Surface Of Reduced Graphene Oxide Nanosheets Research Articles

Amine-functionalized reduced graphene oxide-supported silver nanoparticles for superior catalytic reduction of organic pollutants.

In this work, a simple and environmentally friendly approach has been followed to synthesize amine-functionalized reduced graphene oxide (RGO)-supported silver nanoparticle (AgNPs) having superior catalytic efficiency towards the reduction of organic pollutants. RGO/AgNPs nanohybrid was synthesized by a one-pot hydrothermal reduction of silver nitrate in the presence of amino-propyl trimethoxy silane (APTMS)-functionalized graphene oxide (GO) nanosheets. The structural and morphological characterization of as-synthesized RGO/AgNPs nanohybrid was done by using XRD, SEM, TEM, FT-IR, and Raman spectroscopy techniques. APTMS plays an important role in controlling the size of anchored AgNPs on the nanohybrid in the present study. The -NH2 groups on the surface of APTMS-modified GO function as effective and well-organized nucleation centers facilitating uniform growth of discrete and smaller-sized spherical AgNPs on the surface of RGO nanosheets. In the absence of APTMS, the nanohybrid comprised of bigger-sized AgNPs with few hundred of nanometers in dimension. The catalytic efficiency of RGO/AgNPs nanohybrid was evaluated for the reduction of two model organic pollutants: 4-nitrophenol (4-NP) and methylene blue (MB). Due to the synergistic effects of RGO, APTMS, and Ag components, RGO/AgNPs nanohybrid developed in the present study exhibited superior catalytic activity towards the reduction of 4-NP and MB in comparison with previously reported graphene/graphene oxide/reduced graphene oxide-supported AgNPs catalysts. The catalytic reduction of 4-NP and MB followed pseudo-unimolecular kinetics and the rate constants were found to be 18.83 × 10-3 s-1 and 131.5 ×10-3 s-1 respectively for 4-NP and MB. Furthermore, RGO/AgNPs nanohybrid showed admirable recyclability with negligible loss in its activity until five recycle runs. The superior catalytic activity, favorable kinetic parameters, and sustained catalytic efficiency after recycling make RGO/AgNPs nanohybrid a promising catalyst for the reduction of organic pollutants in environmental remediation.

Enhanced oxidative and adsorptive removal of thallium(I) using Fe3O4@TiO2 decorated RGO nanosheets as persulfate activator and adsorbent

• Fe 3 O 4 @TiO 2 decorated RGO nanosheets can act as PS activator and adsorbent for Tl. • Tl(I) was effectively oxidized to Tl(III) by PS in the presence of the adsorbent. • Maximum removal capacity of 673.2 mg/g was achieved at pH 8.0. • 94.7% of ultimate removal capacity could be accomplished within the first 10 min. • High Tl removal was achieved by enhanced adsorption and surface precipitation. In this study, Fe 3 O 4 @TiO 2 decorated reduced graphene oxide (RGO) nanosheets were synthesized by loading iron oxide on the surface of RGO nanosheets and subsequently coating by titanium oxide, which can be employed as the persulfate (PS) activator and high-performance adsorbent toward thallium (Tl). PS could be effectively activated by the Fe 3 O 4 @TiO 2 decorated RGO nanosheets due to the presence of RGO and Fe(II), resulting in the rapid oxidation of Tl(I) to Tl(III). The removal of Tl(I) was found to be pH-dependent, with the removal efficiency of more than 88.5% in the pH range of 8.0–12.0 at the optimal PS dosage of 10 mM and material dosage of 0.2 g/L. The surface precipitation of Tl 2 O 3 and enhanced adsorption affinity toward Tl were deduced to be main mechanisms for the extremely efficient removal of Tl(I) ions during the oxidation and adsorption hybrid process. The maximum removal capacity of the material at pH 8.0 was estimated as 673.2 mg/g based on the fitting result from the Langmuir model. Approximately 94.7% of ultimate removal capacity could be accomplished within the first 10 min at the initial Tl concentration of 8.5 mg/L. The PS catalytic oxidation coupled with the adsorption technique using the prepared Fe 3 O 4 @TiO 2 decorated RGO nanosheets were proven to be a promising approach for Tl(I) removal from water.

