Photocatalytic ozonation of gallic acid in water

Aqueous solutions of gallic acid have been treated with five different oxidation-radiation processes: visible and ultraviolet A radiation (VUVA), TiO2 adsorption, ozonation, VUVA/TiO2 photocatalysis and VUVA/O-3/TiO2 photocatalytic ozonation. With the exception of VLTVA radiation and TiO2 adsorption, ozone and photolytic processes allow for the total removal of gallic acid in a period between 50 and 90 min. The time taken to achieve 100% gallic acid conversion depends on the oxidation process applied, photocatalytic ozonation being the most effective technique. Throughout the process, oxalic and formic acids were identified as byproducts. Some other unidentified compounds probably related to pyruvic, malonic and maleic acids were also detected. The appearance of these compounds can be justified from direct reactions of both hydroxyl radical and ozone in water. Only photocatalytic ozonation leads to total mineralisation of the organic matter in less than 90 min. The photocatalyst used, TiO2, showed good activity and stability (no leaching was observed) after five consecutive photocatalytic ozonation runs with the same semiconductor-catalyst mass. (c) 2006 Society of Chemical Industry.