Application of polymer microspheres with optical whispering gallery mode resonance characteristics in preparation of photocatalyst

Abstract

The application belongs to the technical field of semiconductor photocatalyst preparation, and particularly relates to application of a polymer microsphere with optical whispering gallery mode resonance characteristics in preparation of a photocatalyst, wherein the polymer microsphere with optical whispering gallery mode resonance characteristics is used as a carrier for the first time, and semiconductor nanoparticles are loaded on the surface of the polymer microsphere for preparation of the photocatalyst; the optical whispering gallery mode resonance characteristics of the surface of the polymer microsphere are used to confine photons in the polymer microsphere for a long time through continuous total internal reflection, to enhance the interaction between light and the semiconductor nanoparticles in a full spectrum, and to form an evanescent field on the surface of the polymer microsphere, so that the semiconductor nanoparticles are loaded on the surface of the polymer microsphere, the enhanced light field can be fully utilized, the purpose of enhancing the photocatalytic effect of the semiconductor nanoparticles is achieved, the photocatalytic system is compatible with different semiconductor catalytic systems, has high universality, and provides a new idea for improving the light capture efficiency of the photocatalytic system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor photocatalyst preparation, and particularly relates to application of a polymer microsphere with optical whispering gallery mode resonance characteristics in preparation of a photocatalyst. BACKGROUND

[0002] The photocatalytic mechanism of a semiconductor is as follows: when a beam of light with energy greater than the band gap of the semiconductor irradiates the surface of a substance, the electrons in the valence band of the semiconductor absorb energy and transition to the conduction band, leaving a hole in the valence band, and the electrons and holes migrate to the surface to perform redox reactions. From the perspective of energy conversion, a traditional semiconductor photocatalytic system includes three basic processes: 1) photon absorption process, when the energy of the incident photon and the band gap of the semiconductor catalyst resonate, the photon is absorbed, and at the same time, the electrons in the semiconductor jump from the valence band to the conduction band, generating an electron-hole pair; 2) separation and surface migration of the photo-generated electron-hole pair; 3) the electrons and holes transported to the surface respectively perform reduction and oxidation reactions with the reactants adsorbed on the surface, realizing the conversion of light energy to chemical energy. Therefore, light absorption is the first step of the photocatalytic reaction, so improving the light absorption capacity is one of the keys to improving the photocatalytic efficiency. However, the light absorption cross section of traditional semiconductor catalysts is generally small, the spectral response range is narrow, and the number of photons that can be captured and utilized is very limited, which greatly hinders the construction of high-efficiency photocatalytic systems.

[0003] For a semiconductor substance, light absorption generally occurs only when the energy of the incident photon is greater than or equal to its band gap. Therefore, the capture of light by a semiconductor is directly related to its band structure. In order to improve the light absorption capacity of the semiconductor, researchers have developed various means to regulate the band structure of the semiconductor, broaden its light capture range, and improve its light capture capacity. There are many ways to process the band gap of a semiconductor, such as defect construction, element doping, heterostructure construction, dye sensitization, etc., which are based on electronic regulation. Improving the light capture efficiency of the system will change the intrinsic properties of the catalyst, and the valence band and conduction band positions of different catalysts also need to be fully considered in order to effectively broaden the absorption spectrum of the material and achieve better photocatalytic enhancement effect, which is not conducive to the reference and promotion of different semiconductor catalyst systems.

[0004] In view of the problems of low light trapping efficiency and non-universality of different semiconductor photocatalytic systems, researchers introduce a special optical structure, such as a photonic crystal, into the photocatalytic system to change the local electromagnetic field mode density, confine the light beam in a small space for a long time, and enhance the interaction between light and matter. Compared with the band regulation strategy, the introduction of the optical structure does not change the intrinsic activity of the catalyst, mainly controls the behavior of the photon to improve the light trapping efficiency of the system, and does not need to match the valence band and conduction band positions of the catalyst, and has high universality and is suitable for various catalytic systems. However, the periodic microstructure of the photonic crystal usually needs a complex and precise template-assisted preparation process, and the light response range of different catalytic systems is different, so the selection of the photonic crystal is also different, and the absorption spectrum of the catalyst must overlap with the photonic band gap of the photonic crystal, otherwise the enhancement effect of the photonic crystal cannot be achieved. The photonic band gap of the photonic crystal is not only determined by its periodic microstructure, but also affected by the refractive index of the material and its surrounding environment, which increases the complexity of the system design and increases the difficulty of the preparation and construction of the photocatalytic system, limiting its application and promotion in the photocatalytic system.

[0005] Therefore, it is of great significance to develop a semiconductor catalyst construction carrier that improves the light trapping capacity of semiconductor catalysts and has universality for catalytic systems. SUMMARY

[0006] In view of the problems of the existing semiconductor photocatalyst, the application provides an application of a polymer microsphere with an optical whispering gallery mode resonance characteristic in preparation of a photocatalyst. The polymer microsphere with the optical whispering gallery mode resonance characteristic is used as a construction carrier of the semiconductor catalyst, and the semiconductor nanoparticles are loaded on the surface of the polymer microsphere. The special whispering gallery mode resonance cavity structure on the surface of the polymer microsphere can effectively confine the photons, and there is no restriction of the optical band gap, so that the resonance of photons of different wave bands can be realized. The interaction between the catalyst and the photons is enhanced by the regulation of the optical structure on the photons, so as to improve the light trapping capacity of the catalyst, and the catalytic performance of the semiconductor catalyst is improved. The application has high universality for different semiconductor catalytic systems.

[0007] To achieve the above purpose, the technical scheme adopted by the application is as follows:

[0008] In a first aspect, the application provides a polymer microsphere with an optical whispering gallery mode resonance characteristic. The particle size of the polymer microsphere is 1-15 μm. The refractive index of the polymer material used to prepare the polymer microsphere is greater than 1.34. The light loss of the polymer material in the wave band range of 320-1000 nm is less than 2 dB / μm.

[0009] The present application firstly starts from the technical concept of improving the light capturing ability of semiconductor catalysts and then improving the catalytic performance thereof, uses a polymer microsphere having optical whispering gallery mode resonance characteristics as a construction carrier of semiconductor catalysts, utilizes the optical whispering gallery mode resonance characteristics of the polymer microsphere, and can confine photons in the polymer microsphere for a long time through continuous total internal reflection, gather a large amount of light energy in a very small space, and when the phase difference between the incident light wave after one round of propagation and the newly incident light wave is equal to an integer multiple of the circumference, the two interfere constructively and resonate, and the interaction between light and semiconductor materials can be enhanced in the full spectrum; and an evanescent field is formed on the surface of the polymer microsphere, and semiconductor nanoparticles are loaded on the surface of the polymer microsphere, so that the enhanced light field can be fully utilized to improve the catalytic performance, and different periodic structures do not need to be constructed for different semiconductor nanoparticles, so that the intrinsic electronic structure of the semiconductor nanoparticles will not be changed and the energy level position does not need to be matched, and the semiconductor catalytic system is compatible with different semiconductor catalysts, has very high universality, and provides a new idea for improving the light capturing efficiency of the photocatalytic system.

