A GA / Ag3PO4 / FeOOH composite catalyst based on graphite from spent lithium-ion battery anodes, its preparation method and its application

Abstract

This invention belongs to the field of environmental catalysis and solid waste resource utilization technology, specifically a GA / Ag3PO4 / FeOOH composite catalyst based on waste lithium battery anode graphite, its preparation method, and its application. The invention first uses waste lithium battery anode graphite as raw material, pre-treating it with high-temperature calcination and pulsed ultrasonic dispersion, and then prepares graphene oxide using a modified Hummers method with interlayer impurity removal. Next, a three-dimensional graphene aerogel framework is constructed through hydrothermal reduction self-assembly, and Ag3PO4 nanoparticles and FeOOH nano-active components are sequentially and in-situ loaded to construct a ternary composite catalyst. This invention has low preparation cost, and the resulting catalyst can achieve low-temperature, high-efficiency CO oxidation under photothermal conditions with good cycle stability. This invention simultaneously realizes the high-value resource utilization of waste lithium battery anode graphite, and has good industrial application prospects in the fields of industrial CO waste gas treatment and air purification.

Description

Technical Field

[0001] This invention belongs to the fields of environmental catalytic materials, air pollution control and solid waste resource utilization technology. Specifically, it relates to a GA / Ag3PO4 / FeOOH composite catalyst based on graphite from waste lithium battery anodes, its preparation method and its application. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the amount of waste lithium batteries generated has exploded, with negative electrode graphite accounting for 10% to 21% of the total battery mass. Currently, waste negative electrode graphite is mostly disposed of through landfill or incineration, which not only causes a serious waste of high-quality carbon resources but also leads to secondary pollution problems such as binder decomposition and electrolyte residue. The traditional Hummers process for preparing graphene oxide (GO) is mainly designed for high-purity natural graphite. When directly used for waste negative electrode graphite, it suffers from problems such as the difficulty in breaking up hard agglomerates after calcination, the inability to effectively remove interlayer lithium intercalation and metal impurities, and uneven oxidation, resulting in poor quality of the final GO. In addition, carbon monoxide (CO) is one of the major air pollutants, and its efficient catalytic oxidation is an important direction for air pollution control. Existing CO catalysts mostly use precious metals as active components, which have problems such as high cost and scarce resources; while Ag3PO4-based non-precious metal catalysts have good visible light response performance, they suffer from defects such as severe photocorrosion, poor cycle stability, and high recombination rate of photogenerated carriers. Therefore, developing a dedicated pretreatment and oxidation process for graphite anodes from waste lithium batteries, constructing a highly efficient and stable Ag3PO4-based composite catalyst, and achieving synergistic development of high-value utilization of waste resources and air pollution control is of significant environmental importance and practical application value. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention aims to provide a GA / Ag3PO4 / FeOOH composite catalyst based on waste lithium-ion battery anode graphite, its preparation method, and its applications. This invention uses waste lithium-ion battery anode graphite as raw material and constructs a ternary composite catalyst with a rich gradient Lewis acidic site structure via a stepwise hydrothermal method. This catalyst achieves efficient CO adsorption and relay activation. Furthermore, relying on a three-dimensional conductive network and the synergistic effect of multi-component interfaces, it effectively accelerates electron transfer, inhibits photocorrosion, and continuously generates reactive oxygen species, significantly improving the catalyst's low-temperature catalytic ability and operational stability. The graphite used in this invention is derived from waste power lithium-ion battery anodes and is suitable for the recycling and reuse of anode graphite from common power lithium-ion batteries such as ternary lithium-ion batteries and lithium iron phosphate batteries. This invention simultaneously solves the dual technical challenges of "high cost of precious metals, poor low-temperature activity and weak stability of non-precious metals" in the field of CO catalytic oxidation, and "low resource utilization rate and serious environmental pollution" of waste lithium-ion battery anode graphite, achieving an organic combination of high-value utilization of waste resources and efficient air pollution control.

[0004] The technical solution of the present invention is described in detail below.

[0005] A method for preparing a GA / Ag3PO4 / FeOOH composite catalyst based on graphite from spent lithium-ion battery anodes includes the following steps: (1) The graphite of the waste lithium battery negative electrode obtained from dismantling is crushed, sieved, roasted, cooled, ground and crushed, water is added to form a suspension, and then ultrasonically dispersed, centrifuged and dried to obtain pretreated graphite powder. (2) Using pretreated graphite powder as raw material, graphene oxide (GO) was prepared by the modified Hummers method. The modified Hummers method adds an interlayer impurity removal step between the low-temperature intercalation reaction stage and the medium-temperature oxidation reaction stage. The interlayer impurity removal step is as follows: filter the graphite suspension after low-temperature intercalation, and wash the obtained solid sample several times with dilute sulfuric acid and anhydrous ethanol to fully remove the metallic impurities lithium, copper, cobalt and manganese embedded in the graphite layers. (3) Add water to solid graphene oxide (GO) to form a suspension, disperse it by ultrasonication to obtain a uniform few-layer graphene oxide (GO) suspension, add silver nitrate and disodium hydrogen phosphate to it, stir evenly in the dark, and then conduct a hydrothermal reaction in a hydrothermal reactor. During the reaction, graphene oxide (GO) is simultaneously reduced and self-assembled into three-dimensional graphene aerogel (GA). At the same time, Ag3PO4 nanoparticles are loaded in situ on the surface of the three-dimensional graphene aerogel (GA) framework. After the reaction is completed, take out the solid sample, wash it, freeze dry it to obtain GA / Ag3PO4 composite intermediate. (4) FeOOH nanorods were grown in situ hydrothermally using GA / Ag3PO4 composite intermediate as a support. After the hydrothermal reaction was completed, the solid sample was taken out, washed and dried to obtain GA / Ag3PO4 / FeOOH composite catalyst.

