Synthesis and characterization of Co₂SiO₄ from rice husk ash

Abstract

Silicate pigments with the general formula MSiO₄ are widely used in the paint, ceramic, and protective coating industries due to their high thermal and chemical stability. In this study, nano-silica was synthesized from rice husk ash (RHA) as a bio-based raw material via the sol–gel method and employed as the silica source for pigment preparation. Subsequently, cobalt silicate (Co₂SiO₄) pigment was successfully synthesized through the sol–gel process, resulting in a desirable blue coloration.

The structural and phase composition of the synthesized pigment was characterized by X-ray-diffraction (XRD), confirming the formation of the cobalt silicate crystalline phase. The morphology and particle size distribution were investigated using scanning electron microscopy (SEM). In addition, the optical properties of the pigment were evaluated by UV–Vis diffuse reflectance spectroscopy (DRS), which revealed strong absorption in the visible region responsible for the blue color of the cobalt silicate pigment. The colorimetric properties were further quantified using the CIE L*a*b* color space, demonstrating high color intensity.

The results indicate that RHA-derived nano-silica is a suitable and sustainable precursor for the synthesis of cobalt silicate pigments, offering an eco-friendly approach for the development of thermally and chemically stable inorganic pigments with promising optical and colorimetric performance.