Oxidative Degradation of Methylene Blue via PDS-Based Advanced Oxidation Process Using Natural Pyrite

摘要

H O - and PDS-based reactions are two typical advanced oxidation processes (AOPs). In this paper, a comparative study of H O /PDS-based AOPs employing natural pyrite as a catalyst to degrade methylene blue (MB) was reported. The adaptive pH range in pyrite/PDS extended from 3 to 11, in contrast to the narrow effective pH range of 3–7 in pyrite/H O . As a result of the iron leaching, a synergistic effect of both homogeneous and heterogeneous catalysis was observed in pyrite/PDS, whereas heterogeneous catalytic oxidation dominated pyrite/H O . Furthermore, the batch results showed that the MB removal by pyrite/PDS was highly dependent on chemical conditions (e.g., pH, pyrite and PDS concentration, temperature). Powerful SO was generated by pyrite rapidly under acidic or weakly acidic conditions, while SO and PDS were assumed by OH under alkaline condition. The lower pyrite loading (from 0.1 to 0.5 g/L) was affected the removal efficiency obviously, while the scavenging of SO did not seem to be remarkable with the excessive amounts of pyrite (>0.5 g/L). Excessive amounts of PDS (>2 mmol/L) might negatively affect the pyrite/PDS system. The reaction temperature that increased from 20 to 40 °C had a positive effect on the degradation of MB. SEM and XRD showed that the passivation of catalyst did not occur due to the strong acid-production ability of pyrite/PDS, inhibiting the formation of Fe-oxide covering the pyrite surface.