Development of a bio-mediated technique of silver-doping on titania

The doping of semiconductor materials is conventionally carried out in chemical and energy intensive processes to have the visible light responsive photocatalytic activity. Herein, we first time report a new and green technique of metal doping viz., bio-mediated doping (BMD) of Ag on onto TiO2 (Ag/TiO2) using the aqueous extract of Sechium edule. The immobilization efficiency of Ag+ at the neutral pH was around 71-84% with the initial amount of Ag varying from 0.25 to 2% (w/w w.r.t. TiO2) and, the immobilized Ag+ was completely doped as no Ag+ ions were detected owing to BMD. The BMD technique had dramatically shifted the optical absorption (similar to 500 nm) to the visible domain and, the band gap of TiO2 was reduced to 2.5 eV. The crystallite size of TiO2 with the increase in Ag-loading was increased significantly because of Ag+ induction into the Ti4+ lattice and, there was about 10% (maximum) phase transformation. In the case of Ag/TiO2, the absolute value of zeta-potentials increased notably at pH > pH(zpc) that had resulted from the rise in oxygen vacancies and, Ag/TiO2 were mostly present as an individual nonclustered unit in water. Ag/TiO2 exhibited 98% degradation of Congo red dye under the visible light illumination. The electron spin resonance spectra confirmed that O-2 formed caused the high photocatalytic activity of BMD Ag/TiO2. (C) 2016 Elsevier B.V. All rights reserved.