A method for preparing a high-efficiency stable charcoal-based nanocatalyst based on joule heating and a regeneration method thereof

Abstract

The application relates to a method for preparing a high-efficiency stable charcoal-based nanometer catalyst based on Joule heating and a regeneration method thereof. The application aims to solve the problems that existing metal nanometer catalysts cannot stably nucleate in charcoal cell walls and charcoal-based nanometer catalysts cannot have high-efficiency catalytic activity and stability. The method comprises the following steps: 1, preparing a transition metal salt solution; 2, carbonizing and activating; 3, acid etching; 4, surface drop coating; and 5, Joule heating treatment. The regeneration method is that the high-efficiency stable charcoal-based nanometer catalyst after passivation is subjected to carbon thermal shock treatment. The application is used for preparing the high-efficiency stable charcoal-based nanometer catalyst based on Joule heating and regeneration.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a charcoal-based nanocatalyst and a regeneration method thereof. BACKGROUND

[0002] Wood, as an abundant and environmentally friendly renewable resource, is regarded as a natural "carbon reservoir" on earth. Wood has anisotropic layered porous structure, good mechanical flexibility and tunable multifunctionality, which makes it widely used in clean energy, catalytic engineering, environmental remediation, intelligent manufacturing and many other fields. Charcoal materials derived from natural wood can not only serve as carriers for functional nanomaterials, but also play a key role in reducing carbon emissions and extending carbon sequestration in the wood industry. In-depth exploration of the interface binding mechanism of charcoal cell walls and functional nanomaterials and its application in clean energy production and water treatment purification are of great significance to the development of low-carbon development and green economy.

[0003] Developing carbon-based nanocatalysts with cost-effectiveness, high catalytic activity and long-term stability is crucial for clean energy production and environmental remediation. In recent years, various interface engineering methods and surface modification strategies have been proposed, such as heteroatom doping, phase engineering, constructing heterojunctions, surface reconstruction, and inducing lattice distortion. However, these methods are complex and costly, and ignore the interaction between nanocatalysts and conductive carbon substrates, leaving room for improvement in manufacturing efficiency. Using charcoal, which is low-cost and can be mass-produced, as a carrier, a low-temperature hydrothermal co-solvent method can achieve high-quality loading of metal nanocatalysts in cell walls. However, due to slow heating rate, cell wall space limitations and migration and aggregation of metal nanoparticles, active sites in charcoal cell walls are unevenly distributed, and even active materials may fall off, resulting in reduced catalytic activity and reaction efficiency. In addition, other common nanomaterial preparation techniques, such as electrochemical deposition, air plasma treatment, microwave heating, chemical vapor deposition and wet chemical methods, cannot solve the problem of stable nucleation of nanocatalysts in charcoal cell walls. Simultaneously achieving high efficiency and long-term stability of catalysts still faces certain challenges. SUMMARY

[0004] The present application aims to solve the problems of existing metal nanocatalysts that cannot stably nucleate in charcoal cell walls and charcoal-based nanocatalysts that cannot simultaneously achieve high catalytic activity and stability, and further provides a method for preparing high-efficiency and stable charcoal-based nanocatalysts based on Joule heating and a regeneration method thereof.

[0005] A method for preparing high-efficiency and stable charcoal-based nanocatalysts based on Joule heating, which is carried out according to the following steps:

[0006] I. Preparation of transition metal salt solution:

[0007] adding the transition metal salt into the solvent and stirring to mix uniformly to obtain a transition metal salt solution;

[0008] The concentration of the transition metal salt solution is 0.05-0.25 mol / L;

[0009] II. Carbonization and activation

[0010] The wood is sequentially subjected to carbonization and activation to obtain the activated wood charcoal;

[0011] III. Acid etching

[0012] The activated wood charcoal is immersed in an acid solution, and etched for 10-30 min at a temperature of 15-35℃, and then ultrasonically cleaned to obtain the acid-treated wood charcoal;

[0013] IV. Surface drop coating

[0014] ①The transition metal salt solution is drop coated onto the surface of the acid-treated wood charcoal to allow the surface to be fully infiltrated, and then the wood charcoal after surface infiltration is vacuum treated;

[0015] ②The step IV ① is repeated for 3-5 times to obtain the drop-coated and infiltrated wood charcoal, which is heated for 8-24 h at a temperature of 50-90℃ to obtain the wood charcoal loaded with metal salt precursors;

[0016] V. Joule heating treatment

[0017] ①The wood charcoal loaded with metal salt precursors is fixed on the copper electrode of a Joule heating device, and subjected to carbon thermal shock treatment for 0.5-2.5 s at a temperature of 700-2400℃ and an argon gas rate of 0.2-0.8 L / min, and then cooled to room temperature;

[0018] ②The step V ① is repeated for 1-3 times to obtain the high-efficiency and stable wood charcoal-based nanocatalyst.

