Hayrettin Yücel

Sorption properties of silicalite-1 of pure silica form : the influence of sorption history on sorption kinetics of critically sized molecules

Abstract Sorption properties of silicalite-1 samples of pure silica form for some parfinic and aromatic hydrocarbons of different molecular sizes were investigated. It was observed that sorption rates and apparent equilibrium capacities for critically sized molecules, m -xylene and o -xylene, depend on the sorption history of the sample. Sorption of m - and o -xylene proceeded extremely slowly on fresh samples of silicalite-1, whereas sorption rates of these molecules on silicalite-1 samples that had passed through a previous p -xylene sorption/regeneration step were significantly faster and equilibrium capacities reached about 92–95% of sorption volume of silicalite-1 when sufficient time was allowed. Uptake curves for m - and o -xylene were of the sigmoid-type, indicative of lattice distortions of silicalite framework. The results of this work, along with some recent, independent studies involving n.m.r. MAS and XRD methotds strongly suggest that sorption of some critically sized molecules causes subtle lattice distortions of high-silica ZSM-5 zeolites, modifying their sorptive behavior.

Short-term antimicrobial properties of mineral trioxide aggregate with incorporated silver-zeolite

The purpose of this in vitro study was to determine whether adding silver-zeolite (SZ) to mineral trioxide aggregate (MTA) would enhance the antimicrobial activity of MTA against Staphylococcus aureus (ATCC #25923), Enterococcus faecalis (ATCC #29212), Escherichia coli (ATCC#25922), Pseudomonas aeruginosa (ATCC #27853), Candida albicans (ATCC #90028), Porphyromonas gingivalis (ATCC #33277), Actinomyces israelii (ATCC #12102), and Prevotella intermedia (ATCC# 15032). SZ was added at 0.2% and 2% mass fraction concentration to MTA powder. The control group was MTA powder with no SZ. The antimicrobial effect test was accomplished by placing freshly mixed MTA specimens on agar plates inoculated with microorganisms and comparing the zones of inhibition at 24, 48, and 72 h. The amounts of silver ion release from MTA specimens were measured with atomic absorption spectrophotometry at 10-min, 24-, 48-, and 72-h periods. The pH of MTA specimens was measured with a pH meter at 10-min, 24-, 48-, and 72-h periods. MTA with 2% and 0.2% SZ specimens showed inhibitory effects on some microorganisms at all time periods, whereas no antimicrobial activity showed for P. intermedia and A. israelii. MTA without SZ inhibited C. albicans, E. Coli, and P. intermedia. The highest silver release was detected in 2% SZ MTA at 24 h. The incorporation of SZ may enhance the antimicrobial activity of MTA.

Antibacterial effect of silver-zeolite containing root-canal filling material.

The aim of this study was to determine the in vitro antibacterial effect of two experimental glass ionomer cements (GICs) on Streptococcus milleri, Staphylococcus aureus, and Enterococcus faecalis after 24 and 48 h incubation by using the agar diffusion inhibitory test. Silver zeolite (SZ) was added at 0.2 and 2% mass fraction concentration to GIC (Endion). The control group was Endion with no SZ. Each of them were prepared to uniform size using a custom-made Teflon mold, and the GIC materials were prepared to form disks (n = 5 per group). The effect of these materials on the growth of three bacteria associated with endodontic infections was determined using the agar diffusion inhibitory test. The amounts of silver ion release from these materials were measured with atomic absorption spectrophotometry at 10 min, 24- and 48-h periods. The pH of samples was measured with a pH-meter at 10 min, 24- and 48-h periods. After the incubation period, the agar plates were evaluated and the degrees of bacterial inhibition were measured in millimeters. A comparison of the mean of the test materials was statistically different in each group of specimens (p < 0.05). Between the two tested materials 2% SZ containing GIC showed the largest zone of inhibition on the agar plates of all the tested strains (p < 0.05). The most inhibition in bacterial growth occurred in E. faecalis. Adding 2% SZ to GIC resulted in a significant increase in the silver release into deionized water. This study demonstrated that GIC had an inhibitory affect on Streptococcus milleri, Staphylococcus aureus, and Enterococcus faecalis and that adding SZ increases that affect proportional to its concentration.

The synthesis and sodium-silver ion exchange of sodalites

Aluminosilicate sodalites of three different types--chlorosodalite, basic sodalite, and oxalate sodalite--have been synthesized in their sodium forms using hydrothermal synthesis. The syntheses were investigated in terms of their relative rates of crystallization and final crystallinities using powder X-ray diffraction. These sodalites were subsequently loaded with silver by aqueous ion exchange. The exchange was studied primarily by monitoring the solution phase. Rate of exchange and equilibrium behavior have been established over the temperature range of 25-80°C for all three types. Extreme selectivity toward silver over sodium was observed, with little dependence on temperature. Both sodium and silver sodalites were characterized by powder diffraction, and crystallographic data for silver sodalites have been derived using Rietveld refinement. Electron micrographs of sodalites have been used for investigations of crystallite morphology and size. Silver sodalites have been observed to manifest various optical properties including photochromic, barochromic, thermochromic, and fluorescent behavior.

Investigation of factors affecting caking tendency of calcium ammonium nitrate fertilizer and coating experiments

Caking of fertilizers is an important problem both to manufacturers and users. Manufacturers must recycle the caked fertilizer to the process resulting in an extra cost and users may have difficulties during the application of the fertilizer to the soil. In the first part of this study major factors which influence caking of a commercial grade calcium ammonium nitrate (CAN) fertilizer were investigated with a laboratory caking apparatus kept in a controlled atmosphere. It was observed that the caking tendency of CAN fertilizer increases almost linearly with pressure exerted on the fertilizer and with moisture content of the fertilizer at a temperature of 35 °C. The results indicate that the phase transition of ammonium nitrate between crystalline forms IV and III plays a significant role in caking of CAN since caking tendency is greatly reduced below the phase transition temperature which occurs at about 32 °C. In the second part of the study, the effectiveness of some coating materials to reduce the caking tendency of CAN fertilizer were tested. Among the materials tested, kieselguhr gave the most satisfactory result under the experimental conditions employed.

Sorption properties of synthetic ferrierite

Limiting sorption volumes of the hydrogen form of a synthetic ferrierite sample were determined for sorbates--water, methanol, propane, hexane, and o-, m-, p-xylenes--at 298 K and at a relative pressure of P/P o = 0.5 using a gravimetric sorption apparatus. Methanol, which has a kinetic diameter significantly smaller than the pore dimensions, was sorbed relatively rapidly and by the greatest amount. The sorption rates of other sorbates were very slow and for some it took several days for equilibrium to be established. The results indicated that, although their kinetic diameters are similar, the adsorption behavior of propane and hexane are quite different. Hexane is able to fill only ten-membered ring channels whereas propane is able to fill both ten- and eight-membered ring channels, at least partially. The inability of the hexane molecules to be sorbed into eight-membered ring channels is attributed to chain length effect. Xylene isomers are sorbed by the H-ferrierite but to smaller extents, consistent with the significantly larger kinetic diameters of these molecules compared to the reported pore dimensions of ferrierite. Among the xylene isomers, p-xylene, with the smallest kinetic diameter of three isomers, is sorbed to a greater extent than either o-xylene or m-xylene.