A gas-liquid interface catalyst, a preparation method and application thereof

Abstract

The present application relates to the technical field of organic waste gas treatment, and particularly relates to a gas-liquid interface catalyst, a preparation method and application thereof. The gas-liquid interface catalyst provided by the present application comprises hydrophilic nano-silica and a hydrophobic N-doped graphene carbon layer coated on the surface of the hydrophilic nano-silica, the hydrophobic N-doped graphene carbon layer anchors active metals through N atoms, and the active metals comprise one or more of Fe, Mn, Co and Cu; the gas-liquid interface catalyst has amphiphilicity. The catalyst provided by the present application overcomes the defects of low •OH yield and poor stability, long VOCs mass transfer path, low mass transfer efficiency, large mass transfer resistance of insoluble VOCs and poor removal effect.

Description

Technical Field

[0001] This invention relates to the field of organic waste gas treatment technology, and in particular to a gas-liquid interface catalyst, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are major precursors to PM2.5 and ozone formation, with annual emissions far exceeding those of NO. X VOCs, along with SO2, are showing a continuous upward trend and have become one of the key and challenging aspects of air pollution control in my country. Currently, the main technologies for treating industrial VOCs emissions include activated carbon adsorption, adsorption concentration-high temperature / catalytic combustion, biodegradation, low-temperature plasma treatment, and photocatalytic oxidation. Among these, activated carbon adsorption has advantages such as simple process and low cost, but it suffers from frequent adsorbent replacement, difficulties in solid waste disposal, and challenges in achieving long-term stable compliance with emission standards. Furthermore, it is not conducive to refined monitoring and source tracing of pollutant emissions. While adsorption concentration-high temperature / catalytic combustion technology has high purification efficiency, its equipment system is complex, requires large construction investment, and has high energy consumption, especially high-temperature combustion which consumes a large amount of fuel, resulting in high carbon emissions. Although technologies such as biodegradation, low-temperature plasma, and photocatalytic oxidation have low-carbon potential, they generally suffer from low treatment efficiency, poor resistance to shock loads, and a tendency to generate secondary pollution, making it difficult to support large-scale industrial applications.

[0003] Hydroxyl radicals (•OH), as strong oxidizing agents, possess a high redox potential (2.8 eV) and are widely used in the treatment of organic waste gases. However, their low generation efficiency and insufficient production volume under industrial conditions greatly limit their practical engineering applications. Recent studies have found that microdroplet technology can significantly enhance the generation rate and instantaneous concentration of •OH, improving the oxidation and purification efficiency of VOCs and providing a new approach for the efficient application of •OH in industrial waste gas treatment. For example, related technologies disclose a solid-liquid spontaneous oxidation mechanism based on the microdroplet interface, inducing in-situ generation of •OH through contact between a solid insulating material rich in hydroxyl functional groups and microdroplets, thereby achieving the oxidative degradation of VOCs. Although the above technologies propose novel microdroplet excitation strategies, they still have the following significant shortcomings:

[0004] (1) Lack of efficient catalytic mechanism: The above technology mainly relies on the reaction of hydroxyl groups on the surface of the insulator with water to generate •OH. No catalyst mechanism is introduced, and hydroxyl groups are easily consumed in the reaction process, resulting in a gradual decrease in the •OH generation rate, which affects the continuous removal efficiency and reaction stability of VOCs.

[0005] (2) The mass transfer path of VOCs is complex and inefficient: The above technologies rely on VOCs to first diffuse from the gas phase to the surface of the droplets, and then penetrate to the solid surface for oxidation reaction. The entire mass transfer path is long and the interface migration efficiency is low, which significantly restricts the reaction rate and overall removal efficiency.

[0006] (3) Limited ability to treat insoluble VOCs: The above technologies have a certain ability to treat easily soluble VOCs (such as ethanol and aldehydes), but for VOCs such as toluene, benzene, and chlorobenzene, which are highly hydrophobic and have high gas-liquid mass transfer resistance, their oxidation reaction kinetics are poor, the purification effect is not ideal, and it is difficult to meet the treatment needs of high-concentration and complex VOC waste gas. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a gas-liquid interface catalyst, its preparation method, and its application. The catalyst provided by this invention overcomes the shortcomings of low •OH yield and poor stability, long VOCs mass transfer pathways and low mass transfer efficiency, as well as high mass transfer resistance and poor removal effect of sparingly soluble VOCs.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] This invention provides a gas-liquid interface catalyst, comprising hydrophilic nano-silica and a hydrophobic N-doped graphene carbon layer coated on the surface of the hydrophilic nano-silica, wherein the hydrophobic N-doped graphene carbon layer anchors an active metal through N atoms, and the active metal includes one or more of Fe, Mn, Co and Cu; the gas-liquid interface catalyst is amphiphilic.

