Surface-Enhanced Raman Spectra of Fulvic and Humic Acids Adsorbed on Copper Electrodes

The surface-enhanced Raman scattering of fulvic or humic acid adsorbed on copper electrodes demonstrates a unique resolution-enhanced effect. The effect is due to chemical binding of humic substances on copper surfaces. It is deduced that only a few kinds of chemically and geometrically favorable groups or portions such as carboxylic ions and pyridine-substituted rings in the humic aggregates specifically bind onto the copper surfaces while the rest dangles in the solutions. Since the rest are far from the surface and their SERS signals are too weak to be observed, the SERS spectra only characterize the binding groups specifically and therefore they are highly resolved and simple. Such a unique resolution-enhanced effect may be valuable to reveal specific clues regarding the binding groups of humic substances, particularly at low concentrations typically found in aquatic environments.