N-doped Na₂Ti₆O₁₃@TiO₂ (denoted as N-NTO@TiO₂) composites are successfully synthesized using a simple two-step process: 1) ball-milling of TiO₂ with Na₂CO₃ followed by heat treatment at 900°C; 2) mixing of the prepared Na₂Ti₆O₁₃ with titanium isopropoxide and calcining with urea at 500°C. The prepared composites are characterized using XRD, SEM, TEM, FTIR, and BET. The N-NTO@TiO₂ composites exhibit well-defined crystalline and anatase TiO₂ with exposed {101} facets on the external surface. Moreover, dopant N atoms are uniformly distributed over a relatively large area in the lattice of the composites. Under visible light irradiation, ~51% of the aqueous methylene blue is photodegraded by N-NTO@TiO₂ composites, which is higher than the values shown by other samples because of the coupling effects of the hybridization of NTO and TiO₂, N-doping, and presence of anatase TiO₂ with exposed {101} facets.

In this work, TiO₂ 3D nanostructures (TF30) were prepared via a facile wet chemical process using ammonium hexafluorotitanate. The synthesized 3D TiO₂ nanostructures exhibited well-defined crystalline and hierarchical structures assembled from TiO₂ nanorods with different thicknesses and diameters, which comprised numerous small beads. Moreover, the maximum specific surface area of TiO₂ 3D nanostructures was observed to be 191 m²g^-1, with concentration of F ions on the surface being 2 at%. The TiO₂ 3D nanostructures were tested as photocatalysts under UV irradiation using Rhodamine B solution in order to determine their photocatalytic performance. The TiO₂ 3D nanostructures showed a higher photocatalytic activity than that of the other TiO₂ samples, which was likely associated with the combined effects of a high crystallinity, unique features of the hierarchical structure, a high specific surface area, and the advantage of adsorbing F ions.

A facile one-pot wet chemical process to prepare pure anatase TiO₂ hollow structures using ammonium hexafluorotitanate as a precursor is developed. By defining the formic acid ratio, we fabricate TiO₂ hollow structures containing fluorine on the surface. The TiO₂ hollow sphere is composed of an anatase phase containing fluorine by various analytical techniques. A possible formation mechanism for the obtained hollow samples by self-transformation and Ostwald ripening is proposed. The TiO₂ hollow structures containing fluorine exhibits 1.2 - 2.7 times higher performance than their counterparts in photocatalytic activity. The enhanced photocatalytic activity of the TiO₂ hollow structures is attributed to the combined effects of high crystallinity, specific surface area (62 m²g^-1), and the advantage of surface fluorine ions (at 8%) having strong electron-withdrawing ability of the surface ≡ Ti-F groups reduces the recombination of photogenerated electrons and holes.

We report a method for preparing rare earth oxides (Re_xO_y) from the recycling process for spent Ni-metal hydride (Ni-MH) batteries. This process first involves a leaching of spent Ni-MH powders with sulfuric acid at 90°C, resulting in rare earth precipitates (i.e., NaRE(SO₄)₂·H₂O, RE = La, Ce, Nd), which are converted into rare earth oxides via two different approaches: i) simple heat treatment in air, and ii) metathesis reaction with NaOH at 70°C. Not only the morphological features but also the crystallographic structures of all products are systematically investigated using field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD); their thermal behaviors are also analyzed. In particular, XRD results show that some of the rare earth precipitates are converted into oxide form (such as La₂O₃, Ce₂O₃, and Nd₂O₃) with heat treatment at 1200°C; however, secondary peaks are also observed. On the other hand, rare earth oxides, Re_xO_y can be successfully obtained after metathesis of rare earth precipitates, followed by heat treatment at 1000°C in air, along with a change of crystallographic structures, i.e., NaRE(SO₄)₂·H₂O → RE(OH)₃ →Re_xO_y.

