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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization

Designing zeolite catalysts with improved mass transport properties is crucial for restrictive networks of either one- or two-dimensional pore topologies. In this paper we demonstrate the synthesis of finned ferrierite (FER), a commercial zeolite with two-dimensional pores, where protrusions on crystal surfaces behave as pseudo nanoparticles. Catalytic tests of 1-butene isomerization reveal a 3-fold enhancement of catalyst lifetime and an increase of 12 % selectivity to isobutene for finned samples compared to corresponding seeds. Electron tomography was used to confirm the identical crystallographic registry of fins and seeds. Time-resolved titration of Brønsted acid sites confirmed the improved mass transport properties of finned ferrierite compared to conventional analogues. These findings highlight the advantages of introducing fins through facile and tunable post-synthesis modification to impart material properties that are otherwise unattainable by conventional synthesis methods.

2D zeolite↗
DOE OSTI2023

Insights into the Oxidative Degradation Mechanism of Solid Amine Sorbents for CO 2 Capture from Air: Roles of Atmospheric Water

Direct air capture (DAC) processes for extraction of CO 2 from ambient air are unique among chemical processes in that they operate outdoors with minimal feed pretreatments. Here, the impact of humidity on the oxidative degradation of a prototypical solid supported amine sorbent, poly(ethylenimine) (PEI) supported on Al 2 O 3 , is explored in detail. By combining CO 2 adsorption measurements, oxidative degradation rates, elemental analyses, solid-state NMR and in situ IR spectroscopic analysis in conjunction with 18 O labeling of water, a comprehensive picture of sorbent oxidation is achieved under accelerated conditions. Here we demonstrated that the presence of water vapor can play an important role in accelerating the degradation reactions. From the study we inferred the identity and kinetics of formation of the major oxidative products, and the role(s) of humidity. Our data are consistent with a radical mediated autooxidative degradation mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Direct Insertion Polymerization of Ionic Monomers: Rapid Production of Anion Exchange Membranes

The limited number of methods to directly polymerize ionic monomers currently hinders rapid diversification and production of ionic polymeric materials, namely anion exchange membranes (AEMs) which are essential components in emerging alkaline fuel cell and electrolyzer technologies. Herein, we report a direct coordination-insertion polymerization of cationic monomers, providing the first direct synthesis of aliphatic polymers with high ion incorporations and allowing facile access to a broad range of materials. We demonstrate the utility of this method by rapidly generating a library of solution processable ionic polymers for use as AEMs. We investigate these materials to study the influence of cation identity on hydroxide conductivity and stability. Furthermore, we found that AEMs with piperidinium cations exhibited the highest performance, with high alkaline stability, hydroxide conductivity of 87 mS cm –1 at 80 °C, and a peak power density of 730 mW cm –2 when integrated into a fuel cell device.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Influence of Ti‐incorporated Zeolite Topology and Pore Condensation on Vapor Phase Propylene Epoxidation Kinetics with Gaseous H 2 O 2

Vapor-phase propylene (C 3 H 6 ) epoxidation kinetics with hydrogen peroxide (H 2 O 2 ) strongly reflects the physical properties of Ti-incorporated zeolite catalysts and the presence of spectating molecules (“solvent”) near active sites even without a bulk liquid phase. Steady-state turnover rates of C 3 H 6 epoxidation and product selectivities vary by orders of magnitudes, depending on the zeolite silanol ((SiOH) x ) density, pore topology (MFI, *BEA, FAU), and the quantity of condensed acetonitrile (CH 3 CN) molecules nearby active sites, under identical reaction mechanisms sharing activated H 2 O 2 intermediates on Ti surfaces. Individual kinetic analyses for propylene oxide (PO) ring-opening, homogeneous diol oxidative cleavage, and homogeneous aldehyde oxidation reveal that secondary reaction kinetics following C 3 H 6 epoxidation responds more sensitively to the changes in zeolite physical properties and pore condensation with CH 3 CN. Thus, higher PO selectivities achieved in hydrophilic Ti-MFI at steady-state reflect the preferential stabilization of transition states for C 3 H 6 epoxidation (a primary reaction) relative to PO ring-opening and oxidative cleavage (secondary reactions) that solvation effects that reflect interactions among condensed CH 3 CN within pores and the extended pore structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Chelator‐Assisted Precipitation‐Based Separation of the Rare Earth Elements Neodymium and Dysprosium from Aqueous Solutions

