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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Photooxidative decomposition and defluorination of perfluorooctanoic acid (PFOA) using an innovative technology of UV–vis/Zn x Cu 1-x Fe 2 O 4 /oxalic acid

Per- and polyfluoroalkyl substances (PFAS) are a large group of perfluorinated organic molecules that have been in use since the 1940s for industrial, commercial, and consumer applications. PFAS are a growing concern because some of them have shown persistent, bioaccumulative and toxic effects. In this work, we demonstrate an innovative technology of UV–vis/Zn x Cu 1-x Fe 2 O 4 /oxalic acid for the degradation of perfluorooctanoic acid (PFOA) in water. The magnetically retrievable nanocrystalline heterogeneous ferrite catalysts, Zn x Cu 1-x Fe 2 O 4 were synthesized using a sol-gel auto-combustion process followed by calcination at 400 °C. The combination of Zn x Cu 1-x Fe 2 O 4 and oxalic acid generate reactive species under UV light irradiation. These reactive species are then shown to be capable of the photodegradation of PFOA. The degree of degradation is tracked by identifying transformation products using liquid chromatography coupled with quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS).

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

Reconceptualizing the Ir III Role in Metallaphotoredox Catalysis: From Strong Photooxidant to Potent Energy Donor

Dual Ir III /L n Ni II metallaphotoredox catalyzed C(sp 3 )–C(sp 2 ) cross-coupling reactions are widely assumed to proceed by photoinduced single electron transfer steps due to the highly oxidizing Ir III * excited state (Ir III = [Ir(dF(CF 3 )ppy) 2 (dtbbpy)] + [PF 6 ] – ; dF(CF 3 )ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine; L n = dtbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). Using time-resolved absorption and emission spectroscopy, we reveal that energy transfer between Ir III * and various LnNi II precatalysts and intermediates with k q ≥ 10 8 M –1 s –1 also drives catalysis. Specifically, the excited states of L n Ni II dihalide precatalysts/organometallic intermediates accessible by energy transfer appear to drive bond homolysis, halogen radical elimination, and reductive elimination reactions that facilitate formation of cross-coupled products. Energy transfer dynamics consequently circumvent the need for photoinduced electron transfer, thereby extending substrate scopes to coupling partners that cannot be oxidized by Ir III *. Within a cross-electrophile coupling model reaction between 4-bromobenzotrifluoride and bromocyclohexane, energy transfer activates the L n Ni II precatalyst at early reaction times before nucleophilic reductants are present. In the absence of Ir III , direct excitation of L n Ni II (Br) 2 also activates the precatalyst to form a L n Ni II (Br)(Aryl) intermediate. To compare energy transfer and electron transfer kinetics, we determined rate constants for reductive quenching by Br – (k SET = 4.1 × 10 8 M –1 s –1 ) and for the subsequent electron transfer from reduced Ir III•– to L n Ni II (Br) 2 (k SET = 4.1 × 10 7 M –1 s –1 ) using Stern-Volmer analysis and pulse radiolysis, respectively. Energy transfer rate constants are competitive with the electron transfer rate constants and energy transfer is a parallel pathway within metallaphotoredox catalysis. Exploiting the energy transfer mechanism, we demonstrate highly selective cross-electrophile coupling between 4-chlorobenzotrifluoride and bromocyclohexane to form exclusively cross-coupled product. Here, with alkyl-trifluoroborate nucleophiles that do not reductively quench IrIII* emission, transmetalation with L n Ni II (Br/Cl)(Aryl) followed by energy transfer also drives excited state reductive elimination to form C(sp 3 )–C(sp 2 ) cross-coupled product. Similarly, energy transfer rather than Ni II oxidation drives C(sp 2 )–OR reductive elimination, despite the strongly oxidizing ability of Ir III *. In total, these reactions demonstrate energy transfer processes from Ir III * to L n Ni II in metallaphotoredox catalysis that can unlock alternative reactive pathways.

