Microscopically tuning the graphene oxide framework for membrane separations: a review

Abstract

Membrane-based separations have been widely applied in gas, water and organic solvent purifications to reduce energy consumption and minimize environmental pollution. In recent years, graphene oxide membranes (GOMs) have attracted...

Chemically Cross-Linked Graphene Oxide as a Selective Layer on Electrospun Polyvinyl Alcohol Nanofiber Membrane for Nanofiltration Application

“…The presence of GA linkages in CGOPVA-50 likely added transport resistance to the GO-selective layer, hence its lower water permeance than that of GOPVA-50. On the other hand, the GA linkages in CGOPVA-50 might have introduced more tortuous paths between the GO nanosheets, hence its enhanced solute rejections than the GOPVA-50 membrane [29,38,58]. Although water permeance was reduced, GA cross-linking in CGOPVA-50 not only ensured the GO layer stability but also improved the solute rejections of the composite NF membrane.…”

“…Multi-layer GO stacking could refine the membrane selectivity by creating tortuous paths for the water and solute, effectively separating the two components. However, stacked GOs are very hydrophilic, which renders them susceptible to damage during membrane operation as the GO sheets can easily detach and re-disperse in water [25,[27][28][29][30]. Thus, the GO-selective layer requires reinforcements to ensure its mechanical stability for longterm application.…”

Covalently Functionalized Graphene for Black Liquor Concentration Membranes

“…7,14,20,37−39 New methods for fine-tuning of the interlayer spacing are crucial to the capture, or exclusion, of target molecules and determining the separation performance of the GO membrane. 7,14,20,23,39 Our group has previously synthesized covalently functionalized graphenes from GO by a Claisen rearrangement. 40,41 Of particular relevance to the work we report herein, allylic alcohols found on the surface of GO are subjected to a Johnson−Claisen [3,3] sigmatropic rearrangement to produce ethyl esters attached to the basal plane via robust C−C bonds that can endure thermal and reductive conditions that degrade other GO derived materials.…”

“…The development of nonthermal separation technologies is imperative to reduce global energy requirements and to address environmental concerns in water purification in the industrial manufacturing, petroleum, chemicals, and paper sectors. − There is a particular need in paper manufacturing with the kraft pulping process, which generates weak black liquor (WBL) as a byproduct. WBL is often concentrated from total solids of ∼18% to ∼75%, which is important to make WBL suitable for combustion. − Since the combustion of the concentrated BL in a recovery boiler generates energy as steam and electricity, BL is regarded as one of the most critical renewable biofuels derived from wood. − However, a series of energy-intensive evaporation processes are used in the WBL concentration. − Besides, WBL is a corrosive high alkaline pH (∼12) complex aqueous fluid/dispersion that typically includes lignin, other organic materials separated from the wood, inorganic salts of Na 2 CO 3 and Na 2 SO 4 , and pulping chemicals of NaOH and Na 2 S and is processed at elevated temperatures (up to 95 °C). − Therefore, nonthermal methods that use separation materials that can endure the harsh separation conditions, have the prospects to significantly reduce energy consumption and bring economic and environmental benefits even with the partial concentration of WBL to a level of ∼30% solids. , Membrane-based separation is a promising alternative to thermal processing and offers the advantages of high energy efficiency, simplicity in the equipment, and the ability to be implemented as compact modules. − , We have been interested in graphene oxide (GO)-based membranes, which have recently received significant attention as a result of their characteristics that include: high water permeability, two-dimensional structures, chemical resistance, mechanical strength, and tunable surface chemistry. − ,,− …”

“…In GO-based separation membranes, the molecular transport pathways can be defined by different physical features: (i) defect pores in the basal plane, (ii) interedge gaps between the sheets, and (iii) interlayer space between the stacked planar sheets. ,, Although it is difficult to manipulate the defect and interedge pores precisely, ,, the interlayer spacing can be controlled by application of physical forces, , intercalation of carbon nanotubes and nanoparticles, − ionic interactions, and chemical modifications. − A narrowed interlayer spacing prevents the flux of molecules and results in low water permeation, and hence an enlargement of the interlayer spacing is vital to create free volume and enhance transport. ,,,− New methods for fine-tuning of the interlayer spacing are crucial to the capture, or exclusion, of target molecules and determining the separation performance of the GO membrane. ,,,, …”