Plasmon activation versus plasmon quenching on the overall photocatalytic performance of Ag/Au bimetal decorated g-C3N4 nanosheets under selective photoexcitation: A mechanistic understanding with experiment and theory

[Display omitted] •Interband plasmonic excitation promotes UV photocatalysis in Ag/Au-g-C3N4.•Optical field intensity reduces at Ag-Au bimetal separation.•The dominance of FRET over PIRET causes a quenched plasmon photocatalysis.•Density functional theory shows bimetals contribute towards valence band of g-C3N4. The exploitation of surface plasmon resonance (SPR) properties of metal nanoparticles (NPs) are considered beneficial for an improved photocatalysis under visible and near infra-red (NIR) photons. Here, on the contrary, we have shown a retarding plasmonic activity in Ag/Au bimetals decorated g-C3N4 nanosheets in rhodamine B (RhB) degradation under UV–vis and green laser. It is argued that Förster-resonance energy transfer (FRET) and plasmon-induced resonance energy transfer (PIRET) counteract with each other on illuminations. The experimental findings, electromagnetic simulation, and density-functional theory (DFT) results infer that reduced optical field intensity at the bimetallic gap, dominance of FRET over PIRET, nearest metal Fermi surface with semiconductor holes, and interfacial trap centers are possibly contributing to a quenched plasmonic photocatalysis. It is further stated that the semiconductor excitation and interband d-sp induced hot electrons over the bimetals are favoring an enhanced photocatalysis under UV light.