Alexander Orlov

Development of a conceptual framework for evaluation of nanomaterials release from nanocomposites: Environmental and toxicological implications

Despite the fact that nanomaterials are considered potentially hazardous in a freely dispersed form, they are often considered safe when encapsulated into a polymer matrix. However, systematic research to confirm the abovementioned paradigm is lacking. Our data indicates that there are possible mechanisms of nanomaterial release from nanocomposites due to exposure to environmental conditions, especially UV radiation. The degradation of the polymer matrix and potential release of nanomaterials depend on the nature of the nanofillers and the polymer matrix, as well as on the nature of environmental exposure, such as the combination of UV, moisture, mechanical stress and other factors. To the best of our knowledge there is no systematic study that addresses all these effects. We present here an initial study of the stability of nanocomposites exposed to environmental conditions, where carbon nanotube (CNT) containing polymer composites were evaluated with various spectroscopic and microscopic techniques. This work discusses various degradation mechanisms of CNT polymer nanocomposites, including such factors as UV, moisture and mechanical damage. An in vivo ingestion study with Drosophila showed reduced survivorship at each dose tested with free amine-functionalized CNTs, while there was no toxicity when these CNTs were embedded in epoxy. In addition to developing new paradigms in terms of safety of nanocomposites, the outcomes of this research can lead to recommendations on safer design strategies for the next generation of CNT-containing products.

A versatile new method for synthesis and deposition of doped, visible light-activated TiO2 thin films

A flexible and widely applicable method allows the deposition of carbon-doped visible light-activated photocatalytic TiO2 thin films on a variety of substrates.

Oxidation of volatile organic compounds on SBA-15 mesoporous molecular sieves modified with manganese.

Catalytic combustion of volatile organic compounds, such as propene, has been studied on manganese modified mesoporous molecular sieves. Powder X-ray diffraction, (29)Si nuclear magnetic resonance, nitrogen sorption and transmission electron microscopy show that the SBA-15 mesoporous silica molecular sieve can be modified with manganese using Mn(2)(CO)(10) or Mn(O(2)CMe)(2) without significant distortion of the host structure. The two products were catalytically active in propene oxidation, with SBA-15 modified with Mn(2)(CO)(10) showing significantly higher activity, possibly due to higher Mn content, than SBA-15 modified with Mn(O(2)CMe)(2).

Exceptional activity of sub-nm Pt clusters on CdS for photocatalytic hydrogen production: a combined experimental and first-principles study

In this work we have explored a new concept of substantially increasing photocatalytic activity for H2 production of conventional semiconductors by modifying them with sub-nm Pt particles. By combining both experimental and theoretical approaches, we have also developed new mechanistic insights into the 17 times increase in photocatalytic activity of Pt modified CdS catalysts.

Photocatalytic hydrogen evolution using nanocrystalline gallium oxynitride spinel

Photocatalytic hydrogen evolution from water was observed over nanocrystalline gallium oxynitride spinel under simulated solar light irradiation (320 nm < λ < 800 nm). Up to 8 μmol h−1 of H2 was evolved without co-catalyst loading. The photocatalyst was synthesized by the ammonolysis of gallium nitrate hydrate (Ga(NO3)3·xH2O). Optical measurements indicate an indirect gap (Eg) in the visible region (Eg = 2.50 eV) which is ascribed to photoexcitations from the N 2p valence states. A direct gap has an onset at ultraviolet energies (Eg = 3.69 eV), which is ascribed to photoexcitations from lower energy O 2p valence states.

Understanding the Interactions of CO2 with Doped and Undoped SrTiO3.

SrTiO3 and doped SrTiO3 have a wide range of applications in different fields. For example, Rh-doped SrTiO3 has been shown to have photocatalytic activity for both hydrogen production and CO2 conversion. In this study, both undoped and Rh-doped SrTiO3 were synthesized by hydrothermal and polymerizable complex methods. Different characterizations techniques including X-ray photoelectron spectroscopy (XPS), XRD, Raman, and UV/Vis spectroscopy were utilized to establish correlations between the preparation methods and the electronic/structural properties of Rh-doped SrTiO3 . The presence of dopants and oxygen vacancies substantially influenced the CO2 interactions with the surface, as revealed by the in situ infrared spectroscopic study. The presence of distinctly different adsorption sites was correlated to oxygen vacancies and oxidation states of Ti and Rh.

