Fourier Transform Surface-Enhanced Raman Spectra of Fulvic and Humic Acids Adsorbed on Au Electrodes

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Abstract
The Fourier transform Surface-enhanced Raman spectra of fulvic and humic acids from sea water adsorbed on an Au electrode were determined. At neutral and basic conditions, the humic acid was hung on the Au surface through its carbonyl groups, and the fulvic acid from the same source was adsorbed in both “end on” and “flat on” configurations. At acidic conditions, both of the fulvic and humic acids were adsorbed on the surfaces through their carboxylate and pyridine-like groups. The SERS behaviours of the humic and fulvic acids at different pH and potentials were from the difference of their chain sizes, charges and flexibility as well as the changes of their conformations. This preliminary study suggested that Fourier transform Surface-enhanced Raman spectroscopy could be used as a powerful probe with which to directly “see” humic substances at low concentrations.