The introduction of colloidal single-layer carbon nitride (SLCN) nanosheets at the stage of the formation of Au nanocrystals (NCs) in aqueous solutions allows the surface plasmon resonance peak position of gold/SLCN composites to be tuned in a relatively broad range of 520–610 nm. The effect is believed to originate from a strong electronic interaction between Au NCs and SLCN nanosheets attached to their surface as capping ligands and resulting in a decrease of the effective electron density on the Au NC surface. The SLCN nanosheets suppress direct interparticle interactions between Au NCs prohibiting additional plasmonic features typical for the Au NC associates. Species similar to SLCN in terms of functionalities but having no conjugated aromatic system, such as polyethyleneimine, only induce aggregation of Au NCs but do not allow the main surface plasmon resonance of the NCs to be tuned demonstrating the crucial role of electronic interaction between the NC surface and the aromatic SLCN sheets for the surface plasmon resonance tuning.
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