Reduced Graphene Oxide Membranes Research Articles

Leaf-veins-inspired nickel phosphate nanotubes-reduced graphene oxide composite membranes for ultrafast organic solvent nanofiltration

Organic solvent nanofiltration (OSN) membranes provide extraordinary opportunities for environment friendly and cost-competitive solvent recovery in petrochemical and pharmaceutical purifications. Currently, membranes that based on two-dimensional (2D) materials are extremely attractive in ultrafast molecular separations owing to the atomic thickness and remarkable physicochemical properties of the 2D nanosheets. Inspired by the structures and functions of vessel element that transport water in leaf veins, nickel phosphate nanotubes-reduced graphene oxide (NPTs-rGO) ultrathin laminar membrane is successfully prepared for ultrafast organic solvent nanofiltration. The in-situ synthetic NPTs can not only contribute to the size-dependent ultrafast molecular separation of the rGO membrane by providing additional molecular transport pathways as well as enlarging the interlayer space of the rGO layer, but also enhance the stability of the resultant membrane. The optimum membrane exhibits a methanol permeance of 670 L m −2 h −1 bar −1 and a high rejection toward molecules greater than 2 nm (MWCO: 650 Da). More importantly, the NPTs-rGO membrane shows promising anti-swelling property under OSN operating conditions. Inspired by leaf veins, this strategy provides insight into designing high-performance lamellar membranes with tubular-channel network, which may promote the fabrication and application of lamellar membranes in OSN. • Inspired by leaf veins, nickel phosphate nanotubes-reduced graphene oxide (NPTs-rGO) composite was applied to develop organic solvent nanofiltration (OSN) membrane. • The OSN performance of the resultant membrane was markedly improved. • The NPTs in the membrane could create tubular transport pathways for solvent. • The resultant NPTs-rGO membrane has superior anti-swelling stability and mechanical strength.

Improved dyes separation performance of reduced graphene by incorporation MoS2 nanosheets

The hydrothermal reduced graphene (rGO) and the layered MoS2 nanosheets prepared by the liquid-phase stripping method were blended, and then the MoS2-rGO composite membranes were prepared on the polyvinylidene fluoride (PVDF) supporting membranes by vacuum filtration method. A variety of characterization methods such as Fourier transform infrared spectrometer (FT-IR), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD) were used to verify the successful introduction of MoS2 into rGO layers and the changes of interlayer structure of the MoS2-rGO membranes. Finally, the effect of MoS2 loading on separation performance of the MoS2-rGO composite membrane was investigated. The results show that the separation performance of the membrane with 33.33% of MoS2 loading (M−rG−3) is the most excellent. The permeability of M−rG−3 membrane is 118.21 L m-2h−1 bar−1, which is about 4.4 times that of the pristine rGO membrane. Meanwhile, the rejection of the M−rG−3 membrane for Methyl blue, Crystal violet, Rhodamine B, and Congo red all exceed 80%.

New Structural Insights into Densely Assembled Reduced Graphene Oxide Membranes

AbstractDensely assembled graphene‐based membranes have attracted substantial interest for their widespread applications, such as compact capacitive energy storage, ion/molecular separation, gas barrier films, and flexible electronics. However, the multiscale structure of densely packed graphene membranes remains ambiguously understood. This article combines X‐ray and light scattering techniques as well as dynamic electrosorption analysis to uncover the stacking structure of the densely stacked reduced graphene oxide (rGO) membranes. The membranes are produced by reducing graphene oxide (GO) membranes with hydrazine, during which the colloidal interactions between GO sheets are modulated by the electrolyte solution. In contrast to the common notion that direct reduction of densely assembled GO sheets in parallel tends to result in significant “graphitization”, this article unexpectedly discovers that the resultant densely packed rGO membrane can still retain the interconnected network nanochannels and show good capacitive performances. This inspires the development of a hierarchical structural model to describe the densely packed rGO membranes. This article further shows that the nanochannel network can be fine‐tuned at the sub‐nanometer level by tailoring the salt concentration and the reduction temperature to render exceptional volumetric capacitance and good rate performance for rGO membranes even with increased packing density.

