Carbon material for catalytic degradation of cod and preparation method and application thereof

Abstract

The application belongs to the technical field of organic wastewater treatment, and discloses a carbon material with good catalytic activity for catalytic degradation of COD as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing biomass powder and a phosphorus-containing acidic solution, placing them in a sealed container for hydrothermal reaction, performing solid-liquid separation after the reaction is completed, and drying to obtain a hydrothermal carbon intermediate; (2) dispersing the hydrothermal carbon intermediate in a solvent, adding an amino donor and an aldehyde group donor, adjusting the pH value to alkaline for in-situ polymerization, so that the polymer is coated on the surface of the hydrothermal carbon intermediate, and after drying, a resin-coated precursor is obtained; (3) performing activation treatment on the resin-coated precursor to obtain the carbon material for catalytic degradation of COD.

Description

Technical Field

[0001] This invention relates to the technical field of organic wastewater treatment, and more specifically, to carbon materials for catalytic degradation of COD, their preparation methods, and applications. Background Technology

[0002] In recent years, with the rapid development of industrial technology, an increasing number of organic pollutants, such as dyes, antibiotics, and pesticides, have been discharged into water bodies. Due to their characteristics of being difficult to degrade, bioaccumulating, persistent, and widely distributed, these pollutants seriously affect human health and ecological balance. Advanced oxidation technologies (AOPs) have broad prospects and application potential in the efficient removal of recalcitrant organic wastewater. Among them, persulfate-based (PDS) AOPs have advantages over hydrogen peroxide-based (H2O2) AOPs, such as easier transport and storage of the oxidant and a wider applicable pH range. Furthermore, the sulfate radicals (SO4•-) generated by PDS activation have a higher oxidation potential and can selectively oxidize organic compounds such as perfluorooctanoic acid and cyanuric acid, which are difficult to oxidize by hydroxyl radicals (•OH), through electron transfer. Therefore, developing technologies for efficiently activating PDS to degrade recalcitrant organic wastewater through non-radical or free radical pathways has rapidly become a research hotspot.

[0003] Common carbon materials for activating photocatalytic degradation of organic pollutants (PDS) include biochar, graphene, carbon nanotubes, and carbon black. However, the performance of undoped or unmodified raw carbon materials activating PDS is generally poor, and the high cost of preparing nanomaterials such as graphene and carbon nanotubes limits their large-scale application. Biochar, as a low-cost and widely available carbon material, possesses a large number of electron donors dispersed on its surface, including oxygen functional groups, persistent free radicals, heteroatoms, and defect structures, giving it great potential as a catalyst. To further improve the catalytic performance of biochar, doping with non-metallic heteroatoms (such as nitrogen, sulfur, boron, oxygen, and phosphorus) has been widely studied due to its low cost and lack of secondary pollution. Among these, nitrogen doping is considered one of the most effective methods to improve the catalytic degradation performance of organic pollutants. By introducing defect sites, pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen, the electronic structure and surface chemical properties of carbon materials can be significantly modulated.

[0004] Although existing nitrogen-doped carbon materials have made some progress in activating PDS to degrade organic pollutants, the following technical bottlenecks and shortcomings still exist:

[0005] Limitations of single-element doping: Existing technologies mostly focus on single nitrogen doping. Although it can improve catalytic activity to some extent, the ability of a single heteroatom to regulate the electron cloud density of the carbon framework is limited, making it difficult to further reduce the activation energy. The lack of synergistic effects from other heteroatoms means that the degradation efficiency and mineralization rate of catalysts in treating complex organic wastewater with high COD values ​​still need to be improved.

[0006] Uneven distribution and easy loss of active sites: Traditional preparation methods usually involve simply mixing biomass directly with a nitrogen source and then pyrolyzing it. This external doping method makes it difficult for nitrogen atoms to be uniformly embedded in the carbon lattice, often remaining only on the surface. Furthermore, nitrogen is easily volatilized and lost during high-temperature pyrolysis, resulting in low nitrogen doping content and uneven distribution of active sites in the final material, which seriously affects the stability and reusability of the catalyst.

