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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Magnetic Properties and Photocatalytic Activity of the TiO{sub 2} Micropowders and Nanopowders Coated by Ni Nanoclusters

In this work, TiO{sub 2} micropowders and nanopowders coated by Ni nanoclusters have been prepared by original electroless deposition method. The presence of Ni nanoclusters at the surface of TiO{sub 2} grains was confirmed by measuring the temperature dependence of magnetization. Optical spectroscopy measurements showed significant increase of light absorption in Ni-coated TiO{sub 2} nanopowders. Photocatalytic properties of TiO{sub 2}/Ni powder were studied with electron paramagnetic resonance spectroscopy as well. It was found that deposition of Ni nanoclusters on a mixture of anatase (76%) and rutile (14%) nanopowder provides best results and the optimal Ni deposition time was determined.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Performance efficiency and kinetic studies of water purification using ZnO and MgO nanoparticles for potassium permanganate

Zinc oxide (ZnO) and Magnesium oxide (MgO) nanoparticles (NPs) have been synthesized by solid–solid reaction technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) were used to investigate the structural properties of ZnO and MgO NPs. XRD indicates that structural of ZnO NPs has a hexagonal structure with space group P63mc. On the other hand, MgO NPs is cubic structure with space group Fm 3-bar m. The photocatalytic efficiency of both ZnO and MgO NPs as a catalyst was illustrated by studying the extreme quantity of potassium permanganate (KMnO{sub 4}) degradation rate in wastewater. KMnO{sub 4} achieved 17% and 25% degradation rate in 180 min for ZnO and MgO NPs, respectively. The experimental data were examined by the kinetic models of pseudo-first and second order as well as intra-particle diffusion. The obtained data is expressed well by the second-order kinetic model for both NPs. Moreover, according to the experimental results, MgO NPs has high-performance water purification as a comparison of ZnO NPs effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Erbium doped anatase TiO{sub 2} nanoparticles for photovoltaic applications

Doping of rare earth metal erbium (Er) into the nanocrystalline titanium dioxide (TiO{sub 2}) was identified to enhance the performance of photocatalytic and photovoltaic applications. Herein, TiO{sub 2} was doped with different concentrations of erbium through hydrothermal method and then employed to photocatalytic and photovoltaic applications. XRD, FT-IR, TEM, AFM, UV–visible DRS and photocatalytic measurements were carried out to examine the impact of erbium doping on TiO{sub 2}. The photovoltaic study revealed that the Er doped TiO{sub 2} exhibited the better power conversion efficiency with high short-circuit current density (J{sub sc}) and open-circuit voltage (V{sub oc}). This enhancement may be due to the reduced charge recombination, increased dye absorption ability and fast photoelectron injection.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Controlled electron transfer by molecular wires embedded in ultrathin insulating membranes for driving redox catalysis

Organic bilayers or amorphous silica films of a few nanometer thickness featuring embedded molecular wires offer opportunities for chemically separating while at the same time electronically connecting photo- or electrocatalytic components. Such ultrathin membranes enable the integration of components for which direct coupling is not sufficiently efficient or stable. Photoelectrocatalytic systems for the generation or utilization of renewable energy are among the most prominent ones for which ultrathin separation layers open up new approaches for component integration for improving efficiency. Recent advances in the assembly and spectroscopic, microscopic, and photoelectrochemical characterization have enabled the systematic optimization of the structure, energetics, and density of embedded molecular wires for maximum charge transfer efficiency. The progress enables interfacial designs for the nanoscale integration of the incompatible oxidation and reduction catalysis environments of artificial photosystems and of microbial (or biomolecular)-abiotic systems for renewable energy.

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

Insights into Acetic Acid Binding and Ketene Formation on Anatase TiO 2 (101)

Understanding the adsorption and reactivity of carboxylic acids on oxide surfaces is of great interest in catalysis for biomass upgrading via ketonization, a carbon–carbon coupling reaction. Herein, we investigate the adsorption and reaction of acetic acid on anatase TiO 2 (101) using scanning tunneling microscopy, infrared spectroscopy, temperature programmed reaction, and density functional theory calculations. We demonstrate the adsorption of acetic acid can form two intermediates: (1) dissociated, bidentate acetate with an associated bridging hydroxyl, and (2) molecular, monodentate acetic acid. The coexistence of ordered phases with increasing monolayer (ML) saturation coverages consisting of (1) pure acetate (0.5 ML), (2) mixed acetate/acetic acid (0.67 ML), (3) mixed acetate/acetic acid (1.0 ML) and (4) pure acetic acid demonstrates similar energetics for both acetate and acetic acid species. Under ultra-high vacuum conditions, the presence of both monodentate acetic acid and bidentate acetate was observed below room temperature, while solely bidentate acetate was observed up to 575 K. The deprotonation of acetic acid produces water at 280 K, while the thermal decomposition of bidentate acetate produces ketene and acetic acid at 645 K. In conclusion, this model study provides detailed insight into the stability and reactivity of carboxylic acid surface-bound intermediates, which could participate during ketonization reactions for biomass upgrading.

