Suk-In Hong

Photocatalytic degradation of the landfill leachate containing refractory matters and nitrogen compounds

Abstract Photocatalytic process was applied to the landfill leachate containing non-biodegradable matter for which biodegradability (BOD/COD) was relatively low. The variations of concentration, apparent first-order rate constants (k′), and removal efficiency were used to describe the degradation behavior of landfill leachate under different conditions, which were various initial pH and photocatalyst concentration. Under the acidic condition, the photocatalytic removal efficiency of landfill leachate was relatively high because there was very low concentration of inorganic carbons that could inhibit the photocatalytic oxidation. To remove ammonium–nitrogen, the photocatalytic reaction must be operated in neutral and/or alkaline solution, and the contribution of photocatalyst in diminution of ammonium–nitrogen might be negligible. The effect of TiO2 concentration was obtained from experimental results and it could demonstrate the relationship of amounts of TiO2 dosage and reaction rate.

Bioconversion of cellulose into ethanol by nonisothermal simultaneous saccharification and fermentation

The kinetic characteristics of cellulase and β-glucosidase during hydrolysis were determined. The kinetic parameters were found to reproduce experimental data satisfactorily and could be used in a simultaneous saccharification and fermentation (SSF) system by coupling with a fermentation model. The effects of temperature on yeast growth and ethanol production were investigated in batch cultures. In the range of 35–45°C, using a mathematical model and a computer simulation package, the kinetic parameters at each temperature were estimated. The appropriate forms of the model equation for the SSF considering the effects of temperature were developed, and the temperature profile for maximizing the ethanol production was also obtained. Briefly, the optimum temperature profile began at a low temperature of 35°C, which allows the propagation of cells. Up to 10 h, the operating temperature increased rapidly to 39°C, and then decreased slowly to 36°C. In this nonisothermal SSF system with the above temperature profile, a maximum ethanol production of 14.87 g/L was obtained.

Core/shell silica-based in-situ microencapsulation: A self-templating method

Core/shell SiO2 and (RSiO1.5)(1-x)-(SiO2)x (R = alkyl) microcapsules were synthesized via a single-step O/W emulsion system using a self-templating method; the facile synthetic process provides an in-situ encapsulation route for a wide range of lipophilic functional compounds.

Comparison of Effective Working Electrode Areas on Planar and Porous Silicon Substrates for Cholesterol Biosensor

Porous silicon-based biosensors were originally developed to further stet the miniaturization of a host of devices. In this paper, we describe the relationship between the enlargement of an electrodes area and its sensitivity for the determination of cholesterol concentrations with covalent binding to immobilized enzymes. For comparison, we conducted a series of experiments using a planar silicon electrode and a porous silicon electrode. We determined the effective surface area of the electrodes using the Randles–Sevcik equation. The active surface area of the planar electrode was approximately 0.1608 cm2, and that of the porous electrode was approximately 0.5054 cm2. Cholesterol oxidase was covalently immobilized on each electrode by silanization. The sensitivities were 0.08567 µA/mM for the planar sensor and 0.2656 µA/mM for the porous sensor. The calculated effective surface area and sensitivity of the porous electrode were about 3.1-fold larger than those of the planar electrode.

The control of valence state: How V/TiO2 catalyst is hindering the deactivation using the mechanochemical method

Various experiments were conducted to improve durability against SO(2) by impregnating the same amount of vanadium in TiO(2) which had the various physical properties. According to those catalysts, the degree of deactivation by SO(2) had various results, and it was found that the production of unreacted NH(3) in selective catalytic reduction reaction should be low. Based on X-ray photoelectron spectroscopy analysis, O(2) on-off test, O(2) reoxidation test and H(2)-temperature programmed reduction experiment, the redox capacity of catalyst was improved due to increasing of non-stoichiometric compounds. Such a non-stoichiometric oxide and redox capacity of catalyst can be enhanced by the ball-milling process, and the production of ammonium sulfate salt can be more easily inhibited by the superior oxidation-reduction capacity of catalyst. We found that this result is caused by producing and increasing of V(x+) (x<or=4), Ti(y+) (y<or=3) which are non-stoichiometric chemical species of catalyst.

An Electrochemical Biosensor Array for Rapid Detection of Alanine Aminotransferase and Aspartate Aminotransferase

An increment of alanine aminotransferase (ALT) or aspartate aminotransferase (AST) in human serum indicates an abnormal symptom of the liver. Hence, an electrochemical biosensor array that uses micro electro mechanical systems technology is required for rapid and integrated measurement of ALT/AST. Here we describe a biosensor array consisting of two glutamate sensors. It turned out that porous silicon layers formed on each working electrode were useful to increase the effective surface area. This biosensor array was constructed with platinum electrodes and a polydimethylsiloxane (PDMS) microchannel. Electrodes in sampling wells minimized a cross-interference effect and permitted multiple sampling by immobilization with glutamate oxidase using a silanization technique. The device sensitivities derived from semi-logarithmic plots were 0.145 μA/(U/l) for ALT and 0.463 μA/(U/l) for AST over a range of 1.3 U/l to 250 U/l. Hene, this ALT/AST biosensor array can be applied in diagnostic and home use.

