Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalysts. The composite photocatalyst is of a yolk-coupled eggshell structure with a cavity, the yolk structure is a nano-porous carbon core, and the eggshell structure is a nano-silver modified titanium dioxide shell. According to the Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst disclosed by the invention, high-efficiency adsorption and selective trapping of toxic pollutants in air can be realized by utilizing nano-porous carbon, and the synergistic purification capability of catalytic oxidation degradation of the toxic pollutants in the air can be realized by utilizing nano-silver modified titanium dioxide. The Yolk-Shell structure can improve the photocatalytic activity and the structural stability of the catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and more specifically, to a yolk-shell structured nano-silver modified titanium dioxide-porous carbon composite photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Volatile organic compounds (VOCs) not only promote the formation of ozone and secondary organic aerosols (SOA), but also have environmental hazards such as biological toxicity. Long-term exposure to low concentrations of VOCs can induce a series of acute and chronic diseases such as respiratory diseases and chronic poisoning, and even cancer. Therefore, it is particularly important to research and develop new green and efficient air purification technologies and materials.

[0003] Titanium dioxide (TiO2) is a common photocatalyst that can catalytically degrade VOCs. During the catalytic oxidation degradation of VOCs, some partially oxidized intermediate products or by-products may be generated. These substances usually have a relatively high molecular weight and strong polarity, resulting in relatively high boiling points and being not easily volatile. For example, during the catalytic oxidation of VOCs (such as toluene, styrene, etc.), if the oxidation is incomplete, aldehydes, ketones, organic acids, tar-like polymers, etc. may be formed. These high-boiling products are likely to accumulate on the surface of the catalyst, covering the active sites, and ultimately leading to catalyst deactivation.

[0004] The existing technology improves the photocatalytic activity through the composite technology of TiO2 and porous carbon. Most of the technologies mainly adopt the coupling of closely packed TiO2 nanoparticles and porous carbon. Although this technology can enhance the photocatalytic oxidation activity of TiO2 by improving the photogenerated electron transfer efficiency at the coupling interface, limited by the closely packed morphology of TiO2, it often causes problems such as low capture and conversion efficiency of VOCs and low photon utilization efficiency, which will severely limit the selective capture and catalytic oxidation of VOCs by the composite structure in complex scenarios. In addition, due to the limitation of the exposed active sites of the closely packed TiO2 nanoparticles, incomplete oxidation of VOCs often leads to the accumulation of high-boiling conversion products, resulting in the occupation of active sites and catalyst deactivation. Moreover, after some intermediate products of pollutants are captured by the photocatalyst, the volume of the photocatalyst will expand, reducing the structural stability of the photocatalyst and thus reducing the service life of the photocatalyst.

[0005] Chinese Patent CN115487796A discloses a preparation method of a composite photocatalyst, which includes the following steps: S1. Using nano-hydrothermal carbon as a template, titanium salt as a raw material, and alcohol solution as a solvent, obtaining a precursor of titanium ion adsorbed on hydrothermal carbon by liquid-phase adsorption method; S2. Heat-treating the precursor obtained in step S1 at 500-950°C for 4h under the protection of inert gas to obtain a carbon-titanium composite; S3. Placing the carbon-titanium composite obtained in step S2 in an air atmosphere with a certain oxygen volume ratio, and performing exposure heat activation treatment at 400-500°C for 2h to obtain a composite photocatalyst with a titanium dioxide-porous carbon integrated nano-multistructure, which can be used for degrading toluene. After the toluene is adsorbed to saturation by this composite photocatalyst, the degradation efficiency of the catalyst for toluene is stable at 95% after 350min of light irradiation. It can be seen that both step S2 and step S3 of the preparation method of this composite catalyst require high temperature for a long time to prepare a rich pore structure, and the long-time heat treatment will cause great energy consumption and increase production costs. The composite photocatalyst prepared by this method has a nano-multistructure of ribbon-like interweaving, and titanium dioxide and multi-level pores show obvious integrated uniform distribution. However, the photocatalytic activity and long-term structural stability of this composite photocatalyst with a titanium dioxide-porous carbon integrated nano-multistructure still need to be further improved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and deficiencies that the structure of the existing titanium dioxide porous carbon composite photocatalyst for photocatalytic VOCs has room for further improvement in photocatalytic activity and structural stability, and to provide a Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst, which has a yolk-coupled eggshell structure with a cavity, the yolk structure is a nano-porous carbon core, and the eggshell structure is a nano-silver modified titanium dioxide shell. This Yolk-Shell structure and the modification of nano-silver can improve the photocatalytic activity and structural stability of the catalyst.

