Begum Tokay

Effects of ultrasound on the synthesis of silicalite-1 nanocrystals.

Application of power ultrasound, offers potential in the degree of control over the preparation and properties of nanocrystalline zeolites, which have become increasingly important due to their diverse emerging applications. Synthesis of silicalite-1 nanocrystals from a clear solution was carried out at 348 K in the absence and presence of ultrasound of 300 and 600 W, in an attempt to investigate the effects of sonication, in this respect. Variation of the particle size and particle size distribution was followed with respect to time using a laser light scattering device with a detector set to collect back-scattered light at an angle of 173°. Product yield was determined and the crystallinity was analyzed by X-ray diffraction for selected samples collected during the syntheses. Nucleation, particle growth and crystallization rates all increased as a result of the application of ultrasound and highly crystalline silicalite-1 of smaller average particle diameter could be obtained at shorter synthesis times. The particle size distributions of the product populations, however, remained similar for similar average particle sizes. The rate of increase in yield was also speeded up in the presence of ultrasound, while the final product yield was not affected. Increasing the power of ultrasound, from 300 to 600 W, increased the particle growth rate and the crystalline domain size, and decreased both the final particle diameter and the time required for the particle growth to reach completion, while its effect on nucleation was unclear.

Synthesis of hydrophobic MIL-53(Al) nanoparticles in low molecular weight alcohols: systematic investigation of solvent effects

The effects of using low molecular weight alcohols, methanol (MeOH) and ethanol (EtOH), for the synthesis of MIL-53(Al) are investigated and the results are directly compared with analogous synthesis in water and N,N-dimethylformamide (DMF). We have successfully synthesised MIL-53(Al), termed MIL-53(MeOH), using MeOH as the solvent and employing a reaction temperature of 150 °C, lower than that typically used for analogous water or DMF-based reactions. Several unique properties are observed for MIL-53(MeOH). The breathing phenomenon which is known for MIL-53(Al) derivatives, prepared using water or DMF as the reaction solvent, is not observed for samples prepared from MeOH and the framework adopts and remains in the large-pore form. Thus, measurement of N2-isotherms and calculation of internal surface areas have verified that the synthesis of MIL-53(MeOH) leads to a product which is highly porous with only minimal or no activation required. Furthermore, X-ray diffraction measurements and scanning electron microscopy at different humidity levels reveal a reversible loss of crystallinity at high humidity levels for MIL-53(MeOH) which was not observed previously for other MIL-53 derivatives. In contrast, the synthesis of MIL-53(Al) in ethanol leads to a product with low crystallinity.

Metal-organic framework thin films on a surface of optical fibre long period grating for chemical sensing

An optical fibre long period grating (LPG) modified with a thin film of HKUST-1, a material from metal organic framework (MOF) family, was employed for the detection of carbon dioxide. The sensing mechanism is based on the measurement of the change of the refractive index (RI) of the coating that is induced by the penetration of CO2 molecules into the HKUST-1 pores. The responses of the resonance bands in the transmission spectrum of an LPG modified with 40 layers of HKUST-1 upon exposure to carbon dioxide in mixture with nitrogen were investigated.

Detection of volatile organic compounds using optical fibre long period grating modified with metal organic framework thin films

An optical fibre long period grating (LPG) modified with a thin film of ZIF-8, a zeolitic immidazol framework (ZIF) material, a subgroup of the metal organic framework (MOF) family, was employed for the detection of organic vapours. ZIF-8 film was deposited onto the surface of the LPG using an in-situ crystallization technique. The sensing mechanism is based on the measurement of the refractive index (RI) change induced by the penetration of the chemical molecules into the ZIF-8 pores. An LPG modified with 5 growth cycles of ZIF-8 responded to exposure to methanol and ethanol vapours.