Nanorose-like ZnCo2O4 coatings synthesized via sol–gel route: morphology, grain growth and DFT simulations

Abstract

Ternary cobalt-based metal oxide (ZnCo2O4) has been successfully coated onto aluminum substrate via sol–gel method. The coatings were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and UV–Vis–NIR spectrophotometry. Thermal degradation of the coatings was probed by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Model of crystal growth kinetics and density functional theory (DFT) calculations further probed the crystalline structure evolution. The predicted ZnCo2O4 crystalline structures were confirmed by XRD and EDX. The grain growth kinetic model for ZnCo2O4, derived from Lifshitz–Slyozov–Wagner (LSW) theory, determined that the growth of crystalline phases is unaffected by the annealing temperature; however, the crystallites’ sizes decreased with the increase in precursor concentration. DFT analysis indicated that structural energy stability between the bulk state and slabs of ZnCo2O4 was at two oxygen layers (O-layers) with an optimum grain width of 17.21 A. Interestingly, the morphology of ZnCo2O4 represented a rose-like template structure formed by inter-connecting layers of nanosheets. This unique surface morphology enhanced the optical absorptance properties up to α = 70.7%.