Ion-Imprinted Mesoporous Silica for Selective Removal of Uranium from Highly Acidic and Radioactive Effluent

Ultra-High Performance of Hyper-Crosslinked Phosphate-Based Polymer for Uranium and Rare Earth Element Adsorption in Aqueous Solution

In this work, a new type of hyper-crosslinked phosphate-based polymer (HCPP) polymerized by bis(2-methacryloxyethyl)phosphate has been developed for uranium and rare earth element (REE) extraction in an aqueous solution. The influence of the pH value, contact time, initial concentration, temperature, and competing ions on uranium adsorption of HCPP is investigated in detail. HCPP exhibits a maximum uranium adsorption capacity of up to 800 mg g^-1 at pH = 6.0 and excellent selectivity toward uranium adsorption over coexisting ions, because of the high affinity between HCPP and uranium ions and dense phosphate groups on the backbone. It also demonstrates high adsorption performance in both simulated seawater with a high salt concentration and a real nuclear industrial effluent. Besides, the crosslinked network structure of HCPP endows this polymer with high chemical stability and reusability. Furthermore, the adsorption mechanism is probed by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared measurements. It is confirmed that the adsorption of uranium on the adsorbent originates from the interaction between phosphate groups and uranium ions. Meanwhile, HCPP also displays high REE adsorption capacities. This work indicates that the phosphate-based HCPP could be utilized as a promising adsorbent for the effective removal of uranium and REEs from aqueous solution.

A novel ion-imprinted amidoxime-functionalized UHMWPE fiber based on radiation-induced crosslinking for selective adsorption of uranium

A novel uranium-imprinted adsorbent (AO-Imp fiber) was prepared by radiation-induced crosslinking of amidoxime-functionalized ultra-high molecular weight polyethylene fiber (AO fiber). The porous structure was characterized by scanning electron microscopy (SEM) and positron annihilation lifetime (PAL) spectroscopy after ion imprinting. This ion-imprinted fiber exhibited enhanced adsorption selectivity for uranium in the form of both UO2 2- and [UO2(CO3)3]4- in batch experiments. Compared with AO fiber, the adsorption capacity of the AO-Imp(250) fiber for uranium increased from 0.36 mg g-1 to 1.00 mg g-1 in simulated seawater and from 5.02 mg g-1 to 12.03 mg g-1 in simulated acid effluent, while its adsorption capacities for other co-existing metal ions were particularly low. This study provides an approach to prepare ion-imprinted adsorbents without introducing crosslinking reagents, which may be a promising method for uranium extraction.

Size-Selective Separation of Rare Earth Elements Using Functionalized Mesoporous Silica Materials

The separation and preconcentration of rare earth elements (REEs) from mineral concentrates in an economically and environmentally sustainable manner are difficult tasks due to their similar physicochemical properties. Herein, a series of tetradentate phenylenedioxy diamide (PDDA) ligands were synthesized and grafted on large-pore three-dimensional KIT-6 mesoporous silica. In solid-phase extraction, the hybrid sorbents enable a size-selective separation of REEs on the basis of the bite angles of the ligands. In particular, smaller REE³⁺ ions are preferentially extracted by KIT-6-1,2-PDDA, whereas light REEs with larger ionic radius are favored by KIT-6-1,3-PDDA. The exposure of bauxite residue digestion solution containing REEs as well as a number of types of competitive ions (including Th and U) to the sorbents results in selective recovery of target REEs. The possibility of regenerating the mesoporous sorbents through a simple loading-stripping-regeneration process is demonstrated over up to five cycles with no significant loss in REE extraction capacity, suggesting adequate chemical and structural stability of the new sorbent materials.

Petroleum pitch-based porous aromatic frameworks with phosphonate ligand for efficient separation of uranium from radioactive effluents

Porous aromatic frameworks with structural/pore controllability and rigid skeletons present a series of emerging materials for solid phase extraction. However, the complicated monomers or noble metal catalyst, and cumbersome synthetic strategies result in high-cost engineering application of porous aromatic frameworks. Herein, a simple synthetic strategy of porous aromatic frameworks with phosphonate is reported for efficient separation of uranium from radioactive effluents, and petroleum pitch, a low-cost and widely available material, was used as the building block. 4-Vinylbenzylphosphonic acid diethyl ester monomer is introduced to chelate uranium and to improve the aqueous dispersibility of sorbents. The phosphonate functionalized PPAFs take 40 min to achieve adsorption equilibrium, and the maximum sorption capacity reaches 147 mg U/g at pH 1.0. PPAFs exhibit good selectivity over various competing ions and excellent radioresistance in acidic solution. Besides, PPAFs remain almost 100% sorption efficiency and intact structure over 5 sorption-desorption cycles with alkaline eluent. This work not only applies a low-cost material for uranium extraction, but a new idea for the utilization of waste and recycling of resources.

