Bioengineered iron-based heterojunction orientation in optimizing activation pathways for superoxide radical-mediated...

Photocatalytic technology has been widely employed for Cr(VI) remediation. However, the inadequate generation of reactive oxygen species associated with the Cr(VI) reduction, caused by the uncontrollable photo-Fenton reaction, significantly restricts the reduction efficiency. Herein, a bioengineered iron-based heterojunction (Bio-Fe₂O₃/Fe₂(WO₄)₃) was fabricated via a two-step process of biomineralization and calcination, where tungstate was doped into the precursor during iron metabolism in acidophilic bacteria to optimize the heterojunction structure. Bio-Fe₂O₃/Fe₂(WO₄)₃ exhibited a short-range ordered structure and superior photocatalytic performance, achieving 100 % reduction of 20 mg/L Cr(VI) within 60 min by photocatalytic oxalic acid (OA) under simulated light conditions. The system provided robust operation in complex environments, notably, operating effectively under mild solar radiation as an alternative to the simulated light. The heterojunction structure intensified the H₂O₂ activation and selectively boosted the yield of superoxide radical (O₂^·-), the primary Cr(VI)-reducing species, from 48.02 % to 72.96 %. The high oxidation state of Fe in Bio-Fe₂O₃/Fe₂(WO₄)₃ contributed to stronger adsorption performance towards OA and H₂O₂, accompanied with the tendency to take the O₂^·--generated activation pathway. This work provides a broader perspective on the rational design of photocatalysts to modulate the OA photocatalysis and the H₂O₂ activation pathway, selectively elevating the yield of O₂^·- for Cr(VI) reduction.