Cs Adsorption Research Articles

Early stage of Cs activation mechanism for In0.53Ga0.47As (0 0 1) β2 (2 × 4) surfaces: Insights from first-principles calculations

The negative electron affinity (NEA) InxGa1−xAs photocathodes are of particular importance as a fundamental building block for the near infrared sensitivity image intensifier. However, a comprehensive understanding is still lacking of the activation mechanism in order to form NEA state. Here we perform a detailed theoretical research on the early stage of Cs adsorption on the As-rich β2(2 × 4) reconstruction of In0.53Ga0.47As (0 0 1) surface by using first-principles calculations within the framework of density functional theory. Adsorption energies, work functions, dipole moments, band structures and density of states of In0.53Ga0.47As (0 0 1) β2 (2 × 4) surface corresponding to different Cs coverages are investigated. Calculation results indicate that Cs adsorption on In0.53Ga0.47As (0 0 1) β2(2 × 4) surface becomes more and more difficult as Cs coverage increases. Cs-induced [Csn+-In0.53 Ga0.47Asn-] dipoles are perpendicular to the substrate, which will decrease the work function and make the electrons easier to escape to the vacuum. However, excessive Cs adatoms will lead to the dipoles repelling each other, and some electrons return back to the substrate due to the electrostatic depolarization, resulting in the appearance of “Cs-kill” phenomenon and the work function rises again. Consequently, the optimal Cs coverage corresponding to the peak value of the InGaAs photocurrent should be considered in order to prevent the absence of the “Cs-kill” phenomenon. Meanwhile, there emerge new valence bands induced by Cs adsorption ranging from −25 eV to −22 eV and from −13 eV to 9 eV. Due to the combined effect of Cs 5s and 5p state electrons, the Fermi level moves into the conduction band, leading to the adsorption models showing more metallic properties.

Adsorption of Cs onto Biogenic Birnessite: Effects of Layer Structure, Ionic Strength, and Competition Cations

Although the adsorption of cesium (Cs) onto phyllosilicate minerals has been widely studied, the effect of Cs on redox-sensitive biogenic Mn oxide is not well understood. In this study, the structural transformation of biogenic birnessite stimulated by commonly occurring natural heavy metals, and the influence of those metals on the adsorption behavior of Cs over a wide range of concentrations (1 × 10–10 to 0.1 mol/L) was carefully examined via solution chemistry and X-ray absorption fine structure techniques. The Cs was reversibly adsorbed onto the mineral surface to form an outer-sphere coordination for all biogenic birnessite samples. The presence of heavy metals (e.g., Zn and Ni) during bio-oxidation of Mn(II), followed by acid treatment, increased the number of available layer vacancies, which consequently increased the adsorption capacity of Cs in the final product. The analysis of the dependence of sorption values on the ionic strength showed distinct results on biogenic birnessite and chemically s...

Photocatalytic enhancement of cesium removal by Prussian blue-deposited TiO2

After the Fukushima nuclear accident, tremendous efforts were made to treat radiocesium, radiostrontium, and other radioactive materials. For the first time, we demonstrate that a TiO2 photocatalyst can significantly enhance Cs adsorption by Prussian blue-deposited TiO2 (PB/TiO2) under UV irradiation. In this study, we synthesized PB/TiO2 using the photodeposition method. After the Cs ions were adsorbed on the PB/TiO2 in darkness, we then exposed the PB/TiO2 to UV light irradiation. This resulted in a further increase in Cs ion adsorption of more than 10 times the amount adsorbed in darkness. This photocatalytic-enhanced adsorption of Cs ions was not observed on PB mixed with SiO2, nor under visible light irradiation. We investigated the effects of PB concentration, PB/TiO2 concentration, and gas purging on both dark and photocatalytic-enhanced adsorption of Cs ions by PB/TiO2. Based on the results, we suggest that the photocatalytic-enhanced adsorption of Cs ions on PB/TiO2 is due to photocatalytic reduction of PB, which leads to additional adsorption of Cs ions. The change in solution color before and after the reaction, and the change in solution pH in the dark and during UV irradiation strongly support this suggestion. The photocatalytic-enhanced adsorption of Cs ions was equivalent during radioactive 137Cs removal, indicating important applications for pollutant removal from contaminated water.