Hierarchical web-like NiFeMn ternary hydroxides microstructure assembled on reduced graphene oxide for binder-free supercapacitor electrode

In this work, a novel hierarchical web-like microstructure was fabricated by aligning interconnected NiFeMn hydroxide garlands on rGO-modified Ni foam (NiFeMn hydroxide/rGO/Ni foam) with a one-pot two-step hydrothermal method. During the first step at 50 °C, the redox reaction between GO and Ni foam results in the formation of rGO membrane on Ni foam. During the second step at 135 °C, urea decomposed and the produced NH3·H2O reacted with metal cations to form amorphous NiFeMn ternary hydroxide. The obtained binder-free electrode was characterized with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), Raman spectroscopy and Brunauer-Emmett-Teller gas sorptometry measurements (BET). The electrochemical performances of NiFeMn hydroxide/rGO/Ni foam were investigated with cyclic voltammetry (CV) and galvanostastic charge/discharge technique (GCD). NiFeMn hydroxide/rGO/Ni foam presents a high areal capacity of 35.1 C cm−2, capacity retention of 81.1% after 5000 GCD cycles at 30 mA cm−2 and excellent rate capability. The asymmetric supercapacitor (ASC) assembled with NiFeMn hydroxide/rGO/Ni foam and activated carbon (AC) presents a ultra-high energy density of 40.73 W h m−2 at the power density of 79.38 W m−2, suggesting its good application prospect in energy storage.

Enhancing the Dye-Rejection Efficiencies and Stability of Graphene Oxide-Based Nanofiltration Membranes via Divalent Cation Intercalation and Mild Reduction.

Laminar graphene oxide (GO) membranes have demonstrated great potential as next-generation water-treatment membranes because of their outstanding performance and physicochemical properties. However, solute rejection and stability deterioration in aqueous solutions, which are caused by enlarged nanochannels due to hydration and swelling, are regarded as serious issues in the use of GO membranes. In this study, we attempt to use the crosslinking of divalent cations to improve resistance against swelling in partially reduced GO membranes. The partially reduced GO membranes intercalated by divalent cations (i.e., Mg2+) exhibited improved dye-rejection efficiencies of up to 98.40%, 98.88%, and 86.41% for methyl orange, methylene blue, and rhodamine B, respectively. In addition, it was confirmed that divalent cation crosslinking and partial reduction could strengthen mechanical stability during testing under harsh aqueous conditions (i.e., strong sonication).

Graphene nanofiltration membrane intercalated with AgNP@g-C3N4 for efficient water purification and photocatalytic self-cleaning performance

Low water flux and heavy membrane fouling hinder the use of graphene-based membranes for water purification and molecular sieving. To the end, a novel graphene-based membrane, intercalated with Ag nanoparticles anchored g-C3N4 (AgNP@g-C3N4) as pillars and photocatalysts, was fabricated through a mixed-dimensional assembly strategy. The uniform loading of Ag nanoparticles on g-C3N4 can greatly improve the photocatalytic ability of g-C3N4 while creating more water transport channels between reduced graphene oxide (rGO) and g-C3N4 laminates. The resultant rGO/AgNP@g-C3N4 nanofiltration membrane displayed efficient water permeability, superior photocatalytic self-cleaning performance, and owned excellent flexibility and structural stability. The water permeability of the rGO/AgNP@g-C3N4 membrane was considerably improved (210.9 L∙m−2∙h−1∙bar−1) compared to the pure rGO membrane (78.4 L∙m−2∙h−1∙bar−1) due to the larger interlayer spacing and rough surface. After 1 h of visible light irradiation, the decrease of flux produced by pollutant molecule adsorption can recover with a ultrahigh flux recovery ratio (FRR) of 98.1%. Moreover, the high flux of the rGO/AgNP@g-C3N4 membrane remained stable in a cross-flow photocatalytic nanofiltration device. Membrane separation, photocatalytic regeneration, and pollutant degradation by ·OH and ·O2− radicals are proposed as effective cooperation mechanisms.

Two-dimensional nanoporous and lamellar membranes for water purification: Reality or a myth?

