• Proceedings of the Korean Magnestics Society Conference
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• 한국자기학회 2015년도 자성 및 자성재료 국제학술대회
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• pp.149-149
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• 2015

• Bulletin of the Korean Chemical Society
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• 제28권11호
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• pp.2056-2060
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• 2007

A successful combination of “oxygen-assisted chemical vapor deposition (CVD) process” and Co catalyst nanoparticles to grow highly pure single walled carbon nanotubes (SWNTs) was demonstrated. Recently, it was reported that addition of small amounts of oxygen during CVD process dramatically increased the purity and yield of carbon nanotubes. However, this strategy could not be applied for discrete Fe nanoparticle catalysts from which appropriate yields of SWNTs could be grown directly on solid substrates, and fabricated into field effect transistors (FETs) quite efficiently. The main reason for this failure is due to the carbothermal reduction which results in SiO2 nanotrench formation. We found that the oxygen-assisted CVD process could be successfully applied for the growth of highly pure SWNTs by switching the catalyst from Fe to Co nanoparticles. The topological morphologies and p-type transistor electrical transport properties of the grown SWNTs were examined by using atomic force microscope (AFM), Raman, and from FET devices fabricated by photolithography.

• Journal of Soil and Groundwater Environment
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• 제25권1호
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• pp.95-105
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• 2020

In this study, iron nanoparticles impregnated hydrochar (FeNPs@HC) was synthesized using lignocellulosic waste and simple one-pot synthetic method. During hydrothermal carbonization (HTC) process, the mixture of lignocellulosic waste and ferric nitrate (0.1~0.5 M) as a precursor of iron nanoparticles was added and heated to 220℃ for 3 h in a teflon sealed autoclave, followed by calcination at 600℃ in N₂ atmosphere for 1 h. For the characterization of the as-prepared materials, X-ray diffraction (XRD), cation exchange capacity (CEC), fourier transform infrared spectrometer (FT-IR), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), Energy Dispersive X-ray Spectroscopy (EDS) were used. The change of Fe(III) concentration in the feedstock influenced characteristics of produced FeNPs@HC and removal efficiency towards As(V) and Pb(II). According to the Langmuir isotherm test, maximum As(V) and Pb(II) adsorption capacity of Fe_0.25NPs@HC were found to be 11.81 and 116.28 mg/g respectively. The results of this study suggest that FeNPs@HC can be potentially used as an adsorbent or soil amendment for remediation of groundwater or soil contaminated with arsenic and cation heavy metals.

• Journal of Powder Materials
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• 제15권2호
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• pp.148-155
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• 2008

Nano magnetite particles have been prepared by two step reaction consisting of urea hydrolysis and ammonia addition at certain ranges of pH. Three different concentrations of aqueous solution of ferric ($Fe^{3+}$) and ferrous ($Fe^{2+}$) chloride (0.3 M-0.6 M, and 0.9 M) were mixed with 4 M urea solution and heated to induce the urea hydrolysis. Upon reaching at a certain pre-determined pH (around 4.7), 1 M ammonia solution were poured into the heated reaction vessels. In order to understand the relationship between the concentration of the starting solution and the final size of magnetite, in-situ pH measurements and quenching experiments were simultaneous conducted. The changes in the concentration of starting solution resulted in the difference of the threshold time for pH uprise, from I hour to 3 hours, during which the akaganeite (${\beta}$-FeOOH) particles nucleated and grew. Through the quenching experiment, it was confirmed that controlling the size of ${\beta}$-FeOOH and the attaining a proper driving force for the reaction of ${\beta}$-FeOOH and $Fe^{2+}$ ion to give $Fe_3O_4$ are important process variables for the synthesis of uniform magnetite nanoparticles.

• Journal of the Korean institute of surface engineering
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• 제50권4호
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• pp.296-300
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• 2017

NiO nanofibers with Au nanoparticles were synthesized by sol-gel and electrospinning techniques, in which the reduction process by ultraviolet exposure is included for the growth of Au nanoparticles in the electrospinning solution. FE-SEM(Field Emission Scanning Electron Microscopy), TEM(Transmission Electron Microscopy) revealed that the synthesized nanofibers had the diameter of approximately 200 nm. X-ray diffraction showed the successful formation of Au-decorated NiO nanofibers. Gas sensing tests of Au-decorated NiO nanofibers were performed using reducing gases of CO, and $C_6H_6$, $C_7H_8$, $C_2H_5OH$. Compared to as-synthesized NiO nanofibers, the response of Au-loaded NiO nanofibers to CO gas was found to be about 3.4 times increased. On the other hand, the response increases were only 1.1-1.3 times for $C_6H_6$, $C_7H_8$, and $C_2H_5OH$.

• Applied Chemistry for Engineering
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• 제30권2호
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• pp.151-154
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• 2019

We report the effective fabrication processes for more practical monolith catalysts consisting of washcoated alumina on a cordierite honeycomb monolith (CHM) and iron oxides nanoparticles in the alumina prepared by a simple dry coating method. It is confirmed that iron oxide nanoparticles were well deposited into the mesopore of washcoated alumina which is formed on the corner wall of honeycomb channel, and the effect of annealing temperature was evaluated for carbon monoxide oxidation catalysts. $Fe_2O_3/{\gamma}-Al_2O_3/CHM$ catalysts annealed at $350^{\circ}C$ exhibited the most enhanced catalytic activity, 100% conversion efficiency at more than $200^{\circ}C$ operating temperature.

