A method for the conversion of gaseous oxygen to ozone mediated by a porous carbon-based floating cathode

Abstract

The application discloses a method for converting gaseous oxygen into ozone by using a porous carbon-based floating cathode, and belongs to the field of electrochemical water treatment and advanced oxidation technology. The porous carbon-based material is floated on the surface of an electrolyte as a cathode, so that the main part of the material is in an oxygen-containing gas phase, and the lower surface of the material is in contact with the electrolyte to form a gas-liquid-solid three-phase interface. An anode is placed in the electrolyte, and a constant potential is applied to selectively activate gaseous oxygen in the oxygen-containing gas phase on the surface of the cathode and in the pores of the cathode to generate ozone and make the ozone enter the electrolyte. In the application, a three-phase interface catalytic environment is constructed by using a carbon-based floating cathode with a through-pore structure and hydrophobicity, nitrogen-doped sites of a dry catalytic interface are used to regulate the directional conversion behavior of key intermediates, the directional activation of gaseous oxygen is strengthened, the Faraday efficiency of an ozone generation path is improved, and ozone dissolved in water in situ is prepared, so that the first case of ozone generated by cathode-activated oxygen molecules is realized, and the application is suitable for in-situ advanced oxidation water treatment, electrochemical synthesis of chemicals and other fields.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical water treatment and advanced oxidation technology, specifically relating to a method for efficiently and in-situ converting gaseous oxygen into dissolved ozone by using a porous hydrophobic carbon-based floating cathode and optimizing the gas-liquid-solid three-phase interface and controlling nitrogen-doped active sites. Background Technology

[0002] Ozone, due to its strong oxidizing properties, is widely used in water disinfection, wastewater treatment, and oxidative synthesis. Traditional ozone production often employs dielectric barrier discharge (DER), which suffers from high energy consumption, complex equipment, and low product utilization. In recent years, electrochemical in-situ ozone generation has attracted attention due to its ease of operation, lack of need for an external gas source, and ability to be coupled with water treatment processes. Existing electrochemical ozone generation technologies mainly achieve ozone production through anodic water oxidation or oxygen activation pathways, often using oxygenated aqueous solutions as the reaction medium. These methods suffer from the following drawbacks: limited oxygen mass transfer, low Faraday efficiency, high operating potential, high energy consumption, severe competing reactions, and poor electrode stability. This is essentially because, at high potentials, water oxidation to ozone generation is only a secondary competing pathway in the OER, making it difficult to efficiently dominate the reaction.

[0003] More importantly, ozone cannot be generated synchronously at the cathode and anode. In fact, the side reaction of ozone reduction and consumption at the cathode in a single-chamber reactor leads to a decrease in ozone utilization. If the cathode reaction zone in the electrolytic cell could also become a functional zone for ozone production, allowing oxygen molecules in the air to be directly activated by cathode electrons at the gas-solid interface to generate polar and hydrophilic reactive oxygen species (ROS), which are then transferred to the gas-water interface to be converted into ozone and dissolved in the aqueous phase, a completely new electrocatalytic ozone synthesis pathway could be opened up to achieve "oxygen in the air → ozone in water".

[0004] Based on this idea, developing a cathode system that can directly and efficiently convert gaseous oxygen selectively into ozone is of great significance for achieving low-energy consumption and high-stability in-situ ozone production. Summary of the Invention

[0005] This invention provides a method for converting gaseous oxygen into ozone through a porous carbon-based floating cathode. By constructing a porous carbon-based cathode with hydrophobic surface properties and a through-pore structure, a stable gas-liquid-solid three-phase interface is formed by utilizing its floating state on the water surface. Combined with nitrogen doping modification of the gas catalytic interface to regulate the oxygen reduction reaction pathway, a highly efficient and selective electrocatalytic conversion of gaseous oxygen into ozone is achieved, overcoming the problems of limited oxygen mass transfer, low ozone selectivity, and poor electrode stability in the prior art.

[0006] This invention is achieved through the following technical solution: A method for converting gaseous oxygen into ozone through a porous carbon-based floating cathode, the specific steps of which are as follows: (1) A porous carbon-based material is floated on the surface of the electrolyte as a cathode, so that the upper part of the main body is in the oxygen-containing phase and the lower surface is in contact with the electrolyte to form a gas-liquid-solid three-phase interface, and the anode is placed in the electrolyte; (2) By applying a constant potential to the cathode in the above system, gaseous oxygen molecules in the oxygen-containing phase are selectively activated on the cathode surface and in the pores to generate ozone, which then enters the water-based electrolyte.