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

New Insights into Secondary Organic Aerosol Formation at the Air–Liquid Interface

Air-liquid interfacial processing of volatile organic compound oxidation has been suggested as an important source of secondary organic aerosols. However, owing to the lack of techniques for in situ air-liquid interface analysis, the detailed interfacial mechanism remains speculative. To obviate this, the analysis of air-liquid interfacial reactions and the dynamics of glyoxal oxidation as a model volatile organic compound using in situ liquid synchrotron-based vacuum ultraviolet single photon ionization mass spectrometry enabled by the system for analysis at the liquid vacuum interface microreactor is reported. This approach allows for determination of reaction intermediates and oxidation products including polymers and oligomers at the air-liquid interface by mass spectral analysis and appearance energy measurements. Furthermore, an expanded reaction mechanism of photooxidation free radical induced reactions as a source of aqueous secondary organic aerosol formation is proposed based on these new results, suggesting that single photon ionization could be applied to provide unique insights into interfacial chemistry changing the earth atmospheric composition.

aqueous secondary organic aerosol, glyoxal, photoo↗
DOE OSTI2021

Green syntheses of stable and efficient organic dyes for organic hybrid light-emitting diodes

Organic hybrid light-emitting diodes (hybrid-LEDs) employ organic dyes as light converters on top of commercial blue inorganic LEDs, replacing incumbent inorganic phosphor light converters synthesized from rare-earth and/or toxic metallic elements to optimize device environmental sustainability. Here, we present two naturally derived organic dyes for hybrid-LEDs, highlighting stability and efficiency enhancement based on a novel “acceptor–acceptor” molecular design. This “acceptor–acceptor” skeleton comprises theobromine and thiadiazole, two electron-withdrawing groups that lower energy levels and suppress photooxidation. This differentiates these dyes from the widely adopted “donor–acceptor” skeleton, where photooxidation is facilitated by the presence of electron-donating units. Simultaneously, sidechains on organic dyes used to enhance solution processability, crucial for film transparency, introduce an additional photooxidation pathway. With this “acceptor–acceptor” skeleton, the destabilization from sidechains was offset by the stability enhancement from the electronic effects in the backbone. Additionally, when blended within an industrial polymer, poly(styrene-butadiene-styrene) (SBS), their enhanced solubility enables the formation of highly transparent films, crucial for reducing scattering loss in LEDs. Furthermore, resultant dye-SBS films achieved photoluminescence quantum yields (PLQYs) of around 90% under ambient conditions. Taking advantage of their transparency and solution processability, we fabricated a waveguide with this theobromine-dye-SBS composite, which was subsequentially assembled into an edge-lit LED device of no glare and enhanced aesthetics.

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

Effect of Humidity on the Reactive Uptake of Ammonia and Dimethylamine by Nitrogen-Containing Secondary Organic Aerosol

This study investigated the uptake of ammonia (NH3) by secondary organic aerosol (SOA) particles generated via limonene photooxidation or ozonolysis as well as the uptake of dimethylamine (DMA) by limonene ozonolysis, α-cedrene photooxidation, or toluene photooxidation SOA in an environmental chamber between 0–50% relative humidity. In addition to the acid-base equilibrium uptake, NH3 and DMA can react with SOA carbonyl compounds converting them into nitrogen-containing organic compounds (NOCs). The effective reactive uptake coefficients for the formation of NOCs from ammonia were measured on the order of 10−5. The observed DMA reactive uptake coefficients ranged from 10−5 to 10−4. Typically, the reactive uptake coefficient decreased with increasing relative humidity. This is consistent with NOC formation by a condensation reaction between NH3 or DMA with SOA, which produces water as a product. Ammonia is more abundant in the atmosphere than amines. However, the larger observed reactive uptake coefficient suggests that amine uptake may also be a potential source of organic nitrogen in particulate matter.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Dicyanobenzothiadiazole (DCBT) Organic Dye as a Visible Light Absorbing Strong Photoinduced Oxidant with a 16 Microsecond Long–Lived Excited State

