Review of techniques for future manufacturing of ordered and functional porous films: conceivable membranes for water desalination by membrane distillation processes

This review focuses on the fabrication of well-controlled porous films, which can work as conceivable membranes for membrane distillation (MD) processes. The latter is a greener membrane technology that finds large application in water desalination. The development of this technology on industrial size is however limited by the lack on the market of membranes with suitable morphological and physicochemical features, which are necessary to keep stable and durable interfacial area at the entrance of each single pore, provide resistance to wetting and fouling phenomena and amplify productivity-efficiency trade-offs. Fundamentals of MD technology and basic concepts about needed membrane morphology and surface properties are introduced. An overview on breakthrough manufacturing approaches to get high degree of structural order in membranes is provided. Descriptive analysis of each single technique is given together with a discussion about the effects of operating conditions on final morphological properties of the films. Among the various techniques, a special focus is dedicated to micromoulding phase separation, block copolymer self-assembly, breath figure, electrospinning and layer-by-layer methods. For each family of nanostructured membranes, examples of MD testing are reported analyzing the membrane productivity, efficiency and resistance to wetting and fouling. The performance of these membranes is also compared to that of commercial and conventional home-made membranes treated under similar operating conditions with seawater or simulate seawater.