Formation Of Inner-sphere Surface Complexes Research Articles

Simultaneous and continuous stabilization of As and Pb in contaminated solution and soil by a ferrihydrite-gypsum sorbent

For the increasing need of stabilization both cationic and anionic metal(loid)s simultaneously, we newly developed a metal sorbent (FIXALL), consisting mainly of ferrihydrite and gypsum. The objectives of this study were to determine the molecular mechanisms of Pb and As stabilization in an aqueous system and to examine a simultaneous and long-term (up to 754days) effect on Pb and As stabilization in an anthropogenically contaminated soil using the FIXALL sorbent. When the solution contained a low concentration of Pb (5mgL−1), the mechanisms of Pb removal by FIXALL were based chiefly on the formation of inner-sphere surface complex with ferrihydrite. In the highly concentrated Pb solution (1200mgL−1), contrarily, the removal of Pb by FIXALL was the direct consequence of the dissolution of gypsum and subsequent precipitation of PbSO4, which strengthens the drawback of low capability of ferrihydrite for Pb removal. Regardless of initial concentrations, the primary mechanism of FIXALL for As stabilization is attributed to the formation of inner-sphere surface complex with ferrihydrite. A contaminated soil study demonstrated that FIXALL could decrease the concentration of water soluble As and Pb simultaneously and continuously for 754days without notable changes in their chemical species and soil pH.

Fe–Al binary oxide nanosorbent: Synthesis, characterization and phosphate sorption property

Phosphorous removal using efficient treatment approach such as adsorption is vital for the control of eutrophication. In this study, nanosized Fe-Al binary oxide sorbent was synthesized through a modified gel evaporation method and employed for adsorption of phosphate from aqueous system. The nanosorbent was characterized by x-ray diffraction (XRD), scanning electron microscope coupled with energy dispersive x-ray spectroscopy (SEM/EDX), tunneling electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and flame atomic absorption spectroscopy (FAAS). Langmuir model showed the best fit to the experimental data with a maximum adsorption efficiency of 16.4mg/g. Having all parameters optimized, it has been found that the nanosorbent exhibited 99.86% phosphate adsorption efficiency. The effect of co-existing anions on the adsorption of phosphate was also studied and no significant effect on the efficiency of the nanosorbent was observed due to competing ions such as fluoride. Desorbabilty of phosphate was investigated and found to be increased with increasing pH. The results of thermodynamic studies indicated that the process is spontaneous and endothermic. Both macroscopic and microscopic approaches were employed to predict the mechanism of phosphate adsorption on the Fe-Al binary oxide nanosorbent. Accordingly, the phosphate adsorption is presumed to occur via the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface.

Sorption of Cadmium(II) and Zinc(II) from Aqueous Solution by Water Treatment Residuals at Different pH Values

Here, we report on the ability of two different water treatment residues, a Fe-based (Fe-WTR) and an Al-based (Al-WTR) ones, to accumulate Cd(II) and Zn(II) from aqueous solutions at different pH values (pH 4.5, 5.5, and 7.0). Fe-WTR showed a greater Zn(II) and Cd(II) sorption capacity than Al-WTR at all the pH values investigated, in particular at pH 7.0 (e.g., ∼0.200 and ∼0.100 mmol g−1 of Me(II) sorbed by Fe- and Al-WTR at pH 7.0, respectively). The greater capacity of the Fe-WTR to accumulate Me(II) seems to be linked to its higher content of iron and manganese ions and to its higher CEC value compared to Al-WTR. The role of the inorganic and organic fractions of WTRs in metal sorption was also assessed. A higher affinity of Cd(II) with respect to Zn(II) toward functional groups of the organic matter of both WTRs was observed, while Zn(II) showed a stronger association with the inorganic phases. The sorption of both metal ions appeared mainly governed by the formation of inner-sphere surface complexes with the inorganic and organic phases of WTRs, as suggested by the sequential extraction data.

