Facile preparation and electrochemical characterization of graphene/ZnO nanocomposite for supercapacitor applications

Graphene/ZnO nanocomposites were successfully synthesized by microwave-assisted method. The structure, morphology, optical and composition of the obtained samples were characterized using XRD, FT-IR, laser Raman, UV–Vis spectroscopy and XPS analysis. XRD analysis confirmed the presence of graphene/ZnO nanocomposite. FE-SEM image reveals that the homogenous distribution of ZnO nanoparticles on the graphene nanosheets. The electrochemical properties of the graphene/ZnO electrodes were analyzed by cyclic voltammetry and impedance spectroscopy. The results confirmed that the incorporation of ZnO nanoparticles enhanced the capacitive performance of graphene electrode. Graphene/ZnO nanocomposite electrode showed higher capacitance value of 109 F g⁻¹ at a scan rate of 5 mV s⁻¹ in 1 M KCl solution as compared to the graphene electrodes. These results demonstrated the importance and great potential of graphene based composites in the development of high-performance energy-storage systems.     

Comparative characterization to the three kinds of solid-shape FeS

The microstructures of three kinds of the synthetical solid FeS, acting as the solid lubricant, which includes FeS bulk, FeS particles and FeS powder, were studied in this article. Their surface morphologies were investigated with SEM, and XRD was used to study the phase structures, TEM was utilized to observe the micro-morphologies and analyze the microstructures. The results showed that the crystals of solid FeS were composed of many hexagonal single crystals and multi-crystals, with two kinds of crystalline structure, hexagonal structure and face-centered cubic structure. The surface of FeS was in the shape of a floccule except for a little granular figure. The micro-morphology of FeS presented irregular flakes which can be seen from TEM pictures, the size of grains ranging between 0.1 μm and 3 μm.     

Thermally induced microstructure and morphology transformations in molybdenum disulfide–octadecyltrimethylammonim layered nanocomposite

Microstructure of layered nanocomposite compound consisting of molybdenum disulfide single layers and the layers of octadecyltrimethylammonium molecules as well as the structure of destruction products of this hybrid compound were studied by high resolution transmission electron microscopy (HRTEM) and powder X-ray diffraction (XRD) techniques. Changes in composition, ordering and morphology of the host and guest layers of the compound occurring due to release of organic guest from the interlayer space of MoS₂ on heating or on action of electronic beam have been revealed. Removal of the guest was found to initiate formation in the initial layered structure of the packets consisting of a few MoS₂ layers which come close together within the distances of ca. 1–1.5 nm and 0.6–0.7 nm after heating at 250 °C and 400 °C, respectively. Leaving the guest also causes deformations of MoS₂ layers resulting in their non-flat geometry. At 400 °C, strong bending of a part of the sulfide layers with the radius as small as 3–4 nm was observed.     

Simple approach to synthesis Pt/NiO flower microspheres and their electrocatalytic properties

A kind of novel Pt/NiO flower microsphere structure has been successfully fabricated through a two step chemical process. Firstly NiO flower microspheres could be prepared by a hydrothermal method with the assistance of biomolecule (l-glutamic acid). Secondly the Pt/NiO microsphere composition could be synthesized by the reduction of H₂PtCl₆ solution by use of glucose, and the as-deposited Pt nanoparticles with less than 40 nm in size were embedded into the gaps of the adjacent petals. The sample was characterized by XRD, SEM, TEM, EDS et al. This new kind of structure shows excellent electrocatalytic properties compared with that of Pt nanoparticles, which might provide an efficient way to improve the electrocatalytic property of nanomaterials and other applications.     

Preparation of core-shell structured amorphous aluminum hydroxide ultra-fine powders via a microwave-hydrothermal route

By using Al₂(SO₄)₃ aqueous solution and urea as raw materials, spherical and laminar morphology amorphous aluminum hydroxide (Al(OH)₃) ultra-fine powders were synthesized after 120 min reaction time at 150 °C via a microwave-hydrothermal route. It is interesting to note that the spherical particles could be self-encapsulated into the hollow shells which were constructed with the laminar morphology particles to form core-shell structured ultra-fine powders. The microscope analysis revealed that the spherical cores were around 1 μm and the shells were about 2-3 μm in diameter, respectively. To investigate the influencing factors and formation mechanism of the as-obtained core-shell structured amorphous aluminum hydroxide (Al(OH)₃) ultra-fine powders, samples subjected to different reaction durations were also studied.     

