Semiconductor-hydrophobic material interfaces as a new active site paradigm for photocatalytic degradation of...

Photocatalytic degradation of long-chain perfluorocarboxylic acid (PFCA) water contaminants has been reported for numerous of semiconductors, including composite TiO₂ particles decorated with graphitic carbon co-catalysts. While pristine TiO₂ degrades PFCAs inefficiently, the carbon components purportedly enhance activity due to their conductive nature and resultant charge separation enhancement. Yet herein, we present evidence that the catalytic activity of a graphene oxide (GO)-TiO₂ composite from the literature arose not due to from charge separation, but to a unique mode of PFCA adsorption occurring at the interface of TiO₂ and hydrophobic GO. Photocatalytic degradation rates by GO-TiO₂ were compared to those of composites containing nonconductive polymer microparticles (polyethylene, polytetrafluoroethylene). Results showed that polymer-TiO₂ composites performed as well as GO-TiO₂ in degrading both perfluorooctanoic acid and oxalate, a common hole scavenger. Thus, the enhanced activity may occur for any TiO₂-hydrophobic interface, regardless of co-catalyst conductivity. Furthermore, compared to an unmodified reference catalyst, chain length dependence of PFCA degradation by a polymer-TiO₂ composite was found to be less severe, with greater activity toward short-chain species indicating enhanced adsorption behavior. Potential adsorption mechanisms are presented, along with broader implications toward improving the applicability of heterogeneous processes toward a wider range of perfluoroalkyl contaminants.