Study of Anionic Dye Removal from Aqueous Solutions by a Novel Ultrafiltration Ceramic Membrane with Carbon Coating

In this work, we propose a novel ultrafiltration ceramic membrane based on support from fly ash microspheres and selective layer from alumina nanofibers with carbon coating. The membrane is characterized by the average pore size of 19 nm and water permeability of 46 L/m2 h bar. The filtration experiments with aqueous solutions of anionic dyes are performed in cross-flow mode. The membrane demonstrates high rejection of 96–97 and 99.8% for Reactive blue 4 (681 Da) and Direct red 80 (1373 Da), respectively. A lower rejection of 55–60 and 79–81% is found for Orange II (350 Da) and Indigo carmine (466 Da), respectively. The permeate flux is in the range 147–171 L/m2 h at the transmembrane pressure of 5 bars. The solutions with lower dye concentration (20 vs. 100 mg/L) demonstrate higher degree of removal. The adsorption isotherms for considered dyes on the membrane support and selective layer as well as zeta potential of selective layer surface are measured. It allows us to reveal that the dye rejection occurs mainly due to electrostatic repulsion between anionic dyes and negatively charged membranes surface, while the contribution of adsorption to the rejection is minor. The present study provides new insights into the mechanisms of dye removal by ultrafiltration membranes and contributes to the development of solutions for wastewater treatment in dying and textile industries.