Resnick Fellows Fall 2019 Seminar Day Date, Time and Venue TBA
Join us for sustainability science research talks presented by Resnick Graduate and Postdoctoral Fellows! All are invited to attend!
Join us for sustainability science research talks presented by Resnick Graduate and Postdoctoral Fellows! All are invited to attend!
The development of battery technologies independent of Li is necessary to increase sustainability, safety, and performance. Divalent cations such as Mg
Towards this goal, we present the discovery of divalent Zn
The cation conduction is enabled by the chemically soft nature of the P2S6
Natural gas (methane) is a promising clean energy source which can be used to lower Green House Gas emissions and the production of natural gas in the US has increased rapidly in recent years. Methane, however, is itself a source of Green House Gas emissions, and its heating effect is orders of magnitude higher than carbon dioxide. Therefore, the methane leak in the production, transportation and storage of natural gas imposes a strong limitation on its use as a clean energy source.
We propose to monitor and control methane leaking using mid-infrared optical frequency combs. In this frequency comb, an array of equidistantly spaced spectral lines, can be generated using on-chip silica microresonators. Compared to traditional methane detection methods such mass spectrometry, this comb source is compact, cost-effective, sensitive and has the potential of mass production.
Starting from a comb at 1.55 micron, we generated the 3.3 micron frequency comb using difference frequency comb generation. Further development of dual-comb source will also be discussed.
Solar disinfection of drinking water (SODIS) is an approach for water treatment widely used in households without access to fresh water. SODIS is a cheap and straightforward method for water treatment, but it is also time-consuming and often requires up to 48 hours to disinfect water. Photocatalytic materials, such as titanium dioxide (titania, TiO2), can harvest sunlight to promote generation of reactive oxygen species (ROS) that damage and deactivate waterborne pathogens.
In laboratory and pilot plant settings, the use of photocatalysts in the form of nanoparticle suspensions reduces the water treatment time to only a few hours. In a household environment, the need to recover the nanoparticles using complex filtering procedures makes this process expensive and impractical. Household use of a photocatalytic reactor requires a high surface-area, strong, self-supported photocatalyst with deterministic 3D architecture that allows for light delivery inside the bulk of the photocatalyst.
To study the effect of 3D architecture on the photocatalytic performance and to fabricate architected photocatalysts, we have developed an additive manufacturing (AM) process for TiO2. We synthesize pre-ceramic photoresists using hybrid organic-inorganic materials, pattern them using a stereolithography apparatus, and pyrolyze to remove the organic content. The resulting structure is comprised of >99wt% rutile TiO2, as confirmed by spectroscopic measurements and transmission electron microscopy. The proposed titania AM process can be used to create safe and efficient photocatalytic reactors for household water disinfection.
Ammonia and water oxidation are of potential interest for renewable energy conversion technologies, but further understanding is necessary to perform these reactions in a controlled, sustainable, and cost-effective manner. Terminal M≡E species have been invoked in oxidatively-induced E-E coupling chemistries, including for E = O and N. Spin leakage onto E is thought to be an important determinant for the reactivity of such species. However, the impact of the triply-bonded element on the extent of spin leakage and E-E coupling is poorly understood.
To examine this question, we targeted a series of Mo≡E compounds (E = P, N, C) supported by a terphenyl diphosphine ligand, in which the identity of the triply-bonded element is varied, but the metal center and ligand scaffold remain unperturbed. The propensity of the respective compounds to undergo E-E coupling is discussed, and correlated to the extent of spin delocalization on E, as determined via pulse electron paramagnetic resonance spectroscopy.
Power grids are among the most complex and critical networks in modern-day society. The increasing adoption of renewable energy sources, such as solar panels and wind turbines, introduces massive amounts of uncertainty to power grids. Current grids are not equipped to cope with this huge variability in power supply and become correspondingly more vulnerable to contingencies and blackouts. A more sustainable fossil-free yet reliable energy system requires new paradigms that go beyond current worst-case scenario analyses and fully account for this uncertainty.