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

Solution synthesis of two-dimensional zinc oxide (ZnO)/molybdenum disulfide (MoS 2 ) heterostructure through reactive templating for enhanced visible-light degradation of rhodamine B

Numerous inorganic materials have been identified as potential candidates for high-performance photocatalysts. However, their solar-to-energy conversion efficiencies still fail to meet commercial requirements. Here, the main hurdle is the rapid recombination of photoexcited electrons and holes in single-phase materials. A viable predicted approach to suppress charge recombination is coupling two materials to form a two-dimensional (2D) heterostructure that physically separates photoinduced electrons and holes in different layers. In this work, the heterostructure-based paradigm was tested and a scalable solution synthesis of epitaxial ZnO-MoS 2 heterostructure was developed. A 2D ZnO-MoS 2 heterostructure was synthesized under hydrothermal conditions by stabilizing intermediate Zn-hydroxide states on a functionalized MoS 2 surface. Detailed characterization showed the formation of multilayer heterostructure with MoS 2 flakes intercalated between large size ZnO plates. The performance of this heterostructure was evaluated using photocatalytic degradation of rhodamine B. A degradation efficiency of 70% was measured within 90 minutes of visible-light irradiation, almost doubling the efficiency of the corresponding single-phase materials or their physical mixtures.

2D heterostructure↗
DOE OSTI2020

Minimizing energy demand and environmental impact for sustainable NH 3 and H 2 O 2 production—A perspective on contributions from thermal, electro-, and photo-catalysis

There is an urgent need to provide adequate and sustainable supplies of water and food to satisfy the demand of an increasing population. Catalysis plays important roles in meeting these needs by facilitating the synthesis of hydrogen peroxide that is used in water decontamination and chemicals production, and ammonia that is used as fertilizer. However, these chemicals are currently produced with processes that are either very energy-intensive or environmentally unfriendly. This article offers the perspectives of the challenges and opportunities in the production of these chemicals, focusing on the roles of catalysis in more sustainable, alternative production methods that minimize energy consumption and environmental impact. While not intended to be a comprehensive review, the article provides a critical review of selected literature relevant to its objectives, discusses areas needed for further research, and potential new directions inspired by new developments in related fields. For each chemical, production by thermal, electro-, and photo-excited processes are discussed. Problems that are common to these approaches and their differences are identified and possible solutions suggested.

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

Visually resolving the direct Z-scheme heterojunction in CdS@ZnIn 2 S 4 hollow cubes for photocatalytic evolution of H 2 and H 2 O 2 from pure water

We report the direct Z-scheme heterojunction has been recently emerging as an appealing architecture for photocatalysts design. Its efficiency depends on the interfacial and structural features of the photocatalysts. Herein, the two-dimensional ZnIn 2 S 4 nanosheets are grown on the surface of CdS hollow cubes to construct the CdS@ZnIn 2 S 4 hierarchical hollow photocatalysts with chemically bonded interface. The visualized measurements based on spatial-resolved surface photovoltage spectroscopy, combined with other spectroscopic and simulation investigations, clearly disclose that the CdS@ZnIn 2 S 4 hollow cubes constitute a highly efficient direct Z-scheme system. This accounts for the stoichiometric generation of H 2 and H 2 O 2 from pure water observed for the CdS@ZnIn 2 S 4 sulfide-only photocatalysts under visible light irradiation with an apparent quantum efficiency of 1.63 % at 400 nm. The present work demonstrates an effective protocol to achieve comprehensive insights into the charge transfer route at semiconductor heterojunction, and offers a viable way for constructing efficient sulfide-only photocatalysts for driving water splitting reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Photochemical micromotor of eccentric core in isotropic hollow shell exhibiting multimodal motion behavior