Controlled synthesis of Mn3O4/RGO nanocomposites with enhanced lithium-storage performance

In this study, Mn3O4 nanocrystals supported by reduced graphene oxide (RGO) nanosheets have been successfully prepared in one step by a facile hydrothermal method. The characterization results show that the well-crystallized Mn3O4 monocrystals are uniformly dispersed on the surface of RGO nanosheets. Further studies indicate that the synergistic effect between RGO nanosheets and Mn3O4 nanocrystals not only alleviates mechanical deformation of the composite but also improves the transport of ions and electrons. As a result, the resulting Mn3O4/RGO nanocomposites deliver a high specific capacity, along with excellent cycle stability and rate performance when used as anode materials for lithium-ion batteries.

A novel ternary composite aerogel for high-performance supercapacitor

Despite the attractive features of existing supercapacitors (SCs), SC devices still exhibit low mass loading, limited working voltage, low specific capacitance, short cycle life, and unsatisfactory energy density. In this study, we introduced novel self-suspended polyaniline (S-PANI) into a combination of manganese dioxide (MnO2) and reduced graphene oxide (RGO) to propose an efficient SC electrode for energy storage applications. The unique addition of lightweight, highly conductive, exceptionally water-soluble, and unique fibrillar structure S-PANI increased the conductivity of composite aerogels and reduced the ionic diffusion resistance of electrode materials. The introduction of S-PANI significantly improved the dispersion of MnO2 particles and enabled MnO2 to give full play to its pseudopotentiability. The MnO2/S-PANI/P-RGO ternary composite aerogel was prepared by the self-assembly hydrothermal technique where different mass ratios of MnO2, S-PANI, and RGO were used and analyzed. Physical analyses showed that MnO2/S-PANI/P-RGO composite aerogels had a 3D porous network structure and MnO2 nanospheres are evenly disseminated on the surface of RGO nanosheets. The flowable S-PANI reduced the solid-solid contact resistance in the electrode. The developed 3D MnO2/S-PANI/P-RGO composite aerogel electrode displayed a specific capacitance of 571 F g−1 at the current density of 1 A g−1 along with the specific capacitance of 413 F g−1 with an increased current density of 40 A g−1 and the capacity retention rate of 72.6 %. Also, the initial capacitance retention of 96.7 % was attained after 10,000 cycles at a current density of 20 A g−1 is attained, displaying significant and long-term stability of the composite aerogel electrode. In summary, MnO2/S-PANI/P-RGO composite aerogels reported in this study are promising in energy storage applications demanding high specific capacitance and cycle life.

RGO-templated lignin-derived porous carbon materials for renewable high-performance supercapacitors

Porous carbon materials are considered as one of the most promising electrode materials of supercapacitors. However, it is inevitable to use an expensive and high-polluting activation treatment for obtaining porous structure. Herein, we reported a scalable and sustainable approach to fabricate lignin-derived porous carbon materials by combining hydrothermal reaction and high-temperature carbonization without using any chemical or physical activating reagents. During the hydrothermal reaction, industrial waste lignin as a green reducing agent deoxidized graphene oxide (GO) effectively, while reduced GO (RGO) hydrogels as 3D templates transitioned lignin molecules from ellipsoidal to disk-like conformation via non-covalent interactions and orderly aligned them on the surface of RGO nanosheets. Through this way, the intermediate products, lignin reduced GO aerogels (LRGOs), delivered superior pseudocapacitive performance caused by the reversible phenol-quinone structural transition of lignin molecules. Results indicated a highly positive correlation between the pseudocapacitance of LRGOs and the reduction degree of RGO. After carbonization, the carbonized LRGOs (C-LRGOs) presented a hierarchical porous structure and the resulted high specific surface area rendered the material an ideal electrical double layer capacitive behavior showing high specific capacitance (330 F g−1 at 1 A g−1), high energy density (11.3 Wh kg−1) at a power density of 254 W kg−1, as well as reliable cycle performance.