• Progress in 2D nanoporous and lamellar membranes is critically reviewed. • Sub-nanoporous membranes can achieve high water permeance and rejection. • Lamellar membranes provide effective rejection of dye molecules at high water flux. • Enhanced ion rejection by lamellar membranes requires 2D material functionalisation. • Research is required on scalability, stability, fouling and pore size engineering. Wastewater contains only ∼ 1% impurities that are required to be separated precisely for water recycling and reuse applications, particularly in water scare regions. Membrane-based separation has been recognised as an environmentally-friendly and energy-efficient process for effective pollutant removal and clean water production. To further improve the selectivity and water flux of membranes, two-dimensional (2D) materials, such as graphene and those exhibiting graphene-like properties, have been intensively studied for nanoporous and lamellar membrane fabrication in the last decade. Herein, we critically review the progress in 2D membranes for water purification and uniquely discuss the performance governing factors and research gaps from the standpoint of environmental and material chemists, which are critical to realize 2D membrane commercialization. The major points of this review are: (1) among the six types of reviewed 2D membranes, graphene, graphene oxide and reduced graphene oxide membrane have been predominantly studied for water treatment. (2) atomically thin nanoporous membranes with a defined pore size can achieve excellent water permeance and selectivity but large-scale fabrication of nanoporous membranes with uniform shape and size of nanopores remains a challenge. (3) salt separation performance of the pressurized lamellar membranes may not be comparable to commercial nanofiltration membranes. (4) functionalization or crosslinking of 2D materials is inevitable to stabilize 2D membrane pore structure and/or improve molecule separation. (5) membranes fabricated using emerging 2D materials such as born nitride and MXene appear to show better stability than graphene oxide membranes. (6) several aspects, particularly membrane stability, long-term performance, and membrane fouling propensity need attention to realize commercial application of 2D membranes in water treatment.

Partially Reduced Graphene Oxide Membranes Crosslinked by an Anionic Porphyrin: Green Fabrication for High‐Performance Ion Sieving

AbstractGO membranes crosslinked by planar cation (e. g. TMPyP, a cationic porphyrin) meet the requirements of green fabrication, because TMPyP can pre‐assemble on GO sheets. However, their ion sieving performance are unsatisfactory. With shortened water channels, reduced graphene oxide (rGO) membranes owe high water flux, yet the retention of multivalent anions may goes down distinctly on account of Donnan effect decreasing obviously. Herein, we focus on the assembly between partially reduced graphene oxide (p‐rGO) and Anionic planar molecule (tetrasulfonic tetraphenyl porphyrin, TPPS), and then fabricate p‐rGO/TPPS composite membranes via assembling p‐rGO/TPPS sheets on base membrane. Anionic planar molecule is firstly used as crosslinking agent for graphene‐based membranes, which has the advantage of 100% atomic efficiency. The fabricated p‐rGO/TPPS membranes show better sieving performance than GO/TMPyP membranes on both side of rejection of Na2SO4 and water flux. Moreover, water flux go up to around another double though rejection decline slightly as the polyther sulfone (PES) base membrane with large surface pores is used.

Unlocking the limits of diffusion and adsorption of metal-crosslinked reduced graphene oxide membranes for gas separation

Reduced graphene oxide (rGO) membranes have shown promising separation and purification in the fields of water treatment and gas capture due to their unique physicochemical characteristics. However, how to further reduce the transport resistance of rGO membranes and improve separation performance is still a thorny issue. In this work, the reported metal-crosslinked rGO membranes showed a reverse-selective separation behaviors for the adsorbed gas molecules at low pressure. The effect of metal ions on the membrane structure and the separation performance were investigated. Metal ions not only can improve the cross-linking structure and control interlamellar spacing of rGO membranes for the precise molecular sieve, but also can provide abundant metal sites to enhance the affinity, which led to a diffusion-controlled process for the targeted gas molecules. The resulting metal-crosslinked rGO membranes presented outstanding gas permeance and selectivity for gas pairs of the He/CO2, N2/CO2 and Kr/Xe, with the highest selectivity of 21, 11.4 and 4.1, respectively. The work will provide a new avenue towards specific molecule capture for the development of rGO membranes in the fields of natural gas purification and radioactive gas recovery.

