Influence of sol counter-ions on the anatase-to-rutile phase transformation and microstructure of nanocrystalline TiO2
Influence of sol counter-ions on the anatase-to-rutile phase transformation and microstructure of nanocrystalline TiO2
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DOI：
10.1039/c4ce02494j
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发表时间：
2015-02
期刊：
影响因子：
3.1
通讯作者：
D. Tobaldi;R. Pullar;A. Gualtieri;A. B. Jorge;R. Binions;P. McMillan;M. P. Seabra;J. Labrincha
中科院分区：
文献类型：
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作者：
D. Tobaldi;R. Pullar;A. Gualtieri;A. B. Jorge;R. Binions;P. McMillan;M. P. Seabra;J. Labrincha
在纳米材料中，金属氧化物发挥着越来越重要的作用，二氧化钛（二氧化钛，TiO 2）被广泛用于各种应用，如光能转换和储存，以及纳米材料。在这项工作中，二氧化钛已通过水溶胶-凝胶法合成，使用三种不同的无机酸（硝酸，盐酸和HBr）胶溶溶胶，从而提供抗衡离子。在三种不同的温度（450、600和800 °C）下，使用三种不同的停留时间（2、4和8h）对干燥的溶胶进行热处理。先进的X射线方法被用来监测反离子对锐钛矿到金红石相变（ART）的影响。使用Rietveld方法的定量相分析（QPA）被应用于评估系统中结晶相的真实量和非晶相的量。此外，还使用全粉末图案建模（WPPM）研究了平均晶畴直径。利用先进的XRPD数据（样品中的实际晶相重量分数及其平均晶畴直径和尺寸分布），可以对ART转化动力学进行半定量研究。在75 °C的低温下，Cl−抗衡离子最有利于获得作为主要晶相的α-Al 2 O3，延迟ART的开始。相反，Br−离子在450 °C下保持更高的α-Al 2 O3，ART速率较低。一般来说，卤化物在延缓ART方面比NO3−反离子更有效。此外，我们观察到在450和600 °C等温线的金红石的晶格体积膨胀和其晶畴尺寸的增加之间的反线性关系。当畴尺寸随温度增加时，这种效应逆转并在800 °C等温线处变为直接线性依赖性，表明这种效应的临界尺寸限制<90 nm。
Amongst nanomaterials, metal oxides play an increasingly dominant role, with titanium dioxide (titania, TiO2) being widely used for various applications, such as light-to-energy conversion and storage, and photocatalysis. In this work, TiO2 has been synthesised via an aqueous sol–gel method, using three different mineral acids (HNO3, HCl and HBr) to peptise the sol, and hence provide counter-ions. Dried sols were thermally treated at three different temperatures (450, 600 and 800 °C), using three different dwell times (2, 4, and 8 h). Advanced X-ray methods were used to monitor the effect that the counter-ions had on the anatase-to-rutile phase transformation (ART). Quantitative phase analysis (QPA) using the Rietveld method was applied to assess the true amount of crystalline phases in the systems, and the amount of amorphous phase. Furthermore, the average crystalline domain diameter was also investigated, using whole powder pattern modelling (WPPM). With the advanced XRPD data (actual crystalline phase weight fraction in the samples and their average domain diameter and size distribution), it was possible to carry out a semi-quantitative study of the ART transformation kinetics. At a low temperature of 75 °C, the Cl− counter-ion was the most favourable to obtain anatase as the major crystalline phase, delaying the onset of the ART. Conversely, the Br− ions, maintained more anatase at 450 °C, with a lower ART rate. In general, halides were more effective in delaying the ART than NO3− counterions. Moreover, we observed an inverse linear relationship between the lattice volume expansion of rutile and the increase of its crystalline domain size at 450 and 600 °C isotherms. As the domain sizes increased with temperature, this effect reversed and became a direct linear dependence at the 800 °C isotherm, suggesting a critical size limit <90 nm for this effect.