Wet Chemical Synthesis of Molybdenum-Doped Amorphous TiO2Nanoparticles and Studies on Their Photochromic Properties

Undoped and (0.5–5 at%) molybdenum-doped TiO2 nanoparticles were synthesized by a simple and scalable wet chemical method. The as-synthesized materials were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, electron paramagnetic resistance (EPR), and ultraviolet-visible (UV-Vis) spectroscopy techniques. XRD studies showed the formation of crystalline anatase phase of undoped TiO2, whereas Mo-doped samples showed the formation of an amorphous phase. AFM studies showed the formation of spherical-shaped particles with a particle diameter of ∼23 nm in all samples. The photochromic behavior of these materials was studied by making their films in alkyd resin. Films of these materials showed a reversible photochromic color change from beige to brown on exposure to UV light. The coloration and bleaching process was recorded using UV-Vis diffuse reflectance spectroscopy. The maximum color change was observed in 2 at% Mo+6-doped nano-TiO2. The photochromic mechanism of molybdenum-doped nano-TiO2 was also examined using EPR spectroscopy.