Energy Landscape of Water and Ethanol on Silica Surfaces

Abstract

Fundamental understanding of small molecule -silica surface interactions at their interfaces is essential for the scientific, technological and medical communities. We report direct enthalpy of adsorption (∆h ads ) measurements for ethanol and water vapor on porous silica glass (CPG-10), in both hydroxylated and dehydroxylated (hydrophobic) forms. The results suggest a spectrum of energetics as a function of coverage, stepwise for ethanol but continuous for water.The zero coverage enthalpy of adsorption for hydroxylated silica shows the most exothermic enthalpies for both water (-72.7 ± 3.1 kJ/mol water) and ethanol (-78.0 ± 1.9 kJ/mol ethanol).The water adsorption enthalpy becomes less exothermic gradually until reaching its only plateau (-20.7 ± 2.2 kJ/mol water) reflecting water clustering on a largely hydrophobic surface, while the enthalpy of ethanol adsorption profile presents two well separated plateaus, corresponding to strong chemisorption of ethanol on adsorbate-free silica surface (-66.4 ± 4.8 kJ/mol ethanol), and weak physisorption of ethanol on ethanol covered silica (-4.0 ± 1.6 kJ/mol ethanol). On the other hand, dehydroxylation leads to missing water -silica interactions, whereas the number of ethanol binding sites is not impacted. The isotherms and partial molar properties of adsorption suggest that water may only bind strongly onto the silanols (which are a minor species on silica glass), whereas ethanol can interact strongly with both silanols and the hydrophobic areas of the silica surface.

Exploring catalyst passivation with NMR relaxation

“…36 Experimental studies of the adsorption of ethanol at silica suggest a similar coverage. 37 We define the thickness of a single adsorbed layer within a given liquid-saturated pore to be that of the kinetic diameter of the molecule under study, . For methanol, it is therefore assumed that 1 = ≈ 3.6 Å during our relaxation experiments.…”

Thermodynamic complexity of sulfated zirconia catalysts

“…In this context, calorimetry is a powerful tool to probe the interactions and bonding energetics on surfaces or at interfaces. Recently, we have performed a series of systematic thermochemical studies on small moleculesurface interactions using immersion, solution and/or gas adsorption calorimetry [17][18][19][20][21]. In addition, the bonding energetics of CO 2 [22,23], CH 4 [24], water, ethanol [25], N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF) 4 [26] was also investigated for various metal-organic frameworks (MOFs).…”

Adsorption and Photocatalytic Decomposition of Gaseous 2-Propanol Using TiO2-Coated Porous Glass Fiber Cloth

“…When the dried sample is inserted into a reactor filled with gaseous 2-propanol, the 2-propanol and water molecules are competitively adsorbed on the SiO2 walls of the pores. Wu et al clarified that the water and alcohol molecules emit comparatively large adsorption heat when they are adsorbed onto a bare SiO2 surface than that emitted when they are adsorbed onto or when they form cluster with the molecules that have already being adsorbed onto the SiO2 surface [42]. This observation indicates that the weakly and strongly adsorbed molecules coexist on the SiO2 walls of the pores (Figure 9a).…”