[0007] The porous carbon-based material in step (1) is a sheet-like carbon-based integrally molded material with a through-pore structure, including sheet-like porous carbon or sheet-like modified porous carbon. Sheet-like porous carbon includes sheet-like biomass-derived porous carbon, sheet-like carbon aerogel, etc. Sheet-like modified porous carbon is sheet-like porous carbon with hydrophobic modification or hydrophobic combination nitrogen doping modification on the surface.

[0008] The preparation method of the sheet-like biomass-derived porous carbon (obtained via biomass pathway) is as follows: Using sheet-like biomass materials (such as pulp flakes, balsa wood, etc.) as precursors, carbonization is carried out in an inert gas atmosphere at 750~850℃ for 3~5h to obtain sheet-like biomass-derived porous carbon. This method has a wide range of raw material sources and low cost.

[0009] The preparation method of the sheet-like carbon aerogel (obtained via a chemical derivation route) is as follows: 1.5 mL of concentrated hydrochloric acid (37.5% by mass) was added to 15 mL of anhydrous ethanol with stirring. During stirring, 1.61 g of phenol and 5.5 mL of formaldehyde were added. The mixture was kept at 110-130 °C for 11-13 h to obtain an aerogel. The aerogel was then soaked in 100-120 mL of anhydrous ethanol for 22-24 h and dried. After carbonization, the aerogel was kept at 750-850 °C for 3-5 h under an inert gas atmosphere to obtain a sheet-like carbon aerogel with a three-dimensional interconnected pore structure.

[0010] The method for preparing the hydrophobically modified sheet-like porous carbon is as follows: Disperse 0.5-1g of acetylene black powder in 50-60mL of deionized water, and sonicate for 5-10min to obtain an acetylene black dispersion. Add 0.5-1mL of 60% polytetrafluoroethylene dispersion dropwise to the acetylene black dispersion to obtain mixture I. Immerse the sheet-like porous carbon in mixture I for 1-3min, dry at 60℃, and then heat in an inert gas atmosphere at 300-400℃ for 30-60min to obtain sheet-like porous carbon with hydrophobic surface modification. The acetylene black powder can be replaced with conductive carbon material powders such as carbon black or graphene powder.

[0011] The method for preparing the surface-hydrophobic combined with nitrogen-doped modified sheet-like porous carbon is as follows: Disperse 0.5-1g of acetylene black powder in 50-60mL of deionized water, and sonicate for 5-10min to obtain an acetylene black dispersion. Add 0.5-1mL of 60% polytetrafluoroethylene dispersion dropwise to the acetylene black dispersion to obtain mixture II. Place sheet-like porous carbon horizontally and immerse it in mixture II for 1-3min with a thickness of 1 / 3. Dry at 60℃, and then heat at 300-400℃ for 30-60min under an inert gas atmosphere to obtain partially hydrophobically modified sheet-like porous carbon. The acetylene black powder can be replaced with conductive carbon material powders such as carbon black or graphene powder. 0.5-1g of nitrogen-doped graphene powder was dispersed in 5-10mL of anhydrous ethanol and sonicated for 5-10min to obtain a nitrogen-doped graphene dispersion. 0.5-1mL of 60% polytetrafluoroethylene dispersion was added dropwise to the nitrogen-doped graphene dispersion to obtain mixture Ш. Part of the hydrophobically modified sheet-like porous carbon that was not impregnated in mixture Ⅱ was impregnated in mixture Ш for 1-3min. After drying at 60℃, it was kept at 350℃ for 30min under an inert gas atmosphere to obtain hydrophobically combined nitrogen-doped modified sheet-like porous carbon. When used as a cathode, the lower surface in contact with the water surface was not nitrogen-doped, and only the remaining part was nitrogen-doped. The nitrogen-doped upper main body was in an oxygen-containing phase (air or other oxygen-containing gas), and the lower surface was in contact with the electrolyte.

[0012] The electrolyte in step (1) is a conductive aqueous solution containing electrolytes, including sodium sulfate solution, etc.

[0013] The anode in step (1) is a shape-stable electrode such as a Ti electrode, a Ti-based RuO2-IrO2 coated electrode, a Ti-based PbO2 coated electrode, a Pt electrode, or a BDD electrode.

