Photocatalytic degradation of malachite green by pyrite and its synergism with Cr(VI) reduction: Performance and reaction mechanism

• Published in: Separation and purification technology Vol. 154; pp. 168 - 175
• Main Authors: Diao, Zeng-Hui, Xu, Xiang-Rong, Liu, Fu-Ming, Sun, Yu-Xin, Zhang, Zai-Wang, Sun, Kai-Feng, Wang, Shi-Zhong, Cheng, Hefa
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.11.2015
• Subjects: Cr(VI); Degradation; Heavy metals; Malachite green; Organic compounds; Photocatalysis; Photocatalysts; Pyrite; Reduction; Synergism; Pyrite; Cr(VI); Synergism; Photocatalysis; Malachite green
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2015.09.027

[Display omitted] •A synergistic effect between MG oxidation and Cr(VI) reduction was found.•The presence of Cr(VI) could not change kinetic order of MG oxidation.•Dissolved oxygen could enhance MG oxidation but decrease Cr(VI) reduction.•Stability of the pyrite in the mixed system was superior to any single system.•A mechanism for the simultaneous removal of MG and Cr(VI) was proposed. Coexistence of organic compounds and heavy metals in industrial wastewater effluent is a serious environmental problem. In this study, pyrite was successfully employed as a photocatalyst for the simultaneous removal of malachite green (MG) and Cr(VI). The removal efficiency of MG and Cr(VI) were 96.7% and 53.1%, respectively after 120min. The presence of Cr(VI) significantly promoted MG degradation, and the reduction ratio of Cr(VI) was significantly accelerated in the presence of MG, demonstrating an obvious synergism between MG degradation and Cr(VI) reduction. The presence of Cr(VI) did not change the kinetic order of MG degradation. The presence of dissolved oxygen could enhance the degradation ratio of MG, but decrease the reduction ratio of Cr(VI) despite the fact that both Cr(VI) and O2 are competitive electron acceptors. Photocatalytic efficiency of the coexistence system was superior to that of the single system when the catalyst was continuously used for 5 times. A synergistic mechanism involving reactive oxygen species produced from photo-Fenton-like process for the MG degradation, whereas the Cr(VI) reduction mainly by direct electrons of pyrite, not reaction of O2− with Cr(VI) was proposed. This is the first report on the application of pyrite particles as a photocatalyst for the simultaneous removal of organic compounds and heavy metals.