A density functional theory study of the effects of metal cations on the Brøsted acidity of H-ZSM-5

Density functional theory calculations have been carried out to establish the influence of mono- and polyvalent cations on the Brønsted acidity of H-ZSM-5. The zeolite was modeled as a cluster containing 41-45 atoms, in the center of which is an Al⁽¹⁾(OH)SiOAl⁽²⁾(OM)unit, where M⁺ = H⁺, Li⁺, Na⁺, K⁺, Ca(OH)⁺, AlO⁺, Al(OH)⁺ ₂. The local geometry of the Brønsted acid site is affected by the nature of M⁺ and this in turn causes a change in the value of the proton affinity (PA) for the site. The highest value of PA is 330 kcal/mol for M⁺ = H⁺ and the lowest value of PA is 305 kcal/mol for M⁺ = AlO⁺. No correlation was found between the value of PA and the Mulliken charge on Al⁽¹⁾. With the exception of the case where M⁺ = AlO⁺ the binding energy of CO with the Brøsted acid proton is approximately 8.8 kcal/mol, independent of the nature of M⁺. When M⁺ = AlO⁺, the binding energy for CO is 11.1 kcal/mol. The present calculations suggest that different factors affect proton affinity and the binding energy for CO adsorption.     

Characterization of Adsorptive Capacity and Investigation of Mechanism of Cu2+, Ni2+ and Zn2+ Adsorption on Mango Peel Waste from Constituted Metal Solution and Genuine Electroplating Effluent

Abstract

The present study reports the potential of mango peel waste (MPW) as an adsorbent material to remove Cu²⁺, Ni²⁺, and Zn²⁺ from constituted metal solutions and genuine electroplating industry wastewater. Heavy metal ions were noted to be efficiently removed from the constituted solution with the selectivity order of Cu²⁺ > Ni²⁺ > Zn²⁺. The adsorption process was pH-dependent, while the maximum adsorption was observed to occur at pH 5 to 6. Adsorption was fast as the equilibrium was established within 60 min. Maximum adsorption of the heavy metal ions at equilibrium was 46.09, 39.75, and 28.21 mg g for Cu²⁺, Ni²⁺, and Zn²⁺, respectively. Adsorption data of all the three metals fit well the Langmuir adsorption isotherm model with 0.99 regression coefficient. Release of alkali and alkaline earth metal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and protons H⁺ from MPW, during the uptake of Cu²⁺, Ni²⁺, and Zn²⁺, and EDX analysis of MPW, before and after the metal sorption process, revealed that ion exchange was the main mechanism of sorption. FTIR analysis showed that carboxyl and hydroxyl functional groups were involved in the sorption of Cu²⁺, Ni²⁺, and Zn²⁺. MPW was also shown to be highly effective in removing metal ions from the genuine electroplating industry effluent samples as it removed all the three metal ions to the permissible levels of discharge legislated by environment protection agencies. This study indicates that MPW has the potential to effectively remove metal ions from industrial effluents.     

Electrokinetic Properties of Vermiculite and Expanded Vermiculite: Effects of pH,Clay Concentration and Mono- and Multivalent Electrolytes

Abstract

In this study, the zeta potential values of vermiculite and expanded vermiculite were measured to determine the effect of pH, clay concentration, and various mono- and multivalent electrolytes including NaCl, KCl, NH₄Cl, NaNO₃, NaClO₄, Na₂SO₄, Na₂CO₃, Na₃PO₄·12H₂O, MgCl₂·6H₂O, CaCl₂·2H₂O, BaCl₂, SrCl₂·6H₂O, CuCl₂·2H₂O, CoCl₂·6H₂O, NiCl₂, AlCl₃, and CrCl₃·6H₂O on the electrokinetic properties of vermiculite samples. It was found that generally the measured zeta potential values of expanded vermiculite for the studied systems were slightly more negative than that of vermiculite. The pH profiles of vermiculite and expanded vermiculite at acidic, natural, and basic pH values were obtained to determine the effect of time on the pH values of clay suspensions. The zeta potential measurements showed that the surface charge of clay particles was negative in water. The isoelectric point of vermiculite and expanded vermiculite were determined as pH 2.30 and 2.57, respectively. Divalent cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺), heavy metal ions (Cu²⁺, Ni²⁺, and Co²⁺) and trivalent cations (Al³⁺ and Cr³⁺) were potential determining ions for vermiculite and expanded vermiculite particles. Moreover, divalent and trivalent cations caused the change of surface charge from negative to positive. On the other hand, monovalent cations (Na⁺, K⁺ and NH₄ ⁺), monovalent anions (Cl^?, NO₃ ^?, and ClO₄ ^?) and multivalent anions (SO₄ ^2?, CO₃ ^2?, and PO₄ ^3?) acted as indifferent ions for these clay particles.     

