Engineering Upconversion Semiconductor Nanostructures: Unravelling the Morphology–Performance Relationship for Photocatalytic Hydrogen Generation

Abstract

Earlier, we developed a well-defined TiO₂ upconversion (CeF₃:Ho³⁺) nanosystem (CHT) for effective visible light-assisted photocatalytic hydrogen generation. To further enhance the overall performance of the UC/semiconductor nanocomposite, the synthesis parameters were systematically optimized for a deeper mechanistic insight into the structure–activity relationship. This study highlights the critical role of the synthesis parameters in producing high-performance semiconductor upconversion (UC) composites. It was observed that minor variations in the synthesis route, particularly in fluoride precursor concentrations, significantly influenced the in situ formation and morphology of UC nanoparticles, thereby modulating the overall photocatalytic performance. This work presents an inquiry into the effect of fluoride precursors during the in situ integration stage of upconversion particles. The surface shape of UC particles changes significantly when the concentration of fluoride ions increases. At lower fluoride concentrations, UC particles were found spherical with diameters of (4–8) ± 2 nm, but at higher concentrations, cylindrical UC particles with length (8–16) ± 2 nm and width (2–5) ± 1.5 nm were predominantly formed. The in situ production of these spherical and cylindrical UC particles is heavily governed by fluoride species, resulting in distinct electrical and photophysical characteristics. This article describes all the morphological and physical components that contribute to activity augmentation as well as the significance of the synthesis operation in defining beneficial properties.