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Results for “covalent functionalization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Synthetic Control of Water-Stable Hybrid Perovskitoid Semiconductors

Hybrid metal-halide perovskites and their derived materials have emerged as the next-generation semiconductors with a wide range of applications, including photovoltaics, light-emitting devices, and other optoelectronics. Over the past decade, numerous single-crystalline perovskite derivatives have been synthesized and developed. However, the synthetic methods for these derivatives mainly rely on acidic crystallization conditions. This approach leads to crystals comprising metal halide building blocks, which show problematic stability when directly exposed to water. In this study, a methodology is developed for synthesizing hybrid metal-halide compounds using lead iodide and the zwitterionic bifunctional molecule cysteamine (CYS), to form various perovskitoid structures under a broad pH range. Interestingly, the different pH conditions alter the coordination environment of lead halides, leading to lead-sulfide and lead-nitride covalent bond formation. This modification significantly enhances their stability when in direct contact with water, lasting for months. Photoluminescence measurements and first principal density functional theory (DFT) calculations reveal that the perovskitoids synthesized under basic and acidic pH conditions exhibit a direct bandgap nature, while those synthesized under neutral conditions display an indirect bandgap. This approach opens new avenues for manipulating synthetic methods to develop water-stable hybrid semiconductors suitable for a wide range of applications, such as solid-state light emitters.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Structure−Property Relationships in a Series of Hybrid Halopyridinium Ruthenium(IV) Halides

Reported is the synthesis and characterization of a family of hybrid ruthenium halides consisting of haloruthenium octahedra (X = Cl, Br) charge balanced with halopyridinium (XPy; X= H, Cl, Br, I) organic cations which assemble via noncovalent interactions between ion pairs. Diffuse reflectance spectroscopy showed that compounds containing RuBr 6 2- octahedra displayed a lower bandgap (1.05 eV< x < 1.08 eV) compared to compounds with RuCl 6 2- octahedra (1.22 eV < x < 1.43 eV). Additionally, computational density functional theory (DFT) based natural bonding orbital (NBO) analysis and density of state (DOS) methods were used to characterize second-sphere non-covalent interaction strengths and elucidate molecular orbital perturbations to elucidate their influence on Ru-X orbital constructs and in turn rationalize band gap trends. Analyses showed ligand to metal charge transfer is responsible for the small bandgap energies and are unperturbed by second-sphere interactions. Here, this report serves as a platform for probing the relationship between the structural and photophysical properties within the haloruthenium family of low dimensional transition metal halide perovskites.

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

Calculation and interpretation of classical turning surfaces in solids

Abstract Classical turning surfaces of Kohn–Sham potentials separate classically allowed regions (CARs) from classically forbidden regions (CFRs). They are useful for understanding many chemical properties of molecules but need not exist in solids, where the density never decays to zero. At equilibrium geometries, we find that CFRs are absent in perfect metals, rare in covalent semiconductors at equilibrium, but common in ionic and molecular crystals. In all materials, CFRs appear or grow as the internuclear distances are uniformly expanded. They can also appear at a monovacancy in a metal. Calculations with several approximate density functionals and codes confirm these behaviors. A classical picture of conduction suggests that CARs should be connected in metals, and disconnected in wide-gap insulators, and is confirmed in the limits of extreme compression and expansion. Surprisingly, many semiconductors have no CFR at equilibrium, a key finding for density functional construction. Nonetheless, a strong correlation with insulating behavior can still be inferred. Moreover, equilibrium bond lengths for all cases can be estimated from the bond type and the sum of the classical turning radii of the free atoms or ions.

