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Small nanosized clusters of Co 3 O 4 coated on PTFE (polytetrafluoroethylene) flexible film is reported as a novel supported photocatalyst effective in the fast discoloration of the azo-dye Orange II under simulated solar radiation in the presence of oxone (2KHSO 5 ·KHSO 4 ·K 2 SO 4 ). The photocatalytic discoloration of Orange II on the PTFE/Co 3 O 4 films proceeds within minutes and the process could be repeated many times without a loss in photocatalyst stability. The photodiscoloration proceeds with a photonic efficiency of ∼1. The PTFE seems to act as a structure forming matrix for the colloidal Co 3 O 4 coated on it surface leading to nanosized clusters of Co 3 O 4 . Monitoring the amount of Co 2+ -ions shows the Co 2+ -ions from the PTFE/Co 3 O 4 during the photocatalysis enter the solution and at a later are stage re-adsorbed the Co 3 O 4 crystallographic network (∼8 min). By elemental analysis (EA) the loading of Co-loading per cm 2 PTFE film was found to vary between 1% and 2%. Transmission electron microscopy (TEM) shows the size of the Co 3 O 4 clusters to vary between 3 and 10 nm. Electron dispersive spectrometry (EDS) confirms the presence of Co on the PTFE. X-ray photoelectron spectroscopy (XPS) of the PTFE/Co 3 O 4 films reveal a partial reduction of the Co 3 O 4 after Orange II discoloration leading to a substantial increase of the amount of Co(II) species in the Co 3 O 4 . Physical insight is provided into the catalyst film surface by carrying out Ar-sputtering of the PTFE/Co 3 O 4 surface to remove the catalyst overlayers up to ∼20 nm.

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The presence of residual water and the silanol groups in silicas are of crucial importance for their commercial applications.