I will give an overview of my current research, which aims to develop new mathematical tools to get novel insight in the delicate trade-off between power grids reliability, efficiency, and sustainability in the presence of renewables. Rare stochastic fluctuations of the power injections, amplified by correlations and network effects, can cause line failures, frequency violations, power losses and ultimately blackouts. I will outline how the likelihood of these contingencies can be calculated and how the corresponding network vulnerabilities can be identified, by means of both analytical methods and simulation tools.
Methane is the second most important anthropogenic greenhouse gas in the Earth's climate system, but emission quantification of localized point sources, such as those from oil and gas facilities or pipe leakages is challenging. This results in ambiguous regional budgets and source category distributions.
Recent advancements in airborne remote sensing instruments enable retrievals of methane enhancements at unprecedented resolution of 1-5 m at regional scales. This provides unprecedented mappings of methane emissions over large geographical areas.
In this talk, I will show current research developments in methane point source geolocation and quantification by an airborne remote sensing instrument, namely the next generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG).
The use of Large Eddy Simulation to study the plume structure under a range of background wind speeds and source emission rates will be emphasized. I will present our results that demonstrate the ability to invert source flux rate to a significantly improved accuracy based solely on the column methane retrievals and the plume shape, without the need of any ground measurements, such as local wind speeds.
Cascading failures in power systems exhibit non-local propagation patterns that make the analysis and mitigation of failures difficult. The increasing penetration of renewable energies brings increasing levels of flow fluctuations to the grid, while reducing the system inertia against perturbations at the same time, making the robust operation of power grids even more challenging.
In this work, we propose a distributed control framework inspired by the recently proposed concepts of unified controller and network tree-partition that offers strong guarantees in both the mitigation and localization of cascading failures in power systems.
In this framework, the transmission network is partitioned into several control areas, which are connected in a tree structure, and the unified controller is adopted by generators or controllable loads for fast timescale disturbance response.
Simulation results show that our novel framework greatly improves the system robustness, and localizes the impact of initial failures in the majority of the load profiles that are examined. Moreover, the proposed framework incurs significantly less load loss, if any, compared to current practice, in all of our case studies.
Biological molecules like amino acids, sugars, and other building blocks of nature exist with a specific chirality that is only left- or right-handed. Medicines often have different effects depending on their handedness, which means that it is essential to synthesize these molecules in single-enantiomer form. One of biggest challenges facing synthetic chemists is how to make molecules in only one isomer, while using abundant, inexpensive resources.
We have developed new reactions for making molecules with specific chirality in only one of their handed forms using earth-abundant nickel rather than precious metals as catalysts. Those catalytic reactions can be run under mild reaction conditions, with very good functional-group compatibility to produce high-value chemical feedstocks. In particular, we are able to control the handedness not only at one carbon, but also at two sites within one molecule, which provides more flexibility for drug developers to use our method for making candidate drugs.
Photovoltaics (PVs) offer a promising path to renewable energy generation. The successful development of PV technology involves careful optimization of various aspects, ranging from materials search, device design, to power grid integration. Theoretical or computational device modeling serves as an essential tool for better understanding of important working principles and provides a more systematic approach to device design and optimization. However, existing models are often limited, if not rife with spurious assumptions. The key challenge lies in the different spatial and temporal scales of the multiple processes involved, especially in complex materials.
Recently, the discovery of above-bandgap photovoltage across thin-films of multi-domain ferroelectric perovskites has revitalized the field of photoferroics. This talk focuses on the development of a thermodynamically consistent device model that incorporates light illumination for ferroelectric perovskites. This model offers insights into the ferroelectric-domain-wall-assisted PV mechanism, which is separate from the conventional PV effect in semiconductors. It also provides a framework for future engineering of novel opto-electronic and nano devices.
Two-dimensional van der Waals materials have shown great promise in ultra-light optoelectronic applications, such as solar cells and efficient LEDs. Among them, transition metal dichalcogenides (TMDCs) and two-dimensional organic-inorganic hybrid lead halide perovskites (2DPVSKs) suffer from low photo emission quantum yield and low stability of emission in ambient atmosphere respectively, which largely limits their practical applications.
