Two birds with one stone: Nanostructured MWCNTs- iron-phthalocyanine/imidazolium bromide co-polymer as catalyst for both CO2 valorization and nitro-reduction reactions

Abstract

The straightforward synthesis of a nanostructured hybrid material in which an iron phthalocyanine/imidazolium bromide co-polymer is formed and simultaneously covalently attached to the surface of multi-walled carbon nanotubes (MWCNT) is reported. FePC@MWCNTs , has been characterized using different techniques such as TGA, solid state 13C NMR, XPS, CHN, Raman, TEM, and physisorption. RAMAN analyses confirmed the successful covalent functionalization of the nanotubes and TEM revealed that the MWCNT were covered by the copolymer, enhancing the stability of the nanostructured hybrid material which contains 0.22 mmol/g mmol of iron phthalocyanine, as shown by combining XPS and CHN. FePC@MWCNTs was successfully employed as heterogeneous catalyst for two different processes: the CO₂ cycloaddition with epoxides to synthesize cyclic carbonates, in which FePC@MWCNTs acts as bifunctional catalyst synergistically combining Lewis acid (Fe atoms) and nucleophilic (Br⁻ anions) components without addition of additives (e.g. TBAB, TBAI, BMIM, etc.); and in the synthesis of arylamines through the reduction of nitro groups, which was efficiently accomplished by using microwave heating. The hybrid material demonstrated in both cases excellent catalytic activity, outperforming all the existing phthalocyanine-based systems and resulting recyclable in consecutive catalytic runs. In the CO₂/epoxide cycloaddition and the nitro-reduction reactions, no metal leaching was observed, further confirming the robustness of this material. What makes FePC@MWCNTs particularly noteworthy, beyond its versatility and robustness, is its simplicity and cost-effectiveness: the material is synthesized from low-cost and readily available precursors through straightforward and atom-economical methods, making it a sustainable choice and also a highly practical and cheap solution for catalysis, underscoring its potential as a valuable catalyst, and offering a sustainable alternative in an industry that often relies on more expensive and less efficient solutions. The robustness of the reported nanostructured hybrid opens the way to expanding their application in other fields such as photo-, electrocatalysis or batteries, among others.