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 α-MnO 2 loaded palygorskite (α-MnO 2 /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 α-MnO 2 on the surface of Pal and characterized the surface of the composite. The surface area of α-MnO 2 /Pal composite was 159.13 m 2 /g, which was much higher than that of Pal and α-MnO 2 . The Pal, α-MnO 2 , Mn 2+ , and α-MnO 2 /Pal were used to activate PMS for RhB degradation. Nearly 100% RhB degradation was obtained in α-MnO 2 /Pal + PMS system in 180 min and in α-MnO 2  + PMS system in 300 min, while only 50% degradation was obtained in Pal + PMS system and 71.4% degradation in Mn 2+  + PMS system in 300 min. The degradation fitted the pseudo-first-order reaction kinetics well with rate constant of 0.02041 min −1 for α-MnO 2 /Pal + PMS system, 0.01192 min −1 for α-MnO 2  + PMS system, and 0.00435 min −1 for Mn 2+  + PMS system, respectively. The factors affecting RhB degradation were further investigated. The RhB degradation efficiency increased with the increase of α-MnO 2 /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 − and 1 O 2 . The possible mechanism was further proposed based on the results. The α-MnO 2 /Pal composite showed nearly 50% mineralization ratio in the presence of PMS and an excellent reusability. The results from this study revealed that α-MnO 2 /Pal composite is an effective catalyst to activate PMS for RhB degradation.