[0007] Another object of the present invention is to provide a preparation method of a Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst.

[0008] Still another object of the present invention is to provide an application of a Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst.

[0009] The above objects of the present invention are achieved by the following technical solutions:

[0010] A yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst, wherein the composite photocatalyst has a yolk-coupled eggshell structure with a cavity, the yolk structure is a nano-porous carbon core, and the eggshell structure is a nano silver modified titanium dioxide shell; in the photocatalyst, the mass ratio of silver to titanium dioxide is (0.02-0.1):1.

[0011] The yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst of the present invention can utilize the nano-porous carbon to achieve efficient adsorption and selective capture of harmful pollutants in the air and utilize the nano silver modified titanium dioxide to achieve the synergistic purification ability of catalytic oxidation and degradation of harmful pollutants in the air.

[0012] The yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst of the present invention has a cavity structure, which can enhance light scattering, improve light absorption efficiency, and thus enhance photocatalytic activity. Moreover, it can effectively shorten the ion diffusion path, enhance the electron transport ability, and improve the reaction rate. In addition, during the recycling process of the catalyst, the cavity structure can buffer volume expansion, maintain the structural stability of the material, and extend the service life.

[0013] The composite photocatalyst of the present invention has a yolk-eggshell structure with a cavity, which improves the utilization rate of active sites of TiO2 in the close-packed form, improves the adsorption affinity for VOCs, and prevents the mass transfer of VOCs molecules from being blocked. This multi-interface structure integrating adsorption and catalytic reaction can not only significantly enhance the utilization efficiency of photons, provide more transfer directions for the transfer of interfacial carriers, but also promote the adsorption, reaction and mass transfer processes of VOCs on the multi-interface structure, effectively avoid the formation of high-boiling products and their accumulation on the interface, thereby avoiding the inactivation of the catalyst. The multi-interface structure of the Ag / TiO2 double interface shell layer and the nano carbon core effectively improves the interfacial mass transfer and electron transfer efficiency. The unique local plasma characteristics of nano Ag can not only enhance the separation efficiency of interfacial carriers, but also greatly improve the utilization efficiency of photons by TiO2.

[0014] Preferably, in the photocatalyst, the mass ratio of silver to titanium dioxide is (0.04-0.08):1.

[0015] Preferably, the size of the yolk structure is 40-60 nm, and the size of the eggshell structure is 3-5 nm.

[0016] Preferably, in the composite photocatalyst, the morphology of the porous carbon core is spherical or irregular spherical, and the crystal form of the porous carbon is amorphous or graphite carbon.

[0017] The present invention also protects a method for preparing the above-mentioned yolk-shell structured nano silver-modified titanium dioxide-porous carbon composite photocatalyst, which comprises the following steps:

[0018] S1. Uniformly disperse nano hydrothermal carbon spheres, titanium salts and urea in an alcohol aqueous solution, and obtain product A through the osmotic adsorption method;

[0019] S2. Carry out a hydrolysis reaction on product A to obtain product B;

[0020] S3. Mix product B with a silver salt solution for 10 - 50 min, and treat it by photoreduction to obtain product C;

[0021] S4. Carry out pyrolysis treatment on product C under the protection of an inert atmosphere to obtain product D;

[0022] S5. Carry out etching treatment on product D by the light irradiation method to obtain the yolk-shell structured nano silver-modified titanium dioxide-porous carbon composite photocatalyst;

[0023] Among them, in step S2, the temperature of the hydrolysis reaction is 40 - 85 °C;

[0024] In step S3, the doping amount of Ag ions in the silver salt is 2 - 10% of the theoretical mass of TiO2 generated;

[0025] In step S4, the pyrolysis temperature is 350 - 550 °C, and the pyrolysis time is 2 - 8 h;

[0026] In step S5, the etching time is 0.5 - 8 h.

[0027] The method of the present invention obtains a yolk-shell structured nano silver-modified titanium dioxide-porous carbon composite photocatalyst.

