Study of Rh/TiO2–SiO2 system in photolytic water splitting

Titania silicates (TiO2–SiO2) of various compositions were prepared by a sol–gel method. RhCl3 was used in 0.2 wt% of Rh quantity on the gel surfaces, which were subsequently exposed to UV irradiation in water under a 355-W UV lamp. λ > 370 nm. Both Rh [I] and Rh [III] surface complexes were formed, depending on the gels composition. They also exhibited various efficiency in photo water splitting reaction, the photocatalysts possessing as supports titania-silica gels containing 40 and 50 mol % of TiO2, were the most effective. According to our proposal, the rhodium complexes took part in the oxidative addition and reductive elimination cycle, where two water molecules in photo water splitting reaction, yielding hydrogen – H2 and two hydroxyl radicals. The two hydroxyls radicals, catalytically converted to oxygen atom and water, in the second cycle of the investigated water splitting reaction. Titanium octahedra and silicon tetrahedra linked by Ti–O–Si bridges were thought to be the grouping responsible for activity of the investigated catalysts. Their largest amounts are on the gels containing 40–58 mol % TiO2.