Tarek M. Abdel-Fattah

Adsorption of Divalent Lead Ions by Zeolites and Activated Carbon: Effects of pH, Temperature, and Ionic Strength

Abstract Lead alloy bullets used at the 2600 military small arm ranges and 9000 nonmilitary outdoor shooting ranges in the United States are a source of mobilized lead ions under conditions of low pH, significant changes in ionic strength, changes in the reduction oxidation potential (redox), and through binding metal ions to soil organic matter. Once mobile, these lead ions can contaminate adjacent soil and water. Batch adsorption kinetic and isotherm studies were conducted to compare and evaluate different types of adsorbents for lead ion removal from aqueous media. The effects on lead ion absorption from pH changes, competing ions, and temperature increases were also investigated. Adsorbent materials such as activated carbon and naturally occurring zeolites (clinoptilolite and chabazite) were selected because of their relative low cost and because the zeolites are potential point-of-use materials for mitigating wastewater runoff. Molecular sieves, Faujasite (13X) and Linde type A (5A) were selected because they provide a basis for comparison with previous studies and represent well-characterized materials. The relative rate for lead ion adsorption was: 13X > chabazite > clinoptilolite > 5A > activated carbon. Modeling lead ion adsorption by these adsorbents using the Langmuir and Freundlich isotherm expressions determined the adsorbents’ capacity for lead ion removal from aqueous media. 13X, 5A, and activated carbon best fit the Langmuir isotherm expression; chabazite and clinoptilolite best fit the Freundlich isotherm. Applications of chabazite would require pH values between 4 and 11, clinoptilolite between 3 and 11, while activated carbon would operate at a pH above 7. Ionic competition reduced lead ion removal by the zeolites, but enhanced activated carbon performance. Increasing temperature improved adsorption performance for the zeolites; activated carbon lead ion adsorption was temperature independent.

Probing nanoparticle interactions in cell culture media.

Nanoparticle research is often performed in vitro with little emphasis on the potential role of cell culture medium. In this study, gold nanoparticle interactions with cell culture medium and two cancer cell lines (human T-cell leukemia Jurkat and human pancreatic carcinoma PANC1) were investigated. Gold nanoparticles of 10, 25, 50, and 100 nm in diameter at fixed mass concentration were tested. Size distributions and zeta potentials of gold nanoparticles suspended in deionized (DI) water and Dulbeccos Modified Eagles Media (DMEM) supplemented with fetal calf serum (FCS) were measured using dynamic light scattering (DLS) technique. In DI water, particle size distributions exhibited peaks around their nominal diameters. However, the gold nanoparticles suspended in DMEM supplemented with FCS formed complexes around 100 nm, regardless of their nominal sizes. The DLS and UV-vis spectroscopy results indicate gold nanoparticle agglomeration in DMEM that is not supplemented by FCS. The zeta potential results indicate that protein rich FCS increases the dispersion quality of gold nanoparticle suspensions through steric effects. Cellular uptake of 25 and 50 nm gold nanoparticles by Jurkat and PANC1 cell lines were investigated using inductively coupled plasma-mass spectroscopy. The intracellular gold level of PANC1 cells was higher than that of Jurkat cells, where 50 nm particles enter cells at faster rates than the 25 nm particles.

Synthesis of Nested Coaxial Multiple-Walled Nanotubes by Atomic Layer Deposition

Nested multiple-walled coaxial nanotube structures of transition metal oxides, semiconductors, and metals were successfully synthesized by atomic layer deposition (ALD) techniques utilizing nanoporous anodic aluminum oxide (AAO) as templates. In order to fabricate free-standing tube-in-tube nanostructures, successive ALD nanotubes were grown on the interior template walls of the AAO nanochannels. The coaxial nanotubes were alternated by sacrificial spacers of ALD Al(2)O(3), to be chemically removed to release the nanotubes from the AAO template. In this study, we synthesized a novel nanostructure with up to five nested coaxial nanotubes within AAO templates. This synthesis can be extended to fabricate n-times tube-in-tube nanostructures of different materials with applications in multisensors, broadband detectors, nanocapacitors, and photovoltaic cells.

Copper cation removal in an electrokinetic cell containing zeolite.

Zeolites are used in environmental remediation of soil or water to immobilize or remove toxic materials by cation exchange. An experiment was conducted to test the use a low electric field to direct the toxic cations towards the zeolite. An electrokinetic cell was constructed using carbon electrodes. Synthetic Linde Type A (LTA) zeolite was placed in the cell. Copper(II) chloride dissolved in water was used as a contaminant. The Cu(2+) concentration was measured for ten hours with and without an applied electric field. The removal of the Cu(2+) ions was accelerated by the applied field in the first two hours. For longer time, the electric field did not improve the removal rate of the Cu(2+) ions. The presence of zeolite and applied electric field complicates the chemistry near the cathode and causes precipitation of Cu(2+) ions as copper oxide on the surface of the zeolite. With increased electric field the zeolite farther away from the cathode had little cation exchange due to the higher drift velocity of the Cu(2+) ions. The results also show that, in the LTA Zeolite A pellets, the cation exchange of Cu is limited to a shell of several tens of micrometers.

