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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Monoterpene Photooxidation in a Continuous-Flow Chamber: SOA Yields and Impacts of Oxidants, NO x , and VOC Precursors

We report monoterpene photooxidation plays an important role in secondary organic aerosol (SOA) formation in the atmosphere. The low-volatility products can enhance new particle formation and particle growth, and thus have influences on climate feedbacks. Here, we present the results of α-pinene and Δ-3-carene photooxidation experiments conducted in continuous-flow mode in an environmental chamber under several reaction conditions. The roles of oxidants, addition of NO, and VOC molecular structure in influencing SOA yield are illustrated. SOA yield from α-pinene photooxidation shows a weak dependence on H 2 O 2 concentration, which is a proxy for HO 2 concentration. The high O/C ratios observed in the a-pinene photooxidation products suggest the production of highly oxygenated organic molecules (HOM). Addition of ozone to the chamber during low-NO x photooxidation experiments leads to higher SOA yield. With the addition of NO, the production of N-containing HOMs is enhanced and the SOA yield shows a modest, non-linear dependence on input NO concentration. Carene photooxidation leads to higher SOA yield than α-pinene under similar reaction conditions, which agrees with the lower volatility retrieved from evaporation kinetics experiments. These results improve the understanding of SOA formation from monoterpene photooxidation and could be applied to refine the representation of biogenic SOA formation in models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

De Novo Design of Proteins That Bind Naphthalenediimides, Powerful Photooxidants with Tunable Photophysical Properties

De novo protein design provides a framework to test our understanding of protein function and build proteins with cofactors and functions not found in nature. Here, we report the design of proteins designed to bind powerful photooxidants and the evaluation of the use of these proteins to generate diffusible small-molecule reactive species. Because excited-state dynamics are influenced by the dynamics and hydration of a photooxidant’s environment, it was important to not only design a binding site but also to evaluate its dynamic properties. Thus, we used computational design in conjunction with molecular dynamics (MD) simulations to design a protein, designated NBP (NDI Binding Protein), that held a naphthalenediimide (NDI), a powerful photooxidant, in a programmable molecular environment. Solution NMR confirmed the structure of the complex. We evaluated two NDI cofactors in this de novo protein using ultrafast pump–probe spectroscopy to evaluate light-triggered intra- and intermolecular electron transfer function. Moreover, we demonstrated the utility of this platform to activate multiple molecular probes for protein labeling.

carbonyls↗
DOE OSTI2026

Photooxidative Upcycling of Post-Consumer Polystyrene Plastics into Phenol Using Eosin Y

Phenol is a commodity chemical frequently used in the manufacturing of resins, pharmaceuticals, and polymers. Yet, its industrial production from cumene requires harsh oxidative conditions followed by the Hock rearrangement. Polystyrene (PS) is a widely manufactured commodity polymer; however, it is among the least recycled plastics. Intriguingly, it is composed of contiguous cumene repeats that could serve as a phenol source, enhancing its value as a waste material. In this work, we leverage the similarity between cumene and PS to drive phenol production via a mild photooxidative HAT mechanism. Using Eosin Y under blue light irradiation and atmospheric pressure of oxygen, commercial PS resin was converted into hydroperoxyl PS. Subsequent acid-catalyzed Hock rearrangement afforded up to 21% yield of phenol. The photooxidation system was successfully applied to 8 post-consumer PS plastics, achieving phenol yields up to 23%, comparable to those of the current industrial Hock process. Our method introduces a mild catalytic strategy for converting post-consumer PS into phenol, offering a potential pathway for PS waste valorization.

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

Photooxidation of Organic Sulfide Enhanced by Heavy Atom Effect in Porphyrin Metal–Organic Frameworks with a Sea Topology

The photoactivity of three porphyrin-based metal-organic frameworks (PMOFs) incorporating Al, Ga, and In nodes was systematically evaluated using the photooxidation of an organic sulfide (2-chloroethyl ethyl sulfide, or CEES; a mustard gas simulant). Faster photodegradation of CEES was observed for PMOFs with heavier metal nodes, placing In-PMOF as the most efficient photocatalyst in the series. Guided by this insight, we developed CSLA-10, a MOF integrating In nodes and Sn-doped porphyrin linker to synergistically amplify heavy-atom effects at both the nodes and ligand levels. CSLA-10 exhibited the fastest reported CEES photooxidation to date, achieving a half-life of 38 s in methanol under blue LED irradiation. When grafted onto textiles, CSLA-10 enabled solvent-free CEES degradation in air/O 2 with a half-life of 2.7 min and complete conversion within 7 min, representing the most rapid full degradation reported under solvent-free conditions. Furthermore, this work establishes a dual heavy-atom strategy for enhancing intersystem crossing and singlet oxygen generation in porphyrin MOFs, providing a rational design principle for next-generation photocatalysts for the degradation of toxic organic sulfides.