[0014] In step (2), the cathode potential when a constant potential is applied to the system is -0.5V to -1.0V. vs (RHE), with a current density of 2.5~6.5 mA / cm².

[0015] The cathode of this invention adopts a floating structure with its geometric plane parallel to the ground (i.e., horizontally placed). It always floats on the liquid surface in the reactor, forming a gas-liquid-solid three-phase interface. The anode adopts shape-stable electrodes such as Ti electrode, Ti-based RuO2-IrO2 coated electrode, Ti-based PbO2 coated electrode, Pt electrode or BDD electrode, which can be directly purchased from the commercial market or prepared by existing conventional methods.

[0016] The anode of this invention is arranged in the following configuration: Configuration A (anode located below cathode): The anode is horizontally immersed a certain distance below the liquid surface, parallel and directly opposite the cathode; Configuration B (anode not directly below cathode): The anode is arranged vertically and placed on the side wall of the reactor, which is suitable for situations where it is necessary to avoid the generation of gas at the anode from interfering with the cathode reaction; Configuration C (anode located below cathode and offset from cathode): The anode is horizontally immersed a certain distance below the liquid surface, parallel to and offset from the cathode.

[0017] Compared with the prior art, the present invention has the following outstanding advantages: Constructing a gas-liquid-solid three-phase interface to achieve direct utilization of gaseous oxygen: This invention uses a porous carbon-based cathode, which is floated on the surface of the electrolyte. The main body of the cathode is in the oxygen-containing phase, and the lower surface is in contact with the liquid phase. Gaseous oxygen does not need to be dissolved in water first and can directly diffuse through the porous structure to the reaction site to participate in the electrochemical reduction reaction. This fundamentally breaks through the mass transfer bottleneck of "oxygen must be dissolved before reaction" in traditional methods, and significantly improves the oxygen utilization efficiency and ozone generation rate.

[0018] (2) The present invention effectively avoids the concentration polarization phenomenon at the gas-liquid interface caused by the limited diffusion of dissolved oxygen and significantly reduces the resistance to interfacial charge transfer. Therefore, no additional aeration system is required. In addition, this unique interfacial structure effectively reduces the interference of water quality background on the catalytic reaction.

[0019] (3) Simple preparation and stable structure: The present invention uses a method of impregnation with a mixture of nitrogen-doped graphene and polytetrafluoroethylene to realize the construction of hydrophobic and nitrogen-doped functional layers in one step on the surface of an integrally formed self-supporting carbon-based cathode. The method is simple to operate, highly controllable, and applicable to a variety of carbon-based substrates. The hydrophobicity and catalytic activity are stable for a long time. The base electrode catalyst coating is easy to destabilize, and the catalytic interface does not come into contact with water, thus avoiding the negative effects of electrowetting and the problems of traditional shedding and deactivation.

[0020] (4) The cathode material is widely available and the cost is controllable: The porous carbon-based material used in this invention can be prepared by annealing in an inert gas atmosphere using biomass as a precursor. The raw materials are abundant and the cost is low. The natural hierarchical pore structure of biomass can also be preserved. Alternatively, carbon aerogel can be prepared by using pure chemical precursors through a solvothermal method combined with atmospheric pressure drying and high temperature carbonization process. The pore structure is controllable and the repeatability is good. The two paths can be flexibly selected according to the application scenario, taking into account both performance and economy.

[0021] (5) The electrode configuration is flexible and applicable to a wide range of scenarios: the cathode floats on the liquid surface and the plane is parallel to the ground. It does not require a complex support structure and has good adaptability. The anode can be placed below the cathode to form a vertical electric field, or it can be arranged on the side or staggered. It can be flexibly selected according to different application requirements.

[0022] (6) Mild operating conditions and low energy consumption: This invention operates at normal temperature and pressure, with the cathode potential controlled between -0.5V and -1.0V. vs RHE), with a current density of 2.5~6.5mA / cm², requires no high-voltage power supply or complex gas source equipment, and significantly reduces energy consumption compared to the traditional dielectric barrier discharge method. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of configuration A in Example 1; Figure 2 This is a schematic diagram of configuration B in Example 2; Figure 3 This is a schematic diagram of configuration C in Example 3; Figure 4 The steps for synthesizing the HBT-OZO probe in Example 1; Figure 5 The results are the ozone qualitative analysis results for Example 1; Figure 6 Cyclic experiments were conducted to demonstrate the degradation effect of the porous carbon-based floating cathode on sodium indigo disulfonate solution in Example 1. Figure 7 The sampling and testing methods for nitrobenzene (NB) in Examples 1, 2, and 3, and the degradation effect diagram of nitrobenzene (NB) are shown. Detailed Implementation

[0024] To more clearly illustrate the technical solution of the present invention, a further detailed description of the present invention will be provided below in conjunction with specific embodiments and related drawings. It should also be noted that the present invention is not limited to the embodiments listed below.

