Distribution Coefficient Kd Research Articles

Dense Dithiolene Units on Metal-Organic Frameworks for Mercury Removal and Superprotonic Conduction.

With 2-COOH and 4-SH donors all packed onto the benzene ring, tetrasulfanyl terephthalic acid (TST) is a simple yet fully equipped ligand to move the field of metal-coordination materials─it is now accomplished. The hard-soft carboxyl-thiol synergy is leveraged here in selectively bonding the carboxyl units to Zr(IV) ions to form the same cubic net of UiO-66 (this being based on the terephthalic linker)─with the free-standing dithiolene units equipping the grid of ZrTST. The 3D network of ZrTST averages about 7.6 connections [as in Zr6O4(OH)4(C8H4O4S4)3.8], with the other 4.4 sealed by acetate ions. The ZrTST solid is stable in boiling water (it is formed in water/acetic acid/ethane dithiol) and remains ordered even above 300 °C. The thiol-enabled ZrTST (powder) takes up mercury from water with a high distribution coefficient Kd (e.g., 1.2 × 106 mL·g-1); it also shows proton conductivity (1.9 × 10-3 S·cm-1 at 90 °C and 90% relative humidity), which, most notably, increases to a highest value of 3.7 × 10-1 S·cm-1 after oxidizing the -SH into the -SO3H groups.

Reconstruction of the Long-Term Dynamics of Particulate Concentrations and Solid–Liquid Distribution of Radiocesium in Three Severely Contaminated Water Bodies of the Chernobyl Exclusion Zone Based on Current Depth Distribution in Bottom Sediments

Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of 137Cs particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of 137Cs and its apparent distribution coefficient Kd, based on 137Cs depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain 137Cs vertical profile. Assuming negligible sediment mixing and allowing for 137Cs strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate 137Cs concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional model. Based on the back-calculated particulate 137Cs concentrations, and the available long-term monitoring data for dissolved 137Cs, the dynamics of 137Cs solid–liquid distribution were reconstructed. Importantly, just a single sediment core collected from a lake or pond many years after a nuclear accident seems to be sufficient to retrieve long-term dynamics of contamination.

Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediments to water columns, which may contribute to the long-term contamination of aquatic products. This study systematically investigated the 137Cs activities of sediment–pore water, providing a direct evidence of the remobilisation of bioavailable 137Cs from sediments in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. We observed that the dissolved 137Cs activity concentration of pore water (3.0–65.8 Bq L−1) was one to two orders of magnitude higher than that of reservoir water. Moreover, the distribution coefficient (Kd) values for the 137Cs of sediment–pore water (2.6–14 × 103 L kg−1) decreased with depth. The Kd values were significantly and negatively correlated with the concentration of the major 137Cs competing cation NH4+. Our results strongly indicate a competitive ion exchange process between 137Cs and NH4+ via a highly selective interaction with the frayed edge sites of phyllosilicate minerals, which is the major reason for the variability of Kd values of sediment–pore water, even in the Fukushima case. Additionally, the sediment accumulation rates were relatively high, and the annual depositional rate of exchangeable 137Cs prevailed over the annual diffusive flux of 137Cs from the sediment to the overlying water. This finding indicates that even after 10 years since the FDNPP accident, the bioavailable 137Cs is still continuously supplied from the catchment covered by mountainous forests, and reservoir sediments are a long-term important source of bioavailable 137Cs in the riverine system. Our findings provide important parameter values for mid- and long-term assessments of the radiation impact of radionuclide discharges to freshwater environments.

Aggregated germanium saponite: Removal and retention of polymeric thorium and uranium complexes

The present study concerns the removal of thorium and uranium from aqueous solution, and particularly the effect of clay particle size and morphology on the adsorption of polynuclear actinide complexes by synthetic saponite nanoscale powders. Saponites were synthesized from a reactant mixture containing aluminum nitrate, magnesium nitrate, and either sodium silicate or sodium germanate. The saponite powders were analyzed by TEM, XRD, SAXS, N2-adsorption-desorption isotherms and FT-IR. Ge-saponite contained randomly stacked platelets ≈ 100 nm long and 80 nm wide, while Si-saponite showed roughly spherical agglomerates ≈ 60–80 nm in size. Small-angle X-ray scattering measurements indicated a hierarchical pore network among the plates and their agglomerates. Thorium polymers composed of fractal aggregates of branched filaments were characterized by synchrotron radiation-SAXS. The distribution coefficient (Kd mL/g) values for thorium (20 μg/mL) at pH 4 were: Ge-saponite (105) ≈ Si-saponite (105) > raw saponite (104) ≈ raw saponite (washed) (104). The Kd values for uranium (20 μg/mL) at pH 5.5 were: Ge-saponite (103) ≈ raw saponite (washed) (103) ≈ Si-saponite (103) ≈ raw saponite (103). The difference in uranyl adsorption performance observed between the two nanoparticle forms of saponite was attributed to a larger pore width for Ge-saponite (3.5 nm) compared with Si-saponite (0.8 nm). The results have implications for mineral ore tailings containing thorium(IV) and, by analogy, Pu(IV) in a clay buffer environment within a geological repository for high-level nuclear waste.

