Cation Exchange Mechanism Research Articles

Lanthanum biosorption using sericin/alginate particles crosslinked by poly(vinyl alcohol): Kinetic, cation exchange, and desorption studies

Nowadays, lanthanum removal from wastewater has received attention due to its importance in various industrial applications. Biosorption has been considered a promising process for lanthanum removal from secondary sources. This study aimed to evaluate the use of sericin/alginate/poly(vinyl alcohol) (SAPVA) particles for lanthanum biosorption in batch system. The effect of pH on the biosorption of lanthanum showed that both lanthanum‐uptake (0.103 mol/kg) and calcium‐release (0.155 mol/kg) reach a maximum at equilibrium pH 5.22. Biosorption kinetics was carried in three lanthanum initial concentrations (0.0005, 0.0011, and 0.0017 mol/dm3). The results revealed that the equilibration time was reached between 210 and 450 min and biosorption capacity at equilibrium between 0.050 and 0.152 mol/kg. The kinetic followed the pseudo-second order model and the external diffusion was the main limiting step. Evaluation of cation exchange mechanism showed that the lanthanum biosorption is related to a stoichiometric reaction (2:3 ratio) between calcium and lanthanum. Calcium nitrate under acidic conditions was able to retrieve lanthanum biosorbed in the particles with high efficiency (96.07 ± 2.02%). Regeneration kinetics showed a longer equilibration time (630 min) and lower biosorption capacity at equilibrium (0.138 mol/kg) for the lanthanum initial concentration of 0.0015 mol/dm3. In this case, the experimental kinetic profile of calcium released throughout the lanthanum biosorption was not stoichiometric. Characterization analyzes suggest that the main mechanism involved in lanthanum capture and calcium release was cation exchange between functional groups on the biosorbent particles and lanthanum. Thus, SAPVA particles are a promising biosorbent for lanthanum removal from aqueous solutions.

Separation of hafnium from zirconium in HNO3 solution by solvent extraction with Cyanex572

Extraction and separation of hafnium (Hf) from zirconium (Zr) in HNO3 solution were carried out with Cyanex572 as extractant. Hf could be selectively extracted with an optimized extraction rate of 76.8%, and the separation factor between Hf and Zr could reach up to 15.7 when the concentration of Zr(IV), Hf(IV), H+, NO3− and (NH4)2SO4 in aqueous phase were fixed at 110 g/L, 3.0 g/L, 2.6 M, 1.8 M and 0.8 M, respectively. The stoichiometry and coordination structure of the extracted complex for Hf was investigated by slope analysis, Fourier transform infrared (FT-IR) spectrometry and nuclear magnetic resonance (NMR) spectrometry. It was found that HfO2+ in nitric acid medium could be extracted into the organic phase through two routes. The dominant route was via a cation-exchange mechanism, according to 2HfO2+aq + H2A2 org + 2NO3̄ aq↔ (HfO2+)2·(NO3̄)2·A2 org + 2H+aq. Meanwhile, the subordinate route was coordinate with PO in Cyanex572 extractant. Therefore, it is possible to developing an effective solvent extraction system to separate Hf from Zr by utilizing Cyanex572.

Preparation of coral-like palygorskite-dispersed Fe3O4/polyaniline with improved electromagnetic absorption performance

Palygorskite (Pal) was used as frameworks to disperse Fe3O4 and polyaniline (PANI) nanoparticles for the preparation of coral-like Pal-dispersed Fe3O4/PANI composites with improved electromagnetic absorption performance. The processing was a combination of hydrothermal synthesis and simple mechanical stirring. With increasing content of Pal, specific surface area of the Pal-dispersed Fe3O4/PANI composites was increased from 21.14 m2/g to 29.69 m2/g, while the composites exhibitd fluffy coral-like structure due to the cation exchange mechanism and rich silanol (Si-OH) group of Pal. Since various loss mechanisms and improved impedance matching, the Pal-dispersed Fe3O4/PANI displayed an optimal reflection loss of −62.45 dB and a broad effective absorption bandwidth of 5.05 GHz. Therefore, this work develops an inexpensive framework to disperse nanoparticles for electromagnetic absorption materials, while new application of Pal is proposed.

