Synthesis And Photocatalytic Activity Of Ag Nanoparitcles Decorated TiO₂ Inverse Opals

Recently, the problems of environment pollution and energy shortage become more and more serious with the development of industry. Photocatalytic degradation of harmful toxic pollutants and photocatalytic synthesis using semiconductor photocatalysts have induced extensive attention. Among all these candidates, TiO₂ has been considered the ideal photocatalytic materials and obtained deeply studies. Since TiO₂ are resource-rich, cheap, non-toxic, chemical stability and easy to dopant. However, the photocatalytic activity of TiO₂ was reflected under the ultraviolet light with wavelength shorter than 380 nm. Furthermore, the practical application of TiO₂ was greatly restricted by its lower quantum yield, which comes from the recombination of photogenerated charges. Thus, it is mostly important to modify TiO₂.There are mainly two methods for TiO₂ modification. The one is chemical modification, including metal and nonmetal doping, noble metal deposition and compositing with other semiconductors. The other is physical modification, such as preparation TiO₂ nanotubes/rods, TiO₂ nanowires, TiO₂ nanobelts, TiO₂ composition which has core-shell structure, micro/mesoporous TiO₂ and coupled with photonic crystals gotten ordered porous TiO₂ inverse opals. Based the above ways, we combined physical and chemical modification and fabricated Ag nanoparticles decorated TiO₂ inverse opals. The main works are as following:1. Colloidal crystal templates were prepared on the glass substrates using SiO₂ microspheres via vertical sedimentation.2. SiO₂ templates were filled with TiCl₄ sol through sol-gel dip-coating. Gelation of fillers was by heat treatment, then TiO₂ crystallization by high temperature calcining. The removal of templates was using hot NaOH solution and achieved ordered porous TiO₂ inverse opals finally.3. Ag nanoparticles with average size about 10 nm were deposited on TiO₂ inverse opals by a facile wet chemical route.4. Crystal phase, surface morphology and microstructure, the elemental composition and chemical state,optical properties were investigated by X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS),UV-vis absorption spectra, and photoluminescence spectroscopy (PL). 5. The experiments of methylene blue degradation confirmed that the result catalysts have enhanced photocatalytic activities and stability, especially the visible-light photocatalysis. Furthermore, the remarkable improvement in methylene blue degradation was appearing on TiO₂ inverse opal with optimizing AgNO₃ concentration 10 mM in the precursor solution, which exhibited 4.20 times visible-light reaction rate constant comparing with conventional Ag loaded TiO₂ film without ordered porous structure. This obvious enhanced visible-light photocatalytic activity can be attributed to the synergetic effect of Ag nanoparticles surface plasmon absorption and the multiple scattering effect of inverse opal ordered porous structures.