Self-assembly Of Graphene Oxide Sheets Research Articles

Phenotypic change of mesenchymal stem cells into smooth muscle cells regulated by dynamic cell-surface interactions on patterned arrays of ultrathin graphene oxide substrates

The topographical interface of the extracellular environment has been appreciated as a principal biophysical regulator for modulating cell functions, such as adhesion, migration, proliferation, and differentiation. Despite the existed approaches that use two-dimensional nanomaterials to provide beneficial effects, opportunities evaluating their impact on stem cells remain open to elicit unprecedented cellular responses. Herein, we report an ultrathin cell-culture platform with potential-responsive nanoscale biointerfaces for monitoring mesenchymal stem cells (MSCs). We designed an intriguing nanostructured array through self-assembly of graphene oxide sheets and subsequent lithographical patterning method to produce chemophysically defined regions. MSCs cultured on anisotropic micro/nanoscale patterned substrate were spontaneously organized in a highly ordered configuration mainly due to the cell-repellent interactions. Moreover, the spatially aligned MSCs were spontaneously differentiated into smooth muscle cells upon the specific crosstalk between cells. This work provides a robust strategy for directing stem cells and differentiation, which can be utilized as a potential cell culture platform to understand cell–substrate or cell–cell interactions, further developing tissue repair and stem cell-based therapies.Graphical

Graphene Oxide-Chitosan Aerogels: Synthesis, Characterization, and Use as Adsorbent Material for Water Contaminants.

Porous aerogels, formed by subjecting precursor hydrogels using a freeze-drying process, are certainly one of the most studied and synthetized soft materials, thanks to their important features such as elasticity, swelling behavior, softness, and micro and nanosized pores, which guarantee their applicability in various fields. Typically, these systems are synthetized working with natural or synthetic polymers, but in the last years great interest has been given to proper formulated aerogels able to combine polymeric structures with other moieties such as graphene or graphene oxide. This working strategy can be pivotal in many cases to tune important properties of the final system such as toughness, porosity, elasticity, electrical conductivity, or responsive behavior. In this work we propose the synthesis of chitosan graphene oxide aerogels obtained through self-assembly of graphene oxide sheets and chitosan chains. These three-dimensional systems were chemically characterized with IR and XRD technique and their inner structure was investigated through the scanning electron microscopy (SEM). Moreover, we mechanically characterized the material through dynamic mechanical analysis, showing the stability of these systems. Finally, the adsorption ability of these soft materials has been demonstrated using model molecules to simulate water contaminants showing the efficacy of those graphene-based systems even for the removal of anionic dyes. Complete removal of contaminants was obtained at low concentration of dyes in solution (100 mg/L), while with a higher amount of pollutant in the solution (350 mg/L) high sorption capacity (q > 200 mg/g) was observed.

Microwave Irradiation of Graphene Aerogel and Its Use on the Electromagnetic Interference Shielding of BMI Nanocomposites

In this work, graphene aerogels (GAs) with three-dimensional interconnected networks were prepared by chemical reduction and self-assembly of graphene oxide sheets. After microwave treatment, obtained microwave reduced graphene aerogels (MRGAs) were used in the preparation of bismaleimide (BMI) composites. The results show that the microwave treatment significantly enhanced the quality of GAs, and the three-dimensional networks in the GAs were well retained. Moreover, the MRGAs were highly efficient in endowing BMI with high electrical conductivity and excellent electromagnetic interference shielding effectiveness (EMI SE). The conductivity of MRGA/BMI composites was 42–68% higher than that of GA/BMI composites. When the filler content is 1.6 wt.%, the EMI SE of MRGA/BMI composite was 32.3% higher than that of GA/BMI composite in the X band.

Effect of aromatic amine modified graphene aerogel on the curing kinetics and interfacial interaction of epoxy composites

Aromatic amine modified 3D porous graphene aerogel was prepared through chemical reduction and self-assembly of graphene oxide sheets in one step by using diaminodiphenylmethane (DDM) as a reducing agent, modifying agent, and curing agent. Subsequently, the DDM-modified graphene aerogel (DGA) was fully infiltrated with epoxy resin to obtain the DGA/epoxy composites. The abundant amine groups derived from DDM on the DGA can react with epoxy resin to strengthen the interfacial interaction, further promoted the curing behaviors by significantly lowering the reaction activation energy. The reinforcement of interfacial interaction and well-interconnected frameworks enhanced the effective transfer of stress and electrons in the resulting composites. Thus, the resulting DGA/epoxy composites exhibited excellent compressive properties and high electrical conductivity. This study presented a facile technique for preparing porous graphene aerogel, which simultaneously improved the electrical conductivity and mechanical properties of epoxy composites, and overcame the issues of dispersion and interfacial interaction of traditional nanofillers.

