Yale University
225 Prospect Street
New Haven, CT 06520
phone: 203.432.5215
greenchemistry@yale.edu

Materials

  • MoDRN (Molecular Design Research Network)

     Details...
    The world we live in is made of chemicals. The man-made substances have had revolutionary benefits on our lives as well as unintended consequences. MoDRN (Molecular Design Research Network) is a Green Chemistry and Green Engineering initiative, which focuses on the rational design of chemicals and materials to reduce toxicity.

    Our engineers, chemists, toxicologists and biologists are working to develop a robust, accurate and intuitive set of tools to both inform chemical toxicity levels and help scientists design less hazardous alternatives. 

    The overarching goal of MoDRN is to enable and empower the design, discovery and development of next generation chemicals that possess reduced toxicity. To accomplish this we facilitate engagement of scientists, educators, industry and regulatory bodies in this trans-disciplinary endeavor.

  • Safer Chemical Design Using Quantum Chemistry, Statistical Learning and Mechanistic Toxicology

     Details...
    Current methods for chemical safety assessment is via animal testing, which shoulders high economic and ethical burdens. As such, developing in-silico models to predict the toxicity potential of chemicals and derive principles to guide safer chemical design is very important.

    Chemicals can provide convenience and comfort to modern society. They are generally designed with certain desired functionalities in mind. However, little is understood about the fundamental principles of chemical toxicity that govern the inherent hazards of chemicals. This leaves the concern that commercial chemicals may possess unintended biological activities and provoke adverse consequences to ecological communities including human beings. The current method for chemical safety assessment is via animal testing, which shoulders high economic and ethical burdens. As such, developing in-silico models to predict the toxicity potential of chemicals and derive principles to guide safer chemical design is very important. 
    This research employs an integrated approach to address this question. The method is primarily composed of three components: quantum chemistry, statistical learning and mechanistic toxicology. Density functional theory based quantum mechanical calculations provide electronic parameters of molecular systems with relatively high accuracy. These parameters are linked to the likelihood of invoking undesired biological responses registered by high throughput screening assays through information mining and mechanistic knowledge consultation. The resulting predictive model will be used to drive safer chemical design principles.    
    The results of this project can deliver benefits to both academic and industrial sectors. For academic institutions, these design principles and predictive models can be used for educational materials. For industrial research labs, the predictive models can be used to guide safer chemical design.

  • Oxidative Stress Responses and Chemical Toxicity

     Details...
    Determining the most important physical and chemical properties that result in oxidative stress responses, which are key steps in many human biological toxic endpoints. 

    More efficient methods to screen more chemicals for potential toxicity and prioritization schemes that select chemicals of concern for further testing are needed, since we have such little information currently on chemical toxicity. But we also need to be using this information to think about how chemicals can be designed with green chemistry principles from the start so that costly and extensive toxicity testing may be avoided.   

    We are determining the most important physical and chemical properties that result in oxidative stress responses, which are key steps in many human biological toxic endpoints. 

    New advances in toxicity testing have the ability to change the nature of chemical regulation in the United States and more effectively protect human and environmental health. They can also inform and empower the development of safer chemical design guidelines that allow chemicals and materials manufacturers to design with human and environmental health considerations.

  • Selective C-H Oxidation Using a Heterogeneous Cobalt Catalyst and Green Oxidant

     Details...
    This project aims to develop an efficient system for selective oxidation of a wide range of organic substrates including compounds containing unactivated C-H bonds.  

    Activating C-H bonds is highly attractive to the field of green chemistry because it can provide atom-economic syntheses and permit late-stage functionalization, even of complex organic molecules, without the introduction and removal of directing groups. It also has the potential to convert feedstock chemicals from oil, natural gas, and biomass into higher value chemicals. Since many of the catalysts that are currently employed in C-H activation require precious metals, our current challenge is to replace these catalysts using earth-abundant and cheaper first row transition metals. Using first row metals is more amenable to large scale application. Interestingly, first row metals are employed by enzymes for selective C-H activation reactions in nature.  

