Two-dimensional MWW-type zeolite membranes for efficient dye separation and water purification

Abstract

Two-dimensional (2D) zeolites provide inspiring opportunities for the exploitation of ultra-thin molecular sieve membranes, but it is rarely applied in water treatment membranes. Exfoliated 2D MWW-type nanosheets in liquid hydroxyl-terminated polybutadiene (HTPB) were assembled into the lamellar MH membranes by vacuum filtration. Various techniques were employed to characterize the surface chemical composition and morphology of the MH membranes. The typical ordered layer-like structure built by the stack of MWW nanosheets mainly contributed to the performance of the MH membrane, and the guest role of a small amount of residual HTPB has also been confirmed. The obtained MH membrane exhibited a water permeance of 11.3 L·m−2·h−1·bar−1 with above 99.5 % rejection for Evans Blue (EB). In particular, the rejection of negatively charged dyes with a molecular size greater than 1.5 nm essentially remained above 90.0 %. Moreover, the lamellar MH membrane possessed excellent physicochemical stability. Excellent rejection was guaranteed at different pressures, pH, and successive cross-flow operations. Although there is still a demand for improvement in terms of permeance, the successful preparation of 2D zeolite lamellar membranes fully demonstrates the promising potential of 2D zeolite nanosheets in water purification.