Co- and Mn-Doped ZnO Pigments Synthesized via Ginkgo Biloba Leaf-Assisted Self-Propagating Combustion: Structural and Optical Properties

ZnO-based pigments doped with Co and Mn ions were synthesized via a self-propagating combustion method using Gingko biloba leaves as a bio-derived fuel. Thermogravimetric analysis confirmed an effective combustion interaction between the metal nitrates and the leaf-derived fuel, validating the combustion synthesis process. X-ray diffraction results revealed the formation of single-phase hexagonal wurtzite ZnO for all samples, with successful incorporation of dopant ions without secondary phase formation. The synthesized powders exhibited porous agglomerated morphologies resulting from gas evolution during the combustion process, while FTIR analysis confirmed the formation of Zn–O bonds and the effective removal of organic species after calcination. Optical characterization demonstrated that transition-metal doping significantly modifies the visible and near-infrared reflectance properties of ZnO pigments, producing green Co-doped and black-brown Mn-doped pigments with relatively high NIR solar reflectance. These results indicate that bio-fuel-assisted combustion synthesis provides a simple and effective route for producing functional ZnO-based pigments with tunable optical properties for potential application in thermally functional coating materials.