Mn oxide coated catalytic membranes for hybrid ozonation-membrane filtration: Membrane microstructural characterization

Ceramic ultrafiltration membranes were coated with the hydrated MnO2 using a novel layer-by-layer (LbL) technique. Ozonation of MnCl2 was used to prepare the MnO2 nanoparticles used in the LbL procedure. The coated membranes were then sintered in air at 500 °C for 45 min. Upon sintering, the MnO2 was converted to α-Mn2O3 (as characterized by selected area diffraction of transmission electron microscopy (TEM) images and X-ray diffraction (XRD)). The surface layer was uneven and tended to increase in thickness with increasing number of coatings. The presence of Mn throughout the membrane after sintering indicated that the nanoparticles used to coat the membrane penetrated into the filter and/or residual Mn2+ ions in the coating suspension were sorbed onto the filter and subsequently oxidized to form manganese oxide. The manganese oxide surface layer acted as a catalyst for the oxidation of suspended and dissolved organic carbon when the membrane was used in a combined ozonation-membrane filtration system treating natural water. This catalytic activity manifested itself as improved recovery of the permeate flux due to the oxidation of organic foulants that deposited on the membrane surface.