Method for strengthening degradation of organic pollutants by using acid modified hydrothermal carbon
By enhancing the Fe(III)/Fe(II) cycle through acid-modified hydrothermal carbon, the problem of low degradation efficiency caused by surface defects of hydrothermal carbon was solved, achieving efficient and environmentally friendly degradation of organic pollutants and reducing treatment costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG UNIV OF PETROCHEMICAL TECH
- Filing Date
- 2024-12-09
- Publication Date
- 2026-07-14
AI Technical Summary
Existing hydrothermal carbon has a small number of oxygen-containing functional groups, low porosity, and small specific surface area during the catalytic activation of persulfate, resulting in insufficient Fe(III)/Fe(II) cycle efficiency, making it difficult to efficiently degrade organic pollutants, and conventional methods pose a risk of secondary pollution.
Acid-modified hydrothermal char was used as a catalyst. Through hydrothermal carbonization of biomass and inorganic acid solution, abundant oxygen-containing functional groups were formed and the pore structure was improved, enhancing the Fe(III)/Fe(II) cycling capacity. This resulted in the preparation of highly efficient acid-modified hydrothermal char for degradation systems constructed from iron salts and persulfates.
It significantly improves the efficiency of the Fe(III)/Fe(II) cycle, enhances the degradation effect on organic pollutants, reduces treatment costs, and reduces Fe(III) flocculation and precipitation, thus achieving green and environmentally friendly high-efficiency degradation.
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Figure CN119503998B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of environmental pollution remediation and relates to a method for enhancing the degradation of organic pollutants using acid-modified hydrothermal carbon. Background Technology
[0002] Advanced oxidation technologies based on persulfate have attracted widespread attention in water treatment due to their economic, efficient, environmentally friendly, safe, and stable advantages. Persulfate can be activated through energy input (ultrasound, heat, microwave) and catalyst addition to generate highly reactive species, including sulfate radicals, hydroxyl radicals, singlet oxygen, high-valence metals, and electron transfer, which can then be used to degrade target pollutants. Among the catalysts used to activate persulfate, homogeneous transition metal ions, such as Co(II), exhibit excellent activation performance; however, they are highly ecotoxic and prone to causing secondary pollution. As an alternative catalyst, iron has advantages such as abundant surface resources, low cost, environmental friendliness, good catalytic activation effect, and no risk of secondary pollution, making it the most studied activation material and receiving considerable attention and extensive research in the catalytic activation of persulfate. However, existing studies have found that Fe(II) is consumed and rapidly oxidized to Fe(III) during the catalytic activation of persulfate, and Fe(III) has a weak activation ability for persulfate, which reduces the degradation efficiency of the constructed system for organic pollutants. Meanwhile, the accumulated Fe(III) can also lead to the formation of iron precipitates under neutral or alkaline conditions, which can easily increase the processing cost.
[0003] To address these challenges, researchers have undertaken extensive work to enhance the Fe(III) / Fe(II) cycle. For example, they have employed inorganic homogeneous reducing agents (such as hydroxylamine and sulfites), metal-based reducing agents, and ultraviolet (UV) irradiation to accelerate the Fe(III) / Fe(II) cycle. However, the use of inorganic homogeneous reducing agents (such as hydroxylamine and sulfites) presents problems such as increased chemical oxygen demand, introduction of ecotoxicity, high reagent costs, and difficulty in recycling. Metal-based reducing agents suffer from metal leaching, which can easily cause secondary pollution. UV irradiation consumes a large amount of energy and has low reduction efficiency. Additionally, carbon materials, such as carbon nanotubes, graphene, and biochar, can also promote the Fe(III) / Fe(II) cycle. However, carbon nanotubes and graphene are expensive reagents, and biochar requires high preparation temperatures, resulting in low product yields and weak Fe(II) reduction and regeneration capabilities. Compared to biochar prepared by pyrolysis, hydrothermal carbon has a lower carbon content and a lower degree of aromatization, but it has more oxygen-containing functional groups. Furthermore, it can be directly processed without drying wet biochar, making hydrothermal carbonization a common pretreatment step in the preparation of high-performance biochar. Hydrothermal carbon is a novel carbonaceous material obtained from biomass / biological waste through hydrothermal carbonization, and it can also promote the Fe(III) / Fe(II) cycle. However, hydrothermal carbon prepared by conventional methods still suffers from drawbacks such as low surface oxygen-containing functional groups, small porosity, and small specific surface area. This results in insufficient adsorption and reduction capabilities, making it difficult to enhance the Fe(III) / Fe(II) cycle in the system. Ultimately, this leads to inefficient removal of organic pollutants from the degradation system, and also results in high catalyst consumption and low degradation efficiency, hindering cost reduction and efficient removal of organic pollutants from water. Therefore, obtaining a catalyst with excellent Fe(III) adsorption and reduction capabilities is crucial for achieving efficient degradation of organic pollutants in water. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for enhancing the degradation of organic pollutants by using acid-modified hydrothermal carbon. This method can significantly enhance the Fe(III) / Fe(II) cycle efficiency under the condition of low dosage of acid-modified hydrothermal carbon, thereby significantly improving the degradation effect of iron salt and persulfate degradation system on organic pollutants.
