One-pot fabrication of magnetically recoverable acid nanocatalyst, heteropolyacids/chitosan/Fe ₃O ₄, and its catalytic performance

A magnetically recoverable acid nanocatalyst, heteropolyacids/chitosan/ Fe ₃O ₄ (HSiW-CS-Fe ₃O ₄), was successfully prepared by a one-pot synthesis method. The characterized results by XRD, TEM, TGA, FT-IR and magnetic measurements testified that Keggin-type 12-silicotungstic acid (HSiW) was efficiently immobilized into the cross-linked chitosan (CS) coating on nanometer-sized Fe ₃O ₄ magnetic cores. The prepared HSiW-CS-Fe ₃O ₄ possesses a typical superparamagnetic behavior and has the acid capacity of 0.13 mmol/g. It exhibits higher catalytic activity in the acetalization reaction of benzaldehyde with ethylene glycol, and gives a 99% yield for acetal under mild reaction conditions. Furthermore, the prepared catalysts can be magnetically separated from the reaction system and reused 5 times without the significant loss of catalytic activities. It is also confirmed that the recovered catalysts are not dramatically changed in the physicochemical features. The prepared HSiW-CS-Fe ₃O ₄ may be the promising catalytic material in a mass production of the fine chemicals.