Preparation method and application of sludge biochar / iron-manganese layered bimetallic oxide composite material

Abstract

The invention relates to a sludge biochar modified layered bimetallic oxide, and a preparation method and application thereof. The modified layered bimetallic oxide is prepared from the following main raw materials: domestic sewage aeration tank sludge, NaOH, Na2CO3, FeCl3. 6H2O and MnCl2. 4H2O. The domestic sewage aeration tank sludge is used for preparing dry sludge, the ferric chloride solution and the manganese chloride solution are used for preparing sludge composite layered double hydroxides, and the final layered bimetallic oxide composite sludge biochar catalyst can be prepared by calcining the sludge composite layered double hydroxides. The modified layered bimetallic oxide prepared by the scheme of the invention can effectively degrade bisphenol A, has relatively strong reusability, and still keeps good degradation ability in a relatively wide pH environment.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and specifically designs a preparation method and application of a sludge biochar / iron-manganese layered double metal mixed oxide composite material (SBC / FeMn-LDO). Background Art

[0002] Bisphenol A (BPA), with the molecular formula C 15 H 16 ₁₅H₁₆O₂, consists of a propane skeleton and two benzene rings, each benzene ring containing a hydroxyl group. BPA is poorly soluble in water, with a solubility in water of 1 g·L –1 ⁻¹ at 21.5 °C, has weak volatility, and poor biodegradability. BPA is widely used and is ubiquitous in people's lives. It is a precursor substance for manufacturing plastics, prepared by condensing phenol and acetone in an acidic medium, and is commonly used in the production of products such as polycarbonate plastics, epoxy resins, flame retardants, and coatings. It is an important organic synthesis intermediate and one of the most commonly used plastic additives. BPA generally enters the environment through domestic sewage, agricultural runoff, and industrial wastewater. At the same time, due to its poor biodegradability, it will persist in the environment, seriously threatening the health of humans and animals. Moreover, BPA can disrupt the hormone composition of organisms, causing endocrine disorders, and is a typical endocrine disruptor (EDCs). A large number of studies have shown that BPA has potential biological toxicity, and exposure to BPA can lead to diabetes, cancer, tumors, cardiovascular diseases, and even organ poisoning. In recent years, with the widespread use of BPA products, it has been detected in water bodies, soil, sediments, air, municipal solid waste, drinking water, and food in various basins, and finally enters environmental water bodies through various channels. BPA can be stably maintained in groundwater and sediments for up to 70 days and has now become one of the most trace pollutants detectable in the environment. Facing the current demand for water ecological safety and water quality health in China, it is urgent to develop an efficient and economical BPA treatment method. Therefore, how to effectively treat BPA wastewater has become the focus of attention of many researchers. There are generally three categories of BPA wastewater treatment methods: physical methods, biological methods, and chemical methods.

[0003] The sulfate radical-based advanced oxidation process (SR-AOPs) has been widely studied in the treatment of refractory organic pollutants due to its strong oxidation performance and high removal efficiency. Compared with the hydroxyl radical (HO·) generated by the Fenton system, the sulfate radical (SO 4− ₄·⁻) has a higher redox potential and a longer half-life, which can promote the efficient and continuous degradation of organic pollutants. Peroxymonosulfate (PMS) is a relatively stable strong oxidant that can be activated to generate SO 4−Various activation methods (such as semiconductor, transition metal, carbon-based catalyst, electrochemistry, alkalization, heat, ultraviolet light, and ultrasound) have been applied to PMS activation. Among them, transition metal catalysts (such as Co, Fe, Mn, Cu) are widely used for PMS activation due to their advantages of simple operation, high efficiency, and low cost. However, homogeneous transition metal catalysts can cause harm to the water environment and even human health during the PMS activation process.

