Investigation of transition metal ion doping behaviors on TiO2 nanoparticles

In this research, we have studied the doping behaviors of eight transition metal ion dopants on the crystal phase, particle sizes, XRD patterns, adsorption spectra, anatase fraction, and photoreactivity of TiO2 nanoparticles. The pristine and ion-doped TiO2 nanoparticles of 15.91-25.47 nm were prepared using sol-gel method. Test metal ion concentrations ranged from 0.00002 to 0.2 at.%. The absorption spectra of the TiO2 nanoparticles were characterized using UV-Visible spectrometer. The wavelength of the absorption edge of TiO2 was estimated using the spectra derivative-tangent method. The photoreactivities of pristine and ion-doped TiO2 nanoparticles under UV irradiation were quantified by the decoloring rate of methyl orange. XRD patterns were recorded using a Rigaku D/MAX-2500 V diffractometer with Cu K alpha radiation (50 kV and 250 mA), and particle size and anatase fraction were calculated. Results reveal that different ion doping exhibited complex effects on the studied characteristics of TiO2 nanoparticles. In general, red shift occurred to ion-doped TiO2 nanoparticles, but still with higher TiO2 photoreactivities when doped with Fe3+ and Ni2+ ions. Among the ions investigated, Ni-doped TiO2 nanoparticles have shown highest photoreactivity at the concentration of 0.002 at.%, about 1.9 times that of the pristine TiO2. Ion doping was shown to reduce the diameter and influence the fraction of anatase. Data also indicated that the combination of anatase diameter and ion radius might play an important role in the photoreactivity of TiO2 nanoparticles. This investigation contributes to the understanding of complex ion doping effects on TiO2 nanoparticles, and provides references for enhancing their environmental application.