Publications

A nickel-foam@carbon-shell with a pie-like architecture as an efficient polysulfide trap for high-energy Li-S batteries

by Luo, L; Chung, SH; Chang, CH; Manthiram, A

JOURNAL OF MATERIALS CHEMISTRY A; Volume: 5; Issue: 29; Pages: 15002-15007; DOI: 10.1039/c7ta05277d

A high-loading sulfur cathode is critical for establishing rechargeable lithium-sulfur (Li-S) batteries with the anticipated high energy density. However, its fabrication as well as realizing high electrochemical utilization and stability with high-loading sulfur cathodes is a daunting challenge. We present here a new pie-like electrode that consists of an electrocatalytic nickel-foam as a “filling” to adsorb and store polysulfide catholytes and an outer carbon shell as a “crust” for facilitating high-loading sulfur cathodes with superior electrochemical and structural stabilities. The inner electrocatalytic nickel-foam is configured to adsorb polysulfides and facilitate their redox reactions. The intertwined carbon shell assists to shield the polysulfides within the cathode region of the cell. Both the nickel-foam and the carbon shell have high conductivity and porous space, which serve simultaneously as interconnected current collectors to enhance the redox kinetics and as polysulfide reservoirs to confine the active material. The effectiveness of such a pie-like structure in improving the electrochemical efficiency enables the cathode to host an ultrahigh sulfur loading of 40 mg cm(-2) and attain a high areal capacity of over 40 mA h cm(-2) at a low electrolyte/sulfur (E/S) ratio of 7. The enhanced cyclability is reflected in a high reversible areal capacity approaching 30 mA h cm(-2) at C/5 rate after 100 cycles and excellent rate capability up to 2C rate.

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Efficient Carrier Multiplication in Colloidal Silicon Nanorods.

by Stolle CJ, Lu X, Yu Y, Schaller RD2,3, Korgel BA

Nano Lett. 2017 Aug 4. doi: 10.1021/acs.nanolett.7b02386.

Auger recombination lifetimes, absorption cross sections, and the quantum yields of carrier multiplication (CM), or multiexciton generation (MEG), were determined for solvent-dispersed silicon (Si) nanorods using transient absorption spectroscopy (TAS). Nanorods with an average diameter of 7.5 nm and aspect ratios of 6.1, 19.3, and 33.2 were examined. Colloidal Si nanocrystals of similar diameters were also studied for comparison. The nanocrystals and nanorods were passivated with organic ligands by hydrosilylation to prevent surface oxidation and limit the effects of surface trapping of photoexcited carriers. All samples used in the study exhibited relatively efficient photoluminescence. The Auger lifetimes increased with nanorod length, and the nanorods exhibited higher CM quantum yield and efficiency than the nanocrystals with a similar band gap energy Eg. Beyond a critical length, the CM quantum yield decreases. Nanorods with the aspect ratio of 19.3 had the highest CM quantum yield of 1.6 ± 0.2 at 2.9Eg, which corresponded to a multiexciton yield that was twice as high as observed for the spherical nanocrystals.

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A method to accelerate creation of plasma etch recipes using physics and Bayesian statistics

by Chopra, MJ; Verma, R; Lane, A; Willson, CG; Bonnecaze, RT

ADVANCED ETCH TECHNOLOGY FOR NANOPATTERNING VI; Book Series: Proceedings of SPIE; Volume: 10149; Article Number: UNSP 101490X; DOI: 10.1117/12.2263507

Next generation semiconductor technologies like high density memory storage require precise 2D and 3D nanopatterns. Plasma etching processes are essential to achieving the nanoscale precision required for these structures. Current plasma process development methods rely primarily on iterative trial and error or factorial design of experiment (DOE) to define the plasma process space. Here we evaluate the efficacy of the software tool Recipe Optimization for Deposition and Etching (RODEo) against standard industry methods at determining the process parameters of a high density O-2 plasma system with three case studies. In the first case study, we demonstrate that RODEo is able to predict etch rates more accurately than a regression model based on a full factorial design while using 40% fewer experiments. In the second case study, we demonstrate that RODEo performs significantly better than a full factorial DOE at identifying optimal process conditions to maximize anisotropy. In the third case study we experimentally show how RODEo maximizes etch rates while using half the experiments of a full factorial DOE method. With enhanced process predictions and more accurate maps of the process space, RODEo reduces the number of experiments required to develop and optimize plasma processes.

