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In the study of adsorption of simple adsorbates in microporous materials like zeolites, thermodynamic models of small grand-canonical cells with very local interactions [e.g., see K. G. Ayappa, J. Chem. Phys. 111, 4736 (1999)] have been proven to be able to produce thermodynamic properties in very good agreement with the results of experiments and atomistic simulations. In this paper we present in details the structure and implementation of a thermodynamic partitioning cellular automaton (PCA) devised as a dynamical version of thermodynamic cell models and proposed as an easy environment to perform coarse-grained simulations of adsorption/diffusion of simple interacting molecules in microporous materials. Local evolution rules and memory effects are introduced to make our PCA able to complete the static picture provided by thermodynamic cell models with the simulation of transport properties. [ABSTRACT FROM AUTHOR]

In this second paper we exploit our thermodynamic partitioning cellular automaton (PCA) developed in Paper I [Pazzona et al., J. Chem. Phys. 131, 234703 (2009)] to study interacting molecules adsorbed in microporous materials. We present a mean-field theory of the single cell model at equilibrium followed by a detailed description of the procedure we propose to calculate the chemical potential in the canonical ensemble. Finally we use our approach to simulate transport properties starting from the parameterization devised by Ayappa [J. Chem. Phys. 111, 4736 (1999)] to reproduce the adsorption properties of xenon in zeolite NaA. We report how the correlations included in the PCA evolution rule affect the estimated self-diffusion coefficient. [ABSTRACT FROM AUTHOR]

The adsorption of NO molecules on Pdn clusters of varying size (n=1–6) located in the main channel of mordenite and the interaction of the metallic clusters with the zeolitic framework were investigated using ab initio density-functional calculations under periodic boundary conditions. The supported clusters are created by binding Pdn2+ cations to the inner cavity of a deprotonated Al-exchanged zeolite with an Al/Si ratio of 1/11, such that a charge-neutral system is created. Compared to the highly symmetric structures of the gas-phase clusters, the clusters bound to the zeolitic framework undergo appreciable geometric distortions lowering their symmetry. The distortions are induced by strong interactions with “activated” framework oxygens located close to the charge-compensating Al/Si substitution sites, but the cluster forms also weaker bonds to “nonactivated” oxygen atoms. The interaction with the framework also affects the electronic and magnetic properties of the clusters. While in the gas phase all clusters (except the isolated Pd atom with a closed d10 ground state) have a paramagnetic moment of 2μB, in the zeolite clusters with two to four atoms have zero magnetic moment, while the Pd5 cluster has a magnetic moment of 2μB and for the Pd6 cluster, it is even enhanced to 4μB (but the magnetic energy differences relative to low-spin configurations are modest). Analysis of the magnetization densities shows that in all clusters with zero total moment (singlet ground state), there are sites with excess spin densities of opposite sign. The influence of the cluster-support interaction on the chemical properties of the clusters has been tested by the adsorption of NO molecules. The results demonstrate the interplay between the molecule-cluster and cluster-framework interactions, which can lead to an increase or decrease in the adsorption energy compared to NO on a gas-phase cluster. While on the gas-phase cluster adsorption in low-coordination sites (vertex or bridge) is preferred, for the cluster in the zeolite adsorption in threefold coordinated hollow or twofold bridge sites is preferred. The magnetic properties of the clusters and of the paramagnetic NO molecule play an important role. For the supported clusters with zero magnetic moment, upon adsorption the spin of the molecule is transferred to the cluster (and induces also a modest polarization of the framework). For magnetic clusters, spin pairing induces a reduced magnetic moment of the NO-Pdn complex. The redshift of the NO stretching frequencies is reduced compared to the free clusters by the cluster-support interaction for the smaller clusters, while it remains essentially unchanged for the larger clusters. A detailed electronic analysis of the cluster-support interactions and of the adsorption properties is presented. [ABSTRACT FROM AUTHOR]

Ammonia-nitrogen recovered from synthetic anaerobic membrane bioreactor (AnMBR) permeate facilitated by natural zeolite (clinoptilolite) ion exchange was released during regeneration with tap water into a recirculating, vertical hydroponic system to demonstrate a potential method for nitrogen recovery and reuse from domestic wastewater. Exhausted clinoptilolite leached ammonium into the tap water, which was then used for the hydroponic fertigation of butter crunch lettuce (Lactuca sativa) in vertical hydroponic towers. Crop mass and pigment development of lettuce grown in the zeolite desorption solution were favorable compared to the control (consisting of diluted, synthetic AnMBR permeate). Nitrification occurred faster in the desorption solution compared to the control, resulting in an 11% and 19% increase in fresh and dry mass, respectively, and greater chlorophyll-a and chlorophyll-b development. A system is proposed for implementing vertical trickling hydroponic systems integrated with zeolite regeneration to realize a reusable nutrient recovery system. This work demonstrates the potential of the proposed nutrient recovery system to simultaneously attenuate AnMBR ammonia-nitrogen content, while providing a renewable source of nitrogen for use in soilless agriculture. [ABSTRACT FROM AUTHOR]

The recovery of silver from wastewater is of great significance due to its economic and environmental interest. In this work, zeolitic imidazolate framework-8 (ZIF-8) was chosen to adsorb Ag(I) from wastewater for the first time. The adsorption performance was assessed by adjusting the pH value, uptake time, initial concentration of Ag(I), as well as temperature. The saturated adsorption capacity for Ag(I) onto ZIF-8 can reach 446.7 mg·g−1, which shows that ZIF-8 not only possesses remarkable adsorption performance but also is superior to the reported adsorbents. The selectivity coefficients of ZIF-8 for Ag(I)/Cd(II), Ag(I)/Ni(II), and Ag(I)/Co(II) are 8.242, 8.315, and 136.3, respectively. The Sips adsorption model matches adsorption isotherms of Ag(I) onto ZIF-8 well, and the pseudo-second-order model is more suitable to illustrate the kinetics data. Thermodynamic experiment indicates that the adsorption process of Ag(I) is an exothermic reaction. Mechanism studies suggest that the redox reaction of Ag occur in the adsorption process. In addition, the study of recycling use indicates that the stable adsorption performance being maintained after recycle twice. Thus, a promising adsorbent is introduced to recover Ag(I) from wastewater in this work. [ABSTRACT FROM AUTHOR]

Highlights • N-rich nanoporous carbon with C 3 N-type was synthesized. • The methanol adsorption mainly depends on the porosity structure at high pressure. • The methanol adsorption is determined by the functional groups at low pressures. • The adsorption mechanism between methanol and nitrogen groups is elucidated. Abstract The N-rich nitrogen (25.7%) porous carbon with high surface area was prepared by using N-rich ZIF-8 as a template and precursor and urea as a secondary nitrogen source. Simple pyrolysis of the ZIF-8/urea composite leads to N-rich carbon with C 3 N-type stoichiometry. The content and type of nitrogen functional groups can be tunable by the pyrolysis temperature. The resulting carbons stand out by a highly polarizable microporous structure and thus high affinity for methanol adsorption. The experimental results indicate that the microporous structure of porous carbon is the determinant of methanol adsorption at high pressure, whereas at low pressure, the methanol adsorption dominantly depends on the nitrogen functional groups. To more deeply investigate the interactions between the methanol molecules and carbon framework, we performed the theoretical analysis regarding the adsorption isotherms, binding energy and atomic partial charge using the GCMC and DFT methods. The methanol adsorption capacity is determined by the electrostatic interaction at low relative pressures due to the nitrogen functional groups enhancing the electrostatic potential of carbon surface. While the dispersive interaction becomes dominant at high relative pressures, and thus the methanol adsorption mainly depends on the porosity structure. [ABSTRACT FROM AUTHOR]