Highly stable and activated Cerium-based MOFs superstructures for ultrahigh selective uranium (VI) capture from simulated seawater

Metal-organic frameworks (MOFs) have attracted considerable attention owing to their tunable morphologies, open topological structures, large specific surface areas, and large number of active sites. These characteristics facilitate the potential application of MOFs to uranium extraction from seawater. Through calcination at low temperatures, activated MOFs with transition structures between MOFs and metal oxides can be prepared. Activated MOFs can not only maintain the structural advantages of the original material but can also expose many active metal sites. In this study, we rapidly synthesized Ce (1,3,5-Benzenetricarboxylic acid)3 (H2O)6 with a superstructure comprising one-dimensional nanorods at room temperature. Activated cerium-based metal-organic framework (CeMOF) with strong water stability was obtained via calcination in nitrogen at 150 °C. Furthermore, CeBTC-150 exhibited ultrahigh selectivity for uranium, and the distribution coefficient (Kd) reached approximately 3.5 × 105 mL/g. The proposed method yielded not only an efficient adsorbent for uranium extraction from simulated seawater but also an innovative concept for the extraction of uranium ions from seawater using activated MOFs.

An application research for near-surface repository of strontium-90 sorption kinetic model on mudrocks

Abstract In this study,90Sr was used as the test radionuclide to characterize the sorption kinetics and effects of initial 90Sr activity and remaining 90Sr in solid concentration were simulated for a near-surface repository. The study focused on the sorption characteristics of radionuclides in unsaturated groundwater environment (or vadose zone) is the important information for investigating the near-surface disposal of intermediate and low-level radioactive waste (ILLW). Moreover, the 90Sr sorption experiments reached equilibrium within 56 h, which fit to the first order sorption kinetic model, and the remaining 90Sr in mudrock samples showed obvious sorption equilibrium hysteresis, which fit to the second order sorption kinetic model. Before reaching the maximum sorption capacity, the sorption rate constant increases with 90Sr increasing; the distribution coefficient (Kd) of 56 h decreases with the remaining 90Sr decreasing. In addition, it showed that the slow sorption process dominated before the sorption reaches equilibrium. In fact, a reliable safety assessment methodology for on-going near-surface repository required a lot of the radionuclides parameters with local environment including the radionuclides sorption/desorption rate constant and maximum sorption capacity.

Environmental Fate of Toxic Volatile Organics from Oil Spills in the Niger Delta Region, Nigeria

Over the years, the environmental degradation of ecological resources from crude oil pollution and its human health impacts is receiving more global attention. The utilization of environmental models capable of predicting the fate, transport, and toxicity of chemicals in spilt crude oil can provide essential knowledge required to deal with the complexity associated with the fate of volatile petroleum chemicals in the environment. This paper explores the environmental fate of toxic volatile organics from an oil spill in the Niger Delta Region of Nigeria. Results from the literature implicated sabotage and operational failures from pipelines as primary causes of crude oil spillages. The generation of a fugacity model using EPI Suite™ revealed that Koc values greatly influence the behavior of BTN. Benzene, Toluene, and Naphthalene (BTN) were partitioned into three compartments based on organic-carbon partitioning coefficient (Koc). The organic-carbon partitioning coefficient (Koc) was computed as a function of soil-water distribution coefficient (Kd) and percentage organic matter (%OM). Koc was used to determining the possible risk posed on delicate ecological resources. Aquatic toxicology estimation using Ecological Structural Activity Relationship revealed that all chemicals were not toxic even at over-estimated Koc values. This research established the usefulness of screening level environmental modeling tools in assessing ecological risk and hence helpful in developing site-specific models for monitoring chemicals in the environment, which can assist governments, policymakers, and industries in designing appropriate regional disaster management plans.