Enhanced Electromagnetic Wave Absorption Performance of Co0.5Zn0.5 ZIF-Derived Binary Co/ZnO and RGO Composites

Composites of porous Co0.5Zn0.5 zeolitic imidazolate framework (CZ-ZIF)-derived binary Co/ZnO with reduced graphene oxide (RGO) have been prepared by a wet chemical method and carbonization process. CZ-ZIF-derived Co/ZnO microframes with diameter of about 250 nm were dispersed onto the surface of RGO nanosheets. The impedance matching of the composite could be adjusted by controlling the weight ratio of RGO to Co/ZnO microframes. Due to its porous structure, excellent impedance matching, and dielectric loss characteristics, the Co/ZnO/RGO composite exhibited maximum reflection loss (RL) of − 52.2 dB at 10.96 GHz. Coatings with thickness of 2.0 mm to 4.0 mm showed bandwidth of 5.6 GHz (from 8.72 GHz to 14.32 GHz) for RL of − 10 dB (90% absorption). Additionally, the amount of composite added into paraffin matrix was only 8 wt.%, less than for most electromagnetic (EM) wave absorbers in previous reports. Therefore, such Co/ZnO/RGO composites may be promising candidate EM wave absorbing materials.

Microstructure and Superior Electrochemical Activity of Cu3P/Reduced Graphene Oxide Composite for an Anode in Lithium-Ion Batteries

Transition-metal phosphides/graphene composites are a promising new anode material for use in Li-ion batteries because of their high capacity for Li-ion storage. In this research, the copper phosphide (Cu3P)/reduced graphene oxide (RGO) composite is prepared successfully via a facile solvothermal method. A large quantity of Cu3P nanoparticles deposit uniformly and firmly on the surface of RGO nanosheets, which not only avoid the aggregation of Cu3P nanoparticles, but also prevent the re-stacking of graphene thereby retaining their extensive active surface area. As a result, the introduction of RGO nanosheets into Cu3P nanoparticles and their unique interfacial interaction give Cu3P/RGO composites outstanding electrochemical performance, such as good cycling stability, high initial discharge and reversible capacities. The material displays a high initial discharge and reversible capacity of 1578 mAh g−1 and 954 mAh g−1, respectively, at a current density of 500 mA g−1 and after 80 cycles. Even at the current density of 800 mA g−1, the reversible capacity is still 792 mAh g−1 after 80 cycles.

FeS anchored reduced graphene oxide nanosheets as advanced anode material with superior high-rate performance for alkaline secondary batteries

Abstract A new nanocomposite formulation of the iron-based anode for alkaline secondary batteries is proposed. For the first time, FeS nanoparticles anchored on reduced graphene oxide (RGO) nanosheets are synthesized via a facile, environmentally friendly direct-precipitation approach. In this nanocomposite, FeS nanoparticles are anchored uniformly and tightly on the surface of RGO nanosheets. As an alkaline battery anode, the FeS@RGO electrode delivers a superior high-rate charge/discharge capability and outstanding cycling stability, even at a condition without any conductive additives and a high electrode loading of ∼40 mg cm −2 . At high charge/discharge rates of 5C, 10C and 20C (6000 mA g −1 ), the FeS@RGO electrode presents a specific capacity of ∼288, 258 and 220 mAh g −1 , respectively. Moreover, the FeS@RGO electrode exhibits an admirable long cycling stability with a superior capacity retention of 87.6% for 300 cycles at a charge/discharge rate of 2C. The excellent electrochemical properties of the FeS@RGO electrode can be stemmed from the high specific surface area, peculiar electric conductivity and robust sheet-anchored structure of the FeS@RGO nanocomposite. By virtue of its superior fast charge/discharge properties, the FeS@RGO nanocomposite is suitable as an advanced anode material for high-performance alkaline secondary batteries.

