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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Intrinsically Hierarchical Nanoporous Polymers via Polymerization-Induced Microphase Separation

The synthesis of microporous polymers generally requires postpolymerization modification via hyper-cross-linking to trap the polymeric network in a state with high void volume. An alternative approach utilizes rigid, sterically demanding monomers to inhibit efficient packing, thus leading to a high degree of free volume between polymer side groups and main chains. In this work we combine polymers of intrinsic microporosity with polymerization-induced microphase separation (PIMS), a versatile methodology for the synthesis of nanostructured materials that can be rendered mesoporous. Copolymerization of various styrenic monomers with divinylbenzene in the presence of a poly(lactide) terminated with a chain-transfer agent (PLA-CTA) results in kinetic trapping of a microphase-separated state. Subsequent etching of PLA provides a bicontinuous mesoporous network. Using equilibrium and kinetic nitrogen sorption experiments as well as positron annihilation lifetime spectroscopy (PALS), we demonstrate that variations in the steric characteristics of the styrenic monomer impart the network with microporosity, resulting in hierarchically (meso and micro) porous materials. Additionally, structure–property relationships of the styrenic monomer with total surface area and pore volume indicate that the glass transition temperature (T g ) of the corresponding styrenic homopolymers provides a reasonable measure of the steric interactions and resultant microporosity in these systems. Finally, PALS provides insight into micro- and mesoscopic void volume differences between porous monoliths containing either tert-butyl or TMS-modified styrenic monomers compared to the parent, unmodified styrene.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis of CO 2 -Based Block Copolymers via Chain Transfer Polymerization Using Macroinitiators: Activity, Blocking Efficiency, and Nanostructure

Immortal copolymerization of epoxides/CO 2 using macro-chain-transfer agent (macro-CTA) is a useful method to prepare CO 2 -based block copolymers for manufacturing high value-added materials. Despite a variety of CO 2 -based block copolymers that have been reported using distinct macro-CTAs, issues including catalytic activity and blocking efficiency for the immortal polymerization remain superficially understood. Here, we systematically studied the reaction activity and blocking efficiency by using various macro-CTAs (including PPG, PEG, and PS) in the presence of two classical catalyst systems ((BDI)ZnOAc and SalenCoTFA/PPN-TFA). By analysis of the gel permeation chromatograms via mathematical deconvolution, it comes to a conclusion that the size, nature, and ratio of [macro-CTA]/[Cat.] strongly influence the catalytic activity of the reaction and blocking efficiency for the resultant block copolymers. As a result, thin film self-assembly of PS/PPC block copolymers was investigated, and the results were analyzed by SEM to ascertain the impact of blocking efficiency on nanoassembly.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Poly(olefin)-Based Anion Exchange Membranes Prepared Using Ziegler–Natta Polymerization

Bromoalkyl-functionalized poly(olefin)s were synthesized by copolymerization of 4-(4-methylphenyl)-1-butene with 11-bromo-1-undecene using Ziegler–Natta polymerization. The resulting bromoalkyl-functionalized poly(olefin)s were converted to quaternary ammonium-containing anion-conductive copolymers by reacting the pendant bromoalkyl group with trimethylamine or a custom-synthesized tertiary amine containing pendant quaternary ammonium moieties. Poly(olefin)-based AEMs with three cations per side chain showed considerably higher hydroxide conductivities, up to 201 mS/cm at 80 °C in liquid water, compared to that of samples with only one cation per bromoalkyl site (68 mS/cm, 80 °C, liquid water), likely due to phase separation in the triple-cation structure. More importantly, triple-cation side-chain poly(olefin) AEMs exhibited higher hydroxide conductivity under relative humidity conditions (50%–100%) than typical AEMs based on benzyltrimethylammonium cations. Here, the triple-cation the triple-cation side-chain poly(olefin)-based AEM exhibited an ionic conductivity as high as 115 mS/cm under 95% RH at 80 °C and 11 mS/cm under 50% RH at 80 °C. In addition to high ionic conductivity, the triple-cation side-chain poly(olefin) AEMs exhibited good chemical and dimensional stability. High retention of ionic conductivity (>85%) was observed for the samples in 1 M NaOH at 80 °C over 1000 h. Based on these high-performance poly(olefin) AEMs, a fuel cell with a peak power density of 0.94 W cm –2 (1.28 W cm –2 after iR correction) was achieved under H 2 /O 2 at 70 °C. The results of this study suggest a new, low-cost, and scalable route for preparation of poly(olefin)-based AEMs for anion exchange membrane applications.

