First principles calculations were performed to study the adsorption behaviors of caffein molecule on the pristine and N-doped TiO2 anatase nanoparticles. Both oxygen and nitrogen in the caffein molecule can react with the TiO2 nanoparticle strongly. Thus, the binding sites were located on the oxygen or nitrogen atom of the caffein, while on the TiO2 nanoparticle the binding site occurs on the fivefold coordinated titanium atoms. By counting van der Waals (vdW) interactions, it was found that the adsorption on the N-doped TiO2 is more favorable in energy than the adsorption on the undoped one, indicating the high sensitivity of N-doped TiO2 nanoparticles towards caffein molecules. It means a dominant effect of nitrogen doping on the adsorption properties of pristine TiO2. The large overlaps in the PDOS spectra of the oxygen and nitrogen atoms of the caffein and titanium atom of TiO2 represent a forming Ti-O and Ti-N bonds between them. The molecular orbital calculation results indicate that the HOMOs are strongly localized on the caffein. Charge analysis based on Mulliken charges reveals a considerable charge transfer from the caffein to the TiO2 nanoparticle. Manuscript profile

Density functional theory calculations were performed to investigate vitamin C interaction withN-doped TiO2 anatase nanoparticles. The adsorption of vitamin C on the energy favorable fivefoldcoordinated titanium sites was investigated. Various adsorption geometries of vitamin C towardsthe nanoparticle were examined. Since the adsorption energies of N-doped nanoparticles are higherthan those of undoped ones, the N-doped TiO2 nanoparticles can interact with vitamin C moleculemore strongly. Besides, adsorption on the pristine nanoparticle is less favorable, whereas on theN-doped one, the adsorption process is more energy favorable. The electronic structure analysis wasperformed in view of the density of states and molecular orbitals of the considered nanoparticles withthe adsorbed vitamin C molecule. The significant overlaps between the PDOS spectra of the oxygenatom of vitamin C molecule and titanium atom of TiO2 confirm the chemisorption of vitamin C onthe TiO2 nanoparticle. After the adsorption, the electronic densities in the HOMOs of the adsorptionsystems were mainly distributed over the vitamin C molecule, while the LUMOs were dominant atthe TiO2 nanoparticle. Our calculations shed light on understanding the interaction between vitamin Cand TiO2 nanoparticles, which provides an efficient outline for future experimental studies. Manuscript profile