Aqueous pathways for the formation of zinc oxide nanoparticles

Abstract

We examine the effect of reactant concentrations, temperatures and feeding methods on the morphology of ZnO formed when reacting solutions of ZnSO 4 and NaOH. The catalytic effect of hydroxide in excess relative to the stoichiometric ratio is considered. It is shown that, having fixed other reaction conditions, the end-products, particle structures and size strongly depend on the mole ratio of the precursors. The presence of zinc salt hydroxide species was confirmed at sub-stoichiometric ratios in slightly acidic conditions. At the stoichiometric ratio both zinc hydroxide and zinc oxide are formed, while only zinc oxide forms in an excess of hydroxide. The method of feeding the reactants into the reaction vessel also has a strong influence on the end-product properties, as does the reaction temperature. By control of these parameters the specific surface area could be varied from 10 to 33 m 2 g -1 , the particle shape could be varied from equiaxed, through to star-like and needle-like, and the particle size may be varied from 50 to over 300 nm.

Solution grown ZnO rods: Synthesis, characterization and defect mediated photocatalytic activity

“…2. The major reflections in the XRD pattern of the as-prepared precipitate match well with the Joint Committee on Powder Diffraction Standards data file (No: 38-0385) of Wulfingite -Zn(OH) 2 [24]. Further, the XRD pattern also reveals the presence of trace amount of ZnO along with Zn(OH) 2 .…”

“…The available reports strongly suggested that careful control of synthetic parameters and growth conditions can result in ZnO nanostructures with exotic size, shape and morphology by the sonochemical process. In most of the cases, formation of ZnO occurred via the intermediate formation of Zn(OH) 2 and [Zn(OH) 4 ] 2− [23,24]. In spite of the large number of information available on the growth of ZnO in various forms, there is still considerable uncertainty regarding the possible role of zinc hydroxide, its concentration, the mechanism by which zinc hydroxide converts to zinc oxide and the factors governing the product morphology.…”

Zinc oxide and zinc hydroxide formation via aqueous precipitation: Effect of the preparation route and lysozyme addition

“…The first one is centered about 55e65 C and corresponds to unbound water apparent particularly for R2-DW and R3-DW. The second one was observed between 125 C and 145 C mainly indicating the decomposition of Zn(OH) 2 into ZnO [12,46]. C1-DW with ε-Zn(OH) 2 crystal structure exhibited the highest weight loss and R1-DW with ZnO structure presented negligible weight loss in this temperature range as expected.…”

“…For example, flake-like ZnO structures which seem growing over a common nucleus were reported when equal volume of 4 M NaOH and 0.2 M zinc nitrate were reacted at 60 C [26]. In another study, ZnO crystals with round and sheet like morphology depending on OH À1 :Zn 2þ ratio were obtained at room temperature when OH À1 :Zn 2þ ratio was 2.5:1 or higher [12]. In addition to the clover-like ZnO structures, small amount of plate-like (for R3-DW) and octahedral (for C2-DW and R4-DW) morphologies were also observed.…”

“…Recently, the method of combining the reactants has also been reported to change the morphology [11,12]. For the aqueous precipitation method, different forms of zinc hydroxides, zinc oxide or a mixture of both can be observed depending on the precipitation protocol.…”