Origin of the Surface Peroxo Titanium Species

From the adsorption isotherm established by Boehm for an anatase powder (P-25), the number of charged (Tis-0 ) groups, in equilibrium with a 0.1 M NaOH solution, may be evaluated as equal to ca. 3.8 groups/nm . The capture of the photogenerated 

The photogenerated Tij-O radicals may, in principle, act as (i) surface recombination centres for the conduction band electrons, (ii) electron acceptors towards reduced species present in the solution, or, for example, (iii) undergo conproportionation 

First quantitative assessment, based on the results of spectrophotometric titrations with KMn04 , indicated a concentration of ca. 1.4 peroxo groups per nm of the true 

Volume of oxygen evolved during 5 h of photolysis over Ti02 powder pretreated at various temperatures (under argon). 100 mg of Ti02 rutile dispersed in 25 cm of solution containing 10 mol of AgNOs (from Ref. 188) 

It should also be mentioned that estimates of the concentration of the surface peroxo species, based on the amount of oxygen photoadsorbed at Ti02 powders dispersed in aqueous solution, may lead in some cases to extremely large formal coverages, as the value of 22 peroxide molecules per nm reported by Harbour et al. . This would suggest the formation of three-dimensional peroxide network if it were effectively confirmed that in the latter case the total amount of photoadsorbed oxygen was present in the form of peroxides. 

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