Formation mechanism of hollow microspheres consisting of ZnO nanosheets

Abstract

Hydrangea-like hollow microspherical ZnO has been synthesized via a transformation from layered basic zinc acetate (LBZA) and characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Investigation of the early stages of the crystal growth revealed a non-classic growth mechanism. With increasing reaction time, (1) amorphous spherical aggregates formed initially, followed by (2) surface multiple nucleation, (3) crystallization into LBZA nanosheets which are vertical to the microspheres' surface, (4) surface condensation leading to the formation of hollow microspheres, (5) extension of the crystallization both inwards and outwards, and ( 6) transformation to zinc oxide during annealing in air. The detailed formation mechanism of the hydrangea-like microspheres, consisting of thin (y5.4 nm) LBZA nanosheets, is proposed. The hydrangea-like ZnO exhibited superior photocatalytic performance in dye degradation due to its unique construction and high specific surface area. This work may shed light on crystal engineering of porous microspheres, hollow crystals and thin nanosheets of other materials.

Modification of the Crystalline Structure of ZnO Nanoparticles Embedded Within a SiO2 Matrix due to Thermal Stress Effects

“…Rykl and Bauer 21 reported for first time a crystalline phase of ZnO different to the hexagonal and cubic, which, to our best knowledge, its crystal symmetry remains unidentified. That ZnO phase has also been marginally reported by other authors: in N doped thin films 22 , in porous hollow microspheres 23 and oxidation of Langmuir-Blodgett multilayers 24 . This phase was obtained by Rykl and Bauer at high temperatures (450 °C) and high pressures (600 atm) 21 .…”

Nanošenje fotokatalitičkih ZnO slojeva na podloge različite geometrije

“…layered basic zinc acetate, LBZA), koji zatim žarenjem prelazi u ZnO zadržavajući listićavu morfologiju LBZA. [5][6][7][8][9][10] Hidrotermalna sinteza alternativni je pristup pripravi slojeva sličnih morfologija, [11][12][13][14] no preliminarna istraživanja pokazuju da su takvi slojevi vrlo prhki i znatno slabije vezani na nemodificiranu podlogu od slojeva iz metanolne otopine. Prethodno 15 su ustanovljeni optimalni uvjeti za dobivanje karakteristične cvjetaste morfologije ZnO.…”

Preparation of hierarchical porous Zn-salt particles and their superhydrophobic performance

“…The obtained particles assembled by nanosheet crystals showed a flowerlike, porous structure. Sodium citrate was adopted as the structure indicator, mixed with hexamethylenetetramine [42][43][44] and urea [45][46][47] leading to an ordered growth during the hydrothermal reaction. The morphology of the products exhibited sufficiently high roughness because the crystals of the modified hydrothermal route products varied from those of the columnar type of ZnO.…”