A quasi-homogeneous catalysis and electron transfer chain for biodecolorization of azo dye by immobilized phenazine redox mediator

Abstract

The anaerobic bio-reduction rate of many different contaminants is slow due to the limitations and efficiencies of electron transfer. In this study, the phenazine immobilized in hydrophilic material was tested as a redox mediator (RM) and quasi-homogeneous catalysis to reduce the mass transfer limitation and increase the decolorization efficiency. Neutral red (NR) was immobilized to polyacrylic acid (PAA) hydrogel by chemical reaction and obtained a content of NR as high as 3.58 mmol cm−3 of PAA. The novel functional material (PAA-NR), with three-dimensional polymeric network with high porosity and water contents (92–98%, w/v) achieved 13.5 fold higher in the anaerobic decolorization efficiency compared to the control. The optimal conditions for decolorization with PAA-NR hydrogel were 40 °C and pH 8.0. Additionally, the electron transfer mechanism of decolorization was investigated by testing with six inhibitors. NADH and FAD chains were involved in the decolorization process. PAA-NR acted as an insoluble redox mediator to accelerate Reactive Brilliant Red K-2BP (K-2BP) reduction through mediating electron transfer between the azoreductase and K-2BP, resulting in higher electron transfer and decolotization efficiency. This immobilizing technology extended the RM application and demonstrated high catalytic activity on pollutant anaerobic transformation.