Degradation of Perfluorooctanesulfonate (Pfos) by Sub-Bandgap Irradiation of Hydrogen-Terminated Nanodiamond

Irradiation of aqueous suspensions containing hydrogen-terminated detonation nanodiamond (HND) with sub-bandgap (λexc > 225 nm) excitation leads to the reductive degradation of perfluorooctanesulfonate (PFOS). As evidenced by nanosecond transient absorption spectroscopy (nsTA), we show that 254 nm excitation of HND in water induces the photoemission of electrons producing hydrated electrons (eaq-). A red shift in the eaq- absorption maximum relative to bulk water indicates a disruption in the hydrogen bonding network of the interfacial water layer at the HND surface. A shortening of the eaq- lifetime with the addition of PFOS and accompanying blue shift of the eaq- absorption maximum indicate PFOS reduction and HND/PFOS surface interactions, respectively. Prolonged photolysis of HND/PFOS solutions at 254 nm results in the degradation of PFOS into smaller polyfluoroalkyl derivatives consistent with other advanced reduction processes. The degradation of PFOS by this method is less sensitive to pH than the state-of-the-art UV-sulfite method.