[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0006] A method for enhancing the degradation of organic pollutants using acid-modified hydrothermal carbon is disclosed. The method involves adding acid-modified hydrothermal carbon to a degradation system constructed from iron salts and persulfates to degrade organic pollutants in water. The acid-modified hydrothermal carbon is prepared by hydrothermal carbonization of biomass and inorganic acid solution as raw materials.
[0007] In a further improvement to the above method, the inorganic acid solution is one of sulfuric acid solution, nitric acid solution, and hydrochloric acid solution.
[0008] In a further improvement to the above method, the concentration of the sulfuric acid solution is 0.01 M to 0.5 M; the concentration of the nitric acid solution is 0.01 M to 0.15 M; and the concentration of the hydrochloric acid solution is 0.01 M to 0.15 M.
[0009] A further improvement to the above method, the preparation method of the acid-modified hydrothermal carbon includes the following steps:
[0010] S1. Mix biomass with inorganic acid solution and stir to obtain a biomass mixed suspension;
[0011] S2. The biomass mixed suspension obtained in step S1 is subjected to hydrothermal carbonization treatment to obtain acid-modified hydrothermal carbon.
[0012] In a further improvement to the above method, in step S1, the mass-to-volume ratio of the biomass to the inorganic acid solution is 1 g: 5 mL to 100 mL; the biomass is one of coconut fiber, corn stalks, sawdust, rice straw, banana peel, fruit shells, etc.; and the stirring time is 20 min to 60 min.
[0013] In a further improvement to the above method, in step S2, the hydrothermal carbonization treatment is carried out in a high-pressure reactor; the temperature of the hydrothermal carbonization treatment is 140 ℃~200 ℃; and the time of the hydrothermal carbonization treatment is 6 hours~24 hours.
[0014] The above method is further improved by including the following treatments after the hydrothermal carbonization process: adjusting the pH of the product solution, filtering, washing, and drying; the washing is performed by sequentially washing the filtered precipitate with water and ethanol; the drying temperature is 60 ℃~105 ℃.
[0015] A further improvement to the above method involves adding acid-modified hydrothermal carbon to the degradation system constructed from iron salts and persulfates to degrade organic pollutants in water. This includes the following steps: mixing acid-modified hydrothermal carbon, iron salts, persulfates, and organic pollutant wastewater for an oxidative degradation reaction to complete the degradation of organic pollutants in the wastewater; the amount of acid-modified hydrothermal carbon added is 0.05 g to 0.3 g per liter of the organic pollutant wastewater.
[0016] In a further improvement to the above method, the amount of iron salt added is 0.05 mmol to 0.5 mmol per liter of organic pollutant wastewater.
[0017] In a further improvement to the above method, the iron salt is a trivalent iron salt or a divalent iron salt; the trivalent iron salt is at least one of ferric sulfate, ferric chloride, ferric nitrate, and ferric acetate; and the divalent iron salt is at least one of ferrous sulfate heptahydrate, ferrous chloride, ferrous nitrate, and ferrous ammonium sulfate.
[0018] In a further improvement to the above method, the amount of persulfate added is 0.2 mmol to 1.0 mmol per liter of organic pollutant wastewater.
[0019] In a further improvement to the above method, the persulfate is permonosulfate and / or perdisulfate; the permonosulfate is potassium permonosulfate; and the perdisulfate is at least one of sodium persulfate, potassium persulfate, and ammonium persulfate.
[0020] In a further improvement to the above method, the organic pollutant in the organic pollutant wastewater is at least one of benzoic acid, tetracycline, phenol, bisphenol A, or sulfamethoxazole; and the initial concentration of the organic pollutant in the organic pollutant wastewater is 5 μmol / L to 40 μmol / L.
[0021] In a further improvement to the above method, the initial pH value of the system is controlled to be 3-9 during the oxidative degradation reaction; the temperature of the oxidative degradation reaction is 20 ℃-50 ℃; the oxidative degradation reaction is carried out under stirring conditions of 100 rpm-250 rpm; and the time of the oxidative degradation reaction is 10 min-30 min.