[0028] In step S1 of the present invention, through the "osmotic adsorption method", titanium ions (Ti 4+ ) are adsorbed onto the surface of the nano hydrothermal carbon spheres. The titanium salts are partially hydrolyzed in the solution to release Ti 4+ ions, and urea helps to adjust the pH, promote the uniform dispersion of titanium ions and adsorb them onto the surface of the carbon spheres to form a precursor.

[0029] In step S2 of the present invention, the titanium salt is hydrolyzed to generate Ti(OH)4, and then gradually dehydrated to form a TiO2 gel structure, which is finally loaded on the surface of the carbon spheres.

[0030] In step S3 of the present invention, Ag + ions are adsorbed onto the surface of the TiO2 / carbon composite, and photoreduction is carried out under ultraviolet or visible light irradiation to reduce Ag + ions into nano Ag.

[0031] In step S4 of the present invention, high-temperature pyrolysis can obtain a core-shell structure product of titanium dioxide supported on porous carbon spheres modified with silver nanoparticles.

[0032] In step S5 of the present invention, through a specific illumination time, the core-shell structure obtained in step S4 is etched by light, partially etching away carbon or the inner layer material, and vaporizing the remaining substances such as urea, so as to form a cavity between the TiO2 shell and the carbon core.

[0033] Among them, the light etching in step S5 is directed at the etching of amorphous carbon in the porous carbon core.

[0034] The raw materials used in the present invention are green, environmentally friendly, non-toxic, low in cost, simple in preparation method, and have the potential to obtain good economic benefits.

[0035] Preferably, a method for preparing a yolk-shell structured silver nanoparticle-modified titanium dioxide-porous carbon composite photocatalyst includes the following steps:

[0036] S1. Using the dispersion method, nano-hydrothermal carbon spheres, a titanium salt, and urea are uniformly dispersed in an alcohol aqueous solution, and the precursor product A of nano-hydrothermal carbon adsorbed with titanium ions is obtained by the permeation adsorption method;

[0037] S2. The product A obtained in step S1 is subjected to a hydrolysis reaction at a certain temperature for 2 to 24 hours, and after washing with water, the precursor product B of TiO2 supported on nano-hydrothermal carbon spheres can be obtained;

[0038] S3. The precursor product B obtained in S2 and a silver nitrate solution with a certain concentration are stirred and mixed at room temperature for 10 to 50 minutes, and treated by photoreduction for a period of time to obtain a silver nanoparticle-modified hydrothermal carbon supported TiO2 composite product C;

[0039] S4. The composite product C obtained in step S3 is pyrolyzed under the protection of an inert atmosphere to obtain a core-shell structure product D of titanium dioxide supported on porous carbon spheres modified with silver nanoparticles;

[0040] S5. The core-shell structure product D obtained in S4 is etched by the light method to obtain a yolk-shell structured silver nanoparticle-modified titanium dioxide-porous carbon composite photocatalyst.

[0041] Preferably, in step S1, the titanium salt is one or more of titanium tetrachloride, tetrabutyl titanate, and titanium oxysulfate.

[0042] Preferably, in step S1, the concentration of the titanium salt is 0.1 to 1.5 mol / L, the concentration of the urea is 0.05 to 0.5 mol / L, and the mass ratio of the nano-hydrothermal carbon spheres in the alcohol aqueous solution is 0.1% to 2%.

[0043] Preferably, in step S1, the ultrasonic dispersion method can be used to uniformly disperse the nano hydrothermal carbon spheres, titanium salt, and urea in the alcohol aqueous solution.

[0044] Preferably, in step S1, the penetration adsorption method is the impregnation penetration method at room temperature, and the penetration adsorption time is 1 to 12 h.

[0045] Preferably, in step S2, the hydrolysis reaction temperature is 40 to 85 °C. The hydrolysis reaction time is 2 to 24 h. The hydrolysis reaction temperature can be reached by gradually increasing the temperature.

[0046] Preferably, after hydrolysis in step S2, the reaction product can be washed to neutral with deionized water. Preferably, the water washing method is suction filtration washing or centrifugal washing, where the centrifugal rotation speed is 5000 to 10000 r / min, the washing solvent is deionized water, and the washing degree is to wash to neutral with water.

