Photo-irradiation for preparation, modification and stimulation of polymeric membranes

The recent developments in combining photo-irradiation-based and membrane technologies are analyzed in this review. It is emphasized that the effects of photo-initiated reactions onto properties of polymeric membranes will largely depend on the nature of the membrane's barrier (i.e., porous vs. non-porous, uncharged vs. charged, or involving affinity interactions). For de novo preparation of membranes from low molar mass or soluble precursors, photo-initiated polymerization and photo-cross-linking are the main pathways, while photo-degradation for pore formation is only rarely applied. Membrane functionalization (modification) is described with many examples, organized into photo-cross-linking of membranes and photo-grafting of membrane surfaces, either via “grafting-to” or via “grafting-from” routes. Photo-stimulation of barrier properties is an attractive concept to create stimuli-responsive membranes, and various ways to use photo-chromic moieties for that purpose are discussed. Overall, photo-irradiation-based methods can be very versatile enabling technologies to improve the performance of polymeric membranes in technical separations (e.g., in gas separation, pervaporation, ultra- and microfiltration or as membrane adsorbers) and other processes (e.g., for controlled release or in sensor systems), and they will definitely also contribute to the development of entirely novel membrane-based materials.