LaCoO_3晶格结构内外Mg的同步改性及其光催化性能

Simultaneous Mg-Modification Inside and Outside of LaCoO_3 Lattice and Their Photocatalytic Properties

运用溶胶-凝胶法同步获得了LaCoO_3钙钛矿晶格结构内Mg^(2+)的掺杂改性及晶格结构外MgO的异质结复合改性。观察到了同步改性后LaCoO_3催化剂上水体罗丹明B(RhB)光催化降解活性的显著提升,相同实验条件下最适Mg含量改性LaCoO_3上RhB的降解率从原始LaCoO_3的58%显著提升至98%,表观一级动力学常数为改性前催化剂的4.5倍。运用X射线衍射(XRD)、氮气低温吸附-脱附(BET法)、扫描及透射电子显微镜(SEM,TEM)、傅里叶变换红外光谱(FT-IR)、X光电子能谱(XPS)、紫外-可见漫反射(DRS)及光致发光光谱(PL)等分析和表征系统探讨了改性前后催化剂的理化特征。结果表明,约10%Co^(3+)晶格结点可为Mg^(2+)掺杂取代而LaCoO_3钙钛矿结构基本保持不变,适量Mg^(2+)对Co^(3+)的掺杂取代可形成晶格畸变和杂质能级、衍生Co^(4+)及促进溶氧吸附从而有利于RhB的光催化降解,过量掺杂的Mg则可能成为光生载流子复合中心从而不利于RhB的去除。适量MgO异质结复合改性LaCoO_3一方面赋予复合催化剂较大表面积,利于RhB富集,也赋予丰富的表面羟基利于光生电子的捕获并衍生活性羟基自由基;另一方面还可能通过LaCoO_3与MgO异质结间电子的跃迁和流动以及晶格氧空位抑制光生载流子的复合,提高复合催化剂的光量子效率。

The Mg-doped inside of LaCoO3 lattice and heterojunctions between MgO and LaCoO3 were acquired synchronously through a sol-gel preparation. Significant enhancement in photocatalytic degradation of rhodamine B （RhB） was obtained on the modified catalysts, with the degradation ratio of RhB reaching as high as 98% within 3 h under the experimental conditions, and the quasi-first-order rate constant of the RhB degradation reaction over the mray diffraction （XRD）, N2 adsorption-desorption at low temperature （BET calculation）, scan and transmission electron microscopy （SEM, TEM）, Fourier transformed infrared spectroscopy （FT-IR）, X-ray photoelectron spectroscopy （XPS）, UV-Vis diffuse reflectance spectroscopy （DRS） and photoluminescence spectroscopy （PL）. The results indicated that about 10% of Co3 in LaCoO3 can be substituted by Mg2 while its perovskite-type structure remains unchanging. The moderate Mg-doping improved the photocatalytic performance of LaCoO3 by the donor level of impurities, derivation of Co4 and adsorption of dissolved oxygen. The over Mg-doping suppressed the degradation of RhB for the recombination of photogenerated carriers on impurities. An optimal amount of MgO cooperates harmoniously with LaCoO3 in degradation of RhB by offering high surface area for the enrichment of RhB, abundant superficial hydroxyls for trapping of electrons and derivation of hydroxyl radials, as well as, enhancing the light quantum efficiency through trapping electrons on vacancies of lattice oxygen and migration or jumping of electrons between MgO and LaCoO3.