Single-step synthesis of MWCNT/ZnO nanocomposite using co-chemical vapor deposition method

Single-step synthesis of MWCNT and ZnO nanocomposite was conducted by co-chemical vapor deposition method. Electron microscopic analysis revealed that the fabricated nanostructures consisted of MWCNTs with a diameter of 60-70 nm which were coated with ZnO nanoparticles with an average size of 20-30 nm. The growth of ZnO nanoparticles took place after the formation of MWCNTs. EDS and XRD analyses could confirm the high crystallinity of ZnO deposited on the MWCNT surface. In comparison with pristine MWCNTs and ZnO nanoparticles, the UV absorption of MWCNT/ZnO nanocomposite was changed through modification with ZnO nanoparticles.     

Low-temperature synthesis of magnetically recoverable,superparamagnetic, photocatalytic,nanocomposite particles

A new, simple, low-temperature method for the synthesis of superparamagnetic, photocatalytic, nanocomposite particles for applications in the decomposition of pollutants in water is presented. The method is based on the coating of clusters of superparamagnetic maghemite (γ-Fe₂O₃) nanoparticles with a photocatalytic anatase layer using the hydrolysis of aqueous TiOSO₄. The clusters of an appropriate size between 100 and 200 nm form by the simultaneous agglomeration of the aminopropyl-triethoxy-silane-grafted maghemite nanoparticles with a size of approximately 15 nm in a suspension of diluted TiOSO₄. During a sudden increase of pH with the addition of NaOH the titania is heterogeneously nucleated at the cluster surfaces. If the hydrolysis was conducted at an elevated temperature of 90 °C, the titania layer was nanocrystalline anatase. The composition of the nanocomposite particles, i.e., the thickness of the anatase layer, can be controlled simply by changing the starting TiOSO₄/Fe₂O₃ ratio for low titania contents, and by multiple coatings to get high titania contents. The photocatalytic activity of the nanocomposites was evaluated in the photocatalytic decomposition of formic acid. The activity seems to increase with an increase in the thickness and the crystallinity of the anatase coating, whereas it decreased after the calcination of the as-synthesized nanocomposite. The coating of the maghemite nanoparticles with a thin layer of insulating silica also slightly improves the photocatalytic activity.     

Graphene nanosheets-poly(o-aminophenol) nanocomposite for supercapacitor applications

Graphene nanosheets-poly(o-aminophenol) (POAP/GNS) nanocomposite was fabricated on a platinum surface by potential cycling. Voltammograms of the POAP/GNS/Pt electrode showed an excellent capacitive behavior accompanied with a redox transition with a mid-peak potential of 295 mV. The POAP/GNS nanocomposite displayed a specific capacitance as high as 281.1 F g⁻¹ at 0.1 A g⁻¹ which is almost three times higher than that of pure graphene. The specific energy and power of the nanocomposite material were 25.0 Wh kg⁻¹ and 34.8 W kg⁻¹, respectively. The nanocomposite retained more than 99% of the initial capacitance after 1200 charge/discharge cycles.     

Synthesis, characterization and magnetic properties of CoFe2O4 nanorods

In this work, we demonstrated a new precursor route to synthesize CoFe₂O₄ one-dimensional (1D) nanorods. CoFe₂O₄ nanorods were prepared via the thermal decomposition of CoFe₂(C₂O₄)₃ nanorod precursor, which was prepared by solvothermal method without the assistance of template or surfactant. The microstructure and magnetic property of the obtained products were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric (TG) and differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results showed that the as-prepared CoFe₂O₄ nanorods were built by magnetic nanoparticles after calcining the precursor nanorods at different temperatures, and the size variation of magnetic nanoparticles with calcination temperatures leaded to variable magnetic properties.     

High-density assembly of gold nanoparticles to multiwalled carbon nanotubes using ionic liquid as interlinker

Gold nanoparticles were deposited onto the surface of carbon nanotubes through an interlinker of ionic liquid terminated with hydroxyethyl units at one end and exchangeable chloride counterions at the other end. The morphology, structure, and composition of the resulting hybrids were characterized by transmission electron microscopy and X-ray diffraction. A very high density of gold nanoparticles was homogeneously dispersed and well-separated from one another on the modified multi-walled carbon nanotubes. The optical absorption of the products was observed by UV-visible spectroscopy. The results imply that the obtained carbon nanotube-gold nanocomposites have a good application potential in catalysis, sensor, and fuel cells.     