25 ENERGY STORAGE↗
DOE OSTI2015

Formation of Alternating trans - A - alt - B Copolymers through Ring-Opening Metathesis Polymerization Initiated by Molybdenum Imido Alkylidene Complexes

Ring-opening metathesis polymerization (ROMP) is enabled to prepare trans-poly(A-alt-B) polymers from a 1:1 mixture of A and B where A is a cyclic olefin such as cyclooctene (A 1 ) or cycloheptene (A 2 ) and B is a large norbornadiene or norbornene derivative such as 2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B 1 ) or dimethylspirobicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1'-cyclopropane (B 2 ). The most successful initiators that were examined are of the type Mo(NR)(CHCMe 2 Ph)[OCMe(CF 3 ) 2 ] 2 (R = 2,6-Me 2 C 6 H 3 (1) or 2,6-i-Pr 2 C 6 H 3 (2)). The trans configuration of the AB linkages is proposed to result from the steric demand of B. Both anti-MB and syn-MB alkylidenes are observed during the copolymerization, where B was last inserted into a Mo=C bond, although anti-MB dominates as the reaction proceeds. anti-MB is lower in energy than syn-MB, does not react readily with eitherA or B, and interconverts slowly with syn-MB through rotation about the Mo=C bond. Syn-MB does not readily react with B, but it does react slowly with A (rate constant ~1 M –1 s –1 ) to give anti-MA and one trans-AB linkage. anti-MA then reacts with B (rate constant ~300 M –1 s –1 or larger) to give syn-MB and the second trans-AB linkage. The reaction has been modeled using experimental data in order to obtain the estimated rate constants above. The reaction between anti-MA and A is presented to give rise to AA linkages, but AA dyads can amount to <5%. Several other A and B monomers, initiators, and conditions were researched.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Pd–Methyl Bond Energy─Property Correlations, Noncorrelations, Machine Learning Models, and Application to Polymerization Catalysis

Metal–carbon bonds are a key intermediate in a variety of homogeneous organometallic transformations and often determine the critical thermodynamics and kinetics of catalytic processes. Surprisingly, the influence of different ligands on metal–carbon bond strengths has been largely overlooked. Here, in this study, we evaluated nearly 700 experimental Pd–methyl complexes by calculating their bond dissociation energies using density functional theory (DFT) and compared these bond strengths to several fundamental molecular properties, and this revealed several surprising correlations and noncorrelations. Most surprising was that several fundamental properties, such as the bond length, bond force constant, and bond electron density, have no correlation with bond strength, despite these correlations often holding for main-group compounds. We were indeed able to identify key ligand-dependent chemical features/descriptors that provided a highly accurate machine learning model and provided insight into the general factors that control the Pd–carbon bond strength, such as radical delocalization and nucleophilicity. Insights gained from the Pd–Me bond energy analysis were then applied to CO migratory insertion steps that are part of copolymerization reactions.

binding energy↗
DOE OSTI2026

Understanding the Influence of Chain Architecture on the Transport Quantities of Polymer Electrolytes with Covalently Bonded Anions

