Three-dimensional MnO2 porous hollow microspheres for enhanced activity as ozonation catalysts in degradation of bisphenol A

Three-dimensional (3D) MnO2 porous hollow microspheres (δ- and α- MnO2 PHMSs), with high adsorption and catalytic ozonation performance, were synthesized by a self-template (MnCO3 microspheres) process at room temperature. The synthesized MnO2 PHMSs were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area. The results showed that PHMSs exhibit the excellent adsorption ability and catalytic activity owning to their hollow spherical structure, mesoporous shell and well-defined interior voids, leading to the strong adsorption for bisphenol A (BPA) and the retention of O3 molecules on catalyst. Moreover, the catalytic performance of α-MnO2 PHMSs was better than that of δ-MnO2 PHMSs which was attributed to the richer lattice oxygen of α-MnO2 PHMSs to accelerate O3 decomposition by producing more reactive oxidative species. The degradation efficiency of BPA using 3D α-MnO2 PHMSs was more than 90% in the presence of ozone within 30min reaction time. The probe tests for reactive oxidative species (ROSs) displayed that BPA degradation by catalytic ozonation is dominated by O2- and OH in our present study. Furthermore, the organic compounds as intermediates of the degradation process were identified by LC/MS.