Colloidal Surface Active Maghemite Nanoparticles for Biologically Safe CrVI Remediation: from Core-Shell Nanostructures to Pilot Plant Development

The present study is aimed at the exploration of achievable improvements for Cr-VI ex situ and in situ water remediation by using novel naked colloidal maghemite (gamma-Fe2O3) nanoparticles (surface active maghemite nanoparticles, SAMNs). The reliability of SAMNs for Cr-VI binding and removal was demonstrated, and SAMN@Cr-VI complex was characterized, as well as the covalent nature of the absorption was unequivocally proved. SAMNs were structurally and magnetically well conserved after Cr-VI binding. Thus, in consideration of their affinity for Cr-VI, SAMNs were exploited in a biological model system, mimicking a real in situ application. The assay evidenced a progressive reduction of revertant colonies of Salmonella typhimurium TA100 strain, as maghemite nanoparticles concentration increased, till the complete suppression of Cr-VI mutagen effect. Finally, an automatic modular pilot system for continuous magnetic removal and recovery of Cr-VI from water is proposed. SAMNs, thanks to their colloidal, binding, and catalytic properties, represent a promising tool as a reliable nanomaterial for water remediation by Cr-VI.