Hydrothermal synthesis of CdTe quantum dots–TiO2–graphene hybrid

CdTe–TiO₂–graphene nanocomposites were successfully synthesized via a simple and relatively general hydrothermal method. During the hydrothermal environment, GO was reduced to reduced graphene oxide (RGO), accompanying with the anchoring of TiO₂ nanoparticles on the surface of RGO. In the following process, CdTe quantum dots (QDs) were then in situ grown on the carbon basal planes. The morphologies and structural properties of the as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and fluorescent spectroscopy. It is hoped that our current work could pave a way towards the fabrication of QDs–TiO₂–RGO hybrid materials.     

Free-standing optoelectronic graphene–CdS–graphene oxide composite paper produced by vacuum-assisted self-assembly

Free-standing optoelectronic graphene–CdS–graphene oxide (G–CdS–GO) composite papers were prepared by vacuum-assisted self-assembly. G–CdS hybrids were first prepared by a hydrothermal method and GO acts as a dispersant which makes it easier to disperse them to form relatively stable aqueous suspensions for fabricating paper. Transmission electron microscopy shows that CdS quantum dots (QDs) with an average size of approximately 1–2 nm were distributed uniformly on the graphene sheets. Photoluminescence measurements for the as-prepared G–CdS–GO composite paper showed that the surface defect related emissions of attached CdS QDs decrease and blue shift obviously due to the change in particle size and the interaction of the surface of the CdS QDs with both the GO and the graphene sheets. The resulting paper holds great potential for applications in thin film solar cells, sensors, diodes, and so on.     

Magnetic resonance evidence of manganese–graphene complexes in reduced graphene oxide

We report on EPR and NMR study of reduced graphene oxide (RGO) produced by the Hummers method. We show that this RGO sample reveals isolated Mn²⁺ ions, which originate from potassium permanganate used in the process of the sample preparation. These ions form paramagnetic charge-transfer complexes with the graphene planes and contribute to the ¹³C spin–lattice relaxation.     

Sonochemical synthesis and application of rhodium–graphene nanocomposite

Abstract  

Highly water dispersible rhodium–graphene nanocomposite have been successfully synthesized by the simple reduction of Rh³⁺ salt on poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymer or pluronic-stabilized graphene oxide (GO) nanosheets with borohydride. Rhodium nanoparticles, having average size of 1–3 nm, are homogeneously distributed through out the graphene sheets. Some porous structures of graphene sheets have also been observed after the reduction of pluronic-stabilized GO in the presence of metal ions. The material is very effective for hydrogenation of arenes, especially for benzene as the substrate material at the room temperature and 5 atm pressure of hydrogen.     

P–n junction characteristics of graphene oxide and reduced graphene oxide on n-type Si(111)

The semiconductor behavior of graphene oxide (GO) and reduced graphene oxide (RGO) synthesized by the Hummers method on n-type Si(111) were investigated. Graphene oxide is a product of the oxidation of graphite, during which numerous oxygen functional groups bond to the carbon plane during oxidation. RGO was prepared by adding excess hydrazine to the GO showing p-type semiconductor material behavior. In the C–O bond, the O atom tends to pull electrons from the C atom, leaving a hole in the carbon network. This results in p-type semiconductor behavior of GO, with the carrier concentration dependent upon the degree of oxidation. The RGO was obtained by removing most of the oxygen-containing functionalities from the GO using hydrazine. However, oxygen remaining on the carbon plane caused the RGO to exhibit p-type behavior. The I–V characteristics of GO and RGO deposited on n-type Si(111) forming p–n junctions exhibited different turn-on voltages and slope values.     

Elucidating synthesis of noble metal nanoparticles/graphene oxide in free-scavenger γ-irradiation

Three representative noble metal (Ag, Au and Pt) nanoparticles decorated graphene oxide (NMNPs/GO) composites were fabricated via γ-irradiation without scavenger. The NMNPs/GO composites exhibited the pure and well-dispersed particles structure, which directly illustrated that the GO could be acted as scavenger to benefit reduction and growth of NMNPs. Compared with irradiated GO (IGO), the GO substrate of composites had the lower relative content of hydroxyl groups, meanwhile, the relative contents of carbonyl groups (Pt > Au > Ag) were increased with increasing valence of noble metal. Such results illustrated that the abundant hydroxyl groups could convert the hydrated electrons, hydroxyl and hydrogen radicals to promote the growth of NMNPs on the surface of GO. In addition, the Raman signals of Ag NPs/GO composites were significantly enhanced (6.18 fold more than pristine GO, respectively), exhibiting obvious surface-enhanced Raman scattering activity. Therefore, this paper revealed that the GO could convert the hydrated electrons and radicals to synthetizing NMNPs/GO composites during γ-ray irradiation.     