The adsorption equilibrium and kinetics of CO2, CH4, and N2 on three types of BETA zeolites were investigated at different temperatures and a defined partial pressure range from dynamic breakthrough experiments. The adsorbed amount followed the decreasing order of CO2 > CH4 > N2 for all studied materials. For the same ratio of SiO2/Al2O3, the Na‐BETA‐25 zeolite showed a higher uptake capacity than H‐BETA‐25, due to the presence of a Na+ cationic center. Comparing the same H+ compensation cation, zeolite H‐BETA‐25 expressed a slightly higher adsorption capacity than H‐BETA‐150. Regarding the selectivity of gases, based on their affinity constants, H‐BETA‐150 displayed the best ability. The adsorption kinetics was considered using the zero‐length‐column (ZLC) technique. Response surface methodology (RSM) was applied to evaluate the interactions between adsorption parameters and to describe the process. Natural gas upgrading requires adsorption of CO2, CH4, and N2. Three different types of BETA zeolites were tested regarding the adsorption equilibrium for these gases. Their structure can be easily functionalized in terms of cation exchange and hydrophobicity index by the SiO2/Al2O3 ratio. Langmuir isotherm and response surface methodology were employed for modeling and statistical analysis. [ABSTRACT FROM AUTHOR]

Highlights • An numerical analytical method for a compact adsorption-type oxygen concentrator having two short-length zeolite columns was developed. • Equations for gas velocity under uniform gas pressure over the entire area of the zeolite column were used. • The energy conservation equation for gas includes flow work and gas enthalpy transport which occurs when gas adsorbs/desorbs at a surface of a zeolite particle. Abstract In order to improve the performance of a compact adsorption-type oxygen concentrator, it is necessary to develop an analytical method for a compact concentrator having two zeolite columns of 15–30 cm length. A method which computes the velocity of gas flowing through the zeolite column was developed by assuming that the total gas pressure over the entire area of the column is spatially uniform during pressure swing adsorption (PSA) operation. The energy conservation equation for gas includes flow work and gas enthalpy transport which occurs when gas adsorbs/desorbs at a surface of a zeolite particle. Spatial distributions of gas velocity, oxygen concentration, and gas-zeolite temperatures were analyzed numerically using these equations. The numerical results of the time dependent changes in the discharged oxygen concentration and the temperature distribution of the zeolite column were in agreement with experiment. [ABSTRACT FROM AUTHOR]

Abstract This work was aimed at removing CO 2 from a fire power plant by using the thermal swing adsorption (TSA) process. It is well known that CO 2 adsorption uptake is blocked by the coexistence of steam in the TSA process. In this paper, the influence of desorption temperature and relative humidity in the desorption process on the CO 2 capture performance during the TSA process is kinetically investigated. Under conditions without water, the adsorption decreases by half; when the relative humidity is 1.1% at 393 K, adsorption decreases to 2.5 mg-CO 2 /g honeycomb. The recovery ratio of the CO 2 adsorption performance depends on the relative humidity, not the desorption temperature. Therefore, in the TSA process, it is expected that the influence of steam can be disregarded if a better steam desorption adsorbent is used. This has the added benefit of eliminating the need to remove steam during preprocessing. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic and static adsorption performance of phosphate in the water on the zirconium modified zeolite (Cl2OZr/zeolite) was investigated. Batch adsorption experiments were performed to evaluate the adsorption conditions and selectivity. The experimental results agree well with the pseudo second-order kinetic model. The effects of the dynamic adsorption of phosphate on Cl2OZr/zeolite were studied. The results indicate that the breakthrough time is 480 min and the phosphate removal rate reaches 95% under the optimal conditions. The curves of dynamic adsorption could be fitted by the Thomas model. Cl2OZr/zeolite can be reused and applied to the actual waste water treatment. Comparing previous studies on phosphate removal with different adsorbents, we can see that the Cl2OZr/zeolite has the advantages of wide pH range, relatively short adsorption equilibrium time and reusability. [ABSTRACT FROM AUTHOR]

The synthesis conditions of zeolitic imidazolate framework-8 (ZIF-8) have been optimized by a response surface method using central composite design (CCD) to obtain the high adsorption capability for the Pb(II) removal in aqueous solution. The physic-chemical properties of the as-prepared ZIF-8, such as morphology, structure and chemical composition, were characterized by field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD) and energy-dispersive X-ray photoelectron spectroscopy (XPS), respectively. The adsorption capability, influence factors, isotherms, thermodynamics, kinetics and mechanism of Pb(II) in aqueous solutions were investigated. The optimal parameters of which have the highest adsorption capability for Pb(II) were 200 mL of water as the solvent, and the molar mass ratio of 2-methylimidazole and Zn(NO3)2·6H2O was 45.63. At this condition, the as-prepared ZIF-8 was a pure hexagonal three-dimensional crystal structure. The equilibrium adsorption capacity up to 668 mg/g for 300 mg/L of initial Pb(II) solutions and the adsorption was a spontaneous process. The largest adsorption capacity from Langmuir isotherm model was 686.25 mg/g. The adsorption kinetics followed the pseudo-second-order model. The equilibrium adsorption time and the optimal adsorption pH was 4 h and 6.0–7.0, respectively. The ZIF-8 still kept well adsorption effect after three times of usage. Therefore, this study showed that ZIF-8 is a promising sorbent for removing environmental pollutants. [ABSTRACT FROM AUTHOR]

In this manuscript, the micro-mesoporous crystals with the properties of (H) ZSM-11 zeolites were successfully obtained via one-pot synthesis in the hydrothermal system by using acidified attapulgite (Si-ATP) and cetyltrimethylammonium bromide (CTAB) as a precursor source (PS) and structure-directing agent (SDA), respectively. The effect of Si-ATP/CTAB ratio on controlling the crystal morphology and hierarchical pore structure of products was systematically investigated. The synthesized materials were characterized with XPS, XRD, FTIR, NMR, SEM, TEM and N 2 adsorption-desorption analysis. Results demonstrate that the products possess not only a classical zeolite framework but also an adjustable mesoporous structure accompanied with a variety of Si-ATP/CTAB ratios. Meanwhile Si-ATP/CTAB ratio has a well linear dependence with hierarchy factor (HF) in lower or higher ranges. The MFI crystal transforms gradually to the MEL-structure under the action of CTAB when Si-ATP/CTAB ratio increases to 80: 5. In addition, (H) ZSM-11 zeolite, this ratio of 80: 5, mesoporosity and adsorption capacity of MB molecules was significantly enhanced. Advanced adsorption performance is attributed to the abundance hydroxyl group and the generated mesoporosity of the zeolite surface under the participation of CTAB. The experimental data are well fitted to the Langmuir isotherm model, with a correlation coefficient of 0.9962. The excellent adsorption performance makes such hierarchically porous (H) ZSM-11 zeolites attractive for applications in the field of energy and environment. [ABSTRACT FROM AUTHOR]

