Graphene Composite Membrane Research Articles

Chemical and thermal stability of electrospinned polyvinylidene fluoride/graphene composite membranes

The effect of graphene content, spinning flow rate, and distance on the chemical and thermal stability of electrospinned polyvinylidene fluoride (PVDF)/graphene composite membranes was systematically investigated. Long-duration soaking experiments by three typical solution media, diluted hydrochloric acid, dimethyl sulfoxide, and mixed-solution of lithium hexafluorophosphate/methyl ethyl carbonate, were used to evaluate the chemical stability of the selected samples. The relevant results of relative mass change rate all indicate that the chemical stability of PVDF composite materials increases with increasing graphene content as well as flow rate or decreasing distance. Moreover, there is a clear consistency between thermal stability and chemical stability. The results of the thermal shrinkage rate evidence that the thermal stability of the samples could be enhanced by increasing graphene content, flow rate, and decreasing spinning distance.

Exfoliated Graphene Composite Membrane for the All-Vanadium Redox Flow Battery

Exfoliated Graphene Composite Membrane for the All-Vanadium Redox Flow Battery

Simple Fabrication of Polyvinylidene Fluoride/Graphene Composite Membrane with Good Lipophilicity for Oil Treatment.

Graphene (GE) is an emerging type of two-dimensional functional nanoparticle with a tunable passageway for oil molecules. Herein, polyvinylidene fluoride (PVDF)/GE composite membranes with controllable pore structure were fabricated with a simple non-solvent-induced phase separation method. The change of crystallinity and crystal structure (α, β, γ, etc.) generated is due to the addition of GE, which benefits the design of a suitable pore structure for oil channels. Meanwhile, the hydrophobicity and thermal stability of the composite membrane were obviously enhanced. With 3 wt % GE, the contact angle was 124.6°, which was increased greatly compared to that of the GE-0 sample. Moreover, the rate of the phase transition process was affected by the concentration of casting solution, temperature, and composition of the coagulation bath. For example, the composite membrane showed better oil–water separation properties when the coagulation bath was dioctyl phthalate. In particular, the oil flux and separation efficiencies were up to 2484.08 L/m2·h and 99.24%, respectively. Consequently, PVDF/GE composite membranes with excellent lipophilicity may have good prospects for oily wastewater treatment.

Ultralight, Safe, Economical, and Portable Oxygen Generators with Low Energy Consumption Prepared by Air-Breathing Electrochemical Extraction.

Pure oxygen is vital in medical treatment, first aid, and chemical synthesis. Hypoxia can cause severe damage to the organ systems such as respiratory, digestive, and nervous systems and even directly cause death. Notably, the severe Coronavirus disease 2019 (COVID-19) pandemic has exacerbated the shortage of medical oxygen in the world. Hence, a safe, economical, and portable oxygen supply device is urgently needed. Here, we have successfully prepared a device with air-breathing electrochemical extraction of pure oxygen (ABEEPO) with light weight and high energy efficiency. By renovating the structure of the electrolytic cell, the components bipolar plate and end plate are replaced with a plastic membrane, and the component current collector is replaced with a highly conductive graphene composite membrane electrode. Due to the use of the plastic membrane and graphene composite membrane electrode, the weight of the electrolytic cell is reduced from 1319.4 to 1.6 g, and the flexibility of the electrolytic cell is successfully realized. Through optimizing anode catalysts, working area, and operating voltage, a high flow rate per mass (234 mL h-1 g-1) was achieved at a voltage of 1.2 V. The device exhibits high stability in 2 h. The new portable oxygen production device would be effective for hypoxia treatment.

Sulfate Radical-Based Advanced Oxidation Process for Ciprofloxacin Removal Using Electroconductive Laser-Induced Graphene Composite Membranes

Sulfate Radical-Based Advanced Oxidation Process for Ciprofloxacin Removal Using Electroconductive Laser-Induced Graphene Composite Membranes

Recent advances in application of the graphene-based membrane for water purification

Graphene is an atomic layer thick carbon-based material with unique two-dimensional architecture and extraordinary physiochemical, optical, electrical, and mechanical properties. Graphene and its derivatives show significant promises for the development of nanoporous ultrathin filtration membranes capable of molecular separation properties. Graphene-based nanofiltration membranes featuring distinct laminar structures can offer various novel mass-transport phenomena for purifying water, energy storage and separation, gas separation, and proton conductors. The latest developments in water purification techniques through graphene-based membranes including engineering, design, and fabrication of diverse graphene, graphene-oxide, and graphene-composite membranes are provided here in relation to their application paradigm for purifying water. The critical views on pollutant removal mechanisms for water purification along with optimization measures are specially highlighted. In addition, the challenges, shortcomings, and future prospects are pointed out. The green and large-scale synthesis technology of graphene coupling with advanced membrane fabrication techniques can promote these state-of-the-art nanofiltration membranes for a wide range of applications.

