment in Table 2, range analysis was performed to calculate the average removal rate (K value) of each factor at the same level. The results are shown in Table 3.

[0063] Table 3 Range Analysis Table for Orthogonal Experiments

[0064] According to Table 3, the order of factors affecting oxidation is: water bath time (B) > water bath temperature (C) > hydrogen peroxide concentration (A), among which water bath time has the most significant impact on the removal rate. The optimal combination is A2B2C4 (hydrogen peroxide concentration 15%, water bath time 4h, water bath temperature 80℃), corresponding to Experiment 6, with a removal rate of 99.4% and an adsorption capacity of 24.86mg / g, which is the best among all samples. Therefore, when oxidizing with hydrogen peroxide, zirconium-modified nitrogen-doped biochar is modified by using a 15% hydrogen peroxide solution and water bathing in an 80℃ water bath for 4h.

[0065] For this optimal combination of short-duration high temperature, we hypothesize that the higher temperature (80°C) accelerates the decomposition and oxidation reaction rate of H2O2, enabling rapid mild oxidation of the carbon framework within a short time (4 hours) without significantly damaging the deep, stable zirconium active centers. The moderate concentration provides a suitable oxidation intensity. This combination perfectly meets the requirement of this invention to oxidize the carbon framework without damaging the "nitrogen-zirconium" active centers.

[0066] Example 5 The effect of different modification methods on the phosphorus adsorption performance of biochar.

[0067] 1. Preparation of BC300: The difference between the preparation of BC300 and Example 1 is that only the sieved corn stalk powder is carbonized at 300°C, without introducing nitrogen and zirconium sources, and without chemical modification.

[0068] 2. Preparation of NBC300: Based on BC300, a nitrogen source is introduced for nitrogen doping at a ratio of 1:1. No zirconium source is introduced, and no chemical modification is performed.

[0069] 3. Preparation of ZrBC300: Based on BC300, a zirconium source is introduced to modify zirconium. The zirconium modification method is the same as in Example 1, but no nitrogen source is introduced and no chemical modification is performed.

[0070] 4. Preparation of ZrNBC300: The preparation of ZrNBC300 differs from that in Example 1 in that no chemical modification was performed; otherwise, it is the same as in Example 1.

[0071] 0.1g of O-ZrNBC300 from Example 1, and equal amounts of BC300, NBC300, ZrBC300, and ZrNBC300 prepared in this example were taken respectively, and their phosphorus adsorption performance was tested. A comparison curve of phosphorus removal rates was plotted, and the results are as follows. Figure 4 As shown.

[0072] The phosphorus removal rates of five materials were compared: O-ZrNBC300, ZrNBC300, ZrBC300, NBC300 and BC300 removed phosphorus from 50 mL and 50 mg / L phosphate standard solutions at rates of 99.44%, 95.54%, 98.18%, 92.1% and 6.45%, respectively; the corresponding adsorption capacities were 24.86 mg / g, 23.89 mg / g, 24.54 mg / g, 23.00 mg / g and 1.60 mg / g, respectively.

[0073] By comparing the phosphorus removal rates of five materials, BC300 showed poor phosphorus removal efficiency, indicating that single-carbon-based biochar has limited surface active site types and lacks specific metal or heteroatom doping, often failing to meet the performance requirements for treating complex aquatic environments or special pollutants. When nitrogen and zirconium sources were introduced, such as ZrNBC300, ZrBC300, and NBC300, the phosphorus removal efficiency was significantly enhanced. This indicates that introducing metal elements (such as zirconium and iron) and various nitrogen functional groups such as pyridine nitrogen and graphitic nitrogen into the biochar framework can significantly improve the surface chemical properties, functional group composition, and electronic structure of the material, thereby enhancing its complexation, coordination, or electrostatic interactions with target pollutants and increasing adsorption capacity and reactivity. When combined with hydrogen peroxide, O-ZrNBC300 achieved a near 100% removal rate for high-concentration phosphorus solutions, indicating that the hydrogen peroxide oxidation process can further increase surface oxygen-containing functional groups and regulate pore structure, thus significantly improving the material's overall adsorption performance. By examining the effects of hydrogen peroxide concentration, water bath temperature, and time on material properties through orthogonal design, the optimal combination can be obtained with fewer experiments, which helps to save experimental costs and improve process optimization efficiency.

[0074] The above embodiments demonstrate that without any one of the following: nitrogen-zirconium synergistic modification, a reasonable carbonization temperature, or a hydrogen peroxide oxidation step, it is difficult to obtain the high-performance chemically modified zirconium-doped biochar material described in this invention.

