New High-Pressure Gallium Borate Ga₂B₃O₇(OH) with Photocatalytic Activity

Abstract

The new high-pressure gallium borate Ga2B3O7(OH) was synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 10.5 GPa and 700 °C. For the system Ga-B-O-H, it is only the second known compound next to Ga9B18O33(OH)15·H3B3O6·H3BO3. The crystal structure of Ga2B3O7(OH) was determined by single-crystal X-ray diffraction data collected at room temperature. Ga2B3O7(OH) crystallizes in the orthorhombic space group Cmce (Z = 8) with the lattice parameters a = 1050.7(2) pm, b = 743.6(2) pm, c = 1077.3(2) pm, and V = 0.8417(3) nm(3). Vibrational spectroscopic methods (Raman and IR) were performed to confirm the presence of the hydroxyl group. Furthermore, the band gap of Ga2B3O7(OH) was estimated via quantum-mechanical density functional theory calculations. These results led to the assumption that our gallium borate could be a suitable substance to split water photocatalytically, which was tested experimentally.

Exploration into the Syntheses of Gallium‐ and Indiumborates under Extreme Conditions: M5B12O25(OH): Structure, Luminescence, and Surprising Photocatalytic Properties

“…The M −O bond lengths in the octahedra of Ga2 and In2 are hence slightly longer as in the regular Ga1 and In1 octahedra, respectively. With average interatomic distances of 1.97 and 2.15 Å and individual values ranging from 1.909(2)– 2.065(2) Å for Ga1 and 2.069(2)–2.247(2) Å for In1, the distances are in good agreement with those reported in the literature 3b, 4b, 6, 8. The distorted octahedra exhibit with 2.10 and 2.36 Å larger average distances and also quite uncommon maximal lengths of 2.307(2) Å for Ga2 and 2.748(2) Å for In2.…”

“…Lin and co‐workers showed an activity of roughly 30 μmol h −1  g −1 for Pt‐loaded TiO 2 11. Compared to other recently published borates of the 13th group of the periodic table, the herein described In 5 B 12 O 25 (OH) shows a high hydrogen evolution rate even without commonly employed co‐catalysts, such as Ni, Pt, or Ru 2, 4b, 5, 6, 12…”

“…Typical vibrations of InO 6 or GaO 6 octahedra appear at the lowest wavenumbers up to about 800 cm −1 4b, 6, 15. While those peaks in the IR spectra overlap with bands of the BO 4 bending and stretching vibrations, usually occurring at 800–1150 cm −1 , they can be distinguished in the Raman spectra 16.…”

“…Hydrogen is then retrieved from the storage molecule through ar eformation process.T oe nable this hydrogen liberation, metal borates gained significance in the recent years as possible photocatalysts,aresult amongst other things of their great stability.Especially triel borates not only shifted into our research focus,b ut have been examined for their photocatalytic activity lately by other groups as well. [2] Unlike most other compounds,o ur newly discovered indium borate In 5 [5] and Ga 2 B 3 O 7 (OH) [6] the third known hydroxylated borate.…”

Structure Elucidation and Characterization of the High‐Pressure Nickel Borate Hydroxide NiB3O5(OH)

“…The IR spectrum of a single‐crystal of NiB 3 O 5 (OH) is shown in Figure . One large and two small absorption bands can be found between 3300 and 3600 cm –1 , which we attribute to vibrations associated with the hydroxyl group . The origin of the rather small and broad peaks at ca.…”