Two-dimensional Graphene Oxide Nanosheets Research Articles

Electrostatic-induced ion-confined partitioning in graphene nanolaminate membrane for breaking anion–cation co-transport to enhance desalination

Constructing nanolaminate membranes made of two-dimensional graphene oxide nanosheets has gained enormous interest in recent decades. However, a key challenge facing current graphene-based membranes is their poor rejection for monovalent salts due to the swelling-induced weak nanoconfinement and the transmembrane co-transport of anions and cations. Herein, we propose a strategy of electrostatic-induced ion-confined partitioning in a reduced graphene oxide membrane for breaking the correlation of anions and cations to suppress anion-cation co-transport, substantially improving the desalination performance. The membrane demonstrates a rejection of 95.5% for NaCl with a water permeance of 48.6 L m−2 h−1 bar−1 in pressure-driven process, and it also exhibits a salt rejection of 99.7% and a water flux of 47.0 L m−2 h−1 under osmosis-driven condition, outperforming the performance of reported graphene-based membranes. The simulation and calculation results unveil that the strong electrostatic attraction of membrane forces the hydrated Na+ to undergo dehydration and be exclusively confined in the nanochannels, strengthening the intra-nanochannel anion/cation partitioning, which refrains from the dynamical anion-cation correlations and thereby prevents anions and cations from co-transporting through the membrane. This study provides guidance for designing advanced desalination membranes and inspires the future development of membrane-based separation technologies.

Graphene-Oxide-Modified Metal-Organic Frameworks Embedded in Mixed-Matrix Membranes for Highly Efficient CO2/N2 Separation.

MOF-74 (metal-organic framework) is utilized as a filler in mixed-matrix membranes (MMMs) to improve gas selectivity due to its unique one-dimensional hexagonal channels and high-density open metal sites (OMSs), which exhibit a strong affinity for CO2 molecules. Reducing the agglomeration of nanoparticles and improving the compatibility with the matrix can effectively avoid the existence of non-selective voids to improve the gas separation efficiency. We propose a novel, layer-by-layer modification strategy for MOF-74 with graphene oxide. Two-dimensional graphene oxide nanosheets as a supporting skeleton creatively improve the dispersion uniformity of MOFs in MMMs, enhance their interfacial compatibility, and thus optimize the selective gas permeability. Additionally, they extended the gas diffusion paths, thereby augmenting the dissolution selectivity. Compared with doping with a single component, the use of a GO skeleton to disperse MOF-74 into Pebax®1657 (Polyether Block Amide) achieved a significant improvement in terms of the gas separation effect. The CO2/N2 selectivity of Pebax®1657-MOF-74 (Ni)@GO membrane with a filler concentration of 10 wt% was 76.96, 197.2% higher than the pristine commercial membrane Pebax®1657. Our results highlight an effective way to improve the selective gas separation performance of MMMs by functionalizing the MOF supported by layered GO. As an efficient strategy for developing porous MOF-based gas separation membranes, this method holds particular promise for manufacturing advanced carbon dioxide separation membranes and also concentrates on improving CO2 capture with new membrane technologies, a key step in reducing greenhouse gas emissions through carbon capture and storage.

Renal clearance of graphene oxide: glomerular filtration or tubular secretion and selective kidney injury association with its lateral dimension

BackgroundRenal excretion is one of the major routes of nanomaterial elimination from the body. Many previous studies have found that graphene oxide nanosheets are excreted in bulk through the kidneys. However, how the lateral size affects GO disposition in the kidneys including glomerular filtration, active tubular secretion and tubular reabsorption is still unknown.ResultsThe thin, two-dimensional graphene oxide nanosheets (GOs) was observed to excrete in urine through the kidneys, but the lateral dimension of GOs affects their renal clearance pathway and renal injury. The s-GOs could be renal excreted via the glomerular filtration, while the l-GOs were predominately excreted via proximal tubular secretion at a much faster renal clearance rate than the s-GOs. For the tubular secretion of l-GOs, the mRNA level of basolateral organic anion transporters Oat1 and Oat2 in the kidney presented dose dependent increase, while no obvious alterations of the efflux transporters such as Mdr1 and Mrp4 mRNA expression levels were observed, suggesting the accumulation of l-GOs. During the GO renal elimination, mostly the high dose of 15 mg/kg s-GO and l-GO treatment showed obvious kidney injuries but at different renal compartment, i.e., the s-GOs induced obvious glomerular changes in podocytes, while the l-GOs induced more obvious tubular injuries including necrosis of renal tubular epithelial cells, loss of brush border, cast formation and tubular dilatation. The specifically tubular injury biomarkers KIM1 and NGAL were shown slight increase with mRNA levels in l-GO administrated mice.ConclusionsThis study shows that the lateral size of GOs affected their interactions with different renal compartments, renal excretion pathways and potential kidney injuries.

