In 1– x Ga x BO 3 (0 ≤ x ≤ 0.5) – Solvothermal Synthesis, Morphology, and Performance in Photocatalytic Water Reduction

Partial solid solutions of In 1– x Ga x BO 3 (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 N 2 adsorption–desorption, in order to identify the phase purity and micromorphology. Nanocrystallites of InBO 3 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 Ga 3+ 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 O 2 flow at 350 °C improved the photocatalytic H 2 evolution rate of InBO 3 from 18.2(6) to 29.5(8) µmol h –1  g –1 . A loading of Pt, RuO x , or NiO x as cocatalyst resulted in further enhancement of the H 2 evolution rate, with an optimal value of 56.1(5) µmol h –1  g –1 under UV light.