Nano

With the emerging technology in the 21st century, which requires higher electrochemical performances, metal oxide composite electrodes in particular offer complementary properties of individual materials via the incorporation of both physical and chemical charge storage mechanism together in a single electrode. Numerous works reviewed herein have identified a wide variety of attractive metal oxide-based composite electrode material for symmetric and asymmetric electrochemical capacitors. The focus of the review is the detailed literature data and discussion regarding the electrochemical performance of various metal oxide composite electrodes fabricated from different configurations including binary and ternary composites. Additionally, projection of future development in hybrid capacitor coupling lithium metal oxides and carbonaceous materials are found to obtain significantly higher energy storage than currently available commercial electrochemical capacitors. This review describes the novel concept of lithium metal oxide electrode materials which are of value to researchers in developing high-energy and enhanced-cyclability electrochemical capacitors comparable to Li-ion batteries. In order to fully exploit the potential of metal oxide composite electrode materials, developing low cost, environment-friendly nanocomposite electrodes is certainly a research direction that should be extensively investigated in the future.

Ultrathin Bi₂Te₃ nanoplates have been grown on an oxidized silicon substrate by a modified hot wall epitaxy (HWE) method, in which a quartz plate with holes was employed. The microstructures and optical properties of Bi₂Te₃ nanoplates were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM) and micro-Raman spectroscopy. The results show that ultrathin Bi₂Te₃ nanoplates with the thickness of about six quintuple layers (QLs) are obtained, which is difficult for the traditional HWE technique. The Raman vibration mode from the nanoplates exhibits an obviously red shift with decreasing thickness. The thickness variation of one nanoplate was obtained by the Raman map derived from the vibration frequency of mode and is in good agreement with the AFM result, which indicates that Raman map is an effective method to characterize the thickness difference of ultrathin Bi₂Te₃ nanoplates.

Thermoelectric properties of a C₆₀ molecule coupled to three-dimensional metallic electrodes are studied using Green function formalism in linear response regime. A tight-binding model is used to investigate the effects of the dimerization and coupling geometry on the electrical conductance, thermopower and figure of merit. Increase of the contact points between the molecule and electrodes results in decrease of the number of the peaks of the electrical conductance because of the interference effects. In addition, oscillation of the thermopower is reduced in the multiple contacts. Results show that the increase of the contact points leads to the reduction of the figure of merit. Furthermore, the effect of the phase breaking scattering on the figure of merit is analyzed using the Büttiker probe method.

A wild type virion, bacteriophage T4, was used as an organic template for the controlled synthesis and organization of Pt nanoparticles and nanoshells on its capsid. A long incubation of T4 virions with the metalchloride solution is necessary to the specific binding of the external surface of T4 capsid with Pt^IV by means of interactions between Pt^IV and the chemical functionality found inherently on the surface of the proteinaceous viral capsid. After chemical reduction with dimethylaminoborane (DMAB), the highly dispersive Pt nanoparticles with a uniform size of 3–4 nm were synthesized and covered the whole viral capsid. The packing density of Pt nanoparticles was enhanced by increasing the incubation cycles of the virions in metal salt solution. Moreover, Pt@T4 shell/core structures could be achieved by increasing the amount of metal ions around virons. UV/vis spectroscopy was used to follow the course of the reaction, and the formation mechanism was discussed. Both the small Pt nanoparticles and Pt@T4 shell/core structures show high electrocatalytic activity in electrochemical measurement, and therefore are expected to have potential applications in electrocatalysis.

The zinc phosphate nanocrystals were synthesized by the ultrasonic–hydrothermal synergistic route. The ultrasonic–hydrothermal synergistic route can not only decrease the size of the zinc phosphate material, but also improve the crystallinity of the product. The transmission electron microscopy (TEM) image showed that the needle-like zinc phosphate product was 200–300 nm in length and 70–80 nm in width. The anti-corrosion tests revealed that the salt atmosphere-resistant time about 1056 h was longer than 768 h common zinc phosphate materials in the market. The mechanisms of ultrasonic–hydrothermal synergistic route and anti-corrosion were discussed.

Ibuprofen-loaded poly(methyl methacrylate) nanoparticles with mean diameters smaller than 20 nm were prepared by a novel method. This consists in carrying out a semicontinuous heterophase polymerization, in which a solution of drug-monomer is added on a micellar solution at an appropriate dosing rate. Scanning transmission electron microscopy (STEM) measurements showed number-average diameters in the range 16–19 nm with 1.14–1.15 in polydispersity, determined as the ratio of weight-average to number-average diameter. Drug contents in nanoparticles close to 24% were determined by UV-Vis spectrophotometry, confirming the results obtained from a procedure that combines latex filtration and quasielastic light scattering (QLS) measurements. Differential scanning calorimetry (CDSC) determinations suggest that at the ibuprofen contents attained in this study, crystals and dispersed molecules of the drug coexist inside the nanoparticles. Based on the relative simplicity of the process it is expected that its use will be adopted to prepare ultrafine nanoparticles composed of different hydrophobic polymers and water insoluble drugs.

