Enhanced piezocatalytic, photocatalytic and piezo-/photocatalytic performance of diphasic Ba1−xCaxTiO3 nanowires near a solubility limit

Abstract

Advanced oxidation processes including piezocatalysis and photocatalysis are considered as promising strategies for environmental remediation. More efforts have been made to clarify the factors that can improve the catalytic efficiency in piezocatalysis. Diphasic Ba_1−xCa_xTiO₃ piezoelectric materials near a solubility limit have been found to exhibit potential for piezoelectric performance far beyond their corresponding single-phasic materials. It is interesting to explore how phase structures (single phase and diphase) will influence the catalytic performance of nanoscale piezoelectric materials. In this study, Ba_1−xCa_xTiO₃ nanowires were used as representative materials to explore the influence of phase structures on catalytic performance. It is found that when x = 0.2 (near the solubility limit), the Ba_1−xCa_xTiO₃ nanowires exhibit better piezocatalytic and photocatalytic performance. This can be ascribed to higher spontaneous polarization induced by the interaction of a ferroelectric tetragonal Ba-rich phase and a normal dielectric orthorhombic Ca-rich phase and band alignment of Ba-rich and Ca-rich phases, which can both effectively enhance charge carrier separation rates. In addition, with the simultaneous assistance of ultrasonic vibration and ultra-violet light, there is a coupling catalytic effect of Ba_1−xCa_xTiO₃ nanowires, with a rate constant k_obs of 71% higher than the simple sum-up of the rate constants of piezocatalytic and photocatalytic reactions. The increasing piezo-/photocatalytic degradation efficiency is mainly attributed to increased free charge carrier concentrations (thermally-excited and photo-induced charge carriers) and a strong piezoelectric field induced by the piezoelectric effect, which is beneficial for the separation of free charge carriers. We believe that this work provides mechanistic insights into how phase structures affect catalytic performance and a novel route to furnish environmentally-friendly catalysts that can efficiently utilize multiple energy sources.