In-situ chemical formation of strong stability GO/rGO hybrid membranes for efficient treatment of organic pollutant

In this study, a strong stability graphene oxide (GO)/reduced graphene oxide (rGO) hybrid membranes were successfully prepared by in-situ chemical reduction method. As the reducing agent, ammonia can effectively promote the deoxygenation of GO surface and the restoration of π-conjugation to produce rGO sheets. Moreover, the weakening of hydration and the enhancement of π-π conjugation promoted the interlayer force of GO/rGO membranes; as a result, the hybrid membranes exhibited extraordinary stability in strong acid and alkali solutions. In organic dyes separation application, the hybrid membranes displayed excellent rejection performance, and the rejection rate up to 100%. In addition, they also showed higher water flux (23.72 L m-2h−1 bar−1) comparing to pristine GO membranes (14.35 L m-2h−1 bar−1) and rGO membrane (8.66 L m-2h−1 bar−1). This work will promote the application scope of graphene-based membranes and provide better performance in water treatment.

Realizing ultrahigh nanofiltration performance based on small flake reduced graphene oxide membranes

Graphene - based membranes have attracted considerable attentions in many fields of study such as desalination and water treatment due to their unique physical and chemical characteristics. However, graphene oxide (GO) membranes suffer from a severe permeability-selectivity trade-off, i.e., when high salt rejection rates are obtained, usually the extremely low water permeance (most <1 L m−2 h−1 bar−1) are presented, thus it is now far insufficient to meet the real-world applications. In this work, we demonstrated the feasibility of the small-flakes for reduced graphene oxide (S-rGO) membrane to create more ordered two-dimensional (2D) laminar channels for nanofiltration. The water permeances of S-rGO membrane for rejection Na2SO4 and MgSO4 solutions were 3.7 - and 3.9-fold higher than those of large-flakes rGO (L-rGO) membrane, while the rejections of S-rGO membrane still maintained as high as 87.0 ± 3.8% and 85.4 ± 2.5% for Na2SO4 and MgSO4, respectively. Further, the long-term experiments of the S-rGO membrane demonstrated their high stability. Overall, this work sheds light on the preparing of high nanofiltration performance of GO-based membranes as well as the transport mechanism within 2D laminar channels, and advances the design of GO-based membranes for real world water purification, molecular/ionic sieving, and other environmental applications.

Reduced graphene oxide incorporated polyvinylidene fluoride/cellulose acetate proton exchange membrane for energy extraction using microbial fuel cells

A superior cost-effective cation exchange membrane based on polyvinylidene fluoride (PVDF), cellulose acetate (CA), and reduced graphene oxide (rGO) work as a superior cost-effective cation exchange membrane for the energy extraction application employing microbial fuel cells (MFCs). In this work, waste sugarcane bagasse was used to make CA, and the Tour technique was employed to make GO, which was then transformed to rGO using multiple modifications. To prepare cation exchange membranes, the CA and rGO were doped. The obtained proton conductivity values increased from 0.01 Scm−1 for rG0 to ∼ 0.4 Scm−1 for rG1 when the manufactured membranes were sulfonated. The combination of CA derived from sugarcane bagasse and rGO in the produced membranes may be attributed to this enhancement in proton conductivity. The power density performance of rG1 was compared to that of commercially available high-performance proton exchange membranes. It was revealed that MFC employing the rG1 membrane outperformed several more expensive membranes when it came to energy extraction using MFC. Without any electrode alteration, a columbic efficiency (CE) of 6.17 %, a COD removal efficiency of 92.0 ± 0.8% %, and a power density of more than 118 mW m−2 were reached. As a result, the constructed low-cost new PVDF-based, rGO, and CA membrane (rG1) shown its suitability for increasing MFC efficacy and is recommended for MFC scaling up.

