Recovering Rare Earth Elements from Aqueous Solution with Porous Amine-Epoxy Networks

A lanmodulin-based fluorescent assay for the rapid and sensitive detection of rare earth elements

Sensitive and rapid detection methods for rare earth elements (REEs), including lanthanides (Lns), will facilitate the mining and recovery of these elements. Here, we innovated a rapid, highly selective and sensitive fluorescence detection method for Lns, based on Hans-Lanmodulin, a newly discovered protein with high selectivity and binding affinity for rare earth elements. By labelling the fluorescein moiety FITC onto Hans-Lanmodulin, named as FITC-Hans-LanM. When rare earth ions are present in solution, FITC-Hans-LanM will specifically bind rare earth ions undergoing a conformational change from a disordered state to a dimer, in which the FITC molecules come close to each other, resulting in decreasing fluorescence intensity or even quenching. The assay was responsive to light, medium and heavy rare earth ions. The fluorescence signal has a good linear relationship with Nd3+ concentration in the range of 1-20 nM. The detection limit of the method was 0.512 nM, within 1 min. This method could become a useful technique for the detection and quantification of rare earth elements in environmental and industrial samples.

Recent Developments in Functional Polymers via the Kabachnik-Fields Reaction: The State of the Art

Recently, multicomponent reactions (MCRs) have attracted much attention in polymer synthesis. As one of the most well-known MCRs, the Kabachnik-Fields (KF) reaction has been widely used in the development of new functional polymers. The KF reaction can efficiently introduce functional groups into polymer structures; thus, polymers prepared via the KF reaction have unique α-aminophosphonates and show important bioactivity, metal chelating abilities, and flame-retardant properties. In this mini-review, we mainly summarize the latest advances in the KF reaction to synthesize functional polymers for the preparation of heavy metal adsorbents, multifunctional hydrogels, flame retardants, and bioimaging probes. We also discuss some emerging applications of functional polymers prepared by means of the KF reaction. Finally, we put forward our perspectives on the further development of the KF reaction in polymer chemistry.

High-resolution temporal monitoring of rare earth elements in acidic drainages from an abandoned sulphide mine (iberian pyrite belt, Spain)

Rare earth elements (REE) are strategic elements due to their economic importance. However, the studies dedicated to the distribution and behaviour of REE in aquatic systems have been scarce until a few decades ago. This work studies the seasonal variations of REE concentrations in acid mine drainage (AMD) affected water courses and the factors controlling their mobility under different hydrological conditions. To address this issue, a high-resolution sampling was performed for two years in selected sampling sites. REE concentrations were very high (median values of 2.7-3.4 mg/L, maximum of 7.0 mg/L). These values are several orders of magnitude higher than those found in natural waters, highlighting the importance of AMD processes on the release of REE to the hydrosphere. No good correlations were found between pH and REE concentration, while REE correlated positively (r Spearman coefficient of 0.78-0.94) with EC and negatively (r -0.88 to -0.90) with discharge in AMD-affected streams. A conservative behaviour of REE was observed due to the strongly acidic conditions observed in the study area. The waters also showed an enrichment in MREEs over LREEs and HREEs (mean values of GdN/LaN>1.8 and YbN/GdN < 0.7), typical of AMD waters. An asymmetry in the content of LREE and HREE was observed in AMD samples studied, which could be explained by the preferential dissolution of LREE or HREE-enriched minerals within each waste heaps. Multivariate analysis suggests the influence of Mn-rich minerals existent in the study area as a potential source of LREE.

