Preparation And Performance Investigation Of Surface-Modified Titanium Dioxide Photocatalysts

With the increasing concern over global environmental pollution and energy crisis,photocatalysis technique provides a new, hopeful approach to solve the two major problemsthrough efficient utilization of solar energy. In1972, Fujishima and Honda discovered thephenomenon of photocatalytic splitting of water on a TiO₂electrode under ultraviolet light.This is a groundbreaking work in the field of chemical conversion of solar energy. Since then,TiO₂photocatalyst becomes a hot research topic, and has been considered to be the mostpromising photocatalytic material. Although TiO₂has many advantages such as chemicalstability, non-toxicity, and high photocatalytic activity under UV light, the widespread use ofTiO₂material is limited by its wide bandgap energy, which causes the catalyst to exploit onlya very small proportion （about3⁵%） of solar radiation. Therefore, it is highly desired todevelop strategies of shifting the photo-responsive range of TiO₂to visible spectral region.This thesis focuses on the surface-modification strategy to extend the photo-responsiverange of TiO₂with the aim of achievement of visible light photocatalysis. Firstly, porous TiO₂was selected as host material for surface modification. This host TiO₂material with a largesurface area and anatase structure was prepared by a light-induced approach. Its structuralperformance was optimized by various characterizations such as XRD and N2adsorption.Furthermore, the optimal host material was modified by various metal ions. It is concludedthat iron-ions modification results in the formation of additional surface energy levels in TiO₂,extending the photo-responsive range. By means of surface photovoltage spectroscopy （SPS）, transient photovoltage （TPV） and EPR techniques, we investigated the effects of surfacemodification on interfacial electron transfer. Using the photocatalytic degradation ofmethylene blue （MB） as model reaction, we studied the visible light photocatalyticperformances of the materials. The photocatalytic results show that simple surfacemodification in indeed achieves the ultimate goal of visible-light-driven photocatalysis, andthe photocatalytic erformance of iron-modified TiO₂is superior to that of nitrogen-dopedTiO₂.Secondly，we present a novel in situ reduction strategy to modify porous TiO₂by noblemetal nanoparticles. By using light-induced synthetic route, we successfully prepared aporous TiO₂material with a large number of surface Ti³⁺species. Due to the high reducibilityof Ti³⁺, metal ions can be directly reduced to metal nanoparticles on the surface of porousTiO₂, leading to the formation of a composite material. Interestingly, we found that a largenumber of H2gas released during the process of surface modification. A preliminarymechanism on this phenomenon was provided. Further works on the catalytic application ofthe porous TiO₂/metal nanoparticles are under investigation.