{111}晶面暴露对介孔金红石TiO_2单晶光催化产氢的促进作用（英文）
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摘要
光催化反应发生在半导体材料的表面,材料表面的原子/电子结构直接影响光催化剂的活性或选择性.因此,发展具有特定晶面的半导体光催化剂受到各国学者的普遍关注,被认为是调控光催化材料性能的有效途径之一.自2008年yang等首次合成高表面能{001}晶面占优的锐钛矿Ti O2单晶以来,控制合成暴露不同晶面Ti O2晶体的研究得到了迅猛的发展,已发展了多种方法合成了具有不同晶面的Ti O2晶体.研究表明,选择性地暴露特定的活性晶面能够显著地提高光催化剂的活性或者改变光催化反应的选择性.但是,含有完整晶面构型的Ti O2单晶样品的颗粒尺寸一般都较大,通常为几微米,因而显著增加了光生载流子传输与分离的难度,并且导致材料较小的比表面积,限制了对光催化活性的进一步提高.能否在合成含特定晶面单晶的同时增加多孔结构成为有效解决这一问题的关键.最近,Crossland等采用晶种模板法成功合成了介孔的锐钛矿Ti O2单晶,并且通过光电器件研究证实了采用该思路可进一步提高材料的光电性能.金红石Ti O2在光催化全分解水方面具有独特的优势,然而关于多孔单晶金红石Ti O2的研究相对较少,尤其是合成热力学不稳定的高表面能{111}晶面完全暴露的多孔金红石单晶面临较大的技术挑战因而一直未见文献报道.本文利用晶种模板法,以Ti Cl4溶液为含Ti前驱体、Na F为形貌控制剂、采用水热处理制备出不同比例{111}晶面的介孔金红石单晶.我们前期工作表明,Na F可作为形貌控制剂合成低表面能{110)晶面占优的介孔金红石单晶.本文发现,通过改变Na F的添加量,可有效调变{111}/{110}晶面比例,最终合成完全暴露{111}高表面能的介孔金红石Ti O2单晶.扫描电镜结果显示,当添加20 mg NaF时,合成{110}占优的具有高长径比的介孔晶体;当Na F用量增加到40 mg时{110}晶面进一步缩短;至80 mg时则制备出{111})高能面完全暴露的金红石Ti O2晶体.值得注意的是,对比研究表明,不采用模板合成了与多孔晶体完全相对应的不同{111}/(110}晶面比例的实心金红石晶体.透射电镜及选区电子衍射以及结合X射线衍射进一步证实,多孔的金红石Ti O2晶体与实心金红石单晶均都为单晶结构,孔结构贯穿于样品内部且具有较高的晶面结晶性.氮气吸附实验发现,虽然三个不同晶面比例介孔金红石单晶样品间的形貌具有显著的差异,但比表面积非常相近(分别为24,25,28 m2/g),孔径也都为50 nm左右,该值与所用SiO 2模板球的直径以及TEM观察结果相一致.光催化产氢性能结果表明,选择性的暴露活性晶面显著提高了光催化活性,仅含高能面{111}的介孔金红石单晶样品具有最高的产氢速率(约800μmol h–1 g–1),比常规{110}晶面占优的介孔单晶样品速率提高了约一倍.尤其比实心单晶样品的产氢速率提高了至少一个数量级,这应归结于介孔结构特性所导致的表面反应活性位增加、电子传输距离缩短以及光吸收增强协同作用的结果.
The development of semiconductor photocatalysts with highly reactive facets exposed has great potential to improve their photocatalytic reactivity. We report the synthesis of mesoporous rutile TiO 2 single crystals with tunable ratios of {110} and {111} facets through the seeded-template hydrothermal method. With increasing the amount of morphology controlling agent NaF,the facet ratio of {111} to {110} increases,and eventually the mesoporous rutile TiO 2 single crystals with wholly exposed {111} reactive facets are obtained. The resultant faceted mesoporous single crystals exhibit a superior photocatalytic performance of hydrogen evolution to mesoporous single crystals with a large percentage of thermodynamically stable {110} facets,as well as the solid rutile single crystals. ? 2015,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.
The development of semiconductor photocatalysts with highly reactive facets exposed has great potential to improve their photocatalytic reactivity. We report the synthesis of mesoporous rutile TiO 2 single crystals with tunable ratios of {110} and {111} facets through the seeded-template hydrothermal method. With increasing the amount of morphology controlling agent NaF,the facet ratio of {111} to {110} increases,and eventually the mesoporous rutile TiO 2 single crystals with wholly exposed {111} reactive facets are obtained. The resultant faceted mesoporous single crystals exhibit a superior photocatalytic performance of hydrogen evolution to mesoporous single crystals with a large percentage of thermodynamically stable {110} facets,as well as the solid rutile single crystals. ? 2015,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.
引文
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