Robust structure regulation of geopolymer as novel efficient amine support to prepare high-efficiency CO2 capture solid sorbent

Abstract

Amine functionalized solid sorbents exhibit promising prospects for post-combustion CO2 capture. One of the most significant challenges at present is the development of cost-effective supports with excellent pore structure and surface texture for amine loading. In this study, geopolymer was treated with nitric acid to suitable degrees. Changes in the porosity, surface silanol density, and degree of polymerization of the geopolymer matrix were systematically evaluated using various spectroscopic techniques, and a mechanism for such regulation was proposed. Moreover, these changes were compared with the variation in the amine grafting amounts and CO2 capture capabilities. Geopolymers treated under an appropriate acid condition exhibits an unexpectedly large specifical surface area of 412 m2/g with a superior silanol density of 4.25 mmol/g being achieved, which facilitate a high (3-Aminopropyl)triethoxysilane (APTES) grafting amount of 3.5 mmol N/g. The as-prepared amine functionalized solid sorbent showed a CO2 adsorption capacity of 1.82 mmol/g at 1 atm and 60 ℃, with fast adsorption kinetics and low energy requirement for regeneration, which are competitive with sorbents prepared using traditional silica supports, despite its simple and robust fabrication route. The superior amine grafting capability of the support and CO2 capture performance of the resultant sorbent are related to the special Si-O(Na)-Al network parent structure of the geopolymer matrix, which allows the formation of abundant pore structures and reserved Si-OH groups that are conveniently achieved via the release of Na and Al during acid regulation. Beyond the confines of this study, the present work would provide new opportunities for cost-effective and efficient preparation of materials that require matrices of high porosity and silanol density.