Macroporous Rgo Electrode Decorated with Co3O4 Nanoparticles for Selective Catalytic Electro-Oxidation of Water

OBJECTIVESThe electro-oxidation of H2O to O2 is a promising process to store energy into a green fuel. Its intrinsic high kinetic barrier requires the use of catalysts to lower the applied potential; moreover, it suffers the competition of side-reactions like Cl‒ oxidation to chlorine, an undesirable corrosive by-product. The high concentration of Cl‒ ions in seawater is one of the major obstacles which hinders the direct employment of such widely available resource as the electrolyte for O2 production (Adv. Mater., 2018, 30, 1707261).The benchmark electrocatalysts based on noble metals (Pt, IrO2) are not selective toward Cl‒, and their scarcity prevents their practical large-scale application. Earth-abundant oxides and (oxy)hydroxides of first-row transition metals (FeOOH, NiOOH, Co3O4) are robust and show even higher catalytic performances than Pt/IrO2. Unfortunately they are not selective against Cl‒ oxidation (ACS Catal., 2014, 4, 3701).In this work, we aim to suppress Cl‒ interference on heterogeneous catalysts through a carefully designed electrode architecture. We synthesize a free-standing, conducting, 3D macroporous reduced graphene oxide (rGO) composite with catalytic Co3O4 nanoparticles (NP) selectively deposited just on the internal walls of its closed, not interconnected pores (average diameter 100 µm). The pore walls act as membranes made of multiple stacked rGO nanosheets; the nanochannels between rGO layers have width < 1 nm which previous works have shown to be permeable to water and gases while preventing the diffusion of dissolved ions like Cl‒ (e.g. Nat. Mater., 2017, 16, 1198). Since the catalytic sites are accessible selectively to the substrates able to permeate through the rGO walls, the water electro-oxidation is expected to happen without suffering the competing Cl2 evolution.The most common method for synthesizing 3D rGO porous materials is through self-assembly of graphene oxide (GO) suspensions during hydrothermal reduction. However, this method leads to scaffolds with small open pores with diameters in the micrometer range (e.g. ACS Nano, 2010, 7, 4324). A macroporous closed structure, instead, allows for selectivity together with higher diffusion rates of the permeating species from the outer solution to the reaction sites. For this reason, in our strategy we synthesize the scaffolds starting from emulsions of hexane droplets in water stabilized by GO nanosheets as soft template for the macroporous structure.RESULTSWe modify the amphiphilicity of GO by adding different amounts of surfactants to produce so-called high internal phase emulsions (HIPE) stabilized by GO. These are single phase emulsions characterized by a high amount of emulsified phase (Hex:H2O ratio > 0.75), and a long-term stability (several months). Then, we convert the HIPE in the final 3D scaffolds by triggering the self-assembly of GO sheets through a hydrothermal reduction with slow temperature ramp, at the end of which hexane has entirely evaporated due to its low boiling point.Through this simple process we are able to control the architecture of the rGO scaffolds without polymerizations or post-modifications. We can control the pore size by tuning the templating HIPE droplet size, which we show depends on the GO concentration, hexane to water ratio, hexane to volume ratio, and emulsifying method (time and power). Because of its superior structural homogeneity compared to the conventional diluted emulsions previously reported (J. Mater. Chem. A, 2015, 3, 4018), a HIPE brings several advantages to the final material, i.e. better mechanical properties, very high surface area, and lower electrical resistivity (2.6±1.3 kΩcm).This is also the first study which reports the addition of a metal-organic precursor (of Co3+ in this specific case), or metal oxide NP (specifically Co3O4) functionalized with a hydrophobic layer, in the apolar phase during the preparation of the emulsion template, and then exploits the immiscible nature of the apolar and water phases to selectively decorate with catalytic NP only the internal wall of the closed pores. This feature requires the formation of highly stable initial GO HIPE and cannot be achieved by any other strategy previously reported.SIGNIFICANCE OF THE WORKThe rGO macroporous materials produced are currently under investigation as self-standing electrocatalysts for selective water oxidation with respect to chlorine evolution. We will then test these electrodes for water decontamination and as anodes in energy storage devices.While in this work we focus on Co3O4, our approach allows the encapsulation of any type of nanocatalyst (metal oxide/metal-based NP) inside the closed rGO macropores, just by changing the hydrophobic precursor. Such materials may exhibit electrocatalytic activity and selectivity towards a variety of substrates that can permeate through the rGO walls while suppressing any competitive reaction involving interfering species which are rejected by the rGO walls. Figure 1

