Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process.

Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga0.97N0.9O0.09 is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga0.97N0.9O0.09 of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4M HCl, 100°C and pulp density of 100 kg/m(3,) respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition.

Factors Related to Gait Function in Post-stroke Patients.

[Purpose] Gait function after a stroke is an important factor for determining a patient's ability to independently perform activities of daily living (ADL). The objective of this study was to elucidate the factors associated with gait function in post-stroke patients. [Subjects] Thirty-nine stroke patients (16 females and 23 males; average age 67.82 ± 10.96 years; post-onset duration: 200.18 ± 27.14 days) participated in this study. [Methods] Their gait function, motor function (Manual Muscle Test [MMT] and Brünnstrom stage), level of cognition (Mini-Mental State Examination score [MMSE], and the Loewenstein Occupational Therapy Cognitive Assessment for the Geriatric Population [LOTCA-G]), and ADL (Korean modified Barthel index [K-MBI]) were assessed. [Results] The degree of gait function showed significant positive correlations with the following variables: MMT of the elbow, knee, ankle and wrist; Brünnstrom stage; MMSE; LOTCA-G subscores except motor praxis; K-MBI. Stepwise linear regression analysis revealed the Brünnstrom stage was the only explanatory variable closely associated with gait level. [Conclusion] Gait function of post-stroke patients was related to motor function, cognition, and ADL. In particular, there is a significant association between gait level and the Brünnstrom stages, reflecting the importance of monitoring the motor recovery of gait function in post-stroke patients.

Synthesis of the thermoelectric nanopowder recovered from the used thermoelectric modules.

We fabricated the thermoelectric powder using the used thermoelectric modules in a vehicle. As a starting material, the used thermoelectric modules were collected and separated to substrate, electrode, solder, and thermoelectric parts by a thermal process. The separation process was performed in a wet process at the critical temperature. The solder in the module was the neighbor part of the thermoelectric material with the lowest melting temperature in the module. We focused on the thermal property of the solder to separate the thermoelectric chips in the module. After the separation process, we prepared the pure thermoelectric material by the chemical etching for an impurity removal. Also the thermoelectric nanopowder was fabricated by a chemical reduction reaction using the recycled thermoelectric materials. The recovered nanopowder was confirmed to the phase of bismuth telluride (Bi2Te3) with the particle size of -15 nm.

Improvement of dispersion stability and optical properties of CdSe/ZnSe structured quantum dots by polymer coating.

In this study, CdSe core and CdSe/ZnSe core/shell quantum dots with a narrow size distribution were synthesized in a micro-reactor. A PMMA coating applied to the surface of CdSe/ZnSe core/shell QDs to prevent degradation gave improved dispersion stability compared to the CdSe core and CdSe/ZnSe core/shell. Many previous approaches to dispersion stability have not been quantitatively assessed. The dispersion stability was confirmed by multiple light scattering measurement. Additionally, the PMMA-coated CdSe/ZnSe QDs showed greatly improved optical properties with a photoluminescence quantum yield up to 80%. This structural motif is expected to prevent the degradation of QDs.

Synthesis of ultra-long hollow chalcogenide nanofibers.

Electrospinning and galvanic displacement reaction are combined to fabricate ultra-long hollow chalcogen and chalcogenide nanofibers in a cost-effective and high throughput manner. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions and morphology, thereby imparting control over the composition and shape of the nanostructures evolved during galvanic displacement reaction. It is believed to be a general route to form various ultra-long hollow semiconducting nanofibers.

Tunable synthesis of cuprous and cupric oxide nanotubes from electrodeposited copper nanowires.

Polycrystalline copper oxide nanostructures with different valence/oxidation states (i.e., Cu2O and CuO) were readily synthesized by thermal oxidation of single crystalline copper nanowires at relative low operating temperature (200 to 300 degrees C). Operating temperature of 200 to 250 degrees C in air oxidized copper to Cu2O and further increased temperature (i.e., 300 degrees C) led to form CuO nanostructures. The morphology of nanostructures significantly altered from nanowires to nanotubes which might be attributed to Kirkendall effect. The electrical resistivity of single copper nanowire, Cu2O and CuO nanotube were determined to be 3.4 x 10(-4), 33, and 211 omega cm, respectively.

Preparation and characterization of TiO2 coated Fe nanofibers for electromagnetic wave absorber.

