α-MnO2/Palygorskite composite as an effective catalyst for heterogeneous activation of peroxymonosulfate (PMS) for the degradation of Rhodamine B

The discharging of Rhodamine B (RhB) from wastewater has caused huge environment pollution. Peroxymonosulfate (PMS) oxidation is an effective way to remove it from wastewater. However, finding an environmentally friendly metal to activate PMS is a key step for the oxidation process. In this study, nanorod alpha-MnO2 loaded palygorskite (alpha-MnO2/Pal) was fabricated by a simple hydrothermal method. The analysis of field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the loading of alpha-MnO2 on the surface of Pal and characterized the surface of the composite. The surface area of alpha-MnO2/Pal composite was 159.13 m(2)/g, which was much higher than that of Pal and alpha-MnO2. The Pal, alpha-MnO2, Mn2+, and alpha-MnO2/Pal were used to activate PMS for RhB degradation. Nearly 100% RhB degradation was obtained in alpha-MnO2/Pal + PMS system in 180 min and in alpha-MnO2 + PMS system in 300 min, while only 50% degradation was obtained in Pal + PMS system and 71.4% degradation in Mn2+ + PMS system in 300 min. The degradation fitted the pseudo-first-order reaction kinetics well with rate constant of 0.02041 min(-1) for alpha-MnO/Pal + PMS system, 0.01192 min -1 for alpha-MnO2 + PMS system, and 0.00435 min(-1) for Mn2+ + PMS system, respectively. The factors affecting RhB degradation were further investigated. The RhB degradation efficiency increased with the increase of alpha-MnO2/Pal dosages, PMS dosages and temperatures. The degradation was inhibited at pH > 5.5, while was favorable at pH < 5.5. The major reactive radicals responsible for RhB degradation classified by radical quenching experiment were O-2(center dot-) and O-1(2). The possible mechanism was further proposed based on the results. The alpha-MnO2/Pal composite showed nearly 50% mineralization ratio in the presence of PMS and an excellent reusability. The results from this study revealed that alpha-MnO2/Pal composite is an effective catalyst to activate PMS for RhB degradation.