Chemically Converted Graphene Research Articles

Modulating surface segregation of Ni2P-Ru2P/CCG nanoparticles for boosting hydrogen evolution reaction in pH-universal

• The activity exhibits a volcanic relationship along with Ni/Ru molar ratio. • The average size of Ni 2 P-Ru 2 P on graphene is from 2.98 to 6.40 nm. • The Ni 2 P-Ru 2 P exhibits excellent activity and stability for HER in pH-universal. • The hydrogen adsorption and H 2 O dissociation depend on the Ni/Ru ratio. Transition metal phosphides with high catalytic activity and durability for the hydrogen evolution reaction (HER) are promising candidates. Herein, we synthesized various Ni 2 P-Ru 2 P nano catalysts with different Ni/Ru ratio supported on chemically converted graphene (CCG) under 10 vol% H 2 /Ar 2 atmosphere. The average size of Ni 2 P-Ru 2 P nanoparticles monotonously increases from 2.98 nm to 6.40 nm with the increase of reduction temperature from 500℃ to 800℃. Meanwhile, the ratio of Ru/Ni is also monotonically increase from 0.67 to 0.85 according to the X-ray photoelectron spectroscopy, suggesting the segregation of Ni to the surface. The Ni 2 P-Ru 2 P/CCG-800 shows the best performance for HER with low overpotentials of 21.83 mV (1 M KOH), 113.38 mV (1 M PBS) and 49.42 mV (0.5 M H 2 SO 4 ), when the current density reaches 10 mA cm −2 . Besides, its Tafel slope of Ni 2 P-Ru 2 P/CCG-800 is 56.92 mV dec −1 in 1 M KOH (67.85 mV dec −1 in 1 M PBS, 45.98 mV dec −1 in 0.5 M H 2 SO 4 ). The superior HER activity of Ni 2 P-Ru 2 P/CCG-800 can be ascribed to the synergistic effect of Ni and Ru near surface. Density functional theory calculations reveal that the introduction of Ni atom into Ru 2 P accelerates H 2 O dissociation at Ru sites and H 2 formation at Ni sites.

Supramolecular Modulation of Molecular Conformation of Metal Porphyrins toward Remarkably Enhanced Multipurpose Electrocatalysis and Ultrahigh‐Performance Zinc–Air Batteries

AbstractModulating the intrinsic catalytic activity of molecular catalysts to improve electrocatalytic performance is significant but challenging. Herein, a simple yet effective strategy to induce molecular flattening of Co (III) meso‐tetra (N‐methyl‐4‐pyridyl) porphyrine (Co‐TMPyP) by supramolecular assembly with chemically converted graphene (CCG) via synergistic electrostatic and π–π interactions is reported. This unique variation in molecular conformation leads to a shortened CoN coordination bond and enhanced electron transfer from the porphyrin macrocycle to the metal ion, thereby optimizing the electronic structure of the catalytic active center in Co‐TMPyP molecule. Thus, the flattened Co‐TMPyP on CCG (Co‐TMPyP/CCG) demonstrates remarkable electrocatalytic performance for the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) simultaneously as a tri‐functional molecular catalyst for the first time with a high half‐wave potential of 0.824 V for ORR and a low overpotential for HER (320 mV) and OER (379 mV) at 10 mA cm–2, respectively, not only much better than the pristine Co‐TMPyP but also among the best results of molecular catalysts in each aspect of ORR, OER, and HER achieved thus far. As a practical demonstration, the Co‐TMPyP/CCG catalyst is used to assemble a rechargeable Zn–air battery, which shows the highest specific capacity (793 mAh g–1) and power density (225.4 mW cm–2) among all molecular catalyst‐based Zn–air batteries ever reported.

Solar light‐driven photocatalyst‐enzyme attached artificial photosynthetic system for regeneration and production of 1,4‐NADH and L‐glutamate

AbstractIn artificial photosynthesis process the photocatalyst‐enzyme attached system is a best strategy to utilize solar energy for solar chemical/fuels production. Herein, we prepared a solar light active graphene‐based photocatalyst received by the covalent attachment of 9‐aminoanthracene (AA) chromophore with chemically converted graphene (CCG) for highly efficient 1,4‐NADH regeneration (79.9 %) and conversion of α‐ketoglutarate (α‐KG) in to L‐glutamate (L‐GM) (88.3 %) in 2 hrs. The present result is a benchmark example of highly selective solar light active enzyme based artificial photosynthetic system for selective formation of L‐GM from α‐KG.

