a b s t r a c tDevelopment of new zeolite based materials is essential for a variety of applications in catalysis, separations, and medicine. Increasing the specific surface area and decreasing the micropore diffusion pathlength in zeolites are important factors for improving the performance of zeolites in catalytic applications and these factors can be optimized by decreasing the zeolite particle size. Creation of a hierarchical zeolite material that possesses both micro-and mesopores with very large surface areas and improved mass transport properties is an effective solution. In this study, a facile approach to a one step synthesis of nanocrystalline ZSM-5 zeolite from a single template system in 12-24 h at 140°C and with high yield is presented. ZSM-5 zeolite crystals as small as 6 nm which form mesoporous aggregates of approximately 200 nm in diameter were synthesized using this method. The mesopore volume and size distribution showed a dependence on particle size such that smaller particles lead to higher mesopore volumes and narrower pore size distributions. The size of individual crystals, as well as mesopore surface area and pore volume can be controlled by adjusting the pH of the reaction mixture, as well as the hydrothermal treatment temperature and duration.

In this report, we describe the synthesis and characterization of nanocrystalline silicalite (the purely siliceous form of the zeolite, ZSM-5) of defined crystal size and surface functionalization and determine the effect on the type and degree of cytotoxicity induced in two distinct model cell lines. The silicalite materials were characterized by powder X-ray diffraction, dynamic light scattering and zeta potential, solid state NMR, thermal gravimetric analysis, and nitrogen adsorption using the BET method to determine specific surface area. The silicalite samples were functionalized with amino, thiol, and carboxy groups and had crystal sizes of approximately 30, 150, and 500 nm. The cytotoxicities of the silicalite samples with different crystal sizes and different surface functional groups were investigated using human embryonic kidney 293 (HEK-293) cells and RAW264.7 macrophage cell lines. We used the lactic dehydrogenase release assay to measure damage to the cell membrane, the caspase 3/7 activity assay to measure key molecules involved in apoptosis, and the Annexin V-propidium iodide staining method to provide visual confirmation of the types of cell death induced. We have shown that the impact of size and surface functionalization of silicalite nanoparticles on cell toxicity and mechanism of cell death is cell type-dependent. Thirty nanometer silicalite nanoparticles were nontoxic in RAW264.7 cells relative to untreated controls but caused necrosis in HEK293 cells. Carboxy-functionalized 500 nm silicalite nanoparticles resulted in apoptosis and necrosis in RAW264.7 cells and predominantly activated apoptosis in HEK293 cells.

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As part of our recent effort to attach well-defined molecular photocatalysts to solid-state surfaces, this present study investigates adsorption and photochemical properties of a tricarbonyl rhenium(I) compound, Re(bpy)(CO)3Cl (bpy = 2,2'-bipyridine), in hierarchical mesoporous ZSM-5. The molecular Re(I) catalyst, a Ru(bpy)3(2+) photosensitizer, and an amine-based electron donor were coadsorbed in the mesopores of the hierarchical ZSM-5 through simple liquid-phase adsorption. The functionalized ZSM-5 was then characterized with infrared and UV-visible spectroscopies and was tested in CO2 reduction photocatalysis at the gas-surface interface. In the mesoporous ZSM-5, CO2 molecules were adsorbed on the amine electron-donor molecules as bicarbonate, which would release CO2 upon light irradiation to react with the Re(I) catalyst. The formation of important reaction intermediates, particularly a Re-carboxylato species, was revealed with in situ Fourier transform infrared spectroscopy in combination with isotopic labeling. The experimental results indicate that hierarchical mesoporous zeolites are promising host materials for molecular photocatalysts and that zeolite mesopores are potential "reaction vessels" for CO2 reduction photocatalysis at the gas-solid interface.

We observed surprising difference in the FTIR (Fourier transform infrared) hydroxyl spectra of the structurally isomorphous, proton exchanged H-CHA and H-SAPO-34 molecular sieves when measured by transmission (TR) or diffuse reflectance (DRIFT) techniques. Experimental and density functional theory (DFT) based model evidence is presented in this paper to prove that the essential reason for this spectral difference is that DRIFT emphasizes the vibrations of surface hydroxyl sites. Vibrations of the bulk Brønsted acidic hydroxyls shift to higher frequencies when they become surface species, the IR beam is reflected from approximately the top ~15 to 20 Å thick layer of the particles, hence the proportion of surface related IR bands becomes significant compared to the bulk related ones in the DRIFT spectra while the opposite is valid for the TR spectra. We demonstrate that the surface hydroxyls are Brønsted acidic both on the H-CHA and the H-SAPO-34 particles and the upshifted vibrations noticed primarily in the DRIFT spectra are Al-OH vibrations on the surface even of H-SAPO-34, not P-OH groups as most researchers believe. We also show that the bulk Brønsted sites might involve HO1, HO2 and HO4 type hydroxyls associated with the known geometrically different oxygen positions on both molecular sieves, but only HO1 surface hydroxyls are associated with the red-shifted vibration intensified in the DRIFT spectra. Moreover, a single surface model cannot account for every vibration observed in DRIFT spectra. From the combination of IR vibrations of three adequate surface models one can as properly match the experimental DRIFT spectra as the TR spectra from the combination of the calculated bulk HO1…HO4 vibrations of these molsieve crystals.

Mesoporous aggregates of nanocrystalline zeolites with MFI and BEA frameworks have been synthesized using a one-pot and single structure directing agent. The effect of different reaction conditions, such as temperature, time, pH and water content, on the particle size, surface area and mesopore volume has been studied. Nanocrystalline and mesoporous ZSM-5, β and Y zeolites were modified with different transition metals and the resulting single-and double metal containing catalyst materials were characterized. Nanocrystalline Silicalite-1 zeolite samples with varying particle size were functionalized with different organosilane groups and the cytotoxic activity of the zeolite nanocrystals was studied as a function of particle size, concentration, organic functional group type, as well as the type of cell line. Framework stability of nanocrystalline NaY zeolite was tested under different pH conditions. The synthesized zeolites used in this work were characterized using a variety of physico-chemical methods, including powder X-ray diffraction, Solid State NMR, nitrogen sorption, electron microscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy and X-ray Photoelectron Spectroscopy.

Nanocrystalline zeolites are emerging as important materials for a variety of potential applications in industry and medicine. Reducing the particle size to less than 100 nm results in advantages for nanocrystalline zeolites relative to micrometer-sized zeolite crystals, such as very large total and external specific surface areas and reduced diffusion path lengths. Understanding the physical and chemical properties of zeolite nanocrystals is imperative for further development and application of nanocrystalline zeolites. In this study, the framework stability of nanocrystalline NaY zeolite with a crystal size of 66 nm and Si/Al = 1.74 was investigated at pH 7.4, 4, 2, and 1. The solids and solutions were analyzed using several different analytical techniques. The relative crystallinity and crystal size and morphology of the solids were examined by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The aluminum content, Si/Al, and coordination were monitored by inductively coupled plasma/optical emission spectroscopy (ICP/OES), X-ray photoelectron spectroscopy (XPS), and aluminum-27 solid-state magic-angle spinning NMR. As the acidity of the medium increased, the framework stability of nanocrystalline NaY decreased. Treatment of the zeolite samples at pH 1 resulted in complete degradation of the zeolite framework after 1 h. An increase in Si/Al was also observed, suggesting the selective removal of aluminum at low pH.