化学学报 ›› 2013, Vol. 71 ›› Issue (03): 360-366.DOI: 10.6023/A12121014 上一篇    下一篇

研究论文

基于软硬酸碱理论的单分散中重稀土硫氧化物纳米板的可控合成

顾均, 丁祎, 柯俊, 张亚文, 严纯华   

  1. 稀土材料化学及应用国家重点实验室 北京大学-香港大学稀土材料和生物无机化学联合实验室 北京大学化学与分子工程学院 北京分子科学国家实验室 北京 100871
  • 收稿日期:2012-12-07 出版日期:2013-03-14 发布日期:2013-01-09
  • 通讯作者: 张亚文,严纯华 E-mail:ywzhang@pku.edu.cn;yan@pku.edu.cn
  • 基金资助:

    项目受国家自然科学基金(Nos.21025101,21271011)资助.

Controllable Synthesis of Monodispersed Middle and Heavy Rare Earth Oxysulfide Nanoplates Based on the Principles of HSAB Theory

Gu Jun, Ding Yi, Ke Jun, Zhang Yawen, Yan Chunhua   

  1. Beijing National Laboratory for Molecular Science, State Key Laboratory of Rare Earth Materials Chemistry and Applications PKU-HKU Joint Laboratory in Rare Earth Materials and Bioinorganic Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
  • Received:2012-12-07 Online:2013-03-14 Published:2013-01-09
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 21025101, 21271011).

根据软硬酸碱理论, 中重稀土+3价离子硬度高, 与S2-离子亲合能力弱, 而与O2-离子亲合能力强, 因此很难通过基于高沸点有机溶剂的前驱体热分解法合成中重稀土硫氧化物纳米材料. 发展了制备掺杂或非掺杂的中重稀土(Eu, Gd, Er, Y, Yb)的单分散硫氧化物纳米板的前驱体热分解方法. 密度泛函理论计算表明, 从轻稀土元素到中重稀土元素, 合成硫氧化物所需要的硫元素化学势逐渐升高. 实验结果表明: 在油胺中以H2S气体为硫化试剂, 以分解温度低的稀土乙酰丙酮盐为前驱体在280 ℃条件下反应, 可以有效提高反应体系中硫元素的化学势, 从而利于目标硫氧化物纳米晶的生成. 其中, 所获得的Y2O2S:Eu纳米板在251 nm紫外光激发下可发出红色荧光; 而与体相材料相比, 因其表面原子比例很高且晶化度较低, 导致其荧光寿命较短、量子产率较低.

关键词: 稀土硫氧化物, 纳米材料, 液相合成, 密度泛函理论计算, 荧光

Based on the theory of hard and soft acids and bases, trivalent ions of middle and heavy rare earths belong to very hard acids, which possess weak affinity towards S2- ions but strong affinity to O2- ions. So it is difficult to synthesize middle and heavy rare earth oxysulfide nano-materials through the thermolysis method in high-boiling-point organic solvent. In this article, monodispersed oxysulfide nanoplates of Y, Eu, Gd, Er and Yb were synthesized through this thermolysis method we developed. Both sodium-doped and undoped rare earth oxysulfide nanoplates could be prepared, and the doping of sodium ions could promote the crystallization of the nanoplates. Rare earth acetylacetonates were used as metal precursors and H2S gas as the sulfurizing reagent. The reactions were conducted in oleylamine at 280 ℃ for 1 hour. The thermogravimetric analysis of the precursor showed that the initial decomposition temperature of the rare earth acetylacetonates is about 200 ℃, which is much lower than that of rare earth oleates. The transmission electron microscopy observation and energy dispersive X-ray analyses of the intermediate products during the synthesis of the nanoplates showed that rare earth oxide nanoplates formed firstly at about 220 ℃, and these nanoplates transformed to oxysulfide nanoplates gradually during the temperature ramping period. Density functional theory calculation was used to compare the total free energy of the oxide and oxysulfide of different rare earth elements. According to this thermodynamical comparison, we concluded that, from light rare earths to heavy rare earths, higher chemical potential of sulfur is needed to obtain the oxysulfide rather than oxide. On one hand, H2S gas has higher sulphurizing power than sulfur. On the other hand, a comparatively low reaction temperature favors the dissolving of H2S in oleylamine. As a result, the chemical potential of sulfur in synthetic system could be effectively increased by using rare earth acetylacetonates as the precursors instead of rare earth oleates, and using H2S gas as sulphurizing agent instead of sulfur, which made it possible to prepare middle and heavy rare earth oxysulfide nanoplates in oleylamine. Fluorescent measurements showed that as-synthesized Y2O2S:Eu nanoplates could emit red light under 251 nm ultraviolet light excitation. For Y2O2S:Eu nanoplates, the fluorescence life time was shorter and quantum yield was lower in comparison with the corresponding bulk counterpart, possibly due to its much higher portion of surface atoms as well as lower crystallinity.

Key words: rare earth oxysulfide, nanomaterial, liquid synthesis, density functional theory calculation, fluorescence