Production of theophylline and polyethylene glycol 4000 composites using Gas Anti-Solvent (GAS) process

Production of drug composites can be used to enhance the dissolution rate of poorly-water soluble drugs. In this research, Gas Anti-Solvent (GAS) technique was applied to produce composites between theophylline (THEO) and polyethylene glycol (PEG) by using dense carbon dioxide as an anti-solvent. It was found that the size of the composites decreased as the concentration of PEG 4000 decreased. However, when increasing the temperature the degree of aggregation and particles size were increased. It was also found that a decrease in ethanol amount in the solvent mixture of dichloromethane and ethanol resulted in a decrease of particle size. The theophylline-PEG composites with the highest drug loading of 16.70% were obtained when using the mass ratio of drug and polymer at 2:3 wt.% in the dichloromethane and ethanol solvent of 50:50%v/v and 25 °C. The dissolution rate of the prepared composites in phosphate buffered solution was found to be 20.8 times greater than that of the original material.     

Ni–Zr–Ti–Si–Sn/Cu metallic glass composites prepared by magnetic compaction

Ni–Zr–Ti–Si–Sn/Cu metallic glass (BMG) composites were fabricated by magnetic compaction of powder mixtures. A considerable plastic deformation took place without apparent failure during the dynamic compaction even at room temperature and at a high strain rate. The BMG particles retained their amorphous phase after the dynamic magnetic compaction at 450 °C. The resulting Ni_52.65Zr_28.71Ti_13.57Si_1.33Sn_3.74/60% Cu composite exhibited a remarkable tensile ductility at room temperature combined with high strength: tensile elongation of 28% and ultimate tensile stress up to 1.1 GPa.     

Preparation and characterization of SnO2/carbon nanotube composite for lithium ion battery applications

SnO₂/multi-walled carbon nanotube (MWCNT) composite was prepared via a diffusion method. Firstly the MWCNT was sonicated in a filtrate which was derived from a tin dichloride solution mixed with AgNO₃ solution. Then the SnO₂/MWCNT composite was prepared whereby, after calcination in N₂ atmosphere, the salts inside the MWCNT decomposed to SnO₂. The resulting composite was characterized by transmission electron microscopy, Raman spectroscopy and X-ray diffraction, which indicated that SnO₂ had infiltrated into the MWCNT and filled the interior. The subsequent evaluation of the electrochemical performance in lithium ion batteries showed that the SnO₂/MWCNT composite had a reversible discharge capacity of 505.9 mAh?g^− 1 after 40 cycles, as compared to 126.4 mAh?g^− 1 for pure nano-SnO₂.     

Novel forsterite/polycaprolactone nanocomposite scaffold for tissue engineering applications

Novel highly porous nanocomposite scaffolds consisting of polycaprolactone (PCL) and forsterite nanopowder were prepared by a solvent-casting/particle-leaching method. In addition, the effects of forsterite nanopowder contents on the structure of the scaffolds were investigated to provide an appropriate composite for bone regenerative medicine. Results showed that the scaffolds exhibited high porosity (up to 92%) with open pores of 100-300 μm average diameters. This porosity increased with decreasing forsterite nanopowder content. In addition, the pore walls contained numerous micropores. Microstructure studies showed that the pores were well distributed throughout the structures. Furthermore, the bioactive forsterite nanoparticles were homogenously distributed within the PCL matrix of the scaffolds, which contained up to 30 wt.% forsterite nanopowder. This porous structure with micropores provides the properties required for bone tissue engineering applications.     

Metal sulfide-polymer nanocomposite thin films prepared by a direct formation route for photovoltaic applications

Blends of conjugated polymers and inorganic semiconductors are an interesting class of materials with various applications in the field of plastic electronics. This work presents a direct approach to obtain composites consisting of a conjugated polymer, poly(3-(ethyl-4-butanoate)thiophene) (P3EBT), and a sulfur-based semiconductor (i.e. CdS, PbS or ZnS) using an in-situ formation route. The metal sulfide semiconductor is formed by reaction of the corresponding metal salt (cadmium acetate, zinc acetate or lead thiocyanate) dispersed within the conjugated polymer matrix with thiourea at temperatures below 200 °C. Nanoscaled networks are formed in the case of the CdS- and ZnS-P3EBT composites as shown by X-ray diffraction and transmission electron microscopy investigations, whereas the PbS-P3EBT blend exhibits inorganic structures on the μm-scale. The materials were used as active layer in bulk-heterojunction type hybrid solar cells. First photovoltaic devices containing an active layer of CdS- or ZnS-P3EBT show photovoltaic action, though efficiencies are low (≤ 0.06%).     

Mechanical properties and microstructure of polyetheretherketone-hydroxyapatite nanocomposite materials

For the first time the polyetheretherketone (PEEK)-hydroxyapatite (HA) nanocomposite materials were successfully prepared, and their microstructure and mechanical properties, such as tensile strength, load-displacement and Young's modulus, were examined. The specimens laminated by the PEEK-HA composite layers with 5 vol.% and 15 vol.% HA were also successfully made, which gave a promising mechanical strength and a high HA content on the specimen surface. This novel approach should be of significance in manufacturing PEEK-HA biomaterials with both satisfactory mechanical properties and high bioactivity.     

