Graphene Hydrogel Research Articles

Hydrothermally Reduced Graphene Hydrogel Intercalated with Divalent Ions for Dye Adsorption Studies

Fundamental studies involving divalent ion intercalated graphene-based hydrogel are still lacking in terms of their adsorption behavior towards dye pollutants. In this study, we prepared a self-assembled Mg2+ and Ca2+ intercalated reduced graphene hydrogel (rGH) using hydrothermal treatment to evaluate the intercalation impact on the adsorption capability towards cationic dyes, methylene blue and rhodamine B. The morphological, structural, thermal, and textural properties of the divalent ion intercalated reduced graphene hydrogels were studied using Fourier transform infrared spectrometer, thermogravimetric analysis, Raman spectroscopy, scanning electron microscope-energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area analysis, and X-ray diffraction. The increased adsorption capacity of the divalent ion intercalated reduced graphene-based hydrogels towards the dye molecules resulted from the increase in the specific surface area and pore volume due to the Mg2+ and Ca2+ bridging that formed spaces between the graphene sheets framework. Adsorption kinetics and the equilibrium adsorption isotherm were fitted by a pseudo-second-order alongside intraparticle diffusion kinetic models and Langmuir isotherm respectively. In addition, the divalent ion intercalated reduced graphene hydrogel showed good generation after three cycles of simultaneous adsorption.

Ultra-simple and green two-step synthesis of sodium anthraquinone-2-sulfonate composite graphene (AQS/rGO) hydrogels for supercapacitor electrode materials

As a kind of cheap and easily available organic molecular with Faradic redox activity, quinones can well combined with carbon-materials by non-covalent π–π conjugation and remedy its shortcomings possessing relatively low specific capacitance. However, in previous studies, the combination of quinones and carbon-based materials often requires toxic organic solvent or high energy-consuming and interminable process, greatly hindering their practical application. Here we use water-soluble sodium anthraquinone-2-sulfonate (AQS) and graphene oxide (GO) solution as raw materials to directly obtain AQS composite reduced GO (AQS/rGO) hydrogels by chemical reduction, the whole process of which is performed at relatively low temperature and normal pressure, and only takes a short time, resulting in great promotion in sustainability and efficiency. The AQS/rGO hydrogel exhibiting a high specific capacitance of 387.43 F g−1 at 1 A g−1 and an excellent cycling stability of 91.11% after 10000 cycles at 10 A g−1, has a prodigious improvement for the pure graphene in all aspects. Besides, the maximum energy density of the asymmetric supercapacitor assembled by AQS/rGO-1 hydrogel reaches 15.98 W h kg−1 at the power density of 325.02 W kg−1. This work provide a new idea for the green and efficient preparation of graphene organic quinones composite and has an important significance for its practical application.

Enhanced bacterial disinfection by CuI-BiOI/rGO hydrogel under visible light irradiation.

Compared with traditional layered graphene, graphene hydrogels have been used to construct highly efficient visible light-excited photocatalysts due to their particular three-dimensional network structure and efficient electron transport capacity. In this work, CuI–BiOI/rGO hydrogel with excellent photocatalytic antibacterial activity was prepared and its activity against Escherichia coli and Staphylococcus aureus was evaluated. The result indicates that CuI–BiOI/rGO hydrogel exhibits superior sterilization performance and higher stability than CuI–BiOI and BiOI/rGO, and could completely kill Escherichia coli and Staphylococcus aureus within 40 min. However, only a small amount of Escherichia coli and Staphylococcus aureus can be inactivated by CuI–BiOI and BiOI/rGO hydrogels. Graphene hydrogel plays a significant part in enhancing the disinfection activity of CuI–BiOI/rGO hydrogel. Furthermore, the synergistic effect between CuI of p-type semiconductors, as a hole transport layer, and graphene hydrogel greatly increases the separation and transfer efficiency of photogenerated electron holes excited by BiOI, and further improves the disinfection activity of CuI–BiOI/rGO hydrogel.

Constructing a hierarchically structured KNi0.67Co0.33PO4·H2O-graphene hydrogel/Ni foam electrode for superior all-solid-state supercapacitor.

