Eu(III) uptake on rectorite in the presence of humic acid: A macroscopic and spectroscopic study

Rare earth elements sequestration in phytoliths: Partitioning patterns and influencing mechanism

Rare earth elements (REEs) are integral to numerous high-tech industries, yet their biogeochemical cycling within ecosystems remains inadequately characterized. Recently, phytoliths have been identified as potentially significant sinks for REEs; however, their role in the cycling of these elements has been underestimated. In this work, we investigate the accumulation of REEs in phytoliths (PhytREEs) within the Greater Khingan Mountains region, employing an optimized wet oxidation method combined with heavy liquid flotation to quantify PhytREEs contents in surface soils. The results revealed an elevation-dependent pattern of PhytREEs concentration, with heightened levels at higher altitudes and diminishing concentrations towards the eastern plains. The enrichment coefficient of PhytREEs (ECPhytREEs) was found to be approximately 2.7 %, indicative of a moderately selective sequestration process. The multivariate analysis indicated that terrain complexity, climatic patterns, soil texture, and organic matter significantly influence the uptake and storage of REEs in plants, subsequently affecting their partitioning in phytoliths. Among these factors, the complexation of REEs with organic matter emerged as a pivotal mechanism facilitating their immobilization within phytoliths. Soil characteristics also play a non-negligible role in modulating REEs dynamics. Our findings highlight the predominant influence of climate on PhytREE storage, suggesting that climatic variables are the primary drivers modulating the bioavailability and ultimate sequestration of REEs within phytoliths. This study enhances our understanding of the biotic-abiotic interplay in the sequestration of REEs and underscores the need to incorporate phytoliths into models of terrestrial REE cycling.

Multi-scale modeling of natural organic matter-heavy metal cations interactions: Aggregation and stabilization mechanisms

Interaction between natural organic matters (NOM) and heavy metal cations in aqueous environment are of great significance for maintaining stability of organic carbon and restraining transport of heavy metal contaminants in (bio)geochemical processes. We systematically explore the aggregation process and complexation between NOM and heavy metal cations (Ag⁺, Cd²⁺, Pb²⁺, Zn²⁺, Eu³⁺) under different pH condition by molecular dynamics (MD) simulations, umbrella sampling method, and quantum chemistry calculations. The character of molecular structures NOM-heavy metal complexes and association are quantified. In acidic pH condition, aggregation proceeds via H-bonding and π-π interactions between NOM fragments. In neutral condition, Ag⁺, Cd²⁺, Pb²⁺, and Eu³⁺ can form inner-sphere complexes with the surface carboxylic groups and therefore reduce intermolecular charge repulsion, eventually leading to NOM aggregation, and it shows that even without direct binding, the outer-sphere adsorbed Zn²⁺ can also result in the formation of NOM assemble through H-bonding. Consequently, these heavy metals are capable of promoting NOM aggregation regardless of the complexing ways. Complexing free energy calculations characterized the dynamic processes of cations binding to the carboxylic groups of NOM fragment and the related energy landscape. This study provides quantitative insights for understanding the environmental processes of heavy metals and cycle of C in aquatic ecosystem, and contributes to developing environment-friendly strategies for controlling heavy metal contaminants.

Lanthanide and Ladder-Structured Polysilsesquioxane Composites for Transparent Color Conversion Layers

Ladder-type polysilsesquioxanes (LPSQs) containing phenyl as a high refractive index unit and cyclic epoxy as a curable unit were found to be excellent candidates for a transparent color conversion layer for displays due to being miscible with organic solvents and amenable to transparent film formation. Therefore, the LPSQs were combined with luminescent lanthanide metals, europium Eu(III), and terbium Tb(III), to fabricate transparent films with various emission colors, including red, orange, yellow, and green. The high luminescence and transmittance properties of the LPSQs-lanthanide composite films after thermal curing were attributed to chelating properties of hydroxyl and polyether side chains of LPSQs to lanthanide ions, as well as a light sensitizing effect of phenyl side chains of the LPSQs. Furthermore, Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy and nanoindentation tests indicated that the addition of the nanoparticles to the LPSQs moderately enhanced the epoxy conversion rate and substantially improved the wear resistance, including hardness, adhesion, and insusceptibility to atmospheric corrosion in a saline environment. Thus, the achieved LPGSG-lanthanide hybrid organic-inorganic material could effectively serve as a color conversion layer for displays.