Sorption of Eu3+ on Na-montmorillonite studied by time-resolved laser fluorescence spectroscopy and surface complexation modeling

The influence of pH and concentrations of Eu3+ and NaNO3 on the sorption of Eu3+ to Na-montmorillonite were investigated through batch sorption measurements and time-resolved laser fluorescence spectroscopy. The pH had little effect on the distribution coefficients (Kd) in the range of pH 4–7 at 0.01 M NaNO3, which indicates that the cation exchange reaction is a dominant sorption process. Meanwhile, the Kd strongly depended on pH at 1 M NaNO3, suggesting the formation of inner-sphere surface complexes. A cation exchange model combined with a one-site non-electrostatic surface complexation model was successfully applied to the measured Kd data. Linear free-energy relationship was used to estimate the formation constants of the surface species from those of the corresponding aqueous hydrolyzed species. The TRLFS spectra of Eu3+ sorbed on Na-montmorillonite were processed by parallel factor analysis, which provided the fluorescence spectra, decay lifetimes, and relative intensity profiles of three Eu3+ surface species. These species corresponded to one outer-sphere (factor A) and two inner-sphere (factors B and C) complexes. It turned out that factors A and B correspond to Eu3+ sorbed by ion exchange to permanent charge sites of Na-montmorillonite and inner-sphere complexation with surface hydroxyl groups of the edge faces. Factor C became dominant at relatively high pH and ionic strength and likely corresponded to the precipitation of Eu(OH)3 on the surface of Na-montmorillonite.

RETRACTED: Effects of Bacillus subtilis on the reduction of U(VI) by nano-Fe0

Abstract The effects of Bacillus subtilis ( B . subtilis , a typical model bacterium) on the reduction of U(VI) by nanoscale zero-valent iron (nano-Fe 0 ) were investigated using batch techniques. The reaction products were analysed using spectroscopic techniques, and a kinetics model was developed to elucidate the mechanisms of U(VI) reduction by nano-Fe 0 . The presence of B . subtilis enhanced the U(VI) sorption rate at pH 3.5–9.5 but inhibited the reduction rate of U(VI) to U(IV) at pH > 4.5. According to the FTIR and XRD analysis, the reduction of U(VI) to U(IV) was inhibited due to the formation of inner-sphere surface complexes between the oxygen-containing functional groups of B . subtilis or extracellular polymeric substances with the Fe(II)/Fe(III) generated by nano-Fe 0 , which blocked electron transport from the Fe 0 core to U(VI). Based on the EXAFS analysis, a fitting of U–Fe shell at ∼3.44 A revealed inner-sphere bidentate complexes between uranyl and the oxide film of nano-Fe 0 . For the nano-Fe 0 + B. subtilis system, the U–Fe shell (at ∼3.44 A) and the U–C/P shell (at ∼2.90 A) further indicated the formation of inner-sphere surface complexes. The kinetics model supported that U(VI) reduction was triggered by U(VI) sorption on the oxide shell of nano-Fe 0 . The XPS and XANES analyses showed that reductive precipitation was the main mechanism of U(VI) removal by nano-Fe 0 , whereas the sorption process dominated the removal of U(VI) in the presence of B . subtilis, which was further demonstrated by TEM images.

Surface complexation modeling of inositol hexaphosphate sorption onto gibbsite

The sorption of Inositol hexaphosphate (IP6) onto gibbsite was investigated using a combination of adsorption experiments, 31P solid-state MAS NMR spectroscopy, and surface complexation modeling. Adsorption experiments conducted at four temperatures showed that IP6 sorption decreased with increasing pH. At pH 6, IP6 sorption increased with increasing temperature, while at pH 10 sorption decreased as the temperature was raised. 31P MAS NMR measurements at pH 3, 6, 9 and 11 produced spectra with broad resonance lines that could be de-convoluted with up to five resonances (+5, 0, −6, −13 and −21ppm). The chemical shifts suggest the sorption process involves a combination of both outer- and inner-sphere complexation and surface precipitation. Relative intensities of the observed resonances indicate that outer-sphere complexation is important in the sorption process at higher pH, while inner-sphere complexation and surface precipitation are dominant at lower pH. Using the adsorption and 31P MAS NMR data, IP6 sorption to gibbsite was modeled with an extended constant capacitance model (ECCM). The adsorption reactions that best described the sorption of IP6 to gibbsite included two inner-sphere surface complexes and one outer-sphere complex:AlOH+IP612-+5H+↔Al(IP6H4)7-+H2O3AlOH+IP612-+6H+↔Al3(IP6H3)6-+3H2O2AlOH+IP612-+4H+↔(AlOH2)22+(IP6H2)10-The inner-sphere complex involving three surface sites may be considered to be equivalent to a surface precipitate.Thermodynamic parameters were obtained from equilibrium constants derived from surface complexation modeling. Enthalpies for the formation of inner-sphere surface complexes were endothermic, while the enthalpy for the outer-sphere complex was exothermic. The entropies for the proposed sorption reactions were large and positive suggesting that changes in solvation of species play a major role in driving the sorption process.