[0010] It is found through experiments that the light loss of the polymer material in the wavelength range of 320-1000 nm is less than 2 dB / μm, that is, the polymer material has almost no absorption to light in the ultraviolet-visible wavelength range, which is one of the necessary conditions for photon trapping; and the polymer material with a refractive index greater than 1.34 is selected, which is one of the necessary conditions for photon confinement.

[0011] In addition, the polymer microsphere has no resonance characteristics if the particle size is too small, and the light confinement is stronger and the evanescent field on the surface is smaller if the particle size is too large, which is not conducive to the interaction between light and semiconductor catalysts and reduces the catalytic effect; therefore, only the polymer microsphere with the above-mentioned size conditions and smooth surface can exhibit excellent optical whispering gallery mode resonance characteristics, the photons can propagate along the inner surface of the microsphere in the form of continuous total reflection, the resonance and confinement of the photons are realized, the light capturing ability of the semiconductor catalysts is significantly improved, and the photocatalytic efficiency is improved.

[0012] Preferably, the polymer material is polystyrene or polymethyl methacrylate.

[0013] The polystyrene and polymethyl methacrylate are very suitable for self-assembly to form an isotropic spherical structure due to their good flexibility, and the polystyrene and polymethyl methacrylate have almost no absorption to light in the ultraviolet-visible wavelength range, and the light loss is small, which is conducive to the resonance of the photons.

[0014] In the second aspect, the present application provides a method for preparing the polymer microsphere having the optical whispering gallery mode resonance characteristics, comprising the following steps:

[0015] S1: adding a cross-linking agent and an initiator into styrene or methyl methacrylate as an oil phase;

[0016] S2: adding an aqueous solution containing a surfactant as a water phase;

[0017] S3: adding the oil phase into the water phase for shearing emulsification, initiating a polymerization reaction at 60-95°C, and collecting the precipitate through centrifugation and washing to obtain polystyrene microspheres or polymethyl methacrylate microspheres.

[0018] The styrene monomer solution or the methyl methacrylate monomer solution and the aqueous solution of the surfactant are emulsified under shearing to form a stable oil-in-water emulsion. Under the driving of the isotropic interfacial tension, the oil phase colloidal particles are spherical. In the heating process, the initiator in the oil phase decomposes to generate free radicals, which initiate the polymerization and cross-linking reaction of the monomers. Since the polystyrene and the polymethyl methacrylate have good flexibility and are not easy to crystallize, they will eventually form a microsphere structure under the induction of the spherical oil phase colloidal particles.

[0019] Preferably, the cross-linking agent is divinylbenzene; the initiator is azobisisobutyronitrile or benzoyl peroxide; and the surfactant is cetyltrimethylammonium bromide, sodium dodecylsulfate or sodium dodecylbenzenesulfonate.

[0020] The addition amount of the cross-linking agent in the styrene or methyl methacrylate is 25%-45% (v / v); the concentration of the surfactant in the water phase is 0.1-0.7 mg / mL; and the volume ratio of the oil phase to the water phase is 1:(15-30).

[0021] The initiator generates free radicals at 60-95°C to initiate the polymerization reaction of the styrene monomers or the methyl methacrylate monomers in the oil phase, so the amount of the initiator is not less than 10 mg / mL, and the excess initiator can be removed through washing.

[0022] The surfactant reduces the interfacial energy of the water phase and the oil phase to form a stable oil-in-water microemulsion system, which is helpful to the formation of the polymer microspheres. It has been found through experiments that the concentration of the surfactant has an influence on the particle size of the polymer microspheres. When the concentration of the surfactant is 0.1-0.7 mg / mL, the formed polymer microspheres have a particle size of 1-15 μm and a smooth surface, and exhibit the optical whispering gallery mode resonance characteristics.

[0023] In addition, when the dispersion phase of the surfactant is adjusted to be a solvent such as ethanol instead of water, the particle size of the polymer microspheres formed by the reaction of the surfactant with the oil phase is in the nanometer range instead of the micrometer range, so that the prepared polymer microspheres do not have the optical whispering gallery mode resonance characteristics due to the too small size.

[0024] The crosslinking agent can enhance the interaction between molecules in the polymer microspheres, and enhance the stability of the polymer microspheres in an alcohol system, and the addition amount of the crosslinking agent is preferably 25% to 45%.

[0025] In a third aspect, the present application provides application of the polymer microspheres with the optical whispering gallery mode resonance characteristics in preparation of a photocatalyst.

[0026] The present application is first conceived from the technical idea of improving the light trapping capability of semiconductor nanoparticles and then improving the catalytic performance thereof, and the polymer microspheres with the optical whispering gallery mode resonance characteristics are used as a construction carrier of a semiconductor catalyst. The optical whispering gallery mode resonance characteristics of the polymer microspheres can confine photons in the polymer microspheres for a long time through continuous total internal reflection, enhance the interaction between light and semiconductor materials in a full spectrum, form an evanescent field on the surface of the polymer microspheres, and load semiconductor nanoparticles on the surface of the polymer microspheres with the optical whispering gallery mode resonance characteristics, so as to fully utilize the enhanced light field and achieve the purpose of enhancing the photocatalytic effect of the semiconductor nanoparticles. The present application can be compatible with different catalytic systems and has high universality.

[0027] In a fourth aspect, the present application provides a photocatalyst, which is prepared by loading semiconductor nanoparticles on the surface of the polymer microspheres with the optical whispering gallery mode resonance characteristics after surface modification.

[0028] Preferably, the weight ratio of the semiconductor nanoparticles to the polymer microspheres in the photocatalyst is 1:(1 to 6).

[0029] It is found through experiments that, with the increase of the weight proportion of the PS microspheres in the photocatalyst, the photocatalytic degradation performance of the catalyst shows a trend of first increasing and then decreasing, and the catalytic performance of the photocatalyst reaches the best when the weight ratio of the semiconductor nanoparticles to the polymer microspheres is 1:2.

[0030] Preferably, the semiconductor nanoparticles are at least one of titanium dioxide nanoparticles, zinc oxide nanoparticles and cadmium sulfide nanoparticles.

[0031] Preferably, the particle size of the semiconductor nanoparticles is less than 200 nm.

