Supercapacitors have been known for over fifty years and are considered as one of the potential energy storage systems. Research into supercapacitors is presently based primarily on their mode of energy storage, namely: (i) the redox electrochemical capacitors and (ii) the electrochemical double layer capacitor. The commonly investigated classes of materials are transition metal oxides (notably, ruthenium oxide) and conducting polymers. Recently, many chemically deposited metal oxide thin film electrodes including ruthenium oxide, iridium oxide, manganese oxide, cobalt oxide, nickel oxide, tin oxide, iron oxide, pervoskites, ferrites etc. have been tested in supercapacitors This review presents supercapacitor performance data of metal oxide thin film electrodes. The supercapacitors exhibited the specific capacitance ( ) values between 50 and 1100 F g , which are quite comparable with bulk electrode values; therefore, it is likely that metal oxide films will continue to play a major role in supercapacitor technology. ► Supercapacitor performance of metal oxide thin film. ► Supercapacitors exhibited the specific capacitance between 50 to 1100 F g . ► Metal oxide films play a major role in supercapacitor technology.
Liquid crystals constitute a fascinating class of soft condensed matter characterized by the counterintuitive combination of fluidity and long-range order. Today they are best known for their exceptionally successful application in flat panel displays, but they actually exhibit a plethora of unique and attractive properties that offer tremendous potential for fundamental science as well as innovative applications well beyond the realm of displays. Today this full breadth of the liquid crystalline state of matter is becoming increasingly recognized and numerous new and exciting lines of research are being opened up. We review this exciting development, focusing primarily on the physics aspects of the new research thrusts, in which liquid crystals – thermotropic as well as lyotropic – often meet other types of soft matter, such as polymers and colloidal nano- or microparticle dispersions. Because the field is of large interest also for researchers without a liquid crystal background we begin with a concise introduction to the liquid crystalline state of matter and the key concepts of the research field. We then discuss a selection of promising new directions, starting with liquid crystals for organic electronics, followed by nanotemplating and nanoparticle organization using liquid crystals, liquid crystal colloids (where the liquid crystal can constitute either the continuous phase or the disperse phase, as droplets or shells) and their potential in e.g. photonics and metamaterials, liquid crystal-functionalized polymer fibers, liquid crystal elastomer actuators, ending with a brief overview of activities focusing on liquid crystals in biology, food science and pharmacology.
Novel Al-doped ZnO (AZO) photocatalysts with different Al concentrations (0.5–6.0 mol%) were prepared through a facile combustion method and followed by calcination at 500 °C for 3 h. The obtained nanopowders were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM) combined with EDX, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy and photoluminescence spectroscopy. The XRD patterns of AZO nanopowders were assigned to wurtzite structure of ZnO with the smallest crystallite size about 11 nm consistent with the results from TEM. The doping of Al in ZnO crystal structure successfully suppressed the growth of ZnO nanoparticles confirmed by XRD patterns. The absorption spectra analysis showed that the optical band gap energy ( ) for the AZO nanopowders were in the range of 3.12–3.21 eV and decreased with increasing of Al dopant. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange under visible light ( ≥ 420 nm) and sunlight irradiation. The results showed that the AZO photocatalyst doped with 4.0 mol% Al exhibited five times enhanced photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity could be attributed to extended visible light absorption, inhibition of the electron–hole pair's recombination and enhanced adsorptivity of MO dye molecule on the surface of AZO nanopowders. ► Successful synthesis of ZnO and Al doped ZnO (AZO) photocatalyst with high porosity by combustion method. ► Extended light absorption and efficient charge separation due to aluminum doping. ► Enhanced adsorptivity of MO dye on the catalyst surface. ► Photocatalytic activity enhancement of AZO photocatalyst over pure ZnO.
Due to the highly inhomogeneous distributions of refractive indexes, light propagation in complex media such as biological tissue experiences multiple light scattering events. The suppression and control of multiple light scattering events are investigated because they offer the possibility of optical focusing and imaging through biological tissues, and they may open new avenues for diagnosis and treatment of several human diseases. In order to provide insight into how new optical techniques can address the issues of multiple light scattering in biomedical applications, the recent progress in optical wavefront-shaping techniques is summarized.
Thin films of tin sulphide (SnS) have been grown by sulphurization of sputtered tin precursor layers in a closed chamber. The effect of sulphurization temperature (T ) that varied in the range of 150–450 °C for a fixed sulphurization time of 120 min on SnS film was studied through various characterization techniques. X-ray photoelectron spectroscopy analysis demonstrated the transformation of metallic tin layers into SnS single phase for T between 300 °C and 350 °C. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. Raman analysis showed modes at 95 cm , 189 cm and 218 cm are related to the A mode of SnS. AFM images revealed a granular change in the grain growth with the increase of T . The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.2 eV to 1.6 eV with T . The Hall effect measurements showed that all the films were p-type conducting nature and the layers grown at 350 °C showed a low electrical resistivity of 64 Ω-cm, a net carrier concentration of 2 × 10 cm and mobility of 41 cm V s . With the use of sprayed Zn Mg O as a buffer layer and the sputtered ZnO:Al as window layer, the SnS based thin film solar cell was developed that showed a conversion efficiency of 2.02%.