Mechanistic insight into copper cation exchange in cadmium selenide semiconductor nanocrystals using X-ray absorption spectroscopy

In terms of producing new advances in sustainable nanomaterials, cation exchange (CE) of post-processed colloidal nanocrystals (NCs) has opened new avenues towards producing non-toxic energy materials via simple chemical techniques. The main processes governing CE can be explained by considering hard/soft acid/base theory, but the detailed mechanism of CE, however, has been debated and has been attributed to both diffusion and vacancy processes. In this work, we have performed in situ x-ray absorption spectroscopy to further understand the mechanism of the CE of copper in solution phase CdSe NCs. The x-ray data indicates clear isosbestic points, suggestive of cooperative behavior as previously observed via optical spectroscopy. Examination of the extended x-ray absorption fine structure data points to the observation of interstitial impurities during the initial stages of CE, suggesting the diffusion process is the fundamental mechanism of CE in this system.

Construction of Zeolite-Loaded Fluorescent Supramolecular on-off Probes for Corrosion Detection Based on a Cation Exchange Mechanism.

Metal engineering structures are commonly covered and protected by coatings. However, the early local corrosion under the coatings and at defects is difficult to detect and discover. Visibility to the naked eye means that corrosion has already developed and expanded. Therefore, it is practical significant to detect the early corrosion of coated metal. Based on the formation of iron ions and anodic acidification in the local corrosion process, iron ions and proton responsive fluorescent rhodamine B acylhydrazone on-off probes are prepared by newly improved methods and denoted as RBA. RBA are loaded on the surface and in the lattice cage of zeolite (ZEO) to protect RBA from premature exposure to the corrosive environment and fluorescence quenching. In corrosive environments, the RBA loaded on the surface are released and complex with iron ions in the environment to activate fluorescence characteristics. Simultaneously, due to the cation exchange of ZEO, iron ions enter the lattice cage of ZEO and combine with RBA in the lattice cage to turn on fluorescence. When applied in epoxy coatings, the RBA/ZEO effectively indicate the occurrence of corrosion under the coatings and at defects, and accurately locate the corrosion site. Nano-scale ZEO (or RBA/ZEO) fill the micropores such as pinholes and defects of the coatings, and increase the difficulty of diffusion and penetration of corrosive media into the coatings. The application of RBA/ZEO functional filler not only do not weaken the main anti-corrosion performance of the coatings, but also significantly improve it.

Anion assisted extraction of U(VI) in alkylammonium ionic liquid: Experimental and DFT studies

The extraordinary extraction of metal ions in imidazolium ionic liquid phase containing neutral extractants was most often attributed to the cation exchange mechanism in addition to the usual solvation-type mechanism. The cation exchange mechanism results in an irreversible loss of the ionic liquid cation, which eventually leads to the pollution of aqueous phase also. To minimize the limitations of imidazolium based ionic liquid, strongly hydrophobic ionic liquids containing tetra-alkyl ammonium ion have been introduced and studied for actinide separation. Even though these tetra-alkyl ammonium ionic liquids did not undergo cation exchange, but showed exceptional extraction of actinides for the reason, which was not established so far. To unravel the unique role of these hydrophobic ionic liquids, the extraction behavior of U(VI) was studied in a solution of tri-n-octylmethylammonium nitrate ([N1888 ][NO3]) in conjunction with a neutral ligand, 2-hydroxy-N,N-dioctyl acetamide (DOHyA). The extraction of U(VI) was studied as a function of various extraction parameters and the organic phase obtained after extraction was probed by FTIR and Raman spectroscopy to elucidate the mechanism of U(VI) extraction in ionic liquid phase. The result revealed that U(VI) was extracted into ionic liquid phase by a couple of extraction modes, namely through metal–ligand coordination and by loss-less anion exchange mode and these pathways did not cause any undue burden to the organic and aqueous phases, unlike the traditional imidazolium ionic liquids. Further, DFT studies were performed to elucidate the underlying mechanism of U(VI) complexation in ionic liquid phase. The calculated values of binding energy (ΔE) and Gibbs free energy (ΔG) for the complexation of U(VI) with DOHyA in dodecane and tetra-alkyl ammonium ionic liquids medium were found in good agreement with the experimentally determined complexation trends of U(VI) ion with DoHyA. The DFT calculations further established that the cation exchange mechanism by both the ionic liquids, [N1888][NO3] and [N1888][NTf2] was not feasible, but anion exchange mechanism could be possible as observed in the experimental studies.