[0006] In this invention, in step (1), the sample is sieved through a 40-100 mesh sieve; the calcination temperature is 500-600℃ and the calcination time is 2-4h; the purpose of calcination is to remove PVDF binder, electrolyte residue and organic impurities; in steps (1) and (3), intermittent pulsed ultrasonic dispersion is performed using a cell disruptor during ultrasonic dispersion; in step (1), the ultrasonic power is 300-500W, the working time is 2-5s and the interval is 2-5s, and the total duration is 15-25min; in step (3), the ultrasonic power is 200-400W, the working time is 2-5s and the interval is 2-5s, and the total duration is 10-20min, and the temperature is controlled at ≤40℃.

[0007] In this invention, the improved Hummers method for preparing graphene oxide (GO) in step (2) is specifically as follows: ① Low-temperature intercalation: Add pretreated graphite powder to concentrated sulfuric acid at a solid-liquid mass-volume ratio of 1:20~1:40 g / mL, and stir at 0~5℃ for 1~2h to allow the sulfuric acid to fully intercalate between the graphite layers, thus obtaining an intercalated graphite suspension. ② Interlayer impurity removal: After filtering the intercalated graphite suspension, the obtained solid sample is first washed 2-3 times with dilute sulfuric acid with a concentration of 1-2 mol / L, and then washed 1-2 times with anhydrous ethanol to fully remove the metallic impurities lithium, copper, cobalt and manganese embedded in the graphite layers. ③Medium-temperature oxidation: Add concentrated sulfuric acid and potassium permanganate to the washed wet material in sequence, and stir at a constant temperature of 35~40℃ for 5~7h; wherein: based on 1g of pretreated graphite powder, the amount of concentrated sulfuric acid added is 15~35mL, and the amount of potassium permanganate added is 2~4g. ④ High-temperature hydrolysis: Add deionized water dropwise and stir the reaction at 90~95℃ for 20~40 min; ⑤ Termination of reaction: Add hydrogen peroxide solution dropwise until the system turns bright yellow, separate the solid and liquid, wash and dry the obtained solid to obtain graphene oxide (GO) solid.

[0008] In this invention, in step ⑤, solid-liquid separation is performed by filtration or centrifugation. The obtained solid is first washed 2-3 times by centrifugation with 5wt% hydrochloric acid solution, then washed with deionized water until neutral, and dried at 50-70°C for 10-14 hours.

[0009] In this invention, in step (3), solid graphene oxide (GO) is mixed with water to form a suspension with a concentration of 2-6 mg / mL; the molar ratio of silver nitrate to disodium hydrogen phosphate is 3.5:1-4.5:1, and the mass ratio of Ag3PO4 to GO is 1:1-3:1; the hydrothermal reaction temperature is 160-180℃, and the hydrothermal reaction time is 10-12 h; the solvent used for washing is deionized water and anhydrous ethanol; the freeze-drying conditions are -60 to -55℃, vacuum degree <15 Pa, and drying time is 36-60 h.

[0010] In this invention, step (4) specifically includes: Add the GA / Ag3PO4 complex intermediate to deionized water and ultrasonically disperse for 10-30 min to obtain a dispersion. Add an iron source and urea to the dispersion, stir until homogeneous, and perform hydrothermal reaction at 90-110℃ for 6-10 hours; wherein: the mass ratio of GA / Ag3PO4 to iron source is 1:1-1:5, the molar ratio of iron source to urea is 1:2-1:6, and the iron source is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate; After the hydrothermal reaction is completed, the catalyst is centrifuged, washed 2-4 times with anhydrous ethanol, and vacuum dried at 50-70℃ for 8-14 hours to obtain the GA / Ag3PO4 / FeOOH composite catalyst.

[0011] The present invention also provides a GA / Ag3PO4 / FeOOH composite catalyst prepared by the above preparation method, which uses three-dimensional graphene aerogel GA prepared from waste lithium battery negative electrode graphite as a continuous conductive framework, uniformly loaded with Ag3PO4 nanoparticles with a particle size of 5~20nm on the surface of GA, and spindle-shaped FeOOH nanorods grown in situ on the surface of Ag3PO4.

[0012] In this invention, the GA / Ag3PO4 / FeOOH composite catalyst has a three-dimensional porous network structure with a specific surface area of ​​10~15 m². 2 / g, with a pore size distribution range of 1.2~50nm, and the total residual amount of metal impurities Li, Cu, Co and Mn in the catalyst is <150ppm.

[0013] Furthermore, this invention provides an application of the above-mentioned GA / Ag3PO4 / FeOOH composite catalyst in the photothermal synergistic catalytic oxidation of carbon monoxide; the application method is as follows: a 300~500W xenon lamp is used as a simulated sunlight source, with a light intensity of 80~120mW / cm². 2 The reaction temperature is 80~200℃; the reaction gas composition is 0.5 vol%~2 vol% CO, 15 vol%~25 vol% O2, with N2 as the equilibrium gas; the space velocity is 30000~90000 mL / (g・h); under photothermal conditions, the composite catalyst achieves a 90% CO conversion temperature T0. 90 The temperature ranges from 120 to 135℃, with a complete conversion temperature T. 100 The operating temperature is 140~160℃; after 100 hours of continuous operation, the CO conversion rate remains above 90%.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Achieving high-value resource utilization of waste lithium-ion battery anode graphite: This invention addresses two unique defects of waste anode graphite after roasting: the easy formation of PVDF carbon slag agglomerates and the presence of a large number of lithium / copper / cobalt / manganese metal impurities embedded in the interlayers. A combined scheme of a dual-intermittent pulsed ultrasonic pretreatment process and a low-temperature intercalation post-interlayer impurity removal process is designed. The dual-intermittent pulsed ultrasonic process, through an alternating "work-intermittent" mode, avoids local overheating and excessive fragmentation of graphite sheets caused by continuous ultrasonication, while intermittent cooling ensures that energy continuously acts on the interior of the hard agglomerates, thoroughly breaking down the dense agglomerate structure formed by PVDF decomposition and carbon slag agglomeration. The interlayer impurity removal process utilizes the characteristic of sulfuric acid molecules inserting into the graphite interlayers during the low-temperature intercalation stage, significantly expanding the interlayer spacing, fully exposing the originally encapsulated intercalated metal ions. Then, soluble metal salts are dissolved using dilute sulfuric acid, and the graphite sheets are washed with anhydrous ethanol to prevent recombination, ultimately controlling the total residual metal content of Li, Cu, Co, and Mn in the catalyst to below 150 ppm. The prepared GO is free from metal impurities and has stable quality, which is significantly better than traditional methods, providing a new technical path for the high-value conversion of waste graphite.