General synthesis of ultrafine metal oxide/reduced graphene oxide nanocomposites for ultrahigh-flux nanofiltration membrane

Graphene-based membranes have great potential to revolutionize nanofiltration technology, but achieving high solute rejections at high water flux remains extremely challenging. Herein, a family of ultrafine metal oxide/reduced graphene oxide (rGO) nanocomposites are synthesized through a heterogenous nucleation and diffusion-controlled growth process for dye nanofiltration. The synthesis is based on the utilization of oxygen functional groups on GO surface as preferential active sites for heterogeneous nucleation, leading to the formation of sub-3 nm size, monodispersing as well as high-density loading of metal oxide nanoparticles. The anchored ultrafine nanoparticles could inhibit the wrinkling of the rGO nanosheet, forming highly stable colloidal solutions for the solution processing fabrication of nanofiltration membranes. By functioning as pillars, the nanoparticles remarkably increase both vertical interlayer spacing and lateral tortuous paths of the rGO membranes, offering a water permeability of 225 L m−2 h−1 bar−1 and selectivity up to 98% in the size-exclusion separation of methyl blue.

Minimising non-selective defects in ultrathin reduced graphene oxide membranes with graphene quantum dots for enhanced water and NaCl separation

• Ultrathin GQDs/rGO membranes are prepared through a two-step assembly method. • The strong π–π interaction between GQDs and rGO enables the coverage of defects. • GQDs/rGO membranes achieve both high water permeance and high NaCl rejection. Reduced graphene oxide (rGO) membranes have been intensively evaluated for desalination and ionic sieving applications, benefiting from their stable and well-confined interlayer channels. However, rGO membranes generally suffer from low permeability due to the high transport resistance resulting from the narrowed two-dimensional (2D) channels. Although high permeability can be realized by reducing membrane thickness, membrane selectivity normally declines because of the formation of non-selective defects, in particular pinholes. In this study, we demonstrate that the non-selective defects in ultrathin rGO membranes can be effectively minimised by a facile posttreatment via surface-deposition of graphene quantum dots (GQDs). The resultant GQDs/rGO membranes obtained a good trade-off between water permeance (14 L⋅m −2 ⋅h −1 ⋅MPa −1 ) and NaCl rejection (91%). This work provides new insights into the design of high quality ultrathin 2D laminar membranes for desalination, molecular/ionic sieving and other separation applications.

An efficient cooling solution with 3D interconnected graphene architectures for passive heat dissipation

A 3D hybridized reduced graphene oxide membrane (AR-rGO) was fabricated using a convenient electrochemical deposition method, which possesses a highly efficient passive heat dissipation capability.

FABRICATION AND MODIFICATION OF CHITOSAN/PAHAE NATURAL ZEOLITE/REDUCED GRAPHENE OXIDE (CS/PNZ/rGO)–BASED POLYMER ELECTROLYTE MEMBRANES

Integration of reduced graphene oxide (rGO) to membranes and its effect on the physicochemical properties with chitosan/natural zeolite from Pahae (PNZ) was investigated. Membranes were fabricated using a solution casting method and sulfuric acid crosslinking. The results showed that the CS/PNZ/rGO membrane (0.5% w/w) exhibited the highest tensile strength of 17.8 MPa. All rGO-modified membranes displayed a higher tensile strength than CS/PNZ-based membranes with only 10.8 MPa. The optimum elongation at break properties of CS/PNZ/rGO (1.5% w/w) was 2.9%. The membrane was stable under oxidative stress for 416 min while the CS/PNZ/rGO membrane (1.5% w/w) persisted until 686 min. The modified rGO membranes crosslinked with sulfuric acid were improved through tensile strength and stable against oxidation. As the modified membranes showed desirable properties from our study, it was then possible to be utilized as renewed polymer electrolyte membranes (PEM).

A Novel Generation of Polysulfone/Crown Ether-Functionalized Reduced Graphene Oxide Membranes with Potential Applications in Hemodialysis.

Heavy metal poisoning is a rare health condition caused by the accumulation of toxic metal ions in the soft tissues of the human body that can be life threatening if left untreated. In the case of severe intoxications, hemodialysis is the most effective method for a rapid clearance of the metal ions from the bloodstream, therefore, the development of hemodialysis membranes with superior metal ions retention ability is of great research interest. In the present study, synthetic polysulfone membranes were modified with reduced graphene oxide functionalized with crown ether, an organic compound with high metal ions complexation capacity. The physico-chemical characteristics of the composite membranes were determined by FT-IR, Raman, XPS and SEM analysis while their efficiency in retaining metal ions was evaluated via ICP-MS analysis. The obtained results showed that the thermal stability of reduced graphene oxide was improved after functionalization with crown ether and that the presence of the carbonaceous filler influenced the membranes morphology in terms of pore dimensions and membrane thickness. Moreover, the ability of Cu2+ ions retention from synthetic feed solution was up to three times higher in the case of the composite membranes compared to the neat ones.