Novel Ion-Imprinted Carbon Material Induced by Hyperaccumulation Pathway for the Selective Capture of Uranium

The development of nuclear energy is significant for resource sustainability. Uranium is the main nuclear fuel, and its effective absorption has captured the attention of researchers. In this study, the green technologies hyperaccumulation effect of the plant and ion-imprinted technology were used to prepare the uranium ion-imprinted hierarchically porous carbon material (II-HPC). At the same time, a nonimprinted hierarchically porous carbon (HPC) was prepared for comparison. The adsorption isotherm was fitted to the Langmuir model and maximum sorption capacity of II-HPC was 503.64 mg g^-1 at 298 K. The kinetic data followed the pseudo-second-order model, indicating a dominant role of chemisorption. Initial studies were performed on a lab-scale simulated continuous-flow system for the adsorption kinetics testing of II-HPC in simulated seawater. The results showed that the amount of uranium adsorbed after 35 days was 0.379 mg g^-1, which determined that II-HPC adsorbent is a potential material for enrichment of U(VI) from the seawater.

Recent Advances in the Separation of Rare Earth Elements Using Mesoporous Hybrid Materials

Over the past decades, the need for rare earth elements (REEs) has increased substantially, mostly because these elements are used as valuable additives in advanced technologies. However, the difference in ionic radius between neighboring REEs is small, which renders an efficient sized-based separation extremely challenging. Among different types of extraction methods, solid-phase extraction (SPE) is a promising candidate, featuring high enrichment factor, rapid adsorption kinetics, reduced solvent consumption and minimized waste generation. The great challenge remains yet to develop highly efficient and selective adsorbents for this process. In this regard, ordered mesoporous materials (OMMs) possess high specific surface area, tunable pore size, large pore volume, as well as stable and interconnected frameworks with active pore surfaces for functionalization. Such features meet the requirements for enhanced adsorbents, not only providing huge reactional interface and large surface capable of accommodating guest species, but also enabling the possibility of ion-specific binding for enrichment and separation purposes. This short personal account summarizes some of the recent advances in the use of porous hybrid materials as selective sorbents for REE separation and purification, with particular attention devoted to ordered mesoporous silica and carbon-based sorbents.

Hydrophilic Multitemplate Molecularly Imprinted Biopolymers Based on a Green Synthesis Strategy for Determination of B-Family Vitamins

A novel green synthesis strategy was proposed for preparation of multitemplate molecularly imprinted biopolymers (mt-MIBP) in aqueous media with less consumption of organic solvents, which were subsequently used as sorbents of ultrasound-assisted dispersive solid-phase extraction (d-SPE) for simultaneous recognition and efficient separation of B-family vitamins in juice samples, followed by high performance liquid chromatography (HPLC) determination. The obtained mt-MIBP was fully characterized by SEM, FT-IR, TEM, and BET. It offered high binding capacity, good selectivity, and fast dynamics toward all the templates. Involved parameters in the d-SPE efficiency such as mt-MIBP mass, sonication time, and eluting/washing solvents' types and volumes were concurrently investigated by central composite design with rapidity and reliability. Under the optimum conditions, the developed mt-MIBP-d-SPE-HPLC method exhibited wide linear range, low limits of detection and quantification (LOQs) within 1.2-5.5 μg L^-1 and 4.0-18.4 μg L^-1, respectively, and appropriate repeatability (relative standard deviation values below 4.2%, n = 4). The high selectivity of this method makes it suitable for successful monitoring of vitamins in juice samples with satisfactory recoveries of 75.8-92.7%, 81.1-92.5%, and 84.7-93.8% for vitamins riboflavin (B₂), nicotinamide (B₃), and pyridoxine (B₆), respectively. The present study implied highly promising perspectives of water-compatible eco-friendly mt-MIBP for highly effective multiresidue analysis in complicated matrixes.

Engineering β-ketoenol structure functionality in hybrid silica as excellent adsorbent material for removal of heavy metals from water

A chelating adsorbent based on the chemical modification of silica by an efficient host able to capture toxic metals, is presented.

Synthesis and radiometric evaluation of diglycolamide functionalized mesoporous silica for the chromatographic separation of actinides Th, Pa and U

Grafting of DGA on mesoporous silica affords a sorbent with the potential to separate U from Pa and Th.

A novel U(vi)-imprinted graphitic carbon nitride composite for the selective and efficient removal of U(vi) from simulated seawater

A high selectivity U(vi)-imprinted g-C₃N₄/β-CD sorbent was synthesized and used for selective removal of U(vi). The interaction mechanism is mainly surface complexation and electrostatic attraction.