Formation Mechanisms of ZnO Spherulites and Derivatives

Abstract

ZnO microparticles have been solvothermally synthesized from zinc acetate and formic acid. The resulting microspherulites consist of radially arranged nanorods which undergo a range of re-crystallisation pathways to produce particles with different terminal morphologies. Crystallisation on the particle surface results in hexagonal microdisc decorated hierarchical microspheres. These particles expose only the (0001) crystallographic plane of ZnO and further develop into a sea-urchin like morphology, when the microdiscs grow up along the [0001] direction into hexagonal microrods. Alternatively, crystallisation of the particle core into a ZnO plate, facilitates asymmetric assembly of nanocrystallites, forming a hexagonal cone on one side of the plate. The particle has a mushroom-like terminal morphology. When simultaneous surface and core re-crystallisation takes place, wood gyro-shaped particles are observed, in which all the surface discs face a single direction. The microstructures of the particles were investigated using XRD, electron microscopy and surface colouring with adsorbed charged dyes. Structural studies of the early growth stages and subsequent morphology evolution support a dipole field driven formation mechanism. This work offers an improved understanding of the formation of other spherulites, in particular, naturally occurring mineral calcium carbonate spherulites.

Low-Temperature Growth of ZnO Nanowires from Gravure-Printed ZnO Nanoparticle Seed Layers for Flexible Piezoelectric Devices

“…Since the NPs are roughly spherical, a large variety of crystallographic planes are presumably exposed to the CBD process [82]. Among these, polar surfaces are extremely chemically reactive [83,84] and have been found to be dominant surface nucleation sites for the growth of ZnO NWs in a solution [66]. To this regard, it has been observed that a high seed layer texture along the polar axis is necessary to obtain a high NW density [67,85,86].…”

Preparation and Formation Mechanism of l-Valine Spherulites via Evaporation Crystallization

“…Many factors affect the formation of spherulites, such as supersaturation, impurities, crystal habits, and additives. , Nowadays, an increasing number of researchers seek to explore the preparation methods for spherulites. Some of them have used ions and polymers as additives to induce or promote spherulitic growth. − With the in-depth studies on spherulites, the manufacture of spherulites is becoming increasingly advanced. − For instance, the ions Mn 2+ , Ni 2+ , and Mg 2+ have been shown to promote the formation of calcium carbonate spheres, sodium hexametaphosphate has been found to mediate the core–shell spherulitic crystallization of lithium carbonate, gelatin has been used as an additive to induce the spherical formation process of l -tryptophan, and the presence of Mg and gelatin-agarose has been reported to influence the formation and architecture of mineral aggregate. .…”

Naturally Occurring and Biomimetic Synthesized Calcite Spherulites

“…A cross section SEM image of a spherulite shown in the inset of Figure a demonstrates a radial arrangement of microrods. The principal driving force of the ordering of the nanocrystallites into such a novel microstructure is probably a dipolar field as discussed in the previous reports on the formation of synthesized vaterite spherulites, naturally occurring aragonite spherulites, synthesized ZnO microspheres. , …”

“…The principal driving force of the ordering of the nanocrystallites into such a novel microstructure is probably dipolar field as discussed in the previous reports on the formation of synthesized vaterite spherulites, 16 naturally occurring aragonite spherulites, 17 synthesized ZnO microspheres. 27,28 It was noted that when the reaction time was increased to 24 h, the number of rhombohedral crystals significantly increased and the number of the spherulites decreased. The spherulites almost disappeared when the growth time was further increased to 48 h, leaving only rhombohedral crystals.…”