Thermally Exfoliated Graphene Research Articles

Thermally-exfoliated graphene Oxide/ZnO nanocomposite catalysts for photocatalytic hydrogen evolution and antibacterial activities

Carbon nanomaterials are of great interest due to their enhanced charge separation in hydrogen evolution reactions. Herein, heterostructured TEGO/ZnO nanocomposite catalyst was obtained by combining 3D multilayer graphene-like nanomaterial obtained by green process from recycled carbon source with ZnO to improve photocatalytic activity. Here, photodeposition of MoSx and Pt in aqueous solution is performed on TEGO/ZnO nanocomposite to obtain TEGO/ZnO/MoSx and TEGO/ZnO/Pt by reducing (NH4)2MoS4 and H2PtCl6.6H2O, respectively. Photodeposited MoSx and Pt on TEGO/ZnO nanocomposite resulted in enhanced photocatalytic activity and stability due to increased active sites and enhanced electron transfer ability due to cocatalyst effect. In addition, antibacterial activity of TEGO/ZnO nanocomposite against Escherichia coli and Staphylococcus aureus was investigated by bacterial growth kinetic assay. This work could open up a new nanomaterial for chemical and biological applications.

Rapid Production of Thermally Exfoliated Graphene with a Large Specific Surface Area by Introducing a Spray Predrying Process

Thermal exfoliation of graphite oxide (GTO) is a rapid and efficient method to obtain thermally exfoliated graphene (TEG) on a large scale. Generally, the effect of the thermal exfoliation process is studied to obtain a high specific surface area (SSA), whereas the importance of the predrying process is rarely discussed. In the present work, the influence of spray-assisted predrying on the final exfoliation of GTO was investigated. It was found that the introduction of spray drying did not change the basic units of the thermally exfoliated products comprised of six to eight layers of porous structures. However, it contributed to the formation of loose and more disordered structures, highly susceptible to the destruction caused by the gas generated during thermal exfoliation. Consequently, a higher SSA of 870 ± 74 m2·g–1 with more pores among all the structural units could be obtained. This work helps to understand the influence of spray drying on the TEG, and conveniently associates the predrying and thermal exfoliation processes to achieve a continuous operation.

An effective graphene confined strategy to construct active edge sites-enriched nanosheets with enhanced oxygen evolution

The sluggish kinetics process derived from oxygen evolution reaction (OER), as the crucial half-reaction, is one of key and bottleneck issues for achieving high-efficiency electrochemical water splitting. Herein, we present a thermally exfoliated graphene (TEG) confined strategy to construct active edge sites-enriched layered double hydroxides (LDHs) nanosheets for OER. The TEG as spatially confined skeleton that features large specific surface area and open frameworks with hierarchical interspace structure, is capable of resulting in effectively confined and dispersed growth of the CoFe-LDH nanosheets. This also finally endows the as-made CoFe-LDH/TEG architectures with the maximized exposure of the edge sites, open and interconnected conducting networks, together with intimate interaction between LDH nanosheets and conductive TEG substrate. These unique and superior characteristics guarantee that the as-made CoFe-LDH/TEG architectures enable the capability of intensifying the reaction process, such as fast electrolyte ion and electron transfer, finally delivering an enhanced electrocatalytic activity and reaction kinetics.

Facile preparation of reduced graphene by optimizing oxidation condition and further reducing the exfoliated products

Abstract

Bismuth iron oxide nanocomposite supported on graphene oxides as the high efficient, stable and reusable catalysts for the reduction of nitroarenes under continuous flow conditions

An efficient catalyst made of bismuth, iron and graphene oxide composite was developed for the reduction of nitroarenes with hydrazine hydrate to afford corresponding anilines. We found that the bismuth and graphene remarkably promoted the activity of iron oxide catalyst, so that a mixture of ferric chloride, bismuth nitrate and graphene oxide catalyzed the complete conversion of 4-nitrophenol into 4-aminophenol. Moreover, a catalyst prepared from the co-precipitation of bismuth, iron and graphene oxide nanocomposite (BFGO) exhibited perfect performance, and it could be recovered magnetically and reused for ten cycles without any activity losing. Furthermore, another heterogeneous catalyst tBFGO was constructed from the bismuth iron oxide nanocomposite with thermal exfoliated graphene. It was a robust and sustainable catalyst and was suitable to be used in the continuous flow microreactor. Applying a catalyst cartridge that filled up with tBFGO, a series of functionalized nitroarenes were successfully converted into corresponding anilines with excellent selectivity, and the work-up procedure was very easy. The catalytic activity of the catalyst did not decline within more than 600min under a flow rate of 1mL/min.

