UV pre-activation/thermal initiated grafting of caffeic acid on PVDF for preparation of adsorptive membranes for cesium

Layered metal sulfides with MaSbc- framework (M = Sb, In, Sn) as ion exchangers for the removal of Cs(Ⅰ) and Sr(Ⅱ) from radioactive effluents: a review

Nuclear power has emerged as a pivotal contributor to the global electricity supply owing to its high efficiency and low-carbon characteristics. However, the rapid expansion of the nuclear industry has resulted in the production of a significant amount of hazardous effluents that contain various radionuclides, such as 137Cs and 90Sr. Effectively removing 137Cs and 90Sr from radioactive effluents prior to discharge is a critical challenge. Layered metal sulfides exhibit significant potential as ion exchangers for the efficient uptake of Cs+ and Sr2+ from aqueous solutions owing to their open and exchangeable frameworks and the distinctive properties of their soft S2- ligands. This review provides a detailed account of layered metal sulfides with MaSb c- frameworks (M = Sb, In, Sn), including their synthesis methods, structural characteristics, and Cs+ and Sr2+ removal efficiencies. Furthermore, we highlight the advantages of layered metal sulfides, such as their relatively high ion exchange capacities, broad active pH ranges, and structural stability against acid and radiation, through a comparative evaluation with other conventional ion exchangers. Finally, we discuss the challenges regarding the practical application of layered metal sulfides in radionuclide scavenging.

Cesium removal from wastewater: High-efficient and reusable adsorbent K1.93Ti0.22Sn3S6.43

Efficient and quick removal of radioactive Cs⁺ from wastewater is significant for the safe use of nuclear energy and human health. A novel adsorbent K_1.93Ti_0.22Sn₃S_6.43 (KTSS) was developed for Cs⁺ removal from complex natural water systems. The working mechanism of KTSS for removing Cs⁺ was the synergistic effect of ion exchange and the Cs⋯S binding, which was proved by several characterization techniques. KTSS showed ultrafast kinetics for Cs⁺ adsorption within 1 min with a removal rate of 99%. Meanwhile, KTSS exhibited a higher adsorption capacity of 450.12 mg/g than many other adsorbents to remove Cs⁺ and possessed excellent chemical stability in a wide pH range of 3-12. Thanks to the natural affinity arising from the S^2- ligands, KTSS displayed excellent selectivity for Cs⁺ even in different complex water systems. The separation factors between Cs⁺ and the coexisting ions of Na⁺, K⁺, Mg²⁺, Ca²⁺ were ranged from 408.61 to 7448.20. Fortunately, by eluting with NaNO₃ the adsorbent could realize the green regeneration and cyclic utilization. Furthermore, it was found that KTSS had tremendous advantages in the removal of Cs⁺ in comparison with the other adsorbents. Consequently, it should be considered that KTSS obtained in this study has great potential in applying ultrafast and high-efficient removal of Cs⁺ from wastewater.

Modification of Polyacrylonitrile Ultrafiltration Membranes to Enhance the Adsorption of Cations and Anions

Ion adsorbing ultrafiltration membranes provide an interesting possibility to remove toxic ions from water. Furthermore, it is also possible to recover valuable elements. In this work, we demonstrate two easy strategies to modify polyacrylonitrile membranes with anion and cation adsorbing groups. The membranes were modified to have positively charged amine groups or negatively charged carboxyl groups. The success of the reactions was confirmed using IR spectroscopy and zeta-potential measurements. The membranes carrying negatively charged groups provided a negative zeta-potential and had an isoelectric point at pH 3.6, while the membranes carrying positively charged groups had a positive zeta-potential in the analyzed pH range. Since only the surface of the polymer was modified, the pore size and permeance of the membranes were not drastically affected. The membranes prepared by both modification strategies had a pure water permeance higher than 1000 L/(m² h bar) and a water contact angle of 44.3 and 57.2°, respectively. Therefore, the membranes can be operated at low pressures with reasonable flux. Additionally, SEM images showed that the membranes were still open-pored. Adsorption tests using a positively and a negatively charged dye as well as a toxic cation and an anion were performed to analyze the adsorption behavior. Both membranes were able to adsorb the oppositely charged dyes as well as the copper and chromate ions. Therefore, these membranes are good candidates to purify water streams containing hazardous ions.

Enhanced Specific Mechanism of Separation by Polymeric Membrane Modification-A Short Review

Membrane technologies have found a significant application in separation processes in an exceeding range of industrial fields. The crucial part that is decided regarding the efficiency and effectivity of separation is the type of membrane. The membranes deal with separation problems, working under the various mechanisms of transportation of selected species. This review compares significant types of entrapped matter (ions, compounds, and particles) within membrane technology. The ion-exchange membranes, molecularly imprinted membranes, smart membranes, and adsorptive membranes are investigated. Here, we focus on the selective separation through the above types of membranes and detect their preparation methods. Firstly, the explanation of transportation and preparation of each type of membrane evaluated is provided. Next, the working and application phenomena are evaluated. Finally, the review discusses the membrane modification methods and briefly provides differences in the properties that occurred depending on the type of materials used and the modification protocol.