Effective removal of cesium from wastewater solutions using an innovative low-cost adsorbent developed from sewage sludge molten slag

This study investigates the effective removal of cesium (Cs) from aqueous solution using sewage sludge molten (SSM) slag that has undergone the surface modification with alkali (NaOH) hydrothermal treatment. The raw and modified slags were characterised systematically using the BET method, the FESEM, the XRF, the XRD spectroscopy and the CEC analysis to understand the physicochemical changes of the materials, and its sensitivity to Cs ions adsorption. Batch adsorption experiments were carried out to investigate the effects of adsorbent dose, contact time, solution pH, different initial Cs concentrations, temperature and the effect of competitive ions on Cs adsorption. The adsorption isotherm, kinetic and thermodynamic studies were also evaluated based on the experimental results. A higher Cs removal efficiency of almost 100% (for 20–100 mg/L of initial concentration) was achieved by the modified SSM slag, and the maximum adsorption capacity was found to be 52.36 mg/g. Several types of synthetic zeolites such as zeolite X, zeolite Y, zeolite A, and sodalite were formed on surface of the modified slag through the modification process which might be enhanced the Cs adsorption capacity. Kinetic parameters were fitted by the pseudo-second order model. The adsorption isotherms data of modified slag were well-fitted to the Langmuir (R2 = 0.989) and Freundlich isotherms (R2 = 0.988). The thermodynamic studies indicated that the adsorption process by the modified slag was spontaneous and exothermic. In the competitive ions effect, the modified slag effectively captured the Cs ion in the presence of Na+ and K+, especially at their lower concentrations. Moreover, the modified slag was reused for several cycles after the successful elution process with an appropriate eluting agent (0.5 M H2SO4), without deterioration of its original performance. Therefore, the SSM modified slag could be effectively used as a low-cost potential adsorbent for high Cs adsorption from wastewater.

Thermodynamics, kinetics, and mechanics of cesium sorption in cement paste: A multiscale assessment

Cesium-137 is a common radioactive byproduct found in nuclear spent fuel. Given its 30 year half life, its interactions with potential storage materials---such as cement paste---is of crucial importance. In this paper, simulations are used to establish the interaction of calcium silicate hydrates (C-S-H)---the main binding phase of cement paste---with Cs at the nano- and mesoscale. Different C-S-H compositions are explored, including a range of Ca/Si ratios from 1.0 to 2.0. These calculations are based on a set of 150 atomistic models, which qualitatively and quantitatively reproduce a number of experimentally measured features of C-S-H---within limits intrinsic to the approximations imposed by classical molecular dynamics and the steps followed when building the models. A procedure where hydrated ${\mathrm{Ca}}^{2+}$ ions are swapped for ${\mathrm{Cs}}^{1+}$ ions shows that Cs adsorption in the C-S-H interlayer is preferred to Cs adsorption at the nanopore surface when Cs concentrations are lower than 0.19 Mol/kg. Interlayer sorption decreases as the Ca/Si ratio increases. The activation relaxation technique nouveau is used to access timescales out of the reach of traditional molecular dynamics (MD). It indicates that characteristic diffusion time for ${\mathrm{Cs}}^{1+}$ in the C-S-H interlayer is on the order of a few hours. Cs uptake in the interlayer has little impact on the elastic response of C-S-H. It leads to swelling of the C-S-H grains, but mesoscale calculations that access length scales out of the range of MD indicate that this leads to practically negligible expansive pressures for Cs concentrations relevant to nuclear waste repositories.

