Zinc-Containing Magnetic Oxides Stabilized by a Polymer: One Phase or Two?

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• 作者：Nicholas Baird ; Yaroslav Losovyj ; Ekaterina Yu. Yuzik-Klimova ; Nina V. Kuchkina ; Zinaida B. Shifrina ; Maren Pink ; Barry D. Stein ; David Gene Morgan ; Tianhao Wang ; Mikhail A. Rubin ; Alexander I. Sidorov ; Esther M. Sulman ; Lyudmila M. Bronstein
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2016
• 出版时间：January 13, 2016
• 年：2016
• 卷：8
• 期：1
• 页码：891-899
• 全文大小：467K
• ISSN：1944-8252

文摘

Here we developed a new family of Zn-containing magnetic oxides of different structures by thermal decomposition of Zn(acac)₂ in the reaction solution of preformed magnetite nanoparticles (NPs) stabilized by polyphenylquinoxaline. Upon an increase of the Zn(acac)₂ loading from 0.15 to 0.40 mmol (vs 1 mmol of Fe(acac)₃), the Zn content increases, and the Zn-containing magnetic oxide NPs preserve a spinel structure of magnetite and an initial, predominantly multicore NP morphology. X-ray photoelectron spectroscopy (XPS) of these samples revealed that the surface of iron oxide NPs is enriched with Zn, although Zn species were also found deep under the iron oxide NP surface. For all the samples, XPS also demonstrates the atom ratio of Fe³⁺/Fe²⁺ = 2:1, perfectly matching Fe₃O₄, but not ZnFe₂O₄, where Fe²⁺ ions are replaced with Zn²⁺. The combination of XPS with other physicochemical methods allowed us to propose that ZnO forms an ultrathin amorphous layer on the surface of iron oxide NPs and also diffuses inside the magnetite crystals. At higher Zn(acac)₂ loading, cubic ZnO nanocrystals coexist with magnetite NPs, indicating a homogeneous nucleation of the former. The catalytic testing in syngas conversion to methanol demonstrated outstanding catalytic properties of Zn-containing magnetic oxides, whose activities are dependent on the Zn loading. Repeat experiments carried out with the best catalyst after magnetic separation showed remarkable catalyst stability even after five consecutive catalytic runs.