Method for low-energy rapid synthesis of metal-bonded graphite stable catalyst and application thereof

Abstract

This invention belongs to the fields of nanomaterial preparation, biomass resource utilization, and advanced oxidation water treatment technology. It discloses a method for the rapid synthesis of metal-bonded graphite-stabilized catalysts with low energy consumption and its applications. This invention utilizes the redox thermal effect of filter paper cellulose and metal nitrates to develop an endothermic induction synthesis technology. This technology induces a controlled, intense exothermic reaction in the precursor under mild conditions of 80-135 °C. Utilizing the localized instantaneous high temperature generated within the material, it drives an in-situ topological transformation of cellulose within 15 seconds, forming a graphite framework with minimal defects, while simultaneously achieving atomic-level reduction and stable anchoring of the metal active sites. When this catalyst is integrated into a continuous flow fixed-bed system, it exhibits excellent persulfate activation performance under extremely high hydraulic loads and extremely short hydraulic residence times, maintaining a removal rate of over 99% for organic pollutants, and showing no significant activity decay after 21 days of operation.

Description

Technical Field

[0001] This invention belongs to the fields of nanomaterial preparation, biomass resource utilization and advanced oxidation water treatment technology, and relates to a method for low-energy-consumption rapid synthesis of metal-bonded graphite stable catalysts and their applications. Background Technology

[0002] With the acceleration of global industrialization, the treatment of industrial wastewater containing recalcitrant organic pollutants such as antibiotics, dyes, and endocrine disruptors has become a major challenge in the field of environmental engineering. Among numerous wastewater treatment technologies, heterogeneous catalytic oxidation based on advanced oxidation processes (AOPs) stands out due to the highly reactive free radicals (such as ·OH and SO42-) generated. ·- This process, characterized by its rapid reaction rate, high mineralization degree, and lack of secondary pollution, is widely used in advanced wastewater treatment. In this process, metal-carbon (MC) composite materials serve as the core catalyst; their interfacial bonding strength, conductivity, and structural stability directly determine the purification efficiency, energy consumption level, and long-term operational life of the catalytic system.

[0003] However, existing metal-carbon composite materials face multiple bottlenecks in practical engineering applications. First, traditional supports suffer from insufficient structural stability and electrical conductivity. Existing carbon-based supports, such as activated carbon, carbon black, or ordinary biochar, are mostly composed of amorphous carbon. These materials have low graphitization levels, which not only limits electron transfer efficiency during catalysis, leading to increased ohmic losses, but also makes them highly susceptible to self-oxidation in strongly oxidizing environments (such as persulfate systems), causing the support structure to collapse. In contrast, highly graphitized carbon materials possess excellent electron mobility and mechanical strength, significantly enhancing the electronic synergistic effect between the metal and the support, making them ideal catalytic supports.

[0004] Secondly, traditional graphitization processes suffer from the dual contradiction of high energy consumption and metal agglomeration. Traditional methods for achieving high graphitization levels typically require prolonged, ultra-high temperature (2000-3000℃) heat treatment. This not only consumes enormous amounts of electrical energy, but also, during the prolonged high-temperature calcination process, the supported metal nanoparticles are highly susceptible to thermal migration and aggregation, leading to a significant reduction in active sites and severely inhibiting the intrinsic activity of the catalyst. How to achieve rapid graphitization of the carbon matrix while effectively suppressing the aggregation of metal particles remains a key technical challenge in the preparation of high-performance catalysts.

[0005] Finally, the synthesis efficiency is insufficient to meet the demands of large-scale industrial applications. Existing high-performance graphite-based catalyst synthesis often involves complex chemical assembly, multi-step solvothermal reactions, or lengthy temperature-programmed processes, resulting in long synthesis cycles and low yields. For industrial wastewater projects with massive daily treatment volumes, there is an urgent need for a rapid synthesis technology that can significantly shorten production cycles, reduce energy consumption, and ensure high catalyst stability.

