Thermal Degradation of Vegetable Oils.

Vegetable oils provide lipids and nutrition and provide foods with a desirable flavor, color, and crispy texture when used to prepare fried foods. However, the oil quality is degraded at elevated temperatures, and thus must be examined frequently because of the damage to human health. In this study, sunflower, soybean, olive, and canola oils were examined, and their properties were measured periodically at different elevated temperatures. The unsaturated triglyceride in oils reacted with the environmental oxygen or water vapor significantly changes in optical absorbance, viscosity, electrical impedance, and acid value. We used defect kinetics to analyze the evolution of these oil properties at elevated temperatures. The optical absorbance, viscosity, and electrical impedance follow the second-order, first-order, and zeroth-order kinetics, respectively. The rate constants of the above kinetics satisfy the Arrhenius equation. Olive oil has the lowest rate of color center and dynamic viscosity among the four oils, with the smallest pre-exponential factor and the largest activation energy, respectively. The rate constants of acid reaction also satisfy the Arrhenius equation. The activation energies of the polar compound and acid reaction are almost the same, respectively, implying that the rate constant is controlled by a pre-exponential factor if four oils are compared. Olive oil has the largest rate constant of acid reaction among the four oils, with the lowest pre-exponential factor.

Formation Mechanism and Bandgap Reduction of GaN-ZnO Solid-Solution Thin Films Fabricated by Nanolamination of Atomic Layer Deposition.

Nanolamination of GaN and ZnO layers by atomic layer deposition (ALD) is employed to fabricate GaN-ZnO homogenous solid-solution thin films because it offers more precise control of the stoichiometry. By varying the ALD cycle ratios of GaN:ZnO from 5:10 to 10:5, the (GaN)1- x (ZnO)x films with 0.39 ≦ x ≦ 0.79 are obtained. The formation of solid solution is explained based on the atomic stacking and preferred orientation of the layers of GaN and ZnO. However, the growth rates of GaN and ZnO during the lamination process are different from those of pure GaN and ZnO films. It is found that GaN grows faster on ZnO, whereas ZnO grows slower on GaN. The density functional theory (DFT) calculations are performed using a superlattice model for GaN and ZnO laminated layers fabricated by ALD to understand the difference of density of states (DOS) and evaluate the bandgaps for various atomic configurations in the solid-solution films. The band positions are experimentally defined by ultraviolet photoelectron spectroscopy. Significant bandgap reduction of the solid solutions is observed, which can be explained by the DOS from the DFT calculations. Visible-light-driven photocatalytic hydrogen evolution is conducted to confirm the applicability of the solid-solution films.

Forced flow atomic layer deposition of TiO2 on vertically aligned Si wafer and polysulfone fiber: Design and efficacy of conduit plates and soak function.

The effectiveness of three different designs of conduit plates was verified for even distribution of precursors in a voluminous forced-flow atomic layer deposition (ALD) chamber designed to hold macroscopic elongated substrates vertically. Furthermore, a new "soak function" was introduced in the controlling software of the ALD instrument. This function enabled increase in residence time of the precursor in the chamber without escalating the dosage. The flow of precursors guided by the conduit plates with and without application of the soak function was simulated using computational fluid dynamics. A conformal coating of TiO2 with good uniformity on Si and porous polysulfone fibers was achieved to evidence the design and efficacy of conduit plates and soak function.

Photocatalysis and Hydrogen Evolution of Al- and Zn-Doped TiO2 Nanotubes Fabricated by Atomic Layer Deposition.

Highly homogeneous Al- and Zn-doped TiO2 nanotubes were fabricated by atomic layer deposition (ALD) via nanolaminated stacks of binary layers of TiO2/Al2O3 and TiO2/ZnO, respectively. The bilayers were alternately deposited on the polycarbonate (PC) membrane template by ALD with various cyclic sequences. The nanotubes in a length of 20 µm and a diameter of 220 nm were obtained after removal of the PC membrane by annealing at 450 °C. The effects of doping composition on the photocatalytic and photoelectrochemical (PEC) activities were investigated. Increasing the Al doping reduced the photocatalytic activity of TiO2 due to formation of charge recombination sites and reduction of hydroxide radicals. In contrast, there was an optimal range of Zn doping to get enhanced photocatalytic activity and higher PEC efficiency. With a doping ratio of 0.01, the hydrogen production rate from water splitting was 6 times higher than that of commercial P25 TiO2. The energy-band diagram of Zn-doped TiO2 determined by ultraviolet photoelectron spectroscopy revealed shift up of the Fermi level to provide more electrons to the conduction band. The photoinduced trapped electrons and holes were detected in Zn-doped TiO2 by in situ electron paramagnetic resonance spectroscopy, which revealed that Ti3+ sites on the surface and surface oxygen vacancies played a key role in promoting the photocatalytic process.