[0047] Preferably, in step S3, the silver salt can be silver nitrate. The concentration of the silver nitrate is 0.1 to 1 mol / L.

[0048] Preferably, in step S3, the light source for the photoreduction method is one of a xenon light source or an ultraviolet light source, and the light treatment time for the photoreduction method is 5 to 30 min.

[0049] Preferably, in step S4, the inert atmosphere is one or more of nitrogen, argon, or helium.

[0050] Preferably, in step S5, the light source is one of a xenon light source or an ultraviolet light source. The light source power is 300 to 1000 W.

[0051] Preferably, in step S5, the etching time is 3 to 5 h.

[0052] Preferably, in step S3, the doping amount of Ag ions in the silver salt is 4 to 6% of the theoretical mass of TiO2 generated.

[0053] Preferably, in step S1, the preparation method of the nano hydrothermal carbon includes the following steps: (a) adding glucose to the alcohol aqueous solution, ultrasonically dispersing to obtain a high-concentration glucose alcohol aqueous solution, and first obtaining glucose high-concentration carbide seeds by using a slow-controlled temperature hydrothermal reaction method; (b) stirring, mixing, and dispersing the glucose high-concentration carbide seeds obtained in step (a) and the alcohol aqueous solution to obtain a homogeneous suspension; the alcohol in the alcohol aqueous solution accounts for 0 to 15% of the volume of the dispersion; (c) transferring the suspension obtained in step (b) to a reaction kettle for hydrothermal reaction to obtain a brown reaction product; (d) washing the brown reaction product obtained in step (c) with ethanol and drying to obtain nano hydrothermal carbon spheres.

[0054] The nano-hydrothermal carbon spheres prepared by the above method are rich in oxygen-containing functional group structures such as hydroxyl and carboxyl groups on the surface, and the surface oxygen content accounts for 20% to 40%.

[0055] The nano-porous carbon of the present invention can preferentially adsorb certain specific pollutants.

[0056] Preferably, in step S4, the pyrolysis time is 3 to 4 h.

[0057] In the preparation method of the present invention, the pyrolysis time can be appropriately reduced, which is beneficial to reducing energy consumption and production costs.

[0058] The present invention also protects the application of the above-mentioned Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst in the field of air purification.

[0059] The composite photocatalyst of the present invention can efficiently remove toxic pollutants and can be applied to the field of air purification.

[0060] The present invention also protects the application of the Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst in the degradation of volatile organic compounds.

[0061] Preferably, the volatile organic compounds are one or more of benzene series, aldehydes, ketones, esters, alcohols, and halogenated hydrocarbons.

[0062] Preferably, the benzene series are benzene, toluene, ethylbenzene, xylene, and styrene. <�

[0063] Preferably, the aldehydes are formaldehyde, acetaldehyde, and phenylacetaldehyde.

[0064] Preferably, the esters are ethyl acetate and butyl acetate.

[0065] Preferably, the ketones are acetone, isobutyl ketone, and menthone.

[0066] Preferably, the alcohols are methanol and ethanol.

[0067] Preferably, the halogenated hydrocarbons are dichloromethane and trichloromethane.

[0068] Compared with the prior art, the beneficial effects of the present invention are:

[0069] The present invention discloses a Yolk-Shell structure nano-silver modified titanium dioxide-porous carbon composite photocatalyst, which has a yolk-coupled eggshell structure with a cavity. The yolk structure is a nano-porous carbon core, and the eggshell structure is a nano-silver modified titanium dioxide shell. This Yolk-Shell structure and the modification of nano-silver can improve the photocatalytic activity and structural stability of the catalyst. Description of the Drawings

[0070] Figure 1 This is the TEM image of the composite catalyst obtained in Example 1 of the present invention.

[0071] Figure 2 This is the SEM image of the composite catalyst obtained in Example 1 of the present invention.

[0072] Figure 3 This is the TEM image of the composite catalyst obtained in Comparative Example 1 of the present invention.

[0073] Figure 4 This is the catalytic degradation performance curve of toluene by the composite photocatalyst obtained in Example 1 of the present invention.

