Photocurrent enhancement of heat treated CdSe-sensitized titania nanotube photoelectrode

The self-organized titania nanotube arrays (NTAs) fabricated by anodisation has gained enormous interest due to its high spatial orientation, excellent charge transfer structure, and large internal surface area; all are crucial properties influencing the absorption and propagation of light. In this study, a composite material, CdSe nanoparticle/TiO₂ nanotube arrays (CdSe/TiO₂ NTAs) were assembled through the insertion of CdSe nanoparticles onto the anodized TiO₂ nanotube arrays via electrochemical deposition. The annealing temperature of CdSe/TiO₂ NTAs was varied from 200 to 350 °C and was found to play an important role in controlling the formation of CdSe nanoparticles on TiO₂ NTAs. Characterizations of the films were performed by using field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, high resolution transmission electron microscopes, X-ray diffractometry and UV–visible diffuse reflectance spectroscopy. The transient photocurrent was examined in a three-electrode system under halogen illumination by using the prepared film as the photoanode. It was found that the CdSe nanoparticles were susceptible to spread through electrochemical deposition and formed on the nanotubes by annealing in nitrogen atmosphere. The increment in annealing temperature has resulted in greater amount of CdSe loaded onto TiO₂ nanotube arrays. Therefore, a suitable annealing temperature can enhance the particle interaction, leading to considerable improvement in PEC performance. The sensitized CdSe/TiO₂ NTAs annealed at 250 °C displayed 84 folds improvement in photoconversion efficiency than that of bare TiO₂ NTAs counterparts.     

Synthesis of self-assembled nanorod vanadium oxide bundles by sonochemical treatment

Self-assembled nanorod of vanadium oxide bundles were synthesized by treating bulk V₂O₅ with high intensity sonochemical technique. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and temperature-programmed reduction (TPR) in H₂. Catalytic behaviour of the materials over anaerobic n-butane oxidation was studied through temperature-programmed reaction (TPRn). Catalytic evaluation of the sonochemical treated V₂O₅ products was also studied on microreactor. XRD patterns of all the vanadium samples were perfectly indexed to V₂O₅. The morphologies of the nanorod vanadium oxides as shown in SEM and TEM depended on the duration of the ultrasound irradiation. Prolonging the ultrasound irradiation duration resulted in materials with uniform, well defined shapes and surface structures and smaller size of nanorod vanadium oxide bundles. H₂-TPR profiles showed that larger amount of oxygen species were removed from the nanorod V₂O₅ compared to the bulk. Furthermore, the nanorod vanadium oxide bundles, which were produced after 90, 120 and 180 min of sonochemical treatment, showed an additional reduction peak at lower temperature (850 K), suggesting the presence of some highly active oxygen species. TPRn in n-butane/He over these materials showed that the nanorod V₂O₅ with highly active oxygen species showed markedly higher activity than the bulk material, which was further proven by catalytic oxidation of n-butane.     

Amorphous particle deposition and product quality under different conditions in a spray dryer

Deposition of amorphous particles, as a prevalent problem particularly in the spray drying of fruit and vegetable juices, is due to low-molecular weight sugars and is strongly dependent on the condition of the particles upon collision with the dryer wall. This paper investigates the condition of the amorphous particles impacting the wall at different drying conditions with the aim of elucidating the deposition mechanism and physical phenomena in the drying chamber. A model sucrose-maltodextrin solution was used to represent the low-molecular-weight sugar. Particle deposits were collected on sampling plates placed inside the dryer for analyses of moisture content, particle rigidity (using SEM) and size distribution. Moisture content was adopted as a general indicator of stickiness. Product particles collected at the bottom of the experimental dryer were found to have higher moisture than particle deposits on samplers inside the dryer. Moisture content profile in the dryer shows that apart from the atomizer region, where particles are relatively wet, particle deposits at other regions exhibit similar lower moisture content. At the highest temperature adopted in the experiments, particles became rubbery suggesting liquid-bridge formation as the dominant deposition mechanism. Further analysis on particles size distribution reveals a particle segregation mechanism whereby smaller particles follow preferentially to the central air stream while larger particles tend to re-circulate in the chamber, as predicted in past CFD simulation. The findings from this work will form the basis and provide validating data for further modeling of wall deposition of amorphous particles in spray drying using CFD.     

