TiO2／Ti电极上外加阳极偏压对亚甲基蓝光催化降解的影响

主要研究了在纳米多孔TiO2／Ti电极上外加阳极偏压对亚甲基蓝光催化降解的影响。另外还讨论了在TiO2／Ti中掺杂过渡族金属离子对亚甲基蓝降解情况的影响。降解程度通过亚甲基蓝的褪色情况来表征。实验结果表明，降解效率随着所加阳极偏压的增大而增大，直到阳极偏压达到3．5V，增大速率开始减小。掺杂Mn^2＋和Cr^3＋可以促进光电催化效率，而掺杂Ni^2＋却会降低光电催化效率。离子半径和各离子的功函数可以解释这种现象。     

Photocatalytic activity of manganese, chromium and cobalt-doped anatase titanium dioxide nanoporous electrodes produced by re-anodization method

Transition metal-doped TiO₂ electrodes were prepared by re-anodization and characterized. The structure of these electrodes was investigated by X-ray diffraction and electron diffraction, which mainly showed typical characteristic anatase reflections without any dopant-related peaks. The amount of transition metal dopant in TiO₂ was kept at approximately 1.0 at.%, as measured by energy dispersive X-ray spectroscopy. The effects of different types of dopants on the photocatalytic activity were revealed by measuring the degradation of an organic aqueous solution containing a dye (acid red G) using a combination of ultraviolet (UV) light energy in the presence of these electrodes. The photocatalytic efficiency was remarkably enhanced by the incorporation of Mn ²⁺ and Cr³⁺. Mn²⁺ showed the most significant enhancement. However, Co²⁺ accelerated the rate of acid red G degradation only slightly. Langmuir-Hinshelwood rate expression was employed for the degradation of acid red G by UV/TiO₂ electrodes system. The adsorption equilibrium constant, the rate constant, and the initial degradation rate were determined for different electrodes. The effect of the concentration of Mn²⁺ on the degradation of acid red G was also investigated and the results showed that there is an optimal value (about 1.0 at.%) of the concentration of Mn²⁺ for inducing faster degradation of the dye. The enhanced photocatalytic degradation rate of acid red G in the presence of transition metals is attributed to the increase of the charge separation in these systems.     

Glass formation ability, structure and magnetocaloric effect of a heavy rare-earth bulk metallic glassy Gd55Co20Fe5Al20 alloy

The structure and magnetic entropy changes in melt-spun and annealed LaFe_11.8−xCo_xSi_1.2 (x = 0, 0.4 and 0.8) ribbons have been investigated. It is found that the value of T_c can be increased continuously up to 290 K for x = 0.8 and the phase transition, at T_c from paramagnetic to ferromagnetic, is changed from first- to second-order due to Co substitution. Large values of the magnetic entropy change are 31 and 13.5 J/kg K in the magnetic field change from 0 to 5 T at 201 K for the LaFe_11.8Si_1.2 and at 290 K for the LaFe₁₁Co_0.8Si_1.2 ribbons, respectively. The magnetic entropy change in the LaFe₁₁Co_0.8Si_1.2 ribbons is higher than that reported in the bulk counterpart and that of conventional MCE materials, such as pure Gd. The enhanced magnetic entropy change of ribbons compared to bulk counterpart is attributed to a more uniform microstructure and element distribution resulting from the high cooling rate by melt-spinning.