Structural and visible-near infrared optical properties of (Fe, Mo)-co-doped TiO2 for colored cool pigments

Abstract

Fe and Mo co-doped TiO2 pigments were prepared via solid-phase synthesis, and the samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible–near infrared (UV-VIS-NIR) spectrophotometer. The effects of coloring impurity Fe3+ and compensating impurity Mo6+ on the phase, morphology, chemical structure, and optical properties of TiO2 pigments were systematically studied—especially the mechanism of synergistic effects of visible light color and near-infrared reflectance of TiO2 pigments. The results showed that single doping of Fe3+ or Mo6+ could accelerate the transition of TiO2 pigment from anatase phase to rutile phase. In the (Fe, Mo) co-doped sample, the Mo impurity helped accelerate the A→R crystal phase transition of TiO2, but an excessive amount of Fe impurity could inhibit the phase transition process. The morphology and particle size of the samples were also affected by the type of impurity and the doping concentration. In addition, the doped impurities could form a strong characteristic absorption peak in the visible light spectrum to enhance the absorption of visible light. The sample then gradually changed from white to pink, white gray to orange, etc. In the near-infrared region, the impurity compensation effect between Mo6+ and Fe3+ could be utilized to reduce the free carrier concentration of the TiO2 pigment and weaken its near infrared absorption. By reasonably adjusting the relative contents of Fe and Mo impurities, the developed Ti0.98875Fe0.0075Mo0.00375O2 yellow pigment could finally yield a NIR reflectance of 96%.This is expected to meet the application requirements of colored energy-saving pigments.