[0019] A regeneration method of the high-efficiency and stable wood charcoal-based nanocatalyst, which is performed according to the following steps:

[0020] ①The passivated high-efficiency and stable wood charcoal-based nanocatalyst is fixed on the copper electrode of a Joule heating device, heated to 700-2400℃ at a heating rate of 8000-12000℃ / s, and subjected to carbon thermal shock treatment for 0.5-2.5 s at a temperature of 700-2400℃ and an argon gas rate of 0.2-0.8 L / min, and then cooled to room temperature at a cooling rate of 2000-2500℃ / s;

[0021] 2. Repeat step 1 for 1-3 times, i.e. complete the regeneration method.

[0022] The present application has the following advantages:

[0023] The present application takes advantage of the good adsorption between charcoal defects and liquid metal, combines Joule heating and rapid cooling technology, limits the nucleation of metal nanocatalyst in the cell wall of charcoal, and synchronously realizes the surface and interface regulation of charcoal-based nanocatalyst. Compared with traditional heating modes (such as tube furnace heating), electrochemical deposition, air plasma treatment, wet chemical reduction method, and gas deposition strategy, the Joule heating technology has the advantages of rapid synthesis (0.5-2.5 s), small particle size (particle size range of 10-38 nm), uniform dispersion, and embedded structure. The prepared charcoal-based nanocatalyst not only has high activity in electrocatalytic water decomposition (the oxygen evolution overpotential is 178 mV at a current density of 10 mA cm -2 , and the oxygen evolution overpotential is 320 mV at a current density of 100 mA cm -2 ), but also exhibits long-term stability (stabilized for 146 h at a current density of 100 mA cm -2 ); at the same time, multiple Joule heating treatment can realize the "passivation-regeneration" of charcoal-based single-atom catalyst (i.e. after multiple cycle experiments, the surface of the charcoal-based nanocatalyst is covered with a large amount of degradation intermediates, which reduces the utilization rate of active metal sites; after multiple high-temperature thermal shock treatments, the reaction intermediates can be thermally degraded into graphite carbon layers, which not only promotes the recovery of active metal sites, but also enhances the local electron transfer of the catalyst, thereby realizing the regeneration of the nanocatalyst), and the total cycle number for degrading organic pollutants can reach 20 times (the total cycle number includes the initial cycle number plus the cycle number after regeneration, and the degradation efficiency remains above 90%).

[0024] Drawings of the specification

[0025] Figure 1 Macro photograph of the high-efficiency and stable charcoal-based nanocatalyst prepared in Example 1;

[0026] Figure 2 Temperature-time curve of the Joule heating and rapid quenching treatment in step five ① of Example 1;

[0027] Figure 3 Actual photograph of the Joule heating process in step five ① of Example 1;

[0028] Figure 4 Scanning electron microscope (SEM) image of the longitudinal section of the activated charcoal prepared in step two of Example 1, magnified by 200 times;

[0029] Figure 5 The specific surface area diagram is shown for the activated charcoal prepared in step two of Example 1.

[0030] Figure 6 This is a scanning electron microscope image of a longitudinal section of the acid-treated charcoal prepared in step three of Example 1, magnified 100,000 times.

[0031] Figure 7 The image shows two cross-sectional scanning electron microscope (SEM) images of the highly efficient and stable charcoal-based nanocatalyst prepared in Example 1, magnified 100x;

[0032] Figure 8 This is a scanning electron microscope image of a longitudinal section of the highly efficient and stable charcoal-based nanocatalyst prepared in Example 1, magnified 20,000 times.

[0033] Figure 9 The image shows a longitudinal section scanning electron microscope image of the highly efficient and stable charcoal-based nanocatalyst prepared in Example 1, magnified 60,000 times.

[0034] Figure 10 Transmission electron microscopy image of the highly efficient and stable charcoal-based nanocatalyst prepared in Example 1;

[0035] Figure 11 The particle size distribution diagram of the highly efficient and stable charcoal-based nanocatalyst prepared in Example 1 is shown.

[0036] Figure 12 The images are X-ray diffraction patterns. 1 is the highly efficient and stable charcoal-based nanocatalyst prepared in Example 1, and 2 is the activated charcoal prepared in step 2 of Example 1.

[0037] Figure 13 The graphs show the oxygen evolution reaction (OER) polarization curves of the highly efficient and stable charcoal-based nanocatalysts prepared in Examples 1 to 3. 1 represents Example 1, 2 represents Example 2, and 3 represents Example 3.

[0038] Figure 14 The highly efficient and stable charcoal-based nanocatalyst prepared in Example 1 was tested at 100 mA cm⁻¹. -2 Stability curves at current density;

[0039] Figure 15 The degradation efficiency of Rhodamine B by highly efficient and stable charcoal-based nanocatalysts prepared by different heating processes is shown in the figure. 1 is Example 4, 2 is Example 5, and 3 is Example 6.

[0040] Figure 16 This is a scanning electron microscope (SEM) image of a longitudinal section of the highly efficient and stable charcoal-based nanocatalyst prepared in Example 4 after passivation during the degradation of Rhodamine B.

