A series of semiconductor photocatalysts based on transition metals (M' = V, Cr, Fe, Co, Mn, Mo, Ni, Cu, Y, Ce, and Zr) incorporated TiO2 (Ti/M' = 20 atomic ratio) materials have been synthesized by adopting a one-step liquid flame aerosol synthesis technique. The resulting materials were explored for the destruction of acetonitrile in gas phase under visible light irradiation at ambient conditions. Our H-2-TPR studies revealed the formation of Me-O-Ti bonds, which suggest the strong interaction of dopant metal-TiO2 in all the as-synthesized materials. The reduction peaks in Cr-doped TiO2 shifted to much lower temperatures, due to the increase in the reduction potential of titania and chromium. The strong interaction (formation of Cr-O-Ti bonds) is the main reason that the Cr/TiO2 is an active photocatalyst in visible light. Our XPS studies suggest that the relative atomic percentage value of Ti3+/Ti4+ characterized by XPS was significantly high for our flame-made Cr/TiO2 nanoparticles (Ti3+/Ti4+ = 0.89, 32.9%), whereas, other samples demonstrated poor atomic percentage value of Ti3+/Ti4+ (Ti3+/Ti4+ = 0.08-0.32). The existence of Ti3+ species with narrow band gap is highly beneficial for the promotion of visible light-induced photocatalytic activity. The position of the Cr 2p peaks shifted to lower binding energies in Cr-doped TiO2 nanoparticles. The electrons migrate from the TiO2 nanoparticles to chromium species, which reveals a strong interaction between Cr and TiO2 nanostructure in the interface of flame-made nanoparticles. Conversely, Mn3+ species combined with TiO2 because its surface metal dispersion was kept high after TiO2 loading. However, Mn3+ incorporated catalyst was inactive because of the small energy driving force for electrons to detrap from Mn2+. The UV-vis spectroscopy results of M'-doped TiO2 (M' = Fe, Cr, V, Co, Ce, and Ni) materials showed augmentation of light absorption in the visible range. The Cr, V and Fe (Ti:M' atomic ratio = 20:1) titania aerosol catalysts reduced the bandgap energy of TiO2 to 2.9 eV under visible light irradiation. Among all of the catalysts we tested, the transition metals (M' = Cr, Fe, and V) incorporated materials have shown an impressive catalytic performance in visible light. Among all the catalyst tested, Cr-doped titania demonstrated a superior catalytic performance and the rate constant is about 8-19 times higher than the rest of the metal doped catalysts. Their catalytic performances are correlated with the UV-vis spectrum of each synthesized catalyst to reveal the specific role played by each metal ion. Published by Elsevier B.V.