PhD Candidate, University of Pittsburgh
Establish material design relationships for enhanced functional efficacy and reduced negative impact
The overarching aim of my research is to inform sustainable design of existing and novel nanomaterials. In particular, I focus on carbon nanomaterials (CNMs) due to their unique and tunable physical and chemical properties, which have enabled recent advancements in a wide range of innovative technologies with far reaching impact on the energy capture and conversion, water treatment, and biomedical fields. While CNMs offer many promising benefits, there are concerns about potential adverse impacts elicited through these same unique material properties and result from unintended environmental and human exposure. A sustainable approach to material design – in which the material is intentionally manipulated to maintain functional performance and minimize inherent hazard - is necessary to preclude future unintended consequences from their use and ensure safe commercialization of CNM-enabled devices. The goal of my research is to decouple the causative mechanisms of material structure and surface chemistry as it relates to the electrochemical (desired function) and biological (inherent hazard) activities of two predominant classes of CNMs, graphene and carbon nanotubes. The identification of governing properties on electrochemical and biological activities and further the determination of correlation between these properties, performance and hazard outcomes, inform rational safe design guidelines for CNMs contributing to advancement of sustainable nanotechnology.
Electrochemistry offers a rich range of techniques to probe material properties in different experimental environments, which can be developed to further decouple CNM function and hazard. Thus, I look forward to the opportunity to attend the Gordon Research Conference (GRC) on Electrochemistry. GRCs are the premier conferences drawing international participation and the leaders in the field. Several topics of the upcoming conference are relevant to my current research as well as to areas that I am eager to learn more about, such as Next Generation Electrocatalysts and Bioelectrochemistry. Receipt of the Sparrho Heroes Early Career Researcher Prize will not only support my attendance at the GRC-Electrochemistry, but will also be a sincere honor. I look forward to sharing my research and receipt of the award with the GRC participants.
Abstract: Nanotechnology continues to offer new materials and applications that will benefit society, yet there is growing concern about the potential health and environmental impacts of production and use of nanoscale products. Although hundreds of studies of nanomaterial hazards have been reported, due (largely) to the complexity of the nanomaterials, there is no consensus about the impact these hazards will have. This Focus describes the need for a research agenda that addresses these nanomaterial complexities through coordinated research on the applications and implications of new materials, wherein nanomaterials scientists play a central role as we move from understanding to minimizing nanomaterial hazards. Greener nanoscience is presented as an approach to determining and implementing the design rules for safer nanomaterials and safer, more efficient processes.
Pub.: 12 Feb '09, Pinned: 01 Jul '17
Abstract: The Twelve Principles of Green Chemistry were first published in 1998 and provide a framework that has been adopted not only by chemists, but also by design practitioners and decision-makers (e.g., materials scientists and regulators). The development of the Principles was initially motivated by the need to address decades of unintended environmental pollution and human health impacts from the production and use of hazardous chemicals. Yet, for over a decade now, the Principles have been applied to the synthesis and production of engineered nanomaterials (ENMs) and the products they enable. While the combined efforts of the global scientific community have led to promising advances in the field of nanotechnology, there remain significant research gaps and the opportunity to leverage the potential global economic, societal and environmental benefits of ENMs safely and sustainably. As such, this tutorial review benchmarks the successes to date and identifies critical research gaps to be considered as future opportunities for the community to address. A sustainable material design framework is proposed that emphasizes the importance of establishing structure-property-function (SPF) and structure-property-hazard (SPH) relationships to guide the rational design of ENMs. The goal is to achieve or exceed the functional performance of current materials and the technologies they enable, while minimizing inherent hazard to avoid risk to human health and the environment at all stages of the life cycle.
