Photo-Responsive Water Filtration Membranes Based on Polymerizable Columnar Liquid Crystals with Azo Moieties

New materials developed in the last years promise to contribute significantly to the preparation of membranes with improved performance in water filtration. Specifically, the use of dynamic-responsive systems provides reversibility of the membrane properties. In this work, a reversible photo-switchable membrane based on templated liquid crystals is presented. Crosslinking of a columnar network, formed by the self-assembly of a discotic supramolecular complex with a photo-responsive moiety, results in a switchable filtration membrane. The azo groups in the membrane undergo a photoinduced trans-cis isomerization by irradiation with 365 nm light and relax back to the cis isomer with a lifetime of 5.7 h or within a few minutes by irradiation at 455 nm. The membranes have a light-induced reversible change in the water permeability and molecular weight cut off of poly (ethylene glycol). The effective pore size of the trans isomer (1.2 nm) increases to 1.4 nm for the cis isomer. Rejection of the organic dye Rhodamine B is reversibly switched between 50 and 85% by alternating irradiation at 365 nm and 455 nm. The reversible and specific switching demonstrates the potential of this system for light-controlled separation in nanoporous membranes.