Impact of titanium concentration in structural and optical behaviour of nano Bi2Ce2−x TixO7 (x = 0–1) high NIR reflective and UV shielding yellow and orange pigments

Abstract

A series of environmentally benign UV shielding and NIR reflective pigments Bi2Ce2−x TixO7 (x = 0.25, 0.5, 0.75, 1) with colour ranging from yellow to dark orange were synthesized by solution combustion route. The optical and structural characteristics of the developed pigments were characterized using UV–Vis NIR Spectrophotometer, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results indicated that the incorporation of Ti4+ into Bi2Ce2O7 showed significant increase in crystallite size due to decrease in lattice strain. The calculated crystallite size of Bi2Ce2−xTixO7 is seen to increase from 15 nm to 41 nm as the concentration of a Ti4+ is increased in Ce4+ sites and resulting crystal structure changed from cubic fluorite (fcc) structure to monoclinic. Progressive substitution of Ti4+ in Bi2Ce2O7 lattice showed a red shift in absorption edge to higher wavelength from 450 to 510 nm in the diffuse reflectance spectra resulting in colour change from yellow to reddish brown. The undoped Bi2Ce2O7 pigment showed good yellow hue (b* = 43.89) with the high NIR reflectance of 78.61% and good UV absorbance. The colour and NIR reflectance characters of low cost, nontoxic Ti doped Bi2Ce2−x TixO7 pigments are comparable with the commercially available yellow chrome pigment and BiVO4 (NIR reflectance = 49%). The application of the synthesized pigments was investigated as paint pigments in thermosetting acrylic resin paint formulation for their colouring performance.