    This project aims to develop an efficient system for selective oxidation of a wide range of organic substrates including compounds containing unactivated C-H bonds.  We recently reported the synthesis and characterization of a highly active heterogeneous cobalt water oxidation catalyst formed from simple and abundant starting materials. We are investigating its use in conjunction with an environmentally benign oxidant to selectively oxidize organic substrates under mild reaction conditions. 

    Broad application of C-H oxidation in industry is limited by the cost of late transition metals as a result of their scarcity and the need to recover the metals post reaction due to recycling and toxicity concerns.  First row metals tend to be much more abundant and thus cheaper. The ability to incorporate oxidations late-stage in the synthetic scheme rather than having to use bulky protection groups early on can greatly improve atom-economy, reduce the use of solvents and waste generated, and reduce the overall number of steps required.

    Further refinement of the catalyst and conditions could also yield selective oxidations of complex organic molecules containing multiple functionalities. This would be of great interest in the synthesis of pharmaceuticals and natural products.   

  • Selective Annealing Techniques of Multi-Walled Carbon Nanotube Synthesis

     Details...
    Multi-walled carbon nanotubes (MWNTs) offer a variety of industrially important functions, including tensile strength, electrical conductivity, and antimicrobial activity. We have been synthesizing a matrix of 28 O-functionalized MWNT using a nitric acid technique combined with a selective annealing technique.

    portant functions, including tensile strength, electrical conductivity, and antimicrobial activity. These functions result from various physical and chemical properties. In order to inform industrially relevant and sustainable design, it is crucial to definitively understand the relationships between MWNT physiochemical properties and these functions, particularly cytotoxicity, which could be desirable or undesirable depending on the application. Nanotube cytotoxicity has been attributed to physical characteristics, chemical characteristics, and production method. It has previously been shown that surface oxygen functional group type plays a critical role in increased MWNT toxicity.  However, it has also been proposed that length or aspect ratio is also an important factor in MWNT toxicity. Single walled carbon nanotubes are currently considered a promising antimicrobial material. However, their high relative cost makes the promise of functionalized MWNTs even more appealing. 

    To answer this question, we have been synthesizing a matrix of 28 O-functionalized MWNT. We have been using a nitric acid technique combined with a selective annealing technique for the synthesis. The acid treatment shortens the tubes and adds oxygen surface groups, while annealing under inert conditions selectively removes some of these oxygen groups. This gives us a suite of MWNTs with varying length and oxygen content/group type.

    Since completing that synthesis, we have been characterizing the MWNTs through various techniques, including DLS, SLS, a bacterial toxicity assay, TEM, XPS, etc. We will also be looking to perform other tests and collaborate more. 

    This research could impact the way we use antimicrobial products, including textiles, polymers and more. This will also offer design principles to CNT manufacturers to make CNTs to meet the needs of their clients, so they can effectively use less material, rather than using a large amount of ineffective material. 

     

  • Environmentally and Economically Sustainable Carbon Nanotube Manufacturing

     Details...
    Carbon nanotubes (CNTs) consist of carbon atoms arranged into hollow cylinders with high length-to-diameter ratios. This “nanotube” geometry gives CNTs several unique properties and therefore widely applicable to the structural, electrical, optical, and energy fields. However, as their demand has increased over the past several decades, we must be concerned with the potential environmental impacts associated with CNT production. How to environmentally sustainable produce CNT is a huge issue facing by the CNT manufacturer. 

    STUDY

    Detailed understanding the chemical process in the CNT manufacturing is our first step. Through chemical analytical tools in our lab, we could understand the bond-building steps in nanocarbon formation. With our specially designed reactors, we can deliver trace amounts of any gas and study the role of each gas in nanocarbon formation. By correlating each intermediate concentration with the CNT properties, we can determine the most efficient and direct pathway to form CNTs. We propose that by intentionally delivering only the necessary reactants for CNT production, we can reduce the formation of the unwanted environmental pollutants, reduce the energetic costs of the CNT synthesis, and simultaneously improve the quality of the CNT.

