Enhancing the H2 evolution from water–methanol solution using Mn2+–Mn+3–Mn4+ redox species of Mn-doped TiO2 sol–gel photocatalysts

• The Mn-doped TiO2 sol–gel photocatalysts were obtained.
• The H2 evolution is improved by sacrificial molecule and Mn dopant in TiO2.
• The Mn incorporation in TiO2 enhance the optical absorption in UV–vis region.
• A mixture of oxidation states of Mn is obtained after calcination in air.
• The role of manganese is decrease the electron–hole recombination.

Mn-doped TiO2 materials synthetized by the sol–gel method were obtained and tested in the photocatalytic hydrogen production from a methanol–water solution. The Mn amount was varied between 1.0–10.0%wt. Powder X-ray diffraction patterns and Raman spectra of the synthesized solids showed the anatase as the predominant crystalline phase. A high specific surface area was found in the Mn-doped sol–gel catalysts between 88–136 m2/g while in bare TiO2 sample 64 m2/g only. Mn-doped TiO2 solids evaluated in the production of H2 showed higher photoactivities (1376 μmol h−1 g−1 for 1.0%wt. Mn and 1736 μmol h−1g −1 for 5.0%wt. Mn) in comparison with the bare TiO2 semiconductor (264 μmol h−1g −1). This improvement in photoactivity is suggested as a combination of charge separators Mn2+, Mn3+ and Mn4+ which can act simultaneously as electron and hole traps respectively. The synergetic effect between the manganese oxidation states and electrons transferred from methanol toward TiO2 particles favored the H2 production.

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