Composite of chitosan, sulfonated biochar, and metal-organic framework as a heterogeneous catalyst for Knoevenagel reaction

Abstract

With the aim of designing a bio-based catalytic composite, which benefits from synergistic effect, a triple composite, containing chitosan, sulfonated biochar, and copper-based metal–organic framework components was synthesized. The formation of the composite was confirmed via several characterization techniques and then it was utilized as a heterogeneous catalyst for promoting Knoevenagel condensation reaction in the aqueous environment. The investigation revealed that a variety of substrates readily underwent this reaction, giving products in high yields ranging from 80 % to 95 %. Furthermore, the catalyst demonstrated good recyclability, and stability, maintaining minimal leaching and catalytic activity loss over six consecutive cycles. The comparative analysis of the composite catalyst against control catalysts validated its superior activity, underscoring the synergistic effects of its components. In fact, the reaction was promoted by the functional groups on chitosan and sulfonated biochar, along with the Lewis acidic sites within the metal–organic framework. Furthermore, when combined with the bead structure, this configuration effectively minimized leaching and facilitate catalyst recovery. The kinetic and thermodynamic studies revealed a low activation energy of 16.48 kJ/mol and first-order kinetics. Parameters like activation entropy (ΔS) and enthalpy (ΔH) were also evaluated via the Eyring-Polanyi equation, along with the assessment of the Gibbs energy change (ΔG).