Enhanced simultaneous adsorption of As(iii), Cd(ii), Pb(ii) and Cr(vi) ions from aqueous solution using cassava root husk-derived biochar loaded with ZnO nanoparticles.

This study presents the modification of cassava root husk-derived biochar (CRHB) with ZnO nanoparticles (ZnO-NPs) for the simultaneous adsorption of As(iii), Cd(ii), Pb(ii) and Cr(vi). By conducting batch-mode experiments, it was concluded that 3% w/w was the best impregnation ratio for the modification of CRHB using ZnO-NPs, and was denoted as CRHB-ZnO3 in this study. The optimal conditions for heavy metal adsorption were obtained at a pH of 6–7, contact time of 60 min, and initial metal concentration of 80 mg L−1. The heavy metal adsorption capacities onto CRHB-ZnO3 showed the following tendency: Pb(ii) > Cd(ii) > As(iii) > Cr(vi). The total optimal adsorption capacity achieved in the adsorption of the 4 abovementioned metals reached 115.11 and 154.21 mg g−1 for CRHB and CRHB-ZnO3, respectively. For each Pb(ii), Cd(ii), As(iii), and Cr(vi) metal, the maximum adsorption capacities of CRHB-ZnO3 were 44.27, 42.05, 39.52, and 28.37 mg g−1, respectively, and those of CRHB were 34.47, 32.33, 26.42 and 21.89 mg g−1, respectively. In terms of kinetics, both the pseudo-first-order and the pseudo-second-order fit well with metal adsorption onto biochars with a high correlation coefficient of R2, while the best isothermal description followed the Langmuir model. As a result, the adsorption process of heavy metals onto biochars was chemisorption on homogeneous monolayers, which was mainly controlled by cation exchange and surface precipitation mechanisms due to enriched oxygen-containing surface groups with ZnO-NP modification of biochar. The FTIR and EDS analysis data confirmed the important role of oxygen-containing surface groups, which significantly contributed to removal of heavy metals with extremely high adsorption capacities, comparable with other studies. In conclusion, due to very high adsorption capacities for metal cations, the cassava root husk-derived biochar modified with ZnO-NPs can be applied as the alternative, inexpensive, non-toxic and highly effective adsorbent in the removal of various toxic cations.

Supported nanoparticle synthesis with Au bis-Ethylenediamine: The mechanism of adsorption onto oxides and carbons

Gold bis-ethylenediamine ([Au(en)2]3+ or AuED) is an effective precursor for the preparation of small Au nanoparticles on common catalyst supports. By studying the adsorption of AuED over a wide variety of supports with surveys of uptake versus time and pH, including XAS studies of solution and adsorbed species, we have demonstrated that an electrostatic mechanism accounts for the data much better than the previously postulated cation exchange mechanism. In the electrostatic mechanism 1) uptake-pH curves are volcano-shaped and are higher in amplitude and broader in pH the lower the PZC of the support, 2) AuED complexes retain at least one hydration sheath with diameter 13.3 Å (0.72 complex/nm2) and adsorb as outer sphere complexes, 3) the monolayer limit in aqueous solutions basified with NaOH is not determined by cation exchange stoichiometry but is a steric limit of close-packed, hydrated complexes. They adsorb at a much lower surface density than that of the surface hydroxyl groups and never electrically saturate the surface. 4) The change in AuED speciation at high pH is consistent with a change in the coulombic attraction of a 3+ versus a 2+ complex.Over carbon supports, adsorption is predominantly electrostatic, but an additional parallel mechanism is apparent in proportion to the graphitic nature of the support.Synthesized Au nanoparticles over the oxide and carbon materials was characterized by high sensitivity powder XRD, STEM imaging, and TPR. The resultant nanoparticles were generally smaller than other synthesis methods reported in the literature for silica, titania, alumina, and carbon. The loading limit of electrostatic adsorption is a surface density of about 1 μmol/m2. At loadings less than or equal to this, electrostatic adsorption provides a simple method with which to synthesize well dispersed Au nanoparticles.

