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The Influence of Ethanolamines on the Solvothermal Synthesis of Zinc Oxide: A Combined Experimental and Theoretical Study

The solvothermal synthesis of ZnO particles from zinc acetylacetonate [Zn(acac)2] in the presence of monoethanolamine (MEA) or triethanolamine (TEA) at 170 °C is reported. The structural, optical and morphological characteristics of ZnO particles have been studied by X-ray diffraction, UV-Vis spectroscopy, FE-SEM and TEM/STEM microscopy. The experimental findings are confirmed by means of DFT calculations. On the basis of the results, both experimental and theoretical, the growth mechanism is proposed which initiated the ZnO nucleation process continued by the growth of primary nanoparticles and immediately thereafter the spherical aggregation of ZnO particles. The calculations suggest that the process of ZnO nucleation proceeded mainly through the reaction of small dimers rather than oligomeric or monomeric species. The high chelating efficiency of both ethanolamines towards zinc with tetrahedral geometry is observed, having the same structural motif for the most stable ZnO–MEA and ZnO–TEA dimers. It was found that the way of primary ZnO nanoparticles growth and their spherical aggregation into final particles strongly depend on the type of ethanolamine used and the molar ratio [ethanolamine]/[Zn(acac)2]. The results show that the increase in TEA concentration could potentiate TEA coating on ZnO nanoparticles, which induced the formation of bigger, densely packed spherical aggregates. The reduced band gap energies were noticed with the increased sample microsphere size.

crystal growth ; density functional calculations ; electron microscopy ; nanoparticles ; ZnO

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