Amino Acid Cross-Linked Graphene Oxide Membranes for Metal Ions Permeation, Insertion and Antibacterial Properties

A photo-Fenton self-cleaning membrane based on NH2-MIL-88B (Fe) and graphene oxide to improve dye removal performance

Attapulgite nanofibers and graphene oxide composite membrane for high-performance molecular separation

Electrical, luminescence, and microwave-assisted reduction behaviour of alkali vs. alkaline earth metal ion-modified graphene oxide membranes

Objectives Graphene oxide (GO) membranes are promising materials in many fields such as supercapacitors1, gas and liquid separation2, sensing3, and acoustic transduction4. For these applications, a high efficiency, scalable method for preparing GO membranes without compromising mechanical properties are required.To date, the most commonly used technique to manufacture GO membranes is vacuum filtration. By filtering the GO suspension, GO sheets are stacked and assembled into membranes. However, this technique has several shortcomings. Firstly, this method cannot be used to control the ordering of GO sheets – a property that determines the microstructures and directly influences interactions between sheets. Secondly, this technique is time- and energy-consuming, and the size of the GO membranes produced is limited by the size of the filter5. New Results We report a new method for preparing large scale GO membranes with tunable microstructures and controllable mechanical properties. This method involves injecting the GO suspension through a thin nozzle into a coagulation bath for promoting the gelation of the GO into a membrane. The nozzle moves at a speed coordinated with the injection flow rate to prepare uniformly thick membranes (Fig. 1(a)). The flow rate in the nozzle induces shear stress, which in turn induces the alignment of GO sheets. Therefore, by adjusting the flow rate, the alignment of GO sheets is tunable, and the mechanical property is controllable. By using this technique, we achieved a long continuous GO membrane with high ultimate tensile strength (UTS) of 67-160 MPa at preparation speeds of up to 160 cm/min. As a comparison, the vacuum filtration method takes a day to prepare a single 47 mm diameter GO membrane with a UTS of 70-125 MPa6. Conclusions In this study, we designed a highly efficient flow injection method that allows us to prepare large-scale GO membranes with tunable microstructures rapidly. This in turn allows us to influence interactions between sheets and, most importantly, manipulate the mechanical properties. In this paper, we show the vast improvement in UTS measurements for GO membranes prepared using the flow injection method as opposed to the vacuum-filtration. This technique will enable fast and controllable production of GO membranes for various fields which call for membranes with good mechanical performance.Fig. 1. (a) Schematically drawing of the process of the injection method for GO membranes preparation; (b) UTS of GO membranes prepared under different flow rates Acknowledgments This research is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the McGill Engineering Doctoral Awards (MEDA).

Incorporating multivalent metal cations into graphene oxide: Towards highly-aqueous-stable free-standing membrane via vacuum filtration with polymeric filters

Graphene oxide (GO) membranes hold significant promise for the water purification. However, they also face the problem of structural swelling, which limits their use in water treatment applications. In this work, a novel dual-modulated core-shell metal-organic framework@Chitosan (MOF@CS) was successfully synthesized and used as an intercalation cross-linker to optimize the interlayer spacing and stability of GO membranes. Molecular dynamics simulation confirms that MOF@CS, acting as an intercalator, accelerates the water diffusion rate within the channels of the GO layer compared to a pure GO layer. At the same time, Fourier Transform Infrared Spectroscopy analysis reveals that MOF@CS serves as a cross-linker for covalently cross-linking the GO layer. The nanofiltration performance and stability of the improved MOF@CS-GO composite membranes were significantly enhanced. Compared to the pure GO membranes, the MOF@CS-GO composite membranes exhibited enhanced Congo red rejection rates (from 76.5% to 95.6%) while maintaining a high pure water flux (34.5 L·m-2·h-1·bar-1) and good structural stability (stable dye removal performance over 120 h). This dual regulation strategy is expected to effectively solve the swelling problem of GO membranes in aqueous media and open up avenues for advancing their performance.