Construction of polymer monolithic columns in polypropylene ink-pen tubes for separation of proteins by cation-exchange chromatography.

We describe the synthesis of polymer monoliths inside polypropylene tubes from ink pens. These tubes are cheap, chemically stable, and resistant to pressure. UV-initiated grafting with 5wt% benzophenone in methanol for 20min activated the internal surface, thus enabling the covalent binding of ethylene glycol dimethacrylate, also via photografting. The pendant vinyl groups attached a poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith prepared via photopolymerization. These tubes measured 100-110mm long, with 2mm of internal diameter. The parent monoliths were functionalized with Na2 SO3 or iminodiacetate to produce strong and weak cation exchangers, respectively. The columns exhibited permeabilities varying from 2.7 to 3.3 × 10-13 m2 , which enabled the separation of proteins at 500 µL/min and back pressures<2.8MPa. Neither structure collapse nor monolith detachment occurred at flow rates as high as 2.0mL/min, which produced back pressures between 6.9 and 9.0MPa. The retention times of ovalbumin, ribonuclease A, cytochrome C, and lysozyme in salt gradient at pH 7.0 followed the order of increasing isoelectric points, confirming the cation exchange mechanism. Separation and determination of lysozyme in egg white proved the applicability of the columns to the analysis of complex samples.

A simple cation exchange model to assess the competitive adsorption between the herbicide paraquat and the biocide benzalkonium chloride on montmorillonite

Since adsorption on clay minerals is one of the most popular water-pollutant removal method, it is important to consider the coexistence of several compounds that can affect pollutant retention. In this work, the competitive behaviour between cationic herbicide paraquat (PQ) and a benzalkonium chloride compound (BAC) on montmorillonite (MMT) was performed by adsorption experiments and analysed by a theoretical cation exchange model. Experimental studies included adsorption isotherms, XRD, FTIR and zeta potential (ζ). Binary systems (BAC + PQ) were performed at different initial concentrations ratio BAC/PQ = 0.1; 0.5; 1.0; 2.0 and 3.0. Results showed that at higher BAC initial concentration, the maximum adsorbed PQ amount decreases. X-Ray diffractograms showed that as the BAC/PQ ratio increases, the MMT basal spacing peak shifts to lower angles suggesting that the basal spacing is mainly controlled by the presence of BAC. Besides, the total adsorbed amount (adsorbed PQ plus adsorbed BAC) is closer to clay CEC value (0.91 mEq g−1), at this value ζ ≅ 0 mV suggesting that the adsorption occurs through a cation exchange mechanism. The theoretical model applied was originally developed to describe the exchange of simple cations on clay minerals, however it was effective in predicting the behaviour of larger cations such as PQ and BAC. In this scenario, thermodynamic parameters calculated through the model indicate that cation exchange process is spontaneous towards adsorbed BAC, suggesting that an adsorbed PQ cation is replaced by an equivalent amount of BAC cation (expressed in terms of electrical charge).

Qualitative and relative distribution of Pb2+ adsorption mechanisms by biochars produced from a fluidized bed pyrolysis system under mild air oxidization conditions

