Multiscale structural control of thiostannate chalcogels with two-dimensional crystalline constituents

Chalcogenide aerogels (chalcogels) are amorphous structures widely known for their lack of localized structural control. This study, however, demonstrates a precise multiscale structural control through a thiostannate motif ([Sn₂S₆]^4-)-transformation-induced self-assembly, yielding Na-Mn-Sn-S, Na-Mg-Sn-S, and Na-Sn(II)-Sn(IV)-S aerogels. The aerogels exhibited [Sn₂S₆]^4-:Mn²⁺ stoichiometric-variation-induced-control of average specific surface areas (95-226 m² g^-1), thiostannate coordination networks (octahedral to tetrahedral), phase crystallinity (crystalline to amorphous), and hierarchical porous structures (micropore-intensive to mixed-pore state). In addition, these chalcogels successfully adopted the structural motifs and ion-exchange principles of two-dimensional layered metal sulfides (K_2xMn_xSn_3-xS₆, KMS-1), featuring a layer-by-layer stacking structure and effective radionuclide (Cs⁺, Sr²⁺)-control functionality. The thiostannate cluster-based gelation principle can be extended to afford Na-Mg-Sn-S and Na-Sn(II)-Sn(IV)-S chalcogels with the same structural features as the Na-Mn-Sn-S chalcogels (NMSCs). The study of NMSCs and their chalcogel family proves that the self-assembly principle of two-dimensional chalcogenide clusters can be used to design unique chalcogels with unprecedented structural hierarchy.

Highly selective and easily regenerated porous fibrous composite of PSF-Na2.1Ni0.05Sn2.95S7 for the sustainable removal of cesium from wastewater

The removal of ¹³⁷Cs from radioactive wastewater remains a huge challenge due to the interference of many coexisting ions. Several tin chalcogenides (X₂Sn₃Y₇, XNa, K; YTe, Se, S) were synthesized and screened for highly selective cesium removal from radioactive wastewater. It was found that Na₂Sn₃S₇ showed the best adsorption performance for low cesium concentrations. Especially after nickel doping, the adsorption capacity and thermal stability of the adsorbent were significantly enhanced. Its maximum adsorption capacity reached 436.72 mg·g^-1 within only 5 min and adsorption performance kept active in the pH range of 2-12. After being coated with a porous polysulfone (PSF) fiber, the developed PSF-Na_2.1Ni_0.05Sn_2.95S₇ was applied to natural complex water with cesium concentration of 17.58 mg·L^-1. The separation factors between Cs⁺ and competitive ions ranged from 625.21 to 13123.21. It is noteworthy that NaNO₃ was an efficient regenerating agent and can be easily separated from the CsNO₃ mixture for cyclic utilization. Remarkably, only 45 min in each cycle of adsorption and desorption toward cesium was realized, and the adsorption properties hardly decreased even after 50 consecutive cycles. The above advantages make the proposed material an excellent candidate for efficient Cs⁺ removal and enrichment from wastewater.

Removal of phosphate at low concentration from water by porous PVA/Al2O3 composites

The porous polyvinyl alcohol (PVA)/Al₂O₃ composite by supporting activated alumina on the cross-linked network of PVA has been successfully prepared and its property for the removal of phosphate in aqueous solution was also evaluated. The structure of the PVA/Al₂O₃ was examined by scanning electron microscopy. It showed that the activated alumina particles with an average size of 1 μm were evenly dispersed and fixed in the cross-linked network structure of PVA. The effects of adsorption time, solution temperature, pH, initial concentration of phosphate, Al₂O₃ loading rate, dosage and coexisting ions on the phosphate removal were further studied. The results showed that the highest removal phosphate efficiency of 95% can be obtained with the Al₂O₃ loading rate of PVA/Al₂O₃ being 60 wt.% at pH of 4 at 30 °C. The maximum adsorption capacities of PO43- by PVA/Al₂O₃ suggested by the Langmuir isothermal model was 10.12 mg/g. The adsorption process of phosphate can be fit well with a pseudo-second-order model (R² = 0.9900). The PVA/Al₂O₃ composite exhibited a high selective adsorption of phosphate in the presence of commonly coexisting anions except the obvious effect of CO32- in water. Meanwhile, the PVA/Al₂O₃ composite can be easily separated and recovered due to the granulation of adsorbent. PVA/Al₂O₃ composite also shows the excellent properties of regeneration and recycling use with the removal efficiency of phosphate was 88.93%, 88.38% and 94.34% after three cycles, respectively. It can be proposed that the PVA/Al₂O₃ composite is a promising recyclable adsorbent for removing phosphate at low concentration from aqueous solution.

Efficient Removal of Cs+ and Sr2+ Ions by Granulous (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O/Polyacrylonitrile Composite

The need to effectively and selectively remove radioactive ¹³⁷Cs and ⁹⁰Sr from nuclear waste solutions persists to mitigate their environmental mobility and high radiotoxicity. Because it is difficult to effectively remove them from acidic environments that degrade most sorbents, new sorbent materials are highly desirable. Here, efficient removal of Cs⁺ and Sr²⁺ is achieved by the composite of layered tin sulfide (Me₂NH₂)_4/3(Me₃NH)_2/3Sn₃S₇·1.25H₂O (FJSM-SnS) and polyacrylonitrile (PAN) (FJSM-SnS/PAN). The granulous composite possesses regular particle morphology and good mechanical strength as an engineered form. It shows excellent acid-base and γ-irradiation resistance, high maximum adsorption capacities (q_m) of 296.12 and 62.88 mg/g for Cs⁺ and Sr²⁺ ions, respectively, and high selectivity even in the presence of excess Na⁺ ions or using lake water. Impressively, q_m^Cs of FJSM-SnS/PAN reaches 89.29 mg/g under even acidic conditions (pH = 2.5). The column loaded with FJSM-SnS/PAN granules exhibits high removal rates (R) toward low-concentration Cs⁺ and Sr²⁺ ions under both neutral and acidic conditions. Moreover, the composite can be recycled and reused with high R^Cs and R^Sr. This work highlights the great potential of metal sulfide ion-exchangers in engineered form for the efficient removal of Cs⁺ or Sr²⁺ ions, especially under acidic conditions, for radionuclide remediation.

