A pH-dependent SERS study of thiophene-2-carboxylic acid adsorbed on Ag-sols

SERS is observed for thiophene-2-carboxylic acid (TCA) adsorbed on Ag-sols. The enhancement is maximum when TCA concentration, in Ag-sol, is 5 × 10−3 M. The SER spectra of TCA are different at different pH values, which suggest that the adsorption geometry is pH dependent. This is further supported by the absorption spectra at different pH values. It is inferred that the chemisorption takes place through both the S-atom and COOH group for pH ⩽ 7 and through the π-electronic system for pH=10.5. Quick desulphurization at pH=2 and stable perpendicular and parallel surface bonding for pH=7 and 10.5, respectively, is revealed.