Mianxin Song

Band gap calculation and photo catalytic activity of rare earths doped rutile TiO2

Abstract The density of states (DOS) of 17 kinds of rare earths (RE) doped rutile TiO2 was by using first-principles density functional theory (DFT) calculation. The band gap widths of RE doped rutile TiO2 were important factors for altering their absorbing wavelengths. The results show that RE ions could obviously reduce the band gap widths and form of energy of rutile TiO2 except Lu, Y, Yb and Sc, and the order of absorbing wavelengths of RE doped rutile TiO2 were the same as that of the results of calculation. The ratio of RE dopant was another important factor for the photo catalytic activity of RE doped rutile TiO2, and there was an optimal ratio of dopant. There was a constant for predigesting the calculation difficulty, respectively, which were 0.5mol.% and 100 mol−1 under supposition. The band gap widths of RE doped rutile TiO2 by DFT calculation were much larger than that by experiment. Finally, by transferring the calculation values to experiment values, it could be found and predicted that RE enlarged obviously the absorbing wavelengh of rutile TiO2. In addition, the degree of RE ions edging out the Ti atom using the parameters of RE elements was computed.

Photovoltage response of (XZn)Fe2O4-BiFeO3 (X = Mg, Mn or Ni) interfaces for highly selective Cr3+, Cd2+, Co2+ and Pb2+ ions detection

High-photostability fluorescent (XZn)Fe2O4 (X=Mg, Mn or Ni) embedded in BiFeO3 spinel-perovskite nanocomposites were successfully fabricated via a novel bio-induced phase transfer method using shewanella oneidensis MR-1. These nanocomposites have the near-infrared fluorescence response (XZn or Fe)-O-O-(Bi) interfaces (785/832nm), and the (XZn)Fe2O4/BiFeO3 lattices with high/low potentials (572.15-808.77meV/206.43-548.1meV). Our results suggest that heavy metal ion (Cr3+, Cd2+, Co2+ and Pb2+) d↓ orbitals hybridize with the paired-spin X-Zn-Fe d↓-d↓-d↑↓ orbitals to decrease the average polarization angles (-29.78 to 44.71°), qualitatively enhancing the photovoltage response selective potentials (39.57-487.84meV). The fluorescent kinetic analysis shows that both first-order and second-order equilibrium adsorption isotherms are in line and meet the Langmuir and Freundlich modes. Highly selective fluorescence detection of Co2+, Cr3+ and Cd2+ can be achieved using Fe3O4-BiFeO3 (Langmuir mode), (MgZn)Fe2O4-BiFeO3 and (MnZn)Fe2O4-BiFeO3 (Freundlich mode), respectively. Where the corresponding max adsorption capacities (qmax) are 1.5-1.94, 35.65 and 43.7 multiple, respectively, being more competitive than that of other heavy metal ions. The present bio-synthesized method might be relevant for high-photostability fluorescent spinel-perovskite nanocomposites, for design of heavy metal ion sensors.

Detection mechanism of perovskite BFO (1 1 1) membrane for FOX-7 and TATB gases: molecular-scale insight into sensing ultratrace explosives

Perovskite bismuth ferrite-BFO (1 1 1) membranes, as potential-sensitive electrochemical sensors, are investigated for the detection of high-energy-density materials by molecular dynamics (MD) and density functional theory (DFT) calculations. For the detection mechanism of the sensitive 1, 1-diamino-2, 2-dinitroethylene (FOX-7) gases, both a cation bridge and electrostatic models can be used to explain the STM signatures as 0.02–0.04 V (single) and 0.03~0.05 V (coverage) over a wide range (0–0.1 V) of bias voltages. For insensitive 1, 3, 5-triamino-2, 4, 6-trinitrobenzene (TATB) gases interacting with the surface of a BFO (1 1 1) membrane, the charge signature can be as high as 0.08 V (coverage: 0.06 V). Analysis indicates a significant difference from the detection mechanism observed for FOX-7 gases; that is, the molecularly intact bidentate bridge configuration with only – bonds binds to both Fe and Bi atoms. These differences are attributed so that the surface O2− of BFO will capture a part of the surface electron of the –NO2 group, creating a 2p-hole defect (h+) which annihilates a spinning upward (↑) Fe3+, forming a spinning downward (↓) Fe2+. The –NO2 electron decreases 0.35 e (single FOX-7; coverage FOX-7: 0.24 e) and 0.56 e (single TATB; coverage TATB: 0.06 e). Such a system could open up new ideas in the design and application of BFO-based sensors.

DFT simulation on the temperature-dependent electronic transition of V (Nb or Ta) substituted NiMn2O4

Previously, we reported that the d–p (Mn-3d–O-2p) orbital hybridization induces Mn valence change (Mn3+→Mn4+) in the octahedron. The electron transfer mechanism can be controlled by modifying the Mn-3d orbital in the octahedron. Here, we used the density functional theory (DFT) with generalized gradient approximation (GGA) and two-dimensional correlation analysis (2D-CA) techniques to calculate the electron transfer mechanism of the V (Nb or Ta) substituted NiMn2O4 (NMO) in the temperature range of 50–1500 K. The results show that the heat accumulation accelerates the O-2p4 orbital splitting, inducing charge disproportionation. The V-3d3 substituted Mn increases the intensity and of the partial density of state (PDOS) at conduction band (1–3 eV), this enhances the V-3d3–O-2p4 p–d σ∗ orbital. The Nb-4d3/Ta-5d3 substituted Mn reduces the intensity of the PDOS at conduction band (1–5 eV), this weakens the Nb-4d3/Ta-5d3–O-2p4 p–d σ∗ orbital. This study effectively analyzes the microscopic changes of the electron transfer caused by the heat accumulation, provides a theoretical basis for the design of NMO-based negative temperature coefficient (NTC) thermistors.

Photo Catalytic Activity of Rare Earth La(Y)/Rutile TiO2

The rutile TiO2, La/rutile TiO2 and Y/rutile TiO2 were synthesized by one-step method, and the densities of states were investigated by ab initio method. Firstly, the result of ab initio calculation showed that the band gap of La/rutile TiO2 is less than that of Y/rutile TiO2 and rutile TiO2, and the crystal lattice energy of rare earths (La, Y)/rutile TiO2 are similar to each other. Secondly, the crystal structure and photocatalytic activity of La (Y)/rutile TiO2 are characterized by XRD, DRS, ζ potential and kinetics reaction of photocatalyzing methyl orange. In a word, the photocatalytic activity for degradation of methyl orange on 1.0wt% La/rutile TiO2 was better than those on Y/rutile TiO2 and rutile TiO2.