[0010] This invention provides a method for preparing the gas-liquid interface catalyst described above, comprising the following steps:

[0011] S1. Dissolve hexadecyltrimethylammonium bromide and a weakly basic reagent in water, then mix with a hydrophobic alcohol solvent to obtain a mixture; the volume ratio of water to hydrophobic alcohol solvent is 1:0.02~0.08;

[0012] S2. Add the silicon source to the mixture to carry out a hydrolysis reaction to obtain a silica precursor suspension;

[0013] S3. The silica precursor suspension is subjected to a hydrothermal reaction followed by solid-liquid separation to obtain hydrophilic nano-silica; the temperature of the hydrothermal reaction is 120~160℃;

[0014] S4. The hydrophilic nano-silica is dispersed in water, and the pH value is adjusted to 7.5~9.5. Polydopamine and active metal salt are added to the pH-adjusted dispersion to carry out an adsorption reaction. After solid-liquid separation of the adsorption system, the obtained solid is calcined under a protective atmosphere to form a hydrophobic N-doped graphene carbon layer anchored to the active metal on the surface of the hydrophilic nano-silica, thus obtaining the gas-liquid interface catalyst.

[0015] The mass ratio of the hydrophilic nano-silica to polydopamine is 1:0.25~4.

[0016] Preferably, in step S4, the mass ratio of the hydrophilic nano-silica to the active metal salt is 1:0.2~1.

[0017] Preferably, in step S1, the hydrophobic alcohol solvent includes one or more of n-pentanol, n-butanol, and isoamyl alcohol.

[0018] Preferably, in step S1, the weakly alkaline reagent includes urea or ammonia; the mass ratio of the hexadecyltrimethylammonium bromide to the weakly alkaline reagent is 1:0.5~1.0.

[0019] Preferably, in step S2, the silicon source includes tetraethyl orthosilicate; the volume ratio of water to silicon source in the mixture is 1:0.05~0.10.

[0020] Preferably, in step S3, the hydrothermal reaction time is 6-9 hours.

[0021] Preferably, in step S4, the calcination temperature is 400~600℃ and the time is 4~6 h.

[0022] This invention provides the application of the gas-liquid interface catalyst described in the above-described scheme or the gas-liquid interface catalyst prepared by the preparation method described in the above-described scheme in the treatment of volatile organic waste gas.

[0023] Preferably, the treatment of volatile organic waste gas includes the following steps: mixing the gas-liquid interface catalyst, water, and hydrogen peroxide to obtain a reaction solution; forming the reaction solution into microdroplets; and contacting the volatile organic waste gas with the microdroplets.

[0024] This invention provides a gas-liquid interface catalyst, comprising hydrophilic nano-silica and a hydrophobic N-doped graphene carbon layer coated on the surface of the hydrophilic nano-silica, wherein the hydrophobic N-doped graphene carbon layer anchors an active metal through N atoms, and the active metal includes one or more of Fe, Mn, Co and Cu; the gas-liquid interface catalyst is amphiphilic.

[0025] This invention, by controlling the hydrophilicity and hydrophobicity of the catalyst surface, enables the catalyst to be stably distributed at the microdroplet interface, thereby fully leveraging the advantage of the microdroplet interface in enhancing the catalytic efficiency of H2O2. The results of the examples show that, compared to the bulk H2O2 catalytic reaction in the liquid phase (compared to Fe@SiO2-H2O2), the amount of •OH generated is significantly increased by 2-3 orders of magnitude. In traditional liquid-phase oxidation technologies, VOCs must first undergo a gas-liquid mass transfer process to enter the liquid phase, and then undergo oxidation with •OH through molecular diffusion. Since this invention is based on a catalytic oxidation reaction constructed at the microdroplet interface, VOC molecules only need to undergo mass transfer from the gas phase to the gas-liquid interface to undergo catalytic oxidation, significantly shortening the mass transfer path. The results of the examples show that, compared to the Fe@SiO2-H2O2 system, the mass transfer efficiency is increased by 5-10 times. Because amphiphilic SiO2 nanocatalysts can effectively adhere to the microdroplet interface, and the uniformly sized nanoparticles themselves have obvious Brownian motion, they can continuously collide with the microdroplet interface, generating a larger gas-liquid contact area. Therefore, the mass transfer area of ​​sparingly soluble VOCs is significantly improved. At the same time, sparingly soluble VOCs are directly degraded by •OH at the microdroplet interface, and the VOCs removal efficiency is significantly improved to 95-99%. Attached Figure Description

[0026] Figure 1 XRD patterns of Fe@CSiO2 and Fe@SiO2;

[0027] Figure 2 Aberration-corrected electron micrograph of Fe@CSiO2;

[0028] Figure 3 A comparison of the infrared spectra of Fe@CSiO2 and Fe@SiO2;

[0029] Figure 4 To catalyze the production of H2O2 by Fe@CSiO2 at the microdroplet interface • Fluorescence microscopy imaging of OH;

[0030] Figure 5 This is a reaction flow diagram of continuous flow VOCs waste gas catalytic oxidation based on Fe@CSiO2 microdroplet interface;

[0031] Figure 6 A comparative graph showing the effect of different catalytic materials on the removal of toluene waste gas in a microdroplet interface catalytic oxidation system;

[0032] Figure 7 The graph shows the relationship between surface tension, contact angle, and surface contact energy at the microdroplet interface for catalysts with different PDA contents.

[0033] Figure 8This is a comparison of the toluene removal efficiency of catalysts with different PDA contents in a microdroplet interface catalytic oxidation system. Detailed Implementation

[0034] This invention provides a gas-liquid interface catalyst, comprising hydrophilic nano-silica and a hydrophobic N-doped graphene carbon layer coated on the surface of the hydrophilic nano-silica, wherein the hydrophobic N-doped graphene carbon layer anchors an active metal through N atoms, and the active metal includes one or more of Fe, Mn, Co and Cu; the gas-liquid interface catalyst is amphiphilic.