Chemistry↗
DOE OSTI2025

Atomic-resolution structural and spectroscopic evidence for the synthetic realization of two-dimensional copper boride

Since the first realization of borophene on Ag(111), two-dimensional (2D) boron nanomaterials have attracted substantial interest because of their polymorphic diversity and potential for hosting solid-state quantum phenomena. Here, we use atomic-resolution scanning tunneling microscopy (STM) and field-emission resonance (FER) spectroscopy to elucidate the structure and properties of atomically thin boron phases grown on Cu(111). Specifically, FER spectroscopy reveals charge transfer and electronic states that strongly differ from the decoupled borophene phases observed on silver, suggesting that the deposition of boron on copper results in strong covalent bonding characteristic of a 2D copper boride. This conclusion is reinforced by detailed STM characterization of line defects that are consistent with density functional theory calculations for atomically thin Cu8B14. This evidence for 2D copper boride is likely to motivate future synthetic efforts aimed at expanding the relatively unexplored family of atomically thin metal boride materials.

Science & Technology - Other Topics↗
DOE OSTI2022

Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP 2 S 7 and KCrP 2 S 7

Two thiophosphates, KInP 2 S 7 and KCrP 2 S 7 , were structurally characterized without investigating any optical properties. Herein in this work, KInP 2 S 7 and KCrP 2 S 7 were revisited to investigate their optical and magnetic properties, respectively. Pure polycrystalline samples and crystals of KInP 2 S 7 and KCrP 2 S 7 were grown by high temperature solid state reactions, where mm-sized crystals of KCrP 2 S 7 were collected. KCrP 2 S 7 is isostructural to KInP 2 S 7 , which features a layered structure. KInP 2 S 7 and KCrP 2 S 7 possess close relationship to the layered thiophosphate M 2 P 2 S 6 (M = Fe, Co, Zn, etc.). The bonding pictures of KInP 2 S 7 were studied using the electron localization function (ELF) coupled with crystal orbital Hamilton population (COHP) calculations. The intrinsically distorted [PS 4 ] tetrahedra and [InS 6 ] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. Electronic structure analysis confirmed that the optical properties of KInP 2 S 7 are mainly contributed to by [PS 4 ] tetrahedra together with small amounts of the contributions coming from [InS 6 ] octahedra. Magnetic measurement on mm-sized crystals of KCrP 2 S 7 verified that there is an antiferromagnetic transition around 21 K, and the Cr atoms are trivalent. KInP 2 S 7 is predicated to be an indirect bandgap semiconductor of 2.38 eV, which is confirmed by the UV-Vis measurement of 2.4(1) eV. KInP 2 S 7 is not a type-I phase-matching material and exhibits moderate second harmonic generation (SHG) response (0.51 × AgGaS 2 , sample of particle size of 100 µm). The laser damage threshold (LDT) of KInP 2 S 7 is very high of 5.2 × AgGaS 2 . Bandgap engineering were undergone to enhance the SHG response of KInP 2 S 7 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Multi-layer coatings and methods of preparing the same

A multi-layer coating includes: a first basecoat layer applied over at least a portion of a substrate; and a second basecoat layer applied over the first basecoat layer. The first basecoat layer and second basecoat layer are formed from compositions having a polyhydrazide and core-shell particles dispersed in aqueous mediums. The core-shell particles of the first basecoat composition includes (1) a polymeric core at least partially encapsulated by (2) a polymeric shell comprising urea linkages, and keto and/or aldo functional groups. The polymeric core of the core-shell particles of the first basecoat composition and the second basecoat composition are each independently covalently bonded to at least a portion of the polymeric shell of the core-shell particles.

Xu, Xiangling↗
DOE OSTI2021

Interpretation of multiple solutions in fully iterative GF2 and GW schemes using local analysis of two-particle density matrices

Due to the presence of non-linear equations, iterative Green’s function methods can result in multiple different solutions even for simple molecular systems. In contrast to the wave-function methods, a detailed and careful analysis of such molecular solutions was not performed before. In this work, we use two-particle density matrices to investigate local spin and charge correlators that quantify the charge resonance and covalent characters of these solutions. When applied within the unrestricted orbital set, spin correlators elucidate the broken symmetry of the solutions, containing necessary information for building effective magnetic Hamiltonians. Based on GW and GF2 calculations of simple molecules and transition metal complexes, we construct Heisenberg Hamiltonians, four-spin-four-center corrections, and biquadratic spin–spin interactions. These Hamiltonian parameterizations are compared to previous wave-function calculations.

