Yiang-Chen Chou

Decomposition of aniline in aqueous solution by UV/TiO2 process with applying bias potential.

Application of bias potential to the photocatalytic decomposition of aniline in aqueous solution was studied under various solution pH, bias potentials and concentrations of potassium chloride. The decomposition of aniline by UV/TiO(2) process was found to be enhanced with the application of bias potential of lower voltages; however, the electrolysis of aniline became more dominant as the applying bias potential exceeding 1.0 V. Based on the experimental results and calculated synergetic factors, the application of bias potential improved the decomposition of aniline more noticeably in acidic solutions than that in alkaline solutions. Decomposition of aniline by UV/bias/TiO(2) process in alkaline solutions was increased to certain extent with the concentration of potassium chloride present in aqueous solution. Experimental results also indicated that the energy consumed by applying bias potential for aniline decomposition by UV/bias/TiO(2) process might be much lower than that consumed for increasing light intensity for photocatalysis.

Characterization and Induced Photocurrent of TiO2 Nanotube Arrays Fabricated by Anodization

The fabrication of TiO 2 nanotube arrays (TNTs) by the anodization of titanium foil in electrolyte containing fluoride was carried out in this study. The surface dimension, phase formation, and lattice parameters of TNTs were determined by the field-emission-scanning electron microscopy and X-ray diffractometer, respectively. The induced photocurrent intensity of TNTs was measured by a potentiostat/galvanostat. The well-defined and highly ordered TNTs were formed in glycerol electrolyte with a water content of 20%. The inner diameter of the TNTs was mainly determined by the anodization voltage, while the length of the TNTs was affected by both anodization voltage and anodization time. The length of the nanotube was continually increased with anodization time until the rates of the electrochemical oxidization of Ti foil and the chemical dissolution of the TiO 2 film reached a dynamic equilibrium. The TNTs annealed at 600°C demonstrated the highest induced photocurrent because of the crystallization of anatase and rutile phases. The increase in the tube length and the decrease in the inner diameter induced higher photocurrents under specific conditions of UV illumination because of a higher illuminated area. However, the enhancement of the induced photocurrent was retarded when the length of the TNTs reached 2000 nm due to the limited penetration of incident UV light penetrated through the nanotube.

Effect of platinum on the photocatalytic decomposition of 2‐chlorophenol in aqueous solution by UV/TiO2

Abstract Photocatalytic decomposition of 2‐chlorophenol in aqueous solutions with platinum‐coated TiO2 slurry under UV irradiation was examined, utilizing various solution pH levels, dissolved oxygen levels and UV light intensities. The atomic percentage of platinum deposited on the TiO2 surfaces were identified by X‐ray photoelectron spectroscopy (XPS) to be in the range of 0.12 and 0.99%. The decomposition of 2‐chlorophenol in acidic aqueous solutions by UV/TiO2 was enhanced to certain extents for experiments conducted with platinum‐coated TiO2 containing up to 0.82% platinum because of the formation of Schottky barrier between platinum and TiO2 to prevent the recombination of electric holes and electrons. However, for experiments conducted with TiO2 coated with higher platinum contents, the decomposition rate of 2‐chlorophenol was reduced markedly, possibly because of the depression of the light absorption of TiO2 by the shielding of coated platinum. The photocatalytic decomposition of 2‐chlorophenol in aqueous solution was inhibited for experiments conducted in neutral and alkaline solutions because the presence of platinum increases the repulsion between 2‐chlorophenol species and TiO2 to hinder the adsorption of 2‐chlorophenol species on TiO2. The decomposition rate of 2‐chlorophenol in aqueous solution by UV/TiO2 was found to be improved significantly with increasing UV light intensity.

