Man Park

Molten-salt method for the synthesis of zeolitic materials: I. Zeolite formation in alkaline molten-salt system

Abstract The molten-salt method has been applied for the zeolitization of fly ash and other mineral wastes. Fly ash was converted into zeolitic materials by a simple thermal treatment at molten states of some salt mixtures without any addition of water. Various combinations of salt mixtures were employed for the zeolitization of fly ash, using NaOH, KOH, or NH 4 F as mineralizer, and NaNO 3 , KNO 3 , or NH 4 NO 3 as stabilizer. The resultant zeolitic materials were composed of sodalite and cancrinite as major crystalline phases. This molten-salt method was also confirmed for the facile zeolitization of kaolinite, montmorillonite, and natural zeolite waste. The main zeolite species synthesized by the molten-salt method were dependent on the types of salt mixture and raw material used. The molten-salt method developed in this study could open a new and alternative approach for the mass treatment of these mineral wastes at low cost, as well as for the improvement of the purity and alkalinity of zeolitic materials.

Molten-salt method for the synthesis of zeolitic materials. II. Characterization of zeolitic materials

Characterization of zeolitic materials synthesized by the newly developed molten-salt method was carried out. Their physicochemical properties were investigated and compared to those of zeolitic materials prepared by the conventional hydrothermal method. The molten-salt method exhibited much less elemental loss during the zeolitization process. The product yield based on the reaction weight was about twice as high in the molten-salt method as in the hydrothermal method. The molten-salt method resulted in zeolitic materials with higher purity, larger contents of alkali metals, lower pH values, and lower cation exchange capacity (higher Si/Al ratio). Salt occlusion also took place in the cavities of the resulting zeolites during the zeolitization of fly ash by the molten-salt method. It seems, therefore, apparent that the high temperature and dry conditions in the molten-salt method lead to zeolitic materials which are somewhat different from hydrothermally synthesized zeolitic materials.

Swelling mica-type clays: synthesis by NaCl melt method, NMR characterization and cation exchange selectivity

Several swelling mica-type clays of nominal compositions, NaxSi8−xAlxMg6O20F4·yH2O where x = 4, 3 or 2 were prepared using kaolinite, silica gel or silicic acid, magnesium fluoride and sodium chloride in the temperature range of 800 to 1100 °C after treatment for 5 to 15 h. All the synthetic clays were characterized by powder X-ray diffraction (XRD). Some of the samples were characterized by scanning electron microscopy (SEM) and 27Al and 29Si solid-state magic angle spinning nuclear magnetic resonance (MASNMR) spectroscopy. Powder XRD showed that all syntheses yielded water-swollen micas with c-axis spacing of ∼1.2 nm along with various amounts of anhydrous mica phase with a c-axis spacing of about 0.96 nm. Solid-state 27Al MASNMR spectroscopy of some micas revealed that almost all the Al is present in the tetrahedral environment while solid-state 29Si MASNMR spectroscopy revealed different Si(Al) nearest neighbor environments depending upon the composition of the various mica-type clays. Selective cation exchange studies were performed on some of these micas and they showed that these novel micas are highly selective for cations such as Sr and Ba. These synthetic clays prepared by a cost-effective method are of relevance in remediation of soils and waters contaminated with hazardous metal ions.

Spontaneous nanoparticle formation coupled with selective adsorption in magadiite

The applications of hydrated layered polysilicates, particularly magadiite, have rapidly expanded from selective cation adsorption to fabrication of nanomaterials even without full understanding of their adsorption reactions. This study has successfully elucidated the distinguished adsorption behavior of magadiite, spontaneous nanoparticle formation coupled with selective adsorption reactions. Magadiite exhibited highly reliable and selective adsorption, especially for Cu2+ and Pb2+. The adsorbed heavy metal cations besides Cu2+ and Pb2+ were spontaneously and systematically transformed into the corresponding hydroxide nanoparticles exclusively on the crystal edges and the nanoparticles ultimately sprouted out of the crystals on full growth. Cation selectivity is explained by the compatibility of the interlayer silanol configuration with coordination of the adsorbed cations whereas spontaneous nanoparticle formation by the changes of the silanol configuration through the grafting reaction of the adsorbed cations is due to the high flexibility of the silicate frameworks. These unique adsorption behaviours of hydrated layered polysilicates, particularly magadiite, provide a new strategy not only for developing advanced purification/retrieval technologies but also for tailor-making various nanoparticles.