[0025] The nitrogen-doped graphene powders used in the examples are shown in Table 1, and were prepared using existing techniques (refer to Zhang Junjie, et al. Melamine-cyanurate supramolecule induced graphitic N-richgraphene for singlet oxygen-dominated peroxymonosulfate activation to efficiently degrade organic pollutants [J]): Table 1

[0026] Note: N py N pr N g N o and N t These represent the contents of pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen, nitrogen oxides, and total nitrogen, respectively.

[0027] The polytetrafluoroethylene dispersion used in the examples was purchased from Maclean's and had a mass concentration of 60 wt%.

[0028] Example 1 (1) The pulp is pre-drawn and 60 o After drying, the carbon material is carbonized at 800℃ for 4 hours under a nitrogen atmosphere to obtain biomass-derived carbon material. 1g of acetylene black powder was dispersed in 60mL of deionized water and sonicated for 10min to obtain an acetylene black dispersion. 1mL of 60% polytetrafluoroethylene dispersion was added dropwise to the acetylene black dispersion to obtain mixture II. The portion of biomass-derived carbon material with a transverse thickness of about 1 / 3 was immersed in mixture II for 3min. After drying at 60℃, it was kept at 400℃ under a nitrogen atmosphere for 60min to obtain about 1 / 3 of the hydrophobically modified biomass-derived carbon. 1 g of nitrogen-doped graphene powder was dispersed in 10 mL of anhydrous ethanol and sonicated for 10 min to obtain a nitrogen-doped graphene dispersion. 1 mL of 60% polytetrafluoroethylene dispersion was added dropwise to the above nitrogen-doped graphene dispersion to obtain mixture Ш. 1 / 3 of the hydrophobically modified biomass-derived carbon (size 4 cm × 4 cm × 2 mm) was placed horizontally and the part not impregnated in mixture Ⅱ was impregnated in mixture Ш for 3 min to perform nitrogen doping modification. After drying at 60 °C, it was kept at 350 °C in a nitrogen atmosphere for 30 min to obtain the main part of the nitrogen-doped modified hydrophobic biomass-derived carbon material. (2) Electrode assembly: using, for example Figure 1 The electrode arrangement is as shown in configuration A. The nitrogen-doped modified hydrophobic biomass-derived carbon material of the main body obtained in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The nitrogen-doped modified main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Ti-based RuO2-IrO2 mesh electrode, which is placed horizontally 10mm below the cathode and fixed with electrode clamps. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.75V ( vs (RHE), with the current density stabilized at around 4.2 mA / cm², allows oxygen in the air to be selectively reduced to ozone on the cathode surface and within the channels, which then enters the electrolyte.

[0029] Figure 4The synthesis pathway of the HBT-OZO probe (referring to Yu Long, et al. A fluorescence probe for highly selective and sensitive detection of gaseous ozone based on excited-state intramolecular proton transfer mechanism [J]) is as follows: The HBT-OZO ozone molecular probe uses the fluorophore 2-(2'-hydroxyphenyl)benzothiazole (HBT), which possesses inherent ESIPT properties, as a precursor. A 4-bromo-1-butene structure is introduced at the phenolic hydroxyl position via ether bonding, yielding the derivative HBT-OZO in a "closed" fluorescence state. When HBT-OZO reacts with O3, its olefin side chain is removed via a β-elimination reaction, releasing the HBT molecule and reopening the fluorescence emission channel, producing strong blue fluorescence. HBT-OZO exhibits high selectivity for O3 and can effectively resist other oxidizing agents (such as...). 1 O2, H2O2, ClO⁻, • OH, O2 •⁻ It can resist interference from substances such as O3, and even in the presence of high concentrations of interfering substances, it can still maintain specific recognition of O3.

[0030] The pH of the sodium indigo disulfonate solution (concentration of 300 ppm, containing 0.05 mol / L Na2SO4) was adjusted to 2.0 using 3 mol / L sulfuric acid. Using this solution as the electrolyte, the rapid decolorization phenomenon during electrolysis was investigated, which qualitatively tested ozone production and quantified its total yield over a certain period. The ozone generation was further selectively identified using the ozone-specific probe HBT-OZO, which effectively resists interference from other ROS. The generation of ozone, a strong oxidant, was further verified by the colorimetric reaction of N,N-diethyl-1,4-phenylenediamine sulfate (DPD).

