Byoung-Gyu Kim

Hydrothermal synthesis of titanate nanotubes from TiO2 nanorods prepared via a molten salt flux method as an effective adsorbent for strontium ion recovery

Hydrated titanate nanotubes (TNTs) were hydrothermally synthesized at 160 °C over reaction times of 6–72 h from molten salt TiO2 nanorods (NRs). Most of the TiO2 NRs were transformed into tubular structure within 24–72 h. The samples synthesized over short reaction times (6–24 h) formed admixtures of TNT and untransformed TiO2 NR residues. Strontium ion (Sr2+) adsorption by the as-prepared samples was quantified. The surface area of the TNTs increased the Sr2+ ion adsorption relative to that of the TiO2 NRs. The mechanism underlying Sr2+ adsorption relied on an ion exchange reaction between Sr2+ ions in the stock solution and Na+ ions in an interlayer of the TNTs. TEM, EDAX, and XAFS analysis confirmed that Sr2+ adsorption and Na+ release occurred at the interlayer of the TNT-2D. The maximum adsorption capacity of the TNTs was calculated using the Langmuir equation. TNT (TNT-2D) sample synthesized over 48 h displayed the highest adsorption capacity (113.6 mg g−1), with a Sr2+ uptake having a nearly 99% efficiency.

Adsorption of rare earth metals (Sr2+ and La3+) from aqueous solution by Mg-aminoclay–humic acid [MgAC–HA] complexes in batch mode

The recoveries of Sr2+ and La3+ as rare earth metals (REMs) were studied using Mg-aminoclay–humic acid [MgAC–HA] complexes prepared by self-assembled precipitation due to electrostatic attraction between water-solubilized [MgAC] and water-soluble [HA], and were compared with the recoveries using [MgAC] and [HA]. The influences of pH and Sr2+ and La3+ concentrations in single and binary systems were evaluated. The adsorbents before/after adsorption of Sr2+ and La3+ were characterized by (1) scanning electron microscopy (SEM) micrographs, (2) Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) spectra, and by (3) powder X-ray diffraction (XRD) pattern analysis. After fitting Langmuir and Freundlich isotherms, the Langmuir model was found to present better matches than the Freundlich one: the maximum adsorption capacities of Sr2+ and La3+ were 0.12 mg g−1 and 4.76 mg g−1 in the binary system at room temperature, and the optimal recovery pH was ∼8.0. In practical seawater meanwhile, the recoveries of Sr2+ and La3+ by [MgAC–HA] complexes were the highest in the binary system. However, with further recycling runs, the recoveries of Sr2+ and La3+ were critically diminished due to disassembly in [MgAC–HA] complexes under acidic conditions. Thus, for the purposes of industrial application, we are currently pursuing the enhancement of recyclability for [MgAC–HA] complexes by their encapsulation or direct hydrogel formation.

Synthesis of Li1.6(MnM)1.6O4 (M=Cu, Ni, Co, Fe) and Their Physicochemical Properties as a New Precursor for Lithium Adsorbent

New precursors as a Li adsorbent, Li1.6(MnM)1.6O4 (M=Cu, Ni, Co, Fe), were synthesized by hydrothermal method and their physicochemical properties were discussed. XRD and HRTEM results revealed that the original spinel structure was stabilized by cobalt-doping while Cu-, Ni- and Fe-doping led to structural changes. Such a structural stabilization by Cobalt-doping was maintained after lithium leaching by acid treatment. Li absorption efficiency from seawater was significantly enhanced by using the Cobalt-doped spinel manganese oxide, Li1.6(MnCo)1.6O4, compared to the commercially available Li1.33Mn1.67O4; the adsorbed amount of Li from 1g-adsorbent was 35 and 16 mg by Li1.6(MnCo)1.6O4, and Li1.33Mn1.67O4, respectively.