A tea polyphenol and bimetallic synergistically modified biochar and its preparation method and application in water phosphorus removal

Abstract

The present invention discloses a tea polyphenol and bimetallic synergistically modified biochar, a preparation method thereof, and an application thereof in water phosphorus removal, comprising the following steps: (1) adding biomass to a tea polyphenol solution, first stirring the biomass, then allowing the biomass to stand, and then drying the biomass to a constant weight, thereby obtaining a biomass impregnated with tea polyphenol; (2) adding the biomass impregnated with tea polyphenol to a bimetallic salt mixed solution of a lanthanum salt and a coordinated metal salt, first stirring the biomass, then allowing the biomass to stand, and then drying the biomass to a constant weight, thereby obtaining a composite biomass; and (3) grinding the composite biomass, and then pyrolyzing the biomass under an inert gas atmosphere. The present invention innovatively utilizes the synergistic effect of metallic lanthanum with metals such as calcium, magnesium, and aluminum to optimize the electrochemical properties of the biochar, thereby enabling the biochar to efficiently adsorb and remove inorganic phosphates in water through a variety of advanced physical and chemical mechanisms, such as coordination exchange, ion precipitation, surface complexation, and electrostatic interaction.

Description

Technical Field

[0001] The present invention relates to the technical field of biochar, and in particular to a biochar modified by synergistic synthesis of tea polyphenols and bimetallic compounds, a preparation method thereof, and an application thereof in phosphorus removal from water bodies. Background Art

[0002] When phosphorus concentration in water exceeds the threshold of 0.02 mg / L, it becomes an environmental pollutant. Excess phosphorus triggers explosive growth of aquatic plants and algae, consuming large amounts of dissolved oxygen, ultimately leading to eutrophication and posing a threat to human health through the water cycle. Therefore, developing efficient and environmentally friendly phosphorus pollution control technologies to mitigate its negative ecological effects has become a pressing scientific issue.

[0003] Among the many technologies for treating phosphorus pollution in water environments, adsorption offers significant advantages due to its wide applicability and efficient resource recovery potential. Biochar-based adsorption technology, in particular, is becoming a research hotspot due to its low cost, renewability, and environmental friendliness. However, single biochar materials are limited in their adsorption efficiency and selectivity due to their negative surface charge and insufficient affinity for phosphate, making them difficult to directly apply to the treatment of complex water environments. Therefore, modifying biochar to enhance its selective adsorption of phosphate has become a key research direction.

[0004] Among various biochar modification methods, metal doping has attracted considerable attention because it can maintain the biochar's original pore structure while also modulating its surface charge, enhancing its dispersibility, and increasing its active sites. This, in turn, significantly improves its phosphate capture capacity through electrostatic attraction. However, the precise design of metal-doped biochar and its effectiveness in phosphorus removal remain underdeveloped. Summary of the Invention

[0005] The main purpose of the present invention is to provide a tea polyphenol and bimetallic synergistically modified biochar with higher phosphorus adsorption capacity and less influence by water humus and inorganic anions, as well as a preparation method and application in water phosphorus removal.

[0006] To achieve the above object, the present invention provides a method for preparing biochar synergistically modified by tea polyphenols and bimetallic compounds, comprising the following steps:

[0007] (1) Tea polyphenols immersion treatment

[0008] Adding biomass to the tea polyphenol solution, stirring it first, then letting it stand, and then drying it to a constant weight to obtain biomass impregnated with tea polyphenols;

[0009] (2) Double metal salt impregnation treatment

[0010] The biomass impregnated with tea polyphenols is added to a mixed solution of a double metal salt of a lanthanum salt and a complex metal salt, stirred, allowed to stand, and then dried to a constant weight to obtain a composite biomass impregnated with tea polyphenols and a double metal salt;

[0011] (3) Preparation of biochar by pyrolysis

[0012] The composite biomass is ground and then pyrolyzed under the protection of an inert gas atmosphere to obtain the tea polyphenol and bimetallic synergistically modified biochar.

