The perforated ZnO nanoflakes with high degree of crystallinity and uniformity were synthesized via the hydrothermal-assisted sol-gel technique without any template. ZnCl 2 was used as a Zn-containing precursor, causing the oriented growth of particles. The observation of a hole on the facet of the as-synthesized particles was discussed in this work. XRD, TEM, and DRS were used to investigate the prepared powder and a simple mechanism was suggested to explain the hole formation on the surface of nanoflakes. As a result, the synthesized powder included pure ZnO with direct band gap energy of 3.24 eV. The range of particle size was within 1 lm in diameter and \50 nm in thickness. A circle hole with 300-500 nm in diameter was observed on the facet of the as-synthesized particles.

ZnO powder was synthesized via a hydrothermally assisted sol-gel method. Synthesis variables including Znprecursor type, pH value, time, and temperature of hydrothermal treatment were analyzed using the Taguchi approach.The experimental procedures were defined based on the L9 array for four variables in three levels. The influences of those variables on the response parameters, i.e. crystallite size, crystallinity, band gap energy ( Eg) , and degradation constants ( k) , were evaluated. XRD results and Eg values showed that ZnO wurtzite appeared to be the only crystalline phase in the samples. Taguchi analysis predicted that the optimized conditions to achieve the highest photoactivity are as follows: Zn-precursor = zinc acetate, pH = 8, t = 2 h, and T = 150 • C. The optimized sample was synthesized based on the mentioned conditions and characterized. The obtained results confirmed the prediction of the Taguchi method and the highest k value was observed.