Adsorption of Water Molecule on Calcium Fluoride and Magnesium Fluoride Surfaces: A Combined Theoretical and Experimental Study

Abstract

The adsorption and dissociation of H2O molecule on various surfaces of MgF2 and CaF2 have been investigated theoretically by using a dispersion-corrected density functional theory based method. The calculated adsorption energy of H2O molecule on the low index CaF2(110) and CaF2(111) surfaces ranges from −0.20 to −0.50 eV, smaller than those on the low index MgF2(001) and MgF2(110) with values from −0.80 to −1.06 eV. The modeling shows that the dissociation of water molecule is possible on the high index CaF2(210) surface and the low index MgF2(001) and MgF2(110) surfaces as revealed by the calculations that the dissociated states of H2O are thermodynamically more stable. Furthermore, for MgF2(001) and MgF2(110) surfaces, the dissociation process is almost barrierless, suggesting that the OH groups on the surfaces could be formed easily. These theoretical predictions suggest that MgF2 is superior to CaF2 in terms of water adsorption affinity, and high temperatures may be needed to remove the adsorbed water molecules and the OH groups on the surfaces, which were confirmed by the in situ FT-IR spectra of the synthesized MgF2 and CaF2 samples. The broad peak for CaF2 ranging from 3100 to 3600 cm–1 can be completely removed with a temperature of 573 K, while a higher temperature of 923 K is required for MgF2.

Ion Adsorption and Desorption at the CaF2‐Water Interface Probed by Flow Experiments and Vibrational Spectroscopy

“…Obtaining such insights is very challenging, as is clear from the common mineral fluorite (i.e., calcium fluoride, CaF 2 ). There are numerous studies elaborating on the structure and dynamics of the fluorite‐water interface, its surface potential, streaming potential, and surface chemistry [5–17] . In 2004, Miller et al [7] .…”

Preparation of CaF2 Microspheres with Nanopetals for Water Vapor Adsorption

“…The FT-IR spectra for both FL-CaF 2 and FL-CaF 2 -R are almost identical to those for CaF 2 nanoparticles reported in our previous work. 33 It is found that: (1) the adsorbed water molecules cannot be completely desorbed by the prolonged evacuation at low temperatures, implying that CaF 2 interacts with the adsorbed water molecules strongly; (2) the adsorbed water molecules on the fresh sample will be completely desorbed under vacuum at temperatures up to 573 K for 7 h, which is in good agreement with the observation by Barraclough and Hall 14 who claimed that the strongly adsorbed water molecules might be "trapped" on the specific surface of CaF 2 during the synthesis; and (3) after the fresh sample is outgassed at 573 K, the readsorbed water molecules on the CaF 2 surface can be completely desorbed under vacuum at 473 K for 3 h.…”

Fabrication of Metal-Insulator-Metal Nanostructures Composed of Au-MgF2-Au and Its Potential in Responding to Two Different Factors in Sample Solutions Using Individual Plasmon Modes

“…The disk-stacked MIM nanostructures are expected to have two LSP modes that generate electric fields outside the MIM nanostructures and inside the insulator layer, and are expected to independently respond to the changes in two phases: the surrounding medium and inside the insulator layer. In addition, by introducing MgF 2 , which is known to adsorb hydroxyl groups of water molecules [40,41] as the insulator layer, the MIM nanostructures are expected to respond to the hydroxyl group by the LSP mode, which generates electric fields inside the insulator layer. By combining the individual mode distribution and the adsorption characteristics of MgF 2 , the MIM nanostructures are expected to monitor the information of both the RI change in the solution and the changes within the MgF 2 layer (corresponding to the interaction of molecules in solution with MgF 2 ).…”