Chemical research in our group explores the properties and chemical reactions associated with nanoscale materials. Nanoparticles are an interesting class of materials because of their high ratio of surface area to volume and the variation of their properties with particle size. Our research spans the disciplines of physical chemistry (especially kinetics), materials chemistry, environmental science, and biochemistry. Specific projects described below include the study of trace organic compounds found in Arctic sediments, nanoparticle toxicity towards plants, synthesis and toxicity of naturally occurring nanoparticles, development and testing of materials for space flight, and kinetics of photochemical reactions on nanoparticle surfaces.
Contact Dr. W or talk with any members of our research group to learn more about these exciting projects.
Influence of Climate Change on the Concentrations of Trace Organic Compounds in Arctic Sediments
Due to my interest in environmental chemistry, I was asked to continue the research conducted by Dr. Mary Sohn upon her retirement. This geochemical research, conducted by PhD students Ms. Salomey Sasu and Mr. Dami Ajadi, explores the relationship between concentrations of trace organic compounds found in sediments and the impact of climate change. The Arctic Ocean and its marginal seas are key areas for understanding the global climate system. Climate change causes increased terrigenous materials to be carried into the ocean as well as higher production of marine organic matter in the ocean. Dr. John Trefry’s research group has collected core samples of sediments from various stations including H30, H32, H24 and Barc5 in the Chukchi Sea which is in the Arctic Ocean. The objectives of this study are to isolate and determine the identities of saturated and unsaturated alkanes and fatty acids in Chukchi Sea sediments. Concentrations of these species in the sediments provide information to the effects of climate change on the organic chemistry of the sediments. The origin of alkanes and fatty acids in sediments (whether terrestrial, aquatic, or a combination of the two) and reactivity (weather labile or stable) will be determined. Additionally, concentrations of arsenic in the Chukchi Sea samples have been obtained from Dr. Trefry’s research group. Hence, arsenic remobilization in the sediments will be compared with the concentrations of alkanes and fatty acids and see if there is any correlation.
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Phytotoxicity of Nanoparticles to Plants and Applications to Phytoremediation
This project, initiated by Mr. Lenny Bernas (MS Chemistry, 2016) investigates the environmental impact of metal cations and commercially synthesized metallic nanoparticles on the health of aquatic plants. Effects were characterized based on photosynthetic function, lipid peroxidation, soluble carbohydrates, total phenolics, total flavonoids, percent scavenging, percent chelating, and total metal absorption. Students interested in this type of research can explore the impact of different metal nanoparticles on E. densa or other plants. Due to the strong biological component of this project, we are collaborating with Dr. Andrew Palmer in the Department of Biological Sciences.
Results of Lenny's research addressed the toxicities of silver cations and commercially synthesized silver nanoparticles (AgNps) towards Egeria Densa (E. densa). (Manuscripts describing the outcomes of this research are in preparation.) This plant was chosen because it is a fast-growing aquatic organism and is commonly used to monitor water quality and heavy metal accumulation. Compared to larger and smaller Ag nanoparticles, silver cations are most toxic to the plants because they enter cells through ion channels and generate reactive oxygen species (ROS), which induce oxidative bursts throughout the plant. Declines were observed in all of the parameters studied, demonstrating the deleterious effects of Ag+ on plants. Silver nanoparticles were mainly adsorbed to the exposed leaf surfaces on stalks of E. densa and the small, 2 nm AgNps induced significant lipid peroxidation at low concentrations of AgNps. This caused declines in photosynthesis, as seen by the degradation of chlorophyll a and carotenoids. 15 nm AgNps exposures showed similar effects to the 2 nm AgNps exposures, but also caused damage to the antioxidant scavenging system. Differences in plant health are demonstrated in the picture below of E. densa plants exposed to Ag+ and 15 nm diameter Ag nanoparticles. Because of similarities to the Ag+ exposures, the mechanism of the 15 nm AgNps toxicity was attributed to the release of silver cations from the nanoparticles adsorbed to the surface of the cell walls. The silver cations showed dose-dependent increase in silver content in the stem tissue, whereas the nanoparticles showed increases in silver content in the leaves, demonstrating different mechanisms of translocation into the plants.
Silver removal from solutions was also monitored for 48 hours in the presence of stalks of E. densa. There was 87% removal of the Ag+ after 48 hours in 0.25 and 0.5 ppm Ag+ exposures, and over 70% removal of 2 and 15 nm AgNps at like concentrations. These results demonstrate that E. densa can remove silver from its aqueous environment and serves as an effective phytoremediant.