Fabrication of TiO2 on porous g-C3N4 by ALD for improved solar-driven hydrogen evolution.

Porous graphitic carbon nitride (P-g-C3N4) thin sheets were fabricated by a one-step calcination of a mixture of urea, melamine, and ammonia chloride at 550 °C. P-g-C3N4 showed 48% higher photocatalytic H2 production from methanol aqueous solution than conventional urea-derived graphitic carbon nitride (g-C3N4) because the existence of numerous pores reduces the recombination rate of charge carriers. In order to further enhance the photocatalytic activity, TiO2 was uniformly deposited on P-g-C3N4 by 60-300 cycles of atomic layer deposition (ALD) to form the TiO2@P-g-C3N4 composite. They exhibited much higher photocatalytic hydrogen production rates than both TiO2 and P-g-C3N4. Among all composites, the sample deposited with 180 ALD cycles of TiO2 showed the highest H2 production because of optimal diffusion length for electrons and holes. It also performed better than the sample of g-C3N4 deposited with 180 cycles of TiO2.

Uniform coating of Ta2O5 on vertically aligned substrate: A prelude to forced flow atomic layer deposition.

Uniform tantalum oxide thin films, with a growth rate of 0.6 Å/cycle, were fabricated on vertically aligned, 10 cm-long, silicon substrates using an innovative atomic layer deposition (ALD) design. The ALD system, with a reaction chamber depth of 13.3 cm and 18 vertical enclosed channels (inner diameter 1.3 cm), was coupled with a shower-head type precursor conduit plate bearing 6 radial channels. This design enabled deposition on 6 silicon substrates at a time. The degrees of non-uniformity of deposits along the length of the silicon wafer and across different positions in the ALD chamber were found to be 1.77%-6.21% and 3.27%-5.45%, respectively. A further advantage of the design is that the conduit plate may be modified and the number of channels increased to process 18 substrates simultaneously, thus moving toward efficient and expedited ALD systems.

Direct formation of anatase TiO2 nanoparticles on carbon nanotubes by atomic layer deposition and their photocatalytic properties.

TiO2 with different morphology was deposited on acid-treated multi-walled carbon nanotubes (CNTs) by atomic layer deposition at 100 °C-300 °C to form a TiO2@CNT structure. The TiO2 fabricated at 100 °C was an amorphous film, but became crystalline anatase nanoparticles when fabricated at 200 °C and 300 °C. The saturation growth rates of TiO2 nanoparticles at 300 °C were about 1.5 and 0.4 Å/cycle for substrate-enhanced growth and linear growth processes, respectively. It was found that the rate constants for methylene blue degradation by the TiO2@CNT structure formed at 300 °C were more suitable to fit with second-order reaction. The size of 9 nm exhibited the best degradation efficiency, because of the high specific area and appropriate diffusion length for the electrons and holes.

Distribution pattern and allocation of defects in hydrogenated ZnO thin films.

A polycrystalline ZnO thin film prepared by atomic layer deposition was annealed in hydrogen at 10 bar and 350-450 °C. Hydrogenation induced simultaneous formation of oxygen and zinc vacancies whose concentrations were closely related to the temperature of treatment. Spatial distributions of these defects were analyzed by photoluminescence confocal mapping which revealed that their localized appearances are linked to each other. It was also demonstrated that nanomechanical mapping of elastic modulus distribution could be used to assess the allocation of accumulated defects on the topmost surface of ZnO with a depth resolution of only several atomic layers. The higher the temperature of hydrogenation, the higher the concentration, and more uniform the distribution of surface defects. In addition, the correlation between the surface morphology and the accumulated defects was established.

