Molecular dynamics simulations of uranyl and uranyl carbonate adsorption at aluminosilicate surfaces

Multiscale computational simulation of pollutant behavior at water interfaces

The investigation of pollutant behavior at water interfaces is critical to understand pollution in aquatic systems. Computational methods allow us to overcome the limitations of experimental analysis, delivering valuable insights into the chemical mechanisms and structural characteristics of pollutant behavior at interfaces across a range of scales, from microscopic to mesoscopic. Quantum mechanics, all-atom molecular dynamics simulations, coarse-grained molecular dynamics simulations, and dissipative particle dynamics simulations represent diverse molecular interaction calculation methods that can effectively model pollutant behavior at environmental interfaces from atomic to mesoscopic scales. These methods provide a rich variety of information on pollutant interactions with water surfaces. This review synthesizes the advancements in applying typical computational methods to the formation, adsorption, binding, and catalytic conversion of pollutants at water interfaces. By drawing on recent advancements, we critically examine the current challenges and offer our perspective on future directions. This review seeks to advance our understanding of computational techniques for elucidating pollutant behavior at water interfaces, a critical aspect of water research.

Interaction Between the Transferrin Protein and Plutonium (and Thorium), What's New?

Transferrin (Tf) is a glycoprotein that transports iron from the serum to the various organs. Several studies have highlighted that Tf can interact with metals other than Fe(III), including actinides that are chemical and radiological toxics. We propose here to report on the behavior of Th(IV) and Pu(IV) in comparison with Fe(III) upon Tf complexation. We considered UV-Vis and IR data of the M2 Tf complex (M=Fe, Th, Pu) and combined experimental EXAFS data with MD models. EXAFS data of the first M-O coordination sphere are consistent with the MD model considering 1 synergistic carbonate. Further EXAFS data analysis strongly suggests that contamination by Th/Pu colloids seems to occur upon Tf complexation, but it seems limited. SAXS data have also been recorded for all complexes and also after the addition of Deferoxamine-B (DFOB) in the medium. The Rg values are very close for apoTf, ThTf and PuTf, but slightly larger than for holoTf. Data suggest that the structure of the protein is more ellipsoidal than spherical, with a flattened oblate form. From this data, the following order of conformation size might be considered:holoTf Collapse

Key Words

• Plutonium
• SAX
• Transferrin
• XAS
• metalloprotein

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MESH Headings

• Transferrin/chemistry
• Plutonium/chemistry
• Thorium/chemistry
• Ferric Compounds
• Scattering, Small Angle
• X-Ray Diffraction

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Grants

• Ministère de l'Enseignement supérieur, de la Recherche et de l'Innovation

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Affiliation(s)

Cyril Zurita Université Côte d'Azur, CNRS, Institut de Chimie de Nice, 06108, Nice, France
Satoru Tsushima Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01328, Dresden, Germany Internationnal Research Frontiers Initiative, Institute of Innovative Research, Tokyo Institute of Technology, Meguro, 152-8550, Tokyo, Japan
Pier Lorenzo Solari Synchrotron SOLEIL, L'Orme des Merisiers, 91190, Saint Aubin, France
Denis Menut Synchrotron SOLEIL, L'Orme des Merisiers, 91190, Saint Aubin, France
Sandrine Dourdain ICSM, Université de Montpellier, CEA, CNRS, ENSCM, Marcoule, France
Aurélie Jeanson Université Côte d'Azur, CNRS, Institut de Chimie de Nice, 06108, Nice, France
Gaëlle Creff Université Côte d'Azur, CNRS, Institut de Chimie de Nice, 06108, Nice, France
Christophe Den Auwer Université Côte d'Azur, CNRS, Institut de Chimie de Nice, 06108, Nice, France

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Microscopic insights into the variations of antibiotics sorption to clay minerals

