Abstract
Schwertmannite (Sch), a good geo-sorbent for immobilizing molybdate oxyanion in natural environment, has been used as an efficient Fenton-like catalyst in the remediation of organic pollutants. However, what's the influence of immobilized molybdate (Moimm) on the catalytic activity of Sch and what's the catalytic difference between Moimm and dissolved molybdate (Modiss) in H2O2 activation are still unknown. In this study, we first find a dual mechanism of Mo-Sch involved in phenol oxidation. At low Moimm loadings (0.01Mo-Sch and 0.05Mo-Sch), phenol oxidation is predominantly mediated by HO radicals generated from dissolved Fe(III) or surface Fe(III) on Sch, whereas at high loadings (1Mo-Sch and 10Mo-Sch), OOH as well as 1O2 generated from monomeric Mo complexes on Sch under acidic conditions also play important roles in phenol oxidation. Unlike Mo-Sch, Modiss forms dimeric Mo2O3(O2)42− with H2O2 under acidic conditions, which can oxidize phenol directively or via OOH radicals, generated from dissolved Mo2O3(O2)42−. The dimerization of Modiss with H2O2 inhibits 1O2 generation. During the experiments, Modiss can also interfere with the chain reactions between dissolved Fe(III) and H2O2, accelerating H2O2 decomposition via an O2 generation pathway, which significantly reduces the utilization efficiency of H2O2 in phenol oxidation.
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