Metal-organic frameworks↗
DOE OSTI2022

Water-Accelerated Photooxidation of CH 3 NH 3 PbI 3 Perovskite

Optical absorbance is used to study the kinetics of methylammonium lead iodide (MAPbI 3 ) thin film degradation in response to combinations of moisture, oxygen, and illumination over a range of temperatures. 105 degradations were conducted over 41 unique environmental conditions. We discover that water acts synergistically with oxygen in a water-accelerated photo-oxidation (WPO) pathway. This pathway is the dominant pathway at 25 °C and is 10, 100, 1000, and >1000 times faster than dry photooxidation (DPO), degradation via hydrate formation, thermal degradation, and blue light degradation, respectively. We find that the rate determining step for DPO is proton abstraction from methylammonium while for WPO it is proton abstraction from water, which occurs at a faster rate and results in water acting as an accelerant for photooxidation of MAPbI 3 . A full kinetic rate equation is derived and fitted to the data to determine activation energies and rate constants.

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

Nanoconfinement-induced shift in photooxidative degradation pathway of polystyrene

Polymer nanocomposites with high concentrations of nanoparticles (NPs) possess exceptional mechanical, transport, and thermal properties. To enable their widespread use in structural applications and functional coatings, it is crucial to understand how nanoconfinement and the polymer-NP interface influence polymer degradation under various environmental conditions, including prolonged UV exposure. In this study, we investigate the photooxidative degradation of polystyrene (PS)-confined in the interstices of SiO 2 NP films. These nanocomposite films are prepared by the capillary rise infiltration (CaRI) of PS into interstices of SiO 2 NP packings, and subsequently subjected to UV irradiation. Our investigation reveals that PS degradation progresses uniformly across the thickness, with degradation initiating from the center of the NP interstitial pores and extending towards the NP surface. We rationalize this degradation mechanism based on the disparity in the surface energies of PS and the NP surface, as well as slow oxygen diffusion through confined PS. Here, we also demonstrate that packing smaller NPs at a given thickness or thicker packing of a specific NP size facilitates photooxidative degradation, highlighting the critical role of the number of interstitial pores in influencing degradation processes.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ultraviolet Photooxidation of Smectite-Bound Fe(II) and Implications for the Origin of Martian Nontronites

Clay minerals detected with orbital and in situ instruments in ancient Martian terrains constrain Mars' climate and aqueous alteration history. Early in its history, Mars experienced an atmospheric redox change and iron-bearing clay minerals may preserve the effects of that transition. Ferrous smectites, the thermodynamically predicted product of chemical weathering of basalts under anoxic conditions, may have undergone oxidation by exposure to chemical oxidants in the atmosphere or regolith, or by direct photooxidation at the surface. To assess these potential oxidation pathways, ferrous trioctahedral smectites of varying initial iron content were synthesized and subjected to oxidation by ultraviolet (UV) irradiation. Experimental UV irradiation under an anoxic atmosphere equivalent to approximately 7 years of flux on the Martian surface caused partial oxidation of smectite-bound Fe (Fe 3+ /ΣFe = 16–18%) and octahedral sheet contraction. Metal-OH vibrational bands in visible/near infrared (VNIR) reflectance spectra of oxidized smectites changed in band depth and asymmetry with higher iron content. X-ray diffraction patterns of UV irradiated samples indicate the formation of a mixed di- and trioctahedral smectite or a secondary nontronite phase, possibly on the surfaces of higher iron content smectites. Furthermore, these experiments suggest that UV irradiation is able to oxidize structurally bound iron in smectites without the presence of other chemical oxidants. Photooxidation may have influenced the mineralogy, both syndepositionally and postdepositionally, of Martian alteration assemblages formed near the surface and this process needs not be limited to one part of their formation history.

58 GEOSCIENCES↗
DOE OSTI2024

Photooxidation of Polyolefins to Produce Materials with In-Chain Ketones and Improved Materials Properties

Herein, we report a selective photooxidation of commodity postconsumer polyolefins to produce polymers with in-chain ketones. The reaction does not involve the use of catalyst, metals, or expensive oxidants, and selectively introduces ketone functional groups. Under mild and operationally simple conditions, yields up to 1.23 mol % of in-chain ketones were achieved. Installation of in-chain ketones resulted in materials with improved adhesion of the materials and miscibility of mixed plastics relative to the unfunctionalized plastics. The introduction of ketone groups into the polymer backbone allows these materials to react with diamines, forming dynamic covalent polyolefin networks. This strategy allows for the upcycling of mixed plastic waste into reprocessable materials with enhanced performance properties compared to polyolefin blends. Mechanistic studies support the involvement of photoexcited nitroaromatics in consecutive hydrogen and oxygen atom transfer reactions.

