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Results for “photooxidation”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Multistep catalytic abiotic CO2 conversion to sugars through C1 intermediates

Carbon dioxide (CO2) to multicarbon (Cn) upgrading for commodity chemicals, fuel production, or artificial food synthesis using renewable energy input is a golden target for researchers in sustainable carbon emission reduction. Here, we explore and analyze a flexible modular roadmap for the task, utilizing sequential electro-, photo-, and organocatalysis to develop a strategy for CO2 conversion using the key and elusive formaldehyde precursor of interest for sugar generation. We study the electrochemical carbon dioxide reduction reaction to methanol in a flow cell and its discontinuous photooxidation to formaldehyde (PMOR) with excellent selectivity. Utilizing a highly active N-heterocyclic carbene catalyst enables tunable generation of C4-C6 aldoses without undesirable byproducts, with carbon conversion yield reaching 60 to 80% for desired pentose, tetrose, and triose product mixtures and over 20% for hexose. This approach presents a roadmap for CO2 valorization, aiming to bridge carbon waste streams with sustainable sugar synthesis and opening broad avenues for green chemical production.

CO2 valorization↗
DOE OSTI2023

Synthesis and functionalization of electron-deficient perfluoroalkyl porphyrin building blocks for supermolecular systems

Synthetic strategies for electron-deficient meso-perfluoroalkylporphyrins bearing diverse functional groups are described. Scalable and efficient syntheses for 5-triisopropylsilylethynyl-10,15,20-tris(heptafluoropropyl)porphyrin and 5-triisopropylsilylethynyl-10,20-bis(heptafluoropropyl)porphyrin that equip meso-ethynyl functional groups via the bilane route have been established, along with a refined route to [5,15-bis(heptafluoropropyl)porphinato]zinc(II). meso-Position halogenation of [5,15-bis(heptafluoropropyl)porphinato]zinc(II) was achieved by selective meso-nitration and subsequent reduction, diazonium salt formation, and iodination reactions. Computational data describe the low energy excited states of these chromophores and the electronic structural factors that control reactivity of these meso-perfluoroalkyl substituted porphyrin complexes. meso-Functionalized [5-triisopropylsilylethynyl-10,20-bis(heptafluoropropyl)porphinato]zinc(II) and [5-iodo-10,20-bis(heptafluoropropyl)porphinato]zinc(II) building blocks lay the foundation for the construction of highly conjugated multiporphyrin arrays that feature electronic structural properties important for the development of n-type materials and high potential photooxidants.

Chemistry↗
DOE OSTI2024

Aqueous Titania Interfaces

Water–metal oxide interfaces are central to many phenomena and applications, ranging from material corrosion and dissolution to photoelectrochemistry and bioengineering. In particular, the discovery of photocatalytic water splitting on TiO 2 has motivated intensive studies of water-TiO 2 interfaces for decades. So far, a broad understanding of the interaction of water vapor with several TiO 2 surfaces has been obtained. However, much less is known about liquid water–TiO 2 interfaces, which are more relevant to many practical applications. Probing these complex systems at the molecular level is experimentally challenging and is sometimes possible only through computational studies. This review summarizes recent advances in the atomistic understanding, mostly through computational simulations, of the structure and dynamics of interfacial water on TiO 2 surfaces. The main focus is on the nature, molecular or dissociated, of water in direct contact with low-index defect-free crystalline surfaces. The hydroxyls resulting from water dissociation are essential in the photooxidation of water and critically affect the surface chemistry of TiO 2.

density functional theory↗
DOE OSTI2023

Initial dynamic photoactive materials testing of an atmospheric chamber intended for radioactive and hazardous gases

Radioisotopes and hazardous gases can have undetermined environmental pathways. Researchers at Pacific Northwest National Laboratory constructed a chamber that complies with the requirements needed for an atmospheric reaction platform and the safety principles of interacting with hazardous dispersible sources to enable the environmental testing of these gases. Initial dynamic testing showed inter-chamber mixing completed from minutes to 1.5 hours. The photooxidation of butyl iodine showed the presence of signals from reaction products, and intermediaries for up to 50 hours. Current detection limits of the chamber and analytical collection and testing approach were shown to be in the single-digit parts per billion levels. In conclusion, the comparisons between the measured oxidation trends and literature show the utility of performing laboratory experiments to validate the results of modeling for larger-scale scenarios.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Innovative mercury treatment technology options for the liquid waste system at the Savannah River Site: scoping studies