In this study, we explore heterostructures of these materials as a solution to these problems, with semiconducting double layers of transition metal dichalcogenides built via exfoliation and dry viscoelastic stamping. We observed over a 700 fold enhancement of the trion emission peak of bilayer WS2 photoluminescence in such a heterostructure. The giant photoluminescence increase in the bilayer WS2 is attributed to charge transfer from the 2D PVSK. Emission enhancement in WS2 by the 2D PVSK shows the promise of making heterostructures such as these, and may provoke further studies of van der Waals heterostructures leading to energy-efficient and lower-cost optoelectronic devices.
Most energy requirements of modern life can be fulfilled by renewable energy sources, but it is impossible in the near future to provide an alternative energy source to replace combustion in airplanes. Combustion in aviation can be made sustainable by introducing alternative jet fuels, which can be synthesized from renewable sources like agricultural wastes, solid wastes, oils, and sugars. These alternative fuels can be used in commercial flights only after a long and rigorous certification procedure by the Federal Aviation Agency (FAA) and ASTM International.
This research aims to expedite the certification process for quicker testing of alternative fuels, by predicting the turbulent flame behavior of fuels from laminar combustion. The goal is to identify a small subset of the laminar flame parameters of the fuel that affect turbulent combustion. Multiple Direct Numerical Simulations (DNS) for the turbulent combustion of different fuels are performed, over a wide range of chemistry and turbulence properties. The laminar flame properties that collapse the data would be identified, and the proposed certification procedure would test only for these significant parameters of the new alternative fuels, thereby making it more efficient and economical.
The rhizosphere contains several species of biocontrol bacteria that produce phenazines, toxic molecules which help keep phytopathogenic fungi at bay. However, there are biocontrol strains of fungi which are also susceptible to phenazine assault and must live directly next to phenazine producers.
We have isolated a plant-promoting biocontrol fungus, Aspergillus ustus, that was found with an adherent bacterial partner, Paraburkholderia S0S3. P. SOS3 is able to detoxify and sequester phenazines, including the environmentally relevant phenazine-1-carboxylic acid (PCA). Intriguingly, P. SOS3 only does so in the presence of A. ustus, allowing the fungus to grow even in the presence of phenazines and phenazine-producing bacteria. This appears to be accomplished by a structural rearrangement of P. SOS3.
In the absence of PCA, P. SOS3 is dispersed throughout the fungal colony. However, in the presence of PCA this bacterium forms spheres within the fungal colony that appear to reduce and sequester PCA, permitting A. ustus growth. This behavior appears to be species-specific as other biocontrol bacteria cannot effectively protect A. ustus.
Given that the relative abundance of phenazine producers in the soil rises with temperature, understanding how biocontrol fungi interact with partnered bacteria to withstand these kinds of stresses is important to the future of agriculture in a warmer climate.
Lithium ion batteries, with their outstanding energy and power density, play a critical role in energy storage in areas from portable electronics to electrical vehicles. Lithium ion batteries with solid-state electrolytes present a safer and more reliable alternative to traditional organic liquid electrolytes, which are flammable. The formation of lithium dendrites, which is a major challenge in lithium ion battery design, is still observed in solid state oxide electrolytes despite their high strength. Structural imperfections, such as the grain boundaries and interconnected pores, serve as pathways for lithium dendrite formation, which leads to short-circuit formation in the battery.
The focus of this work is to develop an electrolyte with minimal imperfections for reliable all-solid-state batteries by use of an oligocrystal design. The processing-structure relationship is systematically explored, and a highly dense (> 99%) electrolyte with grain sizes > 200 m is obtained. This combination of large grain size with no interconnected pores could significantly suppress the nucleation and propagation of lithium dendrites, and enhance the mechanical and electrochemical reliability of the all-solid-state batteries.
Technologies to produce useful chemicals from renewable energy (photoelectrochemical cells/artificial photosynthesis) rely on efficient conversion of water to dioxygen to serve as a source of protons and electrons. One aspect of improving these systems is to design and synthesize highly active water oxidation catalysts that are composed of earth-abundant elements.