Adaptive motion behavior in response to different environmental stimuli is ubiquitous in biology and enables creatures to achieve a diversity of complex tasks, but not typically observed in synthetic systems. In this report we propose a design of chemically-powered micromotors actively performing multimodal motion behaviors with the external stimulus changing. They have isotropic outer surfaces but inherent inner mass asymmetry, such as eccentric core-in-hollow shell TiO 2 (E-TiO 2 ) microspheres. Their motion behavior can be spontaneously transformed among random Brownian propulsion (stochastic walk), negative phototaxis (moving against incident light), and negative photogravitaxis (moving against gravity) when the light intensity, illumination direction, or fuel concentration change. At a low light intensity and/or low H 2 O 2 fuel concentration, the E-TiO 2 micromotors perform directional movement away from light based on the dominated diffusiophoresis by the photocatalytic reaction over the isotropic shell. With the increase of light intensity or fuel concentration, there are more and more photons or fuels to reach the eccentric core and the contribution of the photocatalytic reaction over it to the diffusiophoresis gradually becomes dominant. In this case, the E-TiO 2 micromotors perform stochastic walks near the substrate due to their Brownian random rotational reorientations. The micromotors are single component, have low density, and can be synthesized in a large scale and at a low cost. This work will facilitate the development of multifunctional micro/nanomotors with varying behaviors and functions depending on environmental cues, e.g., enabling efficient search and delivery operations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Transition-metal doped titanate nanowire photocatalysts boosted by selective ion-exchange induced defect engineering

Defect engineering through elemental doping is an efficient way to boost the performance of semiconductor photocatalysts. For this work, transition-metal (TM) doped titanate nanowires (TNWs) were prepared via ion-exchange over the titanate precursors and demonstrated for the Rhodamine B (RhB) degradation under ultraviolet (UV) light irradiation. The ion-exchange of selective ions (V 5+ , Cr 3+ , Ni 2+ , and Zn 2+ ) with protons from pristine TNWs resulted in the hierarchical meso-porosity of nanowires with large pores of ~5–20 nm by TM doping and small pores of ~3.6–4.5 nm inherited from pristine TNWs, which facilitates the mass transfer while maintaining high surface area and active sites. Meanwhile, the TM intercalation partially reduces the Ti 4+ to Ti 3+ and narrows the optical bandgap, which, together with oxygen vacancies and superoxide radicals from pristine TNWs, enhance the adsorption and photocatalytic degradation performance of RhB. This work helps to elucidate the effects of transition-metal doping and provides a rational strategy towards high performance titanate-based photocatalysts for efficient and sustainable wastewater treatment.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tracing the transient reaction kinetics of adsorbed species by in situ/operando infrared spectroscopy

The dynamic reaction behavior (i.e., transient responses) of IR-observable adsorbed species and gaseous products obtained from transient kinetic studies provide valuable kinetic and mechanistic information, namely: the abundance of active intermediates and their reactivity distribution, the chemical structure of IR-observable active and spectator species, the sequence of their formation, and the kinetically significant and rate-determining step under reaction conditions of practical catalysis. We discuss the use of transient response data to elucidate the reaction mechanisms of several gas-solid reactions: CO/H 2 , CO/H 2 /C 2 H 4 , photocatalytic oxidation of ethanol, and the CO 2 -amine reaction. The IR coupled with transient kinetic techniques is especially useful for investigating the mechanisms of photocatalytic reactions because both photogenerated electrons and many adsorbed species are IR-active (exhibiting measurable IR bands), and their evolution occurs on a time scale of seconds at ambient temperature. We highlight the key features and limitations of in situ IR with transient kinetics, as well as their significance in catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A cobalt mimochrome for photochemical hydrogen evolution from neutral water

Here, a system for visible light-driven hydrogen production from water is reported. This system makes use of a synthetic mini-enzyme known as a mimochrome (CoMC6*a) consisting of a cobalt deuteroporphyrin and two attached peptides as a catalyst, [Ru(bpy) 3 ] 2+ (bpy = 2,2'-bipyridine) as a photosensitizer, and ascorbic acid as a sacrificial electron donor. The system achieves turnover numbers (TONs) up to 10,000 with respect to catalyst and optimal activity at pH 7. Comparison with related systems shows that CoMC6*a maintains the advantages of biomolecular catalysts, while exceeding other cobalt porphyrins in terms of total TON and longevity of catalysis. Herein, we lay groundwork for future study, where the synthetic nature of CoMC6*a will provide a unique opportunity to tailor proton reduction chemistry and expand to new reactivity.