The efficient enrichment of U(vi) by graphene oxide-supported chitosan

Graphene oxide-supported chitosan (GO-Ch) composites were synthesized using a covalent method for U(VI) adsorption and were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and extended X-ray absorption fine structure (EXAFS). The characteristic results indicated that Ch was successfully grafted onto GO. The adsorption of U(VI) on GO-Ch was investigated under different environmental conditions. The adsorption kinetics showed that the adsorption of U(VI) on GO-Ch followed the pseudo-second-order equation. The maximum adsorption capacity of U(VI) on GO-Ch at pH 4.0 and T = 303 K calculated from the Langmuir model was 225.78 mg g−1. Thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that U(VI) adsorption on GO-Ch was an endothermic and spontaneous process. The batch desorption indicated U(VI) cannot be completely desorbed from GO-Ch without intervention, suggesting the irreversible adsorption of U(VI) on GO-Ch. The analysis of FT-IR spectra suggested that the interaction mechanism of U(VI) on GO-Ch was mainly chemical adsorption by –NH2 and –COOH groups. According to EXAFS analysis, the peaks at ∼2.9 A can be satisfactorily fitted by the U–C/N shell, revealing the formation of inner-sphere surface complexes. It is demonstrated that the GO-Ch nanocomposite can be a promising material for the preconcentration and solidification of U(VI) from large volumes of aqueous solution.

Simultaneous adsorption and reduction of U(VI) on reduced graphene oxide-supported nanoscale zerovalent iron

The reduced graphene oxide-supported nanoscale zero-valent iron (nZVI/rGO) composites were synthesized by chemical deposition method and were characterized by SEM, high resolution TEM, Raman and potentiometric acid-base titrations. The characteristic results showed that the nZVI nanoparticles can be uniformly dispersed on the surface of rGO. The removal of U(VI) on nZVI/rGO composites as a function of contact time, pH and U(VI) initial concentration was investigated by batch technique. The removal kinetics of U(VI) on nZVI and nZVI/rGO were well simulated by a pseudo-first-order kinetic model and pseudo-second-order kinetic model, respectively. The presence of rGO on nZVI nanoparticles increased the reaction rate and removal capacity of U(VI) significantly, which was attributed to the chemisorbed OH− groups of rGO and the massive enrichment of Fe2+ on rGO surface by XPS analysis. The XRD analysis revealed that the presence of rGO retarded the transformation of iron corrosion products from magnetite/maghemite to lepidocrocite. According to the fitting of EXAFS spectra, the UC (at ∼2.9Å) and UFe (at ∼3.2Å) shells were observed, indicating the formation of inner-sphere surface complexes on nZVI/rGO composites. Therefore, the nZVI/rGO composites can be suitable as efficient materials for the in-situ remediation of uranium-contaminated groundwater in the environmental pollution management.

Phosphate removal from aqueous solutions by a nano-structured Fe–Ti bimetal oxide sorbent

Phosphate removal from water is of vital importance to control eutrophication. Adsorption is one of the most popular technologies for phosphate removal. In this study, iron oxide-based sorbents with different Fe/Ti molar ratios were synthesized by coprecipitation method. Results showed that the Fe–Ti bimetal oxide prepared with a Fe/Ti molar ratio of 20:1 was the optimal sorbent for phosphate removal. Transmission electron microscopic (TEM) image analyses indicate that the Fe–Ti bimetal oxide was nano-structured aggregates. The sorption kinetic data could be described better by the pseudo-second-order equation indicating its chemisorption nature. The boundary layer (film) diffusion was the rate-limiting step of sorption process. The equilibrium sorption data were well fitted with the Langmuir and Freundlich models. The phosphate sorption capacity calculated from Langmuir equation was 35.4mg/g at pH 6.8. Thermodynamics experiments showed that the phosphate sorption was spontaneous and endothermic. The results of ionic strength effect together with zeta potential, FTIR and XPS analyses demonstrated that the main mechanism of phosphate sorption was the replacement of surface hydroxyl groups (M–OH) by phosphate via formation of inner-sphere surface complex. The spent Fe–Ti bimetal oxide could be effectively regenerated by NaOH solutions.

