Graphene-based membranes for organic solvent nanofiltration

Abstract

Different from the conventional polymeric separation membranes having a wide flexible-pore size distribution, layered graphene-based films with interconnected nanochannels provide narrowly well-defined nanopore-size distribution and thus are extremely advantageous for precise liquid filtration and separation. Recently, considerable progress has been achieved in graphene-based membranes for molecular sieving in water. For example, it was found that sub-micrometer-thick graphene oxide (GO) membranes were almost impermeable to liquids, vapors, or gases but allowed unimpeded permeation of water [1] because of the nearly frictionless flow of water molecules through the two-dimensional hydrophobic nonoxidized capillaries. Moreover, it was further demonstrated that GO membranes could act as molecular sieves to block all solutes with hydrated radii > 0.45 nm when immersed in water [2], in which size exclusion appears to account for this behavior. For smaller sizefitted solutes that can enter in nanochannels, GO membrane could achieve more accurate ion selectivity via the diverse interactions between ions and sp 2 clusters or oxygen-containing functional groups on GO basal planes [3].The findings mentioned above implicate that GO membranes are extremely promising for a broad spectrum of separation due to their tunability in pore size to remove various target solutes, including expansion by inserting large spacers and decrease by reducing, crosslinking, etc. [4]. Consequently, most existing studies focused on the adjustment of pore structure for high flux and retention. The representative novel nanostrandchanneled GO membrane exhibited 10-time higher permeance than the conventional polymeric separation membranes [5]. However, graphene-based membranes confronted with some crucial challenges in practical industrial applications, such as scale-up of membranes to large-area, the narrow interlayer spacing in water for highly effective desalination, molecular transport mechanism confined in nanocapillaries, stability in water for long periods of time, especially graphene-based membranes used for organic solvent nanofiltration (OSN).Over the past two years, some successes have been achieved in these aspects. Large-area GO membranes were accessible by an industrially adaptable method of blade coating, which aligned the discotic nematic phase of GO on a porous support [6]. The highly ordered GO membranes formed organized channels and demonstrated outstanding water permeability. Another alternative method is spray coating GO aqueous dispersion and few-layered graphene to yield robust membranes that are easy and scalable to produce [7]. The hybrid layered membranes maintained effective NaCl rejection near 85% and 96% for an anionic dye. The achievement of 97% high rejection for NaCl is a significant breakthrough due to the controllable limited swelling of GO laminates in water [8]. The ion permeation rates were found to decrease exponentially with decreasing sieve size because of dehydration effects whereas water transport was sligh...

Graphene‐Based Advanced Membrane Applications in Organic Solvent Nanofiltration

“…Thereafter, exploration of the state‐of‐the‐art performance of GO‐based membranes in OSN processes is conducted as reviews in this field mainly emphasize polymeric membranes. [ 10,87–90 ] Subsequently, the transport properties of GO‐based membranes under different configurations in organic solvents are illustrated, followed by the conclusion and potential prospects of GO‐based membranes in OSN applications.…”