A monolithic supercapacitor electrode of a KNi0.67Co0.33PO4·H2O-graphene composite hydrogel supported on Ni foam (KNCP-GH/NF) is first prepared by a one-step hydrothermal method, which achieves notable improvements in the electrode surface area and mass-loading of active materials. The KNCP-GH/NF electrode enjoys a hierarchical open-porous structure, where the KNCP-GH composite hydrogel fills in the voids in NF and the porous graphene hydrogel (GH) simultaneously provides a large support surface for growing active KNCP nanoflowers. Accordingly, the KNCP-GH/NF electrode exhibits a strikingly high capacity of 3240 mC cm-2 (876 C g-1) at 2 mA cm-2 and a satisfactory rate performance with 78.3% retention at 100 mA cm-2. Further, an all-solid-state asymmetric supercapacitor, constituted by using KNCP-GH/NF and Fe2P/GH/NF as the cathode and anode, respectively, and PVA-KOH as the solid-state gel electrolyte, delivers a high energy density of 69.2 W h kg-1 (3.9 mW h cm-3) and a power density of 13 229 W kg-1 (720 mW h cm-3) as well as notable cyclability with 81.2% capacity retention after 10 000 charge/discharge cycles. These attractive performances suggest a promising potential for a hierarchically structured KNCP-GH/NF electrode for the high-performance energy storage application.

An anthraquinone-decorated graphene hydrogel based on carbonized cotton fibers for flexible and high performance supercapacitors

Schematic illustration of the preparation procedure of DAQ–CGH.

N/O co-enriched graphene hydrogels as high-performance electrodes for aqueous symmetric supercapacitors.

In this study, an easy one-pot hydrothermal strategy was used to prepare N/O co-enriched graphene hydrogels (NOGHs) using graphene oxide (GO) solution and n-propylamine as a reactant. The n-propylamine can be used not only as a reductant, nitrogen dopant and structure regulator, but also as a spacer to inhibit the agglomeration of graphene sheets. Benefiting from the synergistic effect between the heteroatoms (N, O), 3D porous structures and high specific surface area, the as-prepared NOGH samples present excellent electrochemical properties. Remarkably, the NOGH-140 based binder-free symmetric supercapacitor shows a high specific capacitance of 268.1 F g−1 at the current density of 0.3 A g−1 and retains 222.5 F g−1 (82.9% of its initial value) at 10.0 A g−1 in 6 M KOH electrolyte. Furthermore, the assembled device also displays a notable energy density (9.3 W h kg−1) and outstanding cycling performance (1.8% increase of its initial specific capacitance after 10 000 cycles at 10 A g−1). The simple preparation method and excellent electrochemical properties indicate that NOGHs can be used as electrode materials for commercial supercapacitors.

Diffusion driven nanostructuring of metal–organic frameworks (MOFs) for graphene hydrogel based tunable heterostructures: highly active electrocatalysts for efficient water oxidation

Double-stage molecular diffusion control is achieved in an ‘organic-graphene hydrogel’ biphasic system to yield tunable MOF-based functional hydrogel-hybrids, with excellent water oxidation performance (with a low onset potential and Tafel slope of 44.3 mV dec−1).

Catalysis-induced performance enhancement of an electrochemical microcystin-LR aptasensor based on cobalt-based oxide on a B, N co-doped graphene hydrogel.

Microcystin detection is of great significance and an urgent need because of its damage to water environments and human health. In this paper, an electrochemical aptasensor was developed by combining a 3D cobalt-based oxide modified boron and nitrogen co-doped graphene hydrogel (3D BNG/Co) with a DNA aptamer for sensitive detection of microcystin (MC-LR) through differential pulse voltammetry (DPV) technology. By using 3D BNG/Co as a catalyst and [Fe(CN)6]3-/4- as a redox probe, the catalytic current signal was 3.8 times higher than that of the bare glassy carbon electrode, which can better monitor the electron conduction on the electrode surface and then improve the sensitivity. The as-fabricated electrochemical aptasensor displayed a wide detection range (0.1-1000 pmol L-1), low detection limit (0.03 pmol L-1), good sensitivity, and repeatability, which has potential applications for the protection of the ecological environment and human health.

An all-lignin-based flexible supercapacitor based on a nitrogen-doped carbon dot functionalized graphene hydrogel

In this manuscript, the synthesis of a nitrogen-doped carbon dot functionalized graphene hydrogel and its application as a supercapacitor electrode have been reported.