Initial data on adsorption of Cs and Sr to the surfaces of microplastics with biofilm

The adsorption of radiocesium and radiostrontium onto a range of natural materials has been well quantified, but not for the new media of environmental plastics, which may have enhanced adsorption due to surface-weathering and development of biofilms. Microplastic samples were deployed in freshwater, estuarine and marine conditions, then characterised using infrared spectroscopy to document changes to the plastic surface (vs interior). Synchrotron elemental mapping data revealed surfaces that were well-covered by accumulation of reactive water solutes and sulphur, but, in contrast, had highly discrete coverage of elements such as Fe and Ti, indicating adhered mineral/clay-associated agglomerates that may increase overall adsorption capacity. Plastics that had been deployed for nearly five months adsorbed radionuclides in both freshwater and estuarine conditions with the highest Kd for cesium (Cs) in freshwater (80 ml g−1) and lowest for strontium (Sr) in estuarine conditions (5 ml g−1). The degree of Cs and Sr adsorption onto plastics appears to be approximately 2–3 orders of magnitude lower than for sediment reference values. While lower than for sediments, adsorption occurred on all samples and may indicate a significant radionuclide reservoir, given that plastics are relatively buoyant and mobile in water regimes, and are increasing in global aquatic systems.

The adsorption of Cs+ from wastewater using lithium-modified montmorillonite caged in calcium alginate beads

The increasing nuclear energy consumption has posed serious environmental concerns (e.g. nuclear leakage), and the removal of radionuclides such as cesium becomes an urgent issue to be solved currently. In this research, a novel non-toxic adsorbent lithium-modified montmorillonite clay encapsulated in calcium alginate microbeads (MCA/Li) was fabricated by using ion-exchange method and then used successfully in the remediation of cesium-contaminated wastewater. Analyses of scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the physicochemical properties of adsorbent MCA/Li, such as internal crystal structure, constituent elements, and functional groups. The effects of concentration ratios (sodium alginate/montmorillonite), solution pH, contacting time and initial Cs+ concentration on the adsorption behavior were carefully investigated via batch adsorption experiments. The adsorbent MCA/Li exhibited higher selectivity and removal efficiency towards Cs+ with the maximum adsorption capacity of 100.25 mg/g. In the kinetics study, the pseudo-first-order fitted the cesium adsorption data of MCA/Li better than the pseudo-second-order. The adsorption mechanism studies revealed the process followed the Langmuir isotherm model, which suggested that Cs+ adsorption onto MCA/Li is a monolayer homogeneous adsorption process. The research findings indicated this novel adsorbent MCA/Li demonstrated great potential in radioactive wastewater treatment due to its convenience in synthesis, high adsorption capacity, and low cost.

Chitosan/CaCO3-silane nanocomposites: Synthesis, characterization, in vitro bioactivity and Cu(II) adsorption properties

Chitosan nanocomposites containing 2, 5, 8wt% of calcium carbonate-γ-aminopropyl triethoxy silane (CS/CC-ATS NCs) were prepared by ultrasonic irradiation. After characterizing of physicochemical properties of the obtained CS/CC-ATS NCs, their performance was evaluated for both the bone-like apatite mineralization and the removal of Cu(II). The field emission-scanning electron microscopy images from the in vitro bioactivity of the CS and the CS/CC-ATS NC 5wt% displayed that the hydroxyapatite was produced on the samples surface. However, the distribution of it on the surface of CS/CC-ATS NC 5wt% was better than the pure CS. The uptake of Cu(II) on the CS/CC-ATS NC 5wt% was studied under different adsorption conditions such as contact time, the initial concentration of metal ion and adsorbent amount. The results of isothermal adsorption of the pure CS and the CS/CC-ATS NC 5wt% were well fitted by Langmuir model for Cu(II) with adsorption capacity of 33.33 and 33.90mg·g−1, respectively. As a result, the CS/CC-ATS NC has great potencies in both the bone tissue engineering and the uptake of toxic metal from solution.

Breakthrough studies of the adsorption of Cs from freshwater using a mesoporous silica material containing ferrocyanide

The selectivity and fast exchange kinetics of porous silica adsorbents containing Cu or K ferrocyanide make them ideal candidates for the column decontamination of 137Cs effluents. The exchange thermodynamics of the K+ ions in Sorbmatech® (S202, one such adsorbent) with the major cations present in natural (fresh or sea) water have recently been studied in competition with Cs+ sorption to properly model batch data. This article reports an evaluation of this material for continuous, column processes of freshwater decontamination. Experimental data show that its performance is excellent under these conditions, with a steep breakthrough curve of Cs at column exit. The sorption capacity of S202 is completely retained at high flow rates (up to 10 m·h−1 Darcy velocity) and its column behavior remains ideal down to a height/diameter ratio of 2. A reactive transport model accounting for dispersive flow through the bed coupled to ion diffusion and exchange inside the porous adsorbent grains accurately reproduces the experimental data.