Selenium(IV) Uptake by Maghemite (γ-Fe2O3)

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11). Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing ((2)C) and bidentate mononuclear edge-sharing ((1)E) inner-sphere surface complexes was observed, with a trend toward solely (1)E complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the Se(IV)O3 unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters.

Water treatment residues as accumulators of oxoanions in soil. Sorption of arsenate and phosphate anions from an aqueous solution

Here we report a survey addressed to determine, at different pH values (pH 4.0, 7.0 and 9.0), the ability of two different water treatment residues, a Fe-based (Fe-WTR) and an Al-based (Al-WTR), to accumulate arsenate and phosphate anions from an aqueous solution and to define the mechanism which regulate the sorption of these anions. Fe-WTR showed a greater As(V) and P(V) sorption capacity respect to Al-WTR at all the pH values investigated, in particular at pH 4.0. The greater capacity of the Fe-WTR to accumulate phosphate at pH 4.0 seems to be linked to the higher content of manganese ions compared to Al-WTR, which can give rise, with phosphate ions, to the formation of MnHPO4 precipitates. Sequential extraction of As(V)- or P(V)-WTRs suggested that the main mechanism governing the sorption of both two anions likely involve the formation of inner-sphere surface complexes [Fe/Al–O–As(P)]. Such a coordination mode was supported by the FT-IR spectra that exhibit well resolved band at 865cm−1 and 1040cm−1 attributable to ν(As–O) or ν(P–O) stretching vibration, respectively.

Adsorptive removal of U(VI) and Th(IV) from aqueous solutions using polymer-based electrospun PEO/PLLA fibrous membranes

Fibrous membranes based on poly(ethylene oxide) and poly(l-lactide) fabricated by electrospinning were evaluated for the first time as substrates for the adsorption of tetravalent thorium (Th(IV)) and hexavalent uranium (U(VI)) from aqueous media. The membranes consisted of microfibers with diameters of approximately 2 μm as revealed by scanning electron microscopy. The adsorption of Th(IV) and U(VI) on the membrane was investigated as a function of pH, ionic strength and initial metal concentration under normal atmospheric conditions. The experimental data indicated increased affinity of the membrane for Th(IV) and U(VI), which was pH depended and reaches maximum values (>90 %) for Th(IV) and U(VI) at pH 3 and pH 6.5, respectively. The maximum adsorption capacity (qmax) at optimum conditions was evaluated from the Langmuir isotherm and was found to amount 50.08 and 9.3 mmol kg−1 for Th(IV) and U(VI), respectively. In addition, studies on the effect of ionic strength on the adsorption efficiency did not show any significant effect indicating that the adsorption of Th(IV) and U(VI) on the membrane was most probably based on specific interactions and the formation of inner-sphere surface complexes. The significantly higher adsorption efficiency of the membrane for Th(IV) in acidic media (pH ≤ 3) could be utilized for a pH-triggered, selective separation of Th(IV) from U(VI) from aqueous media.

Copper(II) removal from aqueous solutions by adsorption on non-treated and chemically modified cactus fibres

The adsorption efficiency of a biomass by-product (cactus fibres) regarding the removal of copper(II) from aqueous solutions has been investigated before and after its chemical treatment. The chemical treatment of the biomass by-product included phosphorylation and MnO2-coating. The separation/removal efficiency has been studied as a function of pH, Cu(II) concentration, ionic strength, temperature and contact time. Evaluation of the experimental data shows that the MnO2-coated product presents the highest adsorption capacity, followed by the non-treated and phosphorylated material. Regarding the effect of ionic strength/salinity on the adsorption, in contrast to the removal efficiency of the phosphorylated product, which is significantly affected, the MnO2-coated and non-treated material don't show any effect, indicating the formation of inner-sphere surface complexes. The adsorption reaction is in all cases endothermic and relatively fast, particularly the adsorption on the MnO2-coated product. The results of the present study indicate that for the removal of bivalent metal-ions from contaminated waters the MnO2-coated material is expected to be the most effective adsorbent and an alternative to MnO2 resins for the treatment of environmentally relevant waters.