[0041] Figure 17A longitudinal section scanning electron microscope image of the high-efficiency stable charcoal-based nanocatalyst prepared in Example Four after passivation and regeneration by joule heating treatment;

[0042] Figure 18 A transmission electron microscope image of the high-efficiency stable charcoal-based nanocatalyst prepared in Example Four after passivation and regeneration by joule heating treatment;

[0043] Figure 19 A graph of the degradation efficiency of rhodamine B by the high-efficiency stable charcoal-based nanocatalyst prepared in Example Four during 20 cycles. DETAILED DESCRIPTION

[0044] Specific embodiment one: the present embodiment is a method for preparing a high-efficiency stable charcoal-based nanocatalyst based on joule heating, which is performed according to the following steps:

[0045] I. Preparation of a transition metal salt solution:

[0046] The transition metal salt is added to the solvent and stirred until mixed evenly to obtain a transition metal salt solution;

[0047] The concentration of the transition metal salt solution is 0.05 mol / L to 0.25 mol / L;

[0048] II. Carbonization and activation:

[0049] The wood is sequentially subjected to carbonization treatment and activation treatment to obtain the wood charcoal after activation treatment;

[0050] III. Acid etching:

[0051] The wood charcoal after activation treatment is immersed in an acid solution, and etched for 10 min to 30 min at a temperature of 15°C to 35°C, and then ultrasonically cleaned to obtain the wood charcoal after acid treatment;

[0052] IV. Surface drop coating:

[0053] ①The transition metal salt solution is drop coated onto the surface of the wood charcoal after acid treatment, so that the surface is fully infiltrated, and then the wood charcoal after surface infiltration is vacuum treated;

[0054] ②Step IV ① is repeated 3 to 5 times to obtain the wood charcoal after drop coating and immersion, and the wood charcoal after drop coating and immersion is heated for 8 h to 24 h at a temperature of 50°C to 90°C to obtain the wood charcoal after loading of the metal salt precursor;

[0055] V. Joule heating treatment:

[0056] ①The charcoal after loading the metal salt precursor is fixed on the copper electrode of the Joule heating device, and is subjected to carbon thermal shock treatment at a temperature of 700-2400°C and an argon gas rate of 0.2-0.8 L / min for 0.5-2.5 s, and then is cooled to room temperature;

[0057] ②The step five ① is repeated 1-3 times to obtain the high-efficiency and stable charcoal-based nanometer catalyst.

[0058] In step two, the pretreated wood is carbonized in a vacuum tube furnace, and the overall morphology of the cell wall of the wood can be completely retained and converted into the main structure of the charcoal material; then the charcoal is heated in a CO2 atmosphere to obtain the activated charcoal.

[0059] The purpose of step two is to convert the natural wood into charcoal by pyrolysis and carbonization, which not only imparts good electrical conductivity to the wood, but also maintains the hierarchical porous structure; and the charcoal activated by CO2 has a certain degree of defect.

[0060] The principle of step two is that during the low-temperature carbonization process, the structure of the cell wall and cell cavity will change significantly. The wood components such as cellulose, hemicellulose and lignin in the cell wall form a graphite structure in amorphous carbon through dehydration, decarboxylation and intramolecular condensation, and the carbon layer presents a vortex layer, disordered microstructure, and defects, nanopores and voids on the surface. At the same time, CO2 can be confined in the hierarchical porous structure and react with impurities such as amorphous carbon in the wood to etch carbon atoms in the cell wall of the wood, thereby opening the pores with small pore size, and then forming new micropores under the continuous activation; the removal of carbon atoms is conducive to the realization of the disordering and surface reconstruction of the structure, thereby resulting in a certain defect structure of the treated wood.

[0061] In step three, the activated charcoal is immersed in an acid solution for etching treatment, and then the pH of the solution is adjusted to neutral to obtain the acid-treated wood.

[0062] The purpose of step three is to introduce an acid etching method to treat the activated charcoal, and further introduce defect sites on the surface of the charcoal substrate.

[0063] The mechanism of step three is that after the activated charcoal is immersed in an acid solution (such as nitric acid), an oxidation reaction can occur to generate carbon dioxide, nitrogen oxides and water. This oxidation reaction can change the surface properties of the charcoal substrate, such as increasing the surface roughness, etching the surface of the carbon substrate, and even destroying the local structure, thereby further introducing defects in the charcoal substrate.

[0064] Principle of Step Four: The hierarchical porous structure of charcoal helps the penetration of transition metal salt solution, and fully impregnates into the charcoal cell wall; the surface drop-coating treatment can achieve uniform dispersion of metal salt precursors, avoiding particle agglomeration during high-temperature impact.

[0065] Principle of Step Five ①: In the wood cell wall, the defect-driven limited nucleation of metal nanocatalysts is due to the good adsorption of metal droplets at defect sites at high temperature. After Joule heating and rapid quenching, the charcoal can induce continuous fission of metal particles to form small-particle-size and well-dispersed nanoparticles, and can also promote the derivation of crystalline graphite structure from carbon atoms adjacent to metal nanocatalysts through continuous high-temperature impact, thereby realizing the self-encapsulation of high-entropy alloy nanoparticles in the charcoal cell wall and forming a highly efficient and stable charcoal-based nanocatalyst.

