Vanadium and bismuth doped FePO4 as Near Infra Red (NIR) reflective pigment for energy saving application

Abstract

In the current investigation a series of NIR reflective pigments were synthesised using naturally abundant iron based phosphates. FePO4, Vanadium (V) doped FePO4 of composition FeP1-xVxO4 (x = 0, 0.05, 0.1, 0.15, 0.2), Bismuth (Bi) doped FePO4 of composition BiyFe1-yPO4 (0.03, 0.05, 0.15) and Bi and V co-doped FePO4 of composition Bi0.03Fe0.97P0.8V0.2O4 were prepared by following co-precipitation method. All the tailored materials were characterized using Powder X-ray Diffraction Analysis (PXRD), Fourier Transformed Infra Red (FT-IR), X-ray Photo electron spectroscopy (XPS), Ultra visible Diffuse Reflectance Spectra (UV-DRS), Scanning Electron Microscopy (SEM) techniques and Commission Internationale de l’Eclairage (CIE-LAB) colour parameters. Strain in lattice was observed by the substitution of comparatively bigger V5+ ion into P5+ hence shift in high intense peak was observed. Doping of small amount of Bi3+(x = 0.03) into Fe3+ lattice leads to the introduction of Bi2O3 as secondary phase and the intensity of bismuth oxide phase was increased as the doping concentration increases. Existence of Fe2+ along with Fe3+ was noticed in Bi0.03Fe0.97P0.8V0.2O4 which was confirmed through XPS technique. Reddish brown FePO4 (b* = 17.49) has changed into mustard yellow (b* = 40.47) as the V5+concentration increases from 0 to 0.2. Bi0.03Fe0.97PO4 has turned into reddish orange. 60% reflectance was observed in the NIR region as a result of co-doping of bismuth (Bi) and vanadium (V) into FePO4. Hence V and Bi doped FePO4 materials can serve as potential cool pigments.