Effects of TiO2 nanotube array dimension and annealing temperature on the Acid Red 4 degradation in aqueous solution by photocatalytic process

Degradation of Acid Red 4 (AR4) by photocatalytic processes with TiO(2) nanotube arrays (TNTs) of various dimensions was carried out in this study. TNTs was fabricated by the anodization of titanium foil in electrolyte containing fluoride. The dimension and the induced photocurrent of TNTs were determined by a field-emission scanning electron microscopy and a potentialstat/galvanostat, respectively. The well-defined and highly-ordered TNTs were formed at the anodization voltage ranging from 10 to 40 V in water/glycerol solution (20:80 wt.%) containing 0.5 wt.% NH(4)F. TNTs annealed at 600 degrees C was found to induce the highest photocurrent and to exhibit the preeminent performance of AR4 degradation. The apparent first-ordered reaction rate constant for AR4 degradation was roughly linearly dependent on the induced photocurrent of TNTs, despite the dimension of nanotubes. The depths of incident UV light penetration through the nanotubes and of AR4 diffusion inside nanotubes restricted the degradation of AR4.

Selective reduction of NO by photo-SCR with ammonia in an annular fixed-film photoreactor

Gaseous NO was photocatalytically reduced at room temperature by photo-assisted selective catalytic reduction (photo-SCR) with ammonia over TiO2 in this study. NO reduction efficiency and N2 selectivity were determined from gases composition at the outlet stream of photoreactor. Effect of operating conditions, e.g. light intensity and inlet concentrations of ammonia and oxygen, on the NO reduction efficiency and N2 selectivity were discussed to determine the feasible operating condition for photocatalytic reduction of NO. Experimental results showed that selective catalytic reduction of NO with ammonia over TiO2 in the presence of oxygen was a spontaneous reaction in dark. The photoirradiation on the TiO2 surface caused remarkable photocatalytic reduction of NO to form N2, NO2, and N2O under 254 nm UV illuminations, while almost 90% of N2 selectivity was achieved in this study. The ammonia and oxygen molecules played the roles of reductant and oxidant for NO reduction and active sites regeneration, respectively. The reduction of NO was found to be increased with the increase of inlet ammonia and oxygen concentrations until specific concentrations because of the limited active sites on the surface of TiO2. The kinetic model proposed in this study can be used to reasonably describe the reaction mechanism of photo-SCR.

The effect of surfactants on the ozonation of o‐cresol in aqueous solutions in a rotating packed contactor

Steady‐state dissolved ozone concentrations were maintained relatively constant for experiments on ozone dissolution conducted in the presence of various amounts of sodium dodecyl sulphate (SDS) and Triton X‐100 (TX‐100), an anionic surfactant and a nonionic surfactant, respectively. Ozonation in a rotating packed contactor has been shown to be feasible for achieving nearly complete decomposition of o‐cresol within about 10 minutes of reaction time for most experiments conducted. The temporal decomposition behaviour of o‐cresol in aqueous solution by ozonation was described by a two‐step pseudo‐first‐order reaction kinetics. Even though the presence of SDS and TX‐100 slightly affected the decomposition rate constant of o‐cresol by ozonation in the rotating packed contactor, the mineralization of total organic carbon was apparently reduced with the addition of SDS and TX‐100.

Ozone Transfer and Decomposition of Isopropyl Alcohol by H2O2/Ozone Process in a Rotating Packed Contactor

Abstract Ozone transfer and decomposition of isopropyl alcohol in aqueous solution by H2O2/O3 process in a rotating packed contactor was studied under various operational conditions. Decomposition of isopropyl alcohol by H2O2/O3 process in a rotating packed contactor has been shown to be feasible and can be described with a simplified pseudo-first order kinetic model. Both the overall ozone transfer coefficient and the decomposition rate of isopropyl alcohol by H2O2/O3 process in the rotating packed contactor were enhanced with the increase of rotor speed. The decomposition rate was greatly affected by the rotor speed for experiments conducted at lower gas/liquid flow rate ratio. The decomposition of isopropyl alcohol was favored to occur in neutral and alkaline solutions; however, the decomposition rate of isopropyl alcohol for experiment conducted at pH 11 was found to be hindered. The decomposition of isopropyl alcohol was accelerated with increasing H2O2/O3 molar ratio. However, for experiments conducted in neutral and alkaline solutions, excessive additions of H2O2 might serve as scavenger for OH• free radicals to inhibit the decomposition of isopropyl alcohol.