[0015] This invention reconstructs the core process of the Hummers process to solve the instability problem of waste graphite oxidation: The traditional Hummers process of "continuous intercalation-oxidation" is broken down into a step-by-step independent process of "low-temperature intercalation → interlayer impurity removal → medium-temperature oxidation". This avoids the consumption of oxidant by residual impurities in the interlayer during the oxidation stage, effectively improves the sufficiency of intercalation and the stability of the oxidation process, and significantly reduces the ineffective consumption of oxidant. It solves the problems of large fluctuations in reaction degree and poor batch consistency of products when the traditional method is used to treat waste graphite, and lays the foundation for the preparation of high-performance catalysts.

[0016] Constructing a ternary composite catalyst to significantly improve catalytic performance and stability: This invention constructs a GA / Ag3PO4 / FeOOH ternary composite catalyst in situ via a stepwise hydrothermal method. GA acts as a three-dimensional conductive framework to accelerate electron transfer, Ag3PO4 exhibits strong photocatalytic activity, and FeOOH utilizes Fe... 3+ / Fe 2+ The redox cycle continuously generates reactive oxygen species and inhibits the photocorrosion of Ag3PO4 at its source. CO temperature-programmed desorption tests show that a gradient distribution of Lewis acidic sites forms on the surface of this ternary composite material. Weakly acidic sites are responsible for the rapid adsorption of CO molecules in the gas phase, medium-to-strong acidic sites act as core active centers to achieve efficient CO activation, and strongly acidic sites promote the rapid desorption of the reaction product CO2 and release the active sites. These three synergistically construct a multi-stage relay catalytic reaction system of "adsorption-activation-desorption." Specifically, the catalyst prepared in Example 1 exhibits a Tg of CO under photothermal conditions. 90 As low as 122℃, T 100Even at temperatures as low as 142℃, the conversion rate remains at 95.2% after 100 hours of continuous operation, reaching the performance level of precious metal catalysts.

[0017] The preparation process is simple, low-cost, and suitable for large-scale production: This invention uses waste lithium battery negative electrode graphite as the main raw material and adopts post-intercalation impurity removal without adding a separate impurity removal process. It simply breaks down the traditional Hummers method's continuous intercalation-oxidation process into three steps: "low-temperature intercalation → interlayer impurity removal → medium-temperature oxidation". All operations are completed within the same reaction system, without the need for additional equipment or material transfer. The overall process flow is shortened, the comprehensive cost is reduced, and it is more suitable for industrial-scale production. The entire preparation process does not require complex equipment or harsh conditions. The process is simple, controllable, green, and environmentally friendly, and has good prospects for industrial application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 : Preparation route diagram of GA / Ag3PO4 / FeOOH ternary composite catalyst.

[0020] Figure 2 SEM image of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 1.

[0021] Figure 3 TEM image of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 1.

[0022] Figure 4 XRD diffraction pattern of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 2.

[0023] Figure 5 XPS spectrum of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 3.

[0024] Figure 6 High-resolution Fe 2p XPS spectrum of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 3.

[0025] Figure 7 CO temperature-programmed desorption curve of GA / Ag3PO4 / FeOOH prepared in Example 2.

[0026] Figure 8 Activity curves (a) and stability test curves (b) of the GA / Ag3PO4 / FeOOH ternary composite catalysts prepared in Examples 1, 2 and 3. Detailed Implementation

[0027] This invention details the preparation method and performance characterization of a GA / Ag3PO4 / FeOOH composite catalyst based on graphite from spent lithium-ion battery anodes through the following embodiments. The parameters in each embodiment are optimized and adjusted within the scope defined in the claims to form a tightly bonded ternary composite catalyst, achieving highly efficient photothermal synergistic catalytic oxidation of carbon monoxide. The preparation method roadmap is shown below. Figure 1 As shown.

[0028] Example 1

[0029] Pretreatment of graphite from waste lithium-ion battery anodes: The graphite from the dismantled waste lithium-ion battery anodes was crushed and sieved to 60 mesh. 2g was weighed and placed in a muffle furnace and calcined at 550℃ for 3h. After naturally cooling to room temperature, it was ground and crushed. 40mL of deionized water was added to prepare a suspension. The suspension was then subjected to intermittent pulsed ultrasonic dispersion using a cell disruptor with the following parameters: power 400W, working time 3s, intermittent time 3s, total duration 20min. After centrifugation at 6000r / min for 10min, the suspension was dried at 60℃ for 12h to obtain pretreated graphite powder.

[0030] Improved Hummers method for preparing graphene oxide (GO): ① Low-temperature intercalation: Add 2g of pretreated graphite powder to 60mL of 98wt% concentrated sulfuric acid, place in an ice-water bath, and stir for 1.5h at 0~5℃ to allow the sulfuric acid to fully intercalate between the graphite layers to form graphite sulfate; ② Interlayer impurity removal: Filter the intercalated graphite suspension, wash twice with 1.5mol / L dilute sulfuric acid aqueous solution, and then wash once with anhydrous ethanol to remove lithium ions, copper, cobalt, manganese, and other metallic impurities embedded between the graphite layers; ③ Medium-temperature oxidation: Add 50mL of [unspecified solution] to the washed wet material. 98wt% concentrated sulfuric acid, slowly add 6g potassium permanganate, and stir at 37℃ for 6h; ④ High-temperature hydrolysis: slowly add 120mL deionized water, control the system temperature at 90~95℃, and continue stirring for 30min; ⑤ Termination of reaction: slowly add 30wt% hydrogen peroxide solution until the system turns bright yellow, first centrifuge with 5wt% hydrochloric acid solution (6000r / min, centrifuge for 10min) twice, then wash with deionized water until neutral, and dry at 60℃ for 12h to obtain GO solid.