In photosynthesis, water oxidation is performed by a transition metal cluster known as the oxygen-evolving complex (OEC). It is an attractive template for man-made water oxidation since it is one of the most active catalysts for this reaction while being composed of abundant elements (calcium, manganese, and oxygen). However, the high complexity of photosynthetic machinery makes it challenging to elucidate the mechanism of water oxidation by OEC.
Small molecule clusters related to the biological catalyst have been synthesized to examine the influence of neighboring transition metals on the ability of a manganese center to bind and activate water. These synthetic clusters are able to stabilize species related to key intermediates proposed in the OEC mechanism, including manganese–aquo, –hydroxide, and metal–oxo moieties.
Green chemistry, also referred to as sustainable chemistry, is an area of chemistry and chemical engineering focused on designing both products and processes that minimize the generation and use of hazardous substances. As scientists, how do we start applying the elegant 12 principles of Green Chemistry in our everyday work? I will share how Amgen embedded a green culture at an early stage of our development process that had real downstream effects on the chemical engineers tasked with manufacturing these new pharmaceuticals. I will highlight numerous synthetic examples, and then share why the importance of an internal Green Chemistry Award highlights the shared goal of reducing environment impacts.
This event is jointly sponsored by Chemical Engineering and the Resnick Sustainability Institute.
Ligand design is imperative to the formulation of new catalysts, molecules that serve to accelerate chemical reactions, without themselves being consumed – a cornerstone of the green chemistry movement. As part of our group’s ongoing efforts into the catalytic reduction of robust small-molecules (e.g., N2, CO, CO2 etc.) for access to high-value chemical feedstocks, we have stressed judicious ligand choice as key to achieving selective and sustainable reactivity.
This presentation will focus on the design, synthesis, characterization, and ensuing coordination chemistry of two new ligand scaffolds (with an eye toward application in small-molecule activation). First, the reactivity of a diphosphinoborane with nickel and platinum precursors will be highlighted, generating eta(3)-P,B,P complexes - the first examples of P,B,P-based allyl analogues. Secondly, the 9-phosphatriptycene-10-borate anion will be introduced. A fusion of two ubiquitous organometallic reagents, triphenylphosphine and tetraphenylborate, the synthesis, characterization, and coordination behavior of this species with iron and cobalt will be provided.
Small molecules – such as N2, H2 and CO2 – are key players in a sustainable economy, acting as feedstocks and fuels. Due to their inert nature, catalytic conversion of these molecules is critical, and transition metal complexes have proven effective for this task. However, designing effective catalysts is difficult: small molecule transformations involve many redox steps, proton transfers, and fleeting intermediates. Due to these challenges, theory is critical for elucidating and characterizing catalytic mechanisms. However, Density Functional Theory (DFT) — the workhorse computational method for describing the structure and reactivity of molecules — can be inaccurate for transition metal complex catalysts.
Projection-based embedding offers a simple framework for achieving the higher accuracy of wavefunction theories at a low cost comparable to that of DFT. In this talk, we apply projection-based embedding to a Co-centered CO2-to-CO reduction catalyst. We examine the key step of CO2 binding to the complex and determine the role of intramolecular hydrogen bonds in stabilizing bound CO2. Contrary to proposed mechanisms for similar complexes, we demonstrate that intramolecular hydrogen bonding is unfavorable and does not play a role in the catalysis.
Photoelectrochemical (PEC) solar fuel generation, including water splitting and CO2 reduction, represents a promising scheme for large-scale renewable energy production. Our desired PEC systems integrate semiconducting light-absorbers with electro-catalytic materials allowing for direct and efficient solar-to-fuel conversion. Unfortunately, many state-of-art semiconductors suffer from serious material corrosion and are not considered structurally robust when immersed in aqueous electrolytes, despite their superior photovoltaic performance.
Herein, starting from Ⅲ-Ⅴ semiconductors, we probe corrosion chemistry at the electrode/electrolyte interface under different pH/potential conditions. Thus, the regions where the chemical, electrochemical and photoelectrochemical corrosion occur are identified. Furthermore, both the detailed corrosion pathway and quantitative corrosion kinetics are comprehensively evaluated and measured. Equipped with this understanding, common principles may be devised to minimize/protect the semiconductor surface from rapid corrosion and enable construction of stable PEC devices for sustainable solar fuel production.
