High reversible capacity of SnO2/graphene nanocomposite as an anode material for lithium-ion batteries

A gas–liquid interfacial synthesis approach has been developed to prepare SnO₂/graphene nanocomposite. The as-prepared nanocomposite was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller measurements. Field emission scanning electron microscopy and transmission electron microscopy observation revealed the homogeneous distribution of SnO₂ nanoparticles (2–6 nm in size) on graphene matrix. The electrochemical performances were evaluated by using coin-type cells versus metallic lithium. The SnO₂/graphene nanocomposite prepared by the gas–liquid interface reaction exhibits a high reversible specific capacity of 1304 mAh g⁻¹ at a current density of 100 mA g⁻¹ and excellent rate capability, even at a high current density of 1000 mA g⁻¹, the reversible capacity was still as high as 748 mAh g⁻¹. The electrochemical test results show that the SnO₂/graphene nanocomposite prepared by the gas–liquid interfacial synthesis approach is a promising anode material for lithium-ion batteries.     

Enhanced cycling performance of Fe3O4-graphene nanocomposite as an anode material for lithium-ion batteries

Fe₃O₄-graphene nanocomposite was prepared by a gas/liquid interface reaction. The structure and morphology of the Fe₃O₄-graphene nanocomposite were characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The electrochemical performances were evaluated in coin-type cells. Electrochemical tests show that the Fe₃O₄-22.7 wt.% graphene nanocomposite exhibits much higher capacity retention with a large reversible specific capacity of 1048 mAh g⁻¹ (99% of the initial reversible specific capacity) at the 90th cycle in comparison with that of the bare Fe₃O₄ nanoparticles (only 226 mAh g⁻¹ at the 34th cycle). The enhanced cycling performance can be attributed to the facts that the graphene sheets distributed between the Fe₃O₄ nanoparticles can prevent the aggregation of the Fe₃O₄ nanoparticles, and the Fe₃O₄-graphene nanocomposite can provide buffering spaces against the volume changes of Fe₃O₄ nanoparticles during electrochemical cycling.     

Mn3O4 nanoparticles embedded into graphene nanosheets: Preparation, characterization, and electrochemical properties for supercapacitors

Mn₃O₄/graphene nanocomposites were synthesized by mixing graphene suspension in ethylene glycol with MnO₂ organosol, followed by subsequent ultrasonication processing and heat treatment. The as-prepared product consists of nanosized Mn₃O₄ particles homogeneously distributed on graphene nanosheets, which has been confirmed by field emission scanning electron microscopy and transmission electron microscopy analysis. Atomic force microscope analysis further identified the distribution of dense Mn₃O₄ nanoparticles on graphene nanosheets. When used as electrode materials in supercapacitors, Mn₃O₄/graphene nanocomposites exhibited a high specific capacitance of 175 F g⁻¹ in 1 M Na₂SO₄ electrolyte and 256 F g⁻¹ in 6 M KOH electrolyte, respectively. The enhanced supercapacitance of Mn₃O₄/graphene nanocomposites could be ascribed to both electrochemical contributions of Mn₃O₄ nanoparticles, functional groups attached to graphene nanosheets, and significantly increased specific surface area.     

Preparation and characterization of tin oxide,SnO2 nanoparticles decorated graphene

SnO₂ nanoparticles/graphene (SnO₂/GP) nanocomposite was synthesized by a facile microwave method. The X-ray diffraction (XRD) pattern of the nanocomposite corresponded to the diffraction peak typical of graphene and the rutile phase of SnO₂ with tetragonal structure. The field emission scanning electron microscope (FESEM) images revealed that the graphene sheets were dotted with SnO₂ nanoparticles with an average size of 10 nm. The X-ray photoelectron spectroscopy (XPS) analysis indicated that the development of SnO₂/GP resulted from the removal of the oxygenous groups on graphene oxide (GO) by Sn²⁺ ions. The nanocomposite modified glassy carbon electrode (GCE) showed excellent enhancement of electrochemical performance when interacting with mercury(II) ions in potassium chloride supporting electrolyte. The current was increased by more than tenfold, suggesting its potential to be used as a mercury(II) sensor.     

