Sulfidation Mechanism of Pure and Cu-Doped ZnO Nanoparticles at Moderate Temperature: TEM and In Situ XRD Studies

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• 作者：Igor Bezverkhyy ; Jonathan Skrzypski ; Olga Safonova ; Jean-Pierre Bellat
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：July 12, 2012
• 年：2012
• 卷：116
• 期：27
• 页码：14423-14430
• 全文大小：661K
• 年卷期：v.116,no.27(July 12, 2012)
• ISSN：1932-7455

文摘

Sulfidation mechanism of pure and Cu-doped ZnO nanoparticles (Cu_0.03Zn_0.97O and Cu_0.06Zn_0.94O) at 250 and 350 掳C was studied by transmission electron microscopy (TEM) and in situ synchrotron XRD. For nondoped ZnO, we observed by TEM that partial reaction with H₂S is accompanied by the formation of voids at the ZnO/ZnS interface. This phenomenon (known as the Kirkendall effect) confirms that sulfidation of nanosized ZnO by gaseous H₂S proceeds via the outward growth of ZnS: Zn²⁺ and O^{2鈥?/sup> are transferred to the external (ZnS/gas) surface, where zinc is combined with sulfur and oxygen reacts with protons yielding H₂O. During sulfidation of Cu-doped ZnO, the cavities do not form, showing that the sulfidation proceeds by another mechanism, the inward growth, which implies that S2鈥?/sup> anions diffuse from the external surface to the internal ZnO/ZnS interface, where they exchange with O2鈥?/sup> anions. The change of the transformation mechanism is attributed to a significant acceleration of sulfur transport (lattice or grain boundary) through the Cu-containing ZnS layer due to the presence of sulfur vacancies formed after the charge compensation of Cu1+ replacing Zn2+. The conclusion about the enhanced sulfur diffusion in Cu-containing ZnS is further supported by the time-resolved in situ XRD measurements. It is found that in the case of nondoped ZnO the size of formed ZnS crystallites remains constant during reaction. In contrast, a pronounced crystalline growth takes place in Cu-doped samples during sulfidation under rather mild conditions (250 掳C for Cu_0.06Zn_0.94O) pointing out a high mobility of sulfur anions in Cu-containing ZnS particles.}