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Magnetic biochar functionalized with Prussian blue (MBC-PB) was synthesized as an effective and economical adsorbent for removing cesium from aqueous solutions. Its physicochemical properties were characterized and cesium adsorption experiments were conducted. The cesium adsorption reaction was mainly physisorption and exothermic. MBC-PB had a maximum Cs capacity of 52.63 mg/g and adsorption equilibrium was reached within 1 h. Its removal efficiency was highest at pH 8 and it also effectively removed cesium coexisting with Na with a high distribution constant. These results suggest that MBC-PB has potential for use in actual Cs contaminated aqueous environments. [ABSTRACT FROM AUTHOR]

To effectively remove cobalt, magnetic biochar was modified with chitosan and ethylenediaminetetraacetic acid (CMBC–EDTA), and its properties were examined through surface area and pore size analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, and vibration sample magnetometry. Moreover, according to the Langmuir isotherm model, the maximum capacity of CMBC–EDTA reached 0.7311 mol·kg−1. Over 50% of 50 ppm Co2+ was removed within 20 min, and the adsorption equilibrium was reached after 2 h. At pH 3–7, the 20 ppm Co2+ removal efficiency was more than 90%, and it decreased rapidly below pH 2. [ABSTRACT FROM AUTHOR]

A method of chemically bonding copper ferrocynide (CuFC) to the surface of a PVDF hollow-fibre membrane (PVDF-CuFC) was designed and the resulting PVDF-CuFC was applied to the effective removal of aqueous cesium (Cs). In order to chemically immobilize CuFC on the surface of the PVDF hollow-fibre membrane, carboxyl groups were introduced onto the membrane surface (PVDF-COOH) to peptide bond with amine groups from CuFC. The introduction of the carboxyl group onto the surface of the PVDF hollow-fibre membrane was confirmed by Fourier-transform infrared spectroscopy (FT-IR), while the immobilization of CuFC was confirmed by scanning electron microscopy with energy dispersed spectroscopy, FT-IR, and thermogravimetric analysis. The PVDF-CuFC showed higher Cs adsorption kinetics and adsorption capacity than PVDF-COOH. Moreover, as the initial pH increased, the amount of Cs adsorption by PVDF-CuFC also increased. However, the amount of Cs adsorption at pH 10 was slightly less. The applicability of PVDF-CuFC as a filter type adsorbent for the treatment of a Cs-contaminated water source is demonstrated by continuous filtration experiments. [ABSTRACT FROM AUTHOR]

Composite beads consisting of Ca alginate mixed with zinc ferrocyanide (ZnFC) and Cyanex 272 were synthesized in order to selectively adsorb Cs+ and Co2+ from water. Their physicochemical properties of the synthesized composite beads were characterized using various techniques, including FESEM, EDX, FTIR, and TGA. The ZnFC/Cyanex 272/alginate (ZCA) composite beads were then tested as an adsorbent for the selective removal of Cs+ and Co2+ from an aqueous solution. The adsorption capacity increased with increasing ZnFC and Cyanex 272 contents. The adsorption process followed the Langmuir model and pseudo-second-order kinetics. The ZCA composite beads exhibited excellent selectivity toward Cs+ and Co2+ even in the presence of competitive cations (K+, Na+, Fe2+, and Ni2+). The adsorption capacity of the ZCA composite beads for Cs+ and Co2+ was almost maintained after three times of adsorption-desorption process. [ABSTRACT FROM AUTHOR]

A magnetically separable Co(II)-imprinted polymer based on mesoporous silica (mag@silica-CIP) was synthesized for use as an adsorbent for the selective removal of Co(II). The optimal pH for Co(II) adsorption was found to be 5. Increasing the amount of the Co(II)-imprinted polymer layer on the surface of mag@silica led to an increase in the maximum adsorption capacity for Co(II). The mag@silica-CIP selectively adsorbed Co(II) even in the presence of competing species such as Fe(II), Ni(II), and Mn(II) ions. Thermodynamic experiments revealed that the adsorption of Co(II) by mag@silica-CIP is an endothermic and spontaneous process. [ABSTRACT FROM AUTHOR]

