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Anisotropy in Stable Conformations of Hydroxylate Ions between the {001} and {110} Planes of TiO2 Rutile Crystals for Glycolate, Lactate, and 2-Hydroxybutyrate Ions Studied by Metadynamics Method.
ACS Omega ( IF 3.7 ) Pub Date : 2019-06-25 , DOI: 10.1021/acsomega.9b01100
Hiroki Nada 1 , Makoto Kobayashi 2 , Masato Kakihana 2
Affiliation  

Control over TiO2 rutile crystal growth and morphology using additives is essential for the development of functional materials. Computer simulation studies on the thermodynamically stable conformations of additives at the surfaces of rutile crystals contribute to understanding the mechanisms underlying this control. In this study, a metadynamics method was combined with molecular dynamics simulations to investigate the thermodynamically stable conformations of glycolate, lactate, and 2-hydroxybutyrate ions at the {001} and {110} planes of rutile crystals. Two simple atom-atom distances were selected as collective variables for the metadynamics method. At the {001} plane, a conformation in which the COO- group was oriented toward the surface was found to be the most stable for the lactate and 2-hydroxybutyrate ions, whereas a conformation in which the COO- group was oriented toward water was the most stable for the glycolate ion. At the {110} plane, a conformation in which the COO- group was oriented toward the surface was the most stable for all three hydroxylate ions, and a second most stable conformation was also observed for the lactate ion at positions close to the {110} plane. For all three hydroxylate ions (α-hydroxycarboxylate ions), the stability of the most stable conformation was higher for the {110} plane than for the {001} plane. At both planes, the stability of the most stable conformation was highest for the 2-hydroxybutyrate ion and lowest for the glycolate ion. Supposing that all three hydroxylate ions serve to decrease the surface free energy at the rutile surface and that a more stable conformation at the rutile surface leads to a greater decrease in the surface free energy, the present results partially explain experimentally observed differences in the changes in growth rate and morphology of rutile crystals in the presence of glycolic, lactic, and 2-hydroxybutyric acids.

中文翻译:

通过元动力学方法研究了 TiO2 金红石晶体 {001} 和 {110} 平面之间羟基离子对乙醇酸根、乳酸根和 2-羟基丁酸根离子稳定构象的各向异性。

使用添加剂控制 TiO2 金红石晶体生长和形态对于功能材料的开发至关重要。对金红石晶体表面添加剂热力学稳定构象的计算机模拟研究有助于理解这种控制的机制。本研究将元动力学方法与分子动力学模拟相结合,研究了乙醇酸根、乳酸根和2-羟基丁酸根离子在金红石晶体{001}和{110}面上的热力学稳定构象。选择两个简单的原子间距离作为元动力学方法的集体变量。在{001}平面,COO-基团朝向表面的构象被发现对于乳酸盐和2-羟基丁酸盐离子是最稳定的,而COO-基团朝向水的构象是最稳定的。对乙醇酸根离子最稳定。在{110}平面,COO-基团朝向表面的构象对于所有三个羟基离子来说是最稳定的,并且在靠近{110}平面的位置还观察到乳酸根离子的第二稳定构象。 } 飞机。对于所有三种羟基离子(α-羟基羧酸根离子),{110} 平面的最稳定构象的稳定性高于 {001} 平面。在两个平面上,2-羟基丁酸根离子的最稳定构象的稳定性最高,乙醇酸根离子的最稳定构象的稳定性最低。假设所有三种羟基离子都用于降低金红石表面的表面自由能,并且金红石表面更稳定的构象导致表面自由能更大的降低,本结果部分解释了实验观察到的变化的差异。在乙醇酸、乳酸和 2-羟基丁酸存在下金红石晶体的生长速率和形态。
更新日期:2019-06-25
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