Microwave-assisted synthesis of ZnO micro-javelins

Abstract

The microwave (MW)-assisted formation of ZnO micro-javelins from zinc nitrate and urea in aqueous solution is described. The particles (named as 'micro-javelins' because of their high aspect ratio and needle-like tips) grow hexagonally with well-defined facets in the h01 10i direction and pointed tips in (0001) direction. Powder X-ray diffraction patterns show the appearance of a strikingly dominant (1000) orientation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations reveal the morphological evolution of these hexagonal ZnO particles with time. The effect of precursor concentrations, counterion type and MW irradiation power and their consequent influence on pH and Zn 2+ ion concentration are investigated. A mechanism for the formation of the micro-javelins is postulated. The microwave induced supersaturation of Zn(OH) + species under the weakly basic pH condition and the initial growth through the (000 1) direction (oxygen-rich face) are proposed to be the key factors that dictate the formation of these ZnO micro-javelins. The present one-step microwave process is a straightforward and a reproducible method for the bulk synthesis of defect-free ZnO micro-javelins, which would find potential applications in microelectronic devices (e.g. lasers, cantilevers in surface probing equipment, etc.).

Antibacterial properties of F-doped ZnO visible light photocatalyst

“…Moreover another distinct band originating from C H bonds has been observed at 2936 cm −1 and symmetric and asymmetric stretching bands of acetate species at 1658 cm −1 , 1319 cm −1 ( COO ), and 815 cm −1 ( COO ) [23]. After calcination at 500 • C, the intensity of the bands associated with the presence of organic residue was significantly reduced and a strong peak at ∼450 cm −1 attributed to Zn O bond became apparent [23,24]. It was also noted that the peak at 2936 cm −1 is predominant in the pure ZnO sample compared to the F-doped samples due to the presence of unburned carbon from the precursors.…”

“…The spectrum of ZnO precursor dried at 80 • C revealed bands at ∼3500 cm −1 contributed to the presence of OH stretching bonds [24]. Moreover another distinct band originating from C H bonds has been observed at 2936 cm −1 and symmetric and asymmetric stretching bands of acetate species at 1658 cm −1 , 1319 cm −1 ( COO ), and 815 cm −1 ( COO ) [23]. After calcination at 500 • C, the intensity of the bands associated with the presence of organic residue was significantly reduced and a strong peak at ∼450 cm −1 attributed to Zn O bond became apparent [23,24].…”

Formation and Dissolution of Twin ZnO Nanostructures Promoted by Water and Control over Their Emitting Properties

“…[1][2][3][4] The shortening of processing times, increase in product yields and enhancement of material properties are the main advantages of this synthetic technique. [5] Among metal oxides, ZnO is one of the most investigated semiconductor materials and accordingly it has been successfully synthesised under microwave irradiation in different sizes and morphologies, [6][7][8][9] crystalline orientation (c axis growth vs. a axis growth) [10] and quality (crystalline vs. amorphous). [11] The reasons for such interest can be ascribed to its unique properties: ZnO has a wide band gap (3.37 eV at 300 K) with a large exciton binding energy of 30-70 meV that makes it suitable for opto-electronic, catalytic and biological applications.…”

A conceptual change in crystallisation mechanisms of oxide materials from solutions in closed systems

“…The decomposition pathway of urea-dissolved-in-water under heat has been documented and is presented in Supplementary Information Fig. S6 online 43 . Under continuous MW heating, initially hydroxides (OH − ) and bicarbonates (HCO 3 − ) are formed.…”