Preparation of SnO2–graphene from SnS–graphene oxide for enhanced reversible lithium ion storage

SnO₂–graphene nanocomposites (SnO₂–GNS) have been prepared through a simple hydrothermal reaction with SnS–graphene oxide composites as the precursor. The composite material as prepared was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis, and thermogravimetric analysis. The results indicate that SnO₂ nanoparticles possess a good dispersion on the surface of graphene. Electrochemical tests demonstrate the high reversible lithium ion storage properties of SnO₂–GNS. The nanocomposites retained a reversible capacity of 503 mAh?g^?1 after 40 cycles. Moreover, the composite material exhibited higher capacity and better cyclic performance compared to free SnO₂ nanoparticles physically mixed with graphene in the relative weight ratio. The results suggest that the combination of SnO₂ and graphene leads to synergistic performance, which enhances lithium ion storage properties of the overall system.     

S-shaped current–voltage characteristics of polymer composite films containing graphene and graphene oxide particles

The resistive switching effects in composite films containing polyfunctional polymers, such as derivatives of carbazole (PVK), fluorene (PFD), and polyvinyl chloride (PVC), and also graphene particles (Gr) and graphene oxide (GO), the concentration of which in the polymer matrices varied in the range from 1 to 3 wt % corresponding to the percolation threshold in such systems, have been studied. The analysis of the elemental composition of the investigated composites by means of X-ray photoelectron spectroscopy have shown that the oxidation degree of Gr in GO is about 9 to 10%. It has been established that a sharp conductivity jump characterized by S-shaped current-voltage curves and the presence of their hysteresis occurs upon applying a voltage pulse to the Au/PVK (PFD; PVC): Gr (GO)/ITO/PET structures, where ITO is indium tin oxide, and PET is poly(ethylene terephthalate), with the switching time, t, in the range from 1 to 30 μs. The observed effects are attributed to the influence of redox reactions taking place on the Gr and GO particles enclosed in the polymer matrix, and the additional influence of thermomechanical properties of the polymer constituent of the matrix.

     

Solid-state synthesis of molybdenum–vanadium mixed oxide of tubular morphology

The thermally stimulated processes in the disperse carbon–V₂O₅: MoO₃ mixed oxide composite at 400°C were studied by electron microscopy, Raman spectroscopy, and EPR. The mixed oxide phase recrystallized to form tubulene-like structures in the form of rolled lamellae.     

Hydrolysis precipitation synthesis of monodisperse α-Fe2O3 nanorods/graphene oxide nanocomposites

A nanocomposite of graphene oxide supported by monodisperse rod-like α-Fe₂O₃ nanocrystals (GO/α-Fe₂O₃ nanocomposites) has been fabricated through a simple hydrolysis precipitation route in a water–ethanol system. The nanocomposites were characterized by X-ray diffraction, Raman spectra and transmission electron microscopy, respectively. The GO/α-Fe₂O₃ nanocomposites are GO nanosheets decorated randomly by α-Fe₂O₃ nanorods with diameters in the range of 3–5 nm and lengths of 20–30 nm, while only hollow α-Fe₂O₃ microspheres constructed by the radically oriented single-crystalline nanorods are observed in the absence of GO. Compared with pure α-Fe₂O₃ nanoparticles, α-Fe₂O₃/GO nanocomposites exhibited excellent photocatalytic activity as evident from the degradation of rhodamine B in water under UV irradiation. The superior photocatalytic activity performance of α-Fe₂O₃/GO nanocomposites could be attributed to the synergetic effect between the conducting GO nanosheets and monodisperse α-Fe₂O₃ nanorods.     

Hydrazine reduced exfoliated graphene/graphene oxide layers and?magnetoconductance measurements of Ge-supported graphene layers

Inexpensive production and characteristic magnetoconductance fluctuation of Ge-supported stable graphene/graphene oxide layers are being reported. The changeover from graphite to graphene oxide structure during synthesis was evident from X-ray diffraction patterns whereas development of mono and bilayer graphene/graphene oxide was confirmed by electron microscopy studies. Responding to applied magnetic fields (up to 0.3 T), the Ge-supported graphene layers are shown to exhibit prominent magnetoconductance steps and are attributed to the alteration of Landau levels across the Fermi surface. While low-cost fabrication process is attractive for large scale production, the advantage of short synthesis time and understanding magneto-transport mechanism would find relevance in graphene-based nanodevices and circuits.     

Laser ablative approach for the synthesis of cadmium hydroxide–oxide nanocomposite

Cadmium hydroxide/oxide nanocomposite material is synthesized by pulsed laser ablation of cadmium metal in double distilled water. As-synthesized cadmium hydroxide/oxide particles transforms into pure oxide after annealing at 350 °C for 9 h. As-obtained particles are spherical in shape with 15 nm average diameter, while spherical as well as rod shaped nanostructures are formed after annealing. PL spectrum of annealed powder has peaks corresponding to the defect levels rather than the band gap transitions.     

