Catalyst for heterogeneous catalytic ozonation and preparation method and application thereof

Abstract

The invention provides a catalyst for heterogeneous catalytic ozonation and a preparation method and application thereof. The method for preparing the catalyst comprises the following steps: providing biomass derived from bamboo; contacting the biomass with a chemical stripping agent and reacting under hydrothermal reaction conditions to strip hemicellulose and lignin from the biomass so as to obtain a stripped biomass; subjecting the exfoliated biomass to a pyrolysis process to obtain a carbon skeleton; and loading a metal on the carbon skeleton to obtain the catalyst. The mechanical strength and stability of the obtained catalyst base material can be improved, and the specific surface area of the catalyst base material can be increased, so that the prepared catalyst has an improved organic matter removal effect.

Description

Technical Field

[0001] This disclosure generally relates to the field of wastewater treatment technology, and specifically to catalysts for heterogeneous ozone catalytic oxidation, their preparation methods, and uses. Background Technology

[0002] Ozone (O3) is a strong oxidant that can decompose organic pollutants into short-chain intermediates, thus degrading them. It is commonly used in wastewater treatment. In systems utilizing ozone to oxidize organic pollutants, O3 typically reacts directly with organic matter in molecular form, or through chain reactions to generate highly reactive oxidants, such as hydroxyl radicals (·OH), which then react indirectly with organic matter, achieving a more thorough oxidation effect. The use of catalysts can significantly improve the efficiency of hydroxyl radical generation by ozone, thereby enhancing the degradation of organic pollutants.

[0003] Based on water solubility, catalysts can be classified into homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts suffer from problems such as difficulty in separation and easy loss, and are prone to causing secondary pollution of water bodies. Compared with homogeneous catalysts, heterogeneous catalysts are easy to separate from water bodies and do not cause secondary pollution. Therefore, heterogeneous catalysts are more widely used in the ozone catalytic oxidation treatment of wastewater, a process called heterogeneous catalytic ozonation (HCO).

[0004] As heterogeneous catalysts, two-dimensional (2D) carbon frameworks have attracted considerable research interest due to their significant characteristics, such as strong binding sites, high specific surface area, excellent electron mobility, and applicability. However, large-scale production of these catalysts remains a major challenge due to high cost, crystallinity, and limited yield, hindering their industrial-scale application in HCO processes.

[0005] Furthermore, modifying the two-dimensional carbon framework with metals can improve its stability and enable the metals to enhance O3 conversion by acting as redox mediators. However, to date, due to the complexity, uneconomical nature, and immaturity of industrial-scale metal coating schemes, the catalytic activity of two-dimensional carbon frameworks used in HCO processes remains rather unsatisfactory and unclear. Summary of the Invention

[0006] One objective of this invention is to provide a method for preparing a catalyst for heterogeneous ozone catalytic oxidation, and the catalyst provided by this method. The method of this invention uses bamboo or its residues as a substrate material. Through chemical exfoliation, the hemicellulose and lignin (partially) in the bamboo or its residues are hydrolyzed, improving the mechanical strength, stability, and specific surface area of ​​the resulting catalyst substrate, thereby enhancing the removal of organic matter.

[0007] In a first aspect, the present invention provides a method for preparing a catalyst, comprising:

[0008] Provides biomass derived from bamboo;

[0009] The biomass is contacted with a chemical stripping agent and reacted under hydrothermal conditions to strip hemicellulose and lignin from the biomass, thereby obtaining stripped biomass.

[0010] The stripped biomass is subjected to a pyrolysis process to obtain a carbon skeleton; and

[0011] Metals are loaded onto the carbon framework to obtain the catalyst.

[0012] In some embodiments, the chemical stripping agent includes strong acids such as nitric acid, hydrochloric acid, and sulfuric acid.

[0013] In some embodiments, the hydrothermal conditions include a temperature of 100-200°C, and preferably, a reaction time of 1-5 hours.

[0014] In some embodiments, the volume concentration (v / v) of the strong acid in the chemical stripping agent is 5-20% during the stripping step.

[0015] In some embodiments, the pyrolysis process is carried out at a temperature of 400-700°C, preferably for 1-5 hours.

[0016] In some embodiments, the step of loading metal onto the carbon framework includes:

[0017] A slurry is obtained by mixing metal salts, a carbon skeleton, and water; and

[0018] The slurry is heated to obtain a carbon skeleton loaded with metal.

[0019] In some implementations, the slurry is heated by microwave.

[0020] In some embodiments, the slurry is heated to 50-100°C.

[0021] In some embodiments, the metal is selected from copper, zinc, manganese, and nickel.

[0022] In a second aspect of the invention, a catalyst prepared according to the method described in the first aspect is also provided.

[0023] In some embodiments, the catalyst has a concentration of 50-600m. 2 The specific surface area is / g; and / or the catalyst has a pore size of 1-2nm.

[0024] In some embodiments, the metal to carbon skeleton in the catalyst has a weight ratio of 0.01-5.

[0025] In some embodiments, the catalyst has an oxygen content of 5-50% by weight, and / or the catalyst has a nitrogen content of 1-3% by weight, and / or the catalyst has a carbon content of 40-85% by weight.

[0026] In a third aspect of the invention, the use of the catalyst prepared according to the method of the first aspect or the catalyst according to the second aspect for wastewater treatment, particularly for electroplating wastewater treatment, is also provided. Attached Figure Description

[0027] The above and other objects and features of this disclosure will become apparent from the following description of this disclosure when taken in conjunction with the accompanying drawings.

[0028] Figure 1 A schematic diagram of a chemical stripping process for biomass derived from bamboo, according to one embodiment, is shown.

[0029] Figure 2 A schematic diagram of (a) the metal modification process according to one embodiment is shown, and (b) the material structure obtained by modifying the metal on the stripped carbon skeleton.

[0030] Figures 3a to 3f The OA removal rates (%) of catalysts prepared with carbon skeletons treated with different metal loading ratios and different concentrations of nitric acid are shown. The experimental conditions were: [OA] concentration = 1 Mm, [O3] flow rate = 150 mL / min, [O3] concentration = 10 mg / L, [Cu@EC]O = 1 g / L, pH = 8.5 (using 2 mM NaHCO3 solution as buffer).

