Unique Structures and Vibrational Spectra of Protic Ionic Liquids Confined in TiO₂ Slits: The Role of Interfacial Hydrogen Bonds

Abstract

The ionic liquid (IL)/titanium dioxide (TiO2) interface exists in many application systems, such as nanomaterial synthesis, catalysis, and electrochemistry systems. The nanoscale interfacial properties in the above systems are a common issue. However, directly detecting the interfacial properties of nanoconfined ILs by experimental methods is still challenging. To help better learn about the interfacial issue, molecular dynamics simulations have been performed to explore the structures, vibration spectra, and hydrogen bond (HB) properties at the IL/TiO2 interface. Ethylammonium nitrate (EAN) ILs confined in TiO2 slit pores with different pore widths were studied. A unique vibrational spectrum appeared for EAN ILs confined in a 0.7 nm TiO2 slit, and this phenomenon is related to interfacial hydrogen bonds (HBs). An analysis of the HB types indicated that the interfacial NH3 + group of the cations was in an asymmetric HB environment in the 0.7 nm TiO2 slit, which led to the disappearance of the symmetric N–H stretching mode. In addition, the significant increase in the HB strength between NH3 + groups and the TiO2 surface slowed down the stretching vibration of the N–H bond, resulting in one peak in the vibrational spectra at a lower frequency. For the first time, our simulation work establishes a molecular-level relationship between the vibrational spectrum and the local HB environment of nanoconfined ILs at the IL/TiO2 interface, and this relationship is helpful for interface design in related systems.

Atomistic Molecular Dynamics Simulations of Lipids Near TiO2 Nanosurfaces

“…It can readily form hydrogen bonds with the oxygen bridges and hydroxyl groups on the TiO 2 surface. 63 Our data suggests that this binding mode is one of the main binding modes for POPE adsorption on the TiO 2 surface. A relatively short N–TiO 2 distance of 0.28–0.30 nm is typical for a hydrogen bond.…”

“…The ethanolamine group within the POPE lipid headgroup contains a positively charged, hydrogen-bond-donating fragment −NH 3 + . It can readily form hydrogen bonds with the oxygen bridges and hydroxyl groups on the TiO 2 surface . Our data suggests that this binding mode is one of the main binding modes for POPE adsorption on the TiO 2 surface.…”

Recent advances in theoretical investigation of titanium dioxide nanomaterials. A review

“…Moreover, the orientation of IL ions was depended on the width of TiO 2 , which significantly affects the microstructure of the EAN: the smaller is the TiO 2 wall, the stronger is hydrogen bonding of NH 3 + with the TiO 2 surface that results in lying down of cations along the TiO 2 wall. The increase of the width of the slits leaded to decreasing of the hydrogen bond strength and proportion between IL and TiO 2 and, consequently, to the interfacial reorientation of IL ions [137].…”

“…Chemisorption of solvent molecules and ligands onto the TiO 2 surface may strongly affect its electronic structure [133]. For these reasons, growing interest has been focused on modeling and simulation of TiO 2 in the non-aqueous environment [134][135][136][137][138][139].…”

“…Recently, particular interest has been paid to studying the interaction mode between TiO 2 and various ILs at the molecular level [136]. Dai et al studied the role of interfacial hydrogen bonding between the TiO 2 slits of different widths and ethylammoinium nitrate (EAN), determining the orientation of nanoconfined IL ions on the (100) rutile surface by combining of MD simulations and vibrational spectroscopy [137]. MD simulations were carried out with the NVT ensemble at T=353K by using the all-atom FF for the EAN IL, developed by Acevedo and Tirado-Rives [141].…”