Back Cover Chem. Eng. Technol. 1/2016

AbstractReduced Graphene Oxide Composite of Gallium Zinc Oxynitride Photocatalyst with Improved Activity for Overall Water SplittingIncreasing the level of greenhouse gases would put human health and nutrition in danger in the near future. Holding the CO2 level on its current level requires invention, development, and implementation.Solar energy is the most abundant source of energy on the planet. There are various methods to harvest solar energy. Converting the solar irradiation to hydrogen fuel through water splitting on the surface of a visible light activated photocatalyst, is one of the most promising technologies, and has grasped significant attention lately.Gallium‐zinc oxynitride (GaN:ZnO) solid solution has demonstrated outstanding activity for overall water splitting under visible light. However, like other proposed photocatalysts, a high rate of photo‐excited charge recombination limits its efficiency. Since the electrons tend to move towards the media with higher conductivity and electron mobility, fabrication of nanocomposites of highly conductive materials and photocatalyst would be beneficial.This article proposes a method to address the challenging obstacle in the overall solar water splitting process: the undesirable charge recombination. For the first time, reduced graphene oxide (RGO) was utilized as electron sink in an integrated composite with GaN:ZnO solid solution. Precursors and individual components of GaN:ZnO‐RGO composites have been characterized via various techniques.Fabrication of GaN:ZnO‐RGO not only improved the distribution of GaN:ZnO solid solution over the surface of RGO nanosheets, but also enhanced the rate of charge separation, as confirmed through scanning electron microscopy (SEM) and photoluminescence (PL) analysis. Reduction of graphene oxide (GO) to RGO was confirmed through X‐ray photoelectron spectroscopy (XPS) narrow scan analysis. Moreover, evidence of nanoparticles and aggregates of Rh, as the active sites of the water splitting reaction observed on the surface of RGO nanosheets, suggest the existence of sufficient electron density for photo‐reduction of the Rh precursor.Since the immobilized photocatalyst thin film on the surface of a conductive substrate is believed to be an ideal design for practical application, the proposed integrated photocatalytic system effectively contributes toward the designing of a feasible solar harvesting device. The technique reported in this article, can be applied for various photocatalysts in order to develop a highly efficient photocatalytic system. Authors believe that the presented scientific report would offer benefits to researchers not only in material synthesis and characterization area, but also in the field of electrochemistry and photonics.Babak Adeli and Fariborz TaghipourReduced Graphene Oxide Composite of Gallium Zinc Oxynitride Photocatalyst with Improved Activity for Overall Water SplittingChem. Eng. Technol. 2016, 39 (1), 142–148DOI: 10.1002/ceat.201500239

Synthesis of FeCo-reduced graphene oxide composite and its magnetic and adsorption properties

The composite of FeCo and reduced graphene oxide (RGO) was synthesized via a facile ultrasonic chemical method. FeCo nanoparticles were firmly dispersed on the surfaces of RGO nanosheets. Interestingly, the graphene scrolls were also observed in the composite. The composite exhibited excellent magnetic property with specific saturation magnetization (Ms) of 78.06emu/g and strong adsorption for Rhodamine-B. The comprehensive properties made the composite have great potential applications in water treatment.

