Berna Topuz

Oriented MFI membranes by gel-less secondary growth of sub-100 nm MFI-nanosheet seed layers

A zeolite membrane fabrication process combining 2D-zeolite nanosheet seeding and gel-free secondary growth is described. This process produces selective molecular sieve films that are as thin as 100 nm and exhibit record high permeances for xylene- and butane-isomers.

Open‐Pore Two‐Dimensional MFI Zeolite Nanosheets for the Fabrication of Hydrocarbon‐Isomer‐Selective Membranes on Porous Polymer Supports

Two-dimensional zeolite nanosheets that do not contain any organic structure-directing agents were prepared from a multilamellar MFI (ML-MFI) zeolite. ML-MFI was first exfoliated by melt compounding and then detemplated by treatment with a mixture of H2 SO4 and H2 O2 (piranha solution). The obtained OSDA-free MFI nanosheets disperse well in water and can be used for coating applications. Deposits made on porous polybenzimidazole (PBI) supports by simple filtration of these suspensions exhibit an n-butane/isobutane selectivity of 5.4, with an n-butane permeance of 3.5×10(-7)  mol m(-2)  s(-1)  Pa(-1) (ca. 1000 GPU).

2D zeolite coatings: Langmuir-Schaefer deposition of 3 nm thick MFI zeolite nanosheets

Stable suspensions of zeolite nanosheets (3 nm thick MFI layers) were prepared in ethanol following acid treatment, which partially removed the associated organic structure-directing agent. Nanosheets from these suspensions could then be dispersed at the air-water interface and transferred to silicon wafers using Langmuir-Schaefer deposition. Using layer-by-layer deposition, control on coating thickness was demonstrated. In-plane X-ray diffraction (XRD) revealed that the deposited nanosheets contract upon calcination similar to bulk MFI crystals. Different methods for secondary growth resulted in preferentially oriented thin films of MFI, which had sub-12-nm thickness in certain cases. Upon calcination, there was no contraction detectable by in-plane XRD, indicating well-intergrown MFI films that are strongly attached to the substrate.

Nanoscale Control of Homoepitaxial Growth on a Two-Dimensional Zeolite

Nanoscale crystal growth control is crucial for tailoring two-dimensional (2D) zeolites (crystallites with thickness less than two unit cells) and thicker zeolite nanosheets for applications in separation membranes and as hierarchical catalysts. However, methods to control zeolite crystal growth with nanometer precision are still in their infancy. Herein, we report solution-based growth conditions leading to anisotropic epitaxial growth of 2D zeolites with rates as low as few nanometers per day. Contributions from misoriented surface nucleation and rotational intergrowths are eliminated. Growth monitoring at the single-unit-cell level reveals novel nanoscale crystal-growth phenomena associated with the lateral size and surface curvature of 2D zeolites.

Investigation of the Permeability of Pure Gases in Sol-Gel Derived Al2O3 Membrane

The preparation, characterization and pure gas permeation of sol-gel derived alumina membranes were investigated in this work. The effects of acid concentration/type and water content on the particle size in the sols and pore size distributions of the unsupported membrane were investigated by N2 adsorption/desorption isotherms and Dynamic Light Scattering. Increasing the H/Al mole ratio from 0.1 to 0.25 caused the hydrodynamic sol particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600C. Unsupported membranes were heat treated in the 200 to 1200 C range for the characterization of the phase structure. Pinhole and crack free alumina membranes about 3 μm (2-layer) in thickness was observed from the SEM pictures with insignificant infiltration. The CO2 permeability through the double layer γ-Al2O3 membrane calcined at 600 C was 2.25*10 mol/m.s.Pa, and had a slight pressure dependence indicating Knudsen Diffusion and Laminar Flow being the effective transport mechanisms. Upon the calcination of a similar 2-layer alumina membrane at 500C, the CO2 permeability decreased to 1.51*10 mol/m.s.Pa. without pressure dependence.

MFI Tipi Zeolit Membranların Yüksek Sıcaklıkta Geri Döngülü Akış Sisteminde Sentezi

Bu calismada, MFI tipi zeolit membranlar makro gozenekli destekler uzerinde yuksek sicaklik ve basinc altinda geri dongulu akis sisteminde sentezlenmis ve MFI tipi zeolit membranlarin ozellikleri uzerine membran sentez sicakliginin etkisi incelenmistir. Membranlarin sentezi 140-160oC araliginda ic tarafi nano boyutta MFI tohum kristalleri ile kaplanmis alumina tupler uzerinde yapilmistir. Membranlar ve sentez sirasinda es zamanli olarak olusan toz malzemeler X-isini kirinimi, taramali elektron mikroskobu, ve tanecik boyut dagilimi olcumleri ile karakterize edilmistir. Elde edilen membranlarda n-C4H10/isoC ulasmasi uygulanan sentez tekniginin yuksek kalitede membran uretimine olanak saglayacagini gostermektedir. 10 ile yapilan secicilik testlerinde ideal secicilik degerinin 20’ye

Effects of Processing on the Properties and Permeability of Pure Gases through Sol-Gel Silica Membranes

N2, O2 and CO2 pure gas permeation through sol-gel derived silica membranes were determined and the effects of processing parameters on the microstructure of the membrane was investigated. Silica sols were prepared in an alcoholic solution by hydrolysis and condensation of TEOS as a function of acid content. The thickness of the silica membranes was determined to be about 2μm and significant infiltration into the support was observed from the SEM pictures. The supported membranes were heat treated in the 50-400 o C. The N2 permeabilities of silica membranes varied in the 2.2*10 -10 –2.7*10 -8 mol/m 2 .s.Pa range for single layer membranes dipped for 10s. in the sol. The CO2 permeability of these membranes varied in the 1.2*10 -9 –6.95*10 -8 mol/m 2 .s.Pa range. The sols became viscous and gelled at 50 o C in 16 hours. The O2 permeability increased with aging time. The optimum dipping time during processing was determined to be 10 seconds. The increase in the acid content of the sols were observed to increase permeabilities of the membranes significantly.