[0075] Furthermore, the structures of the four materials mentioned above—O-ZrNBC300, ZrNBC300, NBC300, and BC300—were observed, and their scanning electron microscope (SEM) images are shown below. Figure 5 As shown. From Figure 5 Figure (a) in the figure represents BC300. It can be clearly observed that the pore structure of the original corn stalk biochar is basically intact. It mainly presents the fibrous, lamellar and pore structure of plant tissue residue. The outline edge is smooth, the pore structure is obvious, the surface is relatively flat, and there are only a few irregular micro particles, which are the original ash and mineral impurities. Figure 5Figure (b) shows NBC300, which has a rougher surface and fragmented or eroded pore walls compared to the original biochar, which is conducive to the formation of more exposed active sites. Figure 5 Figure (c) is a SEM image of ZrNBC300, showing that the carbon-based framework surface is covered with a large number of particles or clusters with moderate brightness, which are slightly larger in size than those of NBC300, but more uniformly distributed. Figure 5 Figure (d) in the figure represents O-ZrNBC300, showing a large number of bright particles or flakes attached to the carbon-based framework, indicating a significant increase in loading, while the substrate maintains a rich porosity and crack structure.

[0076] Optimal material adsorption kinetics and isotherm testing: The sample with the highest removal rate in the orthogonal experiment (i.e., O-ZrNBC300) was selected for adsorption kinetics and isotherm fitting analysis.

[0077] Kinetic tests: With the phosphorus solution concentration fixed at 50 mg / L, samples were taken at 0.5, 1, 2, 4, 8, 12, 24, and 38 h, and pseudo-first-order kinetics, pseudo-second-order kinetics, and the Elovich model were fitted. Isotherm test: With a fixed adsorbent dosage of 0.1g and an adsorption time of 38h, the initial concentrations of phosphorus solution were set to 10, 20, 30, 50, 80, and 100 mg / L, and Langmuir, Freundlich, and Redlich-Peterson models were fitted.

[0078] Figure 6 Table 4 shows the fitting curves for the Elovich model, pseudo-first-order kinetics, and pseudo-second-order kinetics model of phosphorus adsorption by O-ZrNBC300. The fitting parameters are shown in Table 4.

[0079] Table 4. Kinetic model fitting parameters for phosphorus fixation by O-ZrNBC300

[0080] R of the pseudo-second-order dynamic model 2 The value (0.978) is higher than that of the pseudo-first-order model (0.953), and its theoretical equilibrium adsorption capacity (28.55 mg / g) is closer to the experimental value (24.86 mg / g), indicating that the adsorption process is mainly chemisorption, which may involve electron sharing or exchange between active sites on the material surface (such as Zr-OH) and phosphate ions. The Elovich model has a high goodness of fit (R²). E 2 =0.986) further confirms the heterogeneity of the material surface and the non-uniformity of the energy distribution of adsorption sites.

[0081] Figure 7The isothermal adsorption fitting curves for O-ZrNBC300 are shown in Table 5, and the fitting parameters are shown in Table 5.

[0082] Table 5. Fitting parameters of the isotherm model for O-ZrNBC300 phosphorus fixation.

[0083] according to Figure 7 As shown in Table 5, the goodness of fit of the Langmuir model (R1) is... 2 =0.966) is better than the Freundlich model (R2). 2 =0.925), indicating that adsorption tends to occur on a uniform monolayer. The calculated theoretical maximum adsorption capacity is as high as 52.06 mg / g, demonstrating the material's excellent phosphorus fixation potential. The highest R value of the Redlich-Peterson model is... E 2 The value (0.976) and the exponent n are close to 0, suggesting that the adsorption mechanism is a combination of Langmuir monolayer adsorption and Freundlich heterogeneous surface adsorption characteristics, but monolayer chemisorption is dominant.

[0084] Characterization and Validation: Fourier transform infrared spectroscopy (FTIR) analysis was performed on O-ZrNBC300 before and after phosphorus adsorption. The results are as follows: Figure 8 As shown.

[0085] Depend on Figure 8 It can be seen that the infrared spectrum of the material before adsorption is at 3424 cm⁻¹. -1 A broad absorption peak appears at 1640 cm⁻¹, which is attributed to the stretching vibrations of surface-adsorbed water and hydroxyl groups (–OH). -1 The absorption peak at 1417 cm⁻¹ corresponds to the stretching vibration of the carbonyl group (C=O) or the bending vibration of O–H in the water molecule. -1 The nearby peak may be related to the symmetric stretching vibration of the carboxylate (COO–) or the C–N bond (originating from nitrogen doping), 1043 cm⁻¹ -1 The strong peak at 466 cm⁻¹ mainly originates from the stretching vibration of C–O (such as alcohols and phenols). Of particular note is the peak at 466 cm⁻¹. -1 A distinct absorption peak was observed at 466 cm⁻¹, corresponding to the vibration of the Zr–O bond, indicating that zirconium has been successfully loaded onto biochar. After phosphorus adsorption, the infrared spectrum of the material changed significantly: it was located at 466 cm⁻¹. -1 The Zr–O bond vibration peak shifted to 467 cm⁻¹ after adsorption. -1 Furthermore, the strength decreases, indicating that the Zr–O bond directly participates in the reaction, and the phosphate ion (PO4) 3-It is highly likely that the zirconium site will bind via ligand exchange at 1081 cm⁻¹. -1 A new strong absorption peak appeared at 1640 cm⁻¹, corresponding to the stretching vibration of the P=O or P–O bond, which is direct evidence that phosphate ions were successfully fixed on the material surface. Meanwhile, a new strong absorption peak appeared at 1640 cm⁻¹. -1 The C=O peak shifted to 1683 cm⁻¹ -1 And 3424 cm -1 The peak intensity of the O–H stretching vibration at 3420 cm⁻¹ weakened and shifted slightly to 3420 cm⁻¹. -1 These changes collectively indicate that hydroxyl (–OH) groups and oxygen-containing functional groups on the material surface also participate in the adsorption process, possibly forming hydrogen bonds with phosphate groups or undergoing ligand exchange.