[0035] In this invention, the particle size of the gas-liquid interface catalyst is preferably 50-150 nm; the thickness of the hydrophobic N-doped graphene carbon layer is preferably 5-20 nm.

[0036] The gas-liquid interface catalyst provided by this invention has amphiphilic properties and can be stably distributed at the microdroplet interface, thereby giving full play to the advantage of the microdroplet interface in enhancing the efficiency of H2O2 catalytic reaction.

[0037] In traditional liquid-phase oxidation technology, VOCs first need to undergo a gas-liquid mass transfer process to enter the liquid phase, and then undergo an oxidation reaction with •OH through molecular diffusion. Since this invention is based on a catalytic oxidation reaction constructed at a microdroplet interface, VOCs molecules only need to undergo mass transfer from the gas phase to the gas-liquid interface to undergo a catalytic oxidation reaction, and the mass transfer path is significantly shortened.

[0038] Furthermore, since the catalyst can effectively adhere to the microdroplet interface and the nanoparticles themselves have obvious Brownian motion, they can continuously collide with the microdroplet interface, generating a larger gas-liquid contact area. Therefore, the mass transfer area of ​​sparingly soluble VOCs is significantly improved. At the same time, sparingly soluble VOCs are directly degraded by •OH at the microdroplet interface, and the VOCs removal efficiency is significantly improved to 95-99%.

[0039] This invention provides a method for preparing the gas-liquid interface catalyst described above, comprising the following steps:

[0040] S1. Dissolve hexadecyltrimethylammonium bromide and a weakly basic reagent in water, then mix with a hydrophobic alcohol solvent to obtain a mixture;

[0041] S2. Add the silicon source to the mixture to carry out a hydrolysis reaction to obtain a silica precursor suspension;

[0042] S3. The silica precursor suspension is subjected to a hydrothermal reaction followed by solid-liquid separation to obtain hydrophilic nano-silica;

[0043] S4. The hydrophilic nano-silica is dispersed in water, and the pH value is adjusted to 7.5~9.5. Polydopamine and active metal salt are added to the pH-adjusted dispersion to carry out an adsorption reaction. After solid-liquid separation of the resulting adsorption system, the obtained solid is calcined under a protective atmosphere to form a hydrophobic N-doped graphene carbon layer anchored to the active metal on the surface of the hydrophilic nano-silica, thus obtaining the gas-liquid interface catalyst.

[0044] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0045] In this invention, hexadecyltrimethylammonium bromide and a weakly basic reagent are dissolved in water and then mixed with a hydrophobic alcohol solvent to obtain a mixture.

[0046] In this invention, the weakly basic reagent preferably includes urea or ammonia; the mass ratio of the hexadecyltrimethylammonium bromide to the weakly basic reagent is preferably 1:0.5~1.0, and in specific embodiments it can be 1:0.6 or 1:0.8. In this invention, the hydrophobic alcohol solvent preferably includes one or more of n-pentanol, n-butanol, and isoamyl alcohol; the water is preferably deionized water; the volume ratio of the water to the hydrophobic alcohol solvent is preferably 1:0.02~0.08, and in specific embodiments it can be 1:0.04, 1:0.05, or 1:0.06.

[0047] The present invention does not have special requirements on the ratio of hexadecyltrimethylammonium bromide to water, as long as the hexadecyltrimethylammonium bromide is completely dissolved.

[0048] In this invention, the role of the weakly alkaline reagent is to provide weakly alkaline conditions for the hydrolysis of the silicon source.

[0049] In this invention, hexadecyltrimethylammonium bromide (CTAB) is a typical cationic surfactant that can serve as a template for SiO2 polycondensation. Under weakly alkaline conditions, a silicon source (such as tetraethyl orthosilicate) hydrolyzes to generate Si-OH, and CTAB encapsulates or stabilizes the SiO2 precursor Si-OH in solution.

[0050] In this invention, the hydrophobic alcohol solvent has a relatively long hydrophobic chain, which can form a microemulsion or phase-separated structure with water in the silicon-source hydrolysis-condensation system, improving the polarity and dielectric constant of the reaction medium and increasing the TEOS hydrolysis-condensation efficiency. A high water ratio leads to excessively rapid hydrolysis, resulting in an accelerated subsequent condensation process and a relatively low surface Si-OH content; a high alcohol ratio slows down the hydrolysis-condensation process, which, while beneficial for the formation of surface hydroxyl groups, affects the particle morphology of SiO2. Therefore, an appropriate ratio of hydrophobic alcohol solvent to water is beneficial for controlling the Si-OH formation rate, thereby affecting the morphology of SiO2 and the density of surface hydroxyl groups.

[0051] It should be noted that step S1 of the present invention is mainly for generating a solvation environment for SiO2 nanoparticles with uniform particle size. Specifically, this environment refers to an environment that allows the silicon source to undergo hydrolysis.

[0052] After obtaining the mixture, the present invention adds a silicon source to the mixture to carry out a hydrolysis reaction to obtain a silica precursor suspension.