Presently nanocrystalline materials have opened a new chapter in the field of electronic applications, since material properties could be changed by changing the crystallite size and/or thickness of the film. The synthesis of nanocrystalline metal chalcogenide and metal oxide thin films by chemical bath deposition (CBD) method is currently attracting considerable attention as it is relatively inexpensive, simple and convenient for large area deposition. Using CBD and modified CBD (which is also known as successive ionic layer adsorption and reaction, SILAR) methods, a large number of thin films have been deposited. This review is on the status of synthesizing thin films of metal chalcogenide and metal oxides by CBD and SILAR. Properties and applications of the thin films are also summarized.
Chemical mechanical polishing (CMP) of sapphire, GaN, and SiC substrates, which are categorized as hard-to-process materials, is demonstrated with a colloidal silica slurry under acidic and alkaline slurry pH conditions. Atomic level surface flatness was achieved by CMP and was confirmed to be equivalent to an almost ideally minimized surface roughness. By comparing the Preston coefficients under different slurry conditions, differences in the CMP properties among the three substrate materials and difficulties in the CMP of the GaN and SiC substrates are presented. The difference in CMP properties between the (0001) and (000-1) planes of GaN and SiC due to their non-revers crystallographical symmetry is also presented. Oxidation processes that occur during CMP of GaN and SiC are also discussed. By comparing the removal rate among GaN, SiC, and their oxides, it was found that the rate-limiting step in the total CMP process for GaN and SiC was surface oxidation reaction of GaN and SiC.
In this study, we demonstrated that graphene could selectively absorb/desorb NO molecules at room temperature. Chemical doping with NO molecules changed the conductivity of the graphene layers, which was quantified by monitoring the current–voltage characteristics at various NO gas concentrations. The adsorption rate was found to be more rapid than the desorption rate, which can be attributed to the reaction occurred on the surface of the graphene layer. The sensitivity was 9% when an ambient of 100 ppm NO was used. Graphene-based gas sensors showed fast response, good reversibility, selectivity and high sensitivity. Optimization of the sensor design and integration with UV-LEDs and Silicon microelectronics will open the door for the development of nano-sized gas sensors that are extremely sensitive.
This study reports the simple synthesis of MFe2O4 (where M = Cu, Ni, and Zn) nanoparticles by a modified sol-gel method using high purity metal nitrates and aloe vera plant extracted solution. Using of aloe vera extract simplifies the process and provides an alternative process for a simple and economical synthesis of nanocrystalline ferrites. The obtained precursors were characterized by TG/DTA to determine the thermal decomposition and subsequently were cc at different temperatures in the range of 600-900 degrees C for 2 h to obtain the ferrite nanoparticles. The calcined samples were characterized by XRD, FT-IR, SEM, and TEM. All the prepared samples are polycrystalline and have spinel structure with crystallite sizes of 15-70 nm. The crystallite size increases with increasing the calcination temperature. Magnetic properties of the prepared ferrite samples were measured using Vibrating sample magnetometer (VSM). The room temperature magnetic behavior of as-prepared ferrite powders can be explained as the results of the three important factors: impurity phase of a-Fe2O3, cationic distribution in spinel structure, and the surface spin structure of nanoparticles. (C) 2010 Elsevier B.V. All rights reserved.
To investigate the effect of nanofluids on convective heat transfer, an experimental study was performed through a circular straight tube with a constant heat flux condition in the laminar and turbulent flow regime. Stable nanofluids, which were water-based suspensions of alumina and amorphous carbonic nanoparticles, were prepared by two- and one-step methods. The effects of thermal conductivity and supernatant nanoparticles of the nanofluids on convective heat transfer were investigated under different flow regimes. In alumina nanofluids containing 3 vol% of suspended particles, the increment of thermal conductivity and convective heat transfer coefficient was 8% and 20%, respectively. For amorphous carbonic nanofluids, the thermal conductivity was similar to that of water, and the convective heat transfer coefficient increased by only 8% in laminar flow. In a comparison of thermal conductivity and convection, the enhancement of the convective heat transfer was much higher than that of the thermal conductivity of nanofluids. The movements of nanoparticles enhanced the convective heat transfer at the entrance region.
Oxygen electrocatalysis that we first defined is considered as the most important phenomenon in almost all electrochemical industries because it is the most sluggish reaction that governs the overall reaction rate in electrochemical cells. In this review, we cover two main areas of oxygen–water electrocatalysis, oxygen reduction to water and oxygen evolution from water. In particular, it aims to provide the readers with an understanding of the critical scientific challenges facing the development of oxygen electrocatalysts, various unique attributes of recent novel catalysts, the latest developments in electrode construction and the outlook for future generation of oxygen electrocatalysts. This review will be of value to both electrochemists and other applied scientists interested in this field of electrocatalysis. Oxygen–water cycle showing an electrochemical redox reaction in the presence of molecular oxygen in electrochemical energy technologies for the next generation. ► The amount of noble metal in O electrocatalysts greatly reduced. ► An alternative oxygen reduction catalyst of nitrogen–carbon composite. ► New reports on Durable metal oxide support and self-healing catalysts. ► Theoretical approach needed for designing of creative catalyst.