Strong photoinduced oxidants are important to organic synthesis and solar energy conversion, to chemical fuels or electric. For these applications, visible light absorption is important to solar energy conversion and long–lived excited states are needed to drive catalysis. With respect to these desirable qualities, a series of five 5,6–dicyano[2,1,3]benzothiadiazole (DCBT) dyes are examined as organic chromophores that can serve as strong photooxidants in catalytic systems. The series utilizes a DCBT core with aryl groups on the periphery with varying electron donation strengths relative to the core. The dyes are studied via both steady–state and transient absorption and emission studies. Additionally, computational analysis, voltammetry, crystallography, and absorption spectroelectrochemistry are also used to better understand the behavior of these dyes. Ultimately, a strong photooxidant is arrived at with an exceptionally long excited state lifetime for an organic chromophore of 16 µs. Finally, the long–lived excited state photosensitizer is well–suited for use in catalysis, and visible light driven photosensitized water oxidation is demonstrated using a water–soluble photosensitizer.

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

Cumene-to-Phenol Process Mediated by Bromine Radicals through Photoinduced Ligand-to-Metal Charge Transfer

Selective C–H activation via hydrogen atom transfer (HAT) has gained significant interest recently. One industrial application for HAT can be found in the tertiary benzylic C–H bond of cumene for producing phenol, a versatile chemical feedstock for various industries. However, the overall phenol yield remains low using the existing Hock process due to the poor selectivity towards the key reaction intermediate, cumene hydroperoxide (CHP). Here, in this work, we demonstrate an efficient strategy for phenol production through photooxidation of cumene to CHP using iron bromide under blue light irradiation, where bromine radicals (generated in situ via ligand-to-metal charge transfer) are used as hydrogen atom abstractors. Mechanistic studies revealed the cumene-to-CHP conversion occurred via a tertiary C–H bond abstraction by a radical mechanism, and the acetic acid and water additives increased CHP selectivity through stabilizing peroxides. The cumene-phenol process achieved up to 88% yield of CHP in 1 hour and could be used with a wide range of substrates. We thus developed a selective, mild, and efficient phenol production method using iron bromide under photooxidative conditions.

HAT↗
DOE OSTI2023

Water dissociation at the water–rutile TiO 2 (110) interface from ab initio-based deep neural network simulations

The interaction of water with TiO 2 surfaces is of crucial importance in various scientific fields and applications, from photocatalysis for hydrogen production and the photooxidation of organic pollutants to self-cleaning surfaces and bio-medical devices. In particular, the equilibrium fraction of water dissociation at the TiO 2 –water interface has a critical role in the surface chemistry of TiO 2 , but is difficult to determine both experimentally and computationally. Among TiO 2 surfaces, rutile TiO 2 (110) is of special interest as the most abundant surface of TiO 2 ’s stable rutile phase. While surface-science studies have provided detailed information on the interaction of rutile TiO 2 (110) with gas-phase water, much less is known about the TiO 2 (110)–water interface, which is more relevant to many applications. In this work, we characterize the structure of the aqueous TiO 2 (110) interface using nanosecond timescale molecular dynamics simulations with ab initio-based deep neural network potentials that accurately describe water/TiO 2 (110) interactions over a wide range of water coverages. Simulations on TiO 2 (110) slab models of increasing thickness provide insight into the dynamic equilibrium between molecular and dissociated adsorbed water at the interface and allow us to obtain a reliable estimate of the equilibrium fraction of water dissociation. We find a dissociation fraction of 22 ± 6% with an associated average hydroxyl lifetime of 7.6 ± 1.8 ns. These quantities are both much larger than corresponding estimates for the aqueous anatase TiO 2 (101) interface, consistent with the higher water photooxidation activity that is observed for rutile relative to anatase.

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

Seasonal variations in composition and sources of atmospheric ultrafine particles in urban Beijing based on near-continuous measurements