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• Recycling of Rechargeable Batteries: Insights from a Bibliometrics‐Based Analysis of Emerging Publishing and Research Trends
  Jiao Lin, Xiaodong Zhang, Li Cai, Ersha Fan, Shumeng Wu, Su Ma, Feng Wu, Renjie Chen, Li Li
  Advanced Energy and Sustainability Research.2022;[Epub]     CrossRef
• Synthesis of Rare Earth Oxide from NaREE(SO4)2·H2O by Ion Substitution Reaction
  Dae-Weon Kim, Bo-Ram Kim, Hee-Lack Choi
  Journal of the Korean Society of Mineral and Energy Resources Engineers.2020; 57(5): 405.     CrossRef

F-containing TiO₂ nanopowders are synthesized using simple wet processes (precipitation-based and hydrothermal) from ammonium hexafluorotitanate (AHFT, (NH4)2TiF6) as a precursor to apply as a photocatalyst for the degradation of rhodamine B (RhB). The surface properties of the prepared samples are evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results confirm that the synthesized anatase TiO₂ has sphere-like shapes, with numerous small nanoparticles containing fluorine on the surface. The photocatalytic activity of F-containing TiO₂ compared with F-free TiO₂ is characterized by measuring the degradation of RhB using a xenon lamp. The photocatalytic degradation of F-containing TiO₂ exhibits improved photocatalytic activity, based on the positive effects of adsorbed F ions on the surface.

In this study, TiO₂ powders are synthesized from ammonium hexafluoride titanate (AHFT, (NH₄)₂TiF₆) as a precursor by heat treatment. First, we evaluate the physical properties of AHFT using X-ray diffraction (XRD), particle size analysis (PSA), thermogravimetric analysis (TGA), and field-emission scanning electron microscopy (FESEM). Then, to prepare the TiO₂ powders, is heat-treated at 300-1300°C for 1 h. The ratio of anatase to rutile phase in TiO₂ is estimated by XRD. The anatase phase forms at 500°C and phase transformation to the rutile phase occurs at 1200°C. Increase in the particle size is observed upon increasing the reaction temperature, and the phase ratio of the rutile phase is determined from a comparison with the calculated XRD data. Thus, we show that anatase and rutile TiO₂ powders could be synthesized using AHFT as a raw material, and the obtained data are utilized for developing a new process for producing high-quality TiO₂ powder.

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• Photocatalytic activity of rutile TiO2 powders coupled with anatase TiO2 nanoparticles using surfactant
  Jong Min Byun, Chun Woong Park, Young In Kim, Young Do Kim
  journal of Korean Powder Metallurgy Institute.2018; 25(3): 257.     CrossRef

Leaching of MOCVD dust in the LED industry is an essential stage for hydro-metallurgical recovery of pure Ga and In. To recover Ga and In, the leaching behavior of MOCVD scrap of an LED, which contains significant amounts of Ga, In, Al and Fe in various phases, has been investigated. The leaching process must be performed effectively to maximize recovery of Ga and In metals using the most efficient lixiviant. Crystalline structure and metallic composition of the raw MOCVD dust were analyzed prior to digestion. Subsequently, various mineral acids were tested to comprehensively study and optimize the leaching parameters such as acidity, pulp density, temperature and time. The most effective leaching of Ga and In was observed for a boiling 4 M HCl solution vigorously stirred at 400 rpm. Phase transformation of GaN into gallium oxide by heat treatment also improved the leaching efficiency of Ga. Subsequently high purity Ga and In can be recovered by series of hydro processes.

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• Selective Solvent Extraction of In from Synthesis Solution of MOCVD Dust using D2EHPA
  Byoungyong Im, Basudev Swain, Chan Gi Lee, Jae Layng Park, Kyung-Soo Park, Jong-Gil Shim, Jeung-Jin Park
  Journal of the Korean Institute of Resources Recycling.2015; 24(5): 80.     CrossRef
• Fabrication of High Purity Ga-containing Solution using MOCVD dust
  Duk-Hee Lee, Jin-Ho Yoon, Kyung-Soo Park, Myung-Hwan Hong, Chan-Gi Lee, Jeung-Jin Park
  Journal of the Korean Institute of Resources Recycling.2015; 24(4): 50.     CrossRef
• Influence of Oxidation Temperatures on the Structure and the Microstructure of GaN MOCVD Scraps
  Hyun Seon Hong, Joong Woo Ahn
  journal of Korean Powder Metallurgy Institute.1970; 22(4): 278.     CrossRef