Qualitative and relative distribution of Pb2+ adsorption mechanisms was investigated using corn stalk biochars (CSBs) and rice husk biochars (RHBs) produced from a pilot-scale fluidized bed pyrolysis system under mild air oxidization conditions (oxygen content 0–6%) at low temperature (450 °C). Boehm titration, Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS) were used to analyze the characteristics of biochars, and adsorption isotherms and kinetics analysis were studied. The Pb2+ adsorption capacities of CSBs (about 40 mg/g) presented about twice the amount of RHBs (about 22 mg/g), which were mainly caused by cation exchange and precipitation mechanisms, with the contribution content to the total sorption up to 90%. With oxygen content increasing from 0% to 6%, the absorbed lead capacity due to cation exchange of CSBs increased from 19.10 to 30.40 mg/g, and the corresponding contributions to total Pb2+ sorption increased from 49.00% to 73.80%. When the oxygen content of pyrolysis atmosphere increased, the contribution of cation exchange in Pb2+ adsorption exhibited extremely different tendencies in CSBs and RHBs under the combined action of metallic accumulation in ash and non-active silica embedding in the retract process, which plays a dominant role in Pb2+ adsorption. This study suggests that CSBs produced by fluidized bed under mild air oxidation improved cation exchange capacity, and were promising, low-cost biochar for Pb2+ remediation in the aqueous environment.

A batch study on the adsorption/desorption behavior of vancomycin on bentonite nanoparticles in aqueous solutions.

In this study, adsorption/desorption of vancomycin (VAN) on bentonite nanoparticles was investigated in a batch system. Adsorption experiments were carried out as a function of several influential parameters such as adsorbent dosage, pH, contact time and ionic strength. Bentonite nanoparticles were characterized by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, and Fourier transform infrared (FTIR) analyses and the mesoporous structure was revealed. Langmuir, Freundlich, and Temkin isotherm models were applied for the examination of equilibrium data, and Langmuir was found to be the best fit. With the increase in pH and ionic strength, the adsorption capacity decreases, which suggests the adsorption process may be dominated by the cation exchange mechanism. Moreover, VAN desorption from bentonite nanoparticles in two initial VAN loadings was investigated under different concentrations of metallic cations of various valences (Na+, Ca2+, Al3+), and pHs 3-10. Desorption was strongly pH-dependent and the amount of VAN desorbed increased with increasing cations concentrations. The FTIR analysis before and after VAN desorption suggests that the formation of Al-VAN and Ca-VAN complexes on the solid surface and then their detachment from the solid surface may contribute to the higher VAN desorption by Al3+ and Ca2+.

Cu2+ cation-exchange in ZnxCd1-xS thin films for neuromorphic devices

Neuromorphic devices are promising for more efficient informatics systems, containing electronic analog circuits capable of simulating brain synaptic cells to mimic neuro-biological architectures present in the nervous system. Such devices may be employed in a microfluidic system with materials with cationic exchange (CE) mechanisms, to control the conductivity states and allow multilevel switching capabilities. Thus, CE of Cu2+ in ZnxCd1-xS (0 ≤ x ≤ 1) thin films is hereby reported. The CE dynamics are studied as a function of the different Zn and Cd content in the film. Cu2+ ions, provided by a Cu(NO3)2 solution, can replace Zn2+ and Cd2+ ions into the insulating ZnxCd1-xS films, increasing their electrical conductivity. Reversible CE is achieved with the aid of Zn or Cd diethyldithiocarbamate (DTC) solutions. This CE mechanism provides several different conduction states in the film, which are proportional to the dipping time in both Cu(NO3)2 and Zn/Cd-DTC solutions. Electrical and compositional analysis by XPS and EDS are thoroughly investigated to comprehend the cation exchange process. Samples with higher Cd concentration present more efficient CE processes with Cu2+. These results are supported by a comprehensive discussion considering both thermodynamics solubility products, Gibbs free energy of formation, and chemical softness of the elements involved in the reaction, essential to understanding the driving force of the CE processes.

Simultaneous recovery of phosphorus and nitrogen from sewage sludge ash and food wastewater as struvite by Mg-biochar

The drawback of biochar as a soil ameliorant is its low-nutrient content while the bottleneck of struvite production is its high chemical cost. This drew the idea of using designed biochar for nutrient recovery from nutrient-rich wastewater as struvite. Mg-biochar was used for simultaneous P and N recovery from sewage sludge ash (SSA) and food wastewater (FW) by using ground coffee bean (GCB) and palm tree trunk (PTT) waste. PTT Mg-biochar could recover 92.2% of PO43−-P and 54.8% of NH4+-N while GCB Mg-biochar could recover 79.5% of PO43−-P and 38.6% of NH4+-N. Adsorption, precipitation and cation-exchange mechanisms are involved in the Mg-biochar for the simultaneous recovery of PO43−-P and NH4+-N as struvite. Mg-biochars also showed higher struvite selectivity than the control samples. This method not only supports waste recycling and pollution mitigation but also highlights economical struvite production and the benefits of CO2 sequestration.

