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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

2‐Aminobenzenethiol‐Functionalized Silver‐Decorated Nanoporous Silicon Photoelectrodes for Selective CO 2 Reduction

Abstract A molecularly thin layer of 2‐aminobenzenethiol (2‐ABT) was adsorbed onto nanoporous p‐type silicon (b‐Si) photocathodes decorated with Ag nanoparticles (Ag NPs). The addition of 2‐ABT alters the balance of the CO 2 reduction and hydrogen evolution reactions, resulting in more selective and efficient reduction of CO 2 to CO. The 2‐ABT adsorbate layer was characterized by Fourier transform infrared (FTIR) spectroscopy and modeled by density functional theory calculations. Ex situ X‐ray photoelectron spectroscopy (XPS) of the 2‐ABT modified electrodes suggests that surface Ag atoms are in the +1 oxidation state and coordinated to 2‐ABT via Ag−S bonds. Under visible light illumination, the onset potential for CO 2 reduction was −50 mV vs. RHE, an anodic shift of about 150 mV relative to a sample without 2‐ABT. The adsorption of 2‐ABT lowers the overpotentials for both CO 2 reduction and hydrogen evolution. A comparison of electrodes functionalized with different aromatic thiols and amines suggests that the primary role of the thiol group in 2‐ABT is to anchor the NH 2 group near the Ag surface, where it serves to bind CO 2 and also to assist in proton transfer.

Kan, Miao↗
DOE OSTI2026

Mechanistic Insights into CO 2 -to-CO Photoreduction by Proton-Responsive Imidazole–Pyridine Re(I) Complexes

Two Re(I) tricarbonyl complexes with imidazole-pyridine ligands, fac- [Re(CO) 3 (pbiH)Cl], (Re-pbiH), and fac-[Re(CO) 3 (bbzp)Cl] (Re-bbzp), where pbiH= 2-(2-pyridy)benzimidazole, bbzp = 2,6-bis(2-benzimidazolyl)pyridine, were synthesized, and their photophysical, electrochemical, and photochemical properties were investigated for application as photocatalysts for CO 2 -to-CO reduction. Upon light irradiation (λ > 370 nm) in CO 2 -saturated CH3CN using 1,3-dimethyl-2-phenyl-2,3-dihydro-1Hbenzo[ d]imidazole (BIH) as a sacrificial donor, Re-bbzp promotes CO formation with a turnover number (TON CO ) of 45 ± 2, whereas Re-pbiH displayed a significantly lower activity (TON CO = 8 ± 1). The role of the bbzp ligand in the photocatalytic behavior was examined in detail using IR spectroelectrochemistry (IR-SEC) together with in situ FTIR and UV−vis spectroscopy under photocatalytic conditions, revealing the formation of key intermediates involved in CO 2 activation. The superior activity of Re-bbzp was rationalized by its ability to function as a proton relay and two-electron acceptor. The role as a proton relay was further supported by the observation of a kinetic isotope effect (KIE = 1.5) when the deuterated electron donor BID was employed, in agreement with the unusual decrease in catalytic activity observed upon addition of Brønsted bases. Overall, these results provide new insights into the role of ligand-based proton-responsive sites in Re(I) tricarbonyl complexes and their impact on CO 2 reduction photocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Effect of Storage Conditions on Efficacy of Poly(ethylenimine)-Alumina CO 2 Sorbents

Solid amine sorbents are one of the primary components of DAC technologies that allow for the removal of ultradilute CO 2 from the atmosphere. A main drawback in the implementation of solid amine sorbents in industrial-scale DAC applications is their instability under certain operational or storage conditions over an extended period. In this work, the effect of storage temperature and gas composition in the storage headspace on the long-term stability of a poly(ethylenimine)-alumina (PEI/γ-Al 2 O 3 ) sorbent is explored. PEI/γ-Al 2 O 3 sorbents with 70 and 100% pore filling are aged under varying gases (N 2 , O 2 , Ar, 0.04% CO 2 −N 2 , CO 2 , and ambient air) in an oven (40 °C), at common ambient indoor temperature conditions (23 °C), or in a freezer (−4 °C). The CO 2 sorption capacity, as measured by thermogravimetric analysis (TGA), along with FTIR spectra of the fresh and aged sorbents, reveal that at 23 and −4 °C, storage under ambient air or inert gas (Ar) provides reasonable long-term stability, with <13% degradation over 12 and 5 months of storage. Interestingly, with storage at 40 °C, similar levels of deactivation were observed under pure O 2 and N 2 after 4 months of storage, which suggests that nonoxidative thermal reactions can occur under prolonged storage conditions under N 2 . In contrast, with storage under CO 2 , sorbent degradation is substantially suppressed compared to storage under N 2 , ambient air, O 2 , or Ar, yielding sorbents with no observable loss in capacity after 2 months, compared to a 66, 63, and 62% loss under N 2 , ambient air, and N 2 in the same period at 40 °C, respectively. Overall, these findings provide guidance for practical amine sorbent storage in academic or industrial settings where amine sorbents are used for carbon capture.

