Inorganic and Hybrid (Organic⁻Inorganic) Lamellar Materials for Heavy metals and Radionuclides Capture in Energy Wastes Management-A Review

Open-framework hybrid zinc/tin selenide as an ultrafast adsorbent for Cs+, Ba2+, Co2+, and Ni2

Efficient adsorption of radioactive ¹³⁷Cs⁺ and ⁶⁰Co²⁺ and their decay products ¹³⁷Ba²⁺ and ⁶⁰Ni²⁺ bears significance for hazard elimination in case of nuclear emergency, which relies on the adsorption rate enhancement that takes advantages of compositional and structural optimization. Herein, we report a zinc-doped selenidostannate constructed from T2-supertetrahedral clusters, namely K_3.4(CH₃NH₃)_0.45(NH₄)_0.15Zn₂Sn₃Se₁₀·3.4 H₂O (ZnSnSe-1K). The soft Se and micro-porosity synergistically endow this material with a binding affinity to Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺ ions and ultrafast kinetics with R > 97.6% in 2-60 min. In particular, ZnSnSe-1K can remove 99.34% of Cs⁺ in 2 min ⁽K_d^Cs > 1.5 × 10⁵ mL g^-1), contributing to a record rate constant k₂ of 9.240 g mg^-1 min^-1 that surpasses all metal chalcogenide adsorbents. ZnSnSe-1K exhibits good acid/base tolerance (pH = 0-12), and the adsorption capacities at neutral are 253.61 ± 9.15, 108.94 ± 25.32, 45.76 ± 14.19 and 38.49 ± 2.99 mg g^-1 for Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺, respectively. The adsorption performances resist well co-existing cations and anions, and the removal rates can keep above or close to 90% even in sea water. ZnSnSe-1K is employed in continuous column and membrane filtration, both of which shows excellent elimination efficiency (R > 99%) for mixed Cs⁺, Ba²⁺, Co²⁺, and Ni²⁺. Especially, the membrane with an ultrathin (70 µm) ZnSnSe-1K layer can remove 97-100% Cs⁺ in suction filtration with a short contact time of 0.33 s. Combined with the simple synthesis, facile elution and great irradiation resistance, ZnSnSe-1K emerges as a selenide adsorbent candidate for use in environmental remediation especially that involving nuclear waste disposal.

Synthesis and characterization of a novel N-rich porous organic polymer and its application as an efficient porous adsorbent for the removal of Pb(II) and Cd(II) ions from aqueous solutions

In this study, a novel N-rich triazine-based porous organic polymer (NR-POP) was synthesized via Schiff-base condensation. The structure of the synthesized porous polymer was identified using FT-IR, XRD, SEM, EDS, TEM, TGA, and BET analyses. The adsorption efficiency of this polymer was investigated for the removal of lead and cadmium ions pollutants. The adsorption processes of Pb(II) and Cd(II) metal ions by this polymer adsorbent were exothermic and matched by the Langmuir isotherm with a high correlation coefficient (R² = 0.9904, 0.9778), the maximum adsorption capacity (833.33, 178.57 mg g^-1), and the pseudo-second-order kinetic model. Furthermore, NR-POP showed an excellent adsorption selectivity for Pb(II) compared to Cd(II).

Magnetic Ionotropic Hydrogels Based on Carboxymethyl Cellulose for Aqueous Pollution Mitigation

In this work, stabilized ionotropic hydrogels were designed using sodium carboxymethyl cellulose (CMC) and assessed as inexpensive sorbents for hazardous chemicals (e.g., Methylene Blue, MB) from contaminated wastewaters. In order to increase the adsorption capacity of the hydrogelated matrix and facilitate its magnetic separation from aqueous solutions, sodium dodecyl sulfate (SDS) and manganese ferrite (MnFe₂O₄) were introduced into the polymer framework. The morphological, structural, elemental, and magnetic properties of the adsorbents (in the form of beads) were assessed using scanning electron microscopy (SEM), energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy (FTIR), and a vibrating-sample magnetometer (VSM). The magnetic beads with the best adsorption performance were subjected to kinetic and isotherm studies. The PFO model best describes the adsorption kinetics. A homogeneous monolayer adsorption system was predicted by the Langmuir isotherm model, registering a maximum adsorption capacity of 234 mg/g at 300 K. The calculated thermodynamic parameter values indicated that the investigated adsorption processes were both spontaneous (ΔG < 0) and exothermic (ΔH < 0). The used sorbent can be recovered after immersion in acetone (93% desorption efficiency) and re-used for MB adsorption. In addition, the molecular docking simulations disclosed aspects of the mechanism of intermolecular interaction between CMC and MB by detailing the contributions of the van der Waals (physical) and Coulomb (electrostatic) forces.

