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Based on the structure related to the high-temperature superconductor yttrium-barium-copper oxide, two novel high-efficiency visible light photocatalysts were created in this study. The yttrium-barium oxide (YBO) semiconductors Y 2 Ba 3 O 6 (YB3O) and Y 2 Ba 4 O 7 (YB4O) were prepared by a copper-free solid-phase sintering method. They were applied for the effective treatment of dye-containing wastewater by photocatalysis under visible light irradiation. The degradation efficiency of methylene blue (MB) reached more than 95% within 10 min. Stable visible light degradation of methyl orange (MO) was achieved in the presence of YB3O and YB4O. The electron spin resonance technique and active substance capture technique confirmed the presence of superoxide radicals (·O 2 −), hydroxyl radicals (·OH) and holes (h VB +) under visible light illumination. UV–Vis diffuse reflectance spectroscopy analysis showed that the direct optical band gaps of YB3O and YB4O were 2.550 eV and 2.583 eV, respectively, which resulted in their high visible absorption at 486.27 nm and 480.06 nm. After five cycles, the recoveries of YB3O and YB4O reached 67.15% and 72.98%. Therefore, YB3O and YB4O are considered as powerful semiconductor catalysts for the photocatalytic degradation of organic dyes in wastewater. • Synthesis of yttrium -barium oxide (YBO) visible light catalyst. • Y 2 Ba 3 O 6 (YB3O) and Y 2 Ba 4 O 7 (YB4O) show a forbidden band width of 2.550 eV and 2.583 eV respectively. • The effective degradation of methylene blue was achieved within 10 min under visible light. • The mineralization of the total organic carbon in the degraded solutions of both dyes reached close to 80%. [ABSTRACT FROM AUTHOR]

Metal organic frameworks (MOFs) have been well-known and extensively researched due to the high storage /good selectivity for gas molecules. Herein, the structures and electron paramagnetic resonance (EPR) spectra for dicopper paddle wheel MOF compound (Cu2(µ2-O2CCH3)4 with various gas molecule are theoretically investigated by density functional theory (DFT) calculations. The adsorption energies and isotherms (including pure gas molecules and the mixed ones) are calculated for the gas molecules interacting with the unsaturated Cu2(µ2-O2CCH3)4. Both quantities exhibit the roughly consistent orders (e.g. H2S > NH3 > CO2 > CO > H2O > N2 > NO > H2 for isotherms and H2S > NH3 > N2 > CO2 > NO > H2O > H2 > CO for adsorption energies), possibly suggesting that this material may act as a potential adsorbent of these gas molecules. The catalytic property of Cu2(µ2-O2CCH3)4 for oxidation of CO and NO into non-toxic molecules and splitting of H2O into H2 and O2 in the solvent condition are uniformly discussed. Simulation of Grand Canonical Monte Carlo (GCMC) in MS 8.0 and calculations in Langmuir model reveal that Cu2(µ2-O2CCH3)4 has good selectivity for CH4 in natural gas (CH4/CO2/N2) and SO2 in fog (SO2/NO/NO2/H2O/O2), which would exhibit potential environmentally friendly applications. [ABSTRACT FROM AUTHOR]

The spin Hamiltonian parameters (g factors, hyperfine structure constants and zero-field splittings D and E) and local structures for Mn2+ and Ni2+ in [Zn(en)3](NO3)2 single crystal are theoretically investigated from the perturbation calculations for trigonally distorted 3d5 and trigonally (or orthorhombically) distorted 3d8 cluster. The trigonal Mn2+ and Ni2+ centres are found to undergo the moderate angular variations Δβ of 4.5° and 5.2°, respectively, related to host Zn2+ site due to size mismatch. The orthorhombic Ni2+ centre shows the relative axial elongation ratio ρ (≈ 2.5%) and the relative perpendicular bond length variation ratio τ (≈0.2%). For Mn2+ centre, the contributions to g-shifts ΔgCT (or hyperfine structure constants ACT and zero-field splitting DCT) from charge-transfer (CT) mechanism are opposite in sign and five times (or 5% and 8%) in magnitude compared with those from crystal-field (CF) mechanism. For the trigonal Ni2+ centre, ΔgCT (or DCT) are the same (or opposite) in sign and 17% (or 2%) in magnitude related to those from CF mechanism. For the orthorhombic Ni2+ centre, ΔgCT and ECT (or DCT) are same (or opposite) in sign and 16% and 48% (or 442%) in magnitude with respect to those from the CF mechanism. The signs and magnitudes of the trigonal distortion angles δβ (≈ −0.3 and 0.4°) related to an ideal octahedron and the local angular variations Δβ related to the host bond angle are suitably illustrated by those of the axial distortion degree (ADD) and the angular variation degree (AVD) of the systems, respectively. [ABSTRACT FROM AUTHOR]