Recently, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) have become serious problems due to the growth of electronic device and next generation telecommunication. It is necessary to develop new electromagnetic wave absorbing material to overcome the limitation of electromagnetic wave shielding materials. The EMI attenuation is normally related to magnetic loss and dielectric loss. Therefore, magnetic material coating dielectric materials are required in this reason. In this study, TiO2 coated Fe nanofibers were prepared to improve their properties for electromagnetic wave absorption. Poly(vinylpyrrolidone) (PVP) and Iron (III) nitrate nonahydrate (Fe(NO3)3 x 9H2O) were used as starting materials for the synthesis of Fe oxide nanofibers. Fe oxide nanofibers were prepared by electrospinning in an electric field and heat treatment. TiO2 layer was coated on the surface of Fe oxide nanofibers using sol-gel process. After the reduction of TiO2 coated Fe oxide nanofibers, Fe nanofibers with a TiO2 coating layer of about 10 nm were successfully obtained. The morphology and structure of fibers were characterized by SEM, TEM, and XRD. In addition, the absorption properties of TiO2 coated Fe nanofibers were measured by network analyzer.

Fabrication and ink-jet patterning of copper nanoparticles with improved dispersion stability.

Copper (Cu) nanoparticles as the metal nanoparticles in the conductive ink were synthesized using electrochemical reaction. This method is characterized as the synthesis process without any metal salts and the post-treatment of washing and drying. It means that it does not need to consider about oxidized and agglomerated metal nanoparticles during the extra treatments. The Cu nanoparticles were synthesized in the various conditions of electrolyte to investigate the mechanism of the synthesis reaction of Cu nanoparticles. And also, the synthesized Cu nanoparticles were controlled the dispersion stability with the addition of dispersion agent such as PVP and Dextran. Finally, it was achieved the ink-jet printed Cu patterns using the synthesized Cu nanoparticles, and examined the morphology of the patterns.

Growth factors for silver nanoplates formed in a simple solvothermal process.

We synthesized both big and ultra-small silver nanoplates through a simple solvothermal process in a common autoclave. Using this approach, we achieved the reduction of silver nitrate in DMF or ethanol in the presence of PVP as a capping agent. The reduction capacity of PVP was also investigated. Growth factors such as the concentration of silver precursor, quantity of capping agent, reaction time, and temperature have been shown to play important roles in the formation of different sizes and shapes of silver nanoplates. The big plates, over 100 nm in edge length, were found mainly in the shape of a connected triangular. Single triangle plates, truncated triangular plates, and hexangular plates were also found under different reaction conditions. The ultra-small silver nanoplates, 20-100 nm in edge length, were successfully extracted from the solution under different centrifugation conditions. The UV-vis spectrum exhibited intense in-plane dipole absorption peaks varying from 470-630 nm, as reflected by the gradual color change of the solution from orange to red, and finally to blue.

Iron nanofibers synthesized by the electrospinning method for use as a GHz band electromagnetic wave absorber.

In this study, we fabricated Fe nanofibers that had a high aspect ratio and were coated by an oxidation protection layer, because electromagnetic properties are affected by the aspect ratio and oxidized layers. PVP/Fe salt nanofibers were prepared by an electrospinning method using an optimized concentration of PVP solution with Iron(lll) nitrate nonahydrate (Fe (NO3)3.9H2O) solution to apply a high voltage. Subsequently, to prepare the Fe nanofibers, the PVP/Fe salt nanofibers were heated up to 600 degrees C in air and reduced to 450 degrees C in H2. The Fe nanofibers were then coated by PVP to prevent re-oxidation. The S-parameter of the prepared Fe nanofibers was measured by a network analyzer, and the power loss was calculated to estimate the EM absorption ability.

Investigation of shape controlled silver nanoplates by a solvothermal process.

The shape control and growth process of silver nanoplates formed by a solvothermal solution approach was investigated by placing a mixed solution containing silver nitrate, poly(vinyl pyrrolidone) (PVP), N,N-dimethylformamide (DMF) or ethanol in an autoclave and examined the products under various reaction conditions. The formation process in ethanol proceeds slowly taking more than 10h to form a suspension of hexangular single plates, which are no more than 50nm in edge length, while the process in DMF is relatively rapid forming large single plates within 2-4h. These separate nanostructures can be fused extensively toward the edge region to form a larger mass. The different sized plates fused together grew to large films or belts but maintained the same thickness. Apart from the reaction time and temperature, appropriate amounts of PVP and DMF were also found to be critical to the shape control. Relatively small triangular plates with average edge lengths of 20-50nm could be separated easily from the product. UV-vis absorption spectroscopy showed that these nanoplates exhibit a strong absorption band from 470 to 630nm. Compared with other methods, our synthesis is mass-productive, rapid and easily operated. The newly formed silver nanoplates may have many potential applications in the biological, chemical, and electrical industries.