CO oxidation over CuO catalysts prepared with different precipitants

CuO catalysts, prepared by the precipitation method using different precipitants such as ammonium hydroxide, sodium hydroxide, sodium carbonate and sodium hydrogen carbonate were applied to CO oxidation. Among the catalysts studied, CuO synthesized with sodium hydrogen carbonate showed the highest activity for CO oxidation. With the water vapor present in the feed gas, the catalytic activity decreased considerably due to reduction in the number of active sites by competitive adsorption between water vapor and CO. The H₂-TPR and CO-TPD results showed that existing Na⁺ cations and HCO ₃ ^? and CO_3/2? anions on the CuO surface could weaken the copper-oxygen bond strength and accelerate the mobility of oxygen on the surface or lattice. Finally, the morphology of the CuO crystals was dependent on the precipitants, and the introduction of Na⁺ cations and various anions resulted in the formation of smaller crystals.     

The effect of some soluble inorganic admixtures on the early hydration of portland cement

The effects of the soluble chlorides, bromides, nitrates, sulphates and acetates of Ca²⁺, Mg²⁺, Li⁺, Na⁺ and Zn²⁺ as well as the corresponding mineral acids on the early hydration of neat Portland cement pastes have been studied. Both the cations and anions are ranked according to their general effectiveness as accelerators of the hydration of the Ca₃SiO₅ phase: Ca²⁺>Mg²⁺>Li⁺>Na⁺>H₂O>Zn²⁺ and OH^? >Cl^?>Br^? >NO₃^?SO₄²～H₂O > CH₃CO₂^?.     

Multi-ion migration of Ca2+, Mg2+, Na+ and K+ in the CREDI process

In this paper, the migration of Ca²⁺, Mg²⁺, Na⁺ and K⁺ in cation-bed electrodeionisation was studied. The results showed that it was longer for divalent cations to be balanced compared with monovalent cations. At relatively low current densities, the membrane fluxes of monovalent cations were higher than that of divalent cations, whereas the results were reversed at relatively high current densities. In the resin phase, it was observed that the ionic transport was in relation to various hydration ionic radii. The reaction orders for Ca²⁺, Mg²⁺, Na⁺ and K⁺ were 2, 2, 1 and 1.5, respectively.     

Functionalized graphene sheets coordinating metal cations

Interactions of metal cations such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ with ammonia-treated graphene sheets (G) and thermal stability of metal cations coordinated with oxygen- and nitrogen-containing functional groups on G were investigated by rinsing G coordinated with metal cations (G-Metal) in 2-propanol using sonication and by heating G-Metal at 773 K, respectively. Monovalent alkali metal cations, divalent alkaline-earth metal cations, divalent transition metal cations such as Mn²⁺, and the other metal cation such as Zn²⁺ were removed by rinsing because of either no interaction or weak interactions between metal cations and G including various thermally stable nitrogen- and oxygen-containing functional groups. Trivalent transition metal cations such as Cr³⁺ and Fe³⁺ were agglomerated by heat treatment at 773 K, whereas divalent transition metal cations such as Co²⁺, Ni²⁺, and Cu²⁺ remained without severe agglomeration. Phenanthroline-like groups on edges of graphene showed the strongest interaction with Ni²⁺ among all of investigated nitrogen- and oxygen-containing functional groups as results of density functional theory calculation. The thermal stability of NNi bonding was confirmed as above 873 K as results of heat treatment of a standard compound (Ni phthalocyanine) in a glass ampoule.     