[0032] The particle size of the semiconductor nanoparticles is less than 200 nm, on the one hand, so as to facilitate the loading of the semiconductor nanoparticles on the surface of the polymer microspheres, and on the other hand, since the evanescent field on the surface of the polymer microspheres is only about hundreds of nanometers, if the particle size of the semiconductor nanoparticles is too large, it is not conducive to the interaction of the semiconductor nanoparticles with the resonance photons.

[0033] In a fifth aspect, the present application provides a method for preparing the photocatalyst, which comprises the following steps:

[0034] S1: adding a crosslinking agent, an initiator and a coupling agent into styrene or methyl methacrylate as an oil phase;

[0035] S2: adding an aqueous solution containing a surfactant as an aqueous phase;

[0036] S3: adding the oil phase into the aqueous phase for shearing emulsification, and obtaining surface-modified polystyrene microspheres or surface-modified polymethyl methacrylate microspheres after washing;

[0037] S4: dispersing semiconductor nanoparticles into the surface-modified polystyrene microspheres or the surface-modified polymethyl methacrylate microspheres in an alcohol solution to form a dispersion, and loading the semiconductor nanoparticles on the surface of the polystyrene microspheres or the polymethyl methacrylate microspheres by stirring to obtain the photocatalyst.

[0038] Preferably, the weight ratio of the polystyrene microspheres to the semiconductor nanoparticles is (1-6):1; the coupling agent is n-octyltriethoxysilane; and the addition amount of the coupling agent in the styrene or the methyl methacrylate is 1%-10% (v / v).

[0039] Preferably, the alcohol solution is an ethanol aqueous solution or a methanol aqueous solution, and the volume fraction of the ethanol aqueous solution or the methanol aqueous solution is 75%-95%.

[0040] The synthesis mechanism of the photocatalyst is described below by taking the polystyrene microspheres as an example: during the polymerization of the styrene molecules, the coupling agent n-octyltriethoxysilane (OTES) molecules are slightly separated from the generated polystyrene molecules due to the difference in polarity. Since the polarity of the OTES is between the aqueous phase and the polystyrene, the OTES molecules tend to be distributed on the surface of the polystyrene (PS) microspheres under the action of the interfacial tension to reduce the interfacial energy of the system, thereby realizing the modification of the OTES on the surface of the PS microspheres.

[0041] Preferably, the above method meets one of the following conditions:

[0042] a) when the semiconductor nanoparticles are titanium dioxide nanoparticles, adding acetic acid into the dispersion in step S4, and the addition amount of the acetic acid is 0.25%-2.5% (v / v);

[0043] b) when the semiconductor nanoparticles are cadmium sulfide nanoparticles, adding ammonia into the dispersion in step S4, and the addition amount of the ammonia is 0.25%-2.5% (v / v).

[0044] The acid can effectively catalyze the hydrolysis of the silane coupling agent on the surface of the polymer microspheres, and the OTES molecules can be hydrolyzed to generate Si-OH, so that the polymer microspheres have the ability to couple with the semiconductor nanoparticles, and the surface of the polymer microspheres is convenient for the coupling and loading of the nanoparticles TiO2.

[0045] Different from the loading of TiO2, the semiconductor nanoparticle ZnO is not stable under acidic conditions and can react with acid, so the loading of ZnO cannot be carried out under the condition of acid catalysis, and the silane coupling agent can be hydrolyzed as much as possible by sufficient stirring for a long time, in which case, ZnO can also be better coated on the surface of the polymer microspheres.

[0046] The surface of cadmium sulfide nanoparticles has poor connectivity due to the lack of the action of functional groups such as hydroxyl groups, so the OTES on the surface of the polymer microspheres needs to be fully hydrolyzed to fully play its connecting role during the loading process. Cadmium sulfide and ZnO are both catalysts that are not resistant to acid, but cadmium sulfide can remain stable in an alkaline environment and does not react with ammonia, so ammonia water can be used instead of acid to catalyze the hydrolysis of the silane coupling agent.

[0047] Like acid catalysis, ammonia catalysis also needs to be controlled in amount, and too much ammonia water can lead to too fast hydrolysis, which is not conducive to the loading of semiconductor nanoparticles on the surface of the polymer microspheres, so the addition amount of acetic acid and ammonia water needs to be controlled at 0.25% to 2.5% (v / v).

[0048] Compared with the prior art, the present application has the following beneficial effects:

[0049] Based on the method of microemulsion polymerization, the present application successfully prepared polymer microspheres with whispering gallery mode (WGM) resonance characteristics, and the surface of the polymer microspheres was modified by a silane coupling agent, thereby realizing the effective loading of the polymer microspheres with WGM resonance characteristics and classical semiconductor materials such as TiO2, ZnO and CdS. Using dye photodegradation as a model reaction, it is successfully verified that the polymer microspheres with WGM resonance characteristics have a significant enhancement effect on the photocatalytic efficiency of the constructed semiconductor photocatalyst, which provides a new idea for improving the light capture efficiency of the photocatalytic system. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 It is a scanning electron microscope graph of the PS spheres of different sizes in Example 1;

[0051] Figure 2 It is a fluorescence microscope photo and the corresponding luminescence spectrum of the polystyrene microspheres of three different sizes in Example 1 under the excitation of pump light;

[0052] Figure 3 It is a scanning electron microscope graph of the TiO2-PS catalyst prepared in Example 2;

[0053] Figure 4 It is a graph of the photocatalytic degradation of crystal violet by the TiO2-PS catalyst in Example 3;

[0054] Figure 5Figure for photocatalytic degradation of crystal violet by TiO2-PS catalysts with different particle sizes prepared in Example 5;

[0055] Figure 6 Figure for light field simulation and local amplification of TiO2-PS catalysts with different particle sizes;

[0056] Figure 7 Figure for scanning electron microscope of catalyst samples in Example 6;

[0057] Figure 8 Figure for photocatalytic degradation of crystal violet by catalysts in Example 6;

[0058] Figure 9 Figure for scanning electron microscope of photocatalyst ZnO-PS prepared in Example 7;

[0059] Figure 10 Figure for photocatalytic degradation of crystal violet by photocatalyst ZnO-PS prepared in Example 7;

[0060] Figure 11 Figure for photocatalytic degradation of crystal violet by pure zinc oxide nanoparticles;

[0061] Figure 12 Figure for scanning electron microscope of CdS-PS catalyst prepared in Example 8;

[0062] Figure 13 Figure for photocatalytic degradation of crystal violet by CdS-PS catalyst prepared in Example 8;

[0063] Figure 14 Figure for photocatalytic degradation of crystal violet by pure cadmium sulfide nanoparticles. DETAILED DESCRIPTION

[0064] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with specific examples. Those skilled in the art should understand that the specific examples described herein are only used to explain the present application, and are not used to limit the present application. The test methods used in the examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available unless otherwise specified.

