Understanding the Bonding Nature of Uranyl Ion and Functionalized Graphene: A Theoretical Study

Uranyl (UO2+2) structuring and dynamics at graphene/electrolyte interface

The physicochemical phenomena at the solid/electrolyte interfaces govern various industrial processes ranging from energy generation, storage, and catalysis to chemical separations and purification. Adsorption-based solid/liquid extraction methods are promising for the selective and rapid separation of nuclear (such as uranium) and other critical materials. In this study, we quantified the adsorption, complexation, and dynamics of UO2+2 ions on the graphene surface in various electrolyte media (LiNO3, NaNO3 and CsNO3) using all-atom molecular dynamics simulations, in combination with network theory based subensemble analysis, enhanced sampling, and temporal analysis. We observe that the choice of background electrolyte impacts the propensity of UO2+2 adsorption on the graphene surface, with LiNO3 being the most favorable at both low and high uranyl-nitrate concentrations. Even though UO2+2 primarily retained its coordination with water and interacted via the outer-sphere mechanism with graphene, the interfacial segregation of NO3- increased the number of contact ion pairs (CIPs) between UO2+2 and NO3- ions, and the residence times of UO2+2 within the interfacial region. This study provides a fundamental understanding of the structure and dynamics of UO2+2 on the solid surface necessary to design advanced adsorption-based separation methods for energy-relevant materials.

Adsorption of uranium (VI) complexes with polymer-based spherical activated carbon

Adsorption processes with carbon-based adsorbents have received substantial attention as a solution to remove uranium from drinking water. This study investigated uranium adsorption by a polymer-based spherical activated carbon (PBSAC) characterised by a uniformly smooth exterior and an extended surface of internal cavities accessible via mesopores. The static adsorption of uranium was investigated applying varying PBSAC properties and relevant solution chemistry. Spatial time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed to visualise the distribution of the different uranium species in the PBSAC. The isotherms and thermodynamics calculations revealed monolayer adsorption capacities of 28-667 mg/g and physical adsorption energies of 13-21 kJ/mol. Increasing the surface oxygen content of the PBSAC to 10 % enhanced the adsorption and reduced the equilibrium time to 2 h, while the WHO drinking water guideline of 30 µgU/L could be achieved for an initial concentration of 250 µgU/L. Uranium adsorption with PBSAC was favourable at the pH 6-8. At this pH range, uranyl carbonate complexes (UO2CO3(aq), UO2(CO3)22-, (UO2)2CO3(OH)3-) predominated in the solution, and the ToF-SIMS analysis revealed that the adsorption of these complexes occurred on the surface and inside the PBSAC due to intra-particle diffusion. For the uranyl cations (UO22+, UO2OH+) at pH 2-4, only shallow adsorption in the outermost PBSAC layers was observed. The work demonstrated the effective removal of uranium from contaminated natural water (67 µgU/L) and meeting both German (10 µgU/L) and WHO guideline concentrations. These findings also open opportunities to consider PBSAC in hybrid treatment technologies for uranium removal, for instance, from high-level radioactive waste.

Adsorption and diffusion of actinyls on the basal gibbsite (001) surface: a theoretical perspective

Actinides are an important component of nuclear fuel for nuclear power and affect human health, and a key process in the transport of radionuclides in the environment is adsorption on mineral surfaces. In this work, we have used density functional theory (DFT) to investigate the microscopic adsorption and diffusion mechanisms of actinyls, U(V), U(VI), Np(V), Np(VI) Pu(V), and Pu(VI), on the gibbsite (001) surface. Actinyls(VI) are attached to the gibbsite surface through two An-Os bonds, which results in a bidentate inner sphere mode, while actinyls(V) favor a monodentate inner sphere adsorption mode with the gibbsite (001) surface. The solvent effects were considered through an explicit water cluster model. All the actinyls studied can be efficiently adsorbed on the gibbsite (001) surface with binding energies ranging from -113.9 kJ mol-1 to -341.2 kJ mol-1. Electronic structure analyses indicate that the cooperation of the An-Os bonds and hydrogen bonds leads to high adsorption stability of the actinyls with the gibbsite surface. The diffusion barriers of the actinyls on the gibbsite surface were determined, and the high energy barriers indicate that this type of gas-phase diffusion process is not likely to take place.