[0066] Regeneration principle of charcoal catalyst: During the cyclic degradation test, the decrease in degradation efficiency is mainly due to the accumulation of degradation intermediates on the catalyst surface and the depletion of active metal sites. The reaction intermediates loaded on the passivated charcoal-based nanocatalyst can be pyrolyzed into a carbon layer after multiple Joule heating high-temperature impacts. The newly formed carbon layer promotes the interfacial electron transfer between the metal sites and the reaction system, thereby realizing the high efficiency and secondary activation regeneration of the charcoal-based nanocatalyst.

[0067] The beneficial effects of the present embodiment are:

[0068] The present embodiment utilizes the good adsorption between charcoal defects and liquid metal, combines Joule heating and rapid cooling technology, and makes the metal nanocatalyst limited nucleate in the charcoal cell wall, while realizing the surface and interface regulation of the charcoal-based nanocatalyst. Compared with traditional heating modes (such as tube furnace heating), electrochemical deposition, air plasma treatment, wet chemical reduction method, and gas deposition strategies, the Joule heating technology has the advantages of rapid synthesis (0.5s-2.5s), small particle size (particle size range of 10nm-38nm), uniform dispersion, and embedded structure. The prepared charcoal-based nanocatalyst not only has high efficiency in electrocatalytic water splitting for oxygen evolution (the oxygen evolution overpotential is 178mV at a current density of 10mA cm -2 , and exhibits long-term stability (the oxygen evolution overpotential is 320mV at a current density of 100mA cm -2 ). -2The charcoal-based single-metal-atom catalysts can be stable for 146 h at a current density; meanwhile, multiple joule heating treatments can achieve the "passivation-regeneration" of the charcoal-based single-metal-atom catalysts (i.e., after multiple cycle experiments, the surface of the charcoal-based nano-catalyst is covered by a large amount of degradation intermediates, thereby reducing the utilization rate of active metal sites; after multiple high-temperature thermal shock treatments, the reaction intermediates can be thermally degraded into graphite carbon layers, which not only promotes the recovery of active metal sites, but also enhances the local electron transfer of the catalyst, thereby achieving the regeneration of the nano-catalyst), and the total cycle number of the degradation of organic pollutants can reach 20 times (the total cycle number includes the initial cycle number plus the cycle number after regeneration, and the degradation efficiency is maintained at more than 90%), and the charcoal-based nano-catalyst prepared has wide application in the fields of clean energy production, water treatment, etc.

[0069] Specific embodiment two: different from the specific embodiment one, the transition metal salt in step one is one or a combination of several of iron salt, cobalt salt, nickel salt, chromium salt and manganese salt; the solvent in step one is distilled water or anhydrous ethanol; the stirring and mixing in step one is specifically under the condition that the stirring speed is 300 rpm-600 rpm, and the stirring time is 12 h-36 h. The others are the same as the specific embodiment one.

[0070] Specific embodiment three: different from the specific embodiment one or two, the iron salt is ferric nitrate, ferric chloride or ferric acetate; the cobalt salt is cobalt nitrate, cobalt chloride or cobalt acetate; the nickel salt is nickel nitrate, nickel chloride or nickel acetate; the chromium salt is chromium nitrate, chromium chloride or chromium acetate; and the manganese salt is manganese nitrate, manganese chloride or manganese acetate. The others are the same as the specific embodiment one or two.

[0071] Specific embodiment four: different from the specific embodiment one to three, the wood in step two is pretreated wood, and the pretreatment is specifically performed according to the following steps: the wood is soaked in distilled water or an ethanol solution, ultrasonic cleaning is performed under the condition that the power is 100 W-300 W for 1 h-3 h, and then vacuum drying is performed under the condition that the temperature is 40 ℃-80 ℃ for 1 h-24 h to obtain the pretreated wood. The others are the same as the specific embodiment one to three.

[0072] Specific embodiment five: different from the specific embodiment one to four, the wood thickness in step two is 0.5 mm-2.5 mm; and the wood in step two is coniferous wood or broad-leaved wood, and the cutting mode is transverse cutting or chordwise cutting. The others are the same as the specific embodiment one to four.

[0073] Embodiment six: the difference between this embodiment and one of the embodiments one to five is that in step two, the wood is sequentially subjected to carbonization treatment and activation treatment, which is carried out according to the following steps: the wood is subjected to carbonization treatment at a temperature of 800-1200°C and a nitrogen flow rate of 0.2-0.6 L / min for 4-8 h, and then cooled to room temperature to obtain the carbonization-treated wood, and then the carbonization-treated wood is subjected to activation treatment at a temperature of 660-860°C and a carbon dioxide flow rate of 0.05-0.2 L / min for 2-10 h, and then cooled to room temperature to obtain the activated wood. The other steps are the same as those in the embodiments one to five.

[0074] Embodiment seven: the difference between this embodiment and one of the embodiments one to six is that in step three, the concentration of the acid solution is 5-25 wt%; in step three, the acid solution is nitric acid solution or hydrochloric acid solution; and in step three, the ultrasonic cleaning is carried out according to the following steps: using distilled water or anhydrous ethanol as the washing liquid, and carrying out ultrasonic cleaning at a power of 200-500 W until the pH of the solution is neutral. The other steps are the same as those in the embodiments one to six.