[0006] In summary, there is an urgent need to develop a novel synthesis technology that can achieve efficient graphitization of biomass and strong chemical bonding of metal active sites in a single step under mild and low-energy conditions. This technology should effectively prevent metal aggregation at high temperatures, constructing metal-bonded graphite-based catalysts with ultra-high chemical stability, thereby overcoming the cost and stability bottlenecks of heterogeneous catalytic oxidation processes in engineering applications. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for rapidly preparing metal-bonded graphite catalysts using self-heating chemical (SIH) technology and its application in a long-lasting fixed-bed reactor. This method uses biomass cellulose as a reducing agent and carbon source, and metal nitrate as an oxidant and active component precursor. Through a redox reaction of both under mild induction conditions (80 °C), a transient self-heating process (>1200 °C) is triggered. Utilizing the localized high temperature generated by this process, the dehydrogenation and carbonization of cellulose, graphitization transformation, and reduction and anchoring of the metal component are completed in situ within an extremely short time (<20 s). This invention not only significantly reduces the energy consumption of graphite-based catalyst synthesis but also achieves strong chemical bonding of metal active sites on a stable graphite support through rapid thermochemical synergy.

[0008] The technical solution of the present invention: A method for the rapid synthesis of metal-bonded graphite-stabilized catalysts with low energy consumption, comprising the following steps: Step 1: Prepare a 3-9 mM solution of metal nitrate (selected from one or more combinations of copper nitrate, iron nitrate, cobalt nitrate, and nickel nitrate), and add it dropwise to the filter paper cellulose at a liquid-to-solid ratio of 10 mL:1 g until it is completely wetted. Step 2: Dry the moistened filter paper cellulose at less than 65°C for 40-60 minutes to allow the metal nitrates to be uniformly anchored on the surface of the filter paper cellulose, thus obtaining a cellulose mixture with anchored metal ions. Step 3: Increase the temperature to 80-135℃ at a heating rate of 10℃ / min to induce a violent self-heating redox reaction in the cellulose mixture anchored to metal ions; the reaction process lasts for 15s, generating local instantaneous high temperature (1250 ℃), causing the filter paper cellulose to dehydrogenate and carbonize and transform into a graphite framework, while the metal is simultaneously reduced and anchored on the graphite framework. Step 4: The product is washed with ethanol and deionized water to remove unreacted impurities, yielding a stable catalyst of metal-bonded graphite (MC-SIH).

[0009] A method for constructing a fixed-bed reactor using a metal-bonded graphite-stabilized catalyst obtained by the above preparation method includes the following steps: 1) Preparation of activated carbon fiber: Cellulose and magnesium chloride are mixed and heated at 125 °C for 16-28 h. The mixture is then washed with acid, anhydrous ethanol and deionized water in sequence and dried to obtain activated carbon fiber. 2) In-situ loading: Metal-bonded graphite stabilized catalyst and activated carbon fiber are mixed in water at a mass ratio of 5:1-1:5 (preferably 2:1) and interfacial induced assembly is carried out at 20-100 ℃ (preferably 60-90 ℃). The reaction is stirred or shaken for 1-48 hours (preferably 12-24 hours) to obtain supported catalytic fiber material. This process achieves high-density and strong anchoring of catalyst particles on the fiber surface through interfacial chemical bonding (such as coordination bonds, electrostatic attraction or hydrogen bonding synergy).

[0010] 3) Filling: Fill the reaction column with supported catalytic fiber material to construct a fixed-bed reactor.

[0011] The fixed-bed reactor is used for the catalytic activation of persulfate degradation of organic wastewater, and its operating parameters are as follows: influent hydraulic retention time of 9.9-37.3 s, hydraulic load of 800-24,000 L / h. -1 m -2 .

[0012] Under continuous flow operation conditions, the fixed-bed reactor maintains a removal rate of over 99% for tetracycline or methyl red, with a stable operating time of no less than 21 days, and the operating cost of wastewater treatment is no higher than 1.25 CNY / ton.