Abstract Tannery industrial effluent is rich in heavy metals and basic dyes as bromocresol purple (BCP), poses an economic problem and a serious danger to the environment. This research had evaluated the importance of the adsorption properties of a modified clinoptilolite (CL) (a type of zeolite) for the removal of BCP dye and some heavy metals as total chromium (tCr) in the ammoniac phase. The modified adsorbent was prepared by mixing solid waste (SW) and CL in a ratio 10:1. The CL, SW, and CL-SW materials were characterized and the adsorption behavior of the later to BCP and tCr was completely studied. The batch removal showed the optimal conditions for BCP adsorption: pH (6.5), time ( t ) (60 min), temperature ( T ) (303.15 K), sorbent dosage ( m ) (60.4 mg), and initial concentration ( C o ) (11.7 mg/L). Moreover, the optimum conditions for tCr removal were: pH (8.8), t (55 min), T (303.15 K), m (400 mg), and C o (16.0 mg/L). Cr desorption mechanism was an ion exchange reaction. The experimental data of tCr were best fitted by the Freundlich isotherm and the pseudo-second-order kinetic model. The maximum adsorption capacities of BCP and tCr onto the CL-SW were 175.5 mg/g and 37 mg/g, respectively. Thermodynamic studies revealed that the adsorptions were spontaneous and endothermic with an increase of entropy. The CL modified adsorbent seems to be a good and efficient for the removal of dyes as BCP and such heavy metals including Cr. Surprisingly, this treatment has largely improved the physicochemical properties of the industrial wastewater and proved a new concept “Polluter Cleans Polluters (PoClPos)”. Graphical abstract Image 1 Highlights • The structure of the clinoptilolite was mesoporous (2∼50 nm) at 303.15 K. • Recycling can exert adverse effects on crystalline phase. • [Cr(NH 3 ) 6 ]3+ ions are bonded to the negative vacant sites on the modified surface. • The concentration of Cr has a major influence on the response variable. • Freundlich model was suitable for Cr adsorption with maximum q e (37.0 mg/g). [ABSTRACT FROM AUTHOR]

Adsorptive desulfurization of sulfur compounds in transportation fuels, such as benzothiophenes from gasoline and jet fuels and dibenzothiophenes from diesel, can be inhibited by diffusion limitations in porous materials as well as the presence of aromatic hydrocarbons. In this study we demonstrate that adsorptive desulfurization using bimetal-exchanged mesoporous Y zeolites can overcome these challenges without sacrificing high sulfur adsorption capacity. The mesopores shorten the diffusion path length toward the internal active sites of the zeolite, while the metals (in this study Ce and Cu), not only create relatively stronger bonds, but also multiple adsorption configurations. The bimetallic mesoporous Y zeolites were prepared using a templated top-down approach, followed by the introduction of the metals, Cu and Ce, via ion-exchange. The ability of each zeolite to remove sulfur compounds is demonstrated by fixed-bed experiments. Model fuels were prepared using benzothiophene and dibenzothiophene in octane, benzene and naphthalene. The adsorption mechanisms of benzothiophene and dibenzothiophene were further studied, at the molecular level, using in-situ Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS). Our results indicate that the metals display high affinity for the aforementioned sulfur compounds, via either π-complexation or σ bond interaction. Specifically, Ce-exchanged Y zeolites exhibit multiple adsorption modes, as they can adsorb the sulfur compounds via the both configurations. Furthermore, the mesoporosity in Y zeolites enable the adsorption of dibenzothiophene with a diffusion coefficient of 4.5x greater than the parent Y zeolite. In conclusion, bimetallic mesoporous Y zeolites exhibited DBT capacity of almost 50 mL/g, five times more than parent Y, due to both improved mass transfer and high adsorption energy. [ABSTRACT FROM AUTHOR]

In recent years, the use of both natural and synthetic zeolites in livestock feeds fed to lactating cows has increased, mainly to improve their performance, health, and to protect against mycotoxins intoxication. Data of scientific literature were compiled to analyze the effects of the incorporation of non-nutritional adsorbent zeolite on production performance and ruminal environment parameters of lactating cows. At moderate levels (200–400 g/cow/day), milk yield was increased by zeolite. Milk fat and protein contents and DMI were not altered and all ruminal parameters were improved: acetate was enhanced, propionate was reduced and consequently, acetate to propionate ratio was increased. The rumen pH was increased and rumen ammonia nitrogen was reduced. When the level of zeolite exceeded 400 g/d/cow, all production and ruminal parameters were negatively altered. These data suggest that zeolite level in the diet has a significant effect on the response of dairy production and ruminal environment characteristics. [ABSTRACT FROM AUTHOR]

The removal of Pb2+, Cd2+, and Hg2+, which act as endocrine disruptors, from aqueous solutions was performed using a NaP1-type zeolite synthesized from a hazardous aluminum waste. The effects of parameters such as pH, contact time, adsorbent dose, initial cation concentration, and coexisting cations on the adsorption efficiency and capacity of the adsorbent were evaluated. Single-cation adsorption was found to be a fast process well described by the pseudo-second-order kinetic model. Equilibrium was reached in the first 15 min achieving high removal efficiencies: 98.9%, 93.3%, and 99.3% for Pb2+, Cd2+, and Hg2+, respectively. The removal of the metal cations could occur via a homogeneous and physical adsorption process that was satisfactorily described by the Sips isotherm. The maximum adsorption capacities, obtained from the Sips isotherm model, were 245.75, 4.43, and 0.22 mg/g for Pb2+, Cd2+, and Hg2+, respectively. In multi-cation adsorption, the zeolite presented the greatest affinity for Pb2+ (due to its smallest cationic size) compared with Cd2+ and Hg2+. The Pb2+ removal efficiency remained practically constant in presence of Hg2+ and Cd2+, reaching efficiencies near 100% at very low contact times (<5 min). Thus, this zeolite could become an alternative adsorbent to eliminate heavy metals from waters. A synergic effect on the environmental protection could be achieved: the end-of-waste condition of a hazardous waste as well as the water decontamination. [ABSTRACT FROM AUTHOR]

This study examined the sorption performance of synthesized nanosized zeolite for the elimination of Cs+ and Sr2+ cations in a binary metal system. The influence of pH, sorbent amount, temperature, and contact time was studied. The relationship between each of these parameters and the removal efficiency was investigated. An analysis of the rate data was performed using both pseudo-first- and second-order reaction models. The ranking of three equilibrium sorption isotherm models used (Redlich-Peterson, Langmuir, and Freundlich) with a variety of numbers of parameters was determined using the corrected Akaike’s information criterion. The results demonstrate that a pseudo-second-order model fits the sorption kinetic data better than a pseudo-first-order model. The isotherm model rank order that best described the data statistically was Redlich-Peterson > Langmuir > Freundlich for the cesium ions and Langmuir > Redlich-Peterson > Freundlich for the strontium ions. Our results revealed that the existence of Sr2+ caused a significant reduction of Cs+ sorption in the binary metal mixture according to a lumped parameter model and vice versa. The results show that the synthesized material’s surface had a relatively stronger affinity for Cs+ than for Sr2+. [ABSTRACT FROM AUTHOR]

Natural zeolite has been recognized as a useful adsorbent for wastewater treatment for removing cations. Natural zeolite is a kind of porous material with large specific surface area but limited adsorption capacity. In recent years, emphasis has been given to prepare the surface modified zeolite using various procedures to enhance the potential of zeolite for pollutants. Modification treatment for zeolite can greatly change surface chemistry and pore structure. The article describes various modification methods of zeolite, and introduces the removal mechanisms of common pollutants such as ammonium, phosphorus and heavy metals. In addition, this review paper intends to present feasibility of applying modified zeolite to constructed wetlands which will be beneficial to achieve higher removal effect. [ABSTRACT FROM AUTHOR]

Pressure drop changes in a fixed bed of synthetic zeolite NaA and natural clinoptilolite from Ai-Dag field (Azerbaijan) are studied as functions of the incoming gas flow rate. Conditions for attaining the maximum adsorbent capacity during adsorptive separation of a CH4/CO/CO2/N2 gas mixture are created in the zeolite fixed bed if the pressure drop is maintained in a certain range. A system of equations describing the relationships of the pressure drop during gas-phase adsorption in a clinoptilolite fixed bed and the incoming gas flow rate that ensure the most complete utilization of the adsorbent capacity is proposed. [ABSTRACT FROM AUTHOR]

