Development of a method for nuclide leaching from glass fiber in HEPA filter

For the disposal of the high efficiency particulate air (HEPA) glass filter to environment, the glass fiber should be leached to lower its radioactive concentration. To derive the optimum method for removal of Co and Cs from HEPA glass fiber, four methods were applied in this study. Results of electrochemical leaching of glass fiber by 4.0 M HNO₃–0.1 M Ce(IV) solution showed that the removal efficiency of ¹³⁴Cs, ¹³⁷Cs, and ⁶⁰Cs from glass fiber after 5 h was 96.4, 93.6, and 93.8%, respectively. Results by 5 wt% NaOH solution showed that the removal efficiency of ¹³⁴Cs, ¹³⁷Cs, and ⁶⁰Cs after 30 h was 81.7, 82.1, and 10.0%, respectively. Results by repeat 2.0 M HNO₃ solution showed that the removal efficiencies of ¹³⁴Cs, ¹³⁷Cs, and ⁶⁰Cs after 2 h of three repetitions were 96.2, 99.4, and 99.1%, respectively. Finally, results by repeat 4.0 M HNO₃ solution showed that the removal efficiencies of ¹³⁴Cs, ¹³⁷Cs, and ⁶⁰Cs after 4 h of three repetitions were 100, 99.9, and 99.9%, respectively, and their radioactivities were below 0.1 Bq/g. Therefore, the chemical leaching method by 4.0 M HNO₃ solution was considered as an optimum one for removal of cesium and cobalt from HEPA glass fiber for self disposal. Also the removal efficiencies of ⁶⁰Co, ¹³⁴Cs, and ¹³⁷Cs from the waste-solution after its precipitation-filtration treatment for reuse of 4.0 M HNO₃ waste-solution were 88.0, 95.0, and 99.8%.     

Analysis of the HDO content in heavy water by ATR-FTIR

The applicability of ATR-FTIR for the determination of the HDO content in heavy water (D₂O) was investigated. Two groups of calibration standard solutions, of low contents (0–1 n% H₂O in heavy water) and of higher contents (0–10 n% H₂O in heavy water) were prepared by adding properly calculated amount of H₂O to D₂O by weight. The absorbances at 3400 cm⁻¹ (ν, O–H) against the calibration standards were measured five times using two kinds of interchangeable IREs (1 bound and 9 bound reflections). And four calibration curves were obtained by linear least square fit of the measured absorbances for the four different measurement conditions, which are (1) for low contents group using 1 bound reflection, (2) for low contents group using 9 bound reflections, (3) for higher contents group using 1 bound reflection, (4) for higher contents group using 9 bound reflections. Determined contents (c ₀) of each calibration standards for the four measurement conditions were obtained by the calibration curves and compared to the calculated contents (c _cal). The uncertainty sources were considered when the HDO in heavy water is determined according to the procedure of this work. The uncertainties u(c ₀) of the determined contents (c ₀) for the four different measurement conditions were calculated.     

Enhancement of surface wettability via the modification of microtextured titanium implant surfaces with polyelectrolytes

Micrometer- and submicrometer-scale surface roughness enhances osteoblast differentiation on titanium (Ti) substrates and increases bone-to-implant contact in vivo. However, the low surface wettability induced by surface roughness can retard initial interactions with the physiological environment. We examined chemical modifications of Ti surfaces [pretreated (PT), R(a) ≤ 0.3 μm; sand blasted/acid etched (SLA), R(a) ≥ 3.0 μm] in order to modify surface hydrophilicity. We designed coating layers of polyelectrolytes that did not alter the surface microstructure but increased surface ionic character, including chitosan (CHI), poly(L-glutamic acid) (PGA), and poly(L-lysine) (PLL). Ti disks were cleaned and sterilized. Surface chemical composition, roughness, wettability, and morphology of surfaces before and after polyelectrolyte coating were examined by X-ray photoelectron spectroscopy (XPS), contact mode profilometry, contact angle measurement, and scanning electron microscopy (SEM). High-resolution XPS spectra data validated the formation of polyelectrolyte layers on top of the Ti surface. The surface coverage of the polyelectrolyte adsorbed on Ti surfaces was evaluated with the pertinent SEM images and XPS peak intensity as a function of polyelectrolyte adsorption time on the Ti surface. PLL was coated in a uniform thin layer on the PT surface. CHI and PGA were coated evenly on PT, albeit in an incomplete monolayer. CHI, PGA, and PLL were coated on the SLA surface with complete coverage. The selected polyelectrolytes enhanced surface wettability without modifying surface roughness. These chemically modified surfaces on implant devices can contribute to the enhancement of osteoblast differentiation.     

Facile synthesis of TiO2 inverse opal electrodes for dye-sensitized solar cells

Engineering of TiO(2) electrode layers is critical to guaranteeing the photoconversion efficiency of dye-sensitized solar cells (DSSCs). Recently, a novel approach has been introduced for producing TiO(2) electrodes using the inverted structures of colloidal crystals. This paper describes a facile route to producing ordered macroporous electrodes from colloidal crystal templates for DSSCs. Using concentrated colloids dispersed in a volatile medium, the colloidal crystal templates were obtained within a few minutes, and the thickness of the template was easily controlled by changing the quantity of colloidal solution deposited. Here, the effects of the structural properties of the inverse opal TiO(2) electrodes on the photovoltaic parameters of DSSCs were investigated. The photovoltaic parameters were measured as a function of pore ordering and electrode film thickness. Moreover, DSSC applications that used either liquid or viscous polymer electrolyte solutions were investigated to reveal the effects of pore size on performance of an inverse opal TiO(2) electrode.     