[0031] Figure 4 Physicochemical analyses of EC and Cu@EC are shown, where a and b are SEM analyses of EC; c and d are SEM-EDS analyses of EC; e is XRD analysis of the unexfoliated raw carbon skeleton (CK) and EC; f and g are SEM analyses of Cu@EC; h, i, and j are SEM-EDS analyses of Cu@EC; and k is XRD analysis of the unexfoliated raw Cu@EC.

[0032] Figure 5 The pH values ​​of EC, Mn@EC and Cu@EC are shown. zpc analyze.

[0033] Figure 6a The correlation between viscosity and shear rate is shown; Figure 6b The correlation between shear stress and shear rate under different catalyst dosages is shown; Figure 6c and Figure 6d This represents the fitting of various pseudoplastic rheological models.

[0034] Figure 7 The dissolved ozone in the system with and without a catalyst is shown. The experimental conditions were: [O3] flow rate = 300 mL / min, [O3] concentration = 16 mg / L, [Cu@EC]0 = 1 g / L, pH = 8.5 (using 2 mM NaHCO3 solution as buffer).

[0035] Figure 8 The removal rate of oxalic acid (OA) by Cu@EC synthesized using PO, impregnation, and microwave-assisted methods is shown. The experimental conditions were: OA concentration = 1 mM, O3 flow rate = 300 mL / min, O3 concentration = 16 mg / L, Cu@EC O = 1 g / L, pH = 8.5 (using 2 mM NaHCO3 solution as buffer).

[0036] Figure 9 The removal rate of nitrobenzene by Cu@EC synthesized using PO, impregnation, and microwave-assisted methods is shown. The experimental conditions were as follows: [nitrobenzene] concentration = 100 μL / L, [O3] flow rate = 300 mL / min, [O3] concentration = 16 mg / L, [Cu@EC]O = 1 g / L, pH = 8.5 (using 2 mM NaHCO3 solution as buffer).

[0037] Figures 10a-10b show the HCO3 treatment process of electroplating wastewater with and without a catalyst. The experimental conditions were as follows: COD concentration = 4500 mg / L, TOC concentration = 1625.3 mg / L, Ni concentration = 58.9 mg / L, O3 flow rate = 300 mL / min, O3 concentration = 40-60 mg / L, Cu@EC0 = 1 g / L, pH = 9.7 (using 2 mM NaHCO3 solution as buffer).

[0038] Figure 11 The OA removal rates of the carbon skeleton stripped with different metals are shown. The experimental conditions were as follows: nitric acid concentration of the treated carbon skeleton: 10-15%, O3 concentration: ~10 mg / L, O3 flow rate: 150 mL / min, pH 8.5, OA concentration: 1 mM, buffer NaHCO3 concentration: 2 mM, catalyst dosage: 1 g / L, total volume of solution to be treated: 100 mL, and run time: 30 min.

[0039] Figure 12The stability test results of Cu@EC synthesized by microwave-assisted method in the embodiments of the present invention are shown under the condition of O3 presence. The experimental conditions were as follows: nitric acid concentration of the carbon skeleton: 10-15%, O3 concentration: ~60 mg / L, O3 flow rate: 300 mL / min, OA concentration: 1 mM, catalyst dosage: 1 g / L, total amount of wastewater solution to be treated: 100 mL, and running time: 120 min.

[0040] Figure 13 The changes in OA concentration over time when treating wastewater using PO and Cu@EC synthesized by microwave-assisted method in the embodiments of the present invention are shown. The experimental conditions were as follows: nitric acid concentration of the carbon skeleton being treated: 10-15%, O3 concentration: ~20 mg / L, O3 flow rate: 300 mL / min, pH 8.5, OA concentration: 1 mM, buffer solution NaHCO3 concentration: 2 mM, catalyst dosage: 1 g / L, total volume of wastewater to be treated: 300 mL, and running time: 60 min. Detailed Implementation

[0041] definition

[0042] Throughout the application, where a composition is described as having, including, or containing specific components, or a process is described as having, including, or containing specific process steps, it is contemplated that the compositions taught by the present invention may also consist substantially of the listed components or consist substantially of the listed process steps.

[0043] In this application, when an element or component is referred to as being included in and / or selected from the list of listed elements or components, it should be understood that the element or component can be any one of the listed elements or components, or the element or component can be selected from a group consisting of two or more listed elements or components. Furthermore, it should be understood that the elements and / or features of the compositions or methods described herein can be combined in various ways, whether explicitly stated or implicit, without departing from the spirit and scope of the teachings of this invention.

[0044] It should be understood that the order of steps or the sequence of actions is not important as long as the teachings of this invention remain operable. Furthermore, two or more steps or actions can be performed simultaneously.

[0045] Unless otherwise expressly stated, the use of the singular in this document includes the plural (and vice versa). Furthermore, when the term “about” is used before a quantity value, this teaching also includes the specific quantity value itself, unless otherwise specified. As used herein, the term “about” is a variation of ±10%, ±7%, ±5%, ±3%, ±1%, or ±0% of an index value, unless otherwise stated or inferred.

[0046] In this invention, the term "optional" refers to two embodiments in which the features (e.g., components, steps, etc.) defined by the term may or may not be present.

[0047] The “normal temperature” conditions mentioned in this invention refer to general temperature or room temperature, which is usually defined as 20-25°C, for example, a temperature condition of 25°C.

[0048] The advantages and features of the present invention will become clearer from the following description of preferred embodiments and illustrative examples. The scope of the invention is not limited to any of the specific embodiments described herein.

[0049] Ozone catalytic oxidation technology is an advanced oxidation technology based on ozone. It combines the strong oxidizing properties of ozone with the adsorption and catalytic characteristics of catalysts, effectively addressing the problem of incomplete degradation of organic matter. Ozone catalytic oxidation is classified into homogeneous catalytic ozonation and heterogeneous catalytic ozonation based on the phase of the catalyst. Heterogeneous catalytic ozonation utilizes a solid catalyst to accelerate the oxidation reaction in the liquid (or gas) phase under normal pressure. The catalyst exists in a solid state, making it easy to separate from water, resulting in less secondary pollution and a simplified treatment process.