The sorption characteristics of Cs and competitive ion exchange with other alkali cations and Sr on three natural zeolites, chabazite, stilbite, and heulandite, were investigated. Chabazite showed the most rapid sorption of Cs, followed by heulandite and then stilbite, and this was closely related to its high cation exchange capacity (CEC) and low Si/Al ratio. The kinetic data for all zeolites were best explained by a pseudo-second-order rate model. The sorption process involved multiple steps and is influenced by the CEC values of the zeolites. The equilibrium adsorption isotherms of the three zeolites were best fitted by both the Langmuir and Freundlich models. The exchange isotherms of Cs and the other investigated cations clearly showed that chabazite showed higher selectivity for Cs than for the others. At lower equivalent fractions of Cs in solution, the selectivities for the other cations showed the following trend: Na > Li > Sr > K > Rb. However, for stilbite and heulandite, the selectivity for Cs is only higher at lower equivalent fractions, and isotherms show sigmoidal shapes mainly because there are more than two sorption sites for Cs while chabazite has one site. Those trends were confirmed by Kielland plots. [ABSTRACT FROM AUTHOR]

An investigation was carried out to determine the extent of relations between various structural properties of zeolite frameworks and their experimental water adsorption capacities. For this aim, average water capacity values were determined for different zeolite frameworks by utilizing water adsorption capacities reported in the literature for related materials. It was observed that the theoretical surface areas and volumes available for water adsorption in zeolites as well as the fractal dimensions of these materials exhibited some correlation with their experimental adsorption capacities. The results might give an indication of the potential for development of different zeolite frameworks, regarding their water adsorption capacities. Analogue materials of known zeolite framework structures, with different chemical compositions, which may allow for relatively high water adsorption capacities, may be prepared for such an improvement. The investigations may also be informative for the development of new zeolite-like adsorbents with relatively high capacities. [ABSTRACT FROM AUTHOR]

Thermodynamics, kinetics and selectivity of H 2 and D 2 on zeolite 5A have been investigated by isotherm adsorption/desorption and thermal desorption spectroscopy (TDS) at temperatures below 77 K. The experimental adsorption isotherms show an increasing amount of gas adsorbed with decreasing temperature from 77 K to 30 K, and D 2 /H 2 adsorption ratio is slightly larger than 1. In addition, the enthalpy of D 2 ( ΔH ) adsorption obtained from adsorption isotherms is for different uptakes always larger than for H 2 indicating a stronger D 2 adsorption. The kinetics of H 2 adsorption/desorption is faster than of D 2 at different temperatures (30–50 K), pressures (10-400 mbar) and gas composition due to the faster H 2 self-diffusion in zeolite 5A at low temperature. Furthermore, D 2 /H 2 selectivity increases gradually and reaches a constant value with increasing loading time and pressure, and it is 8.83, 6.42, 4.98, 3.96 and 4.04 at 30, 35, 40, 50 and 60 K at 50 mbar, respectively. The D 2 /H 2 separation in zeolite 5A is controlled by the thermodynamic equilibrium of adsorption under the experimental conditions applied here. To the best of our knowledge, this is the first report on the hydrogen isotope selectivity of zeolite 5A at temperatures below 77 K. [ABSTRACT FROM AUTHOR]

Zeolites are known as good adsorbents with ion exchange capacity because of their unique physiochemical properties. Their capability of metal ion immobilization makes them a good candidate as an alternative to the chromatography resins. In this study, two types of nanozeolite microspheres including ZSM-5 (Si/Al∼ 27) and 13X (Si/Al ∼ 1.3) were synthesized. The Ni +2 ions were immobilized on the synthesized zeolites along with a local clinoptilolite (Si/Al ∼ 7.53). Batch adsorption/desorption experiments were performed for the purification of the scFv antibodies using these zeolites. All the zeolites showed a high-speed adsorption kinetics with the shortest time for ZSM-5-Ni +2 , reaching the maximum adsorption (100%) in less than 3 min in the pHs ranging from 6.5 to 7.5. In addition to the metal affinity, the hydrophobic property showed to be one of the most effective factors on the adsorption of scFvs. As a result, the less hydrophilic zeolite ZSM-5 was found to be the best adsorbent of scFvs. The mixed mode performance of zeolites by the combination of the metal affinity and the cation exchange properties were analyzed. The Ni +2 -immobilized natural clinoptilolite was the only one that displayed a mixedmode capability. In the elution step, the Ni +2 -immobilized ZSM-5 provided a markedly higher scFv purity (∼90%) with an acceptable purification yield (60%) just by the metal affinity mode. Taken all, relatively short desorption times (∼10 min) of the scFv antibodies along with the high adsorption/desorption yields make the ZSM-5-Ni +2 as a promising metal affinity chromatography media for the low concentration scFv solutions. [ABSTRACT FROM AUTHOR]

Pollution of groundwater and surface water compartments is one of the major concerns related to the use of glyphosate in plant-protection products, and is attributed to the postulated endocrine-disrupting activity of the compound. There is a consensus that glyphosate cannot be inactivated in water by the addition of other substances that may also be foreign to that compartment. Therefore, a good, environment-friendly solution would involve use of natural zeolite-bearing rock to remove glyphosate from water. The main purpose of this study was to demonstrate that the content of glyphosate in water can be reduced by 50% through its adsorption on natural zeolites. An additional purpose was to identify the mechanism underlying the process – demonstrated to be adequately characterized by Freundlich and Langmuir isotherms. In natural zeolite-bearing rock with grain diameter <0.02 mm, the maximum monolayer adsorption capacity was 3.66 mg glyphosate/g sorbent. Glyphosate was shown to be adsorbed inside medium-sized heulandite channels with internal diameters of 0.4–0.6 nm; moreover, the adsorption of glyphosate onto heulandite crystal was shown to be a physisorption, unaccompanied by the formation of chemical bonds. [ABSTRACT FROM AUTHOR]

Producer gas originating from the gasification of biomass has a complex composition, especially compared to its coal or gas based counterparts. Separation of these mixtures is a crucial step in a commercial process, which can effectively be achieved by selective adsorption. In this paper the adsorptive separation of ethylene from a typical complex gas mixture containing N 2 , H 2 , CH 4 , C 2 H 4 , C 2 H 6 , CO and CO 2 on zeolites [Ca]A and [Ag]A using a set-up for high throughput screening is described. It was shown that [Ca]A has a high ethylene adsorption capacity, whereas ethane and CO 2 are co-adsorbed. Desorption of ethylene from [Ca]A is slow, but the adsorption capacity could be restored fully. In addition, the material is stable over 15 subsequent adsorption/desorption cycles without loss in performance. On the other hand, [Ag]A has a high adsorption selectivity for ethylene. However, its stability and ethylene recovery from the material is low, since only 80% of the original ethylene adsorption capacity was recovered after the first cycle. The adsorption capacity and selectivity decreases even further in subsequent cycles. This decrease in adsorption capacity and selectivity is caused by the reduction of the Ag + ion to metallic silver and agglomeration to larger particles due to the presence of reducing gases, e.g. ethylene, CO and H 2 , in the gas stream. [ABSTRACT FROM AUTHOR]

