Investigation in Mediated Heterogeneous Oxygen Reduction of Immobilized Laccase

Abstract

Dynamics of heterogeneous catalysis on oxygen reduction for Lac based electrode capped with a layer of Chitosan-multi-wall carbon nano-tubes complex in the presence of dissolved mediator, was investigated on the basis of precondition that the detainment of substrate and mediator could be neglected. Rates of steps involved in the whole catalytic cycle were determined by the means of UV–Vis spectroscopy, atomic adsorption spectroscopy, linear sweeping voltammetry and cyclic voltammetry in combination with rotating disk electrode technique. These kinetic parameters were normalized under the same dimension. Thus rate determining step was verified to be the diffusion of external mediator. Results also revealed the fact from analysis in changes of morphology and electric conductivity after protein incorporation into nano-composite that random adsorption of enzyme molecules on the conductive support resulted in the decrease in conductive area of nano-composite and hindered the direct electron transfer between active sites in enzyme molecules and conductive matrix. Non-oriented arrangement of protein molecules on the matrix also crippled the mechanical stability of nano-complex with enzyme resulting from weak interaction between incorporated protein molecules and carrier. Catalytic effect on dissolved oxygen reduction reaction for electrode which was over-coated by a layer of nano-complex with immobilized Laccase consisting of Chitosan and multi wall carbon nano-tubes, were found to be restrained by diffusion of electron relay.