[0031] Figure 5 The results of ozone qualitative analysis in Example 1 are shown in the figure. As can be seen from the figure, an acidic sodium indigo disulfonate solution (with a sodium indigo disulfonate concentration of 300 ppm, a Na2SO4 concentration of 0.05 mol / L, and the pH of the sodium indigo disulfonate solution adjusted to 2.0 with 3 mol / L sulfuric acid) was used as the electrolyte, and the floating cathode system was completely decolorized within 20 min. The generation of O3 was verified by the colorimetric reaction of N,N-diethyl-1,4-phenylenediamine sulfate (DPD). Note that H2O2 of the same concentration could not cause DPD to develop color. The O3 generated in the cathode electrocatalytic process was identified by the ozone-specific probe HBT-OZO, which can effectively resist interference from other ROS.

[0032] Figure 6The results of 50 cycles of electrolysis of indigo disulfonate solution using the electrochemical system of Example 1 were used to test the decolorization efficiency. The concentration of indigo disulfonate solution was 300 ppm, the concentration of Na2SO4 was 0.05 mol / L, and the pH of indigo disulfonate solution was adjusted to 2.0 with 3 mol / L sulfuric acid, with a volume of 100 mL. As shown in the figure, after 50 consecutive cycles (20 min / cycle), the system maintained its high efficiency in treating acidic indigo. No coating peeling was observed on the electrode surface, and the hydrophobicity of the main body remained good.

[0033] Example 2 (1) 1.5 mL of 37.5% concentrated hydrochloric acid was added to 15 mL of anhydrous ethanol while stirring. 1.61 g of phenol was added during stirring, followed by the rapid addition of 5.5 mL of formaldehyde. Then, the aerogel was obtained by solvothermal incubation at 120 °C for 12 h. The aerogel was then immersed in 110 mL of anhydrous ethanol for 24 h and then 75 °C for 24 h. o Drying at C, then passing through an inert gas atmosphere at 800°C. o Carbonization was carried out at C for 4 hours to obtain carbon aerogel with a three-dimensional interconnected pore structure. 1g of acetylene black powder was dispersed in 60mL of deionized water and sonicated for 10min to obtain an acetylene black dispersion. 1mL of 60% polytetrafluoroethylene dispersion was added dropwise to the acetylene black dispersion to obtain mixture II. The portion of the carbon aerogel material with a transverse thickness of about 1 / 3 was immersed in mixture II for 3min. After drying at 60℃, it was kept at 400℃ under a nitrogen atmosphere for 60min to obtain a carbon aerogel with about 1 / 3 hydrophobic modification. 1 g of nitrogen-doped graphene powder was dispersed in 10 mL of anhydrous ethanol and sonicated for 10 min to obtain a nitrogen-doped graphene dispersion. 1 mL of 60% polytetrafluoroethylene dispersion was added dropwise to the above nitrogen-doped graphene dispersion to obtain mixture Ш. 1 / 3 of the hydrophobic modified carbon aerogel (size 4 cm × 4 cm × 2 mm) was placed horizontally and the part not immersed in mixture Ⅱ was immersed in mixture Ш for 3 min to perform nitrogen doping modification. After drying at 60 °C, it was kept at 350 °C in a nitrogen atmosphere for 30 min to obtain the main part of the nitrogen-doped modified hydrophobic carbon aerogel. (2) Electrode assembly: using, for example Figure 1 The electrode arrangement is as shown in configuration A. The nitrogen-doped modified hydrophobic carbon aerogel obtained in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The nitrogen-doped modified main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Pt electrode, which is placed horizontally 10mm below the cathode and fixed with an electrode clamp. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.75V ( vs The current density is stabilized at around 4.2 mA / cm², which allows oxygen in the air to be selectively reduced to ozone on the cathode surface and in the channels, and then enters the electrolyte. Tests have confirmed that ozone is indeed dissolved in the electrolyte.

