Efficient hydroxyl radical production and sulfanilamide degradation during oxygenation of microbially reduced metal-organic frameworks

Incubation of iron-reducing bacteria with Fe(III) could generate center dot OH to decompose organic pollutants under redox fluctuation conditions. However, the Fe(III)/Fe(II) transformation efficiency and therefore yields of center dot OH production in systems using Fe(III)-bearing minerals as respiration substrate of bacteria is unsatisfying. Here, we showed that different iron- and iron-copper-based metal-organic frameworks (Fe-MOFs and FeCu-MOFs) can mediate electron transfer from Shewanella oneidensis MR-1 to O2 through their Fe(III)/Fe(II) cycling during anoxic-oxic transition, resulting in generation of reactive oxygen species including center dot O2-, H2O2 and center dot OH. While 3 g/L of MIL-101(Fe) demonstrated faster Fe(III)/Fe(II) cycling, better yields of center dot OH production (69.0 mu mol/mmol Fe(II) oxidation) and sulfanilamide removal (81.5 % in 24 h) than iron-bearing minerals and the rest two FeMOFs (MIL-53(Fe) and MIL-88B(Fe)), Fe0.75Cu0.25-B surpassed the performance of MIL-101(Fe) and other FeCu-MOFs with different Fe/Cu ratios, which might be attributed to its larger surface area, higher amounts of associated Fe(II), and synergistic effects between Fe and Cu species. Moreover, both MIL-101(Fe) and Fe0.75Cu0.25-B maintained structure stability and persistent catalytic activity during four continuous redox cycles in 48 h, the center dot OH production and sulfanilamide degradation of which exceeded those of one-time operation in the same duration. This study revealed the efficacy of combining bacteria and MOFs for center dot OH production, and provided promising alternatives for oxidative degradation of contaminants.