Amino-functionalized POSS nanocage-intercalated titanium carbide (Ti3C2Tx) MXene stacks for efficient cesium and strontium radionuclide sequestration

Modification of Ti3C2Tx nanostructure with KH2PO4 and chitosan for effective removal of strontium from nuclear waste

Nanostructure titanium carbide MXene (Ti3C2Tx) was modified with KH2PO4 and chitosan to effectively remove strontium from nuclear wastewater. Nuclear waste includes radionuclides of uranium, thorium, strontium, and cesium, which are classified depending on the concentration of radionuclides. Nuclear waste with a high strontium concentration is the production waste of radiopharmaceutical production centers. Ti3C2Tx was synthesized from Ti3AlC2 using HF40% and HF in situ (MILD-Ti3C2Tx) in 24 h at 313.15 and 333.15 K. Morphology, structure, and functional groups were investigated using the XRD, SEM, EDS, FTIR, and BET analyses. The Sr(II)'s adsorption capacity on Ti3C2Tx-HF and Ti3C2Tx-HF in situ was obtained as 61.9 and 253.5 mg g-1, respectively (temperature, 298.15 K; pH, 7.00; contact time, 180 min; and Sr(II) concentration, 150 mg l-1). Ti3C2Tx-HF in situ showed fourfold adsorption due to more hydroxyl functional groups and larger interlayer spacing. Ti3C2Tx was modified with KH2PO4 and chitosan to investigate the mechanism of change of Sr(II)'s adsorption capacity, which increased to 370 and 284 mg g-1, respectively. The structural results of modified Ti3C2Tx showed that the surface functional groups increased when modified with chitosan. In addition, modification with KH2PO4, through encapsulating large amounts of KH2PO4 between Ti3C2Tx layers, increased the possibility of Sr(II) diffusion between layers and electrochemical interactions with hydroxyl groups, and thus, increased its adsorption. Some experiments were designed to investigate the effect of parameters like initial concentration of Sr(II), contact time, temperature, and pH solution, as well as modified- and unmodified-Ti3C2Tx on adsorbent. The results revealed that the adsorption process of Sr(II) with pristine and modified-Ti3C2Tx follows pseudo-second-order kinetics and Freundlich heterogeneous isotherm model. Freundlich model isotherm indicates the presence of various functional groups on the surface and between the pristine and modified Ti3C2Tx layers. Electrostatic reactions and intra-sphere complexation were the two dominant mechanisms of the adsorption process.

Effective radioactive strontium removal using lithium titanate decorated Ti3C2Tx MXene/polyacrylonitrile beads

A lithium titanate-decorated Ti3C2Tx MXene (LTO-MX) composite was synthesized through etching and alkali processes, and subsequently immobilized using polyacrylonitrile (PAN) polymer via a phase inversion method. In the batch study, the strontium adsorption behavior followed the Redlich-Peterson isotherm and the pseudo-second-order kinetic models. The maximum adsorption capacity for strontium reached 24.05 mg/g. Furthermore, a continuous fixed-bed column study was performed using the LTO-MX PAN beads to remove strontium from aqueous solutions. The dynamic behavior of column adsorption was examined under various operating parameters such as initial strontium concentration, flow rate, and bed height. Dynamic modeling was employed to describe adsorption breakthrough properties based on these experimental data. Both the Thomas and Yoon-Nelson models accurately simulated the breakthrough curves. The proposed mechanisms for strontium adsorption included encapsulation, electrostatic attraction, cation exchange, and surface complexation. These results demonstrate the effectiveness of LTO-MX PAN beads as adsorbents for the continuous removal of strontium from radioactive wastewater.