Pub.: 09 May '15, Pinned: 01 Jul '17
Abstract: Multiwalled carbon nanotubes (MWNTs) are utilized in a number of sectors as a result of their favorable electronic properties. In addition, MWNT antimicrobial properties can be exploited or considered a potential liability depending on their intended application and handling. The ability to tailor electrochemical and antimicrobial properties using economical and conventional treatment processes introduces the potential to significantly enhance product performance. Oxygen functional groups are known to influence several MWNT properties, including redox activity. Here, MWNTs were functionalized with oxygen groups using standard acid treatments followed by selective reduction via annealing. Chemical derivatization coupled to X-ray photoelectron spectroscopy was utilized to quantify specific surface oxygen group concentration after variable treatment conditions, which were then correlated to observed trends in electrochemical and antimicrobial activities. These activities were evaluated as the potential for MWNTs to participate in the oxygen reduction reaction and to have the ability to promote the oxidation of glutathione. The compiled results strongly suggest that the reduction of surface carboxyl groups and the redox activity of carbonyl groups promote enhanced MWNT reactivity and elucidate the opportunity to design functional MWNTs for enhanced performance in their intended electrochemical or antimicrobial application.
Pub.: 24 Apr '14, Pinned: 01 Jul '17
Abstract: Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.
Pub.: 02 Feb '13, Pinned: 01 Jul '17
Abstract: Graphene is a wonder material with many superlatives to its name. It is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a benchtop experiment. This review analyzes recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.
Pub.: 23 Jun '09, Pinned: 01 Jul '17
Abstract: It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.
Pub.: 03 Mar '12, Pinned: 01 Jul '17
Abstract: Graphene and its derivatives are promising candidates for important biomedical applications because of their versatility. The prospective use of graphene-based materials in a biological context requires a detailed comprehension of the toxicity of these materials. Moreover, due to the expanding applications of nanotechnology, human and environmental exposures to graphene-based nanomaterials are likely to increase in the future. Because of the potential risk factors associated with the manufacture and use of graphene-related materials, the number of nanotoxicological studies of these compounds has been increasing rapidly in the past decade. These studies have researched the effects of the nanostructural/biological interactions on different organizational levels of the living system, from biomolecules to animals. This review discusses recent results based on in vitro and in vivo cytotoxicity and genotoxicity studies of graphene-related materials and critically examines the methodologies employed to evaluate their toxicities. The environmental impact from the manipulation and application of graphene materials is also reported and discussed. Finally, this review presents mechanistic aspects of graphene toxicity in biological systems. More detailed studies aiming to investigate the toxicity of graphene-based materials and to properly associate the biological phenomenon with their chemical, structural, and morphological variations that result from several synthetic and processing possibilities are needed. Knowledge about graphene-based materials could ensure the safe application of this versatile material. Consequently, the focus of this review is to provide a source of inspiration for new nanotoxicological approaches for graphene-based materials.
Pub.: 16 Jan '14, Pinned: 01 Jul '17
Abstract: Two-dimensional materials have become a major focus in materials chemistry research worldwide with substantial efforts centered on synthesis, property characterization, and technological application. These high-aspect ratio sheet-like solids come in a wide array of chemical compositions, crystal phases, and physical forms, and are anticipated to enable a host of future technologies in areas that include electronics, sensors, coatings, barriers, energy storage and conversion, and biomedicine. A parallel effort has begun to understand the biological and environmental interactions of synthetic nanosheets, both to enable the biomedical developments and to ensure human health and safety for all application fields. This review covers the most recent literature on the biological responses to 2D materials and also draws from older literature on natural lamellar minerals to provide additional insight into the essential chemical behaviors. The article proposes a framework for more systematic investigation of biological behavior in the future, rooted in fundamental materials chemistry and physics. That framework considers three fundamental interaction modes: (i) chemical interactions and phase transformations, (ii) electronic and surface redox interactions, and (iii) physical and mechanical interactions that are unique to near-atomically-thin, high-aspect-ratio solids. Two-dimensional materials are shown to exhibit a wide range of behaviors, which reflect the diversity in their chemical compositions, and many are expected to undergo reactive dissolution processes that will be key to understanding their behaviors and interpreting biological response data. The review concludes with a series of recommendations for high-priority research subtopics at the “bio-nanosheet” interface that we hope will enable safe and successful development of technologies related to two-dimensional nanomaterials.
