One step co-sintering synthesis of gradient ceramic microfiltration membrane with mullite/alumina whisker bi-layer for high permeability oil-in-water emulsion treatment

Developing a permeation property and reducing the cost for ceramic microfiltration membrane are significant challenges and target. In this study, a gradient structure ceramic microfiltration membrane with mullite/alumina whisker bi-layer was successfully prepared using the dry-pressing method and one-step co-sintering process. In addition, the co-sintering conditions of substrate and whisker layer, the pore size regulations of whisker layer and emulsified oily wastewater filtration performance of the ceramic microfiltration membranes were systematically investigated. The gradient structure ceramic microfiltration membranes with high bonding strength and flexural strength were obtained under a co-sintering temperature of 1300 °C, and the average pore size of ceramic membrane was approximated in 120 nm, through the coordinated adjustment of the gradient layer by mullite whisker and alumina whisker. The filter performance results showed that with the synergistic effect of high porosity and low tortuosity of the whisker stacking membrane structure, the obtained ceramic membrane exhibited high permeability performance and oil rejection efficiency. The separation fluxes of oil-in-water emulsion with 500 and 1000 mg/L were 901 and 547 L/(m2·h·bar), respectively, and the oil rejection efficiency was higher than 99%. Even after 10 filtration cycles, the separation flux was still steady at 415 L/(m2·h·bar) for the separation process of oil-in-water emulsion with 1000 mg/L. In conclusion, the excellent pore structure of ceramic membrane with whisker layer endowed the separation flux for the oil-in-water emulsion, and the one-step co-sintering indicated a promising practical application for reducing the cost of ceramic microfiltration membranes.