Experimental investigation of the important influence of pretreatment process of thermally exfoliated graphene on their microstructure and supercapacitor performance

Thermal exfoliation is a popular approach to prepare thin-layered graphene in large scale. Generally believed that the microstructure and surface chemistry of the products could tailored by the variation of ambient gas pressure, temperature, acid and organic substances during thermal exfoliation of graphite oxide (GO). In this work, we investigated the effect of physical pre-treatment process and acid assisting on the texture, surface state and electrochemical performance of the resulting thermal exfoliated graphene, and found that the different physical pre-treatment process had great influence on the microstructure and specific surface area of graphene. Especially the graphene formed by sonication treatment consisted by thin layers with lots of wrinkles delivered the highest specific surface area of 678m2/g. Adding volatile acid in the process of pre-treatment could decrease their specific surface area. But the graphene obtained with acid assisting was possessed of larger pore volume and improved conductivity which promoted their electrochemical performance effectively. The important role of physical pre-treatment process and acid assisting process in expansion-exfoliation of GO was discussed in detail in this work.

N-doped carbon layer coated thermally exfoliated graphene and its capacitive behavior in redox active electrolyte

A nitrogen-doped carbon layer coated thermally exfoliated graphene (NC-TEG) is prepared by in-situ polymerization of p-phenylene diamine (PD) with thermally exfoliated graphene (TEG) and subsequent high temperature pyrolysis (600°C for 1h in argon gas environment). Fourier transfer infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy confirm the formation of poly-(p-phenylene diamine) layers on the TEG surfaces with a nitrogen doping level of ~6.1%. Physisorption analysis indicates that NC-TEG not only has the enlarged surface area, but also forms hierarchical three dimensional structures with several micro and meso-pores compared to pristine TEG. Due to the synergic effect of nitrogen atoms in the carbon structures and augmented surface area, the capacitance measured from cyclic voltammetry and galvanic charge–discharge increases to 282.5Fg−1 from the 95.1Fg−1 of TEG. Moreover, the PD monomer acts as a reversible faradaic agent. The capacitive performance of the NC-TEG electrode is investigated in different mixed electrolytes. The specific capacitance is significantly increased to 635.6Fg−1 in a mixed electrolyte of 0.025M PD and 2M KOH. After 10,000 cycles, the capacitive retention shows remarkable stability as high as 87.4%.

Effects of acid vapour mediated oxidization on the electrochemical performance of thermally exfoliated graphene

The surface modification of thermally exfoliated graphene (TEG) is an important technique for alteration of its hydrophobic nature and the resolution of its limited dispersibility. We have developed an easy acid-vapour-mediated method to functionalize the inert TEG surface with oxygen functional groups. The effects of oxygen functional groups on the capacitive performances of TEG were investigated with various reaction times. Ultraviolet–visible, Fourier transform infrared and Raman spectroscopy analyses demonstrated that the dispersibility of TEG was improved due to defect augmenting as the extent of oxidation progressed. Quantitative analyses of functional groups of the oxidized TEG samples (O-TEGs) were performed by thermogravimetric analysis and X-ray photoelectron spectroscopic studies. Physisorption surface analysis showed that the pore volumes of O-TEGs were greater than that of the pristine TEG, whereas the specific surface areas of O-TEGs were lower than that of pristine TEG. Electrochemical performances of the O-TEG samples were measured through cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy analysis. A maximum specific capacitance of 175.2Fg−1 was recorded at a current density of 1Ag−1 for the O-TEG oxidized for 2h. Retention of specific capacitance for the sample was ∼97% after 5000 charge–discharge cycles.