Abstract. Understanding the composition and sources of atmospheric ultrafine particles (UFPs) is essential in evaluating their exposure risks. It requires long-term measurements with high time resolution, which are scarce to date. We performed near-continuous measurements of UFP composition during four seasons in urban Beijing using a thermal desorption chemical ionization mass spectrometer, accompanied by real-time size distribution measurements. We found that UFPs in urban Beijing are dominated by organic components, varying seasonally from 68 % to 81 %. CHO organics (i.e., molecules containing carbon, hydrogen, and oxygen) are the most abundant in summer, while sulfur-containing organics, some nitrogen-containing organics, nitrate, and chloride are the most abundant in winter. With the increase of particle diameter, the contribution of CHO organics decreases, while that of sulfur-containing and nitrogen-containing organics, nitrate, and chloride increases. Source apportionment analysis of the UFP organics indicates contributions from cooking and vehicle sources, photooxidation sources enriched in CHO organics, and aqueous/heterogeneous sources enriched in nitrogen- and sulfur-containing organics. The increased contributions of cooking, vehicle, and photooxidation components are usually accompanied by simultaneous increases in UFP number concentrations related to cooking emission, vehicle emission, and new particle formation, respectively, while the increased contribution of the aqueous/heterogeneous composition is usually accompanied by the growth of UFP mode diameters. The highest UFP number concentrations in winter are due to the strongest new particle formation, the strongest local primary particle number emissions, and the slowest condensational growth of UFPs to larger sizes. This study provides a comprehensive understanding of urban UFP composition and sources and offers valuable datasets for the evaluation of UFP exposure risks.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Online characterization of primary and secondary emissions of particulate matter and acidic molecules from a modern fleet of city buses

The potential impact of transitioning from conventional fossil fuel to a non-fossil-fuel vehicle fleet was investigated by measuring primary emissions via extractive sampling of bus plumes and assessing secondary mass formation using the Gothenburg Potential Aerosol Mass (Go:PAM) reactor from 76 in-use transit buses. Online chemical characterization of gaseous and particulate emissions from these buses was conducted using chemical ionization mass spectrometry (CIMS) with acetate as the reagent ion, coupled with the Filter Inlet for Gases and AEROsols (FIGAERO). Acetate reagent ion chemistry selectively ionizes acidic compounds, including organic and inorganic acids, as well as nitrated and sulfated organics. A significant reduction (48 %–98 %) in fresh particle emissions was observed in buses utilizing compressed natural gas (CNG), biodiesels like rapeseed methyl ester (RME) and hydrotreated vegetable oil (HVO), and hybrid-electric HVO (HVO HEV ) compared to diesel (DSL). However, secondary particle formation from photooxidation of emissions was substantial across all the fuel types. The median ratio of particle mass emission factors of aged to fresh emissions increased in the following order: DSL buses at 4.0, HVO buses at 6.7, HVO HEV buses at 10.5, RME buses at 10.8, and CNG buses at 84. Of the compounds that can be identified by CIMS, fresh gaseous emissions from all Euro V/EEV (Enhanced Environmentally friendly Vehicle) buses, regardless of fuel type, were dominated by nitrogen-containing compounds such as nitrous acid (HONO), nitric acid (HNO 3 ), and isocyanic acid (HNCO), alongside small monoacids (C 1 –C 3 ). Notably, the emission of nitrogen-containing compounds was lower in Euro VI buses equipped with more advanced emission control technologies. Secondary gaseous organic acids correlated strongly with gaseous HNO 3 signals (R 2 =0.85–0.99) in Go:PAM, but their moderate to weak correlations with post-photooxidation secondary particle mass suggest that they are not reliable tracers of secondary organic aerosol formation from bus exhaust. Our study highlights that non-regulated compounds and secondary pollutant formation, not currently addressed in legislation, are crucial considerations in the evaluation of environmental impacts of future fuel and engine technology shifts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Solar photolysis of water

Hydrogen is produced by the solar photolysis of water in a first photooxidation vessel with a transparent wall in the presence of a water soluble photooxidizable reagent and an insoluble hydrogen recombination catalyst. Simultaneously oxygen is produced in a second photoreduction reactor with a transparent wall in the presence of an insoluble photoreduction reagent catalyst. When spent, the solution from the first reactor is fed into the second reactor. A reaction occurs in the dark in which the redox reagents are regenerated, and the regenerated photooxidation reagent solution is recycled to the first reactor. The photoreduction-catalyst is a bifunctional reagent catalyst including a transition metal salt together with a hydroxyl or chlorohydroxyl decomposition catalyst of high area.

