Publications

Protonated Oxide, Nitrided, and Reoxidized K2La2Ti3O10 Crystals: Visible-Light-Induced Photocatalytic Water Oxidation and Fabrication of Their Nanosheets

by Kawashima, K; Hojamberdiev, M; Wagata, H; Yubuta, K; Domen, K; Teshima, K

ACS Sustainable Chemistry & Engineering; JAN 2017; Volume: 5; Pages: 232-240; DOI: 10.1021/acssuschemeng.6b01344

Protonated lanthanum titanium oxide H2La2Ti3O10 and oxynitride H2La2Ti3O10-3/2x,N-x crystals were synthesized from the oxide, nitrided, and remddized layered K2La2Ti3O10 crystals prepared by solid-state reaction through proton exchange. Here, we investigated the holding time of nitridation of oxide K2La2Ti3O10 crystals influencing their crystal structure, shape, and absorption wavelength and band gap energy. The XRD and SEM results confirmed that the crystal structure and plate-like shape of the parent oxide were maintained after nitridation at 800 degrees C for 10 h, and the color of crystals was changed from white to dark green. However, no clear absorption edges were observed in the UV vis diffuse reflectance spectra of the nitrided crystals due mainly to the reduced titanium species (TO.), which act as the recombination center of the photogenerated charge carriers. To decrease the amount of the reduced titanium species, the nitrided crystals were further rewddized at 400 degrees C for 6 h. After partial reoxidation, the absorption intensity in the longer wavelength region was reduced, and the absorption edges appeared at about 449-460 nm. The photocatalytic activity for the water oxidation half reaction was evaluated only for the protonated samples. The protonated reoxidized K2La2Ti3O10 crystals showed the O-2 evolution rate of 180 nmol.h(-1) (for the photocatalytic water oxidation) under visible-light irradiation, and the unexpected photocatalytic decomposition of N2O adsorbed onto the photocatalyst surfaces was observed for the protonated oxide and protonated nitrided layered K2La2Ti3O10 crystals. Furthermore, lanthanum titanium oxide [La2Ti3O10](2-) and oxynitride [La2Ti3O10-3/2xN](2-) nanosheets were successfully fabricated by proton exchange and mechanical exfoliation (sonication) of the oxide, nitrided, and rewddized K2La2Ti3O10 crystals. The TEM results revealed that the lateral sizes of the fabricated nanosheets grown along the (001) direction are 270-620 nm. Apparently, the colloidal suspensions of the fabricated nanosheets showed a Tyndall effect, implying their good dispersion and stability for several weeks in water.

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A Hybrid Chemo-/Grapho-Epitaxial Alignment Strategy for Defect Reduction in Sub-10 nm Directed Self-Assembly of Silicon Containing Block Copolymers

by Blachut, G; Sirard, SM; Maher, MJ; Asano Y; Someya, Y; Lane, AP; Durand, WJ; Bates, CM; Dinhobl, AM; Gronheid, R; Hymes, D; Ellison, CJ; Wilson, CG

Chemistry of Materials; DEC 27 2016; Volume: 28; Pages: 8951-8961; DOI: 10.1021/acs.chemmater.6b03633

The directed self-assembly (DSA) of a 20 nm full-pitch silicon-containing block copolymer (BCP), poly(4-methoxystyrene-b-4-trimethylsilylstyrene), was performed using a process that produces shallow topography for hybrid chemo-/grapho-epitaxy. This hybrid process produced DSA with fewer defects than the analogous conventional chemo-epitaxial process, and the resulting DSA was also more tolerant of variations in process parameters. Cross-sectional scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) confirmed that BCP features spanned the entire film thickness on hybrid process wafers. Both processes were implemented on 300 mm wafers initially prepatterned by 193 nm immersion lithography, which is necessary for economic viability in high-volume manufacturing. Computational analysis of DSA extracted from top-down SEM images demonstrates the influence of process parameters on DSA, facilitating the optimization of guide stripe width, guide stripe pitch, and prepattern surface energy. This work demonstrates the ability of a hybrid process to improve the DSA quality over a conventional chemo-epitaxial process and the potential for high volume manufacturing with high-x, silicon-containing BCPs.

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Interactions and design rules for assembly of porous colloidal mesophases.

by Lindquist BA, Dutta S, Jadrich RB, Milliron DJ, Truskett TM.

Soft Matter. 2017 Jan 30. doi: 10.1039/c6sm02718k. [Epub ahead of print]

Porous mesophases, where well-defined particle-depleted ‘void’ spaces are present within a particle-rich background fluid, can be self-assembled from colloidal particles interacting via isotropic pair interactions with competing attractions and repulsions. While such structures could be of wide interest for technological applications (e.g., filtration, catalysis, absorption, etc.), relatively few studies have investigated the interactions that lead to these morphologies and how they compare to those that produce other micro-phase-separated structures, such as clusters. In this work, we use inverse methods of statistical mechanics to design model isotropic pair potentials that form porous mesophases. We characterize the resulting porous structures, correlating features of the pair potential with the targeted pore size and the particle packing fraction. The former is primarily encoded by the amplitude and range of the repulsive barrier of the designed pair potential and the latter by the attractive well depth. We observe a trade-off with respect to the packing fraction of the targeted morphology: greater values support more spherical and monodisperse pores that themselves organize into periodic structures, while lower values yield more mobile pores that do not assemble into ordered structures but remain stable over a larger range of packing fraction. We conclude by commenting on the limitations of targeting a specific pore diameter within the present inverse design approach as well as by describing future directions to overcome these limitations.