[0065] Example 1 Preparation, characterization and optical whispering gallery mode resonance characteristic analysis of polystyrene microspheres

[0066] In this embodiment, polystyrene is taken as an example to provide a preparation method of polymer microspheres polystyrene with optical whispering gallery mode resonance characteristics, which comprises the following steps:

[0067] (1) Measure 10 mL of styrene and add 3 mL of crosslinking agent divinylbenzene (the volume fraction of the crosslinking agent is 30% of the styrene) and 100 mg of initiator azobisisobutyronitrile (the mass concentration of the initiator in styrene is 10 mg / mL) to it in sequence. Mix and dissolve them to form the oil phase.

[0068] (2) Prepare 400 mL of 0.7 mg / mL hexadecyltrimethylammonium bromide (CTAB) aqueous solution as the aqueous phase.

[0069] (3) The oil phase was added to the aqueous phase and sheared and emulsified for 10 min using an emulsion shearing machine at a shear rate of 4000 rad / min to completely emulsify the aqueous and oil phases. Then, the polymerization reaction was carried out in a 90℃ water bath for 12 hours. The precipitate was collected by centrifugation and then washed with ethanol and water by centrifugation to obtain polystyrene microspheres (PS microspheres).

[0070] Based on the above method, the concentration of CTAB in the aqueous phase of step (2) was adjusted to 0.7 mg / mL, 0.4 mg / mL and 0.1 mg / mL respectively, and polystyrene microspheres were obtained by the above method.

[0071] In addition, CTAB was dissolved in ethanol to prepare an alcohol solution of 400 mL with a concentration of 0.7 mg / mL of CTAB as the aqueous phase. The water bath temperature in step (3) was adjusted from 90 °C to 70 °C. Under the condition that other conditions remained unchanged, polystyrene balls were obtained.

[0072] II. Characterization of the polystyrene spheres prepared above

[0073] Scanning electron microscope (SEM) images of the spherical polystyrene obtained by the above method are shown below. Figure 1 As shown, where, Figure 1 Image a shows polystyrene spheres prepared with the ethanol phase, exhibiting a nanometer-scale (200–300 nm) particle size rather than a micrometer-scale. Scanning electron micrographs of the polystyrene microspheres prepared with CTAB concentrations of 0.7 mg / mL, 0.4 mg / mL, and 0.1 mg / mL in the aqueous phase are shown below. Figure 1 b、 Figure 1 c and Figure 1 As shown in d, the particle size range of the prepared PS microspheres is 1–3 μm, 3–7 μm, and 5–15 μm, respectively.

[0074] Depend on Figure 1It can be seen that the concentration of CTAB in the emulsion system is related to the particle size of the PS balls. When the concentration of CTAB in the system is reduced, the interfacial tension between the dispersed phase (water phase) and the continuous phase (oil phase) will be increased, which will promote the oil phase to aggregate to form larger colloidal particles to reduce the contact area of the two phases and reduce the surface energy of the system, so that the particle size of the PS balls is increased with the decrease of the concentration of CTAB in the dispersed phase. Therefore, the size of the microspheres can be effectively controlled (1-15 μm, Figure 1 ) by changing the concentration of CTAB in the dispersed phase (0.1-0.7 mg / mL).

[0075] When the dispersed phase is adjusted from water to ethanol, the interfacial energy between the two phases becomes very small, and under the driving of the entropy increase effect, the oil phase styrene and the dispersed phase are completely miscible. At this time, the system is changed from emulsion polymerization to dispersion polymerization, and with the progress of the polymerization reaction, the generated polystyrene is gradually precipitated from the ethanol solution and aggregated into nanoscale spherical structure under the action of interfacial tension.

[0076] III. Analysis of the optical whispering gallery mode resonance characteristics of the prepared PS balls

[0077] Since PS itself does not emit light, it is difficult to directly introduce photons into the cavity, so it is difficult to directly verify the optical whispering gallery mode resonance characteristics of the surface of the PS balls. Considering that PS has excellent material compatibility, it can be effectively complexed with non-polar organic dye small molecules to realize the introduction of fluorescence signal. Therefore, the optical whispering gallery mode resonance characteristics of the PS microspheres are explored by the modulation effect of the PS microsphere structure on the fluorescence spectrum of the dye. Coumarin 6 is selected as the light-emitting medium. On the one hand, it has strong fluorescence signal, and on the other hand, it is a π-conjugated molecule with delocalized π electrons, which can have large π-π interaction with the phenyl groups in the polystyrene chain, so that it has better compatibility with the main body material of the cavity and avoids damaging the structure of the PS microspheres.

[0078] By adding 10 mg of coumarin 6 to the styrene in step (1), the concentration of CTAB in the water phase is adjusted as above to prepare PS balls of different sizes, so as to verify the optical whispering gallery mode resonance characteristics of PS balls of different sizes.

[0079] The resonance characteristics of the coumarin 6 doped PS microspheres can be characterized by a micro-spectral test system, and the fluorescence microscope photos obtained by the test are as follows: Figure 2 a、 Figure 2 b and Figure 2As shown in Figure c, all three PS spheres of different sizes emitted uniform green fluorescence, proving that the dye molecules can be uniformly mixed with the polystyrene material. Furthermore, the fluorescence at the edges of the spheres was significantly stronger than at other locations, forming a bright ring band, indicating that the fluorescence emitted by the dye can propagate within the microspheres and be reflected at the boundaries. Simultaneously, we observed obvious cavity modulation in the spectra collected from the edges of the microspheres, with a series of regular spike signals appearing in the fluorescence spectrum of coumarin 6 (e.g., ...). Figure 2 d、 Figure 2 e and Figure 2 f) This is because the total internal reflection of the dye fluorescence at the boundary of the PS sphere causes photons to circulate along the edge of the sphere (normally they can circle more than ten times), resulting in traveling wave coherence and forming the WGM resonant cavity effect.

[0080] Depend on Figure 2 The modulation spectrum and the mode spacing (Δλ), resonant wavelength (λ), microsphere diameter (D), and material refractive index (n) of the microsphere-based WGM cavity will satisfy the equation: λ 2 / Δλ=nπD, through linear fitting, λ 2 There is a clear linear relationship between / Δλ and the diameter D of the microsphere. The refractive index of the polystyrene microsphere is calculated to be 1.52 (n=k / π) from the slope k of the fitted linearity. This is basically consistent with the intrinsic refractive index (1.59) of polystyrene, the main material of the microsphere. This indicates that the photons that satisfy the WGM resonance are well confined within the PS microsphere and have very weak interaction with the substrate. Based on the above analysis, it can be considered that the PS microspheres with a size of 1~15μm prepared by this invention have optical resonance characteristics with a high quality factor.

