Evidence of charge transfer across the organic-inorganic hetero-junction based visible light driven photo-catalyst

Organic-inorganic hetero-junction based catalysts with efficient charge separation ability for superior photo-catalytic activity have been developed by chemical methods. Titanium dioxide (TiO2) and polypyrrole (PPy) as single photo-catalyst have been investigated and compared with TiO2/PPy hetero-junction composite. TiO2/PPy composite has enhanced efficiency for the degradation of toxic organic dye methylene blue (MB) through the charge transfer route. Broad curves in UV-Vis spectra arise due to polaron and bipolaron in PPy and TiO2/PPy composite. The de-localized polaron (Landé g factor value of 1.99) was further detected by electron spin resonance (ESR). The effect of polaron-bipolaron on the structure of as-synthesized PPy and TiO2/PPy composite has been explored by Raman spectroscopy. The oxidation state of different species and electronic structures below the Fermi level has been investigated by x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), which provides molecular orbitals insight and charge transfer state across the hetero-junction TiO2/PPy composite. Collectively, UPS and UV-Vis spectroscopy gives the energy positions (valence/ HOMO band and conduction band (C.B.)/LUMO) for TiO2 and PPy having straggled type band alignment which confirms the hetero junction in the composite.