The Preparation And Photocatalytic Activities Of TiO₂ And TiO₂/SrTiO₃ Photonic Crystals

The current rapid industrial development causes serious energy and environmental issues. Photocatalysts could convert solar enenrgy into chemical energy and achieve photodgradation and water splitting （H2 or O2 evolution） .As a result,photocatalysis could be a practicable solution of energy and environmental issues.TiO₂ is the most widely studied photocatalyst because of its chemically stability,biological non-toxicity and low cost. Unfortunately, owing to its wide band gap （Eg =3.2 eV）, TiO₂ only absorbs the UV light of solar spectrum. Several strategies, such as doping, heterojuction, co-catalysts and nanosizing were thoroughly investigated to improve the photocatalytic performance of TiO₂.Photonic crystals are some manufactured periodic structures form by two materials which have different dielectric constant. Similar to the electrons in crystals,photons in photonic crystals are influenced by the periodic structure. Photonic band gap and slow photon effect are the two main characteristics of photonic crystals.In this work, firstly, monodisperse polystyrene colloidal were synthesized by dispersion polymerization method. Secondly, opal templates were synthesized onto FTO conductive glass by vertical deposition method （solvent-evaporation-induced self-assembling ）. Thirdly, TiO₂ precursors were infiltrated into the intervals of opal templates by sol-gel methods, then TiO₂ inverse opal photonic crystals were synthesized after annealing. Finally, TiO₂/SrTiO₃ photonic crystals were synthesized by hydrothermal method. Main conclusions are as follow:（1） Monodisperse polystyrene latex colloidal were synthesized by dispersion polymerization method （initiator: KPS, stabilizer: PVP）. Beads sizes were controlled by the amount of KPS. Opal templates were synthesized onto FTO by solvent-evaporation-induced convective assembling method. FTO hydrophily,evaporation temperatures, colloidal concentrations, sizes and materials of vessels were optimized to synthesize high quality opal templates.（2） TiO₂ precursors were infiltrated by sol-gel method. High quality TiO₂ inverse opal photonic crystals were synthesized by controlling the ratios of sol and speeds of dip-coating. The photonic bang gap （PBG） would be controlled by the sizes of PS spheres.（3） TiO₂/SrTiO₃ heterojunction was synthesized by hydrothermal method. The sizes and amounts of SrTiO₃ could be controlled by hydrothermal reaction time. With the optimized reaction time ,the photo-current could enhanced 82%, and photocatalytic activities of TiO₂/SrTiO₃ photonic crystals had increased 56% due to the heterojunction function of charge separation.