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Environmental Impact of Naturally Occurring Nanoparticles
Naturally occurring nanoparticles (NNPs), derived from biological, geological and chemical processes, are a far greater source of nanoparticulate matter compared to current amounts of engineered nanoparticles (ENPs), yet little is known about the potential toxicity of NNPs. A preliminary study involving silver nanoparticles formed through the reduction of Ag+ with humic acids has been published (PDF). The influence of silver NNPs and cations is shown below for the waterweed . Students interested in pursuing this collaborative project with Dr. Andrew Palmer can study the effects of other naturally occurring nanoparticles on a variety of plants and algae.
Stable inorganic NNPs form from metal cations through reactions with natural organic matter (NOM). Examples include metal oxide, metal sulfide, and noble metal nanoparticles. Since the NOM coatings for NNPs originate in the same environment where the particles form, inorganic NNPs can be especially stable and therefore less toxic compared to ENPs coated with materials that are incompatible with the natural environment. Alternatively, NOM adsorbed on the nanoparticle surface may interact more favorably with biological cells, leading to greater toxicity. Variations in NPP size and shape, surface coatings, stability, etc. could all influence the potential toxicity of these particles on organisms in the environment. The purpose of this research is to (1) synthesize these nanoparticles in the laboratory using procedures that mimic the geological and chemical processes under which these NNP form in the environment and (2) investigate the bioaccumulation and toxicity of NPPs towards different photoautotrophs which inhabit either fresh water, salt water, or soil environments.
Naturally occurring nanoparticles are a largely unexplored class of environmental toxicants. The presence of these particles may be increased by the oxidation or dissolution of ENPs which cause the release of metal cations into the environment, providing a new source of material for inorganic NNP production. Distinguishing between the toxicity of ENPs and NPPs will help determine which source should be of greater concern to researchers and manufacturers. Photoautotrophs are excellent systems for modeling heavy metal stress and bioaccumulation in response to nanoparticle toxicity. The insight provided by these studies will help us to better understand the role of NNPs in the ecosystem as well as better understand the potential effects of ENPs. These findings will impact policy decisions on water management and manufacturing waste disposal. Discovering that NNP toxicity is lower than toxicity of ENPs will encourage the use of green chemistry principles for the manufacture of NNPs and their use in many applications. Thinking long-term, we hope to standardize the organisms and protocols utilized here for the broader community of researchers to exploit for future studies into nanomaterial toxicity, bioaccumulation, environmental and biological stability, and their transformations over time.
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Development and Testing of Materials for Space Flight
The harsh conditions of space flight pose challenges for developing and testing materials that are not experienced in a chemistry laboratory. Our group works closely with scientists and engineers in other departments, NASA, and companies to synthesize and analyze materials that will help us explore the final frontier.
Our most recent project is a collaboration with Drs. Tracy Gibson (URS Federal Services) and Martha Williams (NASA) and the students and faculty from Florida Tech's Mechanical and Aerospace Engineering (MAE) Department. Drs. Marcus Wilde and Hamid Hefazi (MAE) supervised the construction of a device to test a new method of repairing damage to electrical wires that can be performed easily in low gravity. This method is useful for both space flight and airline industries. The wire repair process was tested onboard a sounding rocket launched from Wallops Flight Facility in Virginia. Data collected during the rocket flight and the samples collected after it landed demonstrated the feasibility of the method but more testing is required before the process is ready for implementation.
A previous project also involved a collaboration with Drs. Gibson and Rudi Wehmschulte of the Chemistry Department. Our group synthesized ferrimagnetic FePt nanoparticles that could be used in a polymer composite for radiation shielding.
Photochemical Reaction Kinetics
We have an ongoing interest elucidating the mechanisms of chemical reactions that occur on the surface of nanomaterials. Often, these reactions involve the interaction of light (photochemistry) with the nanoparticles acting as reaction catalysts. The diagram below illustrates the process of TiO nanoparticles absorbing light which produces electrons and holes capable of performing reduction and oxidation reactions, respectively. Applications of such materials include environmental remediation and chemical sensors. The study of transforming chemical pollutants to more benign products is a long-standing research effort in our lab. We are also interested in photoresponsive nanoparticles synthesized within nanosized pores on a substrate. Preparing nanoparticles in confined spaces is an effective way to produce nanoparticles with the desired properties.
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