The transmittance and sheet resistance of chemically and heat reduced graphene oxide film

The graphene oxide (GO) sheets were prepared from Hummer’s method. The reduced process is important to graphene related materials for widely functional use in many photoelectric fields. Chemically and heat reduced treatment are carried out in this research and the electrical and optical properties of reduced GO films are measured. The size of GO sheets was examined by transmission electron microscopy with a size of about 5–6 µm. The chemically converted graphene (CCG) film are made by spin coating method. We used different GO concentration and different spin coating times to investigate the properties of graphene transparent conductive films. As the decrease of the GO concentration of solution and the times of spin coating, the transmittance is higher. The electrical property of the mixing of GO and CCG is more stable than the GO sheets only, this is discussed in this research and it is cause by the stacking condition of sheets. The conductivity of reduced graphene oxide film come from GO is lower than that come from CCG, we suppose that is because that the overlapping is less (i.e. film-forming ability) in the former, the transmittance and sheet resistance are 56 T% and 50 kohm/sq.

Plasmonic metamaterial-based chemical converted graphene/TiO2/Ag thin films by a simple spray pyrolysis technique

Graphene based hybrid nanostructures have received special attention in both the scientific and technological development due to their unique physicochemical behavior, which make them attractive in various applications such as, batteries, supercapacitors, fuel cells, solar cells, photovoltaic devices and bio-sensors. In the present study, the role of plasmonic metamaterials in light trapping photovoltaics for inorganic semiconducting materials by a simple and low cost spray pyrolysis technique has been studied. The plasmonic metamaterials thin film has been fabricated by depositing chemically converted graphene (CCG) onto TiO2-Ag nanoparticles which has a low resistivity and a low electron–hole recombination probability. The localized surface plasmon resonance at the metal-dielectric interface for the Ag nanoparticles has been observed at 403nm after depositing chemical converted graphene (CCG) on the TiO2-Ag thin film. The results suggest that the stacking order of the CCG/TiO2/Ag plasmonic metamaterials samples did not change the band gap of TiO2 while it changed the conductivity of the film. Thus the diffusion of the noble metals in the glass and TiO2 matrices based thin films can trap the light of a particular wavelength by mean of plasmonic resonance and may be useful for superior photovoltaic and optoelectronic applications.

Remarkable Dependence of Exciplex Decay Rate on Through-Space Separation Distance between Porphyrin and Chemically Converted Graphene

A series of chemically converted graphenes (CCGs) covalently functionalized with multiple zincporphyrins (ZnPs) through tuned lengths of linear oligo-p-phenylene bridges (ZnP-phn-CCG, n = 1–5) were prepared to address the bridge length effect on their photodynamics. Irrespective of the bridge length, photoexcitation of ZnP-phn-CCG led to exclusive formation of an exciplex state, which rapidly decayed to the ground state without yielding the completely charge-separated state. The notable dependence of the exciplex lifetime as a function of separation distance between the porphyrin and CCG has been observed for the first time, supporting the hypothesis that the decay to the ground state is dominated by the through-space interaction rather than the through-bond one. The basic information on the interaction between ZnP and CCG in the excited state will provide us with deeper insight on the intrinsic nature of the exciplex state as a function of donor–acceptor interaction.

Ultra-endurance flexible all-solid-state asymmetric supercapacitors based on three-dimensionally coated MnOx nanosheets on nanoporous current collectors

Three-dimensional (3D) porous current collector is effective in enhancing the energy density per surface area of batteries and supercapacitors due to its ability for high mass loading of active materials and efficient electron and ion transport. Herein, we report a facile method to construct a nanoporous Ni architecture on the surfaces of flexible carbon cloth (Ni@CC). By electrodeposition of ultrathin MnOx nanosheets on the 3D Ni@CC nanoporous current collectors, we achieved an areal specific capacitance of 906.6mFcm−2 at 1mAcm−2, which is much higher than 353.2mFcm−2 using bare CC as the current collector. Employing the 3D MnOx@Ni@CC positive electrode and a chemically converted graphene (CCG) negative electrode, we assembled a flexible all-solid-state asymmetric supercapacitor (AASC) in a Na2SO4/polyvinyl alcohol (PVA) gel electrolyte. The AASC can achieve a superior energy density of 1.16mWhcm−3 at a current density of 1mAcm−2 and excellent cyclability with 81.5% capacity retention after 10,000 charging/discharging cycles. More importantly, the AASC can maintain over 85.7% of its original capacitance even after 200 bending cycles. These results demonstrate the great potential for application of 3D Ni@CC scaffolds in flexible, high performance wearable electronics and energy storage devices.

