Adsorption and activation of molecular oxygen over atomic copper(I/II) site on ceria.

Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, we achieve selective oxygen (O2) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3d orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a [Cu(I)O2]3- site selectively adsorbs molecular O2, forming a rarely reported electrophilic η2-O2 species at 298 K. Assisted by neighbouring Ce(III) cations, η2-O2 is finally reduced to two O2-, that create two Cu-O-Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s-1 at 373 K and 0.01 bar PCO. The unique electronic structure of [Cu(I)O2]3- site suggests its potential in selective oxidation.

High-performance carbon/MnO2 micromotors and their applications for pollutant removal.

The wide applications of particulate micromotors in practice, especially in the removal of environmental pollutants, have been limited by the low production yields and demand on high concentration of fuel such as H2O2. Carbon/MnO2 micromotors were made hydrothermally using different carbon allotropes including graphite, carbon nanotube (CNT), and graphene for treatment of methylene blue and toxic Ag ions. The obtained micromotors showed high speed of self-propulsion. The highest speed of MnO2-based micromotors to date was observed for CNT/MnO2 (>2 mm/s, 5 wt% H2O2, 0.5 wt% surfactant). Moreover, different from previous studies, even with low H2O2 concentration (0.5 wt%) and without surfactant addition, the micromotors could also be well dispersed in water by the O2 stream released from their reaction with H2O2. The carbon/MnO2 micromotors removed both methylene blue (>80%) and Ag ions (100%) effectively within 15 min by catalytic decomposition and adsorption. Especially high adsorption capacity of Ag (600 mg/g) was measured on graphite/MnO2 and graphene/MnO2 micromotors.

Nanogenerator power output: influence of particle size and crystallinity of BaTiO3.

Lead-free piezoelectric nanogenerators made with BaTiO3 offer an attractive energy harvesting solution towards portable, battery-free medical devices such as self-powered pacemakers. Here, we assembled nanogenerators made of thin, flexible poly(vinylidene fluoride-co-hexafluoropropylene) films containing either polycrystalline BaTiO3 nanoparticles of various sizes or commercial monocrystalline particles of 64 or 278 nm in average diameter. The nanoparticles were prepared by hydrogen-driven flame aerosol technology and had an average diameter of 24-50 nm with an average crystal size of about 10 nm. The rapid cooling during nanoparticle formation facilitated the synthesis of polycrystalline, multi-domain, piezoelectrically active tetragonal BaTiO3 with a high c/a lattice ratio. Using these particles, 2 µm thin polymer nanocomposites were formed, assembled into nanogenerators that exhibited a 1.4 V time-averaged output, almost twice that of the best commercial BaTiO3 particles. That output was maintained stable for over 45 000 cycles with each cycle corresponding to a heartbeat of 60 bpm. The exceptional piezoelectric performance of these nanogenerators is traced to their constituent polycrystalline nanoparticles, having high degree of domain orientation upon poling and exhibiting the flexoelectric effect, polarization induced by a strain gradient.

Multiwavelength Light-Responsive Au/B-TiO2 Janus Micromotors.

Conventional photocatalytic micromotors are limited to the use of specific wavelengths of light due to their narrow light absorption spectrum, which limits their effectiveness for applications in biomedicine and environmental remediation. We present a multiwavelength light-responsive Janus micromotor consisting of a black TiO2 microsphere asymmetrically coated with a thin Au layer. The black TiO2 microspheres exhibit absorption ranges between 300 and 800 nm. The Janus micromotors are propelled by light, both in H2O2 solutions and in pure H2O over a broad range of wavelengths including UV, blue, cyan, green, and red light. An analysis of the particles' motion shows that the motor speed decreases with increasing wavelength, which has not been previously realized. A significant increase in motor speed is observed when exploiting the entire visible light spectrum (>400 nm), suggesting a potential use of solar energy, which contains a great portion of visible light. Finally, stop-go motion is also demonstrated by controlling the visible light illumination, a necessary feature for the steerability of micro- and nanomachines.

Multifunctional superhydrophobic polymer/carbon nanocomposites: graphene, carbon nanotubes, or carbon black?

Superhydrophobic surfaces resisting water penetration into their texture under dynamic impact conditions and offering simultaneously additional functionalities can find use in a multitude of applications. We present a facile, environmentally benign, and economical fabrication of highly electrically conductive, polymer-based superhydrophobic coatings, with impressive ability to resist dynamic water impalement through droplet impact. To impart electrical conductivity, the coatings were prepared by drop casting suspensions with loadings of different kinds of carbon nanoparticles, namely, carbon black (CB), carbon nanotubes (CNT), graphene nanoplatelets (GNP) and their combinations, in a fluoropolymer dispersion. At 50 wt % either CB or CNT, the nanocomposite coatings resisted impalement by water drops impacting at 3.7 m/s, the highest attainable speed in our setup. However, when tested with 5 vol % isopropyl alcohol-water mixture, i.e., a lower surface tension liquid posing a stiffer challenge with respect to impalement, only the CB coatings retained their impalement resistance behavior. GNP-based surfaces featured very high conductivity ∼1000 S/m, but the lowest resistance to water impalement. The optimal performance was obtained by combining the carbon fillers. Coatings containing CB:GNP:polymer = 1:1:2 showed both excellent impalement resistance (up to 3.5 m/s with 5 vol % IPA-water mixture drops) and electrical conductivity (∼1000 S/m). All coatings exhibited superhydrophobic and oleophilic behavior. To exemplify the additional benefit coming from this property, the CB and the optimal, combined CB/GNP coatings were used to separate mineral oil and water through filtration of their mixture.

