Fractal growth of ZrO₂nanoparticles induced by synthesis conditions

Abstract

Strong changes in morphology and phase composition of zirconia nanoparticles can be induced by altering the growth conditions during nanoparticle synthesis. Here, we demonstrate that fractal ZrO 2 nanocrystals showing high specific surface area can be obtained in the nonaqueous synthesis by variation of temperature and precursor concentration. The growth process was studied in detail revealing a size increase from 2.7 to 7 nm as well as a change in the polymorphic composition from tetragonal to monoclinic zirconia. TEM measurements of samples withdrawn over the course of the synthesis showed that particles grow from roundish to dendritic shapes during the phase transformation. In contrast to the common assumption that the phase transition is controlled by thermodynamics, our data shows that the transition is rather governed by kinetics.

Mechanistic Aspects in the Formation, Growth and Surface Functionalization of Metal Oxide Nanoparticles in Organic Solvents

“…Driessche and co‐workers proposed a similar dibenzyl ether elimination mechanism for the microwave assisted synthesis of cubic ZrO 2 nanocrystals from Zr(O i Pr) 4 and benzyl alcohol, based on GC‐MS analysis . Ether elimination remained the main reaction pathway even if the synthesis was performed in a 1.5 L batch reactor . Zimmermann and Garnweitner studied the formation of anatase nanoparticles by the reaction of titanium(IV) isopropoxide in benzyl alcohol following an ether elimination pathway.…”

“…presented a detailed mechanistic study on the fractal growth of ZrO 2 nanoparticles considering chemical as well as crystallization aspects. Systematic change of the precursor concentration and reaction temperature made it possible not only to tune the ratio of tetragonal‐to‐monoclinic zirconia, but also to grow either spherical or fractal morphologies …”

“…[117] Ether elimination remained the main reaction pathway even if the synthesis was performed in a1.5 Lbatch reactor. [158] Zimmermann andGarnweitnerstudied the formation of anatase nanoparticles by the reaction of titanium(IV)i sopropoxide in benzyl alcohol following an ether elimination pathway.B esides the ether elimination byproducts spontaneous water released ue to catalytic condensation of benzyla lcohol to dibenzyle ther at the Ti center led to an increase of pressure in the reactionsystem causing instant nucleation and fast growth of the crystalline anatasen anoparticles. [159] According to 1 HNMR data, an analogous ether elimination reaction was also found for the formation of anatase TiO 2 nanoparticles prepared from the reactiono ft itaniumi sopropoxide with benzyl alcohol on the surface of carbon nanomaterials using microwave heating.…”

“…Systematic change of the precursor concentration and reaction temperature made it possible not only to tune the ratio of tetragonal-to-monoclinic zirconia, but also to grow either spherical or fractal morphologies. [158] The solvent not only influences the crystal phase, but also the crystallinity.Acomparison between benzyl alcohol and triethylene glycol (TEG) for the synthesis of magnetite/maghemite nanoparticles showed that at shorter reaction times the particles in benzyla lcohol were of much better crystallinity than those in TEG. [253] This observation is important for magnetic nanoparticles, because the magnetic properties are directly linked to the crystallinity.…”

Formation of Aluminum‐Doped Zinc Oxide Nanocrystals via the Benzylamine Route at Low Reaction Kinetics

“…This synthesis route provides timeresolved access to measurement technologies in terms of particle formation analysis, as will be shown in this work. For synthesizing highly crystalline metal oxide nanostructures, the non-aqueous sol-gel synthesis is used, wherein crystalline precursors are dissolved in aromatic solvents and converted to nanoscale crystals with defined sizes, narrow particle size distributions, and adjustable morphologies, at moderate temperatures [10][11][12][13][14]. The work by Zellmer et al [14] has shown timeresolved studies of crystal growth of AZO nanocrystals via the benzylamine route, preferably at high temperatures (~200°C), high precursor concentrations (~50 g L -1 ), and relatively short reaction times (~30 min).…”