Adsorption behaviors and mechanisms of Fe/Mg layered double hydroxide loaded on bentonite on Cd (II) and Pb (II) removal

In this study, FeMg-LDH loaded with bentonite (FeMg-LDH@bentonite) was prepared using the facile co-precipitating method in situ to remove heavy metals from water and then characterized using XRD, SEM, TEM, FTIR, BET, TGA, and XPS. Pb (II) and Cd (II) were selected as the representative heavy metals to evaluate the adsorption capability of the FeMg-LDH@bentonite. The batch adsorption method was adopted to test the effects of the contact time, pH, initial concentration, different cations, and temperatures. The kinetic study indicated that the adsorption of heavy metals onto FeMg-LDH@bentonite was well fitted by the pseudo-second-order method. Isotherms were effectively simulated based on the Langmuir model. The maximal adsorption capability of Cd (II) and Pb (II) can reach 510.2 mg/g and 1397.62 mg/g, exceeding those of conventional adsorbents. The adsorption mechanisms of FeMg-LDH@bentonite demonstrating that there may exist surface complexation, ion exchange, and chemical deposition between FeMg-LDH@bentonite and heavy metals. Moreover, FeMg-LDH@bentonite was found to have a promising application for practically treating wastewater with heavy metals and can be used for various environmental water pollution treatments. The material may be used for heavy metal contaminated soil in the future.

Hydrogel Adsorbents for the Removal of Hazardous Pollutants—Requirements and Available Functions as Adsorbent

Over the last few decades, various adsorption functions of polymer hydrogels for the removal of hazardous pollutants have been developed. The performance of hydrogel adsorbents depends on the constituents of the gels and the functions produced by the polymer networks of the gels. Research on hydrogels utilizing the characteristic functions of polymer networks has increased over the last decade. The functions of polymer networks are key to the development of advanced adsorbents for the removal of various pollutants. No review has discussed hydrogel adsorbents from the perspective of the roles and functions of polymer networks in hydrogels. This paper briefly reviews the basic requirements of adsorbents and the general characteristics of hydrogels as adsorbents. Thereafter, hydrogels are reviewed on the basis of the roles and functions of the polymer networks in them for the removal of hazardous pollutants by introducing studies published over the last decade. The application of hydrogels as adsorbents for the removal of hazardous pollutants is discussed as well.

Application of carbon dots and their composite materials for the detection and removal of radioactive ions: A review

Radioactive ions with high-heat release or long half-life could cause long-term influence on environment and they might enter the food chain to damage human body for their toxicity and radioactivity. It is of great importance to develop methods and materials to detect and remove radioactive ions. Carbon dots and their composite materials has been applied widely in many fields due to their plentiful raw materials, facile synthesis and functional process, unique optical property and abundant functional groups. This comprehensive review focuses on the preparation of CDs and composite materials for the detection and adsorption of radioactive ions. Firstly, the recent-developed synthetic methods for CDs were summarized briefly, including hydrothermal/solvothermal, microwave, electrochemistry, microplasma, chemical oxidation methods, focusing on the influence of CDs properties. Secondly, the synthetic methods for CDs composite materials were classified to four categories and summarized generally. Thirdly, the application of CDs for radioactive ions detection and adsorption were explored and concluded including uranium, iodine, europium, strontium, samarium et al. Finally, the detection and adsorption mechanism for radioactive ions were searched and the perspective and outlook of CDs for detection and adsorption radioactive ions have been proposed based on our understanding.

