DFOB-Induced Dissolution of Anatase, Rutile, and Food-Grade TiO2 Nanoparticles

Titanium dioxide nanoparticles (TiO2 NPs) are prevalent in products of everyday use, especially in food additives, paints, and consumer products. Their favorable properties include inertness in an aqueous environment. In this study, nanosized anatase, rutile, and food-grade TiO2 particles were investigated with the treatment of the siderophore desferrioxamine B (DFOB), and their physicochemical, spectroscopic, and microscopic natures were revealed under different pH conditions. The formation of a Ti(IV)-DFOB complex in solution is evident from electrospray ionization mass spectroscopy. Dissolved Ti was analyzed by UV/visible and inductively coupled plasma optical emission spectroscopy and was found in the micromolar range (ca. 1-60 μM) over days. At all pH values, dissolution is more extensive for food-grade NP than for anatase and rutile. Near neutral pH, Fourier transform infrared spectroscopy (FTIR) data suggest that siderophore adsorption is more prominent than Ti dissolution. Scanning electron microscopy data reveals erosion of the TiO2 surface with DFOB. A comprehensive kinetic profile supports multiple dissolution steps associated with anatase and rutile, with fewer steps for food-grade NPs. The addition of small organic acids shows mostly synergistic effects toward dissolution. This study will be helpful for considering TiO2 applications in the food processing industry and for predicting its environmental fate in the presence of avid ligands.