Ce and Fe doped gahnite: Cost effective solar reflective pigment for cool coating applications

Abstract

In the current investigation, a new series of Ce doped gahnites of the formula ZnAl2-xCexO4 (x = 0–0.04), Fe doped gahnites of the formula ZnAl2-yFeyO4 (y = 0–0.5) and Ce and Fe co-doped gahnites of the formula ZnAl2-x-yCexFeyO4 (x = 0–0.04; y = 0–0.5) with high near infrared (NIR) reflectance were fabricated to mitigate the heat island effect. All the designed pigments were characterized by powder X-ray diffraction (PXRD), Fourier transformed infra red spectroscopy (FT-IR), Ultraviolet-Diffuse reflectance spectroscopy (UV-DRS). Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscopy (TEM) and CIE-L*a*b* colour values. Band gap of the white gahnite of the formula ZnAl2O4 (Eg = 3.8 eV) shifted to 2.70 eV and 2.15 eV for the pigments ZnAl1.96Ce0.04O4 and ZnAl1.5Fe0.5O4 respectively. Ce doped gahnites broadened the absorption centre from 250 nm to 350 nm in the UV spectrum and resulted in yellow colour. Whereas Fe doping introduced additional electronic transition between 440 nm and 490 nm and exhibited reddish yellow colour. NIR reflectance of ZnAl1.96Ce0.04O4, ZnAl1.5Fe0.5O4 and ZnAl1.78Fe0.2Ce0.02O4 was found to be 86%, 65%, 80% respectively between 700 and 2500 nm regions. Good thermal and chemical stability along with high NIR reflectance made the prepared pigments as a potential candidate to design cool roofing materials.