Plasmon-assisted and electrostatic-driven photocatalysis at the sharp tips of au nano-bipyramids in aqueous phase

Surface-enhanced Raman scattering (SERS) combined with plasmonic photocatalysis is an effective method for the in-situ analysis of molecular reaction mechanism, which has been widely employed to study the transformation process and reaction mechanism of azobenzene molecules. However, achieving highly sensitive monitoring of reactant molecules and precisely controlling the catalytic products remain significant challenges. In this study, citrate-capped gold nanobipyramids (cit-Au NBPs) were used as the plasmonic substrate, which not only utilize the "lightning rod effect" at the tips of the bipyramids to construct an extremely strong localized electric field, but also precisely drive positively charged reactants (such as p-nitroaniline) to the catalytic region at the tips through electrostatic adsorption by the negatively charged citrate on the surface. Based on this synergistic effect, the highly sensitive in-situ SERS monitoring of complex reaction process was achieved. Specifically, the plasmon-driven oxidative coupling and reduction process of p-nitroaniline under light irradiation and after the addition of NaBH₄ were clearly defined. Furthermore, comparative studies on nanoparticles with different morphologies and surface ligands demonstrated the critical roles of tip-induced plasmonic enhancement and electrostatic driving in this highly efficient catalytic system. In addition, the feasibility and promising selectivity of this strategy were verified by the catalysis of p-aminophenol and o-phenylenediamine. This strategy significantly improves the efficiency of plasmonic catalysis and the SERS detection sensitivity of trace intermediates, providing an excellent platform for in-situ monitoring of complex and rapid catalytic reactions.