Process intensification of uniform loading of SnO2 nanoparticles on graphene oxide nanosheets using a novel ultrasound assisted in situ chemical precipitation method

In this paper, a novel ultrasound assisted, solution-based chemical synthesis method for the preparation of SnO₂–graphene nanocomposite is presented. Graphene oxide (GO) was prepared by the modified Hummers–Offeman method in presence of ultrasonic irradiation. Further loading of SnO₂ on GO was carried out with an ultrasound assisted solution-based synthesis route. The prepared GO and SnO₂–graphene nanocomposite were characterized by XRD, TEM, FTIR spectra, TGA and DTA analysis in order to confirm the formation of graphene–SnO₂ nanocomposite. TEM analysis of ultrasonically prepared graphene–SnO₂ composite shows the uniform and fine loading of SnO₂ particles (3–5 nm) on graphene nanosheets. However agglomerated morphology was observed in case of conventionally prepared graphene–SnO₂ composite. The cavitational effects generated due to the ultrasonic irradiations during the synthesis of graphene–SnO₂ composite improve the fine and uniform loading of SnO₂ on graphene nanosheets by oxidation–reduction reaction between GO and SnCl₂·2H₂O compared to conventional synthesis methods. The formed material was used for the preparation of anode in lithium ion batteries and its electrochemical performance was characterized by cyclic voltammetry and charge/discharge cycles. It is found that the capacity of SnO₂–graphene nanocomposite based Li-battery is stable for around 120 cycles, and the battery could repeat stable charge–discharge reaction.     

A nanocomposite of graphene/MnO2 nanoplatelets for high-capacity lithium storage

A nanocomposite of graphene/MnO₂ nanoplatelets was prepared by one-step chemistry route at room temperature. The microstructure was characterized by X-ray diffraction, N₂ absorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Both TEM and SEM images show that MnO₂ nanoplatelets are homogeneously distributed on the graphene nanosheets. The electrochemical properties were tested by cyclic voltammetry, galvanostatic charge–discharge experiments. The nanocomposite exhibited high lithium capacity (905?mAh?g^?1 at 100?mA?g^?1). The superior lithium storage capability can be attributed to the “open” structure: the large effective surface area and short diffusion paths.     

A facile route to carbon-coated SnO2 nanoparticles combined with a new binder for enhanced cyclability of Li-ion rechargeable batteries

Carbon-coated SnO₂ nanoparticles were prepared by a novel facile route using commercial SnO₂ nanoparticles treated with concentrated sulfuric acid in the presence of sucrose at room temperature and ambient pressure. The key features of this method are the simple procedure, low energy consumption, and inexpensive and non-toxic source materials. As-prepared core/shell nanoparticles were characterized by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The electrochemical measurements showed that the carbon-coated SnO₂ nanoparticles with 10% carbon and using carboxymethyl cellulose (CMC) as a binder displayed the best electrochemical performance with the highest specific capacity of 502 mAh g⁻¹ after 50 cycles at a current density of 100 mA g⁻¹. In addition, owing to the water solvability of CMC, the usage of CMC as binder makes the whole electrode fabrication process cheaper and more environmental friendly.     

Photocatalytic reduction synthesis of SrTiO3-graphene nanocomposites and their enhanced photocatalytic activity

SrTiO₃-graphene nanocomposites were prepared via photocatalytic reduction of graphene oxide by UV light-irradiated SrTiO₃ nanoparticles. Fourier transformed infrared spectroscopy analysis indicates that graphene oxide is reduced into graphene. Transmission electron microscope observation shows that SrTiO₃ nanoparticles are well assembled onto graphene sheets. The photocatalytic activity of as-prepared SrTiO₃-graphene composites was evaluated by the degradation of acid orange 7 (AO7) under a 254-nm UV irradiation, revealing that the composites exhibit significantly enhanced photocatalytic activity compared to the bare SrTiO₃ nanoparticles. This can be explained by the fact that photogenerated electrons are captured by graphene, leading to an increased separation and availability of electrons and holes for the photocatalytic reaction. Hydroxyl (·OH) radicals were detected by the photoluminescence technique using terephthalic acid as a probe molecule and were found to be produced over the irradiated SrTiO₃ nanoparticles and SrTiO₃-graphene composites; especially, an enhanced yield is observed for the latter. The influence of ethanol, KI, and N₂ on the photocatalytic efficiency was also investigated. Based on the experimental results, ·OH, h⁺, and H₂O₂ are suggested to be the main active species in the photocatalytic degradation of AO7 by SrTiO₃-graphene composites.

