Titanium dioxide nanoparticles with disordered outermost layer sturctures have significantly enhanced light absorption and photocatalytic properties and thus receiving enhanced attention in recent years. Engineering the outermost layers using in situ magnesium doping to tailor the band-edge of TiO2 nanoparticles was achieved via a flame aerosol reactor. The distribution of doped elements in nanoparticles could be controlled in a high temperature flame process, and which could be predicted by the comparison of different characteristic time scales, such as reaction time, coagulation time, and sintering time is proposed. In situ magnesium doping on the outermost layers effectively tailored the conduction band and electron structure of the TiO2 nanoparticles, and simultaneously improved the maximum photocurrent as well as the maximum photovoltage in dye-sensitized solar cells. These improvements were largely attributed to red-shifted light absorption, and rapid photoelectron injection into the conduction band. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 870-880, 2017