Sorbent extraction behavior of cesium and strontium from nitric acid solutions using a new high thermal stability material

In this study a new low-cost carbonaceous material was prepared from husks of opuntia-ficus-indica as a starting material (precursor) which was accomplished by chemical activation route using H3PO4 impregnation. The material has been identified by different analytical tools. The sorption performance of Cs(I) and Sr(II) from HNO3 solutions was examined through batch system. Variations of the distribution coefficients (Kd) as a function of HNO3 concentration in the range 0.001–5.0 M were presented. Some of separation probabilities were suggested. The results attained signals that the Sr(II) selectivity is higher than that of Cs(I) at high molarities. The retention capacity (qe) of Cs(I) and Sr(II) ions increased with growing temperature. The capacities at 0.001 M HNO3 are 34 and 108 mg/g for Cs(I) and Sr(II), respectively. Whereas, at 2.0 M HNO3 capacities were about 4 and 37 mg/g for each of Cs(I) and Sr (II), respectively. This studies demonstrates that the prepared carbonaceous sorbent is an economically effective sorbent for retention of Cs(I) and Sr(II) species from HNO3 solutions. Cs(I) and Sr(II) removal potential was tested from simulated low- and intermediate-level radioactive waste samples.

Self-templated formation and characterization of polyhedral CoS hollow nanocage (HNC) for heavy metal ions (Ag+, Cd2+, Cu2+, Pb2+ and Zn2+) removal in aqueous solutions

The contamination of water by heavy metal ions can easily cause serious environmental problems and damage to the human body hands down. Using zeolitic imidazolate framework-67 (ZIF-67) as a sacrificial template, polyhedral CoS hollow nanocages (HNC) were successfully synthesized by self-template approach as adsorbents for heavy metal ions removal. The CoS HNCs suggested good chemical stability and extremely efficient heavy metal ions removal of Ag+, Cd2+, Cu2+, Pb2+ and Zn2+, which can be ranked in the order of Ni2+ ≪ Zn2+, Cd2+ < Pb2+, Cu2+, Ag+. The saturation adsorption for Ag+ reached 2147.944 mg g−1 and exhibited high distribution coefficients (Kd) > 107 mL g−1. The CoS HNCs can rapidly reduce the Ag + concentration from ppm level to trace level of 1 ppb. It has been proved that the rapid and selective adsorption was achieved via the hierarchical pore structure of the CoS HNCs can better disperse these metal vacancies with super affinity and the S2−, reduce the mass transfer distance and accelerate mass transfer. It is expected that such a CoS HNCs could be a promising alternative to conventional materials for the adsorption of heavy metal ions.

Preliminary investigation of the presence of PFOS and PFOA in water and sediment in Cau river

Perfluoro-octane sulfonate (PFOS) and Perfluoro-octanoic acid (PFOA) are recognised as emerging environmental pollutants because of their high persistence in various environmental matrices and toxic effects on humans and animals. The objectives of this study were to preliminarily investigate the occurrence of PFOS and PFOA in the water and sediment of the Cau river in Thai Nguyen city. The concentration of PFOS and PFOA in water ranged from &lt;LOQ-0.67 ng/l and 0.05-8.11 ng/l; 1.19-4.73 ng/g, and 0.17-1.78 ng/g in sediment, respectively. The highest total concentrations of PFOS and PFOAwere recorded in the areas that directly received wastewater from domestic and industrial activities. The water-sediment distribution coefficient (Kd) was relatively different for PFOS and PFOA, with Kd ranged from 20.51-72.83 l/g and 1.21-20.31 l/g for PFOS and PFOA, respectively. This result suggested the distribution of PFOS and PFOA between water and sediment, in which PFOS will preferentially deposit in the sediment, and PFOA will tend to distribute in the liquid phase of the aquatic environment.

