Preparation Of Nanometer TiO₂ Catalyst Doped With Upconversion Luminescence Agent And Investigation On Degradation Of Dyestuff Wastewater Using Visible Light

The environment and the sources of energy are main problems people facing and demanding prompt solutions in the 21 century. With unique functions such as reaction under room temperature and being directly drived by solar energy, photocatalysis becomes one kind of ideal technology for enviromental pollution treatment and production of clean sources of energy, moreover it has a broad application prospect and significant economic benefits in the fields of enviromental protection; clean sources of energy; health and medical treatment; building materials; auto industry and food fresh keeping and so on. Therefore, photocatalysis is regarded highly by scientific communities, government departments and enterprises.TiO₂ as photocatalyst has widely been used to photodegrade these organic pollutants for its proper bandwidth, relatively high catalytic reactivity, physical and chemical stability, avirulence and cheapness and so on. However, the ultraviolet light (λ< 387 nm) must be required to irradiate the TiO₂ photocatalyst for its broad band-gap (Eg = 3.2 eV). In general, the sunlight only contains 5% ultraviolet light. Hence, the photocatalytic degradation method treating wastewaters needs costly equipments and large numbers of energies as light source, which restricts the common application of TiO₂ photocatalysis. Much research work has been drawn on modifing TiO₂ catalysts, making the TiO₂ powders as photocatalysts absorb the solar light at large extent. To improve catalytic activity in visible light, some people prepared nano TiO₂ particles with quanta size effect. Many modified methods were adopted such as doping of transition-metal ions, doping of non-metal ions combination of narrow band-gap semiconductors, dyes sensitization and surface chelation and derivation, besides, some special treatment methods( UV light irradiation, ultrasonics disperse and H2O2 dipping) were aslo used. These methods indeed do its work in extending the range of absorption wavelength of TiO₂ catalysts, however, catalytic ability cound not be improved throughly. the electron-cavity pairs generated by excitation of various wavelength lights are different, because their oxidation-reduction potentials are different. To obtain cavities with higher oxidation potential, the ulthraviolet lights must be used for excitation TiO₂. Therefore, we thought whether there are some substances which can turn visible lights into ultraviolet lights to satisfy the requirement of TiO₂ photocatalysts. Fortunately, the upconversion luminescence materials containing rare earth metal ions are just what we want to adulterate to general TiO₂ photocatalysts.In this work, two new upconversion luminescence agents containing Erbium (Er) element was synthesized and then mixed into TiO₂ powder to prepare novel doped TiO₂ photocatalyst with upconversion luminescence. Its photocatalytic activity was checked through the photocatalytic degradation reaction of various hazardous dyes as model compound under the visible light irradiation emitted by three basic color lamps and solar light irradiation, with comparation of undoped TiO₂ catalyst. The characters of upconversion luminescence was detected by upconversion fluorescent spectrum, doped and undoped TiO₂ powder was charactered by XRD and TEM; Process of degradation was detected by UV-Visible spectrum and ions spectrum. The results show that the degradation ratio of dyes in the presence of doped TiO₂ powder under visible light irradiation within certain time period was obviously higher than the corresponding degradation ratio in the presence of undoped TiO₂ powder,which realized the purpose to degrade hazardous compound in industrial wastewater by visible light. In addition, under solar light irradiation directly, it also show higher degradation ratio, which proved a promising method using sunlight for treating the industry dye wastewater in great force.