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This paper deals with the kinetic and isotherm studies of manganese ion removal by zeolite X and its hierarchically porous composites as ion-exchange materials. A hydrothermal treatment was applied to grow a layer of zeolite X over diatomite and carbon surfaces. The hierarchically porous composites used for Mn 2+ ion removal showed higher ion-exchange capacity when compared to pure zeolite X under same conditions. A thermodynamic study of the rate of ion-exchange revealed that the intra-particle diffusion rate constant of zeolite X/carbon and zeolite X/diatomite was higher than that of pure zeolite X indicating that the intra-particle diffusion was enhanced when zeolite was prepared in form of hierarchically porous composites. The study showed that the thickness of boundary film of zeolite X/carbon and zeolite X/diatomite was less than that of pure zeolite X indicating ion diffusion resistance to the active sites was reduced when the composites were utilised. The experimental data showed good agreement with Freundlich model. The calculated thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicated the ion-exchange process of Mn 2+ ion by zeolite X and its composites was spontaneous, endothermic and the randomness increased at the liquid/solid interface under the conditions studied. The results of kinetic study showed that the ion-exchange of Mn 2+ ion by zeolite X and its composites followed a pseudo second order kinetic model indicating Mn 2+ ion removal is a chemical reaction related to valence forces. The encapsulation of Mn 2+ ion was successfully achieved by vitrification and geopolymerization processes demonstrating the efficacy of both processes for environmental management. [ABSTRACT FROM AUTHOR]

The modification of the water/organic interface with size-selective membranes is presented as a means to elucidate the mechanism of facilitated ion transfer processes. In particular, an interfacial or organic phase complexation reaction is observed for the transfer of Cu2+ ions facilitated by dibenzo-18-crown-6, whereas the complexation process for the 1,4,7,10-tetrathiacyclododecane facilitated transfer of the same ion is suggested to occur within the aqueous phase. The contrasting transfer mechanism is discussed in terms of the solution phase behaviour of the thio-ether ligand. [Copyright &y& Elsevier]

The use of kaolin as a silica source in the synthesis of zeolites has been achieved using a novel synthetic approach. The technique reported allows the use of impure kaolin as a starting material to produce pure ZSM-5 zeolite. This is important as it is extremely difficult and time consuming to remove all impurities from natural kaolin. This is also the first report of the direct synthesis of a high silica zeolite from kaolin without the use of an external silica source. [ABSTRACT FROM AUTHOR]

Stabilisation of metal species using hydroxyl‐rich dealuminated zeolites is a promising method for catalysis. However, insights into the interactions between the hydroxyl groups in zeolite and noble metals and their effects on catalysis are not yet fully understood. Herein, comparative studies were conducted using Pt catalysts supported on hydroxyl‐rich dealuminated Beta (deAl‐Beta) and the pristine proton‐form Beta (H‐Beta) for catalytic oxidation of toluene. The findings suggest that during impregnation the Pt precursor (i. e., Pt(NH3)4(NO3)2) interacted with different sites on deAl‐Beta and H‐Beta, leading to the formation of supported Pt nanoparticles with different physicochemical properties. In detail, for H‐Beta, the Pt precursor interacted with Al‐OH and isolated external Si‐OH sites, yielding Pt NPs with a higher Pt0 proportion of ~71 % compared to ~57 % Pt0 on deAl‐Beta. Comparatively, abundant hydroxyl groups on deAl‐Beta such as silanol nest and isolated internal Si‐OH stabilised highly active Pt‐O species. The resulting Pt/deAl‐Beta exhibited improved activity and anti‐coking ability than Pt/H‐Beta in catalytic toluene oxidation. For example, the temperature for 50 % toluene conversion was 193 °C for Pt/deAl‐Beta vs. 232 °C for Pt/H‐Beta, and the coke deposition was 1.7 % vs. 6.7 % (after the 24‐h longevity test), respectively. According to the toluene‐temperature programmed desorption (toluene‐TPD), 1H nuclear magnetic resonance (1H NMR) relaxation and in situ diffuse reflection Fourier transform spectroscopy (in situ DRIFTS) characterisation, the enhanced performance of Pt/deAl‐Beta could be ascribed to (i) the active Pt‐O sites stabilised by hydroxyl groups, which interact with toluene easily for conversion, and (ii) the acid‐free feature of the deAl‐Beta support, which avoids the formation of coke precursors (such as benzoate species) on the catalyst surface. Findings of the work can serve as the design guidelines for making effective supported metal catalysts using zeolitic carriers. [ABSTRACT FROM AUTHOR]

