Preparation method and application of nano-confined zirconium phosphate biochar composite material

Abstract

The application discloses a kind of preparation method and application of nano confined zirconium phosphate biochar composite material, belong to environmental functional material technical field, its steps are: (1) peanut shell is crushed and mixed with potassium bicarbonate, pyrolysis activation is carried out under protective atmosphere, after washing ash with dilute hydrochloric acid, mesoporous biochar carrier is prepared;(2) zirconium oxychloride octahydrate is configured into precursor solution and is introduced into the carrier, and continuous stirring is carried out to promote zirconium ion to be fully diffused and impregnated in the mesoporous channel inside the carrier, (3) add phosphoric acid solution to carry out in-situ precipitation reaction, after washing, dry and obtain composite material.The application utilizes the channel confined effect of carrier, realizes the uniform dispersion of zirconium phosphate active component in the pore of biochar at nanoscale, effectively solves the problem of nano-particle agglomeration.The obtained material has excellent selective adsorption performance for heavy metals in wastewater, and the application process is simple, raw materials are cheap, and has wide application prospect in the field of heavy metal wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, specifically relating to a method for preparing and applying a nano-confined zirconium phosphate biochar composite material. Background Technology

[0002] Against the backdrop of rapid global industrialization, wastewater containing heavy metals discharged from industries such as mining, smelting, electroplating, and battery manufacturing poses a severe threat to global aquatic ecosystems. Lead (Pb) and cadmium (Cd), as typical highly toxic heavy metal pollutants, exhibit extremely high levels of concealment, recalcitrant degradation, and bioaccumulation. Even at extremely low concentrations, Pb and Cd can be amplified through the food chain and enter the human body, irreversibly damaging the nervous system, kidney function, and skeletal structure. Therefore, achieving deep removal and compliant discharge of lead and cadmium from complex wastewater is an urgent need to safeguard aquatic environmental safety and human health.

[0003] For the treatment of heavy metal wastewater, existing methods such as chemical precipitation, membrane separation, and electrochemical methods, while possessing a certain engineering application basis, generally face technical bottlenecks such as high consumption of chemical reagents, the generation of large amounts of secondary sludge containing heavy metals, or high operating energy consumption. Adsorption, due to its simple operation, low cost, and potential for resource recovery, is considered one of the most effective means of deep removal of heavy metals. Among numerous adsorption materials, inorganic ion exchangers (such as zirconium phosphate) exhibit extremely high specific coordination and ion exchange capabilities in capturing heavy metal ions due to their unique crystal structure, abundant surface free protons, and excellent chemical stability. However, pure inorganic nano-zirconium phosphate particles have fatal flaws in practical water treatment: their extremely high surface energy makes them prone to severe aggregation in the aqueous phase, leading to a sharp reduction in effective specific surface area and significant masking of active sites; simultaneously, ultrafine powder materials face significant solid-liquid separation challenges in engineering applications, making them difficult to use directly in fixed-bed column chromatography or conventional filtration separation, easily causing pipeline blockage or loss with the effluent, resulting in secondary pollution.

[0004] Biochar, as an environmentally friendly porous material with abundant carbon negatives and a wide availability, has been extensively explored for applications in environmental remediation due to its well-developed pore network and rich surface functional groups. However, conventional biochar, without deep pore formation and modification, is often predominantly microporous, resulting in high mass transfer resistance and limited absolute adsorption capacity for heavy metals. More critically, it struggles when faced with high concentrations of common background ions (such as Ca2+). 2+ Mg 2+ Na + When dealing with complex real-world water bodies containing heavy metals such as humic acid and natural organic matter, traditional biochar, which relies on non-specific electrostatic adsorption, is easily interfered with by competing ions, resulting in a significant decrease in the adsorption selectivity for target heavy metals and making it difficult to meet the ultra-low emission requirements of complex heavy metal wastewater.