[0074] Figure 5 This is the catalytic degradation performance curve of toluene by the composite photocatalyst obtained in Example 2 of the present invention. Detailed implementation manners

[0075] The present invention will be further described below in conjunction with the detailed implementation manners, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0076] Example 1

[0077] A Yolk-Shell structured nano-silver modified titanium dioxide-porous carbon composite photocatalyst, the composite photocatalyst has a yolk-coupled eggshell structure with a cavity, the yolk structure is a nano-porous carbon core, and the eggshell structure is a nano-silver modified titanium dioxide shell. In the photocatalyst, the mass ratio of silver to titanium dioxide is 0.05:1.

[0078] The preparation method of the above Yolk-Shell structured nano-silver modified titanium dioxide-porous carbon composite photocatalyst includes the following steps:

[0079] S1. Preparation of nano-hydrothermal carbon spheres (HTCS): The nano-hydrothermal carbon spheres (HTCS) were prepared with reference to the preparation method in Example 2 of Chinese Patent Application CN113697794A. The preparation method of nano-hydrothermal carbon (HTCS) is as follows: Weigh 20 g of glucose and add it to 80 mL of ethanol aqueous solution (the volume ratio of ethanol to water is 3:2). Ultrasonic dispersion and dissolution can obtain a clear and transparent glucose ethanol aqueous solution. Transfer the glucose ethanol aqueous solution to a high-pressure reaction kettle with a polytetrafluoroethylene substrate, heat it to 165 °C at a heating rate of 0.2 °C / min, keep the temperature constant for 8 h, and then naturally cool to room temperature to obtain a brownish-red translucent high-concentration carbide seed of glucose. Use a pipette to measure 25 mL of the high-concentration carbide seed of glucose into 70 mL of ethanol aqueous solution (the volume ratio of ethanol to water is 1:20) to obtain a homogeneous mixed solution. Transfer the mixed solution to a high-pressure reaction kettle with a polytetrafluoroethylene substrate, gradually heat it to 180 °C at a heating rate of 4 °C / min, react for 10 h, and naturally cool to room temperature to obtain a brown turbid product. Using ethanol as a detergent, centrifuge and wash the product 3 - 4 times at 11000 r / min, and then place it in a freeze dryer for 15 h to obtain dendritic ultrafine nano-hydrothermal carbon spheres.

[0080] Weigh 0.2 g of nano-hydrothermal carbon (HTCS) and 0.1 g of sodium dodecyl sulfate (SDS). Add 30 mL of ethanol, 30 mL of water, and 10 mL of urea aqueous solution (0.1 mol / L) to each of them respectively. Ultrasonically treat for 30 min at room temperature, and then add 629 μL of 2 M TiCl4 ethanol solution under the condition of rapid stirring. Adsorb and permeate at room temperature for 6 h to obtain the precursor product A of nano-hydrothermal carbon adsorbed with titanium ions.

[0081] S2. Gradually heat the product A to 53 °C for hydrolysis reaction treatment for 24 h. The sample is centrifuged and washed with water to obtain the product B.

[0082] S3. Redisperse the product B in 60 mL of ethanol aqueous solution (30 mL of water: 30 mL of alcohol), add 120 μL of silver nitrate (the doping amount of Ag ions in silver nitrate is 5% of the theoretical mass of TiO2 generated). Under the condition of stirring, irradiate with 450 W xenon lamp for 15 min. The sample is centrifuged and washed 3 times, and freeze-dried for 10 h to obtain the nano-silver-modified hydrothermal carbon-supported TiO2 composite product C;

[0083] S4. Place the product C in a tubular furnace, heat it to 500 °C at a heating rate of 5 °C / min under the protection of an inert atmosphere for pyrolysis treatment, and keep it for 4 h to end, obtaining the nano-silver-modified porous carbon sphere-supported titanium dioxide core-shell structure product D.

[0084] S5. Add the product D into the reaction tube and perform photoetching for 5 h with a 450 W xenon lamp to obtain the yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst.

[0085] Example 2

[0086] A preparation method of a yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst, which is different from Example 1 in that: in step S5, the photoetching time is 2 h.

[0087] The rest is the same as that in Example 1 and will not be described herein again.

[0088] Example 3

[0089] A preparation method of a yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst, which is different from Example 1 in that: in step S3, the doping amount of Ag ions in silver nitrate is 7% of the theoretical mass of TiO2 generated, that is, the amount of silver nitrate is 168 μL.

[0090] The rest is the same as that in Example 1 and will not be described herein again.

