Novel Single-Crystal Hollandite K_1.46Fe_0.8Ti_7.2O₁₆ Microrods: Synthesis, Double Absorption, and Magnetism

Abstract

Novel multifeatured hollandite K1.46Fe0.8Ti7.2O16 (KFTO) was synthesized by a simple hydrothermal method. Magnetic KFTO microrods were well controlled to long rectangular rods with pyramid-shaped tops. A KFTO growth mechanism was proposed on the basis of examining phase and morphology of the samples acquired at different reaction times. The KFTO morphology was confirmed by the calculated surface energies. The UV–vis diffuse reflectance spectra of KFTO microrods showed double absorption with band gaps of 2.01 and 2.16 eV, which was further confirmed by photoluminescence. First-principles studies revealed that the double absorption and magnetic properties originate from the d–d transitions of Fe3+ under the crystal field. The magnetic property could be applied in ferromagnetic semiconductor devices and the double absorption could be applied in visible-light harvesting. This work highlights the multifunctional KFTO microrods with low cost and environmental friendliness.

Polymorphism and Molten Nitrate Salt-Assisted Single Crystal to Single Crystal Ion Exchange in the Cesium Ferrogermanate Zeotype: CsFeGeO4

“…These band gaps are consistent with the yellowish-brown appearance of the materials indicating that they mostly absorb in the blue green (500–560 nm or 2.20–2.48 eV) region of the visible light spectrum. Additionally, these values are consistent with the optical band gap for Fe 2 O 3 ( E g = ∼2.10 eV) and other complex iron containing oxides, all of which have orange to reddish-brown appearance. , …”

New Rubidium-Containing Mixed-Metal Titanium Hollandites

“…All title compounds crystallize in the tetragonal space group I 4/ m . The crystal growth mechanism for a potassium hollandite, K 1.46 Fe 0.8 Ti 7.2 O 16 , has been discussed in detail by Hassan et al Similar arguments can be made for the rubidium hollandites; briefly, the TiO 2 undergoes dissolution in molten RbCl-RbF flux presumably forming structural building blocks of TiO 6 8– octahedra. The transition metal cations, once dissolved in the flux, connect to the TiO 6 8– building blocks to occupy Ti sites due to the nearly identical ionic radii of Ti 4+ and M x + , for example, 0.64 and 0.61 Å for Fe 3+ and Ti 4+ ions, respectively.…”

“…A plethora of Ba-containing Ti-based hollandites are known, − in contrast to the smaller number of known Na- or K-containing phases. − Recently, Knyazev et al for the first time prepared the M 2 Fe 2 Ti 6 O 16 (M = Na, K, Rb, Cs) family as polycrystalline powders by a conventional solid state route and reported on their thermal expansion coefficients obtained using high-temperature X-ray diffraction. This work demonstrates the ability of the hollandite structure to accommodate larger alkali metals in its channels …”

Controlled Fabrication of K2Ti8O17 Nanowires for Highly Efficient and Ultrafast Adsorption toward Methylene Blue

“…The KOH mineralizer plays double functions in the current hydrothermal reaction, providing potassium ion source and a feasible alkaline environment to fully dissolve the raw materials. In the initial stage of the reaction, TiO 2 particles dissolve in the alkaline solution as structural units of distorted TiO 6 octahedra at high temperature, high pressure, and high alkali concentration . These free TiO 6 octahedra reassemble themselves to link together through sharing edges by constructing hydroxyl bridges between the titanium ions and configure a zigzag structure .…”