Self-assembly of graphene oxide sheets: the key step toward highly efficient desalination.

Lamellar graphene oxide (GO) membranes are new membrane materials for seawater desalination due to their selective sub-nanometer interlayer two-dimensional channels. In general, the reliable and precise desalination of GO membranes is still heavily dependent on thick membranes that usually have a low water flux. The trade-off between the water flux and ion rejection is a long-lasting problem that restricts the development of highly efficient desalination membranes. In this work, we theoretically predicted that this trade-off can be broken by the self-assembly of GO sheets during the membrane preparation. Our molecular dynamics (MD) simulations indicate that the high-water permeability of the GO membrane is due to the frictionless flow of water in the 2D nanochannels enclosed by the non-oxidized regions of neighboring GO sheets, while the oxidized regions are responsible for the high ion rejection rate. Meanwhile, the MD simulations of the self-assembly processes of GO sheets in aqueous solutions just demonstrate that the oxidized regions of neighboring GO sheets are prone to stacking with each other, while the non-oxidized regions of neighboring GO sheets are inclined to matching with each other. Therefore, more interlayer nanochannels for fast water flow and ion rejection will be formed, respectively, after the full assembly of GO sheets during membrane preparation. Finally, based on our results, a new but simple method has been proposed to prepare GO membranes with superior desalination performance via deposition rate control.

3D Graphene-based macro-mesoporous frameworks as enzymatic electrodes

An efficient method was developed to fabricate three-dimensional (3D) graphene-based nanomaterials with hierarchical macro-mesoporous structures as novel enzymatic electrode materials. The 3D continuously interconnected macropores were generated by hydrothermal self-assembly of graphene oxide sheets to form 3D graphene-based frameworks, and uniform mesopores on the surface of graphene frameworks were obtained by replicating the previously synthesized mesoporous silica. Due to the integration of macropores that can promote the efficiency of mass transfer, and mesopores that can facilitate enzyme immobilization and electron transfer, the unique 3D graphene-based macro-mesoporous frameworks with narrow mesopore size distribution, large surface area and high electrical conductivity can be applied as an excellent platform to immobilize glucose oxidase as enzymatic electrodes, displaying enhanced glucose-sensing properties. This approach can be utilized to fabricate various 3D hierarchical macro-mesoporous nanomaterials for application in a broad range of sensors, supercapacitors, batteries and catalysis.

Elastic three-dimensional graphene sponge fabricated by the liquid crystals of controlled large graphene oxide sheets

Three-dimensional graphene (3DG) sponge has attracted increasing attention because it combines the unique properties of cellular materials and the excellent performance of graphene. Preparation of 3DG sponge depends mainly on the self-assembly of graphene oxide sheets. In the case of using uniform large graphene oxide and ultralarge graphene oxide sheets, the nematic liquid crystals (LCs) phases are formed at low concentration. After chemical reduction, the LCs of GO solution are converted to 3DG sponges with a high degree of orientation, offering a new methodology to regulate the controlled large GO sheets. The orientation of GO solution can be inherited by 3DG sponge, making the sponge to have a large-scale ordered network structure. The 3D elastic graphene sponges have low density and good elasticity, promising for the applications in strain sensing, shock damping, and energy cushioning. Our work explores a novel strategy for organizing the ordered alignment of controlled large GO sheets and exploring the relationship between the microstructures and mechanical properties of 3DG sponge.

Analyte-driven self-assembly of graphene oxide sheets onto hydroxycamptothecin-functionalized upconversion nanoparticles for the determination of type I topoisomerases in cell extracts.

