Photocatalytic degradation of methamidophos by UV irradiation in the presence of nano-TiO2

In this paper, photocatalytic degradation of methamidophos (o,s-dimethylphosramidothooate) by nano-TiO2 was studied, and the effect factors (such as the nature and the concentration of the TiO2 photocatalyst, and the environment (pH, oxidant additives) of treatment solution, etc.) of this process were systemically investigated. It was found that nano-TiO2 has higher photocatalytic activity than that of bulk-sized counterparts, and the pretreatment temperature and the concentration of the nano-TiO2 used in photocatalysis both exhibited a direct effect on this process; in addition, in the presence of nano-TiO2, the change of initial pH value of the treatment solution and addition of oxidants (KIO4, K2S2O8, and H2O2) to this solution both showed an obviously positive effect on this degradation process, markedly enhancing the degradation rate of methamidophos. Under optimal condition (such as 0.04% KIO4 to the treatment solution), the degradation rate of methamidophos could reach about 83.55% in the first 5 min, which is obviously faster than the degradation speed reported in the literature. Langmuir-Hinshelowood rate expression was employed for the degradation of methamidophos by the UV/TiO2 system and adsorption equilibrium constant and rate constant were determined to be 2.02 m/M and 0.0027 mM/min, respectively.