Influence of method of synthesis on the colour and NIR reflective properties of bismuth and vanadium doped cerium phosphate

Abstract

Inorganic pigment with NIR reflectance properties could mitigate the energy consumption used for controlling the indoor temperature in buildings. This work presents an environmentally benign pigment series of Bi3+ and V5+ doped CePO4 of formula Ce1-xBixP1-yVyO4 (x = y = 0.02 to 0.5) by coprecipitation and hydrothermal methods. Doping of metal ion could tune the band gap of CePO4 approximately from 3.01 to 2.4 eV mainly due to the introduction of additional V3d orbital in the conduction band. Doping changed the color of the compound from white to yellow color. The synthesized compounds were characterized by XRD for phase identification, FT-IR for functional group analysis, UV-DRS to determine the sample's reflectance and band gap, CIE – L*a*b* for color values and SEM techniques for morphology studies. XPS analysis was conducted to confirm the oxidation state of Ce, V and Bi in the compound. Among the series of individual and co-doped CePO4 series, the compound Ce0.8Bi0.2(P0.8V0.2O4) synthesized from the precipitation method exhibited a high yellow value (b* = 24.58) with single-phased monoclinic system and 75.05% NIR solar reflectance. The same compound prepared by the hydrothermal method exhibited less yellow value (b* = 18.96) and 75.67% NIR solar reflectance. Good chemical stability in acid and alkaline medium was observed.