Tuning plasmonic reactivity: Influence of nanostructure, and wavelength on the dimerization of 4-NTP

Hot electrons generated in plasmonic nanoparticles are considered a key candidate for their ability to promote reduction reactions of organic molecules selectively. Such chemical transformations can occur when molecules are adsorbed on the surface of plasmonic nanoparticles interacting with an external incident electromagnetic field. The so-called localized surface plasmon resonance phenomenon, induced by the electromagnetic field, is responsible for the generation of energetic electrons which in turn can be transferred to the molecule, causing its reduction. It is known that such plasmon-induced hot carrier reactions mainly occur in proximity of the so-called hot spots, areas of the plasmonic particle with enhanced electromagnetic field. In this study, we discuss the photocatalytic performances via hot-electron transfer of three different silver nanoplatforms (nanospheres, nanoplatelets, and nanoflowers) for the conversion of 4-nitrothiophenol (4-NTP) to dimercaptoazobenzene (DMAB). The reaction was monitored via surface-enhanced Raman spectroscopy (SERS), irradiating the sample with a 532 nm or a 785 nm laser line. In both cases, we noticed a clear correlation between particle morphologies and reaction kinetic, useful for identifying the more favorable silver nanocatalyst. Moreover, measurements carried out by the 785 nm laser radiation revealed an unexpected conversion of 4-NTP to 4-aminothiophenol (4-ATP) on silver nanoflowers in the absence of reducing agents. This innovative approach opens up the interesting possibility of developing plasmonic nanoparticle-based catalysts with sustained performance while reducing the presence of chemical reactants and providing an alternative and cleaner synthetic chemical route.