The Effects of Preparation Conditions for a BaNbO2N Photocatalyst on Its Physical Properties

BaNbO2N is a semiconductor photocatalyst active for water oxidation under visible-light irradiation up to lambda=740 nm. It is important to understand the nitridation processes of precursor materials to form BaNbO2N to tune the physical properties and improve the photocatalytic activity. Comprehensive experiments and analyses of temperatures, durations, ammonia flow rates, and barium/niobium ratios in the precursor during the nitridation process reveals that faster ammonia flow rates and higher barium/niobium ratios in the precursors help to suppress reduction of pentavalent niobium ions in the nitridation products and that the use of a precursor prepared by a soft-chemistry route allows the production of BaNbO2N at lower temperatures in shorter times than the use of physical mixtures of BaCO3 and Nb2O5 because the niobium species is dispersed among the barium species. BaNbO2N prepared by the soft-chemistry route exhibits comparatively higher activity than that prepared from physical mixtures of BaCO3 and Nb2O5, probably because of lower nitridation temperatures, which suppress excessive dissociation of ammonia, and thereby reduce pentavalent niobium ions, and intimate interaction of niobium and barium sources, which lowers the densities of mid-gap states associated with defects.