In1–xGaxBO3 (0 ≤ x ≤ 0.5) – Solvothermal Synthesis, Morphology, and Performance in Photocatalytic Water Reduction

Partial solid solutions of In1–xGaxBO3 (0 ≤ x ≤ 0.5) were synthesized by the solvothermal method, and they were characterized by powder X-ray diffraction, scanning and transmission electron microscopy, UV/Vis absorption spectroscopy, and N2 adsorption–desorption, in order to identify the phase purity and micromorphology. Nanocrystallites of InBO3 exhibit a particular anisotropic growth along the [110] direction, forming spindlelike morphology (with a diameter of ca. 20 nm and a length of ca. 200 nm). These nanocrystallites further aggregate into microspheres. With Ga3+ substitution, the anisotropic growth was depressed; the nanocrystallites thus exhibited a typical rodlike morphology. Metal borates are well-known optical materials; however, their photocatalytic properties have been rarely studied. Here, post-annealing under O2 flow at 350 °C improved the photocatalytic H2 evolution rate of InBO3 from 18.2(6) to 29.5(8) µmol h–1 g–1. A loading of Pt, RuOx, or NiOx as cocatalyst resulted in further enhancement of the H2 evolution rate, with an optimal value of 56.1(5) µmol h–1 g–1 under UV light.