[0031] GO dispersion and hydrothermal in-situ assembly loading: 120 mg of solid GO was weighed and added to 30 mL of deionized water to prepare a 4 mg / mL suspension. A second intermittent pulsed sonication was performed using a cell disruptor with the following parameters: power 300 W, working time 3 s, intermittent time 3 s, total duration 15 min, and temperature control ≤40℃ to obtain a homogeneous few-layer GO suspension. 0.340 g of silver nitrate and 0.080 g of disodium hydrogen phosphate were added, and the mixture was stirred evenly in the dark and transferred to a 50 mL high-pressure reactor. The mixture was then hydrothermally reacted at 170℃ for 11 h. After the reaction, the mixture was allowed to cool naturally to room temperature, washed twice with deionized water and twice with anhydrous ethanol, and then freeze-dried at -56℃ and vacuum <12 Pa for 48 h to obtain the GA / Ag3PO4 complex intermediate.

[0032] Preparation of GA / Ag3PO4 / FeOOH ternary composite catalyst: 0.03 g of GA / Ag3PO4 composite intermediate was weighed and added to 25 mL of deionized water, and ultrasonically dispersed for 20 min; 0.054 g of ferric chloride and 0.06 g of urea were added, and the mixture was magnetically stirred for 15 min until no visible particles were observed; the mixture was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 100 °C for 8 h; after the reaction, the mixture was cooled to room temperature, centrifuged at 6000 r / min for 10 min, washed three times with anhydrous ethanol, and vacuum dried at 60 °C for 12 h to obtain the target catalyst, denoted as catalyst A. The specific surface areas of the aerogel and the ternary composite material were measured to be 345.2 m² using an Autosorb-1 fully automated specific surface area analyzer from Quantachrome, USA. 2 / g and 10.3m 2 / g, the catalyst pore size distribution ranges from 1.2-35.5nm. Using a Varian 720ES inductively coupled plasma optical emission spectrometer (ICP-OES), the total residual amount of metal impurities (Li, Cu, Co, Mn, etc.) from spent lithium battery negative electrode graphite in the catalyst was measured to be 78.3ppm, far below the industry-accepted requirement of ≤150ppm for total metal impurities in recycled graphite. SEM images of the GA / Ag3PO4 / FeOOH ternary composite catalyst (…). Figure 2 The results show that the catalyst particles are uniformly distributed on the GA surface. Figure 3 The image shows a TEM image of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 1. It can be seen that the surface of the three-dimensional graphene aerogel (GA) is loaded with Ag3PO4 nanoparticles with a particle size of 6~18nm and spindle-shaped FeOOH nanorods with a length of about 200nm.

[0033] Example 2

[0034] Pretreatment of graphite from waste lithium-ion battery anodes: The graphite from the dismantled waste lithium-ion battery anodes was crushed and sieved to 40 mesh. 2g was weighed and placed in a muffle furnace and calcined at 500℃ for 4h. After naturally cooling to room temperature, it was ground and crushed. 40mL of deionized water was added to prepare a suspension. The suspension was then subjected to intermittent pulsed ultrasonic dispersion using a cell disruptor with the following parameters: power 300W, working time 2s, intermittent time 2s, total duration 25min. After centrifugation at 6000r / min for 10min, the suspension was dried at 50℃ for 14h to obtain pretreated graphite powder.

[0035] Improved Hummers method for preparing graphene oxide (GO): ① Low-temperature intercalation: Add 2g of pretreated graphite powder to 40mL of 98wt% concentrated sulfuric acid, place in an ice-water bath, and stir for 2h at 0~5℃ to allow the sulfuric acid to fully intercalate between the graphite layers to form graphite sulfate; ② Interlayer impurity removal: Filter the intercalated graphite suspension, wash three times with 1mol / L dilute sulfuric acid solution, and then wash twice with anhydrous ethanol to remove lithium ions, copper, cobalt, manganese, and other metallic impurities embedded between the graphite layers; ③ Medium-temperature oxidation: Add 30mL of 98wt% concentrated sulfuric acid to the washed wet material, slowly add 4g of potassium permanganate, and stir at a constant temperature of 35℃ for 6h; ④ High-temperature hydrolysis: Slowly add 120mL of deionized water, control the system temperature at 90~95℃, and continue stirring for 30min; ⑤ Termination of reaction: Slowly add 30wt% hydrogen peroxide solution until the system turns bright yellow, first using 5wt%... The solution was centrifuged in hydrochloric acid solution (6000 r / min, 10 min) and washed three times. Then it was washed with deionized water until neutral and dried at 50 °C for 14 h to obtain solid GO.

[0036] GO dispersion and hydrothermal in-situ assembly loading: 120 mg of solid GO was weighed and added to 60 mL of deionized water to prepare a 2 mg / mL suspension. A second intermittent pulsed sonication was performed using a cell disruptor with the following parameters: power 200 W, working time 2 s, intermittent time 2 s, total duration 20 min, and temperature control ≤40℃, to obtain a homogeneous few-layer GO suspension. 0.194 g of silver nitrate and 0.041 g of disodium hydrogen phosphate were added, and the mixture was stirred evenly in the dark and transferred to a 100 mL high-pressure reactor. The mixture was then hydrothermally reacted at 160℃ for 12 h. After the reaction, the mixture was naturally cooled to room temperature, washed twice with deionized water and twice with anhydrous ethanol, and then freeze-dried at -60℃ and vacuum <15 Pa for 60 h to obtain the GA / Ag3PO4 complex intermediate.

