Speaker
Description
Transition to renewable energy is essential for sustainable development, with solar energy offering particularly promising route. Plasmon-active materials enable use of up to 70% of the solar spectrum in the visible and infrared ranges, providing low-energy alternative to UV-driven processes. Noble metal nanostructures (e.g. Au, Ag) exhibit localized surface plasmon resonance upon irradiation allowing efficient energy transfer to chemical systems and enabling reactions under mild conditions with high selectivity [1]. However, plasmon catalysis faces key challenges that hinder its industrial implementation among which the unclear reaction mechanism remains critical. In this pursuit, model reactions play central role. The most widely used system is the azo coupling of p-nitrothiophenol (PNTP) that leads to the formation of 4,4’-dimercaptoazobenzene (DMAB) under laser irradiation (Fig.1a). Despite its popularity with over 3000 published studies, its validity remains questionable.
In this work, we critically reassess the azo coupling as a model reaction for plasmon catalysis. Using X-ray photoelectron (XPS) and Raman spectroscopies, we demonstrate that plasmon excitation induces thiol desorption from Au nanoparticles via Au-S bond cleavage accompanied by thiol oxidation. Analysis of the N1s and S2p regions reveals a reaction pathway significantly more complex than commonly assumed (Fig.1b-d). This discrepancy highly impact on the plasmon catalysis mechanism conclusions made using azo coupling and show that PNTP azo coupling does not meet the criteria of reliable model reaction, namely simplicity and well-defined products. As an alternative, alkoxyamine homolysis can be used as a more suitable model reaction due to its well-established mechanism and straightforward kinetics. The adoption of appropriate model reactions is crucial for advancing mechanistic understanding and accelerating progress in plasmon catalysis.
References
1. S. Linic et al., Nat. Mater, 2015, 14, 567-576