[0053] In this invention, the silicon source preferably comprises tetraethyl orthosilicate; the volume ratio of water to silicon source in the mixture is preferably 1:0.05~0.10, and in specific embodiments it can be 1:0.0625, 1:0.07, 1:0.08 or 1:0.09. In this invention, the silicon source is preferably added dropwise, and there are no special requirements for the rate of addition; it can be added dropwise.

[0054] In this invention, the hydrolysis reaction time is preferably 3-5 hours, and in specific embodiments, it can be 3 hours, 4 hours, or 5 hours. In this invention, the hydrolysis reaction is preferably carried out under stirring conditions. This invention does not have special requirements for the stirring rate; any stirring rate well-known in the art is acceptable. In step S2, the silicon source undergoes a hydrolysis reaction under alkaline conditions to form a Si-OH precursor.

[0055] After obtaining the silica precursor suspension, the present invention performs a hydrothermal reaction on the silica precursor suspension and separates the solid and liquid components to obtain hydrophilic nano-silica.

[0056] In this invention, the hydrothermal reaction temperature is 120~160℃, and the preferred time is 6~9 h. In specific embodiments, the hydrothermal reaction temperature can be 120℃, 130℃, 140℃, 150℃, or 160℃, and the hydrothermal reaction time can be 6 h, 7 h, 8 h, or 9 h. This invention accelerates the condensation reaction of Si-OH precursors through hydrothermal reaction to generate SiO2 nanoparticles. The hydrothermal temperature also affects the particle size and surface hydroxyl density of the SiO2 nanoparticles. Excessively high hydrothermal temperatures lead to dehydration of surface hydroxyl groups, condensing into Si-O-Si, affecting hydrophilicity; excessively low hydrothermal temperatures, while retaining more surface Si-OH and enhancing surface hydrophilicity, result in weaker crystal order, which is not conducive to the formation of uniformly sized SiO2 nanoparticles. In this invention, controlling the hydrothermal temperature at 120~160℃ yields SiO2 nanoparticles with good hydrophilicity and uniform particle size.

[0057] The present invention does not have any special requirements for the solid-liquid separation method; any solid-liquid separation method well known in the art is acceptable, such as filtration.

[0058] After completing the solid-liquid separation, the present invention preferably further includes washing the hydrophilic nano-silica with deionized water until neutral, and then drying it at 90°C.

[0059] After obtaining hydrophilic nano-silica, the present invention disperses the hydrophilic nano-silica in water, adjusts the pH value to 7.5~9.5, adds polydopamine and active metal salt to the pH-adjusted dispersion to carry out an adsorption reaction, and after solid-liquid separation of the resulting adsorption system, calcines the obtained solid under a protective atmosphere to form a hydrophobic N-doped graphene carbon layer anchored to the active metal on the surface of the hydrophilic nano-silica, thus obtaining the gas-liquid interface catalyst.

[0060] In this invention, urea is preferably used to adjust the pH value to 7.5-9.5. In specific embodiments, the pH value can be adjusted to 7.5, 8, 8.5, or 9.5. The purpose of adjusting the pH value in this invention is to enable polydopamine to be effectively adsorbed onto silica nanoparticles, and further thermal decomposition can generate a hydrophobic N-doped graphene carbon layer.

[0061] The present invention does not have special requirements on the amount of water used, as long as it can disperse the hydrophilic nano-silica evenly.

[0062] In this invention, the mass ratio of the hydrophilic nano-silica to polydopamine is 1:0.25~4, and in specific embodiments it can be 1:0.25, 1:0.5, 1:1, 1:2, 1:3 or 1:4, preferably 1:1.

[0063] In this invention, the mass ratio of the hydrophilic nano-silica to the active metal salt is preferably 1:0.2~1, and in specific embodiments it can be 1:0.2, 1:0.4, 1:0.5, 1:0.7 or 1:1. In this invention, when the active metal is Fe, the active metal salt is preferably ferric nitrate nonahydrate; when the active metal is Mn, the active metal salt is preferably manganese sulfate; when the active metal is Cu, the active metal salt is preferably copper nitrate.

[0064] In this invention, the adsorption reaction time is preferably 3-5 hours, and in specific embodiments it can be 3 hours, 4 hours, or 5 hours. Preferably, the adsorption reaction is carried out under stirring conditions.

[0065] This invention does not have any special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art is acceptable, such as vacuum filtration or centrifugation. In this invention, after completing the solid-liquid separation, it is preferable to further include drying the obtained solid before calcining it.

[0066] In this invention, the calcination temperature is preferably 400~600℃, and the calcination time is preferably 4~6 h. In specific embodiments, the calcination temperature can be 400℃, 450℃, 500℃, 550℃, or 600℃, and the calcination time is preferably 4 h, 5 h, or 6 h. In this invention, the protective atmosphere is preferably a nitrogen atmosphere.

[0067] In this invention, step S4 mainly regulates the hydrophobicity of SiO2 nanoparticles and loads catalytically active components. By adjusting the polydopamine ratio, the hydrophobicity of SiO2 nanoparticles can be further regulated. Simultaneously, N atoms can anchor Fe atoms, forming Fe-N structured nanoclusters or single-atom active sites, thereby enhancing catalytic activity.

