Application of ZnO Nano Rods for the Batch Adsorption of Cr(VI): A Study of Kinetics and Isotherms

The present study reports the synthesis of nano Zinc Oxide (ZnO) and its adsorption behaviour. The ZnO obtained by precipitation method were found to be well-defined nano rods arranged like flower. The shape, size and structure of ZnO were characterized from X-Ray Diffraction (XRD), Energy Dispersive X-ray (EDX) and Scanning Electron Microscope (SEM) analysis. These nano rods were utilized for the adsorption of hexavalent chromium ions [Cr(VI)] from their aqueous solution by using batch adsorption technique. Different physico-chemical parameters such as metal ion concentration, pH, dosage level and equilibrium contact time were studied during adsorption. The amount of chromium adsorption increases with increase in adsorbent dosage, whereas the adsorption was maximum in the first 40 min with optimum value of pH 3. The kinetic of adsorption was best fitted by the pseudo-second-order rate equation. Similarly, the equilibrium adsorption data were fitted well by both Temkin and Freundlich adsorption isotherm models in comparison to Langmuir adsorption model. The adsorption of chromium was supported by EDX and SEM analysis. Moreover, the change in the SEM morphology of ZnO nano rods into nano sheets after adsorption is an interesting observation of the present investigation.