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.