Enhanced adsorption of phosphate from aqueous solution by nanostructured iron(III)–copper(II) binary oxides

Phosphate is one of the main elements causing eutrophication and hence the development of high-efficiency and low-cost technologies for phosphate removal from water is of vital importance to alleviate the situation. In this study, nanostructured Fe–Cu binary oxides were synthesized via a facile coprecipitation process and its performance on phosphate removal was systematically evaluated. The as-prepared adsorbent with a Cu/Fe molar ratio of 1:2 was proved to possess the highest phosphate adsorption capacity. The adsorption isotherm data gave better fit to the Langmuir model, with a maximum phosphate adsorption capacity of 35.2mgg−1 at pH 7.0±0.1. Kinetic data correlated well with the pseudo-second-order kinetic model, indicating that the adsorption process might be chemical sorption. Thermodynamic data validated that the phosphate adsorption was an endothermic process. The solution pH has a big impact on the phosphate adsorption on the sorbent and acidic condition was favorable for the adsorption. The coexisting Cl−, SO42- and HCO3- anions had no significant influence on phosphate adsorption, while the present F− and SiO32- could suppress its adsorption, especially at high concentration level. The phosphate adsorption might be mainly achieved by the replacement of surface sulfate and hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. Moreover, the spent Fe–Cu binary oxide could be effectively regenerated by NaOH solution for reuse. The high phosphate uptake capability and good reusability of the Fe–Cu binary oxide make it a potentially attractive adsorbent for the removal of phosphate from water.

Surface mechanism of the boron adsorption on alumina in aqueous solutions

ABSTRACT The adsorption of boron (boric acid) from aqueous solutions on alumina has been investigated at pH 8.0, I = 0.1 M NaClO4, T = 22 ± 3°C, and under normal atmospheric conditions. The characterization of the adsorbed species was performed by Raman spectroscopy and the spectroscopic speciation was assisted by theoretical DFT calculations. Evaluation of the spectroscopic data points to the formation of inner-sphere surface complexes and indicates the formation of two different types of adsorbed boron species. The theoretical calculations corroborate the spectroscopic data and indicate that at low boron concentration the monodentate surface species dominates, whereas increased boron concentration favors the formation of a bidentate surface species. Assuming low coverage, the conditional formation constant for the monodentate surface species has been evaluated to be log β ∗ = 4.1 ± 0.1.

Uranium adsorption by non-treated and chemically modified cactus fibres in aqueous solutions

The adsorption efficiency of Opuntia ficus indica fibres regarding the removal of hexavalent uranium [U(VI)] from aqueous solutions has been investigated prior and after the chemical treatment (e.g. phosphorylation and MnO2-coating) of the biomass. The separation/removal efficiency has been studied as a function of pH, uranium concentration, adsorbent mass, ionic strength, temperature and contact time. Evaluation of the experimental data shows that biosorption is strongly pH-depended and that the MnO2-coated product presents the highest adsorption capacity followed by the phosphorylated and non-treated material. Experiments with varying ionic strength/salinity don’t show any significant effect on the adsorption efficiency, indicating the formation of inner-sphere surface complexes. The adsorption reactions are in all cases exothermic and relatively fast, particularly regarding the adsorption on the MnO2-coated product. The results of the present study indicate that adsorption of uranium from waters is very effective by cactus fibres and particularly the modified treated fibres. The increased adsorption efficiency of the cactus fibres is attributed to their primary and secondary fibrillar structure, which result in a relative relative high specific surface available for sorption.

