A highly efficient and recyclable living biocatalyst using Shewanella@polydopamine@NH2-doped carbon dot biohybrids and polypyrrole immobilized melamine foam for microbial-photoreduction of Cr(VI)

A novel living biocomposite was engineered to boost environmental Cr(VI) remediation. Photosensitive biohybrids were firstly configured through an inward-to-outward assembly of NH2-doped carbon dots (NCDs), polydopamine (PDA) and wild Shewanella oneidensis MR-1 cells to generate microbial-photoreduction of Cr(VI) at the nanoscale. Then, biohybrid-derived biofilms were implanted onto the surface of melamine foam (MF) through an in-situ polypyrrole (PPy)-heterojunction to form highly conductive living MF/PPy/biohybrid biocomposites at a macroscale. Bacterial biomass immobilized onto the surface of MF and the efficacy of related biocomposites for Cr(VI) reduction increased with increasing pyrrole (PY) monomer concentrations (0.15 -> 0.60 mL). In a 50 mg/L-Cr(VI) reduction system conducted under visible light illumination, biocomposites treated with 0.60 mL PY monomer displayed the highest Cr(VI) reduction efficiency (100%) with the shortest reaction time (24 h) during the first reduction cycle and significantly outperformed other biocomposite formulations over longer time periods (36-72 h). The living biocomposites exhibited an outstanding recyclability (>4 cycles) in subsequent reduction cycles. Overall, a reliable amalgamation of all living/non-living components integrated into the biocomposite ensured an efficient biocatalyst framework for Cr(VI) reduction and recyclable use.