Michael Severance

Rapid crystallization of faujasitic zeolites: mechanism and application to zeolite membrane growth on polymer supports.

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications.

Contrast of the biological activity of negatively and positively charged microwave synthesized CdSe/ZnS quantum dots.

Quantum dots (QDs) are semiconductor nanocrystals that have found use in bioimaging, cell tracking, and drug delivery. This article compares the cytotoxicity and cellular interactions of positively and negatively charged CdSe/CdS/ZnS QDs prepared by a microwave method using a murine alveolar macrophage-like cell culture model. Keeping the core semiconductor the same, QD charge was varied by altering the surface capping molecule; negatively charged QDs were formed with mercaptopropionic acid (MPA-QDs) and positively charged QDs with thiocholine (THIO-QDs). The size and charge of these two QDs were investigated in three types of media (RPMI, RPMI + FBS, and X-VIVO serum-free media) relevant for the biological studies. MPA-QDs were found to have negative zeta potential in RPMI, RPMI + FBS, and serum-free media and had sizes ranging from 8 to 54 nm. THIO-QDs suspended in RPMI alone were <62 nm in size, while large aggregates (greater than 1000 nm) formed when these QDs were suspended in RPMI + FBS and serum-free media. THIO-QDs retained positive zeta potential in RPMI and were found to have a negative zeta potential in RPMI + FBS and nearly neutral zeta potential in serum-free media. In a cell culture model, both MPA-QDs and THIO-QDs caused comparable levels of apoptosis and necrosis. Both QDs induced significant tumor necrosis factor-alpha (TNF-α) secretion only at high concentrations (>250 nM). Both types of QDs were internalized via clathrin-dependent endocytosis. Using real-time, live cell imaging, we found that MPA-QDs interact with the cell surface within minutes and progress through the endocytic pathway to the lysosomes upon internalization. With the THIO-QDs, the internalization process was slower, but the pathways could not be mapped because of spectroscopic interference caused by QD aggregates. Finally, MPA-QDs were found to associate with cell surface scavenger receptors, while the THIO-QDs did not. This study indicates that the surface charge and aggregation characteristics of QDs change drastically in biological culture conditions and, in turn, influence nanoparticle and cellular interactions.

Fabrication of zeolite/polymer multilayer composite membranes for carbon dioxide capture: Deposition of zeolite particles on polymer supports.

Membranes, due to their smaller footprint and potentially lower energy consumption than the amine process, offer a promising route for post-combustion CO2 capture. Zeolite Y based inorganic selective layers offer a favorable combination of CO2 permeance and CO2/N2 selectivity, membrane properties crucial to the economics. For economic viability on large scale, we propose to use flexible and scalable polymer supports for inorganic selective layers. The work described in this paper developed a detailed protocol for depositing thin zeolite Y seed layers on polymer supports, the first step in the synthesis of a polycrystalline zeolite Y membrane. We also studied the effects of support surface morphology (pore size and surface porosity) on the quality of deposition and identified favorable supports for the deposition. Two different zeolite Y particles with nominal sizes of 200 nm and 40 nm were investigated. To obtain a complete coverage of zeolite particles on the support surface with minimum defects and in a reproducible manner, a vacuum-assisted dip-coating technique was developed. Images obtained using both digital camera and optical microscope showed the presence of color patterns on the deposited surface which suggested that the coverage was complete. Electron microscopy revealed that the particle packing was dense with some drying cracks. Layer thickness with the larger zeolite Y particles was close to 1 μm while that with the smaller particles was reduced to less than 0.5 μm. In order to reduce drying cracks for layers with smaller zeolite Y particles, thickness was reduced by lowering the dispersion concentration. Transport measurement was used as an additional technique to characterize these layers.

Physicochemical and Toxicological Properties of Commercial Carbon Blacks Modified by Reaction with Ozone

Ozonation of two commercial carbon blacks (CBs), Printex 90 (P90) and Flammruss 101 (F101), was carried out and changes in their morphology, physical properties, and cytotoxicity were examined. The hypothesis examined was that different methods of manufacture of CBs influence their chemical reactivity and toxicological properties. Structural changes were examined by X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy, and electron paramagnetic resonance spectroscopy (EPR). Introduction of surface oxygen functionality upon ozonation led to changes in surface charge, aggregation characteristics, and free radical content of the CBs. However, these changes in surface functionality did not alter the cytotoxicity and release of inflammation markers upon exposure of the CBs to murine macrophages. Interaction of macrophages with F101 resulted in higher levels of inflammatory markers than P90, and the only structural correlation was with the higher persistent radical concentration on the F101.

Influence of crystallite size on cation conductivity in faujasitic zeolites.

The influence of particle size on the ionic conductivity of ceramic materials is an active area of research, and novel effects are observed as particles approach the nanoscale in size. Zeolites are crystalline aluminosilicates with ion-exchangeable cations that are responsible for ionic conductivity at high temperatures. In this paper, we present systematic results for the first time of ionic conductivity in alkali metal ion-exchanged faujasitic zeolites with morphologies ranging from a zeolite membrane, micrometer-sized, submicrometer, and nanoparticles of zeolite. Using impedance spectroscopy in the range of 10 MHz to 0.1 Hz, we have obtained the activation energy (E(act)) of cation motion with these various morphologies in the temperature range of 525-625 °C. Overall, the E(act) decreases with Si/Al ratio. Surface modification of the zeolite particles was carried out with a silylating agent, which upon high temperature calcination should lead to the formation of a monolayer Si-O-Si film on the particle surface. This surface modification had minimal influence on the E(act) of micrometer-sized zeolites. However, E(act) increased rapidly as the zeolite particle approached the nanoscale. These observations led us to propose that, for the high-temperature, low-frequency (10(4)-10(5) Hz), long-range ionic conduction in zeolites, cation hopping across grain boundaries is relevant to ion transport, especially as the size of the crystallite approaches the nanoscale. Intergrain boundaries are more defective in the nanosized zeolite and contribute to the higher E(act).