Nitrogen-Rich Porous Organic Polymers from an Irreversible Amine-Epoxy Reaction for Pd Nanocatalyst Carrier

Nitrogen-rich porous organic polymers were fabricated through a nonreversible ring-opening reaction from polyamines and polyepoxides (PAEs). The epoxide groups reacted with both primary and secondary amines provided by the polyamines at different epoxide/amine ratios with polyethylene glycol as the solvent to form the porous materials. Fourier-transform infrared spectroscopy confirmed the occurrence of ring opening between the polyamines and polyepoxides. The porous structure of the materials was confirmed through N₂ adsorption-desorption data and scanning electron microscopy images. The polymers were found to possess both crystalline and noncrystalline structures, as evidenced by X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) results. The HR-TEM images revealed a thin, sheet-like layered structure with ordered orientations, and the lattice fringe spacing measured from these images was consistent with the interlayer of the PAEs. Additionally, the selected area electron diffraction pattern indicated that the PAEs contained a hexagonal crystal structure. The Pd catalyst was fabricated in situ onto the PAEs support by the NaBH₄ reduction of the Au precursor, and the size of the nano-Pd was about 6.9 nm. The high nitrogen content of the polymer backbone combined with Pd noble nanometals resulted in excellent catalytic performance in the reduction of 4-nitrophenol to 4-aminophenol.

Critical review of functionalized silica sorbent strategies for selective extraction of rare earth elements from acid mine drainage

The ubiquitous and growing global reliance on rare earth elements (REEs) for modern technology and the need for reliable domestic sources underscore the rising trend in REE-related research. Adsorption-based methods for REE recovery from liquid waste sources are well-positioned to compete with those of solvent extraction, both because of their expected lower negative environmental impact and simpler process operations. Functionalized silica represents a rising category of low cost and stable sorbents for heavy metal and REE recovery. These materials have collectively achieved high capacity and/or high selective removal of REEs from ideal solutions and synthetic or real coal wastewater and other leachate sources. These sorbents are competitive with conventional materials, such as ion exchange resins, activated carbon; and novel polymeric materials like ion-imprinted particles and metal organic frameworks (MOFs). This critical review first presents a data mining analysis for rare earth element recovery publications indexed in Web of science, highlighting changes in REE recovery research foci and confirming the sharply growing interest in functionalized silica sorbents. A detailed examination of sorbent formulation and operation strategies to selectively separate heavy (HREE), middle (MREE), and light (LREE) REEs from the aqueous sources is presented. Selectivity values for sorbents were largely calculated from available figure data and gauged the success of the associated strategies, primarily: (1) silane-grafted ligands, (2) impregnated ligands, and (3) bottom-up ligand/silica hybrids. These were often accompanied by successful co-strategies, especially bite angle control, site saturation, and selective REE elution. Recognizing the need to remove competing fouling metals to achieve purified REE "baskets," we highlight techniques for eliminating these species from acid mine drainage (AMD) and suggest a novel adsorption-based process for purified REE extraction that could be adapted to different water systems.

Highly efficient recovery of heavy rare earth elements by using an amino-functionalized magnetic graphene oxide with acid and base resistance

In the application of various magnetic materials for water treatment, control of surface resistance to acid and alkali corrosion remains largely overlooked, which could greatly extend their service life. We herein prepare amino grafted magnetic graphene oxide composites using a simple one-step cross-link reaction between the graphene oxide and magnetic Fe₃O₄/C nanoparticles. The as-prepared magnetic graphene oxide composites have long-term stability under acid and alkali solutions and shows an excellent performance in removing Ho(III), a representative rare earth element (REE) from water. The observed adsorption capacity of 72.1 mg Ho(III)/g exceeded that of most magnetic materials previously reported. Regeneration of the magnetic composites was realized in acid and alkali solutions but their structural integrity and physicochemical properties retained even after 18 adsorption-desorption cycles. The current adsorbent also shows excellent adsorption performance for other heavy REEs, such as Er(III), Eu(III), Lu(III), Tm(III), Y(III) and Yb(III). This work can provide a new strategy for constructing an acid and base resistance magnetic graphene oxide for the high-efficient recovery of heavy REEs from aqueous solution.