Occlusion potential of zeolites for mixed and non-nitrate salts

Abstract Occluded salts in the form of salt complexes exhibit the interesting properties unattainable in bulk state. In this study, occlusion of non-nitrate salts and co-occlusion of mixed nitrate salts were attempted to further expand occlusion potential of zeolites. The non-nitrate salts such as KClO 3 and KH 2 PO 4 were occluded by mordenite, although they do not establish stable molten state. Their occlusions were confirmed by 27 Al NMR spectra, N 2 adsorption/desorption isotherms and thermal analyses. The occluded amounts were relatively less compared to those of nitrate salts. On the other hand, thermal treatment of Na–P1 with a mixture of NH 4 NO 3 and KNO 3 resulted in co-occlusion of both NH 4 NO 3 and KNO 3 by Na–P1 below the melting temperature of KNO 3 . The salts in solid state could be introduced into and occluded by zeolites through the interaction with the molten salt present in the salt mixture. The use of salt mixture could lead to co-occlusion of the salts that could be hardly applicable to salt occlusion. Therefore, this study clearly shows that a variety of salts could be applied to salt occlusion by zeolites.

Conversion of Fly Ash to Swelling Mica: A New Approach for Recycling Fly Ash

Swelling mica exhibits unique characteristics for purification of drinking water contaminated by heavy metals and for selective removal of Sr2+ and Ba2+ ions from nuclear waste solution. As a new approach to recycle fly ash, conversion of fly ash to swelling mica has been attempted and ion-exchange properties of fly ash-derived swelling mica (referred to hereinafter as FA-swelling mica) were examined in this study. Thermal treatment of fly ash with MgO in the presence of excess NaF led to the formation of swelling mica along with trace quantities of impurities. A swelling mica of good quality was obtained from the reactant ratio of fly ash 1 g : MgO 0.75 g : NaF 1.75 g. Unlike gel or kaolinite-derived synthetic Na-4-micas, FA-swelling mica exhibited heterogeneity in its framework. Its uptake capacity for Sr2+ ions was estimated to be 17.4 meq/100 g from 0.1 mM SrCl2 aqueous solution and 5.0 meq/100 g from 0.5 N NaCl solution containing the same Sr2+ concentration. These capacities are less than that of metakaolin-derived Na-4-mica. However, its ion exchange capacity for divalent transitional metal ions was estimated to be 284 meq/100 g from their inaqueous solutions and 206 meq/100 g from the 0.5 N NaCl solution containing the mixed metal ions of Cd2+, Co2+, Mn2+, Ni2+ and Zn2+ each at 1 mN concentration. These capacities are comparable to that of metakaolin-derived Na-4-mica. Its selectivity for transition metal ions is as follows: Zn2+ > Ni2+ ≥ Co2+ ≥ Cd2+ > Mn2+ and this is consistent with the ΔG° values from Gibbs-Duhem equation. These results clearly showed that fly ash could be converted to swelling mica with high uptake capacity for divalent transitional metal ions. Therefore, conversion of fly ash to highly pure swelling mica will lead to a resource from waste.