Heavy metals are continuously contaminating the surface and subsurface water. The adsorption process is an attractive alternative for removing the heavy metals because of its low cost, simple operation, high efficiency and flexible design. In this study, influences of β-zeolite and Cu-modified β-zeolite on preparation of granular activated carbons (GACs) from a composite of powder activated carbon (PAC), methylcellulose as organic binder, bentonite as inorganic binder and water were investigated. A number of granular samples were prepared by controlling the weight percentage of binder materials, PAC and zeolites as a reinforcing adsorbent. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction techniques were employed to characterize zeolite, modified zeolite and produced GAC. The produced GACs were used as the adsorbent for removal of Zn2+ , Cd2+ and Pb2+ ions from aqueous solutions. The results indicated that the adsorption of metals ions depended on the pH (5.5) and contact time (30 min). Maximum adsorption of 97.6% for Pb2+, 95.9% for Cd2+ and 91.1% for Zn+2 occurred with a new kind of GAC made of Cu-modified β-zeolite. The ZnP+, CdP+ and PbP+ ions sorption kinetics data were well described by a pseudo-second order model for all sorbents. The Langmuir and Freundlich isotherm models were applied to analyze the experimental equilibrium data. [ABSTRACT FROM AUTHOR]

In present research, a simplistic hydrothermal method was adopted for one-step synthesis of nanozeolite beta (NZB) having an average particle size of 18 nm with Si/Al ratio 46.67, surface area 328 m 2 /g, pore volume 0.287 cm 3 /g, and pore diameter 3.5 nm. The surface of the synthesized NZB was modified with 0.5 wt% hexadecyltrimethylammonium bromide (HDTMA-Br) and used as an adsorbent for the removal of two phytoestrogens daidzein and coumestrol from aqueous solutions. The surface properties and surface charge of NZB considerably changed after modification with HDTMA-Br, which resulted in enhanced removal of daidzein (92–98% from 7 to 27%) and coumestrol (93.5–99% from 5 to 9.2%). The surface modified zeolite beta (SMZB) has similar physical characteristics as of NZB with an average particle size of 20 nm, surface area 299.8 m 2 /g, pore volume 0.263 cm 3 /g, and pore diameter 3.51 nm. The influence of various parameters was examined by conducting a sequence of batch experiments. The adsorption equilibrium was achieved in less than 3 h with saturation capacity of 40.74 mg/g and 42.87 mg/g for daidzein and coumestrol, respectively. The Freundlich isotherm and fractional order kinetic models represented the adsorption data very closely. The thermodynamic parameters indicated that sorption of both phytoestrogens onto SMZB is spontaneous and exothermic. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (NZVI) has a high adsorption capacity for heavy metals, but it forms aggregates easily. In this study, zeolite-supported nanoscale zero-valent iron (Z-NZVI) was synthesized from a simplified liquid-phase reduction of iron(III) salts which simultaneously adsorbed As(III), Cd(II) and Pb(II) from aqueous solution and soil. Scanning electron micrographs showed that aggregation was eliminated and the NZVI evenly dispersed onto the surface of zeolite. FTIR spectra reveal that NZVI was protected from oxidization on the surface of Z-NZVI. XRD and XPS patterns confirmed the formation of Cd(OH) 2 , Pb 0 , and FeAsO 4 in Z-NZVI after adsorption. The experimental maximum adsorption capacity of Z-NZVI was 11.52 mg As(III)/g, 48.63 mg Cd(II)/g, and 85.37 mg Pb(II)/g at pH 6, respectively, much higher than that of zeolite. Batch experiments indicate that various adsorption mechanisms including electrostatic adsorption, ionic exchange, oxidation, reduction, co-precipitation, and complexation coexisted with the selected heavy metals. Due to the formation of multiphase compounds on the Z-NZVI, the synergy and competition among heavy metals were concurrent. Most arsenic, cadmium and lead in the soil samples were immobilized after mixing with 30 g/kg Z-NZVI. These results suggest that Z-NZVI has great potential for treating water and soil multi-contaminated with heavy metals. [ABSTRACT FROM AUTHOR]

The energy transition from fossil to renewable energy requires the development and integration of efficient energy storages. For thermal energy storage, concepts based on adsorption are promising. One key challenge is to overcome limitations of the storage performance by the heat and mass transfer. Against this background, a closed low-pressure adsorber with zeolite 13X honeycomb adsorbent is studied numerically to identify the limiting factors. The focus of the study is on the adsorption process with the heat extraction limited to the end of the zeolite honeycomb arrangement. A detailed model which takes effects of rarefied gas flow (e.g. slip) as well as cooling effects by the inflowing vapour into account is derived. The model is applied to study the mass transport, heat transport and adsorption over a broad range of relevant geometry and process parameters. The simulations demonstrate that the adsorption process is not limited by the mass transport and isobaric conditions can be assumed in most of the studied cases. In addition, special effects of rarefied gas flow are found to be negligible. Regarding the heat transport, the convective cooling by the vapour is found only to be significant for a very short initial time period. Further analysis show that the process is mainly limited by the heat transport. Only for short channels and wide channel diameters the process becomes limited by the adsorption. [ABSTRACT FROM AUTHOR]

The aim of this work was to reduce/minimize Li in Li-LSX by replacing the 70% Li+ cations in Li-LSX that are bonded to the interior or inaccessible sites which are not used for adsorption. Thus, mixed-cation LiCa-LSX containing minimum lithium were prepared by exchanging small fractions of Li+ into Ca-LSX, followed by dehydration under mild conditions to avoid migration/equilibration of Li cations. Comparisons of adsorption isotherms of N2/O2 and heats of adsorption for the LiCa-LSX samples with that for pure-cation Li-LSX and Ca-LSX provided strong evidence that significant amounts of these Li cations indeed remained on the exposed sites (SIII). The mixed-cation LiCa-LSX samples were compared against the pure-cation Ca-LSX and Li-LSX based on their performance for oxygen production by PSA, via model simulation. The results showed that the mixed-cation LiCa-LSX samples yielded significantly higher O2 product productivities at the same product purity and recovery than their pure-cation precursor (Ca-LSX). © 2017 American Institute of Chemical Engineers AIChE J, 64: 406-415, 2018 [ABSTRACT FROM AUTHOR]

A composite material (PAN-Na-Y-zeolite) was prepared by polymerization of acrylonitrile in the presence of Na-Y zeolite. The composite was functionalized by amidoximation through the reaction of hydroxylamine on nitrile groups of the composite. The sorbent (APNa-Y-zeolite) was fully characterized by FTIR spectrometry, XRD diffraction, thermogravimetric analysis, scanning electron microscopy, zetametry and BET analysis. The sorption properties of APNa-Y-zeolite were investigated for the recovery of Cu(II), Cd(II) and Pb(II) from synthetic solutions before being tested for the purification of local tap water. Sorption properties were characterized through the study of pH effect, uptake kinetics, sorption isotherms. The pseudo-second order rate equation fitted well kinetic profiles. Sorption isotherms were modeled using the Langmuir, the Freundlich and the Sips equations. Thermodynamic parameters were evaluated through variation of temperature. While the sorption of Cu(II) and Cd(II) was endothermic, Pb(II) recovery was exothermic. Metal ions were successfully desorbed using 5 M HCl solutions. High concentrations of NaCl hardly alter sorption performance, contrary to humic acid that slightly reduces metal binding. [ABSTRACT FROM AUTHOR]

The strength of the acid sites in isostructural hierarchical porous zeolites increases in the order BSiO < GaSiO < AlSiO, and the concentration in the structural types increases in the order MTW < BEA < MOR. Zeolite materials with BEA and MOR topology, which consist of nanocrystals with ultrathin-layer morphology, are characterized by a marked decrease of the adsorption potential compared with isostructural materials with nanorods or nanosphere morphology due to a 1.5-fold decrease in the isosteric heats of adsorption of triethylamine. [ABSTRACT FROM AUTHOR]