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

The role of nonmetallic ion substitution in perovskite LaCoO 3 for improved oxygen evolution reaction activity

Transition metal perovskite (ABO 3 ) is an emerging type of oxygen evolution reaction (OER) electrocatalyst that shows reasonably good activity and moderate stability. Although efforts have been made to improve perovskite’ OER performance by various element substitution at A/B-site, the influence of ion, particularly non-metallic ion, substitutions on the OER mechanism are rarely studied. More and more evidence has shown that the metal-center theory has failed to explain lots of OER-related phenomena. Therefore, it is urgent to understand how the cation and anion sites in perovskite determine OER performance. In this work, we used a Fe and P co-doped LaCoO 3 as a model system to explore the influence of substitution in perovskite by combining operando/ex-situ X-ray characterization and density functional theory (DFT). We observed enhanced OER catalytic activities in co-doped materials, which are attributed to the stronger transition-metal-oxygen-bonding-covalency (TMOBC). The detailed analyses by O K-edge XAS, electrochemical performance, and DFT suggest that the hybridization between O 2p and transition metal 3d e g orbitals could be a more credible descriptor of perovskite for OER, which is the combination of e g orbital theory and TMOBC theory. The finding in our work provides insights into the OER catalysis mechanism on metal oxides, which could guide new design of cost-effective oxide electrocatalysts.

25 ENERGY STORAGE↗
DOE OSTI2022

Electroluminescence from Single-Walled Carbon Nanotubes with Quantum Defects

Individual single-walled carbon nanotubes with covalent sidewall defects have emerged as a class of photon sources whose photoluminescence spectra can be tailored by the carbon nanotube chirality and the attached functional group/molecule. Here we present electroluminescence spectroscopy data from single-tube devices based on (7, 5) carbon nanotubes, functionalized with dichlorobenzene molecules, and wired to graphene electrodes. We observe electrically generated, defect-induced emissions that are controllable by electrostatic gating and strongly red-shifted compared to emissions from pristine nanotubes. The defect-induced emissions are assigned to excitonic and trionic recombination processes by correlating electroluminescence excitation maps with electrical transport and photoluminescence data. At cryogenic conditions, additional gate-dependent emission lines appear, which are assigned to phonon-assisted hot-exciton electroluminescence from quasi-levels. Similar results were obtained with functionalized (6, 5) nanotubes. We also compare functionalized (7, 5) electroluminescence data with photoluminescence of pristine and functionalized (7, 5) nanotubes redox-doped using gold(III) chloride solution. This work shows that electroluminescence excitation is selective toward neutral defect-state configurations with the lowest transition energy, which in combination with gate-control over neutral versus charged defect-state emission leads to high spectral purity.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Photoenzymatic Catalysis in a New Light: Gluconobacter “Ene”-Reductase Conjugates Possessing High-Energy Reactivity with Tunable Low-Energy Excitation

Non-natural light-driven enzymatic reactivity was recently developed to perform the highly stereoselective reactions required for pharmaceutical synthesis. However, photoenzymes require high-intensity light to function because of the poor absorption properties of their photoactive intermediates. Inspired by the modular architecture of photosynthesis, we designed a conjugate composed of a covalently linked photoenzyme and a light antenna to separate light capture from catalysis. Spectroscopic characterization of the conjugate showed the presence of efficient energy transfer from the light-harvesting components to the photoenzyme. In the presence of energy transfer, a ~4-fold increase in product yield was observed for intramolecular hydroalkylation of alkenes, and reactivity was enabled for intermolecular hydroalkylation of alkenes. As a result, these improvements establish the power of incorporating nature’s design into non-natural photoenzymatic catalysis.

