Photocatalytic degradation of acephate in pak choi, Brassica chinensis, with Ce-doped TiO₂

The photocatalytic degradation of acephate was investigated using Ce-doped TiO₂ (TiO₂/Ce) hydrosol. In contrast to previous research conducted under artificial light in the laboratory, this study investigated the decomposition of acephate in a field trial. The results show that acephate can be efficiently degraded by the TiO₂/Ce system under natural field conditions; the degradation efficiency was affected by the dosage of the photocatalyst and acephate. The optimum dosage of TiO₂/Ce was 2400 g a.i.ha⁻¹, and the photodegradation efficiency of acephate reached 93.5% after 20 h at an acephate dosage of 675 g a.i.ha⁻¹. Ultra-performance liquid chromatography/mass spectrometry (UPLC/MS) analysis detected and identified four degradation products—methamidophos, phosphorothioic acid O,O,S-trimethyl ester, S-methyl methanethiosulfonate and phosphorous acid—that were formed during the TiO₂/Ce photodegradation of acephate. Based on the structural identification of the degradation products, a probable photodegradation pathway was proposed, and the first decomposition step may be the cleavage of the C‒N bond of acephate. Subsequently, the P‒S and P‒O bonds may be oxidized gradually or simultaneously to complete the mineralization.