Jeong Eun-Suk, Hwang In-Hui, Han Sang-Wook
Department of Physics Education, Institute of Fusion Science, and Institute of Science Education, Jeonbuk National University, Jeonju 54896, Korea.
X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States.
Langmuir. 2020 Sep 8;36(35):10565-10576. doi: 10.1021/acs.langmuir.0c01903. Epub 2020 Aug 28.
The crystallization mechanism of transition-metal oxides (TMOs) in a solution was examined based on ZnO crystallization using in-situ x-ray absorption fine structure (XAFS) measurements at the Zn K edge and semi-empirical quantum chemistry (SEQC) simulations. The XAFS results quantitatively determine the local structural and chemical properties around a zinc atom at successive stages from Zn(NO) to ZnO in an aqueous solution. The results also show that a zinc atom in Zn(NO) ions dissolves in a solution and bonds with approximately three oxygen atoms at room temperature (RT). When hexamethylenetetramine (CHN) is added to the solution at RT, a stable Zn-O complex consisting of six Zn(OH)s is formed, which is a seed of ZnO crystals. The Zn-O complexes partially and fully form into a wurtzite ZnO at 60 and 80 °C, respectively. Based on the structural properties of Zn-O complexes determined by extended-XAFS (EXAFS), SEQC simulations clarify that Zn-O complexes consecutively develop from a linear structure to a polyhedral complex structure under the assistance of hydroxyls (OHs) in an aqueous solution. In a solution with a sufficient concentration of OHs, ZnO spontaneously grows through the merging of ZnO seeds (6Zn(OH)s), reducing the total energy by the reactions of OHs. ZnO crystallization suggests that the crystal growth of TMO can only be ascribed to Ostwald ripening when it exactly corresponds to the size growth of TMO particles.
基于在锌K边的原位X射线吸收精细结构（XAFS）测量和半经验量子化学（SEQC）模拟，以氧化锌结晶为例研究了过渡金属氧化物（TMO）在溶液中的结晶机制。XAFS结果定量地确定了水溶液中从Zn(NO)到ZnO连续阶段锌原子周围的局部结构和化学性质。结果还表明，Zn(NO)离子中的锌原子在室温（RT）下溶解在溶液中并与大约三个氧原子键合。当在室温下向溶液中加入六亚甲基四胺（CHN）时，形成了由六个Zn(OH)组成的稳定的Zn-O络合物，这是ZnO晶体的晶种。Zn-O络合物分别在60和80℃时部分和完全形成纤锌矿ZnO。基于扩展XAFS（EXAFS）确定的Zn-O络合物的结构性质，SEQC模拟表明，在水溶液中羟基（OH）的辅助下，Zn-O络合物从线性结构连续发展为多面体络合物结构。在具有足够浓度OH的溶液中，ZnO通过ZnO晶种（6Zn(OH)）的合并自发生长，通过OH的反应降低总能量。ZnO结晶表明，当TMO的晶体生长与TMO颗粒的尺寸增长完全对应时，TMO的晶体生长只能归因于奥斯特瓦尔德熟化。