Thermodynamic control over the competitive anchoring of N719 dye on nanocrystalline TiO2 for improving photoinduced electron generation

TiO(2) electrodes, sensitized with the N719 dye at high immersion temperatures during the sensitization process, were found to have large fractions of weakly bound N719 on the electrode surface, which resulted in dye aggregation and decreased device longevity. These disadvantages were ameliorated using a low-temperature stearic acid (SA)-assisted anchoring method described here. The activation energy (ΔE(NS)(++)) and relative fraction of strongly bound N719 were twice as large as the respective values obtained without the use of SA. Slowing of adsorption, both by thermal means and through SA-mediated processes, effectively controlled the binding mode of N719 on the surface of TiO(2). The resulting sensitized electrodes displayed enhanced device longevity and improved generation of photoinduced electrons.     

Synthesis of highly ordered mesoporous CeO<Subscript>2</Subscript> and low temperature CO oxidation over Pd/mesoporous CeO<Subscript>2</Subscript>

Highly ordered mesoporous cerium dioxide (meso-CeO₂) was successfully synthesized using a facile solvent-free infiltration method from a mesoporous silica template, KIT-6. The meso-CeO₂ material, thus obtained, exhibited well-defined mesostructure and high surface area (153 m² g⁻¹). The physicochemical properties of meso-CeO₂ material and Pd-supported on meso-CeO₂ (Pd/meso-CeO₂) were characterized by electron microscopy, X-ray diffraction, N₂ adsorption–desorption, and temperature-programmed experiments. The Pd/meso-CeO₂ catalyst exhibited excellent catalytic activity for CO oxidation compared with those of other Pd/CeO₂ catalysts which were prepared using nanocrystalline CeO₂ and bulk-CeO₂ as the supports. Moreover, a hydrogen pretreatment of the Pd/meso-CeO₂ catalyst resulted in a remarkable increase of catalytic activity (T ₁₀₀ = 52 °C).     

Selective hydroisomerization of n-dodecane over platinum supported on zeolites

In this study, in order to develop catalysts for the selective isomerization of higher paraffin, the hydroisomerization reaction of n-dodecane was performed as a model reaction. Pt/ZSM-48, Pt/HZSM-5, Pt/HY, and Pt/SAPO-11 were examined for the selective hydroisomerization of n-dodecane. The catalysts were characterized via X-ray powder diffraction, N₂ adsorption, and the temperature-programmed desorption of ammonia. Among the catalysts studied, the Pt/HZSM-48 catalyst exhibited the best isomerization selectivity in the hydroisomerization reaction of n-dodecane, which is attributed to the moderate acid sites and medium-sized pores present in the HZSM-48. The highest iso-dodecane yield was obtained at a reaction temperature of 280 °C in the Pt/HZSM-48 catalyst. The optimal selectivity of the n-dodecane hydroisomerization over the Pt/SAPO-11 catalyst was obtained at approximately 300 °C, which was slightly higher than that of the Pt/HZSM-48 catalyst.     

Effects of dual initiators and catalytic additives on atom transfer radical polymerization of styrene

The effect of two initiators, so-called dual initiators system on atom radical transfer polymerization (ATRP), were studied with dimethyl-2,6-dibromohepanedioate (DMDBHD) and ethyl-2-bromoisobutyrate (EBIB). Cu(I)Br as catalyst and N,N,N??,N??,N??-pentamethyl-diethylenetriamine as ligand were employed for styrene ATRP. Interestingly, bimodal MWD were shown for the dual initiator system, and one of the peaks had higher molecular weight (MW) and the other had lower MW compared to a one-initiator system. The lower MW peak in bimodal peaks seemed to be mainly resulting from EBIB and the higher MW peak from DMDBHD. Furthermore, methylaluminoxane (MAO) was fed into the ATRP reaction to observe the effect of it on ATRP. As the MAO/CuBr molar ratio in feed increased from 0 to 1, the molecular weight and conversion increased without a notable change in PDI and curve shape of GPC. The conversion in the presence of MAO was also increased with the increase in MAO/CuBr molar ratio. The effect of Cp^*TiCl₃ on the ATRP was opposite to that of MAO. As the Cp^*TiCl₃/CuBr molar ratio increased from 0 to 1, the conversion of polymerization was down from 56 to 35%. Furthermore, the molecular weight was drastically decreased from 10,000 to 5,500, but their PDI did not show a significant change. These results can elucidated by the retarding effect of Cp^*TiCl₃ on the propagation of polymerization.     

Curvature effect on nanometer-scale surface properties of phospholipid layers

Phospholipid bilayers were formed through liposome fusion on surfaces with different curvatures that were defined with silica spheres deposited on silicon water. Prior to the fusion, the surfaces became hydrophobic with octadecyltrimethoxysilane solution. Using atomic force microscope, surface forces were measured on dipalmitoylphosphatidylcholine (DPPC) layers and dioleoylphosphatidylcholine (DOPC) layers upon the curvature at 25°C. The short-range repulsions were higher at 20 and 100 nm curvatures than other curvatures for the DPPC layer, while they were lower for the DOPC layer. Since it was known that the forces are related to its low mechanical stability of the lipid layer, this opposite behavior was analyzed in terms of stability upon the curvature, which appears to be eventually determined by the correlation between the lipid molecule geometry and the surface curvature.     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.