Polyaniline–Graphene Hydrogel Hybrids via Diffusion Controlled Surface Polymerization for High Performance Supercapacitors

The intricate design of nanomaterials through the controlled diffusion process is natural for biological bodies; however, understanding this mechanism for the development of morphology tuned nanoma...

Nitrogen-doped nanoporous graphene induced by a multiple confinement strategy for membrane separation of rare earth.

SummaryRare earth separation is still a major challenge in membrane science. Nitrogen-doped nanoporous graphene (NDNG) is a promising material for membrane separation, but it has not yet been tested for rare earth separation, and it is limited by multi-complex synthesis. Herein, we developed a one-step, facile, and scalable approach to synthesize NDNG with tunable pore size and controlled nitrogen content using confinement combustion. Nanoporous hydrotalcite from Zn(NO3)2 is formed between layers of graphene oxide (GO) absorbed with phenylalanine via confinement growth, thus preparing the sandwich hydrotalcite/phenylalanine/GO composites. Subsequently, area-confinement combustion of hydrotalcite nanopores is used to etch graphene nanopores, and the hydrotalcite interlayer as a closed flat nanoreactor induces two-dimensional space confinement doping of planar nitrogen into graphene. The membrane prepared by NDNG achieves separation of Sc3+ from the other rare earth ions with excellent selectivity (∼3.7) through selective electrostatic interactions of pyrrolic-N, and separation selectivity of ∼1.7 for Tm3+/Sm3+.

Construction of N, S‐co‐doped graphene/polyaniline composite as free‐standing electrode material

SummaryHerein, N, S‐co‐doped graphene hydrogel (N/SGH) was first prepared by one‐pot feasible hydrothermal approach using thiourea as a dopant for both N and S sources. And then, polyaniline (PANI) was grown on the surface of N, S‐co‐doped graphene hydrogel via simple adsorption of aniline monomer and in situ polymerization process. The N, S‐co‐doped graphene/polyaniline (N/SGH/PANI) composite hydrogel was fabricated as a free‐standing and binder‐free electrode material. Due to the co‐doped synergistic effect, the N/SGH electrode exhibited enhanced electrochemical performances. The N/SGH electrode displays a specific capacitance of 130.4 F/g at 0.5 A/g. Compared with pure graphene hydrogel (GH), the specific capacitance of N/SGH and N‐doped graphene (NGH) electrodes at 0.5 A/g increased by 53% and 20%, respectively. PANI pseudocapacitor material was introduced to further improve its capacitive performance. The resultant N/SGH/PANI composite electrode could achieve a max specific capacitance of 236.5 F/g at 0.5 A/g. In addition, N/SGH/PANI composite electrode showed stable cycle performance with the capacity retention of 95.1% after 1000 cycles performed at 10 A/g. Those provide a fabrication strategy for the design of high‐performance supercapacitors electrode materials.

On-Demand Hydrophobic Drug Release Based on Microwave-Responsive Graphene Hydrogel Scaffolds.

Electromagnetically driven drug delivery systems stand out among stimulus-responsive materials due to their ability to release cargo on demand by remote stimulation, such as light, near infrared (NIR) or microwave (MW) radiation. MW-responsive soft materials, such as hydrogels, generally operate at 2.45 GHz frequencies, which usually involves rapid overheating of the scaffold and may affect tissue surrounding the target location. In contrast, 915 MHz MW penetrate deeper tissues and are less prone to induce rapid overheating. In order to circumvent these limitations, we present here for the first time a graphene-based hydrogel that is responsive to MW irradiation of ν=915 MHz. This system is a candidate soft scaffold to deliver a model hydrophobic drug. The graphene present in the hydrogel acts as a heat-sink and avoids overheating of the scaffold upon MW irradiation. In addition, the microwave trigger stimulates the in vitro delivery of the model drug, thus suggesting a remote and deep-penetrating means to deliver a drug from a delivery reservoir. Moreover, the MW-triggered release of drug was observed to be enhanced under acidic conditions, where the swelling state is maximum due to the swelling-induced pH-responsiveness of the hydrogel. The hybrid composite described here is a harmless means to deliver remotely a hydrophobic drug on demand with a MW source of 915 MHz. Potential use in biomedical applications were evaluated by cytotoxicity tests.