The electronic and optical properties of Cs adsorbed GaAs nanowires via first-principles study

In this study, we investigate the Cs adsorption mechanism on (110) surface of zinc-blende GaAs nanowire. The adsorption energy, work function, dipole moment, geometric structure, Mulliken charge distribution, charge transfer index, band structures, density of state and optical properties of Cs adsorption structures are calculated utilizing first-principles method based on density function theory. Total-energy calculations show that all the adsorption energies are negative, indicating that Cs adsorption process is exothermic and Cs covered GaAs nanowires are stable. The work function of nanowire surface has an obvious decrease after Cs adsorption. Besides, the ionization of nanowire surface is enhanced as well. More importantly, Cs adsorption contributes to a lower side shift of bands near Fermi level, and the corresponding band gap disappears. Additionally, the absorption peak and energy loss function after Cs adsorption are far higher than those before adsorption, implying better light absorption characteristic of nanowire surface after Cs adsorption. These theoretical calculations can directly guide the Cs activation experiment for negative electron affinity GaAs nanowire, and also lay a foundation for the further study of Cs/O co-adsorption on the nanowire surface.

Uptake of Cesium and Some Typical Metals onto Hybrid Calix[4]crown Adsorbent with Silica Carrier by Host–Guest Recognition

A new silica adsorbent, C7C6CalixSi, was prepared by intermolecular hybridization. It was achieved by introducing and immobilizing a macrocyclic C7C6Calix into the pores of the hybrid silica carrier specially developed. FT-IR, SME, TG-DSC, BET, and XAR were utilized to characterize the structure of the adsorbent. C7C6Calix was successfully introduced into the macroporous silica carrier by self-assembly. The adsorption of Cs and other typical metals toward C7C6CalixSi was investigated in the range of 0.4 to 5.0 M HNO3. C7C6CalixSi had an excellent adsorption ability and selectivity for Cs over others, except for Rb. The adsorption capacity of Cs was 0.1233 mM/g at the optimal adsorption conditions of 1.0 M HNO3, 298 K, and a contact time of 120 min. The experimental results fitted well with the Langmuir model. The thermodynamic parameters ΔH°, ΔG°, and ΔS° of Cs uptake were obtained. The stability of C7C6CalixSi was evaluated by TOC content. Some valuable adsorption data of the silica adsorbent in the chem...

Effective adsorption and collection of cesium from aqueous solution using graphene oxide grown on porous alumina

Graphene oxide (GO) with a large surface area was synthesized by the direct growth of GO on porous alumina using chemical vapor deposition to study the Cs adsorption mechanism in aqueous solutions. Electronic structure analysis employing in situ near-edge X-ray absorption fine structure spectroscopy and X-ray photoelectron spectroscopy measurements clarifies the Cs atoms bond via oxygen functional groups on GO in the aqueous solution. The Cs adsorption capacity was found to be as high as 650–850 mg g−1, which indicates that the GO/porous alumina acts as an effective adsorbent with high adsorption efficiency for radioactive nuclides in aqueous solutions.

Rapid and highly efficient cesium removal by newly synthesized carbomer encapsulated potassium copper hexacyanoferrate composite

Copper hexacyanoferrate–carbomer composite (CuHCF-carbomer) was synthesized and used as an ion exchanger for the removal of hazardous cesium ion from aqueous solution. The composite composition, properties and morphology were characterized by several techniques namely, FTIR, SEM, EDX, XRD and TGA-DSC. The influence of pH of aqueous solution, initial concentration, shaking time and solution temperature on the adsorption of cesium onto CuHCF-carbomer composite were studied by batch technique. Maximum adsorption capacity value of 1.74 mmol g−1 of Cs+ on CuHCF-carbomer was obtained at pH 9, 9 mmolL−1 Cs+, and 25 °C. Adsorption isotherms, kinetic and thermodynamic parameters of the adsorption process were obtained and used to describe the adsorption of Cs+. In addition, column method was used in the same purpose of Cs+ ion removal. The effect of bed depth and flow rate on the adsorption characteristics of composite was examined at the optimum conditions of pH = 9 and initial Cs+ concentration = 5 mmoL−1. Thomas and Yoon–Nelson kinetic models were applied to evaluate column adsorption performance. Moreover, the prepared composite could be regenerated effectively by 2 M KCl and was used successfully for five times.