Atmospheric chemistry↗
DOE OSTI2021

In Situ ATR-FTIR Study of the Cathode–Electrolyte Interphase: Electrolyte Solution Structure, Transition Metal Redox, and Surface Layer Evolution

We present a study of the lithium nickel manganese cobalt oxide (LiNi 0.6 Mn 0.2 Co 0.2 O 2 , NMC622) cathode-electrolyte interphase (CEI) during galvanostatic charging and discharging using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) methods to investigate the voltage dependent electrolyte solution structure changes at the interface, transition metal (TM) redox chemistry, and cathode/electrolyte interfacial layer evolution. Furthermore, our in situ cell design provides both reliable electrochemical device testing and strong FTIR vibrational absorption signals near the cathode surface. Specifically, advanced spectral analysis elucidates changes of near-surface Li+ ion (de)solvation by solvent molecules during galvanostatic cycling. Moreover, cathode metal-oxygen vibrational absorptions, sensitive to TM redox behaviors and subsequent local structural variations, were correlated to cathode de-lithiation (and lithiation) and electrolyte solution structure changes. In addition, we have detected the formation and evolution of a CEI surface layer on the NMC622 cathode that contributes to the cell's capacity fade.

25 ENERGY STORAGE↗
DOE OSTI2025

Hydrogen Adsorption, Reactivity, and Catalysis on Colloidal Iron Carbide Nanoparticles

Supported iron carbide particles have long served as catalysts for CO hydrogenation (the Fischer Tropsch synthesis, FTS) and continue to be attractive. Despite this, little is known about their chemistry. Reported here is a colloidal Fe x C nanoparticle (NP) model system that allows direct observation of surface hydrogen and CO, as well as quantification of the surface H. Dodecylamine-capped Fe x C NPs (DDA-Fe x C NPs) were synthesized through solution-phase carburization of Fe NPs and form stable colloids in low-polarity organic solvents. Treatment of these colloids with H 2 or D 2 produced highly hydrogenated materials, and FTIR spectra of DDA-Fe x C-D n showed that most of the D binds to carbides, with at least four distinct v(C-D) modes. The surface C-H(D) bonds were all reactive, transferring hydrogen to alkenes and other reagents in solution. Titration and ICP measurements showed a 0.17:1 ratio of added H:total Fe, or roughly. 40 H per 1.8 nm DDA-Fe x C NP. Conversely, CO was preferentially bound to surface Fe sites, with FTIR spectra showing a single broad v(CO) that shifted with CO coverage or co-adsorption of H 2 . The DDA-Fe x C NPs were active catalysts for both olefin hydrogenation and the FTS, under mild conditions and without catalyst pre-treatment. The CO hydrogenation reactions yielded a broad distribution of long-chain linear paraffins and olefins. Though quantitative comparisons with typical FTS results are not possible because of our use of sealed batch reactors and other factors, the observations of high catalytic reactivity demonstrate the relevance of this model system to iron-carbide catalysis. DFT calculations on model slab surfaces with varying iron carbide stoichiometries revealed that the thermodynamically preferred surface adsorption sites are C for H ads and Fe for CO ads . A variety of binding sites and binding energies were found for each adsorbate. We are unaware of previous studies indicating that a diverse array of C-H bonds is the primary source of reactive H on iron carbides. Experimentally, the diversity of *C-H sites was evident in reactions with H-atom donors and abstractors of different strengths, from both the reaction stoichiometries and IR spectra. The different surface–H binding energies correlate with the v(C-D) stretching frequencies. Furthermore, these insights into complex iron carbide surfaces and catalysis could assist catalyst design, and they showcase the importance of stoichiometric studies of reaction intermediates.

