Nanoscale metal oxides for removing inorganic contaminants

Regulations on inorganic aqueous contaminants are becoming increasingly strict as research brings to light the negative impact of these contaminants on human health and the environment. Inorganic contaminants enter the environment from anthropogenic sources such as mining and industrial waste. The goal of our research is to develop a treatment process that both removes these inorganic contaminants while minimizing negative externalities associated with the process.

We are examining metal oxide nanoparticles, particularly iron oxides, as a possible treatment technology for these contaminants. The metal oxide nanoparticles are able to change the form of the contaminant for easier removal as well as remove the contaminant from solution. Furthermore, we are in the process of isolating and synthesizing iron oxide nanoparticles from mine waste, thereby closing industrial loops and turning mine waste into a value-added product.

Funding: [1] National Science Foundations, Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment Systems, 2020-2025; [2] Superfund Research Center, Metals and Metals Mixtures: Cognitive Aging, Remediation, and Exposure Sources (MEMCARE), 2020-2025

Sustainable remediation using nanopowder metal oxide-impregnated chitosan beads

The depletion of natural resources and the damage being done to the environment as a result of increased demand for these resources has been felt over the past several decades. Our focus is on the development and implementation of a universal and sustainable heavy metal remediation technology to offset the risks posed by wastewater runoff from anthropogenic practices.

While many technologies for specific metal remediation already exist, there is no single technology that addresses a large variety of related contaminants. Current efficient removal technologies have the drawback of being highly specific, and this lack of universality results in a difficult and unsustainable use-phase as wastewater is often contaminated with many metals.

This project seeks to develop a nanopowder metal oxide-impregnated chitosan bead (MICB) adsorbent to be used for sustainable removal of arsenic and selenium from solution. Chitosan, a waste product from shellfish, also adsorbs metals like mercury, copper, and cadmium which often coexist with arsenic and selenium. The current work attempts to increase the selectivity of MICB adsorbent in highly complex environments, which are commonly seen in wastewater runoffs.

Funding: [1] National Science Foundations, Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment Systems (NEWT), 2020-2025; [2] Superfund Research Center, Metals and Metals Mixtures: Cognitive Aging, Remediation, and Exposure Sources (MEMCARE), 2020-2025

Utilizing supercritical fluids (SCFs) as green solvents for biodiesel and nanoparticle synthesis applications

SCFs for Nanotechnology

To advance sustainable nanotechnology, green synthesis methods that can produce a variety of high-quality nanoparticles are vital. Supercritical fluid synthesis is a promising green synthesis method since it not only can finely control nanoparticle features such as composition, size, shape, and surface features for many different nanoparticle compositions, but, in addition, it utilizes a greener synthetic route than alternatives through the employment of green solvents such as water, ethanol, and carbon dioxide. Supercritical fluid synthesis controls nanoparticle features by utilizing the unique properties associated with solvents in their supercritical state, when a solvent is at a temperature and pressure above its critical point. From this state to the subcritical state, properties such as density, dielectric constant, and solubilizing capacity, among others, change drastically and allow for conditions to control size, shape, and/or surface of nanoparticles. The solvent state and these properties are easily adjusted through changes in temperature and pressure allowing the supercritical fluid synthesis in-situ crystallization to be tuned to yield desired nanoparticle features. This work investigates the effect of untested process conditions on nanoparticle features with the goal of composition, size, shape, and surface control. 

SCFs for an Integrated Biorefinery

An alternative and sustainable method for bio-oil conversion to biodiesel for a sustainable liquid fuel source is the use of heterogeneous catalysts and supercritical carbon dioxide process. Unlike homogeneous catalysts which contaminate biodiesel product and need costly downstream processing, the heterogeneous catalysts can be easily recovered from the product, used in a fixed bed for continuous operation process, and can be reused. Use of supercritical carbon dioxide as a solvent is advantageous because it is inherently green and has the potential for selective conversion of triglycerides in the oil. Applying this process to different bio-oils gives insight into the overall conversion of fatty acid chains and selectivity. Carbon dioxide’s potential for selective conversion can help transform conventional biodiesel plants to integrated biorefineries that utilize all fractions of biomass and have the ability produce high value products from the unconverted triglycerides such as chemical products, polymers, pharmaceuticals, etc., along with biofuels, benefitting the biofuel industry both economically and environmentally.

