Synthesis of Mn-sensitized TiO ₂ nanoparticles: influence of sequence of reagents on phase composition and photocatalytic activity

A new approach has been developed to synthesize manganese-containing titanium dioxide materials by hydrolysis of titanyl sulfate. The samples were studied by a complex of methods (synchrotron radiation X-ray powder diffraction, high-resolution scanning electron microscopy with energy-dispersive X-ray spectroscopy, absorption spectroscopy). The sequence of the added reagents effects the phase composition (anatase or mixtures of anatase and “η-TiO₂”), size of crystallites, nanoparticles and agglomerates, manganese content, and oxidation state (Mn³⁺, Mn²⁺/Mn³⁺, or Mn³⁺/Mn⁴⁺). The Mn-doped TiO₂ samples have been proven to have high photocatalytic activity for methyl orange (MO) under visible light. The rate of MO degradation reached 0.0046 min⁻¹ (50 % in 150 min) for the sample containing a mixture of anatase (75 %) and “η-TiO₂” (25 %) with a high degree of amorphism; the sample is characterized by the smallest size of crystallites (44.3 Å), the largest size of nanoparticles (33 nm) and agglomerates (10 μm), and the lowest manganese content (0.3 at. %) with the ratio Mn³⁺:Mn⁴⁺ = 1:1. The resultant Mn-doped titania has potential applications in photocatalysis and environmental protection.