08 HYDROGEN↗
DOE OSTI2026

Structural and physicochemical insights into pH-responsive poly(DEAEMA- co -HEMA)-grafted mesoporous silica nanoparticles

Mesoporous silica nanoparticles (SiO 2 ) grafted with responsive polymer shells are versatile hybrid systems. Understanding their three-dimensional organization in the hydrated state remains a significant challenge. Here, in this study, SiO 2 nanoparticles were functionalized with a poly(DEAEMA-co-HEMA) shell via a “grafting-from” polymerization strategy in aqueous media. Successful surface modification was confirmed by FTIR, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, N 2 sorption, and ζ-potential, yielding grafting contents of 22% (p1 DEAEMA-co-HEMA ) and 49% (p2 DEAEMA-co-HEMA ). Small-angle neutron scattering (SANS) with solvent contrast variation was employed to elucidate the solution-state core–shell architecture of p1 and p2 hybrids at pH 2, where the grafted polymer shell is protonated and highly hydrated. Near contrast matching of the silica core, theoretically estimated at 58% D 2 O, suppressed the scattering intensity, enhancing sensitivity to the polymer shell. Constrained core–shell ellipsoid modeling across solvent contrasts revealed a systematic increase in shell thickness, overall particle dimensions, and shell anisotropy with increasing grafting content. In solution, the hydrated polymer shells were markedly more extended and structurally anisotropic than suggested by dry-state techniques structural characterization, highlighting the importance of solution-state structural analysis for accurately describing grafted polymer architectures.

Core-shell biomaterials↗
DOE OSTI2020

Selective hydrogenation of CO 2 and CO over potassium promoted Co/ZSM-5

The utilization of CO 2 as a C 1 feedstock for synthesis of value-added chemicals and fuels could both mitigate the negative effects associated with increasing CO 2 emissions and decrease dependence on fossil fuels as part of a future circular carbon economy. Co-based catalysts have been well-developed for Fischer-Tropsch synthesis (FTS), but replacing the CO reactant with CO 2 (CO 2 -FTS) typically results in low selectivity toward desirable light olefins. To better understand the structure-property relationships of Co-based catalysts, and extend promising FTS results to CO 2 -FTS, we have studied the effect of a potassium promoter and acidic properties of ZSM-5 on catalytic performance. The selectivity of FTS and CO 2 -FTS is shown to be a strong function of Si/Al ratio in co-impregnated catalysts, with findings supported by in situ XAFS and FTIR, demonstrating light olefin selectivity can be tuned by Si/Al ratio and the method of introducing the K promoter.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tunable structure and reinforcement of polyvinyl alcohol (PVA) hydrogels using fungal chitin particles

Polysaccharides, including chitin, are one of the most abundant biopolymers in nature and are increasingly recognized as a sustainable alternative to petroleum-derived plastics and synthetic fillers in polymer composites. Traditionally sourced from crustacean shells, chitin offers mechanical strength and biocompatibility with limitations also in processability and functionality. Fungal-derived chitin material represents a promising alternative, with advantages including scalable fermentation on low-cost substrates, absence of shellfish allergens, and tunable molecular architectures that vary by species, developmental stage, and growth environment. Here, in this study, we systematically examined chitinous materials obtained from taxonomically and functionally distinct fungi, Laccaria bicolor, Trichoderma reesei and Rhizopus oryzae, to assess their structural, chemical, and morphological properties as reinforcement agents in polymer composites. Mild alkaline pretreatment was employed to obtain mycelium chitin particles, thereby improving accessibility to chitin and co-occurring β-D-glucans while maintaining microparticle integrity. Comprehensive FTIR and solid-state NMR analyses revealed species-specific differences in chemical composition and microstructure, with R. oryzae exhibiting a unique spectral signature. These fungal-derived chitin were then incorporated into poly(vinyl alcohol) (PVA) hydrogels, where they acted as reinforcing fillers without the need for additional chemical crosslinkers. Comparative evaluation of hydrogel properties demonstrated that fungal chitin significantly enhanced mechanical performance, with all mycelium fillers mitigating the water weakening in PVA hydrogels. R. oryzae-derived composites tripled the hydrogel tensile strength while the submicron fibrous morphology in L. bicolor contributes to over 45 % tensile improvement in dry PVA composites. Our findings highlight the potential of fungal biomass as a tunable, sustainable platform for producing chitin-based reinforcing agents.

