Thomas C.-K. Yang

Photocatalytic inactivation of Escherichia coli and Lactobacillus helveticus by ZnO and TiO2 activated with ultraviolet light

Abstract The photocatalytic inactivation of Gram negative Escherichia coli and Gram positive Lactobacillus helveticus by both TiO2 and ZnO with 365-nm ultraviolet (UV) light was studied in a batch reactor. Almost all the initial E. coli cell (108 CFU/ml) were inactivated in 40 min in the presence of 2 g/l ZnO. Photocatalytic inactivation of bacteria was found to follow first order kinetics with the highest rate constants being 4.5×10−1 and 2.2×10−1/min for E. coli and L. Helveticus, respectively, treated with 2 g/l ZnO. A similar bactericidal tendency was found in the UV–TiO2 system, where the rate constants were 3.7×10−1 and 1.8×10−1/min for E. coli and L. Helveticus, respectively. The use of air as the purging gas, providing a stronger oxidising environment to both strains, gives a higher catalytic effect on bacteria inactivation than that of nitrogen.

Expert system of a crude oil distillation unit for process optimization using neural networks

Abstract An expert system of crude oil distillation unit (CDU) was developed to carry out the process optimization on maximizing oil production rate under the required oil product qualities. The expert system was established using the expertise of a practical CDU operating system provided by a group of experienced engineers. The input operating variables of the CDU system were properties of crude oil and manipulated variables; while the system output variables were defined as oil product qualities. The knowledge database of the CDU operating model can be built using the input–output data with an approach of artificial neural networks (ANN). The built ANN model can be applied on predicting the oil product qualities with respect to the system input variables. In addition, a design of experiment was implemented to analyze the effect of the system input variables on the oil product qualities. Optimal operating conditions were then found using the knowledge database with an optimization method according to a defined objective function. The built expert system can provide on-line optimal operating information of the CDU process to the operators corresponding to the change of crude oil properties.

Intrinsic photocatalytic oxidation of the dye adsorbed on TiO2 photocatalysts by diffuse reflectance infrared Fourier transform spectroscopy

Abstract Photocatalytic oxidation of aqueous pollutants by semiconductor photocatalysts was found efficient. The overall process by which the heterogeneous photocatalysis proceeds includes: the sequence of the adsorption of reactants, surface reaction and the desorption of final products. As a result, factors such as, the presence of oxygen concentration, pH values of the aqueous solution, pore properties for photocatalyst particles all determine the rate of photodegradation. This study is to concentrate on the photocatalytic mechanisms of the intrinsic reaction occurred on the photocatalysts and the adsorbed dye in air atmosphere. Additionally, the photocatalytic activities of adsorbed dyes prepared under different pH values were also examined and the solid-state results were compared with the aqueous systems at the same pH conditions. Dark adsorption experiments at different pH conditions showed that the saturation amount of dyes adsorbed on the catalysts differs significantly. However, the solid-state photodegradation rates of adsorbed dyes on TiO 2 at various pH values only showed slightly different, which is opposite to the results obtained from the aqueous systems. This evidence reveals that the external and internal mass transport processes are rate-controlling steps that restricted the photodegradation reaction of aqueous dyes at different pH conditions. Furthermore, this investigation supports a proposed direct photocatalytic mechanism for aqueous systems that the photocatalytic oxidation always begins with the adsorption process and the adsorbed dye will then be attacked by the excited hole–electron pairs and hydroxyl radicals from TiO 2 surface to produce final products.

Effect of glass composition on the densification and dielectric properties of BaTiO3 ceramics

An ongoing research goal of thick film capacitors and multilayer capacitors is to lower the firing temperature of the dielectrics. This paper presents the results of using three simple glass systems including PbO–B2O3, PbO–SiO2, and Bi2O3–B2O3 as sintering aids for hydrothermal synthesized BaTiO3. Glasses with different ratios of the modifier/glass former were employed. Effects of adding these glass systems on the BaTiO3 ceramics sintered at 850°C were investigated through measuring and analyzing the density, grain size and dielectric property. It was found that BaTiO3 sintered with glasses composed of 90 mol% PbO–10 mol% SiO2 or 90 mol% PbO–10 mol% B2O3 to 60 mol% PbO–40% B2O3 are helpful to reduce the firing temperature for typical thick film and MLCC applications. They possess high dielectric constant (≈1650) due to their high densification characteristics with the grain size of ≈0.7 μm. In addition, glasses composed of 90 mol% Bi2O3–10 mol% B2O3 to 40 mol% Bi2O3–60 mol% B2O3 are beneficial for thin dielectric layer applications, on account of the high sintering density and a small grain size of ≈0.1 μm with an acceptable K value.

Kinetic analysis of the thermal oxidation of metallocene cyclic olefin copolymer (mCOC)/TiO2 composites by FTIR microscopy and thermogravimetry (TG)

A new amorphous engineering thermoplastic, metallocene cyclic olefin copolymer (mCOC) is considered as a promising material for optical, electrical and mechanical applications. To further expand its application in electro-optic devices, the improvement of mCOCs thermophysical and dielectric properties has been achieved by the addition of suitable inorganic fillers. In the present study, TiO2 powder was chosen to be mixed with mCOC to form a polymer composite. The change of thermal stability of the mCOC composite due to the presence of TiO2 is examined by a thermogravimetry (TG) and an in situ FTIR microscopy equipped with a hot stage. As a result, reaction mechanisms of polymer degradation with and without the filler are obtained. In addition, kinetics of thermal oxidation of filler-free mCOC and mCOC/TiO2 composite are quantitatively achieved by means of non-isothermal weight-loss data analysis.

