Jun-Won Jang

Nano zero-valent iron impregnated on titanium dioxide nanotube array film for both oxidation and reduction of methyl orange.

Here, we demonstrated that nano zero-valent iron (nZVI) impregnated onto self-organized TiO(2) nanotube thin films exhibits both oxidation and reduction capacities in addition to the possible electron transfer from TiO(2) to nZVI. The TiO(2) nanotubes were synthesized by anodization of titanium foil in a two-electrode system. Amorphous TiO(2) (amTiO(2)) nanotubes were annealed at 450 °C for 1 h to produce crystalline TiO(2) (crTiO(2)) nanotubes. The nZVI particles were immobilized on the TiO(2) array film by direct borohydride reduction. Field emission scanning electron microscopy (FE-SEM) analysis of the crystalline TiO(2) nanotube with nZVI (nZVI/crTiO(2)) indicated that the nZVI particles with a mean particle diameter of 28.38 ± 11.81 nm were uniformly distributed onto entire crTiO(2) nanotube surface with a mean pore diameter of 75.24 ± 17.66 nm and a mean length of 40.07 μm. Environmental applicability of our proposed nZVI/TiO(2) nanotube thin films was tested for methyl orange (MO) degradation in the aqueous system with and without oxygen. Since oxygen could facilitate the nZVI oxidation and inhibit electron transfer from crTiO(2) to nZVI surface, MO degradation by nZVI/crTiO(2) in the presence of oxygen was significantly suppressed whereas nZVI/crTiO(2) in the absence of oxygen enhanced MO degradation. MO degradation rate by each sample without oxygen were in following order: nZVI/crTiO(2) (k(obs) = 0.311 min(-1)) > nZVI/amTiO(2) (k(obs) = 0.164 min(-1)) > crTiO(2) (k(obs) = 0.068 min(-1)). This result can be explained with a synergistic effect of the significant reduction by highly-dispersed nZVI particles on TiO(2) nanotubes as well as the electron transfer from the conduction band of crTiO(2) to the nZVI on the crTiO(2) for the degradation of MO.

Carboxymethyl chitosan-modified magnetic-cored dendrimer as an amphoteric adsorbent.

Carboxymethyl chitosan-modified magnetic-cored dendrimers (CCMDs) were successfully synthesized in a three step method. The synthesized samples were characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, thermogravimetry analysis, zeta potential analyzer, X-ray photoelectron spectroscopy, surface area analysis, and Fourier transform infrared spectroscopy. The CCMD exhibited selective adsorption for anionic and cationic compounds at specific pH conditions. With the substitution of amino groups of MD with carboxymethyl chitosan moieties, the adsorption sites for cationic compounds were greatly increased. Since the adsorption onto CCMD was mainly electrostatic interaction, the adsorption of MB and MO was significantly affected by the pHs. The optimal adsorption pH values were 3 and 11 for MO and MB. The maximal adsorption of MO and MB on the CCMD at pH values of 3 and 11 were 20.85mgg(-1) and 96.31mgg(-1), respectively. Reuse of the CCMD as an adsorbent was experimentally tested through adsorption and desorption with simple pH control. More than 99% and 91% of the initial adsorption of MB and MO on the CCMD was maintained with five consecutive recycling.

Iron oxide nanotube layer fabricated with electrostatic anodization for heterogeneous Fenton like reaction

Iron oxide nanotubes (INT) were fabricated with potentiostatic anodization of zero valent iron foil in 1M Na2SO4 containing 0.5wt% NH4F electrolyte, holding the potential at 20, 40, and 60V for 20min, respectively. Field emission scanning electron microscopy and X-ray diffractometry were used to evaluate the morphology and crystalline structure of the INT film. The potential of 40V for 20min was observed to be optimal to produce an optimal catalytic film. Cyanide dissolved in water was degraded through the Fenton-like reaction using the INT film with hydrogen peroxide (H2O2). In case of INT-40V in the presence of H2O2 3%, the first-order rate constant was found to be 1.7×10(-2)min(-1), and 1.2×10(-2)min(-1) with commercial hematite powder. Degradation of cyanide was much less with only H2O2. Therefore, this process proposed in this work can be an excellent alternative to traditional catalysts for Fenton-like reaction.

