Catalytic ozonation of 4-chloronitrobenzene by goethite and Fe2+ -modified goethite with low defects: A comparative study

In this study, Fe2+-modified goethite with low defects (alpha-Fe(Fe2+)OOH) was synthesized and characterized. Results revealed that alpha-Fe(Fe2+)OOH is a nano magnetic material with goethite (alpha-FeOOH)-type structures and has fewer Lewis acid of Fe3 on its surface. Moreover, alpha-Fe(Fe2+)OOH was effective in catalytic ozonation of 4-chloronitrobenzene (4-CNB), which is a probe contaminant that cannot be efficiently removed through sole ozonation. The removal of 4-CNB increased with ozone concentration and alpha-Fe(Fe2+)OOH dosage, but decreased with the presence of carbonate, sulfate and phosphate. The catalytic activity of alpha-Fe(Fe2+)OOH also showed a dependence on solution pH. The presence of humic acid accelerated 4-CNB removal at low concentration but inhibited the removal at high concentration. In comparison with alpha-FeOOH, alpha-Fe(Fe2+)OOH significantly enhanced hydroxyl radicals generation and reduced Fe ions release in this process. The hydroxyl groups of Fe3+ on alpha-FeOOH and alpha-Fe(Fe2+)OOH surface was active site for ozone decomposition into hydroxyl radicals. Introducing Fe2+ significantly increased the density of surface hydroxyl groups relative to alpha-FeOOH. This enhancement significantly promoted hydroxyl radicals generation and 4-CNB degradation in the solution.