[0075] Embodiment eight: the difference between this embodiment and one of the embodiments one to seven is that in step four ①, the transition metal salt solution is drop-coated onto the surface of the acid-treated wood charcoal at a drop-coating amount of 2-5 mL / cm 2 . 2 . The surface of the wood charcoal is fully infiltrated, and then the surface-infiltrated wood charcoal is subjected to vacuum treatment at a temperature of 15-25°C and a vacuum degree of 10-10 kPa for 24-72 h. The other steps are the same as those in the embodiments one to seven.

[0076] Embodiment nine: the difference between this embodiment and one of the embodiments one to eight is that in step five ①, the wood charcoal after loading the metal salt precursor is fixed on the copper electrode of the joule heating device, heated to 700-2400°C at a heating rate of 8000-12000°C / s, and subjected to carbon thermal shock treatment at a temperature of 700-2400°C and an argon flow rate of 0.2-0.8 L / min for 0.5-2.5 s, and finally cooled to room temperature at a cooling rate of 2000-2500°C / s. The other steps are the same as those in the embodiments one to eight.

[0077] Embodiment ten: the regeneration method of the high-efficiency and stable wood charcoal-based nanocatalyst, which is carried out according to the following steps:

[0078]

[0079] ②Repeat step 1-3 times in step 1, namely, the regeneration method is completed.

[0080] The beneficial effects of the present application are verified by the following examples:

[0081] Example 1:

[0082] A method for preparing high-efficiency stable charcoal-based nanocatalyst based on Joule heating, which is carried out according to the following steps:

[0083] I. Preparation of transition metal salt solution:

[0084] Under the condition of 500 rpm, the transition metal salt is added to the solvent and stirred for 24 h to obtain a transition metal salt solution;

[0085] The concentration of transition metal salt in the transition metal salt solution is 0.05 mol / L; the transition metal salt is a combination of iron salt, cobalt salt, nickel salt, chromium salt and manganese salt with a molar ratio of 1:1:1:1:1; the solvent is anhydrous ethanol;

[0086] The iron salt is ferric chloride; the cobalt salt is cobalt chloride; the nickel salt is nickel chloride; the chromium salt is chromium chloride; and the manganese salt is manganese chloride;

[0087] II. Carbonization and activation:

[0088] Under the condition of 1000℃ and nitrogen flow rate of 0.2L / min, the wood is carbonized for 6h, and after cooling to room temperature, the carbonized wood is obtained, and then under the condition of 760℃ and carbon dioxide flow rate of 0.05L / min, the carbonized wood is activated for 6h, and after cooling to room temperature, the activated charcoal is obtained;

[0089] The wood is pretreated wood, and the pretreatment is carried out according to the following steps: the wood is soaked in distilled water, ultrasonic cleaning is carried out under the condition of 200W for 2h, and then vacuum drying is carried out under the condition of 60℃ for 12h to obtain the pretreated wood;

[0090] The thickness of the wood is 2mm; the wood is basswood, and the cutting method is transverse cutting;​

[0091] III. Acid Etching:

[0092] The activated charcoal was immersed in an acid solution and etched for 20 minutes at 25°C. Then, it was ultrasonically cleaned with distilled water at 400W until the pH of the solution was neutral, thus obtaining the acid-treated charcoal.

[0093] The concentration of the acid solution is 10 wt%; the acid solution is a nitric acid solution.

[0094] IV. Surface coating:

[0095] ① The application rate is 3 mL / cm 2 A transition metal salt solution was drop-coated onto the surface of acid-treated charcoal to fully impregnate the surface. Then, the impregnated charcoal was vacuum-treated for 48 hours in a vacuum environment at 25°C and 20Pa.

[0096] ② Repeat step 4① 3 times to obtain the drip-coated and impregnated charcoal. Heat the drip-coated and impregnated charcoal at 80℃ for 24 hours to obtain charcoal loaded with metal salt precursor.

[0097] V. Joule heating treatment:

[0098] ① The charcoal loaded with metal salt precursor was fixed on the copper electrode of the Joule heating device, heated to 1800℃ at a heating rate of 11000℃ / s, and subjected to carbon thermal shock treatment for 2s at a temperature of 1800℃ and an argon gas rate of 0.2L / min. Finally, it was cooled to room temperature at a cooling rate of 2500℃ / s.

[0099] ② Repeat step 5① once to obtain a highly efficient and stable charcoal-based nanocatalyst.

[0100] Example 2: This comparative experiment differs from Example 1 in that the transition metal salts mentioned in step 1 are a combination of iron, cobalt, nickel, and manganese salts in a molar ratio of 1:1:1:1. Everything else is the same as in Example 1.

[0101] Example 3: This comparative experiment differs from Example 1 in that the transition metal salts mentioned in step 1 are iron, cobalt, and nickel salts in a molar ratio of 1:1:1. Everything else is the same as in Example 1.

[0102] Example 4: This comparative experiment differs from Example 1 in that the transition metal salt mentioned in step 1 is a cobalt salt; in step 5, the temperature is increased to 700℃ at a heating rate of 11000℃ / s, and then subjected to carbon thermal shock treatment for 2s at a temperature of 700℃ and an argon gas flow rate of 0.2L / min. Everything else is the same as in Example 1.

