Ion Exchange Kinetics Research Articles

Anisotropy of Anion Diffusion in All-Inorganic Perovskite Single Crystals.

Ion diffusion is a fundamentally important process in understanding and manipulating the optoelectronic properties of semiconductors. Most current studies on ionic diffusion have been focusing on perovskite polycrystalline thin films and nanocrystals. However, the random orientation and grain boundaries can heavily interfere with the kinetics of ion diffusion, where the experimental results only reveal the average ion exchange kinetics and the actual ion diffusion mechanisms perpendicular to the direction of individual crystal facets remain unclear. Here, the anion (Cl, I) diffusion anisotropy on (111) and (100) facets of CsPbBr3 single crystals is demonstrated. The as-grown single crystals with (111) and (100) facets exhibit anisotropic growth with different halide incorporation, which lead to different resulting optoelectronic properties. Combined experimental characterizations and theoretical calculations reveal that the (111) CsPbBr3 shows a faster anion diffusion behavior compared with that of the (100) CsPbBr3, with a lower diffusion energy barrier, a larger built-in electric field, and lower inverse defect formation energy. The work highlights the anion diffusion anisotropic mechanisms perpendicular to the direction of individual crystal facets for optimizing and designing perovskite optoelectronic devices.

Construction and ReO4− adsorption of ionic covalent organic frameworks by solvothermal synthesis based on Zincke reaction

Rhenium is one of the highly scarce and important metals, and its capture is significant for resource recovery. As the latest generation ion exchange materials, ionic covalent organic frameworks (iCOFs) are desired for the acquisition of Re with large adsorption capacity, excellent selectivity, high stability and well-defined pore structures yet seldom reported. In this paper, two highly ordered iCOFs (TABD-COF and TAPB-COF) are successfully constructed via Zincke reaction by the common solvothermal synthesis. In particular, the morphology and crystallinity of iCOFs can be tuned by adjusting the reaction conditions and the structures of precursors. The analysis of PXRD, SEM, and TEM confirms that the two iCOFs exhibit highly ordered crystalline structures with multilayer stacking. TABD-COF and TAPB-COF perform relatively good thermally stability and high chemical stability in both acidic and basic conditions. Both of the two iCOFs show excellent adsorption performance for aqueous ReO4− (714 mg g−1 for TABD-COF, 633 mg g−1 for TAPB-COF) and fast ion exchange kinetics, in which 98 % of ReO4− are captured within 3 mins and 5 mins. Moreover, they also have outstanding trapping efficiency of ReO4− at excesses of competing anions. This work broadens the synthesis of iCOFs via Zincke reaction and provides two novel iCOFs for efficient capture of ReO4− in complex systems.

Research in Industrial Use of Ion Exchange and Simulation

We investigated the industrial use of ion exchange technology as well as the modeling of fixed bed, multicomponent ion exchange processes. In this paper we report on both fields of this research. We have developed a complex technology for the selective separation of the long-live radionuclides and the partial recycling of boric acid from radioactive evaporator bottom residue. A wastewater treatment system has been developed by using a cesium-selective inorganic ion exchanger. The selective separation of 137Cs, 134Cs from high salt concentration and strongly alkaline evaporator bottom residue in Paks NPP has a volume reduction factor of about 3500–6500 at the value of the decontamination factor DF > 100, for the samples of four evaporator bottom residue tanks of the NPP. Some important classes of ion exchangers do possess uniform internal pore structures and bring all parts of the solíd structure into much closer contact with the liquid. Such materials are porous organic resins. For these types of exchangers, we have modified Mansour's multicomponent adsorption model and developed a computer program to describe multicomponent breakthrough, cocurrent, and counter-current elution curves for ion exchangers. In addition, we have developed a subroutine for the calculation of multicomponent ion exchange kinetics according to Nernst-Planck equation and successfully tested it. This subroutine will be added to the multicomponent ion exchange breakthrough and elution simulation program to have a real multicomponent ion exchange simulation program. In this paper we report about these research results too.

Halide Ion Mixing across Colloidal 2D Ruddlesden-Popper Perovskites: Implication of Spacer Ligand on Mixing Kinetics.