In situ DRIFT and kinetic studies of photocatalytic degradation on benzene vapor with visible-light-driven silver vanadates.

The visible-light active silver vanadates with different types of crystallines (Ag(4)V(2)O(7) and Ag(3)VO(4) phases) were synthesized by an environmentally friendly aqueous process. The parameters of hydrothermal temperature and hydrothermal time were tuned to maximize the photocatalytic efficiency for the decomposition of benzene vapor under visible-light irradiation. The quantum efficiencies of the photocatalysts are compared on the basis of the crystalline phases, surface area, intensity of surface hydroxyl groups, and Brönsted acid sites. From the results of DRIFTS studies, the photocatalytic activities strongly depend on the intensities of the Brönsted acidity and hydroxyl groups presented on the silver vanadates. The sample synthesized at 140 degrees C and 4h (HM140) exhibits the best photocatalytic activity; it has a reaction rate constant (k(app)) of 1.42 min(-1), much higher than that of P25 (k(app)=0.13 min(-1)). For an irradiation time of 720 min, the mineralization yields of benzene were 48% and 11% for HM140 and P25, respectively. Based on the short-term decrease of benzene concentration and the long-term increase of CO(2) concentration, the photocatalytic ability of the HM140 sample is significantly superior to that of P25. The highest activity can be attributed to the synergetic effects of the richest Brönsted acid sites, and a favorable crystalline phase combined with abundant surface hydroxyl groups.

Liquid-phase sintering and chemical inhomogeneity in the BaTiO 3 –BaCO 3 –LiF system

An ongoing goal of multilayer capacitor research is to lower the firing temperature of the dielectric. This paper gives a detailed study of sintering BaTiO 3 with LiF flux, which lowers the firing temperature through liquid-phase sintering. A detailed set of experiments is discussed concerning microstructural evolution and corresponding dielectric properties under a number of processing variables, including amount of LiF, sintering temperature, and particle size. Different scales of chemical inhomogeneity were observed in this system, which reflect two underlying mechanisms: solution reprecipitation with limited grain growth at low temperatures, which resulted in distinct core–shell structures, and flux volatility, which gave rise to microscopic chemical inhomogeneity at higher sintering temperatures.

Effect of processing conditions on the crystallinity and structure of carbonated calcium hydroxyapatite (CHAp)

Previous synthesis routes created apatites in low crystallinity and high crystallinity states, but a wider range will extend the design capabilities of apatites for hard tissue replacements. While high crystallinity apatites are more conventional, this work investigated lower crystallinity variations from an amorphous state to low crystallinity apatite. Carbonated hydroxyapatite was prepared by precipitating an amorphous phase followed by crystallization at 650 °C at slow (5 °C min−1) and fast heating rates (60 °C min−1). The effect of processing conditions on crystallinity and structural changes was evaluated by thermal analysis, X-ray diffraction, transmission electron microscopy, Fourier transform infrared and Raman spectroscopy. Furthermore, peak deconvolution of IR and Raman spectra resolved the carbonate and phosphate bands and revealed the carbonate and crystalline phase content in CHAp. Similar to precipitation of crystalline apatites, the crystallization at elevated temperature led to carbonate in both the phosphate and hydroxyl positions. Heating at 650 °C provided a nanosized spherical hydroxyapatite containing carbonate controlled by the heating rate. This creates a mechanism for creating a large range in crystallinity with a greater resorption capability for regenerative medicine.

Dielectric and thermal studies of inorganic microfillers on polymer microwave substrates—metallocene cyclic olefin copolymers (COC)

Metallocene cyclic olefin copolymers (mCOCs) are considered as potential candidates for both optical markets and electric applications because of their high transparency in the visible and near UV regions, and their high electrical resistance. In the microelectronic packaging industries, the propagation velocity of electromagnetic waves on the substrates is inversely proportional to the square root of the dielectric constant. Additionally, extents of energy losses and the elimination of stray electromagnetic radiation are all related to Dk properties. As a result, finding a way to lower Dk values for packaging materials is a trend in high-performance computing devices. This paper investigates the dielectric and thermophysical properties of mCOC by adding to it various proportions of microfillers. Three microfillers, all made up of soda-lime-borosilicate glass, were used in the tests. One of the microfillers was the original glass without surface treatment, while the other two have the methacrylato chromic chloride (MCC) treatment, and epoxy silane treatment, respectively. They were mixed with the melted mCOC and then molded to disks of 30 mm diameter and 1 mm thickness. Thermophysical properties such as the bulk density, heat capacity and thermal conductivity were measured at room temperature to understand the thermal stability and heat transport performance of the composites. Additionally, dielectric properties were measured at room temperature at 1 MHz frequency, in order to evaluate electronic wave transport characteristics and extent of energy loss.

Catalysis of oxidation of carbon monoxide on supported gold nanoparticle

Gold used to be considered to have no catalytic activity. In the 1980s, however, Masatake Haruta found that nano-sized gold particles supported by metal oxides can catalyze the oxidation of carbon monoxide. This work examines the oxidation of carbon monoxide (CO) and the adsorption/desorption behaviors on nano-sized gold catalyst at room temperature by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Carbonate, bicarbonate and carboxylate were observed. The effects of various factors (relative humidity, CO gas concentration, and total surface area) on the CO conversion efficiency were studied using the response surface designs in the Experiment Design Method. The results indicate that the conversion efficiency of CO was high when the ratio of CO and O(2) was close to 1:1. The gas concentration is the most important factor, followed by the weight of gold catalyst, followed by relative humidity. An appropriate humidity enhances the catalytic reaction in the long-term.