New insights into the role of zero-valent iron surface oxidation layers in persulfate oxidation of dibutyl phthalate solutions

Batch tests were conducted to investigate the effect of initial pH on the degradation of dibutyl phthalate (DBP), the formation and evolution of iron corrosion products, and the role of iron oxides on the further degradation of DBP in zero-valent iron (ZVI)–persulfate system. The study indicated that the half-lives for the oxidation of DBP by persulfate activated with ZVI were 30–176   min at pH 3.0–11.0. The constituents and the morphology of the iron corrosion coating along different initial pH and over reaction time were investigated with Raman spectroscopy , X-ray photoelectron spectroscopy and Scanning electron microscopy. The results illustrated that magnetite (Fe 3 O 4 ), wustite (FeO), hematite (α-Fe 2 O 3 ) and goethite (α-FeOOH) were identified as the corrosion products. In alkaline and neutral solutions, the inner layer of iron oxides was mainly composed of α-Fe 2 O 3 with some α-FeOOH while the outer layer mostly consisted of Fe 3 O 4 and α-FeOOH. Oppositely, the iron oxides formation in acidic solution mainly consisted of Fe 3 O 4 , α-FeOOH and a small amount of α-Fe 2 O 3 and FeO in the inner layer, the outer layer was mostly composed of α-Fe 2 O 3 and some α-FeOOH. These iron corrosion coatings exhibited an inhibitory effect on the degradation of DBP, which may be due to that the iron oxides hindered the electron transfer from ZVI core to the solid–liquid interface.