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

Non-covalent planarizing interactions yield highly ordered and thermotropic liquid crystalline conjugated polymers

Controlling the multi-level assembly and morphological properties of conjugated polymers through structural manipulation has contributed significantly to the advancement of organic electronics. In this work, a redox active conjugated polymer, TPT–TT, composed of alternating 1,4-(2-thienyl)-2,5-dialkoxyphenylene (TPT) and thienothiophene (TT) units is reported with non-covalent intramolecular S⋯O and S⋯H–C interactions that induce controlled main-chain planarity and solid-state order. As confirmed by density functional theory (DFT) calculations, these intramolecular interactions influence the main chain conformation, promoting backbone planarization, while still allowing dihedral rotations at higher kinetic energies (higher temperature), and give rise to temperature-dependent aggregation properties. Thermotropic liquid crystalline (LC) behavior is confirmed by cross-polarized optical microscopy (CPOM) and closely correlated with multiple thermal transitions observed by differential scanning calorimetry (DSC). This LC behavior allows us to develop and utilize a thermal annealing treatment that results in thin films with notable long-range order, as shown by grazing-incidence X-ray diffraction (GIXD). Specifically, we identified a first LC phase, ranging from 218 °C to 107 °C, as a nematic phase featuring preferential face-on π–π stacking and edge-on lamellar stacking exhibiting a large extent of disorder and broad orientation distribution. A second LC phase is observed from 107 °C to 48 °C, as a smectic A phase featuring sharp, highly ordered out-of-plane lamellar stacking features and sharp tilted backbone stacking peaks, while the structure of a third LC phase with a transition at 48 °C remains unclear, but resembles that of the solid state at ambient temperature. Furthermore, the significance of thermal annealing is evident in the ∼3-fold enhancement of the electrical conductivity of ferric tosylate-doped annealed films reaching 55 S cm −1 . More importantly, thermally annealed TPT–TT films exhibit both a narrow distribution of charge-carrier mobilities (1.4 ± 0.1) × 10 −2 cm 2 V −1 s −1 along with a remarkable device yield of 100% in an organic field-effect transistor (OFET) configuration. This molecular design approach to obtain highly ordered conjugated polymers in the solid state affords a deeper understanding of how intramolecular interactions and repeat-unit symmetry impact liquid crystallinity, solution aggregation, solution to solid-state transformation, solid-state morphology, and ultimately device applications.

Chemistry↗
DOE OSTI2021

Strong Magnetocrystalline Anisotropy Arising from Metal–Ligand Covalency in a Metal–Organic Candidate for 2D Magnetic Order

Layered metal–organic frameworks are promising candidates for new two-dimensional magnets, as their synthetic programmability of these materials can provide a route to diverse structural and electronic properties. However, such framework materials typically lack the heavy elements that engender magnetocrystalline anisotropy in the monolayer ferromagnets reported to date. Alternative sources of magnetic anisotropy are therefore needed in these materials. Here, we report the synthesis of single crystals of the framework material (NMe 4 ) 2 [Fe 2 L 3 ] (H 2 L = 3,6-dichloro-2,5-dihydroxybenzoquinone) and evaluate the angular dependence of its magnetic properties. Oriented-crystal magnetization measurements reveal strong uniaxial anisotropy, where the easy axis is aligned with the crystallographic c axis. While the spin carriers of this structure are isotropic $S = ^5/_2$ Fe III metal centers and $S = ^1/_2$ organic linkers, the anisotropy energy of the framework material is comparable to that of reported 2D ferromagnets. Density functional theory calculations indicate that the observed magnetocrystalline anisotropy arises from ligand-to-metal charge transfer that enhances the magnetic anisotropy of the otherwise isotropic Fe centers, suggesting that metal–ligand covalency can be utilized as a general additive for the development of 2D magnets. These results in this study show the possibility for (NMe 4 ) 2 [Fe 2 L 3 ] to retain magnetic order down to the 2D monolayer limit. In addition, the combination of large magnetic anisotropy and semiconducting character in (NMe 4 ) 2 [Fe 2 L 3 ] highlights its potential as a new 2D magnetic semiconductor.

