Poly(ionic liquid)-coated hydroxy-functionalized carbon nanotube nanoarchitectures with boosted catalytic performance for carbon dioxide cycloaddition

Abstract

Poly(ionic liquid)s (PILs) bearing high ionic densities are promising candidates for carbon dioxide (CO2) fixation. However, efficient and metal-free methods for boosting the catalytic efficiencies of PILs are still challenging. In this study, a novel family of poly(ionic liquid)-coated carbon nanotube nanoarchitectures (CNTs@PIL) were facilely prepared via a noncovalent and in-situ polymerization method. The effects of different carbon nanotubes (CNTs) and PILs on the structure, properties, and catalytic performance of the composite catalysts were systematically investigated. Characterizations and experimental results showed that hybridization of PIL with hydroxyl- or carboxyl-functionalized CNTs (CNT-OH, CNT-COOH) endows the composite catalyst with increased porosity, CO2 capture capacity, swelling ability and diffusion rate with respect to individual PIL, and allows the CNTs@PIL to provide H-bond donors for the synergistic activation of epoxides at the interfacial layer. Benefiting from these merits, the optimal composite catalyst (CNT-OH@PIL) delivered a super catalytic efficiency in the cycloaddition of CO2 to propylene oxide, which was over 4.5 times that of control PIL under metal- and co-catalyst free conditions. Additionally, CNT-OH@PIL showed high carbon dioxide/nitrogen (CO2/N2) adsorptive selectivity and could smoothly catalyze the cycloaddition reaction with a simulated flue gas (15% CO2 and 85% N2). Furthermore, the CNT-OH@PIL exhibited broad substrate tolerance and could be readily recycled and efficiently reused at least 12 times. Hybridization of PIL with functionalized CNTs provides a feasible approach for boosting the catalytic performance of PIL-based solid catalysts for CO2 fixation.