In this study, the adsorption behaviors of methanol, methanal, toluene, ethylbenzene, and styrene molecules in FAU, FER, CON, and MWW zeolites were investigated. The adsorption isotherms of the five adsorbates in the four zeolites at 298 and 350 K were simulated using grand canonical Monte Carlo simulations. Moreover, binary component adsorptions were considered. The results revealed that the saturated adsorption capacity of single components in different zeolites decreased in the order of FAU > MWW > CON > FER, and the adsorption capacity of the five adsorbates in the same zeolite decreased in the order of methanal > methanol > toluene > styrene > ethylbenzene. The equilibrium adsorption capacity slightly decreased with increasing temperature. In terms of binary component adsorption, intense competition existed between the smaller adsorbed molecules. As the differences among the molecular structures increased, the competition in adsorption became more intense. [ABSTRACT FROM AUTHOR]

The adsorption of acetic acid and methanol on H-Beta zeolite as a model of reaction of first step of the esterification reaction has been investigated with TGA-IR coupled, ATR-FTIR spectroscopy together with Density Functional Theory (DFT) calculations at M06–2X/6-31G(D) level. From the theoretical viewpoint, different models of adsorption of acetic acid and methanol on the surface of H-Beta zeolite are studied. TGA-IR experiments show that both reactants are molecularly adsorbed on H-Beta, beyond 200 °C for methanol and 250 °C for acetic acid other species are also formed due to the surface reactivity being strongly adsorbed on the catalyst. Results from ATR-FTIR spectroscopy and theoretical calculations reveal that the predominant adsorption mode of acetic acid involves the ads_AA(C O) complex where the acetic acid is molecularly adsorbed by the carbonyl group on the Brønsted acid site of catalyst, and the OH group is oriented to the Al-O-Si bridge. The mechanism of adsorption of both acetic acid and methanol is also discussed at molecular level. The complexes where the acetic acid is adsorbed by the carbonyl group are clearly the most stable one. [ABSTRACT FROM AUTHOR]

Paracetamol (acetaminophen (ATP)) at toxic concentrations to human is successfully adsorbed onto MFI -type zeolite ZSM-5 (Si/Al = 30) stepwise under conditions approaching human serum composition. While the speed of adsorption in physiological serum at 37 °C is fast enough to be accomplished in a 4 h standard dialysis session, maximum adsorption levels at equilibrium concentration is reduced when the solution becomes more complex. In pure water, at the highest equilibrium concentrations, the adsorption is almost doubled. Thermogravimetric measurements confirm paracetamol adsorption inside the micropores. Rietveld-analysis on powder X-ray diffraction data proves that after adsorption, paracetamol is located at the intersection of the straight and zigzag channel of the ZSM-5 zeolite. 1 H MAS NMR experiments performed on ZSM-5 zeolite after paracetamol adsorption confirm the absence of interaction between paracetamol molecules and water molecules and/or between the paracetamol molecules themselves. In conclusion, elimination of paracetamol at toxic concentrations in human serum (by ultrafiltration of blood) is a smart way to eliminate selectively such a molecule by physisorption without further interference onto other biochemical equilibria. [ABSTRACT FROM AUTHOR]

We employ grand canonical Monte Carlo and molecular dynamics simulations to systematically study the adsorption and diffusion of C1 to C4 alkanes in hierarchical ZSM-5 zeolite with micropores (-1 nm) and mesopores (>2 nm). The zeolite is characterized by a large surface area of active sites on the microporous scale with high permeability and access to the active sites, which arises from the enhanced transport at the mesoporous scale. We model this zeolite as a microporous Na+-exchanged alumino-sillicate zeolite ZSM-5/35 (Si/Al = 35) in which cylindrical mesopores with a diameter of 4 nm have been built by deleting atoms accordingly. We use the TraPPE and Vujić-Lyubartsev force fields along with the Lorentz-Berthelot combining rules to describe adsorbate-adsorbate and adsorbate-adsorbent interactions. The performance of the force fields is assessed by comparing against experimental single-component adsorption isotherms of methane and ethane in microporous ZSM-5/35, which we measured as part of this work. We compare the adsorption isotherms and diffusivities of the adsorbed alkanes in the dual-porosity zeolite with those in microporous ZSM-5/35 and discern the specific behavior at each porosity scale on the overall adsorption, self-diffusion, and transport behavior in zeolites with dual micro/mesoporosities. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass-derived ethanol offers a potential alternative to fossil-derived fuels. However, the energy-intensive nature of its recovery process, i.e., a sequence of two distillation columns – beer and rectification columns - enriching from 5 to 37, and 37–93 wt%, respectively, limits its environmental and economic benefits. In this paper, we assess the potential of using zeolite membranes for bioethanol recovery. Atomistic-level and molecular dynamic simulations are performed to determine adsorption and diffusion properties of the ethanol-water mixture in zeolite membranes. These properties are modeled using the real adsorption solution theory and the Maxwell-Stefan equations to describe permeation through the zeolite membranes. A comparison of steady state permeance and selectivity predicted by the model with the values from experiments suggests that the simulated membranes are more permeable and selective than the real membranes. This is attributed to the presence of structural non-idealities and hydrophilic defects in real membranes, while the adsorption and diffusion properties obtained using molecular simulations reflect the behavior in ideal crystals. Thus, a reduced diffusivity model with an empirical relation for enhanced water adsorption is used to capture similar performance as that obtained by real membranes. This model is further used in developing conceptual process designs to assess the viability of zeolite membranes for bioethanol enrichment in industry. Both hydrophobic and hydrophilic zeolite membranes are considered. Hydrophobic zeolite membranes show potential for energy savings but lack in separation performance. On the other hand, hydrophilic zeolite membranes can achieve the separation target but result in no energy savings. Thus, a configuration that uses a combination of hydrophobic and hydrophilic membranes is proposed. It can achieve the separation target and results in 15% energy savings over distillation. Techno-economic analysis suggests that ~ 10-fold improvements in permeation or equivalent cost reductions are required for economic viability of this scheme. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-8 (ZIF-8) membranes are highly suitable as H 2 -selective walls in membranes reactors used for water gas shift reactions because of their efficient molecular sieving properties that favor H 2 transport, coupled with their high thermal stability and processability. In this study, we adopted an in-situ counter diffusion method to fabricate a ZIF-8 membrane; Zn sources, already placed inside a porous support, were allowed to diffuse out and react with the 2-methylimidazole (mim) molecules in the bulk phase. Because the reaction rates between the Zn source and the mim molecule were very high, their diffusion rates played a key role in determining the final properties of the membranes. To control the diffusion rate, a hierarchically structured support, i.e., a γ-Al 2 O 3 layer-coated α-Al 2 O 3 disc (γ-/α-Al 2 O 3 disc), was used in addition to an intact α-Al 2 O 3 disc. ZIF-8 membranes in the α-Al 2 O 3 disc (membrane ZIF-8_α) were primarily formed on top similar to a conventional supported-membrane, whereas those in the γ-/α-Al 2 O 3 disc (membrane ZIF-8_γα) were produced inside the support. As desired, membrane ZIF-8_γα showed marked H 2 separation performance with a maximum (max) H 2 /CO 2 separation factor (SF) of ~9.9 ± 1.2 at 250 °C (vs. a max H 2 /CO 2 SF of ~7.5 ± 0.2 for membrane ZIF-8_α). Although both type membranes persisted at 200 and 250 °C for up to 72 h, at a higher temperature of 300 °C, the membrane performance started deteriorating after ~2 h and ~10 h for membranes ZIF-8_α and ZIF-8_γα, respectively. This indicates that the γ-Al 2 O 3 layer served as a protective layer for preserving the performance of the ZIF-8 membrane. The performance at 300 °C was completely degraded due to the eventual conversion of ZIF-8 into ZnO phases. [ABSTRACT FROM AUTHOR]