AgBr crystals containing impurity Rh2+ with and without a next nearest neighbor silver vacancy (VAg) in the [001] axis are theoretically studied. The defect structures, bandgap, Mulliken charge, density of states, ultraviolet-visible (UV-Vis) and electron paramagnetic resonance spectra are analysed for two distinct (i.e. tetragonally elongated and compressed) centres by using density functional theory calculations. The results demonstrate that the structural, photoelectric and spectroscopic properties of AgBr are significantly changed after Rh substitution. The covalency of Rh-Br bonds in the two centres is stronger than that of pure AgBr according to the larger magnitudes of the overlap population. Compared to pure AgBr, Rh doping also results in significantly enhanced red shifts of absorption bands in the UV-Vis region and some new d-d transitions in the visible and near-infrared regions. Meanwhile, the bandgap of Rh-doped AgBr is about 10 % narrower than that of pure AgBr. As a result, the visible light activity may be enhanced in AgBr:Rh systems. Rh dopants can induce the magnetic moments of about 1.73 μB for both centres. Therefore, transition-metal Rh dopants may effectively modulate the electronic, optical and magnetic properties of AgBr. [ABSTRACT FROM AUTHOR]

Abstract: From the perturbation formulas for g factors for an orthorhombically compressed octahedral 3d9 group, g factors, and local structures for the [Cu(en)3]2+ groups in Cu(en)3SO4 and Cu(en)3Cu(CN)3 powders are theoretically investigated. The local structure of Cu2+ in Cu(en)3Cu(CN)3 is evaluated by analyzing the experimental g factors and found to exhibit moderate axial compression ΔZ (≈0.018 Å) and planar bond length variation ΔR (≈0.015 Å) related to an ideal octahedron due to the Jahn-Teller effect. The larger experimental axial anisotropy Δg (= (gx + gy)/2 − gz) of Cu(en)3SO4 than Cu(en)3Cu(CN)3 is mainly ascribed to the larger ΔZ (≈0.053 Å) in the former. The calculated g factors for both systems show reasonable agreement with experiment by including the charge transfer (CT) contributions to gz, which have the same sign and much larger magnitude compared to the conventional crystal-field ones and should be included. [ABSTRACT FROM AUTHOR]