• Journal of Microbiology and Biotechnology
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• 제26권5호
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• pp.829-836
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• 2016

Penicillin G acylase (PGA) was immobilized on magnetic Fe₃O₄@chitosan nanoparticles through the Schiff base reaction. The immobilization conditions were optimized as follows: enzyme/support 8.8 mg/g, pH 6.0, time 40 min, and temperature 25 ℃. Under these conditions, a high immobilization efficiency of 75% and a protein loading of 6.2 mg/g-support were obtained. Broader working pH and higher thermostability were achieved by the immobilization. In addition, the immobilized PGA retained 75% initial activity after ten cycles. Kinetic parameters V_max and K_m of the free and immobilized PGAs were determined as 0.113 mmol/min/mg-protein and 0.059 mmol/min/mg-protein, and 0.68 mM and 1.19 mM, respectively. Synthesis of amoxicillin with the immobilized PGA was carried out in 40% ethylene glycol at 25 ℃ and a conversion of 72% was obtained. These results showed that the immobilization of PGA onto magnetic chitosan nanoparticles is an efficient and simple way for preparation of stable PGA.

• Journal of Magnetics
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• 제22권2호
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• pp.169-174
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• 2017

In this work, lithium ferrite ($Li_{0.5}Fe_{2.5}O_4$) nanoparticles were prepared via mechanochemical processing and subsequent heat treatment at a relatively low ($600^{\circ}C$) calcining temperature. The raw materials used were high purity $Fe_2O_3$ and $Li_2CO_3$ that were milled for between 2 and 20 h. The milled powders were then calcined at temperatures of 500 and $600^{\circ}C$ for 5 h in air. XRD results show that optimum conditions to obtain single phase lithium ferrite nanoparticles with a mean crystallite size of about 23 nm, using Scherrer's formula, are 10 h milling and calcination at $600^{\circ}C$. Saturation magnetization and coercivity of the single phase Li ferrite nanoparticles are 44.6 emu/g and 100 Oe respectively, which are both smaller than those of the bulk Li ferrite. The Curie temperature of the single sample was determined by a Faraday balance, which is $578^{\circ}C$ and smaller than that of bulk Li ferrite.

• Journal of the Korean Ceramic Society
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• 제50권3호
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• pp.231-237
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• 2013

Thermodynamic modeling of the $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ complex ferrite system has been adopted as a rational approach to establish routes to better synthesis conditions for pure phase $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ complex ferrite. Quantitative analysis of the different reaction equilibria involved in the precipitation of $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ from aqueous solutions has been used to determine the optimum synthesis conditions. The spinel ferrites, such as magnetite and substitutes for magnetite, with the general formula $MFe_2O_4$, where M= $Fe^{2+}$, $Co^{2+}$, and $Ni^{2+}$ are prepared by coprecipitation of $Fe^{3+}$ and $M^{2+}$ ions with a stoichiometry of $M^{2+}/Fe^{3+}$= 0.5. The average particle size of the as synthesized $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$, measured by transmission electron microscopy (TEM), is 14.2 nm, with a standard deviation of 3.5 nm the size when calculated using X-ray diffraction (XRD) is 16 nm. When $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ ferrite is annealed at elevated temperature, larger grains are formed by the necking and mass transport between the $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ ferrite nanoparticles. Thus, the grain sizes of the $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ gradually increase as heat treatment temperature increases. Based on the results of Thermogravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC) analysis, it is found that the hydroxyl groups on the surface of the as synthesized ferrite nanoparticles finally decompose to $Ni_{0.5}Zn_{0.4}Cu_{0.1}Fe_2O_4$ crystal with heat treatment. The results of XRD and TEM confirmed the nanoscale dimensions and spinel structure of the samples.

• Clean Technology
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• 제21권1호
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• pp.39-44
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• 2015

This study investigated the effects of six metal oxide nanoparticles (NPs: CuO, NiO, TiO₂, Fe₂O₃, Co₃O₄, ZnO) on seed germination and germination index (G.I) for five types of seeds: Brassica napus L., Malva verticillata L., Brassica olercea L., Brassica campestris L., Daucus carota L. NPs of CuO, ZnO, NiO show significant toxicity impacts on seed activities [CuO (6-27 mg/L), ZnO (16-86 mg/L), NiO (48-112 mg/L)], while no significant effects were observed at > 1000 mg/L of TiO₂, Fe₂O₃, Co₃O₄. Tested five types of seed showed different sensitivities on seed germination and root activity, especially on NPs of CuO, ZnO, NiO. Malva verticillata L. seed was highly sensitive to toxic metal oxide NPs and showed following EC₅₀s : CuO 5.5 mg/L, ZnO 16.4 mg/L, NiO 53.4 mg/L. Mostly following order of toxicity was observed, CuO > ZnO > NiO > Fe₂O₃ ≈ Co₃O₄ ≈ TiO₂, where slightly different toxicity order was observed for carrot, showing CuO > NiO ≈ ZnO > Fe₂O₃ ≈ Co₃O₄ ≈ TiO₂.