An in situ SERS study of substrate-dependent surface plasmon induced aromatic nitration

Here we demonstrate the surface plasmon (SP) induced nitration of aromatic rings by an in situ surface enhanced Raman spectroscopy (SERS) technique. The size feature of the as-prepared Au, Ag and Ag@PDA@Au hierarchical structures allows monitoring the entire reaction process on a single hierarchical structure. With benzenethiol (BT) and HNO₃ as reactants, SP induced aromatic nitration can be successfully realized without the assistance of a conventional acid catalyst, H₂SO₄. Experimental and theoretical studies confirm that the nitration reaction leads to para-nitrothiophenol (p-NTP). While control experiments show that SP here functions as a local heating source and the presence of metal is also necessary for this nitration reaction. This SP induced aromatic nitration reaction also displays SERS substrate-dependent reaction kinetics, which proceeds more rapidly on the Au surface. Higher laser power can generate a stronger photothermal effect, and thus an accelerated reaction rate for this reaction. We believe this finding may broaden the research areas in the SP assisted or induced catalytic reactions.