Tuning Electronic and Optical Properties of TiO2 as a Visible Light Photocatalyst A DFT Investigation

Abstract

Semiconductor photocatalysis promises to alleviate the energy crisis by harnessing solar energy and provide an ideal solution to address the other environmental challenges. Doping TiO2 with noble metals, transition metals, cations, anions has yielded very promising results in enhancing photocatalytic activity of TiO2 in the visible region and its role in generating alternate forms of energy. Here, using first-principles density functional theory, the modulated electronic and optical properties of TiO2 with Pt/Ag substitutional dopants of varying concentration are investigated. Our calculations reveal the significant decreasing trend in the band gap of TiO2 while increasing the Pt (direct band gap) and Ag (indirect band gap) impurity concentration from 4.17% to 8.33% to 12.5%. Density of states reveal strong hybridization between the impurity bands with Ti-(3d) and O-(2p) bands near the Fermi level. The charge transfer mechanism depicts the delocalized electron cloud forming a strong bonding between the dopants (Pt/Ag) and oxygen of TiO2. Moreover, the absorption spectra of the Pt doped TiO2 structures have a broad peak at the visible range of energy spectrum with maximum absorption. The calculated reflectivity, energy loss function and extinction coefficient show the enhanced optical properties of doped TiO2 compared to its pristine form. The obtained results predict the way to tailor the optical properties of Pt/Ag-doped TiO2 as an efficient photocatalyst in the visible region. An exciting research frontier recently has been the use of two- dimensional sheets exclusively composed of reactive facets of TiO2 catalyst to explore the possibility of enhanced photocatalytic activity. We have investigated the optical properties of bulk and two-dimensional TiO2 nanosheets, narrowing on how reduced dimensionality and dimension enhance the photocatalytic reactivity of TiO2.