Funding: National Science Foundations, Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment Systems (NEWT), 2020-2025; 

Enabling the Integrated Biorefinery

There is an increasing demand to produce energy and materials from renewable resources.  Full utilization of biomass feedstocks, analogous to petroleum refining, is critical to reduce economic and environmental barriers to large-scale fuel production.  To advance this goal and the implementation of the integrated biorefinery, Zimmerman’s group has made novel and significant contributions to the fundamental chemistry and underlying process engineering to produce value-added chemicals from biomass as well as assessment of environmental benefits and impacts.  We have focused on surfactants as a chemical class, assessing renewable feedstocks, developing the novel, patented class of c-glycosides, and established green transformations for their production.

Further, for the last several years, Zimmerman’s group has been developing new approaches for microalgal feedstocks for the production of fuels and chemicals.   Our group has uniquely combined empirical and life cycle data to suggest optimal applications of biobased feedstocks and process train selection considering resource and energy inputs as well as biomolecular composition.  We have demonstrated the viability of supercritical carbon dioxide as an extraction solvent for wet biomass meeting or exceeding the performance of organic solvents while providing increased selectivity, decreased hazards, and minimized downstream processing.  Expanding on these findings, a selective, efficient, one-pot separation technology for the extraction and transesterification of lipids from crude biomass for fuel as well as higher value applications has been demonstrated. This novel system relies on thermodynamically favorable phase behavior in a low temperature, moderate pressure carbon dioxide-expanded methanol system.

Funding: National Science Foundation: Collaborative Research: SusChem: Enabling the Biorefinery: Isolation, Fractionation, and Transformation of Bio-based Feedstocks into Fuels and Chemical Products.

Advancing Sustainable Nanotechnology: Safter CNTs and CNT Enabled Products

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).

Ongoing research projects 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.

Funding: National Science Foundations, Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment Systems (NEWT), 2020-2025

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

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.

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.

Funding: Yale Tobacco Center of Regulatory Science, NIH Grant, 2015-2023.
Anesthetic and synthetic cooling flabors in e-cigarettes: chemistry, respiratory effects and behavioral pharmacology, NIH Grant, total budget $502,500, 2018-2021.


Modeling large-scale copper recycling to support transition to sustainable economy

Economic growth and low carbon economy exaggerate the growth of copper demand in economic activities like vehicle electrification and renewable energy generation. Besides, copper production is associated with significant energy consumption and environmental impact. Although copper flow analysis and future copper demand in economy has been extensively studied in literature, little research focuses on various copper-bearing scrap types and the long-term energy consumption and environmental impact associated with copper recycling. Large-scale metal recycling needs full consideration of technology and economic factors to put forward strategies on the micro and the macro levels, which have yet to be studied.

The overall objective of this work is to show the detailed copper flows in economy considering various types of copper scrap and to assess the effect of improvement in large-scale copper recycling on global energy consumption and environmental impacts. Industrial ecology tools like material flow analysis (MFA) and life cycle assessment (LCA) will be utilized. A systems model analyzing life-cycle impact of recycling technologies is being built. This work then assesses future copper demand to meet human basic needs and long-term energy consumption and environmental impact. Building on the above components, this project will generate optimized recycling solutions for decision maker in terms of improving material efficiency and reducing environmental impact without compromising human welfare.

Water Withdrawal and Water-Use Efficiency in the U.S

As one of the 17 United Nations Sustainable Development Goals (SDGs), “clean water and sanitation (SDG 6)” has strong linkages with all other SDGs in many ways, both scientifically and culturally/societally. An aspirational target of it deals with water scarcity, aiming to ensure that there is sufficient water for the global population, economy and environment by increasing water-use efficiency across socioeconomic sectors. Two indicators have been defined to track progress for this target: the change in water-use efficiency over time, and the level of water stress. Such information would allow researchers and policymakers to assess to which extent the economic growth depends on the use of water resources and to keep track of the physical availability of water resources within specific geopolitical regions. Although global water-use efficiency data is made available by the U.N.., currently, there is lack of research on the time-series WUE across sectors within the United States, at both state and county levels. 
The overall objectives of this project involve collecting and processing water withdrawal, water use and associated economic data, as well as evaluating the changes in national and regional WUE within the U.S. between the years of 1980 and 2015. Specifically, WUE in the agriculture, the mining and manufacturing, and the service sectors will be compared and analyzed. Water scarcity is also expected to be incorporated to assess local water stress.