Adsorption Characteristics of Heavy Metal Ions on Phytogenic ZnO Nanoparticles Synthesized Using Coriandrum Sativum Extract

The present study demonstrates the adsorption behavior of heavy metal ions such as “Pb” and “Cr” present in industrial wastewater on phytogenic ZnO nanoparticles. The ZnO nanoparticles were prepared through a green-synthesis route employing Coriandrum Sativum leaf extract as a natural reducing agent. Structural analysis revealed that the as-synthesized nanoparticles contained a mixed phase of amorphous zinc hydroxide (Zn (OH)۲) and crystalline ZnO, which completely transforms to pure hexagonal wurtzite structure upon annealing. Morphologically, the unannealed samples exhibited large, irregular clusters, whereas the annealed samples showed more uniform and well-dispersed nanoparticles. The average crystallite size was estimated to be ۷۰.۶۲ nm for the ۴۵۰℃ sample and ۸۵.۶۰ nm for the ۶۰۰℃ sample. The optical band gap remained nearly constant, with values of ۳.۱۰ eV and ۳.۱۳ eV for the ۴۵۰℃ and ۶۰۰℃ annealed samples, respectively. Both samples demonstrated excellent adsorption capacities, with the ۴۵۰℃ annealed ZnO exhibiting superior removal efficiencies of ۸۴.۸۵% for “Pb” and ۹۹.۹۹% for “Cr” ions. In contrast, the ۶۰۰℃ annealed ZnO achieved ۷۷.۶۹% and ۷۴.۵۲% removal efficiencies for “Pb” and “Cr” ions, respectively. Adsorption data fitting using the Langmuir and the Freundlich models showed that the Langmuir model provided a comparatively better empirical correlation, which may suggest a predominance of monolayer adsorption on relatively homogeneous surface sites within the limitations of the dataset.

کلیدواژه ها:

Nanoadsorbents ، Green synthesis ، ZnO ، Coriandrum sativum (Coriander) ، Water purification