[0013] Furthermore, in step (1), the biomass is any one of straw, rice husk, and sawdust, the tea polyphenol is any one of catechin, catechin gallate, gallocatechin, and gallocatechin gallate, the concentration of the tea polyphenol solution is 0.01 to 0.1 mmol / L, and the ratio of the biomass to the tea polyphenol solution is 5 g:100 mL to 20 g:100 mL.

[0014] Furthermore, in step (1), the stirring treatment conditions are a rotation speed of 100 to 200 r / min and a time of 6 to 12 hours.

[0015] Furthermore, in step (2), the lanthanum salt is lanthanum chloride, and the coordinated metal salt is any one of calcium chloride, magnesium chloride, and aluminum chloride. In the bimetallic salt mixed solution, the concentration of the lanthanum salt is 0.1 to 0.5 mmol / L, and the concentration of the coordinated metal salt is 0.01 to 0.1 mmol / L.

[0016] Furthermore, in step (2), the stirring treatment conditions are a rotation speed of 100 to 200 r / min and a time of 6 to 18 hours.

[0017] Furthermore, in steps (1) and (2), the drying temperature is 40-80°C.

[0018] Furthermore, in step (3), the inert gas is nitrogen or argon.

[0019] Furthermore, in step (3), the pyrolysis treatment process is: heating to 200-600°C at a rate of 5-25°C / min and pyrolyzing for 1-6 hours.

[0020] The present invention also provides a tea polyphenol and bimetallic synergistically modified biochar, which is prepared according to the above preparation method.

[0021] The present invention also provides an application of the tea polyphenols and bimetallic synergistically modified biochar as a water phosphorus removal agent.

[0022] The present invention also provides a method for removing phosphate from water, comprising the following steps: adding the above-mentioned tea polyphenols and bimetallic synergistically modified biochar to a phosphate-containing water body, wherein the initial phosphate concentration of the water body is 5 to 200 mg / L, and the amount of tea polyphenols and bimetallic synergistically modified biochar is 0.1 to 10.0 g / L, and then reacting for 4 to 24 hours under the conditions of a stirring speed of 150 to 250 r / min, a temperature of 20 to 25°C, and an initial pH value of 5 to 11.

[0023] The present invention significantly optimizes the microstructure and electrochemical properties of biochar through the synergistic modification strategy of tea polyphenols and bimetallics, and realizes the efficient adsorption and removal of inorganic phosphates. Lanthanum (La) has a smaller ionic radius and a higher charge density, has a stronger affinity for phosphates, and can effectively adsorb phosphates. However, loading a single lanthanide metal will result in a small number of adsorption sites on the surface of biochar. Based on this, the present invention increases the loading of calcium, magnesium, and aluminum to improve the adsorption performance of biochar and improve the surface properties, providing more ways to remove phosphates. Calcium and magnesium are alkaline metals, and the solubility of calcium phosphate or magnesium phosphate formed by them and phosphate radicals is extremely low, making phosphate radicals very easy to precipitate. Aluminum may enable phosphate radicals to combine with aluminum oxides through surface complexation and adsorption to form a stable surface complex, thereby promoting the removal of phosphates.

[0024] The beneficial effects of the present invention are embodied in:

[0025] (1) This invention innovatively utilizes the synergistic effect of lanthanum with other metals such as calcium, magnesium, and aluminum to optimize the electrochemical properties of biochar. This strategy significantly optimizes the surface charge distribution and reactivity of biochar, enabling it to efficiently adsorb and remove inorganic phosphate from water through a variety of advanced physical and chemical mechanisms such as coordination exchange, ion precipitation, surface complexation, and electrostatic interactions.

[0026] (2) This invention innovatively utilizes the synergistic effect of tea polyphenols and lanthanide bimetallic compounds to modify biochar. The phenolic hydroxyl groups in tea polyphenols act as active functional groups, effectively promoting the uniform distribution and conversion of lanthanide bimetallic compounds on the biochar surface, forming a stable metal oxide / hydroxide composite structure. This process not only significantly increases the specific surface area and porosity of the biochar, but also creates abundant active sites, thereby greatly improving the biochar's adsorption capacity and rate for phosphate.

