What are titania photocatalysts?-An exploratory correlation of photocatalytic activity with structural and physical properties

This article reports on an exploratory statistical analysis of the photocatalytic activity of titanium(IV) oxide (TiO₂; titania) using forty commercially available titania samples. Five photocatalytic reactions were examined as test reactions for the evaluation of photocatalytic activity of the samples: oxygen liberation along with silver deposition, methanol dehydrogenation, acetic acid decomposition, acetaldehyde decomposition and synthesis of pipecolinic acid from L-lysine. Six structural and physical properties of the samples were measured: specific surface area (BET), density of defective sites (DEF), primary particle size (PPS), secondary particle size (SPS) and existence of anatase (ANA) and rutile (RUT) phases. Correlations of photocatalytic activities for the five kinds of reactions with structural and physical properties of 35 (out of 40) titania samples were obtained, and photocatalytic activities were empirically reproduced by a linear combination of six properties with good to fair reliability. While a portion of the results could be interpreted using a conventional mechanism, significant activity dependence on properties, not yet disclosed, was suggested.