Reduction of methylene blue by sulfide ion in the presence and absence of oxygen: simulation of the methylene blue-O2-HS- CSTR oscillations

Abstract

A mechanism is discussed which reproduces in simulations the oscillations during the methylene-blue catalyzed reduction of O2 by HS− in a continuous-flow, strirred tank reactor (CSTR). It contains 14 reactions and is based on experiments and simulations of simpler reactions including the reduction of MB+ by HS− in the absence and presence of O2 and the reactions of H2O2 and O2 with HS−. All experiments on component reactions as well as the CSTR oscillations can be simulated by the same set of reactions and rate constants. The major dynamic feature of the mechanism is the competition for MB. by the oxidizing agents O2 and H2O2 and the reducing agents HS− and HS.. The species MB. is the radical intermediate between the colored (MB+) and colorless (MBH) forms of methylene blue.