[0081] Example 2: Preparation of photocatalysts using polystyrene microspheres as a building block

[0082] This embodiment provides a method for preparing a photocatalyst using polystyrene microspheres as a building block, comprising the following steps:

[0083] (1) Take 10 mL of styrene and add 3 mL of crosslinking agent divinylbenzene (the volume fraction of the crosslinking agent is 30% of the styrene), 100 mg of initiator azobisisobutyronitrile (the mass concentration of the initiator in the styrene is 10 mg / mL) and 1 mL of coupling agent n-octyltriethoxysilane (the volume fraction of the coupling agent is 10% of the styrene) as the oil phase.

[0084] (2) Prepare 400 mL of 0.7 mg / mL hexadecyltrimethylammonium bromide aqueous solution as the aqueous phase.

[0085] (3) The oil phase is added to the water phase and sheared and emulsified by an emulsion shearing machine for 10 min at a shearing rate of 4000 rad / min to completely emulsify the water phase and the oil phase, and then the polymerization reaction is carried out in a water bath at 90°C for 12 hours, and the precipitate is collected by centrifugation, and then washed by ethanol and water in turn to obtain the surface-modified polystyrene microspheres.

[0086] (4) 200 mg of TiO2 nanoparticles are dispersed in 200 mL of ethanol, and the dispersion is treated by shearing (4000 rad / min) for 1 h using an emulsion shearing machine, and then divided into 20 portions, each containing 10 mg of TiO2. One portion of the TiO2 nanoparticle ethanol dispersion and 20 mg of the surface-modified polystyrene microspheres are dispersed in 75% aqueous ethanol to form a dispersion, and the total volume of the dispersion is 40 mL. 200 μL of acetic acid (0.5% by volume in the dispersion) is added to the dispersion, and the mixture is stirred in a water bath at 30°C for 6 h to ensure that the OTES on the surface of the microspheres is completely hydrolyzed, and the TiO2 nanoparticles are loaded on the surface of the polystyrene microspheres to obtain the photocatalyst (TiO2-PS), and the weight ratio of TiO2 to polystyrene microspheres in the photocatalyst is 1:2.

[0087] The scanning electron microscope (SEM) images of the TiO2 nanoparticles in the TiO2 nanoparticle ethanol dispersion are shown in Figure 3 a and Figure 3 b. The scanning electron microscope (SEM) images of the surface-modified polystyrene microspheres are shown in Figure 3 c and Figure 3 d. Compared with the unmodified polystyrene microspheres Figure 1 b), the spherical structure of the PS microspheres does not change significantly, and the surface remains smooth to ensure that the PS microspheres still have WGM resonance characteristics. The scanning electron microscope (SEM) images of the prepared photocatalyst are shown in Figure 3 e and Figure 3 f. It can be seen that the TiO2 is uniformly coated on the surface of the polystyrene microspheres, and the dispersed TiO2 nanoparticles are hardly visible on the substrate. The above morphology results show that the loading method used in the present application can successfully coat the TiO2 nanoparticles on the surface of the polystyrene microspheres.

[0088] Example 3 Analysis of the catalytic performance of the photocatalyst

[0089] In this example, pure PS microspheres and pure titanium dioxide are used as controls to analyze the catalytic performance of the photocatalyst prepared in the present application by analyzing the photocatalytic degradation effect of crystal violet dye.

[0090] 80 mL of 30 mg / L crystal violet dye solution is added to the TiO2 nanoparticles, the photocatalyst prepared in Example 2, and the surface-modified PS microspheres prepared in step 3 of Example 2, respectively, and stirred in the dark for 30 min, and then irradiated with UV light at a power density of 0.5 KW / m2 Photocatalytic degradation was carried out under illumination. During the photodegradation process, samples were taken, centrifuged, and the dye supernatant was collected every 20 minutes. The samples were then photographed and UV absorption curves were measured. Images showing the change in dye concentration over time are shown below. Figure 4 As shown,

[0091] Figure 4 In the text, “PS:TiO2=0:1” represents pure TiO2 nanoparticles, “PS:TiO2=2:1” represents the photocatalyst prepared by the method described in Example 2, and “PS(20mg)without TiO2” represents the surface-modified PS microspheres prepared by step (3) of Example 2. Figure 4 In the diagram, "-30" indicates 30 minutes of stirring in the dark before photodegradation, which indicates that the dye has reached adsorption equilibrium. "0" indicates the start of illumination; "20" indicates 20 minutes of illumination.

[0092] Depend on Figure 4 It can be seen that during the degradation process, the dye fades slowly and changes color little before TiO2 loading, while after TiO2 is loaded onto the surface of polystyrene microspheres, the dye color almost completely fades within 120 minutes. Compared with the degradation by pure TiO2, the photodegradation rate of the photocatalyst prepared in this invention is significantly improved. Through detection and calculation of the degradation rate, the photodegradation rate (K value) of pure titanium dioxide on the dye is 0.0026 min. -1 The K value of the photocatalyst sample of this invention is 0.0259 min. -1 The rate is 9.96 times that of pure titanium dioxide, indicating that the photocatalyst prepared by loading titanium dioxide onto the surface of the PS microspheres described in this case has a catalytic rate enhancement effect of 9.96 times compared to pure titanium dioxide.

[0093] Photodegradation experiments were conducted on PS microspheres modified with silane coupling agents under the same illumination conditions. It was observed that the dye color did not change over time. This indicates that the PS microspheres modified with silane coupling agents do not possess photocatalytically active groups, and their presence has no effect on the TiO2-PS catalytic degradation process.

[0094] The light intensity of the catalytic experiment was adjusted to 2 KW / m 2 Both pure TiO2 and photocatalyst (TiO2-PS) showed a more pronounced decreasing trend, but according to the fitting results, their K values ​​were 0.0131 min. -1 With 0.1161min -1, the catalytic degradation rate of the photocatalyst (TiO2-PS) is still nearly 9 times that of pure TiO2, and the enhanced catalytic effect of the photocatalyst prepared by the application relative to pure TiO2 does not change with the change of light intensity. This shows that when the catalyst of the application is applied to actual production, high photocatalytic efficiency can be achieved at high power density, and has high practical application value.

[0095] In addition, the above photocatalytic degradation test was carried out with methyl orange, rhodamine 6G dye and the like, and the same catalytic degradation rule was shown. The PS microspheres and the PS microspheres modified by silane coupling both do not have photocatalytic activity, and the photocatalytic performance of the photocatalyst prepared by the application is significantly better than that of pure titanium dioxide nanoparticles.