[0013] The beneficial effects of this invention are: (1) Ultra-low energy graphitization: Utilizing internal chemical energy to replace external heat sources. Traditional graphitization requires 7.62 × 10⁻⁶ kilowatt-hours. 6 The energy consumption is reduced by 6 orders of magnitude compared to the previous method, which requires only 1.16 kJ / g.

[0014] (2) Heterojunction enhancement mechanism: A Cu2O / CuO heterostructure was formed on the catalyst surface. According to DFT calculations, this interface enhanced the electron density, reduced the O2O bond breaking energy (adsorption energy -3.11 eV), and significantly improved the degradation efficiency of pollutants such as tetracycline (TC).

[0015] (3) Engineering performance: The catalyst forms a strong chemical bond with the support, with virtually no mass loss within the range of 40-800 °C, and can withstand ~8000 L h. -1 m -2 High-flux flushing. Attached Figure Description

[0016] Figure 1 The temperature monitoring curve during the SIH reaction process (internal heat release can reach 1250 °C).

[0017] Figure 2 This section provides heterostructure analysis of the catalysts; where A represents CuO, Cu₂O, Cu-C-SIH, and the direct calcination thermal synthesis (Cu-C-DTS) catalyst (800-4000 cm⁻¹). -1 FTIR spectra of CuO, Cu₂O, Cu-C-SIH, and direct calcination thermal synthesis (Cu-C-DTS) catalysts (400-700 cm⁻¹). -1 C is the FTIR spectrum of Cu-C-SIH, used for carbon structure analysis (the metal phase was completely removed by treatment with nitric acid, hydrochloric acid, and ammonium hydroxide); D is the XPS Cu 2p spectrum of Cu-C-SIH, used for copper elemental analysis; E is the normalized Cu K-edge XANES spectrum of Cu-C-SIH and reference samples (Cu foil, Cu2O, CuO); F is the Cu K-edge FT-EXAFS spectrum of Cu foil, Cu2O, CuO, and Cu-C-SIH catalyst; G is the EXAFS fitting curve of Cu-C-SIH in R space; H is the WT-EXAFS plot of Cu foil; I is the WT-EXAFS plot of Cu2O; J is the WT-EXAFS plot of CuO; K is the WT-EXAFS plot of Cu-C-SIH.

[0018] Figure 3 For the long-term operating performance of the Cu-C-SIH@FC system (catalyst loading = 1.5 g, [PDS] = 2 mM, [TC] = 10 mg L), -1 (T = 298 K). Detailed Implementation

[0019] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0020] Example 1: Preparation and characterization of Cu-C-SIH catalyst; First, using a molecular-level dispersion process, 1 g of filter paper cellulose (as a reducing agent and carbon source) was impregnated in 10 mL of a 6 mM copper nitrate solution (as an oxidizing agent and precursor of the metal active component) to ensure sufficient contact between copper ions and the cellulose molecular chains. Subsequently, pre-drying was performed at 65 °C to remove the solvent, allowing nitrates to be uniformly anchored on the fiber substrate surface. Then, the ambient temperature was increased to 135 °C at a rate of 10 °C / min, thereby inducing a spontaneous redox reaction between cellulose and nitrate ions. Figure 1 As shown, the system generates localized temperatures as high as 1250 °C within less than 20 seconds through the instantaneous release of chemical internal energy. This rapid heating process causes cellulose to instantly dehydrogenate and transform into a highly crystalline graphite framework, while simultaneously reducing and in-situ anchoring copper species. Figure 2 As shown, in-depth characterization using XRD, XPS, and EXAFS confirmed that the product possesses an excellent ordered graphite structure, and that strong chemical bonds with a bond length of approximately 3.01 Å are formed between Cu atoms and the graphite support. This atomic-level interfacial contact not only significantly enhances the charge transfer rate but also effectively suppresses the thermal migration and aggregation of copper nanoparticles at high temperatures through an extremely short heat treatment cycle, maintaining a high degree of dispersion of active sites.

