Magnetically recoverable PANI@α-Fe2O3-montmorillonite for fast simultaneous removal of Cr(VI) and OG dye from synthetic and actual wastewater.

Multifunctional adsorbents capable of simultaneously removing heavy metals and organic dyes hold significant real-world application potential. Polyaniline-coated α-Hematite-Montmorillonite (PANI@α-Fe2O3-Mt) was designed via an interfacial polymerization technique and used to remove concurrently Cr(VI) and OG dye from water. Its well-integrated structure provided high stability and abundant active sites, facilitating the efficient elimination of OG dye and Cr(VI) from water. Box-Behnken design analysis showed excellent predictive performance and to be a suitable process optimization tool for the removal of OG and Cr(VI), achieving R2 values of 0.999 and 0.998, respectively. Both pollutants fitted well to the pseudo-second-order model (PSO) in the kinetic study, reaching the adsorption equilibrium within 50 min for OG and 60 min for Cr(VI). Multilayer adsorption of OG and Cr(VI) onto PANI@α-Fe2O3-Mt was confirmed through the Freundlich isotherm model, demonstrating highest uptake capabilities of 250.189 mg g-1 for OG and 284.90 mg g-1 for Cr(VI), surpassing those reported with many other adsorbents. OG adsorption is governed by electrostatic and π-π interactions, hydrogen bonding, while Cr(VI) removal involves electrostatic attraction, reduction to Cr(III), and chelation by nitrogen moieties. Collectively, the results demonstrate that the uniform PANI coating on the α-Fe2O3-Mt surface produced a novel and highly efficient bio-adsorbent, effectively removing OG and Cr(VI) ions from contaminated water. Due to its magnetic properties, PANI@α-Fe2O3-Mt could be easily recovered and reused, suggesting facile and cost-effective process. In fact, PANI@α-Fe2O3-Mt achieved 90.89 % OG and 87.5 % Cr(VI) removal in real wastewater, with reusability sustaining 83.54 % and 80.11 % efficiency over four cycles.