[0050] The heterogeneous ozone catalytic oxidation process can be divided into three stages: ① When O3 dissolves in the liquid phase, the catalyst adsorbs and activates it, generating a large number of hydroxyl radicals (·OH); ② Organic pollutants are adsorbed on the catalyst surface to form surface chelates; ③ ·OH reacts with the chelates in an oxidation reaction. In the HCO process, the catalyst interacts with ozone to produce highly active oxidants, such as (·OH), thereby effectively degrading organic pollutants into carbon dioxide. The catalytic ozone process not only improves degradation efficiency but also reduces the amount of ozone required, minimizing the formation of harmful byproducts. In summary, this technology has great potential in controlling organic pollution and promoting a cleaner, healthier environment. However, the limitations of currently used catalysts in large-scale economic production and continuous operation hinder the industrial-scale application of the HCO process.

[0051] This invention utilizes biomass as a precursor for carbonaceous materials to develop a graphene-like carbon framework. This framework possesses a two-dimensional planar structure similar to graphene and exhibits high mechanical strength and stability. This method aligns with the concept of "turning waste into treasure" and holds great potential in addressing the challenges associated with large-scale catalyst production.

[0052] Among various raw materials, bamboo or its residues have significant application advantages. For example, bamboo has a closed and multi-layered structure and contains high levels of natural solid cellulose crude fiber, carbon, and silicon dioxide. Large bamboo forests exist in many parts of China, such as Jiangsu, Sichuan, and Chongqing. Benefiting from these favorable natural conditions, processing bamboo waste biomass into environmentally friendly, sustainable, and cost-effective two-dimensional carbon skeletons is of great significance. When using bamboo waste biomass as a catalyst substrate, this invention involves careful pretreatment of the biomass to obtain ideal catalyst substrate properties, such as a large specific surface area and crystallinity of the carbon skeleton.

[0053] This invention provides a pretreatment method for biomass exfoliation. Biomass exfoliation refers to separating layered materials into thinner sheets or two-dimensional frameworks similar to high-quality graphene-like sheets. Specifically, this invention employs a chemical exfoliation method for biomass exfoliation. This method is more scalable and ideal for biomass exfoliation because it selectively hydrolyzes lignin and hemicellulose under mild conditions and promotes high crystallinity of cellulose, thus facilitating further processing into high-quality graphene-like sheets. The exfoliation method provided by this invention helps improve the performance of two-dimensional materials, such as increasing the surface area, improving electron mobility, and increasing exposed active sites, which is crucial for improving the catalytic performance of catalysts in HCO3 and other functional applications.

[0054] Modifying a carbon framework with metals can improve the stability of the two-dimensional carbon framework and enhance the conversion of O3 by acting as a redox medium. To date, industrial-scale metal coating schemes have been complex, uneconomical, and immature, resulting in less than ideal and unclear catalytic activity in the HCO process. Therefore, developing simple and economical catalysts that precisely incorporate metals onto high specific surface area carbon substrates is an effective strategy to improve atom utilization and the uniformity of active sites. In this invention, metal modification can be achieved via a microwave-assisted method. The rapid increase in temperature accelerates the growth of the metal on the carbon framework surface, contributing to the metal's dispersibility and stability. Most importantly, even without any binder, the metal will not peel off from the carbon framework due to the strong covalent bonds generated by the microwave-assisted method.

[0055] This invention first provides a method for preparing a catalyst, comprising:

[0056] Provides biomass derived from bamboo;

[0057] The biomass is contacted with a chemical stripping agent and reacted under hydrothermal conditions to strip hemicellulose and lignin from the biomass, thereby obtaining stripped biomass.

[0058] The stripped biomass is subjected to a pyrolysis process to obtain a carbon skeleton; and

[0059] Metals are loaded onto the carbon framework to obtain the catalyst.

[0060] In the method of this invention, the biomass can be derived from various parts of bamboo, such as bamboo leaves, bamboo pith (branches), bamboo shoots, bamboo sap, bamboo roots, and bamboo culms (culm stalks, culm bases, culm stems), etc. There is no particular limitation on the bamboo species used in the method of this invention; common bamboo species can be used in the above-described method for preparing the catalyst.

[0061] The chemical exfoliation method described in this paper can yield carbon frameworks with high crystallinity, high functionality, and high specific surface area. Specifically, chemical exfoliation helps to prepare two-dimensional materials with superior properties, such as increasing specific surface area to improve electron mobility and exposing more active sites, which is crucial for catalysis and other functional applications.

[0062] In some embodiments, the biomass derived from bamboo is first washed and completely dried, and preferably pulverized to a size of, for example, 1-3 mm. In some embodiments, the biomass derived from bamboo is in powder form, for example, having a particle size of less than 1 mm.

[0063] In some embodiments, the chemical stripping agent includes strong acids such as nitric acid, hydrochloric acid, and sulfuric acid. In a preferred embodiment, the chemical stripping agent may include nitric acid.

[0064] The hydrothermal reaction conditions described in this invention refer to a chemical process in which water, as a solvent, reacts with other substances under high pressure and high temperature. Hydrothermal reactions are typically carried out in a closed reaction vessel (e.g., an autoclave), with reaction temperatures usually above 100°C and pressures above atmospheric pressure, to increase the reaction rate and alter the composition of the reaction products.

[0065] In some embodiments, the hydrothermal reaction conditions of the present invention include reacting at a temperature of 100-200°C.

[0066] In some embodiments, the hydrothermal reaction can be carried out at temperatures of 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, and 200°C, or within any two of these temperatures. A preferred reaction temperature is 100-150°C, more preferably 110-130°C. At this reaction temperature, efficient hydrolysis of hemicellulose and lignin is more favorable.