[0096] Example 4 Analysis of the influence of the loading ratio of PS microspheres and titanium dioxide on the catalytic performance of the photocatalyst TiO2-PS

[0097] Referring to the preparation method of the photocatalyst TiO2-PS in Example 2, the weight ratio of TiO2 to polystyrene microspheres in the photocatalyst was adjusted to 1:1, 1:4 and 1:6, respectively. The catalytic performance of the catalysts with different loading ratios of PS microspheres and titanium dioxide was detected and calculated according to the catalytic performance analysis method described in Example 3, and the results are shown in Table 1.

[0098] Table 1

[0099] TiO2:PS 1:1 1:2 1:4 1:6 K value 0.0159 0.0259 0.0255 0.0202

[0100] As can be seen from Table 1, with the increase of the weight proportion of PS microspheres, the photocatalytic degradation performance of the photocatalyst TiO2-PS shows a trend of first increasing and then decreasing. When TiO2:PS = 1:2, the catalytic performance of the photocatalyst reaches the best, and with the increase of the weight proportion of PS microspheres, the catalytic performance decreases. This may be due to the fact that too much PS microspheres cause the light shielding effect of the balls to be enhanced, which affects the absorption of light by the catalyst.

[0101] Example 5 Analysis of the catalytic effect of the catalyst prepared by loading titanium dioxide on PS microspheres of different sizes

[0102] As can be seen from Example 1, PS microspheres of different sizes can be prepared by adjusting the concentration of CTAB in the dispersed phase. Referring to the preparation method of the photocatalyst described in Example 2, the concentration of CTAB in the aqueous phase was adjusted to 0.7 mg / mL and 0.4 mg / mL, and the particle size range of the prepared PS microspheres was 1-3 μm and 3-7 μm, respectively. When the dispersed phase of CTAB is ethanol, the particle size of the prepared PS balls is 200-300 nm.

[0103] The catalysts of different sizes of PS spheres supporting TiO2 were prepared according to the preparation method of the photocatalyst in Example 2, and the catalytic rates of different photocatalysts were detected and calculated according to the photocatalytic test of 30 mg / L crystal violet dye solution under the light intensity of 0.5 KW / m2 as described in Example 3, and the results are shown in Table 1. 2 Table 1 Figure 5 Figure 5 In Table 1, "small spheres" means the photocatalyst prepared by supporting TiO2 on PS microspheres with a particle size range of 200-300 nm, "middle spheres" means the photocatalyst prepared by supporting TiO2 on PS microspheres with a particle size range of 1-3 μm, and "large spheres" means the photocatalyst prepared by supporting TiO2 on PS microspheres with a particle size range of 3-7 μm.

[0104] Figure 5 As can be seen from Table 1, the degradation rate of the photocatalyst prepared by supporting TiO2 on nano-sized PS microspheres is consistent with that of pure TiO2, indicating that the use of nano-sized PS microspheres for supporting TiO2 has no enhancing effect on photocatalytic degradation. As can be seen from the fitting results of the degradation rate, the C / C0-time curve of the catalyst prepared from large-sized PS microspheres is above that of the middle-sized PS microspheres, and the K value thereof is 0.0175 min -1 , which is less than the K value (0.0247 min -1 ) of the catalyst prepared from middle-sized PS microspheres.

[0105] The size effect existing in the degradation process of the above TiO2-PS catalysts can be explained by light field simulation of different sizes of whispering gallery mode resonators. The light field distribution of PS microspheres with different sizes (0.8 μm, 2 μm, 5 μm) is shown in Figure 2. In Figure 2, (a) is the light field simulation diagram of the whispering gallery mode resonator of 0.8 μm (small-sized PS spheres), (b) is the light field simulation diagram of the whispering gallery mode resonator of 2 μm (middle-sized PS spheres), (c) is the light field simulation diagram of the whispering gallery mode resonator of 5 μm (large-sized PS spheres), (b1) is the local enlarged view of the middle-sized PS spheres, and (c1) is the local enlarged view of the large-sized PS spheres. Figure 6

[0106] Due to the diffraction effect of light, the small-sized spheres of nano-scale have no confining effect on the light field, and the light field around the small-sized spheres is diffusely distributed, and it is difficult to form WGM resonance and achieve effective confinement of photons, so the small-sized spheres have no any enhancing effect on the catalytic performance of TiO2. The middle-sized spheres of 2 μm have good confining effect on the light field, and the light field is concentratedly distributed at the edge of the cavity, and there is a strong evanescent field on the outer surface of the cavity, which can be effectively coupled and overlapped with the surface semiconductor nanoparticles to improve the light absorption capacity thereof. The optical confining effect of the large-sized spheres is stronger than that of the middle-sized spheres, and the light can be better confined in the interior of the cavity, but compared with the 2 μm spheres, the surface evanescent field of the large-sized microspheres is smaller,​​​Figure 6 c1), far lower than the middle ball ( Figure 6 b1), not conducive to the absorption and utilization of resonant photons by semiconductor nanoparticles on the surface of the microspheres, so the photocatalytic performance of the photocatalyst prepared by loading semiconductor nanoparticles on large-size microspheres is slightly lower than that of the microspheres of medium size. The light field simulation is consistent with the experimental results, further verifying that the PS microspheres enhance the photocatalytic effect of semiconductor nanoparticles based on the photon confinement effect of the optical WGM resonant cavity on the surface of the PS microspheres. At the same time, the above results also show that the size of the PS microspheres is directly related to the enhancement effect, and the PS microspheres of about 1-3 μm have the best enhancement effect, at which the PS microspheres can not only satisfy the effective confinement of photons, but also generate a large range of evanescent field on the surface, ensuring the efficient utilization of semiconductor nanoparticles.

[0107] Example 6 Effect of loading method on the photocatalytic performance of the catalyst TiO2-PS

[0108] In this example, 20 mg of pure PS microspheres without functional group modification were physically mixed with 10 mg of TiO2, and then loaded by stirring for a long time, followed by alcohol washing and water washing to obtain the product. The specific preparation method is as follows:

[0109] (1) 10 mL of styrene was measured, and 3 mL of crosslinking agent divinylbenzene (volume fraction of crosslinking agent was 30% of styrene), 100 mg of initiator azobisisobutyronitrile (mass concentration of initiator in styrene was 10 mg / mL) and 1 mL of coupling agent n-octyl triethoxysilane (volume fraction of coupling agent was 10% of styrene) were added in sequence as the oil phase.

[0110] (2) 400 mL of 0.7 mg / mL aqueous solution of cetyltrimethylammonium bromide was prepared as the water phase.

[0111] (3) The oil phase was added to the water phase and sheared and emulsified by an emulsion shearing machine for 10 min at a shearing rate of 4000 rad / min to completely emulsify the water phase and the oil phase, and then the polymerization reaction was carried out in a 90°C water bath for 12 hours. The precipitate was collected by centrifugation, and then washed with ethanol and water by centrifugation to obtain the surface-modified polystyrene microspheres.

