Enthalpies of Immersion in Caffeine and Glyphosate Aqueous Solutions of SBA-15 and Amino-Functionalized SBA-15.

Mesostructured silica SBA-15 and amino-functionalized silica SBA-15-NH were synthesized, and then, characterization, adsorption capacity, and immersion enthalpies in caffeine and glyphosate on SBA-15 and SBA-15-NH were evaluated. The enthalpy parameter was determined using a local construction Tian-type heat conduction calorimeter. Calorimetric studies in caffeine solutions exhibit negative enthalpy values; exothermic process characteristics for SBA-15 were between -13.90 and -194.06 J g and those for SBA-15-NH were between -7.22 and -60.34 J g, and the adsorption capacity of caffeine was better in SBA-15 than that in SBA-15-NH. In contrast, the enthalpies of immersion in glyphosate solutions were -5.06 to -56.2 J g and the immersion of SBA-15-NH in each solution generated enthalpy values of -9.06 to -41.2 J g, but the adsorption capacity of glyphosate was better in the amino-functionalized SBA-15. The results show that functionalization of SBA-15 produced differences in physicochemical characteristics of solids, since energy and affinity for the calorimetric liquids are related to the surface properties of solids as well as the chemical nature of the target molecule, immersion enthalpy, was different.