Preparation of a magnetic solid acid Fe₃O₄@PS‐SO₃H and its use in hydrolysis of cellulose

BACKGROUND In order to improve the catalytic performance and stability of magnetic solid acid for cellulose hydrolysis in the aqueous phase, this study first modified the surface of magnetite (Fe 3 O 4 ) nanoparticles (NPs) with oleic acid. Then, in an oil‐in‐water (O/W) emulsion system, polystyrene (PS) was coated on the Fe 3 O 4 NPs through emulsion polymerization. Finally, magnetic solid acid Fe 3 O 4 @PS‐SO 3 H was prepared by sulfonation. RESULTS The obtained Fe 3 O 4 @PS‐SO 3 H was characterized by transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, infrared, X‐ray diffraction, X‐ray photoelectron spectroscopy and thermogravimetric analysis, and its acid densityand magnetic properties determined. Applied to cellulose hydrolysis, it exhibited 35.28 emu·g −1 saturation magnetization and 3.56 mmol·g −1 maximum acid density. At 140 °C and 1:1 acid to substrate ratio, cellulose hydrolysis with Fe 3 O 4 @PS‐SO 3 H gave a glucose yield of ≤64.14% in 10 h. The solid acid was conveniently recycled with a magnet and reused for further cellulose hydrolysis. It maintained good catalytic activities after five cycles. CONCLUSION The magnetic solid acid with a polystyrene backbone prepared by emulsion polymerization exhibits efficient and stable catalytic performance, in line with the trend of green development in ‘bio‐refining’, and lays the foundation for the development of composite solid acids.