[0103] Example Five: The difference between this comparative experiment and Example One is that: the transition metal salt in Step One is cobalt salt; in Step Five, the temperature is raised to 1200°C at a rate of 11000°C / s, and the carbon thermal shock treatment is carried out at a temperature of 1200°C and an argon gas rate of 0.2 L / min for 2 s. The others are the same as Example One.

[0104]

[0105] Figure 1 The macro photograph of the high-efficiency stable charcoal-based nanocatalyst prepared in Example One. As can be seen from the figure, the charcoal after carbonization, activation and Joule heating treatment presents a rigid and complete structure.

[0106] Figure 2 The temperature-time curve of the Joule heating and rapid quenching treatment in Step Five ① of Example One. As can be seen from the figure, the charcoal surface loaded with metal salt precursors is instantaneously heated to 1800°C within 0.16 s after the application of direct current pulse; the metal salt precursors are converted into molten metal droplets within 2 s, and the nanoparticles are uniformly dispersed on the surface of the charcoal electrode after rapid cooling.

[0107] Figure 3 The actual picture of the Joule heating process in Step Five ① of Example One. As can be seen from the figure, the ultra-high temperature generated by Joule heating can achieve sufficient heating of the charcoal electrode.

[0108] Figure 4 The longitudinal section scanning electron microscope picture of the activated charcoal prepared in Step Two of Example One, enlarged 200 times. As can be seen from the figure, the activated charcoal presents a hierarchical porous structure.

[0109] Figure 5 The specific surface area graph of the activated charcoal prepared in Step Two of Example One. As can be seen from the figure, the specific surface area of the activated charcoal can reach 754 m 2 g -1 , which proves that more smaller pores are opened after activation, and new micropores are formed.

[0110] Figure 6 The longitudinal section scanning electron microscope picture of the acid-treated charcoal prepared in Step Three of Example One, enlarged 100000 times. As can be seen from the figure, the acid solution etches on the surface of the carbon base and even destroys the local structure, thereby further introducing defects into the charcoal base.

[0111] ​Figure 7 Cross-section and longitudinal-section scanning electron microscope images of the high-efficiency stable charcoal-based nanocatalyst prepared in Example One, magnified 100 times. As can be seen from the images, the charcoal-based nanocatalyst presents a multi-channel structure with low bending degree, which helps to enhance mass transfer in the process of electrochemical energy conversion.

[0112] Figure 8 Longitudinal-section scanning electron microscope image of the high-efficiency stable charcoal-based nanocatalyst prepared in Example One, magnified 20000 times. As can be seen from the image, the high-entropy alloy nanoparticles are densely and uniformly dispersed in the entire wood channel.

[0113] Figure 9 Longitudinal-section scanning electron microscope image of the high-efficiency stable charcoal-based nanocatalyst prepared in Example One, magnified 60000 times. As can be seen from the image, most of the high-entropy alloy nanoparticles present a semicircular shape, indicating that the particles have been embedded into the charcoal cell wall, which enables them to accelerate the interfacial charge transfer between the charcoal substrate and the catalyst during the oxygen evolution reaction.

[0114] Figure 10 Transmission electron microscope image of the high-efficiency stable charcoal-based nanocatalyst prepared in Example One; as can be seen from the image, after Joule heating impact, the surrounding of the high-entropy alloy nanoparticles presents a few-layer graphite carbon structure, further strengthening the interfacial charge transfer between the charcoal substrate and the catalyst.

[0115] Figure 11 Particle size distribution graph of the nanocatalyst in the high-efficiency stable charcoal-based nanocatalyst prepared in Example One. As can be seen from the image, the particle size range of the high-entropy alloy nanoparticles is 10nm-38nm. Compared to the catalyst with several hundred nanometer particle size prepared by traditional heating methods such as tube furnace pyrolysis, the charcoal-based nanocatalyst prepared by this Joule heating method significantly improves the utilization rate of active sites and increases the accessibility of active centers to electrolyte ions. This smaller particle size is mainly due to the continuous fission of particles at carbon defects during the Joule heating process.

[0116] Figure 12 X-ray diffraction spectrum, 1 is the high-efficiency stable charcoal-based nanocatalyst prepared in Example One, and 2 is the activated charcoal prepared in Step Two of Example One. As can be seen from the image, the high-entropy alloy nanoparticles exhibit a single-phase alloy structure.

[0117] Figure 13 Oxygen evolution reaction (OER) polarization curve graph of the high-efficiency stable charcoal-based nanocatalyst prepared in Examples One to Three, 1 is Example One, 2 is Example Two, and 3 is Example Three. As can be seen from the image, the charcoal-based nanocatalyst prepared in Example One has an oxygen evolution overpotential of 178mV at an electric current density of 10mAcm -2 -2, and an OER activity of 10.2mAcm -2The overpotential for oxygen evolution at a current density of 100 mA cm-2 is 320 mV, and the complexity and synergistic effect of the high-entropy configuration help to accelerate the OER kinetics.