[0004] Heterogeneous metal catalysts, on the other hand, have been widely used due to their advantages of low energy consumption, catalytic stability, and reusability. In addition, bimetallic catalysts have attracted much attention because the synergistic effect between different metal ions can improve the catalytic activity. In particular, the Mn-Fe bimetallic catalyst has the advantages of environmental friendliness, high efficiency, and low cost, and has great potential catalytic ability for PMS. Although the Mn-Fe bimetallic catalyst shows excellent catalytic performance in activating PMS, the bimetallic material particles are limited by their aggregates in the liquid-phase reaction, and only the active sites at the edge of the aggregates participate in the reaction. Layered structure materials have abundant active sites due to the high surface area obtained from the charge balance between cations and anions. These two characteristics can enhance the synergistic effect between Mn and Fe. Layered double hydroxides (LDHs) are ideal precursors for preparing layered metal oxides due to their unique structure and flexible ion-exchange properties. The calcined layered double oxides (LDOs) products have the following characteristics: (1) a large number of exposed Mn and Fe active sites; (2) a high surface area; (3) more dispersed metals than the original LDHs metals. Due to these characteristics, LDOs have received extensive attention in catalysis and adsorption and have been selected as efficient catalysts to activate oxidants to degrade organic pollutants in the advanced oxidation process. In recent years, a large number of studies have been carried out on the mechanism of action of the LDO / PMS system. The main important pathways for activating PMS by LDO can be summarized as follows: the metal ions exposed on the catalyst surface act as active sites for PMS activation to generate active free radicals. In addition, the surface hydroxyl groups of heterogeneous catalysts are crucial for the activation of PMS.

[0005] The surface of biochar contains a large number of hydrophilic oxygen-containing groups that can form hydrogen bonds with water molecules, while the internal hydrophobic aromatic structure prefers to enrich the more hydrophobic BPA pollutants, promoting the optimization of the catalytic degradation effect of the catalyst. In addition, the electron transfer ability of the oxygen-containing functional groups (such as -OH and -OOH) of sludge biochar (SBC) can indirectly or directly activate PMS to generate free radicals. Due to the special properties of Fe (such as reducibility, catalytic activity, and magnetism), the SBC-Fe composite material can exhibit the synergistic effect of SBC and Fe. Some studies have shown that the introduced biochar promotes the activation of PMS by CoFe layered double hydroxides (CoFe-LDH). Using sludge as the raw material for biochar can utilize domestic sewage sludge as solid waste, and the metal elements contained in the sludge can provide additional active metal sites to catalytically degrade the pollutant BPA, reducing the dosage of FeMn-LDO while providing better degradation efficiency. It is more economical and efficient than using FeMn-LDO alone. Although transition metals have been recognized as efficient catalysts for activating persulfate, some metals such as Cu, Mn, Co, Fe, and Mo exhibit high catalytic activity, but in practical applications, the working pH value range is narrow, metal ions are easily dissolved out causing secondary pollution, and the powder catalyst requires post-treatment and is not easy to recycle. The LDO composite with biochar is expected to improve the dissolution of metal ions.

[0006] In this study, sludge MnFe-LDH was used as the precursor and calcined at 600 °C for 5 h to obtain a composite material with high efficiency in degrading BPA. The preparation of the above materials and their application in BPA-polluted water bodies provide new ideas and technical support for the emergency treatment of actual BPA pollution, and have very important practical significance for environmental sustainable development. Summary of the Invention

[0007] In order to overcome the disadvantages of metal ion escape, low catalytic activity, and easy agglomeration in the PMS system in the prior art, the present invention provides a layered double hydroxide composite sludge biochar catalyst material with higher catalytic activity and not easy to agglomerate.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a layered double hydroxide / sludge biochar material. The main raw materials of the modified biochar include: domestic sewage aeration tank sludge, NaOH, Na2CO3, FeCl3·6H2O, and MnCl2·4H2O. The domestic sewage aeration tank sludge is used to prepare dry sludge, and the ferric chloride solution and manganese chloride solution are used to prepare sludge composite layered double hydroxides. The final sludge biochar composite layered double metal oxide catalyst can be prepared by calcining the sludge composite layered double hydroxides.

[0009] The above-mentioned sludge composite layered double hydroxide, the specific preparation process includes: after filtering the domestic sludge by suction filtration, washing it with deionized water until the washing liquid is neutral, drying it at 85 °C for 24 h, and then grinding the dried sludge through a 100-mesh sieve to obtain dry sludge.

[0010] The above-mentioned sludge composite layered double hydroxide, the specific production process includes: adding 2 - 8 g of dry sludge to 40 ml of deionized water to obtain a sludge suspension. Mixing 0.9895 g of MnCl₂·4H₂O and 1.35 g of FeCl₃·6H₂O into 100 mL of deionized water to obtain a metal salt solution, and dissolving 1.4 g of NaOH and 1.59 g of Na₂CO₃ in 100 mL of deionized water to obtain an alkaline solution. Slowly drop the metal salt solution and the alkaline solution into the dry sludge suspension simultaneously, stir continuously, and adjust the pH to 10.0 - 11.0. After stirring for 4 h, age at 60 °C for 24 h. Centrifuge and collect the obtained mixture, and wash it thoroughly with deionized water until the pH is close to neutral. Dry the brown product in an oven overnight to obtain the sludge composite layered double hydroxide.