Understanding the adsorption behavior of antibiotic molecules on minerals is crucial for determining the environmental fate and transport of antibiotics in soils and waters. However, the microscopic mechanisms that govern the adsorption of common antibiotics, such as the molecular orientation during the adsorption process and the conformation of sorbate species, are not well understood. To address this gap, we conducted a series of molecular dynamics (MD) simulations and thermodynamics analyses to investigate the adsorption of two typical antibiotics, tetracycline (TET) and sulfathiazole (ST), on the surface of montmorillonite. The simulation results indicated that the adsorption free energy ranged from - 23 to - 32 kJ·mol^-1, and - 9 to - 18 kJ·mol^-1 for TET and ST, respectively, which was consistent with the measured difference of sorption coefficient (K_d) for TET-montmorillonite of 11.7 L·g^-1 and ST-montmorillonite of 0.014 L·g^-1. The simulations also found that TET was adsorbed through dimethylamino groups (85% in probability) with a molecular conformation vertical to the montmorillonite's surface, while ST was adsorbed through sulfonyl amide group (95% in probability) with vertical, tilted and parallel conformations on the surface. The results confirmed that molecular spatial orientations could affect the adsorption capacity between antibiotics and minerals. Overall, the microscopic adsorption mechanisms revealed in this study provide critical insights into the complexities of antibiotics adsorption to soil and facilitate the prediction of adsorption capacity of antibiotics on minerals and their environmental transport and fate. This study contributes to our understanding of the environmental impacts of antibiotic usage and highlights the importance of considering molecular-level processes when assessing the fate and transport of antibiotics in the environment.

Atomistic insights into migration mechanism of graphene-based membranes on soil mineral phases

Graphene-based membranes (GBM) will migrate in the soil and enter the groundwater system or plant roots, which will eventually pose potential risks to human beings. The migration mechanism of GBM depends on the interface behavior of complex soil components. Herein, we use molecular dynamics (MD) simulations to probe the interface behavior between GBM and three type minerals (quartz, calcite and kaolinite). Based on the investigation of binding energy, maximum pulling force and barrier energy, the order of the difficulty of GBM adsorption and desorption on the three minerals from small to large is roughly: quartz, calcite and kaolinite respectively. The graphene-oxide (GO), improves the binding energy and energy barrier, making GBM difficult to migrate in soil. Remarkably, a larger GBM sheet and high velocity external load improve GBM migration in soil to a certain extent. These investigations give the dynamic information on the GBM/mineral interaction and provide nanoscale insights into the migration mechanisms of GBM in soil.

Y(III) Sorption at the Orthoclase (001) Surface Measured by X-ray Reflectivity

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. We apply in situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of the Y³⁺ concentration, [Y³⁺], at pH 7 and 5. With [Y³⁺] ≥ 1 mM at pH 7, we observe an inner-sphere (IS) sorption complex at a distance of ∼1.5 Å from the surface and an outer-sphere (OS) complex at 3-4 Å. Based on the adsorption height of the IS complex, a bidentate, binuclear binding mode, in which Y³⁺ binds to two terminal oxygens, is proposed. In contrast, mostly OS sorption is observed at pH 5. The observed maximum Y coverage is ∼1.3 Y³⁺/A_UC (A_UC: area of the unit cell = 111.4 Ų) for all the investigated pH values and Y concentrations, which is in the expected range based on the estimated surface charge of orthoclase (001).

Force Field Parameterization of Actinyl Molecular Cations Using the 12-6-4 Model

In this work, a set of 12-6-4 force fields (FFs) parameters were developed for the actinyl molecular cations, AnO2n+ (n = 1, 2), from uranium to plutonium for classical molecular dynamics (MD) for four water models: TIP3P, SPC/E, OPC3, and TIP4Pew. Such a non-bonded potential model taking into account the induced dipole between the metallic center and the surrounding molecules has shown better performances for various cations than the classic 12-6 non-bonded potentials. The parametrization method proposed elsewhere for metallic cations has been extended to these molecular cations. In contrast to the actinyl 12-6 FFs from the literature, the new models reproduce correctly both solvation and thermodynamic properties, thanks to the inclusion of the induced dipole term (C4). The transferability of such force fields was assessed by performing MD simulations of carbonato actinyl species, which are highly implicated in actinide migration or actinide extraction from seawater. A highly satisfying agreement was found when comparing the EXAFS signals computed from our MD simulation to the experimental ones. The set of FFs developed here opens new possibilities for the study of actinide chemistry.

Interaction of Th(IV), Pu(IV) and Fe(III) with ferritin protein: how similar?