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

Robust Self-Healing Adhesives Based on Dynamic Urethane Exchange Reactions

Thermoset polyurethanes (PUs) have been successfully reprocessed as covalent adaptable networks (CANs) by catalyzing carbamate exchange. Here we extend bond exchange beyond the internal network cross-links to create a dynamic urethane adhesive. Interfacing PU CANs to substrates with nucleophilic functional groups creates adhesives capable of reversible transcarbamoylation with the substrate, which has not been demonstrated previously by CAN adhesives. Two types of thermoset PU films were synthesized, one containing the green carbamate exchange catalyst Zr(tmhd)4 and the other containing no catalyst. Although otherwise identical in chemical and network properties, as indicated by FT-IR spectroscopy and dynamic mechanical thermal analysis (DMTA), the film containing catalyst showed dynamic bond exchange behavior through stress relaxation analysis. When evaluated as an adhesive, the CAN film exhibited self-healing properties and retained its adhesive strength for five cycles, which is attributed to reversible covalent bonding to the glass substrate. Furthermore, this work expands industrially relevant CANs to structural adhesives and demonstrates their potential value in an application that presently employs PUs as single-use materials.

adhesive↗
DOE OSTI2023

A previously uncharacterized divisome-associated lipoprotein, DalA, is needed for normal cell division in Rhodobacterales

ABSTRACT The bacterial cell envelope is a key subcellular compartment with important roles in antibiotic resistance, nutrient acquisition, and cell morphology. We seek to gain a better understanding of proteins that contribute to the function of the cell envelope in Alphaproteobacteria . Using Rhodobacter sphaeroides , we show that a previously uncharacterized protein, RSP_1200, is an outer membrane (OM) lipoprotein that non-covalently binds peptidoglycan (PG). Using a fluorescently tagged version of this protein, we find that RSP_1200 undergoes a dynamic repositioning during the cell cycle and is enriched at the septum during cell division. We show that the position of RSP_1200 mirrors the location of FtsZ rings, leading us to propose that RSP_1200 is a newly identified component of the R. sphaeroides ’ divisome. Additional support for this hypothesis includes the co-precipitation of RSP_1200 with FtsZ, the Pal protein, and several predicted PG L,D-transpeptidases. We also find that a ∆ RSP_1200 mutation leads to defects in cell division, sensitivity to PG-active antibiotics, and results in the formation of OM protrusions at the septum during cell division. Based on these results, we propose to name RSP_1200 DalA (for division-associated lipoprotein A) and postulate that DalA serves as a scaffold to position or modulate the activity of PG transpeptidases that are needed to form envelope invaginations during cell division. We find that DalA homologs are present in members of the Rhodobacterales order within Alphaproteobacteria . Therefore, we propose that further analysis of this and related proteins will increase our understanding of the macromolecular machinery and proteins that participate in cell division in Gram-negative bacteria. IMPORTANCE Multi-protein complexes of the bacterial cell envelope orchestrate key processes like growth, division, biofilm formation, antimicrobial resistance, and production of valuable compounds. The subunits of these protein complexes are well studied in some bacteria, and differences in their composition and function are linked to variations in cell envelope composition, shape, and proliferation. However, some envelope protein complex subunits have no known homologs across the bacterial phylogeny. We find that Rhodobacter sphaeroides RSP_1200 is a newly identified lipoprotein (DalA) and that loss of this protein causes defects in cell division and changes the sensitivity to compounds, affecting cell envelope synthesis and function. We find that DalA forms a complex with proteins needed for cell division, binds the cell envelope polymer peptidoglycan, and colocalizes with enzymes involved in the assembly of this macromolecule. The analysis of DalA provides new information on the cell division machinery in this and possibly other Alphaproteobacteria.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Determination of Thiol Protonation States by Sulfur X-ray Spectroscopy in Biological Systems

Cysteine is one of the most functionally diverse of the proteinogenic amino acids, owing to its reactive thiol side chain that can undergo deprotonation to form a strongly nucleophilic thiolate. However, few techniques can directly interrogate sulfur charge and covalency in cysteine, particularly in proteins. X-ray spectroscopies provide an element specific probe of sulfur. We demonstrate the sensitivity of S Kβ and Kα X-ray emission spectroscopy (XES) to cysteine ionization and compare it to S K-edge X-ray absorption spectroscopy (XAS) in the physiologically relevant biomolecules l-cysteine and N-acetyl-l-cysteine at room temperature in solution phase. Kβ XES and K-edge XAS are most sensitive to chemical changes at the cysteine thiol and can be used to evaluate the composition of thiol/thiolate mixtures. Furthermore, these results provide a foundation for assessing the pK a of functionally significant cysteine residues in proteins and open the door to time-resolved studies of cysteine-dependent enzymes.

