Title : Selective photocatalysis of bilirubin by imprinted hollow TiO2 microspheres
Titanium oxide or titania is a material extensively studied and employed as a photocatalyst. It has been found that titania in the format of hollow microspheres allows for a significant improvement of the photonic efficiency against the solid format of titania, due to multiple light diffraction and reflection process. Catalysis, especially photocatalysis, is a major field of application of hollow microspherical TiO2 (HMTO). The photocatalysis events consist of surface phenomena that require the adsorption of the substrate molecules or other structures to TiO2 prior to the catalyzed reactions. Invariably, the HMTO materials developed thus far consisted of typical metal oxide networks deprived of any special selectivity feature. It means that the surfaces of these photocatalysts were not able of recognizing a certain targeted and the limited number of chemical structures or sub-structures, against all the others. Such recognition would be of great usefulness in practical applications. For example, on the degradation of the certain specified enantiomer of a drug during the synthesis of that drug, or on the degradation of an organoleptically undesired compound in beer production. One possible route to the achievement of recognition at the surface of HMTO materials is sol-gel molecular imprinting. The main goal of this work was to develop synthesis procedures leading to novel recognitive HMTO where, for the first time, enhanced photonic efficiency and high selectivity in titania photocatalysis will be combined. The recognition ability will be introduced by the molecular imprinting technique. So far, it has been possible to optimize a synthesis route to obtain the HMTO with bilirubin imprints, with particle diameter in the range 800 - 1500 nm, shell thickness in the range 37-170 nm, surface area in the range 50-145 m2/g and mesoporosity (3.4 nm < pore size < 10.2 nm). Batch adsorption tests were performed using the template (bilirubin), an analogue (protoporphyrin), and ascorbic acid, known as a chemical interferent in the quantification of bilirubin. With these tests, it was possible to adjust adsorption isotherms, by non-linear regression, and prove the selectivity of imprinted hollow TiO2 microspheres (MIP-HMTO), since there was a slight increase in the amount adsorbed from the template-bilirubin in the MIP-HMTO (qmax = 22 mg/g), compared to non-imprinted hollow TiO2 microspheres (NIP-HMTO) (qmax = 17 mg/g), and also a pronounced decrease in the analog (MIP-HMTO qmax = 3 mg/g; NIP-HMTO qmax = 17 mg/g). Finally, photocatalysis tests are being carried out with a UV LED (365 nm) to confirm the photocatalytic potential of MIP-HMTO compared to NIP-HMTO.