Fabrication Of Photonic Crystal Particles And Their Applications In Photocatalysis

Recently,inverse opal TiO₂ photonic crystal（PC）as three-dimensional ordered macroporous material has received extensive attention because of its photonic band gaps（PBGs）and photon localization effect.PC can be used as highly active photocatalysts,because it can improve the photon absorption efficiency.As far as we know,most research is focused on the fabrication and application of PC membranes rather than PC powders.It is well known that photocatalysts in the form of powder has shown higher catalytic activity than that of membranes.Here we explored the fabrication of PC particles and further investigated their application in photocatalysis.We fabricated TiO₂ photonic crystal beads and explored their catalytic activity,and then investigated the effect of light scattering of PC particles on the catalytic activity of photocatalysts powders by adding PC particles into photocatalysts powders.The research details are as follows.Firstly,a new method,namely extractant assisted–microemulsion method,was developed to fabricate photonic crystal beads（PCBs）.PS（Polystyrene）microspheres aqueous suspension was added as dispersion phase into continuous phase of a mixture of n-octanol,butanol and a surfactant.W/O droplets formed in the mixture as an emulsion.Then PS opal photonic crystal beads（PS opal PCBs）were obtained after the solvent in W/O droples was fully extracted by continuous phase.The factors that may affect the sizes,morphology and quality of PCBs were explored.It was shown that the average sizes of PCBs became smaller and the quality became worse with the increase of the surfactant.When the volume ratio of n-octanol and butanol was higher than 1:1,the PCBs were polyhedral,while when the ratio was less than or equal to 1:1,the PCBs were spherical.The PS particle’s content of the suspension mainly affected the sizes of PCBs,and the average sizes increased with the increase of PS particle’s content.Secondly,we prepared inverse opal TiO₂ PC membranes through fabricating the PS opal PC membranes,filling the PC membranes with TiO₂ through liquid phase deposition（LPD）technique and subsequent calcinating the PC membranes to remove the PC membrane templates.To obtain the PC particles,the inverse opal TiO₂ membranes were ground by ultrasonication.The prepared PC particles were about 5-40 μm,and their PBGs were fully maintained.Thirdly,using PEG2000 as mesopore-forming agent and PS opal PCBs as templates,we fabricated the macro/mecroporous inverse opal TiO₂ PCBs for the first time and explored the effect of mesopore-forming agents content on the catalytic activity of macro/mecroporous inverse opal TiO₂ PCBs using photodegradation of methyl orange（MO）as the probe reaction.The results showed that the catalytic activity of inverse opal TiO₂ PCBs was enhanced when mecropores were formed in the inverse opal TiO₂ PCBs,and the enhancement was related to the content of PEG2000.When the PEG2000 was 2.1 wt%,the samples showed the highest catalytic activity.Compared with the samples prepared without the PEG2000 mesopore-forming agent,the reaction rate constant of inverse opal TiO₂ PCBs increased by 41% because of their large surface area and the enhancement of mass transport process inside the TiO₂ PCBs.Finally,we synthesized CdS sensitized TiO₂（CdS/TiO₂）nanoparticles as the visible light responsible photocatalysts,and added TiO₂ inverse opal particles into CdS/TiO₂ to explore the effect of light scattering of inverse opal TiO₂ particles on the catalytic activity of CdS/TiO₂ using photodegradation of MO as probe reaction.The results showed that inverse opal TiO₂ particles could improve the catalytic activity of CdS/TiO₂ and the enhancement was related to the position of PBGs of inverse opal particles.When the PBGs were located at the absorption peaks of CdS/TiO₂,the best catalytic activity could be achieved.Because PC particles had strong reflection of light with its wavelength located in PBGs,leading to the multiple scattering of light in the reaction system,the activity of CdS/TiO₂ was enhanced.Moreover,the catalytic activity of CdS/TiO₂ showed a trend of first increase and then decline with the amount of PC particles since the photocorrosion of CdS/TiO₂ could be attributed to the strong light scattering of PC particles.