[0068] It is important to note that optimizing the hydrophilicity / hydrophobicity of SiO2 nanoparticles is crucial for ensuring the catalytic oxidation of VOCs at the microdroplet interface. It is essential to emphasize that excessive hydrophilicity of SiO2 particles weakens their adhesion to the droplet interface, while excessive hydrophobicity hinders the activation reaction of the aqueous oxidant (H2O2). Therefore, this invention cleverly achieves controllable adjustment of the hydrophilic / hydrophobic functional groups on the catalyst surface through the synergistic regulation of a hydrophobic alcohol solvent and polydopamine, thereby balancing the hydrophilicity / hydrophobicity of the SiO2 nanoparticle catalyst. Furthermore, the polydopamine pyrolysis process generates a large number of unsaturated N coordination bonds, which effectively anchor iron atoms, resulting in highly dispersed active sites on the SiO2 nanoparticle surface, thus improving the efficiency of the catalytic reaction at the microdroplet interface.

[0069] The catalyst of this invention has a simple preparation process, can efficiently activate H2O2 without introducing external energy under normal temperature and pressure conditions, and has strong stability and can be recycled multiple times.

[0070] This invention provides the application of the gas-liquid interface catalyst described above in the treatment of VOCs waste gas.

[0071] The present invention does not have any special requirements on the type of VOCs waste gas, and any VOCs waste gas well known in the art can be used, such as easily soluble VOCs (e.g., ethanol, aldehydes) and poorly soluble VOCs (toluene, benzene, chlorobenzene).

[0072] In this invention, the treatment of VOCs waste gas preferably includes the following steps: mixing the gas-liquid interface catalyst, water and hydrogen peroxide to obtain a reaction solution; forming the reaction solution into microdroplets; and contacting the VOCs waste gas with the microdroplets.

[0073] In this invention, the concentration of the gas-liquid interface catalyst in the reaction solution is preferably 0.1~1.0 g / L, and the concentration of H2O2 is preferably 2~20.0 mmol / L; in specific embodiments, the concentration of the gas-liquid interface catalyst in the reaction solution can be 0.1, 0.3, 0.5, 0.8 or 1.0 g / L, and the concentration of H2O2 can be 2.0, 6.0, 8.0, 12.0, 16.0 or 20.0 mmol / L.

[0074] The present invention does not impose any special requirements on the preparation method of the microdroplets; any preparation method well known in the art can be used. In the embodiments of the present invention, the reaction solution is specifically introduced into a microdroplet generator to form microdroplets with uniform particle size, which are then evenly distributed in the reaction chamber.

[0075] In this invention, the liquid-to-gas ratio of the reaction liquid to the volatile organic waste gas is preferably 3~9 L / m³. 3 In specific embodiments, the value can be 3, 4, 5, 6, 7, 8, or 9 L / m. 3 .

[0076] The present invention does not impose any special limitation on the method of contacting the volatile organic waste gas with the micro-droplets. In the present invention, specifically, after the micro-droplets are evenly distributed in the reaction chamber, VOCs waste gas is introduced into the bottom of the reaction chamber.

[0077] The following detailed description of the gas-liquid interface catalyst, its preparation method, and its application provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0078] Example 1

[0079] S1. Weigh 1.5 g cetyltrimethylammonium bromide and 0.9 g urea and dissolve them in 80 mL of deionized water. Add 4.0 mL of n-pentanol and stir magnetically for 30 min to form a homogeneous mixture.

[0080] S2. Add 5.0 mL of tetraethyl orthosilicate (TEOS) dropwise to the above mixture and stir continuously for 3 h to obtain a milky white suspension;

[0081] S3. The suspension was transferred to a hydrothermal reactor and reacted at 130℃ for 6 h. After the reaction was completed, it was naturally cooled to room temperature, filtered, washed with deionized water until neutral, and then dried at 90℃ to obtain hydrophilic SiO2 nanoparticles.

[0082] S4. Take 0.5 g of the above hydrophilic SiO2 nanoparticles and add them to 100 mL of deionized water. Adjust the pH of the solution to 8 with urea. Then add 0.5 g of polydopamine (PDA) and 0.25 g of ferric nitrate nonahydrate in sequence. Stir the reaction under constant temperature for 3 h. Collect the product by centrifugation, filter and dry it. Then calcine it at 550 °C for 3 h in a nitrogen atmosphere to obtain an amphiphilic Fe@CSiO2 gas-liquid interface catalyst with a carbon coating on the surface.

[0083] Comparative Example 1

[0084] This comparative example is essentially the same as steps S1 to S4 in Example 1, except that polydopamine was not added in step S4 when preparing the Fe@SiO2 catalyst. Therefore, the Fe@SiO2 catalyst obtained in this comparative example is a hydrophilic material, and its surface is not coated with a hydrophobic graphene carbon layer, thus lacking amphiphilic structural characteristics.