[0027] (3) The present invention converts agricultural waste such as straw, rice husks, and sawdust into functional biochar materials, thereby achieving a green upgrade from low-value waste to high-value adsorbents, opening up a new path for the design of biochar-based adsorption materials, and also providing a scientific basis and practical methods for the effective treatment of phosphorus pollution (such as sodium phosphate, sodium hydrogen phosphate, and sodium dihydrogen phosphate) in water bodies (such as network sewage, rural sewage, tap water, river water, and lake water). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the SEM image of the biochar modified synergistically by tea polyphenols and bimetallic compounds prepared in Example 1. DETAILED DESCRIPTION

[0029] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0030] Unless otherwise specified, the raw materials, reagents, or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0031] Example 1

[0032] Preparation of biochar modified by synergistic interaction of tea polyphenols and bimetallic compounds

[0033] The preparation steps are as follows:

[0034] (1) Tea polyphenols immersion treatment

[0035] 10 g of corn straw powder with a particle size of 0.5 to 1.0 mm was added to 100 mL of a catechin solution with a concentration of 0.05 mmol / L, and then stirred at a speed of 200 r / min for 10 hours, and then allowed to stand for 24 hours. After that, it was filtered with filter paper, and the filter cake was dried at 60°C to constant weight to obtain a biomass impregnated with tea polyphenols.

[0036] (2) Double metal salt impregnation treatment

[0037] 8 g of the biomass impregnated with tea polyphenols obtained in step (1) was added to 100 ml of a mixed solution of a bimetallic salt containing 0.5 mmol / L lanthanum chloride and 0.05 mmol / L calcium chloride, and then stirred at 150 r / min for 18 h, allowed to stand for 24 h, and then filtered with filter paper. The filter cake was dried at 60°C to constant weight to obtain a composite biomass impregnated with tea polyphenols and bimetallic salts.

[0038] (3) Preparation of biochar by pyrolysis

[0039] The composite biomass obtained in step (2) was ground through an 80-mesh sieve, and then heated to 400°C at a rate of 20°C / min under nitrogen atmosphere, and pyrolyzed at this temperature for 2 hours. After the pyrolysis was completed, it was cooled to room temperature to obtain tea polyphenols and bimetallic synergistically modified biochar.

[0040] Example 2

[0041] Preparation of biochar modified by synergistic interaction of tea polyphenols and bimetallic compounds

[0042] The preparation method of this embodiment is the same as that of Example 1, except that the calcium chloride in step (2) is replaced by magnesium chloride.

[0043] Example 3

[0044] Preparation of biochar modified by synergistic interaction of tea polyphenols and bimetallic compounds

[0045] The preparation method of this embodiment is the same as that of Example 1, except that the calcium chloride in step (2) is replaced by aluminum chloride.

[0046] Comparative Example 1

[0047] Preparation of biochar

[0048] The preparation method of this comparative example is the same as that of Example 1, except that steps (1) and (2) are omitted, and the straw biomass raw material is directly subjected to pyrolysis treatment.

[0049] Comparative Example 2

[0050] Preparation of biochar

[0051] The preparation method of this comparative example is the same as that of Example 1, except that step (1) is omitted and the bimetallic compound is directly impregnated on the straw biomass.

[0052] Comparative Example 3

[0053] Preparation of biochar

[0054] The preparation method of this comparative example is the same as that of Example 1, except that step (2) is omitted and the biomass impregnated with tea polyphenols is directly subjected to pyrolysis treatment.

[0055] Comparative Example 4

[0056] Preparation of biochar

[0057] The preparation method of this comparative example is the same as that of Example 1, except that the bimetallic salt mixed solution in step (2) is replaced by a 0.5 mmol / L lanthanum chloride solution.

[0058] Comparative Example 5

[0059] Preparation of biochar

[0060] The preparation method of this comparative example is the same as that of Example 1, except that the bimetallic salt mixed solution in step (2) is replaced by a 0.05 mmol / L calcium chloride solution.