Multi-dimensional Pt/Ni(OH)2/nitrogen-doped graphene nanocomposites with low platinum content for methanol oxidation reaction with highly catalytic performance

Direct methanol fuel cell has been widely recognized as the ideal renewable energy conversion device. However, it still suffers from two major limitations: the heavy use of precious metal platinum and the sluggish kinetics of methanol oxidation catalytic reaction, which have prevented its large-scale commercialization. Therefore, it is considered desirable to design rational and greatly effective catalysts. In this work, multi-dimensional ternary composite electrocatalysts of Pt/Ni(OH)2/nitrogen-doped graphene catalysts have been synthesized with 0D Pt nanoparticles on the 2D Ni(OH)2 nanosheets supported by 3D porous nitrogen-doped graphene hydrogel, and with a low amount (4.26 wt%) of Pt. Notably, the multi-dimensional porous structure design, abundant hydroxyl species, and mutual interactions of ternary catalysts endow high activity promoting the poisonous CO or CO-like intermediates oxidation and propelling the kinetics of sluggish MOR. These novel Pt/Ni(OH)2/NG catalysts exhibit an excellent mass activity of 2.99 A mg−1Pt for methanol electrooxidation, which is about 2.8 and 4.8 times higher than those of commercial PtRu/C and Pt/C, respectively. Furthermore, both durability and CO tolerance of Pt/Ni(OH)2/NGs electrocatalysts are significantly improved.

Rapid Hard‐Tissue‐Embedding Method for Embedding Graphene Nanomaterials: A Multilayered Graphene Hydrogel Membrane

AbstractGraphene has attracted great interest for its uses in tissue regeneration. Multilayered graphene hydrogel (MGH) membranes show great potential as barrier membranes in guided bone regeneration. However, when using the conventional methyl methacrylate‐embedding process, the MGH membrane swells and loses its natural form, which seriously limits the observation of bone regeneration. A rapid embedding method is developed by adding the cross‐linker tetra(ethylene glycol)diacrylate and increasing the polymerization temperature (45 °C) and initiator concentration (64% benzoyl peroxide in penetration liquid). By the rapid embedding method, the shape and properties of the MGH membrane can be well preserved, and the bone tissue can also be well embedded. The resulting blocks have uniform hardness, which makes it possible to obtain thin sections using a cutting and grinding procedure. The rapid embedding method has no significant effect on the conventional methods of bone regeneration detection. The interface between the MGH membrane and new bone tissue can be clearly observed. This new hard‐tissue‐embedding method can lead to better observation of the interaction between bone and graphene, providing an optimized experimental technology for the study of hard tissue regeneration with graphene in the future.

A novel edge-rich structure of CuO/Co3O4 derived from Prussian blue analogue as a high-rate and ultra-stable electrode for efficient capacitive storage

Metal oxides derived from Prussian blue (PB) and Prussian blue analogues (PBAs) are usually used as electrode materials of supercapacitors (SCs). However, the disadvantage is few external active sites. We have successfully developed a novel yet facile strategy to prepare a novel Cu-Co mixed metal oxide (CuO/Co3O4) derived from Cu-based PBA (Cu3[Co(CN)6]2•9H2O), which can form the edge-rich structure to expose more active sites. The edge-rich structure greatly improves charge storage kinetics of electrode material, and the capacitive contribution can even reach 99% at a scan rate of 10 mV s − 1. Even at a low specific surface area, this novel electrode material possesses excellently ultra-stable and high-rate performance in 2 M KOH aqueous electrolyte (76.7% capacity retention when the current density increases from 1 to 10 A g − 1). Moreover, the hybrid supercapacitor (HSC) fabricated with the positive electrode edge-rich CuO/Co3O4 and the negative electrode nitrogen-doped graphene hydrogel (NDGH) delivers remarkable cycling stability (After 7000 cycles, 98.9% capacity is maintained). These excellent electrochemical performances can be attributed to a novel edge-rich structure, which is beneficial for exposing active sites in the external surface and thus promotes the capacitive contribution for fast redox reaction. This strategy opens up a new avenue for promoting electrochemical performance by mediating interfaces and can be extended to the fields of battery and electrocatalysis.