Poly(β-hydroxyl amine)s: Valuable Building Blocks for Supramolecular Elastomers with Tunable Mechanical Performance and Superior Healing Capacity

Supramolecular elastomers integrated with high mechanical toughness and excellent self-healing ability offer attractive applications in various fields such as biomedical materials and wearable electronics. However, the multistep preparation process for creating functional polymer precursors and the expensive stock materials required are two factors that limit the widespread use of supramolecular elastomers. Herein, for the first time, poly(β-hydroxyl amine)s generated by amine-epoxy polymerization were used in the development of supramolecular polymer materials. Based on the novel silicon-containing poly(β-hydroxyl amine)s synthesized by the polymerization between 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 3-amino-1,2-propanediol, dually cross-linked supramolecular elastomers with both hydrogen bonding and metal coordination were achieved, displaying adjustable mechanical properties with the tensile strength varying from 0.70 MPa to 2.52 MPa, respectively. Thanks to the dynamic nature of the supramolecular interactions, these elastomers exhibited favorable hot-pressing reprocessability and excellent self-healing performance, with the healing efficiency reaching up to 98% at 60 °C for 48 h. Potential applications for photoluminescent materials and flexible electronic devices were demonstrated. We believe that its simplicity of synthesis, adjustable mechanical properties, and robust self-healing capacities bode well for future applications of this new supramolecular elastomer.

Graphene oxide (GO)-based nanosheets with combined chemo/photothermal/photodynamic therapy to overcome gastric cancer (GC) paclitaxel resistance by reducing mitochondria-derived adenosine-triphosphate (ATP)

BACKGROUND

Paclitaxel (PTX) has been suggested to be a promising front-line drug for gastric cancer (GC), while P-glycoprotein (P-gp) could lead to drug resistance by pumping PTX out of GC cells. Consequently, it might be a hopeful way to combat drug resistance by inhibiting the out-pumping function of P-gp.

RESULTS

In this study, we developed a drug delivery system incorporating PTX onto polyethylene glycol (PEG)-modified and oxidized sodium alginate (OSA)-functionalized graphene oxide (GO) nanosheets (NSs), called PTX@GO-PEG-OSA. Owing to pH/thermal-sensitive drug release properties, PTX@GO-PEG-OSA could induced more obvious antitumor effects on GC, compared to free PTX. With near infrared (NIR)-irradiation, PTX@GO-PEG-OSA could generate excessive reactive oxygen species (ROS), attack mitochondrial respiratory chain complex enzyme, reduce adenosine-triphosphate (ATP) supplement for P-gp, and effectively inhibit P-gp's efflux pump function. Since that, PTX@GO-PEG-OSA achieved better therapeutic effect on PTX-resistant GC without evident toxicity.

CONCLUSIONS

In conclusion, PTX@GO-PEG-OSA could serve as a desirable strategy to reverse PTX's resistance, combined with chemo/photothermal/photodynamic therapy.

Understanding Selectivity of Mesoporous Silica-Grafted Diglycolamide-Type Ligands in the Solid-Phase Extraction of Rare Earths

Rare earth elements (REEs) and their compounds are essential for rapidly developing modern technologies. These materials are especially critical in the area of green/sustainable energy; however, only very high-purity fractions are appropriate for these applications. Yet, achieving efficient REE separation and purification in an economically and environmentally effective way remains a challenge. Moreover, current extraction technologies often generate large amounts of undesirable wastes. In that perspective, the development of selective, reusable, and extremely efficient sorbents is needed. Among numerous ligands used in the liquid-liquid extraction (LLE) process, the diglycolamide-based (DGA) ligands play a leading role. Although these ligands display notable extraction performance in the liquid phase, their extractive chemistry is not widely studied when such ligands are tethered to a solid support. A detailed understanding of the relationship between chemical structure and function (i.e., extraction selectivity) at the molecular level is still missing although it is a key factor for the development of advanced sorbents with tailored selectivity. Herein, a series of functionalized mesoporous silica (KIT-6) solid phases were investigated as sorbents for the selective extraction of REEs. To better understand the extraction behavior of these sorbents, different spectroscopic techniques (solid-state NMR, X-ray photoelectron spectroscopy, XPS, and Fourier transform infrared spectroscopy, FT-IR) were implemented. The obtained spectroscopic results provide useful insights into the chemical environment and reactivity of the chelating ligand anchored on the KIT-6 support. Furthermore, it can be suggested that depending on the extracted metal and/or structure of the ligand and its attachment to KIT-6, different functional groups (i.e., C═O, N-H, or silanols) act as the main adsorption centers and preferentially capture targeted elements, which in turn may be associated with the different selectivity of the synthesized sorbents. Thus, by determining how metals interact with different supports, we aim to better understand the solid-phase extraction process of hybrid (organo)silica sorbents and design better extraction materials.