[0007] The contradiction between pore structure and specific surface area: Ordinary biochar materials often suffer from underdeveloped pore structures and small specific surface areas, limiting the contact between pollutants and active sites. Although conventional chemical activation can create pores, it easily disrupts the graphitization of the carbon framework, leading to decreased conductivity and hindering electron transfer. Maintaining a high specific surface area while constructing an ordered carbon structure (such as a core-shell structure or a graphitized structure) that facilitates electron transport remains a major challenge in the preparation of high-performance carbon catalysts. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a carbon material with good catalytic activity for the catalytic degradation of COD, its preparation method and application, and the technical solution is as follows:

[0009] A method for preparing carbon materials for catalytic degradation of COD includes the following steps:

[0010] (1) Mix biomass powder with a phosphoric acid solution, place it in a sealed container for hydrothermal reaction, and after the reaction is completed, perform solid-liquid separation and dry to obtain hydrothermal carbon intermediate;

[0011] (2) The hydrothermal carbon intermediate is dispersed in a solvent, an amino donor and an aldehyde donor are added, the pH is adjusted to alkaline and an in-situ polymerization reaction is carried out, so that the polymer is coated on the surface of the hydrothermal carbon intermediate. After drying, a resin-coated precursor is obtained.

[0012] (3) The resin-coated precursor is activated to obtain the carbon material that catalyzes the degradation of COD.

[0013] As a further improvement to the above preparation method: in step (1), the biomass powder is selected from at least one of bamboo powder, wood powder, straw powder, fruit shell powder or sugarcane bagasse, and passes through a 60-200 mesh sieve; the phosphoric acid solution is phytic acid solution, phosphoric acid solution or ammonium dihydrogen phosphate solution, with a mass fraction of 5-10 wt%.

[0014] As a further improvement to the above preparation method: in step (1), the solid-liquid ratio of biomass powder to phosphoric acid solution is 1g:(30-50mL), the temperature of the hydrothermal reaction is 160-220℃, and the reaction time is 6-24 hours.

[0015] As a further improvement to the above preparation method: in step (2), the amino donor is selected from melamine, urea or thiourea; the aldehyde donor is selected from formaldehyde solution, acetaldehyde or glutaraldehyde.

[0016] As a further improvement to the above preparation method: in step (2), the molar ratio of the amino donor to the aldehyde donor is (1.2-2):1; the mass ratio of the hydrothermal carbon intermediate to the total amount of amino and aldehyde donors is 1:(0.8-1); the solid-liquid ratio of the hydrothermal carbon intermediate to the solvent is 1g:(30-50mL), and the solvent is deionized water; the pH value is adjusted to 8.0-9.5, the temperature of the in-situ polymerization reaction is 70-95℃, and the reaction time is 2-5 hours.

[0017] As a further improvement to the above preparation method: in step (3), the activation treatment includes the following steps: ball milling and mixing the resin-coated precursor with the activator until uniform, followed by high-temperature pyrolysis under an inert atmosphere, and finally post-treatment of the pyrolysis product; the activator is selected from at least one of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium hydroxide or zinc chloride.

[0018] As a further improvement to the above preparation method: the mass ratio of the resin-coated precursor to the activator is 1:(0.5-2), the heating rate of the high-temperature pyrolysis is 2-5℃ / min, the pyrolysis temperature is 700-900℃, and the holding time is 1-4 hours.

[0019] As a further improvement to the above preparation method: the post-treatment includes acid washing, water washing, alcohol washing and drying in sequence; the acid washing uses hydrochloric acid solution or nitric acid solution with a concentration of 0.5-2.0 mol / L.

[0020] The carbon material for catalytic degradation of COD was prepared by the method described above.

[0021] A method for purifying organic wastewater involves using a catalyst to perform advanced oxidation treatment on the organic wastewater. The catalyst includes carbon materials prepared by the above-mentioned preparation method that catalyze the degradation of COD.

[0022] The advantages of the carbon material for catalytic degradation of COD, its preparation method, and its application of the present invention are as follows:

[0023] (1) This invention innovatively employs a phosphoric acid-containing solution-assisted hydrothermal pretreatment for phosphorus doping. The large atomic radius of phosphorus atoms induces lattice distortion and defects in the carbon plane, adjusting the electron spin density of the carbon material and providing abundant attachment sites for subsequent catalytic reactions. Furthermore, the phosphoric acid-containing solution not only acts as an acidic catalyst to promote the dehydration and carbonization of biomass during the hydrothermal stage, but also effectively acts as an activator to etch the carbon framework, significantly increasing the specific surface area and mesopore volume of the material, thus solving the problem of underdeveloped pore structure in ordinary biochar.

