Redox Reactivity of Colloidal Nanoceria and Use of Optical Spectra as an In Situ Monitor of Ce Oxidation States
Redox Reactivity of Colloidal Nanoceria and Use of Optical Spectra as an In Situ Monitor of Ce Oxidation States
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DOI：
10.1021/acs.inorgchem.8b02598
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发表时间：
2018-11-19
影响因子：
4.6
通讯作者：
Mayer, James M.
中科院分区：
文献类型：
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作者：
Damatov, Delina;Laga, Stephanie M.;Mayer, James M.
纳米级氧化铈在催化、生物医学、可再生能源和许多其他领域越来越受到关注。其多功能性源自于形成包含 Ce3+ 和 Ce4+ 离子的非化学计量氧化物的能力。这项工作描述了胶体氧化铈纳米晶体（称为纳米二氧化铈）在非常温和的溶液条件下的氧化和还原反应性。例如，所制备的纳米二氧化钛将氢醌氧化为苯醌，同时还原一些 Ce4+ 离子。在乙醇存在下通过紫外线照射制备的高度还原的纳米二氧化钛将氢醌氧化回苯醌。这种反应性和相关的反应性允许在不改变尺寸或其他性质的情况下调节纳米晶体中的平均铈氧化态。纳米二氧化铈中 Ce3+ 和 Ce4+ 的含量通过 X 射线吸收光谱和反应的化学计量（使用 H-1 NMR 光谱测量）测定。结果首次证明纳米二氧化钛的吸光度与样品中 Ce3+ 的百分比呈线性相关。吸收的减少（能带边缘的蓝移）是由于 Ce3+ 量的增加，而不是量子限制效应。这些发现证明了纳米二氧化铈易于溶液反应，并建立了紫外-可见光谱作为原位测定二氧化铈纳米材料中 Ce 氧化态的强大新工具。
Nanoscale cerium oxide is of increasing interest in catalysis, biomedicine, renewable energy, and many other fields. Its versatility derives from the ability to form nonstoichiometric oxides that include both Ce3+ and Ce4+ ions. This work describes oxidation and reduction reactivity of colloidal cerium oxide nanocrystals, termed nanoceria, under very mild solution conditions. For instance, the as-prepared nanoceria oxidizes hydroquinone to benzoquinone, with reduction of some of the Ce4+ ions. Highly reduced nanoceria, prepared by UV irradiation in the presence of ethanol, oxidize hydroquinone back to benzoquinone. This and related reactivity allow tuning of the average cerium oxidation state in the nanocrystals without changes in size or other properties. The amounts of Ce3+ and Ce4+ in the nanoceria were determined both by Xray absorption spectroscopy and from the stoichiometry of the reactions, measured using H-1 NMR spectroscopy. The results demonstrate, for the first time, that the optical absorbance of nanoceria is linearly related to the percent Ce3+ in the sample. The decrease in absorption (blue-shift of the band edge) is due to increasing amounts of Ce3+, not to a quantum confinement effect. These findings demonstrate the facile solution reactivity of nanoceria and establish UV-visible spectroscopy as a powerful new tool for in situ determination of Ce oxidation states in ceria nanomaterials.