Harnessing Chitosan Beads as an Immobilization Matrix for Zero-Valent Iron Nanoparticles for the Treatment of Cr(VI)-Contaminated Laboratory Residue

Abstract

Nanocomposites (NCs) consisting of zero-valent iron nanoparticles (nZVI) immobilized inchitosan (CS) were prepared and employed for the removal of hexavalent chromium (Cr(VI)) fromboth synthetic and real wastewater. Medium (MCS)- and high (HCS)-molecular-weight chitosan andstabilization with carboxymethylcellulose (CMC) and different nZVI loads were explored. Characterizationthrough scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDS)and X-ray diffraction (XRD) revealed millimeter-sized spheres with micrometer-sized nZVI clustersrandomly distributed. Better nanoparticle dispersion was observed in NCs from the CMC-MCS andHCS combinations. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that CS bindsto Fe(II) or Fe(III) on the surface of nZVI through its functional groups -CONH-, -N-H, and -C-OHand through the -COO− functional group of CMC, forming a bidentate bridge complex. Through experimentswith synthetic waters, it was found that the elimination of Cr(VI) was favored by loweringthe pH, obtaining the maximum percentage of Cr(VI) removal at pH 5.5. With real waters, it wasshown that increasing the mass of NCs also improved the removal of Cr(VI), following a pseudosecond-order adsorption kinetics. The synthesized materials show great potential for applications inenvironmental remediation, showing good efficiency in the removal of Cr(VI) in wastewater.