Tianhong Zhou

Nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO2 ceramics doped with 2.5 mol% Ta and different concentrations of Ca were obtained by sintering at 1300degreesC. As a varistor material, the nonlinear electrical behavior and dielectric properties of these ceramics were investigated. The ceramics have nonlinear coefficients a in the range 2.0-5.5 and high relative dielectric constants. The effects of Ca on the density, nonlinear electrical behavior, resistivity and dielectric properties of the Ta-doped TiO2 ceramics were also studied. The sample doped with 0.75 mol% Ca and 2.5 mol% Ta exhibits the highest nonlinear coefficient and a comparatively lower relative dielectric constant. By analogy to a grain-boundary defect model, the nonlinear electrical behavior of the TiO2 system is explained

Crystal structure and infrared spectra of Na2Al2B2O7

The structure of Na2Al2B2O7 has been refined on X-ray powder diffraction data collected in transmission mode by Rietveld techniques because the polycrystalline samples exhibit a strong tendency of preferred orientation and the single crystals are of poor quality. Final refinement on powder diffraction data converged to agreement factors R-p=6.54%, R-wp=8.55% with R =5.24%. The title compound crystallizes in a trigonal space group P-31c. Lattice parameters are refined to be a=4.8113(1) Angstrom and = 15.2781(3) Angstrom. The structure consists of infinite [Al2B2O7](x) sheets stacking along c-axis and Na atoms in both the inter-sheets and intra-sheets. Infrared spectra of both Na2Al2B2O7 and Na2Ga2B2O7 are reported and a brief interpretation is given based on the structures. High quality X-ray powder diffraction data and results of thermal analysis are also presented

Fabrication of Ag3PO4/GO/NiFe2O4 composites with highly efficient and stable visible-light-driven photocatalytic degradation of rhodamine B

Effective visible-light-driven Ag3PO4/GO/NiFe2O4 Z-scheme magnetic composites were successfully fabricated by a simple ion-exchange deposition method. The Ag3PO4/GO/NiFe2O4 (8%) composite exhibited excellent photocatalytic activity (degradation efficiency was ∼96% within 15 min and kinetic constant reached 0.1956 min−1) and stability when compared to Ag3PO4, NiFe2O4, and Ag3PO4/NiFe2O4 for rhodamine B (RhB) degradation. Furthermore, by electrochemical and fluorescence measurements, the Ag3PO4/GO/NiFe2O4 (8%) material also showed larger transient photocurrent, lower impedance, and longer fluorescence lifetime (7.82 ns). Comparing the activity result dependence with characterization results, it was indicated that photocatalytic activity depended on fast charge transfer from Ag3PO4 to NiFe2O4 through GO sheet. The h+ and ·O2− species played important roles in RhB degradation under visible-light. A possible Z-scheme mechanism is proposed over the Ag3PO4/GO/NiFe2O4 (8%) composite. This study might provide a promising visible light responsive photocatalyst for the photocatalytic degradation of organic dyes in wastewater.

Highly efficient visible-light-driven photocatalytic degradation of rhodamine B by a novel Z-scheme Ag3PO4/MIL-101/NiFe2O4 composite

The effectiveness of metal–organic frameworks (MOFs) as solid-state electron mediators for rhodamine B (RhB) degradation in a Z-scheme photocatalysis system is demonstrated. Novel Z-scheme Ag3PO4/MIL-101/NiFe2O4 (APO/MOF/NFO) composites were synthesized by an in situ precipitation method and employed to degrade RhB dye under visible-light irradiation. The photocatalytic activity results demonstrated that the Z-scheme APO/MOF/NFO(20%) photocatalyst showed relatively improved photocatalytic activity and stability in the degradation of RhB over the individual APO, NFO and APO/NFO materials. By the electrochemical and fluorescence measurements, the APO/MOF/NFO(20%) material also showed a larger transient photocurrent, lower impedance, and longer fluorescence lifetime (7.68 ns). Comparing the activity results with the characterization results, it was indicated that the photocatalytic activity depends on the rapid transfer of electrons from APO to NFO through the three-dimensional structure of the MOF. Furthermore, the possible mechanism for the photodegradation process of APO/MOF/NFO(20%) was proposed to illustrate excellent photocatalytic activity. The present study has paved a new way for using the attractive MOF in the design of a new and efficient system for organic dye degradation in wastewater.

Synthesis and characterization of CoCuMnOx spinel ceramic thin films for spectral selectivity absorption

CoCuMnOx ceramic films were deposited onto stainless steel (SS) substrates by a convenient and innovative aqueous solution chemical method. With this approach, the ubiquitous, inexpensive, and nontoxic water acting as a green solvent was employed to dissolve metal salts, chelating agent, and wetting agent, all of which are low-cost and available commercially. The obtained aqueous solution precursor, showed long-term stability and reproducibility, and could be utilized to prepare CoCuMnOx ceramic films for solar absorber applications. X-ray diffraction (XRD) peaks of the ceramic thin film that was annealed at 450 °C for 1 h corresponded to that of crystalline CoCuMnOx in the JCPDS database. Then, the influence of deposition parameters such as annealing temperature and withdrawal speed on chemical ingredients, film thickness, surface features, and optical properties of the ceramic films was investigated in detail. The result indicated that CoCuMnOx ceramic films exhibited a good spectral selectivity, which was obtained at a 500 °C annealing temperature with different withdrawal speeds. Subjected to an accelerated thermal stability test at 246 °C, the prepared ceramic films showed excellent thermally stability and performance criterion (PC) values below 0.05.