    IMPACT

    Understanding the mechanism of CNT formation on the molecular level could lead to a CNT manufacturing market that will simultaneously improve production efficiency, CNT quality, and environmental sustainability. This successful experience could also be applied to other emerging nanomaterial productions and fabrications in future.

     

    PUBLICATIONS 

    Early Evaluation of Potential Environmental Impacts of Carbon Nanotube Synthesis by Chemical Vapor Deposition. Environ. Sci. Technol., 2009, 43(21), 8367-8373

    Multiple Alkynes React with Ethylene To Enhance Carbon Nanotube Synthesis, Suggesting a Polymerization-like Formation Mechanism. ACS Nano, 2010, 4(12), 7185-7192

  • Red-Mud Neutralization via Water Oxidation

     Details...
    This project explores the use of electricity, potentially comes from renewable sources, to speed up the neutralization of red mud using water as a reagent. 

    Aluminum is one of the most commonly used metals in our society, because of its abundance and harmless nature. Each year, almost 50,000 tonnes of aluminum orbs are mined from different sites around the globe. However, aluminum ore refining from aluminum oxide, which is the raw materials form for aluminum production, generates enormous amount of highly alkaline waste known as red-mud. Depending on the quality (amount of aluminum present) 1 ton of aluminum oxide production can generate 1 to 2.5 tonnes of red-mud waste. The current economical viable disposal strategy for red mud are either discharging them deep into the ocean or storing it in open pond sites to absorb CO2 which would slowly neutralized from the formation of carbonic acid. Neither of them is long-term nor ecologically friendly. Upon neutralization of the alkalinity, red-mud could be an excellent addictive/dopant for construction materials production or can serve as natural filters for heavy metal ions removal. As such, there is a strong initiative in developing a cost effective and rapid method to neutralize red-mud.  

    In 2013, the Anastas group reported a robust earth abundant metal water oxidation catalyst (Co-DPPE) that excels at operating in alkaline environment. The propensity of this catalyst lends itself to the red-mud neutralization objective. In the presence of an anodic polarization at a low voltage, the Co-DPPE catalyst can turn (oxidize) water into oxygen gas and hydrogen ions, which are the acid components needed for neutralizing the red mud. Current investigation focuses on the overall energetic efficiency of the system and studies on how the catalyst would function under mock conditions with lab prepared alkaline solution.

    In short, this project explores the use of electricity, potentially comes from renewable sources, to speed up the neutralization of red mud using water as a reagent. With this technology, strongly alkaline red mud waste, which are typically neutralized by storing in open pond site for years, can be turned into useful building block materials within a much shorter time frame.

  • Reclaiming Speciality and Rare Earth Metals from Electronic Waste

     Details...
    This ongoing research project focuses on building a novel technology to reclaim and separate specialty and rare earth metals from E-Waste. Our focus is on using nano-enabled materials to increase recycling efficiencies for these valuable materials.

    Electronic waste (E-Waste), also known as Waste Electrical and Electronic Equipment (WEEE), is the term used to describe end-of-life appliances that use electricity. It includes discarded items such as computers, consumer electronics (e.g., cell phones, tablets, and laptops) and kitchen appliances. Many of these advanced electronics products contain specialty metals (e.g., yttrium, osmium, and indium) and rare earth elements. As new products increasingly rely on these valuable materials, concern has risen surrounding the environmental, economic, and sociopolitical stability of the long-term supply of these metals. In addition, the consumer products we use in our everyday lives tend to have short product lifetimes (< 5 years!) and low recycling rates (< 1%!). Furthermore, some of the metals have established toxicities (e.g., CdSe or GaAs) and others have very poorly understood global cycles (e.., In and Hf). These factors compound to make metal recovery in E-Waste a critical need in the industry and for the environment.  

    We have an ongoing research project that focuses on building a novel technology to reclaim and separate these specialty and rare earth metals from E-Waste. Our focus is on using nano-enabled materials to increase recycling efficiencies for these valuable materials. In doing so, we have developed a filter apparatus using polymer amended-carbon nanotube (CNT) filters that can selectively separate two metals from a mixed metal waste stream.  

