Rebecca E. Olsen

Effects of catalyst thickness on the fabrication and performance of carbon nanotube-templated thin layer chromatography plates

The effects of iron catalyst thickness on the fabrication and performance of microfabricated, binder-free, carbon nanotube (CNT)-templated, thin layer chromatography (TLC) plates are demonstrated. The iron catalyst was deposited at thicknesses ranging from 4 to 18 nm in increments of 2 nm. Its thickness plays a key role in governing the integrity and separation capabilities of microfabricated TLC plates, as determined using a test dye mixture. Atomic force microscopy and scanning electron microscopy show that smaller and more numerous catalyst nanoparticles are formed from thinner Fe layers, which in turn govern the diameters and densities of the CNTs. The average diameter of the Fe nanoparticles, Dp, is approximately six times the initial Fe film thickness, tFe: Dp ≈ 6tFe. After deposition of relatively thick silicon layers on CNTs made with different Fe thicknesses, followed by oxidation, all of the resulting CNT-templated SiO2 wires had nearly the same diameter. Consequently, their surface areas were v...

Determination of the magnetic contribution to the heat capacity of cobalt oxide nanoparticles and the thermodynamic properties of the hydration layers

We present low temperature (11 K) inelastic neutron scattering (INS) data on four hydrated nanoparticle systems: 10 nm CoO·0.10H(2)O (1), 16 nm Co(3)O(4)·0.40H(2)O (2), 25 nm Co(3)O(4)·0.30H(2)O (3) and 40 nm Co(3)O(4)·0.026H(2)O (4). The vibrational densities of states were obtained for all samples and from these the isochoric heat capacity and vibrational energy for the hydration layers confined to the surfaces of these nanoparticle systems have been elucidated. The results show that water on the surface of CoO nanoparticles is more tightly bound than water confined to the surface of Co(3)O(4), and this is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to water on Co(3)O(4) nanoparticles. This supports the trend, seen previously, for water to be more tightly bound in materials with higher surface energies. The INS spectra for the antiferromagnetic Co(3)O(4) particles (2-4) also show sharp and intense magnetic excitation peaks at 5 meV, and from this the magnetic contribution to the heat capacity of Co(3)O(4) nanoparticles has been calculated; this represents the first example of use of INS data for determining the magnetic contribution to the heat capacity of any magnetic nanoparticle system.

Optimizing the synthesis and properties of Al-modified anatase catalyst supports by statistical experimental design

The important variables in the synthesis of stable, high surface area, aluminum-modified anatase TiO2 catalyst supports were identified and optimized using statistically designed experiments (DOEs). The first DOE examined ten variables at two levels and a second DOE studied eight variables at three levels. Equations were developed to predict the conditions to obtain the highest surface area and pore volume at the desired pore diameter and predict the pore diameter range that may be obtained. Confirmation trials closely matched predicted surface areas, pore volumes, and pore diameters in all but one trial. Rinsing order (before or after calcination) was the most significant factor. Other important factors were calcination temperature, mol% aluminum, and water addition speed. The results of this study demonstrate (a) the power of DOEs in identifying and controlling synthesis variables in relatively few experiments and (b) how analysis of factor effects can provide insight into the formation mechanism.

Functionalization/passivation of porous graphitic carbon with di-tert-amylperoxide.

Porous graphitic carbon (PGC) particles were functionalized/passivated in situ in packed beds at elevated temperature with neat di-tert-amylperoxide (DTAP) in a column oven. The performance of these particles for high performance liquid chromatography (HPLC) was assayed before and after this chemistry with the following analytes: benzene, toluene, ethyl benzene, n-propyl benzene, n-butyl benzene, p-xylene, phenol, 4-methylphenol, phenetole, 3,5-xylenol, and anisole. After the first functionalization/passivation, the retention factors, k, of these compounds decreased by about 5% and the number of theoretical plates (N) increased by ca. 15%. These values of k then remained roughly constant after a second functionalization/passivation but a further increase in N was noticed. In addition, after each of the reactions, the peak asymmetries decreased by ca. 15%, for a total of ca. 30%. The columns were then subjected twice to methanol at 100°C for 5h at 1 mL/min. After these stability tests, the values of k remained roughly constant, the number of plates increased, which is favorable, and the asymmetries rose and then declined, where they remained below the initial values for the unfunctionalized columns. Functionalized and unfunctionalized particles were characterized by scanning electron microscopy and BET measurements, which showed no difference between the functionalized and unfunctionalized materials, and X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS), where ToF-SIMS suggested some chemical differences between the functionalized and unfunctionalized materials. In particular ToF-SIMS suggested that the expected five-carbon fragments from DTAP exist at higher concentrations on DTAP-functionalized PGC. First principle calculations on model graphitic surfaces suggest that the first addition of a DTAP radical to the surface proceeds in an approximately isothermal or slightly favorable fashion, but that subsequent DTAP additions are then increasingly thermodynamically favorable. Thus, this analysis suggests that the direct functionalization/passivation of PGC with DTAP is plausible. Chemometric analyses of the chromatographic and ToF-SIMS data are also presented.

Synthesis and Thermodynamics of Porous Metal Oxide Nanomaterials

Porous metal oxide nanoparticles is a new class of material of great scientific and technological importance with a wide range of applications. In this article, we briefly review the synthetic methods and thermodynamic properties of such materials. We compare and summarize common synthetic routes of such materials including solid-state, solution- phase (co-precipitation, sol-gel, microemulsion, solvothermal/hydrothermal, non-aqueous), and vapor-phase methods. As for the thermodynamics of porous metal oxide nanoparticles, we review experimental determinations, mainly by calorime- try, on surface and interfaces energetics. The interplay among particle size, surface area, morphology, surface stabilizer, phase stability, and redox potentials is discussed.

The Blind Men and the Elephant as a Metaphor for Surface Analysis, as Applied to the Preparation and Analysis of New, Highly Stable Materials for Separations Science

Most of us heard the story of the blind men and the elephant as children. In this old tale from India each man in a group of blind men touches a different part of an elephant. Each walks away with a different experience and subsequently argues that the elephant is like a spear (the tusk), a rope (the tail), a wall (the flank), etc. Only the combination of their stories would have provided a complete, or at least more complete, picture of what an elephant really is.

Practical comparison of traditional and definitive screening designs in chemical process development

Traditional Screening Designs, such as resolution III 2k-p fractional factorials are used routinely in the initial stages of process development. These designs are used to determine which process variables have the largest effect on process outcomes. Once a screening design is complete and the data are analysed, follow-up experiments are normally required in order to develop useful prediction equations involving the important variables and to identify the optimal process operating conditions. Recently developed definitive screening designs allow researchers to identify important variables and optimum process conditions after one set of experiments, eliminating the need for follow-up experiments. This leads to the question: What is now the role of traditional and definitive screening designs in process optimisation? We share our insights gained from using both of these designs in developing a process to produce catalyst support material to shed light on these questions.