Butanol recovery using ionic liquids as green solvents

AbstractBACKGROUNDConsistent rising energy demand due to depleting conventional resources leads to the development of alternative energy sources. Biobutanol is a promising fuel because of its high energy content. However, the fermentative technique of butanol generation by the acetone−butanol−ethanol procedure utilizing solventogenic Clostridium has serious constraints. It represses microbial movement (ordinarily ≥10 g L−1) and influences its production. To extricate butanol from aging broth, there are different separation techniques. To conquer these issues, ionic liquids can be utilized as novel extractants replacing ordinary unstable solvents.RESULTSIn the present paper, separation of butanol (simulated) from aqueous media utilizing typical hydrophobic ionic liquids – 1‐hexyl‐3‐methylimidazolium bis(trifluoromethanesulfonimide) (HMIM[NTF2]), 1‐hexyl‐3‐methylimidazolium hexafluorophosphate (HMIM[PF6]) and other solvents; oleyl alcohol (OA), tri‐n‐butyl phosphate (TBP) and their blends – has been carried at 298 ± 1 K. Results were compared with TBP, which was taken as a conventional reference solvent. Extraction efficiency was observed in the range TBP &gt; 85–87% for OA &gt; 55–85 for HMIM[NTF2] &gt; 26–66% for HMIM[PF6], respectively. From the equilibrium experiments, distribution coefficients (Kd) values were observed in the range of TBP (7–23) &gt; OA (5–7) &gt; HMIM[NTF2] (1.2–5.6) &gt; HMIM[PF6] (0.36–1.94), respectively.CONCLUSIONThe present study shows how extractant–diluent combinations can be used to obtain a non‐toxic extractant to tune characteristics of ionic liquids and improve fluid properties by significantly increasing distribution coefficients and extraction efficiencies. This could be helpful for separation of butanol from aqueous phase. © 2021 Society of Chemical Industry (SCI).

A simple empirical model for phenanthrene adsorption on soil clay minerals

Soil clay minerals are effective substrate adsorbents of polycyclic aromatic hydrocarbons (PAHs) in natural soil. The adsorbed PAHs result in long-term contamination of soils. In this paper, a typical PAH phenanthrene (Phe) and nine high purity clay minerals are selected as representative PAH pollutants and adsorbents, respectively. A series of experiments have been conducted to disclose the relationship between the Phe adsorption effect of these clay minerals and their physical properties, including specific surface area (SSA), cation exchange capacity (CEC) and contact angle (CA). Molecular simulation methods are performed to explore the mechanism of clay mineral structure on Phe adsorption at the molecular level. Density functional theory (DFT) calculation suggests that the adsorption of Phe on clay minerals is mainly due to the van der Waals effect. The strength of the O-H-π effect is greater than that of the hydrophobic effect of Phe adsorption. Molecular dynamic (MD) simulations imply that the hydration effect of cations hinders the Phe hydrophobic adsorption by occupying the adsorption sites. Based on the mechanism explored, a simple empirical model is proposed, and the adsorption distribution coefficient Kd of clay mineral and water phases can be precisely predicted by the three physical properties of clay minerals, without rigorous quantitative analysis of soil clay minerals.

An Improved Speciation Method Combining IC with ICPOES and Its Application to Iodide and Iodate Diffusion Behavior in Compacted Bentonite Clay.

An accurate and effective method combining ion chromatography (IC) and inductively coupled plasma optical emission spectrometry (ICP-OES) was applied in this work to qualitatively and quantitatively analyze individual and co-existing iodide (I−) and iodate (IO3−) at various concentrations. More specifically, a very strong linear relationship for the peak area for the co-existing I− and IO3− ions was reached, and a high resolution value between two peaks was observed, which proves the effectiveness of our combined IC-ICP-OES method at analyzing iodine species. We observed lower accessible porosity for the diffusion of both I− and IO3− in samples of bentonite clay using IC-ICP-OES detection methods, where the effective diffusion coefficient varied based on the anion exclusion effect and the size of the diffusing molecules. In fact, the distribution coefficients (Kd) of both I− and IO3− were close to 0, which indicates that there was no adsorption on bentonite clay. This finding can be explained by the fact that no change in speciation took place during the diffusion of I− and IO3− ions in bentonite clay. Our IC-ICP-OES method can be used to estimate the diffusion coefficients of various iodine species in natural environments.

Soil-soil solution distribution coefficients of global fallout 239Pu and 237Np in Japanese paddy soils

239Pu and 237Np are long-lived radionuclides that emit alpha rays, and once released into the environment, they are present there for a long period of time. Therefore,239Pu and 237Np are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure to humans. Mobilities of these radionuclides in the environment are of particular interest; therefore, in this study, we have made the first-time determination of the soil-soil solution distribution coefficient (Kd, L/kg) using global fallout 239Pu and 237Np in soil. The Kd values were determined by extracting these radionuclides from 23 soil samples using a laboratory batch method. The desorption Kd values of 239Pu were found to vary from 3.2 × 103 to 1.4 × 105 L/kg, and their geometric mean (GM) and arithmetic mean (AM) were 2.3 × 104 L/kg and 3.2 × 104 L/kg, respectively. The desorption Kd values of 237Np ranged from 8.9 × 102 to 2.1 × 104 L/kg, and their GM and AM were 4.1 × 103 L/kg and 6.4 × 103 L/kg, respectively. A comparison between the obtained Kd values of 239Pu and 237Np indicated that the former were about 6-fold higher than the latter in Japanese paddy field soils. Pearson's correlation analysis suggested that the main factors contributing to the sorption and desorption of Pu isotopes in Japanese paddy soils were related to the amounts of Fe and Mn oxides, while the sorption and desorption of 237Np in them would be controlled by an ion-exchange reaction, and/or complex-formation with organic matter, especially in Fluvisols.