A novel fluorescence sensor for uranyl ion detection based on a dansyl-modified peptide

It is of great significance to sensitively and selectively detect uranyl ion (UO₂²⁺) in environmental and biological samples due to the high risks of UO₂²⁺ to human health. However, such suitable sensors are still scarce. A novel fluorescence sensor based on a dansyl-modified peptide, Dansyl-Glu-Glu-Pro-Glu-Trp-COOH (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. As the first linear peptide-based fluorescence sensor for UO₂²⁺, D-P5 exhibited high selectivity and sensitivity to UO₂²⁺ over 27 metal ions (UO₂²⁺, Cr³⁺, Cu²⁺, Ba²⁺, Hg²⁺, Pb²⁺, Co²⁺, Ag⁺, Fe³⁺, Ca²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Cd²⁺, Zn²⁺, Al³⁺, Dy³⁺, Er³⁺, Gd²⁺, Ho³⁺, La³⁺, Lu³⁺, Pr³⁺, Sm³⁺, Tm³⁺) by a turn-off fluorescence response in 10 mM HEPES buffer (pH 6.3). The effects of anions such as S^2-, NO₃^-, SO₄^2- CO₃^2-, HCOO^-, antioxidant ascorbic acid and 4-nitrophenyl acetate on the selectivity for UO₂²⁺ detection were also studies. D-P5 sensor could be used for detecting UO₂²⁺ in a good linear relationship with concentration in the range of 0-8.0 μM with a low limit of detection of 83.2 nM. Furthermore, the interaction of the sensor with UO₂²⁺ was characterized by ESI-MS, IR, XPS and ITC measurements. The 1:1 binding stoichiometry between the sensor and UO₂²⁺ was measured by the job's plot and further verified by ESI-MS. The binding constant of the sensor with UO₂²⁺ was calculated to be 9.8 × 10⁴ M^-1 by modified Benesi-Hildebrand equation. ITC results showed that theΔH^θ andΔS^θ for the interaction of D-P5 with UO₂²⁺ were -(7.167 ± 1.25) kJ·mol^-1 and 66.5 J·mol^-1·K^-1, respectively. Time-resolved fluorescence spectroscopy indicated that the mechanism of fluorescence quenching of D-P5 by UO₂²⁺ ion was static quenching process. In addition, this sensor displayed a good practicality for UO₂²⁺ detection in lake water sample without tedious sample pretreatment.

Adsorption of chloramphenicol from water using Carex meyeriana Kunth-derived hierarchical porous carbon with open channel arrays

A carbon material with both open macrochannel arrays and abundant micro/mesopores was prepared, characterized, and applied for removing chloramphenicol (CAP) from water. In the preparation process, Carex meyeriana Kunth (CM) with natural channel arrays was used as the precursor for producing the biochar, and NaOH was used for removing silicon and formatting micro- and mesopores of the porous carbon. The product (PCCM) exhibited the highest specific surface area (2700.24 m² g^-1) among the reported CM-derived porous carbons. The adsorption performances of PCCM were evaluated through batch adsorption experiments. The maximum adsorption capacity of PCCM toward CAP was 1659.43 mg g^-1. The adsorption mechanism was investigated with the aid of theoretical calculations. Moreover, PCCM exhibited better performance than other porous carbon adsorbents in fixed-bed experiments, which may be due to its structural advantages.

A Novel Triphenylamine-Based Flavonoid Fluorescent Probe with High Selectivity for Uranyl in Acid and High Water Systems

