Dahyun Choi

Stable and magnetically reusable nanoporous magnetite micro/nanospheres for rapid extraction of carcinogenic contaminants from water

We report the growth of porous magnetite microspheres via a template-free hydrothermal route at relatively low temperatures. The growth parameters including the concentration of reactant, reaction temperature and reaction time were examined for the formation of nanopores in the microspheres. Ascorbic acid played a crucial role in the formation of nanoporous microspheres, and also acts as a reducing agent, resulting from Fe3+ conversion into Fe2+ iron during the hydrothermal process. The resulting samples were used to remove acid orange 7 (AO7) and Cr(VI) from water at room temperature via adsorption. The maximum AO7 adsorption capacity calculated from the Langmuir–Freundlich model was found to be 69.13 mg g−1 for an optimum porous structure, which is significantly greater than that of structures formed without ascorbic acid (i.e., 4.61 mg g−1). Simultaneously, the Cr(VI) removal performance of the porous structure (i.e., 96.98 mg g−1) was found to be superior than that of pristine structure (i.e., 10.67 mg g−1). The enhanced removal activity was attributed to the existence of a large number of nanopores, resulting in a large specific surface area of 87.36 m2 g−1. Recycling tests were carried using a magnetic field to separate the powder samples from water, and the samples were found to be stable for up to three cycles. These results show that these porous microspheres have potential applications in cost-effective wastewater treatment.

Oxidation Prevention Properties of Reduced Graphene Oxide Mixed with 1-Octanethiol-Coated Copper Nanopowder Composites

1-Octanethiol-coated Cu nanoparticles were mixed with reduced graphene oxide rGO to fabricate Cu nanoinks with enhanced oxidation prevention. Graphene oxide GO was synthesized using modified Hummer’s method and rGO was reduced from GO using hydrazine hydrate. Copper nanoinks were fabricated with varying concentrations of rGO Cu : rGO ratios of 100 : 1, 500 : 1, and 1000 : 1 wt.%. The coating layers on the copper nanoparticles and rGO were observed using transmission electron microscopy and characterized by X-ray photoemission spectroscopy, X-ray diffraction, and Raman spectroscopy. It was observed that surface roughness increased as the concentration of rGO in Cu patterns increased, and an optimized Cu : rGO weight ratio of 1,000 : 1 was established. After sintering, the electrical properties and corrosion resistance of copper patterns both with and without rGO were measured and monitored for 200 days. The copper pattern with rGO Cu : rGO = 1,000 : 1 was found to maintain its initial resistivity 1.63 × 10−7 Ω·m for 150 days. Corrosion tests were conducted to confirm the oxidation prohibition of rGO. The resistance polarization Rp of the copper pattern was measured to be 1.5 times higher than that of the copper pattern without rGO. Thus, rGO was shown to prevent oxidation and improve the conductivity of copper patterns.

Fabrication of high quality carbonaceous coating on Cu nanoparticle using poly(vinyl pyrrolidone) and its application for oxidation prevention

A novel method of carbonaceous coating on the surface of copper particles was developed through a chemical vapor deposition (CVD) process to prevent the oxidation of copper nanoparticles (CNPs). The types of poly(vinyl pyrrolidone) (PVP) used were K-12 (M W 3,500) and K-30 (M W 45,000). The amounts of PVP used ranged from 10 to 50 wt %. Additionally, processing temperatures of 900 and 875 °C were tested and compared. The optimum CVD process conditions for the carbonaceous coating were as follows: 875 °C processing temperature, 50 wt % K12 PVP solution, and gas conditions of . The resistivity change in the fabricated copper pattern was confirmed that the initial resistivity value of the ink with a mixing ratio of carbonaceous-coated CNPs to 1-octanethiol-coated CNPs of (w/w) maintained its initial resistivity value of 2.93 × 10−7 Ωm for more than 210 days.