A study on adsorption mechanism of organoarsenic compounds on ferrihydrite by XAFS

Anthropogenic organoarsenic compounds which were used such as agrochemicals, pesticides, and herbicides can have a potential as a source of arsenic pollution in water. In the process, the adsorption of arsenic onto mineral surface in soil may play an important role to affect arsenic distribution in solid-water interface. However, adsorption structures of organoarsenic compounds on the iron-(oxyhydr)oxides are not well known. In this study, extended X-ray absorption fine structure (EXAFS) spectroscopy was employed to know the adsorption structure of methyl- and phenyl-substituted organoarsenic compounds (methylarsonic acid (MMA), dimethylarsinic acid (DMA), phenylarsonic acid (PAA), and diphenylarsinic acid (DPAA) onto ferrihydrite which can be a strong adsorbent of arsenic. EXAFS analysis suggests that the formation of inner-sphere surface complex for all organoarsenic compounds with ferrihydrite regardless of the organic functional groups and the number of substitution. The As-Fe distances are around 3.27 , which suggests both mono-and bi-dentate inner-sphere complexes by DFT calculations. The corresponding coordination numbers (CNs) are less than two, suggesting that coexistence of both structures of inner-sphere complexes.

Microscopic level investigation of Ni(II) sorption on Na-rectorite by EXAFS technique combined with statistical F-tests

Extended X-ray absorption fine structure (EXAFS) spectroscopy combined with statistical F-tests is used to investigate the local atomic structures of Ni(II) adsorbed on Na-rectorite. The EXAFS analysis results of Ni(II) sorption samples indicate that the first coordination shell consists of ∼6 O at the Ni–O interatomic distance (R) of ∼2.04Å. The presence of Ni backscattering at RNi–Ni=∼3.06Å in the second coordination shell suggests the formation of Ni(II) precipitate. The results of F-tests show that the Ni(II) precipitate is Ni–Al layered double hydroxide (LDH). Our results demonstrate that Ni(II) ions are retained via different mechanisms depending on solution conditions. At low pH, Ni retention is controlled mainly by the outer-sphere surface complexation. With increasing pH, outer-sphere and inner-sphere surface complexation dominate Ni uptake. Furthermore, Ni surface loading increases with temperature increasing at pH 6.5 due to the formation of inner-sphere surface complexes and Ni–Al LDH. The formation of Ni–Al LDH becomes the dominate mechanism at the elevated pH and temperature. In the presence of humic substances, the sorption of Ni(II) on Na-rectorite is dominated by the formation of ternary surface complexes. These results are important to understand the physicochemical behavior of Ni(II) in the natural environment.

Uranium(VI) adsorption on graphene oxide nanosheets from aqueous solutions

Single-layered graphene oxide (GO) prepared by the Hummers method was used to adsorb U(VI) ions from aqueous solutions. The U(VI) sorption was studied as a function of solution pH, ionic strength, and initial concentration of U(VI) using a batch method in air. It is found that the sorption is rapid, strongly dependent on pH, attaining a plateau at pH 4.0–7.5, and independent of the ionic strength. This suggests the formation of inner-sphere surface complexes of U(VI) on GO. The maximum sorption capacity of GO for U(VI) was evaluated to be 299mg/g at pH 4.0, ranking it among the most effective sorbents reported for U(VI) so far. The abundant oxygen-containing functional groups of GO were demonstrated to play crucial roles in the sorption. Using the distribution coefficients obtained at different temperatures, thermodynamic parameters were also calculated, showing that the sorption is endothermic and spontaneous. GO could be a promising sorbent material applied in the environmental cleanup of uranium pollution and the enrichment of uranium from large volumes of solution.

Investigation of radionuclide 60Co(II) binding to TiO2 by batch technique, surface complexation model and DFT calculations

The interaction between radionuclides and solid/water interfaces is important to understand the physicochemical processes of radionuclides in the natural environment. Herein, the interaction of 60Co(II) with TiO2 in aqueous solution as a function of pH and ionic strength was studied by using batch technique combined with surface complexation model and density functional theory (DFT) calculations. The batch experimental results showed that the adsorption of 60Co(II) was dependent on pH and independent of ionic strength, indicating the formation of inner-sphere surface complexes on TiO2 surfaces. The results of surface complexation models and DFT calculations indicated that the surface species of 60Co(II) adsorbed on TiO2 followed the trend: B structure (i.e., 60Co(II) was linked to one bridge oxygen site) was the dominant surface species at low pH, and TT structure (i.e., 60Co(II) was linked to two terminal oxygen sites) became the important surface complex at neutral and alkaline pH values. These results demonstrated that a multi-technique approach could lead to definitive information on the structures of adsorbed 60Co(II) at the molecular level at the TiO2/water interfaces, as well as realistic models to rationalize and accurately evaluate the macroscopic manifestations of radionuclide adsorption phenomena.