Facile synthesis and photocatalytic activity of ZnO–CuO nanocomposite

Nanostructured ZnO–CuO composite with an open and porous surface was successfully prepared through a simple one-step homogeneous coprecipitation method under low temperature (80 °C), without using any organic solvent or surfactant. The as-prepared samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis spectroscopy. The results demonstrated that the ZnO–CuO nanocomposite presented a hierarchical 3D morphology composed of flower-like ZnO microstructures adorned with leaf-like CuO nanopatches. The photocatalytic activity of ZnO–CuO nanocomposite was evaluated by the photodegradation of rhodamine B under the simulated sunlight irradiation, and compared with those of the monocomponent oxides synthesized by the identical synthetic route and their physical mixture in the approximate molar ratio as that of the nanocomposite. The results indicated that the ZnO–CuO nanocomposite exhibited an appreciable photocatalytic activity, which was mainly attributed to the extended photo-responding range and the increased charge separation rate in the nanocomposite.     

Ultrasound assisted synthesis of polyacrylic acid–nanoclay nanocomposite and its application in sonosorption studies of malachite green dye

Synthesis of nanoclay nanocomposite has been undertaken by using polyacryalic acid (PAA) in aqueous medium and ultrasound environment and its application in dye removal has been investigated. The synthesized product was characterized by using FTIR and XRD techniques. The sonosorption capacity of the product namely PAA–nanoclay composite was determined by choosing malachite green (MG) dye as a model pollutant. The effects of various parameters such as nanocomposite loading, pH, various process conditions etc. have been studied. On comparing the results obtained with that of nanoclay as an adsorbent, it was found for an initial concentration of 500 mg/l, the PAA–nanoclay nanocomposite exhibited higher percentage of pollutant removal (68%) and for nanoclay it was 54%. The adsorption data has been correlated using Langmuir and Freundlich models. The fit of the Freundlich isotherm model was found to be good in the entire range of concentration for the experimental sorption data obtained on the nanoclay nanocomposite. A plausible reaction mechanism for use of PAA–nanoclay nanocomposite as an adsorbent is also proposed.     

Sonochemical synthesis of monodispersed magnetite nanoparticles by using an ethanol–water mixed solvent

The magnetite nanoparticles were synthesized in an ethanol–water solution under ultrasonic irradiation from a Fe(OH)₂ precipitate. XRD, TEM, TG, IR, VSM and UV/vis absorption spectrum were used to characterize the magnetite nanoparticles. It was found that the formation of magnetite was accelerated in ethanol–water solution in the presence of ultrasonic irradiation, whereas, it was limited in ethanol–water solution under mechanical stirring. The monodispersibility of magnetite particles was improved significantly through the sonochemical synthesis in ethanol–water solution. The magnetic properties were improved for the samples synthesized under ultrasonic irradiation. This would be attributed to high Fe²⁺ concentration in the magnetite cubic structure.     

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.     

Fabrication and electrochemical performance of graphene–ZnO nanocomposites

Graphene–ZnO nanocomposites were synthesized successfully through a one-step solvothermal approach. The morphology, structure, and composition of the prepared nanocomposites were investigated by scanning electron microscopy(SEM), transmission electron microscope(TEM), laser micro Raman spectroscopy, and Fourier transform infra-red spectroscopy(FT-IR). The outcomes confirmed that this approach is comparatively steady, practicable, and operable compared with other reported methods. The electrochemical performance of the graphene-ZnO electrodes was analyzed through cyclic voltammetry, altering-current(AC) impedance, and chronopotentiometry tests. The graphene–ZnO electrodes exhibited an improved electrode performance with higher specific capacitance(115 F·g-1), higher electrochemical stability, and higher energy density than the graphene electrodes and most reported graphene–ZnO electrodes. Graphene–ZnO nanocomposites have a steady reversible charge/discharge behavior, which makes them promising candidates for electrochemical capacitors(ECs).     

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.     