Developing a fluorescent probe for UO₂²⁺, which is resistant to interference from other ions such as Cu²⁺ and can be applied in acidic and high-water systems, has been a major challenge. In this study, a "turn-off" fluorescent probe for triamine-modified flavonoid derivatives, 2-triphenylamine-3-hydroxy-4H-chromen-4-one (abbreviated to HTPAF), was synthesized. In the solvent system of dimethyl sulfoxide:H₂O (abbreviated to DMSO:H₂O) (v/v = 5:95 pH = 4.5), the HTPAF solution was excited with 364 nm light and showed a strong fluorescence emission peak at 474 nm with a Stokes shift of 110 nm. After the addition of UO₂²⁺, the fluorescence at 474 nm was quenched. More importantly, there was no interference in the presence of metal ions (Pb²⁺, Cd²⁺, Cr³⁺, Fe³⁺, Co²⁺, Th⁴⁺, La³⁺, etc.), especially Cu²⁺ and Al³⁺. It is worth noting that the theoretical model for the binding of UO₂²⁺ to HTPAF was derived by more detailed density functional theory (DFT) calculations in this study, while the coordination mode was further verified using HRMS, FT-IR and ¹HNMR, demonstrating a coordination ratio of 1:2. In addition, the corresponding photo-induced electron transfer (PET) fluorescence quenching mechanism was also proposed.

The strong interaction of actinyl ions with fullerenol driven by multiple hydrogen bonds

The removal of actinides from radioactive wastewater is an important subject with the continuous application of nuclear energy. All-electron density functional theory (DFT) calculations were carried out to understand the adsorption behaviors of actinyl ions on C₆₀(OH)₂₄ fullerenol in this work. The outer-sphere (OS) bonding mode is more stable than the inner-sphere one because of the formation of multiple hydrogen bonds in the OS mode. The actinyl(VI) ions can be more efficiently absorbed by fullerenol than actinyl(V) ones. The bonding nature of actinyl ions with C₆₀(OH)₂₄ was revealed by various electron density topological analyses. Multiple hydrogen bonds formed in the OS complexes show moderate bond strength with partial covalent nature and are responsible for their high stability. IR spectra were fingerprinted to distinguish the interaction modes of actinyl ions with C₆₀(OH)₂₄.

Adsorption of actinide ion complexes on C60O: An all-electron ZORA-DFT-D3 study

All-electron DFT study was performed to understand the structures, binding natures and spectra of actinide ions complexes (Np(V), Pu(V) and Pu(VI)) adsorbed on C₆₀O surface. The stabilities of the outer-sphere complexes are comparable with the inner-sphere complexes due to the existence of hydrogen bonding. The Pu(VI) ion complex can be more efficiently absorbed on C₆₀O relative to other studied complexes, Np(V) and Pu(V). The bonding natures in the studied complexes were revealed with quantum theory of atoms in molecules (QTAIM), independent gradient model (IGM) and noncovalent interaction (NCI) analyses. The hydrogen bonding can be clearly found in the infrared spectra of the outer-sphere complexes, which can help us to distinguish the complex modes of actinide ion complexes with C₆₀O.

Benzotriazole decorated graphene oxide for efficient removal of U(VI)

There is a need to develop highly efficient materials for capturing uranium from nuclear wastewater. Here, 5-methylbenzotriazole modified graphene oxide (MBTA-GO) was used to adsorb U(VI) from aqueous solution. By the trials of different conditions, we found that the removal of U(VI) from acidic solution was strongly dependent on pH but independent of ionic strength. The U(VI) adsorption was perfectly conformed to the pseudo-second-order kinetics and the adsorption isotherms were simulated by the Langmuir model well. A high removal capacity (q_max = 264 mg/g) for U(VI) at pH 3.5 was obtained. XPS, EXAFS analyses and DFT calculations revealed that the mechanism of uranium capture was ascribed to (i) the surface complexation by benzotriazole and carboxyl groups (providing lone pair electrons) on MBTA-GO and (ii) enhanced synergistic coordination ability of delocalized π-bond of triazole group toward U due to the transfer of electrons from graphene sheet to benzotriazole. DFT calculations further demonstrated that benzotriazole displayed stronger binding with U(VI) compared to carboxyl group due to higher binding energy of [Side/Surface-U-MBTA-GO] (79.745, 54.986 kcal/mol) than [MBTA-GO-COOH-U] (27.131 kcal/mol). This work will provide valuable insight into designing novel nitrogen-containing adsorbents for practical application in wastewater treatment.