Nigerian kaolin is converted into pure zeolite-A by calcination of the kaolin at 650 °C for ten minutes, followed by mixing the obtained metakaolin with a zeolite seed, NaOH, and H2O (autoclave, 100 °C, 3 h). [ABSTRACT FROM AUTHOR]

A hierarchical structured composite made from clinoptilolite supported on date stones carbon is synthesized using two techniques. The composites are manufactured by fixing a natural zeolite (clinoptilolite) to the porous surface of date stones carbon or by direct hydrothermal synthesis on to the surface to provide a supported high surface area ion-exchange material for metal ion removal from aqueous streams. The fixing of the clinoptilolite is achieved using sucrose and citric acid as a binder. The composites and pure clinoptilolite were compared to test the efficacy for the removal of Sr 2+ ions from an aqueous phase. The encapsulation of the Sr 2+ using either vitrification or a geo-polymer addition was tested to ensure that the hazardous waste can be made safe for disposal. The hierarchical structured composites were shown to achieve a higher ion exchange capacity per gram of zeolite than the pure clinoptilolite (65 mg/g for the pure natural clinoptilolite and 72 mg/g for the pure synthesized clinoptilolite) with the synthesized composite (160 mg/g) having higher capacity than the natural clinoptilolite composite (95 mg/g). The rate at which the equilibria were established followed the same trend showing the composite structure facilitates diffusion to the ion-exchange sites in the zeolite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical ZSM-5 with siliceous shell is produced by chelation-alkaline treatment. • Microwave irradiation facilitates the chelation-alkaline treatment efficiently. • Catalytic HDPE pyrolysis is conducted over the hierarchical ZSM-5. • Kinetics and product quality of HDPE pyrolysis are improved over hierarchical ZSM-5. A new microwave (MW) assisted chelation-alkaline strategy was developed to produce hierarchical ZSM-5 zeolites (with external surface area of 203 m2/g) in minutes, leading to the formation of heterogeneous structure with a high-silica shell and aluminium-rich core (silicon-to-aluminium ratios of 49.2 and 37.6, respectively). The zeolites were assessed comparatively by catalytic pyrolysis of high-density polyethylene (HDPE). Compared to the mesoporous ZSM-5 zeolite prepared by the conventional alkaline treatment (via desilication by the NaOH aqueous solution), the hierarchical zeolite by the MW-assisted method showed comparable kinetics in catalytic pyrolysis of HDPE, but with the improved stability in the cyclic pyrolysis-regeneration tests. The improved stability could be due to the better-preserved structural integrity thanks to the relatively milder surface etching by the MW-assisted chelation dealumination method. In addition, compared to the parent ZSM-5, the product distribution of HDPE catalytic pyrolysis over the hierarchical ZSM-5 zeolite showed a higher portion of oil products (i.e., 12 wt% vs. 6.9 wt%) and an improved alkane-to-olefin ratio in the oil products (2.22 vs. 1.86, respectively) due to the reduced acidity and improved hydrogen transfer ability. The MW-assisted chelation-alkaline treatment could be a new strategy to regulate the trade-off between stability and activity of zeolites for catalytic applications. [ABSTRACT FROM AUTHOR]

Abstract: A series of composite membranes based on zeolite A and Nafion 117 have been fabricated for direct methanol fuel cells. The external surface of zeolite A has been modified to enhance the interface bonding between inorganic zeolite crystals and Nafion ionomer. The modified zeolite samples have been characterised using a combination of thermal analysis and spectroscopic techniques. Methanol permeability of Nafion 117 could be reduced by as much as 86% by incorporating functionalised zeolite NaA crystals into the membrane. The effect of different functionalisation level is discussed. [Copyright &y& Elsevier]