Type I topoisomerases (TOPOI), a potential diagnostic biomarker and a target for chemotherapeutic agents, play essential roles in DNA replication, transcription, chromosome segregation, and recombination. It is essential to develop analytical methods for accurate detection of TOPOI in biological fluids for early diagnosis of diseases. Here we show an assay for TOPOI on the basis of the target-induced self-assembly of graphene oxide (GO) sheets onto hydroxycamptothecin-functionalized upconversion nanoparticles (HCPT-UCNPs). The dipole-dipole coupling of HCPT-UCNPs (donor) and GO (acceptor) regulated by TOPOI enables Förster resonance energy transfer between the donor and the acceptor. Integration of minimal autofluorescence and highly specific affinity into the developed nanosensor allows reliable detection of TOPOI in the nanomolar range with the detection limit of 0.29nM. The detection of TOPOI in breast cancer cells with recoveries from 96.3 to 103.7% shows the availability of the proposed assay in complicated samples. Graphical abstract ᅟ.

One-Step Laser Patterned Highly Uniform Reduced Graphene Oxide Thin Films for Circuit-Enabled Tattoo and Flexible Humidity Sensor Application.

The conversion of graphene oxide (GO) into reduced graphene oxide (rGO) is imperative for the electronic device applications of graphene-based materials. Efficient and cost-effective fabrication of highly uniform GO films and the successive reduction into rGO on a large area is still a cumbersome task through conventional protocols. Improved film casting of GO sheets on a polymeric substrate with quick and green reduction processes has a potential that may establish a path to the practical flexible electronics. Herein, we report a facile deposition process of GO on flexible polymer substrates to create highly uniform thin films over a large area by a flow-enabled self-assembly approach. The self-assembly of GO sheets was successfully performed by dragging the trapped solution of GO in confined geometry, which consisted of an upper stationary blade and a lower moving substrate on a motorized translational stage. The prepared GO thin films could be selectively reduced and facilitated from the simple laser direct writing process for programmable circuit printing with the desired configuration and less sample damage due to the non-contact mode operation without the use of photolithography, toxic chemistry, or high-temperature reduction methods. Furthermore, two different modes of the laser operating system for the reduction of GO films turned out to be valuable for the construction of novel graphene-based high-throughput electrical circuit boards compatible with integrating electronic module chips and flexible humidity sensors.

Graphene oxide/chitosan sponge as a novel filtering material for the removal of dye from water

Although graphene oxide (GO)-based materials are attractive media for water treatment, their separation from water for reuse remains a challenge. This study investigated the self-assembly of GO sheets in the presence of chitosan (CS), a natural polyaminosaccharide, into sponges. We found that about 93% of added CS could be combined with GO, regardless of the CS concentration. There exists an upper critical gelation limit, below which hydrogel forms and above which precipitation takes place. Results indicate that upon freeze-drying, a stable GO/CS sponge was generated only at a CS content of ≥9%. Sponges with CS content between 9% and 41% had good filtering performance. The sponges were characterized with XRD, SEM and FTIR measurements and the interaction between GO and CS was analyzed. The GO/CS sponge with CS content of 9% had adsorption capacity of 275.5 mg/g for methylene blue (MB), a model dye molecule. Both electrostatic attraction and hydrophobic interactions are responsible for MB adsorption by GO/CS sponges. The GO/CS sponge could be regenerated for repeated use using 0.5 M NaOH solution as desorption reagent. Our fixed-bed column studies illustrate that the GO/CS sponge performed well as a filtering material for removing MB from water.

Water-soluble triphenylphosphine-derived microgel as the template towards in-situ nitrogen, phosphorus co-doped mesoporous graphene framework for supercapacitor and electrocatalytic oxygen reduction

In this work, we endowed the hydrophobic triphenylphosphine (TPP) with vinyl group as a new copolymerization monomer to synthesize water-soluble microgels, in which the hydrophilic and positively charged TPP-derived chain segments are mainly located at the surface. These synthesized microgel is simultaneously used as a soft template and phosphorus dopant to fabricate nitrogen, phosphorus co-doped mesoporous graphene framework (NP-PG) via a facile hydrothermal process containing graphene oxide and ammonia. Self-assembly of graphene oxide sheets and microgels induced by their electrostatic interaction enable a tight contact between them, which would confine the phosphorus doping mostly in the pore walls. The obtained NP-PG, as a metal-free electrocatalyst for oxygen reduction, shows a comparable electrocatalytic activity to commercial Pt/C catalyst with a peak potential of −0.18V (vs. Ag/AgCl) and long-term durability. Additionally, it can also be used as a supercapacitor electrode to achieve a high specific capacitance of 245Fg−1 at 0.5Ag−1 and 95% of capacitance retention even after 3000cycles at 5Ag−1.