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

Whole-Voltage-Range Solid-Solution Reaction in Layered Oxide Cathode of Sodium-Ion Batteries

Layered manganese-based oxides (LMOs) are promising cathode materials for sodium-ion batteries (SIBs) due to their versatile structures. However, the Jahn–Teller effect of Mn 3+ induces severe distortion of MnO 6 octahedra, and the resultant low symmetry is responsible for the gliding of MnO 2 layers and then inferior multiple-phase transitions upon Na + extraction/insertion. Here, hexagonal P2-Na 0.643 Li 0.078 Mn 0.827 Ti 0.095 O 2 is synthesized through the incorporation of Li and Ti into the distorted orthorhombic P'2-Na 0.67 MnO 2 to function as a phase-transition-free oxide cathode. Further, it is revealed that Li in both the transition-metal and Na layers enhances the covalency of Mn–O bonds and allows degeneracy of Mn 3d e g orbitals to favor the formation of hexagonal phase, and the high strength of Ti–O bonds reduces the electrostatic interaction between Na and O for suppressed Na + /vacancy rearrangements. These collectively lead to a whole-voltage-range solid-solution reaction between 1.8 and 4.3 V with a small volume variation of 1.49%. This rewards its excellent cycling stability (capacity retention of 90% after 500 cycles) and rate capability (89 mAh g -1 at 2000 mA g -1 ).

25 ENERGY STORAGE↗
DOE OSTI2025

A theoretical study of the bonding properties of R 4 Sb 3 compounds

Here, this study investigates the electronic structure and bonding properties of rare-earth antimonide compounds, specifically Yb 4 Sb 3 and La 4 Sb 3 , utilizing density functional theory calculations. The analysis reveals that Yb 4 Sb 3 exhibits a predominantly ionic character whereas La 4 Sb 3 displays a greater degree of covalent bonding. Moreover, the presence of divalent ytterbium leads to p-type conduction at high temperatures in Yb 4 Sb 3 . Conversely, La 4 Sb 3 displays n-type conduction because of a larger electronic transfer from the rare-earth metal towards antimony. These findings provide valuable insights into the structural and electronic properties that govern the performance of R 4 Sb 3 compounds, contributing to the development of advanced materials for thermoelectric energy conversion.

36 MATERIALS SCIENCE↗
NASA NTRS2014

Improved Composites Using Crosslinked, Surface-Modified Carbon Nanotube Materials

Individual carbon nanotubes (CNTs) exhibit exceptional tensile strength and stiffness; however, these properties have not translated well to the macroscopic scale. Premature failure of bulk CNT materials under tensile loading occurs due to the relatively weak frictional forces between adjacent CNTs, leading to poor load transfer through the material. When used in polymer matrix composites (PMCs), the weak nanotube-matrix interaction leads to the CNTs providing less than optimal reinforcement.Our group is examining the use of covalent crosslinking and surface modification as a means to improve the tensile properties of PMCs containing carbon nanotubes. Sheet material comprised of unaligned multi-walled carbon nanotubes (MWCNT) was used as a drop-in replacement for carbon fiber in the composites. A variety of post-processing methods have been examined for covalently crosslinking the CNTs to overcome the weak inter-nanotube shear interactions, resulting in improved tensile strength and modulus for the bulk sheet material. Residual functional groups from the crosslinking chemistry may have the added benefit of improving the nanotube-matrix interaction. Composites prepared using these crosslinked, surface-modified nanotube sheet materials exhibit superior tensile properties to composites using the as received CNT sheet material.

polymer matrix composite↗