Adsorption-synergized reduction of Cr(vi) using Gypsum@PANI composite: unraveling mechanism and advanced statistical...

Cr(vi) is categorized as a top-priority hazardous contaminant. The subsequent adsorption/reduction of Cr(vi) into Cr(iii) has emerged as a powerful process for detoxifying Cr(vi)-laden waters. Herein, a newly designed Gypsum@Polyaniline (Gypsum@PANI) composite was applied for the detoxification of Cr(vi) ions in aqueous solutions. The as-developed Gypsum@PANI composite exhibited a mesoporous texture abundantly decorated with amine/imine groups. Based on the response surface modeling, the Cr(vi) adsorption effectiveness reached 93.86% under optimized conditions (pH 2, adsorbent dosage of 0.35 g L^-1, contact time of 4 h, Cr(vi) concentration of 20 mg L^-1 at 25 °C). Freundlich and pseudo-second order models satisfactorily represented the Cr(vi) adsorption. The maximum uptake capacity was found to be 310.36 mg g^-1. Advanced statistical physics assessment highlighted that Cr(vi) adsorption proceeded via multi-anchorage and multi-molecular pathways. Likewise, the thermodynamic functions proved the spontaneity of the adsorption process, accompanied by energy release and increased disorder. XPS analysis evidenced that the adsorbed Cr(vi) ions were reduced to the less toxic Cr(iii) form. The Gypsum@PANI demonstrated encouraging reusability with a Cr(vi) removal yield of 91% after five successive cycles. Overall, the experimental and theoretical findings asserted that the Gypsum@PANI composite has great potential for the detoxification of Cr(vi) ions in wastewater.