Study On Preparation, Doping And Photocatalytic Activity Of TiO₂ Colloid Via Microwave-Irradiation

Environment pollution and energy resource crisis are the hot topics today and, effective utilization of solar energy to solve pollution problems attains much attention now. With outstandingly characteristics in widely utilization of solar energy, low energy consumption, moderate reaction condition, convenient operation, no secondary pollution, and good oxidation degradation for bio-refractory organic pollutants, the semiconductor oxide heterogeneous photocatalytic technology is a hot research topic in environment science. Among those semiconductor oxides, TiO₂ has excellent photoelectric perfermance, which can activate photoelectron, occuring redox reaction on surface, decomposing most organic pollutants and mineralizing them into CO₂, H2O and other small inorganic molecules completely under light irradiation. TiO₂ is also chemical stable, safe and imnoxious, abundant source. However, the energy band-gap of TiO₂ in the anatase crystalline is wide (Eg≈3.2eV) and it can only catalyze the degradation of persistent organic pollutants under ultraviolet light (300 nm～400 nm) irradiation, which accounts for only a small part (3%～5%) of solar energy with low. quantun yield. The present work is focused on preparation of doped TiO₂ to get good photocatalytic performance catalyst.Using Ti(SO4)2 as precursor, water worked as the solvent, a white precipitation of Ti(OH)4 was obtained by the addition of ammonia aqueous adjusting the pH as 7～8, HNO3 was used as peptizer, CdS was used as doping agent. Then, the mixture aqueous was microwave heated for different hours at low temperature for crystallization. Finally, nanocrystalline TiO₂ sol was obtained. The effects of pH , microwave heating temperature and titanium source on the photocatalysis activity were investigation.The results indicated that CdS doped nanosize TiO₂ colloid photo-catalytic activity is under the follow conditions: pH=1.0, microwave power, 800W; microwave reaction time, 1.5h; microwave reaction temperature, 90℃. Sulfur ions (S6+) substituted partially for the lattice titanium ions (Ti4+), which resulted in the localized crystal deformation of TiO₂ and the bandgap between valence band and conduction band narrowed. chemical valence state was changed by S4+ that it entered TiO₂ lattice., and it destroyed charge balance of original system. In order to maintain charge balance, little titanium ion released redundant electron and changed into higher valence. Uv absorption edge was moved 20 nm, S had entered TiO₂ lattice, and chemical bond was formatted, so photoresponse range of TiO₂ collid was changed.Nitrogen was existed in two doped states: Nitrogen was existed in two doped states: one was substitutional N impurity, which formation joint of Ti-N-Ti doping, another was interstitial impurity by chemical-adsorption of NH3 or NH4+; and the bandgap between valence band and conduction band narrowed. Visible-light photocatalytic activity obtained by N, S-codoped nanosize TiO₂, because of a new impurity was formed.The photocatalytic activity of the sol was evaluated on the degradation of methylene orange, methlene blue and rhodamine B under the UV irradiation or visible-light. The results showed the CdS doped TiO₂ sol had high photocatalytic activity. With the sol prepared under the optimized conditions, the degradation of the methylene orange reached 97.1% in 30 min. it exhibited high photocatalytic activity.