The Savannah River Site (SRS) Liquid Waste System (LWS) contains liquids, salts and sludges that are currently being processed into final wasteforms for disposition, specifically, waste glass for sludges, solids and liquids containing high levels of radioactivity, and saltstone grout for low activity decontaminated liquid solutions. The LWS also contains approximately 60,000 kg of mercury present in the following physical and chemical forms, specifically: a) ionic inorganic mercury, organomercury (e.g., methylmercury), and other minor components found in LWS fluids b) mercury solids such as oxides, hydroxides, amalgams sulfides and sorbed mercury, c) accumulations of dense liquid elemental mercury, and d) vapor phase elemental and organomercury mercury found in tank headspace gas and in evaporators. An effective and proactive management strategy of the mercury present in the LWS is needed to support processing of LWS wastes into glass and saltstone. Sustainable processing of the LAWS to completion requires mercury removal from the LWS at a rate of approximately 2,900 kg/yr. This removal can be accomplished through existing mercury treatment systems or newly implemented LWS “purge points”. The chemical speciation of mercury has emerged as the key factor that controls mercury behavior in the LWS. For example, past studies demonstrated that mercury speciation is adversely impacting the performance of existing removal systems so that significant levels of mercury are recycled from the Defense Waste Processing Facility (DWPF) back to the tank farm. Consequently, mercury concentrations have slowly increased in the LWS tank fluids over time. The presence of organo-mercury has also been identified as the cause of increased mercury leaching from saltstone. In response to these challenges, the Department of Energy (DOE) Office of Environmental Management (EM-TD) Technology Development Program has supported a series of scoping studies predicated on manipulating or controlling mercury speciation and mercury behaviors within the constraints of LWS waste chemistry and safety conditions. The intent of these studies was to rapidly triage potential technology options and develop a technically based go / no go recommendation for further work. This composite report presents the results of three scoping studies: 1) advanced photooxidation processes, 2) chemical reduction, and 3) mercury getters.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Estimation of secondary organic aerosol viscosity from explicit modeling of gas-phase oxidation of isoprene and α -pinene

Abstract. Secondary organic aerosols (SOA) are major components of atmospheric fine particulate matter, affecting climate and air quality. Mounting evidence exists that SOA can adopt glassy and viscous semisolid states, impacting formation and partitioning of SOA. In this study, we apply the GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) model to conduct explicit chemical modeling of isoprene photooxidation and α-pinene ozonolysis and their subsequent SOA formation. The detailed gas-phase chemical schemes from GECKO-A are implemented into a box model and coupled to our recently developed glass transition temperature parameterizations, allowing us to predict SOA viscosity. The effects of chemical composition, relative humidity, mass loadings and mass accommodation on particle viscosity are investigated in comparison with measurements of SOA viscosity. The simulated viscosity of isoprene SOA agrees well with viscosity measurements as a function of relative humidity, while the model underestimates viscosity of α-pinene SOA by a few orders of magnitude. This difference may be due to missing processes in the model, including autoxidation and particle-phase reactions, leading to the formation of high-molar-mass compounds that would increase particle viscosity. Additional simulations imply that kinetic limitations of bulk diffusion and reduction in mass accommodation coefficient may play a role in enhancing particle viscosity by suppressing condensation of semi-volatile compounds. The developed model is a useful tool for analysis and investigation of the interplay among gas-phase reactions, particle chemical composition and SOA phase state.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1972

Oxidation of vehicle components by photoproduced holes.

The oxidation by ZnO holes of vehicle components in thermal control coatings has been examined to develop experimental methods to study such reactions and to identify what components to avoid because of their instability when in the presence of u.v.-produced holes. Two methods were used that show consistent results. An electrochemical technique with a single crystal ZnO anode was used for quantitative comparisons, and electron spin resonance was used to study more practical powder/vehicle systems. Alcohols and dioxane were shown to be readily oxidized by ZnO holes, whereas acetonitrile, neopentane, and ethyl acetate were oxidation resistant. Some resistance to the photooxidation was provided by recombination centers.

Sancier, K. M.↗
NASA NTRS1973

Venus - Composition and structure of the visible clouds

It is proposed that the visible cloud deck on Venus is composed of droplets of sulfuric acid. These are formed by the very rapid photooxidation of carbonyl sulfide in the upper atmosphere. The clouds are best described as an extensive haze since the predicted particulate scale height probably exceeds the gas scale height within the layer. The predicted mixing ratio for water is .000001 (lower limit), and for both carbonyl sulfide and sulfur dioxide it is .0000001 (upper limit); these are in good agreement with observations. Gaps in the layer are not possible unless the planetary scale dynamics produce cloud turnover times of less than a few days. Under these conditions, the water mixing ratio could approach .0001, and the formation of a thin hydrochloric acid haze at high altitude above the main cloud is possible.

Prinn, R. G.↗
NASA NTRS1976

Reaction of NH2 with NO and O2

Experiments were performed on the photooxidation of NH3 at room temperature and the photolysis of NH3-NO mixtures in order to determine the reaction paths of NH2 with O2. NH3 was photolyzed (NH3 + E yields NH2 + H) in the presence of O2 above 0.6 torr at 213.9 nm and 25 C, producing N2 and N2O. Only N2 and N2O were produced with any significant quantum yield, and their quantum yield was invariant with reaction conditions, which imposes a great number of constraints reducing the number of possible reactions greatly. It is argued that the N2 must be produced from the NH2O2 radical which was produced by the reaction between NH2 and O2. Subsequent reactions leading to N2 and N2O are speculative. In the photolysis of NH3 in the presence of NO and NO-O2 mixtures, the products identified were N2, H2, and N2O. Without the presence of O2, the reaction scheme after photolysis is (2) NH2 + NO yields N2 + H2O, (3) H + NO + M yields HNO + M, (4) H + HNO yields H2 + NO, and (5) 2HNO yields N2O + H2O. The average value for the ratio k3 times the square root of k5 divided by k4 was computed to be (1.6 plus or minus 0.6) times 10 to the minus 28th cm to the exponent 9/2 per square root sec. In addition, the presence of 113 mtorr of O2 had no effect on the quantum yields of N2 or H2, so it appears that it does not deactivate electronically excited NH3.