Halide ion exchange seen in metal halide perovskites provide a substantial opportunity to control their halide composition and corresponding optoelectronic properties. Halide ion mixing across colloidal 3D perovskite nanocrystals have been extensively studied while the mixing within colloidal 2D counterparts remain underexplored. In this study, the halide ion exchange kinetics across colloidally stable 2D Ruddlesden-Popper layered bromide (Br) and iodide (I) perovskites using two different spacer ligands such as aromatic phenethylammonium (PEA) versus linear butyammonium (BA) is demonstrated. The halide exchange kinetic rate constant (k), as determined by tracking time-dependent absorbance changes, indicates that Br/I halide mixing in 2D PEA-based perovskites (2.7 × 10-3 min-1 ) occurs at an order of magnitude slower than in 2D BA-based perovskites (3.3 × 10-2 min-1 ). Concentration (≈1mM to 100mM) and temperature-dependent (50 to 80 °C) kinetic studies further allow for the determination of activation barrier for halide ion mixing across the 2D layered perovskites with 75.2 ± 4.4kJ mol-1 (2D PEA) and 57.8 ± 7.8kJ mol-1 (2D BA), respectively. The activation energy reveals that the type of spacer cations plays a crucial role in controlling the halide ion mobility and halide stability due mainly to the internal ligand chemical interaction within 2D structures.

Sorption of Lead, Zinc and Copper from Simulated Wastewater by Amberlite Ir-120 Resin

The presence of heavy metals in the environment is major concern due to their toxicity. In the present study a strong acid cation exchange resin, Amberlite IR 120 was used for the removal of lead, zinc and copper from simulated wastewater. The optimum conditions were determined in a batch system of concentration 100 mg/L, pH range between 1 and 8, contact time between 5 and 120 minutes, and amount of adsorbent was from 0.05 to 0.45 g/100 ml. A constant stirring speed, 180 rpm, was chosen during all of the experiments. The optimum conditions were found to be pH of 4 for copper and lead and pH 6 for zinc, contact time of 60 min and 0.35 g of adsorbent. Three different temperatures (25, 40 and 60°C) were selected to investigate the effect of adsorption temperature on heavy metals adsorption onto Amberlite IR. The equilibrium data were analyzed by the Langmuir and Freundlich isotherms. The thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes were calculated. Moreover, in order to understand the heavy metal extraction kinetics in the presence of Amberlite IR 120, the ion exchange kinetics was also studied. The ion exchange kinetics data were regressed by the pseudo first-order, second-order models. The results obtained show that the Amberlite IR 120 strong acid cation exchange resin performed well for the removal of lead, zinc and copper.

Kinetics of ion exchange on inorganic sorbents

In recent years, the problems associated with water use have sharply escalated worldwide. One of the main methods used for these purposes is ion exchange. In turn, the most promising ion-exchange materials are inorganic ion exchangers - substances with exceptionally high selectivity concerning ions of certain elements. In connection with life, it is necessary to understand ion exchange mechanisms on inorganic ion exchangers since they have significant differences in the unit vector of classical ion exchange resins. A theoretical analysis was conducted, which made it possible to reveal some features of the sorption kinetics of inorganic ion exchange materials. It has been found that when working in the region of concave isotherms, a significant slowdown of the mass transfer process is possible even on very sorbent granulates. This effect is associated with reversing sorption processes involving highly selective sorbents. In this regard, difficulties can be encountered when using displacement desorption, which is associated with maintaining high concentrations of the displacing agent and the low rate of the ion exchange process. The rate of sorption on inorganic ion exchange materials depends in a certain way on the concentration of sorbed ions in an external solution. This dependence manifests itself even in the absence of external diffusion inhibition. In this case, the determining factor is the distribution of electrolytes between the pore space of the granule and the free volume of the solution. The rate of mass transfer processes with the participation of inorganic sorbents can be affected not only by the permeability of granulates but also by inhibition at the level of homogeneous sections of the solid phase. The simplest way to detect such deceleration is to compare the data of the kinetic experiment with the theoretical results related to the model that ignores deceleration at the level of homogeneous sections of the solid phase. In such a comparison, it is necessary to consider possible distortions due to the finite width of particle size fractions, the discrepancy between the particle shape and the calculated one, etc.

Some molecular-sieve peculiarities of natural zeolite of Georgia

Ion exchange property of fibrous zeolite scolecite of Georgian origin has been studied against mono (Li, Na, NH4, K Cs and Rb), divalent (Sr, Ba Ca, Mg) and transition (Cd, Cu, Mn, Zn, Co and Ni) metal cations. Selectivity series of the above cations for scolecite have been compiled. The structure of scolecite, charge and sizeof the cations (both in hydrated and dehydrated state) and cation concentration in the solution (0.1N, 0.3N, 0.5N 1.0N and 1.5N) greatly influence on the ion-exchange property and selectivity order of scolecite. Dynamic Exchange Capacity (DEC) values for the studied cations on scolecite have been calculated. Kinetics of ion exchange in dynamic conditions for the above cations has been studied. Analysis of the obtained data shows that the external diffusion processes have influence on the establishment of equilibrium between the ions on the surface and in the micro porous structure of scolesite. The time of dynamic exchange equilibrium is directly proportional to the cation radios.