[0067] In some embodiments, the reaction time of the hydrothermal reaction can be, for example, 1-5 hours or longer. In some embodiments, the reaction time of the hydrothermal reaction can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, or a longer period of time.

[0068] In the method of the present invention, different degrees of biomass stripping are achieved by using chemical stripping agents of varying concentrations. In some embodiments, the volume concentration (v / v) of the strong acid in the chemical stripping agent is 1-20%. In some embodiments, the volume concentration of the strong acid in the chemical stripping agent can be 5-20%, preferably 10-15%. In some embodiments, the volume concentration of the strong acid in the chemical stripping agent can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range thereof.

[0069] In some embodiments, the pyrolysis process is carried out at a temperature of 400-700°C, preferably 450-650°C, more preferably 500-600°C. In some embodiments, the pyrolysis process can be carried out at temperatures of 450°C, 460°C, 470°C, 485°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, or 650°C, or within any two of the above temperatures. At these pyrolysis temperatures, effective carbonization of the exfoliated carbon skeleton of the present invention is more favorable.

[0070] In some embodiments, the reaction time of the pyrolysis reaction can be, for example, 1-5 hours or longer. In some embodiments, the reaction time of the pyrolysis reaction can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, or a longer period of time.

[0071] In some embodiments, the step of loading metal onto the carbon framework includes:

[0072] A slurry is obtained by mixing a metal salt carbon skeleton with water; and

[0073] The slurry is heated to obtain a carbon skeleton loaded with metal.

[0074] In some embodiments, the metal is selected from copper, zinc, manganese, and nickel.

[0075] The metal salts used in this invention can be selected from water-soluble salts of the aforementioned metals, such as nitrates, hydrochlorides, sulfates, or permanganates (e.g., KMnO4).

[0076] In some embodiments, the slurry can be heated by microwaves, i.e., a microwave-assisted synthesis of metal-loaded carbon frameworks. Microwave-assisted synthesis facilitates the growth of metals at metal-nitrogen / oxygen coordination sites on the carbon framework, during which metal ions adsorb onto the functionalized carbon through in-situ interactions to form a metal-carbon framework. Furthermore, microwave irradiation thermally catalyzes the formation of a fluffy metal-carbon framework.

[0077] In some embodiments, the metal salt is poured into deionized water containing the carbon framework. The resulting slurry is placed in a microwave oven and heated at a microwave power of 400-1200 watts for 10-60 seconds, then stirred to obtain a homogeneous suspension. The suspension is then microwaved again for 90-150 seconds to obtain a fluffy carbon framework product (metal@EC). Microwave powers that can be used are 400 watts, 500 watts, 600 watts, 700 watts, 800 watts, 900 watts, 1000 watts, 1100 watts, or 1200 watts, preferably 600-1000 watts, and more preferably 750-850 watts.

[0078] The present invention also provides catalysts prepared according to the foregoing method.

[0079] In some embodiments, the catalyst has a concentration of 50-600m. 2 Specific surface area per g, for example, having 50 m² / g 2 / g, 100m 2 / g, 150m 2 / g、200m 2 / g、250m 2 / g、300m 2 / g, 350m 2 / g、400m 2 / g、450m 2 / g、500m 2 / g、550m 2 / g、600m 2 Specific surface area per g.

[0080] Because chemical stripping agents are generally strong oxidizers, they oxidize the carbon skeleton during the chemical stripping process, increasing the oxygen content in the carbon skeleton structure to some extent. In some embodiments, the catalyst has an oxygen content of 5-50% by weight, for example, 45%, 40%, 30%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, or 5%.

[0081] In some embodiments, the catalyst has a nitrogen content of 1-3% by weight, for example, an oxygen content of 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3.0%.

[0082] In some embodiments, the catalyst has a carbon content of 40-85% by weight, such as 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%, or any range thereof.

[0083] In some embodiments, the catalyst has a pore size of 1-2 nm, for example, pore sizes of 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, and 2 nm.

[0084] In some embodiments, the weight ratio of the metal to the carbon skeleton in the catalyst is 0.01-5, preferably 0.1-2, and more preferably. In some embodiments, the weight ratio of the metal to the carbon skeleton in the catalyst can be 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any range thereto.

[0085] In addition, the present invention also provides the use of the catalyst prepared according to the foregoing method or the catalyst for wastewater treatment, particularly electroplating wastewater treatment.

[0086] The catalyst described in this invention can be used to treat various industrial and domestic wastewaters, such as dyeing and printing wastewater, electroplating wastewater, pharmaceutical wastewater, municipal sewage, landfill leachate, coal chemical wastewater, pesticide wastewater, and membrane concentrate. It can effectively remove dyes and organic matter from wastewater, reducing its environmental harm and enabling it to meet relatively stringent emission standards.

[0087] Specific embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that various modifications are possible without departing from the scope of the invention as described above. The following embodiments are provided for illustrative purposes only.

[0088] Example

[0089] To verify and understand the performance of the obtained nanoscale metal-supported catalyst, the inventors used it in a suspension reactor of HCO to degrade the target compounds oxalic acid (OA) and nitrobenzene. Oxalic acid (kO3 = 0.04 M) was used... -1 ·s -1 ) and nitrobenzene (0.09±0.02M) -1 ·s -1 These pollutants are targeted because they are resistant to ozone and therefore cannot be removed by ozone processes alone. Furthermore, the hydroxyl radicals (·OH) formed when ozone reacts with a catalyst directly oxidize them to CO2 and H2O without forming any intermediate products, which would otherwise also remove ·OH and complicate the quantification of the process's effectiveness.

[0090] I. Material Preparation

[0091] All chemical reagents, including copper nitrate trihydrate (Cu(NO3)2·3H2O), sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), sodium hydroxide (NaOH), and nitric acid (HNO3), were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0092] All solutions were prepared in distilled water (from Origin Water purifier, D8008, Beijing Juyuanxing Technology Development Co., Ltd.).

[0093] Indigo stock solution is prepared by dissolving 0.6 g·L⁻¹ potassium indigo trisulfonate in 20.0 mM phosphate buffer solution and should be stored in the dark before use.