Jayanty, R. K. M.↗
NASA NTRS1977

Hydrogen quantum yields in the 360 nm photolysis of Eu/2+/ solutions and their relationship to photochemical fuel formation

Water decomposition by a cyclic photoredox process is discussed in general terms. Thermodynamics determines the wavelength of the charge-transfer band corresponding to electron transfer to or from water of hydration of a cation. These relationships indicate that it is unlikely that a photoreduction reaction resulting in water decomposition will occur in the sea-level solar range of wavelengths. Such is not the case for photooxidation, and an example is known: the photolysis of Eu(2+) in aqueous solution. Hydrogen quantum yields have been determined for this reaction. They are sufficiently high (about 0.3) as to offer encourangement for the further exploration of photoredox reactions as a means of solar energy conversion.

Ryason, P. R.↗
NASA NTRS1977

Photocatalytic oxidation mechanism of alkanes in contact with titanium dioxide

Isobutane was photooxidized on titanium dioxide between -16 and +180 C in tertiary butanol and acetone. The formation of tertiary butanol preceded the formation of acetone. Above 20 C the latter compound became clearly predominant. The reaction kinetics obeyed a steady state model of oxygen chemisorption with the involvement of isobutane in the physisorbed phase.

Formenti, M.↗
NASA NTRS1978

Hydrogen from the solar photolysis of water

Developments related to the study of photosynthesis are examined and aspects of photosensitization by solids are considered. It is pointed out that solids photosensitization for solar photochemical fuel formation is now an extremely active research area as a consequence of the promising results obtained with semiconductor photoelectrodes. The investigation of water decomposition schemes involving heterogeneous reactions is likely to be a productive area. As is the case for photosynthesis, the known examples of water decomposition by solids photosensitization involve charge separation processes immediately following light absorption. Homogeneous photoredox reactions are also discussed, taking into account thermochemical and photochemical cycles leading to the formation of a photooxidized ion, hydrogen quantum yields in the photo-oxidation aqueous ions, and thermochemical and photochemical cycles leading to the formation of a photoreduced ion.

Ryason, P. R.↗
NASA NTRS1978

Solar photolysis of water

A cyclic process is described for the solar photolysis of water, including a first stage in which water is reduced in the presence of a Eu(+2) photooxidizable reagent producing hydrogen and spent oxidized Eu(+3) reagent. The spent reagent Eu(+3) is reduced by means of a transition metal ligand complex reductant, RuL(+3) in a photoexcited state, such as a ruthenium pyridyl complex. Due to competing reactions between the photolysis and regeneration products, the photooxidation reaction must be separated from the regeneration in space and time by supporting the reagent and/or the reductant on solid supports and utilizing pH, wavelength and flow control to maximize hydrogen and oxygen production.

Ryason, P. R.↗
NASA NTRS1979

Summary of southeastern Virginia urban plume measurement data for August 4 and 5, 1977

The measurement program was conducted to define the characteristics of the Southeastern Virginia urban plume with emphasis on the photooxidant species. The measurement area was a rectangle approximately 200 km by 60 km centered in the Hampton Roads area of Tidewater Virginia. This area includes the cities of Norfolk, Virginia Beach, Chesapeake, Newport News, and Hampton. The data set presented includes aircraft measurements for ozone, nitrogen oxides, carbon monoxide, methane, and meteorological parameters such as dewpoint temperature. Surface level data for ozone are presented for 10 stations located throughout the test area. Comprehensive meteorological data from existing National Weather Service stations and special locations selected for the urban plume program are summarized.

Gregory, G. L.↗
NASA NTRS1982

Modelling of polymer photodegradation for solar cell modules

A computer program which simulates the complex processes of photooxidation which take place in a polymer upon prolonged exposure outdoors causing it to fail in photovoltaic and other applications. The method calculates from an input data set of elementary reactions and rates the concentration profiles of all species over time.

Guillet, J. E.↗
NASA NTRS1983

Fluorescence from polystyrene - Photochemical processes in polymeric systems, 7

Results are presented for measurements of the fluorescence spectra of polystyrene in dilute solution and in pure solid films. It is determined that a major potential source of experimental error is the concurrent photooxidative degradation in air which may obscure fluorescence emission from monomeric sites in solid films at 25 C. The fluorescence spectra of oriented films are evaluated in terms of the monomer to excimer fluorescence intensity ratio and the excimer 'red shift'. The monomer to excimer fluorescence intensity ratio is determined to be significantly higher in fluid solution than in solid film.

Gupta, M. C.↗