[0021] Example 2 Based on Example 1, by replacing the copper nitrate solution with equimolar amounts of iron nitrate, cobalt nitrate, or nickel nitrate solutions, metal-bonded graphite catalysts such as Fe-C-SIH, Co-C-SIH, or Ni-C-SIH can be obtained under the same SIH reaction conditions. This universal synthesis strategy not only ensures that strong chemical bonds can be formed between different metal active centers and the graphite matrix, but also avoids the severe aggregation problem of active components commonly found in traditional long-term high-temperature calcination processes through a rapid reaction mechanism, thereby achieving low-energy consumption and large-scale preparation of high-performance catalysts.

[0022] Application Example 1: Antibiotic wastewater degradation experiment; In heterogeneous catalytic oxidation experiments, the Cu-C-SIH catalyst prepared in Example 1 was applied to the treatment of wastewater containing 10 mg / LTC. In the presence of 2 mM persulfate (PDS), the TC removal rate consistently reached over 99.9% within only 20 minutes. This superior performance is mainly attributed to the synergistic effect of the Cu2O / CuO heterostructure constructed by the SIH process and the high-conductivity graphite framework (see...). Figure 2 AC) Figure 2 abcd? According to electron paramagnetic resonance (EPR) testing, the system generated a large number of hydroxyl radicals (·OH) and sulfate radicals (SO4) during the reaction. ·-The active oxide species is ·OH. DFT calculations further confirmed that the strong electronic synergistic effect between the metal and the graphite support significantly reduced the breaking energy of the OO bonds in the PDS molecule, accelerating the formation rate of active oxygen species. Compared to catalysts prepared by long-term pyrolysis at 700 °C using traditional methods, this invention effectively solves the activity inhibition problem caused by metal thermal aggregation, resulting in a several-fold increase in catalytic rate and exhibiting extremely high intrinsic activity.

[0023] Application Example 2: Long-term operation of fixed beds; To verify the stability of the catalyst of this invention in long-term operation, 1.5 g of Cu-C-SIH catalyst supported on AFC fibers was packed into a simulated fixed-bed reactor with a diameter of 1 cm for long-term operation experiments. Industrial wastewater containing TC and methyl red (MR) was introduced, achieving a hydraulic retention time (HRT) of only 37.3 s and a treatment load as high as 8000 L / h. -1 m -2 Under these conditions, the system ran continuously for 21 days. For example... Figure 3 As shown, the removal rates of TC and MR remained above 99% throughout the entire operation cycle, with no significant activity decay observed. Thanks to the strong chemical bond between the catalyst and the support, the content of heavy metal ions leached from the effluent was extremely low, fully complying with stringent environmental emission standards. Preliminary calculations indicate that the reagent and energy consumption cost of this process is only 1.25 CNY / ton, fully demonstrating its enormous potential in low-energy, large-scale wastewater remediation projects.

[0024] Comparative Example 1: Preparation and comparison of traditional pyrolysis samples (Cu-C-DTS); To compare the effect of heat treatment on the catalyst, Cu-C-DTS samples were prepared using a conventional impregnation-pyrolysis method. 1 g of cellulose was impregnated in 10 mL of a 6 mM copper nitrate solution (same as the precursor in Example 1) and dried at 65 °C. Subsequently, the dried mixture was placed in a tube furnace and, under a nitrogen atmosphere, slowly heated to 700 °C at a rate of 5 °C / min, and held at this temperature for 2 hours for conventional carbonization. During this process, due to the slow heating rate and long heat treatment time, significant thermal migration and Oswald ripening of metal atoms occurred at high temperatures, leading to severe agglomeration of the metal nanoparticles.