The rare earth elements (REEs) are critical resources for many clean energy technologies, but are difficult to obtain in their elementally pure forms because of their nearly identical chemical properties. Here, an analogue of macropa, G-macropa, was synthesized and employed for an aqueous precipitation-based separation of Nd 3+ and Dy 3+ . G-macropa maintains the same thermodynamic preference for the large REEs as macropa, but shows smaller thermodynamic stability constants. Molecular dynamics studies demonstrate that the binding affinity differences of these chelators for Nd 3+ and Dy 3+ is a consequence of the presence or absence of an inner-sphere water molecule, which alters the donor strength of the macrocyclic ethers. Leveraging the small REE affinity of G-macropa, we demonstrate that within aqueous solutions of Nd 3+ , Dy 3+ , and G-macropa, the addition of HCO 3 − selectively precipitates Dy 2 (CO 3 ) 3 , leaving the Nd 3+ −G-macropa complex in solution. With this method, remarkably high separation factors of 841 and 741 are achieved for 50 : 50 and 75 : 25 mixtures. Further studies involving Nd 3+ :Dy 3+ ratios of 95 : 5 in authentic magnet waste also afford an efficient separation as well. Finally, G-macropa is recovered via crystallization with HCl and used for subsequent extractions, demonstrating its good recyclability.

Gao, Yangyang↗
DOE OSTI2025

Blocky Selective Postpolymerization C–H Functionalization of Polyolefins

C–H functionalization of commodity polyolefins affords functional materials derived from a high-volume, low-cost resource. However, current postpolymerization modification strategies result in randomly distributed functionalization along the length of the polymer backbone, which has a negative impact on the crystallinity of the resultant polymers, and thus the thermomechanical properties. Here, we demonstrate an amidyl radical mediated C–H functionalization of polyolefins to access blocky microstructures, which exhibit a higher crystalline fraction, larger crystallite size, and improved mechanical properties compared to their randomly functionalized analogues. Taking inspiration from the site-selective C–H functionalization of small molecules, we leverage the steric protection provided by crystallites and target polymer functionalization to amorphous domains in a semicrystalline polyolefin gel. The beneficial outcomes of blocky functionalization are independent of the identity of the pendant functional group that is installed through functionalization. Here, the decoupling of functional group incorporation and crystallinity highlights the promise in accessing nonrandom microstructures through selective functionalization to circumvent traditional tradeoffs in postpolymerization modification, with potential impact in advanced materials and upcycling plastic waste.

Neidhart, Eliza K. [The University of North Caroli↗
DOE OSTI2025

De Novo Design of High‐Affinity Miniprotein Binders Targeting Francisella Tularensis Virulence Factor

Abstract Francisella tularensis poses considerable public health risk due to its high infectivity and potential for bioterrorism. Francisella‐like lipoprotein (Flpp3), a key virulence factor unique to Francisella, plays critical roles in infection and immune evasion, making it a promising target for therapeutic development. However, the lack of well‐defined binding pockets and structural information on native interactions has hindered structure‐guided ligand discovery against Flpp3. Here, we used a combination of physics‐based and deep‐learning methods to design high‐affinity miniprotein binders targeting two distinct sites on Flpp3. We identified four binders for site I with binding affinities ranging between 24–110 nM. For the second site, an initial binder showed a dissociation constant ( K D ) of 81 nM, and subsequent site saturation mutagenesis yielded variants with sub‐nanomolar affinities. Circular dichroism confirmed the topology of designed miniproteins. The X‐ray crystal structure of Flpp3 in complex with a site I binder is nearly identical to the design model (Cα root‐mean‐square deviation (RMSD): 0.9 Å). These designed miniproteins provide research tools to explore the roles of Flpp3 in tularemia and should enable the development of new therapeutic candidates.

Gokce‐Alpkilic, Gizem [Molecular Engineering and S↗
DOE OSTI2026

Tuning the Mechanical Properties of Crosslinked Copolymers via Sequence and Solvent‐Selective Swelling for Vat Photopolymerization

Block copolymers (BCPs) offer distinct advantages for vat photopolymerization by enabling mechanically programmable network structures through microphase-separated morphologies that can be kinetically trapped during curing, yielding properties unattainable in homogeneous resins. However, the respective roles of repeat-unit sequence and solvent environment, together with their interplay in directing network formation and mechanical performance, remain unclear. Here, we synthesize a series of CO 2 -based polycarbonate copolymers comprising a crosslinkable glassy poly(vinyl cyclohexene carbonate) (PVCHC, A block) and a non-crosslinkable soft poly(propylene carbonate) (PPC, B block). The polymer sequence is systematically varied (ABA, BAB, and statistical), and solvent choice controls block-selective swelling to jointly control gelation behavior, microphase morphology, and mechanical response through changes in the accessibility and local environment of photocrosslinkable vinyl groups during network formation, as revealed by photorheology and small angle x-ray scattering. By tuning polymer sequence and curing solvent, we transform nominally identical formulations from brittle to highly ductile materials, achieving a three-orders-of-magnitude range in toughness (0.003 to 9.1 MJ m −3 ). These results establish clear structure–processing–property relationships and identify polymer sequence and selective solvation as powerful strategies for programming both printability and performance of block copolymer resins for additive manufacturing.

