The growth of zeolites A, X and mordenite in space

Zeolites are a class of crystalline aluminosilicate materials that form the backbone of the chemical process industry worldwide. They are used primarily as adsorbents and catalysts and support to a significant extent the positive balance of trade realized by the chemical industry in the United States (around $19 billion in 1991). The magnitude of their efforts can be appreciated when one realizes that since their introduction as 'cracking catalysts' in the early 1960's, they have saved the equivalent of 60 percent of the total oil production from Alaska's North Slope. Thus the performance of zeolite catalysts can have a profound effect on the U.S. economy. It is estimated that a 1 percent increase in yield of the gasoline fraction per barrel of oil would represent a savings of 22 million barrels of crude oil per year, representing a reduction of$400 million in the United States' balance of payments. Thus any activity that results in improvement in zeolite catalyst performance is of significant scientific and industrial interest. In addition, due to their 'stability,' uniformity, and, within limits, their 'engineerable' structures, zeolites are being tested as potential adsorbents to purify gases and liquids at the parts-per-billion levels needed in today's electronic, biomedical, and biotechnology industries and for the environment. Other exotic applications, such as host materials for quantum-confined semiconductor atomic arrays, are also being investigated. Because of the importance of this class of material, extensive efforts have been made to characterize their structures and to understand their nucleation and growth mechanisms, so as to be able to custom-make zeolites for a desired application. To date, both the nucleation mechanics and chemistry (such as what are the 'key' nutrients) are, as yet, still unknown for many, if not all, systems. The problem is compounded because there is usually a 'gel' phase present that is assumed to control the degree of supersaturation, and this gel undergoes a continuous 'polymerization' type reaction during nucleation and growth. Generally, for structure characterization and diffusion studies, which are useful in evaluating zeolites for improving yield in petroleum refining as well as for many of the proposed new applications (e.g., catalytic membranes, molecular electronics, chemical sensors) large zeolites (greater than 100 to 1000 times normal size) with minimum lattice defects are desired. Presently, the lack of understanding of zeolite nucleation and growth precludes the custom design of zeolites for these or other uses. It was hypothesized that the microgravity levels achieved in an orbiting spacecraft could help to isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation, which occurs since zeolites are twice as dense as the solution from which they are formed. This was expected to promote larger crystals by allowing growing crystals a longer residence time in a high-concentration nutrient field. Thus it was hypothesized that the microgravity environment of Earth orbit would allow the growth of large, more defect-free zeolite crystals in high yield

Pseudoboehmite as a drug delivery system for acyclovir

Herpes simplex virus is among the most prevalent sexually transmitted infections. Acyclovir is a potent, selective inhibitor of herpes viruses and it is indicated for the treatment and management of recurrent cold sores on the lips and face, genital herpes, among other diseases. The problem of the oral bioavailability of acyclovir is limited because of the low permeability across the gastrointestinal membrane. The use of nanoparticles of pseudoboehmite as a drug delivery system in vitro assays is a promising approach to further the permeability of acyclovir release. Here we report the synthesis of high purity pseudoboehmite from aluminium nitrate and ammonium hydroxide containing nanoparticles, using the sol–gel method, as a drug delivery system to improve the systemic bioavailability of acyclovir. The presence of pseudoboehmite nanoparticles were verified by infrared spectroscopy, transmission electron microscopy, and X-ray diffraction techniques. In vivo tests were performed with Wistar rats to compare the release of acyclovir, with and without the addition of pseudoboehmite. The administration of acyclovir with the addition of pseudoboehmite increased the drug content by 4.6 times in the plasma of Wistar rats after 4 h administration. We determined that the toxicity of pseudoboehmite is low up to 10 mg/mL, in gel and the dried pseudoboehmite nanoparticles.The authors thank the Mackenzie Presbyterian University, Texas Tech University, Mack Pesquisa, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES), Cnpq, and FAPESP (grant 2010/19157-9 and grant 2017/22396-4) for the sponsorship to this project

A slice of an aluminum particle: Examining grains, strain and reactivity

Micron-scale aluminum (Al) particles are plagued by incomplete combustion that inhibits their reactivity. One approach to improving reactivity is to anneal Al particles to increase dilatational (volumetric) strain which has also been linked to increased combustion performance. While optimal annealing temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on particle combustion performance. This study examines the effect of quenching after annealing Al microparticles to 100, 200 and 300 °C on intra-particle dilatational strain and reactivity. Synchrotron X-ray diffraction analysis of the particles reveals the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatational strain of the aluminum-core, alumina-shell particles. The annealed and quenched Al particles were then combined with a metal oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a critical annealing temperature of 300 °C is reached and performance is maintained for each annealing temperature regardless of cooling rate. These results show that altering the mechanical properties and combustion performance of Al particles is strongly dependent on the annealing temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic deformation mechanisms on strain are also considered and additional experimental results are shown on the microstructure of an Al particle. Focused ion beam milling of an Al particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al particles. This confirmed that the Al microparticles have a polycrystalline structure shown by grains all exceeding 100 nm in size