Ferritin is the main protein of Fe storage in eukaryote and prokaryote cells. It is a large multifunctional, multi-subunit protein consisting of heavy H and light L subunits. In the field of nuclear toxicology, it has been suggested that some actinide elements, such as thorium and plutonium at oxidation state +IV, have a comparable `biochemistry' to iron at oxidation state +III owing to their very high tendency for hydrolysis and somewhat comparable ionic radii. Therefore, the possible mechanisms of interaction of such actinide elements with the Fe storage protein is a fundamental question of bio-actinidic chemistry. We recently described the complexation of Pu(IV) and Th(IV) with horse spleen ferritin (composed mainly of L subunits). In this article, we bring another viewpoint to this question by further combining modeling with our previous EXAFS data for Pu(IV) and Th(IV). As a result, the interaction between the L subunits and both actinides appears to be non-specific but driven only by the density of the presence of Asp and Glu residues on the protein shell. The formation of an oxyhydroxide Th or Pu core has not been observed under the experimental conditions here, nor the interaction of Th or Pu with the ferric oxyhydroxide core.

Molecular Dynamics Simulation of Ion Adsorption and Ligand Exchange on an Orthoclase Surface

Orthoclase (K-feldspar) is one of the natural inorganic materials, which shows remarkable potential toward removing heavy metal ions from aqueous solutions. Understanding the interactions of the orthoclase and metal ions is important in the treatment of saline wastewater. In this paper, molecular dynamics simulations were used to prove the adsorption of different ions onto orthoclase. The adsorption isotherms show that orthoclase has remarkable efficiency in the removal of cations at low ion concentrations. Aluminol groups are the preferential adsorption sites of cations due to higher negative charges. The adsorption types and adsorption sites are influenced by the valence, radius, and hydration stability of ions. Monovalent cations can be adsorbed in the cavities, whereas divalent cations cannot. The hydrated cation may form an outer-sphere complex or an inner-sphere complex in association with the loss of hydration water. Na+, K+, and Ca2+ ions mainly undergo inner-sphere adsorption and Mg2+ ions prefer outer-sphere adsorption. On the basis of simulation results, the mechanism of ion removal in the presence of orthoclase is demonstrated at a molecular level.

How Does Iron Storage Protein Ferritin Interact with Plutonium (and Thorium)?

The impact of the contamination of living organisms by actinide elements has been a constant subject of attention since the 1950s. But to date still little is understood. Ferritin is the major storage and regulation protein of iron in many organisms, it consists of a protein ring and a ferrihydric core at the center. This work sheds light on the interactions of early actinides (Th, Pu) at oxidation state +IV with ferritin and its ability to store those elements at physiological pH compared to Fe. The ferritin-thorium load curve suggests that Th^IV saturates the protein (2840 Th atoms per ferritin) in a similar way that Fe does on the protein ring. Complementary spectroscopic techniques (spectrophotometry, infrared spectroscopy, and X-ray absorption spectroscopy) were combined with molecular dynamics to provide a structural model of the interaction of Th^IV and Pu^IV with ferritin. Comparison of spectroscopic data together with MD calculations suggests that Th^IV and Pu^IV are complexed mainly on the protein ring and not on the ferrihydric core. Indeed from XAS data, there is no evidence of Fe neighbors in the Th and Pu environments. On the other hand, carboxylates from amino acids of the protein ring and a possible additional carbonate anion are shaping the cation coordination spheres. This thorough description from a molecular view point of Th^IV and Pu^IV interaction with ferritin, an essential iron storage protein, is a cornerstone in comprehensive nuclear toxicology.

Redox mechanism and stability of uranyl phosphites at mineral surfaces: Cooperative proton/electron transfer and high efficacy for Uranium(VI) reduction

Uranium phosphites have recently emerged as promising materials to remediate radioactive contamination. In this study, the redox mechanisms of uranyl phosphites at mineral surfaces have been addressed by periodic DFT calculations with dispersion corrections. Different from other ligands, the phosphite anions (H₂PO₃^-, HPO₃^2-) are efficient reducing agents for uranyl reduction, and the redox reactions are divided into three steps, as isomerization between two phosphite anion isomers (Step 1), conformational transition (Step 2) and dissociation of the water molecule (Step 3). A second water molecule is critical to lower the activation barriers of Step 1, and all activation barriers are moderate so that the redox reactions occur favorably under normal conditions, which are further dramatically accelerated by the highly exergonic Step 3. Accordingly, formation of uranyl phosphites becomes an effective approach to manage uranium pollution. Moreover, the lower activation barriers for H₂PO₃^- rather than HPO₃^2- rationalize the superior reduction activities of uranyl phosphites and the enhanced stability of U(IV) products at lower pH conditions. Owing to the cooperative proton/electron transfer, the U(VI) reduction to U(IV) and P(III) oxidation to P(V) are completed within one step, with transition states being featured by the U(V) and P(IV) species.

