Amine-functionalised monolithic silica adsorbents for CO2 capture

Abstract

This study explored the CO₂ adsorption properties of amine-functionalised siliceous monoliths with enhanced efficiency for CO₂ capture. Silica cylindrical monolithic macroscopic structures were successfully prepared from the polymerization of the silica source (TEOS) condensed on surfactant Pluronic P-123 or F-127, and using acrylamide. Previously synthesized SBA-15 was also used to prepare the monolithic structure. Materials were functionalised by grafting with two aminosilanes, 3-(trimethoxysilyl)propylamine (AP) and N¹-(3-trimethoxysilylpropyl)diethylenetriamine (DT). A positive correlation was found between the amount of amines grafted and the total CO₂ uptake under pure and dry conditions. Nevertheless, the efficiency of amines (mol of CO₂ per mol of N) was lower for highly loaded samples due to reduced site accessibility. DT functionalization of the monoliths was found to produce the best results within the concentrations studied, surpassing AP-functionalized monoliths, with P-123 monolith-2DT reaching a CO₂ uptake as high as 108 mg g⁻¹ at 1 bar and 156 mg g⁻¹ at 5.5 bar (both at 45 °C). They also achieved CO₂ uptakes at 0.15 bar which were 54–87% of the values in pure CO₂, indicating the obtention of highly selective sorbents. Moreover, aminated monoliths also showed stable uptakes over 5 adsorption–desorption cycles and over 20 cycles in the case of P-123 monolith-2DT, where it maintained 79% of its initial capacity under pure CO₂ and 85% of it under 15% CO₂.