[0112] (4) Take 200 mg TiO2 nanoparticles dispersed in 200 mL ethanol, and use an emulsion shearing machine to shear and disperse (4000 rad / min) for 1 h. Then divide the sample into 20 portions, each containing 10 mg TiO2. Take one portion of the TiO2 nanoparticle ethanol dispersion and mix it with 20 mg of surface-modified polystyrene microspheres in 75% ethanol aqueous solution to form a dispersion. The total volume of the dispersion is 40 mL. Stir the dispersion in a 30°C water bath for 12 h. In the absence of acid catalysis, try to load the TiO2 nanoparticles onto the surface of the polystyrene microspheres by physical action by extending the stirring time as much as possible to prepare a photocatalyst sample.

[0113] The scanning electron microscope image of the catalyst sample is shown in Figure 7 It can be seen that most of the TiO2 is still in a dispersed state, and the coating of TiO2 on the surface of the PS microspheres is very uneven. The degradation of crystal violet by the catalyst is shown in Figure 8 The photocatalytic degradation rate is faster than that of TiO2, and the change in dye concentration is relatively obvious. From the K value obtained by fitting in Figure 8 d, the catalytic degradation rate is close to twice that of pure TiO2. This is because although there is no active group connected, part of the TiO2 can still be attached to the surface of the PS microspheres by physical action under the action of long-time stirring, and the resonant cavity can therefore play a weak role. As can be seen from the comparison with the TiO2-PS catalyst prepared in Example 2 (shown in Figure 3 ), the silane coupling agent plays a key connecting role. Adding acid catalysis helps to hydrolyze the silane coupling agent to form active groups, which facilitates the close loading of TiO2 on the surface of the PS microspheres. The enhancement of the photocatalytic degradation performance of the catalyst TiO2-PS is due to the close connection between TiO2 and the PS microspheres, so that the WGM resonant cavity on the surface of the PS can fully play a role in TiO2.

[0114] Example 7

[0115] This example takes semiconductor nanoparticles zinc oxide as an example to provide a method for preparing a photocatalyst using polystyrene microspheres as a construction carrier, which comprises the following steps:

[0116] (1) Measure 10 mL of styrene, and then add 3 mL of divinylbenzene (30% by volume fraction of styrene), 100 mg of azobisisobutyronitrile (10 mg / mL of initiator in styrene), and 1 mL of n-octyltriethoxysilane (10% by volume fraction of styrene) as an oil phase.

[0117] (2) Prepare 400 mL of a 0.7 mg / mL aqueous solution of cetyltrimethylammonium bromide as an aqueous phase.

[0118] (3) The oil phase is added to the water phase and sheared and emulsified by an emulsion shearing machine for 10 min at a shearing rate of 4000 rad / min to completely emulsify the water phase and the oil phase, and then the polymerization reaction is carried out in a 90℃ water bath for 12 hours, and the precipitate is collected by centrifugation, and then washed by ethanol and water by centrifugation to obtain the surface-modified polystyrene microspheres;

[0119] (4) 200 mg of ZnO nanoparticles are dispersed in 200 mL of ethanol, and sheared and dispersed by an emulsion shearing machine (4000 rad / min) for 1 h, and then divided into 10 parts, each containing 20 mg of ZnO nanoparticles. One part of the ZnO nanoparticle ethanol dispersion is taken and mixed with 40 mg of the surface-modified polystyrene microspheres to form a dispersion in 75% ethanol aqueous solution, and the total volume of the dispersion is 40 mL. Stirring is carried out in a 30℃ water bath for 6 h to ensure that the OTES on the surface of the microspheres is fully hydrolyzed, and the ZnO nanoparticles are loaded on the surface of the polystyrene microspheres to obtain the photocatalyst ZnO-PS.

[0120] The scanning electron microscope image of the photocatalyst ZnO-PS is shown in Figure 9 , and it can be seen that the ZnO nanoparticles are uniformly wrapped on the surface of the PS microspheres, and almost no dispersed ZnO nanoparticles are visible on the substrate.

[0121] 80 mL of 30 mg / L crystal violet dye solution is added to the photocatalyst ZnO-PS sample, and stirring is carried out in the dark for 30 min, and then photocatalytic degradation is carried out under the condition of 1 KW / m 2 light irradiation, and the degradation results are shown in Figure 10 . Figure 10 a-d are the dye concentration change photos taken at intervals of 20 min, the absorbance curves taken at intervals of 20 min, the curves of the ratio of the dye concentration to the initial concentration C / C0 with time within 120 min, and the first-order kinetic fitting curves. As shown in Figure 10 a, the color change of the crystal violet degraded by ZnO-PS is obvious, as shown in Figure 10 c, the change of the dye concentration with time is significant, and the degradation rate is fast, as shown in Figure 10 d, the K value of the crystal violet degraded by ZnO-PS is 0.0284 min -1 .

[0122] 200 mg of ZnO nanoparticles are dispersed in 200 mL of ethanol, and sheared and dispersed for 1 h, and then divided into 10 parts, each containing 20 mg of ZnO, and directly dried as a control group.

[0123] Similarly, 80 mL of 30 mg / L crystal violet dye solution is added to the control group sample, and stirring is carried out in the dark for 30 min, and then photocatalytic degradation is carried out under the condition of 1 KW / m 2 light irradiation. Figure 11a-c are the photos of dye concentration change sampled at intervals of 20 minutes, the curve of the ratio of dye concentration to initial concentration C / C0 versus time within 120 minutes and its first-order kinetics fitting curve. As shown in a, the color of crystal violet solution is not changed obviously after 120 minutes of ZnO degradation. As shown in b, the color of crystal violet solution is changed obviously after 120 minutes of ZnO degradation. As shown in c, the change of dye concentration with time is slow during the degradation of ZnO. As shown in d, the K value of ZnO degrading crystal violet is 0.0059 min Figure 11 a, the color change of crystal violet is not obvious during the degradation of ZnO. As shown in Figure 11 b, the color change of crystal violet is obvious during the degradation of ZnO. As shown in c, the change of dye concentration with time is slow during the degradation of ZnO. As shown in d, the K value of ZnO degrading crystal violet is 0.0059 min Figure 11 -1. -1 .

[0124] Example 8

[0125] This example takes semiconductor nanoparticle cadmium sulfide as an example to provide a method for preparing a photocatalyst by using polystyrene microspheres as a construction carrier, which comprises the following steps:

[0126] (1) 10 mL of styrene is measured, and 3 mL of divinylbenzene (the volume fraction of the crosslinking agent is 30% of the styrene), 100 mg of azobisisobutyronitrile (the mass concentration of the initiator in the styrene is 10 mg / mL) and 1 mL of n-octyltriethoxysilane (the volume fraction of the coupling agent is 10% of the styrene) are sequentially added to the styrene as an oil phase.