Clinoptilolite zeolites were modified through acid treatment followed by Ca(OH) 2 conditioning. The modified zeolite adsorbent (H-Zeo-CaOH) has built-in dual functions for desalination and pH neutralization. The modified zeolites were evaluated using synthetic saline water and groundwater spiked with brine produced during potash mining, and characterized using multiple instrumental techniques. Batch adsorption experiments were conducted for (1) zeolites treated with acids of varying strengths, (2) Ca(OH) 2 -conditioned acid-treated zeolites, and (3) natural zeolites. Acid-treated zeolites, with or without Ca(OH) 2 conditioning, exhibited dramatically improved Na + removal. Na + removal from saline water (1000–5000 mg Na + /L) using the modified zeolites ranged from 45 to 88%, whereas natural zeolites achieved approximately 25%. The modified zeolites desalinated the brine-impacted groundwater (73–87% Na + removal), despite abundant K + ions in the groundwater, which are highly competitive for adsorption sites. The acid treatment caused dealumination within the zeolites, generating acidified zeolites with a high affinity for Na + and a large porosity. Sodium adsorption sites, visualized by synchrotron-based scanning transmission X-ray microscopy, correlated with alumina (>Al-O-Na) in the modified zeolites. The effluent, which is normally highly acidic due to protonic exchanges in acid-treated zeolites, was neutralized by the concomitant release of hydroxyl ions only when using the H-Zeo-CaOH adsorbent. [ABSTRACT FROM AUTHOR]

Experimental measurements and molecular simulations were used to investigate the effect of adsorption-induced changes in zeolite crystal size on the separation performance of NaA zeolite membrane for dehydration of alcohols. The vapor permeation (VP) separations of water/IPA showed a dramatic decrease in selectivity due to increase of IPA flux as the feed water concentration decreased. However, in the case of water/methanol and water/ethanol mixtures, the alcohol fluxes were almost independent of the feed water concentration. Permporosimetry measurements as well as molecular simulations show that at low loading of water, NaA crystals contract slightly, while they expand at higher loadings, which significantly affects the intercrystalline defects. In addition, at low water loadings intercrystalline defects are not blocked by water adsorbed at the defect sites. Both methanol and ethanol can enter the zeolite to reduce the crystal contraction. However, isopropanol cannot enter the NaA crystal and is thus unable to mitigate the effects of low water loadings. Based on this knowledge, the presence of methanol or ethanol in the water/isopropanol mixtures with low water content was expected to improve the dehydration performance of NaA zeolite membrane. This result was also observed for the dehydration of water/other large molecular mixture. Our studies here provide an improved understanding of the permeation and separations for NaA zeolite membrane. [ABSTRACT FROM AUTHOR]

To determine the role of zeolite's exchangeable cations such as Ca 2 + and Na + in the adsorption of phosphate on zirconium-modified zeolite (ZrMZ), the adsorption behaviors and mechanisms of phosphate on ZrMZ, NaCl-treated ZrMZ and CaCl 2 -treated ZrMZ in the absence and presence of ammonium were comparatively investigated in this study. Results showed that coexisting ammonium promoted the adsorption of phosphate on the raw, NaCl-treated and CaCl 2 -treated ZrMZs. In the absence of ammonium, the treatment of ZrMZ with NaCl inhibited the phosphate adsorption, but the treatment of ZrMZ with CaCl 2 enhanced the adsorption of phosphate. In the presence of ammonium, the treatment of ZrMZ with NaCl suppressed the adsorption of phosphate, but the effect of CaCl 2 treatment on the phosphate adsorption depended upon coexisting ammonium amount. In the presence of a certain amount of ammonium (5–30 mg N/L), the treatment of ZrMZ with CaCl 2 improved the phosphate adsorption efficiency. The mechanism for phosphate adsorption onto ZrMZ was the exchange of surface hydroxyl groups with phosphate ions and the formation of phosphate inner-sphere coordination complexes, and the enhancement of phosphate adsorption onto ZrMZ by coexisting Ca 2 + could be attributed to the formation of CaHPO 4 0 species in the calcium/phosphate solution and the formation of phosphate-bridged ternary complex ( Zr)(OPO 3 H)Ca on the adsorbent surface. The increased phosphate adsorption induced by CaCl 2 treatment could be attributed to the increase in the amount of released Ca 2 + from ZrMZ, and the decreased phosphate adsorption induced by NaCl treatment could be attributed to the decrease in the amount of released Ca 2 + from ZrMZ. This work suggests that the exchangeable Ca 2 + in ZrMZ plays an important role in the phosphate adsorption, and its release enhances the adsorption of phosphate. [ABSTRACT FROM AUTHOR]

An attractive approach to reduce anthropogenic emission of carbon dioxide (CO2) would be to valorize it into value-added products (e.g. alcohols or dimethylether) by chemical recycling. However, in most of these important reactions, water is produced as a byproduct that limits CO2 conversion thermodynamically and can lead to the deactivation of catalysts. Water removal in sorption-enhanced reaction process (SERP) would allow the overcoming of these drawbacks and several zeolites (SOD, LTA, and FAU) have been selected to assess their potential to adsorb water in-situ at high temperatures. This work aims to study the water adsorption capacity and kinetics in a large temperature range of 25-250 °C and evaluate the potential of the selected adsorbents for in-situ water removal in the reverse water gas shift (RWGS) reaction. For all zeolites, the water uptake showed an important decrease at higher temperatures but the capacity at 250 °C was still significant. While the poor adsorption kinetics of SOD limit its use, FAU-13X powder gave better results than LTA-4A, which were confirmed by a more important increase of CO concentration at the exit of the reactor for the RWGS reaction. Transient adsorption data obtained in this study were fitted by a double stretched equation and the kinetic constants were determined. These results are essential to model and design an efficient SERP process and determine the optimal reaction conditions. [ABSTRACT FROM AUTHOR]

The effect of electromagnetic fields on the adsorption-desorption properties of natural zeolites is a new direction in the theory of physical and chemical processes associated with the surface characteristics of aluminosilicates. The influence of two types of fields, an ultrahigh-frequency electromagnetic field (UHF EMF) and a weak pulsed magnetic field (WPMF) is considered. Modes for treatment of natural zeolite (clinoptilolite) and its activated forms for the most effective sorption of formaldehyde, water, and a mixture thereof were found. It was shown that the preadsorption activation of zeolite in a UHF EMF enhances the selectivity of water vapor sorption, whereas treatment of the sorbent in a WPMF largely affects the selectivity of the absorption of formaldehyde vapors. The decreased desorption of formaldehyde as a result of activation of the mineral in a UHF EMF, as well as complete absence of formaldehyde desorption when a WPMF was used as an activator, was detected. [ABSTRACT FROM AUTHOR]

Magnetite-zeolite composites (MZCs) and an MZC modified with poly( N -isopropylacrylamide) (PNIPAM) (PMZ) were prepared in this study as adsorbents for Cs + ions. The ratios of the removal of these magnetic adsorbents from suspensions using high-gradient magnetic separation (HGMS) were examined. The structures of these adsorbents were examined using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetry. From these measurements, it was confirmed that the magnetite was deposited on the zeolite for the MZC samples and PNIPAM was immobilized on an MZC for the PMZ sample. The saturated amount of Cs + adsorption of the zeolite, MZCs, and the PMZ were almost the same at 0.66, 0.68, and 0.65 mmol/g, respectively. The ratios of the removal of the zeolite, an MZC (10.7 wt% magnetite loading), and the PMZ (at 20 °C and 50 °C) adsorbents from suspensions using HGMS were 33, 85, 92, and 96 wt%, respectively. It was concluded that the PMZ adsorbent was the most effective for the adsorption of Cs + and could be removed most effectively from suspensions using HGMS at 50 °C. [ABSTRACT FROM AUTHOR]

