Tominaka Satoshi, Yamada Hiroki, Hiroi Satoshi, Kawaguchi Saori I, Ohara Koji
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
Research and Utilization Division, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-gun, Hyogo 679-5198, Japan.
ACS Omega. 2018 Aug 9;3(8):8874-8881. doi: 10.1021/acsomega.8b01693. eCollection 2018 Aug 31.
The formation of titanium dioxides, such as rutile and anatase, is known to proceed through the formation of a lepidocrocite-type layered structure under hydrothermal conditions, but the nucleation of this intermediate is still not understood well. Here, the nucleation of lepidocrocite-type layered titanates under hydrothermal conditions is observed by tracking the structural changes by in situ time-resolved pair distribution function analyses. We found that titanate clusters or corrugated layered prestructures having <1 nm domains with lepidocrocite-type connectivity were formed even before thermal treatment in alkaline aqueous solution. Upon thermal treatment, a two-dimensional layered structure grew directly from the prestructure, not from the amorphous polymeric hydroxide dissolved in the solution. Thus, we conclude that the formation of the lepidocrocite-like prestructure is the key for forming a layered titanate under hydrothermal conditions.
众所周知，在水热条件下，诸如金红石和锐钛矿等二氧化钛的形成过程会经过纤铁矿型层状结构的形成阶段，但这种中间体的成核过程仍未被充分理解。在此，通过原位时间分辨对分布函数分析追踪结构变化，观察了水热条件下纤铁矿型层状钛酸盐的成核过程。我们发现，即使在碱性水溶液中进行热处理之前，就已形成了具有纤铁矿型连通性、域尺寸小于1纳米的钛酸盐簇或波纹状层状预结构。经过热处理后，二维层状结构直接从预结构生长而来，而非从溶解在溶液中的无定形聚合氢氧化物生长而来。因此，我们得出结论，类纤铁矿预结构的形成是水热条件下形成层状钛酸盐的关键。
