From Pigment to Photocatalyst: CdSe/CdS Solutions Mimicking Cadmium Red for Visible-Light Dye Degradation

This study explores the dual functionality of cadmium-based pigments (CdS, CdSe, and CdS1−xSex solid solutions) as historical colorants and visible-light photocatalysts. Synthesized pigments here replicated hues of traditional cadmium reds. At the same time, their photocatalytic efficiency was evaluated using model dyes, such as indigo carmine (anionic) and fuchsine (cationic), as a representative of heritage materials. Structural and optical characterization confirmed tunable bandgaps (1.63–2.28 eV) and phase-dependent microstructures, with CdS1−xSex composites exhibiting compositional heterogeneity. Photocatalytic tests revealed specific degradation mechanisms. Indigo carmine degradation was dominated by superoxide radicals (O2•−), while fuchsine degradation relied on photogenerated electrons (e′). Scavenger experiments highlighted the synergistic role of reactive oxygen species (ROS) and charge carriers, with CdS and CdSe showing the highest activity. Intermediate composites displayed selective reactivity, suggesting trade-offs between phase homogeneity and surface interactions. Reduced photocatalytic efficiency in composites aligns with cultural heritage needs, where pigment stability under light exposure is critical. This work bridges material science and conservation, demonstrating how the compositional tuning of CdS1−xSex can balance color fidelity, photocatalytic activity, and longevity in art preservation.