PACS

61.46. + w; 78.67.Bf; 78.66.Sq     

Microwave-assisted one-pot synthesis of metal/metal oxide nanoparticles on graphene and their electrochemical applications

An effective synthesis strategy of hybrid metal (PtRu)/metal oxide (SnO₂) nanoparticles on graphene nanocomposites is developed using a microwave-assisted one-pot reaction process. The mixture of ethylene glycol (EG) and water is used as both solvent and reactant. In the reaction system for the synthesis of SnO₂/graphene nanocomposite, EG not only reduces graphene oxide (GO) to graphene, but also results in the formation of SnO₂ facilitated by the presence of a small amount of water. On the other hand, in the reaction system for preparation of PtRu/graphene nanocomposites, EG acts as solvent and reducing agent for reduction of PtRu nanoparticles from their precursors and reduction of graphene from graphene oxide. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) characterizations confirm the feasibility of the microwave-assisted reaction system to simultaneously reduce graphene oxide and to form SnO₂ or PtRu nanoparticles. The as-synthesized SnO₂/graphene hybrid composites show a much higher supercapacitance than the pure graphene, and the as-prepared PtRu/graphene show much better electrocatalytic activity for methanol oxidation compared to the commercial E-TEK PtRu/C electrocatalysts.     

Bivalent tin ion assisted reduction for preparing graphene/SnO2 composite with good cyclic performance and lithium storage capacity

Co-precipitation method of SnCl₂·2H₂O and graphene oxide (GO) solution was performed to fleetly prepare graphene/SnO₂ composite. The structure and composition of the nanocomposite were detected by means of XRD, SEM, TEM and FT-IR. The GO was reduced by bivalent tin ions to graphene nanosheet (GNS) via solution reaction and SnO₂ nano-crystals with size of 4–6 nm were homogeneously distributed on the matrix of GNS. It was found that the disorder degree of graphene in GNS/SnO₂ composite prepared by the bivalent tin ion assisted reduction method was much lower than that of GNS obtained via pyrolysis reduction. The possible mechanism for this phenomenon was discussed in detail. The N₂ adsorption tests showed an ink-bottle-like pore structure of GNS/SnO₂ and the SnO₂ nanoparticles were confined in the interlayer of GNS without agglomeration. These structural features were desirable and enabled GNS/SnO₂ an excellent anode material in lithium ion battery. The electrochemical tests showed that the composite could deliver a reversible capacity of 775.3 mAh/g and capacity retention of 98% after 50 cycles.     

Fabrication of graphene/prussian blue composite nanosheets and their electrocatalytic reduction of H2O2

In this work, graphene/prussian blue (PB) composite nanosheets with good dispersibility in aqueous solutions have been synthesized by mixing ferric-(III) chloride and potassium ferricyanide in the presence of graphene under ambient conditions. Transmission electron microscopy (TEM) shows that the average size of the as-synthesized PB nanoparticles on the surface of graphene nanosheets is about 20 nm. Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) patterns have been used to characterize the chemical composition of the obtained graphene/PB composite nanosheets. The graphene/PB composite nanosheets exhibit good electrocatalytic behavior to detection of H₂O₂ at an applied potential of −0.05 V. The sensor shows a good linear dependence on H₂O₂ concentration in the range of 0.02-0.2 mM with a sensitivity of 196.6 μA mM⁻¹ cm⁻². The detection limit is 1.9 μM at the signal-to-noise ratio of 3. Furthermore, the graphene/PB modified electrode exhibits freedom of interference from other co-existing electroactive species. This work provides a new kind of composite modified electrode for amperometric biosensors.     

Fabrication of SnO2/SnS2 hybrids by anchoring ultrafine SnO2 nanocrystals on SnS2 nanosheets and their photocatalytic properties

Ultrafine SnO₂ nanocrystals with sizes of ~4 nm have been successfully loaded on the SnS₂ nanosheets to fabricate SnO₂/SnS₂ hybrids via a facile hydrothermal method. The obtained samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminence (PL) and electrochemical impedance spectroscopy (EIS). The experimental results indicate that the SnO₂ nanocrystals of ~4 nm are well dispersed and intimately anchored on the SnS₂ nanosheets to form nanosized heterojunctions, which can be favorable to the separation of photo-generated holes and electrons. Consequently, the SnO₂/SnS₂ hybrids demonstrate obviously enhanced photocatalytic activities for reduction of Cr (VI) under visible light compared with both the bare SnO₂ and SnS₂.     

