Enhanced removal of Cr(VI) and Mo(VI) from polluted water using L-cysteine doped polypyrrole/bentonite composite

Abstract

The demand for clean water and soil drives high efficiency, less expensive, and eco-friendly clay-composites as adsorbents for remediation of heavy metals polluted environment. We have developed a new water remediation technique by using an organic-inorganic composite, L-cysteine doped polypyrrole modified bentonite (L-cys/PPy/BT) for removal of Cr(VI) and Mo(VI). The L-cys/PPy/BT showed maximum adsorption capacities of 318.5 and 65.4 mg/g for Cr(VI) and Mo(VI) respectively. For Cr(VI) and Mo(VI) the sorption process on L-cys/PPy/BT followed the Freundlich and Langmuir isotherm models, respectively. Furthermore, the pseudo-second-order kinetic model described the adsorption behavior of Cr(VI) and Mo(VI). Moreover, the thermodynamic parameters indicated that sorption processes were endothermic and spontaneous. Mechanistic assessment revealed that adsorption of Mo(VI) on L-cys/PPy/BT could be attributed to chelation, electrostatic attraction and ion-exchange of Mo(VI) with the imine/amine functional groups in the material's matrix, while electrostatic attraction, ion exchange, chelation and redox reaction played a significant role in the removal of Cr(VI). This research provides a new approach for the use of clay materials as potential sorbents for removal of heavy metal ions in contaminated water.