[0094] The ozone stock solution was prepared by continuously bubbling O3(g) (~4% O3(g) / O2(g) mixture) in distilled water (1L) for 30 minutes. The ozone stock solution was obtained by UV spectroscopy at 253 nm (molar absorptivity = 3200 nm). -1 cm -1 ) Determine the ozone concentration in the stock solution.

[0095] All experiments were conducted under constant pH conditions of 8.5 ± 0.1, using 2 mM NaHCO3 as the buffer solution.

[0096] If necessary, 2 mM NaOH and 2 mM HNO3 solutions were also prepared for initial pH adjustment. Synthesis wastewater containing 2 mM NaHCO3 and 1 mM OA, and nitrobenzene synthesis wastewater with a mass concentration of 120 mg / L were prepared to test the catalyst performance.

[0097] In the following examples, the intrinsic viscosity of the oil phase or water phase was tested at room temperature using a rheometer in rotational mode.

[0098] II. Catalyst Preparation

[0099] 1. Preparation of carbon framework

[0100] The bamboo used as a biomass source was collected from Yixing, Jiangsu, China. The collected samples were washed and completely dried in the sun. The bamboo was then pulverized into fine bamboo powder and stored for chemical stripping.

[0101] For chemical exfoliation, 1 kg of bamboo powder was dissolved in an aqueous nitric acid (HNO3) solution and then reacted in an autoclave at 120°C for 2 hours. The exfoliated bamboo powder was collected, filtered, dried (100°C, 24 hours), and then pyrolyzed in a muffle furnace under nitrogen atmosphere at 550°C (heating rate 5°C / min, 2 hours). The exfoliated carbon skeleton (EC) (380 g) obtained after pyrolysis was washed with deionized water (DI) until the pH reached neutral, and then stored in a sealed glass container for further processing.

[0102] Figure 1 The illustration shows an embodiment of the method of the present invention in which biomass derived from bamboo comprises cellulose, hemicellulose and lignin, is pretreated according to the method of the present invention to remove hemicellulose and lignin, and then pyrolyzed and carbonized to obtain the removed carbon skeleton.

[0103] To obtain carbon skeletons with different degrees of exfoliation, 1 kg of bamboo powder was dissolved at different volume concentrations (v / v).

[0104] The hemicellulose and lignin were exfoliated to different degrees in aqueous nitric acid solutions of 5%, 10%, 15%, and 20% (by volume of nitric acid) to study the structure and composition of the different carbon skeletons obtained.

[0105] Comparative Example 1 is a carbon skeleton (unpeeled original carbon skeleton) prepared by pyrolysis of untreated bamboo powder using the same method as described above.

[0106] The composition of each carbon framework was tested and analyzed. Specifically, the morphology of EC and metal@EC was characterized using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The catalyst was chemically characterized using X-ray powder diffraction (XRD). The specific surface area was determined by analyzing N2 adsorption isotherm data using the Bruner-Emmett-Taylor (BET) model. The particle size distribution and average diameter of the prepared carbon framework were determined using a Micromeritics Nano Plus HD-3 instrument. The results are shown in Table 1.

[0107] Table 1. Characterization results of the unexfoliated raw carbon skeleton and carbon skeletons with different degrees of exfoliation.

[0108]

[0109] As shown in Table 1, the original carbon skeleton sample (Comparative Example 1) has a small surface area, pore size, and pore volume, reflecting its complete and dense structure, as it retains the natural structure rich in lignin, cellulose, and hemicellulose.

[0110] The carbon skeleton samples obtained by exfoliating bamboo biomass using 5% HNO3 showed high oxygen content, indicating that bamboo contains abundant oxygen-rich components such as hemicellulose and partially hydrolyzed lignin. The oxygen-containing groups in these components can form reaction sites on the carbon skeleton surface, making it more susceptible to electrophilic attack by oxidants (O3). Compared to carbon structures chemically exfoliated with higher concentrations of nitric acid, the carbon skeleton synthesized with lower concentrations of nitric acid showed higher oxygen content, but the structure was not yet fully stable and exhibited lower stability.

[0111] The carbon skeleton sample obtained by exfoliation with 10-15% HNO3 yielded the highest surface area (537.09 m²). 2 The increased carbon content ( / g) indicates that the internal structure of the carbon skeleton is fully exposed and porosity is formed. The increased carbon content suggests that hemicellulose and lignin are more extensively hydrolyzed, leaving more carbon-rich material and reducing the likelihood of electrophilic attack by oxidants, thus improving the stability of the carbon structure. At the maximum value of 15% in this range, the specific surface area decreases slightly, which is related to the partial collapse or reorganization of the pore network. Furthermore, the increase in pore volume indicates the formation of a large number of macropores or mesopores, which also explains the slight decrease in surface area despite the increase in porosity.

[0112] When the HNO3 concentration increased to 20%, the specific surface area decreased significantly to 57.38 m². 2 / g, this could be due to excessive stripping leading to pore structure collapse or aggregation, as evidenced by the sharp decrease in pore volume. Furthermore, carbon content can also decrease due to excessive removal of carbonaceous materials (carbon in hemicellulose and lignin) or the formation of residues with low carbon density.

[0113] These results indicate that a 10-15% nitric acid concentration is highly suitable for generating carbon frameworks with high specific surface area and pore size, making them more suitable as catalyst substrates. The following examples all utilize carbon frameworks treated with 10-15% nitric acid (by volume) for metal loading and related testing.

[0114] 2. Loading metals onto a carbon framework

[0115] In one embodiment, metallic copper can be loaded onto a carbon framework using a microwave-assisted method. Specifically, different amounts of the metal salt Cu(NO3)2 are poured into deionized water containing 1% carbon framework by weight, wherein the weight ratio of metal salt to carbon framework is 0.1, 0.5, 1, and 2, respectively. The resulting slurry is placed in a microwave oven and heated at 800 watts for 30 seconds, then stirred to obtain a homogeneous suspension. After thorough stirring, it is microwaved again for 120 seconds to obtain a fluffy carbon framework (metal@EC). The resulting carbon framework product is then completely dried and stored.