additive manufacturing↗
DOE OSTI2022

Bio‐based glycerol plasticizers for flexible poly(vinyl chloride) blends

Abstract A series of glycerol‐based compounds were investigated for their application as plasticizers for flexible poly(vinyl chloride) (PVC) blends. The effect of plasticizer chemical structure on the performance, migration behavior, and blend morphology were evaluated and compared to blends produced using the commercial plasticizer dioctyl terephthalate (DOTP). Blends containing 40 phr (parts per hundred rubber) of glycerol‐based plasticizer showed a considerable reduction (between 54 to 86°C) in glass transition temperature ( T g ) relative to neat PVC ( T g ~ 80°C). Tensile testing of samples prepared with the glycerol analogs demonstrated higher ductility (elongation at break values of up to 97%) than DOTP (elongation at break value of 75%) at identical plasticizer loadings. The surface morphologies showed excellent incorporation of the glycerol plasticizers functionalized with alkyl chains longer than four carbons in length into the PVC matrix, whereas droplet formation was observed in blends with shorter chain glycerol derivatives. Leaching behavior of the plasticized samples were evaluated into different media and showed that plasticizers comprised of branched, or longer alkyl chains produced 2‐ to 4‐fold lower migration rates compared to those with shorter alkyl chains into polar solutions.

Halloran, Matthew W.↗
DOE OSTI2020

Neurosensory and Sinus Evolution as Tyrannosauroid Dinosaurs Developed Giant Size: Insight from the Endocranial Anatomy of Bistahieversor sealeyi

Tyrannosaurus rex and other tyrannosaurid dinosaurs were apex predators during the latest Cretaceous, which combined giant size and advanced neurosensory systems. Computed tomography (CT) data have shown that tyrannosaurids had a trademark system of a large brain, large olfactory bulbs, elongate cochlear ducts, and expansive endocranial sinuses surrounding the brain and sense organs. Older, smaller tyrannosauroid relatives of tyrannosaurids developed some, but not all, of these features, raising the hypothesis that tyrannosaurid-style brains evolved before the enlarged tyrannosaurid-style sinuses, which might have developed only with large body size. This has been difficult to test, however, because little is known about the brains and sinuses of the first large-bodied tyrannosauroids, which evolved prior to Tyrannosauridae. Here we present the first CT data for one of these species, Bistahieversor sealeyi from New Mexico. Bistahieversor had a nearly identical brain and sinus system as tyrannosaurids like Tyrannosaurus, including a large brain, large olfactory bulbs, reduced cerebral hemispheres, and optic lobes, a small tab-like flocculus, long and straight cochlear ducts, and voluminous sinuses that include a supraocciptal recess, subcondyar sinus, and an anterior tympanic recess that exits the braincase via a prootic fossa. When characters are plotted onto tyrannosauroid phylogeny, there is a two-stage sequence in which features of the tyrannosaurid-style brain evolved first (in smaller, nontyrannosaurid species like Timurlengia), followed by features of the tyrannosaurid-style sinuses (in the first large-bodied nontyrannosaurid tyrannosauroids like Bistahieversor). This suggests that the signature tyrannosaurid sinus system evolved in concert with large size, whereas the brain did not.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Hierarchical assemblies of polypeptoids for rational design of advanced functional nanomaterials

Polypeptoids (poly-N-substituent glycines) are a class of highly tailorable peptidomimetic polymers. Polypeptoids have identical backbones as polypeptides (poly-C-substituent glycines), but sidechains of polypeptoids are appended to backbone nitrogen rather than α-carbon of polypeptides. As a result, peptoid backbone lacks of chirality and hydrogen bond donors. This unique structure gives polypeptoids a combined merit of both high stability as synthetic polymers and biocompatibility as biopolymers. In addition, peptoid sequences can be engineered precisely to assemble specific crystalline patterns such as spheres, fibers, ribbons, tubes, and sheets, which shows promising potentials of polypeptoids for different applications such as antimicrobials, catalysts, drug delivery, and templating inorganic materials. In this review, we summarize recent investigations into hierarchical self-assembly pathways and molecular structures of peptoid crystals that are of interest as templates for fabricating functional materials for potential biomedical, biochemical, and bioengineering applications. Furthermore, this review provides a summary of recent experimental and computational studies of polypeptoid assembly in solution and solid-liquid interfaces, current achievements in the field, and discusses future challenges and opportunities for the rational design of self-assembled polypeptoid nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Enhancing Biomass Productivity by Forecast‐Informed Pond Operations

