Heterogeneous sono-Fenton process using pyrite nanorods prepared by non-thermal plasma for degradation of an anthraquinone dye

Natural pyrite (NP) was treated using oxygen and nitrogen non-thermal plasmas to form modified catalysts. Cleaning effect of the O₂ plasma by chemical etching leads to removal of impurities from catalyst surface and sputtering effect of the N₂ plasma results in formation of pyrite nanorods. The mentioned plasmas were applied separately or in the order of first O₂ and then N₂, respectively. The catalytic performance of the plasma-modified pyrites (PMPs) is better than the NP for treatment of Reactive Blue 69 (RB69) in heterogeneous sono-Fenton process (US/H₂O₂/PMP). The NP and the most effective modified pyrite (PMP₄) samples were characterized by XRD, FT-IR, SEM, EDX, XPS and BET analyses. The desired amounts were chosen for operational parameters including initial pH (5), H₂O₂ concentration (1 mM), PMP₄ dosage (0.6 g/L), dye concentration (20 mg/L), and ultrasonic power (300 W). Moreover, the effects of peroxydisulfate and inorganic salts on the degradation efficiency were investigated. Gas chromatography-mass spectrometry (GC-MS) method was applied to identify the generated intermediates and a plausible pathway was proposed for RB69 degradation. Environmentally-friendly modification of the NP, low amount of leached iron and repeated reusability at milder pH are the significant privileges of the PMP₄. The phytotoxicity test using Spirodela polyrrhiza verified the remarkable toxicity removal of the RB69 solution after the treatment process.