Fig. 1. SERS spectra of MHTP (a) and OHTP (b) pre-adsorbed on a roughened Ag electrode in KCl solution of pH 2, 7 and 12 at OCP

Fig. 2. Potential-dependent SERS spectra of MHTP pre-adsorbed on a roughened Ag electrode in KCl solution of pH 7 (a) and 12 (b)

Fig. 3. (a) SERS spectra of MHTP pre-adsorbed on a roughened Ag electrode in KCl solution of pH 2, 7 and 12 at negative potential; (b) Relative ratio of band intensities at 1 021 cm^-1 (TP) to 880 cm^-1 (MHTP) at different pH values

Fig. 4. (a) SERS spectra of OHTP pre-adsorbed on a roughened Ag electrode in KCl solution of pH 2, 7 and 12 at negative potential; (b) Relative ratio of band intensities at 991 cm^-1 (TP) to 830 cm^-1 (OHTP) at different pH values