Enabling higher photoelectrochemical efficiency of TiO2via controlled formation of a disordered shell: an alternative to the hydrogenation process.

A simple one-step and low-temperature process was developed to form an amorphous overlayer on the crystalline TiO2 film by atomic layer deposition. This composite structure is beneficial for improved photoelectrochemical efficiency since the as-deposited amorphous layer showed unique properties such as local disorder and presence of oxygen vacancies.

Extremely high efficient nanoreactor with Au@ZnO catalyst for photocatalysis.

We fabricated a photocatalytic Au@ZnO@PC (polycarbonate) nanoreactor composed of monolayered Au nanoparticles chemisorbed on conformal ZnO nanochannel arrays within the PC membrane. A commercial PC membrane was used as the template for deposition of a ZnO shell into the pores by atomic layer deposition (ALD). Thioctic acid (TA) with sufficient steric stabilization was used as a molecular linker for functionalization of Au nanoparticles in a diameter of 10 nm. High coverage of Au nanoparticles anchored on the inner wall of ZnO nanochannels greatly improved the photocatalytic activity for degradation of Rhodamine B. The membrane nanoreactor achieved 63% degradation of Rhodamine B within only 26.88 ms of effective reaction time owing to its superior mass transfer efficiency based on Damköhler number analysis. Mass transfer limitation can be eliminated in the present study due to extremely large surface-to-volume ratio of the membrane nanoreactor.

HNO3-assisted polyol synthesis of ultralarge single-crystalline Ag microplates and their far propagation length of surface plasmon polariton.

We developed a HNO3-assisted polyol reduction method to synthesize ultralarge single-crystalline Ag microplates routinely. The edge length of the synthesized Ag microplates reaches 50 µm, and their top facets are (111). The mechanism for dramatically enlarging single-crystalline Ag structure stems from a series of competitive anisotropic growths, primarily governed by carefully tuning the adsorption of Ag(0) by ethylene glycol and the desorption of Ag(0) by a cyanide ion on Ag(100). Finally, we measured the propagation length of surface plasmon polaritons along the air/Ag interface under 534 nm laser excitation. Our single-crystalline Ag microplate exhibited a propagation length (11.22 µm) considerably greater than that of the conventional E-gun deposited Ag thin film (5.27 µm).

Toward highly efficient photocatalysis: a flow-through Pt@TiO2@AAO membrane nanoreactor prepared by atomic layer deposition.

A Pt@TiO2@AAO membrane nanoreactor was fabricated by atomic layer deposition. The photodegradation test of methylene blue demonstrated that the nanoreactor shows efficient photocatalysis performance. It exhibited ~28% photodegradation of methylene blue after ten flow-through cycles, corresponding to about 2.7 × 10(-2) s of contact time of methylene blue with Pt@TiO2 nanotubes.

Preparation and characterization of molecularly homogeneous silica-titania film by sol-gel process with different synthetic strategies.

Three silica-titania thin films with various degrees of molecular homogeneity were synthesized by the sol-gel process with the same precursor formula but different reaction paths. The dried films prepared by a single spin-coating process have a thickness of 500-700 nm and displayed no cracks or pin holes. The transmittances and refractive indices of the samples are >97.8% in the range of 350-1800 nm and 1.62-1.65 at 500 nm, respectively. The in-plane and out-of-plane chemical homogeneities of the films were analyzed by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. For the film with the highest degree of homogeneity, the deviations of O, Si, and Ti atomic contents in both in-plane and out-of-plane directions are less than 1.5%, indicating that the film is highly molecularly homogeneous. It also possesses the highest transparency and the lowest refractive index among the three samples.

Deposition of platinum on oxygen plasma treated carbon nanotubes by atomic layer deposition.

Platinum nanoparticles were deposited on oxygen plasma treated carbon nanotubes (CNTs) by atomic layer deposition (ALD). The treatment time with oxygen plasma generated by microwaves under a power of 600 W varied from 5 to 20 s. The number of ALD cycles was controlled at 5-125. X-ray photoelectron spectroscopic analysis indicated that oxygen plasma can graft oxygen-containing functional groups to the CNT surface to act as nucleation sites for growth of Pt nanoparticles. Formation of very uniform and well distributed Pt nanoparticles of a size of 1.60-4.80 nm was achieved. The growth rate of Pt nanoparticles could be controlled by the number of ALD cycles and oxygen plasma treatment time. This offers a dry process to deposit well-dispersed metallic nanoparticles on selected support materials.