(Ba<Subscript>0.93</Subscript>Nd<Subscript>0.07</Subscript>)TiO<Subscript>3</Subscript> thin films prepared by sol–gel method as a potential dielectric resonator antenna application

In this paper, we report the application of Neodymium (Nd) doped barium titanate thin films (Ba_1-xNd_x) TiO₃ with x = 0 and 0.07 as dielectric resonator antenna. The films were prepared using the sol–gel method and dip-coating technique. Barium acetate, titanium (IV) isopropoxide and neodymium (III) acetate hydrate were used as precursors while glacial acetic acid and acetylacetone were used as solvents. Si wafers were used as a substrate with dipping times varying from 10, 30, and 50 s. The 0.07 films were >800 nm thick and crystallized after being annealed at 800°C for 30 min. The films were tested as dielectric resonator antenna. It was found that, on the actual antenna circuit, the resonant frequency decreased as the (Ba_0.93Nd_0.07) TiO₃ films thickness increased (from 0.8379, to 5.4525 μm). All samples resonate in the range of 8.68–8.83 GHz with quasi omni-directional radiation patterns.     

Slip effects on unsteady mixed convection of hybrid nanofluid flow near the stagnation point

The unsteady mixed convection of the Al2O3-Cu/H2O hybrid nanofluid flow near the stagnation point past a vertical plate is analyzed. The bvp4c technique is used to solve the resulting ordinary differential equations. The combined effects of the velocity and thermal slip are addressed. The effects of different relevant physical parameters are studied numerically. The results show that the heat transfer rate is reduced when the volume fraction of the nanoparticles increases, while the unsteadiness...     

Unsteady flow of a Maxwell hybrid nanofluid past a stretching/shrinking surface with thermal radiation effect

Applied Mathematics and Mechanics - The non-Newtonian fluid model reflects the behavior of the fluid flow in global manufacturing progress and increases product performance. Therefore, the present...     

Nonlinear optical characterization of phosphate glasses based on ZnO using the Z-scan technique

The nonlinear optical properties of a phosphate vitreous system [(ZnO)_x-(MgO)_30-x-(P₂ O₅)₇₀], where x=8, 10, 15, 18, and 20 mol% synthesized through the melt-quenching technique have been investigated by using the Z-scan technique. In the experiment, a continuous-wave laser with a wavelength of 405 nm was utilized to determine the sign and value of the nonlinear refractive (NLR) index and the absorption coefficient with closed and opened apertures of the Z-scan setup. The NLR index was found to increase with the ZnO concentration in the glass samples by an order of 10^-10 cm²·W^-1. The real and imaginary parts of the third-order nonlinear susceptibility were calculated by referring to the NLR index (n₂) and absorption coefficient (β) of the samples. The value of the third-order nonlinear susceptibility was presented by nonlinear refractive or absorptive behavior of phosphate glasses for proper utilization in nonlinear optical devices. Based on the measurement, the positive sign of the NLR index shows a self-focusing phenomenon. The figures of merit for each sample were calculated to judge the potential of phosphate glasses for application in optical switching.     

ESR spectra and thermal diffusivity of Zn–Al layered double hydroxide

Zn–Al–NO₃–LDH was synthesized using the co-precipitation method at pH 7±0.1 and ratio Zn/Al=4. The heat treatment of LDH was studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) to investigate the stability of the LDH structure. The in situ electron spin resonance (ESR) spectra of fresh LDH from room temperature up to 190 °C were obtained, which are due to the presence of nitrate radicals in LDH interlayer. ESR spectra of sintered LDH below 200 °C (ex situ ESR spectra) were investigated, which are also due to the nitrate radicals. However, at 200 °C and above, spectra were due to the oxygen vacancies of ZnO, which was formed during the thermal treatment of LDH. Thermal diffusivity of LDH as a function of in situ temperatures results in a nonlinear relation, which is due to the changing water content of LDH when temperature increases. However, thermal diffusivity of LDH as a function of sintered temperatures showed a linear relation and the slope of these data demonstrated the dependency between thermal diffusivity and water content of LDH below 200 °C. For temperature above 180 °C, the thermal diffusivity behavior was mainly due to the ZnO phase in LDH.     

Experimental study of the effect of slotted blades on the Savonius wind turbine performance

This study investigates the effect of Reynolds number on the performance of Savonius wind turbine with slotted blades. The turbine performance investigation was based on the torque coefficient( Ct), power coefficient( Cp), and tip speed ratio( TSR). The experiment used two number of blade configuration, blade overlap ratio of 10%, 12.5% and 20%, slotted position of 15%, 20%, 25% and 35%, and also slotted gap width of 3 mm, 5 mm, 7 mm, and 9 mm. The wind speed carried out in this experiment are 5.94 m/s, 6.46 m/s, 6.99 m/s, and 7.27 m/s, which are generated from the fan blowers as a wind source. The Savonius turbine with 10% overlap ratio shows the best performance. The highest Cp obtained is 0.138 by the variation of a 3 mm gap with Re of 1.44 × 10~4 and 0.526 TSR.