[0022] Compared with the prior art, the advantages of the present invention are as follows:
[0023] (1) In view of the shortcomings of hydrothermal carbon, such as the small number of oxygen-containing functional groups on the surface, the small number of reducing components, the small porosity and specific surface area, and the resulting defects such as poor adsorption and reduction capacity of hydrothermal carbon for Fe(III), this invention creatively proposes a method to enhance the degradation of organic pollutants by using acid-modified hydrothermal carbon. Acid-modified hydrothermal carbon is added to the degradation system constructed by iron salt and persulfate to degrade organic pollutants in water. The acid-modified hydrothermal carbon used is prepared by hydrothermal carbonization of biomass and inorganic acid solution as raw materials. Compared with conventional hydrothermal carbon preparation methods, the hydrothermal carbonization of biomass under acidic conditions in this invention has the following advantages: (a) Under the action of inorganic acid-assisted hydrothermal carbonization, the organic matter in the biomass will form more functional groups (such as carboxyl groups, amino groups, phenolic hydroxyl groups, etc.) during the hydrothermal carbonization process and expose them on the surface of the hydrothermal carbon. Compared with pore electrostatic adsorption, these functional groups have stronger adsorption selectivity and higher adsorption stability, thus stronger adsorption of characteristic pollutants and Fe(III), enabling more Fe(III) to be reduced to Fe(II), which is beneficial to improving the recycling efficiency of Fe(II); (b) Under the action of inorganic acid-assisted hydrothermal carbonization, the hydrothermal carbonization reaction can be promoted, enabling more biomass to be converted into hydrothermal carbon. At the same time, under the action of acidic ions, the pore structure of the hydrothermal carbon can be effectively improved, significantly increasing the surface area and pore size of the hydrothermal carbon, and can... It can change structural defects, thereby exposing more adsorption sites and active sites, which can not only improve the adsorption capacity of hydrothermal carbon for characteristic pollutants and Fe(III), but also improve the catalytic reduction ability of hydrothermal carbon for Fe(III), making Fe(II) regeneration efficiency higher, and promoting the Fe(III) / Fe(II) cycle in the system, thus making the system more effective in degrading organic pollutants; (c) Biomass components can decompose at lower temperatures, undergoing hydrolysis and dehydration, and forming carbon-rich solid products through aldol condensation, cycloaddition, aromatization and polymerization. Moreover, these reactions are further enhanced under the action of inorganic acid-assisted hydrothermal carbonization, which can not only activate the surface of hydrothermal carbon and increase the number of surface active sites, but also oxidize some unstable functional groups, which is conducive to increasing the content of reducing components, making hydrothermal carbon exhibit better reduction performance.In the method of this invention, the acid-modified biochar has the advantages of abundant oxygen-containing functional groups on the surface, a large number of reducing components, abundant pore structure with large pore size and large specific surface area. It exhibits excellent adsorption capacity for characteristic pollutants and Fe(III), especially excellent catalytic reduction capacity for Fe(III). Therefore, adding acid-modified hydrothermal char to the degradation system constructed by iron salt and persulfate can significantly enhance the Fe(III) / Fe(II) circulation effect in the system. On the one hand, it can significantly increase the concentration of active species in the iron salt / persulfate oxidation system, so as to better construct a free radical / non-free radical coexisting oxidation system dominated by high concentration of sulfate free radicals and high-valence iron. Thus, the free radical / non-free radical coexisting oxidation system can be used to efficiently remove different types of organic pollutants in different environmental media. On the other hand, it can also significantly improve the utilization rate of iron salt, which is conducive to reducing treatment costs and significantly reducing Fe(III) flocculation and precipitation, making it more green and environmentally friendly.
[0024] (2) In this invention, the inorganic acid solution used is one of sulfuric acid solution, nitric acid solution, and hydrochloric acid solution. Simultaneously, by optimizing the type and concentration of the acidic solution (0.01M–0.5M for sulfuric acid solution, 0.01M–0.15M for nitric acid solution, and 0.01M–0.15M for hydrochloric acid solution), the number of adsorption sites and catalytically active sites on the surface of hydrothermal carbon can be significantly increased while simultaneously increasing biochar yield, thereby obtaining acid-modified hydrothermal carbon with high yield and excellent performance. In particular, when the concentration of the inorganic acid solution is too low, the increase in oxygen-containing functional groups on the surface of the hydrothermal carbon is not significant, and the enhancement effect on Fe(III) adsorption and reduction is not significant, making it difficult to promote the degradation effect of the system on organic pollutants. Meanwhile, when the concentration of inorganic acid solution exceeds 0.5 M, it can completely corrode hydrothermal carbon in the hydrothermal reaction, causing the corresponding modified hydrothermal carbon to completely dissolve. For example, when the concentration of nitric acid and hydrochloric acid reaches 0.5 M, the material obtained by hydrothermal carbonization reaction completely dissolves, and no solid product can be obtained. Attached Figure Description
[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.