Fabrication of zero valent iron (ZVI) nanotube film via potentiostatic anodization and electroreduction

Zero valent iron has been successfully used for the degradation of a wide range of contaminants. However, this reaction of using ZVI particle produces a large quantity of iron sludge. To solve the problem, we report the synthesis of self-organized nanoporous zero valent iron film treated with anodization and electro-reduction of iron foil. The iron nanotubes were fabricated in 1 M Na(2)SO(4) + 0.5 wt% NaF electrolyte by supplying constant electric currents of 50 mV/s, and holding the potential at 20, 40 and 60 V for 20 min. Nanoporous shape was produced by anodic oxidation of iron film. After anodizing process, electro-reduction of nanoporous iron film converted crystallization iron oxide to zero valent iron. Electro-reduction process was carried out by electro-reducing with powersupply to and holding the potential at 20 V for 20 min. The surface of iron nanotube film was examined by BET and the thickness of the oxidized films was evaluated by scanning electron microscope (SEM). The crystalline structures of the fabricated films were evaluated using X-ray diffraction (XRD).

Kinetic Studies of Nanoscale Zero-Valent Iron and Geobacter lovleyi for Trichloroethylene Dechlorination

Nanoscale zero-valent iron (nZVI) has recently received much attention for remediation of soil and groundwater contaminated with trichloroethylene (TCE). But there have been many debates on the toxic or inhibitory effects of nZVI on the environment. The objective of this study was to investigate the effects of nZVI on the activity of Geobacter lovleyi and to determine the potent effect of combination of abiotic and biotic treatment of TCE dechlorination. TCE degradation efficiencies of Geobacter lovleyi along with nZVI were more increased than those when nZVI was solely used. The amount of total microbial protein was increased in the presence of nZVI and hydrogen evolved from nZVI was consumed as electron donor by Geobacter lovleyi. In addition, dechlorination of TCE to cis-DCE by Geobacter lovleyi along with nZVI in respiking of exogenous of TCE shows that the reactivity of Geobacter lovleyi was also maintained. These results suggest that the application of Geobacter lovleyi along with nZVI for the dehalorination is beneficial for the enhancement of TCE degradation rate and reactivity of Geobacter lovleyi.

Synthesis of Multi-Terminalized Magnetic-Cored Dendrimer for Adsorption of Chromium and Enhancement of Magnetic Recovery

A chrome absorbent that is useful in rapid magnetic recovery and recycling was developed though a synthesis of MultiTerminalized Magnetic-core Dendrimer (MTMD). Divergence through coprecipitation and rotation growth was used for synthesis. The dendrimer was multi-terminilized through methyl propionate and glutaric acid. The property analysis of the synthesized sample was performed through XRD, FT-IR, TEM, EDS, TGA and zeta potential analyzer. A magnetic-core of MTMD had a magnetite crystal and the size of 4th generation dendrimer was identified to be from 15 nm to 20 nm. Through the analysis of the TGA, the rate of the dendrimer branch for the first generation dendrimer was about 7% and 3% of diminished weight occurred as the generation grows. Also, the potential of the dendrimer when multi-terminalized, had variation from 25.26 mV to -6.53 mV. As a result of MTMD adsorption experiment, it absorbed more than 80% within 5 minutes and indicated absorptivity of 6.308 mg/g. When it was compared with COOH Dendrimer (COOH-D) after magnetic recovery, the recovery time was rapidly reduced by more than half and it could recover 100% within 30 minutes. In case of the regeneration experiment that used chrome, it was identified to maintain the same adsorptivity for four runs.