[0024] (2) This invention innovatively employs an in-situ resin polymerization coating scheme for nitrogen doping. By generating a resin layer through in-situ polymerization on the surface of phosphorus-containing hydrothermal carbon, a compact precursor structure of "biochar core-resin polymer shell" is constructed, overcoming the defects of the traditional physical mixing method mentioned in the background art, which results in uneven nitrogen source distribution and easy volatilization and loss at high temperatures. The resin layer (such as melamine-formaldehyde resin, etc.) is a high-quality precursor with high nitrogen content. During pyrolysis, it is transformed into a carbon layer rich in highly active sites such as pyridine nitrogen and graphitic nitrogen. Due to the anchoring effect of the biochar core, nitrogen is firmly confined to the surface of the carbon skeleton, which greatly improves the nitrogen retention rate and doping uniformity.

[0025] (3) This invention innovatively employs a strategy combining phosphoric acid solution-assisted hydrothermal pretreatment with in-situ resin polymerization coating to achieve synergistic co-doping of nitrogen and phosphorus. The co-doping of nitrogen and phosphorus atoms breaks the electroneutrality of the carbon surface. Due to the difference in electronegativity between nitrogen, phosphorus and carbon, a large number of active sites are formed in the carbon matrix, which not only optimizes the adsorption energy of persulfate molecules by the catalyst, but also significantly reduces the activation energy of electron transfer. The inner biochar framework provides excellent conductive channels and structural support, which, combined with the catalytic sites of the outer layer, effectively promotes the directional transfer of electrons from organic pollutants to persulfate, thereby greatly improving the degradation efficiency and mineralization rate of COD.

[0026] (4) This invention utilizes the combined effect of resin pyrolysis and high-temperature activation by activators to further optimize the pore structure and mass transfer performance of the material. During the high-temperature stage, the gas generation from the pyrolysis of the resin layer and the deep etching by the activator (such as an alkaline activator) work together to not only remove surface impurities and expose the previously embedded nitrogen and phosphorus active sites to the maximum extent, but also to construct a hierarchical and interconnected pore network inside the carbon material. This effectively reduces the diffusion resistance of reactants (organic pollutants and persulfates) inside the catalyst, significantly improves the mass transfer efficiency, and ensures the efficient and continuous catalytic reaction.

[0027] The embodiments of the invention provided in this specification will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages of the embodiments of the invention provided in this specification will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments of the invention provided in this specification. Attached Figure Description

[0028] The accompanying drawings, which form part of the embodiments of the invention provided in this specification, are used to aid in understanding the embodiments of the invention provided in this specification. The content provided in the drawings and the related descriptions in the embodiments of the invention provided in this specification can be used to explain the embodiments of the invention provided in this specification, but do not constitute an undue limitation on the embodiments of the invention provided in this specification. In the drawings:

[0029] Figure 1 This is a SEM image of the carbon material in Example 1 of the present invention. Detailed Implementation

[0030] The embodiments of the invention provided in this specification will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the embodiments of the invention provided in this specification based on these descriptions. Before describing the embodiments of the invention provided in this specification in conjunction with the accompanying drawings, it should be particularly noted that:

[0031] The technical solutions and features provided in the embodiments of the invention provided in this specification, including the following description, can be combined with each other without conflict.

[0032] Furthermore, the embodiments of the inventions provided in this specification mentioned below are generally only a part of the embodiments of the inventions provided in this specification, and not all of them. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the inventions provided in this specification without creative effort should fall within the scope of protection of the embodiments of the inventions provided in this specification.

[0033] Regarding the terminology and units in the embodiments of the invention provided in this specification: The terms "comprising," "including," "having," and any variations thereof in the description, claims, and related parts of the embodiments of the invention provided in this specification are intended to cover non-exclusive inclusion. Furthermore, other relevant terms and units in the embodiments of the invention provided in this specification can be reasonably interpreted based on the relevant content of the embodiments of the invention provided in this specification.

[0034] Example 1

[0035] The method for preparing carbon materials for catalytic COD degradation in this embodiment includes the following steps:

[0036] (1) Select bamboo powder as biomass raw material and sieve it to 60-200 mesh. Disperse the bamboo powder in 8wt% phytic acid solution according to the solid-liquid ratio of 1g:40mL and place it in a closed high-pressure reactor. Perform hydrothermal reaction at 180℃ for 12 hours. After the reaction, perform solid-liquid separation and drying to obtain a hydrothermal carbon intermediate rich in phosphorus.