Electrically-Transduced Chemical Sensors Based on Two-Dimensional Nanomaterials

Electrically-transduced sensors, with their simplicity and compatibility with standard electronic technologies, produce signals that can be efficiently acquired, processed, stored, and analyzed. Two dimensional (2D) nanomaterials, including graphene, phosphorene (BP), transition metal dichalcogenides (TMDCs), and others, have proven to be attractive for the fabrication of high-performance electrically-transduced chemical sensors due to their remarkable electronic and physical properties originating from their 2D structure. This review highlights the advances in electrically-transduced chemical sensing that rely on 2D materials. The structural components of such sensors are described, and the underlying operating principles for different types of architectures are discussed. The structural features, electronic properties, and surface chemistry of 2D nanostructures that dictate their sensing performance are reviewed. Key advances in the application of 2D materials, from both a historical and analytical perspective, are summarized for four different groups of analytes: gases, volatile compounds, ions, and biomolecules. The sensing performance is discussed in the context of the molecular design, structure-property relationships, and device fabrication technology. The outlook of challenges and opportunities for 2D nanomaterials for the future development of electrically-transduced sensors is also presented.

Carboxylated carbon nanotubes corked with tetraalkylammonium cations: A concept of nanocarriers in aqueous solutions

An explicit water molecular dynamics simulations were used to probe (6,6) and (9,9) single-walled carbon nanotubes, functionalized with three carboxylate ion groups at each of the two openings, as potential nanocarriers in aqueous solutions. Three tetraalkylammonium cations (i.e., tetraethyl-, tetrapropyl-, and tetrabuthylammonium) were tested as corks to cap the nanotube openings. The variation of the sizes of the nanotubes (diameter) and of the cork cations (bulkiness) allowed us to select the proper corks that fit the nanotube openings best. Smaller tetraalkylammonium ions could easily fit the openings, but since they are less hydrophobic compared to their larger analogues they showed less affinity for the interior of the nanotubes. On the other hand, the hydrophobicity (and thus the affinity for the nanotubes) can be adjusted through the increase of tetraalkylammonium cation size, providing that the cork still fits the opening. Additionally, an external electric field was tested as a means of nanotube uncorking. The field is capable of disjoining corked ions from the functionalized nanotube openings, triggering in this way a potential cargo release stored inside the nanotubes.

N, P, and S Codoped Graphene-Like Carbon Nanosheets for Ultrafast Uranium (VI) Capture with High Capacity

The development of functional materials for the highly efficient capture of radionuclides, such as uranium from nuclear waste solutions, is an important and challenging topic. Here, few-layered N, P, and S codoped graphene-like carbon nanosheets (NPS-GLCs) that are fabricated in the 2D confined spacing of silicate RUB-15 and applied as sorbents to remove U(VI)ions from aqueous solutions are presented. The NPS-GLCs exhibit a large capacity, wide pH suitability, an ultrafast removal rate, stability at high ionic strengths, and excellent selectivity for U(VI) as compared to multiple competing metal ions. The 2D ultrathin structure of NPS-GLCs with large spacing of 1 nm not only assures the rapid mass diffusion, but also exposes a sufficient active site for the adsorption. Strong covalent bonds such as P-O-U and S-O-U are generated between the heteroatom (N, P, S) with UO2 2+ according to X-ray photoelectron spectroscopy analysis and density functional theory theoretical calculations. This work highlights the interaction mechanism of low oxidation state heteroatoms with UO2 2+, thereby shedding light on the material design of uranium immobilization in the pollution cleanup of radionuclides.

Selective sorption of uranium from aqueous solution by graphene oxide-modified materials

The effect of competing ions on the sorption behaviour of uranium onto carboxyl-functionalised graphene oxide (COOH-GO) were studied in batch experiments in comparison to graphene oxide (GO) and graphite. The effect of increasing the abundance of select chemical functional groups, such as carboxyl groups, on the selectivity of U sorption was investigated. In the course of the study, COOH-GO demonstrated superior performance as a sorbent material for the selective removal of uranyl ions from aqueous solution with a distribution coefficient of 3.72 ± 0.19 × 10³ mL g⁻¹ in comparison to 3.97 ± 0.5 × 10² and 2.68 ± 0.2 × 10² mL g⁻¹ for GO and graphite, respectively.