Adsorbate-dependent uptake behavior of topographically bi-functionalized ordered mesoporous silica materials

Abstract Novel behaviors such as adsorbate-dependent pore opening and functionality-controlled uptake have been accomplished by the bifunctionalized ordered mesoporous silica developed here. SBA-11 was topographically functionalized with two different functional groups by step-wise functionalization. Bulky and flexible tert-butylphenethyl (BP) groups were topographically grafted around the pore entrance and on the external surface, while small dimethyl (DM) groups were attached on the inner pore surface. The resulting bifunctionalized SBA-11 exhibited the selective malathion scavenger, which was not observed by the corresponding mono-functionalized SBA-11s. The uptake behaviors of the functionalized SBA-11s for malathion and toluene strongly suggest that the bulky and flexible BP groups are locally grafted around the pore entrance to act as a functional pore window. The interaction among the adsorbate, BP and DM groups induces a specific rearrangement of functional pore window which leads to the discriminative uptake. Therefore, the functionalized OMMs equipped with the pore window, the nanosized functional vessels, could be developed into the adsorbate-discriminating adsorbents for highly selective removal/recovery of specific organic molecules.

Guest-cooperative templating system for as-synthesis loading of guest molecules into ordered mesoporous silica materials

A guest-cooperative templating system utilizing an interdependent micelle assembly of surfactant and guest has been developed to overcome the major disadvantages of as-synthesis loading methods such as low loading capacity and limitation on the type of guests. This system employs unique surfactants which cannot be effective in templating OMMs without suitable guests. Performance of the guest-cooperative templating system was evaluated using a nonionic surfactant, brij 78 [(C18H37 (O–CH2CH2)20OH)] with a bulky hydrophilic head and an essential oil, eugenol, as a cooperative hydrophobic guest. High resolution TEM and SEM images reveal that a well-ordered hexagonal mesostructure is crystallized in a form of sphere-like particles. Reliable eugenol loading capacities could be increased nearly up to 10 wt%. It is also found that an elevated loading of eugenol leads to its increased stability within the mesopore. Therefore, this study successfully shows that maximized exploration of effective pore space could be realized through an interdependent micelle assembly of structurally different surfactant and guest.

Functional characterization of a chemical defoliant that activates fruit cluster Leaf defoliation in ‘Fuji’ apple trees

The removal of fruit cluster leaves was shown to be a valuable method for controlling fruit quality and producing high-grade apples. A chemical defoliant that functions as an activation switch was shown to turn on the genes necessary for fruit cluster leaf defoliation. Elucidating the mechanism involved in leaf defoliation is crucial to our understanding of the use of chemical defoliants in fruit trees. To gain insight into chemical defoliant-mediated leaf defoliation, we first confirmed the occurrence of ethylene production by applying a chemical defoliant on fruit cluster leaves. Then, we used RNA-seq analysis to obtain a series of transcriptome profiles for genes and proteins involved in leaf senescence induction. Within 2 days of applying the chemical defoliant to apple trees, 1-aminocyclopropane carboxylic acid (ACC) oxidase, ACC synthase, a chlorophyll binding protein, and polygalacturonase-related genes were up-regulated at least sixfold. An in vitro enzyme assay showed that lanolin oil activates ACC synthase activity, a key regulatory enzyme in the ethylene pathway. We also showed that chemical defoliant decreased the light saturation point and total chlorophyll content. Then, we used a polygalacturonase activity assay to confirm the effects of chemical defoliant on leaf senescence in vivo. Furthermore, treatment with chemical defoliant resulted in a significant increase in the chromaticity value of a*, whereas L* and b* decreased in the apple fruit. Taken together, we conclude that chemical defoliant could selectively affect fruit cluster leaves, which suggested that it can be used as a selective defoliant.

Post-isomorphic substitution of trivalent metal cations for Ca2+ in portlandite crystals

Isomorphic substitution, position replacement of one cation by another of similar size, leads to incorporation of a variety of cations into solid crystals without any significant changes to the primary crystal structures. To date, isomorphic substitution has been known to take place almost exclusively via co-crystallization of the cations during formation of the crystals. We report here the discovery of isomorphic substitution of trivalent metal cations for Ca2+ ions in portlandite crystals at room temperature as evidenced by the transient appearance of metastable phase, the formation of Ca-based layered double hydroxides at high pH, the distinct shift of suspension pH after phase transition, and the in situ topochemical reaction. This post-crystallization isomorphic substitution provides an innovative pathway for the synthesis of materials through chemical manipulation of crystals as well as a new insight into interpretation on their weathering and transformation processes.