Rare earth elements in a historical mining district (south-west Spain): Hydrogeochemical behaviour and seasonal variability

This work deals with the distribution of rare earth elements (REE) in the abandoned Tharsis mines under different hydrological conditions. High concentrations of REE were observed; mean value of 1747 μg/L. The highest concentrations of REE were recorded during the dry period (DP, mean of 2220 μg/L) due to high evaporation and strong water-rock interactions. However, some sampling points showed the highest REE concentrations during the wet period (WP) due to the washing out of large dumps during intense rainfall. The concentration of REE shows a positive correlation with electrical conductivity (EC) and a negative correlation with pH because more acidic conditions enhance dissolution of minerals. However, the highest concentrations of REE occurred in samples with intermediate levels of metal pollution and EC values. The highest correlations of middle REE (MREE) and heavy REE (HREE) occurred with elements related to hydrothermal mineralisation of Mn and Ni, associated with sulphide deposits. The normalised patterns of the AMD sources showed an enrichment of MREE over light REE (LREE) and HREE in all samples. The use of REE patterns as geochemical tracers confirmed the conservative behaviour of REE in the fluvial network, that is, they are not affected by the precipitation of mineral phases. The quantification of REE released from AMD sources to water bodies reveals that, although the highest concentrations occur during the DP, the main load of REE occurs during the WP, due to the highest discharges, with 6.62 kg/day of LREE, 1.12 kg/day of MREE, and 0.54 kg/day of HREE.

Ultrapermeable Organic Solvent Nanofiltration Membranes with Precisely Tailored Support Layers Fabricated Using Thin-Film Liftoff

Thin-film composite (TFC) membranes are favored for precise molecular sieving in liquid-phase separations; they possess high permeability due to the minimal thickness of the active layer and the high porosity of the support layer. However, current TFC membrane fabrication techniques are limited by the available materials for the selective layer and do not demonstrate the level of structural control needed to substantially advance organic solvent nanofiltration (OSN) membrane technology. In this work, we employ the newly developed thin-film lift-off (T-FLO) technique to fabricate polybenzimidazole (PBI) TFC membranes with porous support layers uniquely tailored to OSN. The drop-cast dense PBI selective layers endow the membranes with an almost complete rejection of common small dye molecules. The polymeric support layer is optimized by a combinatorial approach using four different monomers that alter the cross-linking density and polymer chain flexibility of the final composite. These two properties substantially affect the porogen holding capacity of the reticular polymer network, leading to the formation of different macropore structures. With a 150 nm thick PBI selective layer and fine-tuning of the support layer, the resulting membrane achieves stable and superior permeance of 14.0, 11.7, 16.4, 11.4, 17.1, and 19.7 L m^-2 h^-1 bar^-1 for water, ethanol, methanol, isopropanol, tetrahydrofuran (THF), and acetonitrile, respectively.

