表面结构决定了晶体材料的许多重要的物理化学性质.可控制备具有特定表面结构的微纳米晶体,从而实现对晶体材料性能的改善,引起了广泛的关注.本课题组近期相关的研究表明,晶体生长体系中,生长单元的过饱和度决定了晶体的表面结构.基于已有研究结果,本文通过调节混合溶剂体系中乙二醇和水的相对体积比及Na OH的用量,改变晶体生长体系中生长单元的过饱和度,合成了亚微米尺寸的Na Ta O3立方体、削角立方体、削角削棱立方体和准球体.低过饱和度条件下,形成的Na Ta O3颗粒是低能{100}晶面裸露的立方体;随过饱和度的增加,立方体的角和棱逐渐削去,裸露表面能更高的晶面;极高过饱和度条件下,则形成准球体Na Ta O3颗粒.这种准球体的形成难以用经典的晶体生长理论加以解释.通过研究同样受过饱和度影响的二维晶核生成功(Whkl),发现在极高的过饱和度的条件下,晶体生长趋于各向同性,合理地解释了准球体的形成机制.
Spin-polarized density functional theory(DFT)calculations are carried out to determine the site preference of H adsorption on Pd(100)surface and subsurface.We carefully scrutinize the energy difference between different patterns at=0.50 ML and confirm the LEED observation that surface adsorption can form c(2×2)ordering structure.On the contrary,we disclose that p(2×1)structure become more favorable than c(2×2)for subsurface adsorption.These site preferences are rationalized via an analysis of the layer and orbital resolved density of states.Furthermore,we propose that the interstitial charge as a key factor determining the preferred H adsorbed site.
This paper describes a robust method for the synthesis of high-quality ZIF-8 nanocrystals using reverse micelles as discrete nanoscale reactors.The precise size control of ZIF-8 nanocrystals is conveniently achieved by tuning the concentration of precursors,reaction temperatures,the amount of water,and the structure of surfactants.The as-synthesized ZIF-8 nanocrystals are of narrow distribution and tunable size.A size-dependent catalytic activity for Knoevenagel condensation reaction is further demonstrated by using ZIF-8 nanocrystals with different sizes as the catalysts.This facile method opens up a new opportunity in the synthesis of various ZIFs nanocrystals.