Self-assembly of metal–organic frameworks and graphene oxide as precursors for lithium-ion battery applications

We fabricated composites of Fe₂O₃/reduced graphene oxide as lithium-ion batteries anode material with controlled structures by employing self-assembly of metal–organic frameworks (MOFs) and polymer-functionalized graphene oxide as precursors. By electrostatic interaction, the negatively charged MOFs, Prussian Blue (PB), are assembled on poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene oxide (positive charge). Then the PB cubes become FeOOH nanosheets when treated with sodium hydroxide. Upon further annealing, the FeOOH nanosheets transform to Fe₂O₃ nanoparticles while the graphene oxide become reduced graphene oxide simultaneously. It was found that the composites have good performance as anode of lithium-ion battery. This work shows a new way for self-assembling MOFs and 2D materials.     

A hybrid electrochemical–thermal method for the preparation of large ZnO nanoparticles

A simple and efficient two-step hybrid electrochemical–thermal route was developed for the synthesis of large quantity of ZnO nanoparticles using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The bath concentration and current density were varied from 30 to 120 mmol and 0.05 to 1.5 A/dm². The electrochemically generated precursor was calcined for an hour at different range of temperature from 140 to 600 °C. The calcined samples were characterized by XRD, SEM/EDX, TEM, TG-DTA, FT-IR, and UV–Vis spectral methods. Rietveld refinement of X-ray data indicates that the calcined compound exhibits hexagonal (Wurtzite) structure with space group of P63mc (No. 186). The crystallite sizes were in the range of 22–75 nm based on Debye–Scherrer equation. The TEM results reveal that the particle sizes were in the order of 30–40 nm. The blue shift was noticed in UV–Vis absorption spectra, the band gaps were found to be 5.40–5.11 eV. Scanning electron micrographs suggest that all the samples were randomly oriented granular morphology.     

Rapid and efficient synthesis of colloidal gold nanoparticles by?arc discharge method

The microstructural (XRD and SEM) and dielectric behavior of Pb(Zr_0.54Ti_0.46)O₃ (PZT 54/46) ceramic system with donor (La, Nb and La+Nb) doping was studied. For all Nb-doped PZT samples, only one (tetragonal) phase was found, which confirms the compositional shifts near the morphotropic phase boundary. For La- and La+Nb-doped samples, there are two (rhombohedral and tetragonal) phases. Dielectric characteristic behavior (1/ε) for La- and La+Nb-doped PZT was associated with two-phase transitions: Ferro–Ferro at low temperature and Ferro–Para at Curie temperature. For Nb-doped samples, only one phase transition is observed, which indicates the presence of a single ferroelectric phase.     

High quality nitrogen-doped zinc oxide thin films grown on ITO by sol–gel method

Highly transparent N-doped ZnO thin films were deposited on ITO coated corning glass substrate by sol–gel method. Ammonium nitrate was used as a dopant source of N with varying the doping concentration 0, 0.5, 1.0, 2.0 and 3.0 at%. The DSC analysis of prepared NZO sols is observed a phase transition at 150 °C. X-ray diffraction pattern showed the preferred (002) peak of ZnO, which was deteriorated with increased N concentrations. The transmittance of NZO thin films was observed to be ~88%. The bandgap of NZO thin films increased from 3.28 to 3.70 eV with increased N concentration from 0 to 3 at%. The maximum carrier concentration 8.36×10¹⁷ cm⁻³ and minimum resistivity 1.64 Ω cm was observed for 3 at% N doped ZnO thin films deposited on glass substrate. These highly transparent ZnO thin films can be used as a window layer in solar cells and optoelectronic devices.     

Concept of infrared photodetector based on graphene–graphene nanoribbon structure

We study the mechanisms of photoconductivity in graphene layer–graphene nanoribbon–graphene layer (GL–GNR–GL) structures with the i-type gapless GL layers as sensitive elements and I-type GNRs as barrier elements. The effects of both an increase in the electron and hole densities under infrared illumination and the electron and hole heating and cooling in GLs are considered. The device model for a GL–GNR–GL photodiode is developed. Using this model, the dark current, photocurrent, and responsivity are calculated as functions of the structure parameters, temperature, and the photon energy. The transition from heating of the electron–hole plasma in GLs to its cooling by changing the incident photon energy can result in the change of the photoconductivity sign from positive to negative. It is demonstrated that GL–GNR–GL photodiodes can be used in effective infrared and terahertz detectors operating at room temperature. The change in the photoconductivity sign can be used for the discrimination of the incident radiation with the wavelength 2–3 μm and 8–12 μm.     

Controllable synthesis of layered Co–Ni hydroxide hierarchical structures for high-performance hybrid supercapacitors

A facile solvothermal method is developed for synthesizing layered Co–Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co–Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co_0.5Ni_0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g⁻¹ at a galvanic current density of 1 A g⁻¹ and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co–Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.