Theoretically unraveling the separation of Am(iii)/Eu(iii): insights from mixed N,O-donor ligands with variations of central heterocyclic moieties

With the fast development of nuclear energy, the issue related to spent nuclear fuel reprocessing has been regarded as an imperative task, especially for the separation of minor actinides. In fact, it still remains a worldwide challenge to separate trivalent An(iii) from Ln(iii) because of their similar chemical properties. Therefore, understanding the origin of extractant selectivity for the separation of An(iii)/Ln(iii) by using theoretical methods is quite necessary. In this work, three ligands with similar structures but different bridging frameworks, Et-Tol-DAPhen (La), Et-Tol-BPyDA (Lb) and Et-Tol-PyDA (Lc), have been investigated and compared using relativistic density functional theory. The electrostatic potential and molecular orbitals of the ligands indicate that ligand La is a better electron donor compared to ligands Lb and Lc. The results of QTAIM, NOCV and NBO suggest that the Am-N bonds in the studied complexes have more covalent character compared to the Eu-N bonds. Based on the thermodynamic analysis, [M(NO₃)(H₂O)₈]²⁺ + L + 2NO₃^- = [ML(NO₃)₃] + 8H₂O should be the most probable reaction in the solvent extraction system. Our results clearly verify that the relatively harder oxygen atoms offer these ligands higher coordination affinities toward both of the An(iii) and Ln(iii) ions compared to the relatively softer nitrogen atoms. However, the latter possess stronger affinities toward An(iii) over Ln(iii), which partly results in the selectivity of these ligands. This work can afford useful information on achieving efficient An(iii)/Ln(iii) separation through tuning the structural rigidity and hardness or softness of the functional moieties of the ligands.

Increase in the reduction potential of uranyl upon interaction with graphene oxide surfaces

Coordination of uranyl (U(vi)) with carboxylate groups on functionalized graphene oxide (GO) surfaces has been shown to alter the reduction potential of the sorbed uranium ion.

In situ X-ray absorption fine structure study on the polymerization of isoprene assisted by Nd-based ternary catalysts

Polymerization processes of isoprene catalyzed by four catalysts with different alkylaluminums were detected by in situ XAFS technique. The catalytic mechanism of the neodymium-based ternary catalyst was discussed based on the structure information.

Dynamics of Humic Acid and Its Interaction with Uranyl in the Presence of Hydrophobic Surface Implicated by Molecular Dynamics Simulations

This work targeted a molecular level of understanding on the dynamics of humic acid (HA) and its interaction with uranyl in the presence of hydrophobic surface mimicked by a carbon nanotube (CNT), which also represents a potential intruder in the environment accompanying with the development of nanotechnology. In aqueous phase, uranyl and HA were observed to build close contact spontaneously, driven by electrostatic interaction, leading to a more compact conformation of HA. The presence of CNT unfolds HA via π-π interactions with the aromatic rings of HA without significant perturbation on the interaction strength between HA and uranyl. These results show that the hydrophilic uranyl and the hydrophobic CNT influence the folding behavior of HA in distinct manners, which represents two fundamental mechanisms that the folding behavior of HA may be modulated in the environment, that is, uranyl enhances the folding of HA via electrostatic interactions, whereas CNT impedes its spontaneous folding via van der Waals (vdW) interactions. The work also provides molecular level of evidence on the transformation of a hydrophobic surface into a hydrophilic one via noncovalent functionalization by HA, which in turn affects the migration of HA and the cations it binds to.

New Insight into GO, Cadmium(II), Phosphate Interaction and Its Role in GO Colloidal Behavior

This study establishes the relationship between the graphene oxide (GO) colloidal behavior and the co-adsorption of Cd(II) and phosphate (P(V)) on GO. Results reveal that the interactions among GO, Cd(II), and P(V) exhibit a significant dependence on solution chemistry and addition sequences and that these interactions subsequently affect the GO colloidal behavior. The GO aggregation is pH-dependent at pH < 4.0 and depends apparently on the binding ability of Cd(II) to GO at pH > 4.0. When the components were added simultaneously, the presence of P(V) enhances the GO binding capacity toward Cd(II), confirmed by theoretical calculation, resulting in the greater destabilizing influence of Cd(II) + P(V) on GO than Cd(II) at pH 3.0-9.5, while the formation of Cd3(PO4)2 precipitate leads to a lower destabilizing influence of Cd(II) + P(V) on GO than Cd(II) at pH > 9.5. Both pH and addition sequence affect the destabilizing ability of Cd(II) + P(V). These new insights are expected to provide valuable information not only for the application of GO as a potential adsorbent in multicomponent systems for heavy metal ion and oxyanion co-removal but also for the fate and risk assessment of GO after serving as heavy metal ion and oxyanion carrier.