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Integrative FourD omics approach profiles the target network of the carbon storage regulatory system.

by Sowa SW, Gelderman G, Leistra AN, Buvanendiran A, Lipp S, Pitaktong A, Vakulskas CA, Romeo T, Baldea , Contreras LM.

Nucleic Acids Res. 2017 Jan 26. pii: gkx048. doi: 10.1093/nar/gkx048. [Epub ahead of print]

Multi-target regulators represent a largely untapped area for metabolic engineering and anti-bacterial development. These regulators are complex to characterize because they often act at multiple levels, affecting proteins, transcripts and metabolites. Therefore, single omics experiments cannot profile their underlying targets and mechanisms. In this work, we used an Integrative FourD omics approach (INFO) that consists of collecting and analyzing systems data throughout multiple time points, using multiple genetic backgrounds, and multiple omics approaches (transcriptomics, proteomics and high throughput sequencing crosslinking immunoprecipitation) to evaluate simultaneous changes in gene expression after imposing an environmental stress that accentuates the regulatory features of a network. Using this approach, we profiled the targets and potential regulatory mechanisms of a global regulatory system, the well-studied carbon storage regulatory (Csr) system of Escherichia coli, which is widespread among bacteria. Using 126 sets of proteomics and transcriptomics data, we identified 136 potential direct CsrA targets, including 50 novel ones, categorized their behaviors into distinct regulatory patterns, and performed in vivo fluorescence-based follow up experiments. The results of this work validate 17 novel mRNAs as authentic direct CsrA targets and demonstrate a generalizable strategy to integrate multiple lines of omics data to identify a core pool of regulator targets.

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Handling Input Dynamics in Integrated Scheduling and Control

by Baldea, M; Touretzky, CR; Park, J; Pattison, RC; Harjunkoski, I

PROCEEDING OF 2016 IEEE INTERNATIONAL CONFERENCE ON AUTOMATION, QUALITY AND TESTING, ROBOTICS (AQTR); Book Series: IEEE International Conference on Automation Quality and Testing Robotics; Pages: 381-386; Published: 2016

Coordinating production scheduling decisions with the process control system requires considering the evolution of the process over multiple time scales and at multiple levels of detail. From a mathematical perspective, this requires dealing with process models that are large-scale, ill-conditioned and involve both continuous and discrete variables (the former related to physical states, while the latter reflect production management decisions). In this paper, we introduce a novel methodology for time scale-bridging between production scheduling and process control. We use process operating data to obtain low-order models of the closed-loop behavior of the process, which are then incorporated in the production scheduling framework. The theoretical developments are accompanied by an illustrative case study on a methyl methacrylate process, showing excellent economic results and significantly improved computational performance.

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Enabling glucose/xylose co-transport in yeast through the directed evolution of a sugar transporter.

by Li, H; Schmitz, O; Alper, HS

Applied Microbiology and Biotechnology. 2016 Dec;100(23):10215-10223. Epub 2016 Oct 11.

The capacity to co-transport glucose and xylose into yeast has remained a technical challenge in the field. While significant efforts have been made in transporter engineering to increase xylose transport rates, glucose-based inhibition still limit most of these transporters. To address this issue, we further engineer sugar transporter proteins to remove glucose inhibition and enable glucose/xylose co-transport. Specifically, we start with our previously derived CiGXS1 FIM mutant strain and subjugate it to several rounds of mutagenesis and selection in a hexose metabolism null strain. Through this effort, we identify several mutations including N326H, a truncation in the C-terminal tail, I171F, and M40V as additionally dominant for reducing glucose inhibition. The resulting transporter shows substantially improved xylose transport rates in the presence of high quantities of glucose including up to 70 g/L glucose. Moreover, the resulting transporter enables co-utilization of glucose and xylose with glucose rates on par with a wild-type transporter and xylose rates exceeding that of glucose. These results demonstrate that major facilitator superfamily hexose transporters can be rewired into glucose-xylose co-transporters without functional inhibition by either substrate. These results enhance the potential of using lignocellulosic biomass as a feedstock for yeast.

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Identification of gene knockdown targets conferring enhanced isobutanol and 1-butanol tolerance to Saccharomyces cerevisiae using a tunable RNAi screening approach.

by Crook, N; Sun, J; Morse, N; Schmitz, A; Alper, HS

Applied Microbiology and Biotechnology. 2016 Dec;100(23):10005-10018. Epub 2016 Sep 21.