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Recent advances in hemophilia B therapy

by Horava, SD; Peppas, NA

Drug Delivery and Translational Research; Jun 2017; Volume: 7; Issue: 3; Pages: 359-371; DOI: 10.1007/s13346-017-0365-8

Hemophilia B is a hereditary bleeding disorder caused by the deficiency in coagulation factor IX. Understanding coagulation and the role of factor IX as well as patient population and diagnosis are all critical factors in developing treatment strategies and regimens for hemophilia B patients. Current treatment options rely on protein replacement therapy by intravenous injection, which have markedly improved patient lifespan and quality of life. However, issues with current options include lack of patient compliance due to needle-based administration, high expenses, and potential other complications (e.g., surgical procedures, inhibitor formation). As a result, these treatment options are also limited to developed countries. Recent advantages in hemophilia B treatment have focused on addressing these pain points. Emerging commercial products based on modified factor IX aimto reduce injection frequency. Exploratory research efforts have focused on novel drug delivery systems for orally administered treatment and gene therapy as a potential cure. Such alternative treatment methods are promising options for hemophilia B patients worldwide.

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Sacrificial Crystal Templated Hyaluronic Acid Hydrogels As Biomimetic 3D Tissue Scaffolds for Nerve Tissue Regeneration

by Thomas, RC; Vu, P; Modi, SP; Chung, PE; Landis, RC; Khaing, ZZ; Hardy, JG; Schmidt, CE

ACS Biomaterials Science & Engineering; Jul 2017; Volume: 3; Issue: 7; Pages: 1451-1459; DOI: 10.1021/acsbiomaterials.7b00002

Pores are key features of natural tissues and the development of tissues scaffolds with biomimetic properties (pore structures and chemical/mechanical properties) offers a route to engineer implantable biomaterials for specific niches in the body. Here we report the use of sacrificial crystals (potassium dihydrogen phosphate or urea) that act as templates to impart pores to hyaluronic acid-based hydrogels. The mechanical properties of the hydrogels were analogous to the nervous system (in the Pascal regime), and we investigated the use of the potassium dihydrogen phosphate crystal-templated hydrogels as scaffolds for neural progenitor cells (NPCs), and the use of urea crystal-templated hydrogels as scaffolds for Schwann cells. For NPCs cultured inside the porous hydrogels, assays for the expression of Nestin are inconclusive, and assays for GFAP and BIII-tubulin expression suggest that the NPCs maintain their undifferentiated phenotype more effectively than the controls (with glial fibrillary acidic protein (GFAP) and Billtubulin expression at ca. 50% relative to the chemically/mechanically equivalent not templated control hydrogels). For Schwann cells cultured within these hydrogels, assays for the expression of S100 protein or Myelin basic protein confirm the expression of both proteins, albeit at lower levels on the templated hydrogels (ca. 50%) than on the chemically/mechanically equivalent not templated control hydrogels. Such sacrificial crystal templated hydrogels represent platforms for biomimetic 3D tissue scaffolds for the nervous system.

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A Conversation with John McKetta

by McKetta, JJ Jr; Truskett, TM

Annual Review of Chemical and Biomolecular Engineering; Jun 7 2017; doi: 10.1146/annurev-chembioeng-060816-101315

John J. McKetta, Jr. is a foundational figure in chemical engineering education and energy policy in the United States. An authority on the thermodynamic properties of hydrocarbons and an energy adviser to several US presidents, McKetta helped to educate and mentor thousands of students at the University of Texas at Austin for over 40 years, many of whom became leading figures in the energy and petrochemical industries, as well as in academia. As dean of the College of Engineering, McKetta helped to establish a bioengineering program, which later became the Biomedical Engineering Department, at the University of Texas at Austin, and was a tireless advocate for excellence and a focus on the student. At age 100, McKetta recalls the challenges and opportunities he faced in childhood, his memories of the emergence of petrochemical engineering, and his views on chemical engineering education and the people it has impacted in the United States over the past 100 years.

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Charged poly(N-isopropylacrylamide) nanogels for use as differential protein receptors in a turbidimetric sensor array

by Culver, HR; Sharma, I; Wechsler, ME; Anslyn, EV; Peppas, NA

The Analyst; Jul 26 2017; doi: 10.1039/c7an00787f

Due to the high cost and environmental instability of antibodies, there is precedent for developing synthetic molecular recognition agents for use in diagnostic sensors. While these materials typically have lower specificity than antibodies, their cross-reactivity makes them excellent candidates for use in differential sensing routines. In the current work, we design a set of charge-containing poly(N-isopropylacrylamide) (PNIPAM) nanogels for use as differential protein receptors in a turbidimetric sensor array. Specifically, NIPAM was copolymerized with methacrylic acid and modified via carbodiimide coupling to introduce sulfate, guanidinium, secondary amine, or primary amine groups. Modification of the ionizable groups in the network changed the physicochemical and protein binding properties of the nanogels. For high affinity protein-polymer interactions, turbidity of the nanogel solution increased, while for low affinity interactions minimal change in turbidity was observed. Thus, relative turbidity was used as input for multivariate analysis. Turbidimetric assays were performed in two buffers of different pH (i.e., 7.4 and 5.5), but comparable ionic strength, in order to improve differentiation. Using both buffers, it was possible to achieve 100% classification accuracy of eleven model protein biomarkers with as few as two of the nanogel receptors. Additionally, it was possible to detect changes in lysozyme concentration in a simulated tear fluid using the turbidimetric sensor array.

