Treatment of coliphage MS2 with palladium-modified nitrogen-doped titanium oxide photocatalyst illuminated by visible light.

A palladium-modified nitrogen-doped titanium oxide (TiON/-PdO) photocatalytic fiber was synthesized on a mesoporous activated carbon fiber template by a sol-gel process. Calcination of the coated fibers resulted in a macroporous interfiber structure and mesoporous photocatalyst coating. Atomic ratios of major photocatalyst constituents determined by X-ray photoelectron spectroscopy analyses were N/Ti approximately equal to 0.1 and Pd/-Ti approximately equal to 0.03. X-ray diffraction analyses revealed that the photocatalyst had an anatase structure and palladium additive was present as PdO. Triplicate batch experiments performed with MS2 phage (average initial concentration of 3 x 10(8) plaque forming units/mL) and TiON/PdO photocatalyst at a dose of 0.1 g/L under dark conditions revealed the occurrence of virus adsorption on the photocatalyst fibers at a rate that resulted in equilibrium within 1 h of contact time with corresponding virion removals of 95.4-96.7%. Subsequent illumination of the dark-equilibrated samples with visible light (wavelengths greater than 400 nm and average intensity of 40 mW/cm2) resulted in additional virus removal of 94.5-98.2% within 1 h of additional contact time. By combining adsorption and visible-light photocatalysis, TiON/PdO fibers reached final virus removal rates of 99.75-99.94%. Spin trapping electron paramagnetic resonance (EPR) measurements confirmed the production of *OH radicals by TiON/PdO under visible light illumination, which provided indirect evidence about MS2 phage being potentially inactivated.