Preparation And Performance Of Visible-light Photocatalysts For Hydrogen Generation Via Fe³⁺ Linking TiO₂ And Xanthene Dyes

Three xanthene dyes (EosinY, ErythrosinB and Rosebengal) were fixed respectively on TiO₂ via Fe³⁺ coupling to prepare xanthene-Fe³⁺-TiO₂ sensitized photocatalysts. Using triethanolamine (TEOA) as an electron donor, their photocatalytic activity (xanthene-Fe³⁺-TiO₂) for hydrogen generation was improved greatly under visible light irradiation (λ=420 nm) compared with that of xanthene-TiO₂ (without Fe³⁺ coupling). The UV-vis absorption characterization indicates that xanthene-Fe³⁺-TiO₂ has stronger absorption than xanthene-TiO₂. The adsorption experiment and FTIR characterization show that Fe³⁺ coupling can enhance the adsorption amount and intensity of xanthenes on TiO₂.Therefore, their the photocatalytic activity is improved greatly via Fe³⁺ coupling. Effect of structure of xanthene dyes on the activity of the sensitized TiO₂ photocatalysts was discussed.MutilayeF-sensitized(mu-EosinY-Fe³⁺-TiO₂(a)) via co-adsorption of EosinY and Fe³⁺, Monolayer-sensitized(mo-EosinY-Fe³⁺-TiO₂ (b)) photocatalysts via Fe³⁺ linking EosinY with TiO₂, and Monolayer-sensitized photocatalysts via EosinY adsorbing on TiO₂ without Fe³⁺( EosinY-TiO₂(c) ) have been prepared and characterized. The activities of these catalysts were evaluated by hydrogen generation under visible light irradiation (λ=420 nm) in the presence of triethanolamine (TEA) as an electron donor. Activity of multilayer-sensitized photocatalyst is better than that of monolayer one. Maximal hydrogen evolution rate of Mutilayer-sensitized photocatalysts (a) increased by a factor of 1.8 compared to that of Monolayer-sensitized photocatalysts (b), and by a factor of 3.0 compared to that of Monolayer-sensitized photocatalysts without Fe³⁺ (c) . The highest apparent quantum yield of mu-EosmY-Fe³⁺-TiO₂ reached 19.1%. Photoelectrochemical experiment is consistent with the order of the catalyst activity. The adsorption experiment and UV-vis DRS results show that the multilayer-sensitized TiO₂ samples have higher visible-light harvesting efficiency than the monolayer one due to high dye loading. Fourier transform infrared (FTIR) characterization confirms that the multilayer Eosin Y on TiO₂ by Fe³⁺ linkage has indeed 3-dimensional polymeric structure. For mo-EosinY-Fe³⁺-TiO₂, Fe³⁺ links only TiO₂ and Eosin Y; whereas for mu-EosinY-Fe³⁺-TiO₂, all the 3 possible donor sites of EosinY (carbonyl, phenolate and carboxylate groups) , are utilized in coordinating with Fe³⁺ form 3-dimensional polymeric structures i.e. Mutilayer-sensitized photocatalysts. The Mutilayer-sensitized dye shows a better photosensitization in comparison with Monolayer-sensitized dyes due to its large dye absorption, and "antenna effect", which improve the visible light harvesting and electron transfer between the dye molecules and TiO₂.