Adsorption Behaviour and Kinetics of Zearalenone on Hydroxyl-Fe-Al-Intercalated Montmorillonite

Pristine montmorillonite (Mont) was used as raw materials to prepare hydroxyl-Fe-pillared Mont, hydroxyl-Al-pillared Mont, and hydroxyl-Fe-Al-pillared Mont composites. By varying the OH/Fe and Fe/Al molar ratios during the preparation of the pillared Mont, the adsorption capacity of zearalenone (ZEA) and the kinetics were elucidated. The characterization of X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy reveals the adsorption mechanism of pristine and modified Mont. The results indicated that the ZEA adsorption capacity is Mont (0.05 mg/g) &lt;&lt; 1.5OH/Fe-Mont (0.28 mg/g) &lt;&lt; OH/Al-Mont (0.51 mg/g) &lt; 0.5Fe/Al-Mont (0.56 mg/g) in the condition of pH = 8 and 37°C, in which both 0.5Fe/Al-Mont and OH/Al-Mont reached maximum adsorption capacity and 1.5OH/Fe-Mont attained 5 times the capacity of Mont. Adsorption isotherm studies revealed that Freundlich adsorption isotherms best represented the experimental data. The kinetic data for ZEA adsorption revealed that the Mont adsorption capacity for ZEA equilibrates in 1 hour and is best described using the pseudo-second-order rate equation. The XRD analysis indicated that the amplification of Fe-dominant pillared Mont interlayer spacing is the main reason for the observed increases in the adsorption capacity of ZEA, while Al-dominant pillared Mont has a relatively stable Keggin structure; therefore, interlayer spacing is not the primary mechanism for changes in the adsorption capacity of both OH/Al-Mont and Al-dominant pillared Mont. An FT-IR analysis demonstrated that cationic exchange was the dominant mechanism that allowed ZEA and hydroxyl-Al ions to enter the Mont interlayers, while this cationic exchange mechanism was not the dominant mechanism used by hydroxyl-Fe entering the Mont layers.

Asymmetric diglycolamide in BmimNTf2 as an effective solvent system for the uranyl extraction

The extraction behavior of uranyl from the nitric acid medium using an asymmetric diglycolamide, DMDODGA, in BmimNTf2 was studied. The effects of the concentration of HNO3, DMDODGA and temperature on the distribution ratio were discussed. The distribution ratio of uranyl into BmimNTf2 liquid is much higher than that into hydrocarbon diluents. The extraction mechanism was investigated by UV-visible spectroscopic and extraction experiments that all agree the cation-exchange mechanism. Formation of the 1:2 U/DMDODGA complexes was analyzed using the slope analysis method. In addition, uranyl can be effectively separated from perrhenate using DMDODGA-BmimNTf2 system.

Development of Biomass-Based Anion Exchanger for the Removal of Trace Concentration of Phosphate from Water

Aluminum loaded saponified Mango Waste i.e. Al (III)–SMW adsorbent, which functions as anion exchanger, was developed by loading Al (III) onto lime treated Mango waste biomass. The characterization of adsorbent was done by an Energy Dispersive X-ray (EDX) spectroscopy and chemical analysis techniques. Elemental analysis showed an exchange of Ca (II) or K (I) from SMW with Al (III) during loading reaction via cation exchange mechanism. Phosphate adsorption is strongly pH-dependent and maximum adsorption occurs at pH around 7– 9. The maximum uptake capacity of Al (III)–SMW for phosphate was found to be 3.28 mg/g from the Langmuir isotherm model. The residual concentration of phosphate was sharply decreased by increasing the amount of Al (III)–SMW and reached less than 0.07 mg/L (from 9.7 mg/L) with the use of only 6 g/L of Al (III)–SMW whereas higher than 7 g/L successfully removed 100% of phosphate from water. The adsorbed phosphate was successfully desorbed and the adsorbent was regenerated using dilute alkali solution. Therefore, the Al (III)–SMW adsorbent investigated in this research work is expected to be a potential material for the treatment of water polluted with a trace amount of phosphate from aqueous solution.

