The impregnation of mesoporous silica with diaminohexane by means of supercritical CO2: A possible CO2 solid sorbent

Among solid sorbents, silica is particularly interesting thanks to its stability and versatility. With this in mind, we developed a silica sorbent impregnated with amino groups to increase its ability to capture CO2. A commercial mesoporous silica (type SBA-15) was impregnated with a diamine (diaminohexane) by using supercritical CO2 as a green solvent. The so obtained sorbent was physico-chemically characterized and its adsorption behavior was investigated by means of volumetric isotherms at room temperature (and data were fitted by Langmuir models) and in situ Fourier Infrared Spectroscopy. The results prove that the impregnation with supercritical CO2 is effective and the resulting material is able to capture CO2. Although the CO2 capture capacity value of the impregnated material is comparable to that of the pristine one (0.89 mmol/g and 0.94 mmol/g, respectively, at 25 °C), the impregnated sorbent is significantly more efficient in capturing CO2 at low pressure. Chemisorption and, secondary, physisorption are observed. Both phenomena are reversible at room temperature, allowing an easy regeneration of the sorbent. The material, moreover, is stable also at higher temperature, proving to be compatible with thermal regeneration processes. Finally, Langmuir modeling indicates a dual-site behavior, with stronger adsorptions sites attributed to amines, and weaker sites attributed to silica.