Here, we use a combination of experiments and coarse-grained molecular dynamics simulations to elucidate the structure–property relationships in polymer electrolytes obtained by the copolymerization of poly(vinyl ethylene carbonate─lithium styrene bis(trifluoromethanesulfonyl)imide) or p(VEC-LiSTFSI). Experiments show that the conductivity reduces with increasing anion (i.e., STFSI) fraction on the chain, and the cation transference number (t + ) is found to be dependent on the anion fraction. Furthermore, a significant fraction of unpolymerized VEC monomers are observed. Since it is inherently difficult to experimentally control the chain architecture and the amount of unpolymerized VEC in these systems, we perform coarse-grained molecular dynamics simulations on model polymer systems with different chain architectures to mimic the plausible experimental systems. Specifically, we look at the differences in transference numbers arising from (i) a random copolymer of VEC and STFSI monomers; (ii) a blend of VEC-STFSI copolymer with VEC monomers; and (iii) a ternary blend of the VEC homopolymer, STFSI homopolymers, and VEC monomers. The ternary blend model demonstrates the closest resemblance with the experimental transference numbers and diffusivities. The lithium diffusivity obtained from the coarse-grained models with VEC monomers (plasticizers) is about 1.5 times that of the model without VEC monomers, showing that the plasticizing effect of VEC monomers is modest. We rationalize the experimental observations based on aggregate and cluster analyses obtained from molecular simulations. This work reveals that polymer electrolyte chain architecture and plasticizers can critically influence the transport properties, and these parameters should be considered when designing single ion conducting polymeric electrolytes.

cluster distribution↗
DOE OSTI2020

Adhesive Polymers as Efficient Binders for High-Capacity Silicon Electrodes

The major cause for capacity fading of silicon nanoparticle (SiNP)-based electrodes is the immense pressure applied toward the conductive networks during the charge/discharge process. While numerous efforts have been devoted to investigating different types of polymer binders, the rational design of an adhesive binder with pressure sensitivity has rarely been reported. Herein, a series of pressure-sensitive adhesives (PSAs) synthesized via copolymerization of 2-ethylhexyl acrylate (2-EHA) and acrylic acid (AA) are evaluated as polymer binders for SiNP-based electrodes. The balance between the density of interaction groups and viscoelastic properties is systematically investigated for efficient binding performance. The SiNP-based electrode using PSA with 20 mol % of 2-EHA (Si-PSA-20%) exhibits excellent electrochemical performance, achieving a capacity retention of 83% at the 100th cycle compared with 54% for Si-PAA after activation. Si-PSA-20% also delivers a superior cycling performance at a high current density (1731 mAh g –1 after 350 cycles vs 719 mAh g –1 after 150 cycles for Si-PAA, 1.8 A g –1 ) and at high mass loading of active materials (capacity retention of 74 vs 38% for Si-PAA after 100 cycles, SiNP content ~1.2 mg cm –2 ). Atomic force microscopy (AFM), peel tests, and Car–Parrinello molecular dynamics (CPMD) simulations are employed to understand their binder performance. The novel design and systematical investigation of PSAs as binders will definitely be appealing for not only the Si electrode but also for other high-energy-density electrode materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Elucidating Design Rules toward Enhanced Solid-State Charge Transport in Oligoether-Functionalized Dioxythiophene-Based Alternating Copolymers

This study investigates the solid-state charge transport properties of the oxidized forms of dioxythiophene-based alternating copolymers consisting of an oligoether-functionalized 3,4-propylenedioxythiophene (ProDOT) copolymerized with different aryl groups, dimethyl ProDOT (DMP), 3,4-ethylenedioxythiophene (EDOT), and 3,4-phenylenedioxythiophene (PheDOT), respectively, to yield copolymers P(OE3)-D, P(OE3)-E, and P(OE3)-Ph. At a dopant concentration of 5 mM FeTos 3 , the electrical conductivities of these copolymers vary significantly (ranging between 9 and 195 S cm –1 ) with the EDOT copolymer, P(OE3)-E, achieving the highest electrical conductivity. UV–vis–NIR and X-ray spectroscopies show differences in both susceptibility to oxidative doping and extent of oxidation for the P(OE3) series, with P(OE3)-E being the most doped. Wide-angle X-ray scattering measurements indicate that P(OE3)-E generally demonstrates the lowest paracrystallinity values in the series, as well as relatively small π–π stacking distances. The significant (i.e., order of magnitude) increase in electrical conductivity of doped P(OE3)-E films versus doped P(OE3)-D or P(OE3)-Ph films can therefore be attributed to P(OE3)-E exhibiting both the highest carrier ratios in the P(OE3) series, along with good π–π overlap and local ordering (low paracrystallinity values). Furthermore, these trends in the extent of doping and paracrystallinity are consistent with the reduced Fermi energy level and transport function prefactor parameters calculated using the semilocalized transport (SLoT) model. Observed differences in carrier ratios at the transport edge (c t ) and reduced Fermi energies [η(c)] suggest a broader electronic band (better overlap and more delocalization) for the EDOT-incorporating P(OE3)-E polymer relative to P(OE3)-D and P(OE3)-Ph. Ultimately, we rationalize improvements in electrical conductivity due to microstructural and doping enhancements caused by EDOT incorporation, a structure–property relationship worth considering in the future design of highly electrically conductive systems.

