Photocatalytic efficiency and self-cleaning properties under visible light of cotton fabrics coated with sensitized TiO2

A simple and reproducible one-pot process for the elaboration of cotton fabrics coated with sensitized TiO2 was developed. A molecular precursor [Ti(OR)3(O2C-AQ)] was prepared starting with anthraquinone-2-carboxylic acid (AQ-COOH) and characterized by FTIR, CPMAS NMR and XPS. Hydrolysis of mixtures of [Ti(OR)3(O2C-AQ)] and Ti(OR)4 at low temperature in an aqueous medium leads to pale yellow cotton fabrics together with the corresponding free P-TiO2/AQ powders. The diffuse reflectance UV spectra confirmed the shift of absorption towards the visible range. From FTIR, CPMAS NMR and XPS analysis of the samples (cotton pieces and powders), it was shown that AQ-COOH was not only adsorbed on Titania but tightly bond through a carboxylate complex as in the molecular precursor. Anatase polymorph was always characterized by XRD even in the absence of a calcination step. Examination by SEM of treated cotton tissues before and after washing showed stable and homogeneous coating of TiO2 particles on the cotton fibers.The photocatalytic properties of the samples were investigated, with special care to visible light activation. Under UV light, acetone mineralization was observed, while under filtered visible light, no acetone mineralization occurred. However efficient singlet oxygen addition to di-n-butyl sulfide was evidenced under visible light. Sulfoxide and sulfone were obtained in better yields using sensitized TiO2 than using un-modified TiO2 or Anthraquinone alone treated fabrics. Optimum results were obtained with low level of sensitizing AQ-COOH relative to TiO2 (8%) and no reactivity improvement was noticed with higher AQ-COOH levels. The cotton pieces coated with sensitized TiO2 also displayed self-cleaning properties towards wine stain, either under solar illumination or even in indoor light.The better efficiency of sensitized TiO2-coated cotton is accounted for by a synergy effect between TiO2 and AQ-COOH, enhancing the formation of Reactive Oxygen Species (singlet oxygen and/or superoxide radical-anion). However, under these conditions, the production of hydroxyl radical seems to be ruled out.

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► TiO2 sensitized with anthraquinone-2-carboxylic acid (AQ-COOH) was prepared from a molecular precursor [Ti(OR)3(O2C-AQ)].
► Coated cotton pieces and modified TiO2 powders were prepared and characterized.
► Bonding between AQ-COOH and TiO2 through a carboxylate complex was demonstrated.
► Under visible light, no acetone mineralization but synergy effect leading to significant singlet oxygen production.