Jungho Ryu

Titania nanofibers as a photo-antenna for dye-sensitized solar hydrogen

Directionally grown TiO(2) nano-architectures can serve as effective platforms for photogenerated charges to flow vectorially through the architecture framework, promising an unexpectedly high efficiency. This study demonstrates that directionally aligned TiO(2) nanofibers (TNF) obtained via a simple rearrangement of randomly scattered TiO(2) nanoparticles (TNP) exhibit significantly enhanced activity in terms of hydrogen production from water under visible light (λ > 420 nm). It has been found that Eosin Y (EY)-sensitized hydrogen production with TNF is greater than those with TNP and commercial TiO(2) samples (Degussa P25 and Hombikat UV-100) by a factor of 7 and >140, respectively, in the presence of triethanolamine (TEOA) as an electron donor. The annealing of TNF at elevated temperatures reduces the amount of H(2) produced and changes various physicochemical properties. Attempts have been made to find correlation factors between hydrogen production and reaction parameters (e.g., pH-dependent EY adsorption, surface area, pore size, particle size, and anatase-to-rutile ratio), none of which have provided an apparent correlation. It was suggested that the interparticle electron transfer is facilitated when TiO(2) nanoparticles are physically interconnected, and TNF might work as a robust photo-antenna for efficiently collecting the photogenerated electrons. The photocurrent measurements in visible light-irradiated EY/TiO(2) suspensions indicate that the photocurrent of TNF is 50% higher than that of TNP, supporting the photo-antenna mechanism of TNF.

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.

A Synergistic Effect of Surfactant and ZrO2 Underlayer on Photocurrent Enhancement and Cathodic Shift of Nanoporous Fe2O3 Photoanode.

Augmenting the donor density and nanostructure engineering are the crucial points to improve solar water oxidation performance of hematite (α-Fe2O3). This work addresses the sluggish water oxidation reaction associated with hematite photoanode by tweaking its internal porosity. The porous hematite photoanodes are fabricated by a novel synthetic strategy via pulse reverse electrodeposition (PRED) method that involves incorporation of a cationic CTAB surfactant in a sulfate electrolyte and spin-coated ZrO2 underlayer (UL) on FTO. CTAB is found to be beneficial in promoting the film growth rate during PRED. Incorporation of Zr4+ ions from ZrO2 UL and Sn4+ ions from FTO into the Fe2O3 lattice via solid-state diffusion reaction during pertinent annihilation of surfactant molecules at 800 °C produced internally porous hematite films with improved carrier concentration. The porous hematite demonstrated a sustained photocurrent enhancement and a significant cathodic shift of 130 mV relative to the planar hematite under standard illumination conditions (AM 1.5G) in 1 M NaOH electrolyte. The absorption, electrochemical impedance spectroscopy and Mott-Schottky analyses revealed that the ZrO2 UL and CTAB not only increased the carrier density and light harvesting but also accelerated the surface oxidation reaction kinetics, synergistically boosting the performance of internally porous hematite photoanodes.

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.