A facile preparation of edge etching, porous and highly reactive graphene nanosheets via ozone treatment at a moderate temperature

A simple method to modify thermal-exfoliated graphene nanosheets (T-GNS) by using streaming ozone under different time and temperature is described in this paper. The results indicated that a wide variety of oxygen-containing groups such as COH, COC, CO and COOH could be introduced on the surface of T-GNS by ozone treatment. Especially when ozone modification was taken under 80°C for 20min, the atomic ratio of O/C was increased to 0.503, and the percentage of carboxyl groups was up to 14.37%, which was more than 10times compared with the original T-GNS. In addition, it is worth mentioning that ozone treatment under a moderate temperature could cause etching on the edge of T-GNS and form porous structure in basal plane. As a result, the dispersion of ozone-treated T-GNS in aqueous solution was greatly improved, and the enhanced oxygen-containing groups and dispersion would facilitate its further functionalization and application.

Thermally exfoliated graphene based counter electrode for low cost dye sensitized solar cells

Graphene obtained from thermal exfoliation of graphite oxide are highly wrinkled and have large surface area. Their wrinkled nature is expected to give them excellent catalytic activity. Herein, we demonstrate the use of thermally exfoliated graphene (TEG) as cost effective electrocatalyst for the tri-iodide reduction in dye sensitized solar cells (DSSCs). X-ray diffraction, Raman and Infra red spectroscopy and electron microscopy studies confirm the defective and wrinkled nature of TEG. BET surface area measurement show a large surface area of ∼ 470 m2/g. The counter electrode was fabricated by drop casting a slurry of TEG dispersed in a Nafion:Ethanol solution on fluorine doped tin oxide (FTO) substrates. The use of Nafion prevented film “peel off,” thus ensuring a good substrate adhesion. Electrochemical impedance spectroscopy reveals that TEG had a catalytic performance comparable to that of Pt, suggesting its use as counter electrode material. As expected, the DSSC fabricated with Nafion solubilized TEG/FTO as counter electrode shows an efficiency of about 2.8%, comparable to Pt counter electrode based DSSC which has an efficiency of about 3.4%.

Preparation of magnetic CoFe 2O 4-functionalized graphene sheets via a facile hydrothermal method and their adsorption properties

Magnetic CoFe 2O 4-functionalized graphene sheets (CoFe 2O 4–FGS) nanocomposites have been synthesized by hydrothermal treatment of inorganic salts and thermal exfoliated graphene sheets. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that cobalt ferrite nanoparticles with sizes of 10–40 nm are well dispersed on graphene sheets. OH − was recognized as a tie to integrate the inorganic salts with the graphene sheets, which made reaction started and developed on the surface of graphene sheets and formed cobalt ferrite nanoparticles on graphene sheets. The adsorption kinetics investigation revealed that the adsorption of methyl orange from aqueous solution over the as-prepared CoFe 2O 4–FGS nanocomposites followed pseudo-second-order kinetic model and the adsorption capacity was examined as high as 71.54 mg g −1. The combination of the superior adsorption of FGS and the magnetic properties of CoFe 2O 4 nanoparticles can be used as a powerful separation tool to deal with water pollution.

Nano-Engineered Spacing in Graphene Sheets for Hydrogen Storage

Thermally exfoliated graphene (TEG) sheets were functionalized and cross-linked by in situ diazonium reactions in super acids. The degree of functionalization was monitored by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Compared with the original TEG material, the functionalized TEGs show improved hydrogen uptake capacities, which could be attributed to the proppant effect of the grafted functional groups and charge transfer between the sulfonic addends and the graphene sheets. This method provides a possible route to further increase the hydrogen storage capacity of graphene materials by cross-linking and nanospace engineering.

Decoration, Migration, and Aggregation of Palladium Nanoparticles on Graphene Sheets

As a two-dimensional carbon nanomaterial, graphene has a high surface area and good chemical stability; therefore, its potential applicability in composite materials and as a catalyst support is high. Here, we report a facile process to decorate graphene sheets with well-dispersed Pd nanoparticles. By the in situ formation and adhesion of Pd nanoparticles to the thermally exfoliated graphene (TEG) sheets suspended in a solvent, a Pd/TEG composite was prepared and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer−Emmett−Teller (BET) surface area analysis. The migration and aggregation of Pd nanoparticles on the graphene sheets was directly observed by scanning transmission electron microscopy. As the composite was heated to 700 °C, there was little movement of the Pd nanoparticles; on heating to 800 °C, well below the melting temperature, the Pd nanoparticles began to migrate, coalesce, and agglomerate to form larger particles. The aggregation behavior was fu...