Iron
complexes of tetra-amido macrocyclic ligands (Fe-TAML)
are
recognized to be effective catalysts for the degradation of a wide
range of organic contaminants in homogeneous conditions with the high
valent Fe(IV) and Fe(V) species generated on activation of the Fe-TAML
complex by hydrogen peroxide (H2O2) recognized
to be powerful oxidants. Electrochemical activation of Fe-TAML would
appear an attractive alternative to H2O2 activation,
especially if the Fe-TAML complex could be attached to the anode,
as this would enable formation of high valent iron species at the
anode and, importantly, retention of the valuable Fe-TAML complex
within the reaction system. In this work, we affix Fe-TAML to the
surface of carbon black particles and apply this “suspension
anode” process to oxidize selected target compounds via generation
of high valent iron species. We show that the overpotential for Fe(IV)
formation is 0.17 V lower than the potential required to generate
Fe(IV) electrochemically in homogeneous solution and also show that
the stability of the Fe(IV) species is enhanced considerably compared
to the homogeneous Fe-TAML case. Application of the carbon black-supported
Fe-TAML suspension anode reactor to degradation of oxalate and hydroquinone
with an initial pH value of 3 resulted in oxidation rate constants
that were up to three times higher than could be achieved by anodic
oxidation in the absence of Fe-TAML and at energy consumptions per
order of removal substantially lower than could be achieved by alternate
technologies.