Doped Titania Nanocrystals Explained By Experimental And DFT Characterizations

Doped nanostructured TiO2 is a photocatalytic promising material exploiting significant activity in the visible region.[1-5] However, its exact photocatalytic mechanism is still under debate. Here we present characterization results of doped titania nanoparticles through HR-XRPD, EXAFS, HR-TEM, UV–Vis spectroscopy, N2 adsorption – desorption isotherm, EDX analysis, DRS. A photoelectrochemical characterization was also carried out by means of photocurrent and photovoltage measurements.[6] Average Ti nearest neighbors distances were obtained from EXAFS (see picture as an example), lattice parameters from HR-XRPD and electronic density of states from DRS and photoelectrochemical experiments. The latter are weere compared with DFT calculations at different levels of theory. As for N-doping, we found that N substitutes O at low levels of doping, whereas O vacancies creation is observed at higher N concentrations.[1] To achieve a better understanding of the structural and photocatalytic role of the guest N species, we compared HR-XRPD results with periodic DFT simulations of defective and doped anatase through a wide concentration range.[6] This comparison is discussed considering also the outcomes provided by photocatalytic experiments. In this way, we rationalize the correlation among doping and the observed photocatalytic performances. We also found that doping sometimes induces high crystallinity and slows the recombination of photogenerated electrons and holes in TiO2,[2] modifying the absorption spectra with specific features in the visible region. We investigated the effects of the dopant on the band energy level, surface area, pore volume and crystal size, complementing experimental results with plane-wave bulk DFT calculations. We provided strong evidence that electronic photoexcitation enhancements are generated by the presence of dopant extra orbitals just below the conduction band.