[0091] Comparative Example 1

[0092] A preparation method of a titanium dioxide-porous carbon composite photocatalyst, which is different from Example 1 in that silver nitrate is not added.

[0093] The rest is the same as that in Example 1 and will not be described herein again.

[0094] Result Detection

[0095] Perform relevant performance tests on the catalysts of the above examples and comparative examples:

[0096] (1) TEM and SEM

[0097] Figure 1 The TEM image of the composite catalyst obtained in Example 1 of the present invention. Figure 1 (a) in it shows the selected area electron diffraction (SAED) pattern, demonstrating the morphology of the material. Figure 1 (b) in it shows that the lattice spacing is 0.331 nm, which is consistent with the interplanar spacing of the anatase plane, and is identified as anatase crystal, indicating that titanium dioxide crystal is synthesized. Figure 1 (c) in it shows two different lattice structures, indicating that titanium dioxide is successfully loaded on the carbon spheres. Figure 1 (d) in it shows the distribution of different elements. It can be seen that the carbon element is concentrated in the inner layer, the titanium element wraps the carbon spheres, a cavity is formed between the titanium element and the carbon element, and nano Ag is uniformly distributed on the TiO2 shell structure, forming a tight composite system.

[0098] Figure 2 This is the SEM image of the composite catalyst obtained in Example 1 of the present invention. It can be seen that the composite photocatalyst has a yolk-coupled eggshell structure with cavities.

[0099] Figure 3 This is the TEM image of the composite catalyst obtained in Comparative Example 1 of the present invention. Figure 3 (a) in it shows the yolk-shell structure, and the outer shell and the inner core structure are clearly visible. Figure 3 (b) in it shows the interface where the two substances are combined. Figure 3 (c) in it shows that the lattice of Ti is successfully coated on the surface. Figure 3 (d) in it is the distribution of different elements. It can be seen that the carbon element is concentrated in the inner layer, the titanium element wraps the carbon sphere, and a cavity is formed between the titanium element and the carbon element.

[0100] (2) Photocatalytic test

[0101] Take 0.08 g of the samples prepared according to each example and comparative example and add them to the photocatalytic reactor, which is horizontally fixed at a distance of 12 cm from a 300 W xenon lamp, and then continuously introduce toluene (40 ± 1 ppmv) gas. The toluene gas first reaches adsorption equilibrium on the photocatalyst, and then the photocatalytic reaction starts under illumination.

[0102]

[0103] Figure 1 This is the catalytic degradation performance curve of toluene using the catalyst obtained in Example 1. The results show that the sample has a strong degradation ability for the removal efficiency of toluene. Its degradation efficiency for toluene reaches 99%. During the continuous degradation of 600 min, its degradation efficiency for toluene is stable above 99% and there is no obvious downward trend. The CO2 production is as high as 1799 ppmv.

[0104] The highest performance of the catalyst obtained in Example 2 for catalytic degradation of toluene is above 90%. During the continuous degradation of 600 min, its degradation efficiency for toluene is stable at about 80%. At the same time, the production of CO2 decreases. This shows that compared with Example 1, reducing the time of photolithography leads to incomplete formation of the yolk-shell structure, resulting in weakened electron mass transfer and adsorption effects, and a certain degree of reduction in catalytic activity.

[0105] The performance of the catalyst obtained in Example 3 for catalytic degradation of toluene was up to about 99%. During the continuous degradation for 600 min, the average degradation efficiency was about 85%. Compared with Example 1, the degradation efficiency of the catalyst in Example 3 for toluene decreased to a certain extent. This shows that more nano-Ag will, to a certain extent, inhibit the photocatalytic activity of the material.

[0106] The performance of the catalyst obtained in Comparative Example 1 for catalytic degradation of toluene reached about 99% in the first 300 min. After continuous degradation for 300 min, its degradation efficiency for toluene was poor and the sample was severely deactivated. The CO2 production was 775 ppmv. It is speculated that due to the absence of nano-Ag, the reduction of photocatalytic efficiency led to the accumulation of by-products, which inhibited the migration of photogenerated electrons between the inner and outer layers, thus resulting in a decrease in the pollution removal efficiency.