Phosphine-Induced Phase Transition in Copper Sulfide Nanoparticles Prior to Initiation of a Cation Exchange Reaction.

Cation exchange reactions of colloidal copper sulfide nanoparticles are widely used to produce derivative nanoparticles having unique compositions, metastable crystal structures, and complex heterostructures. The copper sulfide crystal structure plays a key role in the mechanism by which cation exchange occurs and the product that forms. Here, we show that digenite copper sulfide nanoparticles undergo a spontaneous phase transition to tetragonal chalcocite in situ, prior to the onset of cation exchange. Room-temperature sonication of digenite (Cu1.8S) in trioctylphosphine, a Lewis base that drives cation exchange, extracts sulfur to produce tetragonal chalcocite (Cu2S). The subtle structural differences between digenite and tetragonal chalcocite are believed to influence the accessibility of cation diffusion channels and concomitantly the mechanism of cation exchange. Structural relationships in nanocrystal cation exchange are therefore dynamic, and intermediates generated in situ must be considered.

Synthesis and characterization of nylon 6 polymer nanocomposite using organically modified Indian bentonite

In this present research work two different organic compounds are applied for the modification of Indian origin bentonite. One is with n-hexadecyltrimethylammonium bromide (CTAB), intercalated with an interlayer of bentonite via cation exchange mechanism. Whereas, another with 3-Aminopropyl trimethoxysilane (APTES) interlayer functionalization with bentonite –OH group. APTES and CTAB–intercalated bentonites samples were further cross modified with CTAB and APTES to obtain novel co-surfactant locked organo bentonite modeling (CLOM) like matrices. Original and modified bentonite samples were comparatively evaluated by advanced characterization techniques such as, powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermal gravimetric analysis (TGA). Moreover, the applicability of the developed CLOM like materials were investigated in nylon 6 nanocomposite preparation by melt compounding method using a micro twin co-rotated extruder. Additionally, CLOM-nylon-6 polymer nanocomposites were characterized by wide angle X-ray diffraction, TGA, differential scanning calorimetry, atomic force microscopy and tensile strength measurement. The observed thermograph results confirmed no significant difference in the thermal properties of the developed composites. Whereas, the significant variation observed in the tensile strength results particularly for developed composite 5% of N6-OAMSB and N6 AMOSB 5 showed 111.5 and 76.6% respective enhancement in tensile strength results when compared with a bare nylon-6 polymer.

Diverse Physiological Functions of Cation Proton Antiporters across Bacteria and Plant Cells.

Membrane intrinsic transport systems play an important role in maintaining ion and pH homeostasis and forming the proton motive force in the cytoplasm and cell organelles. In most organisms, cation/proton antiporters (CPAs) mediate the exchange of K+, Na+ and Ca2+ for H+ across the membrane in response to a variety of environmental stimuli. The tertiary structure of the ion selective filter and the regulatory domains of Escherichia coli CPAs have been determined and a molecular mechanism of cation exchange has been proposed. Due to symbiogenesis, CPAs localized in mitochondria and chloroplasts of eukaryotic cells resemble prokaryotic CPAs. CPAs primarily contribute to keeping cytoplasmic Na+ concentrations low and controlling pH, which promotes the detoxification of electrophiles and formation of proton motive force across the membrane. CPAs in cyanobacteria and chloroplasts are regulators of photosynthesis and are essential for adaptation to high light or osmotic stress. CPAs in organellar membranes and in the plasma membrane also participate in various intracellular signal transduction pathways. This review discusses recent advances in our understanding of the role of CPAs in cyanobacteria and plant cells.