Adsorption isotherms of quercetin onto

The quantity of titania grafted to the surface of non-porous particles was determined following titania dissolution and complexation with H2O2, where the complex absorbs light at 407 nm (calibration curve, Fig. S2) [35]. The amount of grafted titania on the particles increased linearly with the amount of titania precursor used during grafting (Fig. 3). From this analysis, the amount of titania on the particle surface is determined to be 0.33, 1.17, 2.61 and 9.83 mg of TiO2 per gram silica. Guo and Dong determined that monolayer coverage of titania corresponds to approximately 1.9 mg TiO2/m2 surface area [26]. The average diameter of non-functionalized particles (450 nm), approximate density of AC 261066 (2.2 g/cm3) and equations for volume and surface area of a sphere were used to calculate the bulk surface area of the materials to determine TiO2 grafting. This surface area was used to convert the measured values of TiO2 grafted to the particles (in mg TiO2/g silica) to surface coverage (in mg TiO2/m2 silica). This approach to surface area estimation was taken instead of BET analysis of nitrogen adsorption because of the reduced accuracy of gas adsorption measurements for low specific surface areas. Titania coating densities for synthesized particles are 0.05, 0.19, 0.43 and 1.6 mg TiO2/m2, which ranges from a light to near monolayer titania coverage (2.6–84% of a monolayer) on the nonporous particles. The use of non-porous, spherical silica particles ensured that all surfaces were uniform and equally accessible to functional groups during functionalization as well as dissolution analysis.