Poly[poly(oxypropylene) phosphate] macroionophores for transport and separation of cations in a hybrid: Cation‐exchange polymer and liquid membrane system

Poly[poly(oxypropylene) phosphate]s (PPOPP, M_n = 5800, 8100, 10,400), with different POP units (400, 1200, 2000), were synthesized and applied as cation‐selective macroionophores in a multimembrane hybrid system (MHS). The solution of PPOPP in dichloroethane formed the flowing liquid membrane (FLM) circulating between two polymer cation‐exchange membranes, and subsequently, between two polymer‐made pervaporation (PV) membranes. It was found that the PPOPP macroionophores activate the preferential transport of Zn²⁺ cations from aqueous solutions containing competing Cu²⁺, Ca²⁺, Mg²⁺, K⁺, and Na⁺ cations. The following separation orders were observed for PPOPPs with POP‐400 and POP‐1200: Zn²⁺ > Cu²⁺ ? Ca²⁺, Mg²⁺, K⁺, Na⁺, and for PPOPP with POP‐2000: Zn²⁺ > Cu²⁺,Ca²⁺ ? Mg²⁺, K⁺, Na⁺. Always, the particular cations are separated as: Zn²⁺ > Cu²⁺, Ca²⁺ > Mg²⁺, and K⁺ > Na⁺. The properties of PPOPPs were compared to respective transport and separation characteristics corresponding to those of respective poly(propylene glycol)s and poly(oxypropylene) bisphosphates. The results of investigation indicate that the bifunctional character of PPOPPs is caused by the presence of ionizable groups and probably pseudocyclic POP structures. By comparing the separation of cations in the simple MHS[FLM] system and the system supported by pervaporation unit [MHS[FLM‐PV] it was found that continuous dehydration of an organic FLM improves the system overall performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1436–1445, 2004     

Rapid Separation of Tl+ and Pb2+ from Various Binary Cation Mixtures Using Dicyclohexano-18-crown-6 Incorporated into Emulsion Membranes

Abstract

Relative transport rates of metal cation nitrates (Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺) in a water-toluene-water emulsion membrane system were measured. The toluene component contained the surfactant Span 80 and the crown ether dicyclohexano-18-crown-6. The aqueous receiving phase contained Li₄P2O₇. When each metal cation was individually present in the aqueous source phase, metal extraction was complete within 10 min with the order of extraction being Tl⁺ > Cs⁺ > Ag⁺ > Rb⁺ > K⁺ ≥m Na⁺ and Pb⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺ for uni-and bivalent cations, respectively. Significant extraction was found for all cations except Na⁺, K⁺, and Ba²⁺. Some metal ions were concentrated nearly 10-fold in a 10-min period. Relative transport rates were determined when binary cation mixtures of either Tl⁺ or Pb²⁺ were present at equal concentrations with each of the remaining metal ions in the source phase. Tl⁺, when present with either Na⁺, Cs⁺, or Rb⁺, was selectively extracted from the source phase. Complete and nearly exclusive extraction of Pb²⁺ was observed in the presence of all cations including Tl⁺. The enrichment ratios of Pb²⁺ in the binary mixtures were approximately 10 while those of the second cation were less than 0.5 except for Sr²⁺ which was 0.86. Corresponding separation factors for Pb²⁺ ranged from 1000 to > 6000.     

Complexation of poly(methyl methacrylate-g-propylene oxide) and alkali-metal ions

Summary Copolymers of poly(methyl methacrylate-g-propylene oxide) with grafted branches having different molecular weights were complexed with K⁺, Na⁺ and Ca²⁺. The efficiency of the graft copolymers in binding cations was evaluated from salt distribution equilibria in water-methylene chloride. Among the used cations, K⁺ was more easily complexed than Na⁺ and Ca²⁺.     

The influence of hydrogen- and cation-underpotential deposition on oxide-mediated Pt dissolution in proton-exchange membrane fuel cells

In order to fully understand the influence of a lower potential limit on platinum dissolution and the likely mechanism for mass and surface-area loss under potential cycling conditions, the dissolution of a Pt catalyst in a N₂-saturated 0.5 M H₂SO₄ solution was examined using an electrochemical quartz nanobalance (EQCN) flow cell, a rotating ring-disk electrode (RRDE) and inductively coupled plasma mass spectroscopy (ICP-MS). Due to the observation that cycling to a lower potential limit, which coincides with the hydrogen under-potential (H_UPD) region, results in a decrease in the dissolution rate, cations capable of interfering with the hydrogen UPD process (Zn²⁺, Li⁺, Na⁺, K⁺, and Cd²⁺) were introduced to the solution. Larger rates of mass loss were observed in the presence of these cations during the cycling process in the UPD region, despite apparently negligible effects on the behavior with more positive lower potential limits or on oxide formation and stripping. It was found that the quantity of soluble Pt species produced during the electrochemical reduction of PtO₂ was proportional to the charge associated with oxide stripping at the disk electrode during the RRDE experiment.     

