分层组织的纳米结构TiO2用于MEMS应用
Hierarchically organized nanostructured TiO2 for photocatalysis applications
摘要：
采用无模板反应脉冲激光沉积（PLD）技术制备纳米TiO 2分级结构。通过适当选择沉积参数，证明了对TiO 2微结构形态的精细控制，从经典的致密/柱状膜到超细纳米颗粒（<10 nm）的不同层次组装的茂密森林，直到更无序的气凝胶型结构。相应地，膜密度相对于本体TiO 2膜而变化，孔隙度从48%到超过90%。这些结构相对于在400摄氏度下的热处理是稳定的，这导致晶体有序化，但不会导致纳米级的形态变化。无论是作为沉积和退火膜表现出非常有前途的光催化性能，甚至优于标准Degussa P25粉末，作为一个模型分子的硬脂酸的降解证明。所观察到的动力学与PLD生长材料的特殊形态相关。我们发现，三维多尺度分层形态增强了反应动力学，并为质量传输和光子吸收创造了理想的环境，最大限度地提高了表面积与体积比，同时通过作为分配通道的大的树间空间提供了易于访问的孔隙率。报道的策略提供了一种通用的技术，通过超细纳米粒子的分级组装来制造高纵横比的3D二氧化钛微结构。除了光催化和催化应用之外，这种材料可能对同时需要高表面体积比和有效质量传输的应用感兴趣。
英文摘要：
A template-free process for the synthesis of nanocrystalline TiO2 hierarchical microstructures by reactive Pulsed Laser Deposition (PLD) is here presented. By a proper choice of deposition parameters a fine control over the morphology of TiO2 microstructures is demonstrated, going from classical compact/columnar films to a dense forest of distinct hierarchical assemblies of ultrafine nanoparticles (<10 nm), up to a more disordered, aerogel-type structure. Correspondingly, film density varies with respect to bulk TiO2 anatase, with a degree of porosity going from 48% to over 90%. These structures are stable with respect to heat treatment at 400 centigrade degrees, which results in crystalline ordering but not in morphological changes down to the nanoscale. Both as deposited and annealed films exhibit very promising photocatalytic properties, even superior to standard Degussa P25 powder, as demonstrated by the degradation of stearic acid as a model molecule. The observed kinetics are correlated to the peculiar morphology of the PLD grown material. We show that the 3D multi-scale hierarchical morphology enhances reaction kinetics and creates an ideal environment for mass transport and photon absorption, maximizing the surface area-to-volume ratio while at the same time providing readily accessible porosity through the large inter-tree spaces that act as distributing channels. The reported strategy provides a versatile technique to fabricate high aspect ratio 3D titania microstuctures through a hierarchical assembly of ultrafine nanoparticles. Beyond photocatalytic and catalytic applications, this kind of material could be of interest for those applications where high surface-to-volume and efficient mass transport are required at the same time.
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