Insights into the competitive adsorption of pollutants on a mesoporous alumina–silica nano-sorbent synthesized from coal fly ash and a waste aluminium foil

A highly efficient and low-cost alumina–silica nano-sorbent was fabricated and characterized to understand the key factors responsible for its superiority over the existing adsorbents in treating the industry-discharged wastewater for the removal of dyes and heavy metals. As compared to the properties of raw fly ash, the following fundamental improvements were observed for the alumina–silica nano-sorbent: (a) transformation of throttled mesopores into slit-type pores, (b) increment in the surface area by 65-fold, (c) change in the morphology from spherical particles to a flake-type structure with sharp edges, (d) reduction in the average crystal size from 61.143 to 27.176 nm, and (e) increase in the pore volume from 0.005 to 0.50 cm³ g⁻¹. These desired properties of the nano-sorbent were obtained by blending a waste aluminium foil with fly ash. This process increased the ratio of alumina to silica from 0.59 : 1 to an optimum ratio of 1.9 : 1, beyond which the particles agglomerated and the pore volume reduced. Eventually, the precipitated hydroxides were calcined at 700 °C that favoured the formation of γ-alumina. Moreover, this heat treatment changed its crystallinity and morphology of γ-alumina, which abruptly enhanced its activity towards the pollutants. The obtained product (nano-sorbent) was tested for the removal of lead and malachite green from a model wastewater solution over a wide range of initial pollutant concentrations and adsorbent dosages. After observing almost complete removal capacity and reusability for the pollutants, we propose this synthesized adsorbent as a universal material for treating industrial wastewater.

A highly efficient and low-cost alumina–silica nano-sorbent was fabricated and characterized to realize the key factors responsible for its superiority over the existing adsorbents in treating the wastewater for the removal of dyes and heavy metals.

Abiotic reduction of uranium(VI) with humic acid at mineral surfaces: Competing mechanisms, ligand and substituent effects, and electronic structure and vibrational properties

Abiotic reduction represents an attractive technology to control U(VI) contamination. In this work, an abiotic route of U(VI) reduction with humic acid at mineral surfaces is proposed and reaction mechanisms are addressed by periodic density functional theory calculations. Different influencing factors such as ligand effect, content of CO₃^2- ligands and substituent effect are inspected. The coordination chemistry of uranyl(VI) surface complexes relies strongly on substrates and ligands, and the calculated results are in good agreements with experimental observations available. For the OH^- ligand, two competitive mechanisms co-exist that respectively produce the U(IV) and U(V) species, and the former is significantly preferred because of lower energy barriers. Instead, the NO₃^- ligand leads to the formation of U(V) while for the Cl^- ligand, the U(VI) surface complex remains very stable and is not likely to be reduced because of very high energy barriers. The U(V) and U(IV) complexes are the predominant products for low and high CO₃^2- contents, respectively. Accordingly, the abiotic reduction processes with humic acid are efficient to manage U(VI) contamination and become preferred under basic conditions or at higher CO₃^2- contents. The U(VI) reduction is further promoted by introduction of electron-donating rather than electron-withdrawing substituents to humic acid. Electronic structure analyses and vibrational frequency assignments are calculated for the various uranium surface complexes of the reduction processes, serving as a guide for future experimental and engineered studies. The molecular-level understanding given in this work offers an abiotic route for efficient reduction of U(VI) and remediation of U(VI)-contaminated sites at ambient conditions.

Gibbsite (100) and Kaolinite (100) Sorption of Cadmium(II): A Density Functional Theory and XANES Study of Structures and Energies

Due to the potential toxicity of cadmium (Cd²⁺) and its presence in various waste products found in the environment, it is necessary to develop methods to attenuate and remediate Cd²⁺ waste. Sorption of Cd²⁺ to mineral surfaces is a potential route to accomplish this goal. This work focused on improving our molecular-scale understanding of the chemistry of Cd²⁺ interactions with gibbsite and kaolinite mineral surfaces. Plane-wave density functional theory (DFT) energy minimization calculations and molecular dynamics simulations were used to study the adsorption energies and the nature of the bonds between Cd²⁺ and the mineral surfaces for possible inner- and outer-sphere surface complexes. Models resulting from the DFT calculations were used to calculate theoretical XANES spectra that were compared with experimental Cd L_III XANES of aqueous Cd²⁺ as a proxy for outer-sphere Cd²⁺ hydrated complexes associated with the mineral surfaces. These studies suggest that Cd²⁺ would favorably bond to the (100) surfaces of both kaolinite and gibbsite through a bidentate mononuclear interaction. However, the results indicate that mixtures of surface complexes on these minerals are likely.

