Insights into mechanisms behind photocatalytic degradation of organic dyes using cadmium doped zinc oxide

A deep understanding of dye–photocatalyst interactions is essential for the rational design of Cd-doped ZnO under real-world conditions. Here, density functional theory (DFT) and time-dependent DFT calculations are used to investigate ZnO nanoclusters interacting with methyl orange (MO) as a model organic dye. The effects of Cd-to-Zn substitution on structural, electronic, optical and adsorption properties are examined. Dispersion interactions prove crucial for stabilizing the MO–nanocluster complexes in aqueous environments. Cd substitution brings the LUMO levels of the dye and the cluster into closer alignment, potentially facilitating interfacial charge transfer. Population analyses reveal a scheme-dependent, Cd-content-sensitive charge redistribution at the interface, consistent with a possible electron-donor role for MO. Excited-state and molecular-orbital analyses further clarify the Cd influence on photoexcitation. These results extend current views of photocatalytic dye degradation, which are typically centred on reactive oxygen species, by highlighting processes that can occur at ROS-free catalytic sites on Cd-doped ZnO surfaces.