[0026] Figure 1 The graph shows the degradation effect of Fe(III) / persulfate system on sulfamethoxazole under different acid-modified hydrothermal carbon and unmodified hydrothermal carbon conditions in Example 1 of the present invention.
[0027] Figure 2The graph shows the degradation rate of sulfamethoxazole by the Fe(III) / persulfate system under different acid-modified hydrothermal carbon and unmodified hydrothermal carbon conditions in Example 1 of the present invention.
[0028] Figure 3 This is a graph showing the concentration changes of Fe(III) reduced to Fe(II) in different acid-modified hydrothermal carbon / Fe(III) systems in Example 2 of the present invention.
[0029] Figure 4 This is a graph showing the variation of Fe(II) concentration in different acid-modified hydrothermal carbon / Fe(III) / persulfate systems in Example 2 of the present invention.
[0030] Figure 5 This is a graph showing the variation of Fe(III) concentration in different acid-modified hydrothermal carbon / Fe(III) / persulfate systems in Example 2 of the present invention.
[0031] Figure 6 The graph shows the degradation effect of sulfamethoxazole on the 0.1 M nitric acid modified hydrothermal carbon / Fe(III) / persulfate system under different pH conditions in Example 3 of the present invention. Detailed Implementation
[0032] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.
[0033] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values of more than three repeated experiments.
[0034] Example 1
[0035] A method for enhancing the degradation of organic pollutants using acid-modified hydrothermal carbon specifically involves adding acid-modified hydrothermal carbon to a degradation system constructed from iron salts and persulfates to degrade sulfamethoxazole in water, including the following steps:
[0036] A conical flask was used to conduct the degradation experiment in a 100 mL system with a sulfamethoxazole concentration of 25 μM. After adding sulfamethoxazole and the corresponding amount of water, the pH of the solution was adjusted to 3.0 with 0.5 M sulfuric acid (unless otherwise specified). The solution was placed in a water bath shaker, and acid-modified hydrothermal carbon (0.1 g / L), potassium persulfate complex salt PMS (0.2 mM), and ferric sulfate (Fe(III), 0.2 mM) were added. The oxidative degradation reaction was carried out at 30℃ and 150 rpm for 30 min to complete the degradation of sulfamethoxazole in the water.
[0037] In this embodiment, the acid-modified hydrothermal carbon is prepared by hydrothermal carbonization of coconut fiber and inorganic acid solution, including the following steps:
[0038] After separating the coconut fiber raw materials, wash and drain them, then transfer them to a beaker and place them in an oven to dry completely. Cut the dried coconut fiber raw materials into small pieces and tear them apart. Use a crusher to crush the materials thoroughly, pass them through a 100-mesh sieve, and obtain coconut fiber. Seal the coconut fiber in a sealed bag and transfer it to a desiccator for storage.
[0039] Preparation of acid-modified hydrothermal carbon: 1 g of coconut fiber was accurately weighed using an electronic balance and added to separate reaction vessels, which were then labeled. 30 mL of different types and concentrations of inorganic acid solutions (sulfuric acid, nitric acid, and hydrochloric acid) were selected and added to different reaction vessels. The vessels were stirred in a magnetic stirrer for 30 min to obtain a mixed suspension of coconut fiber. The reaction vessels were then assembled and placed in a 180 ℃ oven for hydrothermal carbonization for 12 hours. After the reaction was complete, the mixture was cooled to room temperature, removed, and allowed to stand until layered. The surface oil was then poured off. The material was washed with deionized water until neutral using a vacuum pump, and then placed in a vacuum drying oven at 60 ℃ until completely dry. After drying, the material was ground into powder, dispensed into centrifuge tubes, and labeled for later use.
[0040] Table 1. Numbering of Acid-Modified Hydrothermal Carbons Prepared Under Different Types and Concentrations of Inorganic Acid Solutions
[0041]
[0042] In this embodiment, unmodified hydrothermal carbon was also prepared, using water instead of inorganic acid solution, with other conditions remaining the same.
[0043] In this embodiment, before performing high-performance liquid chromatography (HPLC) analysis, 1.0 mL of sample was drawn using a syringe at specified time intervals (0, 1, 3, 5, 10, 15, 30 min), filtered through a 0.45 μm filter, quenched with excess sodium thiosulfate solution, and the concentration of sulfamethoxazole in the sample was measured. The degradation efficiency of sulfamethoxazole was then calculated, and the results are as follows: Figure 1 As shown.
