Recent progress in the nanoarchitectures of bismuth oxyhalides (BiOX) and binary bismuth oxyhalides (BiOX/BiOY, where X, Y = F, Cl, Br, and I; X ≠ Y) and their heterostructures.

Bismuth oxyhalides (BiOX, where X = F, Cl, Br, I) have emerged as an important class of materials whose layered crystal structures and distinctive optoelectronic properties make them attractive candidates for environmental remediation and energy conversion. Recent research has focused extensively on designing BiOX nanostructures and BiOX/BiOY (X, Y = F, Cl, Br, I; X ≠ Y) heterojunctions to attain optimal utilization for the target applications. In this review, the morphosynthesis of BiOX nanoparticles and the heterostructures of BiOX, including BiOX supported on solid substrates, is introduced. Synthetic approaches for BiOX/BiOY heterojunctions, both unsupported and supported on substrates, are also examined, with an emphasis on the relationship between heterostructure design and the resulting optical and photocatalytic behaviour. In addition, BiOXxY1-x (X, Y = F, Cl, Br, I; X ≠ Y) solid solutions are discussed and distinguished from two-phase heterojunctions. Applications of well-defined BiOX nanoparticles, BiOX/BiOY heterojunctions, and their support-immobilised heterostructures in photo- and electrocatalysis, adsorption and separation, and biomedical use are also discussed.