A new magnetic heterogeneous catalyst for fast degradation of rhodamine B by peroxymonosulfate oxidation: Monodisperse-porous and Fe3O4 incorporated manganese oxide microspheres

A new synthetic method, "staged shape templating decomposition" suitable for transition or rare-earth metal oxide microspheres was developed for obtaining magnetic, uniform and porous manganese oxide (MagMnO(x)) microspheres. The microspheres 4.7 mu m in size were obtained with a specific surface area of 45.5 m(2) g(-1). Fe3O4, Mn5O8, MnO2 and Mn2O3 phases were shown by X-ray diffraction spectroscopy. Mn2+, Mn3+ and Mn4+ states were observed on the surface by X-ray photoelectron spectroscopy. Catalase-like and oxidase-like activities of MagMnO(x) microspheres were explained by coexistence of Mn and Fe crystallites in a mesoporous structure with a sufficiently large surface area and a particle interior with large mesopores facilitating substrate diffusion. The maximum substate consumption rates for catalase-like and peroxidase-like activities were determined as 15.6 mM/min and 20.3 mu M/min, respectively. By considering their ROS generation ability, MagMnO(x) microspheres were evaluated as a heterogeneous catalyst for rhodamine B (Rh B) removal via peroxymonosulfate (PMS) activation. Rh B was removed in the periods shorter than 15 min via chemical degradation with a limited physical adsorption. Superoxide anion (O-2(-center dot)) and singlet oxygen (O-1(2)center dot) radicals generated by MagMnOx-PMS system were responsible for degradation of Rh B. The highest apparent first order rate constant for Rh B degradation was calculated as 0.5771 min-1. The apparent first order rate constant increased with increasing MagMnO(x) and PMS concentrations and decreasing initial Rh B concentration. Rh B was almost completely removed in each of five recycling runs and only lower than 1.5 % w/w of Fe and Mn contents of MagMnO(x) microspheres were leached over five recycling runs. The catalyst with large particle size, resistant to agglomeration exhibited high removal rate, low dye adsorption, high magnetization, and high reusability for Rh B removal via peroxymonosulfate activation.