Pub.: 29 Feb '16, Pinned: 01 Jul '17
Abstract: This article reports a direct chemical pathway for antioxidant deactivation on the surfaces of carbon nanomaterials. In the absence of cells, carbon nanotubes are shown to deplete the key physiological antioxidant glutathione (GSH) in a reaction involving dissolved dioxygen that yields the oxidized dimer, GSSG, as the primary product. In both chemical and electrochemical experiments, oxygen is only consumed at a significant steady-state rate in the presence of both nanotubes and GSH. GSH deactivation occurs for single- and multi-walled nanotubes, graphene oxide, nanohorns, and carbon black at varying rates that are characteristic of the material. The GSH depletion rates can be partially unified by surface area normalization, are accelerated by nitrogen doping, and suppressed by defect annealing or addition of proteins or surfactants. It is proposed that dioxygen reacts with active sites on graphenic carbon surfaces to produce surface-bound oxygen intermediates that react heterogeneously with glutathione to restore the carbon surface and complete a catalytic cycle. The direct catalytic reaction between nanomaterial surfaces and antioxidants may contribute to oxidative stress pathways in nanotoxicity, and the dependence on surface area and structural defects suggest strategies for safe material design.
Pub.: 06 Aug '11, Pinned: 01 Jul '17
Abstract: Health and environmental impacts of graphene-based materials need to be thoroughly evaluated before their potential applications. Graphene has strong cytotoxicity toward bacteria. To better understand its antimicrobial mechanism, we compared the antibacterial activity of four types of graphene-based materials (graphite (Gt), graphite oxide (GtO), graphene oxide (GO), and reduced graphene oxide (rGO)) toward a bacterial model-Escherichia coli. Under similar concentration and incubation conditions, GO dispersion shows the highest antibacterial activity, sequentially followed by rGO, Gt, and GtO. Scanning electron microscope (SEM) and dynamic light scattering analyses show that GO aggregates have the smallest average size among the four types of materials. SEM images display that the direct contacts with graphene nanosheets disrupt cell membrane. No superoxide anion (O(2)(•-)) induced reactive oxygen species (ROS) production is detected. However, the four types of materials can oxidize glutathione, which serves as redox state mediator in bacteria. Conductive rGO and Gt have higher oxidation capacities than insulating GO and GtO. Results suggest that antimicrobial actions are contributed by both membrane and oxidation stress. We propose that a three-step antimicrobial mechanism, previously used for carbon nanotubes, is applicable to graphene-based materials. It includes initial cell deposition on graphene-based materials, membrane stress caused by direct contact with sharp nanosheets, and the ensuing superoxide anion-independent oxidation. We envision that physicochemical properties of graphene-based materials, such as density of functional groups, size, and conductivity, can be precisely tailored to either reducing their health and environmental risks or increasing their application potentials.
Pub.: 20 Aug '11, Pinned: 01 Jul '17
Abstract: The upstream and downstream environmental impacts of engineered nanomaterials (ENMs) are increasingly realized, and have motivated research to advance promising applications while precluding adverse impacts. Life-cycle assessment (LCA) is a comprehensive tool that considers the entire lifetime of a material, product or process—from raw material acquisition to end-of-life—and can be used to characterize these impacts as various environmental and human health categories. The motivation for this highlight stems from the curiosity of experimentalists and theorists researching the environmental and biological impacts that could result from widespread implementation of nanotechnology. In particular, we are motivated to identify how our research on the nano–bio interface can liaise with the nano-LCA community to advance nano-LCA in a safe and sustainable manner. As such, this highlight focuses on four recent nano-LCA publications that survey across several system levels and address the topics of: (i) upstream impacts from nanoparticle synthesis, (ii) extended lifetimes through the incorporation of ENMs in paints, (iii) integration of nano-specific data into existing life-cycle models, and (iv) the establishment of a nano-specific LCA framework.
Pub.: 06 Feb '17, Pinned: 30 Jun '17