[0107] The above results can illustrate that the photocatalyst of the present invention has high photocatalytic activity and long-term structural stability. It can also illustrate that the catalyst prepared by the present invention can effectively promote the formation rate of oxidative free radicals such as hydroxyl radicals and superoxide radicals, promote the degradation and mineralization of toluene enriched on the surface of the photocatalyst, and at the same time avoid problems such as product accumulation and catalyst deactivation caused by interfacial mass transfer problems.

[0108] (3) Regeneration of the catalyst.

[0109] Utilizing the thermal stability of TiO2 and porous carbon, the adsorbed pollutants and by-products are removed by heating the catalyst at a high temperature, usually at about 500 °C, to remove the organic substances on the surface and the accumulated by-products, thereby restoring the catalytic activity. This process needs to be carried out in an inert gas (such as argon) atmosphere to avoid damage to the catalyst surface caused by oxidation reactions and ensure the long-term stability and effectiveness of the catalyst.

[0110] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst, characterized in that, The composite photocatalyst has a yolk-coupled eggshell structure with cavities. The yolk structure is a nanoporous carbon core, and the eggshell structure is a titanium dioxide shell modified with silver nanoparticles. In the photocatalyst, the mass ratio of silver to titanium dioxide is (0.02 - 0.1):

1.

2. The Yolk-Shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst according to claim 1, characterized in that, In the photocatalyst, the mass ratio of silver to titanium dioxide is (0.04 - 0.08):

1.

3. The yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst according to claim 1, characterized in that, In the composite photocatalyst, the morphology of the porous carbon core is spherical or irregularly spherical, and the crystal form of the porous carbon is amorphous or graphite carbon.

4. The preparation method of the Yolk-Shell structured silver-modified titanium dioxide-porous carbon composite photocatalyst according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1. Uniformly disperse nano-hydrothermal carbon spheres, titanium salts, and urea in an alcohol aqueous solution, and obtain product A through the osmotic adsorption method. S2. Hydrolyze product A to obtain product B. S3. Mix product B with a silver salt solution for 10 - 50 min, and treat it by photoreduction to obtain product C. S4. Pyrolyze product C under the protection of an inert atmosphere to obtain product D. S5. Etch product D by the light irradiation method to obtain the Yolk-Shell structured silver-modified titanium dioxide-porous carbon composite photocatalyst. Among them, in step S2, the temperature of the hydrolysis reaction is 40 - 85 °C. In step S3, the doping amount of Ag ions in the silver salt is 2 - 10% of the theoretical mass of TiO2 generated. In step S4, the pyrolysis temperature is 350 - 550 °C, and the pyrolysis time is 2 - 8 h. In step S5, the etching time is 0.5 - 8 h.

5. The preparation method of the yolk-shell structured silver-modified titanium dioxide-porous carbon composite photocatalyst according to claim 4, characterized in that, In step S5, the etching time is 2 - 6 h.

6. The preparation method of the yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst according to claim 4, characterized in that, In step S5, the etching time is 3 - 5 h.

7. The preparation method of the yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst according to claim 4, characterized in that, In step S1, the preparation method of the nano-hydrothermal carbon includes the following steps: (a) Add glucose to an alcohol aqueous solution, and ultrasonically disperse it to obtain a high-concentration glucose alcohol aqueous solution. First, obtain glucose high-concentration carbide seeds by the method of slow-controlled temperature hydrothermal reaction. (b) Stir and mix the glucose high-concentration carbide seeds obtained in step (a) with the alcohol aqueous solution to obtain a homogeneous suspension. The alcohol in the alcohol aqueous solution accounts for 0 - 15% of the volume of the dispersion. (c) Transfer the suspension obtained in step (b) to a reaction kettle for hydrothermal reaction to obtain a brown reaction product. (d) Wash the brown reaction product obtained in step (c) with ethanol and obtain nano-hydrothermal carbon spheres through drying treatment.

8. The preparation method of the yolk-shell structured nano silver modified titanium dioxide-porous carbon composite photocatalyst according to claim 4, characterized in that, In step S4, the pyrolysis time is 3 - 4 h.

9. Use of the Yolk-Shell structured silver-modified titanium dioxide-porous carbon composite photocatalyst according to any one of claims 1 - 3 in the degradation of volatile organic compounds.

10. The application according to claim 9, wherein The volatile organic compounds are one or more of benzene series, aldehydes, ketones, esters, alcohols, and halogenated hydrocarbons.

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