[0044] Figure 1 This is a graph showing the degradation effect of the Fe(III) / persulfate system on sulfamethoxazole under different acid-modified hydrothermal carbon and unmodified hydrothermal carbon conditions in Example 1 of the present invention. Figure 1As shown, due to the poor activation performance of unmodified hydrothermal carbon for persulfate, the degradation efficiency of sulfamethoxazole in the system constructed from unmodified hydrothermal carbon and persulfate was only 8.4% within 30 minutes, a result similar to that of the Fe(III) / persulfate system without hydrothermal carbon. In the unmodified hydrothermal carbon / Fe(III) / persulfate system, the degradation efficiency of sulfamethoxazole was significantly improved, reaching 52.0%. Compared to these, in this invention, the introduction of an inorganic acid solution during the preparation of hydrothermal carbon can significantly improve the degradation performance of sulfamethoxazole in the Fe(III) / persulfate system by modifying the hydrothermal carbon with acid. Specifically, compared to the unmodified hydrothermal char / Fe(III) / persulfate system, when the sulfuric acid solution concentrations were 0.01 M, 0.1 M, 0.2 M, and 0.5 M, the sulfuric acid-modified hydrothermal char, when added to the Fe(III) / persulfate system, showed that the degradation efficiency of sulfamethoxazole increased to 58.0%, 61.5%, 83.0%, and 67.5% respectively after 30 minutes of degradation reaction. This indicates that the sulfuric acid-modified hydrothermal char obtained after modification with sulfuric acid solutions of concentrations of 0.01 M-0.5 M can further improve the degradation efficiency of sulfamethoxazole in the Fe(III) / persulfate system. In particular, the effect of sulfuric acid-assisted modification was optimal when the sulfuric acid solution concentration was 0.2 M, and the resulting sulfuric acid-modified hydrothermal char exhibited superior adsorption and catalytic reduction capabilities. Compared to the unmodified hydrothermal char / Fe(III) / persulfate system, when the concentrations of nitric acid solution were 0.01 M and 0.1 M, the degradation efficiency of sulfamethoxazole by the prepared nitric acid-modified hydrothermal char, when added to the Fe(III) / persulfate system, increased to 63.0% and 88.0% respectively after 30 minutes of degradation reaction. This indicates that the nitric acid-modified hydrothermal char obtained after modification with nitric acid solution at concentrations of 0.01 M-0.2 M can further improve the degradation efficiency of sulfamethoxazole in the Fe(III) / persulfate system. In particular, the nitric acid-assisted modification effect was best when the concentration of nitric acid solution was 0.1 M, and the resulting nitric acid-modified hydrothermal char had superior adsorption and catalytic reduction capabilities. Furthermore, increasing the concentration of the nitric acid solution significantly reduced the degradation performance of the nitric acid-modified hydrothermal char in the system constructed with Fe(III) and persulfate. Specifically, at a nitric acid solution concentration of 0.2 M, the degradation efficiency of the system for sulfamethoxazole was only 24.0%. Notably, at a nitric acid solution concentration of 0.5 M, the solid hydrothermal char sample prepared with the assistance of the nitric acid solution was dissolved by acid corrosion, making it impossible to obtain a solid sample of nitric acid-modified hydrothermal char. In addition, the hydrochloric acid-modified biochar prepared after modification with hydrochloric acid solution exhibited similar degradation performance to that of the nitric acid solution in the system constructed with Fe(III) and persulfate.
[0045] Figure 2 This is a graph showing the degradation rate of sulfamethoxazole in the Fe(III) / persulfate system under different acid-modified hydrothermal carbon and unmodified hydrothermal carbon conditions in Example 1 of the present invention. The data on the degradation of sulfamethoxazole in the Fe(III) / persulfate system by the above-mentioned acid-modified and unmodified hydrothermal carbon were fitted with a pseudo-first-order kinetic rate equation to obtain the degradation rate (…). k obs ).like Figure 2 As shown, the first-order kinetic rate of sulfamethoxazole degradation in the unmodified hydrothermal carbon / Fe(III) / persulfate system is 10.66 × 10⁻⁶. -2 min -1 Compared to other methods, the first-order kinetic rates of sulfamethoxazole degradation in the systems constructed from different acid-modified hydrothermal chars with Fe(III) and persulfate in this embodiment were significantly improved. Specifically, the addition of nitric acid-modified hydrothermal char, obtained by modification with 0.1 M nitric acid solution, to the Fe(III) / persulfate system significantly enhanced the system's activity in degrading sulfamethoxazole, achieving a first-order kinetic rate of 29.43 × 10⁻⁶. -2 min -1 The degradation rate of sulfamethoxazole was 2.8 times that of the unmodified hydrothermal char / Fe(III) / persulfate system. After modification with 0.2 M sulfuric acid solution, the sulfuric acid-modified hydrothermal char, when added to the Fe(III) / persulfate system, significantly improved the degradation activity of sulfamethoxazole, achieving a first-order kinetic rate of 25.09 × 10⁻⁶. -2 min -1 Furthermore, the enhanced rate of sulfamethoxazole degradation in the Fe(III) / persulfate system by these acid-modified hydrothermal carbons corresponds precisely to... Figure 1 Degradation kinetics in [the study].
