VSC Adsorptive Properties in Ion Exchanged Zeolite Materials in Gaseous and Aqueous Medium

摘要

The microporous materials, zeolite, were synthesized and the H_2S adsorption into microporous material was studied. Zeolite has three dimensional framework structure in which SiO_4 and AlO_4 tetrahedrons are bonded, and generally contains alkali metal or alkali-earth metal atoms as univalent or bivalent cations. These electrostatic effects result in the surface potential of zeolite materials, and may influence the adsorptive properties. Two kinds of zeolite materials, LTA (Zeolite A) and MFI (ZSM-5), which have different Si/Al ratios, were synthesized by a wet method. Some starting materials were dissolved in water, and the mixture was heated, filtered, washed, and dried. The Ag-doped zeolite materials were prepared as follows. The sample was put into 2M silver nitrate solution and stirred. The obtained specimen was filtered and washed with water, then dried at 90°C for 24 hrs. The samples, identified by powder X-ray diffraction method, were put into a 5 L glass flask filled with H_2S gas. The initial concentration of H_2S was 30 ppm. When 0.02 g of LTA was applied, the concentration of H_2S fell to 84% for first 2 hours, and was decreased with time. The equilibrium did not seem to reach even for 24 hours. The amount of LTA was increased to be 0.2 g, and then the concentration of H_2S was decreased to be less than 20% for 24 hrs. In case of Ag-doped LTA, the concentration of H_2S dropped to be 24% for 2 hrs and to be almost 0% for 4 hrs. The exchanges of alkali metal or alkali-earth metal atoms to univalent or bivalent metal ions zeolite material remarkably improves the H_2S reduction. The amount of adsorbed H_2S onto LTA was larger than that onto MFI. The difference in the amount of adsorbed H_2S between two types of zeolites can be explained by the surface potential. Polarity of zeolites depends on their Si/Al ratio. XRD patterns of the LTA and H_2S adsorbed LTA specimens seem to be almost identical, and the peaks corresponding to Ag_2S was not observed. So sulfur may be included in zeolite structure. The XRD analysis should be investigated in great detail for further study. H_2S in aqueous medium was also found to adsorb into microporous material, which was confirmed by the headspace gas chromatography with flame photometric detector. The microporous material should be expected to be an adsorbent material, useful for health in mouth.