[0061] Structural characterization and determination of biochar modified by synergistic reaction of tea polyphenols and bimetallic compounds

[0062] Figure 1 This is the SEM image of the biochar modified by tea polyphenols and bimetallic synergistically prepared in Example 1. It can be seen that the surface of the modified biochar is wrinkled.

[0063] The specific surface area, pore volume and pore diameter of the biochar prepared in each embodiment and comparative example were measured, and the results are shown in Table 1.

[0064] Table 1

[0065]

[0066]

[0067] It can be seen that the specific surface area of ​​the biochar prepared in Example 1 is as high as 425.08 m 2 / g, the pore volume and pore diameter are 0.21cm 3 / g, and 4.26 nm. The specific surface properties of the biochars produced in Examples 2 and 3 were similar to those in Example 1. However, the original biochar produced in Comparative Example 1 had a much smaller specific surface area than the modified biochar, and its pore structure was coarser and more uneven. The specific surface properties of the biochars produced in Comparative Examples 2-4 were also significantly lower than those shown in Examples 1-3.

[0068] Experimental study on phosphorus removal from water by biochar modified with tea polyphenols and bimetallic compounds

[0069] 1. Phosphate removal test of single phosphate body

[0070] Test method: 100 mL of a 50 mg / L sodium phosphate aqueous solution was added to a beaker, followed by 0.1 g of biochar sample. The pH was then adjusted to 6.0 with 0.1 mmol / L sodium hydroxide and / or hydrochloric acid. The reaction was stirred at 200 rpm and 25°C for 4 hours. The residual phosphate concentration was measured using a UV-visible spectrophotometer. The phosphorus removal results are shown in Table 2.

[0071] Table 2

[0072] Biochar samples Initial total phosphorus concentration Total phosphorus concentration after treatment Total phosphorus removal rate Example 1 50mg / L 0.01mg / L 99.98％ Example 2 50mg / L 3.27mg / L 93.46％ Example 3 50mg / L 3.91mg / L 92.19％ Comparative Example 1 50mg / L 34.93mg / L 30.15％ Comparative Example 2 50mg / L 15.42mg / L 69.15％ Comparative Example 3 50mg / L 21.63mg / L 56.74％ Comparative Example 4 50mg / L 9.83mg / L 80.35％ Comparative Example 5 50mg / L 12.49mg / L 75.03％

[0073] 2. Water phosphorus removal test in the presence of competitive ions

[0074] Test Method: 100 mL of an aqueous solution (containing 50 mg / L sodium phosphate, 100 mg / L sodium chloride, 50 mg / L sodium sulfate, and 5 mg / L sodium nitrate) was added to a beaker, followed by 0.1 g of biochar sample. The pH was then adjusted to 6.0 with 0.1 mmol / L sodium hydroxide and / or hydrochloric acid solution. The mixture was stirred at 200 rpm and 25°C for 4 hours. The residual phosphate concentration was determined using a UV-visible spectrophotometer. The phosphorus removal results are shown in Table 3.

[0075] Table 3

[0076] Biochar samples Initial total phosphorus concentration Total phosphorus concentration after treatment Total phosphorus removal rate Example 1 50mg / L 5.00mg / L 90.00％ Comparative Example 1 50mg / L 44.86mg / L 10.28％ Comparative Example 2 50mg / L 30.13mg / L 39.75％ Comparative Example 3 50mg / L 36.82mg / L 26.37％ Comparative Example 4 50mg / L 16.93mg / L 66.15％ Comparative Example 5 50mg / L 23.02mg / L 53.97％

[0077] From the above, it can be seen that the phosphorus removal effect of the biochar prepared in Example 1 of the present invention is less affected by the interference of competitive anions, while the phosphorus removal effects of the biochars prepared in Comparative Examples 1-5 are greatly affected.

[0078] 3. Phosphorus removal test in water in the presence of humus

[0079] Test method: 100 mL of an aqueous solution (containing 50 mg / L sodium phosphate and 2 mg / L fulvic acid) was added to a beaker, followed by 0.1 g of biochar sample. The pH was then adjusted to 6.0 with 0.1 mmol / L sodium hydroxide and / or hydrochloric acid. The mixture was stirred at 200 rpm and 25°C for 4 hours. The residual phosphate concentration was measured using a UV-visible spectrophotometer. The phosphorus removal results are shown in Table 3.

