Controlled engineering of Bi4O5Br2 and BiOBr via interactions between imidazolium ionic liquids and medium during synthesis as a simple method for enhancement of photocatalytic activity†

Ionic liquid-mediated synthesis of Bi₄O₅Br₂ and BiOBr was carried out in non-polar solvents (glycerol, ethylene glycol) and a polar solvent (0.1 M mannitol). The effect of elongation of alkyl side chains (C4mim⁺, C8mim⁺, and C16mim⁺) of imidazolium ionic liquids, which act as a source of bromide and template, on the morphological, optical, and photocatalytic properties of materials was investigated. The crystallite size, morphology, particle size, energy bandgap, and exposure of (110), (001), and (102) facets were effectively tuned by selecting the proper ionic liquid–solvent system. The self-assembly of ILs and their role in forming Bi-based crystallites in non-polar and polar solvents differed. The most effective 5-fluorouracil was photooxidized over the samples prepared in C4mim⁺ – 0.1 M mannitol solution, while the best Cr(vi) photoreduction occurred with the sample formed in C4mim⁺ – glycerol. Molecular dynamics simulation correlated the length of alkyl side chains of imidazolium ILs with an increase in the number of “free” –OH groups of the solvent, which interacted with BiOBr nuclei during synthesis, fine-tuning its photocatalytic activity.