Removal of Cr(VI) using polyacrylonitrile/ferrous chloride composite nanofibers

Remediation materials for the immobilization of hexavalent chromium in contaminated soil: Preparation, applications, and mechanisms

Hexavalent chromium is a toxic metal that can induce severe chromium contamination of soil, posing a potential risk to human health and ecosystems. In recent years, the immobilization of Cr(VI) using remediation materials including inorganic materials, organic materials, microbial agents, and composites has exhibited great potential in remediating Cr(VI)-contaminated soil owing to the environmental-friendliness, short period, simple operation, low cost, applicability on an industrial scale, and high efficiency of these materials. Therefore, a systematical summary of the current progress on various remediation materials is essential. This work introduces the production (sources) of remediation materials and examines their characteristics in detail. Additionally, a critical summary of recent research on the utilization of remediation materials for the stabilization of Cr(VI) in the soil is provided, together with an evaluation of their remediation efficiencies toward Cr(VI). The influences of remediation material applications on soil physicochemical properties, microbial community structure, and plant growth are summarized. The immobilization mechanisms of remediation materials toward Cr(VI) in the soil are illuminated. Importantly, this study evaluates the feasibility of each remediation material application for Cr(VI) remediation. The latest knowledge on the development of remediation materials for the immobilization of Cr(VI) in the soil is also presented. Overall, this review will provide a reference for the development of remediation materials and their application in remediating Cr(VI)-contaminated soil.

Synthesis of Electrospun Polyvinyl Butyral/Bentonite Nanofiber Film for Cationic Dye Removal

The textile industry is a common and relevant sector worldwide that generates significant environmental pollution via the discharge of dye-containing wastewater. In this direction, the electrospinning technology can be used to produce adsorbing nanofibers for the treatment of wastewater polluted by dyes and other toxic compounds. The nanofibers obtained by this technology are light and thin, thus providing several advantages (e.g., high surface area) to improve the efficacy of adsorption processes. In this direction, this study reports the preparation of nanofibers from polyvinyl butyral (PVB) and bentonite via electrospinning. This study also reports PVB/bentonite nanofiber mat and its application in adsorbing the cationic dye (methylene blue) from an aqueous solution. The morphology and water contact angles of these nanofibers were analyzed. Results showed that the maximum dye adsorption of these nanofibers was 66.63 mg/g along with 32% removal at pH 9 and 27 ± 2°C. The dye adsorption on these nanofibers was exothermic and pH-dependent, with the best adsorption capacities obtained under alkaline conditions. The adsorption mechanism of this dye molecule on these PVB/bentonite nanofiber mats was associated with van der Waals forces, hydrogen bonding, and electrostatic interactions. This novel composite is an interesting material with improved properties that can be applied to the removal of cationic dyes from wastewater.

Fe/C materials prepared by one-step calcination of acidified municipal sludge and their excellent adsorption of Cr(VI)

Biochar derived from municipal sludge can be applied to adsorption. But it usually requires activation and pickling due to the generation of impurities such as metal oxide particles, which is uneconomical. Here, a facile strategy, acidification-one-step calcination, was developed and sludge-based Fe-C materials with good Cr(VI) removal effect were obtained by regulating the amount of hydrochloric acid. The results show that the adsorption capacity of Fe/C-5 (the best sample) for Cr(VI) was 150.84 mg g^-1. According to the Langmuir isotherm and pseudo-second-order kinetic model, the removal of Cr(VI) by Fe/C-5 is spontaneous and endothermic chemisorption process. In addition, Fe/C-5 has good ability to remove Cr(VI) under the interference of coexisting ions, and has good cycle stability. The removal of Cr(VI) by Fe/C-5 is considered to be synergistic process of adsorption and reduction. The Fe atoms were highly dispersed in Fe/C-5 and tightly bonded with C atoms, which not only strengthened the Cr(VI) adsorption by electrostatic attraction, but also activated the C atoms in the biochar material, so that the C atoms can reduce Cr(VI) to Cr(III) under acidic conditions. This may be due to the fact that acid pretreatment converted the iron in municipal sludge in the form of Fe-O/OH to free Fe³⁺ and entered the C lattice during the calcination process. In this work, Fe-C materials with excellent Cr(VI) adsorption capacity were prepared by one-step calcination method, which has important reference significance for the resource utilization of municipal sludge.