[0005] To overcome the dual challenges of easy aggregation of inorganic nanomaterials and poor selectivity of conventional biochar, the "nanoconfinement" strategy has emerged. By confining inorganic nanoparticles within the pores of a porous support, steric hindrance can effectively suppress nanoparticle aggregation, while the porous carbon framework can enhance the overall hydraulic properties of the material to achieve rapid solid-liquid separation. However, existing composite processes often employ simple physical mixing, direct co-precipitation, or conventional impregnation methods. Due to the difficulty in overcoming the microporous mass transfer resistance of the precursor, most of the inorganic active components often accumulate disorderedly on the outer surface of the biochar. This not only fails to achieve true "pore confinement" but also makes the materials highly susceptible to detachment under hydraulic shear or fluid scouring, further clogging the original pores and significantly reducing the material's cycle stability and removal efficiency. Therefore, developing a nano-confined biochar composite material with a well-developed mesoporous structure, strong interfacial bonding force, and stable in-situ growth of zirconium phosphate active components within the pores, using renewable agricultural waste as raw material, has significant theoretical and practical value for achieving efficient and selective removal and engineering application of heavy metals such as Pb and Cd in wastewater. Summary of the Invention

[0006] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows: A method for preparing a nano-confined zirconium phosphate biochar composite material includes the following steps: Step S1: After mixing biomass waste with a pore-forming activator, the mixture is pyrolyzed and activated to obtain large-pore expanded biochar. Then, the biochar is acid-washed to remove ash and washed with water until neutral. After drying, the mesoporous biochar carrier is obtained. Step S2: The mesoporous biochar carrier is placed in a zirconium oxychloride octahydrate precursor solution containing alcohols and acids, and is mixed and impregnated by continuous stirring to allow zirconium ions to fully diffuse and enter the pores of the mesoporous biochar carrier, thereby obtaining a zirconium-loaded intermediate suspension. Step S3: Add phosphorus source solution to the zirconium-loaded intermediate suspension, and carry out in-situ precipitation reaction under constant temperature stirring conditions. After the reaction is completed, filter out the solid, wash and dry it to obtain nano-confined zirconium phosphate biochar composite material.

[0007] Furthermore, in step S1: The biomass waste is peanut shells with a particle size of 0.2-1 mm after being crushed; the pore-forming activator is potassium bicarbonate; the mass ratio of peanut shells to potassium bicarbonate is 1:5. The heating rate for pyrolysis activation is 10–20 °C / min; the temperature for pyrolysis activation is 600 °C; and the activation time is 1 h. The acid washing and ash removal process uses a dilute hydrochloric acid solution with a concentration of 0.05–0.2 mol / L. The solid-liquid ratio of the macroporous expanded biochar to the dilute hydrochloric acid solution is 5–10 g / L. The acid washing and ash removal process takes 20–24 hours.

[0008] Furthermore, the heating rate for the pyrolysis activation is 15°C / min.

[0009] Furthermore, in step S2: The solvent of the zirconium oxychloride octahydrate precursor solution is an aqueous solution containing ethanol and hydrochloric acid, wherein the mass fraction of ethanol is 25% to 35% and the mass fraction of hydrochloric acid is 3% to 7%; the mass concentration of zirconium oxychloride octahydrate in the zirconium oxychloride octahydrate precursor solution is 80 to 120 g / L. The solid-liquid ratio of the mesoporous biochar carrier to the zirconium oxychloride octahydrate precursor solution is 2-5 g / L. The blending and impregnation time is 10-15 hours.

[0010] Furthermore, in step S3: The phosphorus source solution is a phosphoric acid solution with a mass fraction of 25% to 35%; The reaction temperature for the in-situ precipitation is 55–65°C; the reaction time for the in-situ precipitation is 10–15 h. The drying temperature is 40–50°C.

[0011] Furthermore, the reaction temperature for the in-situ precipitation is 60°C.

