Sulfonic acid-functionalized chitosan-Fe3O4/covalent triazine framework as an efficient and reusable magnetic nano-catalyst for fructose conversion into 5-hydroxymethylfurfural

A sulfonic acid-functionalized magnetic nano-catalyst based on a chitosan-supported Fe 3 O 4 /covalent triazine framework (CS-Fe 3 O 4 /CTF-SO 3 H) was successfully prepared via a stepwise assembly and post-synthetic sulfonation strategy. The structural, morphological, thermal, and magnetic features of the nano-catalyst were comprehensively characterized using fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), and vibrating sample magnetometry (VSM) analyses, confirming the successful construction of a robust and magnetically recoverable acidic framework. The catalytic performance of CS-Fe 3 O 4 /CTF-SO 3 H was evaluated in the dehydration of fructose to 5-hydroxymethylfurfural (HMF) in DMSO. Under optimized reaction conditions (fructose: 75 mg, catalyst loading: 21 wt%, 120 °C, 30 min), an outstanding HMF yield of 98.7% was achieved. Comparative catalytic studies underlined negligible activity for pristine CS and non-functionalized CTF, whereas sulfonated counterparts exhibited remarkably enhanced performance, highlighting the crucial role of Brønsted acid sites. Hot filtration and recyclability tests confirmed the heterogeneous nature of the catalyst and its excellent stability over multiple reaction cycles, with only a minor decrease in acidity. The combination of high catalytic efficiency, magnetic separability, and reusability makes CS-Fe 3 O₄/CTF-SO 3 H a promising solid acid nano-catalyst for biomass-derived carbohydrate valorization.