[0037] (2) The hydrothermal char intermediate was dispersed in deionized water, with a solid-liquid ratio of 1 g:40 mL. An amino donor (selected from melamine) and an aldehyde donor (selected from formaldehyde) were added to the dispersion, with the molar ratio of amino donor to aldehyde donor controlled at 2:1, and the mass ratio of the hydrothermal char intermediate to the total mass of the added amino and aldehyde donors at 1:1. The pH of the reaction system was adjusted to 9, and the temperature was raised to 80°C under closed stirring conditions for 4 hours for in-situ polymerization. After the reaction was completed, the precursor with a "biochar core-resin polymer shell" structure was obtained through solid-liquid separation and drying.

[0038] (3) The resin-coated precursor and the activator (selected from sodium carbonate) were ball-milled and mixed evenly at a mass ratio of 1:1. The mixed powder was placed in a tube furnace and heated to 800°C at a heating rate of 3°C / min under an inert atmosphere and held at that temperature for 2 hours. After natural cooling, the heat-treated product was first immersed in a 1 mol / L hydrochloric acid solution and stirred at room temperature for 6 hours. Then, it was washed with water and alcohol until neutral. After drying, the carbon material for catalytic degradation of COD was obtained.

[0039] Figure 1 This is a SEM image of the carbon material in this embodiment. (Example:) Figure 1 As shown, carbon materials have abundant pores.

[0040] Biological wastewater often has a high COD content and contains other impurities such as salts that affect COD degradation. This invention involves adding carbon materials and / or PS (potassium persulfate, specifically potassium persulfate) to a batch of biological wastewater (COD concentration of 98 mg / L, denoted as CO) for catalytic degradation experiments. The dosage of carbon materials was 0.4 g / L, and the dosage of PDS was 4 mol / L. Samples were taken at regular intervals to test the COD concentration (denoted as C), and the COD removal rate was calculated using the formula "COD removal rate = (1 - C / C0) × 100%".

[0041] Tests showed that both the carbon material and PDS have a certain degradation effect on COD. During the initial use and reaction at room temperature for 1 hour, the COD removal rate of PDS was 14.3%, and that of the carbon material was 33.5%. However, when both carbon material and PDS were added simultaneously, the COD removal rate reached 62% after 30 minutes of reaction, with the fastest COD concentration reduction. After 1 hour of reaction, the COD removal rate reached 82.6%, and the COD concentration of the treated water met the discharge standards. This demonstrates that the carbon material and PDS of this invention can synergistically reduce COD, thereby improving wastewater purification. Furthermore, the carbon material still maintained a 75.4% COD removal rate even after 5 reuses, exhibiting good stability.

[0042] Example 2

[0043] Compared with Example 1, the difference in the preparation method of carbon material for catalytic degradation of COD in this example is that the hydrothermal reaction temperature in step (1) is 160°C and the reaction time is 24 hours.

[0044] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this embodiment was 79.4%.

[0045] Example 3

[0046] Compared with Example 1, the preparation method of carbon material for catalytic degradation of COD in this example is different in that the hydrothermal reaction temperature in step (1) is 220°C and the reaction time is 6 hours.

[0047] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this embodiment was 80.1%.

[0048] Example 4

[0049] Compared with Example 1, the preparation method of carbon material for catalytic degradation of COD in this example is different in that: in step (2), the amino donor is urea, the aldehyde donor is glutaraldehyde, and the molar ratio of amino donor to aldehyde donor is controlled at 1.2:1.

[0050] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this embodiment was 76.5%.

[0051] Example 5

[0052] Compared with Example 1, the preparation method of carbon material for catalytic degradation of COD in this example is different in that: the amino donor in step (2) is thiourea, the aldehyde donor is acetaldehyde, and the molar ratio of amino donor to aldehyde donor is controlled at 1.6:1.

[0053] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this embodiment was 78.2%.

[0054] Example 6

[0055] Compared with Example 1, the preparation method of carbon material for catalytic COD degradation in this example is different in that: the activator is potassium carbonate, and the mass ratio of resin-coated precursor to activator is 1:0.5.

[0056] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this embodiment was 77.8%.

[0057] Example 7

[0058] Compared with Example 1, the preparation method of carbon material for catalytic COD degradation in this example is different in that the activator is sodium bicarbonate, and the mass ratio of resin-coated precursor to activator is 1:2.

[0059] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this embodiment was 78.9%.

