Surface Properties of High-Performing Bi₂₄O₃₁Br₁₀ and its Acid-Driven Conversion to BiOX Photocatalysts (X = Cl, Br)

Bismuth oxyhalides, including Bi24O31X10 and BiOX (X = Cl and Br), are emerging materials for photocatalysis. In this study, we demonstrate the transformation of Bi24O31X10 (X = Br and Cl) into pure-halide and mixed-halide solid solutions (ss) of BiOX by suspending the Bi24O31X10 powder in HX(aq) acid solutions. The photocatalytic activity of all BiOX and Bi24O31X10 materials were screened for the photooxidation of benzylamine to N-benzylidenebenzylamine under UV irradiation, i.e., a reaction involving a hydrogen transfer reaction. The catalytic properties of the acid-derived BiOX were impacted by both the parent Bi24O31X10 precursor the acid concentration used in the transformation and the halide content. BiOBr and BiOCl-ss materials derived from Bi24O31Br10 exhibited better catalytic performance compared to those derived from Bi24O31Cl10, and parent Bi24O31Br10 exhibited the highest catalytic activity of all materials. The superior properties of parent Bi24O31Br10 and all Bi24O31Br10-derived materials were then scrutinized by investigating the mechanism of the light-assisted hydrogen transfer of Bi24O31X10 by using inelastic neutron scattering (INS) and X-ray photoelectron spectroscopy (XPS). Bi24O31Br10 exhibited a remarkably higher capability of abstracting and binding H-atoms in comparison with Bi24O31Cl10, which is essential for reactions involving an H-transfer. We propose that this property explains the difference in the catalytic activity between the two Bi24O31X10 materials.