Fabrication of Positively and Negatively Charged, Double-Shelled, Nanostructured Hollow Spheres for Photodegradation of Cationic and Anionic Aromatic Pollutants under Sunlight Irradiation

Abstract A novel approach to prepare double-shelled, nanostructured hollow spheres with positively and negatively charged was proposed. If the difference in isoelectric points between M x O and N y O was large enough, at a certain pH range, the inner and outer shell of double-shelled M x O@N y O hollow spheres were positively and negatively charged, respectively. A proof-of-concept was shown, using WO 3 and TiO 2 as anionic and cationic building subunits, respectively. The nanoparticles of WO 3 and TiO 2 were coated successively onto the functionalized polystyrene (PS) template beads, the resulted PS@WO 3 @TiO 2 nanocomposites were calcined at elevated temperature, and then double-shelled WO 3 @TiO 2 hollow spheres were obtained. The dispersity, morphology, size, and lattice of these hollow spheres were tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The presence and purity of both WO 3 and TiO 2 phases were confirmed by electron energy loss mapping analysis and X-ray diffraction analysis (XRD). The specific surface area and the average pore diameter of these hollow spheres were 53.04 m 2 /g and 8.042 nm, respectively. The photocatalytic activity for the degradation of cationic and anionic aromatic pollutants was in the order of double-shell hollow spheres WO 3 @TiO 2  > single-shell WO 3 -TiO 2  > P25, i.e., the synergistic effect of coupling TiO 2 with WO 3 on photocatalytic performance was proved by us.