Development of Nylon 6 nanofibers modified with Cyanex-272 for cobalt recovery

With a worldwide ever increasing demand for metals, particularly for the manufacture of electronics and batteries, there is not only a concurrent need to recover these materials from their subsequent waste streams but also a need to make advancements to do this via development of more efficient and eco-friendly processes for metal recovery; solid-phase extraction can be considered a promising alternative to conventional processes. This work studied the production of novel nanofibers modified with Cyanex 272 and their application in the recovery of cobalt present in aqueous solution The nanofibers produced by forcespinning were characterized by SEM, FT-IR and TGA and the extraction of cobalt was evaluated by variation of the pH, solid:liquid (S:L) ratio, extraction time and Cyanex 272 content in the nanofibers. The best extraction efficiency was 99.96%, achieved under the following conditions: pH 8; (S:L) ratio of 1:200; 25% of Cyanex 272; Extraction time of 60 min. The maximum extraction capacity obtained was 15.46 mg Co/g of nanofiber and 70.15 mg Co/g of extractor. In successive reuse cycles, the results demonstrated that the extraction efficiency was maintained at over 85%. The findings showed that Nylon 6/Cyanex 272 nanofibers are a new robust and promising material for the recovery of heavy metals from aqueous solution, confirming that nanofibers have an efficiency similar to conventional liquid-liquid extraction, without the disadvantage of volatile organic compounds emissions generated by the use of organic diluents.

Production of polyacrylonitrile nanofibres modified with Cyanex 272 for recovery of gallium from solution

The objectives of this work were to develop polyacrylonitrile nanofibres modified with the commercial Cyanex 272 extractor and apply them for the recovery of gallium present in aqueous solution. The nanofibres were produced using the centrifugation technique, employing Forcespinning® equipment. The average nanofibre diameter ranged from 530 to 840 nm. The highest adsorption of gallium was achieved at pH 2.5, with a pseudo-second order kinetic model and the Freundlich equilibrium isotherm model providing the best fits of the experimental data. The thermodynamic parameters showed that the adsorption was spontaneous, favourable, and endothermic. The maximum capacity of the PAN/Cyanex 272 nanofibres for the recovery of gallium was 38.93 mg g^-1. In successive reuse cycles, the nanofibres showed a small decrease of the adsorption capacity for the metal after the first cycle, while the efficiency remained constant in the subsequent cycles. The desorption efficiency remained constant throughout the cycles, with values in the range 80%-90%. The findings demonstrated that PAN/Cyanex 272 nanofibres have excellent potential for use as adsorbents, providing good capacity for the recovery of gallium and satisfactory stability during reuse in several cycles.

Waste Moringa oleifera seed pods as green sorbent for efficient removal of toxic aquatic pollutants

In the present study, biosorption of chromium (Cr(VI)) ions and Naphthol blue black (NBB) dye using Moringa oleifera seed pods powder (MPP) as green biosorbent was investigated. Three different sizes of MPP viz. fine fraction (<53 μm), coarse fraction (>250 μm) and mixed fraction were investigated. The biosorbent was characterized by pHzpc, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) in order to get an insight of the surface charge, functional groups, and morphology of the biosorbent, respectively. The biosorption studies were conducted with Cr(VI) and NBB dye and different parameters, such as solution pH, contact time, initial concentration of the pollutant, adsorbent dosage and co-existing ions were examined. Experimental results revealed that the maximum removal of Cr(VI) and NBB dye was observed at pH 1 and 2, respectively and the equilibrium was achieved in ca. 180 min. The removal efficiency of Cr(VI) by fine, mixed and coarse fraction was 91.8, 74.9, 52.6%, respectively, whereas for NBB dye, the removal efficiency for the same fractions was 97.5, 33.6, 18.9%, respectively. The removal efficiency of Cr(VI) and NBB dye was influenced in the presence of competing ions. The biosorption isotherm and kinetic data were best correlated with Langmuir isotherm and pseudo-second order kinetic model, respectively. Column studies were also conducted with MPP by studying different flow rates and adsorbates concentrations to check the practical applicability of MPP in removing target metal and dye pollutants.