Ju-Hyeon Lee

Photocatalytic ZnO nanopowders prepared by solution combustion method for noble metal recovery

Nano-sized ZnO powder was synthesized by solution combustion method (SCM). Using this ZnO nanopowder as a photocatalyst, it was tried to recover silver from the silver-plating wastewater that was discharged by noble metal plating industries. The photocatalytic efficiency of ZnO nanopowder, as one of optical properties, was compared with other photocatalysts such as commercial TiO2 and commercial ZnO. The ZnO nanopowder showed three folds higher photocatalytic efficiency than any other commercial photocatalysts. Other electro-optical measurements such as photoluminescence (PL) measurement, electrical resistivity and carrier concentration measurement also showed very consistent results. The recovery of gold from gold plating wastewater was also tried. The recovery efficiency was improved by about 25% by adding methanol as a scavenger to the gold plating wastewater. It took 45 min to completely recover gold from the wastewater.

Rapid Ag recovery using photocatalytic ZnO nanopowders prepared by solution-combustion method

The study of photocatalytic reactions is a recently emerging area out of the field of catalytic chemistry. In general, photocatalytic reaction is an interaction between molecules and surfaces including electron transfer between molecules and catalysts. Semiconductors are usually used for photocatalysts because their carrier concentration can be controlled [1, 2]. Recent studies have mainly concentrated on environmental problems such as purification of contaminated water or air [3, 4]. Semiconductors for photocatalytic reactions should have characteristics such as high optical activity, high optical stability, high sensitivity for UV-visible light and low fabrication cost [2, 5]. Many researchers have paid attention to oxide semiconductors because of their wide band gap energy and ease of handling [6–9]. Nano-sized particles have different physical and chemical properties compared to bulk materials. High catalyst activity may be expected because of their large surface area and different surface properties, such as surface defects, when these nano-sized particles are used as catalysts. The fabrication of nano-sized particles with high stability and dispersibility in solution is essential to obtain high photocatalytic activity [10, 11]. In this paper, synthesis of ZnO was tried to obtain the nano-sized semiconductor particles for photocatalytic application. Two methods are generally used to obtain such ZnO powder. One is vapor method and the other is sol-gel method. In the case of vapor method, the resulting powders contain agglomerates rather than separated particles because it is very difficult to control the reaction conditions during the process. This means that the vapor method is not a satisfactory method to obtain nano-sized ZnO powders. On the other hand, the sol-gel method could provide uniform ZnO powders. However, it is required to control the reaction condition strictly because of the violent hydrolysis reaction in the air during synthetic process. In addition, this method is not attractive because metal alkoxide as a starting source is very expensive. This is why the method is still not commercialized but is being tried only in a small laboratory scale [12, 13]. Park et al. proposed the solution combustion method to synthesize highly pure and fine ceramic powders. Using this method, the heating and evaporation of metal nitrate solution with glycine results in self-firing and generates intense heat by exothermic reaction [14]. This intense heat is used to synthesize the powders. In this study, nano-sized ZnO powders were prepared using this solution combustion method. Their characteristics and photocatalytic efficiency were also investigated. Zn(OH)2 (Junsei, Japan) powder solved in nitric acid was used as the starting material (oxidant), and glycine(H2NCH2COOH, Yakuri pure chemicals co. Ltd, Japan) was used as a fuel, in order to synthesize ZnO powder. The starting material was dissolved in distilled water in a beaker. Then the glycine was added to the starting solution in the beaker. The solution was then heated on a hot plate with stirring. As the distilled water evaporated, the solution became viscous and generated small bubbles. The nitric acid group (NO3 ) reacted with the fuel and intense heat was generated (the temperature rises to 1500–1800 ◦C). This high temperature resulted in a high pressure, which leads to an explosion. ZnO powder was formed by this high temperature and high pressure and was collected in a collector that was placed above the beaker. In this paper, this process is referred to the solution combustion method. In general glycinenitrate process (GNP), oxide powders are synthesized adding the fuel in equilibrium state (fuel/oxidant = 1). However, in this study after calculating the oxidation number by the general GNP method, ZnO powder was prepared by fuel lean state considering the vapor pressure of Zn or ZnO. Five different ZnO powders were prepared with the variation of the fuel/oxidant ratio. X-ray diffractometer (XRD) measurement was performed to examine the crystalline state of the prepared ZnO powder. As shown in Fig. 1, single phase ZnO was obtained by the above method; the ZnO powder with fuel/oxidant ratio of 0.8 showed the highest XRD peaks and hence was assumed to be the most crystalline. As shown in Fig. 2, the photoluminescence spectra of commercial ZnO powder showed two peaks: one is in the vicinity of 500 nm, and the other one is near 400 nm. The peak near 500 nm probably came from the energy transition between O vacancy level and Zn vacancy level as shown in Fig. 3. The UV peak near 400 nm might be from band to band transition. However, ZnO powder synthesized by the solution combustion method showed only one sharp peak near 390 nm that was slightly shifted to UV side. This peak is equivalent to the energy gap of ZnO (∼3.2 eV). These results indicate

