Modified titanium dioxide photocatalysts for the enhanced photodegradation of organic substrates

Two approaches to generate TiO₂ photocatalyst for the enhanced photodegradation of substrates are described. One approach includes the surface modification of TiO₂, with a layer consisting of a N,N′-bipyridinium π-acceptor layer. The resulting photocatalyst reveals superior photocatalytic activity as compared to the non-modified TiO₂ for the decomposition of π-donor substrates such as 1,4-dimethoxybenzene (1), 1,2-dimethoxybenzene (2) and indole (3). The enhanced photocatalytic activity of the modified TiO₂, V²⁺-TiO₂ is attributed to the concentration of the pollutant at the heterogeneous catalyst surface via the formation of supramolecular π donor-acceptor complexes. A second approach to improve the photocatalytic activity of TiO₂, involves its doping with Fe(III)-Phthalocyanine, Fe(III)-Pc. The Fe(III)-Pc doped TiO₂, Fe(III)-Pc/TiO₂ is formed by the sol-gel method. The series of organic substrates p-nitrobenzoic acid (5), p-aminobenzoic acid (6), p-chlorophenoxyacetic acid (7), salicylic acid (8) and aniline (9), is effectively degraded by the Fe(III)-Pc/TiO₂ catalyst compared to the non-modified catalyst. Photodegradation of the organic pollutants in the presence of Fe(III)-Pc/TiO₂ is substantially enhanced as compared to non-modified TiO₂ and leads to complete mineralization. The enhanced activity of the Fe(III)-Pc doped TiO₂, is attributed to the synergistic generation of OH radical, the active species in the degradation of the organic substrates, at the semiconductor surface, via the photochemical cleavage of light-induced generated H₂O₂ at the semiconductor surface.