Tunable Photocatalytic Efficiency of Nanocomposites for Environmental Applications

Titanium dioxide (TiO2) is one of the most efficient photocatalyst due to its excellent potocatalytic properties for organic pollutants. However, the large band gap of TiO2 and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. The photocatalytic efficiency of TiO2 can be enhanced by modification of surface and by inhibiting electron hole recombination rate with doping of Ag. The Ag doped TiO2 act as electron trapping to reduce the recombination rate of photogenerated electron–hole pairs. The electron storage on Ag nanoparticles shift the Fermi level of Ag-TiO2 nanocomposite thin film to more negative potential, and this improves the photocatalytic performance of film by capturing the photogenerated electrons. However, photocatalytic efficiency of TiO2 under solar radiation is very low due to its large band gap. In the present case photocatalytic efficiency of TiO2 is improved by doping nitrogen into TiO2 which creates deep level as well as oxygen vacancies located at 0.71–1.18 eV below the conduction band of TiO2. The introduction of localized N2p energy level of dopant above the O2p valence band maximum of TiO2 leads to band gap narrowing, which further causes shifting of absorbance of N-TiO2 from UV light to visible light region. Hence nitrogen doped TiO2 shows higher photocatalytic activity than that of pure TiO2. The as-synthesized TiO2-SnO2 composite showed excellent photocatalytic efficiency under UV light irradiation compared to pure TiO2 and SnO2. When a large band gap semiconductor (SnO2) is coupled with a small band gap semiconductor (TiO2) with a more negative CB level, CB electrons can be injected from the small band gap semiconductor to the large band gap semiconductor. Thus, a wide electron hole separation is achieved. This separation can help in enhancing of photocatalytic efficiency. Further the semiconductor quantum dots have been great attention as a material for solar energy conservation into electricity due to their electrical and optical properties. Semiconductor quantum dots show promising developments for the next generation of solar cells.