Highly efficient removal of uranium(VI) from aqueous solutions by poly(acrylic acid-co-acrylamide) hydrogels

One-pot synthesis of brewer's spent grain-supported superabsorbent polymer for highly efficient uranium adsorption from wastewater

High-efficient and fast adsorption of uranium is important to reduce the hazards caused by the uranium contamination of water environment due to the increased human activities. Herein, brewer's spent grain (BSG)-supported superabsorbent polymers (SAP) with different cross-linking densities are prepared as cheap and eco-friendly adsorbents for the first time via one-pot swelling and graft polymerization. A 7 wt% NaOH solution is used to swell BSG before grafting and subsequently neutralize the acrylic acid to control the reaction rate without producing alkaline wastewater. Compared with the traditional methods, swelling improves the grafting density and the utilization of raw materials due to the increased disorder degree of the BSG fibers. This results in the grafting of abundant carboxyl and amide groups onto the BSG backbone, forming a strongly hydrophilic polymer network of the BSG-SAP. Compared with the reference polymers without BSG, BSG-SAP presents higher adsorption capacity and enhanced reusability. The highly cross-linked BSG-SAP (BSG-SAP-H) shows an outstanding adsorption capacity of U(VI) (1465 mg/g at pH₀ = 4.6), a fast adsorption rate (81% of equilibrium adsorption capacity in 15 min), and a high selectivity in the presence of competing ions. Adsorption mechanism studies reveal the involvement of amide groups, a bidentate binding structure between UO₂²⁺ and the carboxyl groups, and a cation exchange between Na⁺ and UO₂²⁺. More importantly, the adsorption capacity of BSG-SAP-H reaches 254.4 mg/g in the fixed-bed column experiment at a low initial concentration (c₀(U) = 30 mg/L) and keeps 80% of the adsorption capacity after four cycles, indicating a great potential for uranium removal from wastewater. This work shows a suitable approach to explore the untreated biomass to prepare SAP with enhanced adsorption performance via a general and low-cost strategy.

Sulfur edge in molybdenum disulfide nanosheets achieves efficient uranium binding and electrocatalytic extraction in seawater

Electrochemical extraction of uranium in seawater provides a promising strategy for the persistent supply of fuel in the nuclear industry. However, current operation voltage for the electrochemical extraction of uranium in seawater generally requires a high applied voltage (∼-5 V). Herein, we constructed S-terminated MoS₂ nanosheets with abundant electrochemically active S-edge sites for efficient binding and reduction of uranium. In 100 ppm of uranium-spiked seawater at an applied voltage of -3 V, the S-terminated MoS₂ nanosheets exhibited a considerable extraction capacity of 1823 mg g^-1. After 30 min electrolysis in 100 mL of real seawater with 100 times concentrated uranium (330 ppb), the extracted uranium (29.5 μg) consumes electricity of 8.7 mW h. Moreover, we concentrated 12 L of real seawater (3.3 ppb) into 20 mL of aqueous solution containing 1752.6 ppb U by adding a reverse potential. In the mechanistic study, we directly observed the uranium clusters and single atoms confined by the S-edge at atomic resolution, which served as the intermediate and accounted for the boosted uranium extraction in seawater.

Elaboration of composite based on the incorporation of marble particles into polymeric framework for the removal of Co(II) and Eu(III)

The incorporation of marble particles into the framework of composite material through the polymerization of acrylic acid (AA) and acrylamide acid (AM) using induced gamma irradiation was performed. The novel poly[AA-AM]-marble composite was characterized by multiple analytical instruments such as: energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) analysis, differential thermal analysis-thermogravimetric analysis (DTA-TGA), Fourier transformer infrared (FTIR), surface area measurements using Brunauer–Emmett–Teller (BET) method and scanning electron microscope (SEM). Radioisotopes of fission (152+154Eu) and activation products (60Co) are the major environmental threats. Sorption of stable isotopes of cobalt and europium onto the synthesized composite material as the sorbent is applied. Sorption kinetics of Eu3+ and Co2+ were computed. The obtained results were analyzed by pseudo-first- and second-order, intraparticle diffusion, and Elovich kinetic models. It is deduced that the pseudo-second-order was more fitted and a chemisorption mechanism was suggested. The sorption capacity for Eu3+ and Co2+ on the prepared composite material was measured at the contact time (2 h) and pH = 4 (for Eu3+), pH = 6 (for Co2+) and it was found to be 91.2 and 13.1 mg/g, respectively. A promising result for the decontamination of both Eu and Co ions was obtained in various aquatic ecosystem applications such as: river water, tap water and groundwater.

Hydrolytically stable foamed HKUST-1@CMC composites realize high-efficient separation of U(VI)

HKUST-1@CMC (HK@CMC) composites that show good acid and alkali resistance and radiation resistance were successfully synthesized by introducing carboxymethyl cellulose (CMC) onto the surface of HKUST-1 using a foaming strategy. For the first time, the composites were explored as efficient adsorbents for U(VI) trapping from aqueous solution, with encouraging results of large adsorption capacity, fast adsorption kinetics, and desirable selectivity toward U(VI) over a series of competing ions. More importantly, a hybrid derivative film was successfully prepared for the dynamic adsorption of U(VI). The results show that ∼90% U(VI) can be removed when 45 mg L-1 U(VI) was passed through the film one time, and the removal percentage is still more than 80% even after four adsorption-desorption cycles, ranking one of the most practical U(VI) scavengers. This work offers new clues for application of the Metal-organic-framework-based materials in the separation of radionuclides from wastewater.

An Ion-Crosslinked Supramolecular Hydrogel for Ultrahigh and Fast Uranium Recovery from Seawater

Large-scale uranium extraction from seawater is a crucial but challenging part of nuclear power generation. In this study, a new ion-crosslinked supramolecular Zn²⁺ -poly(amidoxime) (PAO) hydrogel that can super-efficiently adsorb uranium from seawater is explored. By simply mixing two solutions of zinc chloride and PAO, a supramolecular Zn²⁺ -PAO hydrogel is achieved via the interaction between zinc cations and amidoxime anions. In contrast with existing amidoxime-functionalized hydrogel-based adsorbents having low PAO contents and fiber-based adsorbents with weak hydrophilicity, the PAOs can be directly crosslinked using a small quantity of superhydrophilic zinc ion. Thus, a supramolecular hydrogel is formed, having both a high content of well-dispersed PAOs and good hydrophilicity. Relative to reported adsorbents, this low-cost hydrogel membrane exhibits outstanding uranium adsorption performance, reaching 1188 mg g^-1 of M_U /M_{dry gel} in 32 ppm uranium-spiked water. More importantly, after immersion in natural seawater for only 4 weeks, the uranium extraction capacity of the Zn²⁺ -PAO hydrogel membrane reaches 9.23 mg g^-1 of M_U /M_{dry gel} . This work can provide a general strategy for designing a new type of supramolecular hydrogel, crosslinked by various bivalent/multivalent cation-crosslinkers and even many other superhydrophilic supramolecular crosslinkers, for the high-efficient and massive extraction of uranium from seawater.