Surface Adsorption and ROS Formation in α-Ag2WO4: Linking Theory and Photocatalytic Performance

Abstract Understanding the relationship between surface structure and photocatalytic performance is essential for the development of semiconductor materials. In this study, hexagonal α-Ag2WO4 rods were investigated using a theoretical-experimental approach, highlighting the influence of surface-dependent reactivity on the generation of reactive oxygen species (ROS). Density functional theory calculations showed that the surfaces (001) and (101) favor H2O adsorption and activation to form •OH radicals, while the (010) surface increased O2 adsorption. Furthermore, coadsorption calculations revealed a synergistic interaction between H2O and O2, which favors ROS generation. The experimental data obtained for α-Ag2WO4 samples synthesized via a coprecipitation route in water, ammonia, and ethanol as solvents indicate the ability to tune defect and morphology without affecting its hexagonal structure. The highest crystallinity and anisotropy were observed for the samples synthesized in water. On the other hand, synthesis in ethanol yields higher defect densities and sub-coordinated silver quantum cluster-rich surfaces. The photocatalytic activity was evaluated considering rhodamine B under UV light, with and without air bubbling. The samples synthesized in aqueous medium exhibited enhanced response (approximately 76% removal), which can be ascribed to the greater reactivity of (001)/(101) exposed surfaces, and •OH radical generation, whose presence was confirmed by coumarin probes and scavenger tests. Under bubbling conditions, the sample synthesized in an ethanolic medium exhibited complete dye degradationover 10 times faster compared to samples synthesized in waterwhich may be related to O2 reduction activation pathways rather than H2O-based mechanisms. DMA probing experiments and scavengers’ tests revealed higher •O2− and 1O2 generation under O2-rich conditions, suggesting a higher availability of active sites for the reduction of oxygen into ROS species as a result of the defect-rich samples synthesized in ethanol. This work provides a practical strategy for tailoring α-Ag2WO4 particle morphologyengineering surfaces and controlling exposed facetsenabling selective ROS formation for enhanced photocatalytic response, which is essential for the rational development of advanced semiconductor photocatalysts.