Peppermint-Mediated Green Synthesis of Nano ZrO 2 and Its Adsorptive Removal of Cobalt from Water.

Zirconium oxide nanoparticles (ZrO₂NPs) were green synthesized for the first time using an aqueous peppermint extract as a precipitating and capping agent. Addition of the extract to Zr⁴⁺ solution was followed by calcination of the resulting precipitate at 570 and 700 °C to form ZrO₂NPs570 and ZrO₂NPs700, respectively. These oxides were characterized using X-ray diffraction, transmission electron microscopy, and BET surface area analysis, and used as adsorbents for cobalt ions (Co²⁺) in water. The effects of pH, initial Co²⁺ concentration, ZrO₂NPs mass, and contact time on adsorption efficiency were studied. Characterization results showed formation of cubic ZrO₂ with average crystallite sizes (XRD data) of 6.27 and 7.26 nm for ZrO₂NPs570 and ZrO₂NPs700, respectively. TEM images of the two oxides exhibited nearly spherical nanoparticles and BET surface area measurements indicated the formation of mesoporous oxides having surface areas of 94.8 and 62.4 m²/g, respectively. The results of the adsorption study confirmed that the synthesized ZrO₂NPs can be efficiently used for the adsorption of Co²⁺ from water. The uptake of Co²⁺ from the treated solution is favored at pH values higher than its point of zero charge (6.0). In addition, the adsorption of Co²⁺ by ZrO₂ follows a pseudo-second order kinetics (R² = 1.0) and can be explained by the Langmuir adsorption isotherm (R² = 0.973). [ABSTRACT FROM AUTHOR]