Solar photocatalysis of carbaryl rinsate promoted by dye photosensitization

In this study, carbaryl (a carbamate insecticide) rinsate was treated by a novel technology – solar photocatalysis assisted with a dye photosensitizer (methylene blue (MB) or rose Bengal (RB)). The major advantage of this technology is to employ effectively natural solar light instead of artificial lamps as an irradiation source, leading to a considerable decrease in energy consumption and operation cost. Results showed that an increased mineralization and toxicity reduction efficiency for carbaryl rinsate was achieved by adding dyes into the solar photocatalytic system. Among the conditions studied, adding 1 × 10−6 M of MB, which corresponded to 1% of the initial concentration of carbaryl rinsate in the system, renders the most effective microtoxicity reduction of carbaryl rinsate. As a result, a carbaryl removal percentage of 66.2%, a mineralization efficiency of 26.2%, and a toxicity reduction of 44.6% could be achieved. The mineralization of carbaryl was found to follow the pseudo-first order reaction kinetics. The decomposition mechanism of carbaryl was further investigated through identification of the intermediates to elaborate the influence of dye photosensitizer on the solar photocatalysis of carbaryl. On the basis of the intermediates identified, it was believed that hydrolysis, hydroxylation and quinonation may be the major mechanisms for decomposing carbaryl in the process of solar photocatalysis with the aid of dye photosensitizer. On the strength of results obtained in this study, it was revealed that solar photocatalysis along with the aid of a dye photosensitizer, such as MB or RB, was a greatly feasible approach for the pollution control of pesticide rinsate.