Decontamination of radioactive cesium-contaminated soil/concrete with washing and washing supernatant- critical review

We reviewed washing of radioactive Cs-contaminated concrete and soil based on the fate of Cs in concrete and soil, including sorption materials for treatment of supernatant solution. In non-aged cement materials (the calcium silicate hydration (C-S-H) phase), it was possible to decontaminate Cs using ion exchange with monovalent cations, such as NH₄⁺. The clay components in the soil and aggregates were important factors in optimization of the efficiency and mechanism for Cs decontamination with washing solution. The parameters (reagent component, pH, and temperature) of the washing solution should be determined considering soil mineral type (here, weathered biotite (WB) with vermiculite), since monovalent cations such as NH₄⁺ and K⁺ can inhibit Cs decontamination due to collapse of the hydrated and expanded interlayer regions with cation exchange. In this case, hydrothermal treatment or H₂O₂ dosing was necessary to expand the collapsed interlayer region for Cs removal by washing with cation exchange or organic acids. Acid and a chelating agent significantly enhanced Cs-release with dissolution of the adsorbent layer containing iron and aluminum oxides. The important characteristics of important and emerging sorption materials for treatment of the radioactive Cs-contaminated supernatant after washing treatment are discussed. Sorbents for treatment of washing supernatant are divided in to two main categories. Clay minerals, metal hexacyanoferrates, and ammonium molybdophosphates are discussed in the inorganic class of materials. Hypercrosslinked polymers, supramolecular sorbents, carbon nanotubes, and graphene oxide are covered in the carbon-based sorbents for Cs removal from water.

Novel One-Pot Solvothermal Synthesis of High-Performance Copper Hexacyanoferrate for Cs+ Removal from Wastewater

Efficient removal of radioactive cesium from complex wastewater is a challenge. Unlike traditional precipitation and hydrothermal synthesis, a novel vast specific surface area adsorbent of copper hexacyanoferrates named EA-CuHCF was synthesized using a one-pot solvothermal method under the moderate ethanol media characterized by XRD, SEM, EDS, BET, and FTIR. It was found that the maximum adsorption capacity towards Cs+ was 452.5 mg/g, which is far higher than most of the reported Prussian blue analogues so far. Moreover, EA-CuHCF could effectively adsorb Cs+ at a wide pH range and low concentration of Cs+ in geothermal water within 30 minutes, and the removal rate of Cs+ was 92.1%. Finally, the separation factors between Cs+ and other competitive ions were higher than 553, and the distribution coefficient of Cs+ reached up to 2.343 × 104 mL/g. These properties suggest that EA-CuHCF synthesized by the solvothermal method has high capacity and selectivity and can be used as a candidate for Cs+ removal from wastewater.

Enhanced kinetics and super selectivity toward Cs+ in multicomponent aqueous solutions: A robust Prussian blue analogue/polyvinyl chloride composite membrane

Developing effective adsorbents for ¹³⁷Cs removal from complex wastewater systems has been a significant challenge. Although existing spheres adsorbents could improve the post-separation ability and practical operability, the adsorption kinetics are still significantly retarded due to the large intra-particle diffusion resistance. Here, we demonstrate the efficiency of a robust Prussian blue analogue/polyvinyl chloride composite membrane (PPM), which was easily prepared by a simple solvent evaporation method. In virtue of the less dense layer and ion-sieving functionality, it showed enhanced kinetics (5 h) and super selectivity (S_F = 248.3-5388.6) towards Cs⁺. New PPM was robust within a wide pH range (2-10) and exhibited favorable removal capacity (152.8 mg/g), placing it at an outstanding material for Cs⁺ removal among other adsorbents. Moreover, PPM could be simply eluted and reused using a KCl solution as eluent. A study of the adsorption mechanism confirmed an ion-exchange action during the removal process. Thus, PPM is considered to be a promising candidate for the removal of Cs⁺ from multicomponent aqueous solutions.

Sandwich membranes based on PVDF-g-4VP and surface modified graphene oxide for Cu(II) adsorption

UV photo-preactivation/thermally-induced grafting was employed for grafting 4-vinylpyridine (4-VP) on polyvinylidene fluoride (PVDF), and graphene oxide (GO) was modified with 4'-carboxy-2,2':6',2"-terpyridine (CTPy). Then sandwich PVDF-g-4VP/GO-CTPy/polytetrafluoroethylene (PTFE) membrane was fabricated for adsorption of Cu (II) as a model. The membrane formation, static adsorption thermodynamics, kinetics and dynamic adsorption/desorption were studied. The results showed that, the addition of polyethylene glycol (PEG 4000) as porogen can significantly increase the porosity and adsorption capacity of the membranes. The adsorption could be well described by the Langmuir model and pseudo-second-order kinetic model. The breakthrough volume and saturated volume increased with rising GO-CTPy contents. The adsorption capacity of sandwich membranes was much higher than that of mixed matrix membranes. The sandwich membrane also exhibited excellent reusability in dynamic adsorption/desorption cycles, demonstrating great potential in adsorption of trace Cu (II).