Cherie L. Geiger

Essential fatty acids and phenolic acids from extracts and leachates of southern cattail (Typha domingensis P.)

We have been able to isolate several phytotoxic compounds from aqueous extracts and leachates of cattails (Typha domingensis) using activated charcoal as an absorbant, followed by successive extraction with organic solvents, analysis by GC/MS, and structural elucidation by NMR spectroscopy when possible. The phytotoxins were identified as essential fatty acids (linoleic acid and alpha-linolenic acid) and phenolic compounds of known phytotoxic activity (caffeic acid from the aqueous extracts; caffeic, p-coumaric, and gallic acid from the leachates). Both extracts and the phytotoxins in the extracts have the potential of inhibiting the growth and chlorophyll production of several ecologically relevant species.

Dechlorination comparison of mono-substituted PCBs with Mg/Pd in different solvent systems

It is widely recognized that polychlorinated biphenyls (PCBs) are a dangerous environmental pollutant. Even though the use and production of PCBs have been restricted, heavy industrial use has made them a wide-spread environmental issue today. Dehalogenation using zero-valent metals has been a promising avenue of research for the remediation of chlorinated compounds and other contaminants that are present in the environment. However, zero-valent metals by themselves have shown little capability of dechlorinating polychlorinated biphenyls (PCBs). Mechanically alloying the metal with a catalyst, such as palladium, creates a bimetallic system capable of dechlorinating PCBs very rapidly to biphenyl. This study primarily aims to evaluate the effects of solvent specificity on the kinetics of mono-substituted PCBs, in an attempt to determine the mechanism of degradation. Rate constants and final byproducts were determined for the contaminant systems in both water and methanol, and significant differences in the relative rates of reaction were observed between the two solvents.

Ultrasound pretreatment of elemental iron: kinetic studies of dehalogenation reaction enhancement and surface effects

This work presents data showing the kinetic improvement afforded by ultrasound pretreatment and illustrates the physical and chemical changes that take place at the iron surface. First-order rate constants improved as much as 78% with 2h of ultrasound pretreatment. Scanning electron microscopy (SEM) and surface area analysis were used for confirmation of the physical changes that take place after ultrasound was used on iron surfaces exposed to a variety of conditions. X-ray photoelectron spectroscopy was used to determine chemical surface characteristics before and after ultrasound use. SEM and surface area analysis showed that ultrasound use clears the iron surface of debris increasing the surface area up to 169%. In addition, exposure to ultrasound alters ratios of surface species, such as adventitious carbon to carbonyl carbon and iron to oxygen, and removed hydroxides thus making the iron more reactive to reductive dehalogenation.

Dechlorination of polychlorinated biphenyls using magnesium and acidified alcohols.

Polychlorinated biphenyls (PCBs) were widely used in industry until their regulation in the 1970s. However, due to their inherent stability, they are still a widespread environmental contaminant. A novel method of degradation of PCBs (via hydrodehalogenation) has been observed using magnesium powder, a carboxylic acid, and alcohol solvents and is described in this paper. The rates of degradation were determined while varying the type of acid (formic, acetic, propionic, butyric, valeric, benzoic, ascorbic, and phosphoric), the amount of magnesium from 0.05 to 0.25 g, the amount of acetic acid from 0.5 to 50 μL and the concentration of PCB-151 from 0.1 to 50 μg/mL, as well as the alcohol solvent (methanol, ethanol, propanol, butanol, octanol, and decanol). The results of these studies indicate that the most rapid PCB dechlorination is achieved using a matrix consisting of at least 0.02 g Mg/mL ethanol, and 10 μL acetic acid/mL ethanol in which case 50 ng/μL of PCB-151 is dechlorinated in approximately 40 min.

The use of mechanical alloying for the preparation of palladized magnesium bimetallic particles for the remediation of PCBs

The kinetic rate of dechlorination of a polychlorinated biphenyl (PCB-151) by mechanically alloyed Mg/Pd was studied for optimization of the bimetallic system. Bimetal production was first carried out in a small-scale environment using a SPEX 8000M high-energy ball mill with 4-μm-magnesium and palladium impregnated on graphite, with optimized parameters including milling time and Pd-loading. A 5.57-g sample of bimetal containing 0.1257% Pd and ball milled for 3 min resulted in a degradation rate of 0.00176 min(-1)g(-1) catalyst as the most reactive bimetal. The process was then scaled-up, using a Red Devil 5400 Twin-Arm Paint Shaker, fitted with custom plates to hold milling canisters. Optimization parameters tested included milling time, number of ball bearings used, Pd-loading, and total bimetal mass milled. An 85-g sample of bimetal containing 0.1059% Pd and ball-milled for 23 min with 16 ball bearings yielded the most reactive bimetal with a degradation rate of 0.00122 min(-1)g(-1) catalyst. Further testing showed adsorption did not hinder extraction efficiency and that dechlorination products were only seen when using the bimetallic system, as opposed to any of its single components. The bimetallic system was also tested for its ability to degrade a second PCB congener, PCB-45, and a PCB mixture (Arochlor 1254); both contaminants were seen to degrade successfully.

