Efficiency of a novel cysteine-polypyrrole@silver phosphate nanocomposite for hazardous Cr(VI) removal: Experimental study and statistical optimization modeling

Abstract

• Novel stable Cys-PPy@Ag 3 PO 4 nanocomposite was fabricated and fully characterized. • Response Surface Methodology optimized the Cr(VI) adsorption conditions. • Cys-PPy@Ag 3 PO 4 showed a Q m value of 149.76 mg.g -1 per the Langmuir isotherm model. • N- and S- groups of Cys-PPy@Ag 3 PO 4 effectively immobilizes converted Cr(III) ions. • Cys-PPy@Ag 3 PO 4 retains 86.12 % Cr(VI) removal after four adsorption–desorption cycles. A novel cysteine functionalized-Polypyrrole@silver phosphate (Cys-PPy@Ag 3 PO 4 ) nanocomposite, synthesized through chemical polymerization was used for fully reducing Cr(VI) to Cr(III) and successfully capturing the Cr(III), representing a major leap in Cr(VI) remediation technology. Assorted analytical approaches, such as Fourier-transforms infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron (XPS) spectroscopy, Brunauer-Emmett-Teller (BET), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), were implemented to explore the morphology and removal mechanism. The nanocomposite exhibited a mesoporous structure enriched with nitrogen/oxygen functional groups, which improved the diffusion, adsorption, and reduction of Cr(VI) ions. At pH 2, 96.50 % of Cr(VI) was removed using 0.5 g.L −1 of adsorbent in 60 min. Besides, the maximum uptake capability was 149.76 mg.g −1 , and both Freundlich isotherm and PSO kinetic models perfectly aligned with the adsorption experimental findings for Cr(VI) species. Analysis of thermodynamic factors revealed that Cr(VI) adsorption was endothermic and spontaneous, enhancing the disorder of Cr(VI) species on the nanocomposite surface. XPS and FT-IR analysis proved that Cr(VI) ions were electrostatically adsorbed and subsequently converted to Cr(III), which were then immobilized through chelation with imine/sulfonate groups and electrostatic attraction with carboxylate groups. The nanocomposite showcased effortless regenerability through basification and outstanding reusability. Overall, Cys-PPy@Ag 3 PO 4 proved highly effective in removing Cr(VI) from water. This study focuses on the synthesis of a novel adsorbent with reduction capabilities. Thus, the hazardous Cr(VI) ions were successfully removed from aqueous solutions, providing an alternative for environmental remediation. Hence, the reductive behavior of the synthesized adsorbent converted the toxic Cr(VI) into Cr(III). This adsorbent was regenerated with basic media, enabling its usage for 4 cycles, and reducing spent adsorbent disposal. Thus, the desorption process favored not only the adsorbent reuse but also the attainment of a less harmful effluent-containing Cr(III).