Correlation investigation on the visible-light-driven photocatalytic activity and coordination structure of rutile Sn-Fe-TiO2 nanocrystallites for methylene blue degradation

• The relationship between activity and coordination of Sn-Fe-TiO2 was investigated.
• Fe3+ preferentially substituted tetrahedrally coordinated Ti4+.
• Sn-Fe-0.1 exhibited the highest photocatalytic activity.
• The highest activity was attributed to the proper ratio of unsaturated Fe and Ti.
• Mechanism of Sn-Fe codoped TiO2 photocatalyst was proposed.

Rutile Sn-Fe-TiO2 photocatalysts with high visible-light-driven activity were synthesized by an improved soft chemical solution process for investigating the potential correlation between their photocatalytic performance and coordination structure. The prepared photocatalysts were systematically characterized by XRD, BET, Raman, TEM, UV–vis, XPS, XAFS and Mössbauer techniques. Their photocatalytic performances were evaluated by degrading the model pollutant of methylene blue aqueous solution under visible light irradiation (λ ≥ 400 nm). The results indicated that tin and iron ions could substitute Ti4+ in the rutile TiO2 lattice, and specially, iron ions were located at tetrahedrally coordinated titanium sites. Their visible-light-driven photocatalytic activities were found to culminate at a very low level of iron doping (Fe/Ti = ∼0.1 at.%, Sn/Ti = 2.0 at.%), this was 5-fold of P25 and 2-fold of undoped rutile TiO2. It was confirmed that besides the high surface area, fine crystallinity, enhanced visible light absorption and optimized oxygen vacancy concentration, the mole ratio of tetrahedrally coordinated iron and titanium was also essential to modify their visible-light-driven photocatalytic properties.

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