*2.3. Synthesis of Nanocrystalline Fe-Doped ZnO*

Fe-doped ZnO was prepared using a precipitation route as previously described [15]. Briefly, Zinc nitrate hexahydrate (5.948 g), ferric chloride (0.108 g) and trisodium citrate (5.882) were dissolved in 500 mL distilled water and stirred at 80 ◦C for 60 min. Then 250 mL of NaOH (250 mM) was slowly added dropwise into the solution using a burette until yellowish-white precipitate was formed. The precipitate was allowed to come to room temperature and was then centrifuged (10,000 rpm, which corresponds to 9391 g force, 10 min, Eppendorf 5424, USA), and rinsed with distilled water thrice. The precipitate was then dried at 70 ◦C overnight followed by calcination at 500 ◦C. The calcined Fe-doped ZnO powder was characterized as mentioned in our previous paper and used for photocatalytic applications.
