Sulfonic acid-functionalized core-shell Fe_(3)O_(4)@carbon microspheres as magnetically recyclable solid acid catalysts

摘要

Green and recyclable solid acid catalysts are in urgent demand as a substitute for conventional liquid mineral acids.In this work,a series of novel sulfonic acid-functionalized core-shell Fe_(3)O_(4)@carbon microspheres(Fe_(3)O_(4)@C-SO_(3)H)have been designed and synthesized as an efficient and recyclable heterogeneous acid catalyst.For the synthesis,core-shell Fe_(3)O_(4)@RF(resorcinol-formaldehyde)microspheres with tunable shell thickness were achieved by interfacial polymerization on magnetic Fe_(3)O_(4)microspheres.After high-temperature carbonization,the microspheres were eventually treated by surface sulfonation,re sulting in Fe_(3)O_(4)@C-x-SO_(3)H(x stands for carbonization temperature)microspheres with abundant surface SO_(3)H groups.The obtained microspheres possess uniform core-shell structure,partially-graphitized carbon skeletons,superparamagnetic property,high magnetization saturation value of 10.6 emu/g,and rich SO_(3)H groups.The surface acid amounts can be adju sted in the range of 0.59-1.04 mmol/g via sulfonation treatment of carbon shells with different graphitization degrees.The magnetic Fe_(3)O_(4)@C-x-SO_(3)H microspheres were utilized as a solid acid catalyst for the acetalization reaction between benzaldehyde and ethylene glycol,demonstrating high selectivity(97%)to benzaldehyde ethylene glycol acetal.More importantly,by applying an external magnetic field,the catalysts can be easily separated from the heterogeneous reaction solutions,which later show well preserved catalytic activity even after 9 cycles,revealing good recyclability and high stability.