In this research, four types of low cost and high performance ceramic microfiltration (MF) membranes have been employed in an in-line adsorption-MF process for oily wastewater treatment. Mullite, mullite-alumina, mullite-alumina-zeolite and mullite-zeolite membranes were fabricated as ceramic MF membranes by low cost kaolin clay, natural zeolite and α-alumina powder. Powdered activated carbon (PAC) and natural zeolite powder in concentrations of 100-800 mg L-1 were used as adsorbent agent in the in-line adsorption-MF process. Performance of the hybrid adsorption-MF process for each concentration of PAC and natural zeolite powder was investigated by comparing quantity of permeation flux (PF) and total organic carbon (TOC) rejection during oily wastewater treatment. Results showed that by application of 400 mg L-1 PAC in the adsorption-MF process with mullite and mullite-alumina membranes, TOC rejection was enhanced up to 99.5% in comparison to the MF only process. An increasing trend was observed in PF by application of 100-800 mg L-1 PAC. Also, results demonstrated that the adsorption-MF process with natural zeolite powder has higher performance in comparison to the MF process for all membranes except mullite-alumina membranes in terms of PF. In fact, significant enhancement of PF and TOC rejection up to 99.9% were achieved by employing natural zeolite powder in the in-line adsorption-MF hybrid process. [ABSTRACT FROM AUTHOR]

The adsorption of molecules on metal nanoparticles can be sterically controlled through the use of zeolite crystals, which enhances the product selectivity in hydrogenations of reactants with more than one reducible group. Key to this success was the fixation of Pd nanoparticles inside Beta zeolite crystals to form a defined structure (Pd@Beta). In the hydrogenation of substituted nitroarenes with multiple reducible groups as a model reaction, the Pd@Beta catalyst exhibited superior selectivity for hydrogenation of the nitro group, outperforming both conventional Pd nanoparticles supported on zeolite crystals and a commercial Pd/C catalyst. The extraordinary selectivity of Pd@Beta was attributed to the sterically selective adsorption of the nitroarenes on the Pd nanoparticles controlled by the zeolite micropores, as elucidated by competitive adsorption and adsorbate displacement tests. Importantly, this strategy is general and was extended to the synthesis of selective Pt and Ru catalysts by fixation inside Beta and mordenite zeolites. [ABSTRACT FROM AUTHOR]

Powder LSX zeolite samples of high phase purity and near 100% crystallinity have been synthesized in NaK, K, Na, and Li forms. The effect of the chemical nature and content of the exchange cation and air calcination temperature on the degree of crystallinity and the porous structure characteristics and adsorption properties of the mentioned LSX zeolite forms were established by X-ray diffraction and adsorption methods. [ABSTRACT FROM AUTHOR]

In this work, NaY zeolite is explored as a possible “template” to obtain porous materials type ZTC from the adsorption of heavy crude oil in a water-oil model system (emulsion). In order to produce the adsorbents, a cationic surfactant is selected to facilitate the adsorption of the crude oil into the pores of the zeolite and to get the composite, which was activated with controlled thermal treatments (T: 700–800 °C and t: 0.5–1 h) in inert conditions (N 2 gaseous). The starting materials, composite and porous carbons were characterized using structural/surface analysis techniques (API Gravity, SARA, IR, XRD, XRF, TGA, Langmuir isotherms, BET and SEM). The results showed that four types of mesoporous carbons were produced with specific surface areas between 70 ± 1 m 2 /g and 220 ± 3 m 2 /g, average pore volumes between 0.144 cm 3 /g and 0.40 cm 3 /g and average pore widths between 4.9 nm and 8.3 nm. The activation conditions of 800 °C and 1 h allowed to make the carbonaceous material with the best surface characteristics (220 ± 3 m 2 /g, 0.27 cm 3 /g, and 4.9 nm). Therefore, it is concluded that under assay conditions employed, the heavy crude oil, as a mixed model (water-oil), from an aqueous environment is a starting material suitable for preparation of “mesoporous” carbons. [ABSTRACT FROM AUTHOR]

Volatilized ammonia loss (VAL) and toxicity are major disadvantages on urea amendment. In order to mitigate, slow (or) controlled release urea based fertilizers are prepared with low cost materials. Therefore, micro and nano-sized adsorbents such as zeolite, biochar were impregnated with urea @1:1 ratio for fertilizer formulations. The objective of the study was to evaluate the VAL rate. To study the effect of soil texture, incubation experiment on two different soils of Tamil Nadu (Typic Haplustalf and Vertic Ustropepts) with 4 physically mixed, 4 fabricated, conventional urea and control without urea determined. Fertilizer formulations were surface applied @ 250 kg N ha-1 and assessed the VAL rate for 16 days. The trapped ammonia was observed with colour change from pink to greenish and titrated with diluted sulfuric acid. Initial 3 days VAL rate was high on urea, physically mixed adsorbent fertilizers than urea impregnated fertilizers and colour change was observed on every 4-6 h of both soils. In contrast, the urea impregnated fertilizers had colour change after 9-10 h regardless of adsorbent and soils. The fabricated fertilizer observed VAL rate on gradual with low quantity on T5- Zeourea (13.5 days, 15.1 days) T6- Nano-zeourea (15.5 days, 16 days), T9- Biourea (7.5 days, 7.1 days) and T10- Nano-biourea (9 days, 9.7 days) than T2- Urea (5.5 days, 4.6 days) of Alfisols and Inceptisols respectively. Cumulative VAL rate percentage was low on T5- Zeourea (30 %, 34 %), T6- Nano-zeourea (28 %, 29.3 %) T9- Biourea (39 %, 41.5 %) and T10- Nano-biourea (36 %, 37.5 %) of Alfisols and Inceptisols, respectively on comparison with other fertilizer type. It is concluded that the surface amendment of physically mixed fertilizers not influenced any change on both soils. Urea impregnation influenced on days and cumulative VAL percentage. Our study elucidates that micro and nano porous adsorbents are potential substrate to reduce VAL rate of urea in both soils. [ABSTRACT FROM AUTHOR]

The results of the study of removal of nonylphenol, octylphenol and their ethoxylates from real industrial and municipal wastewater are presented. Industrial wastewater was pre-treated by coagulation with FeCl3 and adsorption on zeolite, before discharging into municipal sewer system. Their removal efficiencies in primary sedimentation tank of municipal WWTP were very low. From the practical point of view, the highest and the most significant removal efficiencies within the whole WWTP were observed for nonylphenol and nonylphenol ethoxylates. Dominancy of abiotic mechanisms of alkylphenols removal follows from adsorption measurements. Activated sludge cultivated in lab-scale extended aeration tank accounted for relatively high adsorption affinity to these substances. Activated sludge sampled from municipal wastewater treatment plant (MWWTP) receiving industrial wastewater containing alkylphenols accounted for very low adsorption affinity to these pollutants. Significantly higher removal efficiency of octylphenol ethoxylates was observed with the O3/granular active carbon (GAC) process compared to the ozonation process alone. Lower toxicity impact of intermediates and products of ozonation treatment on Vibrio fischeri was measured in comparison to the O3/GAC process. Actually, the municipal WWTP effluent discharge concentration values complies with EQS values, including nonylphenols. [ABSTRACT FROM AUTHOR]