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

Cocontinuous Nanostructures by Microphase Separation of Statistically Cross-Linked Polystyrene/Poly(2-vinylpyridine) Networks

Cocontinuous polymeric nanostructures have drawn considerable attention due to their ability to combine distinct, percolation-dependent properties of two different polymer domains. Randomly end-linked copolymer networks (RECNs) have previously been shown to support the formation of disordered cocontinuous nanostructures across wide composition windows in a robust way. However, achieving highly efficient linking of telechelic polymers with excellent end-group fidelity often requires complex synthetic routes. As an alternative, we study here statistically cross-linked copolymer networks (SCCNs) composed of polystyrene and poly(2-vinylpyridine) (PS and P2VP) with cross-linkable allyl pendent groups that are conveniently synthesized by controlled radical copolymerization. Via selective extraction of P2VP, coupled with gravimetry, small-angle X-ray scattering, and electron microscopy, we find disordered cocontinuous phases across wide composition ranges (up to ≈ 35 wt %), approaching values previously determined for RECNs. Remarkably, even for samples that appear to exhibit full percolation, a substantial fraction of P2VP (≈ 20–30 wt %) cannot be removed, which we ascribe to short strands between nearby cross-linkers that are physically embedded within PS domains. Here, the resulting PS porous monoliths with residual surface P2VP layers enable facile surface modification to resist protein adsorption and templating of porous gold nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Electronic and Morphological Studies of Conjugated Polymers Incorporating a Disk-Shaped Polycyclic Aromatic Hydrocarbon Unit

As more research findings have shown the correlation between ordering in organic semiconductor thin films and device performance, it is becoming more essential to exercise control of the ordering through structural tuning. Many recent studies have focused on the influence of side chain engineering on polymer packing orientation in thin films. However, the impact of the size and conformation of aromatic surfaces on thin film ordering has not been investigated in great detail. Here we introduce a disk-shaped polycyclic aromatic hydrocarbon building block with a large π surface, namely, thienoazacoronenes (TACs), as a donor monomer for conjugated polymers. Here, a series of medium bandgap conjugated polymers have been synthesized by copolymerizing TAC with electron donating monomers of varying size. The incorporation of the TAC unit in such semiconducting polymers allows a systematic investigation, both experimentally and theoretically, of the relationships between polymer conformation, electronic structure, thin film morphology, and charge transport properties. Field effect transistors based on these polymers have shown good hole mobilities and photoresponses, proving that TAC is a promising building block for high performance optoelectronic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Chemically and Mechanically Recyclable Vitrimers from Carbon Dioxide-Based Polycarbonates

Designing thermoset materials with dynamic crosslinks is an important strategy to mitigate rising global carbon dioxide emission levels. The development of polymers from sustainable feedstocks, with efficient manufacturing methods, for high-value applications, and with circular end-of-use solutions is essential for advancing material technologies. One approach involves exploiting carbon dioxide itself as feedstock to create high performance, sustainable materials, by enchaining 50 mol% CO2 via copolymerization with epoxides to yield polycarbonates. This work describes the synthesis, end-functionalization, and curing of poly(propylene carbonate) (PPC) and poly(cyclohexene carbonate) (PCHC) into beta-hydroxy ester vitrimers. These vitrimers demonstrate the ability to be mechanically reprocessed up to 3 times with retention of the material’s properties through dynamic transesterification exchange reactions. The polycarbonate vitrimers with gel fractions exceeding 90 % exhibit high tensile strength (> 50 MPa) and Young’s modulus (> 2 GPa), achieved by varying repeat unit structure in the polymer backbone from the low Tg PPC to the more rigid high Tg PCHC structures. Owing to an entropically favorable chain back-biting mechanism, the network chains can be cleaved and depolymerized into cyclic small molecules. In the case of PCHC, this process enables repolymerization back to polycarbonates with 69 wt.% CO2 retention through life-cycles. The promising mechanical performance and recyclability of these CO2-based polycarbonate vitrimers indicate their potential for sustainable, high-performance materials, paving the way for future innovations in circular polymer technologies and carbon capture utilization.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Dithieno[3,2-c:3′,2′‑ h ][2,6]naphthyridine-4,9(5H,10H)-dione-Based Conjugated Polymers for High Stable n‑Type Organic Electrochemical Transistors