[0060] Compare with Example 1

[0061] Compared with Example 1, the preparation method of the carbon material for catalytic degradation of COD in this comparative example is different in that step (1) is not performed, and bamboo powder is directly reacted with amino donor and aldehyde donor.

[0062] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this control example was 58.3%.

[0063] Compare with Example 2

[0064] Compared with Example 1, the preparation method of the carbon material for catalytic degradation of COD in this comparative example is different in that step (2) is not performed, but melamine, hydrothermal carbon intermediate and activator are directly ball-milled and mixed and then heat-treated.

[0065] Tests showed that the COD removal rate of the carbon material and PDS reacted with the biological wastewater for 1 hour in this control example was 62.7%.

[0066] The carbon material for catalytic degradation of COD in this invention is prepared by the preparation method described in any of the above embodiments.

[0067] An embodiment of the organic wastewater purification method of the present invention is to use a catalyst to perform advanced oxidation treatment on the organic wastewater, wherein the catalyst includes carbon materials for catalytic degradation of COD prepared by the preparation method described in any of the above embodiments.

[0068] The embodiments of the invention provided in this specification have been described above. Those skilled in the art will be able to implement the embodiments of the invention provided in this specification based on these descriptions. All other preferred embodiments and implementations obtained by those skilled in the art based on the above description of the embodiments of the invention provided in this specification without inventive effort should fall within the protection scope of the embodiments of the invention provided in this specification.

Claims

1. A method for preparing carbon materials for catalytic degradation of COD, characterized in that: Includes the following steps: (1) Mix biomass powder with a phosphoric acid solution, place it in a sealed container for hydrothermal reaction, and after the reaction is completed, perform solid-liquid separation and dry to obtain hydrothermal carbon intermediate; The solid-liquid ratio of biomass powder to phosphoric acid solution is 1g:(30-50mL), the hydrothermal reaction temperature is 160-220℃, and the reaction time is 6-24 hours; (2) The hydrothermal carbon intermediate is dispersed in a solvent, an amino donor and an aldehyde donor are added, the pH is adjusted to alkaline and an in-situ polymerization reaction is carried out, so that the polymer is coated on the surface of the hydrothermal carbon intermediate. After drying, a resin-coated precursor is obtained. The molar ratio of the amino donor to the aldehyde donor is (1.2-2):1; the mass ratio of the hydrothermal char intermediate to the total amount of amino and aldehyde donors is 1:(0.8-1); the solid-liquid ratio of the hydrothermal char intermediate to the solvent is 1g:(30-50mL), and the solvent is deionized water; the pH value is adjusted to 8.0-9.5, the temperature of the in-situ polymerization reaction is 70-95℃, and the reaction time is 2-5 hours; (3) The resin-coated precursor is activated to obtain the carbon material that catalyzes COD degradation; wherein the activation treatment includes the steps of: ball milling and mixing the resin-coated precursor with an activator until uniform, then performing high-temperature pyrolysis under an inert atmosphere, and finally performing post-treatment on the pyrolysis product; the activator is selected from at least one of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium hydroxide or zinc chloride. The mass ratio of the resin-coated precursor to the activator is 1:(0.5-2), the heating rate of the high-temperature pyrolysis is 2-5℃ / min, the pyrolysis temperature is 700-900℃, and the holding time is 1-4 hours.

2. The preparation method according to claim 1, characterized in that: In step (1), the biomass powder is selected from at least one of bamboo powder, wood powder, straw powder, fruit shell powder or sugarcane bagasse, and passes through a 60-200 mesh sieve; the phosphoric acid solution is phytic acid solution, phosphoric acid solution or ammonium dihydrogen phosphate solution, with a mass fraction of 5-10 wt%.

3. The preparation method according to claim 1, characterized in that: In step (2), the amino donor is selected from melamine, urea or thiourea; the aldehyde donor is selected from formaldehyde solution, acetaldehyde or glutaraldehyde.

4. The preparation method according to claim 1, characterized in that: The post-treatment includes sequential acid washing, water washing, alcohol washing, and drying; the acid washing uses a hydrochloric acid solution or nitric acid solution with a concentration of 0.5-2.0 mol / L.

5. A carbon material for catalytic degradation of COD, characterized in that: It is prepared by the preparation method according to any one of claims 1-4.

6. A method for purifying organic wastewater, characterized in that: Advanced oxidation treatment of organic wastewater is performed using a catalyst, wherein the catalyst comprises a carbon material for catalytic degradation of COD prepared by the preparation method described in any one of claims 1-4.

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