Effect of calcination temperatures on the performance of rectorite for cadmium immobilization in soil: Freeze-thaw, plant growth, and microbial diversity

The immobilization of cadmium (Cd(II)) in soil using calcined rectorite (REC) was investigated in this research. The results of immobilization show that a small amount of REC calcined at 700 °C (REC-700 °C) could effectively immobilize 90% of Cd(II) in soil, while the immobilization efficiency of REC only reached 42%. Moreover, the immobilization efficiency of REC calcined at 300 °C and 500 °C (REC-300 °C and REC-500 °C) were lower than REC. To investigate the mechanism, the materials before and after immobilization were fully analyzed by Fourier transform infrared spectroscopy (FT-IR), powdery X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM). The results indicate that the structure of REC has been changed after calcination at different temperatures and Cd(II) was successfully immobilized on materials. Losing free water, structural water and OH groups respectively, the layer spacing of REC-300 °C and REC-500 °C was shrunk. However, the crystal structure of REC was destroyed after calcination at 700 °C, resulting in the generation of new phases. According to the XRD result, more cadmium hydroxide (Cd(OH)₂) were produced on REC-700 °C, indicating that more OH groups were formed during immobilization. Furthermore, Tessier test demonstrates that Cd(II) in soil changed from exchangeable state and water soluble state to carbonate bound state and iron manganese oxide bound state during immobilization. The result of microbial community indicates that REC-700 °C can restore the microbial composition of Cd(II)-contaminated soil. The effects of pH, freeze-thaw, REC dosage, and initial heavy metal concentration were also evaluated to provide a theoretical basis for the subsequent application of the material in the remediation of contaminated soil.

NanoTafla Nanocomposite as a Novel Low-Cost and Eco-Friendly Sorbent for Strontium and Europium Ions

Now the wide use of nanooxides is attributed to their remarkable collection of properties. Nanocomposites have an impressive variety of important applications. A thermal decomposition approach provides a more optimistic method for nanocrystal synthesis due to the low cost, high efficiency, and expectations for large-scale production. Therefore, in this study a new eco-friendly nanooxide composite with sorption characteristics for europium (Eu(III)) and strontium (Sr(II)) was synthesized by a one-step thermal treatment process using earth-abundant tafla clay as a starting material to prepare a modified tafla (M-Taf) nanocomposite. The synthesized nancomposite was characterized by different techniques before and after sorption processes. Different factors that affected the sorption behavior of Eu(III) and Sr(II) in aqueous media by the M-Taf nanocomposite were studied. The results obtained illustrated that the kinetics of sorption of Eu(III) and Sr(II) by the M-Taf nanocomposite are obeyed according to the pseudo-second order and controlled by a Langmuir isotherm model with maximum sorption capacities (Q _max) of 25.5 and 23.36 mg/g for Eu(III) and Sr(II), respectively. Also, this novel low-cost and eco-friendly sorbent has promising properties and can be used to separate and retain some radionuclides in different applications.

High-performance removal of radionuclides by porous organic frameworks from the aquatic environment: A review

Dealing with unwanted nuclear waste is still a serious issue from the point of view of humans and the environment because of its harmful and dangerous effects. Recently, porous organic frameworks (POFs) have gained an increasing concern as effective materials in the removal of various types of hazardous metal ions, especially radioactive metal ions. POFs are a unique class that included covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) with strong covalent bonds, large surface area, high adsorption capacity, tunable porosity, and a porous structure with more efficient than conventional adsorbents. This review highlights the recent developments of POFs for the rapid elimination of radionuclide. The unique characteristics, adsorption properties, and interaction mechanisms between radioactive metal ions and the POF-based materials are summarized. Also, prospects for enhancing the performance of POFs to capture radioactive metal ions are discussed.

Fabrication, functionalization and advanced applications of magnetic hollow materials in confined catalysis and environmental remediation

Magnetic hollow-structured functional hybrid materials with unique architectures and preeminent properties have always been an area of extensive research. They represent a subtle collaboration of hollow architecture, mesoporous nanostructure and magnetic character. Owing to the merits of a large void space, low density, high specific surface area, well-defined active sites and facile magnetic recovery, these materials present promising application projections in numerous fields, such as drug delivery, adsorption, storage, catalysis and many others. In this review, recent progress in the design, synthesis, functionalization and applications of magnetic hollow-meso/nanostructured materials are discussed. The first part of the review has been dedicated to the preparation and functionalization of the materials. The synthetic protocols have been broadly classified into template-assisted and template-free methods and major trends in their synthesis have been elaborated in detail. Furthermore, the benefits and drawbacks of each method are compared. The later part summarizes the application aspects of confined catalysis in organic transformations and environmental remediation such as degradation of organic pollutants, dyes and antibiotics and adsorption of heavy metal ions. Finally, an outlook of future directions in this research field is highlighted.

