Alcoholic Solvent Influence on ZnO Synthesis: A Joint Experimental and Theoretical Study

Abstract

Zinc oxide nanoparticles were prepared by a solvothermal synthesis using various alcoholic reaction solvents including ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-octanol, at 170 °C. The nucleation and growth processes of the ZnO nanoparticles were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) characterization, and they were corroborated by means of quantum chemical calculations at the density functional theory level (DFT). On the basis of the results of joint microstructural and theoretical study, the nucleation and preferential growth mechanism of ZnO nanoparticles is proposed. The effect of various alcoholic solvent on the overall shape and growth rate along the preferential c-axis of ZnO nanoparticles were corroborated by means of theoretical simulations of interface-solvent interaction by using nanoclusters (ZnO)n (n = 12 and 36). The (ZnO)36–CH3(CH2)nOH (n ≤ 7) interaction has been found to be spontaneous exergonic process only in the presence of 1-butanol as reaction medium with ΔG*INT = −4.95 kcal mol–1, whereas endergonic in the presence of all remaining alcohols used (ΔG*INT > 0). The results of X-ray diffraction size-strain analysis reveal that solely the use of 1-butanol as solvent leads to rather isotropic crystallite shape (Dv⊥c-ax ∼12 nm, Dv∥c-ax ∼12 nm), whereas in the presence of all remaining alcohols used ZnO nanoparticles grew prevailing in the c-direction to form nanorods. The alcohols of different size and polarity acts as a solvent and reactant as well as controlling agents for crystal growth, providing different binding interactions involved in both the nucleation processes and preferential growth of ZnO nanoparticles. The calculated values of EO···H and EZn–O of (ZnO)36–CH3(CH2)7OH (1-octanol) interaction indicate a weaker interaction of the nonpolar 1-octanol and polar a little positively charged Zn surface of ZnO crystal as well as a higher preferential growth rate along the c-axis in comparison to polar alcoholic media.