Simple preparation of Mn-N-codoped TiO₂ photocatalyst and the enhanced photocatalytic activity under visible light irradiation

Graphical abstract: - Highlights: • Mn-N-codoped TiO₂ were synthesized by a simple sol-gel synthesis method. • Mn-N-TiO₂ exhibited a strong absorption at 400–650 nm. • Mn and N codoping enhanced the thermal stability of TiO₂ structure. • Mn-N-TiO₂ showed significant photocatalytic activity under visible light for RhB. - Abstract: Mn-N-codoped TiO₂ nanocrystal photocatalysts responsive to visible light were synthesized by a simple sol-gel method and calcined at different temperatures. The catalysts with different Mn contents were characterized by XRD, BET, UV-vis DRS, XPS and ESR analyses and their photocatalytic activities for Rhodamine B degradation were studied under visible light irradiation. The results showed that the codoping of Mn and N ions inhibited the growth of crystalline size and the transformation from anatase to rutile phase. The XPS results showed that the introduction of a small amount of Mn facilitated further N uptake. Mn-TiO₂ and Mn-N-TiO₂ exhibited strong visible light absorptions at 400–650 nm. Mn-TiO₂ showed significant photocatalytic activity under visible light irradiation compared to pure TiO₂, and the activity was further enhanced by codoping Mn and N into TiO₂. The highest photocatalytic activity was achieved on 0.25%Mn-N-TiO₂ calcined at 400 °C. The synergistic effect of Mn and N ions narrowed the band gap of TiO₂ and inhibited the recombination of the photogenerated electrons and holes, leading to a great improvement in the photocatalytic activity in the visible light region