Cisplatin-induced self-assembly of graphene oxide sheets into spherical nanoparticles for damaging sub-cellular DNA.

This report describes the hitherto unobserved cisplatin induced self-assembly of 2D-graphene oxide sheets into 3D-spherical nano-scale particles. These nanoparticles can encompass dual DNA damaging drugs simultaneously. A combination of confocal microscopy, gel electrophoresis and flow cytometry studies clearly demonstrated that these novel nanoparticles can internalize into cancer cells by endocytosis, localize into lysosomes, and damage DNA, leading to apoptosis. Cell viability assays indicated that these nanoparticles were more cytotoxic towards cancer cells compared to healthy cells.

Preparation and electrochemical properties of Fe2O3/reduced graphene oxide aerogel (Fe2O3/rGOA) composites for supercapacitors

A simple hydrothermal process for fabrication of a nanocomposite comprising Fe2O3 anchored on three-dimensional (3D) reduced graphene oxide aerogel (rGOA) was developed by using Fe(NO3)3 and graphene oxide (GO) as precursors and urea as precipitation agent. The morphology and structure of the Fe2O3/reduced graphene oxide aerogel (Fe2O3/rGOA) composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and Raman spectroscopy. An interconnected 3D network structure, which can allow rapid electrolyte ions diffusion and fast electron transport, was formed by the self-assembly of graphene oxide sheets decorated with Fe2O3 nanoparticles. The particle sizes of Fe2O3 ranged from 30 to 50 nm and were hardly affected by the amount of Fe2O3 loaded into rGOA. The electrochemical properties of the Fe2O3/rGOA composites were studied using cyclic voltammetry and galvanostatic charge/discharge measurement by a three-electrode system. The as-prepared Fe2O3/rGOA composites exhibited a specific capacitance as high as 522 F g−1 at 20 A g−1 within the operated voltage window (−1.1 to 0.3 V). The excellent electrochemical performance of Fe2O3/rGOA was interpreted to be due to the synergistic effect of Fe2O3 particles and rGOA.

Gamma-ray irradiation-induced reduction and self-assembly of graphene oxide into three-dimensional graphene aerogel

Three-dimensional (3D) graphene aerogel (GA) with honeycomb-like porous structure and high C/O ratio was successfully prepared from graphene oxide (GO) dispersions in isopropanol/water solution by simple γ-ray irradiation and freeze-drying processes. Under irradiation, GO sheets suspending in the mixture were reduced and self-assembled mainly due to the restoration of π-π conjugated structure. The microstructure of GA was observed under different magnifications and the pores are quite uniform with pore size around 10µm. The reduction effect of GO was confirmed comprehensively by different characterizations. Briefly, γ-ray irradiation is an effective and green method for the reduction and self-assembly of GO sheets.

Fabrication, Characterization, and Biocompatibility of Polymer Cored Reduced Graphene Oxide Nanofibers.

Graphene nanofibers have shown a promising potential across a wide spectrum of areas, including biology, energy, and the environment. However, fabrication of graphene nanofibers remains a challenging issue due to the broad size distribution and extremely poor solubility of graphene. Herein, we report a facile yet efficient approach for fabricating a novel class of polymer core-reduced graphene oxide shell nanofiber mat (RGO-CSNFM) by direct heat-driven self-assembly of graphene oxide sheets onto the surface of electrospun polymeric nanofibers without any requirement of surface treatment. Thus-prepared RGO-CSNFM demonstrated excellent mechanical, electrical, and biocompatible properties. RGO-CSNFM also promoted a higher cell anchorage and proliferation of human bone marrow mesenchymal stem cells (hMSCs) compared to the free-standing RGO film without the nanoscale fibrous structure. Further, cell viability of hMSCs was comparable to that on the tissue culture plates (TCPs) with a distinctive healthy morphology, indicating that the nanoscale fibrous architecture plays a critically constructive role in supporting cellular activities. In addition, the RGO-CSNFM exhibited excellent electrical conductivity, making them an ideal candidate for conductive cell culture, biosensing, and tissue engineering applications. These findings could provide a new benchmark for preparing well-defined graphene-based nanomaterial configurations and interfaces for biomedical applications.