[0046] comprehensive Figure 1 and Figure 2 It can be seen that adding the acid-modified hydrothermal carbon prepared in this invention to the Fe(III) / persulfate system can significantly enhance the degradation performance of the system for sulfamethoxazole, and can significantly improve the degradation rate and degradation effect of sulfamethoxazole, which is beneficial to achieving efficient removal of organic pollutants in water.
[0047] Example 2
[0048] The effect of acid-modified hydrothermal carbon prepared under different concentrations and types of inorganic acid solutions in Example 1 of this invention on the iron speciation in the Fe(III) / persulfate system was investigated, including the following steps:
[0049] (1) Fe(II) concentration detection. 2.0 mL of 1,10-phenanthroline (10 mM) and 0.4 mL of saturated sodium acetate (NaAc) solution were added to a 10 mL centrifuge tube beforehand. Then, 2.6 mL of the filtered filtrate was transferred at different degradation reaction time points, added to the centrifuge tube, and mixed well. After standing for 10 min, the absorbance of Fe(II) was detected at a wavelength of 510 nm by ultraviolet spectrophotometry, and the concentration was determined by the standard curve.
[0050] (2) Detection of total Fe concentration. 0.8 mL of hydroxylamine hydrochloride (10 mM), 2.0 mL of 1,10-phenanthroline (10 mM), and 0.4 mL of saturated sodium acetate solution were added to a 10 mL centrifuge tube beforehand. Then, at different degradation reaction time points, 1.8 mL of the filtered liquid was transferred to the centrifuge tube, mixed, and allowed to stand for 10 min. The absorbance of Fe(II) was then measured at 510 nm using ultraviolet spectrophotometry, and the concentration was determined using a standard curve. The saturated sodium acetate solution served as a pH buffer. The concentration of Fe(III) in the degradation reaction was equal to the total Fe concentration minus the concentration of Fe(II).
[0051] Figure 3 This is a graph showing the concentration changes of Fe(III) reduced to Fe(II) in different acid-modified hydrothermal carbon / Fe(III) systems in Example 2 of the present invention. Figure 3 It can be seen that the unmodified hydrothermal char can directly and continuously reduce Fe(III) to generate 61.72 μM Fe(II) within 30 minutes. Compared with the unmodified hydrothermal char, the acid-modified hydrothermal char of this invention has a significantly enhanced ability to reduce Fe(III). Specifically, the nitric acid-modified hydrothermal char prepared by modification with 0.1 mM nitric acid solution and the sulfuric acid-modified hydrothermal char prepared by modification with 0.2 mM sulfuric acid solution showed that the Fe(II) concentration in the system increased to 93.10 μM and 87.83 μM respectively within 30 minutes. In addition, the nitric acid-modified hydrothermal char and the hydrochloric acid-modified hydrothermal char prepared by modification with 0.2 mM nitric acid solution and hydrochloric acid solution showed that the Fe(II) concentration in the system decreased to 44.11 μM and 20.83 μM respectively within 30 minutes. Therefore, the amount and trend of Fe(III) reduced to Fe(II) by acid-modified hydrothermal char prepared under different conditions are related to the... Figure 1 and Figure 2 The degradation performance of the acid-modified hydrothermal carbon / Fe(III) / persulfate system constructed in this study is consistent with that of sulfamethoxazole.
[0052] Figure 4 This is a graph showing the variation of Fe(II) concentration in different acid-modified hydrothermal carbon / Fe(III) / persulfate systems in Example 2 of the present invention.
[0053] Figure 5 This is a graph showing the variation of Fe(III) concentration in different acid-modified hydrothermal carbon / Fe(III) / persulfate systems in Example 2 of the present invention.