The local structures for various Rh2+ centers in AgCl are theoretically studied using density functional theory (DFT) with periodic CP2K program. Through geometry optimizing, the stable ground states with minimal energies and electronic structures are obtained for the tetragonally elongated (TE), orthorhombically elongated (OE), and tetragonally compressed (TC) centers, and the corresponding g and hyperfine coupling tensors are calculated in ORCA level. The calculations reveal obvious Jahn–Teller elongation distortions of about 0.109 and 0.110 Å along [001] axis for TE and OE centers without and with 1 next nearest neighbor (nnn) cation vacancy VAg in [100] axis, respectively. Whereas TC center with 1 nnn VAg along [001] axis exhibits moderate axial compression of about 0.066 Å due to the Jahn–Teller effect. For OE and TC centers with 1 nnn VAg, the ligand intervening in the central Rh2+ and the VAg is found to displace away from the VAg by about 0.028 and 0.024 Å, respectively. The present results are discussed and compared with those of the previous calculations based on the perturbation formulas by using the improved ligand field theory. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR)gfactors and local structures for Ni3+in LiAlyCo1–yO2as the cathode materials for lithium-ion batteries are theoretically investigated at various Al concentrationsy(= 0.1, 0.5, 0.8 and 1.0). The [NiO6]9–clusters are subject to the tetragonal elongation distortions along theC4axis owing to the Jahn–Teller effect and the different degrees of distortions are characterised by the slightly increasing relative elongation ratioρ(and also crystal-field strength and covalency) withy. In pure LiAlO2(y = 1.0), the [NiO6]9–cluster exhibits the largestρ(≈1.4%) and an additional relative variation ratioτ(≈1.4%) of the planar bond lengths, responsible for the perpendicularganisotropyδg= (gx–gy). The number of impurity Ni3+centres increases from one aty = 0 and 1.0 to two aty = 0.1 and 0.8 and reaches the maximum four aty = 0.5, in accordance with the increasing degree of disorder of the systems. The distinct impurity centres for the sameymay be accompanied by the comparable energies of the ground and near excited states, similar to ‘resonant states’ with slightly different local elongation distortions and tetragonal level splittings. The present studies will be helpful to understand the relationships between local structures and performances of LiAlyCo1–yO2type cathode materials. [ABSTRACT FROM PUBLISHER]

The spin Hamiltonian parameters ( g factors g // , g ⊥ , hyperfine structure constants A // , A ⊥ and superhyperfine parameters A z ′ , A x ′ and A y ′ ) and defect structures for Ag 2+ in NaF and CsCdF 3 crystals are theoretically studied using the improved perturbation formulas of these quantities for a 4d 9 ion in a tetragonally elongated octahedron. The contributions from both the crystal-field and charge transfer mechanisms are taken into account, and the relevant model parameters are quantitatively obtained from the cluster approach in a consistent way. The impurity centers are found to undergo the relative tetragonal elongations of about 9.4% and 8.2% for Ag 2+ in NaF and CsCdF 3 , respectively, along the C 4 axis due to the Jahn–Teller effect. By employing the few adjustable parameters, the calculated spin Hamiltonian parameters based on the above uniform formulas and the local tetragonal elongation distortions agree well with the experimental data. Despite dominant ionicity of the hosts, the charge transfer contributions are actually important to the spin Hamiltonian parameters (e.g., about 20% for the g -shifts) due to strong covalency of impurity Ag 2+ . [ABSTRACT FROM AUTHOR]

The defect structures for Co 2+ in ZnO microwires, thin films and bulks are theoretically investigated by analyzing the electron paramagnetic resonance (EPR) parameters (zero-field splitting D, g factors g // and g ⊥ and hyperfine structure constants A // and A ⊥ ) for trigonally distorted tetrahedral 3d 7 clusters in a consistent way. The impurities Co 2+ are found to suffer the displacements (≈0.046, 0.044 and 0.045 Å) away from the ligand triangles along the C 3 axis in ZnO microwires, thin films and bulks, respectively, which considerably reduce the trigonal distortions of the Zn 2+ sites in the hosts. Apart from the contributions from the conventional crystal-field (CF) mechanism, those from the charge-transfer (CT) mechanism are important and should be included in the EPR analysis. The defect structures and spectral properties of the three ZnO:Co 2+ systems are discussed. [ABSTRACT FROM AUTHOR]

The EPR g factors for the oxygenated and nonoxygenated BaCuO 2+ x are theoretically studied from the perturbation formulas of the g factors for an orthorhombically elongated octahedral 3d 9 complex based on the cluster approach. The relative axial elongation ratios (≈1% and 0.6%) along c axis and the relative planar bond length variations (≈6.9% and 8.9%) are found for the oxygenated and nonoxygenated systems, respectively. The above local orthorhombic distortions of the Jahn–Teller nature around Cu 2+ can suitably account for the axial and perpendicular anisotropies of the observed g factors. The present studies can be useful to understand the influences of this parasitic phase BaCuO 2+ x on the EPR behaviours and superconductivity of the R 123 high T c superconductors. [ABSTRACT FROM AUTHOR]