Browsing by Subject "Zeolite"

Now showing 1 - 4 of 4

Open Access
Europium (II)-Doped Microporous Zeolite Derivatives with Enhanced Photoluminescence by Isolating Active Luminescence Centers
(American Chemical Society, 2011-10-21) Yang, X. Y.; Tiam, T. S.; Yu, X. B.; Demir, Hilmi Volkan; Sun, X. W.
Solid-state reaction is the most common method for preparing luminescent materials. However, the luminescent dopants in the hosts tend to aggregate in the high-temperature annealing process, which causes adverse effect in photoluminescence. Herein, we report a novel europium (II)-doped zeolite derivative prepared by a combined ion-exchange and solid-state reaction method, in which the europium (II) ions are isolated to a large extent by the micropores of the zeolite. Excited by a broad ultraviolet band from 250 to 420 nm, a strong blue emission peaking at 450 nm was observed for these Eu-embedded zeolites annealed at 800 degrees C in a reducing atmosphere. The zeolite host with pores of molecular dimension was found to be an excellent host to isolate and stabilize the Eu2+ ions. The as-obtained europium (II)-doped zeolite derivative showed an approximately 9 fold enhancement in blue emission compared to that of the general europium (111)-doped aluminosilicates obtained by conventional solid-state reaction, indicating that, by isolating active luminescence centers, it is promising to achieve highly luminescent materials. Also, the strong blue emission with broad UV excitation band suggests a potential candidate of phosphor for ultraviolet excited light-emitting diode.
Open Access
Femtosecond laser assisted synthesis of silicate-1 zeolite
(2022-01) Hagverdiyev, Mehdi
Zeolites are microporous (pore sizes < 2 nm) inorganic aluminosilicate materials with well-defined molecular pores and high surface areas used widely for various chemical processes, primarily as catalysts, sorbents, and ion exchangers. Aside from 40 types of natural zeolite, 253 different synthetic zeolitic framework types are synthesized and recognized by the International Zeolite Association (IZA). Zeolite synthesis requires moderate temperatures between 50°C - 270°C and high pressures (up to 120 bar). A fundamental challenge in zeolite synthesis is to elucidate and control the nucleation and growth of the zeolite crystals. The main reason for this is the fast kinetics of zeolite synthesis and rapid conformational transitions between quasi-equilibrium phases. Zeolite synthesis is a complex process because more than 40 different types of silica polymerization and depolymerization reactions occur simultaneously in a reaction mixture (i.e., precursor suspension). Reaction time scales of the silica polymerization are within the range of picoseconds and femtoseconds. Using the traditional hydrothermal synthesis method, which is occurring near thermal equilibrium, it is impossible to control the system at the time scale of these simultaneous polymerization reactions due to the slow energy deposition, which can be from 24 hours to several days. Other types of zeolite synthesis methods such as microwave synthesis are capable of depositing high energies in short time scales. However, the synthesis method is lacking the control of the excess heating of the full volume of the precursor suspension. During microwave heating, several hot spots form inside the precursor suspension, causing the boiling of the liquid. Growth by inhomogeneous heating leads to the formation of fused (i.e., interconnect) crystals instead of the discrete ones that dominate the end product in microwave-assisted synthesis method of zeolites. Here, we introduce a novel femtosecond laser-assisted synthesis method for the synthesis of Silicalite-1 zeolites. Femtosecond laser pulses ensure the delivery of a precise amount of energy per area within a given time interval, and therefore the spatiotemporal control over the energy delivered to the precursor suspension could be done on the time scale of the polymerization reactions of the zeolite synthesis. Thanks to the femtosecond laser pulses, the appropriate environment for zeolite synthesis, such as local high temperature and local high pressure (shock waves), has been created. In the laser-assisted synthesis method, the time required for zeolite synthesis decreased drastically compared to the hydrothermal method, overall control and product quality increased compared to the microwave synthesis method of zeolites. Unlike other rapid synthesis methods such as microwave synthesis, the uncontrollable temperature rise over the full volume of precursor suspension was not observed, resulting in 'discrete' crystals in the final product. Energy intake of the transparent precursor suspension was achieved through multiphoton absorption of the femtosecond laser pulses inducing steep spatiotemporal thermal gradients. Since surface tension of fluid is a function of temperature, surface tension gradients form as well, causing Marangoni flow. The ‘stirring effect’ of these flows leads to the distribution of the formed clusters evenly to the system, which is not attained by static hydrothermal synthesis of zeolites. It is proposed that vigorous flow induced in the laser-assisted synthesis assembles nuclei/polymerized clusters much faster than the other synthesis methods, which may be the reason for the drastically reduced reaction times compared to hydrothermal synthesis (i.e., 30 - 48h for hydrothermal vs. 3h - 5h for laser-assisted syntheses). Growth kinetics of the Silicalite-1 zeolite was examined in detail. In addition, templatefree nanosized microporous Zeolite Y, and mesoporogen-free hierarchical ZSM-5 zeolites with micro and meso-porosity were synthesized with reduced reaction times through laser-assisted synthesis method (i.e., 24 - 45h for hydrothermal vs. 1 - 5h for laser-assisted syntheses), which is important in terms of green synthesis approaches drawing attention in recent years.
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Jeolojik yapının kurbanları: Karain Köyü ve kansere yakalanan yerliler
(Bilkent University, 2020) Polat, Ekrem; Işıksaçan, Salih; Karakollukçu, Oğulcan; Doğan, Muhammed Agah; Kuzgun, Abdurrahman
1970'li yıllarda Nevşehir'in Ürgüp ilçesine bağlı Karain köyünde ölüm oranı ve hasta sayısı oldukça yüksekti. İlk başlarda bu hastalıklara verem teşhisi konuldu. Göğüs Hastalıkları Uzmanı Dr. Yusuf İzzettin Barış'ın Karainli bir hastayı muayene etmesi sonucunda gerçek ortaya çıktı. Dr. Barış yaptığı testler sonucunda hastaya akciğer zarı kanseri anlamına gelen mezotelyoma teşhisi koydu ve ekibiyle birlikte Karain köyünde bir çalışma başlattı. Bu çalışmalar sonucunda köyün jeolojik yapısında bulunan eriyonitin kansere sebep olduğu ortaya çıkarıldı. Köyde yapılan çalışmalar uluslararası bir boyut kazandı ve birçok yabancı bilim insanı da Karain köyünde çalışmalar yaptı. Köyde artan çalışmalardan rahatsızlık duymaya başlayan köy halkı kanser için alınan tedbirlere uymadı ve köyü terk etmedi. Günümüzde ise köyde yaşam devam etmektedir.
Open Access
The sorption behavior of CS + ion on clay minerals and zeolite in radioactive waste management: sorption kinetics and thermodynamics
(Springer, 2011) Yildiz, B.; Erten, H. N.; Kış, M.
In this work, Cs+ ion sorption on some clays and zeolite were investigated. 137Cs was used as a tracer. Activities were measured with a NaI crystal gamma counter. The particle size distribution was determined by a laser sizer. Surface area of the particles were determined by BET (Brunauer, Emmett and Teller method). Structure analysis was made by using X-ray diffraction. The chemical compositions of the solid samples were determined using a ICAP-OE spectrometer. Kinetic and thermodynamic parameters were determined. Due to very high uptake results; clay and zeolite can be proposed as a good sorbents in waste management considerations.