NH2-MXene/OXG nanocomposite hydrogel with efficient photothermal antibacterial activity for potentially removing biofilms

The adhesion of bacteria to the surface leads to formation of biofilms causing numerous infection problems in implanting medical devices or interventional therapy. Traditional treatment for such problems is generally to administrate patients with antibiotics or antifungal agent. Alternatively, devices are taken out of the body to mechanically destroy the biofilm and re-used by surgery. In this study, a straightforward method was developed to remove biofilms using a MXene-based photothermal hydrogel. The hydrogel consists of dynamic crosslinking network formed by Schiff-base reaction between aldehyde-containing xyloglucan (OXG) and amine-containing MXene (NH2-MXene), which showed efficient killing of both gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) bacteria upon near-infrared (NIR) laser irradiation. The NH2-MXene/OXG nanocomposite hydrogel showed a high photothermal antibacterial efficiency and stable photothermal conversion, demonstrated by efficient removal of biofilms ex vivo.

Efficient sequestration of cesium ions using phosphoric acid-modified activated carbon fibers from aqueous solutions

In this study, acid-modified activated carbon fibers (ACF-Ps) were synthesized by phosphorylation. Three different types of ACF-based adsorbents functionalized with PO43-, P2O74-, or P3O105- ions, namely, ACF-P1, ACF-P2, and ACF-P3, were prepared by phosphorylating ACF with trisodium phosphate (Na3PO4), sodium dihydrogen pyrophosphate (Na2H2P2O5), and sodium tripolyphosphate (Na5P3O10), respectively, and utilized as adsorbents to remove cesium ions (Cs+) from aqueous solutions. Among the tested adsorbents, ACF-P3 exhibited the highest Cs+ adsorption capacity of 37.59 mg g-1 at 25 °C and pH 7 which is higher than that of ACF (5.634 mg g-1), ACF-P1 (19.38 mg g-1), and ACF-P2 (30.12 mg g-1) under the same experimental conditions. More importantly, the Cs+ removal efficiencies of ACF-P3 (82.90%), ACF-P2 (66.2%), ACF-P1 (34.2%) were 29.3-, 23.4-, and 12.11-fold higher than that of un-treated ACF (2.83%). The results suggested that the phosphorylation with Na5P3O10 is highly suitable for Cs+ adsorption which effectively functionalizes ACF with a greater number of phosphate functional groups. Adsorption and kinetic data well-fitted the Langmuir isotherm and pseudo-second-order model, respectively, which indicated the monolayer adsorption of Cs+ onto ACF-P1, ACF-P2, and ACF-P3 which were largely controlled by chemisorption. Overall, phosphoric acids containing different phosphate-based polyanions (PO43-, P2O74-, or P3O105-) enriched -OH and/or -COOH surface functional groups of ACF in addition to P-containing surface groups (PO, C-P-O, C-O-P, and P-O) and facilitated the Cs+ adsorption through surface complexation and electrostatic interactions.

Recent Advancement in Emerging MXene-Based Photocatalytic Membrane for Revolutionizing Wastewater Treatment

MXene-based photocatalytic membranes provide significant benefits for wastewater treatment by effectively combining membrane separation and photocatalytic degradation processes. MXene represents a pioneering 2D photocatalyst with a variable elemental composition, substantial surface area, abundant surface terminations, and exceptional photoelectric performance, offering significant advantages in producing high-performance photocatalytic membranes. In this review, an in-depth overview of the latest scientific progress in MXene-based photocatalytic membranes is provided. Initially, a brief introduction to the structure and photocatalytic capabilities of MXene is provided, highlighting their pivotal role in promoting the photocatalytic process. Subsequently, in pursuit of the optimal MXene-based photocatalytic membrane, critical factors such as the morphology, hydrophilicity, and stability of MXenes are meticulously taken into account. Various preparation strategies for MXene-based photocatalytic membranes, including blending, vacuum filtration, and dip coating, are also discussed. Furthermore, the application and mechanism of MXene-based photocatalytic membranes in micropollutant removal, oil-water separation, and antibacterial are examined. Lastly, the challenges in the development and practical application of MXene-based photocatalytic membranes, as well as their future research direction are delineated.

