Reduction pathway and mechanism of chloronitrobenzenes synergistically catalyzed by bioPd and Shewanella oneidensis MR-1 assisted by calculation

Abstract

Although microbial synthesized palladium nanoparticles (bioPd) have been demonstrated to exhibit a great activity toward dechlorination of several chlorinated pollutants, there is no systematic investigation into the substituent effect on dechlorination. Chloronitrobenzenes are widely used for manufacturing and known as persistent pollutants with recalcitrance of biodegradation for nitro groups. In this work, bioPd was synthesized by Shewanella oneidensis MR-1. The dechlorination of 2-chloronitrobenzene, 4-chloronitrobenzene and 2,4-dichloronitrobenzene catalyzed by bioPd were investigated. Simultaneous dechlorination and nitro reduction were observed by synergistic catalysis of bioPd and S. oneidensis MR-1. Pd concentration was optimized for the reduction. Producing profiles of intermediates changed with the ratio of Pd to cell, supporting a size- or shape-controlled catalytic activity of bioPd. The removal of chloro atoms at para-position was easier than that at ortho-position in 2,4-DCNB, suggesting a position effect on the reduction, which was further supported by the frontier molecular orbital and frontier electron density of 2,4-DCNB according to density functional theory.