Tuning Electrical Conductivity of Inorganic Minerals with Carbon Nanomaterials.

Conductive powders based on Barite or calcium carbonate with chemically converted graphene (CCG) were successfully synthesized by adsorption of graphene oxide (GO) or graphene oxide nanoribbons (GONRs) onto the mineral surfaces and subsequent chemical reduction with hydrazine. The efficient adsorption of GO or GONRs on the surface of Barite and calcium carbonate-based mineral particles results in graphene-wrapped hybrid materials that demonstrate a concentration dependent electrical conductivity that increases with the GO or GONR loading.

Oxygen-reduction reaction strongly electrocatalyzed by Pt electrodeposited onto graphene or graphene nanoribbons

Pt nanoclusters with Pt porous dendritic structures on top (high porosity materials) were electrodeposited at a low overpotential onto glassy carbon (GC) electrodes modified with graphite (GR), multiwalled carbon nanotubes (MWCNT), graphene oxide (GO), graphene oxide nanoribbons (GONR), chemically converted graphene (CCG), and graphene nanoribbons (GNR). The electrochemical profiles of these materials were investigated using cyclic voltammetry and microgravimetry (electrochemical quartz microbalance). Their electrocatalytic activity towards the oxygen-reduction reaction (ORR) was studied employing hydrodynamic cyclic voltammetry. Physical characterization of the samples was based on transmission electron microscopy (TEM), scanning electron microscope (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray microanalysis (EDX). Pt electrocatalysts electrodeposited onto CCG and GNR exhibited high electrocatalytic activity towards ORR when compared with commercial Pt (10 wt.%) on carbon and high stability after 10 000 potential scans, suggesting the possibility of applying these catalysts to acid fuel cells—viable even in economic terms, as very low amounts of finely dispersed Pt per cm2 onto thin CCG or GNR films were required to produce the electrocatalysts. GC electrodes modified with Pt electrodeposited onto GR, MWCNT, GO, or GONR exhibited poor electrocatalytic activity.

All-Solid-State High-Energy Asymmetric Supercapacitors Enabled by Three-Dimensional Mixed-Valent MnOx Nanospike and Graphene Electrodes.

Three-dimensional (3D) nanostructures enable high-energy storage devices. Here we report a 3D manganese oxide nanospike (NSP) array electrode fabricated by anodization and subsequent electrodeposition. All-solid-state asymmetric supercapacitors were assembled with the 3D Al@Ni@MnOx NSP as the positive electrode, chemically converted graphene (CCG) as the negative electrode, and Na2SO4/poly(vinyl alcohol) (PVA) as the polymer gel electrolyte. Taking advantage of the different potential windows of Al@Ni@MnOx NSP and CCG electrodes, the asymmetric supercapacitor showed an ideal capacitive behavior with a cell voltage up to 1.8 V, capable of lighting up a red LED indicator (nominal voltage of 1.8 V). The device could deliver an energy density of 23.02 W h kg(-1) at a current density of 1 A g(-1). It could also preserve 96.3% of its initial capacitance at a current density of 2 A g(-1) after 10000 charging/discharging cycles. The remarkable performance is attributed to the unique 3D NSP array structure that could play an important role in increasing the effective electrode surface area, facilitating electrolyte permeation, and shortening the electron pathway in the active materials.

Synthesis, characterization and cytotoxicity of polyethylene glycol coupled zinc oxide–chemically converted graphene nanocomposite on human OAW42 ovarian cancer cells

