Abstract
The immobilization of zerovalent iron nanoparticles (nZVI) is a way to facilitate their use in continuous flow systems for the treatment of aqueous pollutants. In this work, two types of nZVI (powdered, NSTAR; and slurry suspended, N25) were immobilized in millimetric alginate beads (AL) by coagulation, forming nanocomposites (NCs). These NCs, N25@AL and NSTAR@AL, were structurally studied and tested for Cr(VI) removal. For both NCs types, SEM analysis showed a uniform distribution of the nanoparticles in micron-scale agglomerates, and XRD analysis revealed the preservation of α-Fe as the main iron phase of the immobilized nanoparticles. Additionally, Raman spectroscopy results evidenced a partial oxidation of the initially present magnetite. For both nZVI types, the Cr(VI) removal efficiency increased with temperature, decreased with pH, and did not show any significant change in anoxic or oxic conditions. On the other hand, N25@AL resulted a faster removal agent than NSTAR@AL; however, both materials had the same maximum removal capacity: 133 mg of Cr(VI) per gram of nZVI at pH 3. Cr(III) formed during the removal of Cr(VI) was retained by the alginate matrix, constituting a clear advantage against the use of free nZVI in suspension at acidic pH.
Highlights
Accepted: 15 December 2021Iron-based nanoparticles (NPs), as zerovalent iron or iron oxides, have been used for the removal of a wide range of pollutants, including metals and metalloids in water [1,2,3,4]
The structure of the shell depends on the synthesis procedure: though the nZVI obtained by borohydride reduction are covered by a smooth amorphous oxide layer, the nZVI produced by thermal reduction with H2 present different domains of crystalline oxide structures [8]
NANOFER 25 (N25) and NANOFER STAR (NSTAR) nZVI were purchased from Nanoiron s.r.o.; their main physicochemical characteristics can be found in the supplementary material document (SM)
Summary
Iron-based nanoparticles (NPs), as zerovalent iron (nZVI) or iron oxides (nFeOx), have been used for the removal of a wide range of pollutants, including metals and metalloids in water [1,2,3,4]. Compared with their bulk counterparts, nanomaterials have a higher density of surface reaction per unit mass, displaying a notably higher reactivity for surface-mediated processes. Some NPs are manufactured in a way to provide a Published: 7 February 2022
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