Zinc oxide (ZnO) nanowire (NW) films were synthesized at low temperature (95°C) through amine-assisted solution process and used as photoanode for the fabrication of dye-sensitized solar cells (DSSCs). It was found that with the addition of polyethyleneimine (PEI) and ammonium hydroxide (NH₄OH) in growth solution, the NWs were smaller in diameter and longer in length by prolonging the growth time without refreshing the growth solution. A reasonable overall conversion efficiency of 1.25% was achieved with photoanode based on ZnO NWs containing PEI and NH₄OH. However, DSSC fabricated with ZnO NWs not containing PEI and NH₄OH showed low conversion efficiency of 0.58%. All the DSSCs exhibited almost similar values of open circuit voltage (V_OC) and fill factor (FF). Interestingly, DSSC based on ZnO NWs with PEI and NH₄OH obtained two times higher short circuit current density (J_SC) compared to ZnO NWs photoanode without PEI and NH₄OH. The increase in efficiency and J_SC with the length of NWs is attributed to the increase in internal surface area for sufficient dye loading and light harvesting.

Nanocomposites of n-type Zinc Oxide (ZnO) and p-type copper phthalocyanine (CuPc) were synthesized using solution route and the electrical properties of heterojunctions of ZnO and CuPc in the nanocomposite film was studied. For comparison, electrical properties of bilayer heterojunction devices using ZnO nanostructure drop cast film and thermally evaporated CuPc were also studied. Rectification ratio (RR) of about 28 and 5.5 was obtained at 4 V for devices with nanocomposite film and bilayer heterojunctions indicating improved formation of p–n junction characteristics for nanocomposite films. Values of ideality factor, barrier height at the p–n junction interface and series resistance were estimated using different methods like semilog plots, Cheung and Norde's methods. Ideality factor estimated from semilog plots and Cheung's methods were found to be higher than unity indicating deviation from ideal diode behavior. Barrier height estimated from different methods was about 0.7 eV. Series resistance measured using Cheung and Norde's methods were found to be about 92 KΩ and 21 KΩ, respectively. Bilayer heterojunction devices exhibited much higher series resistance, ideality factor and barrier height as estimated using all the above-mentioned methods as compared to the devices with nanocomposite film. The above results indicate intimate mixing and improved interface between ZnO and CuPc in the in situ synthesized nanocomposite film thereby offering improved p–n junction characteristics.

Palygorskite (denoted as Pal) was used as an economical carrier of hybrid photocatalyst TiO₂–Fe_xO_yvia an in situ depositing technique (marked as Pal–TiO₂–Fe_xO_y). The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), brunner-emmet-teller (BET) measurements, X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectra measurements. Results showed that TiO₂–Fe_xO_y composite particles with average size of about 10 nm were loaded onto the Pal fibers' surface. Fe_xO_y acted not only as magnetic source but also took part in the formation of TiO₂–Fe_xO_y heterojunction structure, which resulted in the obvious absorption in visible light region for the obtained Pal–TiO₂–Fe_xO_y composite photocatalyst. The obtained Pal–TiO₂–Fe_xO_y shows excellent photocatalytic activity toward photodegradation of Methyl orange (MO) under visible light irradiation and the degradation ratio reached 94% within 180 min. Moreover, Pal–TiO₂–Fe_xO_y could be readily recovered from the reaction solution by the magnet. Possible mechanism for the enhancement was also proposed.

Amine-promoted process has been applied in conventional preparation of quantum dots (QDs) for years. However, the required amine quantity was large in a typical promotion procedure. For example, large amine amount was demanded in the organic phase method for polarity and solubility adjustment. Meanwhile, it was also essential for aqueous synthesis to achieve competitive coordination ability. In order to impel the promotion more efficiently, 1,2-diaminoethane (DAE) was selected in this study to decrease amine dosage while accelerating reaction rate in aqueous synthesis. Based on its bidentate structure and high formation constant, the reaction time at high temperature was efficiently shortened. Additive species and quantities were varied for comparison under different conditions. At room temperature, QDs with limited DAE were successfully generated within 3 h while the hydrazine group failed even after 100 h' storage. The optical properties of the QDs obtained using DAE additive were better than the other groups. QDs with higher quantum yield (QY) were also obtained through adjusting total ion strength. More attractive result was found in QDs' structure. Since the reaction was efficiently shortened in our method, CdS impurity reported in conventional CdTe QDs synthesis was eliminated.

Poly(vinylidene fluoride) (PVDF) nanocomposites were prepared by melt-mixing. The dispersion of clay platelets and rheology of nanocomposites were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and rheometric mechanical spectrometer (RMS). The transformation of α to β and γ phase in PVDF was induced by the addition of nanoclay and subsequently the isothermal crystallization kinetics of neat PVDF and its nanocomposite have been investigated. The interaction between clay nanofillers and PVDF macromolecular chains induced the change of conformation from trans-gauche to all-trans crystal structure in PVDF segment. The isothermal crystallization of PVDF/clay nanocomposites was carried out by Differential Scanning Calorimetry (DSC) technique. The influence of clay platelets on nucleation crystallization rate and Avrami exponent were studied. PVDF/clay nanocomposite showed higher crystallization rate indicating that nanoclay has acted as an effective nucleation agent. This nucleation effect of nanoclay increased the Avrami exponent and decreased the degree of crystallinity.