ABSTRACT Microalgal cultivation for biofuels and proteins holds significant promise but faces challenges in achieving economically viable biomass productivity under variable environmental conditions. This study introduces a forecast‐informed pond operation (FIPO) system that uses numerical weather prediction (NWP) ensemble forecasts and the biomass assessment tool (BAT) to optimize daily dilution rates for enhanced biomass production. In contrast to the current practice, where fixed dilution rates are based on operator experience, the FIPO system determines the optimal dilution rate based on future weather forecasts and biomass growth conditions. Our experiments validate the effectiveness of FIPO in both short‐ and long‐term growth scenarios. In short‐term experiments, FIPO increased biomass production by 21.3% compared to batch growth and 7.4% over fixed dilution (60% every 3 days) operations. The NWP forecast‐informed operations achieved biomass production nearly identical to that using perfect weather forecasts, highlighting the accuracy of current NWP forecasts for guiding pond operations. In long‐term experiments, FIPO resulted in biomass production increases of 13.3% and 17.8% compared to two fixed dilution rates (60% every 3 days and 20% daily). These findings underscore the viability of using NWP forecasts to optimize microalgal cultivation systems. By adjusting daily dilution rates in response to forecasted weather, operators can achieve higher biomass yields and mitigate risks associated with environmental variability. This study provides a foundation for future research and practical applications in commercial‐scale microalgal production.

Yan, Hongxiang [Energy and Environment Directorate↗
DOE OSTI2023

Derivatization of Mirror-Image L -Nucleic Acids with 2'-OMe Modification for Thermal and Structural Stabilization

To further expand the functionality and enhance the stability of mirror-image nucleic acids as advanced agents for basic research and therapeutic design, we have synthesized 2'-deoxy-2'-methoxy- L -uridine phosphoramidite and incorporated it into L -DNA and L -RNA by solid-phase synthesis quantitatively. We found that the thermostability of L -nucleic acids is dramatically improved after introducing the modifications. Moreover, we successfully crystallized both L -DNA and L -RNA duplexes containing the 2'-OMe modifications and sharing identical sequences. Crystal structure determination and analysis revealed the overall structures of the mirror-image nucleic acids, and for the first time it was possible to interpret the structural deviations caused by 2'-OMe and 2'-OH groups in the oligonucleotides, which are very similar. In conclusion, this novel chemical nucleic acid modification has the potential to be used to design nucleic acid-based therapeutics and materials in the future.

2'-OMe-modifications↗
DOE OSTI2022

Generalized Brønsted‐Evans‐Polanyi Relationships for Reactions on Metal Surfaces from Machine Learning

Abstract Brønsted‐Evans‐Polanyi (BEP) relationships, i. e., a linear scaling between reaction and activation energies, lie at the core of computational design of heterogeneous catalysts. However, BEPs are not general and often require reparameterization for each class of reactions. Here we construct generalized BEPs (gBEPs), which can predict activation energies for a diverse dataset of reactions of C, O, N and H containing molecules on metal surfaces. In a first step we develop a set of descriptors based on scaling relationships that can capture the change in chemical identity of reactants during the reaction. Subsequently, we use the reaction energy, these descriptors and a single descriptor for the surface structure to parameterize machine learning based regression approaches for the prediction of activation energies. The best approach we developed shows a Mean Absolute Error (MAE) of 0.11 eV for the training set (80 % of the data set) and 0.23 eV for the test set (20 % of the data set). The methodology presented here allows to calculate activation energies within fractions of seconds on a typical personal computer and due to its generality, accuracy and simplicity in application it might prove to be useful in transition metal catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

CO as a Probe Molecule to Study Surface Adsorbates during Electrochemical Oxidation of Propene

