New insights into the electron-transfer mechanism of Cr(VI) activation by carbon materials for simultaneously enhanced Cr(VI) detoxicate and acetaminophen oxidation: the role of defect structures.

Hexavalent chromium (Cr(VI)) is a widely recognized toxic heavy metal pollutant, yet its intrinsic oxidative potential remains underutilized. The observation that Cr(V) generated during sulfite- or photocatalyst-mediated Cr(VI) reduction exhibits efficient oxidation of coexisting organic compounds has prompted exploration of potential Cr(VI)-based heterogeneous catalytic systems. Herein, waste polyethylene was upcycled via a controlled salt-template pyrolysis strategy to synthesize carbon nanoscale catalysts (LCSs) with engineered defect structures. These LCSs synergistically amplified the oxidative capacity of potassium dichromate (PCr), achieving rapid degradation of diverse organic micropollutants and concurrent Cr(VI)-to-Cr(III) reduction. Combined theoretical and experimental analyses demonstrate that vacancy defects function as intrinsic active sites, enhancing polarization charge distribution and electron density redistribution on LCSs surfaces to amplify interfacial reactivity and electron mobility. This defect-driven electronic modulation enables efficient charge transfer between acetaminophen (ACP) and PCr. Furthermore, life cycle and techno-economic analyses highlighted the enhanced environmental and economic merits of the LCSs/PCr system, exhibiting a two-thirds reduction in carbon emissions compared to conventional processes and a 50 % reduction in operational costs. This work reveals defect structures' critical role in Cr(VI) catalysis systems, redefining chromium pollution control through Cr(VI) repurposing as catalytic assets and advancing sustainable water decontamination.