Amide/imide-based conjugated polymers have been utilized as n-type OECT materials and have demonstrated promising device performance. However, their performance remains insufficient in terms of both efficiency and stability, which limits their practical applications. The development of conjugated polymers based on amide and imide groups represents a promising approach to address this issue. Here, in this study, we introduced dithieno­[3,2-c:3′,2′-h]­[2,6]­naphthyridine-4,9­(5H,10H)-dione (TVTDA) into the design of the OECT materials for the first time. By copolymerizing it with (E)-2,2′-(ethene-1,2-diyl)­bis­(thiophene-3-carbonitrile), we prepared two polymers, TVTDA-2CNTVT-ST and TVTDA-2CNTVT-BR, which contain linear or branched ethylene glycol side chains, respectively. OECT devices based on these polymers demonstrate n-type charge transport characteristics, achieving promising μC* values of 7.17 and 26.5 F cm –1 V –1 s –1 for TVTDA-2CNTVT-ST and TVTDA-2CNTVT-BR, respectively. The higher electron mobility and μC* of TVTDA-2CNTVT-BR can be attributed to its mixed edge-on and face-on stacking mode, larger crystalline coherence length, and larger domain size in the thin film. To our delight, the OECT devices based on both polymers exhibit good operational stability after operating in an aqueous solution for 2000 s, with current retention rates exceeding 93%, representing the high level among the OECT devices based on amide/imide-conjugated polymers. Our study demonstrates that the TVTDA unit holds great potential for constructing high-performance n-type OECT materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A lyotropic liquid crystal-templated nanofiltration membrane with thermo- and pH-responsive 3D transport pathway

We produce controlled nanostructured membranes from cross-linking of self-assembled diacrylated poloxamers. At sufficiently high concentrations, poloxamers form lyotropic liquid crystals (LLCs), such as lamellar (L α ), cubic packing of spherical micelles, and hexagonal packing of rod-like micelles in water (H 1 ). We use the H 1 phase as a template to produce orderly packed nanofibrous membranes. The obtained membrane has a continuous 3D transport pathway and can alter its nanofiltration (NF) properties in response to changes in temperature and pH. The formulation includes Pluronic P84-diacrylate (P84DA), a thermoresponsive component that acts as both macromer and structure-directing amphiphile. P84DA facilitates changes in membrane pore size with temperature due to its thermoresponsiveness when it is in contact with water. Furthermore, the precursor contains acrylic acid (AAc) as the charged component, which upon copolymerization with P84DA, not only enables ion separation through Donnan exclusion but also imparts pH-responsive behavior for the separation of ionic species. The membrane performance is studied and compared with a commercial NF membrane (NF270). We show that the synthesized NF membrane has separation properties adjustable with temperature and pH with exceptional resistance to fouling by various solutes due to its highly hydrophilic surface. Furthermore, the membrane shows an outstanding sulfate over chloride ion selectivity, which is a requirement for salt fractionation applications. Deducted from separate experiments, the ideal chloride/sulfate selectivity for magnesium cation is about 2.38 at low ionic strengths. This study is done on a model system to show the capability of incorporating pH-responsiveness in LLC templated membranes, in which the pH-responsive range can be designed by changing the charged groups of comonomer in the formulation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Controlling Complex Coacervation via Random Polyelectrolyte Sequences

The utilization of chemical sequence control in polymeric materials is key to enabling material design on par with biomacromolecular systems. One important avenue for scalable sequence-controlled polymers leverages the random copolymerization of distinct monomers, with the statistical distribution of the monomeric sequence arising from reaction kinetics following a first-order Markov process. Here we utilize the framework of the random phase approximation (RPA) to develop a theory for the phase behavior of symmetric polyelectrolyte coacervates whose chemical sequences are dictated by simple statistical distributions. We find that a high charge "blockiness" within the random sequences favors the formation of denser and more salt-resistant coacervates while simultaneously increasing the width of the two-phase region. Here, we trace these physical effects to the increased cooperativity of Coulomb interactions that results from increased charge blockiness in oppositely charged polyelectrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