Bistability and pH Hysteresis of Graphene Oxide Solution in Circle Acid–Base Titration

Abstract Although the dispersion of graphene oxide in solution has been well studied, there still exists mysteries. Here the graphene oxide was synthesized by the modified Hummers method. By the circle acid–base titration, we reported a bistable and pH hysteretic behavior of the graphene oxide in aqueous solution. To interpret the phenomena, a varying pKa mechanism based on the self-assembly of graphene oxide sheets in the circle titration is proposed.

Rational Design of Graphene-Based Aerogels for High-Performance Supercapacitors

Recently, graphene (GN) aerogels with porous three-dimensional (3D) structures have attracted intensive attention because of their ultrahigh specific surface area, high conductivity and multiple electronic transport pathways. Up to date, a variety of strategies coupled with various chemical or physical cross-linkers, such as organic binders [1], ion linkages [2] and ion coordination [3], have been applied to fabricate 3D graphene gels. However, most of the cross-linkers (e.g. organic reagents and metal ions) used are environmentally harmful or expensive, and, more importantly, unexpected impurities and elements could be introduced in the resultants. On the other hand, although graphene electrode can fundamentally provide a specific capacitance up to 550 F/g [4], the specific capacity achieved so far is still far from the theoretical value, which is largely limited by the unexpected restacking of graphene sheets to greatly reduce its available surface. Various spacers, such as carbonaceous materials [5] and metal oxides [6], have been employed into the GN to inhibit the restacking and improve capacitive performance. However, graphene/metal oxide composites usually suffer a low rate performance and poor stability, and the performance of graphene/carbon was still unsatisfied due to the low specific capacity of spacers.Herein, we have demonstrated a novel, simple, low-cost and green approach to produce graphene-based aerogels via the self-assembly of graphene oxide sheets in the alcohols. The as-prepared aerogles have shown special internal structures formed by self-assemble graphene sheets, whereby both macro- and mesopores for ionic transport have been achieved. In order to improve the electrochemical performance of the graphene aerogels, we have introduced ordered porous carbon (PC) with high specific capacity as an effective spacer to rationally design GN/PC aerogels [7]. The ordered porous carbon (PC) with high specific surface area and good capacitance was introduced as a spacer to efficiently inhibit the restacking of graphene (GN) sheets, which has significantly enhanced the specific surface area and facilitated the transmission of ions and electrons in the as-synthesized porous hybrid structure. The all-state-solid electrode fabricated by the as-prepared GN/PC aerogels presented excellent flexibility, and exhibited high specific capacity and good rate performance in polyvinyl acetate/KOH gel electrolyte. Implication of the specific capacities of ~187 F g-1 at 1 A g-1 and 140 F g-1 at 10 A g-1 suggests that the GN/PC aerogels promised great potentials in the development of lightweight high-performance flexible energy storage devices.

Monolithic carbons with spheroidal and hierarchical pores produced by the linkage of functionalized graphene sheets

We report a novel monolithic porous carbon constructed by the hydrothermal self-assembly of graphene oxide sheets with poly (vinyl alcohol) as the linker in the formation process of a three-dimensional (3D) structure. All the pores in this carbon have circular cross-sections and range from micropores to mesopores to macropores and are formed by the gradual removal of trapped water. This 3D graphene network together with unique spheroidal and hierarchical pore structure with macropore openings at the surface allows fast ion and electron transport into the innermost micropores. The carbon not only exhibits excellent capability for removal of dye pollutants and oils but also shows a good performance as an electrode material in lithium ion batteries. Moreover, it is also proved to be an ideal buffer for expanded active materials in electrochemical energy storage.

On the Gelation of Graphene Oxide

Graphene oxide (GO) has been recognized as a unique two-dimensional building block for various graphene-based supramolecular architectures. In this article, we systematically studied the three-dimensional self-assembly of GO sheets in aqueous media to form hydrogels. The gelation of GO can be promoted by different supramolecular interactions, including hydrogen bonding, π-stacking, electrostatic interaction, and coordination. Furthermore, the lateral dimensions of GO sheets also have strong influences on GO gelation. The resulting GO hydrogels exhibited low critical gelation concentrations and good reversibility upon chemical stimulations. These findings indicate that GO has rich supramolecular properties, and its hydrogels may have a variety of technological applications.