Chemical Control of Facet-Selective Photoetching in Wurtzite CdS Photocatalysts

The photocorrosion of visible-light-responsive photocatalysts is considered detrimental, compromising activity and stability. Although CdS photocorrosion has been extensively reported, most studies focus on performance degradation rather than the underlying facet-dependent mechanisms. Consequently, the origins of facet-selective photocorrosion, the role of solution chemistry (pH, chemical species, and hole-scavenging ability), and the impact of excessive photoetching on photocatalytic activity remain poorly understood. In this study, we demonstrated that the photocorrosion of Pt-loaded wurtzite CdS can be harnessed as a controllable postsynthetic strategy for facet engineering. The photoetching behavior of Pt-loaded CdS photocatalysts was systematically investigated in various aqueous solutions, including lactic acid (LA), acetic acid (AA), sodium lactate (NaLac), and pure water, to elucidate the factors governing facet-selective etching. Distinct etching behaviors were observed depending on solution chemistry. In the LA solution, selective etching predominantly occurred on the Cd-terminated (0001) facet, whereas in AA and pure water, preferential etching of {10–10} and {10–11} side facets was observed. These differences were found to arise from variations in the hole-scavenging ability and coordination chemistry. Insufficient hole scavenging in AA and water led to hole accumulation and corrosion of the side facets, whereas strong chelation of Cd 2+ by LA promoted preferential dissolution of the (0001) facet. Light-intensity-dependent experiments revealed that side-facet etching occurs when the carrier generation rate exceeds the hole-consumption capacity of the solution, highlighting the dynamic balance between carrier generation and consumption as a key determinant of etching selectivity. Controlled photoetching of the (0001) facet of Pt-loaded CdS for a short duration generated shallow surface corrugation, resulting in a 2.7-fold enhancement in hydrogen evolution activity. In contrast, excessive etching caused Pt nanoparticle detachment, increased carrier recombination, and reduced activity. These findings establish solution-controlled photoetching as an effective facet-engineering strategy that transforms photocorrosion from a degradation pathway to a design tool for high-performance semiconductor photocatalysts.