Grafting density is an important structural parameter that imparts significant influences over the physical properties of architecturally complex polymers. In this paper, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). ω-norbornenyl poly(D,L-lactide) (PLA) and polystyrene (PS) macromonomers were copolymerized with discrete co-monomers in different feed ratios, enabling precise control over the grafting density. Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers can self-assemble into long-range-ordered lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ N bb α ) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, instead of segregation strengths. A model is pro-posed in which the characteristic ratio (C ∞ ), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ~ N bb f(z) . To the best of our knowledge, this report represents the first study of scaling behavior for the self-assembly of block polymers with variable grafting density. Lastly, the relationships disclosed herein provide valuable insights into conformational changes with grafting density, thus introducing new opportunities for future block polymer design.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hierarchical On-Surface Synthesis of Graphene Nanoribbon Heterojunctions

Bottom-up graphene nanoribbon (GNR) heterojunctions are nanoscale strips of graphene whose electronic structure abruptly changes across a covalently bonded interface. Their rational design offers opportunities for profound technological advancements enabled by their extraordinary structural and electronic properties. Thus far, the most critical aspect of their synthesis, the control over sequence and position of heterojunctions along the length of a ribbon, has been plagued by randomness in monomer sequences emerging from step-growth copolymerization of distinct monomers. All bottom-up GNR heterojunction structures created so far have exhibited random sequences of heterojunctions and, while useful for fundamental scientific studies, are difficult to incorporate into functional nanodevices as a result. In contrast, we describe a hierarchical fabrication strategy that allows the growth of bottom-up GNRs that preferentially exhibit a single heterojunction interface rather than a random statistical sequence of junctions along the ribbon. Such heterojunctions provide a viable platform that could be directly used in functional GNR-based device applications at the molecular scale. Our hierarchical GNR fabrication strategy is based on differences in the dissociation energies of C-Br and C-I bonds that allow control over the growth sequence of the block copolymers from which GNRs are formed and consequently yields a significantly higher proportion of single-junction GNR heterostructures. In conclusion, scanning tunneling spectroscopy and density functional theory calculations confirm that hierarchically grown heterojunctions between chevron GNR (cGNR) and binaphthyl-cGNR segments exhibit straddling Type I band alignment in structures that are only one atomic layer thick and 3 nm in width.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synergistic Removal of Zinc and Copper in Greenhouse Waste Effluent by Struvite

Struvite (MgNH 4 PO 4 ·6H 2 O) can be recovered from wastewaters for mitigation of phosphorus content. However, the interaction of dissolved constituents with struvite is rarely evaluated. Removal of heavy metals and total organic carbon (TOC) in a greenhouse wastewater (GW) by struvite was investigated in this work. Presynthesized struvite was added to GW and removal of Zn (689 μg/L), Cu (151 μg/L), and TOC (51 mg/L) monitored from 1 to 26 d. Metal uptake in sodium nitrate solutions was used to assess competition, and the influence of other GW constituents on sorption. Struvite was also directly precipitated from GW (PPT). Recovered GW solids had 64–247 mg/kg Zn, 12–54 mg/kg Cu, and 1721–8806 mg/kg TOC, with lowest loadings for PPT and highest for 26 d solids. X-ray absorption spectroscopy detected polymerized Zn-phosphate, induced by dissolved phosphorus in GW, and Cu copolymerization, initially limited by aqueous Cu-organic complexation. Sorbed Cu shifts Fourier transform infrared-sensitive phosphate bands and changes the intensities of reflections in X-ray diffraction patterns of struvite more so than Zn. Struvite from GW is more susceptible to thermal decomposition than unreacted struvite, evolving CO(g), CO 2 (g), NH 3 (g), and H 2 O(g). Therefore, struvite from GW sorbs metals and organics, and can release sorbed and structural components to the aqueous and gas phases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