Green synthesis of biocompatiable chitosan–graphene oxide hybrid nanosheet by ultrasonication method

Ultrasound-induced synthesis of chitosan-modified nano-scale graphene oxide (CS-NGO) hybrid nanosheets, which has great potential pharmaceutical applications, in supercritical CO₂ without catalyst was presented for the first time. The preparation process does not require organic solvent and post-processing, and CO₂ easily escapes from the product. The morphology and structure of the CS-NGO, characterized using scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis, confirms that it was combined via the amide linkage, and had excellent dispersibility and stability toward acidic and physiological aqueous solution, which implies that it could be used as a drug-carrier. The sonication power played a crucial role in inducing forming amidation, and the conversion rate increased with the sonication time. The mechanism of this reaction was explained.     

Sonochemical decomposition of noble metal oxides and sonochemical alloying of gold–silver systems

Recently, environmental problems, such as global warming, have become more severe; thus, there is a requirement to implement sustainable development goals in materials processing. In this study, we investigated a low-cost and environmentally-friendly sonochemical process for the synthesis of metal nanoparticles with large specific surface areas and catalysis effects. Au₂O₃ hydrate and Ag₂O were reduced to Au and Ag, respectively, at room temperature in a short time when irradiated with ultrasound in ethanol. Furthermore, when a mixed powder of Au₂O₃ hydrate and Ag₂O was irradiated in ethanol, Au–Ag alloys were obtained in only 10 min. This fast and environmentally friendly alloying technique, known as sonochemical alloying, is promising for alloy syntheses.     

Sonochemical synthesis of nanoplates of two Cd(II) based metal–organic frameworks and their applications as precursors for preparation of nano-materials

Nano plates of two Cd(II)-based metal–organic frameworks, [Cd₂(oba)₂(4-bpdb)₂]_n·(DMF)_x(TMU-8) and [Cd(oba)(4,4′-bipy)]_n·(DMF)_y (TMU-9) were synthesized via sonochemical reaction by using various time and concentrations of initial reagents and power of irradiation and characterized by scanning electron microscopy, X-ray powder diffraction and IR spectroscopy. Moreover, the effect of triethylamine on speed of nucleation during the synthesis was investigated. Thermolysis of these MOFs at 550 °C under air atmosphere yields CdO nanoparticles.     

P–V–T equation of state of rhodium oxyhydroxide

A high pressure X-ray diffraction study of RhOOH was carried out up to 17.44?GPa to investigate the compression behavior of an oxyhydroxide with an InOOH-related structure. A fit to the third-order Birch–Murnaghan equation of state gave K₀?=?208?±?6?GPa, and K′?=?9.4?±?1.3. The temperature derivative of the bulk modulus was found to be ?K/?T?=??0.06?±?0.02?GPa K^?1. The refined parameters for volume thermal expansion were α₀?=?2.7?±?0.3?×?10^?5 K^?1; α₁?=?1.7?±?1.1?×?10^?8 K^?2 in the polynomial form (α(T)?=?α_0?+?α₁(T?300)). Our results show that RhOOH is very incompressible, and has a higher bulk modulus than other InOOH-structured oxyhydroxides (e.g. δ-AlOOH, ε-FeOOH, and γ-MnOOH).     

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.

     

First–principles study of potassium adsorption and diffusion on graphene

Potassium–ion batteries (KIBs) are a new–type of energy storage devices that have attracted increasing attention due to their low cost and the abundant resource of K in the Earth’s crust. Monolayer and multilayer graphene are promising electrode materials for KIBs. Herein, the adsorption and diffusion of potassium atoms on the surface of graphene were studied using the first–principles calculations including the van der Waals interaction. It was determined that K atoms can stably adsorb on the surface of graphene. The climbing image nudged elastic band method was employed to calculate the diffusion barriers of a single K atom and two K atoms on the surface of graphene. The results demonstrated that the diffusion barrier of a single K atom on graphene was low. The interaction between K atoms was considered and it facilitates the K atom diffusion to the second and third nearest–neighbour site of the K adatom, but prevents the K atom diffusion to the far nearest–neighbour site of the K adatom. Moreover, the difference in charge density demonstrates that there was a significant charge transfer from two K adatoms to its nearest–neighbour carbon atoms.     