Selective Recovery of Rare Earth Elements from Coal Fly Ash Leachates Using Liquid Membrane Processes

Coal combustion residues and other geological waste materials have been proposed as a resource for rare earth elements (REEs, herein defined as the 14 stable lanthanides, yttrium, and scandium). The extraction of REEs from residues often generate acidified leachates that require highly selective separation methods to recover the REEs from other major soluble ions in the leachates. Here, we studied two liquid membrane processes (liquid emulsion membranes, LEM, and supported liquid membranes, SLM) and compared them to standard solvent extraction techniques for selective recovery and concentration of REEs from a leachate of coal fly ash. All separation methods involved an organic solution of di(2-ethylhexyl)phosphoric acid dissolved in kerosene or mineral oil and an acid strippant solution of 5 M nitric acid for the liquid-based separations. The LEM configuration, which separated REEs by immersing an acid-in-oil emulsion in the ash leachate, resulted in similar recovery percentages of individual REEs as the conventional solvent extraction approach. The recovery of REEs in the SLM configuration, which involved the impregnation of the solvent in a hydrophobic membrane, was slower than the LEM process. However, the SLM process was notably more selective for the heavy (and higher value) REEs, while the conventional extraction and LEM processes were more selective for the light REEs. A flux-based model of the extraction processes suggested that recovery rates were limited by REE affinity for the solvent chelator in the SLM, while the rates of REEs separation via LEM were limited by diffusive mass transfer across the liquid membrane. Altogether, these results help to identify specific steps in the recovery process that future work should target in the development of scalable liquid membrane separations for REE recovery.

A critical review on remediation, reuse, and resource recovery from acid mine drainage

Acid mine drainage (AMD) is a global environmental issue. Conventionally, a number of active and passive remediation approaches are applied to treat and manage AMD. Case studies on remediation approaches applied in actual mining sites such as lime neutralization, bioremediation, wetlands and permeable reactive barriers provide an outlook on actual long-term implications of AMD remediation. Hence, in spite of available remediation approaches, AMD treatment remains a challenge. The need for sustainable AMD treatment approaches has led to much focus on water reuse and resource recovery. This review underscores (i) characteristics and implication of AMD, (ii) remediation approaches in mining sites, (iii) alternative treatment technologies for water reuse, and (iv) resource recovery. Specifically, the role of membrane processes and alternative treatment technologies to produce water for reuse from AMD is highlighted. Although membrane processes are favorable for water reuse, they cannot achieve resource recovery, specifically selective valuable metal recovery. The approach of integrated membrane and conventional treatment processes are especially promising for attaining both water reuse and recovery of resources such as sulfuric acid, metals and rare earth elements. Overall, this review provides insights in establishing reuse and resource recovery as the holistic approach towards sustainable AMD treatment. Finally, integrated technologies that deserve in depth future exploration is highlighted.

Preparation of diglycolamide polymer modified silica and its application as adsorbent for rare earth ions

Three novel diglycolamide monomers were synthesized and polymerized on silica. The diglycolamide polymer grafted silica were used as adsorbents for rare earth ions. The effects of acid concentration, structure of monomer, initial solution concentration, contact time and coexisting ions on adsorption of rare earth ions were investigated in detail. It was shown that the adsorption capacity increased with increasing acid concentration. Three adsorbents exhibited selectivity for middle and heavy rare earth over light rare earth in different extent. The adsorbent prepared from the monomer having the largest alkyl substituent showed the lowest adsorption capacity but the highest selectivity for different rare earth elements (REEs). Adsorption data were well fitted to the Langmuir isotherm and pseudo-second-order models. The presence of high concentrations (100 fold) of coexisting metal ions, K(I), Cr(II), Cu(II) or Fe(III), does not decrease the adsorption for rare earth ions seriously.

Green separation of rare earth elements by valence-selective crystallization of MOFs

A green valence-selective crystallization strategy of MOFs is developed for the precise separation of Ce element at room temperature.