Monolayer graphene membranes for molecular separation in high-temperature harsh organic solvents

The excellent thermal and chemical stability of monolayer graphene makes it an ideal material for separations at high temperatures and in harsh organic solvents. Here, based on understanding of solvent permeation through nanoporous graphene via molecular dynamics simulation, a resistance model was established to guide the design of a defect-tolerant graphene composite membrane consisting of monolayer graphene on a porous supporting substrate. Guided by the model, we experimentally engineered polyimide (PI) supporting substrates with appropriate pore size, permeance, and excellent solvent resistance and investigated transport across the resulting graphene-covered membranes. The cross-linked PI substrate could effectively mitigate the impacts of leakage through defects across graphene to allow selective transport without defect sealing. The graphene-covered membrane showed pure solvent permeance of 24.1 L m-2 h-1 bar-1 and stable rejection (∼90%) of Allura Red AC (496.42 g mol-1) in a harsh polar solvent, dimethylformamide (DMF), at 100 °C for 10 d.

New leak elements for helium based on single-layer graphene composite membranes

Graphene containing intrinsic pores with molecular dimensions is a highly promising material for standard leak elements because of its minimal and stable gas flow. However, the etching of polymethyl methacrylate (PMMA) during the typical graphene transfer process can cause the rupture of graphene on the porous substrate due to the surface tension as the etchant solution dries out. In this article, we simplified the typical graphene transfer process that enabled the transfer of a PMMA/graphene composite membrane onto a macroporous Cu gasket as the leak element and tested the leak rate, time stability, and response time of the composite membrane. The membrane permeation area depends on the pore size of the Cu substrate, which can be controlled by laser ablation or computer numerical control milling. To ensure the accuracy of time stability, the entire test lasted 60 days. The conductance results for two devices with a permeation size of 50 and 500 μm were about 10−17 and 10−14 m3 s−1, and the maximum variation of conductance in 60 days was 14% and 2.6%, respectively. Accordingly, the permeance of the composite membrane for helium can be calculated as 4.17 × 10−12–1.09 × 10−11 Pa m3 (cm2 s Pa)−1. Moreover, the composite membrane has been proven to have a rapid response of about 2 s to the upstream pressure.

Interfacial Ions Sieving for Ultrafast and Complete Desalination through 2D Nanochannel Defined Graphene Composite Membranes.

The layered graphene membrane has high potential for efficient desalination owing to its frictionless surface and hydrophobic nature. However, it has not been demonstrated so far due to the challenges related to controlling membrane microstructure. Herein, we develop a facile and simple thiol-ene click method to prepare a perfluoro-alkyl grafted graphene (fGraphene) membrane on porous ceramic, which features an ultrahigh antiwetting surface, oriented mesoporous surface entrances, and a well-defined interlamellar spacing of ∼1.1 nm. With vacuum membrane distillation, the fGraphene membranes post ∼100% rejections to the small ions of seawater, at least 1 order of magnitude higher water fluxes than those of commercial membranes and graphene-oxide-based membranes, as well as robust stability in the desalination. Fast NaCl desalinations on the fGraphene membrane were also confirmed by the reverse/forward osmosis tests. The complete rejection of ions and high flux are attributed to the interfacial sieving effect over the 2D nanochannels as well as the vapor-phase transport in the mesoscale channels, which is fundamentally different from the solution-diffusion mechanism of dense polymeric membranes and the size-sieving mechanism of microporous membranes. This work not only demonstrates a special separation effect for complete desalination over the layered graphene-based membrane but also offers a reliable method to functionalize and structure graphene membranes for other potential applications.

Preparation of silk fibroin and graphene composite membrane and its response driving performance test

With the development of materials, intelligent materials have the functions of sensing, controlling and driving objects, self-adaptive repair and so on, so they have been widely used. Silk fibroin fiber is a kind of natural protein, which is formed by silk degumming, insoluble in water, and can be decomposed gradually in alkaline solution without irritation and side effects, so it has a good prospect of biological application. The silk fibroin film was mixed with graphene composites, and the intelligent materials for functional response were prepared by means of the excellent optical and thermal properties of graphene. The biaxially oriented polypropylene film (BOPP) / silk fibroin bilayer composite film was prepared by the simple composite method, which showed good thermal response bending deformation properties. The graphene solution was dripped on one side of the fibroin film by a dripping method. After low-temperature drying, the final BOPP/SF/RGO/PEDOT:PSS composite film was prepared by adding a layer of poly (3meme 4-ethylenedioxythiophene / polystyrene sulfonate) (PEDOT:PSS). The flexible film driver was prepared, which can respond to multiple stimuli under light, heat and humidity.

