FOURIER TRANSFORM SURFACE-ENHANCED RAMAN SPECTRA OF FULVIC ACID FROM WEATHERED COAL ADSORBED ON GOLD ELECTRODES

摘要

Surface-enhanced Raman spectroscopy has been used to demonstrate that fulvic and humic acids can be readily adsorbed on gold surfaces mainly via physical adsorption. Chemically enhanced effects also play a minor role since the surface-enhanced Raman spectroscopic (SERS) signals of a few of specific groups in humic substances are selectively enhanced in some cases. Metal ions in solutions has little influence on the SERS spectra of fulvic acid and it implies that the binding sites of the fulvic acid to metal ions are located at considerable distance from the gold surface. Although the SERS characteristics of fulvic acid with high degrees of humification show some differences from those of the humic substances reported previously, the SERS spectra of all the methylated samples are almost identical. The data show that humic substances are adsorbed to a gold surface via their hydrophobic regions whilst their active sites remain available. SERS spectroscopy on gold electrodes show potential for in situ observation of humic substances in aqueous environment pertinent to their environmental roles.