[0011] Furthermore, the above-mentioned sludge composite layered double hydroxide is calcined at 400 - 600 °C for 5 h under the protection of nitrogen, and then sieved through a 100-mesh sieve to obtain the sludge biochar composite layered double metal oxide.

[0012] Furthermore, the present application also provides an application of the above-prepared sludge biochar composite layered double metal oxide, specifically, it is used to activate peroxymonosulfate (PMS) to degrade organic pollutants in the water environment.

[0013] Furthermore, the organic pollutant is bisphenol A (BPA).

[0014] Furthermore, the volume of the water environment to be degraded is 400 ml, and the pH is 3 - 11.

[0015] Furthermore, the optimal reaction conditions for the degradation of the water environment are: the dosage of the sludge biochar composite layered double metal oxide is 80 mg, the initial concentration of bisphenol A is 20 mg / L, the volume of the bisphenol A solution is 400 ml, pH = 7, the temperature is 25 °C, the dosage of potassium peroxymonosulfate is 0.1 g, and the removal rate of BPA reaches 96.4%.

[0016] Furthermore, the above-mentioned sludge biochar composite layered double metal oxide can be recycled after suction filtration, washing and drying.

[0017] The beneficial effects of the present invention are:

[0018] 1. In this application, the biomass domestic sewage sludge, as a solid waste that needs to be landfilled, recycling it as the biomass for biochar improves economic efficiency. The metal elements contained in the sludge can provide additional active metal sites to catalyze the degradation of pollutant BPA, reducing the dosage of FeMn-LDO while providing better catalytic activity, reducing the escape of metal ions, and being more economical and efficient than using FeMn-LDO alone. Moreover, the disadvantage of easy agglomeration of FeMn-LDO loaded with biochar is also greatly improved.

[0019] 2. The sludge biochar composite layered double metal oxide in this application has a better BPA degradation rate than the single layered double metal oxide alone. This is because after compounding with sludge biochar, the distribution of Fe and Mn is uniform, improving the efficiency of the catalyst. The specific surface area of the composite material is significantly higher than that of the single layered double metal oxide and sludge biochar. This characteristic enables the catalyst to adsorb more pollutants and enrich them at the active sites for degradation. At the same time, the hydroxyl functional groups rich on the surface of biochar can generate a large number of hydroxyl radicals, effectively promoting the progress of the degradation reaction.

[0020] 3. The sludge biochar composite layered double metal oxide material prepared in this application has significant magnetic characteristics, and the catalyst can be rapidly separated and recycled by applying an external magnetic field. This characteristic makes the material show good application prospects in the degradation treatment of bisphenol A (BPA) in the water environment. It not only has high degradation performance but also can realize the recycling of the catalyst, providing a new sustainable solution for the water treatment field. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the drawings and embodiments.

[0022] Figure 1 . Appearance diagram of the material of this application

[0023] Figure 2 . Experimental diagram of the effect of the material of this application on degrading bisphenol A

[0024] Figure 3 . SEM diagram of the material of this application DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025]

Example 1

[0026] (1) Preparation of precursor sludge composite layered double hydroxide: After filtering the domestic sewage sludge by suction filtration, wash it with deionized water until the washing liquid is neutral, put it in an oven at 85 °C and dry it for 24 h, and then grind the dried sludge through a 100-mesh sieve to obtain dry sludge.

[0027] The above-mentioned sludge composite layered double hydroxide, the specific production process includes: adding 2-8 g of dry sludge into 40 ml of deionized water to obtain a dry sludge suspension. Mix 0.9895 g of MnCl2·4H2O and 1.35 g of FeCl3·6H2O into 100 mL of deionized water to obtain a metal salt solution, and dissolve 1.4 g of NaOH and 1.59 g of Na2CO3 in 100 mL of deionized water to obtain an alkaline solution. Slowly drop the metal salt solution and the alkaline solution into the dry sludge suspension at the same time, stir continuously, and adjust the pH to 10.0-11.0. After stirring for 4 h, age at 60 °C for 24 h. Centrifuge and collect the obtained mixed solution, and wash it thoroughly with deionized water until the pH is close to neutral. Dry the brown product in an oven overnight to obtain the sludge composite layered double hydroxide.