Simple Scalable Fabrication of Laser-Induced Graphene Composite Membranes for Water Treatment

Laser-induced graphene (LIG)-polymer composite materials might be potentially useful in many applications, including water purification technology. For example, water treatment membranes with antib...

Mechanism of a Self-Assembling Smart and Electrically Responsive PVDF-Graphene Membrane for Controlled Gas Separation.

The development of science and technology is accompanied by a complex composition of multiple pollutants. Conventional passive separation processes are not sufficient for current industrial applications. The advent of active or responsive separation methods has become highly essential for future applications. In this work, we demonstrate the preparation of a smart electrically responsive membrane, a poly(vinylidene difluoride) (PVDF)-graphene composite membrane. The high graphene content induces the self-assembly of PVDF with a high β-phase content, which displays a unique self-piezoelectric property. Additionally, the membrane exhibits excellent electrical conductivity and unique capacitive properties, and the resultant nanochannels in the membrane can be reversibly adjusted by external voltage applications, resulting in the tailored gas selectivity of a single membrane. After the application of voltage to the membrane, the permeability and selectivity toward carbon dioxide increase simultaneously. Moreover, atomic-level positron annihilation spectroscopic studies reveal the piezoelectric effect on the free volume of the membrane, which helps us to formulate a gas permeation mechanism for the electrically responsive membrane. Overall, the novel active membrane separation process proposed in this work opens new avenues for the development of a new generation of responsive membranes.

Preparation of graphene-coated anodic alumina substrates for selective molecular transport

In this paper, we report graphene composite membranes prepared by transfer of a layer of chemical vapor deposition graphene onto porous anodic alumina (AA) substrates with nominal pore size 20 and 30 nm, referred as 20AA and 30AA. The coated and uncoated substrates were characterized using optical and electron microscopy techniques. The bare substrates exhibited a smooth surfaces with a well-organized array of hexagonal pores, displaying an average pore size of 17 ± 3 (20AA) and 23 ± 3 nm (30AA). The scanning electron microscopy and atomic force microscopy analyses confirmed the successful transfer of graphene layer onto the target substrates. The molecular transport study was performed by introducing 0.5 M potassium chloride (KCl) and deionized water in a Side-bi-Side Franz diffusion cell. The graphene/20AA specimen blocked 66% ions transport, and graphene/30AA membrane about 64%. The ions blockage exceeded 90%, near the characteristics of defect-free graphene when the defects of the transferred graphene were sealed with Nylon 6,6. The results of this study suggest the potential use of graphene on AA substrates for water desalination and gas purification applications. CVD graphene has shown > 90% blockage of KCl molecules when tested on porous alumina substrate (pore size ~ 20 nm).

Temperature Dependence of the Pore Structure in Polyvinylidene Fluoride (PVDF)/Graphene Composite Membrane Probed by Electrochemical Impedance Spectroscopy.

In this paper, graphene was introduced in the PVDF to improve the thermal stability of the pore structure, which is the key feature for the membrane applied for the thermo-osmotic energy conversion (TOEC) process. The PVDF/graphene composite membranes were characterized by a scanning electron microscopy (SEM), a water contact angle measurement, and electrochemical impedance spectroscopy (EIS). It was found that the composite membranes exhibited improved surface hydrophobicity. Moreover, the pores in pure PVDF membrane would expand during the heat process while the existence of graphene in PVDF clearly suppressed the expansion, which implied better thermal stability of the pores in the composite membrane. According to the pore deformation time, the heat conductivities of the membranes were calculated and compared with each other. It confirmed that the composite membrane with higher graphene content exhibited enhanced heat conductivity. EIS can be used to monitor the temperature dependence of the pore structure in aqueous environments.

Scalable graphene composite membranes for enhanced ion selectivity

Unintended defects are a significant problem for mass production of graphene membranes. Herein, we report a method to fabricate scalable CVD graphene polymer membranes through the formation of a polysulfone (PSf) supporting layer, which is capable of duplicating the Cu morphology. Unintended defects were limited by minimizing defects associated with graphene wrinkles and eliminating polymer residues used in the transfer process. Consequently, the KCl leakage by diffusion of raw graphene membranes fabricated with this method was only ~ 0.5% that of the supporting membrane; there was also no water flux under a pressure of 20 bar. Excellent ion selectivity was achieved by controlling the duration of H2 plasma treatment. The selectivity of KCl over NaCl was 2.61, the selectivity of KCl over MgCl2 was 15.62, and the selectivity of NaCl over MgCl2 was 5.98.