Present work reports for the first time on successful synthesis of polyethylene glycol (PEG) coupled ZnO–chemically converted graphene (CCG) nanocomposites (ZGP) as well as pristine nano ZnO (ZO), ZnO–CCG (ZG) and ZnO–PEG (ZP) by adopting facile solvothermal method using zinc acetate dihydrate, graphene oxide and PEG as precursor materials. X‐ray diffraction measurement of samples showed nanocrystalline hexagonal ZnO. Agglomeration of ZnO nanoparticles formed microspheres in ZG, and the agglomeration was found to be decreased in ZGP as revealed from field emission scanning and transmission electron microscopes. Raman and FTIR spectral studies evidenced the presence of chemically interacted CCG and polyethylene glycol in the nanocomposites. Content of the organics in ZGP was determined by thermogravimetric analysis. A mechanism was proposed on the formation of ZGP nanocomposite. From the measurement of in vitro cytotoxicity, quantitative cell viability (CV) of human ovarian cancer cell line, OAW42, was obtained from control to a maximum of 200 µg/ml of sample concentrations. An excellent CV of the cancer cells was observed (nearly ~80% of viable cells at 50 µg/ml dose with respect to the control) for ZGP compared to ZO, ZG and ZP samples. The effective role of CCG and PEG in ZGP nanocomposite for enhancing the cell viability was explained. This simple strategy could be beneficial for synthesis of other metal oxide towards biomedical applications. Copyright © 2015 John Wiley & Sons, Ltd.

Probing Bio-Nano Interactions between Blood Proteins and Monolayer-Stabilized Graphene Sheets.

Meeting proteins is regarded as the starting event for nanostructures to enter biological systems. Understanding their interactions is thus essential for a newly emerging field, nanomedicine. Chemically converted graphene (CCG) is a wonderful two-dimensional (2D) material for nanomedicine, but its stability in biological environments is limited. Systematic probing on the binding of proteins to CCG is currently lacking. Herein, we report a comprehensive study on the interactions between blood proteins and stabilized CCG (sCCG). CCG nanosheets are functionalized by monolayers of perylene leading to significant improvement in their resistance to electrolyte salts and long-term stability, but retain their core structural characteristics. Five types of model human blood proteins including human fibrinogen, γ-globulin, bovine serum albumin (BSA), insulin, and histone are tested. The main driving forces for blood protein binding involve the π-π interacations between the π-plane of sCCG and surface aromatic amonic acid (sAA) residues of proteins. Several key binding parameters including the binding amount, Hill coefficient, and binding constant are determined. Through a detailed analysis of key controlling factors, we conclude that the protein binding to sCCG is determined mainly by the protein size, the number, and the density of the sAA.

Preparation of hybrid transparent electrodes of silver nanowires and chemically converted graphene on abitrary substrate at low temperature

Graphene has been enjoyed significant recent attention due to its potential applications in electronic and optoelectronic devices. Graphene is usually prepared via Hummers' method or modified Hummers' methods. These methods are the most suitable for the large-scale production of single graphene at low cost. But their main drawbacks are the use of strong oxidizing agents which make graphene films separating into small sheets and this extremely decrease the electrical conductivity of graphene. Herein, we report an inexpensive, fast and facile method for preparation of a double layer structured transparent, flexible hybrid electrode from silver nanowires (Ag NWs) with chemically converted graphene (CCG) coating on arbitrary substrate. These films dramatically decreases the resistance of graphene films and exhibited high optical transmittance (82.4 %) and low sheet resistance (18 Ω/ sq), which is comparable to ITO transparent electrode. The ratio of direct conductivity to optical conductivity DC/OP = 104 of this electrode is very close to that displayed by commercially available ITO. Especially, the whole fabrication process is carried out at low temperature. The graphene films are spin coated directly on the substrate without transferring therefore eliminating troubles that are brought from the transfer method.

Synthesis and Characterization of Covalently Linked Graphene/Chitosan Composites

Chitosan, a naturally derived polysaccharide, was covalently linked to chemically converted graphene (CCG) and the properties of the resulting composites were investigated. The composites were prepared using a stable dispersion of CCG in aqueous solvent. The CCG sheets are stabilised in solution by a small number of peripheral charged groups that can be used to form amide linkages with the polymer matrix. Apart from processability and swellability, the synthesized composites exhibited improved mechanical properties and conductivity by the addition of graphene. Graphene incorporation also introduced a control over the extent of swelling in the composites. The synthesized graphene/composites are promising materials for a variety of applications, for example as conducting substrates for the electrically stimulated growth of cells.