Novel Boundary Lubrication Mechanisms from Molecular Pillows of Lubricin Brush-Coated Graphene Oxide Nanosheets.

There are numerous biomedical applications where the interfacial shearing of surfaces can cause wear and friction, which can lead to a variety of medical complications such as inflammation, irritation, and even bacterial infection. We introduce a novel nanomaterial additive comprised of two-dimensional graphene oxide nanosheets (2D-NSCs) coated with lubricin (LUB) to reduce the amount of tribological stress in biomedical settings, particularly at low shear rates where boundary lubrication dominates. LUB is a glycoprotein found in the articular joints of mammals and has recently been discovered as an ocular surface boundary lubricant. The ability of LUB to self-assemble into a "telechelic" brush layer on a variety of surfaces was exploited here to coat the top and bottom surfaces of the ultrathin 2D-NSCs in solution, effectively creating a biopolymer-coated nanosheet. A reduction in friction of almost an order of magnitude was measured at a bioinspired interface. This reduction was maintained after repeated washing (5×), suggesting that the large aspect ratio of the 2D-NSCs facilitates effective lubrication even at diluted concentrations. Importantly, and unlike LUB-only treatment, the lubrication effect can be eliminated over 15 rinsing cycles, suggesting that the LUB-coated 2D-NSCs do not exhibit any binding interactions with the shearing surfaces. The effective lubricating properties of the 2D-NSCs combined with full reversibility through rinsing make the LUB-coated 2D-NSCs an intriguing candidate as a lubricant for biomedical applications.

Reduced Graphene Oxide-Laminated One-Dimensional TiO2-Bronze Nanowire Composite: An Efficient Photoanode Material for Dye-Sensitized Solar Cells.

A facile one-step hydrothermal method was developed to prepare reduced graphene oxide-laminated TiO2–bronze (TiO2-B) nanowire composites (TNWG), which contain two-dimensional graphene oxide nanosheets and TiO2-B nanowires. In the hydrothermal process, the functional groups of graphene oxide were reduced significantly. Dye-sensitized solar cells (DSSCs) were fabricated using TNWG as the photoanode material. The effects of different reduced graphene oxide contents in TNWG on the energy conversion efficiency of the dye-sensitized solar cells were investigated using J–V and incident photon-to-current conversion efficiency characteristics. DSSCs based on a TNWG hybrid photoanode with a reduced graphene oxide content of 8 wt % demonstrated an overall light-to-electricity conversion efficiency of 4.95%, accompanied by a short-circuit current density of 10.41 mA cm–2, an open-circuit voltage of 0.71 V, and a fill factor of 67%, which were much higher than those of DSSC made with a pure TiO2-B NW-based photoanode. The overall improvement in photovoltaic performance could be associated to the intense visible light absorption and enhanced dye adsorption because of the increased surface area of the composite, together with faster electron transport due to reduced carrier recombination.

Fabrication of non-covalently grafted Cu(acac)2 over two-dimensional graphene oxide nanosheets: An environmentally benign noble photocatalyst for visible-light-driven degradation of phenol

Herein, we report the development of a novel recyclable sonochemical non-covalent grafting of Cu(acac)2 over two-dimensional graphene oxide (GO) photocatalyst degrades phenol under visible light irradiation. The photocatalyst was prepared and characterized by XRD, FTIR, SEM, HR-TEM, EDAX, XPS, BET. The results of the analysis suggest the uniform grafting of Cu(acac)2 over the surface of GO. The photodegradation efficiency of GO/Cu(acac)2 was performed both under light and dark. The composite showed up to 90% degradation of phenol in 90 min when irradiated under the visible light. This improved photocatalytic activity may be attributed to the reduction in the band gap of pristine GO owing to the grafting of Cu(acac)2. The Langmuir-Hishelwood pseudo-first-order kinetic model of the degradation was performed and the rate constant (k) in presence of light for the composite was found to be 9.94 × 10−4 min−1 which is almost three times than the rate constant measured in presence of light with pristine GO.