[0116] Figure 2 (a) A schematic diagram of the metal modification process is shown, in which metal ions are adsorbed onto functionalized carbon through in-situ interactions to form a metal-carbon framework. In addition, microwave irradiation thermally catalyzes the formation of the fluffy metal-carbon framework; (b) The resulting material structure with metal modified on the exfoliated carbon framework, wherein the metal is coordinated with oxygen and / or nitrogen on the carbon framework surface.

[0117] As a comparative example, the unstripped original carbon skeleton (CK) was also subjected to metal loading following the same procedure.

[0118] In another example, metallic copper was loaded onto ECs via an impregnation method. ECs were dispersed in deionized water, and then the metal salt Cu(NO3)2 was added dropwise. The pH of the suspension was adjusted to 10 using NaOH solution to promote copper ion formation. Specifically, the metal salt was poured into deionized water containing 1% carbon skeleton, where the weight ratio of metal salt to carbon skeleton was 0.5, and then stirred to obtain a homogeneous suspension. The suspension was then kept in an oil bath (80°C) for 3 hours, and the resulting precipitate was completely dried in an oven (110°C). The dried product was washed with deionized water and centrifuged several times, then dried at 80°C for 12 hours to obtain the final metal@EC product.

[0119] Compared to the impregnation method in the comparative example, the microwave-assisted metal loading method of this invention significantly shortens the preparation time and more effectively reduces TOC (total Organic Carbon). Figure 8 and Figure 9 ).

[0120] Figure 4 Physicochemical analyses of EC and Cu@EC are shown, where a and b are SEM analyses of EC; c and d are SEM-EDS analyses of EC; e is XRD analysis of the unexfoliated raw carbon skeleton (CK) and EC; f and g are SEM analyses of Cu@EC; h, i, and j are SEM-EDS analyses of Cu@EC; and k is XRD analysis of the unexfoliated raw Cu@EC.

[0121] from Figure 4Scanning electron microscopy images a and b show that the exfoliated carbon framework (EC) retains its original bamboo-like structure, and the exfoliation process facilitates the formation of a layer on the surface. After coating with metal (Cu), the Cu@EC particles exhibit the same morphology, and according to the elemental spectrum results, Cu, C, and O are uniformly distributed. Figure 4 (hj). XRD pattern of the catalyst ( Figure 4 The results (e and k) confirm that the main mineral phases of the unexfoliated pristine carbon framework, EC, and metal@EC are calcite (JCPDs#17-0763) and albite (JCPDs#41-1476). Compared to the pristine carbon framework, the diffraction peaks of EC are broadened, weakened, and almost disappear, likely due to the increased nanopores generated during the chemical exfoliation process. Notably, the coating with metal (Cu) reveals the presence of metallic copper, as indicated by characteristic diffraction peaks corresponding to the cubic nature of copper, consistent with reference pattern JCPDS#46-0099. Coating with metal (Cu) on the exfoliated carbon stabilizes copper and preserves its crystal structure.

[0122] III. Catalyst Performance Evaluation and Characterization Methods

[0123] The inventors first investigated the effect of different metal loadings on the removal of organic matter from wastewater. Using carbon skeletons treated with nitric acid at concentrations of 5-20% by volume, copper was loaded onto the carbon skeletons using a microwave-assisted method to obtain metal@EC products. To further confirm their performance in the HCO process, as described above, different weight ratios (0.1, 0.5, 1, and 2) of copper were loaded onto each synthesized carbon skeleton.

[0124] like Figures 3a-3e As shown, pure ozone (PO) and unloaded metal-based carbon frameworks (EC) are essentially ineffective at removing OA. For carbon frameworks treated with 5% volume HNO3, metal loading only slightly improves OA removal rates. Figure 3b This indicates that the optimal metal deposition effect was not achieved, and the promoting effect of the loaded metal on the activation sites was weak.

[0125] For carbon skeletons treated with HNO3 at 10% and 15% volume concentration ( Figure 3c and Figure 3d A loading rate of 0.5% significantly removed OA (approximately 75%). These results are related to the uniform and smooth copper modification of the carbon framework surface, which promotes rapid and significant OA removal. To distinguish between OA oxidation and adsorption, adsorption was also measured using the same amount of catalyst in solution. It was observed that approximately 2 ± 1.5% of TOC was removed by adsorption within 15 minutes, indicating that adsorption had a very weak effect on OA removal.

[0126] For carbon skeletons treated with 20% volume concentration of HNO3 ( Figure 3e Due to the reduced specific surface area of ​​the catalyst particles, particle aggregation, and a slight decrease in surface active sites, the OA removal rate decreased, but it was still significantly higher than that of the unstripped original carbon skeleton.

[0127] In addition, based on Figures 3a-3e The results showed that a loading metal (copper) to carbon skeleton ratio of 0.5:1 was most suitable. At this ratio, carbon skeletons treated with 10% and 15% volume concentrations of HNO3 could achieve OA removal rates as high as 75%. Figure 3f ).

[0128] Based on this ratio, attempts were also made to load other metals, such as Zn, Mn, and Ni, onto the EC. Figure 11 The results showed that Zn@EC (approximately 60%) and Ni@EC (approximately 40%) achieved high OA removal rates and stable metal deposition, but their inactivation after a period of time could result in slightly lower OA removal rates within 30 minutes. Mn@EC achieved a significantly higher OA removal rate (approximately 98%).

[0129] Figure 12 The stability test results of Cu@EC synthesized by microwave-assisted method in the embodiments of the present invention are shown in the presence of O3, wherein the TOC and Cu concentration remained essentially consistent within 120 minutes, indicating that Cu@EC exhibits excellent carbon and metal stability in ozone applications.

[0130] Figure 5 The pH values ​​of EC, Mn@EC and Cu@EC are shown. zpc Analysis. The pH value of zero point charge (pHzpc) was determined using potentiometric titration of solid samples. Two experiments were conducted, each time adding 10 g of solid to 100 mL of 0.1 M NaNO3 electrolyte. One suspension was titrated with 5 M HNO3, and the other with 5 M NaOH. After allowing 10 minutes for pH equilibration, titrations were performed within a pH range of 3 to 11 to avoid solid dissolution.