Sonochemical temperature controlled synthesis of pellet-, laminate- and rice grain-like morphologies of a Cu(II) porous metal–organic framework nano-structures

Nano-structures of the Cu(II) metal–organic framework, {Cu(BDT)(DMF)·CH₃OH·0.25DMF}_n (1), which BDT²⁻ is 1,4-benzeneditetrazolate, have been synthesized by the reaction of H₂BDT with Cu(NO₃)₂·6H₂O via ultrasonic irradiation in three different temperatures, which causes different morphologies. The products were characterized by IR spectroscopy, elemental analysis, scanning electron microscopy and X-ray powder diffraction. This study demonstrates that sonochemistry is a suitable method for preparation of metal–organic framework nano-structures and temperature is an effective parameter on morphologies of Cu(II) metal–organic framework nano-structures.     

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.     

N-doped graphene/Bi nanocomposite with excellent electrochemical properties for lithium–ion batteries

N-doped graphene/Bi nanocomposite was prepared via a two-step method, combining the gas/liquid interface reaction with the rapid heat treatment method. The as-prepared sample was characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), and elemental analyzer. The XRD, FESEM, XPS, and elemental analysis results confirm the successful synthesis of N-doped graphene/Bi nanocomposite. As a result, the prepared N-doped graphene/Bi nanocomposite as an anode material for lithium-ion batteries delivers excellent electrochemical performance. A high lithium storage capacity of about 522 mAh g^?1 in the voltage range of 0.01–3.5 V is obtained. After 50 cycles at different current densities from 50 to 1000 mA g^?1, the specific capacity can still remain 386 mAh g^?1. Even at the high current density of 1000 mA g^?1, the N-doped graphene/Bi nanocomposite can still deliver a specific capacity of 218 mAh g^?1. The excellent electrochemical performance of the N-doped graphene/Bi nanocomposite is supposed to benefit from the high electronic conductivity of nitrogen-doped graphene and the synergistic effect of bismuth nanoparticles and nitrogen-doped graphene.     

Microstructure of pulsed laser deposited ceramic–metal and polymer–metal nanocomposite thin films

Ceramic–metal (MgO combined with Fe, Ti and Ni₈₀Nb₂₀) and polymer–metal (polycarbonate combined with Ag and Pd) nanocomposite multilayers were deposited at room temperature by laser ablation (at 248 nm). The multilayers were characterized by X-ray reflectometry, infrared spectroscopy and transmission electron microscopy. In the case of MgO/metal multilayers, well-layered structures are produced down to layer periodicities of 1.2 nm, necessary for tunneling magnetoresistance devices and X-ray mirrors in the water window. The interface roughness in the case of polymer/metal multilayers is found to be a strong function of the metal layer thickness and also the nature of the metal. PACS 68.55.-a; 81.15.Fg     

Sol–gel nonhydrolytic synthesis of a hybrid organic–inorganic electrolyte for application in lithium-ion devices

A new inorganic–organic hybrid electrolyte was synthesized by a nonhydrolytic sol–gel simple route without specific treatment of the reagents. The hybrid ion conductor is prepared with citric acid (CA), tetraethyl-orthosilicate (TEOS) and ethylene glycol (EG), forming polyester chains. The time-consuming drying step, required in most of the chemical syntheses, is not necessary for the preparation of the present hybrid electrolyte, pertaining to the polyelectrolyte class because only Li⁺ is mobile in the polymeric chain. The effect of the concentration of Li is investigated in terms of the Li-ionic conductivity. The new hybrid conductor is shown to be fully amorphous at room temperature with the vitreous transition temperature around 228 K (−45 °C). The material is solid, transparent and displays an ionic conductivity above 10⁻⁵ (Ω cm)⁻¹, besides presenting a great reproducibility of all these characteristics.