Intermediate products of carbendazim degradation in water from photolysis, TiO₂ photocatalysis, and TiO₂ sorption

This work used TiO₂ photocatalysis under natural sunlight irradiation to degrade residual carbendazim in water by using Degussa P25 suspension, Degussa P25 coated filters, and titanium tetra-isopropoxide (TTiP) sol–gel coated filters. Their induced intermediate products were compared with the natural sunlight photolytic degradation and sorption process under white-light fluorescent lamps. The carbendazim degradation efficiencies from Degussa P25 in the forms of suspension and coated filters were 100% and 99.5%, respectively, with no sorption of carbendazim onto them. For sol–gel coated filters, similar efficiencies of 92.3–96.4% were rapidly obtained due to the synergistic effect from the sorption process. For their intermediate products, photolysis could induce benzimidazole isocyanate, 2-AB, 1,2-phenylenediamine, and monocarbomethoxy-guanidine in stable intensities along with their parent compound, carbendazim. With photocatalysis, carbendazim and benzimidazole isocyanate rapidly decreased within 30–60 min. There was a significant difference between 2 photocatalysts in producing 2-AB and monocarbomethoxy-guanidine that Degussa P25 induced much higher intensities than the sol–gel filters. Moreover, TiO₂ photocatalytic degradation could induce more intensity of 1,2-phenylenediamine than photolytic degradation. With the sorption capability from sol–gel coated filters, the intensities of carbendazim, benzimidazole isocyanate, 2-AB, benzimidazole, and monocarbomethoxy-guanidine were significantly reduced from the aqueous solution.