热处理金红石晶体结构及其光催化活性分析

The Crystal Structure and Photocatalytic Activity of Natural Rutile Modified by Heat Treatment

本文以在氢气气氛中加热和退火处理的天然金红石样品(采自山西某变质矿床)为研究对象,利用单晶和粉晶X-射线衍射(XRD)、环境扫描电子显微镜(ESEM)、紫外-可见漫反射吸收光谱(UV-vis)等矿物学常规测试方法,结合Rietveld方法对实验数据计算和精修的结果,对系列样品的晶体结构及对光催化活性影响进行了系统的研究。实验结果表明,天然金红石中含有的V,Fe等杂质离子以类质同象替代Ti4+离子存在于晶格之中,引起晶格畸变,有助于提高样品的光催化活性。随着温度升高,一方面部分类质同象替代的三价铁离子逐步被还原为二价铁和单质铁,大半径离子逃离晶格引起金红石晶胞参数减小;另一方面,热处理引起晶格膨胀,结果导致样品的晶胞参数变化不明显。同时,热处理金红石样品的可见光响应能力得到大幅提高,900℃样品在600nm处的光吸收强度相对于原样增大了147.2%。在800℃及900℃样品中出现的微量单质铁为金属导体,其费米能级较低,与半导体金红石颗粒接触时可以快速转移光生电子,从而提高体系的可见光响应能力。

The micro-structure and photocatalytic activity of natural rutile, which was heated and annealed under hydrogen atmosphere, was studied here. Several conventional mineralogical test methods were used, such as X-ray diffraction （XRD）, environmental scanning electron microscopy （ESEM）, UV-vis diffusive reflectance absorption spectral analysis and structural refinement using GSAS software with Rietveld method. The natural rutile samples used in this study are found in a metamorphic deposit and collected from Shanxi province, China. The experimental results indicate that V, Fe and other impurities exist in the crystal lattice of natural rutile as isomorphous substitution for Ti ions, which causes distortion of crystal lattice and effectively enhances the photocatalytic activity of the specimens. As the temperature increased, parts of the isomorphous substituted ferric ions were gradually reduced to divalent and elemental iron. On one hand, the unit cell parameters of rutile decreased because of escaping of ions from the lattice, which have larger ionic radii than Ti 4＋ ion. On the other hand, the unit cell parameters would be increased because of thermal expansion caused by the heat treatment. Therefore, no significant change in the unit cell parameters was observed. At the same time, the visible light response abilities of heated rutile samples were largely improved with increasing temperature. Compared to the original sample RZM, the light absorption intensity of sample, which was subjected to heat treatment at 900℃, was enlarged by 147.2 % at 600 nm. Rietveld refinements suggested that a small amount of simple substance iron appeared when the heating temperature reached 800 ℃ and 900 ℃. Iron is a metallic conductor and has lower Fermi level.When iron was in contact with semiconductor rutile particles, the photo-induced electrons could be transferred rapidly, thereby enhancing the visible light response ability of the system.