Structural, morphological, and optical properties of TiO2 thin films synthesized by the electro phoretic deposition technique

In this work, we report the structural, morphological, and optical properties of TiO₂ thin films synthesized by the electro phoretic deposition technique. The TiO₂ film was formed on a doped fluorine tin oxide (SnO₂:F, i.e., FTO) layer and used as a photo electrode in a dye solar cell (DSC). Using spectroscopic ellipsometry measurements in the 200 to 800 nm wavelengths domain, we obtain a thickness of the TiO₂ film in the range of 70 to 80 nm. Characterizations by X-ray diffraction and atomic force microscopy (AFM) show a polycrystalline film. In addition, AFM investigation shows no cracks in the formed layer. Using an ultraviolet–visible near-infrared spectrophotometer, we found that the transmittance of the TiO₂ film in the visible domain reaches 75%. From the measured current–voltage or I-V characteristic under AM1.5 illumination of the formed DSC, we obtain an open circuit voltage V_oc = 628 mV and a short circuit current I_sc = 22.6 μA, where the surface of the formed cell is 3.14 cm².     

One-step electrosynthesis of MnO2/rGO nanocomposite and its enhanced electrochemical performance

We present a facile one-step electrochemical approach to generate MnO₂/rGO nanocomposite from a mixture of Mn₃O₄ and graphene oxide (GO). The electrochemical conversion of Mn₃O₄ into MnO₂ through potential cycling is expedited in the presence of GO while the GO is reduced into reduced graphene oxide (rGO). The MnO₂ nanoparticles are evenly distributed on the rGO nanosheets and act as the spacer to prevent rGO nanosheets from restacking. This unique structure provides high electroactive surface area (1173?m² g^?1) that improves ions diffusion within the MnO₂/rGO structure. As a result, the MnO₂/rGO nanocomposite exhibits high specific capacitance of 473?F?g^?1 at 0.25?A?g^?1, which is remarkably higher (3 times) than the Mn₃O₄/GO prior conversion. In addition, the electrosynthesized nanocomposite shows higher conductivity and excellent potential cycling stability of 95% at 2000 cycles.     

Non-solvolytic synthesis of aqueous soluble TiO2 nanoparticles and real-time dynamic measurements of the nanoparticle formation

Highly aqueously dispersible (soluble) TiO₂ nanoparticles are usually synthesized by a solution-based sol–gel (solvolysis/condensation) process, and no direct precipitation of titania has been reported. This paper proposes a new approach to synthesize stable TiO₂ nanoparticles by a non-solvolytic method - direct liquid phase precipitation at room temperature. Ligand-capped TiO₂ nanoparticles are more readily solubilized compared to uncapped TiO₂ nanoparticles, and these capped materials show distinct optical absorbance/emission behaviors. The influence of ligands, way of reactant feeding, and post-treatment on the shape, size, crystalline structure, and surface chemistry of the TiO₂ nanoparticles has been thoroughly investigated by the combined use of X-ray diffraction, transmission electron microscopy, UV-visible (UV–vis) spectroscopy, and photoluminescence (PL). It is found that all above variables have significant effects on the size, shape, and dispersivity of the final TiO₂ nanoparticles. For the first time, real-time UV–vis spectroscopy and PL are used to dynamically detect the formation and growth of TiO₂ nanoparticles in solution. These real-time measurements show that the precipitation process begins to nucleate after an initial inhibition period of about 1 h, thereafter a particle growth occurs and reaches the maximum point after 2 h. The synthesis reaction is essentially completed after 4 h.     

TiO2-graphene nanocomposite for electrochemical sensing of adenine and guanine

TiO₂-graphene nanocomposite was prepared by hydrolysis of titanium isopropoxide in colloidal suspension of graphene oxide and in situ hydrothermal treatment. It provides an efficient and facile approach to yield nanocomposite with TiO₂ nanoparticles uniformly embedded on graphene substrate. The electrochemical behavior of adenine and guanine at the TiO₂-graphene nanocomposite modified glassy carbon electrode was investigated. The results show that the incorporation of TiO₂ nanoparticles with graphene significantly improved the electrocatalytic activity and voltammetric response towards these species comparing with that at the graphene film. The TiO₂-graphene based electrochemical sensor exhibits wide linear range of 0.5–200 μM with detection limit of 0.10 and 0.15 μM for adenine and guanine detection, respectively. The excellent performance of this electrochemical sensor can be attributed to the high adsorptivity and conductivity of TiO₂-graphene nanocomposite, which provides an efficient microenvironment for electrochemical reaction of these purine bases.     

