No abstract

Sulfidation of nanoscale zerovalent iron (nZVI) has shown some fundamental improvements on reactivity and selectivity toward pollutants in dissolved-oxygen (DO)-stimulated Fenton-like reaction systems (DO/S-nZVI system). However, the pristine microstructure of sulfide-modified nanoscale zerovalent iron (S-nZVI) remains uncovered. In addition, the relationship between pollutant removal and the oxidation of the S-nZVI is largely unknown. The present study confirms that sulfidation not only imparts sulfide and sulfate groups onto the surface of the nanoparticle (both on the oxide shell and on flake-like structures) but also introduces sulfur into the Fe(0) core region. Sulfidation greatly inhibits the four-electron transfer pathway between Fe(0) and oxygen but facilitates the electron transfer from Fe(0) to surface-bound Fe(III) and consecutive single-electron transfer for the generation of HO and hydroxyl radical. In the DO/S-nZVI system, slight sulfidation (S/Fe molar ratio = 0.1) is able to nearly double the oxidative removal efficacy of diclofenac (DCF) (from 17.8 to 34.2%), whereas moderate degree of sulfidation (S/Fe molar ratio = 0.3) significantly enhances both oxidation and adsorption of DCF. Furthermore, on the basis of the oxidation model of S-nZVI, the DCF removal process can be divided into two steps, which are well modeled by parabolic and logarithmic law separately. This study bridges the knowledge gap between pollutant removal and the oxidation process of chemically modified iron-based nanomaterials.

Magnetic carbon nanocages (Mag@CNCs) were synthesized via a green one-step process using pine resin and iron nitrate salt as a carbon and iron source, respectively. To produce Mag@CNCs, pristine materials have been carbonized at high temperature under inert atmosphere. The structural, textural, and surface properties of as-synthesized Mag@CNCs were studied employing microscopic, spectroscopic, and surface physicochemical methods. The obtained results showed that the new Mag@CNCs have significant surface area (177 m2 g–1) with both microporosity and mesoporosity. Moreover, the material exhibits a homogeneous distribution of core–shell-type magnetic nanoparticles within the carbon matrix, formed by iron carbide (Fe3C) and metallic iron (α-Fe), with sizes of 20–100 nm, surrounded by a few graphitic layers-walls. Most importantly, Mag@CNCs were tested as absorbents for As­(III) removal from aqueous solutions, showing a total of 263.9 mg As­(III)-uptake capacity per gram of material at pH = 7, a record sorption capacity value among all previously tested iron-based materials and one of highest values among all reported sorbents so far. The adsorbed As­(III) species are anchored at the surface of Mag@CNCs, as demonstrated by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy measurements. The pH-edge As­(III)-adsorption experiments combined with theoretical surface complexation modeling allowed a detailed understanding of the interfacial properties of Mag@CNCs, and hence the As­(III) uptake mechanism. The analysis revealed that As­(III) binds on two types of surface sites of Mag@CNCs, i.e., on carbon-surface species (C x OH2) and on Fe-oxide layer (FeOH2) of nanoparticles. This exemplifies that the advanced morphology- and surface-driven synergistic properties of the Mag@CNCs material are crucial for its As­(III)-uptake performance.