Efficient detoxification of Cr(VI)-containing effluents by sequential adsorption and reduction using a novel cysteine-doped PANi@faujasite composite: Experimental study supported by advanced statistical physics prediction.

Nowadays, the global spreading of hazardous heavy metals becomes a top-priority environmental challenge, owing to its serious detrimental health outcomes. Herein, a novel cysteine-doped polyaniline@faujasite hybrid composite (Cys-PANi@FAU-50) was synthesized via a facile in-situ polymerization route for the effective detoxification of Cr(VI)-bearing wastewaters. The Cys-PANi@FAU-50 composite displayed an open mesoporous structure richly decorated with nitrogen/oxygen-containing functional groups, which consequently boosted the diffusion, adsorption and reduction of Cr(VI) oxyanions. The Cr(VI) adsorption behavior was satisfactorily tailored via pseudo-second-order law and Langmuir model with a maximum uptake capacity of 384.6 mg/g. Based on the advanced statistical physics theory, the monolayer model with two distinct receptor sites provided a reliable microscopic and macroscopic prediction of the Cr(VI) adsorption process. Stereographically, the Cr(VI) ions were adsorbed through horizontal multi-anchorage and vertical multi-molecular mechanisms on the amine and hydroxyl groups of Cys-PANi@FAU-50, respectively. The thermodynamic functions evidenced that the Cr(VI) adsorption was an endothermic spontaneous process. XPS analysis proved that Cr(VI) ions were electrostatically adsorbed, and subsequently reduced to Cr(III), which were in turn immobilized by chelation with imine/sulfonate groups and electrostatic interactions with carboxylate groups. The Cys-PANi@FAU-50 featured an effortless regenerability and good reusability. Overall, the Cys-PANi@FAU-50 composite owns outstanding potentiality for detoxifying Cr(VI)-laden effluents.

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