Jyung Choi

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.

Microporous Semicrystalline Silica Materials

A new family of microporous semicrystalline silica materials (MSSMs) were developed at room temperature from acidic mixtures of alkyl-substituted silane and tetramethylalkoxysilane. Hydrolyzed alkyl-substituted silica precursors, having hydrophilic silanol groups and hydrophobic alkyl groups, presumably act not only as templates but also as sol stabilizers for continuous pore engineering of silica materials in the micropore region. Depending on the substituted alkyl (SUA) groups in initial sols, MSSMs have distinct broad x-ray diffraction peaks in low 2θ range of 2° to 12°, distinguishable thermal behavior of SUA groups, highly flexible processability, and discrete micropore size with good thermal stability of micropores after the removal of SUA groups. These designer microporous silicas are expected to be useful for molecular sieving applications.

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.

Effect of Molecular Structure of Polyarylates on the Compatibility in Polyarylate/Poly(vinyl chloride) Blends

A homologous series of polyarylates were prepared by condensation poly- merization of three different bisphenols, isophthaloyl, and terephthaloyl chlorides (their molar ratio 5 2:1:1). The resulting polyarylates were tetramethyl bisphenol S- (TMBPS-), bisphenol S- (BPS-), and tetramethyl bisphenol A- (TMBPA-) polyary- lates, and each have structural variants; (1) methyl or no substitution on the biphenyl rings of bisphenol, and/or (2) central group connecting the biphenyl rings with or without polarity. Only the polyarylate having both methyl substitution and polar connector, i.e., TMBPS-polyarylate, was found to be compatible with PVC. The sulfone groups of TMBPS-polyarylate and chlorides of PVC exerted a dipole- dipole interaction only when the tetramethyl substitution on the bisphenol rings was present. In the absence of tetramethyl groups (BPS-polyarylate), incompatibility with PVC was ob- served. The strength of polar interactions appeared to be influenced by the methyl substitution causing electronic rearrangement in bisphenol rings. However, due to the lack of polar connector groups, the inclusion of methyl substitution in TMBPA-polyary- late was found to have no effect on the specific interactions, and hence, the compati- bility with PVC.

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.

Effect of Municipal Sewage Sludge on Soil Chemical Properties and Growth of Rose (Rosa hybrida L.)

This study was conducted to find out the effect of municipal sewage sludge on the growth and heavy metal content of rose and soil chemical properties. Municipal sewage sludge was applied to soil at rate of 0, 3, 5, 10 and 15 ton/10a, the plant height, flower number and stem size of rose were found to be increase in the treatments of sewage sludge. Contents of mineral nutrients in rose stem were determined to be higher at municipal sewage sludge application plots than those of no application. But, there were not any significant increases of heavy metal contents in soil and rose stem with the sludge applications. from the results of this study, it is apparent that the application of municipal sewage sludge would not increase available heavy metals in soil.

Degradation of the Chlorothalonil by Functional Zeolite-KCIO 3 Complex

Salt occlusion in Zeolite is a unique phenomenon that takes place only when the salt size is similar to the window size of host zeolite. -occluded Zeolite, as an environment-friendly oxidant, has a high potential for effective removal of various organic pollutants. This study was carried to investigate the characteristics and the removal kinetics of fungicide chlorothalonil by zeolite- complex. About 10% of was occluded in zeolite pores synthesized by salt-thermal method from fly ash, although the occlusion amount was relatively less compared to that of nitrate salts. By occlusion with , no remarkable changes were found in X-ray diffraction patterns of cancrinite, whereas some decrease of overall peak intensities was found with those of sodalite. Different releasing kinetics of ion were observed in distilled water and soil solution from zeolite- complex. Two reactions, hydration and diffusion, seem to be related with the release of . Therefore, the release isotherm of ion well fitted to the power function model which indicate the release was made by hydration and diffusion. The removal of chlorothalonil by zeolite and reached at reaction equilibrium within 6 hours by 18% and 47% respectively. However, the chlorothalonil removal by the zeolite- complex increased slowly and steadily up to 92% in 96 hours. These findings suggested that zeolite- complex could be applied for effective removal of organic contaminants in the soil and aqueous environment.

Photocatalytic Degradation of Fungicide Chlorothalonil by Mesoporous Titanium Oxo-Phosphate

Titanium mesoporous materials have received increasing attention as a new photocatalyst in the field for photocatalytic degradation of organic compounds. The photocatalytic degradation of chlorothalonil by mesoporous titanium oxo-phoswhate (Ti-MCM) was investigated in aqueous suspension for comparison with , (Degussa, P25) using as an effective photocatalyst of organic pollutants. Mesoporous form of titanium Phosphate has been prepared by reaction of sulfuric acid and titanium isopropoxide in the presence or n-hexadecyltrimethylammonium bromide. The XRD patterns of Ti-MCM are hexagonal phases with d-spacings of 4.1 nm. Its adsorption isotherm for chlorothalonil reached at reaction equilibrium within 60 min under dark condition with 28% degradation efficiency. The degradation ratio of chlorothalonil after 9 hours under the UV radiation condition (254 nm) exhibited 100% by Ti-MCM and 88% by . However, these degradation kinetics in static state showed a slow tendency compared to that of stirred state because of a low contact between titanium matrices and chlorothalonil. Also, degradation efficiency of chlorothalonil was increased with decreasing initial concentration and with increasing pH of solution. As results of this study, it was clear that mesoporous titanium oxo-phosphate with high surface area and crystallinity could be used to photo- catalytic degradation of various organic pollutants.