In-situ growth of Cu nanoparticles on reduced graphene oxide nanosheets and their excellent catalytic performance

Reduced graphene oxide (RGO)-Cu nanocomposites were prepared for the first time through one-pot co-reduction of graphene oxide and Cu2+ ions in ethylene glycol medium. The as-synthesized products were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy. The in-situ grown Cu nanoparticles with adjustable loading amount are uniformly anchored on the surface of RGO nanosheets. The RGO-Cu nanocomposites exhibit extraordinarily superior catalytic performance, with which the catalytic reduction of 4-nitrophenol into 4-Aminophenol can finish within 40s and the apparent rate constant is as high as 6.0min−1 under 25°C. It was found that a suitable copper content is important to optimizing the catalytic activity of the nanocomposites. The kinetics of the reduction reaction at different temperatures was systematically investigated to determine the activation parameters, from which the mechanism of the enhanced catalytic activity is revealed. The RGO-Cu catalysts with excellent catalytic performance and relatively low cost show great promise for the catalytic applications.

Green synthesis of highly reduced graphene oxide by compressed hydrogen gas towards energy storage devices

Herein, we present a new strategy for the mass production of high-quality reduced graphene oxide (RGO) with a surface area of 354 m2 g−1 using high pressure hydrogen as a reducing agent under hydrothermal conditions. The high pressure used is solely generated from the packing of the gas cylinder itself and a pressure meter could simply fulfil the role of monitoring pressure. The reduction process is green without chemical wastes produced. Comparing to other reported methods, the significant advancements of our strategy lie not only in the high-quality RGO with high C/O ratio, conductivity and surface area, but also in the most environment-friendliness and cost-effectiveness, which make the large scale fabrication feasible. Moreover, clean noble metal nanocrystals such as Pt could be easily in situ deposited onto the surface of RGO nanosheets when noble metal salts are introduced into the system. In particular, the prepared RGO and Pt/RGO show exceptional electrochemical performances in supercapacitors and lithium oxygen batteries because of their clean electrochemical surface, good conductivity and large surface area. Our results reveal that the obtained RGO have a specific capacitance of 884.4 F g−1 at a current density of 0.5 A g−1, and the Pt/RGO electrode can deliver discharge–charge capacities of 1000 mAh g−1 for 40 cycles with a high round-trip efficiencies of 74.9% at 50 mA g−1 when used as Li–O2 battery electrodes.

Highly Sensitive Reduced Graphene Oxide Impedance Sensor Harnessing π-Stacking Interaction Mediated Direct Deposition of Protein Probes

Graphene-based electrochemical impedance sensors have recently received much attention due to their outstanding sensing capability and economic viability. In this study, we present a novel means of constructing an impedance sensing platform via harnessing intrinsic π-stacking interactions between probe protein molecules and reduced graphene oxide (RGO) substrate, obviating the need for introducing external chemical groups often required for covalent anchoring of the probes. To achieve this goal, protein molecules used as a probe were denatured to render their hydrophobic residues exposed in order to facilitate their direct π-stacking interactions with the surface of RGO nanosheets. The protein molecules in denatured form, which would otherwise have difficulty in undergoing π-stacking interactions with the RGO surface, were found to uniformly cover the RGO nanosheets at high density, conducive to providing a graphene-based impedance sensing platform capable of detecting a probe-specific analyte at high sensitivity. The proof-of-concept performance of thus-constructed RGO-based impedance sensors was demonstrated via selective detection of biological binding events of antigen-antibody reaction at a femtomolar range. Notably, since the π-stacking interaction can occur on the entire RGO surface, it can desirably exclude a backfill process indispensable for the conventional biosensors to suppress background noise signals. Since the procedure of π-stacking mediated direct deposition of on-purpose denatured protein probes onto the RGO surface is facile and straightforward, the proposed strategy is anticipated to extend its applicability for fabrication of high performance graphene-based bio or chemical sensors.

