Preparation of a visible-light-active TiO2 photocatalyst by RF plasma treatment

In order to realize a visible (vis)-light-active TiO2 photocatalyst, reduction treatment using low-temperature hydrogen plasma with elevated temperatures was applied on anatase TiO2 powder of ST-01 without causing a phase transition to rutile. According to plasma-heat treatment, oxygen was evacuated from ST-01 particles and the colored ST-01, ivory to beige, was obtained. XPS results showed non-stoichiometric, expressed as TiO2−x} and x was increased with the increase of treating time. Plasma-heat treated ST-01 showed new ESR signal at g = 2.003 assigned to electrons trapped at the oxygen-defect site. This signal was strengthened when vis-light illumination was applied. Results of vis-light activity tests, evaluated by photocatalytic oxidation of benzoic acid in liquid phase and 2-propanol in gas phase using vis-light illumination (>406 nm), showed excellent activity while low ST-01 showed almost no activity on both tests.