[0118] Figure 14 The high-efficiency stable charcoal-based nanocatalyst prepared in Example One can be stably operated at a current density of 100 mA cm-2 for 146 h, and the required voltage only increases by 3.6%, indicating that the embedded structure of high-entropy alloy nanoparticles helps to enhance the interface stability of the catalyst. -2 The stability curve at a current density of 100 mA cm-2. As can be seen from the figure, the charcoal-based nanocatalyst can be stably operated at a current density of 100 mA cm-2 for 146 h, and the required voltage only increases by 3.6%, indicating that the embedded structure of high-entropy alloy nanoparticles helps to enhance the interface stability of the catalyst. -2 The stability curve at a current density of 100 mA cm-2. As can be seen from the figure, the charcoal-based nanocatalyst can be stably operated at a current density of 100 mA cm-2 for 146 h, and the required voltage only increases by 3.6%, indicating that the embedded structure of high-entropy alloy nanoparticles helps to enhance the interface stability of the catalyst.

[0119] The degradation experiment process of Rhodamine B (RhB): 150 mL of RhB aqueous solution (concentration of 25 mg / L) was prepared, 300 mg of charcoal-based nanocatalyst and 75 μL of 0.5 mM of potassium persulfate (PMS) were added to trigger RhB degradation, and then 2.0 mL of solution was extracted at the designed time interval, filtered with a polyvinylidene fluoride needle filter (0.45 μm), and immediately measured for the residual concentration of RhB with a UV spectrophotometer. Figure 15 The degradation efficiency of Rhodamine B by the high-efficiency stable charcoal-based nanocatalyst prepared by different heating processes, 1 is Example Four, 2 is Example Five, and 3 is Example Six. As can be seen from the figure, the charcoal-based nanocatalyst prepared in Example Four exhibits high catalytic activity and can remove 99.5% of Rhodamine B within 10 min; as the reaction temperature increases, the number of carbon defect sites will decrease, and the cobalt metal salt will also gradually evaporate, resulting in a decrease in metal loading, which ultimately affects the degradation efficiency of the charcoal-based nanocatalyst.

[0120] After the catalytic reaction, the catalyst was washed with deionized water for 3 times and then dried in an oven at 60°C. The recovered catalyst was used for cyclic degradation experiments under the same conditions, and the degradation experiment process was the same as Figure 15 that described above, and the degradation time was 10 min each time. In each cyclic experiment, the stability and recovery efficiency of the catalyst were evaluated according to the RhB degradation. Figure 16 The longitudinal section scanning electron microscope image of the high-efficiency stable charcoal-based nanocatalyst prepared in Example Four after passivation during the degradation of Rhodamine B. As can be seen from the figure, after 10 cycles of the charcoal-based nanocatalyst, the surface presents a larger nanoflower structure due to the adsorption of degradation intermediates, thereby hindering the continuation of the reaction.

[0121] The regeneration method of the high-efficiency stable charcoal-based nanocatalyst prepared in Example Four, which is carried out according to the following steps:

[0122] ① The passivated high-efficiency stable charcoal-based nanocatalyst was fixed on the copper electrode of a joule heating device, heated to 1600°C at a heating rate of 10000°C / s, and subjected to carbon thermal shock treatment at 1600°C and an argon flow rate of 0.4 L / min for 2 s, and finally cooled to room temperature at a cooling rate of 2400°C / s;

[0123] ② Step ① was repeated twice, i.e., the regeneration method was completed, to obtain the regenerated charcoal-based nanocatalyst.

[0124] Figure 17 The longitudinal section scanning electron microscope image of the passivated high-efficiency stable charcoal-based nanocatalyst prepared in Example Four after joule heating treatment and regeneration. As shown in the figure, after the charcoal-based nanocatalyst was regenerated at a high temperature of 1600°C, the cobalt nanoparticles recovered activity and presented a smooth spherical shape.

[0125] Figure 18 The transmission electron microscope image of the passivated high-efficiency stable charcoal-based nanocatalyst prepared in Example Four after joule heating treatment and regeneration. As shown in the figure, after the charcoal-based nanocatalyst was regenerated at a high temperature of 1600°C, the reaction intermediates coated around the cobalt catalyst were converted into a graphite carbon layer structure, which not only promoted the recovery of active metal sites but also enhanced the local electronic transfer of the catalyst.

[0126] Figure 19 The degradation efficiency of rhodamine B by the high-efficiency stable charcoal-based nanocatalyst prepared in Example Four in 20 cycles; the charcoal-based nanocatalyst used in the first to ninth cycle experiments was prepared in Example Four; the charcoal-based nanocatalyst used in the tenth cycle experiment was passivated and had a significantly decreased degradation efficiency; the charcoal-based nanocatalyst used in the eleventh to twenty-first cycle experiments was passivated and regenerated by joule heating shock treatment; and the cycle process and the degradation process were the same as those of Example Four. As shown in the figure, after the charcoal-based nanocatalyst was subjected to joule heating treatment for multiple times, passivation-regeneration was achieved, and the degradation efficiency of rhodamine B was higher than 90% in 20 cycles. Figure 16 ​

