Heterogenization of Polyoxometalates on the Surface of Plasma-Modified Polymeric Membranes

Novel catalytic membranes have been prepared by linking phosphotungstic acid H3PW12O40 (W12), a polyoxometalate having interesting properties as photocatalyst, on the surface of plasma-modified membranes. Porous flat-sheet membranes made of polyvinylidene fluoride (PVDF) have been prepared by a phase-inversion technique induced by a nonsolvent. These membranes have been modified by plasma treatments on the surface to graft N-containing polar groups that are able to act as binding sites with W12 (PVDF-NH2-W12). A comparison of the surface and bulk properties of the native and modified PVDF membranes has been reported. Catalytic activity of the PVDF-NH2-W12 membranes has been evaluated in the aerobic degradation reaction of phenol in water. Catalytic tests have been carried out in a membrane reactor operating in continuous mode. Better catalytic performances have been observed for the W12 heterogenized on PVDF membrane than for W12 in a homogeneous phase. Moreover, PVDFNH2-W12 membranes have given proof of their complete stability under photooxidation conditions and their good recycle. This study has shown the possibility of heterogenizing catalysts by a controlled modification of the membrane surface via a plasma technique. This new method is very versatile and can be easily extended to other catalysts. Further studies are actually in progress with other catalysts belonging to the polyoxometalates group.