[0037] Preparation of GA / Ag3PO4 / FeOOH ternary composite catalyst: 0.03 g of GA / Ag3PO4 composite intermediate was weighed and added to 25 mL of deionized water, and ultrasonically dispersed for 10 min; 0.03 g of ferric nitrate and 0.033 g of urea were added, and the mixture was magnetically stirred for 15 min until no visible particles were observed; the mixture was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 90 °C for 10 h; after the reaction, the mixture was cooled to room temperature, centrifuged at 6000 r / min for 10 min, washed twice with anhydrous ethanol, and vacuum dried at 50 °C for 14 h to obtain the target catalyst, denoted as catalyst B. The specific surface areas of the aerogel and the ternary composite material were measured to be 323.5 m² using an Autosorb-1 fully automated specific surface area analyzer from Quantachrome, USA. 2 / g and 11.7m 2 The catalyst has a pore size distribution ranging from 1.5 to 41.3 nm. Using a Varian 720ES inductively coupled plasma optical emission spectrometer (ICP-OES), the total residual amount of metallic impurities (Li, Cu, Co, Mn, etc.) from waste lithium-ion battery negative electrode graphite in the catalyst was measured to be 114.7 ppm, far below the industry-accepted requirement of ≤150 ppm for total metallic impurities in recycled graphite. Figure 4 The image shows the XRD diffraction pattern of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 2, confirming the presence of GA, Ag3PO4, and FeOOH in the catalyst. CO temperature-programmed desorption tests were performed on the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 2, and the results are as follows... Figure 7 As shown in the figure, tests revealed that a gradient distribution of Lewis acidic sites formed on the catalyst surface, with three distinct CO desorption peaks at 123℃, 223℃, and 323℃, corresponding to weak, medium, and strong acidity intensities, respectively. Among these, the peak area of ​​the medium-strong Lewis acidic sites accounted for more than 68% of the total peak area, providing ample active sites for the efficient adsorption and relay activation of CO molecules, thus endowing the catalyst with excellent low-temperature catalytic activity.

[0038] Example 3

[0039] Pretreatment of graphite from waste lithium-ion battery anodes: The graphite from the dismantled waste lithium-ion battery anodes was crushed and sieved to 100 mesh. 2g was weighed and placed in a muffle furnace and calcined at 600℃ for 2h. After naturally cooling to room temperature, it was ground and crushed. 40mL of deionized water was added to prepare a suspension. The suspension was then subjected to intermittent pulsed ultrasonic dispersion using a cell disruptor with the following parameters: power 500W, working time 5s, intermittent time 5s, total duration 15min. After centrifugation at 6000r / min for 10min, the suspension was dried at 70℃ for 10h to obtain pretreated graphite powder.

[0040] Improved Hummers method for preparing graphene oxide (GO): ① Low-temperature intercalation: Add 2g of pretreated graphite powder to 80mL of 98wt% concentrated sulfuric acid, place in an ice-water bath, and stir for 1h at 0~5℃ to allow the sulfuric acid to fully intercalate between the graphite layers to form graphite sulfate; ② Interlayer impurity removal: Filter the intercalated graphite suspension, wash twice with 2mol / L dilute sulfuric acid aqueous solution, and then wash once with anhydrous ethanol to remove lithium ions, copper, cobalt, manganese, and other metallic impurities embedded between the graphite layers; ③ Medium-temperature oxidation: Add 70mL of 98wt% concentrated sulfuric acid to the washed wet material. ④ Slowly add 8g of potassium permanganate to concentrated sulfuric acid and stir at 40℃ for 6h; ⑤ High-temperature hydrolysis: slowly add 120mL of deionized water, control the system temperature at 90~95℃, and continue stirring for 30min; ⑥ Termination of reaction: slowly add 30wt% hydrogen peroxide solution until the system turns bright yellow, first centrifuge with 5wt% hydrochloric acid solution (6000r / min, 10min) and wash twice, then wash with deionized water until neutral, and dry at 70℃ for 10h to obtain GO solid.

[0041] GO dispersion and hydrothermal in-situ assembly loading: 120 mg of solid GO was weighed and added to 20 mL of deionized water to prepare a 6 mg / mL suspension. A second intermittent pulsed sonication was performed using a cell disruptor with the following parameters: power 400 W, working time 5 s, intermittent time 5 s, total duration 10 min, and temperature control ≤40℃, to obtain a uniform few-layer GO suspension. 0.485 g of silver nitrate and 0.102 g of disodium hydrogen phosphate were added, and the mixture was stirred evenly in the dark and transferred to a 50 mL high-pressure reactor. The mixture was then hydrothermally reacted at 180℃ for 10 h. After the reaction, the mixture was allowed to cool naturally to room temperature, washed twice with deionized water and twice with anhydrous ethanol, and then freeze-dried at -55℃ and vacuum <10 Pa for 36 h to obtain the GA / Ag3PO4 complex intermediate.

[0042] Preparation of GA / Ag3PO4 / FeOOH ternary composite catalyst: 0.03 g of GA / Ag3PO4 composite intermediate was weighed and added to 25 mL of deionized water, and ultrasonically dispersed for 30 min; 0.15 g of ferric sulfate and 0.135 g of urea were added, and the mixture was magnetically stirred for 15 min until no visible particles were observed; the mixture was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 110 °C for 6 h; after the reaction, the mixture was cooled to room temperature, centrifuged at 6000 r / min for 10 min, washed four times with anhydrous ethanol, and vacuum dried at 70 °C for 8 h to obtain the target catalyst, denoted as catalyst C. The specific surface areas of the aerogel and the ternary composite material were measured to be 314.9 m² using an Autosorb-1 fully automated specific surface area analyzer from Quantachrome, USA. 2 / g and 12.4m 2The catalyst has a pore size distribution ranging from 1.5 to 47.1 nm. Using a Varian 720ES inductively coupled plasma optical emission spectrometer (ICP-OES), the total residual amount of metallic impurities (Li, Cu, Co, Mn, etc.) from waste lithium-ion battery negative electrode graphite in the catalyst was measured to be 141.9 ppm, which is lower than the industry-accepted requirement of ≤150 ppm for total metallic impurities in recycled graphite. Figure 5 The XPS spectrum of the GA / Ag3PO4 / FeOOH ternary composite catalyst prepared in Example 3 shows characteristic peaks for Ag 4d, P 2p, C 1s, Ag 3d, O 1s, Ag 3p, and Fe 2p in sequence, confirming the presence of C, O, P, Ag, and Fe elements in the catalyst, consistent with the elemental composition of the GA / Ag3PO4 / FeOOH ternary composite catalyst. Only characteristic peaks for C, O, P, Ag, and Fe elements were detected in the full XPS spectrum; no signals of impurities such as Li, Cu, Co, and Mn were observed. This is because the detection limit of XPS (approximately 0.1 at.%) is higher than that of ICP-OES, making it impossible to detect trace impurities at the ppm level. Combined with the total residual metal impurities of <150 ppm measured by ICP-OES, this confirms that the interlayer impurity removal process of the present invention effectively removes metal impurities from waste graphite. Figure 6 The high-resolution Fe 2p XPS spectrum indicates that the Fe in FeOOH has a chemical valence of +2 and +3.