Cation-dependent structural instability of graphene oxide membranes and its effect on membrane separation performance

Graphene oxide (GO) membranes have shown enormous promise in desalination and molecular/ionic sieving. However, the instability of GO membranes in aqueous solutions seriously hinders their practical applications. Herein, we report a novel and simple strategy to fabricate stable GO membranes in water-based environments through the insertion of various metal cations from metal foils (e.g., copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) foils) and natural deposition. Based on the cation-π, coordination, and electrostatic interaction between metal cations and GO nanosheets, the aqueous stability and mechanical strength of the membranes are significantly improved. The permeation rates for acetone, toluene, and p-xylene molecules across the GO membrane cross-linked by copper ions with a deposition time of 24 h are 0.966, 0.074, and 0.100 mol m-2 h-1, respectively. Moreover, this membrane displays excellent separation performance, and the separation factor of K+/Mg2+ is up to 68.8 in mono-/multivalent metal cation sieving, which indicate the effective molecular/ionic sieving performance. Meanwhile, the ionic sieving of the GO membrane cross-linked by copper ions has excellent repeatability and long-term stability. The versatility of this natural deposition strategy to fabricate GO membranes cross-linked by metal cations is investigated by using Fe foil, Zn foil, and Ni foil as well as other porous substrates such as polyvinylidene fluoride (PVDF), polyethersulfone (PES), and nylon membranes and filter paper. This fabrication strategy also enables low-cost preparation of large-area GO membranes. Therefore, GO membranes cross-linked by metal cations and prepared by this simple metal cation incorporation strategy have large potential application for molecular/ionic sieving in various solution systems.

Presently carbon allotropes namely graphene, graphene oxide (GO) and reduced graphene oxide (RGO) are being extensively utilized for water purification applications. The presence of myriad types of oxygen functional groups in the GO, however, makes this material very hydrophilic, allowing it to absorb water and to swell in moist or watery environments and to significantly damage its intended performance. In contrast, fully reduced graphene oxide membranes are not stable due to fewer oxide groups which are mainly responsible for GO flakes stacking. In the present work, the aforementioned problems are overcome by optimizing the oxygenated functional groups to develop mildly reduced graphene oxide (MRGO) membrane over PVDF (polyvinylidene fluoride) support. GO is reduced by L-Ascorbic Acid (LAA) with different amounts of wt.% and an optimized MRGO membrane is achieved at 10 wt.% of LAA, which is stable and showing comparatively lower swelling than GO membrane. All related structural and optical characterizations like XRD, SEM, EDAX, Raman, FTIR, and Contact angle have been done to evaluate the effect of mild reduction of GO. The studies are indicative of their potential application in water purification.

Graphene oxide for high-efficiency separation membranes: Role of electrostatic interactions

Graphene oxide (GO) membranes exhibit promising potential in nanofiltration due to their controllable transport channel size and low transport resistance of water molecules, resulting in exceptional water permeability. However, the trade-off between water flux and rejection ratio stemming from tightly packed interlayers poses a challenge to the application of GO membranes in nanofiltration. To overcome this trade-off, a practical method is urgently needed to regulate the interlayer space of GO membranes. In this study, a macrocyclic molecule with a rigid porous structure, cucurbit[6]uril (CB[6]), has been introduced to enlarge and precisely adjust the interlayer distance of GO membranes, effectively addressing the trade-off dilemma. The interlayer distance can be precisely adjusted within a range of 0.46 to 1.35 nm, making it suitable for the removal of small organic molecules from wastewater. Through the optimization of GO and CB[6] quantities, the GO membrane containing 20 µg GO and 49.9 wt% CB[6] (CB6GO-4) demonstrates a high pure water flux (PWF) exceeding 171.3 L m-2h−1 bar−1, more than 5.9 times higher than a pure GO membrane (28.8 L m-2h−1 bar−1), alongside a dye rejection ratio over 92 %, indicating the promising potential of CB[6]-intercalated GO membranes in removing organics from industrial saline wastewater.

Graphene oxide membranes for enhancing water purification in terrestrial and space-born applications: State of the art

Graphene oxide membranes with hierarchical structures used for molecule sieving

Graphene oxide membranes for ion separation: Detailed studies on the effects of fabricating conditions

Preparation of high-performance nanocomposite membranes with hydroxylated graphene and graphene oxide