Chitin↗
DOE OSTI2023

Carbonic Anhydrase Enhanced UV-Crosslinked PEG-DA/PEO Extruded Hydrogel Flexible Filaments and Durable Grids for CO 2 Capture

In this study, poly (ethylene glycol) diacrylate/poly (ethylene oxide) (PEG-DA/PEO) interpenetrating polymer network hydrogels (IPNH) were extruded into 1D filaments and 2D grids. The suitability of this system for enzyme immobilization and CO 2 capture application was validated. IPNH chemical composition was verified spectroscopically using FTIR. The extruded filament had an average tensile strength of 6.5 MPa and elongation at break of 80%. IPNH filament can be twisted and bent and therefore is suitable for further processing using conventional textile fabrication methods. Initial activity recovery of the entrapped carbonic anhydrase (CA) calculated from esterase activity, showed a decrease with an increase in enzyme dose, while activity retention of high enzyme dose samples was over 87% after 150 days of repeated washing and testing. IPNH 2D grids that were assembled into spiral roll structured packings exhibited increased CO 2 capture efficiency with increasing enzyme dose. Long-term CO 2 capture performance of the CA immobilized IPNH structured packing was tested in a continuous solvent recirculation experiment for 1032 h, where 52% of the initial CO 2 capture performance and 34% of the enzyme contribution were retained. These results demonstrate the feasibility of using rapid UV-crosslinking to form enzyme-immobilized hydrogels by a geometrically-controllable extrusion process that uses analogous linear polymers for both viscosity enhancement and chain entanglement purposes, and achieves high activity retention and performance stability of the immobilized CA. Potential uses for this system extend to 3D printing inks and enzyme immobilization matrices for such diverse applications as biocatalytic reactors and biosensor fabrication.

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

Determination of Carbon, Hydrogen, Nitrogen, and Oxygen in Bio-Oils: Laboratory Analytical Procedure (LAP)

The determination of total carbon, hydrogen, and nitrogen in bio-oils is important as these values can be used to track the carbon balance of production processes as well as calculate total oxygen content by difference. Oxygen content of bio-oils is a key metric for production and upgrading strategies as these are typically aimed at reducing oxygen. Oxygenates in bio-oils contribute to poor hydrocarbon miscibility, high acidity, high viscosity, and poor stability. Upgrading of bio-oils via deoxygenation produces hydrocarbons which can be used to generate feedstocks for renewable fuels and chemicals. In this Laboratory Analytical Procedure (LAP), combustion-based ultimate analysis is used to determine the weight percent (wt%) of C, H, and N in bio-oils and upgraded products. Ultimate analysis uses high temperatures and a pure oxygen environment to completely combust organic samples to carbon dioxide (CO 2 ), water (H 2 O), and nitrogen oxides (NO x ). In this procedure the amount of C and H in the sample are quantified by measuring resultant CO 2 and H 2 O with Fourier-transform infrared spectroscopy (FTIR). For N, NO x is reduced to nitrogen (N 2 ) which is measured with a thermal conductivity detector (TCD), providing total N content.

09 BIOMASS FUELS↗
DOE OSTI2023

Novel Co 5 Cluster Based Triazole Bridged Cobalt-Fluorophosphate: Synthesis, Structure, Magnetic and Heterogeneous Catalytic Epoxidation Studies

A novel triazole bridged cobalt fluorophosphate coordination polymer with the formula {Co 5 (1,2,4-triazole) 2 (OH) 2 (PO 3 F) 4 } n has been synthesized. Single crystal X-ray studies reveal that the compound comprises of Co 5 clusters which ultimately build the whole framework, here all cobalt centers are in octahedral geometry established from continuous shape analysis. All the cobalt centers are in Co(II) oxidation state and the results are supported by the bond valence sum (BVS) calculation. The sample has been characterized by single crystal X-ray, powder X-ray, FTIR and TGA analysis. The compound was tested for olefin catalysis performance and magnetism. Magnetization measurements reveal overall antiferromagnetic interactions among the Co(II) ions. The compound is very active in the catalytic transformation of olefins to their corresponding epoxides. In conclusion, catalytic epoxidation studies reveal that cyclohexene and styrene can be converted up to 97% with almost 65% selectivity of products with higher TON numbers.