Recent strategies, progress, and prospects of two-dimensional metal carbides (MXenes) materials in wastewater purification: A review

With the rapid development of industrialization, water pollution directly leads to the serious shortage of fresh water. As reported by the World Water Council, nearly 3.8 billion people will face water scarcity by 2030. Therefore, developing advanced nanomaterials to realize wastewater purification is a major challenge. Two-dimensional (2D) transition metal carbides (MXenes), as the emerging 2D layered nanomaterials, have been investigated for the applications of water purification treatment since first reported in 2011. Over 40 different MXenes have been developed for environmental remediation, and dozens more structures and properties are theoretically predicted. Here, we review the advances from the aspects of synthesis strategies for MXenes, purification mechanism, and their applications in wastewater treatment processes. The major points are 1) the synthesis and modification approaches for MXenes such as multi-layered stacked MXenes and delaminated MXenes 2) a discussion of current water remediation over MXene-based materials, 3) a brief introduction for removal behaviors and deep interaction mechanisms, 4) optimization strategies and key points for boosting the remediation performance of MXenes.

MXene/AgNW composite material for selective and efficient removal of radioactive cesium and iodine from water

Toxic fission products, such as cesium (137Cs) and iodine (129I) are of great concern because of their long half-lives and high solubility in water. The simultaneous removal of Cs and I using a single adsorbent is an area of increasing interest. In this study, MXene/silver nanowire (AgNW) composite was synthesized through physical mixing and employed for simultaneous removal of iodide (I-) and cesium (Cs+) ions from contaminated water. The MXene/AgNW composite demonstrated excellent adsorption capacities of 84.70 and 26.22 mg/g for I- and Cs+, respectively. The experimental data supported the hypothesis of multilayer adsorption of Cs+ owing to the inter-lamellar structures and the presence of heterogeneous adsorption sites in MXene. The interaction between I- and the AgNW involved chemisorption followed by monolayer adsorption. MXene/AgNW composite material exhibited promising results in the presence of competitive ions under extreme pH conditions. Thus, synthesized composite materials holds promising potential as an adsorbent for the remediation of radioactive liquid waste.

Decorating Channel Walls in Metal-Organic Frameworks with Crown Ethers for Efficient and Selective Separation of Radioactive Strontium(II)

Nuclear accidents and the improper disposal of nuclear wastes have led to serious environmental radioactive pollutions. The rational design of adsorbents for the highly efficient separation of strontium(II) is essential in treating nuclear waste and recovering radioactive strontium resources. Metal-organic frameworks (MOFs) are potential materials for the separation of aqueous metal ions owing to their designable structure and tunable functionality. Herein, a novel 3D MOF material MOF-18Cr6, in which 1D channels are formed using 18-crown-6-ether-containing ligands as channel walls, is fabricated for strontium(II) separation. In contrast to traditional MOFs designed by grafting functional groups in the framework pores, MOF-18Cr6 possesses regular 18-crown-6-ether cavities on the channel walls, which not only can transport and intake strontium(II) via the channels, but also prevent blockage of the channels after the binding of strontium(II). Consequently, the functional sites are fully utilized to achieve a high strontium(II) removal rate of 99.73 % in simulated nuclear wastewater. This study fabricates a highly promising adsorbent for the separation of aqueous radioactive strontium(II), and more importantly, can provide a new strategy for the rational design of high-performance MOF adsorbents for separating target substances from complex aqueous environments.

Application of MXene for remediation of low-level radioactive aqueous solutions contaminated with 133Ba and 137Cs

MXene is an innovative multilayered material that has been prepared by an acid-salt (HCl + NH4F) etching route and tested for the removal of 133Ba and 137Cs in radioactive conditions for the first time. MXene has exhibited high uptake capacity of about 154.9 and 121.5 mg g-1 for 133Ba and 137Cs, respectively, in 0.01 mol L-1 solution and using 5 g L-1 of adsorbent at natural pH.

