Kinetics of the Degradation of l-Cysteine at Freshly Prepared Nano-sized MnO_2 Surfaces in the Absence and Presence of TX-100

摘要

Nano-sized colloidal manganese dioxide was synthesized at room temperature by a chemical method in neutral medium without a stabilizing agent. The obtained MnO_2 nano-sized colloid was found to be stable for several months and was characterized by means of UV–Vis spectroscopy, energy-dispersive X-ray spectrometer (EDX) and transmission electron microscopy. The EDX analysis confirmed the presence of Mn and O in the sample. The paper reports on the use of nano-sized colloidal manganese dioxide as an oxidant in the oxidation of cysteine (Cyst) in the absence and presence of surfactant (TX-100) at 35 °C. The study was carried out as functions of [MnO_2], [Cyst], [HClO_4] and temperature. The results show that the reaction proceeds through fast adsorption of Cyst onto the surface of the colloidal MnO_2. Pseudo-first-order rate constants were found to increase with the increase in [TX-100]. This paper reports values of the reaction rates and activation parameters in the absence and presence of surfactant and proposes a plausible mechanism.