ORIGINAL PAPER Solvothermal syntheses of nano- and micro-sized ZnO powders with a controllable morphology D. Lukovic ´ Golic ´ • Z. Brankovic ´ • N. Daneu • S. Bernik • G. Brankovic ´ Received: 2 March 2012 / Accepted: 6 April 2012 / Published online: 17 April 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Zinc oxide powders with different morpholo- gies and grain sizes were synthesized using solvothermal methods from ethanolic zinc acetate solutions in the pres- ence of lithium hydroxide. The inﬂuence of the tempera- ture and the time of the reaction, as well as the pH value of the starting solution, on the ZnO particle size and mor- phology were examined. It was found that an increase in the pH value from 8 to 12 results in a signiﬁcant decrease in the mean particle size. Also, the particles’ morphology can be changed from hexagonal plates and prisms to rods by controlling the reaction time and the temperature. The crystallization mechanism is discussed, based on estab- lished correlations such as the particle size/shape versus the reaction parameters. Dissolution/recrystallisation is the most probable growth mechanism responsible for the ZnO particles’ morphology obtained in the solvothermal (hydrothermal) reactions with a basic solution. The planar structure of the zinc-hydroxy-acetate molecule plays the main role in growing the structures during the sovothermal reactions with a slightly acid solution. Keywords ZnO  Sol–gel  Solvothermal synthesis  Reaction parameters  Particle morphology 1 Introduction Zinc oxide is a very important ceramic material with semiconducting (n-type), pyroelectric and piezoelectric properties. It is a wide-band-gap semiconductor with a large exciton binding energy. These speciﬁc properties open up a number of possibilities for electronic and optical applications. Zinc oxide materials have been used for UV lasers [1], photodetectors [2], solar cells [3, 4], gas sensors [5], piezoelectric generators [6], ﬁeld-effect transistors [7], varistors [8], photocatalysts [9, 10], light-emitting diodes [11, 12] and photonic crystals [13]. Synthetic routes for preparing ZnO nanostructures can be divided into two general groups: vapour-phase methods [14–16] and solu- tion-phase methods [17–19]. The hydrothermal and solvothermal methods, as a type of solution-phase methods, are simple, low-temperature, low-cost methods with a rel- atively high ZnO yield. A variety of ZnO nanostructures, such as nanoparticles [20], nanorods and nanowires [21], nanocombs [22], nanohelices [23], nanorings [24], nanobelts [25], nano- cages [26], have been reported in the literature as a result of different synthesis methods. Zinc acetate dihydrate and zinc nitrate hexahydrate have been widely used as zinc sources in solution chemical methods (hydro- and solvo- thermal methods) due to their higher solubility in water and organic solvents. ZnO nanoparticles were successfully prepared in hydrothermal syntheses using zinc nitrate hexahydrate and ammonium hydroxide [27]. The reactions were carried out at temperatures under 200 °C and the inﬂuence of the pH and the growth temperatures on the microstructure were studied. Spherical ZnO nanoparticles (100–300 nm) were synthesized using the hydrothermal method by the oxidation of zinc acetate in supercritical water with controllable conditions (temperature, pressure D. Lukovic ´ Golic ´(&)  Z. Brankovic ´  G. Brankovic ´ Institute for Multidisciplinary Research, University of Belgrade, Kneza Vis ˇeslava 1a, 11030 Belgrade, Serbia e-mail: danijela@imsi.rs N. Daneu  S. Bernik Joz ˇef S ˇ tefan Institute and Center of Excellence NAMASTE, Jamova 39, 1000 Ljubljana, Slovenia 123 J Sol-Gel Sci Technol (2012) 63:116–125 DOI 10.1007/s10971-012-2773-z