The twenty standard proteinogenic, or protein creating amino acids grant access to a myriad of chemistries that harmonize to give rise to life. If nature can make such wondrous things with only these limited building blocks, new tools should allow us to accomplish even more. Indeed, expanding the protein code beyond the standard amino acids to include non-canonical amino acids (ncAAs) has unveiled pharmaceutical intermediates, biological probes, and natural products. Yet despite their obvious utility, synthesis of ncAAs remains challenging as strict chirality, multiple reactive functional groups, and poor yields stymie effective routes.
Biocatalysis has emerged as a versatile method to overcome these challenges by supplanting nature’s existing machinery to synthesize ncAAs. In conjunction with directed evolution, biocatalysis allows us to access an expanded amino acid alphabet using simple, green chemistries that are accessible to researchers from a broad array of backgrounds and means. My research aims to evolve useful biocatalysts to expand nature’s toolbox, providing a simple and environmentally benign platform for preparation of new tryptophan analogs.
Water is a precious commodity, especially in the state of California. Our state frequently experiences cycles of major state-wide precipitation deficits – most notably the 2012–2015 drought which was the worst to occur in the past 1200 years.
The focus of this work is to develop a state-wide model of the California reservoir network to address the following scientific questions: 1) What are the dependencies among reservoirs? 2) Are there unmodeled phenomena (denoted as latent variables) that are influencing the network globally -And could these latent variables cause a system-wide catastrophe (e.g. exhaustion of multiple large reservoirs)?
For the first time, we developed a statistical model of the California reservoir network that address these questions. Using this model we can obtain a clearer picture of the demands placed on reservoirs during drought, and propose guidelines for policies that can lead to more sustainable water resources.
Land loss on river deltas is dictated by the rates of sea level rise, land subsidence, and sediment deposition. Existing models are based on sustainability of the entire delta; however, land loss can vary spatially because river avulsions periodically and abruptly shift the river course changing the distribution of sediment.
We present new theory and scaled physical experiments demonstrating that the extent of land loss is set by a competition between the avulsion frequency of active distributary channels and the rate of retreat on sediment-starved coastlines.
Results indicate that avulsions occur more frequently under more rapid rates of sea-level rise and land subsidence. More frequent avulsions, in turn leads to reduced durations of lobe abandonment and more even distributions of sediment. Thus, although rates of land loss are greater on average for deltas undergoing higher rates of sea-level rise, the local extremes are muted, resulting in transiently reduced rates of land loss.
Application of our theory to published field data suggests that sustaining modern delta area through the century will require more sediment than previously estimated.
This talk addresses two questions: (1) How Southern California urban water users can achieve sustainability in groundwater basins; and (2) How will agricultural water users in the Central Valley adjust to a sustainable regime of groundwater pumping.
The first part of the talk will discuss the effectiveness of adjudication, a legal settlement among groundwater pumpers, in managing groundwater basins in Southern California. As a form of self-governance, adjudication generally leads to higher water levels in the adjudicated basins. Counter-intuitively however, there is a problem with dynamic efficiency because when compared to competitive pumpers, pumpers in adjudicated basins actually have less efficient extraction patterns in response to surface water availability.
The second part of the talk will discuss the response of the agricultural community to water supply changes in the Central Valley. We explore how reallocation of water through water markets may lead to greater efficiency.
Society relies on organic chemistry to make game-changing molecules for modern life, including high-performance materials, crop-boosting agrochemicals, and life-saving pharmaceuticals. All of these products are essential for life in the 21st century, but the ways we manufacture them are often not sustainable nor environmentally-conscious. Further, there are many remaining grand challenges that can be solved by inventing new molecules, though methods for making them do not yet exist. We need fundamentally better chemical tools to let us make new and old molecules more efficiently, sustainably, and environmentally-consciously.
Our research focuses on developing new tools, catalysts, for making molecules better. We take inspiration from nature in our designs, seeking to use sustainable and abundant solar electricity to drive our reactions just as plants use photosynthetic chemical potential to drive theirs. Our catalytic reactions enable efficient and environmentally-conscious ways to make old molecules and will be useful for inventing new ones.