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.

Applications and toxicity of graphene family nanomaterials and their composites

Graphene has attracted much attention of scientific community due to its enormous potential in different fields, including medical sciences, agriculture, food safety, cancer research, and tissue engineering. The potential for widespread human exposure raises safety concerns about graphene and its derivatives, referred to as graphene family nanomaterials (GFNs). Due to their unique chemical and physical properties, graphene and its derivatives have found important places in their respective application fields, yet they are being found to have cytotoxic and genotoxic effects too. Since the discovery of graphene, a number of researches are being conducted to find out the toxic potential of GFNs to different cell and animal models, finding their suitability for being used in new and varied innovative fields. This paper presents a systematic review of the research done on GFNs and gives an insight into the mode and action of these nanosized moieties. The paper also emphasizes on the recent and up-to-date developments in research on GFNs and their nanocomposites for their toxic effects.

Paving the way for the synthesis of a series of divalent actinide complexes: a theoretical perspective

Recently, the +2 formal oxidation state in soluble molecular complexes for lanthanides (La-Nd, Sm-Lu) and actinides (Th and U) has been discovered [W. J. Evans, et al., J. Am. Chem. Soc., 2011, 133, 15914; J. Am. Chem. Soc., 2012, 134, 8420; J. Am. Chem. Soc., 2013, 135, 13310; Chem. Sci., 2015, 6, 517]. To explore the nature of the bonding and stabilities of the low-valent actinide complexes, a series of divalent actinide species, [AnCp'3](-) (An[double bond, length as m-dash]Th-Am, Cp' = [η(5)-C5H4(SiMe3)](-)) have been investigated in THF solution using scalar relativistic density functional theory. The electronic structures and electron affinity properties were systematically studied to identify the interactions between the +2 actinide ions and Cp' ligands. The ground state electron configurations for the [AnCp'3](-) species are [ThCp'3](-) 6d(2), [PaCp'3](-) 5f(2)6d(1), [UCp'3](-) 5f(3)6d(1), [NpCp'3](-) 5f(5), [PuCp'3](-) 5f(6), and [AmCp'3](-) 5f(7), respectively, according to the MO analysis. The total bonding energy decreases from the Th- to the Am-complex and the electrostatic interactions mainly dominate the bonding between the actinide atom and ligands. The electron affinity analysis suggests that the reduction reaction of AnCp'3→ [AnCp'3](-) should become increasingly facile across the actinide series from Th to Am, in accord with the known An(iii/ii) reduction potentials. This work expands the knowledge on the low oxidation state chemistry of actinides, and further motivates and guides the synthesis of related low oxidation state compounds of 5f elements.

Theoretical insight into the binding affinity enhancement of serine with the uranyl ion through phosphorylation

Various type complexes of uranyl ion with serine and phosphoserine were investigated which showed phosphorylation induced binding affinity enhancement of serine with the uranyl ion.

Interactions between uranium(vi) and phosphopeptide: experimental and theoretical investigations

A phosphorylated pentapeptide (WpTPpTW, P¹) motif was designed as a model to mimic possible U(vi) coordination sites of genuine phosphorylated proteins.

Synergistic Amination of Graphene: Molecular Dynamics and Thermodynamics

Functionalization of graphene using organic moieties constitutes an affordable way to modulate its physical and chemical properties. Finding an exact structural formula of functionalized graphene using experimental approaches is challenging. We studied in detail the thermal stability and thermodynamics of amino- and ethylamino-graphene and found a surprising synergistic effect: more amino groups stabilize functionalized graphene favoring further amination, whereas a small concentration of amino groups is unstable in many cases. The functional groups can be attached either on the same side or simultaneously on different sides of the graphene sheet. Deformation of functionalized graphene is proportional to the number of amino groups. Complete amination leading to formation of the ultimate product, Cx(NH2)x, is hindered sterically. Our study assists in the determination of the structure of chemically modified graphene and makes specific predictions that can be tested and validated experimentally.

