Novel polypyrrole-coated ZnCo2O4 spinel nanostructures for prompt and efficient adsorption of Cr(VI) from wastewater

Abstract

This work designed an innovative polypyrrole/zinc cobaltite spinel oxide (Ppy@ZnCo₂O₄) nanocomposite useful as competitive adsorbent for the elimination of Cr(VI) from wastewater. Assorted analytical approaches were implemented to explore the Ppy@ZnCo₂O₄ structure and morphological aspects. The batch experiments for process optimization through the response surface approach integrated with box-Behnken design (RSM/BBD), confirmed that the quadratic model fits Cr(VI) removal with R² = 0.999. Encouragingly, the Ppy@ZnCo₂O₄ nanocomposite demonstrated outstanding adsorption efficiency for Cr(VI) in wastewater, achieving 97.86 ± 0.58 % removal in just 40 min. The highest uptake capability reached 273.12 ± 1.44 mg.g⁻¹, and the adsorption experimental results aligning well with both the Freundlich isotherm and pseudo-second-order kinetic models. Thermodynamic outcomes revealed that the Cr(VI) adsorption exhibited exothermic and spontaneous behavior, and contributed to a lessening in the disorder of the Cr (VI) species onto the Ppy@ZnCo₂O₄ surface. In addition, mechanism investigation confirmed that Cr(VI) species were initially adsorbed through electrostatic attractions, then converted to Cr(III), and finally anchored by forming chelates with N-containing functional groups of Ppy@ZnCo₂O₄. The as-developed Ppy@ZnCo₂O₄ demonstrated a straightforward regenerability via basification and exceptional reusability. In brief, the Ppy@ZnCo₂O₄ presents considerable promise for proficiently eradicating Cr(VI) species from wastewater.