[0043] Example 4 (Catalytic Performance Test) The photothermal synergistic catalytic oxidation performance of CO was tested using a fixed-bed reactor. 0.1 g of catalyst was weighed and placed in a quartz reaction tube with an inner diameter of 8 mm and a catalyst loading height of 5 mm, secured at the top and bottom with quartz wool. The reaction gas composition was 1 vol% CO, 20 vol% O2, with N2 as the balance gas. The total gas flow rate was 100 mL / min, and the space velocity was 60,000 mL / (g·h). A 300 W xenon lamp was used as a simulated sunlight source with a light intensity of 100 mW / cm². 2 The reaction temperature range was 80~200℃. Samples were taken for testing after stabilizing at each target temperature for 30 min. The concentration of CO before and after the reaction was detected online using an Agilent 7890A gas chromatograph (equipped with a GDX-502 column and a thermal conductivity detector TCD), and the CO conversion rate was calculated. All performance tests were performed in triplicate, and the data were the average of the three experiments, with a relative standard deviation of <5%. The test results showed that the three GA / Ag3PO4 / FeOOH composite catalysts prepared in this invention all exhibited excellent catalytic performance. Among them, catalyst A, prepared using the optimal process parameters, showed the best performance, with its 50% CO conversion temperature (T50) being << 200℃. 50The temperature is 111℃, and the 90% conversion temperature (T) is... 90 The complete conversion temperature is 122℃ (T). 100 The CO conversion rate remained at 95.2% after 100 hours of continuous operation at 142℃. The 50% CO conversion temperature (T5) for catalyst B is... 50 The temperature is 113℃, and the 90% conversion temperature (T) is... 90 The complete conversion temperature is 132℃ (T). 100 The temperature was 157℃, and after 100 hours of continuous operation, the CO conversion rate was 94.1%. The 50% CO conversion temperature (T50) of catalyst C is... 50 The temperature is 113℃, and the 90% conversion temperature (T) is... 90 The complete conversion temperature is 128℃ (T). 100 The temperature was 158℃, and after 100 hours of continuous operation, the CO conversion rate was 94.7%. Figure 8 The figures (a) show the activity curve of the GA / Ag3PO4 / FeOOH ternary composite catalyst and (b) show the stability test curve of catalyst A. The results indicate that all three GA / Ag3PO4 / FeOOH composite catalysts prepared in this invention exhibit excellent photothermal synergistic catalytic oxidation performance of CO, demonstrating that the process parameter range of this invention has good applicability and stability.

[0044] Comparative Example 1: Preparation of a non-aerogel structured rGO / Ag3PO4 / FeOOH composite catalyst (powder) using waste negative electrode graphite. This comparative example uses the exact same waste lithium-ion battery anode graphite raw material as in Example 1, retaining all pretreatment, the modified Hummers method for preparing graphene oxide (GO), and the FeOOH preparation steps, only omitting the hydrothermal reduction self-assembly process of three-dimensional graphene aerogel (GA). Specifically, the prepared GO suspension was directly added to 5 mL of 80 wt% hydrazine hydrate solution for chemical reduction, and the reaction was stirred at 90°C for 2 h to obtain reduced graphene oxide (rGO) powder; then, following the same proportions and steps as in Example 1, Ag3PO4 nanoparticles were loaded onto the surface of the rGO powder and coated with a FeOOH nanolayer to obtain a non-aerogel ternary composite catalyst, denoted as catalyst D.

[0045] The photothermal synergistic catalytic oxidation performance of CO was tested under the same conditions as in Example 4. The test results showed that catalyst D achieved a CO 50% conversion temperature (T50). 50 The conversion temperature is 125℃, and the 90% conversion temperature is (T). 90 The complete conversion temperature is 142℃ (T). 100At 168℃, after 100 hours of continuous operation, the CO conversion rate was only 82.7%. Its catalytic activity and stability were significantly lower than catalyst A in Example 1. The main reason for the performance decline was that the rGO powder obtained by chemical reduction was prone to severe agglomeration, resulting in a specific surface area of ​​only 32.6 m². 2 / g, which is far lower than the specific surface area of ​​three-dimensional graphene aerogels. Agglomeration leads to uneven loading of active components and easy detachment. At the same time, the lack of a continuous conductive framework and three-dimensional porous mass transfer channels results in slow electron transfer rate and hindered diffusion of reactants and products, ultimately leading to a significant reduction in catalytic performance.

[0046] Comparative Example 2: Graphene oxide was prepared using the traditional Hummers method without interlayer impurity removal steps. This comparative example uses the traditional Hummers method to prepare graphene oxide, omitting the "low-temperature interlayer impurity removal" step. The remaining preparation steps and reagent dosages are identical to those in Example 1. Specifically, pretreated waste negative electrode graphite powder is directly added to 98wt% concentrated sulfuric acid, followed by the addition of potassium permanganate in one step. The mixture is then stirred at a constant temperature of 35-40°C for 6 hours. Subsequent high-temperature hydrolysis, reaction termination, washing, and drying steps are consistent with Example 1 to obtain graphene oxide. The target catalyst, denoted as catalyst E, is then obtained through the same hydrothermal composite and FeOOH in-situ growth steps.