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

Effects of Co doping on the structure and physicochemical properties of hausmannite (Mn 3 O 4 ) and its transformation during aging

Hausmannite is a common low-valence manganese oxide mineral with a distorted spinel structure in surficial sediments. Although natural Mn oxides often contain various transition metal (TM) impurities, few studies have addressed the substitution mechanisms of TMs, such as cobalt (Co), with hausmannite and induced changes in the mineral physicochemical properties. In this study, Co-doped hausmannites with final Co/Mn molar ratios of 0.05 and 0.11 were synthesized and characterized by wet chemical analysis, powder X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR), high resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS). Co-doped samples have larger crystallite sizes and smaller specific surface areas than those of the hausmannite without Co. The Co cations exist in a mixed-valence of +3 and + 2. Powder XRD and acid dissolution experiments indicate that Co incorporates into the mineral structures, and increases the mineral structural stability. Co K-edge extended X-ray adsorption fine structure (EXAFS) analysis demonstrates that Co likely substitutes for lattice Mn(III). After aging at room temperature for three years, 14.1 ± 1.9% of pure hausmannite is transformed to manganite while only 2.6 ± 0.7% of manganite appears in the aged Co-doped sample with an initial Co/Mn molar ratio of 0.10. Finally, these results provide new insights into the incorporation mechanisms of TMs into low valence Mn oxides, and the stability of these minerals in natural environments.

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

Hybrid Absorption–Crystallization Strategies for the Direct Air Capture of CO2 Using Phase-Changing Guanidium Bases: Insights from in Operando X-ray Scattering and Infrared Spectroscopy Measurements

Efforts to limit rising concentrations of CO 2 have motivated the development of negative emission technologies. Direct air capture (DAC) of CO 2 is one of the negative emissions technologies that has been proposed for the direct removal of CO 2 from the atmosphere. Phase-changing bis(iminonoguanidine) (BIG) sorbents have been developed for the direct air capture of CO 2 . These phase changing sorbents, specifically glyoxal-bis(iminoguanidine) (GBIG), involve (1) CO 2 absorption with aqueous amino acid salts, such as K- or Na-glycinate to yield bicarbonate-rich solutions, (2) crystallization of the bicarbonate anions with a BIG solid, which regenerates the amino acid, and (3) solid-state CO 2 release from the carbonate crystals and BIG regeneration. Despite the promising potential of these materials, their structural evolution during the thermal regeneration of the BIG solids, chemical regeneration of the sodium or potassium glycinate solvents, and the crystallization behavior of CO 2 -loaded BIG bicarbonate remain to be evaluated and understood in detail. The aim of this study is to probe these knowledge gaps. In situ wide-angle X-ray Scattering (WAXS) results show that CO 2 and water molecules in GBIG bicarbonate are simultaneously released in a single step during the thermal regeneration of the sorbent at 97 – 134 °C. In situ ATR-FTIR measurements showed that sodium glycinate and GBIG bicarbonate are simultaneously generated when GBIG, glycine, and sodium bicarbonate are reacted. The crystallization of GBIG bicarbonate from GBIG and CO 2 -loaded monoethanolamine (MEA) occurs rapidly in the first 10 min of the reaction, as determined using in situ GI-SAXS measurements. Overall, the insights from these studies are essential for the scalable implementation of CO 2 capture technologies using these phase-changing sorbents.

