In Situ SERS Study of Azobenzene Derivative Formation
from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured
Surfaces: What Is the Role of Applied Potential and Used Metal?
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Abstract
The
aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is
a substance that can be easily adsorbed on Au, Ag, and Cu surfaces,
but in some studies, formation of 4,4′-dimercaptoazobenzene
(4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT
on all three SERS-active metals in a spectroelectrochemical cell aiming
at the role of the metal and electrode potential on formation of 4,4′-DMAB
at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB
are observed in a potential range from +0.2 to −0.8 V. Only
at very negative potentials do these bands almost disappear and only
spectral features of 4-ABT are observed. In the case of Ag, a similar
spectral behavior is observed, but relative bands intensities are
weaker than on Au. In the case of Cu, there is no spectral evidence
of 4,4′-DMAB at any potential value. Only characteristic bands
of 4-ABT are observed in the whole potential range; the highest signals
are obtained at potentials around −0.6 V. Experimental results
are supported by DFT calculations. We can conclude that the crucial
aspect of surface photocatalytic formation of 4,4′-DMAB from
4-ABT is the metal. The reaction is very effective on Au, and it is
inhibited on Cu