[0034] Example 3 (1) The pulp is pre-drawn and 60 o After drying, the carbon material is carbonized at 750℃ for 5 hours under a nitrogen atmosphere to obtain biomass-derived carbon material. 1g of acetylene black powder was dispersed in 60mL of deionized water and sonicated for 10min to obtain an acetylene black dispersion. 1mL of 60% polytetrafluoroethylene dispersion was added dropwise to the acetylene black dispersion to obtain mixture II. Biomass-derived carbon material (size 4cm×4cm×2mm) was immersed in mixture II for 3min, dried at 60℃, and then kept at 400℃ for 60min under a nitrogen atmosphere to obtain hydrophobic modified biomass-derived carbon. (2) Electrode assembly: using, for example Figure 1 The electrode arrangement is as shown in configuration A. The nitrogen-doped modified hydrophobic biomass-derived carbon material of the main body obtained in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The nitrogen-doped modified main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Ti-based RuO2-IrO2 mesh electrode, which is placed horizontally 10mm below the cathode and fixed with electrode clamps. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.75V ( vs (RHE), with the current density stabilized at around 4.2 mA / cm², allows oxygen in the air to be selectively reduced to ozone on the cathode surface and within the channels, which then enters the electrolyte.

[0035] Figure 7The sampling and testing methods for nitrobenzene (NB) and the comparison of NB degradation effects under different modification conditions (corresponding to Example 1: hydrophobic biomass-derived carbon material with nitrogen doping modification in the main body, Example 2: hydrophobic carbon aerogel with nitrogen doping modification in the main body, and Example 3: hydrophobic biomass-derived carbon material, respectively) are shown in the figure. It can be seen from the figure that the water sample taken from the porous carbon-based floating cathode system can degrade NB added to the water sample 5 minutes later. The NB concentration is 20 μM. After mixing and reacting for 30 minutes, the NB concentration change was detected by high performance liquid chromatography (Shimadzu, LC-16). It was found that the concentration of oxidant in the water sample increased with the extension of electrolysis time, and the degradation efficiency of NB also gradually increased. At the same time, it was found that the degradation effect of NB by the nitrogen-doped porous carbon material was better than that of the porous carbon material with only hydrophobic modification, indicating that the addition of nitrogen doping sites is beneficial to the directional transformation behavior of key intermediates and enhances the directional activation of gaseous oxygen. Among long-lived reactive oxygen species, only O3 possesses the intrinsic kinetic ability to oxidize and degrade nitrobenzene, suggesting that O3 was generated in the floating cathode system.

[0036] Example 4 (1) The pulp is pre-drawn and 60 o After drying, the carbon material is carbonized at 750℃ for 5 hours under a nitrogen atmosphere to obtain biomass-derived carbon material. 0.5g of acetylene black powder was dispersed in 50mL of deionized water and sonicated for 5min to obtain an acetylene black dispersion. 0.5mL of 60% polytetrafluoroethylene dispersion was added dropwise to the acetylene black dispersion to obtain mixture II. The portion of biomass-derived carbon material with a transverse thickness of about 1 / 3 was immersed in mixture II for 1min. After drying at 60℃, it was kept at 300℃ under a nitrogen atmosphere for 30min to obtain about 1 / 3 of the hydrophobically modified biomass-derived carbon. 0.5 g of nitrogen-doped graphene powder was dispersed in 5 mL of anhydrous ethanol and sonicated for 5 min to obtain a nitrogen-doped graphene dispersion. 0.5 mL of 60% polytetrafluoroethylene dispersion was added dropwise to the above nitrogen-doped graphene dispersion to obtain mixture Ш. 1 / 3 of the hydrophobically modified biomass-derived carbon (size 4 cm × 4 cm × 2 mm) was placed horizontally and the part not impregnated in mixture Ⅱ was impregnated in mixture Ш for 1 min to perform nitrogen doping modification. After drying at 60 °C, it was kept at 350 °C in a nitrogen atmosphere for 30 min to obtain the main part of the nitrogen-doped modified hydrophobic biomass-derived carbon material. (2) Electrode assembly: using, for example Figure 1The electrode arrangement is as shown in configuration B. The nitrogen-doped modified hydrophobic biomass-derived carbon material of the main body obtained in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The nitrogen-doped modified main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Ti-based RuO2-IrO2 mesh electrode, which is placed vertically 6mm to the side and fixed with an electrode clamp. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.85V ( vs The current density is stabilized at around 5.2 mA / cm², which allows oxygen in the air to be selectively reduced to ozone on the cathode surface and in the channels, and then enters the electrolyte. Tests have shown that ozone is dissolved in the electrolyte.