Preparation of Modified Graphene Oxide Nanomaterials for Water and Wastewater Treatment

Because of the population explosion, industrialization and environmental disruption which cause big water crisis to all human beings, the development of high-efficient water treatment technologies is highly desirable. Recently, graphene oxide (GO) has drawn wide attention from the scientific community. the two-dimensional GO nanosheets possess high specific surface area and high surface activity, which make GO-based nanomaterials have great potential in various fields. In this paper, recent methods on modification of graphene oxide nanomaterials are introduced and compared. The prospects of GO-based nanomaterials applied in water treatment from three aspects of absorbent, catalysis and membrane separation are further analysed.

Hierarchical architecture for flexible energy storage.

The introduction of hierarchy and chirality into structure is of great interest, and can result in new optical and electronic properties due to the synergistic effect of helical and anisotropic structures. Herein, we demonstrate a simple and straightforward route toward the fabrication of hierarchical chiral materials based on the assembly of two-dimensional graphene oxide nanosheets (GO) and one-dimensional cellulose nanocrystals (CNCs). The unique layered structure of CNC/GO could be preserved in the solid state, allowing electrode active SnO2 to be loaded for potential applications in energy storage. The resultant SnO2/CNC/reduced GO (SnO2/CNC/rGO) composite could be processed into film, fiber, and textile with an extremely high tensile strength of 100 MPa. The free-standing SnO2/CNC/rGO electrodes exhibit highly improved energy storage performance, with a reversible capacity of ∼500 mA h g-1 maintained for 1500 cycles in the film and ∼800 mA h g-1 maintained for 150 cycles in the textile at a current density of 500 mA g-1. This is attributed to the prepared hierarchical chiral structures. The presented technique provides an effective approach to producing hierarchical functional materials from nanoparticles as building blocks, which might open an avenue for the creation of new flexible energy storage devices.

Synergistic effects of 2D graphene oxide nanosheets and 1D carbon nanotubes in the constructed 3D carbon aerogel for high performance pollutant removal

To create interspace-enlarged and sites-exposed graphene-based adsorbents for pollutant management, three-dimensional macrostructures (3D GTs) were facilely constructed via self-assembly of two-dimensional graphene oxide nanosheets (2D GO) and one-dimensional carbon nanotubes (1D CNTs). Since the existence of CNTs acting like frames may reinforce the mechanical strength of the GO nanosheets, the density of the stable and porous 3D GTs was reduced to 0.2mg/mL which was much lower than the minimum concentration required to form pure GO 3D macrostructures. The 3D GTs exhibited superior adsorption capabilities to emerging pollutants such as oxytetracycline (1729mg/g) and diethyl phthalate (680mg/g), and traditional pollutants such as methylene blue (685mg/g), Cd2+ (235mg/g) and diesel (421g/g). The adsorption capacity of 3D GTs is higher than the reported graphene/GO and CNTs-based adsorbents, which can be attributed to the synergistic effects of GO and CNTs in micro-environment, nano-substrate, and active sites. Firstly, the assembled GO sheets were highly separated and in monolayer form, which created large interspaces in 3D GTs. Secondly, GO and CNTs provided abundant adsorption sites. Thirdly, the micro environment of interspaces in stable 3D GTs could be tuned to achieve selective adsorption to particular pollutant. In short, we propose a super graphene-based adsorbent which is competitive and scalable for water purification.

Degradation of phenol using Fe3O4-GO nanocomposite as a heterogeneous photo-Fenton catalyst

Abstract Hybridizing zero-dimensional nanoparticles with two-dimensional graphene oxide nanosheets has been regarded as one of the most promising way to improve the adsorptive and catalytic performance of nanomaterials. Graphene oxide–iron oxide (Fe3O4-GO) nanocomposites were synthesized using a co-precipitation combining hydrothermal method, and then characterized using XRD, TEM, BET, XPS and VSM to study their structures and functionalities. Fe3O4-GO was used to degrade phenol in a heterogeneous photo-Fenton process. The effects of different parameters, such as GO loading, catalyst dosage, initial concentration of H2O2 and initial pH of the phenol solution on the degradation efficiency were assessed. The results showed that under optimal conditions with UV-light irradiation, about 98.8% phenol and 81.3% TOC of a phenol solution could be removed after 120 min photo-Fenton degradation. It can be seen that UV-light improves significantly the phenol removal in photo-Fenton process. The introduction of GO in the catalyst promotes the photo-Fenton reaction via three roles: increasing adsorption capacity, offering more active sites and accelerating the Fe3+/Fe2+ cycle under UV light irradiation. It was also observed that Fe3O4-GO still showed high catalytic activity after five cycles.