Strippable Polymeric Nanocomposites Comprising "Green" Chelates, for the Removal of Heavy Metals and Radionuclides

The issue of heavy metal and radionuclide contamination is still causing a great deal of concern worldwide for environmental protection and industrial sites remediation. Various techniques have been developed for surface decontamination aiming for high decontamination factors (DF) and minimal environmental impact, but strippable polymeric nanocomposite coatings are some of the best candidates in this area. In this study, novel strippable coatings for heavy metal and radionuclides decontamination were developed based on the film-forming ability of polyvinyl alcohol, with the remarkable metal retention capacity of bentonite nanoclay, together with the chelating ability of sodium alginate and with "new-generation" "green" complexing agents: iminodisuccinic acid (IDS) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC). These environmentally friendly water-based decontamination solutions are capable of generating strippable polymeric films with optimized mechanical and thermal properties while exhibiting high decontamination efficiency (DF ≈ 95-98% for heavy metals tested on glass surface and DF ≈ 91-97% for radionuclides 241Am, 90Sr-Y and 137Cs on metal, painted metal, plastic, and glass surfaces).

Cs Adsorption and CsCl Particle Formation Facilitated by Amino Talc-like Clay in Aqueous Solutions at Room Temperature

Amino talc-like clay with an increased number of active sites and dispersion in a colloidal system has been synthesized and used for contaminant adsorption and support for nanoparticle formation. Amino talc-like clays having different number of layers and aminoalkyl ligands were synthesized and their Cs uptake behavior was examined. Cs uptake through Cs adsorption and CsCl particle formation facilitated by amino talc-like clay in a colloidal aqueous solution at room temperature are reported. The amino talc-like clay demonstrated better Cs uptake with a high initial Cs concentration than talc and montmorillonite. This might have been caused by a high concentration of trapped Cs and Cl ions in exfoliated amino clay, which eventually became CsCl particles. The formation of the CsCl particles in the amino clay depended on the clay concentration and ethanol treatment. The exfoliation of the basal sheets of the amino clay as a result of a high salt concentration and the protonation of amine induced by ethanol treatment was shown to be a precondition for CsCl particle formation. These results could promote amino talc-like clay for high-concentration Cs uptake and the green synthesis of Cs-halide particles in an aqueous solution.

Preparation of MgGa Layered Double Hydroxides and Possible Compositional Variation

Layered double hydroxides (LDHs), shown as the general formula of [M2+1-xM3+x(OH)2]x+(An-)x/n∙yH2O, are useful for various applications such as anion exchangers/adsorbents, catalysts and catalysts' supports, and drug/gene carriers due to their structural, compositional and morphological characteristics and their variation. The x value (M3+/(M2+ + M3+) ratio) in layered double hydroxides (LDHs), corresponding to the layer charge density, is one of the important parameters for controlling the properties of LDHs. The x values in commonly available LDHs are limited (0.2 < x < 0.3). In order to obtain LDHs with x < 0.2, Mg2+ Ga3+-LDHs with interlayer iodide were examined. The linear correlation between lattice parameter a and x value in the products with x of 0.06-0.24 was seen, suggesting the successful substitution of Mg2+ in the brucite-like sheet with Ga3+. Carbonate and dodecyl sulfate types MgGa-LDH were prepared by ion exchange with carbonate anion and reconstruction in aqueous solution of sodium dodecyl sulfate. The products with x of 0.06 were dispersed in water and hexanol better than those with x of 0.24 for MgGa-LDHs containing carbonate and dodecyl sulfate, respectively, suggesting effects of the lower layer charge density on the dispersion.

Ion-Imprinted Polymers: Synthesis, Characterization, and Adsorption of Radionuclides

Growing concern over the hazardous effect of radionuclides on the environment is driving research on mitigation and deposition strategies for radioactive waste management. Currently, there are many techniques used for radionuclides separation from the environment such as ion exchange, solvent extraction, chemical precipitation and adsorption. Adsorbents are the leading area of research and many useful materials are being discovered in this category of radionuclide ion separation. The adsorption technologies lack the ability of selective removal of metal ions from solution. This drawback is eliminated by the use of ion-imprinted polymers, these materials having targeted binding sites for specific ions in the media. In this review article, we present recently published literature about the use of ion-imprinted polymers for the adsorption of 10 important hazardous radionuclides-U, Th, Cs, Sr, Ce, Tc, La, Cr, Ni, Co-found in the nuclear fuel cycle.