A Scaling Approach for Retention Properties of Crystalline Rock: Case Study of the In‐Situ Long‐Term Sorption and Diffusion Experiment (LTDE‐SD) at the Äspö Hard Rock Laboratory in Sweden

AbstractThe in‐situ long‐term sorption and diffusion (LTDE‐SD) experiment performed at the Äspö Hard Rock Laboratory in Sweden aims at increasing knowledge of sorption and diffusion processes of radionuclides in natural fractures and granodiorite matrix under in‐situ conditions. This paper presents a comprehensive modeling exercise focusing on the scaling approach for sorption and diffusion parameters from laboratory to in‐situ conditions using the LTDE‐SD data set for six representative radionuclides. The near‐surface heterogeneities at both the fracture surface and rock matrix were evaluated by the conceptual model with high porosity, diffusivity, and sorption capacity, as well as their gradual changes at the near‐surface zones. The modeling results for non‐sorbing Cl‐36 and weak‐sorbing Na‐22 validated the model concept and parameter estimation of porosity and diffusivity by considering a 5‐mm‐thick disturbed zone with gradual parameter changes and an undisturbed matrix characterized by constant parameters. The effective diffusivities (De) of these cationic and anionic tracers showed typical cation excess and anion exclusion effects; however, the cation excess diffusion was more pronounced due to the heterogeneous pore networks in this granodiorite. The modeling results for high‐sorbing tracers (Cs‐137, Ra‐226, Ni‐63, and Np‐237) with different sorption mechanisms validated the scaling approaches of distribution coefficients (Kd) as a function of particle size and their relation to near‐surface disturbances. Sorption dependence on particle size could be understood in relation to different sorption mechanisms and mineralogical features. This modeling exercise provided key recommendations toward better scaling approaches for estimating reliable De and Kd parameters under in‐situ conditions.

Experimental investigation on buffer/backfill materials for radioactive waste repository downward facing sorption additivity of cesium, strontium and cobalt with different concentrations

Abstract Buffer/backfill materials for radioactive waste disposal sites consist of pure bentonite or bentonite-rock mixtures. In this study, the batch test method was used to obtain the sorption characteristics of important radionuclides such as Cs, Sr and Co on buffer/backfill materials; i. e., mixing Wyoming MX-80 bentonite or local Taiwanese Zhi-Shin bentonite with possible host rock (argillite and granite) in different proportions (0∼100%). The distribution coefficients (Kd) for Cs, Sr and Co were obtained from the experiments. The distribution coefficient for the bentonite-rock mixtures were found, with more than 50% of mixing proportion of bentonite to argillite or granite, to have very similar values to that of pure bentonite. Furthermore, it was clearly found that the sorption of Cs, Sr and Co to bentonite-rock mixtures is decreased as ionic strength of the liquid phase is increased from 0.001M to 1M for NaCl solutions. According to the experimental results, in synthetic groundwater, it is quite convenient and helpful to assess the distribution coefficients (Kd) of Cs, Sr and Co for buffer/backfill materials using batch sorption experiments with bentonite-rock mixtures of fixed mixing proportions.

Benzobisthiazole-bridged white fluorescent emitting covalent organic framework for simultaneous mercury detection and removal

Mercury (Hg2+), a heavy metal ion, is considered one of the most toxic metals on earth and is widespread as an environmental pollutant. Various promising adsorbents have been developed with accessible chelating sites and high affinity for heavy metal ions. Herein, we utilized the advantages of covalent organic frameworks (COFs) and designed benzobisthiazole-bridged (BBT) fluorescent COFs (FCOFs) for Hg2+ sensing applications. The BBT-FCOF nanosheets has a π-π transition, effective electron transfer, and enhanced delocalization within the π orbitals of the BBT ring. It emits a white fluorescence enabling real-time detection of Hg2+ metal ions. The excellent sensing property of BBT-FCOF nanosheets was attributed to the high sensitivity towards Hg2+; this was confirmed by the x-ray photoelectron spectroscopy binding energy of sulfur and nitrogen atom in BBT-FCOF. The limit of detection of Hg2+ was 30 ppb, which is very low compared to other published methods. ICP-mass measurement also proved that BBT-FCOF nanosheets removed almost 99% of Hg and BBT-FCOF distribution coefficient (Kd) was calculated to be 5 × 105 g−1. The recyclability test proved that HCl effectively removed the adsorbed Hg2+ metal ions from BBT-FCOF nanosheets, making it a useful tool for real-time Hg2+ detection and removal from waste water.

