Ag-doped hollow TiO2 microspheres for the selective photo-degradation of bilirubin

Abstract

The surface of highly crystalline hollow TiO2 microspheres was nanostructured to contain recognition sites for bilirubin and simultaneously doped with Ag to achieve a photocatalytic response to visible light irradiation. The molecular imprinting technique was employed to obtain the recognition sites, whereas Ag-doping was tested either during the synthesis or after the complete synthesis by impregnation. Different Ag:Ti molar proportions were studied (1:2; 1:4 and 1:6). From the absorbance spectra in suspensions of the different microspheres, the ratio of 1:6 molAg/molTi was established as allowing for a greater capacity of absorption of visible light. It was possible to confirm a positive catalytic effect of Ag-doping, either with ultraviolet or visible light, especially for molecularly imprinted hollow microspheres doped during the synthesis. The increases in kinetic constants were much higher for molecularly imprinted hollow microspheres doped during the synthesis and calcined at 250 °C (12 min−1 and 9 min−1, for ultraviolet and visible light) compared to the corresponding undoped microspheres (8 min−1 and 5 min−1, for ultraviolet and visible light), leading to imprinting factors of 1.6 and 1.9, for ultraviolet and visible light, respectively. Selective photocatalysis was also confirmed with α values of 1.4 and 1.3 for ultraviolet and visible light, respectively. In conclusion, it was possible to obtain, with success, selective Ag-doped hollow TiO2 microspheres with a higher rate of bilirubin degradation compared to undoped hollow TiO2 microspheres, even with visible light irradiation.