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.