In polymeric proton exchange membranes, the impregnation of filler materials, such as metal–organic frameworks (MOFs), has attracted considerable attention. Aquivion® is a state-of-the-art membrane used in fuel cells and electrolysis applications because of its mechanical stability and elevated proton conductivity at high temperatures. By applying the theory of coordination networks with the incorporation of a high-proton-conductive Co-tri MOF, {[(Co(bpy)(H2O)4](Hbtc).(H2O)1.5}n, the proton conductivity of Aquivion® is improved. Co-tri MOF/Aquivion® composite membranes are prepared in different weight percentages using the solution casting method and are tested within a fuel cell system. The 1-wt.% Co-tri MOF/Aquivion® blend membrane shows an improved cell performance and a 66% increase in proton conductivity compared with that of the pristine Aquivion® membrane. The effect of Co-tri MOF on the Aquivion® membrane's structural morphology and thermal properties is also investigated. [ABSTRACT FROM AUTHOR]

Amine-functionalized graphene oxide/zinc hexacyanoferrate (amino-rGO/ZnHCF) composites were successfully synthesized for the removal of Cs+ from radioactive liquid waste. Their morphologies, surface areas, pore sizes, functional groups, and thermal stabilities were investigated by field-emission transmission electron microscopy, Brunauer–Emmett–Teller analysis, Fourier transform infrared spectroscopy, and thermogravimetry. Adsorption experiments revealed high adsorption capacities at pH 5–7 and stability below pH 9. The dependence of the synthesized composites on the pseudo-second-order model and the Temkin model was also observed. The results of this study indicate that the new amino-rGO/ZnHCF composites are good adsorbent candidates for Cs removal from aqueous solutions. [ABSTRACT FROM AUTHOR]

The effect of Tf2N−, as a common anion in aqueous and ionic liquid (IL) phases, on Cs extraction in the IL system was investigated using C2mimTf2N as an IL and DCH18C6 as an extractant. The "common anion (Tf2N−) effect" operated via the movement of Cs+·Tf2N− from the aqueous phase into the IL phase by extraction in the form of Cs+·extractant·Tf2N−, without any traditional cation exchange. The extraction product was recovered as a precipitate using a small amount of IL, which facilitated precipitation via supersaturation. [ABSTRACT FROM AUTHOR]

The process characteristics of a new solid-liquid Cs+ separation from the radioactive liquid waste using a crown ether dicyclohexano-18-crown-6 as an extractant and an ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were studied. The physicochemical properties of the precipitate containing Cs+ which is an solid-liquid extraction product were investigated to identify the solid-liquid phase separability and Cs+ loading. The Cs+ separation process performances were compared experimentally with those of the conventional adsorption system for pretreatment requirement and the amount of Cs+ waste. It was observed that the solid-liquid separation method using ILs has high Cs+ separation performance especially in the low Cs+ concentration. [ABSTRACT FROM AUTHOR]

Four single crystals of fully dehydrated and partially Zn2+-exchanged zeolites Y (Si/Al = 1.56) were prepared by the static ion-exchange method using a mixed ion-exchange solution in which Zn(NO3)2:NaCl mole ratios were 1:1 (crystal 1), 1:25 (crystal 2), 1:50 (crystal 3), and 1:100 (crystal 4), respectively, with a total concentration of 0.05 M, and followed by vacuum dehydration at 673 K. Their single-crystal structures were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd3¯m and refined to the final error indices R1/wR2 = 0.0459/0.1454, 0.0449/0.1283, 0.0427/0.1284, and 0.0486/0.1680, respectively. Their unit-cell formulas are |Zn25Na25|[Si117Al75O384]-FAU (crystal 1), |Zn19.5Na36|[Si117Al75O384]-FAU (crystal 2), |Zn19.5Na36|[Si117Al75O384]-FAU (crystal 3), and |Zn7Na61|[Si117Al75O384]-FAU (crystal 4), respectively. The degree of Zn2+ exchange decreases from 67 to 19% as the initial concentration of Zn2+ decrease and the initial concentration of Na+ increases in given ion-exchange solutions. [ABSTRACT FROM AUTHOR]

The spontaneous reductive decomposition behavior of HMnO4 in water as a function of the initial HMnO4 concentration and reaction temperature was investigated. The decomposition of HMnO4 was fast in the early stage of the reaction and thereafter slowed down significantly, regardless of the initial HMnO4 concentration. The loss of HMnO4 by spontaneous reductive decomposition increased with increasing reaction temperature. Based on the experimental results and the classical nucleation theory, a mathematical model was developed using a combination of two first-order reactions representing the nucleation and crystal growth of MnO2 to predict the spontaneous reductive decomposition behavior of HMnO4. [ABSTRACT FROM AUTHOR]