Application of a Novel Coarse-Grained Soil Organic Matter Model in the Environment

Soil organic matter (SOM) is ubiquitous in the environment. Intensive efforts have been made to find effective ways to assess the interaction of SOM with contaminants since such interactions are one of the important criteria used to evaluate the migration, persistency and bioavailability of chemicals in the environment. This study aims to extend the application of coarse-grained (CG) dissipative particle dynamics (DPD) to the water/SOM system and predict contaminant mobility in the system. The CG model was based on the Vienna Soil-Organic-Matter Modeler, which can generate flexible condensed-phase models of SOM. A series of DPD simulations was performed to investigate the mobility of perfluorinated sulfonic acids (PFSAs) and hexachlorobutadiene (HCBD). The results indicated that the mobility of PFSAs decreased with increasing length in the carbon chain. In addition, HCBD and hexachlorobenzene (HCB) have similar diffusion coefficients, indicating analogous behavior in SOM. Moreover, water-containing SOM layers may reflect a more realistic situation. This work, coupling the CG method with DPD simulation, provides a new high-efficiency tool to assess the behavior of contaminants in the environment.

Adsorptive environmental applications of MXene nanomaterials: a review

Since titanium carbide Ti3C2 nanosheets were first produced in 2011, an increasing number of members of this new family of two-dimensional transition metal carbides/nitride (MXene) materials have been successfully synthesized. Due to their large specific surface area, hydrophilic nature and abundant highly active surface sites, MXenes have been demonstrated to adsorb a variety of environmental pollutants, including heavy metal ions, organic dyes, radionuclides, and gas molecules, and thus can be used for the removal of pollutants and even sensing. In this review, we summarize the recent research progress on MXene materials in the adsorptive remediation of environmental pollutants and highlight the main challenges in the future to understand the full potential of MXene materials in environmental systems.

Bonding trends across the series of tricarbonato-actinyl anions [(AnO2)(CO3)3]4- (An = U-Cm): the plutonium turn

Actinyl-tricarbonato anions [(AnO₂)(CO₃)₃]^4- (An = U-Cm) in various environments were investigated using theoretical approaches of quantum-mechanics, molecular-mechanics and cluster-models. Cations and solvent molecules in the 2^nd coordination sphere affect the equatorial An←O_eq bonds more than the axial An[triple bond, length as m-dash]O_ax bonds. Common actinide contraction is found for calculated and experimental axial bond lengths of ₉₂U to ₉₄Pu, though no longer for ₉₄Pu to ₉₆Cm. The tendency of U to Pu forming actinyl(vi) species dwindles away toward Cm, which already features the preferred An^III/Ln^III oxidation state of the later actinides and all lanthanides. The well known change from d-type to typical U-Pu-Cm type and then to f-type behavior is labeled as the plutonium turn, a phenomenon that is caused by f-orbital energy-decrease and f-orbital localization with increase of both nuclear charge and oxidation state, and a non-linear variation of effective f-electron population across the actinide series. Both orbital and configuration mixing and occupation of antibonding 5f type orbitals increase, weakening the AnO_ax bonds and reducing the highest possible oxidation states of the later actinides.

Determination of the Structures of Uranyl-Tri-n-butyl-Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

The complex structure of a plutonium uranium refining by extraction (PUREX) process organic phase was characterized by combining results from experiments and molecular dynamics simulations. For the first time, the molecular interactions between tri-n-butyl phosphate (TBP) and the extracted solutes, as well as TBP aggregation after the extraction of water and/or uranyl nitrate, were described and analyzed concomitantly. Coupling molecular dynamics simulations with small- and wide-angle X-ray scattering (SWAXS) experiments can lead to simulated organic solutions that are representative of the experimental ones, even for high extractant and solute concentrations. Furthermore, this coupling is well adapted for the interpretation of SWAXS experiments without preliminary hypothesis on the size or shape of aggregates. The results link together previous literature studies obtained for each level of depiction separately (complexation or aggregation). Without uranium, or at low metal concentration, almost no aggregation was observed. At high uranium concentration, organic phases contain small [UO₂ (NO₃ )₂ (TBP)₂ ]_n polymetallic aggregates (with n=2 to 4), in which the 1:2 U/TBP stoichiometry is preserved.