Hybrid Sorbents for 129I Capture from Contaminated Groundwater

Radioiodine (¹²⁹I) poses a risk to the environment due to its long half-life, toxicity, and mobility. It is found at the U.S. Department of Energy Hanford Site due to legacy releases of nuclear wastes to the subsurface where ¹²⁹I is predominantly present as iodate (IO₃^-). To date, a cost-effective and scalable cleanup technology for ¹²⁹I has not been identified, with hydraulic containment implemented as the remedial approach. Here, novel high-performing sorbents for ¹²⁹I remediation with the capacity to reduce ¹²⁹I concentrations to or below the US Environmental Protection Agency (EPA) drinking water standard and procedures to deploy them in an ex-situ pump and treat (P&T) system are introduced. This includes implementation of hybridized polyacrylonitrile (PAN) beads for ex-situ remediation of IO₃^--contaminated groundwater for the first time. Iron (Fe) oxyhydroxide and bismuth (Bi) oxyhydroxide sorbents were deployed on silica substrates or encapsulated in porous PAN beads. In addition, Fe-, cerium (Ce)-, and Bi-oxyhydroxides were encapsulated with anion-exchange resins. The PAN-bismuth oxyhydroxide and PAN-ferrihydrite composites along with Fe- and Ce-based hybrid anion-exchange resins performed well in batch sorption experiments with distribution coefficients for IO₃^- of >1000 mL/g and rapid removal kinetics. Of the tested materials, the Ce-based hybrid anion-exchange resin was the most efficient for removal of IO₃^- from Hanford groundwater in a column system, with 50% breakthrough occurring at 324 pore volumes. The functional amine groups on the parent resin and amount of active sorbent in the resin can be customized to improve the iodine loading capacity. These results highlight the potential for IO₃^- remediation by hybrid sorbents and represent a benchmark for the implementation of commercially available materials to meet EPA standards for cleanup of ¹²⁹I in a large-scale P&T system.

Amino-functionalized magnetic chitosan beads to enhance immobilization of potassium copper hexacyanoferrate for selective Cs+ removal and facile recovery

Potassium copper hexacyanoferrate (KCuHCF)-incorporated magnetic chitosan beads (HMC) were synthesized for both selective Cs⁺ removal in aqueous solutions and facile recovery of the spent adsorbent. To disperse and immobilize large amounts of the KCuHCF, methyl acrylate and diethylenetriamine were sequentially grafted onto the one-step synthesized magnetic chitosan beads. The additional introduction of amino functionality led to the enriched Cu²⁺ ions on the bead surface to incorporate KCuHCF into the grafting matrix. Consequently, the HMC exhibited a high Cs⁺ capacity calculated to be 136.47 mg g⁻¹ from the Langmuir model, and the equilibrium was established within 4 h. Moreover, the HMC exhibited excellent stability in a wide pH range from 4 to 11 and an outstanding Cs⁺ selectivity (>97%) in seawater (1.11 mg L⁻¹ Cs⁺). From a practical point of view, the HMC was stable during five successive adsorption cycles and easily recovered by magnets, enabling continuous operation to decontaminate a large volume of wastewater.

The magnetic chitosan beads were amino-functionalized by grafting and showed an outstanding removal performance for radioactive Cs⁺.

Towards magnetic responsive chalcogenides for efficient separation in water treatment: facile synthesis of magnetically layered chalcogenide Fe3O4/KMS-1 composite adsorbents and their zinc removal application in water

A novel easily separated magnetic chalcogenide based composite, Fe₃O₄/KMS-1, was successfully synthesized under vigorous stirring of a mixture in ethanol solution.

Metal sulfide ion exchangers: superior sorbents for the capture of toxic and nuclear waste-related metal ions

Metal sulfide ion-exchangers (MSIEs) have emerged as a new class of promising sorbents for the removal of toxic and radioactive metals from wastewater.

Metal sulfide ion-exchangers (MSIEs) represent a new addition to the field of ion exchange materials. This is a growing class of materials that display exceptional selectivity and rapid sorption kinetics for soft or relatively soft metal ions as a result of their soft basic frameworks. Without requiring functionalization, they outperform the most efficient sulfur-functionalized materials. This is the first review focusing on this class of materials; it covers the most important MSIEs, focusing on their synthesis, structural features and ion-exchange chemistry. Furthermore, recent developments in the engineered and composite forms of MSIEs are described. Future research opportunities are also discussed in the hope of inspiring additional scientists to engage in this new area of research on sulfidic ion-exchange materials.

γ-Radiation fabrication of porous permutite/carbon nanobeads/alginic acid nanocomposites and their adsorption properties for Cs+

Novel porous permutite/carbon nanobeads/alginic acid nanocomposites were successfully fabricated and applied for Cs⁺ removal.