The preferred embodiments provide for a process for preparing a TiO.sub.2 thin film. The preferred embodiments also provide for TiO.sub.2 thin films prepared by the process herein, and a method of using TiO.sub.2 thin films for killing bacteria and viruses in an environment under ultraviolet irradiation. The TiO.sub.2 thin films according to the invention have higher photocatalytic activity, and can particularly be used to photocatalytically degrade organic pollutants in air to hereby kill bacteria and viruses therein.