Tracing hydrothermal mineral thenardite in geysers/hot springs of North-western Himalayan belt, Ladakh Geothermal Province, India by hydrogeochemistry, fluid-mineral equilibria and isotopic studies

The present study highlights the first evidence of hydrothermal mineral Thenardite (Na2SO4) from Puga geothermal area, North-western Himalayan belt in Ladakh Geothermal Province, India, which is unequivocal evidence for the presence of high-temperature hydrothermal fluid activity from one of the thickest crust areas of the Earth. The Puga geothermal belt illustrates a fault-bounded hydrothermal system with a clearly defined conductive zone, coinciding with Kiagar Tso fault typically exemplifying a shallow-level medium enthalpic geothermal reservoir. The hydrogeochemistry suggests that thermal and non-thermal waters are of Na-Cl-HCO3 and Ca-Mg-HCO3 type, respectively, with neutral to near alkaline pH. The silica and cation geothermometry reveal sub-surface temperatures around 150 °C and 250 °C, respectively, at shallow depth; however, >250 °C is anticipated at the deepest levels (~3 km). Stable isotope (δD and δ18O) studies explicate depletion of isotopic content for thermal waters over Puga river water and radiogenic isotope (3H) suggests matured thermal waters with ongoing water-rock interactions. The recharge altitude estimation and physiographic studies put forth that geothermal reservoir is recharged with the ice masses located at an altitude of 6458 m above mean sea level (msl) in the west of Puga valley, probably from the highest peak of Polokong La mountain. The two key processes participating in regulation of proportions of the dissolved salts in the thermal waters are silicate weathering and ion-exchange kinetics. The powder X-ray diffraction study reveals a major occurrence of hydrothermal mineral thenardite in the hot spring deposits for the first time along with huge encrustations of trona, borax, calcite and elemental sulfur. The high-temperature fluids encounter thenardite, pyrite, and jarosite-bearing minerals in basement rock causing enrichment of SO42− and Cl− in geothermal waters. The temperature-dependent speciation modelling (50 °C–200 °C) for major ion Na+ reveals the composition of the reservoir fluid (~150 °C): Na+ > NaCO3− > NaSO4− > NaHCO3 > NaF > NaOH. A conceptual evolution model of thermal waters involving the recharge-deep circulation-mixing-discharge of thermal springs is hence put forth in the study using various hydrogeochemical insights.

Solid‐State Field‐Assisted Ion Exchange (Ag → Na) in Soda–Lime Float Glass: Tin Versus Air Side

The application of a DC current allows fast (few minutes) Ag+ → Na+ ion exchange in soda–lime–silicate (SLS) glass. The effect of processing parameters, electric current, and treating time is studied on both air and tin sides of SLS float glass, and non‐Fickian diffusion is revealed. It is shown that ion exchange kinetics are similar on both sides and the tempering process results in similar mechanical properties (crack formation probability after Vickers indentation, hardness, and Young's modulus). However, the structure/microstructure of the tin and air sides is hugely different. In particular, clear silver nanoclustering takes place on the tin side, resulting in ≈8 nm metallic particles in the vicinity of the surface. The formation of nanoparticles is also coupled with a deep structural reorganization of the amorphous network and the Q n units. The nanoparticles’ size decreases moving from the surface to the interior of the glass. Silver nanoparticles are also detected on the air side, although their density and size are largely reduced. Whereas the mechanical properties measured on the air and tin side are similar, significative differences are observed in terms of optical properties.