The transport properties of CO2 and CH4 for chemically modified polysulfones

The sorption and transport properties of pure CO2 and CH4 for a series of polysulfones were measured. The effects of molecular structure of polysulfones on transport properties were studied using chemically modified polysulfones, including TMSPSF (bisphenol-A trimethylsilylated polysulfone), BPSF (bromobisphenol-A polysulfone), and BTMSPSF (bromobisphenol-A trimethylsilylated polysulfone). The effects of operating pressure on the sorption and permeation properties of polysulfones were examined. The permeation properties for a mixture of CO2 and CH4 were also measured and these results were compared with those obtained from the experiments of pure gases. The sorbed concentrations and permeability coefficients are well fitted to a conventional dual-mode model. The permeability coefficients of each gas of a binary mixture are lower than those of pure gases, which shows the competition effect between each component. The permeability coefficients of polysulfones rank in the following order, TMSPSF > BTMSPSF > bisphenol-A polysulfone (PSF) > BPSF. The effect of the substituents on chain packing was related to the gas-permeation properties. Fractional free volume (FFV) calculations and X-ray diffraction were used to judge chain packing. In comparison with PSF, the higher values of permeability coefficients for TMSPSF and BTMSPSF are due to higher FFV and d spacing. The lower permeability coefficients for BPSF is attributed to the strong induced dipole interchain interaction. Addition of bromo substituents to TMSPSF is also found to decrease the permeability coefficients for BTMSPSF, suggesting that the potential increase in FFV due to packing–disrupting bulky trimethylsilyl groups is overridden by the increase in cohesive energy density.

Simultaneous determination of oxygen transport characteristics of six membranes by hexagonal dissolved oxygen sensor system

Abstract In the present study, a hexagonal sensor system composed of a six port measurement device and six different cathodes with one common anode was developed for simultaneous determination of oxygen permeabilities or diffusivities of six different membranes. To minimize experimental variations caused by geometrical differences among six individual electrodes, the current output of each electrode was divided by individual correction factors determined by standardization with a typical membrane of fluorinated ethylene propylene (FEP). The hexagonal sensor system was then used to simultaneously determine the oxygen transport characteristics such as permeabilities or diffusivities of six different polypropylene membranes. The present study showed that a newly developed hexagonal dissolved oxygen sensor system can be used for simultaneous measurement of oxygen transport characteristics of six different membranes.

Fabrication and Electrochemical Characterization of Nanoporous Silicon Electrode for Amperometric Urea Biosensor

We describe a new type of biosensor that employs a modified gold electrode based on nanoporous silicon (NPSi) for the electrochemical detection of urea. Urease (Urs) was covalently immobilized onto an Au/NPSi electrode functionalized with 3-mercaptopropionic acid (3-MPA). Amperometric calibration curves for both NPSi and planar silicon (PLSi)-based urea sensitive electrodes were compared in the range of 0.3 to 4.5 mM urea concentrations. The Michaelis–Menten constant (Km) was determined using the amperometric method. The electrochemical active area (Aea) of the 3-MPA/Au/NPSi electrode was evaluated using cyclic voltammetry (CV) and the result was compared with the 3-MPA/Au/PLSi electrode. Measured sensitivity of the Urs/SAMs/Au/NPSi electrode is ca. 2.05 µA mM-1 cm-2 and that of the Urs/SAMs/Au/PLSi electrode is ca. 1.10 µA mM-1 cm-2. About 1.8 times of sensitivity increase is obtained in the Au/NPSi electrode.

Gas Permeabilities of CO2 and CH4 for Polysulfones Substituted with Bromo and Trimethylsilyl Groups

Bromobisphenol A trimethylsilylated polysulfone (BTMSPSf) was synthesized, and the effect of bromo and trimethylsilyl groups on the pure CO2 and CH4 transport properties of polysulfone was examined. The ideal separation factor for BTMSPSf is reduced by about 10% than that for unmodified polysulfone (PSf), but BTMSPSf is about two times more permeable than PSf. The effect of the substituents on chain packing was related to the gas permeation properties. Fractional free volume (FFV) calculation, d-spacing and cohesive energy density were used to judge chain packing. In comparison with PSf, the higher values of permeability coefficients for BTMSPSf are due to higher FFV and d-spacing. The small decrease in ideal separation for BTMSPSf is explained as follows: the potential increase in FFV due to packing-disrupting bulky trimethylsilyl groups is overridden by the increase in cohesive energy density attributed to the addition of bromo substituents.