Novel Rapid Screening of Basic Immobilized Amine Sorbent/Catalyst Water Stability by a UV/Vis/Cu2+ Technique

Time-consuming thermogravimetric analysis (TGA) decomposition study is a typical practice to assess the stability of fresh and water-treated basic immobilized amine sorbents (BIAS)/catalysts. This work presents a faster and more precise spectroscopic UV/Vis/Cu²⁺ sorbent screening technique that quantifies aqueous amines washed from the BIAS by using UV-active amine/Cu²⁺ complexes. Six BIAS-based catalysts, containing different amine species and a crosslinker within silica, were treated with ultrapure water and then analyzed for their CO₂ capture performance and amine leach resistance/stability by using TGA (catalysts, approximately 4 h) and UV/Vis/Cu²⁺ techniques (wash solution, few minutes). A comparative analysis revealed that directly quantifying washed amines with UV/Vis/Cu²⁺ is 9-127 times more precise than indirect testing of the sorbents by TGA. Similar trends in the H₂ O stability profiles of the catalysts [organic content retained values (OCR)] were reported by both analysis methods, allowing UV/Vis/Cu²⁺ to replace TGA for quantifying unstable leached amines. The UV/Vis/Cu²⁺ OCR results could be used to predict the CO₂ -capture stability profile of the sorbents, confirming the reliability of this technique to rapidly screen catalyst stability and performance.

Dissimilar Materials Bonding Using Epoxy Monolith

The epoxy monolith with a highly porous structure is fabricated by the thermal curing of 2,2-bis(4-glycidyloxyphenyl)propane and 4,4'-methylenebis(cyclohexylamine) in the presence of poly(ethylene glycol) as the porogen via polymerization-induced phase separation. In this study, we demonstrated a new type of dissimilar material bonding method for various polymers and metals coated with the epoxy monolith. On the basis of scanning electron microscopy (SEM) observations, the pore size and number of epoxy monoliths were evaluated to be 1.1-114 μm and 8.7-48 200 mm^-2, respectively, depending on the ratio of the epoxy resin and cross-linking agent used for the monolith fabrication. Various kinds of thermoplastics, such as polyethylene, polypropylene, polyoxymethylene, acrylonitrile-butadiene-styrene copolymer, polycarbonate bisphenol-A, and poly(ethylene terephthalate), were bonded to the monolith-modified metal plates by thermal welding. The bond strength for the single lap-shear tensile test of stainless steel and copper plates with the thermoplastics was in the range of 1.2-7.5 MPa, which was greater than the bond strength value for each bonding system without monolith modification. The SEM observation of fractured test pieces directly confirmed an anchor effect on this bonding system. The elongated deformation of the plastics that filled in the pores of the epoxy monolith, was observed. It was concluded that the bond strength significantly depended on the intrinsic strength of the used thermoplastics. The epoxy monolith bonding of hard plastics, such as polystyrene and poly(methyl methacrylate), was performed by the additional use of adhesives, solvents, and a reactive monomer. The epoxy monolith sheets were also successfully fabricated and applied to dissimilar material bonding.

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.

Mesoporous SiO2 Nanoparticles: A Unique Platform Enabling Sensitive Detection of Rare Earth Ions with Smartphone Camera

Fast and sensitive detection of dilute rare earth species still represents a challenge for an on-site survey of new resources and evaluation of the economic value. In this work, a robust and low-cost protocol has been developed to analyze the concentration of rare earth ions using a smartphone camera. The success of this protocol relies on mesoporous silica nanoparticles (MSNs) with large-area negatively charged surfaces, on which the rare earth cations (e.g., Eu³⁺) are efficiently adsorbed through electrostatic attraction to enable a "concentrating effect". The initial adsorption rate is as fast as 4025 mg (g min)^-1, and the adsorption capacity of Eu³⁺ ions in the MSNs is as high as 4730 mg g^-1 (equivalent to ~ 41.2 M) at 70 °C. The concentrated Eu³⁺ ions in the MSNs can form a complex with a light sensitizer of 1,10-phenanthroline to significantly enhance the characteristic red emission of Eu³⁺ ions due to an "antenna effect" that relies on the efficient energy transfer from the light sensitizer to the Eu³⁺ ions. The positive synergy of "concentrating effect" and "antenna effect" in the MSNs enables the analysis of rare earth ions in a wide dynamic range and with a detection limit down to ~ 80 nM even using a smartphone camera. Our results highlight the promise of the protocol in fieldwork for exploring valuable rare earth resources.

