Fabrication of a novel core-shell-shell temperature-sensitive magnetic composite with excellent performance for papain adsorption.

Herein, a novel temperature-sensitive magnetic composite (Fe 3 O 4 @SiO 2 @P(NIPAM- co -VI)/Cu 2+ ) with a uniform core-shell-shell structure was successfully prepared via a layer-by-layer method. The resulting magnetic composite revealed good magnetic properties and remarkable affinity to papain with a maximum adsorption capacity of 199.17 mg g -1 . The adsorption equilibrium data fitted the pseudo-second-order kinetic and Freundlich models well, and the major thermodynamics parameters indicated that adsorption was an endothermic and spontaneous process. Fe 3 O 4 @SiO 2 @P(NIPAM- co -VI)/Cu 2+ could thermally protect papain, which is attributed to the reversible hydrophilic-hydrophobic transition of the composite at temperatures below and above the lower critical solution temperature. More importantly, the magnetic composite could be recycled at least six times without a remarkable loss in its adsorption capacity, and the process of adsorption and elution had no significant effect on the activity and structure of papain. This work could provide a novel separation method for papain without loss of its activity.