    This technology could offer several advantages including enhanced recovery of high-value specialty minerals using low-cost filters, reduced need for mining rare earth minerals in politically unstable or environmentally undesirable locations, enhanced atom economy during device fabrication, and reduced emissions of toxic elements or nascent industrial minerals that have yet unknown toxicities or environmental impacts.

     

  • Sweeteners and Other Flavor Agents Relevant to Existing and Emerging Tobacco Products

     Details...
    To support ongoing Yale TCORS research into the role flavor additives play in initiation and addiction to existing and emerging tobacco products, the overall objective of this project is to characterize and quantify the composition and quantity of key sweeteners and other flavor additives in salable chewable and dissolvable products as well as e-cigarettes.

    The Family Smoking Prevention and Tobacco Control Act banned the sale of tobacco cigarettes with added artificial and natural flavors.  However, this ban does not extend to chewable or dissolvable tobacco products or to electronic cigarettes.  Of particular concern with these emerging products is that certain flavors, sweeteners in particular, are thought to lower the threshold for adolescent tobacco use initiation and reinforcement.  It is known that these emerging products contain sweeteners and other flavor additives in addition to ground tobacco and nicotine.  However, the specific composition and quantity of these components are not well characterized making it difficult to replicate the impact of actual product formulations on behavior.

    The results of this project will guide the design and implementation of in vivo tests in mice and rats examining the effects of flavors on nicotine consumption and central reward pathways, with the overall goal of ascertaining the role of these additives in initiating and reinforcing tobacco product use, particularly relevant to susceptible users such as adolescents.

  • Advancing Sustainable Nanotechnology: Safer Carbon Nanotubes (CNTs) and CNT-Enabled Products

     Details...
    Carbon nanotubes (CNTs) are a class of nanomaterials that have the potential to significantly impact human health and the environment in both positive and negative ways. The vast number of CNT applications range from antimicrobial coatings, conductive thin films, advanced battery technology, and high strength composites. The unique properties that inspire these promising applications are also the cause of environmental and human health concern. This application-implication paradox serves as the motivation for our research, which focuses on better understanding the underlying physicochemical properties of CNTs that govern specific responses (e.g. antimicrobial and reactivity). 

    We have ongoing research projects that focus on both the molecular and product level. At the molecular level, various techniques are used to systematically modify the surface chemistry of single- (SWNT) and multi-walled (MWNT) carbon nanotubes and thus, alter their physical and chemical properties. At the product level, our work seeks to evaluate the environmental and human health impacts associated with the production and implementation of nano-enabled products. In doing so, we established a quantitative approach to evaluating upstream impact and downstream benefit tradeoffs that can be applied to emerging technologies.   

    The application of our holistic and comprehensive approach to nanomaterial and nano-enabled product systems advances the establishment of property-hazard relationships to simultaneously enhance nanomaterial functional properties and reduce the potential for unintended consequences, ultimately enabling a sustainable future for the nanotechnology industry.

  • Catalytic Transformation of Biomass

     Details...
    Development of new earth-abundant metal catalysts for selective transformation of lignin model compounds and lignocellulosic biomass.

    This project aims to selectively defunctionalize lignin while preserving aromaticity and a useful degree of complexity.  It is important to develop biomass as a renewable source of chemicals but we must strive to do so in a sustainable fashion.  Conversion of lignin from agricultural waste and energy crop residues to higher-value products has potential to produce chemicals and fuels without competing with food resources.  The fundamental catalytic chemistry has already been established for the most part using precious metals.  The price and scarcity of these metals may exclude them from practical applications in industrial-scale biomass conversion.  Our goal is to use cheaper, more abundant metals for these catalytic steps.  The chemistry of the expensive metal complexes can be used to help guide the development of cheaper metal alternatives.  The development of catalysts based on abundant metals would have important impacts beyond biomass chemistry as well.