Effect of exposed facets of bismuth vanadate, controlled by ethanolamine, on oxidative coupling of primary amines

Abstract

This work firstly demonstrates the ethanolamine (ETA)-assisted hydrothermal synthesis of BiVO4, with different ratios of exposed {1 1 0}/{0 1 0} planes and relates this to performance in photocatalytic oxidative coupling of benzylamine under visible light. {1 1 0}-dominant BiVO4 exhibits outstanding photocatalytic activity at room temperature owing to synergistic effects of largely exposed {1 1 0}-oxidative facet along with excellent charge generation and migration abilities, as evidenced by X-ray diffraction patterns, electrochemical impedance spectra, and photocurrent responses. The catalyst can successfully transform benzylamine derivatives to corresponding imines with selectivities of >85%, indicating a wide scope of amine substrates that can be used with the developed catalyst. Based on radical scavenging, spin-trapping EPR, and Mott-Schottky results, a plausible oxidative coupling mechanism via a O2[rad]–-assisted route and band energy diagram of the catalyst are proposed. This work highlights the influence of ETA in controlling resultant exposed crystal facets of the final BiVO4, which is the main factor governing oxidative amine coupling activity. Importantly, the tunability of exposed {1 1 0}/{0 1 0} facet of BiVO4 controlled by ETA as well as a correlation between {1 1 0} facet and the coupling activity of benzylamine firstly disclosed in this work could be readily extended for designing functional catalysts with desired performances.