A bicrystalline titanium dioxide nanofiber with enhanced photocatalytic activity was synthesized from potassium titanate K 2 Ti 2 O 5 via ion exchange and calcination. The nanofiber has a core-shell crystalline structure with a thin TiO 2 (B) phase sheathing the anatase core, as characterized by X-ray diffraction, Raman spectroscopy, and high-resolution transmission microscopy (HRTEM). From HRTEM and local electron diffraction patterns, the two crystalline phases form a coherent interface with the 0.34-nm spacing between the (102) planes of TiO 2 (B) matching that between the anatase (101) lattice planes. The core-shell anatase/TiO 2 (B) nanofiber shows enhanced photocatalytic activity in iodine oxidation reaction with a 20-50% increase in extent of reaction compared to either single-crystal anatase or single-crystal TiO 2 (B) nanofibers. Anatase and TiO 2 (B) have the same band gap value of 3.2 eV, while theoretical calculations show the conduction band (CB) and valence band (VB) energies in anatase are both lower than the corresponding CB and VB energies in TiO 2 (B). The enhanced photocatalytic property may be due to enhanced and concerted charge mobility toward or away from the anatase/TiO 2 (B) interface. The special structure-property relationship can provide a new strategy to design and fabricate efficient photocatalytic and photovoltaic materials.

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The band structure-controlled solid solution of BiOBr x I 1-x was successfully synthesized by a simple solvothermal route. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, UVÀvis diffuse reflectance spectroscopy, and nitrogen sorption/desorption. The resulting BiOBr x I 1-x samples were phase-pure and of three-dimensional (3D) microspheres composed of nanoplates. The samples with different x values exhibited composition-dependent absorption properties in the visible light region and the bandgaps were estimated to be between 1.89 and 2.53 eV. Rhodamine B (RhB) photocatalytic degradation experiments showed that these samples possessed excellent and composition-dependent performance. The highest catalytic performance of the 3D BiOBr 0.2 I 0.8 microspheres may derive from a synergetic effect, including higher surface area, porous structure, and enhancement of light absorbance. Moreover, on the basis of the analysis of the valence band and conduction band, a possible mechanism of photocatalytic activity of BiOBr x I 1-x samples was also proposed.

To study the effects of type and content of cosolvent as well as temperature on the properties of two well-known deep eutectic solvents (DESs), i.e., ChCl/EG (choline chloride + ethylene glycol at a molar ratio of 1:2) and ChCl/Gly (choline chloride and glycerol at a molar ratio of 1:2), the density and viscosity of the mixtures of ChCl/EG or ChCl/Gly with methanol (MeOH) and water (H2O) over the whole compositional range at temperatures from 288.15 to 323.15 K as well as the molar enthalpy of mixing for the mixtures of ChCl/EG or ChCl/Gly + MeOH were experimentally measured. The excess molar volume, viscosity deviation, and excess molar Gibbs energy of activation were further calculated to study the effects of temperature, types of cosolvent and DES, and their contents on the nonideal behavior of these pseudobinary systems. The molar enthalpy of mixing measured in this work was further compared with those with H2O as the cosolvent reported in the literature. It shows that the mixing of these two DESs with MeOH is exothermic, which is opposite compared to those mixed with H2O. Additionally, the nonrandom two-liquid model and Gibbs–Helmholtz equation were combined to represent the experimental results of the enthalpy of mixing.