Reduction of benzo[a]pyrene with acid-activated magnesium metal in ethanol: A possible application for environmental remediation

Persistent organic pollutants (POPs) are a well-known threat to the environment. Substances such as polycyclic aromatic hydrocarbons (PAHs) in contaminated soils and sediments can have severe and long-term effects on human and environmental health. There is an urgent need for the development of safe technologies for their effective degradation. Here we present a new technique using ball-milled magnesium powder and ethanol solvent as a convenient electron transfer/proton source for the partial reduction of PAHs under ambient conditions. The rates of degradation were determined while evaluating the influences of acetic acid and type of ball-milled magnesium added to the reaction mixture. The results of these triplicate studies indicate that with the use of acetic acid as an activator and ball-milled magnesium carbon (Mg/C), this reducing system (Mg-EtOH) is able to achieve a 94% conversion of 250 μg/mL of toxic benzo[a]pyrene into a mixture of less toxic and partially hydrogenated polycyclic compounds within 24h. This methodology can be used as a combined process involving ethanol washing followed by reduction reaction and it can also be considered as an easy handling and efficient alternative process to the catalytic hydrogenation of PAHs.

Improving student learning in calculus through applications

Nationally only 40% of the incoming freshmen Science, Technology, Engineering and Mathematics (STEM) majors are successful in earning a STEM degree. The University of Central Florida (UCF) EXCEL programme is a National Science Foundation funded STEM Talent Expansion Programme whose goal is to increase the number of UCF STEM graduates. One of the key requirements for STEM majors is a strong foundation in Calculus. To improve student learning in calculus, the EXCEL programme developed two special courses at the freshman level called Applications of Calculus I (Apps I) and Applications of Calculus II (Apps II). Apps I and II are one-credit classes that are co-requisites for Calculus I and II. These classes are teams taught by science and engineering professors whose goal is to demonstrate to students where the calculus topics they are learning appear in upper level science and engineering classes as well as how faculty use calculus in their STEM research programmes. This article outlines the process used in producing the educational materials for the Apps I and II courses, and it also discusses the assessment results pertaining to this specific EXCEL activity. Pre- and post-tests conducted with experimental and control groups indicate significant improvement in student learning in Calculus II as a direct result of the application courses.

Kinetic modeling of the H2O2 enhanced incineration of heptane and chlorobenzene

The addition of hydrogen peroxide (H2O2) into a stream of heated air containing volatile organic compounds (VOCs), such as heptane and chlorobenzene, has been found to increase the destruction of those VOCs. Detailed kinetic models for the enhanced oxidation of heptane (44 chemical species, 144 reactions), and chlorobenzene (62 species, 212 reactions) were developed. The computer code CHEMKIN was used for the model simulations, and sensitivity analyses were performed using the code SENKIN. Additional thermodynamic data needed for the model were calculated using the group addition methods of Benson, and the computer code THERM. It was concluded that the H2O2 enhancement effect in the oxidation of heptane occurs by the thermal dissociation of the peroxide molecule, providing two OH radicals, followed by hydrogen abstraction of the heptane molecule by an OH radical. In the un-enhanced case the key reaction is the thermal dissociation of the heptane molecule into two radicals. For chlorobenzene the major VOC destruction pathway seems to be the attack of an HO2 radical to generate the phenoxy radical. The HO2 radicals are supplied by the peroxide indirectly, through OH radical attack on other H2O2 molecules, and by other downstream reactions. This is a plausible explanation for the experimental observation of the need for much higher concentrations of H2O2 with chlorobenzene than with heptane, and for the apparent delay in the destruction of chlorobenzene.

Using hydrogen peroxide or ozone to enhance the incineration of volatile organic vapors

Abstract The destruction of certain hazardous Volatile Organic Compounds (VOCs) by incineration requires high temperatures and long residence times. This oxidation process occurs by a complex series of chemical reactions, initiated and propagated by the reactive radicals: hydroxyl (OH), oxygen atoms (O), hydrogen atoms (H), and hydroperoxyl (HO 2 ). It was postulated that the addition of radical sources—such as hydrogen peroxide (H 2 O 2 ) or ozone (O 3 )—to a heated stream of VOCs in air, would enhance the kinetics of the thermal oxidation. In practice, addition of enhancers to post-flame gases in a real incinerator should result in lower incineration temperatures or shorter residence times to obtain the required destruction and removal efficiency (DRE). In this work, the VOCs studied include n -heptane, chlorobenzene, and isopropanol; less extensive experiments were also conducted on trichloroethylene and heptane/chlorobenzene mixtures. The reactor was a 200 cm long, 6 mm diameter quartz tube, externally heated in a Lindberg tube furnace. The experiments were run isothermally for temperatures from 637°C to 750°C with residence times varying from 0.25 to 1.0 seconds at four or five different concentrations of H 2 O 2 or O 3 . The results of these experiments show that the introduction of H 2 O 2 clearly enhances the destruction of the VOCs tested. Ozone was these to be less versatile than hydrogen peroxide because it was effective in the incineration of the alkane but not on the other compounds.