Fabrication of 3D Polypyrrole/Graphene Oxide Composite Hydrogels with High Performance Swelling Properties

The polypyrrole (PPy)/graphene oxide (GO) composite hydrogels with hierarchical porous structures were fabricated by one-step self-assembly method. The static oxidation polymerization of pyrrole monomer in GO aqueous solution resulted in the formation of three-dimensional (3D) PPy/GO composite hydrogels, which consisted of one-dimensional PPy nanofibers and two-dimensional GO nanosheets. The as-prepared composite hydrogels exhibited shrinking–swelling behavior with cycles of suction and water-supplying. The effects of GO nanosheets content on the swelling properties were investigated. Results showed that the well-dispersed GO nanosheets in the hydrogel networks resulted in a significant improvement in water absorbencies of the hydrogels. PPy/GO composite hydrogels exhibited unobvious variation in the water absorbency even in saline solutions. Such excellent properties in water absorbencies endow the conducting 3D PPy/GO composite hydrogels with great potential applications in electrochemical sensors or controlled release.

One-Dimensional Porphyrin Nanoassemblies Assisted via Graphene Oxide: Sheetlike Functional Surfactant and Enhanced Photocatalytic Behaviors

Surfactant-assisted self-assembly (SAS) has received much attention for supramolecular nanoassemblies, due to its simplicity and easiness in realizing a controllable assembly. However, in most of the existing SAS protocols, the employed surfactants work only as a regulator for a controllable assembly but not as active species for function improvement. In this paper, we report that a porphyrin, zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP), could be assembled to form one-dimensional (1D) supramolecular nanostructures via a SAS method, wherein graphene oxide (GO) plays a fascinating role of sheetlike surfactant. We show that, when a chloroform or tetrahydrofuran solution of ZnTPyP is injected into an aqueous dispersion of GO, 1D supramolecular nanoassemblies of ZnTPyP with well-defined internal structures could be easily formulated in a controllable manner. Our experimental facts disclose that the complexation of ZnTPyP with the two-dimensional GO nanosheets plays an important role in this new type of SAS. More interestingly, compared with the 1D ZnTPyP nanoassemblies formulated via a conventional SAS, wherein cetyltrimethylammonium bromide is used as surfactant, those constructed via our GO-assisted SAS display distinctly enhanced photocatalytic activity for the photodegradation of rhodamine B under visible-light irradiation. Our new findings suggest that GO could work not only as an emergent sheetlike surfactant for SAS in terms of supramolecular nanoassembly but also as functional components during the performance of the assembled nanostructures.

Graphene/quantum dot bionanoconjugates as signal amplifiers in stripping voltammetric detection of EpCAM biomarkers

A sensitive electrochemical immunosensor for the detection of epithelial cell adhesion molecule (EpCAM) antigen, a common marker for tumors of epithelial origin, employing bionanoconjugates as signal-transduction labels has been developed. The bionanoconjugates were fabricated by carboxylation of the two-dimensional graphene oxide nanosheets (GRs) and immobilizing streptavidin and amine-functionalized CdSe quantum dots (QDs) on carboxylated GRs via carbodiimide coupling chemistry, followed by the immunoreaction with the biotinylated secondary antibodies. Since carboxylated GRs have a higher density of active sites, it allows a large number of CdSe QDs to be immobilized onto the surface of the bionanoconjugates, and hence, enhance the sensitivity of the immunosensor. The method enabled detection limits of 100fg/mL and 1pg/mL (based on the S/N=3) in PBS buffer and serum samples, respectively, using anodic stripping voltammetric readout. The immunosensor showed a good selectivity, reproducibility, and long-storage stability, and may become a promising technique for the early detection of tumor biomarker in clinical/biological samples.