CO2 adsorption on cellulose nanofiber-polyethyleneimine functionalized membranes

Abstract

This research addresses two limitations of electrospun membranes consisting of cellulose acetate (CA) and polyethylenimine (PEI) for CO2 capture. Such setbacks are the easy elution of PEI from the CA matrix in the presence of water and their relatively poor mechanical properties. The approach involves the innovative incorporation of oxalic acid-treated cellulose nanofibers (CNF) to increase PEI retention, besides burst and tensile strength. The synergistic effects of CNF and PEI, based on ammonium carboxylate formation, are postulated to enhance CO2 uptake. The study evaluates the adsorption capacity of 14 different membranes, analyzing their physical, mechanical, and chemical properties. It also implies the optimization of the PEI content to prevent elution and ensure proper performance for potential off-gas treatments. In this context, esterification with oxalic acid was deemed a more suitable method to introduce carboxyl groups on cellulose than the well-known TEMPO- mediated oxidation, since the latter resulted in highly viscous CNF suspensions, unfit for electrospinning. Overall, the best performance was attained by membranes containing 4 wt% PEI and CNF pretreated with 75 wt % oxalic acid. CO2 adsorption followed pseudo-first order kinetics, reaching saturation values over 4 mmol/g. Moreover, membranes were reusable, not detecting any significant loss in adsorption capacity along five cycles. All considered, this study proposes a robust solution for sustainable industrial processes, both in terms of resisting stress and in terms of CO2 capture.