Thiol–ene click functionalization of a MCM-41/Fe3O4 nanocomposite with acrylic acid: a magnetically recoverable solid acid catalyst for efficient conversion of sugars to 5-HMF

Abstract

The development of efficient solid acid catalysts is critical for the sustainable production of 5-hydroxymethylfurfural (5-HMF), an important foundational chemical obtained from biomass. In this work, mesoporous silica MCM-41 was prepared and modified with Fe₃O₄ nanoparticles to impart magnetic recoverability. The surface was further functionalized with 3-mercaptopropyltriethoxysilane to introduce thiol groups, followed by a thiol–ene click reaction with acrylic acid to graft carboxylic acid functionalities onto the surface. The resulting magnetically recoverable nanocomposite was comprehensively characterized using FT-IR spectroscopy, acid–base titration, EDX, XRD, BET, TEM, SEM, TGA, and VSM analyses. The nanocomposite combined the high surface area and ordered mesoporosity of MCM-41 with the magnetic separability of Fe₃O₄ nanoparticles. It was used as a solid acid catalyst for the transformation of sugars into 5-HMF. The influences of several reaction parameters like the reaction temperature, catalyst amount, reaction time, and type of solvent were assessed for the transformation of fructose into 5-HMF. The optimized reaction conditions were determined to be a temperature of 120 °C, 30 mg of catalyst, a reaction time of 1 h, and the reaction medium with a dimethyl sulfoxide/H₂O (V/V) ratio of 2/1. Under these conditions, the conversion of fructose resulted in 94% 5-HMF yield. The catalyst also demonstrated outstanding reusability across multiple cycles with a minimal loss of effectiveness. Moreover, the turnover number (TON) and turnover frequency (TOF) were calculated to be 25.2 and 25.2 h⁻¹, respectively, highlighting the efficiency of our developed catalytic system.