The synthesis and characterization of metal nanoparticles using a modified electrolysis method for conductive ink in ink-jet printing technology.

In the ink-jet patterning process, conductive ink composed of metal nanoparticles and solutions, is an important factor for improving properties of printed patterns and processes. In this study, metal (Cu) nanoparticles in conductive ink were synthesized using a modified electrolysis method that extracted to metal nanoparticles from bulk metal plates. The Cu nanoparticles were prepared with a narrow size distribution. The dispersion stability and oxidation properties in conductive inks were also studied. Cu nanoparticles were homogeneous and had a diameter of 15 approximately 20 nm. By addition of PVP, the dispersion and oxidation stability of the metal nanoparticles, which were not oxidized after 2 month, were improved.

Synthesis and electrical property of indium tin oxide nanofibers using electrospinning method.

In this study indium tin oxide (ITO) nanofibers were synthesized using an electrospinning method. The morphological properties of the ITO nanofibers were considered and their specific resistances were measured to determine their applicability as filler for a transparent conducting film. ITO/PVP composite nanofibers were successfully obtained by electrospinning using a precursor solution containing indium nitrate, tin chloride, and poly(vinlypyrrolidone). After the heat treatment of ITO/PVP composite nanofibers at 600 degrees C and 1000 degrees C, ITO nanofibers with an average diameter of about 168 nm and 165 nm were synthesized, respectively.

Production of GDP-L-fucose, L-fucose donor for fucosyloligosaccharide synthesis, in recombinant Escherichia coli.

A recombinant Escherichia coli strain was developed to produce guanosine 5'-diphosphate (GDP)-L-fucose, donor of L-fucose, which is an essential substrate for the synthesis of fucosyloligosaccharides. GDP-D: -mannose-4, 6-dehydratase (GMD) and GDP-4-keto-6-deoxymannose 3, 5-epimerase 4-reductase (WcaG), the two crucial enzymes for the de novo GDP-L-fucose biosynthesis, were overexpressed in recombinant E. coli by constructing inducible overexpression vectors. Optimum expression conditions for GMD and WcaG in recombinant E. coli BL21(DE3) were 25 degrees C and 0.1 mM isopropyl-beta-D-thioglucopyranoside. Maximum GDP-L-fucose concentration of 38.9 +/- 0.6 mg l(-1) was obtained in a glucose-limited fed-batch cultivation, and it was enhanced further by co-expression of NADPH-regenerating glucose-6-phosphate dehydrogenase encoded by the zwf gene to achieve 55.2 +/- 0.5 mg l(-1) GDP-L-fucose under the same cultivation condition.

Fabrication and magnetic characteristics of vertical feco nanowire arrayed in Al2O3 insulator of honeycomb bulkhead structure.

High-density and uniform-sized FeCo alloy nanowires were prepared by electro deposition of Fe2+ and Co2+ into Anodic aluminum oxide (AAO) templates with two different diameters. These templates were fabricated with three-step anodization method. The additional anodization after the 2nd anodization step resulted in the decrease of the thickness of bottom barrier layer. It found an optimum condition to obtain a successful electrodeposition of Fe2+ and Co2+ into AAO templates. The nanowires with the diameters of 25 nm and 80 nm were homogeneously embedded in the AAO templates and their magnetic properties were strongly affected by diameters of nanowire.

Synthesis and electrical properties of (Bi(1/2)Na(1/2))TiO3 (BNT) ferroelectric thin films by liquid sprayed mist chemical vapor deposition technique.

This study aims to synthesize lead-free ferroelectric material, (Bi(1/2)Na(1/2))TiO3 using the Liquid Sprayed Mist Chemical Vapor Deposition (LSMCVD) technique. The mist of precursor solution was vaporized and deposited on two different substrates of Si(100) and (111)Pt/TiO2/SiO2/Si(100) in an oxygen atmosphere. The deposition temperature and time were varied in the range of 400-600 degrees C and 30-90 min. (Bi(1/2)Na(1/2))TiO3 thin film had preferred orientations of (110). The thickness of the thin film deposited was 35-162 nm. The remnant polarization (2Pr) and the dielectric constant were 4.6-16.8 microC/cm2, 325-350, respectively.