Nano-TiO2 catalyzed UV-LED sample pretreatment method for decomposition of humic substances in natural water samples

A photocatalytic digestion device consisting of an ultraviolet light emitting diode (UV-LED) and a nano-TiO2 coated catalyst rod was designed and used for the decomposition of humic substances in natural water samples prior to inorganic elemental analysis. The aim was to develop a green sample pretreatment method by utilizing energy efficient and environmental friendly UV-LED technology. The effects of different experimental variables including pH, UV-LED irradiation time, and hydrogen peroxide concentration were studied using a statistical experimental design. Dissolved organic carbon (DOC) removal was studied as the response. Dissolved organic carbon can interfere in some analytical measurements (for example in electrochemical analysis methods) and after digestion, the possible interfering effects are minimized. The recoveries for some spiked elements (As, Bi, Cd, Co, Cu, Ge, Ni, Pb, Sb, Se and Tl) were studied. It was found that in optimal DOC removal conditions, the recoveries for cadmium, cobalt, nickel and selenium were good. However, lower recoveries for some hydride forming elements were observed, indicating element losses, possibly due to adsorption phenomenon.