The Influence of Hibiscus tiliaceus Leaf Extract as Capping Agent on the Zinc Oxide Properties and its Photo-simultaneous Performance

Polyol method, as one alternative in ZnO synthetic methods, have been developed and generated a nano-ZnO. However, the produced nano-ZnO is unstable due to its small particle size. To overcome the problems, we added Hibiscus tiliaceus leaves’ extract during the ZnO (EZnO) synthesis to change the water content and hydrolysis ratio of Zn2+/water. The addition of H. tiliaceus extract resulted in a shifting peak at (101) plane compared to ZnO synthesized without extract addition (WZnO). The use of H. tiliaceus extracts leads to the formation of large and non-uniform particles compared to the one prepared without the extract, which is in agreement with the intensity of diffraction pattern. The use of H. tiliaceus extracts shifted the bandgap energy to visible range. The performance of WZnO and EZnO samples was tested for simultaneous photo-oxidation of methylene blue and photo-reduction of Cr(VI) ions under UV-C irradiation. The EZnO is equally active as WZnO for Cr(VI) ion photo-reduction but less active for photo-oxidation of methylene blue. The presence of retained organic material in EZnO is plausibly affected by the adsorption and subsequent photo-oxidation of the bulky MB leading to a lower photo-oxidation performance. However, the activity of EZnO was a little bit lower than that of WZnO, revealing that the synergistic of particle size and band gap energy is a crucial factor in photo-removal process. In addition, the presence of phenolic compounds on the EZnO surface might change the nature properties of WZnO, which influence its performance.