Fabrication of TiO2 nanotubes by atomic layer deposition and their photocatalytic and photoelectrochemical applications.

The formation of TiO(2) nanotubes was conducted by atomic layer deposition (ALD) with tris-(8-hydroxyquinoline) gallium (GaQ(3)) nanowires as a template at different substrate temperatures, 50, 100, and 200 °C. TiO(2) nanotubes were formed only at 50 and 100 °C. Although a higher growth rate at 50 °C was observed, nanotubes with better uniformity, conformality, and less residual chloride were obtained at 100 °C because of a different formation mechanism. A photocatalysis test of TiO(2) nanotubes prepared by different cycle numbers at 100 °C was conducted. It showed that TiO(2) nanotubes prepared by 400 cycles of ALD and treated at 700 °C for 1 h to form anatase phase had the best photocatalytic performance. Compared with P-25, the nanotubes showed higher photocatalytic degradation of rhodamine B and water splitting efficiency.

Photocatalytic degradation of rhodamine B by anchored TiO2 nanowires.

Rutile TiO2 nanowires anchored on silica were fabricated by annealing TiO2 nanoparticles dispersed on silicon or quartz substrate by means of a polystyrene nanosphere monolayer template at 1000 degrees C for 1 h without any catalyst. The diameter and length of the nanowires were 30-80 nm and 1-3 microm, respectively. The growth direction of the nanowires is [112]. The photocatalytic activities of TiO2 nanoparticles and anchored nanowires were evaluated. TiO2 nanowires had higher photocatalytic activity for rhodamine B than TiO2 nanoparticles.

The formation of TiO(2) nanowires directly from nanoparticles.

TiO(2) nanowires were fabricated by annealing TiO(2) nanoparticles on silicon substrate at 1000 degrees C in air. When a polystyrene nanosphere monolayer was used as a template to separate the TiO(2) nanoparticles, they could more easily react with the silicon substrate to form Ti(5)Si(3). The TiO(2) nanowires were formed upon further oxidation of Ti(5)Si(3). The diameters and lengths of TiO(2) nanowires were 30-80 nm and 1-3 microm, respectively. The nanowires had a rutile structure with the growth direction [112]. It is believed that the formation of TiO(2) nanowires involved a precipitation process in the mixture of SiO(2) and TiO(2). The nanowires show different photoluminescence behavior from that of the powder.

Comparison of organic and inorganic germanium compounds in cellular radiosensitivity and preparation of germanium nanoparticles as a radiosensitizer.

PURPOSE: The aim of this work is to compare the radiosensitizing effect between organic and inorganic germanium compounds and to investigate whether nanometer-sized germanium particles can act as radiosensitizers. MATERIALS AND METHODS: Bis (2-carboxyethylgermanium) sesquioxide (Ge-132), germanium oxide (GeO(2)) and germanium nanoparticles were used in this study. Cell viability was determined by clonogenic survival assay. Cellular DNA damage was evaluated by alkaline comet assay, confocal microscopy and the cellular level of phospho-histone H2AX (gamma-H2AX). RESULTS: Nanometer-sized germanium particles were fabricated. They have a similar radiosensitizing effect as that of GeO(2). Conversely, Ge-132 did not enhance the radiosensitivity of cells. Comet assay was employed to evaluate the level of DNA damage and confirmed that inorganic germanium compounds enhanced cellular radiosensitivity. Notably, the comet assay indicated that the nanoparticle itself caused a higher level of DNA damage. The possibility that germanium nanoparticles per se caused DNA damage was ruled out when the cellular level of gamma-H2AX was examined. CONCLUSIONS: We demonstrated that inorganic but not organic germanium compounds exerted radiosensitizing effect in cells. Nanometer-sized germanium particles were fabricated and were able to enhance the radiosensitivity of cells. Confounding effect may occur when comet assay is used to estimate the level of DNA damage in the presence of germanium nanoparticles.