Synthesis of Core/Shell ZnO/rGO Nanoparticles by Calcination of ZIF-8/rGO Composites and Their Photocatalytic Activity.

A facile two-step method was developed to prepare core/shell ZnO/rGO particles from ZIF-8/rGO composites. ZIF-8 particles were first grown at the surface of rGO sheets. Next, ZIF-8 particles were transformed into ZnO particles by thermal decomposition under air at 500 °C. All materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller analyses. Results obtained show that ZIF-8 particles strongly associate with rGO sheets and that the calcination of this material produces porous core/shell ZnO/rGO particles with an average diameter of ca. 40 nm. The wt % of rGO associated with ZIF-8 particles was varied from 5 to 20%. The ZnO/rGO (10%) particles exhibit the highest photocatalytic activity for the degradation of the Orange II dye under simulated solar light irradiation of weak intensity (5 mW/cm). This high photocatalytic activity was demonstrated to originate from superoxide O radicals due to the efficient trapping of photogenerated electrons in ZnO by rGO.