Quan-Fu An

Tuning molecular sieving channels of layered double hydroxides membrane with direct intercalation of amino acids

Two-dimensional (2D) materials have been widely used to construct efficient molecular sieving and transport channels in membrane separation. However, controlling the architecture and properties of the separation channel is still a great challenge. In this study, we propose a facile and feasible approach to prepare layered double hydroxide (LDH) composite membranes on tubular ceramic substrates by using amino acids (glycine, serine and alanine) as intercalation molecules. The interlayer spacing formed in the stacked LDH nanosheets provides transport channels for water molecules, and is modified through in situ intercalation of amino acid molecules with different molecular size and hydrophilic properties. The amino acid-intercalated LDH membranes exhibited high permeance without sacrificing rejection compared with pristine LDH membranes. Particularly, the glycine-intercalated LDH composite membrane with expanded hydrophilic transport channels shows a permeance of 566 L m−2 h−1 MPa−1 and a rejection of about 98.5% towards Eriochrome Black T (EBT) molecules. The permeance is 2.2-fold higher than that of the pristine LDH membrane. Moreover, molecular simulation was also used to interpret the intercalation and separation mechanism of the LDH membranes. We anticipate that this study may extend the materials and methods to regulate and control the transport channels in membranes.

A vertically channeled lamellar membrane for molecular sieving of water from organic solvents

Molecular sieve-based membranes are considered to be promising for achieving both high selectivity and permeability. Layered double hydroxides (LDHs) are typical two-dimensional crystalline compounds with highly uniform interlayer galleries that can be used to construct efficient molecular transport pathways. Herein, vertically channeled laminates are constructed on a tubular alumina substrate using CoAl–LDH as building blocks. Good-quality laminates are crystallized by direct nucleation and growth onto the alumina, in which alumina substrates act as both reactants and supports. Vertically aligned interlayer galleries are formed as sieving and transport channels for water molecules with the oriented nucleation effect of NH4F. Compared with the zigzag pathways formed by two dimensional materials parallel to the substrate, the straight vertical channels have higher molecular transfer efficiency. As a result, the robust CoAl–LDH membranes show much higher and more stable organic solvent dehydration performance than most membranes under a wide range of feed conditions. This work thus demonstrates that LDH-based composite membranes are highly promising as the next generation of membranes for molecular sieving.