Ryason, P. R.↗
NASA NTRS1981

Modelling of polymer photodegradation for solar cell modules

A computer model including an integration routine was developed and demonstrated to simulate, in principle, the chemical changes which may occur in the photooxidation of hydrocarbons, using as input data a set of elementary reactions, corresponding rate constants and appropriate starting conditions. Application of this model to the photooxidation of pottant and plastic materials used in the LSA module designs provides a reliable predictive capability regarding the useful lifetime of these materials. An earlier mechanism consisting of 46 reactions was simplified considerably by reducing the number of formal termination steps since it became apparent that the major termination process goes via the peroxy radicals. In addition, new reactions of oxygen with acryl radicals (from Norrish type I) to form peracids, which then decompose to form carbon dioxide are included.

Somersall, A. C.↗
NASA NTRS1981

Modelling of polymer photodegradation for solar cell modules

A computer program developed to model and calculate by numerical integration the varying concentrations of chemical species formed during photooxidation of a polymeric material over time, using as input data a choice set of elementary reactions, corresponding rate constants and a convenient set of starting conditions is evaluated. Attempts were made to validate the proposed mechanism by experimentally monitoring the photooxidation products of small liquid alkane which are useful starting models for ethylene segments of polymers like EVA. The model system proved in appropriate for the intended purposes. Another validation model is recommended.

Somersall, A. C.↗
NASA NTRS1982

Modelling of photodegradation in solar cell modules of substrate and superstrate design made with ethylene-vinyl acetate as pottant material

A computer model which simulates, in principle, the chemical changes in the photooxidation of hydrocarbons using as input data a set of elementary reactions, corresponding kinetic rate data and appropriate initial conditions was developed. The Model was refined and exploited to examine more closely the photooxidation and photostabilization of a hydrocarbon polymer. The results lead to the following observations. (1) The time to failure, tau sub f (chosen as the level of 5% C-H bond oxidation which is within the range anticipated for marked change in mechanical properties) varies as the inverse square root of the light intensity. However, tau sub f is almost unaffected by both the photoinitiator type and concentration. (2) The time to failure decreases with the rate of abstraction of C-H by peroxy radicals but increases with the rate of bimolecular radical termination controlled by diffusion. (3) Of the various stabilization mechanisms considered, the trapping of peroxy radicals is distinctly the most effective, although the concommitant decomposition of hydroperoxide is also desirable.

Somersall, A. C.↗
NASA NTRS1982

Modeling of polymer photodegradation for solar cell modules

It was shown that many of the experimental observations in the photooxidation of hydrocarbon polymers can be accounted for with a computer simulation using an elementary mechanistic model with corresponding rate constants for each reaction. For outdoor applications, however, such as in photovoltaics, the variation of temperature must have important effects on the useful lifetimes of such materials. The data bank necessary to replace the isothermal rate constant values with Arrhenius activation parameters: A (the pre-exponential factor) and E (the activation energy) was searched. The best collection of data assembled to data is summarized. Note, however, that the problem is now considerably enlarged since from a theoretical point of view, with 51 of the input variables replaced with 102 parameters. The sensitivity of the overall scheme is such that even after many computer simulations, a successful photooxidation simulation with the expanded variable set was not completed. Many of the species in the complex process undergo a number of competitive pathways, the relative importance of each being often sensitive to small changes in the calculated rate constant values.

Somersall, A. C.↗
NASA NTRS1983

Modelling of photodegradation in solar cell modules of substrate and superstrate design made with ethylene-vinyl acetate as pottant material

A computer model was developed which can generate realistic concentration versus time profiles of the chemical species formed during photooxidation of hydrocarbon polymers using as input data a set of elementary reactions with corresponding rate constants and initial conditions. The results of computer simulation have been shown to be consistent with the general experimental observations of the photooxidation of polyethylene exposed to sunlight at ambient temperatures. The useful lifetime (5% oxidation) of the unstabilized polyethylene is predicted to vary from a few months in hot weather (100 F) to almost two years in cool weather (45 F) with an apparent net activation energy of 10 kcal/mol. Modelling studies of alternate mechanisms for stabilization of clear, amorphous, linear polyethylene suggest that the optimum stabilizer would be a molecularly dispensed additive in very low concentration which can trap peroxy radicals and also decompose hydroperoxides.

Somersall, A. C.↗