Recent Advances in Layered-Double-Hydroxide-Based Separation Membranes.

The use of two-dimensional materials shows great promise for the development of next-generation membrane materials, thanks to their atomic thinness and the ease with which precise nanochannels can be constructed. Among these materials, layered double hydroxides (LDHs) stand out as an important class, possessing many features that make them ideal for constructing high-performance membranes. LDHs offer many advantages, such as their abundant and tunable interlayer anions, which enable the preparation of membranes with adjustable sub-nanometer pore sizes. Additionally, their hydrophilicity and positive charge characteristics afford them unique benefits. LDHs have been found to be effective in gas separation, ion sieving, and nanofiltration. This review provides a summary of the latest progress in using LDHs for membrane separation. It begins by introducing the basic properties of LDHs, followed by the assembly strategy for LDH membranes. Furthermore, the review presents the research status of LDHs membranes in various fields in a systematic manner. Lastly, the paper highlights some challenges and future prospects for preparing and applying LDHs membranes.

Two-Dimensional LDH Film Templating for Controlled Preparation and Performance Enhancement of Polyamide Nanofiltration Membranes.

Tailored design of high-performance nanofiltration membranes that can be used in a variety of applications such as water desalination, resource recovery, and sewage treatment is desirable. Herein, we describe the use of layered double hydroxides (LDH) intermediate layer to control the interfacial polymerization between trimesoyl chloride (TMC) and piperazine (PIP) for the preparation of polyamide (PA) membrane. The dense surface of LDH layer and its unique mass transfer behavior influence the diffusion of PIP, and the supporting role of the LDH layer allows the formation of ultrathin PA membranes. By only changing the concentration of PIP, a series of membranes with controllable thickness from 10 to 50 nm and tunable crosslinking-degree can be prepared. The membrane prepared with a higher concentration of PIP shows excellent performance for divalent salt retention with water permeance of 28 Lm-2 h-1 bar-1 , high rejection of 95.1 % for MgCl2 and 97.1 % for Na2 SO4 . While the membrane obtained with a lower concentration of PIP can sieve dye molecules of different sizes with a flux of up to 70 Lm-2 h-1 bar-1 . This work demonstrates a novel strategy for the controllable preparation of high-performance nanofiltration membranes and provides new insights into how the intermediate layer affects the IP reaction and the final separation performance.