Utilizing of ash extracted from Iraqi common water reeds as an inexpensive effective silica source in the preparation of ZSM-5 zeolite was investigated for the first time in the present work. This study was conducted using a hydrothermal treatment at autogenous pressure. The molar content of silica (17.84–26.76), sodium oxide (1.71–2.4), water (76.92–304.6), organic template (0.55–2.73), organic solvent (23.46–140.76), and synthesis conditions (crystallization time (24–72 h) and temperature (130–180 °C)) were investigated to obtain high purity ZSM-5 zeolite microspheres. The zeolite samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis by X-Ray (EDAX), N 2 adsorption/desorption isotherms, Thermogravimetric Analyzer (TGA), and Fourier transform infrared spectroscopy (FTIR). XRD pattern of all synthesized samples was compared to XRD pattern of the commercial ZSM-5 zeolite. This work allows using locally available solid waste resulted from a dry natural plant as an inexpensive silica source without using an external source of silica. Also, this is the first report of the direct synthesis of a high purity ZSM-5 zeolite microspheres from common water reeds ash containing highly reactive silica. A gel composition of 2Na 2 O: 26.76SiO 2 : Al 2 O 3 : 2.73TPAOH: 23.46EtOH: 304.6H 2 O gave an outstanding final product of ZSM-5 zeolite microspheres at 180 °C and 27 h. This high crystallinity ZSM-5 zeolite porous microspheres possess Si/Al ratio of 17, a crystal size of 61.419 nm, BET surface area of 277.482 m2/g, a total pore volume of 0.1659 cm3/g, micropore volume of 0.1131 cm3/g, pore width of 5.28 nm, and hierarchical factor of 0.14. Image 1 • High purity ZSM-5 zeolite microspheres can be prepared using the ash extracted from common water reeds (CWRA). • Replacing the toxic chemicals with environmentally friendly silica source. • CWRA allows obtaining high purity ZSM-5 zeolite microspheres using low content of methanol and without the ageing step. • CWRA allows obtaining high purity ZSM-5 zeolite at lower crystallization temperature or shorter crystallization time. [ABSTRACT FROM AUTHOR]

Recent research has demonstrated a new synthesis route for hierarchically porous zeolite composites by mechanical modification of the support surface using ultrasonication in a nanoparticle suspension. It was believed that target zeolites should be added as seeds for the sonication. In this study, the effect of nanoparticles was investigated with ultrasonication to understand the crystallization mechanism of zeolites obtained by the nanoparticles–assisted synthesis. It has been found that the nanoparticles under the influence of ultrasonication generate fissures or cracks as nucleation sites on the carbon surface. These nanoparticles such as zeolite A, γ-Al 2 O 3 , quartz and sand are different from the target zeolite X. Therefore, an amorphous aluminosilicate gel nucleates at those cracks during the hydrothermal treatment. Thus, the mechanical activation of the support surface is the process to induce the formation of strongly attached zeolite X over the template, not a seeding step. This is confirmed as an attachment due to the weak bond between the support and the zeolite for ‘non-seeded’ composites whereas the ‘seeded’ composites have a robust structure which maintains a zeolite coating upon mechanical agitation. [ABSTRACT FROM AUTHOR]

Hierarchical ZSM-5 coatings supported on macrocellular β-SiC foams were prepared by a microwave-accelerated secondary growth method. Under microwave irradiation, differential heating was enabled due to the high microwave-adsorbing ability of SiC leading to the fast assembly of ZSM-5 zeolites on the SiC foams. The effects of crystallisation temperature, time and agitation on the growth of ZSM-5 zeolites on SiC foams were also investigated under microwave heating. A specific surface area of ca. 52 m 2 g −1 was obtained under the optimum condition of 150 °C and 4 h. Comparative studies of conventional hydrothermal and microwave-accelerated synthesis were conducted and the resulting materials were characterised extensively using XRD, SEM and N 2 adsorption. The combination of microwave heating, high microwave absorption of SiC substrates and agitation allowed a much more focused heating across the surface of SiC foams than conventional heating, which suppressed the formation of ZSM-5 crystals in the liquid phase and the consequent sedimentation. Additionally, for the first time, mesoscopic features of ZSM-5 coatings on SiC foam composites (>10 μm) were studied in 3D by X-ray micro computed tomography (μ-CT), providing quantitative information on the quality of the ZSM-5 coating such as the global thickness and distribution of ZSM-5 across the SiC foam supports. It was concluded that microwave-accelerated secondary growth synthesis offered an efficient route to give high quality coatings on structured foams with the good crystal quality and uniform thickness as well as lower energy consumption, especially for the substrate with a high loss tangent. [ABSTRACT FROM AUTHOR]