Luminescence spectroscopic investigations of europium complexes formed in the kaolinite-humic acid/citric acid systems

In the present study, the nature of Eu(III) complexes (Eu(III) was used as a surrogate for Am(III)) formed in kaolinite–humic acid (HA)/citric acid (CA) system was investigated by luminescence spectroscopy. In addition to the ternary system (kaolinite + Eu + L(CA/HA)), the binary system (Eu-L) was also looked at for a better understanding of the complexes formed at the kaolinite surface. The lifetime and emission spectra of Eu-L complexes on the kaolinite surface differ considerably as compared to the same in the aqueous phase. The Eu-HA aqueous complexation shows differences in the excitation spectra with similar decay lifetimes with increasing aqueous HA concentrations. The ligand-to-metal charger transfer (LMCT) in the Eu-HA excitation spectra suggests the complexation of Eu(III) with HA at pH ∼ 4. Although the mode of Eu(III) binding to the kaolinite surface in the presence of CA/HA was the same i.e. metal-bridged ternary complex formation, the local surroundings around the sorbed Eu(III) differ in the two cases. The loading of HA in the Eu-HA-kaolinite system does not have a large effect on the local structure around the sorbed Eu(III) ion, but enhances the percentage of Eu(III) uptake onto the kaolinite surface. The number of H2O molecules in the primary hydration sphere of sorbed Eu(III) differs in the Eu-HA-kaolinite and Eu-CA-kaolinite systems. In addition, Eu(III) assisted precipitation of HA was also seen using a radiometric method.

Design and synthesis of core-shell Fe3O4@PTMT composite magnetic microspheres for adsorption of heavy metals from high salinity wastewater

In this study, a novel magnetic nanoparticles (MNP) modified by an organodisulfide polymer (PTMT) was designed for adsorption of heavy metals (Hg(II), Pb(II) and Cd(II)) from simulated coal chemical high salinity wastewater. The MNP-PTMT nano-composite was synthesize and characterized by SEM, TEM, FTIR, BET, VSM, TGA and XRD. The results indicate that the wanted MNP-PTMT magnetic nanoparticles were successfully obtained by modification. Adsorption experiments were systematically carried out to evaluate the performance of the obtained nanoparticles and to build up the adsorption models. The results demonstrate that the adsorption kinetic and isotherms thermodynamic followed the pseudo-second-order model and the Freundlich equation, respectively. In the presence of the inorganic salt in high salinity wastewater, the adsorption efficiency of MNP-PTMT for heavy metals was still excellent. The magnetic adsorbent could be recovered from aqueous solution by an external magnetic field in 20s and the subsequent regeneration of Hg(II)/Pb(II) loaded MNP-PTMT can be efficiently achieved by using EDTA-2Na solution as desorbent. The novel MNP-PTMT nanoparticles could be used reproductively for five times without apparent decrease in sorption capacity.

Metal-organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal-organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

Nanoscale zero-valent iron functionalized Posidonia oceanica marine biomass for heavy metal removal from water

Because of the excellent reducing capacity of nanoscale zero-valent iron (NZVI), it can be used as alternative materials for the removal of a variety of reducible water contaminants including toxic metals. The current paper reports the research results obtained for self-prepared biosorbent, Posidonia oceanica biomass, activated in alkaline medium and functionalized with NZVI particles. The structural characteristics, surface morphology, and binding properties of the resulting nanobiosorbent are presented. Batch comparative adsorption trials including adsorption kinetics and isothermals onto raw Posidonia, Posidonia-OH and Posidonia-OH-NZVI were investigated on three heavy metal ions: Cd(II), Pb(II), and Cu(II). The nanobiosorbent showed better properties, such as high reactivity and high uptake rate through the sorption process. The toxic metal removal has been monitored in terms of pseudo-first- and pseudo-second-order kinetics, and both Langmuir- and Freundlich-type isotherm models have been used to describe the sorption mechanism. The experimental data of all studied systems showed that the uptake kinetics follow the pseudo-second-order kinetic model and the equilibrium uptake can adopt the Langmuir-type isotherm model which assumes a monolayer coverage as the adsorption saturates and no further adsorption occurs. The thermodynamic results confirm that all sorption processes were feasible, spontaneous and thermodynamically favorable. Zeta potential data displayed that Cd(II), Pb(II), and Cu(II) tend to be reduced after exposure on the Posidonia-OH-NZVI surface. Furthermore, sorption competitions of the metals from binary and ternary systems were carried out onto Posidonia-OH-NZVI in order to gain further insight into the sorption efficiency of this material. Therefore, as a result, the proposed new nanobiosorbent could offer potential benefits in remediation of heavy metal-contaminated water as a green and environmentally friendly bionanocomposite.

