Structural and electronic properties of BiOF with two-dimensional layered structure under high pressure: Ab initio study

WOS: 000454538900007In this work, the crystal structure of the BiOF is studied under high hydrostatic pressure using ab initio calculations. Pressure-volume relationships and structural transitions are investigated using Siesta method. A first-order phase transition from the tetragonal matlockite PbFCl-type structure with space group P4/nmm to the orthorhombic structure with space group Cmcm is successfully observed for BiOF. This phase transition which occur around 19.6 GPa is also analyzed from the total energy and enthalpy calculations. In addition, electronic properties of BiOF are researched during the pressure. By analyzing the energy band structures, it is found that the band gaps P4/nmm and Cmcm phases for the BiOF are 2.74 and 2.47 eV, respectively

Hydrothermal Crystallization of Bismuth Oxychlorides (BiOCl) Using Different Shape Control Reagents

Bismuth oxychloride photocatalysts were obtained using solvothermal synthesis and different additives (CTAB—cetyltrimethylammonium bromide, CTAC—cetyltrimethylammonium chloride, PVP–polyvinylpyrrolidone, SDS–sodium dodecylsulphate, U—urea and TU—thiourea). The effect of the previously mentioned compounds was analyzed applying structural (primary crystallite size, crystal phase composition, etc.), morphological (particle geometry), optical (band gap energy) parameters, surface related properties (surface atoms’ oxidation states), and the resulted photocatalytic activity. A strong dependency was found between the surface tension of the synthesis solutions and the overall morpho-structural parameters. The main finding was that the characteristics of the semiconductors can be tuned by modifying the surface tension of the synthesis mixture. It was observed after the photocatalytic degradation, that the white semiconductor turned to grey. Furthermore, we attempted to explain the gray color of BiOCl catalysts after the photocatalytic decompositions by Raman and XPS studies

DFT Calculations on the Electronic Structures of BiOX (X = F, Cl, Br, I) Photocatalysts With and Without Semicore Bi 5d States

The electronic structures of BiOX (X = F, Cl, Bi-, I) photocalalysts have been calculated with and without Bi 5d states using the experimental lattice parameters, via the plane-wave pseudopotential method based oil density functional theory (DFT). BiOF exhibits a direct band gap of 3.22 or 3.12 eV corresponding to the adoption of Bi 5d states or not. The indirect band gaps of BiOCl, BiOBr, and BiOI are 2.80, 2.36, and 1.75 eV, respectively, if calculated with Bi 5d states, whereas the absence of Bi 5d states reduces them to 2.59, 2.13, and 1.53 eV successively. The Calculated gap characteristics and the falling trend of gap width with the increasing X atomic number agree with the experimental results, despite the common DFT underestimation of gap values. The shapes of valence-band tops and conduction-band bottoms are almost independent of the involvement of Bi 5d states. The indirect characteristic becomes more remarkable, and the conduction-band bottom flattens in the sequence of BiOCl, BiOBr, and BiOI. Both O 2p and X np (n = 2, 3, 4, and 5 for X = F, Cl, Br, and I, respectively) states dominate the valence hands, whereas Bi 6p states contribute the most to the Conduction hands. With the growing X atomic number, the localized X np states shift closer toward the valence-band tops, and the valence and conduction bandwidths evolve in opposite trends. Atomic and bond populations have also been explored to elucidate the atomic interactions, along with the spatial distribution of orbital density. (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 183-190, 200