Hyemin Kim

In-situ one-step synthesis of carbon-encapsulated naked magnetic metal nanoparticles conducted without additional reductants and agents.

C-encapsulated highly pure Ni, Co, and Fe magnetic nanoparticles (MNPs/C) were synthesized by an innovative one-step in-situ plasma in liquid method (solution plasma processing, SPP) without any additional reductants, agents, or treatment. Successful encapsulation of MNPs was demonstrated by using inductively coupled plasma-atomic emission spectrometry and cyclic voltammetry techniques. The obtained X-ray diffraction patterns and transmission electron microscopy images corresponded to MNPs with average diameters of 5 nm and good crystalline structure. The C capsules with spherical shapes (containing onion-like layers) were characterized by uniform sizes (ranging from 20 nm to 30 nm) and chain-like morphologies. The synthesized MNPs/C exhibited superparamagnetic properties at room temperature and might be utilized in data storage, biomedical, and energy applications since various NPs (including bimetallic ones) could be easily prepared by changing working electrodes. This study shows the potential of SPP to be a candidate for the next-generation synthesis method of NPs/C.

Synthesis of colloidal MnO2 with a sheet-like structure by one-pot plasma discharge in permanganate aqueous solution

Stable colloidal MnO2—consisting of MnO2 with a sheet-like structure—was synthesized by solution plasma process (SPP). The synthesis was completed in one-step by discharging the plasma in potassium permanganate (KMnO4) aqueous solution without using any dispersants or stabilizers. An alteration of the manganese oxide oxidation state, from MnO4− to MnO2 as a function of the discharge time, was investigated by UV-vis spectroscopy. Morphology and elemental constituents were observed by TEM and EDS mapping. Results indicated that the discharge time was an important feature for the formation of MnO2 in the SPP system. Specifically at neutral pH (pH = 7), MnO4− was completely reduced to MnO2 within a discharge time of 18 min. After that the obtained MnO2 was converted rapidly to Mn2+. To better understand the possible pathways of MnO2 formation by the SPP, we compared aspects of the reaction under different pH conditions. Formation of MnO2 under additional, controlled pH conditions, i.e. 2 and 12, was studied. Results suggested that hydrogen species played a key role for the reduction of MnO4− in the water-based SPP system. In comparison to the existing routes for the synthesis of MnO2 nanosheets with a single or low number of layers, the SPP holds excellent promise as an effective alternative means regarding its simplicity, time-energy preserving, and scalability.

A simple synthesis method for nanostructured Co-WC/carbon composites with enhanced oxygen reduction reaction activity

Abstract Co nanoparticles (Co NPs) and nanoscale tungsten carbide (WC) are successfully synthesized simultaneously with mesoporous structured carbon black (C) using an innovative simple method, which is known as solution plasma processing (SPP), and NPs are also loaded onto carbon black at the same time by SPP. The introduction of Co NPs led to not only superior oxygen reduction reaction (ORR) activity in terms of onset potential and peak potential, but also to a more efficient electron transfer process compared to that of pure WC. Co-WC/C also showed durability for long-term operation better than that of commercial Pt/C. These results clearly demonstrate that the presence of Co NPs significantly enhanced the ORR and charge transfer number of neighboring WC NPs in ORR activities. In addition, it was proved that SPP is a simple method (from synthesis of NPs and carbon black to loading on carbon black) for the large-scale synthesis of NP-carbon composite. Therefore, SPP holds great potential as a candidate for next-generation synthetic methods for the production of NP-carbon composites.

One-pot synthesis of purple benzene-derived MnO 2 -carbon hybrids and synergistic enhancement for the removal of cationic dyes

MnO2-carbon hybrid (MnO2-C-PBz) was simultaneously synthesized by a one-step solution plasma process (SPP) using a single precursor referred to as “purple benzene”, which was derived from the K+(dicyclohexano-18-crown-6 ether) complex. To clarify the synergistic effects on the cationic dye removal, MnO2-free carbon and carbon-free MnO2 samples were concurrently investigated. The results of adsorption for cationic dyes (methylene blue (MB) and rhodamine B (Rh B)) and anionic dye (methyl orange (MO)) revealed remarkably high affinity for cationic dyes. In particular, MnO2-C-PBz exhibited the highest adsorption capacity for MB, i.e., ~3 times greater than that of the others. In addition, MnO2-C-PBz exhibited a rapid, high decolorization ability at C0 = 10 mg L−1 (within a few seconds, ~99%) and at C0 = 100 mg L−1 (within 30 min, ~81%), and the theoretical maximum monolayer adsorption capacity was 357.14 mg g−1 as calculated from the Langmuir adsorption isotherm equation. Furthermore, compared with carbon-free MnO2, MnO2-C-PBz exhibited quite a good cyclic stability. We expect that our findings give rise to the understanding of the synergistic effects of MnO2-carbon hybrid, as well as role of each components for the cationic dye adsorption, and may open an innovative synthesis approach to inorganic-organic hybrid materials.

Adhesion and Corrosion Resistance of Mg(OH) 2 Films Prepared by Application Principle of Cathodic Protection in Natural Seawater

Cathodic current on a metal tends to increase the neighboring to the metal surface, especially during electro-deposition in seawater. The increased pH at metal/seawater interface results in precipitation of brucite crystal structure- as following formula; , that is typical mechanism of the main calcareous deposits-compound in electro deposited coating films. In this study, the effects of anode and current density on deposition rate, composition structure and morphology of the deposited films were systematically investigated by scanning electron microscopy(SEM) and x-ray diffraction(XRD), respectively in order to overcome the problems such as deposition rate and a weak adhesion between deposit film and metal surface. The adhesion and corrosion resistance of the coating films were also evaluated by anodic polarization test. The electro-deposited film formed by using AZ31-Mg anode had the most appropriate physical properties. Weight gain of electro-deposit films increased with increasing cathodic current. Electro-deposit prepared at current density shows better adhesion than that formed at .