Performance of PVDF Based Membranes with 2D Materials for Membrane Assisted-Crystallization Process

Abstract

Membrane crystallization (MCr) is a promising and innovative process for the recovery of freshwater from seawater and for the production of salt crystals from the brine streams of desalination plants. In the present work, composite polymeric membranes for membrane crystallization were fabricated using graphene and bismuth telluride inks prepared according to the wet-jet milling (WJM) technology. A comparison between PVDF-based membranes containing a few layers of graphene or bismuth telluride and PVDF-pristine membranes was carried out. Among the 2D composite membranes, PVDF with bismuth telluride at higher concentration (7%) exhibited the highest flux (about 3.9 L∙m−2h−1, in MCr experiments performed with 5 M NaCl solution as feed, and at a temperature of 34 ± 0.2 °C at the feed side and 11 ± 0.2 °C at the permeate side). The confinement of graphene and bismuth telluride in PVDF membranes produced more uniform NaCl crystals with respect to the pristine PVDF membrane, especially in the case of few-layer graphene. All the membranes showed rejection equal to or higher than 99.9% (up to 99.99% in the case of the membrane with graphene). The high rejection together with the good trans-membrane flux confirmed the interesting performance of the process, without any wetting phenomena, at least during the performed crystallization tests.

Two-Dimensional Materials: From Discovery to Application in Membrane Distillation/Crystallization Processes

“…Perrotta et al [172] studied the influence of graphene loading in PVDF flat sheet membranes and concluded that a graphene loading leads to a more uniform crystal size distribution (CSD) of NaCl and a lower coefficient of variation (CV) than pristine PVDF, thanks to the assisted water exclusion. Frappa et al [108] studied how the presence of graphene and bismuth telluride in PVDF-based membranes help to obtain purer NaCl crystals. Macedonio et al [56] studied the effect of Bi 2 Se 3 introduced in PVDF membranes as fillers.…”

“…These techniques require the polymer to be soluble in a suitable solvent or in a mixture of solvents. Two-dimensional materials are usually dispersed in the solvent or a mixture of solvent as described in Frappa et al [23,107,108]. In principle, all the main phase inversion techniques can prepare membranes containing 2D materials (non-solvent-induced phase inversion (NIPS), vapor-induced phase separation (VIPS), thermally induced phase separation (TIPS) and evaporation of the solvent, (EIPS)).…”