Improving yeast tolerance to 1-butanol and isobutanol is a step toward enabling high-titer production. To identify previously unknown genetic targets leading to increased tolerance, we establish a tunable RNA interference (RNAi) screening approach. Specifically, we optimized the efficiency and tunability of RNA interference library screening in yeast, ultimately enabling downregulation efficiencies from 0 to 94 %. Using this system, we identified the Hsp70 family as a key regulator of isobutanol tolerance in a single round of screening, with downregulation of these genes conferring up to 64 % increased growth in 12 g/L isobutanol. For 1-butanol, we find through two rounds of iterative screening that the combined downregulation of alcohol dehydrogenase and enolase improves growth up to 3100 % in 10 g/L 1-butanol. Collectively, this work improves the tunability of RNAi in yeast as demonstrated by the discovery of novel effectors for these complex phenotypes.

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Molecular Insights into the Complex Relationship between Capacitance and Pore Morphology in Nanoporous Carbon-based Supercapacitors

by Pak, AJ; Hwang, GS

ACS APPLIED MATERIALS & INTERFACES; Volume: 8; Issue: 50; Pages: 34659-34667; DOI: 10.1021/acsami.6b11192; Published: DEC 21 2016

Electrochemical double layer capacitors, or super capacitors, are high-power energy storage devices that consist of large surface area electrodes (filled with electrolyte) to accommodate ion packing in accordance with classical electric double layer (EDL) theory. Nanoporous carbons (NPCs) have recently emerged as a class of electrode materials with the potential to dramatically improve the capacitance of these devices by leveraging ion confinement. However, the molecular mechanisms underlying such enhancements are a clear departure from EDL theory and remain an open question. In this paper, we present the concept of ion reorganization kinetics during charge/discharge cycles, especially within highly confining subnanometer pores, which necessarily dictates the capacitance. Our molecular dynamics voltammetric simulations of ionic liquid immersed in NPC electrodes (of varying pore size distributions) demonstrate that the most efficient ion migration, and thereby largest capacitance, is facilitated by nonuniformity of shape (e.g., from cylindrical to slitlike) along nanopore channels. On the basis of this understanding, we propose that a new structural descriptor, coined as the pore shape factor, can provide a new avenue for materials optimization. These findings also present a framework to understand and evaluate ion migration kinetics within charged nanoporous materials.

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System-size effects in ionic fluids under periodic boundary conditions

by Thompson, JP; Sanchez, IC

JOURNAL OF CHEMICAL PHYSICS; Volume: 145; Issue: 21; Article Number: 214103; DOI: 10.1063/1.4968040; Published: DEC 21 2016

We investigate the system-size dependence of the thermodynamic properties of ionic fluids under periodic boundary conditions. Following an approach previously developed in the context of quantum Monte Carlo simulations of many-electron systems, we show that the leading-order finite-size artifact in the Coulomb energy per particle of a classical fluid of N structureless ions at given density and temperature is simply -k(B)T(2N)(-1). Analytical approximations for the periodicity-induced size dependence of the excess thermodynamic properties of the fluid in the weak-coupling regime are obtained within the linearized Debye-Huckel theory. Theoretical results are compared with published simulations of the one-component plasma and our own simulations of a primitive-model electrolyte solution. Our work is directly relevant to estimating finite-size corrections in simulations of charged fluids comprising structureless ions embedded in continuous media. We outline in the Appendix how some of our formal results may be generalized to molecular fluids with mobile ions; e.g., electrolyte solutions with explicit solvent. Published by AIP Publishing.

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Quantifying the Interface Energy of Block Copolymer Top Coats

by Sunday, DF; Maher, MJ; Tein, S; Carlson, MC; Ellison, CJ; Wilson, CG; Klinet, RJ

ACS MACRO LETTERS; Volume: 5; Issue: 12; Pages: 1306-1311; DOI: 10.1021/acsmacrolett.6b00684; Published: DEC 2016

Block copolymers (BCPs) have the potential to play a key role in templating materials for nanoscale synthesis. BCP lithography likely will be one of the first examples of BCP-based nanomanufacturing implemented in a production setting. One of the challenges in implementing BCP lithography is that the lamella need to be oriented perpendicular to the substrate. For many systems, this requires control over interfacial energies for both components at the substrate and interface. Top coats can be designed to provide a neutral interface for both blocks on the BCP surface. The preferentiality of the top coat as a function of composition has been determined qualitatively by examining the orientation of a BCP after annealing with a top coat. Measurements of the interfacial width between the top coat and homopolymers allows the interface energy to be quantitatively determined. Resonant soft X-ray reflectivity measurements on top coat/homopolymer pairs were used to extract the Flory-Huggins parameter (chi) and interface energy (gamma) as a function of top coat composition. The difference between chi and gamma for each top coat/homopolymer pair was minimized at compositions that resulted in the top coat promoting perpendicular orientation. As the composition moved away from the neutral point the difference between chi and gamma for each pair grew larger.

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