[0131] In addition, the stability of the catalyst in the presence of ozone was measured by continuously bubbling 60 mg / L O3(g) into the catalyst suspension at a flow rate of 3 L / h for 2 hours, and the concentrations of leached copper and iron were measured using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0132] At pH 8.5, containing 1 g·L -1 After continuously bubbling O3(g) in a Cu@EC suspension for 2 hours, no Cu ions were leached out, and the total organic carbon (TOC) did not increase due to the oxidation of carbon into the solution.

[0133] Based on the titration results, the pH of EC is... zpc Approximately 8.7; pH increases with the deposition of manganese and copper. zpc The acidity of the catalyst increases as the concentration drops to 5.2. Figure 5 Since OA contains a negative charge, Cu@EC also contains a negative charge at pH 8.5, therefore no OA adsorption was observed (the OA adsorption results also prove this point).

[0134] Since this catalyst is typically used in suspensions, the inventors also analyzed the flow characteristics of the catalyst within the suspension reactor, as maintaining the catalyst in suspension and good mixing within the reactor are crucial for reactions occurring in the suspension reactor.

[0135] Rheological properties, including viscosity, shear rate, and shear stress, also affect particle retention in suspensions. For example... Figure 6a As shown, the viscosity of the Cu@EC suspension was the same at different Cu@EC concentrations (0.1 and 1 g / L), confirming that the presence of Cu@EC had no significant effect on the system's viscosity. This observation further indicates that the loading of Cu@EC particles used does not have a significant impact on the rheological properties of the system. The shear rate was increased from 0 s⁻¹. -1 Increased to 300s -1 This can increase the viscosity of Cu@EC suspensions, thus confirming the shear thickening behavior of particulate fluid mixtures. Shear thickening behavior affects the stability of particulate suspensions, particle sedimentation behavior, and the uniformity of particle dispersion. For example... Figure 6b As shown, the increased shear rate enhances the shear stress experienced by the particles, thereby improving particle dispersibility and reducing particle sedimentation. The shear stress and shear rate data obtained by the inventors at catalyst concentrations of 0.1 and 1.0 g / L show good fit to the Herschel-Bulkley model. Figure 6c and 6d The results indicate that both suspensions exhibit non-Newtonian fluid behavior. In summary, all observed rheological behaviors strongly support the use of Cu@EC in suspension reactors.

[0136] The calculated settling velocity of Cu@EC in the reactor is 0.00741 ms. -1 (Lower than the bubble rising speed (0.01 milliseconds)) -1This indicates that the settling velocity of Cu@EC should be very small under these conditions. The short relaxation time of 1.4–6 seconds (the particle's response to changes in surrounding flow conditions) further suggests that these particles readily adapt to flow variations and resist settling. Furthermore, the calculated Froude number (the ratio of inertial force to gravity) is 1.14, indicating that the particle settling behavior is relative to the surrounding hydrodynamics. Therefore, settling can be controlled by adjusting the hydrodynamics.

[0137] The methods for calculating the settling velocity, particle relaxation time, and Frod number are as follows:

[0138] Suspended particles in a liquid medium are affected by two forces: (1) the liquid flow velocity (v) F ) and particle velocity (v P The resistance (F) caused by the difference D (2) the particle mass (F) caused by buoyancy and gravity. G ).

[0139] Taking all the above forces into account, the velocity (v) of a single particle in a steady flow P It can be described by a formula.

[0140]

[0141] Where, ρ P , and v P These represent particle density, particle diameter, and particle velocity, respectively; v F Represents the velocity of the liquid; ρ F Represents fluid density; C D It is the drag coefficient.

[0142] Gravity and buoyancy (F G This is described by Formula 2.

[0143]

[0144] When particles cannot encounter stirring or liquid flow, their direction of motion becomes perpendicular, at which point v F =0 and v P =Particle settling velocity (v) S ).

[0145] therefore

[0146]

[0147] When the settling velocity tends to stabilize Then there is

[0148]

[0149] According to Stokes' Law:

[0150] C D =24 / Re (5)

[0151] therefore,

[0152]

[0153] relaxation time of particles (t) S By influencing the stability and behavior of particles in a fluid medium, it plays a crucial role in maintaining particle suspension. The relaxation time when the particle velocity is close to 0.99 times the fluid velocity is described as follows.

[0154]

[0155] Here, μ F Indicates the viscosity of the liquid medium.

[0156] Froude number (F r The value is calculated using formula S8, which provides the conditions that affect the behavior and stability of particles in fluid media.

[0157]

[0158] Where, ρ SL and ρ GL Let ρ represent the density of the solid-liquid mixture and the density of the gas-liquid mixture (considered as the density of water), respectively. SL The value is determined by formula S9.

[0159]

[0160] C S This indicates the concentration of particles.

[0161] Figure 7 The amount of dissolved ozone in the system is shown with and without a catalyst.

[0162] according to Figure 7 The O3 decay experimental data, calculated using kinetic equations, show that in the presence of a catalyst, the decay rate constant of dissolved O3 is approximately 4.8 ± 0.3 × 10⁻⁶. -3 s -1 and 3.8±0.4×10 -3 s -1 The value was close to that measured in the absence of a catalyst (5.2 ± 0.3 × 10⁻⁶). -3 s -1 This indicates that the ozone decay caused by the interaction with the catalyst is negligible. The effect of Cu@EC on the ozone decay rate is small. Figure 7 The results show that Cu@EC has a very small effect on ozone decay kinetics (10%).

[0163] like Figure 13 As shown, with the prepared Cu@EC catalyst, a significant reduction of approximately 50% in OA concentration was observed within the first 5 minutes of treatment, decreasing from an initial concentration of approximately 1.0 mM to approximately 0.5 mM, and further to below 0.1 mM after about 30 minutes. In contrast, treatment with pure ozone (PO) resulted in an OA concentration still above 0.8 mM after 60 minutes. This indicates that the catalyst of the present invention has a very significant effect on promoting OA removal.