Carbon Cloth Supported Nano-Mg(OH)2 for the Enrichment and Recovery of Rare Earth Element Eu(III) From Aqueous Solution

Nano-Mg(OH)₂ is attracting great attention as adsorbent for pre-concentration and recovery of rare earth elements (REEs) from low-concentration solution, due to its superior removal efficiency for REEs and environmental friendliness. However, the nanoparticles also cause some severe problems during application, including aggregation, blockage in fixed-bed column, as well as the difficulties in separation and reuse. Herein, in order to avoid the mentioned problems, a carbon cloth (CC) supported nano-Mg(OH)₂ (nano-Mg(OH)₂@CC) was synthesized by electrodeposition. The X-ray diffraction and scanning electron microscopy analysis demonstrated that the interlaced nano-sheet of Mg(OH)₂ grew firmly and uniformly on the surface of carbon cloth fibers. Batch adsorption experiments of Eu(III) indicated that the nano-Mg(OH)₂@CC composite maintained the excellent adsorption performance of nano-Mg(OH)₂ toward Eu(III). After adsorption, the Eu containing composite was calcined under nitrogen atmosphere. The content of Eu₂O₃ in the calcined material was as high as 99.66%. Fixed-bed column experiments indicated that no blockage for Mg(OH)₂@CC composite was observed during the treatment, while the complete blockage of occurred to nano-Mg(OH)₂ at an effluent volume of 240 mL. Moreover, the removal efficiency of Mg(OH)₂@CC was still higher than 90% until 4,200 mL of effluent volume. This work provides a promising method for feasible application of nanoadsorbents in fixed-bed process to recycle low-concentration REEs from wastewater.

Sulfonylcalix[4]arene functionalized nanofiber membranes for effective removal and selective fluorescence recognition of terbium(iii) ions

A novel sulfonylcalix[4]arene functionalized aminated polyacrylonitrile (APAN) nanofiber membrane was fabricated, exhibiting good Tb³⁺ adsorption capacity and photoluminescence performance.

Highly Efficient and Selective Recovery of Rare Earth Elements Using Mesoporous Silica Functionalized by Preorganized Chelating Ligands

Separating the rare earth elements (REEs) in an economically and environmentally sustainable manner is one of the most pressing technological issues of our time. Herein, a series of preorganized bidentate phthaloyl diamide (PA) ligands was synthesized and grafted on large-pore 3-dimensional (3-D) KIT-6 mesoporous silica. The synthesized sorbents were fully characterized by N₂ physisorption, FT-IR, ¹³C cross-polarization (CP) and ²⁹Si magic-angle spinning (MAS) NMR, thermogravimetric analysis-differential thermal analysis (TGA-DTA), and elemental analysis. Overall, the grafting of PA-type ligands was found to have significantly improved the extraction performance of the sorbents toward REEs compared to the homogeneous analogues. Specifically, the sorbent modified with the 1,2-phtaloyl ligand shows high preference over lanthanides with smaller size, whereas the 1,3-phtaloyl ligand exhibits selectivity toward elements with larger ion radius. This selectivity drastically changes from the homogeneous models that do not exhibit any selectivity. The possibility of regenerating the mesoporous sorbents through simple stripping using oxalate salt is demonstrated over up to 10 cycles with no significant loss in REEs extraction capacity, suggesting adequate chemical and structural stability of the new sorbent materials. Despite the complex ion matrix and high ionic composition, the exposure of industrial mining deposits containing REEs to the sorbents results in selective recovery of target REEs.