Degradation of diclofenac by pyrite catalyzed Fenton oxidation

We demonstrated that diclofenac can be rapidly and completely oxidized in Fenton reaction system using pyrite as catalyst. The pH of the solution dropped from 5.7 to 4.1–3.2 with addition of different amounts of pyrite (0.5–4.0 mM) as Fe(II) concentration increased to 0.07–0.52 mM. Complete degradation (100%) of diclofenac was observed by pyrite Fenton system within 120 s, while only 65% of diclofenac was removed by classic Fenton system in 180 s. Degradation of diclofenac was significantly inhibited (100–51%) by addition of HO scavenger (t-butanol) but not by O2− scavenger (chloroform), indicating that diclofenac was dominantly oxidized by HO produced during pyrite Fenton reaction. It was suggested that continuous dissolution of aqueous Fe(II) by pyrite Fenton reaction supported the complete degradation of diclofenac. The rate of diclofenac degradation increased as pyrite and H2O2 concentrations increased. 2,6-dichlorophenol, 2-chloroaniline, and 2-chlorophenol were detected as major intermediates but they were rapidly degraded in 120 s. Chloride ions, ammonium, and total organic carbon measurements confirmed that diclofenac finally degraded to further oxidized forms (organic acids, HCl, and CO2).

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pyrite provided proper pH condition (3–4) and appropriate amount of aqueous Fe(II). ► Diclofenac was rapidly degraded (within 120 s) in pyrite suspension with H2O2. ► Diclofenac was finally mineralized to HCl and CO2 by pyrite Fenton system. ► HO was identified as a main reactive radical for diclofenac degradation. ► Continuous dissolution of Fe(II) from pyrite surface enhanced diclofenac degradation.