Electrical and magnetic properties of La0,7Ca0,3MnO3 films prepared by RF magnetron sputtering method for colossal magnetoresistance applications

Abstract La 0.7 Ca 0.3 MnO 3 powders were prepared by solution combustion method. The electrical and magnetic properties of their thin films were investigated for colossal magnetoresistance applications. Sputter targets were prepared using the powders to deposit La 0.7 Ca 0.3 MnO 3 thin films on SiO 2 buffer layered Si substrate by RF magnetron sputtering. The particles were nano-sized and their specific surface area was 49.44 m 2 /g. This fact resulted in the decrease of sintering temperature by 300 °C. It was easy to get high purity La 0.7 Ca 0.3 MnO 3 powders with perovskite structure. The maximum magnetoresistance ratio of 1210% was observed at 96 K. In this study, the La 0.7 Ca 0.3 MnO 3 films showed the colossal magnetoresistance properties, even though the films were deposited on the amorphous SiO 2 substrate and non-epitaxially. This is probably due to the high quality single phase of the thin film.

The effect of Pt impurity at the NiCr/Si interface on the growth of amorphous Cr layer during annealing

Abstract Two sets of samples were prepared; one without and the other with Pt impurity at NiCr/Si interfaces. Following annealing at 475 °C for various time periods, in both cases Cr-rich amorphous interfacial layers form between unreacted NiCr layers and Ni silicide layers. The Pt impurity moves with the amorphous layer (a-layer) and suppresses the growth of the a-layer. The Pt impurity presumably acts as a seed for early nucleation for crystallization of the a-layer. Thus, the segregated a-layers of the samples with Pt impurity (Pt impurity samples) are thinner and thermally less stable than those of the samples without Pt impurity (Pt-free samples).

Co기 초합금 ECY768에서 응고 조직 및 탄화물 형성 거동

【Directional solidification experiments were carried out at 0.5-150

A possible method for large area deposition of a-Si:H thin films using electron cyclotron resonance plasma-enhanced chemical vapor deposition

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A Study on the Fabrication of STS 316L Films by Ion Beam Deposition with Ion Source

/s in the Co-base superalloy ECY 768. As increasing solidification rate, the dendrite length increased and it reached the maximum at 150

Characteristics of La0.7Ca0.3MnO3 Powders Prepared by the Solution Combustion and Solid State Reaction Methods for Colossal Magnetoresistance Applications

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Noncontact sensing of electric potential using electroluminescence effects

/s, where the tip temperature is close to the liquidus. The liquidus and eutectic temperatures could be estimated by comparing the dendrite lengths and the temperature gradients at the solid/liquid interface and those were estimated as

Photocatalytic degradation of TOC from aqueous phenol solution using solution combusted ZnO nanopowders

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