Zinc hexacyanoferrate functionalized magnetic carbon nanotube composites were synthesized to be used as adsorbents for the selective removal of Cs. The synthesized adsorbents exhibited a high adsorption capacity that could be successfully improved by increasing the loading of zinc hexacyanoferrate, which plays a major role in selectively adsorbing and removing Cs from the adsorbent surface. Although the saturation magnetization value for the synthesized adsorbents decreased with increasing zinc hexacyanoferrate loading, the adsorbents could be sufficiently separated by using a permanent magnet. [ABSTRACT FROM AUTHOR]

Selective separation of Cs from liquid radioactive waste by 'precipitation' was observed in a hydrophobic ionic liquid containing the Cs-selective extractant dicyclohexano-18-crown-6. The precipitate was formed by the cation exchange mechanism, which simplified the treatment of Cs after extraction. Solid-liquid extraction is a more economical extraction system than liquid-liquid extraction because it uses smaller quantities of ionic liquids. This work showed the possibility of developing a new method for removing Cs from liquid radioactive waste using solid-liquid phase separation instead of the conventional liquid-liquid separation in an ionic liquid extraction system. [ABSTRACT FROM AUTHOR]

In this study, copper ferrocyanide-functionalized, multi-walled carbon nanotubes (MWCNT-CuFCs) were synthesized. The MWCNT-CuFCs exhibited a high capacity for sorbing Cs from aqueous solutions because of their strong affinity for Cs and high specific surface area. The sorption capacity of the MWCNT-CuFCs for Cs was dependent upon the initial pH of the solution. The sorption ability of the MWCNT-CuFCs for Cs was maintained even in the presence of co-existing ions (K and Na). To determine the degree of Cs desorption from the MWCNT-CuFCs, a column-based desorption experiment was performed. [ABSTRACT FROM AUTHOR]

The formatted ethylenediamine functional group on silica supports gives the desired chelation with copper ferrocyanide for the selective removal of cesium ions. The copper ferrocyanide was well dispersed on the silica surface. Ion exchange capacity tests demonstrated that the functionalization of copper ferrocyanide on silica showed high rate of Cs removal. Loading of the organic functional group on silica at a rate of 30 % supported a high ion exchange capacity (0.92 mmol/g) for Cs ion. The sorption kinetics and the effect of co-existing salt on the efficiency of the composite material for Cs removal were also discussed. [ABSTRACT FROM AUTHOR]

Hydrous manganese oxide-polyacrylonitrile (HMO-PAN) composite was applied for the removal of Co, Sr and Cs from radioactive laundry wastewater. Single- and multi-solute competitive sorptions onto HMO-PAN were investigated. The maximum sorption capacity was in the order of Co (0.573) > Cs (0.551) > Sr (0.310 mmol g). Sorption of the metals occurred via physical adsorption due to weak van der Waals force and ion exchange with Mn in HMO-PAN. Sorption behaviors were not related to the types of the surfactants. Among the tested surfactants, SDBS and SOBS remarkably increased the distribution coefficient of Co and Sr, respectively. [ABSTRACT FROM AUTHOR]

Fishbone as a main backfill material of permeable reactive barrier to remediate groundwater contaminated with Co and Sr was investigated through single- and bi-solute competitive sorptions. The single-solute sorption data were fitted by Freundlich, Langmuir and Dubinin-Radushkevich models. The coefficients of determination ( R > 0.91) indicated that all models fitted well. Maximum sorption capacities ( q) of Co and Sr predicted by the Langmuir model were 0.55 mmol/g and 0.50 mmol/g, respectively. The bi-solute competitive sorption of the metals was analyzed by the Langmuir, competitive Langmuir, Sheindorf-Rebhun-Sheintuch (SRS) and P-factor models. The sorbed amount of one solute in bi-solute system decreased due to competition with the other solute. Langmuir model parameters for single- ( q and b) and bi-solute ( q and b) competitive sorptions were compared to analyze the effect of competition between the metals. The competitive Langmuir, SRS and P-factor models predicted the bi-solute competitive sorption data well ( R > 0.93). [ABSTRACT FROM AUTHOR]

Sorptive removal of Co, Sr and Cs from aqueous solution by SAMMS was investigated. The single-solute sorption data were well fitted by the Freundlich, Langmuir and Dubinin-Radushkevich models (R>0.95). The maximum sorption capacities (q) of the Langmuir model were in the order of Cs (1.14 mmol/g)>Co (0.20 mmol/g)≈Sr (0.195 mmol/g). The bi-solute competitive sorption of the metals was analyzed by the Langmuir, competitive Langmuir, modified extended Langmuir and P-factor models. The sorption of one metal was suppressed by the presence of competing metals. Sorptions of Co and Sr were strongly dependent on the initial solution pH but that of Cs was not. The calculated thermodynamic parameters such as ΔH, ΔS and ΔG showed that sorption of Co onto SAMMS was endothermic, whereas those of Sr and Cs were exothermic. The negative ΔG values indicated all the sorption processes were spontaneous in nature. [ABSTRACT FROM AUTHOR]