Adsorption of 4-n-Nonylphenol and Bisphenol-A on Magnetic Reduced Graphene Oxides: A Combined Experimental and Theoretical Studies

Adsorption of 4-n-nonylphenol (4-n-NP) and bisphenol A (BPA) on magnetic reduced graphene oxides (rGOs) as a function of contact time, pH, ionic strength and humic acid were investigated by batch techniques. Adsorption of 4-n-NP and BPA were independent of pH at 3.0- 8.0, whereas the slightly decreased adsorption was observed at pH 8.0-11.0. Adsorption kinetics and isotherms of 4-n-NP and BPA on magnetic rGOs can be satisfactorily fitted by pseudo-second-order kinetic and Freundlich model, respectively. The maximum adsorption capacities of magnetic rGOs at pH 6.5 and 293 K were 63.96 and 48.74 mg/g for 4-n-NP and BPA, respectively, which were significantly higher than that of activated carbon. Based on theoretical calculations, the higher adsorption energy of rGOs + 4-n-NP was mainly due to π-π stacking and flexible long alkyl chain of 4-n-NP, whereas adsorption of BPA on rGOs was energetically favored by a lying-down configuration due to π-π stacking and dispersion forces, which was further demonstrated by FTIR analysis. These findings indicate that magnetic rGOs is a promising adsorbent for the efficient elimination of 4-n-NP/BPA from aqueous solutions due to its excellent adsorption performance and simple magnetic separation, which are of great significance for the remediation of endocrine-disrupting chemicals in environmental cleanup.

Nanoscale zero-valent iron particles supported on reduced graphene oxides by using a plasma technique and their application for removal of heavy-metal ions

Nanoscale zero-valent iron particles supported on reduced graphene oxides (NZVI/rGOs) from spent graphene oxide (GO)-bound iron ions were developed by using a hydrogen/argon plasma reduction method to improve the reactivity and stability of NZVI. The NZVI/rGOs exhibited excellent water treatment performance with excellent removal capacities of 187.16 and 396.37 mg g(-1) for chromium and lead, respectively. Moreover, the NZVI/rGOs could be regenerated by plasma treatment and maintained high removal ability after four cycles. X-ray photoelectron spectroscopy analysis results implied that the removal mechanisms could be attributed to adsorption/precipitation, reduction, or both. Such multiple removal mechanisms by the NZVI/rGOs were attributed to the reduction ability of the NZVI particles and the role of dispersing and stabilizing abilities of the rGOs. The results indicated that the NZVI/rGOs prepared by a hydrogen/argon plasma reduction method might be an effective composite for heavy-metal-ion removal.

Adsorption and desorption of U(VI) on functionalized graphene oxides: a combined experimental and theoretical study

The adsorption and desorption of U(VI) on graphene oxides (GOs), carboxylated GOs (HOOC-GOs), and reduced GOs (rGOs) were investigated by batch experiments, EXAFS technique, and computational theoretical calculations. Isothermal adsorptions showed that the adsorption capacities of U(VI) were GOs > HOOC-GOs > rGOs, whereas the desorbed amounts of U(VI) were rGOs > GOs > HOOC-GOs by desorption kinetics. According to EXAFS analysis, inner-sphere surface complexation dominated the adsorption of U(VI) on GOs and HOOC-GOs at pH 4.0, whereas outer-sphere surface complexation of U(VI) on rGO was observed at pH 4.0, which was consistent with surface complexation modeling. Based on the theoretical calculations, the binding energy of [G(···)UO2](2+) (8.1 kcal/mol) was significantly lower than those of [HOOC-GOs(···)UO2](2+) (12.1 kcal/mol) and [GOs-O(···)UO2](2+) (10.2 kcal/mol), suggesting the physisorption of UO2(2+) on rGOs. Such high binding energy of [GOs-COO(···)UO2](+) (50.5 kcal/mol) revealed that the desorption of U(VI) from the -COOH groups was much more difficult. This paper highlights the effect of the hydroxyl, epoxy, and carboxyl groups on the adsorption and desorption of U(VI), which plays an important role in designing GOs for the preconcentration and removal of radionuclides in environmental pollution cleanup applications.