Highly efficient and selective Hg(II) removal from water by thiol-functionalized MOF-808: Kinetic and mechanism study

Mercury pollution poses a serious threat to the ecological environment and public health due to its high toxicity and persistence, but there is still a lack of rapid and effective Hg(II) removal technology, especially emergency response of Hg(II) leakage. Herein, an effective metal-organic framework adsorbent, MOF-808-SH, was fabricated by grafting thioglycollic acid on MOF-808 for Hg(II) removal. The MOF-808-SH demonstrated high adsorption capacity of 977.5 mg/g, impressively ultrafast adsorption kinetics (C0 = 10 mg/L, removal > 99 % in 10 s) with a rate constant k of 36.89 g mg−1 min−1, which is dozens of times faster than that of ever reported Hg(II) adsorbents. Batch experiments show that MOF-808-SH exhibits high selectivity toward Hg(II) with a distribution coefficient Kd as high as 5.0×106 mL/g. Moreover, MOF-808-SH exhibits excellent recyclability with a negligible loss of capacity after 6 adsorption-regeneration cycles. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS) unveil that the –SH groups in MOF-808-SH are the key adsorption sites, and specific inner-sphere coordination with Hg(II) is responsible for the high selectivity. In addition, large surface area, well-developed porous structures and high –SH loading of MOF-808-SH reasonably explains ultrafast kinetics and high adsorption capacity for Hg(II). This study indicates the potential of MOF-808-SH to remove Hg(II) from wastewater.

Synthesis, characterization and γ-rays irradiation of cobalt-based metal-organic framework for adsorption of Ce(III) and Eu(III) from aqueous solution

Metal-organic frameworks (MOFs) have important applications in adsorption, because of high porosity, diverse functionalities, and easy modification. Cobalt metal organic frame work (Co-MOF) based on diallylamine as the ligand was synthesized for the adsorption of Ce(III) and Eu(III) from aqueous solutions. Co-MOF was characterized by different spectroscopic techniques such as Fourier Transform-Infrared (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The effects of adsorbent weight, pH of solutions, contact time, metal ion concentrations and gamma irradiation dose were studied. The adsorption efficiency of Ce(III) and Eu(III) onto Co-MOF was 93.3 and 27.47%, respectively, at pH 5.1. The distribution coefficient (Kd) of Ce(III) increased from 17.46 to 2791.30 ml/g, while for Eu(III) increased from 13.15 to 75.75 ml/g with changed the pH from 1.01 to 5.1. The Ce(III) and Eu(III) adsorption data were well fitted to the pseudo second order kinetic and Langmuir adsorption model. The maximum adsorption capacity of Ce(III) and Eu(III) onto Co-MOF were 102.24 and 52.93 mg/g respectively. The adsorption of Ce and Eu was slightly reduced by about 10% with increase dose of gamma radiation up to 400 kGy.

Absorption capacity of hydromorphic soils in relation to heavy metal

Comparative studies of ion-exchange adsorption of Zn(II) and Cu(II) cations by hydromorphic soils of southern Russia have been performed. Various equations (Langmuir, Freundlich, and Dubinin-Radushkevich) were used and the adsorption parameters and adsorption energy were calculated to describe the obtained isotherms. A significant decrease of the distribution coefficient (Kd) with an increase of the metal concentration in an equilibrium solution was revealed. It is shown that the Langmuir equation and, to a lesser degree, the Dubinin-Radushkevich and Freundlich equations are the most suitable model to describe the adsorption processes of Zn(II) and Cu(II) by the soils in all experimental variants. The strong correlation between the parameters of the sorption of metals obtained using a particular chosen model was established. The Langmuir equation provides higher strengths of a bond than the Dubinin-Radushkevich equation. In all cases, the sorption capacity of meadow soil in relation to the studied metals is higher than for alluvial soil due to the low buffering capacity of the latter. Both types of soils characterize with higher affinity to Cu(II) than to Zn(II).