Microstructural evolution and mechanical properties of ultrafine grained Al3Ti/Al–5.5Cu composites produced via hot pressing and subsequent friction stir processing

In situ Al₃Ti/Al–5.5Cu composites fabricated by powder metallurgy and subsequent forging were subjected to multiple pass friction stir processing (FSP) with and without active cooling. The forged sample exhibited lower strength and ductility due to the presence of coarse Al₃Ti clusters with a size range of 50–100 μm and coarse matrix grains. Four-pass FSP in air resulted in the refinement and redistribution of the Al₃Ti clusters, and the generation of micron matrix grains, thereby increasing the strength and ductility of the composites. Furthermore, coarse Al₂Cu particles dissolved and re-precipitated due to a relatively long duration of thermal exposure. Additional two pass FSP with rapid water cooling (FSP-water) dissolved most of the Al₂Cu into the matrix and retained the solutes in solution due to the short duration of thermal exposure. Meanwhile, ultrafine matrix grains with a high density of dislocations were obtained. These microstructural changes led to significant increase in strength and a decrease in ductility in the FSP-water sample. After aging, the FSP-water sample exhibited further increased yield strength and ultimate tensile strength due to the precipitation of metastable Al₂Cu phases. However, the ductility did not decrease due to the decrease of dislocation density after aging.     

High performance graphene-poly (o-anisidine) nanocomposite for supercapacitor applications

Our previous exciting results on graphene (G)-conducting polymer (polyaniline (PANI) and polyethylenedioxythiophene (PEDOT)) supercapacitors have prompted the investigation of G-substituted conducting polymer nanocomposites used as electrode materials in supercapacitors. The solubility of ortho-substituted PANI derivatives in a few common solvents has allowed the fabrication of stretchable films by the casting technique. The G-poly (o-anisidine) (G-POA) nanocomposites were synthesized with different weight ratios of G to o-anisidine by chemical methods, and characterized by various techniques, such as, scanning electron microscopy, transmission electron microscopy, UV–visible spectroscopy, Raman spectroscopy, thermogravimetric analysis and cyclic voltammetry. The electrical conductivity and specific capacitance obtained for the G-POA nanocomposites were found to be dependent on the weight ratios of G to o-anisidine. The specific capacitance and the charging–discharging behavior of the POA and G-POA supercapacitors were investigated in a 2 M H₂SO₄, 0.2 M LiClO₄ and 1 M 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) ionic liquid. The specific capacitance of 380 F g⁻¹ was calculated for the 1:1 weight ratio of G to o-anisidine based G-POA supercapacitor in 2 M H₂SO₄. The presence of the electron-donating group (–OCH₃) in the o-anisidine allows the electrons through the lone pair of nitrogen atoms to enhance the electronic charge transport inside the G-POA supercapacitor electrodes. However, the G-POA-based supercapacitors showed a 27% decrease in the specific capacitance in H₂SO₄ and 16% decrease in the ionic liquid (BMIM-PF₆) after 1000 cycles of charging and discharging. The higher stability and rate capability of the G-POA based supercapacitor in an ionic liquid (BMIM-PF₆) as compared to an aqueous electrolytic supercapacitor opens the door for the fabrication of stable supercapacitors for practical applications.     

The Effect of Variable Binder Content and Sintering Temperature on the Mechanical Properties of WC–Co–VC/Cr3C2 Nanocomposites

WC powders with an average crystallite size of 10 nm were successfully prepared by ball milling of micron-sized tungsten carbide powders. Grain growth inhibitors (VC and Cr₃C₂) with concentrations of 0.6 wt% each were added to nanocomposites of WC–9Co and WC–12Co, in both as-received and milled WC. Powder mixtures were then consolidated using spark plasma sintering technique at 1200 and 1300 °C for 10 min under high vacuum and pressure of 50 MPa. The influence of WC crystallite size, Co content, and sintering temperature over microstructure and mechanical properties of the resulting composites were studied through XRD and FESEM. Densification and attained grain sizes of the sintered products were measured by Archimedes principle and Scherrer procedure, respectively. Moreover, microhardness (H_v30) and fracture toughness were measured and compared for each composition to comparatively assess the individual effect. It was observed that the addition of VC and Cr₃C₂ resulted in decreased densification of the synthesized composites. These grain growth inhibitors were found to limit grain sizes to 131 nm with an average hardness of 1592 H_v30 and fracture toughness of 9.23 Mpam^1/2.