[0037] Example 5 (1) 1.5 mL of 37.5% concentrated hydrochloric acid was added to 15 mL of anhydrous ethanol while stirring. 1.61 g of phenol was added during stirring, followed by the rapid addition of 5.5 mL of formaldehyde. Then, the aerogel was obtained by solvothermal incubation at 110 °C for 13 h. The aerogel was then immersed in 100 mL of anhydrous ethanol for 22 h and then 75 °C. o Drying at C, followed by inert gas atmosphere at 750°C. o Carbonization was carried out at C for 5 hours to obtain carbon aerogel with a three-dimensional interconnected pore structure. 0.8 g of acetylene black powder was dispersed in 55 mL of deionized water and sonicated for 6 min to obtain an acetylene black dispersion. 0.6 mL of 60% polytetrafluoroethylene dispersion was added dropwise to the acetylene black dispersion to obtain mixture II. The portion of the carbon aerogel material with a transverse thickness of about 1 / 3 was immersed in mixture II for 2 min. After drying at 60 °C, it was kept at 300 °C under a nitrogen atmosphere for 50 min to obtain a carbon aerogel with a hydrophobic modification of about 1 / 3. 0.6 g of nitrogen-doped graphene powder was dispersed in 6 mL of anhydrous ethanol and sonicated for 8 min to obtain a nitrogen-doped graphene dispersion. 0.8 mL of 60% polytetrafluoroethylene dispersion was added dropwise to the above nitrogen-doped graphene dispersion to obtain mixture Ш. 1 / 3 of the hydrophobic modified carbon aerogel (size 4 cm × 4 cm × 2 mm) was placed horizontally and the part not immersed in mixture Ⅱ was immersed in mixture Ш for 2 min to perform nitrogen doping modification. After drying at 60 °C, it was kept at 350 °C in a nitrogen atmosphere for 30 min to obtain the main part of nitrogen-doped modified hydrophobic carbon aerogel. (2) Electrode assembly: using, for example Figure 1The electrode arrangement is as shown in configuration C. The nitrogen-doped modified hydrophobic carbon aerogel obtained in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The nitrogen-doped modified main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Pt electrode, which is placed horizontally 10mm below the cathode and fixed with an electrode clamp. It is parallel to the cathode and staggered. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.65V ( vs The current density is stabilized at around 4.2 mA / cm², which allows oxygen in the air to be selectively reduced to ozone on the cathode surface and in the channels, and then enters the electrolyte. Tests have shown that ozone is dissolved in the electrolyte.

[0038] Example 6 (1) The pulp is pre-drawn and 60 o After drying, the carbon material is carbonized at 850℃ for 3 hours under a nitrogen atmosphere to obtain biomass-derived carbon material. (2) Electrode assembly: using, for example Figure 1 The electrode arrangement is as shown in configuration A. The carbon aerogel prepared in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The upper main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Ti-based RuO2-IrO2 mesh electrode, which is placed horizontally 10mm below the cathode and fixed with electrode clamps. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.5V ( vs The current density is stabilized at around 2.5 mA / cm², which allows oxygen in the air to be selectively reduced to ozone on the cathode surface and in the channels, and then enters the electrolyte. Tests have shown that ozone is dissolved in the electrolyte.

[0039] Example 7 (1) The balsa wood was carbonized at 850°C for 3 hours under a nitrogen atmosphere to obtain biomass-derived carbon materials; (2) Electrode assembly: using, for example Figure 3 The electrode arrangement is carried out in configuration C shown. The biomass-derived carbon material prepared in step (1) is used as the cathode (size 4cm×4cm×2mm) and floats on the surface of the electrolyte. The upper main body is in the gas phase and the lower surface is in contact with the electrolyte. The anode is a Ti-based RuO2-IrO2 coated electrode, which is placed horizontally 10mm below the cathode and fixed with electrode clamps. It is parallel to and offset from the cathode. The electrolyte is a Na2SO4 solution with a concentration of 0.05mol / L and a volume of 100mL. (3) Control the cathode potential to -0.65V ( vs The current density is stabilized at around 4.2 mA / cm², which allows oxygen in the air to be selectively reduced to ozone on the cathode surface and in the channels, and then enters the electrolyte. Tests have shown that ozone is dissolved in the electrolyte.

