The mechanism for the stability of graphene oxide membranes in a sodium sulfate solution

Tuning Transport in Graphene Oxide Membrane with Single-site Copper (II) Cations

Controlling the ion transport through graphene oxide (GO) membrane is challenging, particularly in the aqueous environment due to its strong swelling tendency. Fine-tuning the interlayer spacing and chemistry is critical to create highly selective membranes. We investigate the effect of single-site divalent cations in tuning GO membrane properties. Competitive ionic permeation test indicates that Cu²⁺ cations dominate the transport through the 2D channels of GO membrane over other cations (Mg²⁺/Ca²⁺/Co²⁺). Without/With the single-site M²⁺ modifications, pristine GO, Mg-GO, Ca-GO, and Cu-GO membranes show interlayer spacings of ∼13.6, 15.6, 14.5, and 12.3 Å in wet state, respectively. The Cu-GO membrane shows a two-fold decrease of NaCl (1 M) permeation rate comparing to pristine GO, Mg-GO, and Ca-GO membranes. In reverse osmosis tests using 1000 ppm NaCl and Na₂SO₄ as feeds, Cu-GO membrane shows rejection of ∼78% and ∼94%, respectively, which are 5%–10% higher than its counterpart membranes.

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Single-site Cu²⁺ decreases the interlayer spacing of wet graphene oxide membrane

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Single-site Cu²⁺ modifications can enhance salt rejection

Highly Stable and Antibacterial Two-Dimensional Tungsten Disulfide Lamellar Membrane for Water Filtration

Two-dimensional (2D) lamellar membranes consisting of restacked WS₂ nanosheets have shown excellent separation properties for water filtration. The stability, antifouling properties, and antibacterial activities of the WS₂ laminar membranes were investigated for practical application. We discovered that the separation properties of the WS₂ laminar membranes changed slightly after soaking in water for 28 days as well as that of a 45 h-cross-flow filtration, demonstrating an extraordinary operational stability of the WS₂ laminar membranes. The remarkable stability is related to the dominant van der Waals interactions between WS₂ nanosheets. In addition, the WS₂ laminar membranes exhibited excellent antibacterial properties against S. aureus and E. coli with antibacterial rates of 91.3 % and 89.7 %, respectively. These properties of the WS₂ laminar membranes make them promising candidates for application in water filtration.

Combined Effects of Surface Charge and Pore Size on Co-Enhanced Permeability and Ion Selectivity through RGO-OCNT Nanofiltration Membranes

Nanofiltration (NF) has received much attention for wastewater treatment and desalination. However, NF membranes generally suffer from the trade-off between permeability and selectivity. In this work, the coenhancement of permeability and ion selectivity was achieved through tuning the surface charge and pore size of oxidized carbon nanotube (OCNT) intercalated reduced graphene oxide (RGO) membranes. With the increase of OCNT content from 0 to 83%, the surface charge and the pore size were increased. The permeability increased to 10.6 L m^-2 h^-1 bar^-1 and rejection rate reached 78.1% for Na₂SO₄ filtration at a transmembrane pressure of 2 bar, which were 11.8 and 1.3 times higher than those of pristine RGO membrane. The composite membrane also showed 11.1 times higher permeability (11.1 L m^-2 h^-1 bar^-1) and 2.9 times higher rejection rate (35.3%) for NaCl filtration. The analyses based on Donnan steric pore model suggest that the increased permeability is attributed to the combined effects of enlarged pore size and increased surface charge, while the enhanced ion selectivity is mainly dependent on the electrostatic interaction between the membrane and target ions. This finding provides a new insight for the development of high-performance NF membranes in water treatment and desalination.

Recent Developments of Graphene Oxide-Based Membranes: A Review

Membrane-based separation technology has attracted great interest in many separation fields due to its advantages of easy-operation, energy-efficiency, easy scale-up, and environmental friendliness. The development of novel membrane materials and membrane structures is an urgent demand to promote membrane-based separation technology. Graphene oxide (GO), as an emerging star nano-building material, has showed great potential in the membrane-based separation field. In this review paper, the latest research progress in GO-based membranes focused on adjusting membrane structure and enhancing their mechanical strength as well as structural stability in aqueous environment is highlighted and discussed in detail. First, we briefly reviewed the preparation and characterization of GO. Then, the preparation method, characterization, and type of GO-based membrane are summarized. Finally, the advancements of GO-based membrane in adjusting membrane structure and enhancing their mechanical strength, as well as structural stability in aqueous environment, are particularly discussed. This review hopefully provides a new avenue for the innovative developments of GO-based membrane in various membrane applications.

Preparation of freestanding graphene-based laminar membrane for clean-water intake via forward osmosis process

Here, a thin freestanding graphene oxide based laminar membrane was prepared for clean-water intake through a forward osmosis process.

Nanofluidics in two-dimensional layered materials: inspirations from nature

This review highlights the recent progress, current challenges, and future perspectives in the design and application of 2D layered materials for nanofluidic research, with emphasis on the thought of bio-inspiration.