Bamboo-based activated carbon is synthesized by a simple heat treatment with or without KOH activation, and characterized for possible energy storage applications. The KOH activation introduces a very large surface area of more than 3000 m g to the bamboo-based activated carbon, resulting in high specific capacitance, energy density, and power density in an aqueous electrolyte. The specific capacitance retention is more than 91% of the original capacitance after 3000 cycles, proving excellent cyclic stability for supercapacitor applications. Our results indicate that the natural resource of common bamboo could be an essential raw material for the energy storage devices.
As new carbon-based materials, graphene quantum dots (GQDs) many advantages due to the additional unique properties that arise from their nanoscale small size. GQDs are expected to be suitable for various applications. For use of GQDs in various fields, mass production is critically required. To date, many methods for preparing GQDs with good properties and high yield have been introduced. The main synthesis strategies are known as bottom-up and top-down methods. Synthesis of GQDs from small organic molecules, known as the bottom-up approach, is appropriate for controlling the size of GQDs but requires multistep organic reactions and purification at each step. However, the top-down approach of breaking the carbon-carbon bonds of a large carbon source is easy and simple, and therefore suitable for mass production. Here, we briefly introduce the solution-process synthesis of GQDs using a top-down method and recent energy-related applications such as capacitors, lithium ion batteries, and solar cells.
In order to prevent the charge recombination at the interface between the transparent-conducting oxide (TCO) substrate and electrolyte, a TiO compact layer was deposited on the substrate by hydrolysis of TiCl aqueous solution. Optimum thickness of the compact layer was found to be ∼25 nm, which showed ∼24% increase in the power-conversion efficiency compared with the bare cell. Impedance spectra indicated that the interfacial charge-transfer resistance of TCO/electrolyte interface was increased by more than a factor of three with the TiO compact layer at 0.4 V. Moreover, the electron-carrier lifetime of the 25 nm-deposited cell was improved by a factor of five compared with the bare cell. ► We investigate the effect of TiO compact-layer thickness on the performance of DSSC. ► The TiO compact layer is formed by the simple hydrolysis of TiCl . ► The 25 nm-deposited cell exhibits ∼24% higher power-conversion efficiency. ► The electron-carrier lifetime is improved by a factor of five.
Three kinds of nanofluids are prepared by dispersing Al O and AlN nanoparticles-in-transformer oil. The thermal conductivity of the nanoparticle–oil mixtures increases with particle volume fraction and thermal conductivity of the solid particle itself. The AlN nanoparticles at a volume fraction of 0.5% can increase the thermal conductivity of the transformer oil by 8% and the overall heat transfer coefficient by 20%. From the natural convection test using a prototype transformer, the cooling effect of Al O /AlN-oil nanofluids on the heating element and oil itself is confirmed. However, the excess quantity of surfactant has a harmful effect on viscosity, thermal property, chemical stability, and thus it is strongly recommended to control the addition of the surfactant with great care.
Ultrahigh-aspect-ratio V O nanowires were successfully prepared using [VO(O ) (OH )] as the starting material by a template-free hydrothermal route without the addition of organic surfactant or inorganic ions. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The results revealed that the peroxovanadium (V) complexes can be easily transformed to V O nanowires by this hydrothermal route. The uniform nanowires were with width about 50 nm and length about dozens of micron. The BET analysis showed the V O nanowires had a high specific surface area of 25.6 m g . The synthesized V O nanowires performed a high capacitance of 351 F g when used as supercapacitor electrode in 1 mol L LiNO .
Yb /Tm and Yb /Er co-doped NaLuF crystals were synthesized by a facile hydrothermal method. The optical temperature sensing properties of Tm based upon its two thermally coupled energy levels F and H were systematically investigated by means of fluorescence intensity ratio ( ) technique. The 980 nm laser-induced thermal effect on Tm doped NaLuF crystals was studied by using Er doped sample as thermal probe. The temperature sensitivity of Tm in NaLuF : Yb /Tm crystals shows a nonlinear dependence on temperature, and the maximum value is about 0.00045 K at 600 K. The accuracy and reliability of the optical thermometry based on Tm in NaLuF : Yb /Tm crystals has been checked by using Yb /Er co-doped sample as temperature sensing unit. The results demonstrate that NaLuF : Yb /Tm crystals have good sensing stability and may have potential application for the optical thermometry. The optical temperature sensing properties of Tm were systematically investigated, and NaLuF : Yb /Er crystals were adopted as a thermal probe to monitor the laser-induced thermal effect and to verify the accuracy of the temperature detection for Tm in NaLuF : Yb /Tm crystals.