Inactivation of phage MS2 by titanium dioxide photocatalysis.

Abstract

Viral disinfection by near-UV photocatalysis was accomplished in aqueous titanium dioxide suspensions. A photocatalyzed inactivation of phage MS2 of 90% increased to 99.9% after 2 μM Fe (from ferrous sulfate) was added to phosphate-buffered, distilled water containing TiO₂ and 20 μM Tris hydrochloride. Iron additions ranging from 0.2 to 20 μM, showed that a 2 μM Fe concentration produced maximum photoreactivity. The initial rate of MS2 inactivation, in the solution without iron, increased more than twenty-fold when Tris was absent. This rate of inactivation showed an additional nine-fold increase when the MS2 was photocatalyzed in a sample of Tucson groundwater, primarily because of low concentrations of groundwater species that scavenge hydroxyl radicals. A 99.997% inactivation of MS2 was observed after a 1000-ml glass beaker, containing a 100-ml suspension of MS2-spiked groundwater and 1 g l⁻¹ TiO₂, was exposed to sunlight for 10 sec. The hydroxyl radical (OH⋅) was linked to the MS2 destruction by verifying the ability of OH⋅ to inactivate MS2, and by demonstrating that OH⋅ was produced during the photocatalyzed reactions. An OH⋅ source, and competition kinetics techniques, were used to obtain these findings and to produce other evidence of MS2 inactivation by photocatalytically-produced OH⋅. These methods were also used to show that the presence of 2 μM Fe increased the quantity of liquid-phase OH⋅ that was produced during photocatalysis. Measurements showed that most of the added 2 μM Fe partitioned onto the TiO₂ surface, allowing the opportunity for OH⋅ production by Fenton reactions. Experimental results were consistent with proposed photocatalytic mechanisms (involving photocatalysis, diffusion, and Fenton reaction) by which OH⋅ was available on and off the TiO₂ surface. Non-OH⋅ means of MS2 inactivation were evaluated. The MS2 inactivation that occurred in unilluminated solutions to which Fe and TiO₂ were added, was probably caused by the effects of stirring, oxidation by iron, and MS2 enmeshment in aggregating TiO₂ particles.