DFT-study supported synergistic electrochemical supercapacitor performance of Bi2MoS6 nanosheets

Synergistic electrochemical performance of the bismuth molybdenum sulphide (Bi2MoS6, BMS) nanosheets can be beneficial for fast ion exchange kinetics in electrolyte solution for energy storage performance. Bismuth sulphide (Bi2S3, BS), molybdenum sulphide (MoS2, MS), and BMS electrode materials of different morphologies are grown on stainless-steel (SS) conducting substrate using a wet chemical process. A 0 - 1 V operating potential window vs. Ag/AgCl has been utilized for half-cell analysis wherein, 947.4 F g−1 specific capacitance is obtained for BMS nanosheet-like electrode at 0.6 Ag−1 current density with nearly 97 % stability which is better than BS and MS electrode materials. Full understanding of synergistic effect i.e., enhancement of electrochemical properties, has clearly been revealed by applying ab-initio theoretical calculations using density functional theory. The values of power density and energy density of the as-constructed symmetric supercapacitor device by using BMS electrode are respectively found to be 1130 Wkg−1 and 85 Whkg−1. A panel of forty-two LEDs coupled in series has been powered through symmetric device to demonstrating the practical application of the as-prepared nanosheet-type BMS electrode material for commercial feasibility.

Anion‐Modulated Chemical Doping of Organic Hole Conductor Boosts Efficiency and Stability of Perovskite Solar Cells

AbstractChemical doping of organic semiconductors enables significant progress in improving their optoelectronic performance. However, the correlation between doping counter ions and charge‐transport mechanism has not been yet well‐understood. In this study, it is discovered that the anion‐dependent degree of delocalization (DOD) of lithium‐based dopants significantly determines the doping kinetics as well as the conductivity of organic hole transport layer (HTL), leading to large variation in solar cell efficiency and device stability. Specifically, the incorporation of bis(pentafluoroethanesulfonyl) imide (PFSI−) as the anion with a high DOD results in one order of magnitude higher film conductivity and thus an elevated power conversion efficiency (PCE) exceeding 22.1%, much higher than the state‐of‐the‐art lithium bis(trifluoromethane)sulfonimide (LiTFSI) (21.1%) and lithium hexafluorophosphate (LiPF6) (20.0%). Moreover, the dopant LiPF6 with a smaller DOD produces higher doping yield of HTL accompanied by stronger light‐induced PCE fluctuation. Structural analysis reveals anion‐modulated ion exchange kinetics determine the hole‐transport mechanism and device photostability. To mitigate these detrimental effects, a versatile strategy of Li+ solvation is developed to modulate the anion dissociation, enabling simultaneous improvement of device efficiency and stability. This study elucidates an intriguing and generally applicable doping mechanism, and envisages a bright future to further developing efficient and stable organic electronics.

Molecular-level insights into pH regulation of cation adsorption and exchange at clay particle edges

Clay particle edges are often adsorption and catalytic centers while performances are strongly pH-dependent. Microscopic understanding of adsorption of single (Na+, K+, Cs+, Pb2+) and binary (Na+/Cs+, Na+/K+, K+/Pb2+, Na+/Pb2+) metal ions by montmorillonite particle edges under various pH conditions is addressed by molecular dynamics simulations, and mechanisms regarding how pH regulates adsorption of metal ions, ion-specific effects, impacts of co-ions, thermodynamics and kinetics of ion exchange, and immobilization of heavy metals are unraveled. Under all pH conditions, Na+ and Pb2+ with smaller ionic radii have much higher inner-sphere adsorption densities than K+ and Cs+, and pH elevation generates new adsorption configurations that greatly promote adsorption. The promoting extent is apparently larger for Na+ and Pb2+, while ion-specific sequence (Na+ > K+ > Cs+) remains, which is applicable to single and binary metal ions. Impacts of co-ions onto adsorption rely on their identities and become magnified at higher pH although with consistent trends at all pH conditions; e.g., Na+ always inhibits Pb2+ adsorption while the degree of inhibition is larger due to pH elevation. Whether to promote or suppress adsorption by co-ions can be predicted from relative adsorption preference (Na+ > Pb2+ > K+ > Cs+). Stronger competitive adsorption occurs for binary Na+/Pb2+ than other Aa+/Bb+ ions and for the particle edges than basal and interlayer surfaces. As indicated by selectivity coefficients, montmorillonite particle edges are always Na+-selective, while pH elevation significantly enhances Pb2+ selectivity. Specific adsorption at clay particle edges emerges at lower pH for Na+ than Pb2+ (5.3 vs. 6.9) and increases at higher pH, while the increasing extent is larger for Pb2+, indicating pH elevation favors the immobilization of heavy metals. Results significantly enrich the knowledge about the adsorption/exchange of metal ions and the immobilization of heavy metals by clay minerals.