[0012] As a further aspect of the present invention, the present invention also provides a nano-confined zirconium phosphate biochar composite material prepared by the above preparation method, wherein the framework of the nano-confined zirconium phosphate biochar composite material is mesoporous biochar with a particle size of 0.2-1 mm and a specific surface area of ​​550-750 m². 2 / g, total pore volume is 0.25~0.32cm³ 3 / g, with an average pore size of 1.5–2.0 nm; The pores and inner surface of the skeleton are loaded with zirconium phosphate nanoparticles with a mass fraction of 30-45 mg / g.

[0013] As a further aspect of the present invention, the present invention also provides the application of the nano-confined zirconium phosphate biochar composite material prepared by the above preparation method, the specific steps of which are as follows: The nano-confined zirconium phosphate biochar composite material was packed into a fixed-bed adsorption column and used to continuously treat heavy metal ions in wastewater at an empty column flow rate of 5–15 BV / h. After saturation, desorption and regeneration were performed in situ using a mixed solution containing 0.01–0.05 mol / L HCl and 2%–6% CaCl2 as a desorbent. Furthermore, due to the excellent hydrodynamic particle size of this material, in static adsorption applications, a microporous membrane with a pore size of 0.45 μm can be directly used for vacuum filtration to achieve rapid solid-liquid separation between the composite adsorbent material and the purified water.

[0014] Compared with the prior art, the present invention has the following significant advantages: (1) The innovative "impregnation-diffusion-in-situ precipitation" confined process is used to solve the problem of nanoparticle aggregation: This invention utilizes a mixed solvent system of 30% ethanol and 5% hydrochloric acid to effectively reduce the surface tension of the precursor solution, driving high-concentration zirconium ions to overcome microporous resistance and deeply penetrate and anchor within the pores of mesoporous biochar. Subsequently, 30% phosphoric acid is added directly for isothermal in-situ precipitation. The well-developed mesoporous network (1.5–2.0 nm) of the biochar acts as a physical “microreactor,” and the steric hindrance effect restricts the excessive growth and aggregation of zirconium phosphate crystals, allowing them to be stably embedded in the carbon framework as highly dispersed amorphous or nanoscale particles, maximizing the exposure of surface active sites.

[0015] (2) Specific coordination adsorption capacity and anti-interference ability, overcoming the adsorption capacity limitation of biochar: Compared to conventional biochar that relies solely on electrostatic interactions, the nano-zirconium phosphate enriched within the pores of the composite material of this invention provides abundant specific chemical binding sites. When treating highly toxic heavy metal wastewater, this material exhibits excellent adsorption capacity for heavy metals in water through ion exchange and interfacial coordination. Experiments show that the saturated adsorption capacity of this material for cadmium in wastewater can reach 80–100 mg / g, far exceeding that of similar conventional adsorbents.

[0016] (3) Excellent engineering hydraulic properties, overcoming the bottleneck of solid-liquid separation of powder materials: Pure nano-sized zirconium phosphate powder is prone to causing filter membrane clogging and pipeline head loss in water treatment. This invention locks the nano-active components within a large-particle-size mesoporous biochar framework of 0.2-1 mm, endowing the material with excellent hydrodynamic properties. In practical applications, it can not only achieve efficient solid-liquid separation through conventional filter guns, but also be directly packed into fixed-bed adsorption columns for continuous and stable operation at high flow rates of 5-15 BV / h.

[0017] (4) A highly efficient dual regeneration mechanism that balances green and low-carbon benefits with the benefits of a circular economy: After the nano-confined zirconium phosphate biochar composite material prepared by this invention becomes saturated with adsorption, it can be desorbed in situ using a mixed solution of dilute acid (HCl) and calcium salt (CaCl2). + Provides the driving force for protonation replacement, while Ca 2+ This process enhances the extrusion of heavy metals through the common ion effect, achieving rapid emptying and regeneration of adsorption sites. The entire preparation and regeneration process uses peanut shells, an agricultural waste, as a base, resulting in low reagent consumption, long cycle life, and high alignment with the current sustainable development strategy of "treating waste with waste and green and low-carbon" in the field of environmental governance. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process of the present invention; Figure 2 The exchange capacity of cadmium ions (a) and lead ions (b) in water of the nano-confined composite material prepared in Example 1; Figure 3 The exchange capacity of cadmium ions (a) and lead ions (b) in water is shown in Comparative Example 1. Figure 4 Fixed-bed breakthrough curve for cadmium removal from the nano-confined composite material prepared in Example 1; Figure 5 The fixed-bed in-situ cumulative desorption curve of cadmium removal using the nano-confined composite material prepared in Example 1. Detailed Implementation

[0019] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Furthermore, unless otherwise specified, the raw materials, reagents, or devices used in the following embodiments can be obtained from conventional commercial channels or by existing known methods.

