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

Abstract

• PPy-coated ZnCo 2 O 4 spinel nanocomposite was fabricated and fully characterized. • In 40 min, the PPy@ZnCo 2 O 4 successfully reduced 97.86 ± 0.58 % of Cr(VI). • Experimental results are predicted and optimized through the Box-Behnken design. • Electrostatic attraction, redox and chelation are main mechanisms for Cr removal. • PPy@ZnCo 2 O 4 reliably achieves over 83.02 ± 1.66 % Cr(VI) removal across four cycles. This work designed an innovative polypyrrole/zinc cobaltite spinel oxide (Ppy@ZnCo 2 O 4 ) nanocomposite useful as competitive adsorbent for the elimination of Cr(VI) from wastewater. Assorted analytical approaches were implemented to explore the Ppy@ZnCo 2 O 4 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 R 2 = 0.999. Encouragingly, the Ppy@ZnCo 2 O 4 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@ZnCo 2 O 4 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@ZnCo 2 O 4 . The as-developed Ppy@ZnCo 2 O 4 demonstrated a straightforward regenerability via basification and exceptional reusability. In brief, the Ppy@ZnCo 2 O 4 presents considerable promise for proficiently eradicating Cr(VI) species from wastewater.