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Simulation of magnetite nanoparticle mobility in a heterogeneous flow cell

by Lyon-Marion, BA; Becker, MD; Kmetz, AA; Foster, E; Johnston, KP; Abriola, LM; Pennell, KD

Jounral of Enviornmental Science-Nano; Jul 1 2017; Volume: 4; Issue: 7; Pages: 1512-1524;  DOI: 10.1039/c7en00152e

Engineered nanomaterials have been proposed for a range of subsurface applications including groundwater remediation, treatment of contaminated soils, and characterization of flow. The ability to accurately predict nanoparticle (NP) mobility in the environment is critical for assessing NP performance and designing subsurface applications. The objective of this study was to evaluate the ability of a numerical simulator that accounts for the influence of varying electrolyte and NP concentrations to predict experimental observations of polymer-coated magnetite nanoparticle (nMag) transport and retention in a heterogeneous, multi-dimensional flow cell (0.64 m length x 0.38 m height x 1.4 cm internal thickness, referred to as “2.5-dimensional” or “2.5D” due to the internal thickness width). A series of column experiments was performed to independently determine model input parameters, including the maximum NP retention capacity and attachment rate. Localized injection of nMag into the heterogeneous flow cell demonstrated preferential flow around a lower permeability lens and the downward migration of higher density nMag suspensions. Numerical simulations successfully captured the observed flow path of the nMag pulse injections, and provided close fits to spatially distributed aqueous and solid-phase nMag measurements obtained within the heterogeneous flow field. Experimental and modeling results demonstrated that relatively small contrasts in fluid density (e.g., 0.01 g mL(-1)) can result in flow instabilities and downward migration of nMag. This work provides the first direct comparison between model simulations and experimental observations of NP transport and retention in a 2.5D heterogeneous flow domain and demonstrates the importance of accounting for relevant physical and chemical properties in order to accurately describe NP fate and transport.

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Enabling tools for high-throughput detection of metabolites: Metabolic engineering and directed evolution applications.

by Lin, JL; Wagner, JM; Alper, HS

Journal of Biotechnology Advances; Jul 16 2017; doi: 10.1016/j.biotechadv.2017.07.005

Within the Design-Build-Test Cycle for strain engineering, rapid product detection and selection strategies remain challenging and limit overall throughput. Here we summarize a wide variety of modalities that transduce chemical concentrations into easily measured absorbance, luminescence, and fluorescence signals. Specifically, we cover protein-based biosensors (including transcription factors), nucleic acid-based biosensors, coupled enzyme reactions, bioorthogonal chemistry, and fluorescent and chromogenic dyes and substrates as modalities for detection. We focus on the use of these methods for strain engineering and enzyme discovery and conclude with remarks on the current and future state of biosensor development for application in the metabolic engineering field.

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Fundamental Understanding of CO2 Capture and Regeneration in Aqueous Amines from First-Principles Studies: Recent Progress and Remaining Challenges

by Stowe, HM; Hwang, GS

Industrial & Engineering Chemistry Research; Jun 21 2017; Volume: 56; Issue: 24; Pages: 6887-6899; DOI: 10.1021/acs.iecr.7b00213

Aqueous amine-based chemical scrubbing has been considered the most promising near-term solution for CO2 capture from flue gas. However, its widespread implementation is hindered by the high cost associated with the parasitic energy consumption during solvent regeneration, along with degradation and corrosion problems. Computer simulations have been widely used to improve our fundamental understanding of CO2 absorption materials and processes in efforts to design and develop high-performance, cost-effective solvents. Here, we review recent progress in first-principles studies on molecular mechanisms underlying CO2 absorption into aqueous amines and solvent regeneration. We also briefly discuss aspects that remain unclear, such as degradation and corrosion mechanisms, and the reaction-diffusion behavior of CO2 at the solvent/gas interface. This review highlights the increasingly significant role of first-principles-based atomistic modeling in exploring the function and properties of candidate materials, as well as the complex physicochemical phenomena underlying CO2 capture, solvent degradation, and corrosion, especially when direct experimental characterization at the atomic level may be difficult.

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