The preparation of ZnO nanoparticles with a multi-step process is reported. The preparation path included zinc hydroxide nitrate (ZnHN) or zinc hydroxide carbonate (ZnHC) precipitation, their thermal treatment and nano-milling. ZnO preparation was followed in detail by STEM, FT-IR, XRD and TG-MS analyses. In order to demonstrate the efficiency of the nano-milling process, the obtained ZnO nanoparticles were characterized with regard to their photo-catalytic activity of caffeine degradation. The smallest ZnO nanoparticles (similar to 20 nm) with the highest BET surface (similar to 80 m(2) g(-1)) were prepared from ZnHC at 300 degrees C. (C) 2014 Elsevier Ltd. All rights reserved.