Abstract: Composite polymer proton exchange membranes (PEM) were prepared by solution recasting. The composite membranes formed are based on Nafion incorporating a silane functionalized zeolite, mordenite, as an additive. The composite membranes were placed within a single cell DMFC and compared to an MEA featuring a standard Nafion 125μm membrane. The impact of mordenite particle size, the choice of the silane functionalizing agent and the membrane preparation procedure are investigated. A composite ion exchange membrane which featured Nafion and a ground mordenite which was functionalized using glycidoxypropyltrimethoxysilane achieved a power density that outperformed a standard Nafion MEA under all conditions. [Copyright &y& Elsevier]

We report a low-cost, highly energy efficient microwave-assisted chelation (MWAC) method, which enabled the post-synthetic modification of synthetic zeolites for adopting hierarchical structures within minutes. Exemplified by Zeolite Y, hierarchical Y zeolites prepared in this way showed exceptional specific external surface areas of >300 m2 g−1 and mesopore volumes of >0.46 cm3 g−1. Comparative assessments revealed that developed zeolites have shown significantly improved catalytic activities for catalysis involving large substrates, such as catalytic cracking and hydrocracking of plastics. Image 1 • Efficient post-synthetic modification method under microwave irradiation for making hierarchical Y zeolites. • Combination of microwave and chelation to make intracrystalline mesopores in Y zeolites. • The developed method shows significantly reduced energy consumption and improved mesoporosity. • The resulting hierarchical Y zeolites show the improved catalytic activities in catalytic cracking and hydrocracking. [ABSTRACT FROM AUTHOR]

A multiporous zeolite A (A b) was obtained by the addition of the organosilane molecule dimethyl octadecyl [3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC) in the synthesis gel and successfully dispersed in bacterial cellulose forming aerogels for Pb2+ adsorption. Several characterization techniques such as powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and N 2 adsorption-desorption were employed to investigate physical, chemical, and textural properties of the samples. The resulting material is also compared to the conventional microporous zeolite A and shows a positive interaction between zeolite crystals and cellulose nanofibrils, specially when the mesopores are present in the crystal. Improvements are observed for the multiporous samples in both adsorption and ionic exchange processes. The selectivity for Pb2+ in the presence of Cd2+ is enhanced as a result of improved intraparticle diffusion where there is the insertion of mesopores to the structures. From the kinetic models, the pseudo-second order model fits better to the experimental data suggesting chemisorption as the governing process in adsorption and the mesopores seem to have a remarkable role on it. These multiporous materials facilitate the access of Pb2+ to the zeolite inner pores and therefore present high potential to be used for both Pb2+ adsorptive and analytical devices. Image 1 • Multiporous zeolite A is successfully obtained by using a bifunctional surfactant. • Hierarchical materials are obtained with Bacterial cellulose nanofibres. • Better selectivity for Pb2+ in binary system with Cd2+ is achieved for the material. • Materials with potential use for both adsorptive and analytical devices. [ABSTRACT FROM AUTHOR]

The effect of alcohol ratio in solution casting of composite membranes is one of the important factors to their good properties for direct methanol fuel cell (DMFC). The investigation was focused on the effect of alcohol ratio (methanol/ethanol mixture) during the fabrication process on the membrane properties, morphology, chemical resistance, water uptake, proton conductivity and methanol permeability. Alcohol mixture with proportion of 0–5 vol ratio was varied in order to prepare the composite membranes. It was found that the alcohol ratio had insignificant effect on the homogeneity of the composite membranes as the layers of polymer rich and mordenite rich were formed. The ratio had insignificant effect on proton conductivity of the composite membranes. Reducing alcohol ratio from five to three, however, led to 80% chemical resistance reduction and 70% higher methanol permeability. Finally, these composite membranes with five volume ratio of alcohol were used in membrane electrode assembly and tested in a DMFC compared to recast Nafion membrane. The composite membranes gave a maximum power density of 11.5 mW cm−2 at 343.15 K, which was 58% higher than that of recast membrane. • Effect of solvent in solution cast method for composite membrane fabrication was studied. • Amount of solvent in fabrication did not affect filler dispersion. • The higher amount of alcohol in membrane fabrication leads to higher DMFC performance. [ABSTRACT FROM AUTHOR]