Effect of charge and anisotropic diffusivity on ion exchange kinetics in nuclear waste form materials

Motifs of radionuclide absorption particles (absorbers or fillers) for the nuclear waste treatment usually have crystal structures with nano-sized tunnels for fast ion diffusion. On the other hand, the accumulation of ions generates an electric field which affects the ion diffusion. Therefore, the strong anisotropic kinetic properties and the electric field affect ion exchange kinetics, especially in an assembly of these particles which may block the fast diffusion tunnels for each other. In this work, we developed a mesoscale model to describe the effect of anisotropic kinetic properties and electric field on ion exchange kinetics. With the model we simulated the effect of anisotropic diffusivity, electrochemical potential, particle morphology, size and aggregation on ion exchange kinetics during batch experiments. It is found that (1) ion exchange results in charge accumulation inside the particle because different ions have different diffusivities and different diffusion driving forces. The electric neutrality is not preserved; (2) the electric field speeds up the slower diffusion ions (either uptake or release) and slows down the faster diffusion ions to reduce charge accumulation and maintains charge neutrality; (3) the ion exchange becomes very slow at the later stages because (a) diffusion driving force (electrochemical gradient, Cs+ concentration in the solution and Na+ inside the particle) continuously decreases, as observed in batch experiments; and (b) the diffusivity decreases due to the Cs+ concentration dependence of ion diffusivity. This can explain the observed experimental phenomena that the radionuclide capacity usually cannot be reached; (4) for needle-like particle and their clusters, both surface area and diffusion distance along the direction with the fastest diffusivities have significant impact on the ion exchange kinetics.

Novel layered iron antimony thiostannate adsorbent of K1.61Fe0.04Sb0.03Sn3.1S7 for cesium green recovery from geothermal water

To develop a green and efficient cesium adsorbent with high adsorption capacity, rapid kinetics, and good regeneration performance is a tremendous challenge. In this work, potassium iron antimony thiostannate (PIATS) synthesized by the hydrothermal method was utilized for green recovery cesium from geothermal water for the first time. PIATS showed a high adsorption capacity of 401.23 mg/g, which was much higher than other types of adsorbents at present. Meanwhile, PIATS showed rapid ion exchange kinetics (within 3 min) and broad pH resistance (4–12). More importantly, PIATS still showed excellent selectivity to cesium even in geothermal water containing many other coexisted ions (Kd = 1.96 × 104 mL/g), and the separation factors between Cs+ and the coexisted competing ions were ranged from 462.77 to 963.76. Subsequently, the cesium-laden PIATS could be easily eluted with 0.50 mol/L NaNO3 to achieve rapid desorption (within 10 min). The concentration of Cs+ in the elution was enriched more than 11 times higher than that in the original solution. Furthermore, no organic solvents or other toxic reagents were involved during the whole process. Therefore, the adsorption advantages, excellent enrichment ability, and structural stability of PIATS make it a potential recyclable candidate for green cesium recovery from geothermal water.

Effect of PbSO4-Oleate Coverage on Cesium Lead Halide Perovskite Quantum Dots to Control Halide Exchange Kinetics.

The selective control of halide ion exchange in metal halide perovskite quantum dots (PQDs) plays an important role in determining their band gap and composition. In this study, CsPbX3 (X = Cl−, Br−, and I−) PQDs were self-assembled with PbSO4-oleate to form a peapod-like morphology to selectively control halide ion exchange. Considering the distinct absorption and bright luminescence characteristics of these PQDs, in situ UV-Vis. absorption and fluorescence spectroscopies were employed to monitor the time-dependent band gap and compositional changes of the PQDs. We determined that the halide exchange in the capped PQDs is hindered—unlike the rapid anion exchange in noncapped PQDs—by a reduction in the halide exchange kinetic rate depending on the extent of coverage of the PQDs. Thus, we tracked the halide ion exchange kinetics between CsPbBr3 and CsPbI3 PQDs, depending on the coverage, using in situ UV-Vis. absorption/photoluminescence spectroscopy. We regulated the halide exchange reaction rate by varying the capping reaction temperature of the PQDs. The capping hindered the halide exchange kinetics and increased the activation energy. These results will enable the development of white LEDs, photovoltaic cells, and photocatalysts with alternative structural designs based on the divalent composition of CsPbX3 PQDs.

