Bimetallic Ag–M (M = Co, Rh, Ir) alloy microflowers as high-performance plasmonic catalysts for visible-light-driven imine formation: a comparative study via in situ SERS

Abstract

Up to now, plasmonic catalysis studies have heavily depended on noble metals such as Au or Ag, hindering broad application. However, alloying catalytically active transition metals with plasmonic metals has recently emerged as a way to obtain superior performance in plasmonic catalysis. In this work, we demonstrate transition metal-based bimetallic Ag–M (M = Co/Rh/Ir) alloy plasmonic substrates that drive the transformation of benzylamine to N-benzylidenebenzylamine at room temperature under visible light excitation at 457 nm in an aqueous solution. Substrate fabrication was carried out using simple thermolysis of metal alkyl ammonium halide precursors (MToABr, where M = Ag, Co, Rh and Ir) on glass coverslips, and the resulting substrates were thoroughly characterized. Utilizing the localized surface plasmon resonance (LSPR) phenomenon of metals, we employed in situ surface-enhanced Raman scattering (SERS) to monitor the progress of the reaction. The reaction pathway, along with the role of ‘hot-carriers’ in the presence of atmospheric oxygen, was explored by a scavenger-assisted strategy. The formation and time-dependent gradual increase of the imine peak at 1626 cm⁻¹ in comparison to the peak at 1597 cm⁻¹ of benzylamine indicated the extent of the C–N coupling reaction. It was observed that alloying catalytically active transition metals with Ag enhanced the catalytic performance for all bimetallic catalysts investigated, compared to pure Ag. Among bimetallic catalysts, Ag–Co showed the best plasmonic efficiency, but the lowest rate of product formation. Ag–Ir was found to be the best catalyst, demonstrating the highest relative rate of reaction.