[0047] Catalytic performance was tested under the same conditions as in Example 4. The test results showed that catalyst E achieved a CO 50% conversion temperature (T50). 50 The conversion temperature is 128℃, and the 90% conversion temperature is (T). 90 The complete conversion temperature is 145℃ (T). 100 At 172℃, after 100 hours of continuous operation, the CO conversion rate was only 86.3%. The main reason for the performance degradation is that the traditional Hummers method cannot effectively remove metallic impurities such as lithium ions, copper, cobalt, and manganese embedded in the graphite layers. ICP analysis showed that the E impurity content of the catalyst was 368.5 ppm. During the catalytic process, metallic impurities may cover the catalytic active sites, causing performance degradation.

[0048] Comparative Example 3: GA / Ag3PO4 binary composite catalyst without FeOOH coating This comparative example omits the in-situ growth step of FeOOH and only prepares the GA / Ag3PO4 binary composite catalyst. The remaining preparation steps are exactly the same as in Example 1. Specifically, pretreated waste negative electrode graphite is used to prepare graphene oxide via a modified Hummers method, and then the GA / Ag3PO4 composite intermediate is obtained by hydrothermal in-situ assembly and loading. This intermediate is directly used as the target catalyst and is denoted as catalyst F.

[0049] Catalytic performance tests were conducted under the same conditions as in Example 4. The results showed that the initial catalytic activity of catalyst F was close to that of catalyst A, and its CO 50% conversion temperature (T50) was similar. 50 The conversion temperature is 112℃, and the 90% conversion temperature (T) is... 90 The complete conversion temperature is 123℃ (T). 100 The initial temperature was 144℃; however, the stability decreased sharply, with the CO conversion rate dropping below 85% after 20 hours of continuous operation, and only 58.7% after 100 hours. This is because the single Ag3PO4 catalyst is prone to photocorrosion under light irradiation, leading to the loss of active components and structural damage, and the absence of the FeOOH coating layer cannot fundamentally inhibit this process. X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250Xi) was used to characterize and verify the catalyst after 20 hours of continuous reaction under the same photothermal conditions as the catalytic activity evaluation: In the newly prepared Example 1 and this comparative catalyst, Ag exists only in the +1 valence state, and Ag3d... 5 / 2 The peaks were all located at 367.8 eV; after the reaction, only trace amounts of metallic Ag were detected in the ternary catalyst of Example 1. 0 (368.2 eV), its peak area accounts for 3.2% of the total Ag peak area, while the binary catalyst in this comparative example shows obvious metallic Ag. 0 The characteristic peak, with a peak area ratio of 21.7%, directly proves the significant inhibitory effect of the FeOOH coating layer on the photocorrosion of Ag3PO4.

[0050] Comparative Example 4: Preparation of GA / Ag3PO4 / FeOOH Composite Catalyst by Physical Mixing Method This comparative example uses a physical mixing method to prepare a ternary composite catalyst, with all other conditions being exactly the same as in Example 1. Specifically, three-dimensional graphene aerogel GA, Ag3PO4 nanoparticles, and FeOOH nanorods were prepared separately. Following the mass ratio of the three components in Example 1, they were thoroughly ground and mixed in an agate mortar for 30 minutes to obtain a physically mixed ternary composite catalyst, denoted as catalyst G.

[0051] Catalytic performance was tested under the same conditions as in Example 4. The test results showed that catalyst G achieved a CO 50% conversion temperature (T50). 50 The conversion temperature is 135℃, and the 90% conversion temperature is (T). 90 The complete conversion temperature is 156℃ (T). 100At 185℃, after 100 hours of continuous operation, the CO conversion rate was 72.4%. The reason for the significant performance decline is that in the catalyst prepared by the physical mixing method, GA, Ag3PO4 and FeOOH only have loose physical contact, which cannot form the tight interfacial bond obtained by the in-situ growth of this invention. Not only is the active site exposure insufficient, but it is also difficult for the components to achieve efficient synergistic effect, and ultimately the catalytic performance declines significantly.

[0052] The present invention provides a GA / Ag3PO4 / FeOOH ternary composite catalyst based on graphite from waste lithium-ion battery anodes. The three-dimensional graphene aerogel GA, acting as a continuous conductive framework, provides a uniformly loaded, high-specific-surface-area support for Ag3PO4 nanoparticles and FeOOH nanolayers. It not only rapidly transfers photogenerated electrons and suppresses carrier recombination but also provides efficient mass transfer and reaction channels for CO, O2, and photothermal energy. The strong photocatalytic activity of Ag3PO4 and the redox cycling characteristics of FeOOH work synergistically to effectively solve the problems of severe photocorrosion and poor stability of single Ag3PO4 catalysts. The synergistic effect of the three components achieves efficient photothermal synergistic catalytic oxidation of CO at lower temperatures, and the catalyst exhibits good cycling stability. This invention realizes the high-value utilization of graphite from waste lithium-ion battery anodes, with a simple and controllable preparation process. It has broad application prospects in industrial flue gas treatment, indoor air purification, and other fields, achieving synergistic optimization of resource recycling and environmental governance.

