Photocatalytic activity of Fe-modified bismuth titanate pyrochlores: Insights into its stability, photoelectrochemical, and optical responses

This work examines the catalytic activity of a pyrochlore phase bismuth titanate (Bi2Ti2O7–BTO) in driving the photo-assisted decomposition of a model pollutant, methyl orange (MO). The photoactivity of the BTO has been probed with the inclusion of Fe with BTO and with the addition of a co-catalyst- Pt external to the Fe-BTO. The addition of Fe enhances BTO photoactivity by ∼38%, while the presences of Pt along with Fe demonstrate the most favorable increase at 88% compared to the plain BTO. The MO degradation follows a pseudo first order kinetics. Under 100% visible light illumination, all catalysts demonstrate photoactivity. Specifically, a 10%, 15%, and 21% degradation of MO with BTO, Fe-BTO, and Pt/Fe-BTO, respectively, is noted. Stability analysis indicates that a mild oxidative treatment at 350 °C is sufficient to recover ∼86% of the photoactivity lost over 6 h of exposure to photoillumination in 2 h increments. Further, for the first time, complementary photoelectrochemical and optical measurement tools have been used to systematically probe the functioning of BTO in the presence of Fe and Pt. Electrochemical impedance, chronopotentiometry (intermittent illumination studies), and fluorescence measurements reveals (i) Fe aids in visible light assisted charge separation, (ii) Pt is not as effective with visible light as it is with UV, and (iii) a high concentration of hydroxyl radical in the Pt/Fe-BTO is the basis for improved photoactivity of the catalysts. Using bismuth titanate pyrochlore as a case study, this work demonstrates the approach to leverage optical and photoelectrochemical tools for systematic analysis of other multi-metal oxides that belong to the sillenite, delafossites, pyrochlores, and scheelites.