Claims

1. A method for preparing highly efficient and stable charcoal-based nanocatalysts based on Joule heating, characterized in that: Follow these steps: I. Preparation of transition metal salt solutions: The transition metal salt is added to the solvent and stirred until homogeneous to obtain a transition metal salt solution; The concentration of the transition metal salt solution is 0.05 mol / L to 0.25 mol / L; the transition metal salt is one or a combination of several of the following: iron salt, cobalt salt, nickel salt, chromium salt, and manganese salt. II. Carbonization Activation: Wood was carbonized for 4-8 hours at a temperature of 800℃-1200℃ and a nitrogen flow rate of 0.2L / min-0.6L / min. After cooling to room temperature, carbonized wood was obtained. Then, the carbonized wood was activated for 6-10 hours at a temperature of 660℃-860℃ and a carbon dioxide flow rate of 0.05L / min. After cooling to room temperature, activated charcoal was obtained. III. Acid Etching: The activated charcoal was immersed in an acid solution and etched for 10 to 30 minutes at a temperature of 15℃ to 35℃, followed by ultrasonic cleaning to obtain acid-treated charcoal. The concentration of the acid solution is 5wt%~25wt%; the acid solution is a nitric acid solution or a hydrochloric acid solution; IV. Surface coating: The drop volume is 2 mL / cm 2 ~5mL / cm 2 The transition metal salt solution was drop-coated onto the surface of the acid-treated charcoal to fully wet the surface. Then, the charcoal was vacuum-treated for 24h to 72h in a vacuum environment with a temperature of 15℃ to 25℃ and a vacuum degree of 10Pa to 10kPa. Repeat step four After 3 to 5 times, the charcoal after drip coating and impregnation is obtained. The charcoal after drip coating and impregnation is then heated at a temperature of 50℃ to 90℃ for 8 to 24 hours to obtain charcoal loaded with metal salt precursor. V. Joule heating treatment: Charcoal loaded with metal salt precursors was fixed on the copper electrode of a Joule heating device and heated to 1800℃~2400℃ at a heating rate of 8000℃ / s~12000℃ / s. The charcoal was then subjected to carbon thermal shock treatment for 0.5s~2.5s at a temperature of 1800℃~2400℃ and an argon gas flow rate of 0.2L / min~0.8L / min. Finally, the charcoal was cooled to room temperature at a cooling rate of 2000℃ / s~2500℃ / s. Repeat step five One to three times, a highly efficient and stable charcoal-based nanocatalyst was obtained; The highly efficient and stable charcoal-based nanocatalyst can be regenerated after passivation. The regeneration method is carried out according to the following steps: The passivated, highly efficient and stable charcoal-based nanocatalyst was fixed on the copper electrode of a Joule heating device. The temperature was increased to 1800℃~2400℃ at a heating rate of 8000℃ / s~12000℃ / s, and then subjected to carbon thermal shock treatment for 0.5s~2.5s at a temperature of 1800℃~2400℃ and an argon gas flow rate of 0.2L / min~0.8L / min. Finally, the temperature was cooled to room temperature at a cooling rate of 2000℃ / s~2500℃ / s. Repeat steps 1 to 3 times.

2. The method for preparing highly efficient and stable charcoal-based nanocatalysts based on Joule heating according to claim 1, characterized in that... The solvent mentioned in step one is distilled water or anhydrous ethanol; the stirring and mixing mentioned in step one specifically refers to stirring at a speed of 300 rpm to 600 rpm for 12 h to 36 h.

3. The method for preparing highly efficient and stable charcoal-based nanocatalysts based on Joule heating according to claim 1, characterized in that... The iron salt is ferric nitrate, ferric chloride, or ferric acetate; the cobalt salt is cobalt nitrate, cobalt chloride, or cobalt acetate; the nickel salt is nickel nitrate, nickel chloride, or nickel acetate; the chromium salt is chromium nitrate, chromium chloride, or chromium acetate; and the manganese salt is manganese nitrate, manganese chloride, or manganese acetate.

4. The method for preparing highly efficient and stable charcoal-based nanocatalysts based on Joule heating according to claim 1, characterized in that... The wood mentioned in step two is pretreated wood. The pretreatment is carried out in the following steps: the wood is soaked in distilled water or ethanol solution, ultrasonically cleaned for 1h to 3h at a power of 100W to 300W, and then vacuum dried for 1h to 24h at a temperature of 40℃ to 80℃ to obtain pretreated wood.

5. The method for preparing highly efficient and stable charcoal-based nanocatalysts based on Joule heating according to claim 1, characterized in that... The thickness of the wood mentioned in step two is 0.5mm to 2.5mm; the wood mentioned in step two is coniferous or broadleaf wood, and the cutting method is transverse cutting or tangential cutting.

6. The method for preparing highly efficient and stable charcoal-based nanocatalysts based on Joule heating according to claim 1, characterized in that... The ultrasonic cleaning described in step three is carried out in the following steps: using distilled water or anhydrous ethanol as the cleaning solution, ultrasonic cleaning is performed at a power of 200W~500W until the pH of the solution is neutral.

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