Pneumoproteins and biomarkers of inflammation and coagulation do not predict rapid lung function decline in people living with HIV

Chronic obstructive pulmonary disease (COPD) is among the leading causes of death worldwide and HIV is an independent risk factor for the development of COPD. However, the etiology of this increased risk and means to identify persons with HIV (PWH) at highest risk for COPD have remained elusive. Biomarkers may reveal etiologic pathways and allow better COPD risk stratification. We performed a matched case:control study of PWH in the Strategic Timing of Antiretoviral Treatment (START) pulmonary substudy. Cases had rapid lung function decline (> 40 mL/year FEV1 decline) and controls had stable lung function (+ 20 to − 20 mL/year). The analysis was performed in two distinct groups: (1) those who were virally suppressed for at least 6 months and (2) those with untreated HIV (from the START deferred treatment arm). We used linear mixed effects models to test the relationship between case:control status and blood concentrations of pneumoproteins (surfactant protein-D and club cell secretory protein), and biomarkers of inflammation (IL-6 and hsCRP) and coagulation (d-dimer and fibrinogen); concentrations were measured within ± 6 months of first included spirometry. We included an interaction with treatment group (untreated HIV vs viral suppression) to test if associations varied by treatment group. This analysis included 77 matched case:control pairs in the virally suppressed batch, and 42 matched case:control pairs in the untreated HIV batch (n = 238 total) who were followed for a median of 3 years. Median (IQR) CD4 + count was lowest in the controls with untreated HIV at 674 (580, 838). We found no significant associations between case:control status and pneumoprotein or biomarker concentrations in either virally suppressed or untreated PWH. In this cohort of relatively young, recently diagnosed PWH, concentrations of pneumoproteins and biomarkers of inflammation and coagulation were not associated with subsequent rapid lung function decline. Trial registration: NCT00867048 and NCT01797367

A slice of an aluminum particle: Examining grains, strain and reactivity

Micron-scale aluminum (Al) particles are plagued by incomplete combustion that inhibits their reactivity. One approach to improving reactivity is to anneal Al particles to increase dilatational (volumetric) strain which has also been linked to increased combustion performance. While optimal annealing temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on particle combustion performance. This study examines the effect of quenching after annealing Al microparticles to 100, 200 and 300 °C on intra-particle dilatational strain and reactivity. Synchrotron X-ray diffraction analysis of the particles reveals the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatational strain of the aluminum-core, alumina-shell particles. The annealed and quenched Al particles were then combined with a metal oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a critical annealing temperature of 300 °C is reached and performance is maintained for each annealing temperature regardless of cooling rate. These results show that altering the mechanical properties and combustion performance of Al particles is strongly dependent on the annealing temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic deformation mechanisms on strain are also considered and additional experimental results are shown on the microstructure of an Al particle. Focused ion beam milling of an Al particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al particles. This confirmed that the Al microparticles have a polycrystalline structure shown by grains all exceeding 100 nm in size

Electrochemical fabrication of TiO2 -Au nanocomposites

Nanocomposites comprised of electrosynthesized/annealed TiO2 on indium tin oxide substrates, using the electrogeneration of base method, followed by electrodeposited gold clusters are presented, and their photoelectrochemical response is examined. The TiO2 films are nodular with a rough morphology. Gold nanoparticles were electrodeposited onto the electrogenerated TiO2 with galvanostatic pulses. A step photoresponse analysis was employed to characterize the photoelectrochemical behavior of three different forms of the TiO2-Au composite: (i) TiO2 decorated with Au nanoparticles, TiO2/Au, (ii) TiO2 with embedded Au nanoparticles in a sandwichlike fashion, TiO2/Au/TiO 2, and (iii) TiO2 with embedded and decorated Au nanoparticles, TiO2/Au/TiO2/Au. The TiO2/Au composite resulted in the highest photocurrent response under UV irradiation and in a broadening of the photocurrent response to the visible region, although with successive testing a decrease in the photocurrent response was observed. The photoresponse of the buried Au nanoparticles, TiO2/Au/TiO 2, was slightly lower compared to Au decorating the TiO2 electrosynthesized surface, TiO2/Au, but significantly higher than pristine electrosynthesized TiO2. © 2009 The Electrochemical Society