Development of a New Generation of Stable, Tunable, and Catalytically Active Nanoparticles Produced by the Helium Nanodroplet Deposition Method

Nanoparticles (NPs) are revolutionizing many areas of science and technology, often delivering unprecedented improvements to properties of the conventional materials. However, despite important advances in NPs synthesis and applications, numerous challenges still remain. Development of alternative synthetic method capable of producing very uniform, extremely clean and very stable NPs is urgently needed. If successful, such method can potentially transform several areas of nanoscience, including environmental and energy related catalysis. Here we present the first experimental demonstration of catalytically active NPs synthesis achieved by the helium nanodroplet isolation method. This alternative method of NPs fabrication and deposition produces narrowly distributed, clean, and remarkably stable NPs. The fabrication is achieved inside ultralow temperature, superfluid helium nanodroplets, which can be subsequently deposited onto any substrate. This technique is universal enough to be applied to nearly any element, while achieving high deposition rates for single element as well as composite core-shell NPs.

Unexpected visible light driven photocatalytic activity without cocatalysts and sacrificial reagents from a (GaN)1–x(ZnO)x solid solution synthesized at high pressure over the entire composition range

Optical and photocatalytic properties were determined for the solid solution series (GaN)1–x(ZnO)x synthesized at high pressure over the entire compositional range (x = 0.07 to 0.9). We report for the first time photocatalytic H2 evolution activity from water for (GaN)1–x(ZnO)x without cocatalysts, pH modifiers and sacrificial reagents. Syntheses were carried out by reacting GaN and ZnO in appropriate amounts at temperatures ranging from 1150 to 1200 °C, and at a pressure of 1 GPa. ZnGa2O4 was observed as a second phase, with the amount decreasing from 12.8 wt% at x = 0.07 to ∼0.5 wt% at x = 0.9. The smallest band gap of 2.65 eV and the largest average photocatalytic H2 evolution rate of 2.31 μmol h−1 were observed at x = 0.51. Samples with x = 0.07, 0.24 and 0.76 have band gaps of 2.89 eV, 2.78 eV and 2.83 eV, and average hydrogen evolution rates of 1.8 μmol h−1, 0.55 μmol h−1 and 0.48 μmol h−1, respectively. The sample with x = 0.9 has a band gap of 2.82 eV, but did not evolve hydrogen. An extended photocatalytic test showed considerable reduction of activity over 20 hours.

Characterizing Working Catalysts with Correlated Electron and Photon Probes

1. Center for Functional Nanomaterials, Brookhaven National Laboratory, New York, NY 11973 2. Department of Physics, Yeshiva University, New York, NY 10016 3. Department of Chemistry, University of Illinois at Urbana-Champaign, Illinois 61820 4. National Synchrotron Light Source II, Brookhaven National Laboratory, New York, NY 11973 5. Materials Science and Engineering Department, Stony Brook University, Stony Brook 11794 6. Department of Chemical Engineering, Columbia University, New York, NY 10027

Operando and multimodal studies of speciation and activity of Pt catalysts during the hydrogenation of ethylene

The creation of fuels and large volume chemicals (such as olefins) from crude oil feedstocks involves the hydrogenation of unsaturated hydrocarbons. These processes involve numerous catalytic reforming and hydrogenation/dehydrogenation processes, and are generally mediated by supported metal nanoparticle catalysts. These catalysts are generally chosen for their high activity, long term stability and the ease with which they can be regenerated and recovered. However, despite the extensive use of these materials, there are many questions that remain about how specific attributes of the structure and composition of the catalysts are affected by the gases with which they interact. Furthermore, it is critically important to understand how these structural changes affect selectivity, as well as how deactivation occurs because of the conversion process.