Laponites® for the Recovery of 133Cs, 59Co, and 88Sr from Aqueous Solutions and Subsequent Storage: Impact of Grafted Silane Loads

In this study, silylated Laponites^® (LAP) were synthetized with various loads of 3-aminopropyltriethoxysilane (APTES) to evaluate their adsorption properties of ¹³³Cs, ⁵⁹Co, and ⁸⁸Sr during single-solute and competitive experiments. The increase in the initial load of APTES increased the adsorbed amount of APTES in the resulted grafted clay. The characterization of LAP-APTES exhibited a covalent binding between APTES and LAP and emphasized the adsorption sites of APTES for each tested load. In comparison with raw LAP, LAP-APTES displayed significantly higher adsorption properties of Co²⁺, Cs⁺, and Sr²⁺. The competitive adsorption of these three contaminants provides a deeper understanding of the affinity between adsorbate and adsorbent. Therefore, Co²⁺ displayed a strong and specific adsorption onto LAP-APTES. Except for Cs⁺, the adsorption capacity was improved with increasing the load of APTES. Finally, the desorption behavior of the three contaminants was tested in saline solutions. Cs⁺ and Sr²⁺ were significantly released especially by inorganic cations displaying the same valence. Conversely, desorption of Co²⁺ was very low whatever the saline solution. LAP-APTES, therefore, presented suitable adsorption properties for the removal of radionuclides especially for Co²⁺, making this material suitable to improve the decontamination of radioactive wastewaters.

A Comparative Study on Color Stability of Anthocyanin Hybrid Pigments Derived from 1D and 2D Clay Minerals

Anthocyanin extracted from the fresh blue berry fruits was loaded onto different clay minerals including one-dimensional tubular halloysite and fibrous sepiolite, and two-dimensional lamellar kaolinite and montmorillonite to fabricate reversible allochroic hybrid pigments. The effect of the possible interaction mechanism between anthocyanin and clay minerals on the color stability of hybrid pigments was investigated. Due to the difference in the structures and properties of clay minerals, natural anthocyanin was inclined to be absorbed on the surface and intercalated into the interlayer of 2:1 type layered montmorillonite, while it was mainly anchored on the surface of 1:1 type kaolinite and halloysite. By contrast, it was simultaneously loaded on the surface and confined into the nanochannels and/or grooves of 2:1 type chain-layered sepiolite. Interestingly, the resulting hybrid pigments presented good thermal stability and resistance to chemical reagents, as well as reversible gas-sensitive allochroic behavior in HCl or NH₃ gases, especially anthocyanin/sepiolite hybrid pigments due to the shielding effect of the well-defined nanochannels and grooves of sepiolite. Based on this color-change behavior, a simple pH test paper was also prepared with obvious color change at different pH values by coating the filter paper with anthocyanin/sepiolite hybrid pigments.

Technetium Encapsulation by A Nanoporous Complex Oxide 12CaO•7Al2O3 (C12A7)

Technetium (99Tc) is an important long-lived radionuclide released from various activities including nuclear waste processing, nuclear accidents and atmospheric nuclear weapon testing. The removal of 99Tc from the environment is a challenging task, and chemical capture by stable ceramic host systems is an efficient strategy to minimise the hazard. Here we use density functional theory with dispersion correction (DFT+D) to examine the capability of the porous inorganic framework material C12A7 that can be used as a filter material in different places such as industries and nuclear power stations to encapsulate Tc in the form of atoms and dimers. The present study shows that both the stoichiometric and electride forms of C12A7 strongly encapsulate a single Tc atom. The electride form exhibits a significant enhancement in the encapsulation. Although the second Tc encapsulation is also energetically favourable in both forms, the two Tc atoms prefer to aggregate, forming a dimer.