Remarkable enhancement of the electrode performance of nanocrystalline LiMn2O4 via solvothermally-assisted immobilization on reduced graphene oxide nanosheets

A facile solvothermal way to immobilize nanocrystalline LiMn2O4 on the surface of graphene nanosheets is developed to improve the functionality of lithium manganate as lithium intercalation electrode. A solvothermal treatment for the colloidal mixture of graphene oxide (GO) nanosheets and LiMn2O4 nanocrystals gives rise not only to the reduction of GO to reduced graphene oxide (RGO) but also to the immobilization of lithium manganate nanoparticles on the surface of RGO nanosheets. According to powder X-ray diffraction and electron microscopic analyses, the crystal structure and morphology of spinel lithium manganate remain intact upon the composite formation with the RGO nanosheets. The application of larger aldehyde molecule as a reductant leads to the increase of crystallinity and the lowering of Mn oxidation state for the pristine LiMn2O4 and its nanocomposite with the RGO nanosheets. The present LiMn2O4–RGO nanocomposites display promising cathode performances for lithium rechargeable batteries, which are much superior to those of the pristine LiMn2O4 nanocrystals. The observed enhancement of electrode performance upon the composite formation with the RGO nanosheets is attributable both to the improvement of the surface ion transport of nanocrystalline lithium manganate and to the increase of electrical conductivity. The present experimental findings demonstrate that the solvothermal treatment with RGO nanosheets provides an effective way of improving the electrochemical activity of nanocrystalline lithium metal oxides.

A Strong Electronic Coupling between Graphene Nanosheets and Layered Titanate Nanoplates: A Soft‐Chemical Route to Highly Porous Nanocomposites with Improved Photocatalytic Activity

Strongly coupled nanocomposites of layered titanate and reduced graphene oxide (RGO) are synthesized by electrostatically derived self-assembly between negatively charged RGO nanosheets and positively charged TiO(2) nanosols, which is then followed by a phase transition of the anatase TiO(2) component into layered titanate. The resulting nanocomposite consists of thin 2D nanoplates of lepidocrocite-type layered titanate immobilized on the surface of RGO nanosheets. The composite formation with RGO nanosheets is effective not only in promoting the phase transition of anatase TiO(2) nanosols, but also in improving the thermal stability of the layered titanate, indicating the role of RGO nanosheets as an agent for directing and stabilizing layered structures. The layered-titanate-RGO nanocomposites exhibit remarkably expanded surface area with the formation of micropores and mesopores. The composite formation with RGO nanosheets gives rise to the disappearance of the reflectance edge of layered titanate in the diffuse reflectance UV-vis spectra, indicating a strong electronic coupling between the RGO and layered titanate. The strong electronic correlation between the two components is further evidenced by the visible-light-induced generation of photocurrents after the hybridization with RGO. The layered-titanate-RGO nanocomposite shows a higher activity for the photodegradation of organic molecules than uncomposited layered titanate, underscoring the usefulness of graphene hybridization in improving the photocatalyst performance of layered titanate. The experimental findings presented here clearly demonstrate that the self-assembly of metal oxide nanoparticles with RGO 2D nanosheets is quite effective not only in synthesizing porous metal-oxide-graphene nanocomposites with improved photo-induced functionality, but also in achieving strong electronic coupling between RGO and metal oxides.

Sodium citrate: A universal reducing agent for reduction / decoration of graphene oxide with au nanoparticles

A facile method is proposed for the synthesis of reduced graphene oxide nanosheets (RGONS) and Au nanoparticle-reduced graphene oxide nanosheet (Au-RGONS) hybrid materials, using graphene oxide (GO) as precursor and sodium citrate as reductant and stabilizer. The resulting RGONS and Au-RGONS hybrid materials were characterized by UV-vis spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, atomic force microscopy, transmission electron microscopy, and X-ray diffraction. It was found that the RGONS and Au-RGONS hybrid materials formed stable colloidal dispersions through hydrogen bonds between the residual oxygen-containing functionalities on the surface of RGONS and the hydroxyl/carboxyl groups of sodium citrate. The electrochemical responses of RGONS and Au-RGONS hybrid material-modified glassy carbon electrodes (GCE) to three kinds of biomolecules were investigated, and all of them showed a remarkable increase in electrochemical performance relative to a bare GCE.