[0164] To measure the oxidation of organic matter during the HCO3 process, 500 mL of synthetic wastewater (containing 2 mM NaHCO3 and organic matter (OA or nitrobenzene)) and 1 g. L were injected into the reactor. -1 Catalyst. Subsequently, the concentration was 10 mg / L. -1 O3(g) was continuously bubbled into the reactor at a flow rate of 150 mL / min. At desired time intervals, 5 mL samples were drawn from the reactor and aerated with air for 30 seconds to remove any present O3. Samples collected from the reactor section were filtered through a PVDF filter (0.22 μm) and the total organic carbon (TOC) content in the samples (reactor section and permeate) was measured using a TOC analyzer (TOC-LCPH, Shimadzu, Japan). The outlet O3(g) concentration was measured using an O3 gas analyzer.

[0165] As a recalcitrant ozone compound, OA adsorbs and removes approximately 6 ± 0.55% of TOC within 15 minutes, reaching a steady state. Figure 8 However, a significant reduction in TOC was observed with ozone treatment in both the presence and absence of the catalyst. Specifically, the TOC removal rate was approximately 92 ± 3.8% within 15 minutes, indicating that Cu@EC (microwave-assisted method) possesses stronger oxidation capabilities. The excellent TOC removal rate is related to the high surface area and active sites of the catalyst. Furthermore, these results demonstrate that the uniform and controllable growth of copper on the catalyst surface can modulate ozone and organic matter. However, Cu@EC synthesized by the impregnation method in the comparative example failed to achieve significant results because the modification effect of Cu in the impregnation-synthesized catalyst was poor, resulting in low availability of active sites.

[0166] Because nitrobenzene is a compound that is difficult to degrade by ozone, pure ozone treatment only removes 13±2.1% ( Figure 9However, compared to the PO and Cu@EC impregnation method (approximately 22%), the TOC removal rate (approximately 54%) with the addition of the catalyst (Cu@EC microwave-assisted method) was significantly higher. Since the TOC removal rate of the adsorption method was only about 5 ± 1.1% within 15 minutes and reached equilibrium, the TOC removal rate in this case was due to the oxidation process. Overall, the results indicate that the catalyst synthesis was very successful and it possesses a strong oxidizing ability for ozone-recalcitrant compounds.

[0167] Figures 10a-10b show the results of treating electroplating wastewater using the same HCO3 treatment process with and without a catalyst. The chemical oxygen demand (COD) and total organic carbon (TOC) of the wastewater were 4500 mg / L and 1652.3 mg / L, respectively, with a pH of 9.7. The nickel (Ni) content was 58.9 mg / L, existing as a complex bound to organic matter. Complexed nickel cannot be treated by traditional processes such as coagulation, flocculation, adsorption, and ion exchange. Therefore, it is necessary to degrade the organic matter to decompose the nickel-organic complex and promote the release and removal of free nickel.

[0168] In the pure ozone (PO) process (O3 concentration = 40 mg / L, O3 flow rate = 3 L / min), no significant removal of organic matter was observed (Fig. 10a and Fig. 10b). After introducing Cu@EC, a more significant removal effect on organic matter was observed, but more Ni was adsorbed on the catalyst surface because the catalyst contains a negative charge at higher pH values ​​(see...). Figure 5 pH in zpc result).

[0169] Under the same conditions, a very high nickel removal rate (approximately 82%) was observed for MnO@EC. In particular, the oxidation of organic matter in the system was enhanced when the ozone concentration was increased to 60 mg / L. Compared to Cu@EC (approximately 40%) and PO (approximately 60%) conditions, the COD removal rate of MnO@EC was approximately 70%. During this process, a higher nickel adsorption rate (approximately 82%) was also observed for the MnO@EC catalyst.

[0170] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and any improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a catalyst, comprising: Provides biomass derived from bamboo; The biomass is contacted with a chemical stripping agent and reacted under hydrothermal conditions to strip hemicellulose and lignin from the biomass, thereby obtaining stripped biomass. The stripped biomass is subjected to a pyrolysis process to obtain a carbon skeleton; and Metals are loaded onto the carbon framework to obtain the catalyst.

2. The method of claim 1, wherein the chemical stripping agent is selected from strong acids such as nitric acid, hydrochloric acid and sulfuric acid.

3. The method according to claim 1 or 2, wherein the hydrothermal conditions include a temperature of 100-200°C, and preferably, the reaction time is 1-5 hours.

4. The method according to any one of claims 1 to 3, wherein the volume concentration of the strong acid in the chemical stripping agent in the stripping step is 5-20%.

5. The method according to any one of claims 1 to 4, wherein the pyrolysis process is carried out at a temperature of 400-700°C, preferably for 1-5 hours.

6. The method according to any one of claims 1 to 5, wherein the step of loading the metal on the carbon framework comprises: A slurry is obtained by mixing metal salts, carbon skeletons, and water. and The slurry is heated to obtain a carbon skeleton loaded with metal.

7. The method of claim 6, wherein the slurry is heated by microwave.

8. The method according to any one of claims 1 to 7, wherein the metal is selected from copper, zinc, manganese and nickel.

9. The catalyst prepared by the method according to any one of claims 1 to 8.

10. The catalyst according to claim 9, wherein the catalyst has a concentration of 50-600 μm. 2 The specific surface area is / g; and / or the catalyst has a pore size of 1-2nm.

11. The catalyst according to claim 9 or 10, wherein the weight ratio of the metal to the carbon skeleton in the catalyst is 0.01-5.

12. The catalyst according to any one of claims 9 to 11, wherein the catalyst has an oxygen content of 5-50% by weight, and / or the catalyst has a nitrogen content of 1-3% by weight, and / or the catalyst has a carbon content of 40-85% by weight.

13. The use of the catalyst prepared by the method according to any one of claims 1 to 8 or the catalyst according to any one of claims 9 to 12 for wastewater treatment, particularly for electroplating wastewater treatment.

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