[0054] Depend on Figure 4 and Figure 5 It can be seen that in the constructed acid-modified hydrothermal char / Fe(III) / persulfate system, the Fe(III) concentration decreased during the degradation process, and the Fe(II) concentration was detected, further confirming that the acid-modified hydrothermal char can indeed contribute to the reduction of Fe(III). Overall, the total iron concentration fluctuated slightly during the reaction of the constructed system but remained basically unchanged. It is worth noting that the Fe(II) concentration in the constructed acid-modified hydrothermal char / Fe(III) / persulfate system was much lower than that in the hydrothermal char / Fe(III) system. This is attributed to the fact that the Fe(II) generated by reduction is used to activate the persulfate, resulting in a significant decrease in its concentration. In addition, compared with the unmodified hydrothermal char / Fe(III) / persulfate system, the addition of acid-modified hydrothermal char resulted in a higher Fe(II) concentration in the Fe(III) / persulfate system.
[0055] Depend on Figure 3-5 The results show that, compared with unmodified hydrothermal carbon, the acid-modified hydrothermal carbon used in this invention can significantly improve the degradation performance of sulfamethoxazole in the Fe(III) / persulfate system. Specifically, a certain concentration of inorganic acid solution assists in modifying the hydrothermal carbon, endowing the surface of the hydrothermal carbon with abundant functional groups (including carboxyl, amino, and phenolic hydroxyl groups) and persistent free radicals, giving it better reduction properties. This significantly promotes the reduction of Fe(III) to Fe(II), providing more usable Fe(II) to promote the activation of persulfate and generate higher concentrations of active species, thus achieving enhanced degradation of organic pollutants. Moreover, with the increase of inorganic acid solution concentration, the content of functional groups on the surface of the hydrothermal carbon increases significantly, leading to an increase in the amount of active species generated and the degradation efficiency of organic pollutants. In addition, different types of inorganic acid solutions have different effects on the reduction properties of the surface functional groups and persistent free radicals of hydrothermal carbon. It is worth noting that when the concentration of inorganic acid solution is too high, it is easy to corrode the hydrothermal carbon, resulting in a significant reduction in the quality of the hydrothermal carbon product formed by the hydrothermal carbonization reaction, or even complete dissolution, making it impossible to obtain a solid product.
[0056] Example 3
[0057] A method for enhancing the degradation of organic pollutants using acid-modified hydrothermal carbon specifically involves investigating the applicability of a nitric acid-modified hydrothermal carbon / Fe(III) / persulfate system under different initial pH conditions, including the following steps:
[0058] A conical flask was used to conduct a degradation experiment in a 100 mL system with a sulfamethoxazole concentration of 25 μM. After adding sulfamethoxazole and the corresponding water, the pH of the solution was adjusted to 3, 5, 7, 9, and 11 respectively using 0.5 M sulfuric acid or sodium hydroxide. The solution was placed in a water bath shaker, and 0.1 M nitric acid-modified hydrothermal carbon (0.1 g / L), potassium peroxymonosulfate composite salt PMS (0.2 mM), and ferric sulfate (Fe(III), 0.2 mM) prepared in Example 1 were added. The oxidative degradation reaction was carried out at 30 °C and 150 rpm for 30 min to complete the degradation of sulfamethoxazole in the water.
[0059] Figure 6 The graph shows the degradation effect of sulfamethoxazole on the 0.1 M nitric acid modified hydrothermal carbon / Fe(III) / persulfate system under different pH conditions in Example 3 of the present invention. Figure 6 In this study, 0.1 M nitric acid-modified hydrothermal carbon, which exhibits the best performance, was selected as a co-catalyst to investigate the degradation of sulfamethoxazole under different pH conditions. Figure 6 It can be seen that under acidic conditions and even neutral or weakly alkaline environments (pH 3-9), the system constructed by adding 0.1 M nitric acid-modified hydrothermal char exhibits almost identical degradation performance for sulfamethoxazole, with degradation rates all exceeding 90%, achieving good degradation effects. However, at pH 11, the degradation efficiency for sulfamethoxazole significantly decreases to only 24.10%. The reason for the decreased degradation effect of the constructed system under strongly alkaline conditions may be that Fe(III) and its reduction to Fe(II) are easily precipitated under strongly alkaline conditions, reducing the available Fe(II) in the constructed system. In other words, under alkaline conditions, Fe(III) in the constructed system undergoes hydrolysis to generate ferric hydroxide precipitate, leading to a reduction in Fe(II), a decrease in catalytic activation ability, and a significant decrease in the degradation effect of sulfamethoxazole. Therefore, the acid-modified hydrothermal char / Fe(III) / persulfate system constructed in this invention can achieve good degradation performance within a wide pH range of 3-9.
