Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 3Citation - Scopus: 3Hybrid Silica Aerogels From Bridged Silicon Alkoxides: Ultralow Thermal Conductivity for Low-Temperature Applications(Springer, 2025) Abebe, A. M.; Biesuz, M.; Vakifahmetoglu, C.; Cassetta, M.; Soraru, G. D.Hybrid silica aerogels are promising materials for thermal insulation applications. Highly porous aerogels were synthesized from bridged bis(triethoxysilyl)methane BTEM and triethoxysilane TREOS silicon alkoxides via the sol-gel process. The carbon content in the hybrid aerogels decreased with increasing amounts of TREOS. Crack-free monolith aerogels were synthesized through supercritical drying, which is crucial for thermal and optical investigations. The aerogels are characterized by high BET surface areas ranging from 700 to 1400 m(2)/g, pore volumes between 2.0 and 10.5 cm(3)/g, and a maximum porosity of 95%. The thermal conductivity of the aerogels at room temperature was measured via a hot disk apparatus. The materials exhibited ultralow thermal conductivity, reaching a minimum value of 15 mW/mK. This value ranks among the lowest reported values for silica-based aerogels in the literature. Optical transmittance measurements indicated high transparency, exceeding 80% in the visible region. Therefore, these exceptional properties of low density, high optical transparency, and low thermal conductivity make these materials promising candidates for transparent insulation applications.Article Citation - WoS: 23Citation - Scopus: 24Epoxidation of Propene by High-Throughput Screening Method Over Combinatorially Prepared Cu Catalysts Supported on High and Low Surface Area Silica(Springer Verlag, 2012) Düzenli, Derya; Şeker, Erol; Senkan, Selim; Önal, IşıkGas phase epoxidation of propene using molecular oxygen was studied by use of a high-throughput testing technique. A large number of catalysts including promoted and un-promoted Cu were synthesized in a much faster combinatorial fashion using a sol-gel method. Metal catalysts supported on high and low surface area silica were tested and ranked in a high-throughput activity and selectivity testing apparatus at different experimental conditions such as reaction temperature and reactant gas ratio. The amount of Cu loading and the addition of alkali promoters such as K and Li resulted in different tendencies in consumption rate for both silica materials. The maximum PO production rate was obtained as 25.82 μmol/g/ cat./min (2.90 % conv. and 20.49 % selectivity) for 3 % Cu-2.25 % K catalyst supported on high surface area silica. There was no noticeable difference in structural and chemical properties of catalysts after modification with K when examined by XRD and TEM; however, the overall activation energy of un-modified catalysts (92 kJ/mol) decreased to 71 kJ/mol for K-modified catalyst. There was negligible difference between the activation energies calculated for PO production (75 vs. 77 kJ/mol).Article Citation - WoS: 2Citation - Scopus: 3Preparation and Characterization of Diphasic Sol-Gel Derived Unsupported Mullite Membranes(Springer Verlag, 2011) Topuz, Berna; Çiftçioglu, MuhsinDiphasic gels prepared by mixing freshly prepared polymeric silica and polymeric boehmite sols through a modified Al-alkoxide route in mullite compositions led to the crystallization of mullite upon heat treatment at 775°C. Mullite formation was observed at a 100°C higher temperature when diphasic gels were formed by mixing aged polymeric sols containing about 2 nm in diameter boehmite species. These relatively low mullite formation temperatures were attributed to the nanoscale sizes of the polymeric species of the two amorphous phases present in the diphasic gels.Article Citation - WoS: 12Citation - Scopus: 13Single Step Sol-Gel Made Silver Chloride on Titania Xerogels To Inhibit E. Coli Bacteria Growth: Effect of Preparation and Chloride Ion on Bactericidal Activity(Springer Verlag, 2011) Tuncer, Mert; Şeker, ErolWe report the antibacterial efficacies of silver and/or silver chloride containing titania xerogels synthesized with modified single step sol-gel methods against Escherichia coli bacteria. As the silver loading in TiO 2 increases, the amount of the xerogel required to inhibit the growth of the bacteria decreases and also we found that pure TiO2 was not bactericidal. Among modified single step sol-gel methods used in this study, the additional HCl treatment sol-gel route III was very effective to obtain only AgCl crystallites in TiO2. Based on viable cell count method, 0.125 g/L of 29%Ag/TiO2 (made with HNO3 sol-gel route I) was enough to inhibit the growth of E. coli whereas 0.6 g/L of 29%Ag/TiO2 (made with the additional HCl treatment sol-gel route III) was required. However, antibacterial activity of 29%Ag/TiO2 (made with HNO 3 sol-gel route I) after 6 usages was the same as 29%Ag/TiO 2 (made with the additional HCl treatment sol-gel route III).Article Citation - WoS: 36Citation - Scopus: 42Sol-Gel Derived Mesoporous and Microporous Alumina Membranes(Springer Verlag, 2010) Topuz, Berna; Çiftçioğlu, MuhsinStable polymeric and colloidal boehmite sols were prepared by sol-gel process through controlled hydrolysis/condensation reactions. The particle sizes of the colloidal sols were in the 12-25 nm range depending on the process parameters and about 2 nm for polymeric sols. The presence of a significant increase in the microporosity content of the heat treated polymeric membranes relative to the mesoporous colloidal membranes might make the design of thermally stable microporous alumina membranes with controlled pore structures possible. The phase structure evolution in the 600-800 °C range had shown that the crystallization of the gamma alumina in the amorphous matrix starts at about 800 °C. This indicated that the pore structure stability may be enhanced through processing up to this relatively high temperature in polymeric alumina derived unsupported membranes. The permeance values of the two and three layered colloidal alumina membranes were observed to be independent of pressure which implies that the dominant gas transport mechanism is Knudsen diffusion in these structures. This was also supported by the 2.8 nm BJH pore sizes of the colloidal membranes. The Knudsen diffusion equation derived permeances of the polymeric alumina membranes with thicknesses of about 300 nm were determined to be very close to the experimentally determined permeance values. © 2010 Springer Science+Business Media, LLC.