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

All-solid-state Z-scheme BiVO 4 –Bi 6 O 6 (OH) 3 (NO 3 ) 3 heterostructure with prolonging electron-hole lifetime for enhanced photocatalytic hydrogen and oxygen evolution

As a visible-light response photocatalyst, BiVO 4 is widely used in photocatalytic oxygen evolution. In this study, a novel BiVO 4 –Bi 6 O 6 (OH) 3 (NO 3 ) 3 (BBN) heterostructure fabricates via a simple one-pot hydrothermal approach is certified to effectively restrain the recombination of carriers by efficient spatial charge separation. By employing BBN as a reductive-function photocatalyst, a solid-state Z-scheme is constructed to improve the photo-redox capacity of BiVO 4 and hydrogen production is realized in the BiVO 4 –BBN heterostructure for the first time. Furthermore, the solid-state Z-scheme introduced in the BiVO 4 –BBN ensures the photoexcited carriers with the powerful redox capacity to participate in the photocatalytic reaction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interfacial charge transfer in Pt-loaded TiO 2 P25 photocatalysts studied by in-situ diffuse reflectance FTIR spectroscopy of adsorbed CO

The efficiency of photocatalytic systems is strongly depending on the charge carrier transfer from the excited semiconductor to co-catalyst particles attached on its surface. In this study, we investigated the influence of photo-induced charge transfer in photoplatinized TiO 2 P25 photocatalysts by diffuse reflectance FTIR spectroscopy of CO molecules adsorbed on the Pt co-catalyst under well-defined gas phase conditions. In contrast to aqueous conditions, where shifts of the CO stretching vibration of up to 50 cm -1 have been reported, the observed shifts under gas phase conditions are very small (<1 cm -1 ). This demonstrates that the difference in dielectric properties between aqueous electrolytes and vacuum are critical for the development of prominent shifts of adsorbed CO bands upon trapping of photogenerated charge carriers on co-catalyst particles. The experimental findings are discussed in terms of an electrostatic Stark effect, charge screening, co-adsorption, coverage-dependent shifts of the vibrational bands of adsorbed CO and photocatalytic surface reactions.

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

Multifunctional transition metal doped titanium dioxide reduced graphene oxide composites as highly efficient adsorbents and photocatalysts

A series of novel, mesoporous transition metal doped titanium dioxide-reduced graphene oxide composites are synthesized where the dopants were Mn, Co, Ni, Mo, and W. An in-situ synthesis method was used which involves a green, economic, hydrothermal process which can be scaled up easily. The composites show high surface areas (165–245 m 2 /g) and monomodal pore size distributions with average pore diameters in the range of 3–5 nm. The homogeneous distributions of the dopants are seen in SEM-EDX mapping data. The indirect band gaps of the composite materials are in the range of 2.20–2.48 eV. The composites show excellent dye adsorption activities where 100% adsorption of Rhodamine B occurs within 5 min when Mo–TiO 2 /rGO composite is used. Furthermore, the adsorbed dye can either be desorbed or photocatalytically degraded and the composite is reusable up to 10 cycles without losing significant activity. Mo–TiO 2 /rGO composite showed excellent adsorption of both cationic and anionic dyes at neutral pH.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Design of materials with supramolecular polymers

One hundred years ago Hermann Staudinger was strongly criticized by his scientific peers for his macromolecular hypothesis, but today it is hard to imagine a world without polymers. His hypothesis described polymers as macromolecules composed of large numbers of structural units connected by covalent bonds. In the 1990s the concept of supramolecular polymers emerged in the scientific literature as discrete entities of large molar mass comparable to that of classical polymers but built through non-covalent bonds among monomers. Supramolecular polymers exist in biological systems, and potentially blend the physical properties of covalent polymers with unique features such as high degrees of internal order within the polymeric structure, defined shapes, and novel dynamics. This trend article provides a summary of seminal contributions in supramolecular polymerization and provides recent examples from the Stupp laboratory to demonstrate the potential applications of an exciting class of materials composed fully or partially of supramolecular polymers. Finally, in closing, we provide our perspective on future opportunities provided by this field at the onset of a second century of polymers. It is our objective here to demonstrate that this second century could be as prosperous, if not more so, than the preceding one.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Orientation of acetic acid hydrogen bonded to acetate terminated TiO 2 (110)

Acetic acid is a common pollutant for which photocatalytic degradation over titania provides a mitigating strategy. Knowledge of the bonding of acetate/acetic acid to this substrate is needed to aid interpretation of the photocatalytic data. In this work we use ambient pressure near edge X-ray absorption fine structure to measure the coverage and geometry of acetate in the TiO 2 (110) contact layer as well as acetic acid in an additional layer. A saturation coverage of 0.5 monolayers in both layers is found up to an acetic acid pressure of 10 -1 Torr at 266 K. The geometry of acetate appears to be unchanged by adsorption of an additional layer of acetic acid, with the contact layer involving a majority acetate species bidentate bonded to neighboring Ti 5c sites and a minority acetate species bonded in a perpendicular geometry. Acetic acid has a similar geometry dictated by hydrogen bonding to the contact layer as well as the substrate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