Graphene Oxide: A Novel 2‐Dimensional Material in Membrane Separation for Water Purification

Abstract

a significant advantage, greatly facilitates GO deposition from solution using water as a low cost and environment-friendly solvent. [3] Recently, GO has attracted great attention as a novel 2-D membrane material in water purification application because of its excellent mechanical property, atomically thin thickness, excellent dispersion in water, and ease to form compact membrane structure or to be added into polymer matrix. [3,4] Concept demonstration/preliminary studies on using graphene-based membranes for water purification were focused on simulations for single layer graphene/ GO/reduced GO (rGO) with structural defects. Cohen-Tanugi et al., [5] using molecular dynamics (MD) simulation, found that hydrogenated and hydroxylated defects with appropriate sizes on graphene could have 2-3 orders of magnitude higher water permeability than commercial reverse osmosis (RO) membranes but similarly high salt rejection, suggesting great potential of single-layered graphene membranes for desalination. Lin et al. [6] showed by MD simulations that thermally reducing GO with different initial epoxy to hydroxyl ratios and different oxygen concentrations may generate selective defects on rGO for high water permeability and high salt rejection desalination. Figure 2a shows representative structures of rGO after reduction at 2,500 K, when GO flakes with different starting oxygen concentrations and epoxy concentrations or epoxy/hydroxyl ratios are used. With the increase of oxygen concentration and epoxy concentration, rGO becomes more defective and has bigger nanopores because of more carbon removal from the GO matrix. This suggests pores on rGO may be controlled by controlling starting GO composition and reduction conditions. Further, they studied desalination performance of defects on rGO after reduction at different temperatures and using GO with different oxygen concentrations and epoxy concentrations (Figure 2b). Too low oxygen concentration (17%) leads to complete water blocking irrespective of reduction temperature and initial epoxy concentration or epoxy/hydroxyl ratio. At higher initial oxygen concentration (25% and 33%), high water flux and 99% salt rejection can be obtained depending on reduction temperature epoxy/hydroxyl ratio. These promising simulation results, therefore, suggest appropriately reducing GO with desired starting composition As a newly emerging 2-dimensional (2-D) material with sub-nanometer thickness, graphene oxide (GO) has been widely studied either as a pure/skeleton membrane material or as an additive in and a functional coating on matrix membranes for water purification because of its unique physico-chemicomechanical properties. Manipulating or incorporating this novel 2-D material effectively into a membrane structure has been shown to significantly improve membrane performance, including increased water permeability, alleviated fouling, improved antibacterial properties, etc., which will eventually lead to lower energy consumption, longer lifetime, and lower maintenance cost. As the pure/...

A Comprehensive Review on Polymeric Nano-Composite Membranes for Water Treatment

“…These functional groups impart hydrophilicity to GO especially their sheets which due to their superior chemical stability, strong hydrophilicity and high surface area are highly feasible for use as nanofillers (additive) for polymeric membranes to form polymeric nano-composite membranes [149,150]. Due to its planar and 1-atom thick layer structure, graphene oxide is cost effective and exhibits excellent properties such as high conductivity, large surface area, electromagnetic properties, good tensile and mechanical strength [151][152][153]. Graphene oxide based membranes are used in gas and ion separation due to their ability to stack into layers thus forming nanochannels which serve as pores for transport of highly selective ions and molecules.…”

Solar‐Inspired Water Purification Based on Emerging 2D Materials: Status and Challenges

“…[88] Graphene-based materials, the most extensively researched 2D materials, have been widely used in photothermal evaporation, [76,[89][90][91][92][93][94][95][96][97][98][99][100][101][102] photoinduced antimicrobial treatment, [103][104][105][106][107][108] and photocatalytic degradation, [109][110][111][112][113][114][115][116][117][118][119] which have been widely reviewed. [120][121][122][123][124][125][126][127][128][129] Although solar-inspired application based on emerging 2D materials in addition to graphene-based nanomaterials has also made a great improvement, there is no review on this bright direction to systematically summarize the development and analyze the further perspectives.…”

Preparation of stable and superior flux GO/LDH/PDA‐based nanofiltration membranes through electrostatic self‐assembly for dye purification

“…In recent years, graphene oxide (GO) has triggered significant attention as a new type of self-assembly membrane material attribute to possess a unique honeycomb two-dimensional (2D) sheet-like structure, large surface area, hydrophilicity, flexibility, and chemical stability. [12][13][14][15][16] Furthermore, a range of actively functional groups like hydroxyl, epoxide, and carboxyl groups distribute on defects and edges, which can adsorb aromatic organic contaminants and heavy metal ions. 4,[17][18][19] More than this, the 2D nanochannels between self-assembly GO flakes can provide pathways for water permeation.…”