Abstract

A nitrogen-doped carbon catalyst was systematically prepared via a green-chemistry route, using chitosan as an accessible yet reusable biopolymeric precursor. The preparative procedure involved pyrolyzing chitosan under an inert atmosphere at 550 °C, enabling efficient incorporation of nitrogen functionalities into the resulting carbon matrix. Subsequently, a surface modification involved the incorporation of –SO3H groups to furnish the catalyst with a substantial number of Brønsted acidic sites. The incorporation of acidic functionalities together with nitrogen-rich domains is significant. This combination results in a bifunctional surface capable of simultaneously activating both nucleophilic and electrophilic species, broadening the scope of catalytic transformations. The catalytic efficiency of the catalyst was examined using the Michael addition reaction, using chalcone and malononitrile as representative substrates. Under mild conditions (40 °C for 2 h), the catalyst efficiently drove the reaction to produce the corresponding adduct with yields up to 70%. Hence, a synergistic effect between nitrogen and Brønsted acidic sites is necessary to activate bonds and stabilize the transition state to promote reactivity and selectivity. Beyond its catalytic effectiveness, this work highlights the importance of developing green, reusable heterogeneous catalysts from biomass. This approach not only reduces systemic reliance on precious and toxic metal-based systems but also enhances the usability of natural biopolymers, such as chitosan. These previously wasted materials can be rendered useful as catalytic agents. Altogether, this work provides an environmentally friendly and flexible approach to developing carbon-based acid catalysts.