[0080] Table 3

[0081]

[0082]

[0083] The presence of fulvic acid not only occupies the adsorption sites of biochar, but also may interact with phosphoric acid in water, thereby further reducing the adsorption of phosphoric acid, resulting in a reduction in the amount of phosphoric acid adsorbed exceeding the amount of fulvic acid present. From the above, it can be seen that fulvic acid has little effect on the phosphorus removal effect of the biochar prepared in Example 1, Comparative Example 4, and Comparative Example 5. However, for the biochar prepared in Comparative Examples 1-3, the presence of fulvic acid significantly interferes with its phosphorus removal effect.

[0084] 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 in the scope of protection of the present invention.

Claims

1. A method for preparing biochar modified by synergistic use of tea polyphenols and bimetallic compounds, characterized in that: The following steps are involved: (1) Tea polyphenols soaking treatment Adding biomass to the tea polyphenol solution, stirring it first, then letting it stand, and then drying it to a constant weight to obtain biomass impregnated with tea polyphenols; The biomass is any one of straw, rice husk, and sawdust; the tea polyphenol is any one of catechin, gallocatechin, and gallocatechin gallate; the concentration of the tea polyphenol solution is 0.01 to 0.1 mmol / L; and the ratio of the biomass to the tea polyphenol solution is 5 g:100 mL to 20 g:100 mL; (2) Double metal salt impregnation treatment The biomass impregnated with tea polyphenols is added to a mixed solution of a double metal salt of a lanthanum salt and a complex metal salt, stirred, allowed to stand, and then dried to a constant weight to obtain a composite biomass impregnated with tea polyphenols and a double metal salt; The lanthanum salt is lanthanum chloride, and the coordinated metal salt is any one of calcium chloride, magnesium chloride, and aluminum chloride. In the double metal salt mixed solution, the concentration of the lanthanum salt is 0.1 to 0.5 mmol / L, and the concentration of the coordinated metal salt is 0.01 to 0.1 mmol / L. (3) Preparation of biochar by pyrolysis The composite biomass is ground and then pyrolyzed under the protection of an inert gas atmosphere to obtain the tea polyphenol and bimetallic synergistically modified biochar.

2. The method for preparing tea polyphenols and bimetallic synergistically modified biochar according to claim 1, wherein: In step (1), the stirring treatment conditions are a rotation speed of 100 to 200 r / min and a time of 6 to 12 hours.

3. The method for preparing tea polyphenols and bimetallic synergistically modified biochar according to claim 1, wherein: In step (2), the stirring treatment conditions are a rotation speed of 100 to 200 r / min and a time of 6 to 18 hours.

4. The method for preparing tea polyphenols and bimetallic synergistically modified biochar according to claim 1, wherein: In steps (1) and (2), the drying temperature is 40-80°C.

5. The method for preparing biochar modified by synergistic combination of tea polyphenols and bimetallic compounds according to claim 1, wherein: In step (3), the pyrolysis process is as follows: heating to 200-600°C at a rate of 5-25°C / min and pyrolyzing for 1-6 hours.

6. A biochar modified by synergistic action of tea polyphenols and bimetallic compounds, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 5.

7. Use of the tea polyphenols and bimetallic synergistically modified biochar as claimed in claim 6 in phosphorus removal from water.

8. A method for removing phosphate from water, characterized in that: The following steps are involved: The tea polyphenols and bimetallic synergistically modified biochar as described in claim 6 is added to a phosphate-containing water body, the initial phosphate concentration of the water body is 5-200 mg / L, the amount of tea polyphenols and bimetallic synergistically modified biochar is 0.1-10.0 g / L, and then the reaction is carried out for 4-24 hours under the conditions of a stirring speed of 150-250 r / min, a temperature of 20-25°C, and an initial pH value of 5-11.

Images