Department of Physical Chemistry, University of Bucharest, Bd. Regina Elisabeta, no. 4-12, 030018, Bucharest, Romania.
Environ Sci Pollut Res Int. 2010 Jun;17(5):1158-66. doi: 10.1007/s11356-009-0292-4. Epub 2010 Feb 10.
In the present work, we explored the kinetics of dichlorvos (2,2-dichlorvinyl dimethyl phosphate, DDVP) decay through UV-A light-induced TiO(2) photocatalysis at pH 4 and 9, and the formation of degradation intermediates and final products under specific experimental conditions. Experimental observations and theoretical considerations allowed us to suggest the degradation mechanism of DDVP by the UV/TiO(2) process in aqueous solution.
The irradiation experiments were carried out in a photoreactor using a 228-W medium-pressure Hg vapor lamp. The concentration of DDVP, phosphate ion and formaldehyde as reaction intermediate, are determined spectrophotometrically. Chloride ion concentration was measured potentiometrically.
The photocatalytic degradation rate of dichlorvos (DDVP) under UV irradiation (360-380 nm) was optimized with respect to the flow rate of O(2) gas sparged into the solution and photocatalyst concentration for a constant dichlorvos concentration (1.66 x 10(-4) M) at pH 4. Kinetic data were obtained at pH 4 and pH 9 for dichlorvos and the inorganic species released through its photo-induced degradation. The proposed mechanism which assumes the formation of some toxic intermediates resistant to mineralization is supported by theoretical calculations and the observed inorganic mass balances.
The calculated pseudo-first-order rate constants were dependent on the dissolved oxygen level at low O(2) flow rate, but somewhat independent on the initial pH. The decrease of pH during the irradiation suggests the formation of organic acids. The presence of organic intermediates was confirmed also by TOC measurements. A plausible reaction mechanism of DDVP degradation through the UV-A/TiO(2) process was proposed.
在本工作中，我们研究了在 pH 值为 4 和 9 时，通过紫外光诱导 TiO2 光催化二氯松（2,2-二氯乙烯基二甲基磷酸酯，DDVP）衰减的动力学，以及在特定实验条件下形成的降解中间体和最终产物。实验观察和理论考虑使我们能够提出 DDVP 通过紫外/TiO2 过程在水溶液中的降解机制。
辐照实验在使用 228 W 中压汞蒸气灯的光反应器中进行。DDVP、磷酸根离子和甲醛（作为反应中间体）的浓度通过分光光度法测定。氯离子浓度通过电位测定法测量。
在 pH 值为 4 时，优化了紫外光（360-380nm）照射下 DDVP 的光催化降解速率，以优化氧气气体流速和催化剂浓度，使 DDVP 的浓度保持不变（1.66×10(-4)M）。在 pH 值为 4 和 9 时，获得了 DDVP 和通过光诱导降解释放的无机物质的动力学数据。提出的机制假设形成了一些对矿化有抗性的有毒中间体，这得到了理论计算和观察到的无机质量平衡的支持。
计算得到的准一级速率常数取决于低氧气流速下的溶解氧水平，但在初始 pH 值上有些独立。辐照过程中 pH 值的下降表明形成了有机酸。TOC 测量也证实了有机中间体的存在。提出了通过紫外-A/TiO2 过程降解 DDVP 的合理反应机制。