[0040] The above embodiments are only some implementations of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for converting gaseous oxygen into ozone through a porous carbon-based floating cathode, characterized in that, The specific steps are as follows: (1) A porous carbon-based material is floated on the surface of the electrolyte as a cathode, so that its main body is in the oxygen-containing phase and its lower surface is in contact with the electrolyte to form a gas-liquid-solid three-phase interface, and the anode is placed in the electrolyte; (2) Apply a constant potential to the cathode in the above system so that the gaseous oxygen in the oxygen-containing phase is selectively activated on the cathode surface and in the pores to generate ozone, which then enters the electrolyte.

2. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 1, characterized in that, The porous carbon-based material in step (1) is a sheet-like carbon-based material with a through-pore structure, including sheet-like porous carbon or sheet-like modified porous carbon. Sheet-like porous carbon includes sheet-like biomass-derived porous carbon and sheet-like carbon aerogel. Sheet-like modified porous carbon is sheet-like porous carbon with hydrophobic surface modification or hydrophobic combined nitrogen doping modification.

3. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 2, characterized in that, The method for preparing the sheet-like biomass-derived porous carbon is as follows: Using sheet-like biomass materials as precursors, carbonization is carried out by holding at 750~850℃ for 3~5 hours in an inert atmosphere to obtain sheet-like biomass-derived porous carbon.

4. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 2, characterized in that, The preparation method of the sheet-like carbon aerogel is as follows: 1.5 mL of 37.5% concentrated hydrochloric acid was added to 15 mL of anhydrous ethanol under stirring. During stirring, 1.61 g of phenol and 5.5 mL of formaldehyde were added. The mixture was kept at 110-130 °C for 11-13 h to obtain an aerogel. The aerogel was then soaked in 100-120 mL of anhydrous ethanol for 22-24 h and dried. After carbonization, the aerogel was kept at 750-850 °C for 3-5 h under an inert atmosphere to obtain a sheet-like carbon aerogel with a three-dimensional interconnected pore structure.

5. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 3 or 4, characterized in that, The method for preparing sheet-like porous carbon with hydrophobic surface modification is as follows: Disperse 0.5-1g of acetylene black powder in 50-60mL of deionized water, and sonicate for 5-10min to obtain an acetylene black dispersion. Add 0.5-1mL of 60% polytetrafluoroethylene dispersion dropwise to the acetylene black dispersion to obtain mixture I. Immerse the sheet-like porous carbon in mixture I for 1-3min, dry at 60℃, and then keep it at 300-400℃ under an inert atmosphere for 30-60min to obtain sheet-like porous carbon with hydrophobic surface modification.

6. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 3 or 4, characterized in that, The method for preparing sheet-like porous carbon with hydrophobic bonding and nitrogen doping modification is as follows: Disperse 0.5-1g of acetylene black powder in 50-60mL of deionized water, and sonicate for 5-10min to obtain an acetylene black dispersion. Add 0.5-1mL of 60% polytetrafluoroethylene dispersion dropwise to the acetylene black dispersion to obtain mixture II. Place sheet-like porous carbon horizontally and immerse it in mixture II for 1-3min with a thickness of 1 / 3. Dry at 60℃ and then keep it at 300-400℃ under an inert atmosphere for 30-60min to obtain partially hydrophobically modified sheet-like porous carbon. 0.5-1g of nitrogen-doped graphene powder was dispersed in 5-10mL of anhydrous ethanol and sonicated for 5-10min to obtain a nitrogen-doped graphene dispersion. 0.5-1mL of 60% polytetrafluoroethylene dispersion was added dropwise to the nitrogen-doped graphene dispersion to obtain mixture Ш. Part of the hydrophobically modified sheet-like porous carbon that was not impregnated in mixture Ⅱ was impregnated in mixture Ш for 1-3min. After drying at 60℃, it was kept at 350℃ under an inert atmosphere for 30min to obtain hydrophobically combined nitrogen-doped modified sheet-like porous carbon.

7. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 5 or 6, characterized in that, Replace the acetylene black powder with carbon black or graphene powder.

8. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 1, characterized in that, The electrolyte in step (1) is a conductive aqueous solution containing electrolyte.

9. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 1, characterized in that, The anode in step (1) is a Ti electrode, a Ti-based RuO2-IrO2 coated electrode, a Ti-based PbO2 coated electrode, a Pt electrode, or a BDD electrode.

10. The method for converting gaseous oxygen into ozone mediated by a porous carbon-based floating cathode according to claim 1, characterized in that, In step (2), the cathode potential when a constant potential is applied is -0.5V to -1.0V, and the current density is 2.5 to 6.5mA / cm².

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