Sodium tungstate immobilized on plasma-treated PVDF membranes: New efficient heterogeneous catalyst for oxidation of secondary amines to nitrones

New heterogeneous oxidation catalysts have been obtained by immobilizing sodium tungstate (Na2WO4) on plasma-treated poly(vinyldene difluoride) (PVDF) membranes. This new generation of catalytically active membranes has been developed by coupling the advantages of low temperature plasma modification processes with surface chemical immobilization reactions of catalysts. Polymeric membranes with different thicknesses, morphologies and pore dimensions were prepared by a non-solvent induced phase inversion technique. Then the surface of the membranes have been surface modified with NH3 radiofrequency glow discharges in order to graft active amino groups for immobilizing sodium tungstate in a stable way. The new catalytic membranes were successfully used for the oxidation of secondary amines to nitrones in a flat membrane reactor. A conversion to nitrone of 100% in less than 3 h (comparable to the homogeneous system) was achieved with the membrane having smallest pore diameter and finger like morphology.