Jung-Hee Chung

UV/TiO2 and UV/TiO2/chemical oxidant processes for the removal of humic acid, Cr and Cu in aqueous TiO2 suspensions

The objective of this study was to investigate the treatment efficiency of UV/TiO2 and UV/TiO2/chemical oxidant processes for the removal of humic acid and hazardous heavy metals in aqueous TiO2 suspensions. The reaction rate (k) of humic acid and hazardous heavy metals by UV/TiO2 was higher than that of UV illumination alone or TiO2 alone. The removal efficiency for humic acid and Cr(VI) at acid or neutral pH values was higher than that at basic pH values. However, the removal efficiency for Cu(II) at acid pH values was smaller compared with that at neutral or basic pH values. The reaction rate (k) of humic acid and hazardous heavy metals in the TiO2 concentration range of 0.1–0.3 g l−1 increased with increasing TiO2 dosage. However, amounts higher than a TiO2 dosage of 0.3 g l−1 reduced the removal efficiency for humic acid and hazardous heavy metals because of the shielding effect on the UV light penetration in the aqueous solution caused by the presence of excessive amounts of TiO2. The addition of oxidants to the UV/TiO2 system showed an increase in degradation efficiency for the treatment of humic acid and hazardous heavy metals. The optimal concentration of oxidants was: H2O2 50 mg l−1, O3 20 g m−3 and K2S2O8 50 mg l−1, respectively. The degradation efficiency of UV/TiO2/oxidant systems for the removal of humic acid and hazardous heavy metals was much greater when H2O2 was used as the oxidant.

Influence of nitrate, sulfate and operational parameters on the bioreduction of perchlorate using an up-flow packed bed reactor at high salinity.

In this study we have investigated whether electron acceptors, such as nitrate or sulphate ions, competitively inhibit the reduction of perchlorate in brine in continuous up‐flow packed bed bioreactors. The effect of pH and hydraulic retention time (HRT) on the reduction of perchlorate at high salinity has also been examined. Reduction of perchlorate was found to be only moderately influenced by nitrate (under 163 mg N L−1), implying that there was no significant microbial competition for electron acceptors. As a result of microbial diversity, there were few differences between microbial communities fed with a variety of media, suggesting that most nitrate‐reducing bacteria are able to reduce perchlorate at high salinity. Reduction of perchlorate was almost complete at relatively high sulfate levels (1000 mg L−1), neutral pH (6–8) and relatively long HRTs (>10 h).

Degradation mechanism of organic light-emitting device investigated by scanning photoelectron microscopy coupled with peel-off technique

The authors present space-resolved spectroscopic data on organic layers of a degraded organic light-emitting device. The data were obtained using a scanning photoelectron microscope (SPEM) coupled with peel-off technique to directly probe the uncontaminated organic layers, which were covered with cathode layer. The SPEM images of the degraded device show different and small size distributions of tris-8-hydroxy quinoline aluminum (Alq3) and hole-transport layers compared to that of as-prepared device. The analysis indicates that bonding strength between Alq3 and cathode layers and between the Alq3 and hole transport layers becomes weak as the device degrades, presumably due to structural deformation of the organic layers.

Scanning photoelectron microscopic study of top-emission organic light-emitting device degradation under high-bias voltage

The degradation process of a top-emission organic light-emitting device (TOLED) under high-bias voltage was investigated using a scanning photoelectron microscope (SPEM). The TOLED was in situ biased to reveal the degraded area inside the SPEM chamber. The SPEM data showed a volcano-type structure inside the degraded area. The overall results of the spectroscopic analysis suggest that strong degradation was accompanied by an eruption underneath the cathode layer. It is posited that the hot gases from the erupted area separated the cathode layer from the organic layer, forming a large bubble, and that, as the bubble exploded, the pressure of the gas blew away the cathode layer.

Laser-induced surface cleaning of molybdenum field emitter arrays for enhanced electron emission

Visible laser irradiation on molybdenum field emission arrays (Mo–FEAs) was performed as one efficient cleaning method in order to etch off any unnecessary oxidation layers on the FEA surface. Scanning electron microscopy and high-resolution transmission electron microscopy showed clear removal of ultrathin MoO oxide layers at the emitter edge through a photoinduced thermal process. A sharp surface morphology of the emitter tips was also observed due to the crystallization or thermalmigration effect during the laser exposure. The structural enhancement of the FEA was strongly confirmed by a remarkable increase of 40% in the emission current after laser exposure.

BACKWASH BASED METHODOLOGY FOR THE ESTIMATION OF SOLIDS RETENTION TIME IN BIOLOGICAL AERATED FILTER

The concept of solids retention time (SRT) was used for describing the growth of biofilm in a biological aerated filter (BAF) system. The SRT profile was obtained from the change in solids accumulation, estimated from the head loss profile data before and after backwash using the Carmen-Kozeny equation. The SRT profile along the filter bed depth showed the SRT of about 2 days for the lower layer and about 6 days for the upper layer. The overall SRT was determined by the direct estimation of excess solids mass during backwash and of solids retained in the filter bed. The ideal characteristic SRT distribution was maintained by regular backwash, for organic removal and nitrification. The SRT for high organic removal and nitrification is demonstrated by the SRT distribution along the filter bed in this BAF process.

Photoelectron spectrum from a thin organic layer exposed to intense x rays

When an organic layer on a conducting substrate is exposed to intense x rays, such as in scanning photoelectron microscopy (SPEM), the photoelectron spectrum for the exposed area shows a kinetic energy shift towards higher binding energy due to the accumulation of local charges. We present experimental evidence that in the thin organic layer of approximately 100nm thickness in organic light-emitting devices, there exists an unshifted spectral component besides the local-charging-shifted spectral component. This finding enabled us to reliably investigate the chemical structures of organic layers using SPEM, which was shown to be advantageous in obtaining the space-resolved chemical structural information of a specimen.