Theoretical study on electronic properties of p-type GaN nanowire surface covered with Cs

By using density functional theory, we have investigated the Cs adsorption mechanism of Mg-doped GaN nanowire photocathode. The results show that in the GaN nanowire, Mg atoms tend to replace the Ga atoms in the central position, because the position has the lowest formation energy, and the carrier concentration is highest, which shows better conductivity. Besides, Mg doping leads to the Fermi level close to the valence band, exhibiting p-type conductivity. After Cs activation, the most stable adsorption site of Mg-doped nanowires is B N site. After Cs adsorption, the conduction band minimum and the valence band maximum both move to the lower energy, which is favorable for forming the n-type surface state and improving the photoelectron escape probability. This study can be used to guide the Cs adsorption process of Mg-doped GaN nanowires, which is helpful to improve the performance of GaN nanowire-based optoelectronic devices.

Nanoscale spatial analysis of clay minerals containing cesium by synchrotron radiation photoemission electron microscopy

A synchrotron radiation photoemission electron microscope (SR-PEEM) was applied to demonstrate the pinpoint analysis of micrometer-sized weathered biotite clay particles with artificially adsorbed cesium (Cs) atoms. Despite the insulating properties of the clay, we observed the spatial distributions of constituent elements (Si, Al, Cs, Mg, and Fe) without charging issues and clarified reciprocal site-correlations among these elements with nanometer resolution. We found that Cs atoms were likely to be adsorbed evenly over the entire particle; however, we identified an occupational conflict between Cs and Mg atoms, implying that Cs sorption involves ion exchange processes. Spatially resolved X-ray absorption spectra (XAS) of the Cs4,5 M-edge region showed Cs to be present in a monocation state (Cs+) as typically observed for Cs compounds. Further pinpoint XAS measurements were also performed at the Fe L2,3-edge to determine the chemical valence of the Fe atoms. The shapes of the spectra were similar to those for Fe2O3, indicating that Fe in the clay was in a 3+ oxidation state. From these observations, we infer that charge compensation facilitates Cs adsorption in the vicinity of a substitution site where Si4+ ions are replaced by Fe3+ ions in SiO4 tetrahedral sheets. Our results demonstrate the utility of SR-PEEM as a tool for spatially resolved chemical analyses of various environmental substances, which is not limited by the poor conductivity of samples.

Graphene oxide supported filtration of cesium from aqueous systems

Graphene Oxide-Cesium (GO-Cs) composites, in the form of dispersions as well as solid state thin films, were prepared by introducing different concentrations of Cs into aqueous GO dispersions or subphase. Interaction mechanism of Cs with various functional groups of GO and the extent of Cs uptake on GO sheets under different ambient conditions were investigated using FT-IR, Raman, PL and XPS techniques. Cs was noticed to exhibit preferential interaction with hydroxyl groups of GO and furthermore, incorporation of Cs causes significant change in relative ratios of functional groups, inferring a major structural reorganization in the composite sheets. FT-IR and PL studies showed that aged GO samples can accommodate relatively larger quantities of Cs compared to fresh GO sheets, owing to largely available –COOH and free/associated hydroxyl groups in aged GO sheets. Intercalation studies on GO multilayers indicated that extent of Cs uptake on GO layers increases with duration of intercalation as well as quantity of GO available for interaction. Membrane filters of GO were prepared by controlled coating of GO sheets on filter papers and their adsorption and filtration abilities were tested by filtration of aqueous Cs solutions. Aged GO coated membrane filter displayed superior adsorption abilities compared to those coated with fresh GO sheets, which corroborate well with the inferences drawn from the spectroscopic investigations. In the present work, the prepared GO membrane filters showed a maximum Cs adsorption capacity of ∼148 mg/g.

