Titanium dioxide nanotubes offer distinct advantages over films of the same material in the production of hydroxyl radicals and subsequent inactivation of Escherichia coli in wastewater. However, their visible light absorption capabilities are limited. Semiconducting nanocrystals of cadmium sulfide have been used to increase the sensitivity of TiO2 nanotubes to visible light. A small applied potential, using CdS-coated TiO2 nanotube arrays, allowed for total inactivation of E. call in hitherto record short time.