Applicability of montmorillonite, manganese oxide-coated montmorillonite (MOCM) and iron oxide-coated montmorillonite (IOCM) as backfill materials in permeable reactive barrier (PRB) to remediate contaminated groundwater was investigated. Single- and bi-solute competitive sorptions of Co, Sr and Cs were conducted. The Freundlich, Langmuir and Dubinin-Radushkevich models fitted the single-solute sorption data well ( R > 0.95). Maximum sorption capacities ( q) of Co and Sr predicted by the Langmuir model were in the order of MOCM (0.37 mmol/g for Co and 0.28 mmol/g for Sr) > montmorillonite (0.27 mmol/g for Co and 0.19 mmol/g for Sr) ≈ IOCM (0.23 mmol/g for Co and 0.21 mmol/g for Sr), while those of Cs were in the order of montmorillonite (1.11 mmol/g) > MOCM (0.68 mmol/g) > IOCM (0.62 mmol/g). In the bi-solute sorptions, the sorbed amount of one solute decreased due to the presence of the other competing metal ion. Langmuir model parameters for single-solute ( q and b) and bi-solute ( $$ q_{\text{mL}}^{*} $$ and $$ b_{\text{L}}^{ *} $$) sorptions were compared to analyze the effect of competition between the metal ions. The competitive Langmuir ( R > 0.81) and P-factor ( R > 0.82) models predicted the bi-solute competitive sorption data well but not the SRS model (0.003 < R < 0.97). [ABSTRACT FROM AUTHOR]

A study of reductive denitrification of nitrate was conducted. Microscale zero-valent iron (ZVI) and palladium-coated iron (Pd/Fe) were used in the reduction of nitrate with variable pH. The solution pH was controlled by an auto controlling system instead of chemical buffers. Higher reduction rates were achieved with lower pH and lower pH gave the pseudo-first-order kinetics while it was close to the zero-order reaction when the pH of the solution was becoming high and nitrate concentration was higher. As it took several hours to convert intermediates to ammonia completely, the assumption, under which mass loss calculated from the measured ammonia concentration right after the reaction was the mass of nitrogen evolved, could lead to overestimation of the nitrogen selectivity. The current study confirmed that the palladium coating on the iron could increase the nitrogen selectivity, and the Pd/Fe system could also achieve the advantages of coupling of electron source and catalyst with regard to the engineering aspects. [ABSTRACT FROM AUTHOR]

Chromium is a toxic and carcinogenic heavy metal that originates from various human activities. Therefore, the effective removal of chromium from aqueous solutions is an extremely important global challenge. Herein, we report a chitosan-coated iron oxide nanoparticle immobilized hydrophilic poly(vinylidene) fluoride membrane (Chi@Fe2O3–PVDF) which can potentially be used for efficient removal of hexavalent chromium(VI) by a simple filtration process. Membrane filtration is an easy and efficient method for treating large volumes of water in a short duration. The adsorption experiments were conducted by batch and continuous in-flow systems. The experimental data showed rapid capture of hexavalent chromium (Cr(VI)) which can be explained by the pseudo-second-order kinetic and Langmuir isotherm model. The nanocomposite membrane exhibited high adsorption capacity for Cr(VI) (14.451 mg/g in batch system, 14.104 mg/g in continuous in-flow system). Moreover, its removal efficiency was not changed significantly in the presence of several competing ions, i.e., Cl−, NO3−, SO42−, and PO43−. Consequently, the Chi@Fe2O3-PVDF-based filtration process is expected to show a promising direction and be developed as a practical method for wastewater treatment. [ABSTRACT FROM AUTHOR]

Ciprofloxacin (CPX), a widely used antibiotic, was removed by synthesizing graphene oxide/calcium alginate–polyacrylamide (GO/Ca-Alg2–PAM) beads, a three-dimensional double-network complex. The synthesis of GO/Ca-Alg2–PAM beads was performed by crosslinking and cation exchange mechanisms with graphene oxide (GO), sodium alginate (Na-Alg), and polyacrylamide (PAM). The properties of GO/Ca-Alg2–PAM beads were confirmed using field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and a thermogravimetric analysis. Furthermore, isothermal adsorption experiments were performed and fitted using three isothermal adsorption models (Langmuir, Freundlich, and Temkin). The adsorption isotherm experimental data fit well with the Langmuir isotherm model with a qm value of 6.846 mg/g. In addition, the spontaneous reaction of the CPX adsorption using GO/Ca-Alg2–PAM was confirmed by temperature-dependent experiments. [ABSTRACT FROM AUTHOR]