[0127] (2) 400 mL of a 0.7 mg / mL aqueous solution of cetyltrimethylammonium bromide is prepared as an aqueous phase.

[0128] (3) The oil phase is added to the aqueous phase and sheared and emulsified by using an emulsion shearing machine for 10 min at a shearing rate of 4000 rad / min to completely emulsify the aqueous phase and the oil phase, and then the emulsion is subjected to a polymerization reaction in a 90℃ water bath for 12 hours. The precipitate is collected by centrifugation, and then sequentially washed by ethanol and water by centrifugation to obtain surface-modified polystyrene microspheres.

[0129] (4) 200 mg of cadmium chloride is weighed and subjected to hydrothermal preparation of CdS nanoparticles together with sodium sulfide. The prepared CdS nanoparticles are dispersed in 200 mL of ethanol, and then equally divided after shearing and dispersing treatment for 1 h. Each sample contains 5 mg of CdS. One part of the cadmium sulfide ethanol dispersion liquid is taken together with 10 mg of the surface-modified polystyrene microspheres, and then dispersed in 75% of an ethanol aqueous solution to form a dispersion liquid. The total volume of the dispersion liquid is 40 mL. 200 μL of 25% ammonia water (the volume fraction of the ammonia water in the dispersion liquid is 0.5%) is added to the dispersion liquid, and then stirred in a 30℃ water bath for 6 h to ensure that the OTES on the surface of the microspheres is fully hydrolyzed, so that the CdS nanoparticles are loaded on the surface of the polystyrene microspheres to obtain a photocatalyst CdS-PS.

[0130] The scanning electron microscope photo of the photocatalyst CdS-PS is as shown in Figure 12As shown, CdS nanoparticles uniformly wrapped in the PS microspheres surface, the substrate can hardly see the dispersed CdS nanoparticles.

[0131] Different catalysts have different degradation capacity, in the degradation experiment, the amount of catalyst and light intensity are adjusted according to the actual situation. In the CdS-PS sample, 80 mL of 30 mg / L crystal violet dye solution was added, and the light stirring was carried out for 30 min, and then the photocatalytic degradation was carried out under the light intensity of 0.5 KW / m 2 Figure 13 The degradation results are shown in Figure 13 a-d are the photos of the change of dye concentration sampled at intervals of 5 min, the absorbance curves sampled at intervals of 5 min, the curves of the ratio of dye concentration to initial concentration C / C0 with time within 40 min and the first-order kinetic fitting curves. As shown in Figure 13 a, the color change of crystal violet degraded by CdS-WGM cavity is obvious, as shown in Figure 13 c, the change of dye concentration with time is significant, and the degradation rate is fast, as shown in Figure 13 d, the K value of crystal violet degraded by CdS-WGM cavity is 0.076 min -1 .

[0132] 200 mg of cadmium chloride and sodium sulfide were weighed and hydrothermally prepared CdS nanoparticles, and the CdS nanoparticles were dispersed in 200 mL of ethanol and sheared and dispersed for 1 h, and then divided into equal parts, each sample containing 5 mg of CdS. One part of the cadmium sulfide alcohol dispersion was directly dried as a control group.

[0133] Similarly, in the control sample, 80 mL of 30 mg / L crystal violet dye solution was added, and the light stirring was carried out for 30 min, and then the photocatalytic degradation was carried out under the light intensity of 0.5 KW / m 2 . Figure 14 a-c are the photos of the change of dye concentration sampled at intervals of 5 min, the absorbance curves sampled at intervals of 5 min, the curves of the ratio of dye concentration to initial concentration C / C0 with time within 40 min and the first-order kinetic fitting curves. As shown in Figure 14 a, the color change of crystal violet degraded by CdS is not obvious, as shown in Figure 14 c, the K value of crystal violet degraded by CdS is 0.052 min -1 .

[0134] From the experimental results of Example 7 and Example 8, it can be seen that the semiconductor-PS microsphere composite structure is universal for different semiconductor nanoparticle catalysts, and the photocatalytic efficiency is also obviously enhanced after ZnO and CdS are loaded on the surface of PS microspheres.​

Claims

1. A photocatalyst characterized by comprising: The photocatalyst is prepared by loading semiconductor nanoparticles on the surface of polymer microspheres with optical whispering gallery mode resonance characteristics after surface modification of the polymer microspheres; The weight ratio of the polymer microspheres to the semiconductor nanoparticles is (1-6):1; The semiconductor nanoparticles are at least one of titanium dioxide nanoparticles, zinc oxide nanoparticles and cadmium sulfide nanoparticles; The polymer microspheres with optical whispering gallery mode resonance characteristics are surface-modified by the following method: S1: adding a crosslinking agent, an initiator and a coupling agent into styrene or methyl methacrylate as an oil phase; S2: adding an aqueous solution containing a surfactant as an aqueous phase; S3: adding the oil phase into the aqueous phase for shearing emulsification, and then washing to obtain the surface-modified polymer microspheres, wherein the polymer material used for preparing the polymer microspheres is polystyrene or polymethyl methacrylate; The particle size of the polymer microspheres is 1-15 μm; the refractive index of the polymer material used for preparing the polymer microspheres is greater than 1.34; and the light loss of the polymer material in the wavelength range of 320-1000 nm is less than 2 dB / μm; The coupling agent is n-octyl triethoxysilane.

2. The photocatalyst according to claim 1, wherein The particle size of the semiconductor nanoparticles is less than 200 nm.

3. A method for preparing the photocatalyst according to claim 1, characterized by, The method comprises the following steps: S1: adding a crosslinking agent, an initiator and a coupling agent into styrene or methyl methacrylate as an oil phase; S2: adding an aqueous solution containing a surfactant as an aqueous phase; S3: adding the oil phase into the aqueous phase for shearing emulsification, and then washing to obtain the surface-modified polystyrene microspheres or the surface-modified polymethyl methacrylate microspheres; S4: dispersing semiconductor nanoparticles in an alcohol solution to form a dispersion, and then stirring the dispersion to load the semiconductor nanoparticles on the surface of the polystyrene microspheres or the polymethyl methacrylate microspheres, thereby obtaining the photocatalyst.

4. The method of claim 3, wherein the photocatalyst is prepared by the process of claim 1 or 2. The method satisfies one of the following conditions: a) when the semiconductor nanoparticles are titanium dioxide nanoparticles, adding acetic acid into the dispersion in step S4, and the addition amount of the acetic acid is 0.25%-2.5% v / v; b) when the semiconductor nanoparticles are cadmium sulfide nanoparticles, adding ammonia into the dispersion in step S4, and the addition amount of the ammonia is 0.25%-2.5% v / v.

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