Gamma-ray Spectroscopy Using Inorganic Scintillator Coated with Reduced Graphene Oxide in Fiber-Optic Radiation Sensor

In this study, we developed a remote gamma-ray spectroscopy system based on a fiber-optic radiation sensor (FORS) that is composed of an inorganic scintillator coated with reduced graphene oxide (RGO) and a plastic optical fiber (POF). As a preliminary experiment, we measured the transmitted light intensities using RGO membranes of different thicknesses with different wavelengths of emitted light. To evaluate the FORS performance, we determined the optimal thickness of the RGO membrane and measured the amounts of scintillating light and gamma energy spectra using radioactive isotopes such as 60Co and 137Cs. The amounts of scintillating light from the RGO-coated inorganic scintillators increased, and the energy resolutions of the gamma-ray spectra were enhanced. In addition, the gamma-ray energy spectra were measured using different types of RGO-coated inorganic scintillators depending on the lengths of the POFs for remote gamma-ray spectroscopy. It was expected that inorganic scintillators coated with RGO in FORS can deliver improved performance, such as increments of scintillating light and energy resolution in gamma-ray spectroscopy, and they can be used to identify nuclides remotely in various nuclear facilities.

Confining peroxymonosulfate activation in carbon nanotube intercalated nitrogen doped reduced graphene oxide membrane for enhanced water treatment: The role of nanoconfinement effect

Coupling membrane filtration with peroxymonosulfate (PMS) activation is promising to overcome the selectivity-permeability trade-off in membrane-based water treatment. However, the PMS catalytic efficiency of membrane still needs improvement to offset the insufficient reaction time during filtration process. Herein, an oxidized carbon nanotube intercalated nitrogen doped reduced graphene oxide (NRGO-OCNT) membrane with PMS activation function was firstly designed and prepared, which confined PMS activation in membrane interlayer for enhanced water treatment. The influence of confinement scale on membrane performance was studied through changing the OCNT intercalation ratio. Under the optimal confinement condition, the NRGO-OCNT membrane filtration integrated with PMS activation (MFPA) could realize 100% 4-chlorophenol removal at a high permeate flux of 290.2 L m−2 h−1 bar−1 (retention time of only 0.36 s), whose performance was 2.8, 1.7 and 5.0 times higher than that of filtration alone, NRGO MFPA (excessive confinement) and NRGO-OCNT powder-based batch reaction (no confinement), respectively. Moreover, NRGO-OCNT MFPA preferentially removed smaller-sized organics which easily entered and diffused in confined interlayer. The outstanding performance of NRGO-OCNT MFPA was owing to the nanoconfinement effect in appropriate confined interspacing, where the mass transfer rate of reactants was greatly boosted for enhanced generation of SO4− and OH towards pollutant.

Effect of low-dose irradiation on the properties of GO and GO membrane

Reduced graphene oxide (rGO) is supposed to have better stability and adsorption properties than graphene oxide (GO). Here, GO was controllable reduced by γ-ray irradiation at low doses of 0–10 kGy. Both physicochemical characteristics and filtration performance of GO/rGO membranes were investigated. The XPS, FTIR and UV spectra data showed that both the types and contents of the oxygen-containing functional groups changed after irradiation, but were not linearly correlated with the dose. The irradiation doses of 2 and 10 kGy were two important points, at which the largest C/O values were found. Although the types of the oxygen-containing functional groups were different, the rGO membranes at 2 and 10 kGy both showed the largest flux and the lowest rejection during the long-term filtration. The performance of the rGO membrane is highly influenced by the content rather than the types of oxygen-containing functional groups. The rGO membrane was more stable than the GO membrane at low GO load during the long-term filtration. The rejections of both dye and ions decreased along running time and adsorption was the main mechanism. Different performances were found for the long and short-term filtration. The balance of flux and rejection, as well as the long-term test should be paid more attention during the application of GO/rGO membranes.