[0020] This invention discloses a method for preparing and applying a nano-confined zirconium phosphate biochar composite material, comprising the following steps: S1: This invention firstly involves mixing biomass waste (such as peanut shells) with potassium bicarbonate and then performing high-temperature pyrolysis. The high-temperature pyrolysis products of potassium bicarbonate are used to etch the carbon matrix, thereby achieving "pore expansion". Combined with a dilute acid ash removal process, a multi-level porous biochar carrier (LBC) with a well-developed mesoporous structure is prepared.

[0021] S2: Employing an "impregnation-diffusion-in-situ precipitation" strategy: First, the zirconium-containing precursor is dissolved in a specific ethanol / hydrochloric acid mixed solvent. Utilizing the excellent wettability and permeability of the mixed solvent, a high concentration of zirconium ions (Zr) is generated.4+ Overcoming mass transfer resistance, it penetrates deeply and anchors within the mesoporous channels of biochar; S3: Next, phosphoric acid solution is added directly, and under constant temperature stirring, the phosphate ions and zirconium ions in the pores undergo an in-situ precipitation reaction. Due to the spatial confinement effect of the mesoporous channels (i.e., the effect of physical microreactors), the generated zirconium phosphate (ZrP) crystals are strictly confined to the nanoscale and cannot agglomerate, thus anchoring themselves in the carbon framework in a highly dispersed state.

[0022] The nano-confined zirconium phosphate biochar composite material (ZrP-LBC) prepared by this invention not only completely solves the engineering pain points of easy agglomeration and extremely difficult solid-liquid separation of inorganic nanomaterials, but also provides a large number of specific chemical binding sites for the zirconium phosphate active components enriched in its pores. Through strong ion exchange and interfacial coordination, it overcomes the bottleneck of poor selectivity and low capacity of conventional biochar for heavy metal adsorption, thereby achieving efficient and deep removal of heavy metals such as cadmium (Cd) from wastewater. The reaction process principle is detailed in [link to relevant documentation]. Figure 1 .

[0023] Example 1 A method for preparing a nano-confined zirconium phosphate biochar composite material: Stage S1 (Carrier Preparation): Peanut shells were crushed to 0.2–1 mm in a crusher. 5 g of the crushed peanut shells were weighed and mixed evenly with 25 g of potassium bicarbonate (mass ratio 1:5). The mixture was placed in a tube furnace and heated to 600 °C at a heating rate of 15 °C / min under a protective atmosphere, and then pyrolyzed at this temperature for 1 h. After cooling, the resulting solid was added to a 0.1 mol / L dilute hydrochloric acid solution and acid-washed at room temperature for 24 h to remove ash. Subsequently, it was washed with deionized water until neutral, dried, and the mesoporous biochar carrier (LBC) was obtained.

[0024] Stage S2 (Zirconium Source Impregnation): Weigh 8g of zirconium oxychloride octahydrate (ZrOCl2·8H2O) and dissolve it in 80mL of a mixed solvent (containing 30% ethanol and 5% hydrochloric acid) to prepare a precursor solution. Then, weigh 0.2g of the mesoporous biochar support prepared in step S1 and add it to the solution. Stir the solution magnetically for 12 hours at room temperature to allow zirconium ions to fully impregnate the pores of the mesoporous biochar, thus obtaining the zirconium-supported intermediate.