Desalination Aspects of PSSA-g-PEG Copolymer and its Graphene Composite Membranes

In this study, polystyrene sulfonic acid (PSSA) was copolymerized with 1% polyethylene glycol (PEG 600), then Graphene (G) was added at different individually percent of 0.1, 0.5 and 1%, respectively. The resultant membrane designated as (PSSA-g-PEG)/G and was characterized using FTIR, SEM, XRD and TGA analysis. Then, membrane efficiency was determined by measuring the salt rejection and the water flux measured under different parameters such as temperature, pressure and composites concentrations. We found that, increasing temperature and pressure increased membrane water flux, but increasing G portion slightly increased water flux except before and at concentration 0.5% where increasing water flux was growing.

A porous graphene composite membrane intercalated by halloysite nanotubes for efficient dye desalination

Porous reduced graphene oxide (PRGO) was obtained by making pores on graphene oxide layers. Halloysite nanotubes, modified by Poly (sodium-p-styrenesulfonate) (PSS), were used to enlarge the interlayer spacing of PRGO. These two materials were immobilized on membrane surface through a time-saving, facile solvent evaporation method. The sandwich structure, formed through solvent evaporation process, provided additionally continuous pathway for water and salts, thus improving the water permeability of the composite membranes. Comprehensive characterizations of the materials were characterized by FT-IR, TEM, Raman, EDS and XRD. The composite membranes were characterized by SEM, FT-IR and EDS. The composite membranes exhibited a higher separation effect for salts and dye (i.e. 4.7% for MgSO4, 4.7% for MgCl2, 6.8% for NaCl, and 14.3% for Na2SO4; up to 97.9% for Reactive Black 5). The pure water permeation of composite membranes could reach as high as 8.8L/(m2hbar). Hence, the graphene-based hybrid membranes presented a potential application in separation for salts and dyes.

Study and preparation of highly water-stable polyacrylonitrile–kraton–graphene composite membrane for bending actuator toward robotic application

In this article, polyacrylonitrile–kraton–graphene (PAN-KR-GR) ionomeric polymer membrane sandwiched between Pt electrode-based ionic polymer–metal composite (IPMC) actuator is developed. The aim of this study is to design and prepare multifunctional ionic polymer–metal composite membrane for robotic application. The water uptake capacity and ion exchange capacity of polyacrylonitrile–kraton–graphene ionomeric membrane is 133.33% at 45 °C for 8 h of immersion and 1.4 meq g−1 of dry membrane, respectively. Proton conductivity and maximum water loss of ionic polymer–metal composite membrane is 5.26 mS cm−1 and 38% after applying 7 V for 12 min, respectively. Scanning electron micrographs shows the smooth and uniform coating of platinum (Pt). Cyclic voltammetry, linear sweep voltammetry, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and tip displacement of PAN-KR-GR-Pt IPMC membrane are also examined. A multifinger-based gripping system for dexterous handling is developed for robotic application.

Exceptionally strong and robust millimeter-scale graphene–alumina composite membranes

Graphene has attracted attention as a potential strengthening material and functional component in suspended membranes as utilized in micro and nanosystems. Development of a practical and scalable fabrication process is a necessary step to allow the exceptional material properties of graphene to be fully exploited in composite structures. Using standard and scalable microfabrication processes, we fabricated free-standing chemical vapor deposition monolayer graphene-reinforced Al2O3 composite membranes, 0.5 mm in diameter, that are strong and robust. Bulge tests revealed that the graphene reinforcement increased the membrane fracture strength by a factor of at least three and maximum sustainable strain from 0.28% to at least 0.69%. We show that the graphene-reinforced membranes are even tolerant to significant cracking without loss of membrane integrity. The graphene composite membranes’ freestanding area of ∼200 000 μm2 is almost a thousand times larger than suspended graphene membranes reported elsewhere. The presented graphene composite membranes may be seen as representing an interesting new class of durable composite materials warranting further study and having potential for broad applicability in a variety of fields.

Sulfonated Poly(Ether Ether Ketone)/Graphene composite membrane for vanadium redox flow battery

A novel composite membrane of sulfonated poly(ether ether ketone) (SPEEK) and graphene was prepared and investigated in this paper. The scanning electron microscopy images of the composite membrane revealed the presence and the uniformity dispersion of graphene in the SPEEK matrix. The properties of the obtained composite membrane, including the water uptake, swelling ratio, ion exchange capacity (IEC), area resistance, proton conductivity, VO2+ permeability, ion selectivity, single cell performance, chemical stability and mechanical properties are evaluated in detail, compared to the pristine SPEEK membrane and Nafion 117 membrane. Self-discharge test proved that the composite membrane possessed the longest discharge time (61h above 0.8V). At 80mAcm−2, a higher coulombic and energy efficiency for SPEEK/Graphene membrane was obtained, compared with Nafion 117 (96.4% vs 92.8% and 83.8% vs 79.5% respectively). Furthermore, the SPEEK/Graphene composite membrane exhibited high stability in 500 cycle's long time running.