Use of the Bubbling Reactor with the Ru(bpy)23/S2O28 Photosystem for Measuring the Rate of Water Oxidation as Promoted by Different Manganese Oxides

In the current chapter, the use of a bubbling reactor for investigating the activity of different manganese oxides (i.e. Mn2O3, Mn3O4 and MnO2) is described. The most important aspects of water oxidation reaction considered are the role of the catalyst specific surface area (SSA), and the effect of the irradiance on the system. The former was investigated by preparing and testing samples with the same crystal structure, but with different SSA values. Notably, water oxidation catalyst activity does not strictly increase with SSA, but rather depends on the preparation route, which affects the nature of the surface. The effect of the irradiance was studied by using three irradiances conditions (i.e. 0.3, 0.5 and 1.0 sun) and three different catalyst contents (i.e. 10, 20 and 40 mg), evidencing how the increase in irradiance enhances the degradation processes rather than the O2 evolution. On this basis, a kinetic model imposing steady state conditions on transient species was developed, yielding a simple linear combination of two exponentials as expression of. The results show that the ratio between the kinetic constants of the desired (i.e. O2 formation) and undesired path (i.e. dye degradation) decreases at increasing irradiance, evidencing how the role of parasitic reactions, far from being negligible, tends to be overwhelming

Sacrificial Oxidants as a Means to Study the Catalytic Activity of Water Oxidation Catalysts

An overview of the different sacrificial oxidants used in literature is reported, paying particular attention to the “sacrificial pair”, a photosystem made of a Ru-dye (Tris(bipyridine)ruthenium(II) dichloride, working as “antenna” for visible light) and a final electron acceptor (i.e. the persulfate ion). Such sacrificial oxidant is one of the most common in the literature and it was used in all the experiments described in Chap. 4. Different configurations of batch reactors can be used in the sacrificial-oxidant-driven water oxidation (WO) reaction, and three of them (i.e. the Clark-electrode Cell, the Stripping Flow Reactor and the Bubbling Reactor) are described in detail. The effects of both mass transfer limitations and side reactions on the determination of the two parameters describing the activity of water oxidation catalysts (i.e. the O2 production rate and the total evolved O2) are discussed, evidencing how such undesired phenomena occur to a different extent with the three reactor configurations

Hydrogen peroxide route to Sn-doped titania photocatalysts

<p>Abstract</p> <p>Background</p> <p>The work aims at improving photocatalytic activity of titania under Vis light irradiation using modification by Sn ions and an original, simple synthesis method. Tin-doped titania catalysts were prepared by thermal hydrolysis of aqueous solutions of titanium peroxo-complexes in the presence of SnCl₄ or SnCl₂ using an original, proprietary "one pot" synthesis not employing organic solvents, metallo-organic precursors, autoclave aging nor post-synthesis calcination. The products were characterized in details by powder diffraction, XPS, UV–vis, IR, and Raman spectroscopies, electron microscopy and surface area and porosity measurements</p> <p>Results</p> <p>The presence of tin in synthesis mixtures favors the formation of rutile and brookite at the expense of anatase, decreases the particle size of all formed titania polymorphs, and extends light absorption of titania to visible light region >400 nm by both red shift of the absorption edge and introduction of new chromophores. The photocatalytic activity of titania under UV irradiation and >400 nm light was tested by decomposition kinetics of Orange II dye in aqueous solution</p> <p>Conclusions</p> <p>Doping by Sn improves titania photoactivity under UV light and affords considerable photoactivity under >400 nm light due to increased specific surface area and a phase heterogeneity of the Sn-doped titania powders.</p