Preparation and characterization of chitosan–caboxymethyl-β-cyclodextrin entrapped nanozero-valent iron composite for Cu (II) and Cr (IV) removal from wastewater

• Highly efficient CS-NZVI-CMβ-CD composite beads were synthesized to remove Cr (VI) and Cu (II) in solution.
• NZVI gives strength to CS-NZVI-CMβ-CD beads and facilitates magnetic separation.
• CMβ-CD into chitosan incorporates more functional groups for higher sorption.
• Both redox and adsorption processes were proved as the key removal mechanisms.
• Endothermic and exothermic adsorption for Cr (VI) and Cu (II), respectively.

The entrapment of Fe0 nanoparticles within a chitosan–carboxymethyl β-cyclodextrin complex, a nontoxic and biodegradable stabilizer, yields chitosan–Fe0 nanoparticle–carboxymethyl β-cyclodextrin beads that are 2.5 mm in diameter and contain 50% iron by weight. The complete disappearance of Cr (VI) and Cu (II) may involve both physical adsorption and reduction of Cr (VI) to Cr (III) and Cu (II) to Cu (0) while oxidizing Fe0 to Fe (III). The rate of reduction can be expressed by pseudo-second-order reaction kinetics. The rate constants increased with increasing iron loading and initial concentration at pH 6, while the adsorption of Cr (VI) and Cu (II) was found to be endothermic and exothermic, respectively. The apparent activation energies for Cr (VI) and Cu (II) were found to be 71.99 and 18.38 kJ mol−1, respectively. X-ray photoelectron spectroscopy confirmed the reduction process. The equilibrium data could be well described by both Langmuir and Temkin isotherms for describing monolayer adsorption and chemisorption processes, respectively. Both film diffusion and intraparticle diffusion were found to be the rate-limiting steps from the analysis of an intraparticle diffusion model. Thus, the synthesized chitosan–Fe0-nanoparticle–carboxymethyl β-cyclodextrin beads can be a potential material for in situ remediation of contaminated surface and ground water.