On the design and synthesis of titanium dioxide-graphene nanocomposites for enhanced photovoltaic and photocatalytic performance

Abstract

This thesis describes my efforts to incorporate graphene into TiO2 films and photocatalysts and my investigations into the photovoltaic and photocatalytic properties of the resulting composites. The composites were synthesized using a photocatalytic method that effectively dispersed the graphene throughout the nanoparticle TiO2 matrix. The integration of graphene increased the photocurrent generated by the TiO2 in response to UV light tenfold. I attribute this enhancement to the ability of RGO to capture photogenerated electrons from TiO2 and conduct them efficiently to a conducting substrate: transient photocurrent measurements and electroimpedance spectroscopy showed a fourfold increase in the electron lifetime of RGO-TiO2 films. The better electrochemical properties of the RGO-TiO2 composite also resulted in better photocatalytic activity. Composite powders dispersed in solution completely mineralized the organic pollutant phenol three times faster than TiO2 alone. Finally, I observed that the RGO-TiO2 composite demonstrated a photovoltaic and photocatalytic response to visible light. The composite generated a significant photocurrent in the visible spectrum between 440 and 700nm, with a maximum response at 540nm. The strength of the visible response depended on the degree of exfoliation of the RGO, indicating that intimate contact between the two materials is critical to this effect. Ab inito studies of the interface interaction showed that the close proximity of the RGO induced a high-lying valence band and low-lying conduction band in the TiO2 band gap, which may be responsible for the effect.