Advances in Inorganic and Hybrid Ion Exchangers

All-in-one treatment: Capture and immobilization of 137Cs by ultra-stable inorganic solid acid materials HMMoO6·nH2O (M = Ta, Nb)

Capture and immobilization of 137Cs is urgent for radioactive contamination remediation and spent fuel treatment. Herein, an effective all-in-one treatment method to simultaneously adsorb and immobilize Cs+ without high-temperature treatment is proposed. According to the strategy of incorporating high-valency metal ions into molybdates to increase the material stability and affinity towards radionuclides, layered HMMoO6·nH2O (M = Ta (1), Nb (2)) are prepared. Both materials exhibit excellent acid resistance (even 15 mol/L HNO3). They maintain remarkable adsorption capacity for Cs+ in 1 mol/L HNO3 solutions and can selectively capture Cs+ under excessive competitive ions. Furthermore, they show successful cleanup for actual 137Cs-liquid-wastes generated during industrial production. In particular, adsorbed Cs+ can be firmly immobilized in interlayer spaces of materials due to the highly stable anionic framework. The removal mechanism is attributed to ion exchange between Cs+ and interlayer H+ by multiple characterizations. Study of the structure-function relationship shows that the occurrence of Cs+ ion exchange is closely related to plate-like layered structure. This work develops an efficient all-in-one treatment method for capturing and immobilizing radiocesium by ultra-stable inorganic solid acid materials with low energy consumption and high safety for radionuclide remediation.

Robust and Flexible Thioantimonate Materials for Cs+ Remediation with Distinctive Structural Transformation: A Clear Insight into the Ion-Exchange Mechanism

It is imperative yet challenging to efficiently sequester the ¹³⁷Cs⁺ ion from aqueous solutions because of its highly environmental mobility and extremely high radiotoxicity. The systematical clarification for underlying mechanism of Cs⁺ removal and elution at the molecular level is rare. Here, efficient Cs⁺ capture is achieved by a thioantimonate [MeNH₃]₃Sb₉S₁₅ (FJSM-SbS) with high capacity, fast kinetics, wide pH durability, excellent β and γ radiation resistances, and facile elution. The Cs⁺ removal is not significantly impacted by coexisting Na⁺, K⁺, Ca²⁺, Mg²⁺, and Sr²⁺ ions which is beneficial to the remediation of Cs⁺-contaminated real waters. Importantly, the mechanism is directly illuminated by revealing an unprecedented single-crystal to single-crystal structural transformation upon Cs⁺ uptake and elution processes. The superior Cs⁺ removal results from an unusual synergy from strong affinity of soft S^2- with Cs⁺, easily exchangeable [MeNH₃]⁺ cations, and the flexible and robust framework of FJSM-SbS with open windows as trappers.

Comparison of The Sorption Kinetics of Lead(II) and Zinc(II) on Titanium Phosphate Ion-Exchanger

The treatment of heavy metal-contaminated wastewater is an important action to reduce the negative impacts of industrial wastes on water bodies. This work focuses on the application of a low-cost titanium (IV) phosphate sorbent of TiO(OH)H₂PO₄·2H₂O chemical composition toward lead and zinc ions depending on their concentration and the temperature of the solution. The kinetic studies showed that the values of the rate of intraparticle diffusion and the effective diffusion coefficients for Zn²⁺ were considerably higher than those for Pb²⁺. To explain the difference between the sorption kinetics rates for Pb²⁺ and Zn²⁺, the effective radius and dehydration degree of the adsorbed ions were calculated. The sorbent capability of the lead and zinc ion removal and its excellent efficiency in the presence of a high concentration of calcium ions were demonstrated using simulated mine water. Due to the fast kinetics and the high exchange capacity of titanium phosphate toward divalent ions, this sorbent can be considered as a promising material for the concentration and immobilization of heavy metals into the phosphate matrix.

Peroxide-treated metal-organic framework templated adsorbents for remediation of high level nuclear waste

Remediation of legacy nuclear waste is one of the greatest challenges faced by the US Department of Energy, with projected cleanup efforts requiring over five decades and hundreds of billions of dollars. New materials are necessary to accelerate waste processing, achieving time and financial savings. Herein we report a peroxide treatment to a Ti metal-organic framework (MOF) and related MOF-templated adsorbents. The resulting materials displayed exceptional affinity for Am(III), achieving distribution coefficients in excess of 10⁵ mL/g, and out-performing state-of-the-art benchmarks monosodium titanate (MST) and peroxo-treated modified MST (mMST) for removal of ⁸⁵Sr(II) and ^{239, 240}Pu(IV) from legacy nuclear waste simulant.

Efficient and irreversible capture of strontium ions from aqueous solution using metal–organic frameworks with ion trapping groups

Efficient and irreversible capture of radioactive nuclides is an important environmental protection task when disposing of nuclear wastewater.

One-Step Synthesis of Zeolite Membranes Containing Catalytic Metal Nanoclusters

Metal-loaded zeolitic membranes are promising candidates as catalytic membrane reactors. We report a one-step synthesis method to synthesize zeolite membranes containing metal nanoclusters, that has advantages in comparison to multistep methods such as impregnation and ion exchange. Pure-silica MFI zeolite-Pt hybrid membranes were prepared by hydrothermal synthesis with addition of 3-mercaptopropyl-trimethoxysilane (MPS) and a platinum precursor. Composition analysis and mapping by energy-dispersive X-ray spectroscopy (EDX) reveal that Pt ions/clusters are uniformly distributed along the membrane cross-section. High-magnification scanning transmission electron microscopy (STEM) analysis shows that Pt metal clusters in the hybrid zeolite membrane have a diameter distribution in the range of 0.5-2.0 nm. In contrast, a pure-silica MFI membrane synthesized from an MPS-free solution shows negligible incorporation of Pt metal clusters. To characterize the properties of the hybrid (zeolite/metal) membrane, it was used as a catalytic membrane reactor (CMR) for high-temperature propane dehydrogenation (PDH) at 600 °C and 1 atm. The results indicate that Pt metal clusters formed within the MFI zeolite membrane can serve as effective catalysts for high-temperature PDH reaction along with H2 removal via membrane permeation, thereby increasing both conversion and selectivity in relation to a conventional membrane reactor containing an equivalent amount of packed Pt catalyst in contact with an MFI membrane. The hybrid zeolite-Pt CMR also showed stable conversion and selectivity upon extended high-temperature operation (12 h), indicating that encapsulation in the zeolite allowed thermal stabilization of the Pt nanoclusters and reduced catalyst deactivation.