Nanosecond pulse electrical fields used in conjunction with multi-wall carbon nanotubes as a potential tumor treatment

The objectives of this communication were to fabricate pure samples of multi-walled carbon nanotubes (MWCNTs) and to determine their toxicity in tumor cell lines. MWCNTs were dispersed in a concentration of the surfactant T80 that was minimally toxic. Cell-type variation in toxicity to MWCNTs was observed but was not significantly different to unexposed controls. Additionally, we investigated the increased cell killing of the pancreatic cancer cell line PANC1 when exposed to ultrashort (nanosecond) pulsed electrical fields (nsPEF) in the presence of MWCNTs as a potential form of cancer therapy. We hypothesized that the unique electronic properties of MWCNTs disrupt cell function, leading to cell death, when cells are exposed to nsPEF. We observed a 2.3-fold reduction in cell survival in cells pulsed in the presence of MWCNTs compared to pulsed controls. This study demonstrates that ultrashort pulse electrical field applications have enhanced killing effects when cells are previously grown in the presence of MWCNTs, suggesting that the electrical properties of MWCNTs play a vital role in this process and is suggestive of a synergistic interaction between these nanomaterials and electrical fields.

Atomic Layer Deposition of ZrO2 and HfO2 Nanotubes by Template Replication

Highly ordered zirconia and hafnia nanotubes were fabricated by atomic layer deposition (ALD) within the anodic alumina oxide (AAO) template. Scanning electron microscopy and energy-dispersive spectroscopy were used to characterize the morphology and elemental compositions of the different ALD coatings. The diameters of the AAO pores are in the range of 200-300 nm with a thickness of 60 μm. The results indicated that the freestanding nanotubes were uniformly grown through the entire template thickness. The ALD process conformally replicated the AAO template dimensions. The number of ALD cycles controlled the resultant nanotube wall thickness.

Pyrolytic Synthesis of Carbon Nanotubes from Sucrose on a Mesoporous Silicate

Abstract Multi‐wall carbon nanotubes were synthesized from sucrose by a pyrolytic technique using mesopourous MCM‐41 silicate templates without transition metal catalysts. The nanotubes were examined in the carbon/silicate composite and after dissolution of the silicate. High‐resolution transmission electron microscopy study of the multi‐wall nanotubes showed them to be 15 nm in diameter, 200 nm in length and close‐ended. There was variation in crystallinity with some nanotubes showing disordered wall structures.

In vitro stability study of organophosphonic self assembled monolayers (SAMs) on cobalt chromium (Co-Cr) alloy

Surface modification of cobalt chromium (Co-Cr) alloy is being investigated as a possible solution to the biomedical challenges arising from its usage. Self assembled monolayers (SAMs) of organophosphonic octadecylphosphonic acid (ODPA) were formed on the oxide surface of Co-Cr alloy by chemisorption using the solution deposition technique. High quality and well-ordered SAMs were formed which were characterized using Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle measurements and ellipsometry. The resulting monolayers were then exposed to in vitro conditions using phosphate buffered saline (PBS) solution. The samples were analyzed for a period of 1, 3, 7 and 14 days. The resulting samples were characterized using XPS, AFM and Contact angle measurements. XPS atomic concentrations and detailed high energy elemental scans gave an insight into the trends of elemental concentrations over the duration of the study. SAMs were found to be strongly bound to the oxide surface after PBS exposure. AFM gave the topographic details of SAMs presence by island formation before and after SAM formation and also over the duration of the PBS exposure. Contact Angle Measurements confirmed the hydrophobicity of the surface after SAM formation and indicated a slight disorder of the SAM alkyl chain upon exposure to PBS. Thus, ODPA SAMs were successfully coated on Cobalt Chromium (Co-Cr) alloy surface and were found to be stable and strongly bound after PBS exposure.

Dye-Sensitized Solar Cell Based on Polyaniline/Multiwalled Carbon Nanotubes Counter Electrode

This work presented the successful fabrication of dye-sensitized solar cell using polyaniline base (EB), multiwalled carbon nanotubes (MWCNTs), organic dye (rhodamine B or riboflavin), zinc oxide (ZnO), and indium tin oxide (ITO). The electrical properties of the resultant devices were investigated by measuring the current density voltage (-), capacitance voltage (-), and impedance measurements under both dark and illuminated conditions. The photovoltaic cell characteristics, that is, open circuit voltage (), short circuit current density (), and energy conversion efficiency (), were evaluated under illumination and were found to be 0.48 mA/cm2, 400 mV, and 0.224%, respectively, for ITO/EB-MWCNTs/ZnO-rhodamine B/ITO heterostructure. Using impedance spectra, it was found that the series resistances of this type of solar cell are 62 and 60 Ω under darkness and illumination, respectively.

Lead bioaccumulation in emydid turtles of an urban lake and its relationship to shell disease.

Urban runoff contributes significant amounts of heavy metals into receiving waters in which turtles make up a large portion of the biodiversity. Turtles accumulate heavy metals in their body and shell bone, yet little is known about how it affects their health. Studies in vertebrates have shown bioaccumulation of lead to have several deleterious effects such as immunosuppression, impairment of skeletal calcification and competition with calcium ion uptake. This study surveys the bioaccumulation of lead in emydid turtles of an urban lake and investigates the differences based on species, sex, size and its possible relationship to shell disease. Shell disease was quantified and small sections of shell were collected from each specimen and analyzed for lead content using Graphite Furnace Atomic Adsorption Spectrometry. Significant differences of lead accumulation were found between species, yet not with sex or body size. Linear regression comparison of lead concentration and shell disease showed no positive correlation.