Claims

1. A method for preparing a GA / Ag3PO4 / FeOOH composite catalyst based on waste lithium battery negative electrode graphite, characterized in that, Includes the following steps: (1) The graphite of the waste lithium battery negative electrode obtained from dismantling is crushed, sieved, roasted, cooled, ground and crushed, water is added to form a suspension, and then ultrasonically dispersed, centrifuged and dried to obtain pretreated graphite powder. (2) Using pretreated graphite powder as raw material, graphene oxide (GO) was prepared by the modified Hummers method. The modified Hummers method adds an interlayer impurity removal step between the low-temperature intercalation reaction stage and the medium-temperature oxidation reaction stage. The interlayer impurity removal step is as follows: filter the graphite suspension after low-temperature intercalation, and wash the obtained solid sample several times with dilute sulfuric acid and anhydrous ethanol in sequence to fully remove the metal impurities lithium, copper, cobalt and manganese embedded in the graphite layers. (3) Add water to solid graphene oxide (GO) to form a suspension, disperse it by ultrasonication to obtain a uniform few-layer graphene oxide (GO) suspension, add silver nitrate and disodium hydrogen phosphate to it, stir evenly in the dark, and then conduct a hydrothermal reaction in a hydrothermal reactor. During the reaction, graphene oxide (GO) is simultaneously reduced and self-assembled into three-dimensional graphene aerogel (GA). At the same time, Ag3PO4 nanoparticles are loaded in situ on the surface of the three-dimensional graphene aerogel (GA) framework. After the reaction is completed, take out the solid sample, wash it, freeze dry it to obtain GA / Ag3PO4 composite intermediate. (4) FeOOH nanorods were grown in situ hydrothermally using GA / Ag3PO4 composite intermediate as a support. After the hydrothermal reaction was completed, the solid sample was taken out, washed and dried to obtain GA / Ag3PO4 / FeOOH composite catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), the sample is sieved through a 40-100 mesh sieve; the calcination temperature is 500-600℃ and the calcination time is 2-4h; in both steps (1) and (3), intermittent pulsed ultrasonic dispersion is performed using a cell disruptor during ultrasonic dispersion. In step (1), the ultrasonic power is 300~500W, working for 2~5s, with a break of 2~5s, and a total duration of 15~25min; in step (3), the ultrasonic power is 200~400W, working for 2~5s, with a break of 2~5s, and a total duration of 10~20min, with a temperature control of ≤40℃.

3. The preparation method according to claim 1, characterized in that, In step (2), the improved Hummers method for preparing graphene oxide (GO) is specifically as follows: ① Low-temperature intercalation: Add pretreated graphite powder to concentrated sulfuric acid at a solid-liquid mass-volume ratio of 1:20~1:40 g / mL, and stir at 0~5℃ for 1~2h to allow the sulfuric acid to fully intercalate between the graphite layers, thus obtaining an intercalated graphite suspension. ② Interlayer impurity removal: After filtering the intercalated graphite suspension, the obtained solid sample is first washed 2-3 times with dilute sulfuric acid with a concentration of 1-2 mol / L, and then washed 1-2 times with anhydrous ethanol to fully remove the metallic impurities lithium, copper, cobalt and manganese embedded in the graphite layers. ③Medium-temperature oxidation: Add concentrated sulfuric acid and potassium permanganate to the washed wet material in sequence, and stir at a constant temperature of 35~40℃ for 5~7h; wherein: based on 1g of pretreated graphite powder, the amount of concentrated sulfuric acid added is 15~35mL, and the amount of potassium permanganate added is 2~4g. ④ High-temperature hydrolysis: Add deionized water dropwise and stir the reaction at 90~95℃ for 20~40 minutes; ⑤ Termination of reaction: Add hydrogen peroxide solution dropwise until the system turns bright yellow, separate the solid and liquid, wash the obtained solid by centrifugation 2-3 times with 5wt% hydrochloric acid solution, wash it with deionized water until neutral, and dry it at 50-70℃ for 10-14h to obtain graphene oxide GO solid.

4. The preparation method according to claim 1, characterized in that, In step (3), solid graphene oxide (GO) is mixed with water to form a suspension with a concentration of 2-6 mg / mL; the molar ratio of silver nitrate to disodium hydrogen phosphate is 3.5:1-4.5:1, and the mass ratio of Ag3PO4 to GO is 1:1-3:1; the hydrothermal reaction temperature is 160-180℃, and the hydrothermal reaction time is 10-12 h; the solvent used for washing is deionized water and anhydrous ethanol; the freeze-drying conditions are -60 to -55℃, vacuum degree <15 Pa, and drying time is 36-60 h.

5. The preparation method according to claim 1, characterized in that, Step (4) is as follows: Add the GA / Ag3PO4 complex intermediate to deionized water and ultrasonically disperse for 10-30 min to obtain a dispersion. Add an iron source and urea to the dispersion, stir until homogeneous, and perform hydrothermal reaction at 90-110℃ for 6-10 hours; wherein: the mass ratio of GA / Ag3PO4 to iron source is 1:1-1:5, the molar ratio of iron source to urea is 1:2-1:6, and the iron source is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate; After the hydrothermal reaction is completed, the catalyst is centrifuged, washed 2-4 times with anhydrous ethanol, and vacuum dried at 50-70℃ for 8-14 hours to obtain the GA / Ag3PO4 / FeOOH composite catalyst.

6. A GA / Ag3PO4 / FeOOH composite catalyst prepared by the method according to any one of claims 1-5, characterized in that, It uses three-dimensional graphene aerogel GA, prepared from waste lithium battery negative electrode graphite, as a continuous conductive framework. Ag3PO4 nanoparticles with a particle size of 5~20nm are uniformly loaded on the surface of GA, and spindle-shaped FeOOH nanorods are grown in situ on the surface of Ag3PO4.

7. The GA / Ag3PO4 / FeOOH composite catalyst according to claim 6, characterized in that, It has a three-dimensional porous network structure with a specific surface area of ​​10~15m³. 2 / g, with a pore size distribution range of 1.2~50nm, and the total residual amount of metal impurities Li, Cu, Co and Mn in the catalyst is <150ppm.

8. The application of the GA / Ag3PO4 / FeOOH composite catalyst according to claim 6 or 7 in the photothermal synergistic catalytic oxidation of carbon monoxide.

9. The application according to claim 8, characterized in that, A 300-500W xenon lamp is used as the simulated sunlight source, with a light intensity of 80-120mW / cm². 2 The reaction temperature is 80~200℃; the reaction gas composition is 0.5vol%~2vol%CO, 15vol%~25vol%O2, and N2 is the equilibrium gas; the space velocity is 30000~90000 mL / (g・h).

10. The application according to claim 9, characterized in that, The 90% conversion temperature of CO is T 90 The temperature ranges from 120 to 135℃, with a complete conversion temperature T. 100 The operating temperature is 140~160℃; after 100 hours of continuous operation, the CO conversion rate remains above 90%.

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