New Insight into the Aggregation of Graphene Oxide Using Molecular Dynamics Simulations and Extended Derjaguin-Landau-Verwey-Overbeek Theory

A comparative experimental and molecular dynamics (MD) simulation study was carried out to investigate the aggregation of graphene oxide (GO). Mechanisms behind the effects of solution chemistries (pH, metal ions, and tannic acid (TA)) and GO topology (carboxyl content, GO size, and GO thickness) were uncovered. For example, MD results showed that more hydrogen bonds formed between GO and water at higher pH, according well with the increased hydrophilicity of GO calculated based on contact angle measurements. Radial distribution functions analysis suggested Ca²⁺ interacted more strongly with GO than Na⁺, which explained the experimental observations that Ca²⁺ was more effective in accelerating the aggregation process than Na⁺. The adsorption-bridging and steric effects of TA were simulated, and TA was found to be unfolded upon wrapping on GOs, leading to an increased capacity for ion and solvent binding. The evaluations of contributions to GO hydrophilicity, electrostatic energy, and intensities of interactions with metal ions indicated the carboxyl group is the essential functional group in mediating the stability of GO. Overall, by combining MD simulations with experimental measurements, we provided molecular-level understandings toward the aggregation of GO, indicating MD, if used properly, can be applied as a useful tool to obtain insights into the aggregation of nanomaterials.

Adsorption of uranyl species on hydroxylated titanium carbide nanosheet: A first-principles study

In this work, hydroxylated titanium carbide Ti3C2(OH)2, a representative of the two-dimensional transition metal carbides, has been predicted to be an effective adsorbent for uranyl ions in aqueous environments for the first time using density functional theory simulations. The calculations revealed that the uranyl ion can strongly bind with Ti3C2(OH)2 nanosheet in aqueous solution regardless of the presence of anionic ligands such as OH(-), Cl(-) and NO3(-). The bidentate coordination of uranyl to the surface is energetically more favorable than other adsorption configurations, and the uranyl ion prefers to bind with the deprotonated O adsorption site rather than the protonated one on the hydroxylated surface. During the adsorption process, the chemical adsorption as well as the formation of hydrogen bonds is the dominant factor.

Prediction and clarification of structures of (bio)molecules on surfaces

The design of future materials for biotechnological applications via deposition of molecules on surfaces will require not only exquisite control of the deposition procedure, but of equal importance will be our ability to predict the shapes and stability of individual molecules on various surfaces. Furthermore, one will need to be able to predict the structure patterns generated during the self-organization of whole layers of (bio)molecules on the surface. In this review, we present an overview over the current state of the art regarding the prediction and clarification of structures of biomolecules on surfaces using theoretical and computational methods.

Mechanism of adsorption affinity and capacity of Mg(OH)2 to uranyl revealed by molecular dynamics simulation

The redistribution of surface OH groups results in a negative charge site which facilitates the uranyl adsorption.

Synthesis of Hollow Nanotubes of Zn2SiO4 or SiO2: Mechanistic Understanding and Uranium Adsorption Behavior

We report a facile synthesis of Zn2SiO4 nanotubes using a two-step process consisting of a wet-chemical synthesis of core-shell ZnO@SiO2 nanorods followed by thermal annealing. While annealing in air leads to the formation of hollow Zn2SiO4, annealing under reducing atmosphere leads to the formation of SiO2 nanotubes. We rationalize the formation of the silicate phase at temperatures much lower than the temperatures reported in the literature based on the porous nature of the silica shell on the ZnO nanorods. We present results from in situ transmission electron microscopy experiments to clearly show void nucleation at the interface between ZnO and the silica shell and the growth of the silicate phase by the Kirkendall effect. The porous nature of the silica shell is also responsible for the etching of the ZnO leading to the formation of silica nanotubes under reducing conditions. Both the hollow silica and silicate nanotubes exhibit good uranium sorption at different ranges of pH making them possible candidates for nuclear waste management.

Magnesium carbonate basic coating on cotton cloth as a novel adsorbent for the removal of uranium

A magnesium carbonate basic coating on a cotton cloth was prepared by a facile and cost-effective method for uranium(vi) adsorption. The maximum adsorption capacity toward uranium is 370 mg g⁻¹, promoting a promising and effective adsorbent for practical uranium(vi) adsorption.

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.