Antimony retention and transformation: a novel approach using microfluidics and hydrogel, biocomposite nanomagnetite aggregates

Abstract

Antimony (Sb) is a redox sensitive metalloid increasingly recognized as an emerging contaminant of global concern due to its toxicity and widespread occurrence in natural and anthropogenically impacted water systems. It is commonly found in both drinking and wastewater, where it poses potential risks to human health. Magnetite nanoparticles, known as active retention agents for redox-sensitive contaminants, are combined here with polymeric matrices to ease their application in water treatment systems and to enhance their stability, dispersibility, and sorption efficiency. In this study, we assess Sb retention using hydrogel-nanomagnetite aggregates, with and without chitosan coating, under flow-through microfluidic conditions that mimic natural and engineered aquatic environments. Advanced synchrotron-based μ-XRF mapping and μ-XANES spectroscopy were employed for the first time to such integrated system to simultaneously resolve the spatial distribution and oxidation state of sorbed Sb. Antimonate immobilization followed two distinct, input concentration-dependent pathways: (i) reduction to Sb(III), forming stable inner-sphere Fe–O–Sb complexes, or (ii) adsorption via electrostatic and complexation mechanisms. At low Sb(V) concentrations reduction is favored in chitosan-free aggregates, enabling homogeneous Sb(III) diffusion through the media. At higher concentrations, and particularly in chitosan-coated systems, Sb(V) is immobilized predominantly via adsorption, accumulating on the rim of the aggregates. Chitosan enhances Sb(V) sorption by providing positively charged functional groups and, along with pH and Sb input concentration, controls Sb sorption processes. These findings deepen the understanding of Sb retention mechanisms through redox and sorption interactions in polymer-supported magnetite systems, as revealed using microfluidics technology, and provide a new foundation for the development of advanced water treatment technologies with international relevance for mitigating redox-sensitive contaminants.