Controlled Nano-Crystallization for Optimizing of Lead Acid Positive Active Material Using Graphene Nano-Composites

Controlled Nano-Crystallization for Optimizing of Lead Acid Positive Active Material Using Graphene Nano-Composites

Effect of chemically converted graphene as an electrode interfacial modifier on device-performances of inverted organic photovoltaic cells

This study examined the effects of chemically converted graphene (CCG) materials as a metal electrode interfacial modifier on device-performances of inverted organic photovoltaic cells (OPVs). As CCG materials for interfacial layers, a conventional graphene oxide (GO) and reduced graphene oxide (rGO) were prepared, and their functions on OPV-performances were compared. The inverted OPVs with CCG materials showed all improved cell-efficiencies compared with the OPVs with no metal/bulk-heterojunction (BHJ) interlayers. In particular, the inverted OPVs with reduction form of GO showed better device-performances than those with GO and better device-stability than poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)-based inverted solar cells, showing that the rGO can be more desirable as a metal/BHJ interfacial material for fabricating inverted-configuration OPVs.

Highly selective solar-driven methanol from CO2 by a photocatalyst/biocatalyst integrated system.

The successful development of a photocatalyst/biocatalyst integrated system that carries out selective methanol production from CO2 is reported herein. The fine-tuned system was derived from a judicious combination of graphene-based visible light active photocatalyst (CCG-IP) and sequentially coupled enzymes. The covalent attachment of isatin-porphyrin (IP) chromophore to chemically converted graphene (CCG) afforded newly developed CCG-IP photocatalyst for this research endeavor. The current work represents a new benchmark for carrying out highly selective methanol formation from CO2 in an environmentally benign manner.

Aqueous Colloidal Stability of Graphene Oxide and Chemically Converted Graphene

Graphene oxide (GO) was prepared by modified Hummer’s method, and chemically converted graphene (CCG) was prepared by further reduction of the aqueous GO colloid. The effect of pH on particle size, particle charge, and light absorption of the aqueous colloids of GO and CCG was studied with titration against HCl or NaOH, to find the ideal characteristics for a stable dispersion. The GO colloid was stable in the pH range of 4–11, whereas the CCG colloid gained stability at a relatively narrower pH range of 7–10. Poor stability of the colloids was observed for both GO and CCG colloids at both extremes of the pH scale. Both of the colloids exhibited average size of ~1 micron in the low pH range, whereas for higher pH the size ranged between 300 and 500 nm. The UV-Vis spectra showed absorption peak at 230 nm for GO colloids that shifted to 260 nm for the CCG colloid. Such shift can be ascribed to restoring of electronic conjugation of the C=C bonds in CCG.

Remarkable electrochemical stability of one-step synthesized Pd nanoparticles supported on graphene and multi-walled carbon nanotubes

Anodes and cathodes of fuel cells are usually composed of metallic nanoparticles (NPs) dispersed on carbon, in order to increase their active area. Since the degradation of the catalyst affects the performance of the fuel cells, understanding the stability of its components is pivotal to make these systems more reliable. As such, graphene sheets and carbon nanotubes have been employed as alternative supports to improve the stability of anodes in fuel cells. In this context, we have used polyvinylpyrrolidone (PVP) combined with a one-step chemical reduction induced by ethylene glycol to synthesize Pd NPs dispersed on chemically converted graphene (CCG). We compared the electrochemical stability of Pd NPs supported on carbon black (C), multi-walled carbon nanotubes (MWCNTs) and CCG. MWCNTs and CCG make Pd NPs electrochemically more stable than carbon black. Pd/CCG catalysts are more stable than Pd/MWCNTs during the first potential cycles, while Pd/MWCNTs showed a higher long-term stability. These results allow us to consider a competition between agglomeration of NPs and degradation of the support, where the agglomeration seems to be limited by the available surface area of the support.

Anhydrous organic dispersions of highly reduced chemically converted graphene

A straightforward, systematic approach to the reduction of graphene oxide (GO) that affords dispersions of chemically converted graphene (CCG) in anhydrous organic solvents with decreasing basal plane defects is reported. The extent of reduction can be controlled and optimized, resulting in highly reduced dispersible chemically converted graphene (hrCCG) having an O1S/C1S ratio of 0.06, which approaches that of graphite. The hrCCG dispersion in anhydrous dimethylformamide (DMF) was stable for several months at a concentration of 0.5–0.6mgmL−1. This process was found to be easily scalable and could be exploited for the large scale production of hrCCG in DMF and its dispersion in other anhydrous organic solvents. This study demonstrates that the stability of the graphene dispersion is critically dependent on the exfoliation process. The improved elimination of basal defects and the restoration of aromaticity, while maintaining dispersion stability on a large scale in an anhydrous organic solvent, greatly increase the potential of this material for a wide variety of applications.