Evaluating graphene oxide and holey graphene oxide membrane performance for water purification

Reduced Holey Graphene Oxide Membranes for Desalination with Improved Water Permeance

“…Two-dimensional (2D) sheets with atomic thickness are ideal membranes for water purification because of their potential in forming sub-10 nm layers with high water permeance. − For example, single-layer graphene with nanopores deposited on ultrafiltration (UF) membranes exhibited both high water permeance and salt rejection. − However, it remains challenging to synthesize large-area defect-free sheets and generate pores with high density and uniform pore sizes . One approach to overcome these barriers is to prepare oxidized graphene (i.e., graphene oxide or GO), which can be stacked providing sub-nanometer interlayer channels (<0.7 nm) for molecular separations. − Similar to graphene, in-plane nanopores can be generated on the GO sheets (holey GO or HGO) to reduce the tortuosity and thus increase water permeance. − However, the interlayer channels in GO or HGO are often larger than hydrated ions, − and thus, they are mainly investigated for dye removal (larger than 1 nm) or separation of organic solvents, instead of water desalination. ,, Additionally, GO is susceptible to redispersion in water due to its hydrophilicity and the shearing force from the feed flow, making it challenging for long-term underwater operation.…”

“…To improve stability and salt rejection, GO nanosheets can be reduced to partially remove hydrophilic oxygen-containing groups (reduced GO or r-GO), which increases hydrophobicity and decreases interlayer spacing. , For instance, when GO was reduced by hydriodic acid (HI) vapor, increasing the exposure time from 0 to 3 min reduced the layer interspacing from 1.15 to 0.37 nm and thus water permeance from 11 L m –2 h –1 bar –1 (LMH/bar) to ≈2 LMH/bar, while the NaCl rejection increased from 28.6 to 56.9% . There exhibits a tradeoff between stability and water permeability for these r-GO membranes; that is, a higher degree of reduction (or greater stability and higher salt rejection) leads to a lower water permeance …”

“…20 There exhibits a tradeoff between stability and water permeability for these r-GO membranes; that is, a higher degree of reduction (or greater stability and higher salt rejection) leads to a lower water permeance. 12 An effective way to break this tradeoff is to create in-plane nanopores on r-GO sheets to decrease tortuosity and thus increase water permeance without decreasing salt rejection. For example, the membranes fabricated with HGO prepared using 70% HNO 3 and then H 2 reduction (with a Pd catalyst) exhibited a water permeance of 5.3 LMH/bar and Na 2 SO 4 rejection of less than 69%.…”

Construction of facilitated mass transfer composite membranes with triple-layer water nanochannel architecture for forward osmosis process using cGO-coated polysulfone separation membrane as the substrate

“…Moreover, a new peak at 1051.0 cm −1 corresponding to the OH bending appears in the cGO spectrum. 41 These results suggest that more hydroxyl and carboxyl groups are incorporated into the GO nanosheets during the carboxylation process. It can be observed from the SEM images in Fig.…”

Rational ion transport management mediated through membrane structures

“…Inorganic nanosheets, including stacked porous nanosheets (e.g., holey graphene frameworks [HGFs], [170,171] porous carbon, [172][173][174] and TaS 2 [175] ) and hybrid nanosheets (e.g., MXene/rGO [176,177] ) have also been used to construct 3D nanochannels (Figure 8). Duan et al designed a highperformance supercapacitor electrode using 3D HGFs with hierarchical pores (Figure 8A).…”