Evaluation of shape and size effects on optical properties of ZnO pigment

The pigment with optimized morphology would attain maximum diffuse solar reflectance at a lower film thickness and reduce the pigment volume concentration required. This factor would contribute to a reduction in overall weight and possibly extend the durability of the system to longer time scales, specially in space assets. In the present work, five different morphologies of ZnO pigment were synthesized by hydrothermal method. The ZnO pigments were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and N2 adsorption (BET). The optical property of the ZnO pigments was investigated by UV/VIS/NIR spectrophotometer. The results indicated that the optical properties of ZnO powders were strongly affected by the particle size and morphology. The nanorods and microrods ZnO structures showed the minimum spectral reflectance in visible and near infrared regions, whereas the novel nanoparticle-decorated ZnO pigment revealed the maximum spectral reflectance in the same regions. The reflectance spectra of scale-like and submicrorods ZnO were in the middle of the others. The higher surface roughness led to higher light scattering in nanoparticle-decorated ZnO pigment and multiple-scattering in them. These results proved that a significant improvement in the scattering efficiency of ZnO pigment can be realized by utilizing an optimized nanoparticle-decorated pigment.