Determination of Acid-Base Properties of Silicas by Inverse Gas Chromatography: Variation with Surface Treatment

Abstract

The specific component of the free energy of adsorption, ÀÁG SP A , of untreated crystalline and fused silica, and four types of silane coupling agents-treated fused silicas, were estimated by the inverse gas chromatography (IGC) method, using the adsorption of several polar and nonpolar probes on their surfaces at various measuring temperatures. The acid-base properties of the untreated and surface-treated silicas were quantified by their K A and K D parameters, reflecting the ability of the surface to act as an electron acceptor and donor, respectively. Acidic components were detected on the untreated crystalline and fused silica surfaces, but the surface properties of the fused silicas surface-treated with -glycidoxy propyl trimethoxy silane (GMS) and -amino propyl triethoxy silane (AES) were slightly basic, and those of the fused silicas surface-treated with -methacryloxy propyl trimethoxy silane (MTMS) and -mercapto propyl trimethoxy silane (MCMS) were amphoteric.

Fabrication and Characterization of Sulfonated Carbon Materials and Chitosan-Derived Functioned Carbon via Schiff’s Base Process for Separation Purposes

“…The value of free energy change for adsorption (ΔGA) is determined by adding up the adsorption energies resulting from dispersive and specific interactions. As per research, when n-alkanes are used as nonpolar probes, their adsorption occurs solely through dispersive interactions [79]. The negative values of ΔGA indicate a spontaneous transfer of solutes from the mobile phase to the stationary phase for C@Chitosan-COL and Schiff's-C-S under the studied temperature range (313-343 K) (Table 2).…”

Inverse Gas Chromatography Demonstrates the Crystallinity-Dependent Physicochemical Properties of Two-Dimensional Covalent Organic Framework Stationary Phases

“…Dispersive interactions (London forces) in n- alkane adsorption provide information on carbon structure, whereas specific interactions of the COF surface are determined using standard organic polar probes. In addition to dispersive interactions, the adsorption of polar molecules on the stationary phase involves specific components pertaining to various forms of van der Waals’ forces, such as the Keesom orientation force and Debye inductive force, as well as hydrogen bonding, π–π interactions and other noncovalent attractions . The column coated with single-crystalline TAPPy-PDA showed rapid separation of the studied mixture of polar organic probes (ACN, DCM, Et 2 O, THF, and EtOAc) in ∼50 s in real time, equivalent to ∼11 s in adjusted retention (Figure and eq S2).…”

“…In addition to dispersive interactions, the adsorption of polar molecules on the stationary phase involves specific components pertaining to various forms of van der Waals' forces, such as the Keesom orientation force and Debye inductive force, as well as hydrogen bonding, π−π interactions and other noncovalent attractions. 73 The column coated with single-crystalline TAPPy-PDA showed rapid separation of the studied mixture of polar organic probes (ACN, DCM, Et 2 O, THF, and EtOAc) in ∼50 s in real time, equivalent to ∼11 s in adjusted retention (Figure 4 and eq S2). The elution of these polar probes from the single-crystalline TAPPy-PDA COFcoated column followed the order: ACN, DCM, Et 2 O, THF, and EtOAc.…”