[0025] Stage S3 (In-situ Precipitation): 80 mL of a 30% (w / w) phosphoric acid solution was directly added to the reaction system from step S2. The mixture was transferred to a thermostatic magnetic stirrer, and the reaction temperature was maintained at 60°C for 12 hours. After the reaction, the solid was filtered out using a filter gun or vacuum filtration device (e.g., a 0.45 μm filter membrane), and washed repeatedly with deionized water to remove residual free acid and impurities. Finally, the obtained solid was dried in an oven at 45°C to obtain the nano-confined zirconium phosphate biochar composite material (ZrP-LBC).

[0026] Test Example 1 Physicochemical properties and static adsorption performance of the composite material obtained in Example 1: The resulting composite material (ZrP-LBC) retained a well-developed hierarchical porous network in its skeleton. Characterized by BET nitrogen adsorption-desorption testing, the composite material had a specific surface area of ​​650.04 m². 2 / g, total pore volume is 0.28cm³ 3 The average pore size is 1.74 nm (within the typical mesoporous range). Elemental analysis and calculations showed that the actual loading of zirconium phosphate nanoparticles on biochar reached 37.7 mg / g, and no obvious surface agglomerates were observed under SEM, confirming the successful realization of nanoconfinement. In static adsorption experiments, this material exhibited extremely high specific adsorption capacity for cadmium (Cd) in water, with a maximum saturation adsorption capacity of 90 mg / g.

[0027] Example 1: Fixed-bed application of highly efficient cadmium removal nano-confined composite material: Removal of cadmium-containing wastewater: 3 mL of the highly efficient cadmium-removing nano-confined composite material prepared in this embodiment was packed into a glass adsorption column with a diameter of 20 mm and a height of 210 mm. The wastewater contained Cd was used for treatment. 2+ 1 mg / L, Ca 2+ 20 mg / L, Mg 2+ 20 mg / L, Na + 20 mg / L, a peristaltic pump was used to control the wastewater flow from top to bottom through the adsorption column fixed bed, with the effluent flow rate controlled at 18 min through 3 BV (equivalent to an empty column flow rate of approximately 10 BV / h). The dynamic column breakthrough curve results are as follows. Figure 4 As shown. Due to the material's extremely strong specific coordination adsorption capacity, when the Cd concentration in the effluent reaches the stringent breakthrough point of 0.01 mg / L, the corresponding effective treatment bed volume is as high as 340 BV.

[0028] In-situ regeneration and desorption: The exchange-saturated composite material was directly regenerated in situ within the adsorption column. A mixed solution of 0.02 mol / L HCl and 4% CaCl2 was used as the eluent. HCl provided the proton displacement motive force, while CaCl2 enhanced heavy metal desorption through the common ion effect. The in-situ desorption results are as follows: Figure 5 As shown, after elution with a 20 BV mixed regeneration solution, the cumulative desorption rate of cadmium reached as high as 99%. The column was then rinsed with pure water until near neutral, and then wastewater was pumped back in to begin the next batch of continuous operation.

[0029] Comparative Example 1 This comparative example uses unmodified raw biochar (BC). Its preparation process involves directly pyrolyzing peanut shells at 600℃ without potassium bicarbonate pore-expanding activation, and without subsequent zirconium impregnation and in-situ phosphoric acid precipitation loading processes.

[0030] Testing revealed that the virgin biochar in this comparative example had extremely underdeveloped pores and lacked effective specific chemisorption sites on its surface. Under the same static adsorption test conditions, the virgin biochar exhibited extremely low exchange adsorption capacity for cadmium (Cd) in water, with a maximum adsorption capacity of less than 10 mg / g (see Appendix). Figure 3 Furthermore, this is significantly different from the 90 mg / g in Example 1, as shown in the appendix. Figure 2 Therefore, it can be seen that the comparative material has almost no effective deep removal effect on the target low concentration of heavy metals, which fully confirms the decisive role of the "pore expansion + nano-confined loading" dual process of the present invention in improving adsorption performance.