The latest research trends in the removal of cesium from radioactive wastewater: A review based on data-driven and visual analysis

The widespread adoption of nuclear energy has increased the amount of radioactive cesium (Cs) that is discharged into waste streams, which can have environmental risks. In this paper, we provide a comprehensive summary of current advances in aqueous Cs removal by employing a bibliometric analysis. We collected 1580 articles related to aqueous Cs treatment that were published on the Web of Science database between 2012 and 2022. By applying bibliometric analysis combined with network analysis, we revealed the research distribution, knowledge base, research hotspots, and cutting-edge technologies in the field of aqueous Cs removal. Our findings indicate that China, Japan, and South Korea are the most productive countries with respect to Cs removal research. In addition, both historic events and environmental threats might have contributed to research in Asian countries having a higher focus on Cs removal as well as strong international cooperation between Asian countries. A detailed keyword analysis reveals the main knowledge base for aqueous Cs removal and highlights the potential of the adsorption-based method for treating Cs contamination. Furthermore, the results reveal that exploration of functional materials is a popular research topic in the field of Cs removal. Since 2012, novel materials, including Prussian blue, graphene oxide, hydrogel and nanocomposites, have been widely investigated because of their high capacity for Cs removal. On the basis of the detailed information, we report the latest research trends on aqueous Cs removal, and propose future research directions and describe the challenges related to effective Cs treatment. This scientometric review provides insights into current research hotspots and cutting-edge trends in addition to contributing to the development of this crucial research field.

Bifunctional Amine- and Thiol-Modified Ti3C2Tx MXene for Trace Detection of Heavy Metals

Surface functionalization of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, also known as MXenes, is a powerful approach for modification of their physical and chemical properties for new applications. In this study, we demonstrate the synthesis of a bifunctional Ti₃C₂T_x MXene modified with amine and thiol groups through a facile condensation reaction. We successfully employed the resulting NH₂/SH-Ti₃C₂T_x MXene as a solid phase in the ultrasonic-assisted dispersive micro solid-phase extraction (d-μ-SPE) method for the analytical determination of heavy metals at trace levels in food and soil samples. The prepared NH₂/SH-Ti₃C₂T_x MXene showed remarkable performance in the ultrasonic-assisted d-μ-SPE method with limits of detection of 0.12 and 2.30 ng mL^-1, with linear dynamic ranges of 0.50-90 μg L^-1 and 10-120 μg L^-1 for cadmium (Cd²⁺) and lead (Pb²⁺) ions, respectively. Furthermore, the extraction efficiencies were greater than 97%, with a relative standard deviation of less than 3% for five separate batch experiments in the determination of 5.0 μg L^-1 of Cd²⁺ and Pb²⁺. This study shows that NH₂/SH-Ti₃C₂T_x can be used as a simple, rapid, reliable, selective, and sensitive material in the d-μ-SPE method for the trace determination of Cd²⁺ and Pb²⁺ in soil and agricultural products. This study demonstrates the utility of MXenes for analytical chemistry and suggests that further advances in methods for the functionalization of MXenes can open new applications for these already exciting materials.

Highly selective and easily regenerated porous fibrous composite of PSF-Na2.1Ni0.05Sn2.95S7 for the sustainable removal of cesium from wastewater

The removal of ¹³⁷Cs from radioactive wastewater remains a huge challenge due to the interference of many coexisting ions. Several tin chalcogenides (X₂Sn₃Y₇, XNa, K; YTe, Se, S) were synthesized and screened for highly selective cesium removal from radioactive wastewater. It was found that Na₂Sn₃S₇ showed the best adsorption performance for low cesium concentrations. Especially after nickel doping, the adsorption capacity and thermal stability of the adsorbent were significantly enhanced. Its maximum adsorption capacity reached 436.72 mg·g^-1 within only 5 min and adsorption performance kept active in the pH range of 2-12. After being coated with a porous polysulfone (PSF) fiber, the developed PSF-Na_2.1Ni_0.05Sn_2.95S₇ was applied to natural complex water with cesium concentration of 17.58 mg·L^-1. The separation factors between Cs⁺ and competitive ions ranged from 625.21 to 13123.21. It is noteworthy that NaNO₃ was an efficient regenerating agent and can be easily separated from the CsNO₃ mixture for cyclic utilization. Remarkably, only 45 min in each cycle of adsorption and desorption toward cesium was realized, and the adsorption properties hardly decreased even after 50 consecutive cycles. The above advantages make the proposed material an excellent candidate for efficient Cs⁺ removal and enrichment from wastewater.