Synthesis of green cool pigments (CoxZn1-xO) for application in NIR radiation reflectance

Abstract

Reconciling green synthesis, sustainability and production of pigments for protection of solar radiation is a continuous topic of search for unique, versatile and environmental compatible methods. In this perspective, we present the green synthesis of inorganic pigments with reflective properties of infrared radiation in the NIR region. Green powder pigments described by CoxZn1-xO, were obtained via the gelatinization method of starch colloidal suspension with inorganic salts (zinc and cobalt), calcined at different temperatures. Structural, morphological and spectroscopic characterization showed the pigments present Wurtzite crystalline phase with compact hexagonal structure, and monophasic when obtained at a calcination temperature above 800 °C. Colorimetric measurements obtained by the CIEL*a*b* method presented values related to green pigments attributed to cobalt ions, which replace the zinc ions in the Wurtzite matrix and corroborate the composition estimated by X-ray fluorescence analysis for Co0.1Zn0.9O. The pigments' NIR reflectivity increased with the calcination temperature increasing, with R% > 35%; and when the pigment is dispersed in a white paint the increase is R% > 50%. Therefore, our green pigments present great potential to be used as an active material in cold coatings and in solar devices.