[0086] In summary, FTIR analysis confirmed that phosphate interacts with zirconium sites and oxygen-containing functional groups on the material surface, and achieves phosphorus fixation by forming Zr–O–P type inner surface complexes.

[0087] Figure 9 The images show the mapping of O-ZrNBC300 before and after phosphorus adsorption. Before adsorption, C, N, and O elements are uniformly and continuously distributed throughout the biochar framework, confirming successful nitrogen doping and the widespread presence of oxygen-containing functional groups. Zr elements are highly dispersed on the carbon substrate in the form of fine particles or clusters, with a uniform distribution and no large-area agglomeration. This indicates that the modification achieved good loading and dispersion of zirconium species on the biochar surface, providing sufficient and easily accessible active sites for phosphorus adsorption. After phosphorus adsorption, P elements clearly appear in the post-adsorption mapping, and their distribution pattern highly overlaps with that of Zr elements. The signal intensity of P elements is strongest in the Zr-rich areas, directly demonstrating that phosphate ions are specifically adsorbed around the zirconium active sites.

[0088] From the perspective of micro-area elemental distribution, direct evidence is provided for the phosphorus fixation mechanism: phosphorus fixation is not random physical adsorption, but rather achieved through specific chemical interactions with zirconium species loaded on the surface (such as ligand exchange to form inner-layer complexes). This is consistent with the Zr-O bond shift observed in FTIR analysis and the chemisorption mechanism inferred from kinetic and isothermal analyses, jointly constructing the core phosphorus fixation mechanism of "ligand exchange chemisorption dominated by zirconium active sites." Simultaneously, the stable existence and shift of Zr-O bonds in FTIR, and the high co-localization of Zr and P in mapping, demonstrate that the optimized oxidation treatment successfully preserved the core Zr active sites. Furthermore, the newly added oxygen-containing functional groups form a complementary adsorption network with the original nitrogen and zirconium sites, proving the synergistic effect between multiple modifications and oxidation.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation, characterized in that, Includes the following steps: S1, uniformly mix biomass raw material powder with nitrogen source and pyrolyze to obtain nitrogen-doped biochar; S2, nitrogen-doped biochar is mixed evenly with zirconium source solution, shaken, aged, filtered, washed and dried to obtain zirconium-modified nitrogen-doped biochar; S3, zirconium-modified nitrogen-doped biochar is mixed with hydrogen peroxide solution, heated, filtered, centrifuged, washed and dried to obtain chemically oxidized zirconium-modified nitrogen-doped biochar.

2. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 1, characterized in that: In step S1, the mass ratio of the biomass raw material to the nitrogen source is 4:(1~16).

3. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 2, characterized in that: The biomass raw material includes corn stalks, and the nitrogen source includes urea.

4. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 1, characterized in that: In step S1, the pyrolysis temperature is 300~500℃.

5. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 1, characterized in that: In step S2, the mass-to-volume ratio of the nitrogen-doped biochar to the zirconium source solution is 1 g: (45~55) mL, and the concentration of the zirconium source solution is 0.1~0.3 mol / L.

6. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 5, characterized in that: The zirconium source solution includes a zirconium oxychloride solution.

7. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 1, characterized in that: In step S3, the concentration of the hydrogen peroxide solution is 5-30 wt%, and the heating temperature is 30-80°C for 2-4 hours.

8. The method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 1, characterized in that: In step S3, the mass-to-volume ratio of the zirconium-modified nitrogen-doped biochar to the hydrogen peroxide solution is 1 g: (25~35) mL.

9. A zirconium-modified nitrogen-doped biochar based on chemical oxidation, characterized in that: It is prepared by the method for preparing zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in any one of claims 1 to 8.

10. The application of zirconium-modified nitrogen-doped biochar based on chemical oxidation as described in claim 9 in phosphorus removal from water.

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