Adsorption and chemical modification of gallic acid on silver nanoparticles studied by Raman spectroscopy: Effect of anions and cationic pesticide paraquat

In this work, we have carried out a study of the chemical change of gallic acid in solution and on Ag colloids by using UV-vis absorption and surface-enhanced Raman spectroscopy (SERS). Gallic acid is a natural molecule occurring in plants which is involved in processes with important industrial and environmental impact, such as humification or food browning, where a chemical degradation of this phenol is involved. The adsorption of gallic acid on a metal surface can catalyse the chemical modification of the phenols, thus having interest in remediation processes where polyphenols of different nature are involved. Parameters such as pH, light irradiation and phenol concentration were checked in this work in relation to degradation mechanism catalysed by Ag. Finally, we have also tested the influence of the cationic pesticide paraquat in the chemical changes of GA as a possible agent, which may change the humification mechanisms.