Degradation of PVDF in photocatalytic membranes in gaseous environments.

Poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-hexa-fluoropropylene) (PVDF-HFP) are fluoropolymers used for applications including, but not limited to, immobilization of photocatalytic materials for water and air purification due to its high resistance to ultraviolet (UV) exposure and extreme environmental conditions. The stability of these fluoropolymers in combination with titanium dioxide (TiO2) nanopowder was investigated. Membranes were prepared using the phase inversion method. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis after 21 h of intense UV exposure showed a degradation of both PVDF and PVDF-HFP. A decrease in PVDF(-HFP) absorbance relative to TiO2 absorbance in the FT-IR spectra, a decrease of the F (1s) peak and a significant increase of the Ti (2p) peaks in the XPS spectra were observed. It was demonstrated that this degradation results from reaction with TiO2 upon UV exposure. Gas analysis using a quadrupole mass spectrometer (QMS) strongly indicated the gradual formation and subsequent conversion of (highly toxic) carbonic difluoride CF2O, reaching a maximal concentration after 2.5 h and a full removal after 10 h of UV exposure. A strong indication of the production of carbon dioxide (CO2) and tetrafluoromethane (CF4) as end products was obtained.