[0025] The highest TC removal rate of the conventional pyrolysis sample (Cu-C-DTS) is only about 17.5%. Scanning electron microscopy revealed that the copper particles on the Cu-C-DTS surface have diameters mostly between 500-900 nm (indicating severe aggregation), and their effective active surface area is far lower than that of the Cu-C-SIH catalyst prepared by the SIH method of this invention. This comparison strongly confirms that this invention, through self-heating technology, rapidly achieves graphitization transformation while precisely freezing the metal dispersion state and establishing strong chemical bonds, thereby optimizing the activity and stability compared to traditional processes.

Claims

1. A method for low-energy-consumption and rapid synthesis of metal-bonded graphite-stabilized catalysts, characterized in that, The steps are as follows: Step 1: Prepare a metal nitrate solution and add it evenly dropwise onto the filter paper cellulose until it is completely wetted; Step 2: Dry the moistened filter paper cellulose to uniformly anchor the metal nitrates on the surface of the filter paper cellulose, thus obtaining a cellulose mixture with anchored metal ions. Step 3: Raise the temperature to 80-135℃ to induce a violent self-heating redox reaction in the cellulose mixture anchored to metal ions; the reaction process lasts for 15 seconds, generating local instantaneous high temperature, causing the filter paper cellulose to dehydrogenate and carbonize and transform into a graphite framework, while the metal is simultaneously reduced and anchored on the graphite framework. Step 4: The product is washed with ethanol and deionized water to remove unreacted impurities, yielding a metal-bonded graphite-stabilized catalyst.

2. The method for low-energy-consumption rapid synthesis of metal-bonded graphite stable catalysts according to claim 1, characterized in that, The metal nitrate is one or a combination of two or more of copper nitrate, iron nitrate, cobalt nitrate, and nickel nitrate.

3. The method for low-energy-consumption rapid synthesis of metal-bonded graphite stable catalysts according to claim 1, characterized in that, The concentration of the metal nitrate is 3-9 mM.

4. The method for low-energy-consumption rapid synthesis of metal-bonded graphite stable catalysts according to claim 1, characterized in that, Add the metal nitrate solution dropwise evenly to the filter paper cellulose at a liquid-to-solid ratio of 10 mL: 1 g until it is completely wetted.

5. The method for low-energy-consumption rapid synthesis of metal-bonded graphite stable catalysts according to claim 1, characterized in that, In step two, the drying conditions are: drying at less than 65℃ for 40-60 minutes.

6. The method for low-energy-consumption rapid synthesis of metal-bonded graphite stable catalysts according to claim 1, characterized in that, In step two, the temperature rise rate is 10℃ / min.

7. A method for constructing a fixed-bed reactor using a metal-bonded graphite-stabilized catalyst obtained by any one of the preparation methods according to claims 1-6, characterized in that, 1) Preparation of activated carbon fiber: Cellulose and magnesium chloride are mixed and heated at 125 °C for 16-28 h. The mixture is then washed with acid, anhydrous ethanol and deionized water in sequence and dried to obtain activated carbon fiber. 2) In-situ loading: Metal-bonded graphite stabilized catalyst and activated carbon fiber are mixed at a mass ratio of 5:1-1:5 and added to water. The mixture is stirred or shaken at 20-100 °C for 1-48 hours to obtain the supported catalytic fiber material. 3) Filling: The supported catalytic fiber material is filled into the reaction column to construct a fixed-bed reactor.

8. The method according to claim 7, characterized in that, The fixed-bed reactor is used for the catalytic activation of persulfate degradation of organic wastewater, and its operating parameters are as follows: influent hydraulic retention time of 9.9-37.3 s, hydraulic load of 800-24,000 L / h. -1 m -2 .

9. The method according to claim 8, characterized in that, Under continuous flow operation conditions, the fixed-bed reactor maintains a removal rate of over 99% for tetracycline or methyl red, with a stable operating time of no less than 21 days, and the operating cost of wastewater treatment is no higher than 1.25 CNY / ton.

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