[0085] The Fe@CSiO2 catalyst prepared above was characterized for relevant performance. For example... Figure 1 As shown, X-ray diffraction (XRD) patterns reveal characteristic diffraction peaks in the Fe@CSiO2 sample, indicating the simultaneous presence of amorphous SiO2 and graphene structures, suggesting a composite phase structure. In contrast, Fe@SiO2 without carbon coating exhibits only amorphous SiO2. Furthermore, high-resolution transmission electron microscopy (HRTEM) images (…) Figure 2 The results show that Fe@CSiO2 exhibits a spherical monodisperse nanoparticle structure with a particle size of approximately 100 nm, and its surface is coated with a graphene carbon layer approximately 10 nm thick, endowing it with significant hydrophobic characteristics, thus possessing an amphiphilic interface structure with a synergistic hydrophilic-hydrophobic interaction. Infrared spectrum ( Figure 3 This further verified its amphiphilic characteristics. Compared with Fe@SiO2, Fe@CSiO2 showed obvious characteristic absorption peaks of hydrophobic functional groups such as C=C and C–H on its surface, indicating that it has both hydrophilic and hydrophobic functional groups, which is conducive to the occurrence of gas-liquid interface reactions.

[0086] Figure 4 This is a fluorescence microscopy image of Fe@CSiO2-H2O2 participating in the catalytic reaction at the microdroplet interface. It can be observed that the catalyst produces significant green fluorescence at the microdroplet interface, indicating that it can effectively catalyze and activate H2O2 (0.5 mM), generating a high concentration of •OH (6.25 × 10⁻⁶). -11 M). Compared with Fe@SiO2-H2O2 in the liquid phase reaction, its •OH formation concentration (6.01×10) - 13The M value was increased by approximately 104 times, significantly enhancing the catalytic activity (liquid-phase reaction experiments are shown in Example 3 and Comparative Example 4). In summary, the Fe@CSiO2 catalyst prepared in Example 1 exhibits a well-defined amphiphilic structure and excellent microdroplet interfacial catalytic performance, verifying that the gas-liquid interfacial catalyst described in this invention has a reasonable structural design, a feasible preparation process, and good prospects for industrial application.

[0087] Example 2

[0088] This embodiment provides a method for enhancing VOCs gas-liquid mass transfer at the microdroplet interface using Fe@CSiO2 gas-liquid interface catalyst, comprising the following steps:

[0089] S1. Preparation of catalytic absorption solution: Weigh 0.5 g Fe@CSiO2 catalyst, add 1 L of deionized water, and use ultrasonic treatment to make it uniformly dispersed to obtain a stable catalytic absorption solution.

[0090] S2. Generating and distributing microdroplets in the reaction chamber: The absorbent liquid described above is introduced into the microdroplet generator to form microdroplets of uniform size, which are then evenly distributed inside the reaction chamber. The microdroplet flow rate is controlled at 0.2 L / min to ensure the formation of a stable gas-liquid interface system.

[0091] S3. Introducing VOCs waste gas and achieving microdroplet interface mass transfer reaction: VOCs waste gas, represented by toluene, is introduced from the bottom of the reaction chamber through a gas diffusion device, allowing it to fully contact the microdroplets suspended within the reaction chamber. The waste gas flow rate is set to 0.04 m³ / min. At the microdroplet interface, VOCs undergo a gas-liquid mass transfer process with the catalyst, and the overall gas-liquid mass transfer coefficient (…) Kl a It reached 0.176 s -1 .

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 2 is that no catalyst material was added in this comparative example; therefore, only microdroplets were used to absorb VOCs waste gas. The mass transfer effect on VOCs at the gas-liquid interface is not significant. Kl a Only 0.0069 s -1 This further corroborates that amphiphilic Fe@CSiO2 can significantly enhance the gas-liquid mass transfer of VOCs.

[0094] Comparative Example 3

[0095] The difference between this comparative example and Example 2 is that the catalyst used is hydrophilic Fe@SiO2. Because this catalyst is not amphiphilic, it is difficult to form a stable distribution at the microdroplet interface, and its mass transfer enhancement effect on VOCs at the gas-liquid interface is not significant, resulting in an overall... Kl a Only 0.0072 s -1 The effect was significantly lower than that of amphiphilic Fe@CSiO2 in Example 2, further demonstrating that amphiphilic Fe@CSiO2 can significantly enhance the gas-liquid mass transfer of VOCs.

[0096] Mass transfer enhancement mechanism and performance results: In the above mass transfer process, Fe@CSiO2 nanoparticles continuously collide with the microdroplet interface through Brownian motion, significantly increasing the contact frequency per unit area and the exposure rate of reactive sites, thereby effectively improving the overall gas-liquid mass transfer efficiency. Experimental measurements showed that the system in Example 2... Kl a Reached 0.176 s -1 Compared to the hydrophilic Fe@SiO2 catalyst system without a carbon coating, its mass transfer efficiency is increased by approximately 24 times, significantly enhancing the interfacial capture capacity of VOCs. In summary, Example 2 demonstrates that Fe@CSiO2 in a microdroplet system can achieve highly efficient gas-liquid mass transfer of VOCs through the synergistic effect of its physical dynamic behavior (Brownian diffusion) and surface amphiphilic structure, further proving the advantages and feasibility of this catalyst in gas-liquid interfacial reactions.