Ion-cyclotron resonance study of elementary stages of the catalytic oxidation of CO by N2O in the presence of VIA-group metal ions

Gas phase reactions of Mo⁺ and W⁺ ions with the molecules of various oxidants (NO, O₂, N₂O, CH₂O, C₂H₄O) were studied using ion cyclotron resonance. In oxidation with N₂O the mono-, di- and trioxide metal cations are formed consecutively. The trioxide MO₃ ⁺ ions of both metals react with CO to form CO₂ and MO₂ ⁺ ions. In this way, catalytic reaction N₂O + CO N₂ + CO₂ occurs in the gas phase with MoO₃ ⁺ /MoO₂ ⁺ and WO₃ ⁺/WO₂ ⁺ couples as catalysts. The rate constants have been measured for both stages of the catalytic cycle as well as for the stages of the catalyst preparation. Metal-oxygen bond energies were estimated for MoO_x ⁺ and WO_x ⁺ species with various x. The mechanism of CO oxidation with MoO_x ⁺ and WO_x ⁺ cations as catalysts in the gas phase is discussed in comparison with that for the oxidation over classical solid oxide catalysts.     

FTIR study of low-temperature CO adsorption on Cu/silicalite-1

Adsorption of CO on Cu/silicalite reveals the existence of Cu⁺ sites similar in properties to the Cu⁺ cations exchanged in Cu–ZSM-5. In both cases Cu⁺(CO)₂ dicarbonyls are formed at ambient temperature and under CO equilibrium pressure. These species are converted into monocarbonyls after evacuation. At low temperature, as with Cu–ZSM-5, tricarbonyls are formed on part of the Cu⁺ sites on Cu/silicalite-1. However, the polycarbonyls on the Cu/silicalite-1 sample are less stable as compared to Cu–ZSM-5. In addition, a fraction of Cu⁺ sites rather typical for oxide-supported copper is found with Cu/silicalite-1. The location of the different copper cations in Cu/silicalite-1 is discussed.     

Transfer of Monovalent and Divalent Cations in Salt Solutions by Electrodialysis

Abstract

The selectivity mechanism of transport of Na⁺, Ca²⁺ and Mg²⁺ through commercial monovalent‐cation permselective membranes is investigated in batch electrodialysis experiments with synthetic salt solutions containing monovalent and divalent cations. The role of hydration energy, steric effect, kinetic effect as well as effects of permselectivity of cation exchange membrane has been elucidated with electrodialysis of single solutions (NaCl, CaCl₂, MgCl₂). The mechanism of interferences is investigated in (Na⁺/Ca²⁺, Na⁺/Mg²⁺, Ca²⁺/Mg²⁺ and Na⁺/Ca²⁺/Mg²⁺) mixtures.     

Use of the empirical Hill equation for characterization of the effect of added cations on the viscosity of aqueous solutions of partially hydrolyzed polyacrylamide

Summary An empirical method based on the Hill equation has been developed to characterize the effects of added cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) on the viscosities of aqueous solutions of partially hydrolyzed polyacryl-amide.     

13C and 23Na n.m.r. studies of the interactions between cations and kryptofix (2,2) bound to soluble or gel polyacrylamide

Interactions between univalent cations (Li⁺, Na⁺, K⁺, Ag⁺) and bivalent cations (Ba²⁺, Ca²⁺) with kryptofix (2,2) substituted polyacrylamide have been investigated using ¹³C n.m.r. The tendency to form complexes involves the dimensions of both the hydrated ion and the cavity size macrocycle and for Ag⁺ the nature of the interaction site. The sensitivity of the ²³Na n.m.r. method for detecting complex formation in solution from macromolecular species has been applied to the determination of the conditional formation constants of Na⁺ and Ba²⁺ complexes.     

Lichen Substances Affect Metal Adsorption in <Emphasis Type="Italic">Hypogymnia physodes</Emphasis>

Lichen substances are known to function as chelators of cations. We tested the hypothesis that lichen substances can control the uptake of toxic metals by adsorbing metal ions at cation exchange sites on cell walls. If true, this hypothesis would help to provide a mechanistic explanation for results of a recent study showing increased production of physodalic acid by thalli of the lichen Hypogymnia physodes transplanted to sites with heavy metal pollution. We treated cellulose filters known to mimic the cation exchange abilities of lichen thalli with four lichen substances produced by H. physodes (physodic acid, physodalic acid, protocetraric acid, and atranorin). Treated filters were exposed to solutions containing seven cations (Ca²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Mg²⁺, Mn²⁺, and Na⁺), and changes to the solution concentrations were measured. Physodalic acid was most effective at influencing metal adsorption, as it increased the adsorption of Fe³⁺, but reduced the adsorption of Cu²⁺, Mn²⁺, and Na⁺, and to a lesser extent, that of Ca²⁺ and Mg²⁺. Reduced Na⁺ adsorption matches with the known tolerance of this species to NaCl. The results may indicate a possible general role of lichen substances in metal homeostasis and pollution tolerance.     

