Adsorption-coupled reduction mechanism in ZnO-Functionalized MWCNTs nanocomposite for Cr (VI) removal and improved anti-photocorrosion for photocatalytic reduction

Abstract

It is essential to utilize the adsorption-coupled reduction mechanism when using adsorption techniques for heavy metal ions remediation. This particular work deals with the synthesis of ZnO functionalized MWCNTs (ZC) where ZnO nanoparticles are grafted on the functionalized MWCNTs by a facile hydrothermal approach for Cr (VI) removal. The metal ion adsorption behavior of ZC nanocomposites has been examined for removal of Cr (VI), and it was noticed that ZC-10 (10 wt % functionalized MWCNT content) exhibited excellent adsorption capacity and removal efficiency of 94% was accomplished at pH 2. Equilibrium data have been analyzed using various isotherm models and were found to be represented best by the Langmuir adsorption model. Various kinetic models have been used to understand the adsorption process, and the kinetics of adsorption best followed the pseudo-second-order kinetic model. The influence of several operational parameters such as initial pH, Cr (VI) concentration, dosage, agitation speed, and the presence of competing anions were well elucidated and optimized. Thermodynamic parameters revealed that the adsorption of Cr (VI) on ZC-10 adsorbent was spontaneous and endothermic. Additionally, ZC-10 nanocomposite exhibited improved photocatalytic activity under UV–Vis light irradiation in contrast to ZnO as a result of reduced electron-hole pair recombination and improved anti-photocorrosion.