[0097] Example 3

[0098] This embodiment provides a method for the efficient oxidation and degradation of VOCs waste gas by using Fe@CSiO2 catalyst to catalyze H2O2 at the microdroplet interface. The process flow is as follows: Figure 5 As shown, the following steps are performed:

[0099] S1. Preparation of catalytic reaction solution: Weigh 0.5 g of the Fe@CSiO2 catalyst prepared in Example 1 and add it to 1 L of deionized water. Disperse it evenly using ultrasound. Then add 1 mL of 30% hydrogen peroxide (H2O2) solution and mix thoroughly to obtain a homogeneous reaction solution, wherein the concentration of H2O2 is 10 mM.

[0100] S2. Generating and distributing microdroplets in the reaction chamber: The above-mentioned reaction liquid is passed into the microdroplet generator to form microdroplets with uniform particle size, ensuring their uniform distribution within the reaction chamber. The microdroplet flow rate is controlled at 0.2 L / min to establish a stable gas-liquid interface reaction environment.

[0101] S3. Introducing VOCs waste gas and carrying out microdroplet interface catalytic reaction: Waste gas containing VOCs (represented by toluene) is introduced from the bottom of the reaction chamber through a gas diffusion device, allowing it to fully contact the microdroplets suspended within the chamber. At the gas-liquid interface of the microdroplets, the Fe@CSiO2 catalyst effectively activates H2O2, thereby generating active oxide species •OH, which catalytically oxidizes the VOCs, ultimately converting them into harmless products CO2 and H2O. The inlet gas flow rate is set to 0.04 m³ / min, and the liquid-to-gas ratio is 5 L / m³. 3 。

[0102] Comparative Example 4

[0103] The difference between this comparative example and Example 3 is that the catalyst used is hydrophilic Fe@SiO2, which does not enhance gas-liquid interface activity. Due to the lack of synergistic effect from the hydrophobic carbon layer, the activation efficiency of the Fe@SiO2-H2O2 system for H2O2 and the •OH generation capacity at the microdroplet interface are significantly reduced, resulting in a VOCs (represented by toluene) removal rate of only 56.7% after 4 hours (see Example 3). Figure 6 (), which is much lower than 96.5% in Example 3.

[0104] Figure 6 This is a comparative graph showing the removal efficiency of different catalytic materials for toluene waste gas in a microdroplet interface catalytic oxidation system. In this graph, microdroplet + Fe@CSiO2 + H2O2 represents Example 3, microdroplet + Fe@SiO2 + H2O2 represents Comparative Example 4, microdroplet + Fe@CSiO2 represents Example 2, microdroplet + Fe@SiO2 represents Comparative Example 3, and microdroplet absorption represents Comparative Example 2. Experimental results show that under the above reaction conditions, the method of this invention achieves a removal rate of over 95% for typical VOCs pollutants (such as toluene) (see [link to original text]). Figure 6 Furthermore, it maintains high stability within 2 hours of continuous reaction, with no significant performance degradation.

[0105] In summary, this embodiment verifies that Fe@CSiO2 possesses excellent H2O2 catalytic activity under microdroplet interface conditions, enabling efficient and stable degradation of VOCs waste gas, demonstrating outstanding application potential and engineering promotion value.

[0106] Examples 4-6: Fe@CSiO2 catalysts prepared with different PDA ratios

[0107] This embodiment provides Fe@CSiO2 catalysts prepared with different PDA contents. The content is basically the same as S1-S4 in Example 1, the main difference being the PDA content: In Example 1, the PDA content is 0.5g (i.e., Fe@CSiO2 - 0.5g PDA); in Example 4, the PDA content is 0.25g (i.e., Fe@CSiO2 - 0.25g PDA); in Example 5, the PDA content is 1.0g (i.e., Fe@CSiO2 - 1.0g PDA); and in Example 6, the PDA content is 2.0g (i.e., Fe@CSiO2 - 2.0g PDA). Figure 7 As can be seen from the data, the contact angle energy of Fe@CSiO2 gradually increases with the increase of PDA content, indicating that the increase of PDA content can regulate the hydrophobic properties of the catalyst surface. Figure 7 The deeper the red color, the higher the surface contact energy; and when the PDA content is 0.5g (i.e., Fe@CSiO2-0.5gPDA), the catalyst contact angle is 82.5°, indicating that the material has amphiphilic properties. Further calculations of the contact energy between the catalyst and the microdroplet interface show that, compared with the Fe@SiO2 catalyst without PDA, the contact energy between the PDA-modified Fe@CSiO2 series catalysts and the microdroplet interface is significantly increased, indicating that PDA modification is beneficial for catalyst adsorption at the microdroplet interface. Among them, Fe@CSiO2-0.5gPDA has the highest contact energy at the microdroplet interface, therefore, it can be better adsorbed at the microdroplet interface, which is more conducive to inducing catalytic reactions at the microdroplet interface.

[0108] Examples 7-9: Performance of Fe@CSiO2 catalysts with different PDA contents in catalytic activation of H2O2-oxidative degradation of VOCs at the microdroplet interface

[0109] The difference between Example 7 and Example 3 is that the catalyst Fe@CSiO2-0.5gPDA is replaced with Fe@CSiO2-0.25gPDA; the difference between Example 8 and Example 3 is that the catalyst Fe@CSiO2-0.5gPDA is replaced with Fe@CSiO2-1.0gPDA; and the difference between Example 9 and Example 3 is that the catalyst is replaced with Fe@CSiO2-2.0gPDA.

