A Study On Photocatalytic And Photoelectric Properties Of TiO₂

The field of photocatalysis can be traced back more than 80 years to early observations of the chalking of titania-based paints and to studies of the darkening of metal oxides in contact with organic compounds in sunlight. During the past 20 years, it has become an extremely well researched field due to practical interest in air and water remediation, self-cleaning surfaces etc. However, the mechanisms by which certain types of organic compounds are decomposed completely to carbon dioxide and water, for example, have not been quite well understood.In this discussion, using P25-TiO₂ and anatase single crystal with a large percentage of reactive facets as catalysts, we studied their photocatalytic activity in photodegradation of some specific small molecular substrate and dyes under UV irradiation. By contrast with different conditions reaction rates, the operating mechanism of the photocatalytic degradation of trichloroacetic acid (TCA) was investigated. We also discovered a high-selective oxidation reaction by P25-TiO₂ photocatalysis in water. Further, we analyzed anatase single photocatalytic activity combining with its photoelectric properties.1. TiO₂-assisted photocatalytic degradation of TCA under UV irradiation by using P25 and kinetic hydrogen isotope effect is examined to reveal the photocatalytic mechanism. Experimental results demonstrate that TCA shows very similar dechlorination degradation rates under both aerobic and anaerobic conditions. But we detected dichloroacetic acid as the intermediate of TCA degradation only in absence of dioxygen. So we considered that the reduction to DCA is a pathway for TCA degradation under anaerobic condition. We further detected obvious difference in kinetic characteristics between D₂O and H₂O solutions for the TCA degradation and DCA production. Combining with the Arrhenius plots in D₂O and H₂O, we deduced a linear H atom transfer involving a tunneling pathway through nonplanar pericyclic TS.2. For organic synthesis, the selectivity of the TiO₂-photocatalyzed oxidation is unsatisfactory in aqueous system due to the photo-generated holes of TiO₂ and generated OH radical having high oxidative potential. Here, we report a good selectivity photocatalytic oxidation of hydrazo derivatives by a TiO₂ aqueous. When the conversion reached up to 55% , the selectivity is higher then 80%.3. TiO₂ single crystals with highly reactive surfaces have long been studied. Here, we have synthesized uniform anatase TiO₂ single crystals with a high percentage of {001} facets using hydrofluoric acid as a morphology controlling agent by hydrothermal synthesis. We further examined its photoelectric properties by surface photovoltage spectroscopy,surface photocurrent spectroscopy technology. Comparing with P25 and common anatase catalysts, we determined its catalytic activity for degradation of dyes. We analyzed the relationship between its photoelectric properties and catalytic activity.