Publication

Abstract : In the present study, the role of polymeric surfactant polyvinylpyrrolidone (PVP) in enhancing optical absorption of PVP capped TiO 2 nanoparticles in the visible region is investigated. When the PVP capped hydrous amorphous TiO 2 is calcined at temperature less than thermal degradation temperature of PVP, the polymeric surfactant alters the band structure of TiO 2 nanoparticles resulting a significant change in optical absorption by introducing Ti 3+ ions and oxygen vacancies in the band gap. The induced surface modifications of TiO 2 nanoparticles by PVP were studied using micro Raman, XPS, UV–Vis., EPR and photoluminescence spectroscopy. The Raman active mode at 144 cm −1 which is ascribed to anatase TiO 2 is shifted and broadened in PVP capped samples (TP 1 ) due to oxygen related stoichiometry defects. The excess oxygen vacancies in TiO 2 lattice leads to the formation of Ti 3+ ions to maintain the electrostatic balance. The existence of Ti 3+ ions is also confirmed from EPR spectra. The observed red shift of optical absorption spectra is due to reduction in the band gap of PVP capped nanoparticles. Furthermore the deconvoluted Ti2p 3/2 and Ti2p 1/2 XPS peaks shows prominent shoulder peaks at 457.7 and 463.5 eV corresponding to Ti 3+ . The formation of Ti 3+ upper shifts the O1s line of TP1 due to transfer of charges from oxygen atoms of PVP to Ti 4+ ions. Besides PL emission at 481 nm confirms the formation of Ti 3+ due to surface oxygen vacancies induced by PVP. The surface defects Ti 3+ and oxygen vacancies act as trap centers and extend the lifetime of charge carriers. © 2019