[0060] The results above show that, compared with conventional methods, the acid-modified biochar used in this invention has advantages such as abundant oxygen-containing functional groups on the surface, a large number of reducing components, abundant pore structure with large pore size and large specific surface area. It exhibits excellent adsorption capacity for characteristic pollutants and Fe(III), especially excellent catalytic reduction capacity for Fe(III). Therefore, adding acid-modified hydrothermal char to the degradation system constructed by iron salt and persulfate can significantly enhance the Fe(III) / Fe(II) circulation effect in the system. On the one hand, it can significantly increase the concentration of active species in the iron salt / persulfate oxidation system, so as to better construct a free radical / non-free radical coexisting oxidation system dominated by high concentration of sulfate free radicals and high-valence iron. Thus, the free radical / non-free radical coexisting oxidation system can be used to efficiently remove different types of organic pollutants in different environmental media. On the other hand, it can also significantly improve the utilization rate of iron salt, which is conducive to reducing treatment costs and significantly reducing Fe(III) flocculation and precipitation, making it more green and environmentally friendly.
[0061] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.
Claims
1. A method for enhancing the degradation of organic pollutants using acid-modified hydrothermal carbon, characterized in that, The method involves adding acid-modified hydrothermal carbon to a degradation system constructed from iron salts and persulfates to degrade organic pollutants in water. The acid-modified hydrothermal carbon is prepared by hydrothermal carbonization of biomass and inorganic acid solution. The inorganic acid solution is one of sulfuric acid solution, nitric acid solution, and hydrochloric acid solution. The concentration of the sulfuric acid solution is 0.01 M to 0.5 M. The concentration of the nitric acid solution is 0.01 M to 0.15 M; the concentration of the hydrochloric acid solution is 0.01 M to 0.15 M.
2. The method according to claim 1, characterized in that, The preparation method of the acid-modified hydrothermal carbon includes the following steps: S1. Mix biomass with inorganic acid solution and stir to obtain a biomass mixed suspension; S2. The biomass mixed suspension obtained in step S1 is subjected to hydrothermal carbonization treatment to obtain acid-modified hydrothermal carbon.
3. The method according to claim 2, characterized in that, In step S1, the mass-to-volume ratio of the biomass to the inorganic acid solution is 1 g: 5 mL to 100 mL; the biomass is one of coconut fiber, corn stalks, sawdust, rice straw, banana peel, and fruit shells; the stirring time is 20 min to 60 min.
4. The method according to claim 2, characterized in that, In step S2, the hydrothermal carbonization treatment is carried out in a high-pressure reactor; the temperature of the hydrothermal carbonization treatment is 140 ℃~200 ℃; and the time of the hydrothermal carbonization treatment is 6 hours~24 hours.
5. The method according to claim 4, characterized in that, The hydrothermal carbonization process further includes the following steps: pH adjustment, filtration, washing, and drying of the product solution; the washing involves sequentially washing the filtered precipitate with water and ethanol; the drying temperature is 60 ℃~105 ℃.
6. The method according to any one of claims 1 to 5, characterized in that, Adding acid-modified hydrothermal carbon to a degradation system constructed from iron salts and persulfates to degrade organic pollutants in water includes the following steps: mixing acid-modified hydrothermal carbon, iron salts, persulfates, and organic pollutant wastewater for an oxidative degradation reaction to complete the degradation of organic pollutants in the wastewater; the amount of acid-modified hydrothermal carbon added is 0.05 g to 0.3 g per liter of the organic pollutant wastewater.
7. The method according to claim 6, characterized in that, The amount of iron salt added is 0.05 mmol to 0.5 mmol per liter of organic pollutant wastewater; the amount of persulfate added is 0.2 mmol to 1.0 mmol per liter of organic pollutant wastewater; the iron salt is a trivalent iron salt or a divalent iron salt; the trivalent iron salt is at least one of ferric sulfate, ferric chloride, ferric nitrate, and ferric acetate; the divalent iron salt is at least one of ferrous sulfate heptahydrate, ferrous chloride, ferrous nitrate, and ferrous ammonium sulfate; the persulfate is permonosulfate and / or perdisulfate; the permonosulfate is potassium permonosulfate; the perdisulfate is at least one of sodium persulfate, potassium persulfate, and ammonium persulfate; the organic pollutant in the organic pollutant wastewater is at least one of benzoic acid, tetracycline, phenol, bisphenol A, or sulfamethoxazole; the initial concentration of the organic pollutant in the organic pollutant wastewater is 5 μmol / L to 40 μmol / L.
8. The method according to claim 6, characterized in that, The initial pH of the system during the oxidative degradation reaction is controlled to be 3-9; the temperature of the oxidative degradation reaction is 20℃-50℃; the oxidative degradation reaction is carried out under stirring conditions of 100rpm-250rpm; and the time of the oxidative degradation reaction is 10min-30min.