We numerically calculated the effects of pulse modulation (plasma-on and -off times) on the concentration changes of the chemical species (SiH4, SiHx, SiHx+ and polymerized negative ions) and also the growth rate of a-Si : H thin films in the pulsed SiH4 plasmas. During the plasma-on, SiHx is generated quickly by a fast dissociative reaction of SiH4, but, during plasma-off, SiHx disappears rapidly by a reaction with hydrogen and also by the deposition onto the reactor wall. During the plasma-on, the negative ions are polymerized by the reactions with SiH4, but, during the plasma-off, they disappear by neutralization reactions with positive ions. As the plasma-on time increases or as the plasma-off time decreases, the time-averaged concentrations of SiHx and negative ions and also the time-averaged film growth rate increase. This study shows quantitatively that polymerized negative ions, which are not considered to be preferred precursors for the high-quality thin films, can be efficiently reduced by the pulsed plasma process. [ABSTRACT FROM AUTHOR]

Sorption and desorption kinetics of chlorophenols, 2-chlorophenol (2-ChP), 2,4-dichlorophenol (2,4-DChP) and 2,4,5-trichlorophenol (2,4,5-TChP), in montmorillonite modified with hexadecyltrimethyl ammonium cations (HDTMA-mont) were investigated by using laboratory batch adsorbers. To investigate the effect of chemical concentration and sorbent weight on the sorption or desorption rate constants, the initial chemical concentration and sorbent weight were varied from 50 to 150 mg/L and from 0.2 to 1.0 g, respectively. A one-site mass transfer model (OSMTM) and two compartment first-order kinetic model (TCFOKM) were used to analyze kinetics. The OSMTM applicable to desorption rate analysis was newly derived. As expected from the number of model parameters involved, the three-parameter TCFOKM was better than the two-parameter OSMTM in describing sorption and desorption kinetics of chlorophenols in HDTMA-mont. The mass transfer coefficient for sorption (ks) in OSMTM generally increased as K ow value increases, except for 2,4,5-TChP, while the mass transfer coefficient for desorption (k d ) consistently increases as K ow value decreases, due to the weaker hydrophobic interaction between the solute and the organoclay. Since most sorption and desorption complete in an hour and half an hour, respectively, k d values were found to be greater than k s values for all three solutes studied. The fraction of the fast sorption (or desorption) and the first-order sorption (or desorption) rate constants for the fast and slow compartments in TCFOKM were determined by fitting experimental data to the TCFOKM. The results of kinetics reveal that the fraction of the fast sorption or desorption and the sorption rate constants in the fast and slow compartments were in the order 2,4,5-TChP>2,4-DChP>2-ChP, which agrees with the magnitude of the octanol-water partition coefficient, K ow . The first-order sorption rate constants in the fast and slow compartments were found to vary 101–102 hr−1 and 10−3–10−2 hr−1, respectively. However, the desorption rate constants in the fast and slow compartments were not correlated well with K ow . The first-order desorption rate constants in the fast compartment (101−102 hr−1) were found to be much larger than those in the slow compartment (10−3–10−4 hr−1). Sorption affinity and desorption resistance of each chlorophenol in 50% HDTMA-mont were found to show the same tendency: the weakly-sorbed chlorophenol (i.e., 2-ChP) was easily desorbed, while the strongly-sorbed chlorophenol (i.e., 2,4,5-TChP) was rather resistant to desorption. [ABSTRACT FROM AUTHOR]

Mag@silica-Ag composite has a high sorption ability for I− in aqueous solution due to its high surface area and strong affinity for the studied anion. The material adsorbed I− rapidly during the initial contact time (in 45 min, η = 80%) and reached adsorption equilibrium after 2 h. Moreover, mag@silica-Ag proved to selectively remove I− from a mixture of Cl−, NO3− and I−. The adsorption behavior fitted the Langmuir isotherm perfectly and the pseudo-second-order kinetic model. Based on the Langmuir isotherm, the maximum adsorption capacity of mag@silica-Ag was 0.82 mmol/g, which is significantly higher than previously developed adsorbents. This study introduces a practical application of a high-capacity adsorbent in removing radioactive I− from wastewaters. [ABSTRACT FROM AUTHOR]