Structure analysis and photocatalytic properties of spinel zinc gallium oxonitrides

This report describes a detailed structural, electronic, and catalytic characterization of zinc gallium oxonitride photocatalysts with a spinel crystal structure. The bandgap decreases to less than 3 eV with increasing nitrogen content (<3 wt%) and these photocatalysts are active in visible light (λ>420 nm) for the degradation of cresol and rhodamine B. Density functional theory calculations show that this bandgap reduction is in part associated with hybridization between the dopant N 2p states and Zn 3d orbitals at the top of the valence band. X-ray photoelectron measurements indicate that nitrogen is indeed interacting with the oxide precursor through the formation of both nitride- and oxonitride-type species. The incorporation of nitrogen reduces the uniformity of the local structure of the spinel Zn-Ga-O-N (ZGON) species, as reflected in X-ray absorption spectra and Raman measurements relative to zinc gallate, which suggests the presence of defects. The oxonitrides exhibit faster photocatalytic rates of reaction than the oxide precursor. The degradation mechanisms were determined to be via the attack by hydroxyl radicals and holes for rhodamine B and cresol, respectively. Addition of Pt as a co-catalyst increased the rate of photodegradation, a result attributed to better charge separation.     

SrP3N5O: a highly condensed layer phosphate structure solved from a nanocrystal by automated electron diffraction tomography

The oxonitridophosphate SrP₃N₅O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH₂)₃, thiophosphoryl triamide SP(NH₂)₃, SrS, and NH₄Cl enclosed in evacuated and sealed silica‐glass ampoules up to 750 °C. The compound was obtained as nanocrystalline powder with needle‐shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X‐ray powder diffraction data. SrP₃N₅O crystallizes in the orthorhombic space group Pnma (no. 62) with unit‐cell data of a=18.331(2), b=8.086(1), c=13.851(1) Å and Z=16. The compound is a highly condensed layer phosphate with a degree of condensation κ=1/2. The corrugated layers ${{{\hfill 2\atop \hfill \infty }}}The oxonitridophosphate SrP(3)N(5)O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH(2))(3), thiophosphoryl triamide SP(NH(2))(3), SrS, and NH(4)Cl enclosed in evacuated and sealed silica-glass ampoules up to 750 °C. The compound was obtained as nanocrystalline powder with needle-shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X-ray powder diffraction data. SrP(3)N(5)O crystallizes in the orthorhombic space group Pnma (no. 62) with unit-cell data of a=18.331(2), b=8.086(1), c=13.851(1) ? and Z=16. The compound is a highly condensed layer phosphate with a degree of condensation κ=?. The corrugated layers (∞)(2){(P(3)N(5)O)(2-)} consist of linked, triangular columns built up from P(O,N)(4) tetrahedra with 3-rings and triply binding nitrogen atoms. The Sr(2+) ions are located between the layers and exhibit six-, eight-, and ninefold coordination. FTIR and solid-state NMR spectra of SrP(3)N(5)O are discussed as well.