Synchrotron-based photoemission study of electronic structure of the Cs/GaN ultrathin interface

Electronic structure of the Cs/n-GaN nano-interface has been studied in situ via synchrotron-based photoelectron spectroscopy by excitation in the energy range of 70–400 eV. The GaN sample was grown by an original method of epitaxy of low-defect unstressed nanoscaled films on AlGaN/SiC/Si substrate. Changes in the surface state spectra and in the Ga 3d, Cs 4d, Cs 5p, N 1s core level spectra have been revealed under different cesium coverages. The intrinsic surface states for the clean GaN surface at binding energies of ∼5.0 eV and ∼7.0 eV are attenuated during Cs adsorption. Simultaneously three Cs induced surface states are found to arise. Drastic changes in the surface state spectrum were ascertained and shown to be originated from the local interacting Ga dangling bonds and adsorbed Cs atoms initiating the electron redistribution effect with formation of the semiconductor-like Cs/n-GaN interface.

Adsorption Behaviors of Rubidium and Cesium Ions from Aqueous Solution onto Sodium Tetraphenylborate ‐ Polyacrylonitrile (TPB‐PAN)

AbstractIn this study, a novel composite adsorbent of sodium tetraphenylborate – polyacrylonitrile (TPB–PAN) was prepared for investigating adsorption behaviors of rubidium (Rb) and cesium (Cs) ions from their aqueous solutions. Several experimental parameters such as pH, shaking time, initial concentration, and interference ions were routinely evaluated. The experimental results showed that the Rb(I) and Cs(I) were both adsorbed by the adsorbent of TPB‐PAN at pH 7.0, and the adsorption equilibriums were achieved within 2 h. The presence of co‐existing ions did not get involved with Rb(I) and Cs(I) adsorption, indicating the high selectivity of TPB‐PAN adsorbent toward Rb(I) and Cs(I) ions. Under optimum conditions, the maximum adsorption capacities for Rb(I) and Cs(I) ions by the adsorbent of TPB‐PAN were 44.64 mg g−1and 118.48 mg g−1based on the langmuir sorption isotherm study. In addition, the adsorption processes of rubidium and cesium both are exothermic spontaneous process. Therefore, the proposed adsorbent of TPB‐PAN allowed the selective, sensitive, easy to use, cost‐effective, high efficiency, fast kinetics of preconcentration and separation (removal) Rb(I) and Cs(I) ions even in the presence of competing ions. As a consequence, the TPB‐PAN adsorbent can be used potentially for preconcentration and separation Rb(I) and Cs(I) ions from water samples in a wide range of practical applications for removal Rb(I) and Cs(I) ions in environmental aqueous resources.

Effects of NH4+, K+, Mg2+, and Ca2+ on the Cesium Adsorption/Desorption in Binding Sites of Vermiculitized Biotite.

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH4+, K+, Mg2+, and Ca2+ on the adsorption/desorption of Cs+ into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH4+, K+, or Mg2+; we then evaluated the adsorption of Cs+ on three treated VBs, and the desorption by extraction with NH4+, K+, Mg2+, or Ca2+ was further evaluated. Our structural analysis and Cs+ extractability determinations showed that NH4+ and K+ both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs+ to external surface sites on which Cs+ was readily extracted by NH4+, K+, Mg2+, or Ca2+ irrespective of their species, whereas Mg2+ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs+ in collapsed interlayer sites on which the Cs+ desorption was difficult and varied significantly by the cations used in extraction. The order of Cs+ extraction ability from the collapsed interlayers was K+ ≫ Mg2+ ≈ Ca2+ ≫ NH4+. These results could provide important insights into Cs migration in soil and its decontamination for soil remediation.

The adsorption of Sr(II) and Cs(I) ions by irradiated Saccharomyces cerevisiae

Adsorption behavior and mechanism of Sr(II) and Cs(I) in single and binary solutions using irradiated Saccharomyces cerevisiae was investigated. The effects of several environmental factors on Sr(II) and Cs(I) adsorption to irradiated Saccharomyces cerevisiae was determined. The equilibrium experimental data were simulated by different kinetic models and isotherm models. The combined effect of Sr(II) and Cs(I) on Saccharomyces cerevisiae is generally antagonistic. SEM and EDS analyses indicate that crystals formed on the cell surface are precipitate of Sr(II) and Cs(I), respectively.