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 (α-Fe(Fe²⁺)OOH) was synthesized and characterized. Results revealed that α-Fe(Fe²⁺)OOH is a nano magnetic material with goethite (α-FeOOH) -type structures and has fewer Lewis acid of Fe³⁺ on its surface. Moreover, α-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 α-Fe(Fe²⁺)OOH dosage, but decreased with the presence of carbonate, sulfate and phosphate. The catalytic activity of α-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 α-FeOOH, α-Fe(Fe²⁺)OOH significantly enhanced hydroxyl radicals generation and reduced Fe ions release in this process. The hydroxyl groups of Fe³⁺ on α-FeOOH and α-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 α-FeOOH. This enhancement significantly promoted hydroxyl radicals generation and 4-CNB degradation in the solution.