Efficient solvent-free hydrogenation of ketones over flame-prepared bimetallic Pt-Pd/ZrO(2) catalysts.

Named and flamed: Bimetallic Pt-Pd/ZrO(2) catalysts with different Pt/Pd atomic ratios and high dispersion of the metal nanoparticles are prepared by a single-step flame-spray pyrolysis. The catalysts show excellent activity and tunable product selectivity for the solvent-free hydrogenation of the ketone model compounds cyclopentanone and acetophenone.

Mono- and bimetallic Rh and Pt NSR-catalysts prepared by controlled deposition of noble metals on support or storage component.

Mono- and bimetallic Rh and Pt based NOx storage-reduction (NSR) catalysts, where the noble metals were deposited on the Al2O3 support or BaCO3 storage component, have been prepared using a twin flame spray pyrolysis setup. The catalysts were characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy, X-ray diffraction, and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy. The NSR performance of the catalysts was investigated by fuel lean/rich cycling in the absence and presence of SO2 (25 ppm) as well as after H2 desulfation at 750 °C. The performance increased when Rh was located on BaCO3 enabling good catalyst regeneration during the fuel rich phase. Best performance was observed for bimetallic catalysts where the noble metals were separated, with Pt on Al2O3 and Rh on BaCO3. The Rh-containing catalysts generally showed much higher tolerance to SO2 during fuel rich conditions and lost only little activity during thermal aging at 750 °C.

Continuous flame aerosol synthesis of carbon-coated nano-LiFePO(4) for Li-ion batteries.

Core-shell, nano-sized LiFePO(4)-carbon particles were made in one step by scalable flame aerosol technology at 7 g/h. Core LiFePO(4) particles were made in an enclosed flame spray pyrolysis (FSP) unit and were coated in-situ downstream by auto thermal carbonization (pyrolysis) of swirl-fed C(2)H(2) in an O(2)-controlled atmosphere. The formation of acetylene carbon black (ACB) shell was investigated as a function of the process fuel-oxidant equivalence ratio (EQR). The core-shell morphology was obtained at slightly fuel-rich conditions (1.0

Development and characterization of a Versatile Engineered Nanomaterial Generation System (VENGES) suitable for toxicological studies.

A novel system for generation of engineered nanomaterials (ENMs) suitable for in situ toxicological characterization within biological matrices was developed. This Versatile Engineered Nanomaterial Generation System (VENGES) is based on industry-relevant, flame spray pyrolysis aerosol reactors that can scaleably produce ENMs with controlled primary and aggregate particle size, crystallinity, and morphology. ENMs are produced continuously in the gas phase, allowing their continuous transfer to inhalation chambers, without altering their state of agglomeration. Freshly generated ENMs are also collected on Teflon filters for subsequent physicochemical and morphological characterization and for in vitro toxicological studies. The ability of the VENGES system to generate families of ENMs of pure and selected mixtures of iron oxide, silica, and nanosilver with controlled physicochemical properties was demonstrated using a range of state-of-the-art-techniques. Specific surface area was measured by nitrogen adsorption using the Brunauer-Emmett-Teller method, and crystallinity was characterized by X-ray diffraction. Particle morphology and size were evaluated by scanning and transmission electron microscopy. The suitability of the VENGES system for toxicological studies was also shown in both in vivo and in vitro studies involving Sprague-Dawley rats and human alveolar-like monocyte derived macrophages, respectively. We demonstrated linkage between physicochemical ENM properties and potential toxicity.

Flame spray-pyrolyzed vanadium oxide nanoparticles for lithium battery cathodes.

Vanadium pentoxide (V2O5) nanoparticles (30-60 nm) were made by a one-step and scalable flame spray pyrolysis (FSP) process. Optimization of the FSP processing conditions (precursor concentration and injection rate) enhanced the electrochemical performance of these nanoparticles. Increasing the cut-off potential for discharging from 1.5 to 2.5 V vs. Li/Li+ improved the cycle life of these V2O5 nanoparticles. Particles with the lowest specific surface area (approximately 32 m2 g(-1)) and highest phase purity (up to 98 wt%) showed excellent cyclability between 2.5 and 4.0 V vs. Li/Li+, retaining a specific charge of 110 mAh g(-1) beyond 100 cycles at a specific current of 100 mA g(-1), and also superior specific charge of 100 mAh g(-1) at specific current up to 20C rate (or 2000 mA g(-1)).