Simply synthesized apatites precipitated onto porous rice husk charcoal for the extraction of cadmium (II) and copper (II) ions

ABSTRACT A simple low-temperature method for the deposition of apatite on porous charcoal from rice husk is proposed. The deposition was carried out by impregnation and subsequent treatment of porous charcoal with inorganic compounds of phosphorus and calcium, followed by hydrothermal treatment at 120° C. The composites obtained in this way were investigated by XRD, electron microscopy, nitrogen porosimetry and ion-exchange adsorption of copper and cadmium ions. XRD of the synthesized composites showed the formation of hydroxyapatites with different degrees of crystallization. Electron microscopy showed the presence in the composites of pore-channels with a diameter of up to 10 microns in which apatite grains up to 300 nanometers in length are deposited. The study of the kinetics of ion exchange shows that the diffusion of ions into the grains of hydroxyapatite occurs slowly and does not end during 60 days. Adsorption of cadmium and copper ions during 24 hours occurs mainly on the surface of grains and is characterized by a high degree of ion adsorption and solution purification.

De Novo Ion-Exchange Membranes Based on Nanofibers.

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs.

Ion-exchange mechanisms and interfacial reaction kinetics during aqueous corrosion of sodium silicate glasses

The ion-exchange and associated interfacial reaction mechanisms of silicate glasses are critical in elucidating their aqueous corrosion behaviors, surface modification and property changes, hence have potential impact on both science and technology. This work reports findings of the atomic and nanoscale details of the glass–water interfacial reactions revealed by applying reactive force field (ReaxFF) based molecular dynamics (MD) simulations, from which the key mechanisms of the ion exchange, as well as the kinetics of associated interfacial reactions, are elucidated. It was found that the Na+ and H+ ion exchange can happen between two oxygen ions on a single silicon oxygen tetrahedron or adjacent tetrahedra. In addition, the clustered reaction of two non-bridging oxygens mediated by an adjacent water molecule was also identified. The latter reaction might be the main mechanism of water transport after initial surface reactions that consume the non-bridging oxygen species on the surface. Water molecules thus can play two roles: as an intermediate during the proton transfer processes and as a terminator of the clustered reactions. Statistical analyses were performed to obtain reaction kinetics and the results show that silanol formation is a more favored process than the silanol re-formation within the first 3 ns of interfacial reactions. The results obtained thus shed lights on the complex ion-exchange mechanisms during glass hydration and enable more detailed understanding of the corrosion and glass–water interactions of silicate glasses.

Sulfur-encapsulated zeolite micromotors for the selective removal of cesium from high-salt water with accelerated cleanup times

Bubble-propelled sulfur-encapsulated NaX zeolite (S-NaX) micromotors were developed for the selective removal of cesium from high-salt conditions with accelerated cleanup times. NaX was first modified with sulfur to provide additional Lewis acid−base interactions with Cs+ for enhanced Cs+ selectivity, and then Pt was half-deposited on S-NaX for bubble propulsion via the catalytic decomposition of H2O2. The average velocity of the resulting S-NaX/Pt micromotors in 5 wt% H2O2 is 39.7 ± 17.1 μm/s, which is higher than that of a previously reported Cs adsorbent micromotor (35.4 μm/s). The Cs+ ion-exchange kinetics of the S-NaX micromotor is 1.32 times higher than that of the NaX micromotor in a 5 wt% H2O2 solution where the molar ratio of Na+ to Cs+ is 200, even though the sulfur in the S-NaX micromotor causes an adverse effect on the propulsion speed due to the sulfur poisoning effect. Moreover, the S-NaX micromotor in simulated groundwater also exhibited excellent Cs+ removal performance with distribution coefficient (Kd) values at least 3.2 times higher than those of the nonpropelled S-NaX and NaX micromotor, demonstrating the great potential for the treatment of radioactive Cs+-contaminated water.

Synthesis of phillipsite from perlite utilizing mother waters from wet gel EMT preparation and study of the obtained zeolitic material as ion exchanger

In the present paper, a supplementary method was elaborated for synthesis of phillipsite from perlite utilizing mother waters from wet gel EMT preparation. The method is reproducible and cheap—synthesis was performed at mild conditions at 90 °C. One of the obtained phillipsite samples was tested as ion exchanger with solutions containing K+, Cs+ and Sr2+ for simulated radioactive fixation of these ions. The kinetics of ion exchange was adequately described by pseudo-second-order kinetic model equations. The obtained parameters for the ion exchange properties of the synthesized phillipsite show that this material could be used in the Cs+ and Sr2+ removal in decontamination processes. Cation-exchange effectiveness was also tested for Cs+ and Sr2+ solutions, contaminated with model nonionic surfactant Pluronic 123, which may appear as a municiple pollutant.