Insight into the mechanism on micro-electrolysis removal of Cr(VI) by Fe-MOFs derived Fe@C: the crucial role of Fe(II)

Iron-based metal organic frameworks (Fe-MOFs) have been regarded as the ideal precursors for synthesis of iron-carbon micro-electrolysis (IC-ME) materials. However, their conventional autoclave-based fabrication limits large-scale application, and the potential of the resulting Fe@C composites derived from Fe-MOFs for Cr(VI) reduction remains underexplored. Herein, a facile stirring method conducted under ambient conditions was successfully developed. The evolution from Fe-MOFs to Fe@C was comprehensively characterized, and its reductive capacity for Cr(VI) was systematically evaluated. The effect of key experimental parameters including reaction time, initial pH value, electrolyte concentration, catalyst dosage, and environmental matrices on Cr(Ⅵ) removal were investigated in detail on the basis of the concentration variation of Fe ions released into water. The obtained results indicated that the rate of Cr(VI) removal-efficiency change (Δη/Δt) was positively corelated with that of Fe(II) concentration change (Δ C Fe(II) /Δ t) and 98.2% of Cr(VI) was removed within 60 min under the optimized conditions. According to the results of XPS with ion sputtering, Cr(VI) was removed via multiple pathways including adsorption, reduction and co-precipitation. This work not only offers a scalable route for MOFs-derived IC-ME materials, but also provides mechanistic insights into Cr(VI) removal from the perspective of Fe(II) dynamics.