Flux Synthesis of Single Crystal Bismuth Vanadate (BiVO4) Nanowires and their Visible Light Driven Photocatalytic Water Oxidation Properties

Abstract

Bismuth vanadate (BiVO4) is a well-studied semiconductor for visible light active photocatalyst for the oxygen evolution reaction (OER). In this study, single-crystal BiVO4 nanowires were synthesized for the first time. The nanowires are obtained by recrystallization of BiVO4 microparticles from NaVO3 flux in the 550°C – 700°C temperature range. They exhibit an average thickness of 433.4 ± 110.6 nm and lengths exceeding 20 μm. X-ray diffraction and electron microscopy confirm that the nanowires are single crystals in the monoclinic Scheelite structure with the [010] crystal direction oriented along the principle wire axis. The nanowires have an optical band gap of 2.41 eV and oxidize water under visible light (390 mW/cm²) at a rate of 28.75 µmol/h. The apparent quantum efficiency for oxygen evolution is 0.44% at 405 nm. The relatively low photocatalytic activity of the nanowires can be explained by the absence of a facet-induced charge separation mechanism. Indeed, photolabeling experiments with silver (+) and manganese (2+) ions demonstrate that both photoholes and electrons are extracted along the cylindrical nanowire surface. The fiber morphology makes the BiVO4 nanowires uniquely suited for membrane applications in solar energy conversion and photocatalysis.