Holey nitrogen-doped graphene aerogel for simultaneously electrochemical determination of ascorbic acid, dopamine and uric acid

In this paper, holey nitrogen-doped graphene aerogel (HNGA) was synthesized and applied to the concurrently electrochemical determination of small biological molecules including ascorbic acid (AA), dopamine (DA) and uric acid (UA). Firstly, holey graphene hydrogel was synthesized by the hydrothermal reaction in the presence of H2O2, which subsequently was lyophilized and further annealed in the mixed gas of ammonia and argon to obtain HNGA. Electron microscopy characterization exhibited a great number of nanopores formed on the basal surface of graphene sheets, and HNGA possessed a hierarchically porous structure. The unique structure and composition of HNGA make it an ideal material for electroanalytical application through accelerating mass and electron transfer. HNGA modified glassy carbon electrode (HNGA/GCE) displayed significantly enhanced electrochemical response to AA, DA, and UA, namely reducing overpotential, increasing current density, and improving the reversibility. The oxidation peaks of these three biomolecules can be entirely separated with evident peak potential differences which are 0.216 V (AA-DA), 0.120 V (DA-UA), and 0.336 V (AA-UA), which it allowed the determination of the three substances at the same time. This sensor shows high sensitivity for the determination of AA, DA, and UA with the detection limit of 16.7 μM, 0.22 μM, and 0.12 μM (S/N = 3), respectively. The proposed sensor was applicable for the practical sample analysis as well and desirable recovery was obtained.

MOFs-induced high-amphiphilicity in hierarchical 3D reduced graphene oxide-based hydrogel

Micro-nano surface with high-amphiphilic structures possesses fascinating physical properties and promising applications in many areas. Herein, we reported a three dimensional (3D) porous hierarchical architecture with internal crosslinked network structures constructed from metal-organic frameworks (MOFs) and graphene oxide (GO) through a facile self-assembly hydrothermal method. In contrast to conventional 3D graphene hydrogel with strongly hydrophobic structures, the resulting composite exhibited high-amphiphilic features with both highly hydrophilic and oleophilic ability, which could absorb water and oils simultaneously, owing to the synergistic effect between MOFs and reduced graphene oxide. MOFs acted as a dopant and intercalated between reduced graphene oxide layers, which could largely increase the specific surface areas of graphene hydrogels (GH) and artistically adjust the surface structures of pristine GH as well. Accordingly, the 3D porous hierarchical MIL-101-GH materials showed great absorption capacity for oil and water. The advantages of this high amphiphilic properties were proved by constructing a biphasic catalytic system with the introduction of molecular sieve into the 3D MIL-101-GH hybrid. As a result, the designing functionalized foam exhibited good catalytic performance in heterogeneous catalysis for epoxidation of olefins without addition of co-solvents.

In Situ Formation of "Dimethyl Sulfoxide/Water-in-Salt"-Based Chitosan Hydrogel Electrolyte for Advanced All-Solid-State Supercapacitors.

Biodegradable hydrogel electrolytes are particularly attractive in the fabrication of all-solid-state supercapacitors due to environmental benignity and avoiding of leakage. The introduction of "water-in-salt" (WIS) electrolytes into hydrogels will further broaden the electrochemical stability window of aqueous supercapacitors significantly. Meanwhile, the addition of an organic co-solvent can effectively overcome the inevitable salt precipitation and extend the temperature adaptability. Herein, an in situ cross-linking approach was demonstrated without any extra binder to obtain a "dimethyl sulfoxide/water-in-salt"-based (DWIS) chitosan hydrogel electrolyte. Interestingly, the addition of 4-7 mol L-1 of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salts not only conforms to the criterion of WIS, but also promoted the successful gelation through the supramolecular complexation between Li+ -solvated complexes and chitosan chains. A hydrogel-based all-solid-state supercapacitor was fabricated using the DWIS chitosan hydrogel as the electrolyte and separator while nitrogen-doped graphene hydrogel (NG) was used as the electrode. The optimized supercapacitor with a wide operating voltage of 2.1 V showed a high specific capacitance of 107.6 F g-1 at 1 A g-1 , remarkable capacitance retention of 80.1 % after 5000 cycles, a superior energy density of 62.9 Wh kg-1 at a power density of 1025.5 W kg-1 , and excellent temperature stability in the range of -20 to 70 °C. These findings suggest that the as-prepared hydrogel electrolyte holds great potential in the practical application of high-performance solid-state energy storage devices.

Reduction Self-Assembly of Three-Dimensional Graphene Hydrogels: Implication as Adsorbents

We have prepared a three-dimensional (3D) graphene hydrogel with a specific surface area that is comparable to the theoretical specific surface area of two-dimensional graphene. Graphene oxide was ...