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

Comprehensive Dynamics in a Polyelectrolyte Complex Coacervate

The linear viscoelastic response, LVR, of a hydrated polyelectrolyte complex coacervate, PEC, was evaluated over a range of frequencies, temperatures, and salt concentrations. The PEC was a nearly stoichiometric blend of a quaternary ammonium poly([3-(methacrylamido)propyl]trimethylammonium chloride), PMAPTAC, and poly(2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt), PAMPS, an aliphatic sulfonate, selected because they remain fully charged over the conditions of use. Narrow molecular weight distribution polyelectrolytes were prepared using fractionation techniques. A partially deuterated version of PMAPTAC was incorporated to determine its coil radius of gyration, R g , within PECs using small-angle neutron scattering. Chain dimensions were determined to be Gaussian with a Kuhn length of 2.37 nm, which remained constant from 25 to 65 °C. The LVR for a series of matched molecular weight PECs, mostly above the entanglement threshold, exhibited crossovers of modulus versus frequency classically attributed to the reptation time, relaxation between entanglements, and the relaxation of a Kuhn length of units (the “monomer” time). The scaling for zero shear viscosity, η 0 , versus chain length, N, was η 0 ~ N 3.1 , in agreement with “sticky reptation” theory. The lifetime and activation energy, E p , of a pair between polyanion and polycation repeat units, Pol + Pol – , were determined from diffusion coefficients of salt ions within the PEC. The activation energy for LVR of salt-free PECs was 2E p , showing that the key mechanism limiting the dynamics of undoped PECs is pair exchange. An FTIR technique was used to distinguish whether SCN– acts as a counterion or a co-ion within PECs. Doping of PECs with NaSCN breaks Pol + Pol – pairing efficiently, which decreases effective cross-linking and decreases viscosity. Finally, an equation was derived that quantitatively predicts this effect.

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

Insights into the Promotion with Ru of Co/TiO 2 Fischer–Tropsch Catalysts: An In Situ Spectroscopic Study

Although ruthenium is a common promoter for cobalt-based Fischer–Tropsch synthesis (FTS) catalysts, the origin of Ru promotion and promoter concentration effects remains controversial. To gain a fundamental understanding of the Ru promotion effects, we herein performed an in situ spectroscopic study by X-ray absorption spectroscopy (XAS), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS)–Auger of working Co/TiO 2 catalysts (ca. 12 wt % Co, pure anatase TiO2 phase) promoted with different amounts of Ru (0.1–1.2 wt %). At typical FTS conditions (220 °C, 20 bar, H 2 /CO = 2), the activity in terms of both metal-time-yield (MTY) and initial turnover frequency (TOF) was maximized for the catalysts promoted with 0.1–0.2 wt % Ru, for which most of the Ru was alloyed with Co in bimetallic nanoparticles. The analysis of Auger electrons evidenced that the lower (apparent) TOF of accessible Co0 sites in the absence of Ru and at Ru concentrations beyond 0.2 wt % is bridged to the development, under reaction conditions, of FTS-inactive cobalt carbide (CoC x ) and cobalt oxide (CoO x ) patches, respectively, at the outermost surface of cobalt crystallites.

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

Uptake of aqueous heavy metal ions (Co2+, Cu2+ and Zn2+) by calcium-aluminium-silicate-hydrate gels

Highlights: • C-A-S-H gels containing metal ions (Co{sup 2+}, Cu{sup 2+} or Zn{sup 2+}) were precipitated by a sol-gel technique. • Uptake mechanism and immobilization capacity of divalent metal ions by C-A-S-H are elucidated. • Up to ~55–60 mol% of Zn can be incorporated in defective tobermorite-type C-A-S-H. • Metal uptake by C-A-S-H is controlled mainly by isomorphous substitution for Ca ions. • Crystal-chemical features of C-A-S-H gels and implications for practical application are discussed. Calcium-aluminium-silicate-hydrate (C-A-S-H) gels containing heavy metal ions (Me: Co{sup 2+}, Cu{sup 2+} or Zn{sup 2+}) were precipitated at different Me/Si molar ratios to study the uptake mechanism and immobilization capacity. Aqueous solution chemistry and solid-phase characterization using XRD, FTIR, ESEM-EDX, TEM-HAADF and TG-DSC methods reveal threshold values for ion substitution of ~55–60 mol% for Zn, ~30–40 mol% for Co and ~25–30 mol% for Cu in defective tobermorite-type C-A-S-H with (Ca + Me)/(Si + Al) molar ratios from 0.86 to 1.04. At higher aqueous Me concentrations, Me (chloride) hydroxides start to co-precipitate. The uptake mechanism of Me ions by C-A-S-H is based on (i) isomorphous substitution of Me for Ca in the CaO layer, (ii) ion exchange in the interlayer, (iii) tetrahedral substitution (Zn) within the dreierketten chains and (iv) surface adsorption onto the C-A-S-H gel structure. Systematics in crystal-chemistry of Me-bearing C-A-S-H and implications for application and performance in natural and man-made settings are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

FTIR analysis of unaged encapsulants

Fourier transform infrared spectroscopy (FITR) analysis (in ATR mode) of unaged encapsulants (EVA, POE, EPE) from a commercial source.

characterization↗