2D materials assisted membrane crystallization: A new combined theoretical and experimental approach

In the field of nanotechnologies, nano-composite membranes [1-2] enriched with two-dimensional (2D) materials are attracting interest in various areas of the scientific research, due to their peculiar and exceptional electronic properties. Actually 2D materials are becoming promising in membrane technology dedicated to water treatment as well. Specifically, 2D materials confined in defined volumetric spaces can assist mass transfer through membranes under specific conditions. New mechanisms are envisaged to control water sequestration from ion solutions causing quicker ion aggregation processes during Membrane Crystallization (MCr). The latter is part of the membrane technology enabling recovery of valuable salts from seawater and brine. In the recent past [1,3-4], atomistic simulations have provided a detailed picture of the formation of the critical nucleus of salts in supersaturated solution. Herein, for the first time we explore the potential of 2D materials in MCr technology from experimental and computational points of view. A combined molecular approach has been employed to predict and validate the effects of 2D materials on salts nucleation and growth rate when NaCl solution comes in contact with membrane surfaces. Experimental tests and simulations have been performed using different concentrations of exfoliated 2D flakes, designing three different models: pristine PVDF, PVDF with Graphene at 5% wt and PVDF with Graphene at 10% wt. As a first outcome, MD simulation demonstrate how the chemical composition of the membrane surface, can affect the crystallization of salts, while experimental test yield clear the role of the filler in nucleation grow rate, crystal size and shape, but also in the energy of the system [5]. In the overall, the nanomaterials influence kinetics of crystal formation, reducing the nucleation times. Aknowledgment: We acknowledge financial support by the 'Ministero degli Affari Esteri e della Cooperazione Internazionale, Direzione Generale per la Promozione del Sistema Paese' within the framework of the Great Relevance International Project Italy (MAECI)-China (NSFC) 2018-2020 - New Materials, with particular reference to Two-dimensional systems and Graphene (Prot.MAE0088962). Image: Figure. Final NaCl crystals achieved from a) Molecular Dynamiscs simulation and from b) Membrane assisted Crystallization experiments. In both cases a PVDF with Graphene 5% membrane was used. Recent Publications 1. Tsai JH, Perrotta ML, Gugliuzza A, Macedonio F, Giorno L, Drioli E, Tung KL, Tocci E (2018) Membrane -Assisted Crystallization: A molecular view of NaCl Nucleation and Growth, Appl. Sci., 8, 2145. 2. Perrotta ML, Saielli G, Casella G, Macedonio F, Giorno L, Drioli E, Gugliuzza A (2017) An ultrathin suspended hydrophobic porous membrane for high-efficiency water desalination, Appl. Mat. Today, 9, 1-9. 3. Chackraborty D, Patey GN (2013) How Crystals Nucleate and grow in aqueous NaCl solution, J. Phys. Chem. Lett., 4, 573-578. 4. Lanaro G, Patey GN (2016) Birth of NaCl Crystals: Insight from Molecular Simulations, J. Phys. Chem. B., 120, 9076-9087. 5. Espinosa JR, Vega C, Valeriani C, Sanz E (2015) The crystal - fluid interfacial energy and nucleation rate of NaCl from different simulation methods, J. Chem. Phys, 142 , 194709.