The photodimerization of 4-aminothiophenol (PATP) into 4,4\'-dimercaptobenzene (DMAB) has been extensively utilized as a paradigm reaction to probe the role of surface plasmons in nanoparticle-mediated light-driven processes. Here I report the first observation of the PATP-to-DMAB photoreaction in the absence of any plasmonic mediators. The reaction was observed to occur with different kinetics either for PATP adsorbed on non-plasmonic nanoparticles (TiO2 , ZnO, SiO2 ) or deposited as macroscopic droplets. Confocal microRaman spectroscopy enabled to investigate the reaction progress in different plasmon-free contexts, either aerobic or anaerobic, suggesting a new interpretation of the photodimerization process, based on direct laser-induced activation of singlet oxygen species. These results provide new insights in light-driven redox processes, elucidating the role of sample morphology, light and oxygen.

Noble metal-semiconductor nanocomposites have received extensive attention in Surface Enhanced Raman Scattering (SERS) due to their unique properties. In this paper, the Ag-ZnO nanocomposites are prepared by hydrothermal growth and simple chemical reduction immersion. The synthesized nanocomposite material simultaneously integrates the individual enhancement effects of the two materials in the SERS, such as the electromagnetic enhancement of silver nanoparticles and the chemical enhancement of ZnO semiconductor materials. Using this substrate, Rhodamine 6G molecules with a concentration as low as 10-8 M can be detected, and the coupling reaction of PATP can be effectively promoted. The nanocomposite materials prepared by selecting appropriate semiconductor materials and metal materials combined, could be potentially applied, as SERS substrates, in certain catalytic reactions.