[0031] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nano-confined zirconium phosphate biochar composite material, characterized in that, Includes the following steps: Step S1: After mixing biomass waste with a pore-forming activator, the mixture is pyrolyzed and activated to obtain large-pore expanded biochar. Then, the biochar is acid-washed to remove ash and washed with water until neutral. After drying, the mesoporous biochar carrier is obtained. Step S2: The mesoporous biochar carrier is placed in a zirconium oxychloride octahydrate precursor solution containing alcohols and acids, and is blended and impregnated by continuous stirring. Step S3: Add phosphorus source solution to the zirconium-loaded intermediate suspension, and carry out in-situ precipitation reaction under constant temperature stirring conditions. After the reaction is completed, filter out the solid, wash and dry it to obtain nano-confined zirconium phosphate biochar composite material.

2. The method for preparing a nano-confined zirconium phosphate biochar composite material according to claim 1, characterized in that, In step S1: The biomass waste is peanut shells with a particle size of 0.2-1 mm after being crushed; the pore-forming activator is potassium bicarbonate; the mass ratio of peanut shells to potassium bicarbonate is 1:

5. The heating rate for pyrolysis activation is 10–20 °C / min; the temperature for pyrolysis activation is 600 °C; and the activation time is 1 h. The acid washing and ash removal process uses a dilute hydrochloric acid solution with a concentration of 0.05–0.2 mol / L. The solid-liquid ratio of the macroporous expanded biochar to the dilute hydrochloric acid solution is 5–10 g / L. The acid washing and ash removal process takes 20–24 hours.

3. The method for preparing a nano-confined zirconium phosphate biochar composite material according to claim 2, characterized in that, The heating rate for the pyrolysis activation is 15℃ / min.

4. The method for preparing a nano-confined zirconium phosphate biochar composite material according to claim 1, characterized in that, In step S2: The solvent of the zirconium oxychloride octahydrate precursor solution is an aqueous solution containing ethanol and hydrochloric acid, wherein the mass fraction of ethanol is 25% to 35% and the mass fraction of hydrochloric acid is 3% to 7%; the mass concentration of zirconium oxychloride octahydrate in the zirconium oxychloride octahydrate precursor solution is 80 to 120 g / L. The solid-liquid ratio of the mesoporous biochar carrier to the zirconium oxychloride octahydrate precursor solution is 2-5 g / L. The blending and impregnation time is 10-15 hours.

5. The method for preparing a nano-confined zirconium phosphate biochar composite material according to claim 1, characterized in that, In step S3: The phosphorus source solution is a phosphoric acid solution with a mass fraction of 25% to 35%; The reaction temperature for the in-situ precipitation is 55–65°C; the reaction time for the in-situ precipitation is 10–15 h. The drying temperature is 40–50°C.

6. The method for preparing a nano-confined zirconium phosphate biochar composite material according to claim 5, characterized in that, The reaction temperature for the in-situ precipitation is 60℃.

7. A nano-confined zirconium phosphate biochar composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. The nano-confined zirconium phosphate biochar composite material according to claim 7, characterized in that, The framework of the nano-confined zirconium phosphate biochar composite material is mesoporous biochar with a particle size of 0.2–1 mm and a specific surface area of ​​550–750 m². 2 / g, total pore volume is 0.25~0.32cm³ 3 / g, with an average pore size of 1.5–2.0 nm; The pores and inner surface of the skeleton are loaded with zirconium phosphate nanoparticles with a mass fraction of 30-45 mg / g.

9. An application of a nano-confined zirconium phosphate biochar composite material, characterized in that, Application of the nano-confined zirconium phosphate biochar composite material prepared by any one of claims 1 to 6 in wastewater treatment.

10. The application of the nano-confined zirconium phosphate biochar composite material according to claim 9, characterized in that, The specific steps are as follows: The nano-confined zirconium phosphate biochar composite material was packed into a fixed-bed adsorption column and used to continuously treat heavy metal ions in wastewater at an empty tower flow rate of 5–15 BV / h. After saturation, a mixed solution containing 0.01–0.05 mol / L HCl and 2%–6% CaCl2 by mass was used as a desorbent for in-situ desorption and regeneration.

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