Time-dependent DFT and experimental study on visible light photocatalysis by metal oxides of Ti, V and Zn after complexing with a conjugated polymer

Abstract

Density Functional Theory (DFT) and Time Dependent (TD)-DFT studies predict substantial modifications in optical properties of Transition Metal Oxides (TMOs) of Ti, V and Zn by complexing them with conjugated polymer polythiophene (PTh). The TMO nanostructures were synthesized and their complexes with polymers were fabricated using a chemical oxidative polymerization method. Coating of the TMOs with PTh and the nano-dimensional nature of the samples was confirmed by various morphological investigations such as infrared (IR), X-ray diffractographs (XRD), High Resolution Transmission Electron Microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM) techniques. The prepared samples were found to be a visible light driven photocatalyst. The sensitization of the complexes has been explained in terms of relative ordering of frontier orbitals of PTh and the TMO, and PTh qualified as an efficient photosensitizer for all three metal oxides on the basis of its electronic characteristics. Since the Highest Occupied Molecular Orbital (HOMO) of PTh lies well between the band gap of all three TMOs, the electron transfer from donor (PTh) to acceptor (TMO) is facilitated. The appreciable red shift in the absorption spectrum and decrease in the optical band gap calculated by Tauc's plot confirmed substantial reduction in the band gap of the formed complex in comparison to their bare counterparts. The isodensity plots established the PTh–TMO complexes as donor acceptor complexes and intermolecular charge transfer quantified the electron transfer from PTh (donor) to the TMOs (acceptor).