[0110] The performance of Fe@CSiO2 catalysts with different PDA contents in catalytic activation of H2O2-oxidative degradation of VOCs at the microdroplet interface is shown in the figure. Figure 8 .from Figure 8As can be seen, the VOCs removal efficiency first increases and then decreases with the PDA content increasing from 0 to 2.0 g, specifically 56.7%, 77.4%, 96.5%, 85.5%, and 75.4%, respectively. The VOCs removal rate reaches its maximum (96.5%) when the PDA content is 0.5 g (Fe@CSiO2-0.5 g PDA). Compared with other catalysts, the amphiphilic Fe@CSiO2-0.5 g PDA catalyst has the highest surface contact energy, enabling stable adsorption at the microdroplet interface. Therefore, it can efficiently catalyze the activation of H2O2 at the microdroplet interface to generate •OH, thereby oxidizing and degrading VOCs in the waste gas.

[0111] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gas-liquid interface catalyst, characterized in that, The catalyst comprises hydrophilic nano-silica and a hydrophobic N-doped graphene carbon layer coated on the surface of the hydrophilic nano-silica. The hydrophobic N-doped graphene carbon layer anchors an active metal through N atoms. The active metal includes one or more of Fe, Mn, Co and Cu. The gas-liquid interface catalyst is amphiphilic. The preparation method of the gas-liquid interface catalyst includes the following steps: S1. Dissolve hexadecyltrimethylammonium bromide and a weakly basic reagent in water, then mix with a hydrophobic alcohol solvent to obtain a mixture; the volume ratio of water to hydrophobic alcohol solvent is 1:0.02~0.08; S2. Add the silicon source to the mixture to carry out a hydrolysis reaction to obtain a silica precursor suspension; S3. The silica precursor suspension is subjected to a hydrothermal reaction followed by solid-liquid separation to obtain hydrophilic nano-silica; the temperature of the hydrothermal reaction is 120~160℃; S4. The hydrophilic nano-silica is dispersed in water, and the pH value is adjusted to 7.5~9.

5. Polydopamine and active metal salt are added to the pH-adjusted dispersion to carry out an adsorption reaction. After solid-liquid separation of the adsorption system, the obtained solid is calcined under a protective atmosphere to form a hydrophobic N-doped graphene carbon layer anchored to the active metal on the surface of the hydrophilic nano-silica, thus obtaining the gas-liquid interface catalyst. The mass ratio of the hydrophilic nano-silica to polydopamine is 1:0.25~4.

2. The method for preparing the gas-liquid interface catalyst according to claim 1, characterized in that, Includes the following steps: S1. Dissolve hexadecyltrimethylammonium bromide and a weakly basic reagent in water, then mix with a hydrophobic alcohol solvent to obtain a mixture; the volume ratio of water to hydrophobic alcohol solvent is 1:0.02~0.08; S2. Add the silicon source to the mixture to carry out a hydrolysis reaction to obtain a silica precursor suspension; S3. The silica precursor suspension is subjected to a hydrothermal reaction followed by solid-liquid separation to obtain hydrophilic nano-silica; the temperature of the hydrothermal reaction is 120~160℃; S4. The hydrophilic nano-silica is dispersed in water, and the pH value is adjusted to 7.5~9.

5. Polydopamine and active metal salt are added to the pH-adjusted dispersion to carry out an adsorption reaction. After solid-liquid separation of the adsorption system, the obtained solid is calcined under a protective atmosphere to form a hydrophobic N-doped graphene carbon layer anchored to the active metal on the surface of the hydrophilic nano-silica, thus obtaining the gas-liquid interface catalyst. The mass ratio of the hydrophilic nano-silica to polydopamine is 1:0.25~4.

3. The preparation method according to claim 2, characterized in that, In step S4, the mass ratio of the hydrophilic nano-silica to the active metal salt is 1:0.2~1.

4. The preparation method according to claim 2, characterized in that, In step S1, the hydrophobic alcohol solvent includes one or more of n-pentanol, n-butanol, and isoamyl alcohol.

5. The preparation method according to claim 2, characterized in that, In step S1, the weakly alkaline reagent includes urea or ammonia; the mass ratio of the hexadecyltrimethylammonium bromide to the weakly alkaline reagent is 1:0.5~1.

0.

6. The preparation method according to claim 2, characterized in that, In step S2, the silicon source includes tetraethyl orthosilicate; the volume ratio of water to silicon source in the mixture is 1:0.05~0.

10.

7. The preparation method according to claim 2, characterized in that, In step S3, the hydrothermal reaction takes 6 to 9 hours.

8. The preparation method according to claim 2 or 3, characterized in that, In step S4, the calcination temperature is 400~600℃ and the time is 4~6 h.

9. The application of the gas-liquid interface catalyst according to claim 1 or the gas-liquid interface catalyst prepared by any one of claims 2 to 8 in the treatment of volatile organic waste gas.

10. The application according to claim 9, characterized in that, The treatment of volatile organic waste gas includes the following steps: The gas-liquid interface catalyst, water, and hydrogen peroxide are mixed to obtain a reaction solution; the reaction solution is then formed into microdroplets; and volatile organic waste gas is brought into contact with the microdroplets.

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