An overview of porous silica immobilized amines for direct air CO₂ capture

Abstract

An increased level of CO₂ in the atmosphere is identified as a threat to life on planet earth. Since hydrogenation of CO₂ back to fuel is identified as a major solution for both decreasing the emission and meeting the energy demands, the energy-efficient capture of CO₂ is recognized as an inevitably significant step. Small- and large-scale direct air capture (DAC) of CO₂ is a viable solution to address CO₂ discharge from industrial, automobile, and household activities (both point and mobile sources). The real challenge of DAC is to pick 400 molecules of CO₂ for capture from a million gas molecules in the atmosphere. Thus, in this report, we focus on reviewing the literature dealing with the chemical interaction between the sorbate (CO₂) and sorbent which is highly specific. Materials such as metal hydroxides and amine solutions are well discussed in other celebrated reviews and perspectives. Here we focus on inert porous silica immobilized amine materials emphasizing particularly on their advantages compared to other sorbent materials. Furthermore, amine functionalized novel silica materials such as bimodal porous silica and hierarchical silica are discussed highlighting the CO₂ capture mechanism, desorption, and sorbent-regeneration. Both O₂ and CO₂-induced degradation pathways along with measures to retard sorbent degradation are presented. Finally, a brief overview of sustainability and future potential of amine-silica composite materials is presented to gain more insights.