[0028] (2) Preparation of sludge biochar composite layered double metal oxide: Calcinate the above-mentioned sludge composite layered double hydroxide under the protection of nitrogen at 400-600 °C for 5 h, grind it and then sieve it through a 100-mesh sieve to obtain the sludge biochar composite layered double metal oxide. Obtain the material

[0029] The sludge biochar composite layered double metal oxide prepared in Example 1 and the layered double metal oxide without composite sludge biochar were used to degrade BPA. The reaction conditions were: the material dosage was 80 mg respectively, the initial concentration of bisphenol A was 20 mg / L, the volume of bisphenol A solution was 400 ml, pH = 7, the dosage of potassium persulfate was 0.1 g, pH was 7, and the temperature was 25 °C. The removal rate of BPA by the composite sludge biochar layered double metal oxide can reach 96.4% under the above conditions.

[0030] Figure 1 As shown, the material is in the form of brownish-black powder.

[0031] Figure 2 As shown, it is the experimental effect diagram of the degradation of bisphenol A by the composite material of this example.

[0032] Figure 3 As shown, it is the SEM diagram of SBC / FeMn-LDO prepared in this example. It can be seen in the figure that FeMn-LDO adheres to the surface of the sludge biochar material. Among them, FeMn-LDO all presents small spheres of different sizes. The biochar is in the blue frame, and the FeMn-LDO attached to the surface of the biochar is in the red frame. It shows that the composite structure prepared in this application has a high specific surface area on the surface, which can provide a large number of active sites for the degradation of BPA.

Claims

1. A method for preparing a SBC / FeMn-LDO composite material, characterized in that: The specific preparation steps include: (1) Preparation of dry sludge: After filtering the domestic sewage sludge, wash it with deionized water until the washing liquid is neutral, put it into an oven at 85°C for 24 hours, and then grind the dried sludge through a 100-mesh sieve to obtain dry sludge; (2) Preparation of precursor sludge composite layered double hydroxide: Add 2-8g dry sludge to 40ml deionized water to obtain a dry sludge suspension; mix 2.97g MnCl2·4H2O and 1.35g FeCl3·6H2O in 100mL deionized water to obtain a metal salt solution, and dissolve 1.4g NaOH and 1.59g Na2CO3 in 100mL deionized water to obtain an alkaline solution; slowly add the metal salt solution and the alkaline solution to the dry sludge suspension at the same time, stirring continuously, and adjust the pH to 10.0-11.0; after stirring for 4h, age at 60℃ for 24h; collect the obtained mixed solution by centrifugation, and thoroughly wash it with deionized water until the pH is close to neutral; dry the brown product in an oven overnight to obtain a sludge composite layered double hydroxide; (3) Preparation of the final sludge biochar composite layered bimetallic oxide: The sludge composite layered double hydroxide was calcined at 600° C. for 5 h under the protection of nitrogen, ground and then sieved with a 100-mesh sieve to obtain the sludge biochar composite layered bimetallic oxide.

2. The method for preparing a SBC / FeMn-LDO composite material according to claim 1, characterized in that: In the step (2), the mixed metal salt solution Mn 2+ / Fe 3+ =3:1, Mn 2+ +Fe 3+ =0.2mol / L.

3. The method for preparing a SBC / FeMn-LDO composite material according to claim 1, characterized in that: The mixed metal salt solution and the alkaline solution in step (1) are added dropwise by co-precipitation method; wherein the concentration of NaOH in the alkaline solution is 0.35 mol / L, and the concentration of Na2CO3 is 0.15 mol / L.

4. The method for preparing a SBC / FeMn-LDO composite material according to claim 1, characterized in that: The calcination temperature was 600°C and the calcination time was 5 hours.

5. An application of the sludge biochar composite layered bimetallic oxide according to any one of claims 1 to 4, characterized in that: Specifically, it is used to degrade organic pollutants in water environments.

6. The use of the sludge biochar composite layered bimetallic oxide according to claim 5, characterized in that: The organic pollutant is bisphenol A; the pH of the adsorption water environment is 3-11.

7. The use of the sludge biochar composite layered bimetallic oxide according to claim 5, characterized in that: The reaction conditions of the degradation water environment are: material dosage is 80 mg, initial concentration of bisphenol A is 20 mg / L, volume of bisphenol A solution is 400 ml, pH=7, potassium persulfate dosage is 0.1 g, pH is 7, temperature is 25°C; under the above conditions, the removal rate of BPA by composite sludge biochar layered bimetallic oxide can reach 96.4%.

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