Graphene stimulates the nucleation and growth rate of NaCl crystals from hypersaline solution via membrane crystallization

Abstract

Membrane crystallization (MCr) is regarded as a powerful tool for promoting the formation of crystals of salt from hypersaline solutions such as seawater brine. In this kind of process, a hydrophobic membrane is used to remove water in the form of vapor from a saline solution. As a consequence, super-saturation is produced and crystals of salt are formed in the retentate. Today, the major concern is the restricted industrial process scale up for this technology. This is due to the lack of membranes with features designed to handle MCr processes suitably. A higher yield of uniformly sized and shaped crystals is targetable. Herein, composite PVDF–graphene membranes are proposed as interactive interfaces for adjusting nucleation-and-growth events in the MCr process. An experimental in silico study is proposed to examine the steps which precede the crystallization and regulate the formation of crystals. Well-established interactions at the graphene–solution interface are envisaged to stimulate continually water sequestration from ion–water clusters and promote ion–ion aggregation. Reduced nucleation time and increased growth rate of the crystals are detected. Coefficients of variation of 26.7–32.2% are estimated, yielding an indication of a major uniformity of the crystals. Both the experimental and theoretical findings provide interesting indications of the capacity of the graphene to direct the nucleation and growth of minerals on a scale of time and space.