Graphene platelets with a large scale have been synthesized by reduction of graphene oxide (GO) in aqueous solution of hydrazine hydrate under microwave irradiation (MWI). Microstructure of the graphene was characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM) together with the selected area electron diffraction (SAED). The electrochemical properties were evaluated by the analysis of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in 1 M Na₂SO₄ aqueous solution. The results show that the as-prepared materials consist of crumpled, few-layer (~ 3 nm) thick and electronically conductive graphitic sheets. The supercapacitors fabricated using this material possess a low equivalent series resistance (ESR) value ~ 1.6Ω and a high specific capacitance of 285 F ⋅ g^-1. In addition, the graphene reduced under a diverse duration of MWI displays a different interlayer spacing, extent of reduction, level of graphitization and specific capacitances. The duration of MWI and the treatment methods strongly affect the microstructure of graphene, and then dominate its electrochemical properties.

The Bi₂O₃ sphere-like precursors were first synthesized through a simple hydrothermal reaction in the mixture of sodium cholate (SC) and hydrogen peroxide. Thermal decomposition of these precursors would result in the formation of the uniform porous Bi₂O₃ nanospheres with diameters of ca. 80 nm in air at 500°C. The amount of added H₂O₂ and the reaction time were found to play important roles in the formation of Bi₂O₃ sphere-like precursors. The as-prepared porous Bi₂O₃ nanospheres exhibited a very excellent photocatalytic activity for the degradation of rhodamine B (RB) and methyl blue (MB) dyes under visible-light irradiation, which could be attributed to their narrow band gap and high surface area.

3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) nanostructures with different morphologies are prepared on glass substrates at different substrate temperature (T_s) in a molecular beam epitaxy (MBE) system. Scanning/transmission/scanning transmission electron microscopy (SEM/TEM/STEM), X-ray diffraction (XRD), selected area electron diffraction (SAED) and nanobeam diffraction (NBD) techniques are employed in the systematical characterizations of the nanostructures. It is found that the PTCDA nanosheets (NSs), nanowires and nanorods are facile to produce at T_s = 350°C, 330°C and 240°C, respectively; the continuous films are obtained at 180°C and 50°C. XRD studies indicate that only the α-phase polymorph is formed regardless of the T_s. SAED and NBD results show that the nanowire and NS are single crystalline. The optical properties of the prepared PTCDA nanostructures are also found to be influenced by T_s and are correlated with the crystal quality and size. PTCDA nanowires and NSs exhibit an obvious redshift and broadening in the adsorption spectra, and enhanced emission intensity. The improved optical properties facilitate potential applications of these nanostructures in organic optoelectronic devices.

Magnetic Resonance Imaging (MRI) is a noninvasive diagnostic method that provides information on morphological and physiological changes of the internal organs over time. Imaging and measurements can be repeated on the same subject, thereby reducing inter-individual variability effects and hence the number of subjects required. A potential MRI contrast agent consisting of microbubbles embedded with superparamagnetic iron oxide nanoparticles (SPION) in the shell (SPION MBs) was injected intravenously into rats to determine their biodistribution and pharmacokinetics using MR imaging. Agarose phantoms containing SPION MBs were scanned using 3 T MRI to construct a standard curve. Rats were injected with SPION MBs, free SPION or plain MBs and scanned dynamically at 3 T using a clinical MR scanner. The relaxation rate (R2*) was studied over time as a measure of the iron oxide concentrations to enable calculation of the pharmacokinetic parameters. The kinetics of SPION MBs in the liver was fitted to a one-compartment model. Furthermore, the biological fate of SPION MBs was examined via a histological survey of tissue samples using Perls' Prussian blue staining and immunohistochemistry (IHC). 1.2 h after injection of SPION MBs, T2* of the liver had decreased to its minimum. The elimination half-life of SPION MBs was 598.2 ± 97.3 h, while the half-life for SPION was 222.6 ± 26.4 h. Moreover, our study showed that SPION MBs were taken up by the macrophages in the lungs, spleen and liver. MBs labeled with SPION can be used for MR imaging. Moreover, MRI is a reliable and noninvasive tool that can be utilized in pharmacokinetic investigations of future contrast agents using SPION MBs and SPION in the rat.

Colloidal nanoparticles were obtained by green synthesis, embedded in the Opuntia ficus-indica plant extract. Optical measurements allowed us to detect two absorption bands centered in 230 nm and 298 nm. Agglomerates of Pb nanoparticles have size in the range 2–8 nm. The effective absorption cross section of spherical Pb nanoparticles was calculated by applying the Mie theory for colloidal systems and compared to optical absorption measurements of Pb nanoparticles. The Raman spectrum of the samples after the reduction of Pb, shows a band at low wavenumbers centered at 116 cm^-1. Similar bands have been assigned to small Pb and Ag clusters in other experimental results. Additionally, we used the density functional theory (DFT) as well as semi-empirical methods to assign this band to radial breathing modes of Pb metal nanoparticles.