Dihydroxyanthraquinones as stable and cost-effective TiO2 photosensitizers for environmental and biomedical applications

Materials based on titanium(IV) oxide and four dihydroxyanthraquinones were synthesized using a simple impregnation method. The dyes (1,2-, 1,4-, 1,5- and 1,8-dihydroxyanthraquinone) did not alter the physical properties of bare TiO2, but photosensitized it to visible light, up to 600 nm. The materials exhibit good photocatalytic activity in this spectral range. Adsorbed 1,5- and 1,8-dihydroxyanthraquinones revealed exceptional stability compared to previously described semiconductors modified with organic compounds. The spectroscopic characterization of the synthesized materials indicates that photosensitization occurs via an indirect electron transfer mechanism. To exploit their promising properties, appropriate tests were carried out towards the photodynamic inactivation of microorganisms. It was found that upon excitation with green light the tested photomaterials exhibited remarkable activity (3-4 log units) against Gram-negative and Gram-positive bacteria, as well as fungi. Moreover, the addition of inert potassium iodide to the photocatalytic system led to the complete eradication (>7 log units) of studied microorganisms. Elaborated materials appeared exceptionally photoactive under visible light, photostable, and cost-effective and therefore can be considered promising photocatalysts for environmental and biomedical applications.