Composite Graphene and Beyond Graphene Membranes

Many areas around the globe suffer the scarcity of clean and fresh water as well as the access to adequate sanitation due to the exponential increase in the world's population and industrial activities over the last decades. Current state-of-the-art technology allows for the provision of refresh water by processing seawater and brackish water by means of membrane operations and in particularly reverse osmosis plants. Though the reverse osmosis is 10 folds more efficient than thermal processes, it is not yet an intensely competitive technology from an energetic point of view, especially for those countries that suffer important energy shortages. Also, seasonal variations in seawater quality as well as sensitivity to fouling, scaling and brine disposal make the RO-process necessary to the integration with pre-treatment steps, such as nanofiltration, and post-treatment steps, such as membrane distillation and membrane crystallization. Nanofiltration takes advantages of reducing hardness and total dissolved solid with a recover factor up to 50% and energy saving of 25-30%. Membrane Distillation and Crystallization are envisaged as suited processes to handle the brine problems, taking advantages of production of ultra-pure, desalted and demineralized water as well as concentration of aqueous salts or inorganic acids up to high concentrations, and crystallization . Despite the sustainability of integrated membrane processes, there is still a great demand for advanced materials, which can yield more efficient production of clean and safe water while reducing the energy need to produce it. The choice of 2D layered materials for the fabrication of advanced membranes appears to be a reliable route for allocating in the same device complementary functions, including mass, charge and energy transport. Herein, the potentiality of graphene and 2D materials beyond graphene in water processing is discussed. Nanopores, local defects and wrinkling in graphene sheets as well as the insertion of functional groups in the pore edges or between the stacked layers are discerned with the membrane ability to let water pass through, but also to stop pollutants and salts at the interface according to size exclusion, chemical and electrostatic interactions and Donnan's exclusion mechanisms. Electronical features are also examined in relation to the possibility to realize devices for self-sustainable energy recovery, production and storage. Finally, perspectives on the future of 2D electronic materials beyond graphene, including phosphorene, silicene, and other transition metal dichalcogenide, are discussed with an emphasis to the synthesis, characterization and production of nanoporous desalination membranes through which water flow and ion filtering can be regulated .