Solvothermal synthesis of SnO2/graphene nanocomposites for supercapacitor application

A facile solvent-based synthesis route based on the oxidation–reduction reaction between graphene oxide (GO) and SnCl₂·2H₂O has been developed to synthesize SnO₂/graphene (SnO₂/G) nanocomposites. The reduction of GO and the in situ formation of SnO₂ nanoparticles were achieved in one step. Characterization by X-ray diffraction (XRD), ultraviolet-visible (UV–vis) absorption spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy (FESEM) confirmed the feasibility of using the solvothermally treated reaction system to simultaneously reduce GO and form SnO₂ nanoparticles with an average particle size of 10 nm. The electrochemical performance of SnO₂/graphene showed an excellent specific capacitance of 363.3 F/g, which was five-fold higher than that of the as-synthesized graphene (68.4 F/g). The contributing factors were the synergistic effects of the excellent conductivity of graphene and the nanosized SnO₂ particles.     

Novel conductive magnetic nanocomposite based on poly (indole-co-thiophene) as a hemoglobin diagnostic biosensor: Synthesis,characterization and physical properties

The novel conductive nanocomposite has been successfully prepared by emulsion polymerization. First, magnetite nanoparticles were synthesized via coprecipitation reaction. Then, poly (indole-co-thiophene)@Fe₃O₄ nanocomposite was prepared via emulsion copolymerization of indole and thiophene monomers using sodium dodecyl sulfate as an emulsifier and ammonium persulfate as an oxidant in the presence of Fe₃O₄ nanoparticles. Characterization of the synthesized copolymer, Poly (In-co-T), and its magnetic nanocomposite were studied by Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, differential scanning calorimetric, UV-vis spectrophotometer, and vibrating sample magnetometer. Also, the electrical conductivity of copolymer and nanocomposite were determined by four-probe instrument. Results showed a synergic effect in thermal stability by good interaction between polymer chain and magnetic nanoparticles. The conductivity of the nanocomposite was higher than bare copolymer, and increase of nanoparticles content caused an increment in the conductivity of the nanocomposites. The applicable properties of proposed conductive nanocomposite as a base at electrochemical biosensing have been investigated.     

The improved electrocatalytic activity of palladium/graphene nanosheets towards ethanol oxidation by tin oxide

Tin oxide (SnO₂)/graphene nanosheets (GNS) composite was prepared by a simple chemical-solution method as the catalyst support for direct ethanol fuel cells. Then the SnO₂-GNS composites supporting Pd (Pd/SnO₂-GNS) catalysts were synthesized by a microwave-assisted reduction process. The Pd/SnO₂-GNS catalysts were characterized by using X-ray diffraction, transmission electron microscopy and energy-dispersive spectroscopy techniques. The electrocatalytic performances of Pd/SnO₂-GNS catalysts for ethanol oxidation were studied by cyclic voltammetric and chronoamperometric measurements. It was found that compared with Pd/GNS, the Pd/SnO₂-GNS catalyst showed superior electrocatalytic activity for ethanol oxidation when the mass ratio of SnCl₂·2H₂O precursor salt to graphite oxide was about 1:2.     

Binder-free combination of graphene nanosheets with TiO<Subscript>2</Subscript> nanotube arrays for lithium ion battery anode

Binder-free combination of graphene nanosheets with oriented TiO₂ nanotube arrays was designed and achieved via one-step facile electrodeposition. The structure and morphology of as-prepared composite graphene nanosheets/TiO₂ nanotube arrays were studied in terms of SEM, FESEM, EDX, TEM, Raman and FTIR. Furthermore, the corresponding electrochemical performances were evaluated in terms of galvanostatic charge/discharge, cycle stability and AC impedance. As expected, the composite graphene nanosheets/TiO₂ nanotube arrays displayed higher discharge capacity, cycle stability and Li⁺ diffusion coefficient than bare TiO₂ nanotube arrays. High Li-storage activity, superior conductivity and large surface area of graphene nanosheets should be responsible for improved electrochemical performances.