Novel electroblowing synthesis of submicron zirconium dioxide fibers: effect of fiber structure on antimony(v) adsorption

Anion exchange on hydrous zirconium oxide materials: application for selective iodate removal

The radioactive ¹²⁹I is a top-priority radionuclide due to its the long half-life (1.57 × 10⁷ years) and high mobility. Because of the planned and accidental releases to the environment, specific separation technologies are required to limit the potential radiation dose to human beings. Zirconium oxides are known for their adsorption capability and selectivity to oxyanions and here the applicability to selective IO₃ ^- removal has been investigated regarding the uptake mechanism, regeneration and competition caused by other anions, like environmentally relevant SO₄ ^2-. Granular aggregates of hydrous zirconium oxides with and without Sb doping showed high potential for the selective IO₃ ^- removal in the presence of competing anions, like the forementioned SO₄ ^2- (apparent capacity between 0.1-0.4 meq g^-1 depending on SO₄ ^2- concentration). The main uptake mechanism was found to be outer-sphere complexation (ion-exchange) to the protonated hydroxyl groups of hydrous zirconium oxides, but also minor mechanisms were identified including inner-sphere complexation and reduction to I^-. The materials were observed to be easily and successively regenerated using dilute acid. Hydrous zirconium oxides showed high potential for IO₃ ^- removal from waste solutions regarding technical (high selectivity and apparent capacity) and ecological/economic (feasible regeneration) aspects.

Antimony removal from water by pine bark tannin resin: Batch and fixed-bed adsorption

Antimony is present in water by natural causes but is also mobilized in the environment by anthropogenic activities, particularly mining. Considering its toxicological behavior, antimony removal from contaminated groundwater and mine effluents is necessary. In this work, Sb(III) and Sb(V) removal from aqueous solution was studied using a resin prepared from pine bark tannins. Subsequent iron loading of the tannin resin was tested, but this chemical modification was shown not to improve adsorptive properties. Tannin resin (unmodified form) presented a good ability to uptake antimony, with maximum adsorption capacities, evaluated in batch mode, of 30-33 mg g^-1 (Sb(III), pH 6) and 16-47 mg g^-1 (Sb(V), pH 2), depending on the particle size. The performance of the adsorbent was not affected by high levels of sulfate, which characterize most mining-impacted waters, but depending on Sb-load of the water it could be moderately affected by metal cations coexisting in solution. The applicability of the tannin resin on Sb(III) uptake was confirmed in continuous fixed-bed experiments. Breakthrough curves were obtained for different inlet adsorbate concentrations, bed heights, flow rates and aqueous media (distilled water and a simulated mine effluent). The adsorptive capacity of the tannin resin was practically maintained and adsorbent usage rates as low as 0.11 kg m^-3 were determined to treat efficiently (90% removal) 1 mg-Sb(III) L^-1 contaminated water. Overall, tannin resin is a bio-derived sorbent that shows affinity for antimony in both redox states, being stable in pH conditions commonly found in Sb-contaminated waters.

Novel electroblowing synthesis of tin dioxide and composite tin dioxide/silicon dioxide submicron fibers for cobalt(ii) uptake

Nanoscale SnO2 has many important properties ranging from sorption of metal ions to gas sensing. Using a novel electroblowing method followed by calcination, we synthesized SnO2 and composite SnO2/SiO2 submicron fibers with a Sn : Si molar ratio of 3 : 1. Different calcination temperatures and heating rates produced fibers with varying structures and morphologies. In all the fibers SnO2 was detected by XRD indicating the SnO2/SiO2 fibers to be composite instead of complete mixtures. We studied the Co2+ separation ability of the fibers, since 60Co is a problematic contaminant in nuclear power plant wastewaters. Both SnO2 and SnO2/SiO2 fibers had an excellent Co2+ uptake with their highest uptake/K d values being 99.82%/281 000 mL g-1 and 99.79%/234 000 mL g-1, respectively. Compared to the bare SnO2 fibers, the SiO2 component improved the elasticity and mechanical strength of the composite fibers which is advantageous in dynamic column operation.

Beyond the Single-Nozzle: Coaxial Electrospinning Enables Innovative Nanofiber Chemistries, Geometries, and Applications

With an ever increasing scientific, technological, and industrial interest in high surface area, porous nanofiber mats, electrospinning has emerged as a popular method to produce fibrous assemblies for use across biomedical, energy, and environmental applications. However, not all precursor solutions nor complex geometries can be easily fabricated using the traditional single-nozzle apparatus. Therefore, coaxial electrospinning, a modified version of electrospinning that features a concentrically aligned dual nozzle, has been developed. This review will first describe the mechanism of electrospinning two precursor solutions simultaneously and the operational parameters that need to be optimized to fabricate continuous fibers. Modifications that can be made to the coaxial electrospinning process, which enable the fabrication of uniform fibers with improved properties, as well as the fabrication of fibers that are hollow, functionalized, and from "nonspinnable precursors" will be discussed as a means of promoting the advantages of using a coaxial setup. Examples of how coaxially electrospun nanofibers are employed in diverse applications will be provided throughout this review. We conclude with a timely discussion about the current limitations and challenges of coaxial electrospinning.