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

Interpreting accelerated tests on perovskite modules using photooxidation of MAPbI 3 as an example

Solar panels (modules) based on metal halide perovskites are following a fast track to commercialization. Unlike more established solar cell materials, there are not yet decades-long field observations to increase consumer confidence. The "physics and chemistry of failure" approach is used in other industries and estimates product degradation based on laboratory accelerated tests integrated with an understanding of degradation mechanisms. This work uses that approach to quantify the relationship between accelerated tests and projected product behavior for metal halide perovskite modules. Degradation involving photooxidation of methylammonium lead iodide is used to illustrate the method. Acceleration factors in common accelerated tests are found to be low. Conclusions emphasize that the accelerated tests on photovoltaics should not be interpreted as equivalent across module types or as a green light for commercialization unless supported by the appropriate field data or physics and chemistry of failure analysis.

14 SOLAR ENERGY↗
DOE OSTI2026

Post-Modification of Crystalline Peptoid Nanomembranes with Active Nanoparticles for Efficient Photooxidation of a Mustard Gas Simulant

Peptoids (or poly-N-substituted glycines) hold immense potential for assembling into hierarchically structured functional materials via controlled molecular interactions. To create self-assembled materials with tailored functionalities, peptoid sequences are often conjugated with reactive or recognition motifs to enable applications including specific binding, biomimetic catalysis, and fluorescence imaging. However, the direct integration of bulky functional motifs into peptoid sequences can disrupt assembly processes and structural outcomes. Herein, we present a post-modification strategy for functionalizing pre-formed 2D crystalline assemblies. Through introducing clickable active sites, such as azide, alkyne, or thiol groups into a peptoid sequence, site-specific conjugation is achieved post-assembly via efficient “click”-type reactions. This strategy enables the ordered alignment of functional groups and gold nanoparticles (Au NPs) on the surface of 2D peptoid nanomaterials with controlled density, while preserving their high crystallinity and structural integrity. Furthermore, we demonstrated that nanomembranes functionalized with both Au NPs and porphyrins enhance the efficiency and selectivity of the photooxidation of 2-chloroethyl ethyl sulfide, a simulant of sulfur mustard. This innovative strategy lays the groundwork for advancing peptoid-based functional materials across diverse applications, from catalysis to biomedicine.

Chemistry↗
DOE OSTI2026

Operation-Induced BiVO4 Surface Reconstruction Modulates Photoelectrochemical Glycerol Photooxidation Stability and Activity

Abstract Operation-induced surface reconstruction of photoelectrodes is underexplored as a path to control stability and performance. We show how adaptive junctions form via surface reconstruction of BiVO4 during glycerol photooxidation and how these surfaces affect electrolyte-dependent kinetics and durability. Preferential V dissolution in both acidic and alkaline media forms a Bi-rich layer. In situ measurements through a dual-working-electrode platform quantify the changes in photovoltage and charge-transfer resistance derived from adaptive junction formation, while enabling quantitative separation of the driving forces for charge separation and interfacial catalysis. The reconstructed surface in acidic media improves hole-transfer kinetics, functions as a glycerol-oxidation catalyst, and imparts photostability. Surface reconstruction in alkaline media exhibits the opposite behavior, impeding hole injection. This instability is mitigated by trace Ni2+ ions, which drive in situ surface activation without cocatalyst pre-deposition. This study shows the significance of surface reconstruction in the design of durable photoelectrodes for applications targeting organic electro-oxidation.

Yang, Jin Wook↗
DOE OSTI2022

Rapid photooxidation and removal of As(III) from drinking water using Fe-Mn composite oxide

Fe-Mn composite oxide (FMO) is widely applied to the oxidation and removal of As(III) from water. However, As(III) can directly reduce manganese oxides, decreasing the oxidation capacity or reusability and thereby greatly limiting the applicability of FMO. Here, the oxidation capacity and reusability of FMO for As(III) were efficiently improved by light radiation, and the effect of typical coexisting ions (SO 4 2– and Ca 2+ ) on the removal of As(III) was also studied. O 2 •– produced from excited manganese oxide and ligand-to-metal charge transfer in iron oxide-As(III) complex enhanced As(III) oxidation and removal under light radiation. At an initial As(III) concentration of 1000 μg L –1 , the total As concentration was respectively decreased to 11.5, 1.5 and 4.4 μg L –1 under darkness, UV light and sunlight at 180 min, and could be reduced to below the guideline limitation of drinking water (10 μg L –1 ) within 40 and 60 min under UV light and sunlight, respectively. SO 4 2– exhibited negligible effect on As removal efficiency because FMO had obviously lower adsorption capacity and selectivity for SO 4 2– than for As(V). The adsorption of coexisting Ca 2+ on manganese oxide decreased the negative charge on the FMO surface, thereby improving As(III) adsorption and oxidation. FMO exhibited excellent reusability, and a total As removal efficiency of 99.1% was still maintained after five cycles of an adsorption-desorption process under UV light. Finally, this work elucidates the photochemical oxidation and removal mechanism of FMO for As(III), and proposes a low-cost and efficient method for the detoxification of As(III)-contaminated drinking water.

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