Mechanistic elucidation and evaluation of biosorption of metal ions by grapefruit peel using FTIR spectroscopy,kinetics and isotherms modeling,cations displacement and EDX analysis

BACKGROUND: The performance and mechanism of the biosorptive removal of Ni²⁺ and Zn²⁺ from aqueous solution using grapefruit peel (GFP) as a new biosorbent was investigated by using different experimental approaches, such as potentiometric titration, Fourier transform infrared (FTIR) and energy‐dispersive X‐ray spectroscopy (EDX) analysis, chemical blocking of functional groups and concomitant release of cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) from GFP with metal (Ni²⁺, Zn²⁺) uptake. RESULTS: GFP removed Ni²⁺ and Zn²⁺ rapidly, with 84.73% and 92.46% of the equilibrium sorption being reached in 30 min for Ni²⁺ and Zn²⁺, respectively. The equilibrium process was described well by the Langmuir isotherm model, with maximum sorption capacity of 1.33 and 1.51 meq g^?1 for Ni²⁺ and Zn²⁺, respectively. Release of cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and protons H⁺ from GFP during uptake of Ni²⁺ and Zn²⁺ and EDX analysis of GFP before and after metal sorption revealed that the main mechanism of sorption was ion exchange. FTIR spectroscopy showed that carboxyl and hydroxyl groups were involved in the sorption of Ni²⁺ and Zn²⁺. Blocking of these groups revealed that carboxylic group was responsible for 78.57% and 73.31% of Ni²⁺ and Zn²⁺ removal, respectively whereas 22.63% and 28.54% was due to the hydroxyl group. The GFP could be regenerated using 0.1 mol L^?1 HCl, with more than 98% metal recovery and reused for five cycles without any significant loss in its initial sorption capacity. CONCLUSIONS: The study suggests that GFP has promising potential for use as an efficient and cost‐effective biosorbent for the removal and recovery of Ni²⁺ and Zn²⁺ from aqueous solution. Copyright © 2009 Society of Chemical Industry     

Non-Dispersive Solvent Extraction of Neodymium using N,N,N’,N’-Tetraoctyl Diglycolamide (TODGA)

Hollow fiber contactor was used to study non-dispersive extraction (NDSX) of Nd³⁺ ions from aqueous solutions. N,N,N′,N′-tetraoctyl diglycolamide (TODGA) diluted with n-dodecane was used as the organic phase with di-n-hexyl octanamide (DHOA) as the phase modifier. The role of cations (H⁺/Na⁺) on the transport of Nd³⁺ ions has been investigated for this system. It was observed that H⁺ ion has a significant role to play in the Nd³⁺/TODGA complexation reaction. A mathematical model has also been developed to simulate the NDSX process in a hollow fiber contactor. A comparison has also been made between extraction profiles from the NDSX process and the hollow fiber supported liquid membrane (HFSLM) process. It was observed that NDSX gave comparatively faster rates of extraction in the presence of H⁺ ions but slower in the absence of H⁺ ions.     

Influence of K+ and Na+ ions on the degradation of wet‐spun alginate fibers for tissue engineering

A synthetic type of wet‐spun alginate fibers were immersed in simulated body fluid(SBF) composed of K⁺, Na⁺, and Ca²⁺ cations with various concentrations. Experimental measurements revealed that Na⁺ had a greater impact on degradability than that of K⁺ ion. The finding was further confirmed by the characterization of mass loss, ICP, XRD, and theoretical analyses. The degradation process and mechanism were demonstrated through the research on swelling behavior and mass loss. Besides, the wet‐spun alginate fibers were characterized by FT‐IR, XRD, and SEM. The results showed that the degradation mechanism could be attributed to the ion‐exchange between Ca²⁺ of the synthetic alginate fibers and Na⁺, K⁺ of the solutions under the osmotic pressure. The synthetic fibers were swelled and then degraded faster with the presence of Na⁺ ion presented greater influence on degradability compared with K⁺ ion. The degradation results of a mechanical rupture of fibers due to excessive water uptake without the occurrence of any chemical changes in the spun alginates structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44396.