Thin Water Films at Multifaceted Hematite Particle Surfaces

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• 作者：Jean-Fran莽ois Boily ; Merve Ye艧ilba艧 ; Munshi Md. Musleh Uddin ; Lu Baiqing ; Yulia Trushkina ; Germ脿n Salazar-Alvarez
• 刊名：Langmuir
• 出版年：2015
• 出版时间：December 8, 2015
• 年：2015
• 卷：31
• 期：48
• 页码：13127-13137
• 全文大小：659K
• ISSN：1520-5827

文摘

Mineral surfaces exposed to moist air stabilize nanometer- to micrometer-thick water films. This study resolves the nature of thin water film formation at multifaceted hematite (伪-Fe₂O₃) nanoparticle surfaces with crystallographic faces resolved by selected area electron diffraction. Dynamic vapor adsorption (DVA) in the 0鈥?9 Torr range at 298 K showed that these particles stabilize water films consisting of up to 4鈥? monolayers. Modeling of these data predicts water loadings in terms of an 鈥渁dsorption regime鈥?(up to 16 H₂O/nm²) involving direct water binding to hematite surface sites, and of a 鈥渃ondensation regime鈥?(up to 34 H₂O/nm²) involving water binding to hematite-bound water nanoclusters. Vibration spectroscopy identified the predominant hematite surface hydroxo groups (鈭扥H, 渭鈥揙H, 渭₃鈥揙H) through which first layer water molecules formed hydrogen bonds, as well as surface iron sites directly coordinating water molecules (i.e., as geminal 畏鈥?OH₂)₂ sites). Chemometric analyses of the vibration spectra also revealed a strong correspondence in the response of hematite surface hydroxo groups to DVA-derived water loadings. These findings point to a near-saturation of the hydrogen-bonding environment of surface hydroxo groups at a partial water vapor pressure of 鈭? Torr (鈭?0% relative humidity). Classical molecular dynamics (MD) resolved the interfacial water structures and hydrogen bonding populations at five representative crystallographic faces expressed in these nanoparticles. Simulations of single oriented slabs underscored the individual roles of all (hydro)oxo groups in donating and accepting hydrogen bonds with first layer water in the 鈥渁dsorption regime鈥? These analyses pointed to the preponderance of hydrogen bond-donating 鈭扥H groups in the stabilization of thin water films. Contributions of 渭鈥揙H and 渭₃鈥揙H groups are secondary, yet remain essential in the stabilization of thin water films. MD simulations also helped resolve crystallographic controls on water鈥搘ater interactions occurring in the 鈥渃ondensation regime鈥? Water鈥搘ater hydrogen bond populations are greatest on the (001) face, and decrease in importance in the order (001) > (012) 鈮?(110) > (014) 鈮?(100). Simulations of a single (鈭? nm 脳 鈭?6 nm 脳 鈭?6 nm) nanometric hematite particle terminated by the (001), (110), (012), and (100) faces also highlighted the key roles that sites at particle edges play in interconnecting thin water films grown along contiguous crystallographic faces. Hydroxo鈥搘ater hydrogen bond populations showed that edges were the preferential loci of binding. These simulations also suggested that equilibration times for water binding at edges were slower than on crystallographic faces. In this regard, edges, and by extension roughened surfaces, are expected to play commanding roles in the stabilization of thin water films. Thus, in focusing on the properties of nanometric-thick water layers at hematite surfaces, this study revealed the nature of interactions between water and multifaced particle surfaces. Our results pave the way for furthering our understanding of mineral-thin water film interfacial structure and reactivity on a broader range of materials.