Adsorption and Thermogravimetric Studies of Silica-Based Amide Bonded Phases

Abstract

A series of chemically modified porous silicas, which can be used in high-performance liquid chromatography (HPLC), were prepared by a two-step modification process. Aminopropyl groups were first attached to the silica surface and subsequently converted to amides via the reaction with appropriate acid chlorides. Changes in the surface properties of the silica caused by the chemical modification were monitored using elemental analysis and high-resolution thermogravimetry. In addition, complete nitrogen adsorption isotherms were measured at 77 K in the relative pressure range from 10-6 to 0.99. Standard adsorption characterization of the materials included the evaluation of the specific surface area, total pore volume, and pore size distribution. Moreover, adsorption energy distribution functions were calculated from submonolayer adsorption data using the regularization method. It was estimated that about 40% of the available surface silanols were converted to amine groups and about 60% of amines were converted to amides. It was shown that although the chemical modification of the surface does not significantly alter the porous properties of the starting silica, it significantly affects the interaction of nitrogen probe molecules with the surface. Moreover, it was demonstrated that nitrogen adsorption is quite sensitive to the presence or absence of various functional groups on the silica surface and that the information obtained from the adsorption measurements can be utilized for the characterization of silica-based materials used in chromatographic applications.

Fabrication and Characterization of Nanotemplated Carbon Monolithic Material

“…The first one occurred between 25 and 120°C with a gradual weight loss of 0.3%, mainly attributed to adsorbed moisture vaporization, a loss also seen with samples of CM blank resin, NTCM resin, as well as pure samples of C 60 (Figure 1a). The next stage between 120 and 600°C shows a gradual weight loss of ∼0.7% for the FMS, resulting from the deamination of the secondary amino substitute and unreacted primary amine from APS (Figure 1a), which is in agreement with the results of Jaroniec et al 25 T h i sw e i g h tl o s sc o u l da l s oa t t r i b u t e dt ot h ep a r t i a l decomposition of the substituted C 60 molecules, as the pure C 60 showed signs of decomposition beginning at ∼400°C (Figure 1a, C 60 ). The weight loss rate for FMS reached a maximum at ∼530 and ∼700°C, for the third and final stage, respectively, with 5% total weight loss, mainly due to the decomposition of the covalently attached C 60 .…”

A regenerable ruthenium tetraammine nitrosyl complex immobilized on a modified silica gel surface: Preparation and studies of nitric oxide release and nitrite-to-NO conversion

“…This percentage of conversion is near to the physical limit because isonicotinamide groups possibly do not bind orthogonally to the surface but in an angular shape occupying a volume larger than the isonicotinamide ring. These values are in agreement with those reported by Jaroniec and co-workers [82] for the preparation of a series of amide bound phases on silica gel surface. Therefore, the resulting modified surface is a mixture of amine and isonicotinamide functional groups.…”

Surface Properties of Mesoporous Carbon–Silica Gel Adsorbents

“…The use of quasi-isothermal thermogravimetric analysis to characterize various adsorbents has been discussed in detail elsewhere (37,38).…”