A major challenge in the electrochemical oxidation of hydrocarbons is understanding the formation of intermediate species, some of which continue to react, while others are non-reactive or poisonous species that block adsorption of further reactants. Herein we investigate the identity and behavior of adsorbates formed during partial oxidation of propene. We employ two techniques: Electrochemistry-Mass Spectrometry (EC-MS) and Attenuated Total Reflection Infrared Spectroscopy (ATR-FTIR). In both cases, we use CO as a probe molecule, to perturb the ad-layer of propene intermediates. In the EC-MS experiments, propene and its intermediates were quantified by triggering their desorption via displacement with CO. We show evidence for at least two distinct classes of propene adsorbates, via CO displacement and electrochemical stripping. A redshift in the ν(C–O) mode was observed, during IR spectroscopy, reflecting the chemical environment arising from strongly bound propene intermediates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Bipolar Redox‐Active Molecules in Non‐Aqueous Organic Redox Flow Batteries: Status and Challenges

Abstract In this Review, recent advances in the development of organic bipolar redox‐active molecules (BRMs) for redox‐flow batteries (RFBs) are discussed, with special emphasis on their utilization in non‐aqueous systems. BRMs are single molecules that can be used as both anolyte and catholyte. Their unique redox chemistry enables identical components to be present in RFBs, which has distinct advantages in storage, mitigating crossover and compound degradation. Recent scientific innovations have uncovered three main strategies in preparing these bipolar species: developing stable radicals that are capable of both positive and negative redox reactions, covalently bridging electron donor‐acceptor motifs on one single molecule, and forming biredox eutectic mixtures through physically mixing active components. These approaches not only enabled symmetric flow battery design, but also resulted in electroactive materials with improved properties such as solubility, stability, and cell voltage. Nevertheless, much is still to be done. Importantly, developing BRMs that are competitive with vanadium RFBs in all performance indicators (e. g. solubility >1.0 M, voltage output >2.0 V, and cycling longevity >10 000 cycles) remains a challenge. Mechanistic studies including molecular dynamics, plausible degradation processes, and electrode/solution interface are necessary to peer into key parameters that dominate their battery performance. Accordingly, we review the current status and suggest future opportunities in these areas.

Li, Min↗
DOE OSTI2021

Promotion and Tuning of the Electrochemical Reduction of Hetero‐ and Homobimetallic Zinc Complexes**

Abstract Compounds containing multiple metals attract significant interest due to the useful redox and reactivity properties of such species. Here, the electrochemical properties of a family of macrocyclic complexes that feature a zinc(II) center paired with a secondary redox‐inactive metal cation in heterobimetallic (Na + , Ca 2+ , Nd 3+ , Y 3+ ) motifs or homobimetallic (Zn 2+ ) motifs have been investigated. The new complexes were prepared via a divergent strategy, isolated, and structurally characterized with single‐crystal X‐ray diffraction (XRD) analysis. XRD results show that the structures of the complexes are modulated by the identity of the incorporated secondary metal ions. Cyclic voltammetry data reveal that ligand‐centered reduction is promoted in the bimetallic complexes and that the paired metal ions synergistically influence the redox properties of the complexes. Similar to prior work from our group and others, the bimetallic complexes containing stronger Lewis acids undergo more significant reduction potential shifts; contrasting with prior work on complexes containing redox‐active metals, however, the zinc(II) complexes studied here display faster electron transfer (as judged by lower reorganization energies, λ) when incorporating di‐ or tri‐valent Lewis acids in contrast to monovalent (and more weakly acidic) sodium. The quantified trends in these data offer insights that could help distinguish metal‐ versus ligand‐centered reduction of bimetallic complexes.

Kelsey, Shaun R.↗
DOE OSTI2021

Probing the Effects of Acid Electrolyte Anions on Electrocatalyst Activity and Selectivity for the Oxygen Reduction Reaction

The local microenvironment at the electrode-electrolyte interface plays an important role in electrocatalytic performance. Herein, we investigate the effect of acid electrolyte anion identity on the oxygen reduction reaction (ORR) activity and selectivity of smooth Ag and Pd catalyst thin films. Cyclic voltammetry in perchloric, nitric, sulfuric, phosphoric, hydrochloric, and hydrobromic acid, at pH1, reveals that Ag ORR activity trends as follows: HClO 4 >HNO 3 >H 2 SO 4 >H 3 PO 4 >HCl>>HBr, while Pd ORR activity trends as: HClO 4 >H 2 SO 4 >HNO 3 >H 3 PO 4 >HCl>>HBr. Moreover, rotating-ring-disk-electrode selectivity measurements demonstrate enhanced 4 e - selectivity on both Ag and Pd, by up to 35% H 2 O 2 and 10% H 2 O 2 respectively, in HNO 3 compared to in HClO 4 . Relating physics-based modeling and experimental results, we postulate that ORR performance depends greatly on anion-related phenomena in the double layer, for instance competitive adsorption and non-covalent interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