Environmental Remediation and Application of Nanoscale Zero-Valent Iron and Its Composites for the Removal of Heavy Metal Ions: A Review

The presence of heavy metals in the industrial effluents has recently been a challenging issue for human health. Efficient removal of heavy metal ions from environment is one of the most important issues from biological and environmental point of view, and many studies have been devoted to investigate the environmental behavior of nanoscale zerovalent iron (NZVI) for the removal of toxic heavy metal ions, present both in the surface and underground wastewater. The aim of this review is to show the excellent removal capacity and environmental remediation of NZVI-based materials for various heavy metal ions. A new look on NZVI-based materials (e.g., modified or matrix-supported NZVI materials) and possible interaction mechanism (e.g., adsorption, reduction and oxidation) and the latest environmental application. The effects of various environmental conditions (e.g., pH, temperature, coexisting oxy-anions and cations) and potential problems for the removal of heavy metal ions on NZVI-based materials with the DFT theoretical calculations and EXAFS technology are discussed. Research shows that NZVI-based materials have satisfactory removal capacities for heavy metal ions and play an important role in the environmental pollution cleanup. Possible improvement of NZVI-based materials and potential areas for future applications in environment remediation are also proposed.

Effect of different complexing ligands on europium uptake from aqueous phase by kaolinite: batch sorption and fluorescence studies

The fluorescence studies suggested that the Eu(iii) sorbs as Eu(iii)–oxalate complex (binary system) onto kaolinite surface in the ternary system of Eu(iii), oxalic acid and kaolinite at circumneutral pH conditions.

Sorption of radionuclides from aqueous systems onto graphene oxide-based materials: a review

Graphene oxide-based nanomaterials are suitable materials for the preconcentration of radionuclides and heavy metal ions from aqueous solutions in environmental pollution cleanup.

Influences of different environmental parameters on the sorption of trivalent metal ions on bentonite: batch sorption, fluorescence, EXAFS and EPR studies

The presence of long-lived radionuclides in natural aquatic systems is of great environmental concern in view of their possible migration into biospheres of mankind. Trivalent actinides such as (241/243)Am can contribute a great deal to radioactivity for several thousand years. This migration is significantly influenced by various factors such as pH, complexing ions present in aquatic environments, and the sorption of species involving radionuclides by sediments around water bodies. Clay minerals such as bentonite are known to be highly efficient in radionuclide retention and hence are suitable candidates for backfill materials. This study presents experimental results on the interaction of Eu(iii) and Gd(iii) (chemical analogs of Am(iii) and Cm(iii)) with bentonite clay under varying experimental conditions of contact time, pH, and the presence of complexing anions such as humic acid (HA) and citric acid (cit). The sorption of HA on bentonite decreased with increasing the pH from 2 to 8, which was attributed to electrostatic interactions between HA and the bentonite surfaces. The sorption of Eu(iii) on bentonite colloids showed marginal variation with pH (>95%). However, a decrease in Eu(iii) sorption was observed in the presence of HA beyond pH 5 due to the increased aqueous complexation of Eu(iii) with deprotonated HA in the aqueous phase. The complexation of Eu(iii) with citrate ions was studied using Time Resolved Laser induced Fluorescence Spectroscopy (TRLFS) to explain the sorption data. Extended X-ray absorption fine structure (EXAFS) and electron paramagnetic resonance (EPR) investigations were carried out to understand the local chemical environment surrounding Eu(iii) and Gd(iii) (EPR probe) sorbed on bentonite under different experimental conditions. Surface complexation modelling shows the predominant formation of ≡XOEu(+2) (silanol) up to pH < 7, and beyond which ≡YOEu(OH)(+) (aluminol) is responsible for the quantitative sorption of Eu(iii) onto bentonite in the studied pH range.