Criegee intermediates found to have big impact on troposphere

 In a breakthrough paper recently published in the journal Science, researchers from Sandia's Combustion Research Facility, the University of Manchester and Bristol University report direct measurements of reactions of a gas-phase Criegee intermediate using photoionization mass spectrometry.

Criegee intermediates -- carbonyl oxides -- are implicated in autoignition chemistry and are pivotal atmospheric reactants, but only indirect knowledge of their reaction kinetics had previously been available. The article, titled Direct Kinetic Measurements of Criegee Intermediate (CH2OO) Formed by Reaction of CH2I with O2, reports the first direct kinetics measurements made of reactions of any Criegee species, in this case formaldehyde oxide (CH2OO). These measurements determine rate coefficients with key species, such as sulfur dioxide (SO2) and nitrogen dioxide (NO2), and provide new insight into the reactivity of these transient molecules.

The detection and measurement of the Criegee intermediate reactions was made possible by a unique apparatus, designed by Sandia researchers, that uses light from a third-generation synchrotron user facility, Lawrence Berkeley National Laboratory's Advanced Light Source, to investigate chemical reactions that are critical in hydrocarbon oxidation. The intense tunable light from the synchrotron allows researchers to discern the formation and removal of different isomeric species -- molecules that contain the same atoms but are arranged in different combinations.

In the present case, CH2OO can be distinguished from its more stable isomer, formic acid (HCOOH), because of their differing thresholds for photoionization. The Manchester and Bristol researchers recognized that this apparatus could elucidate not only combustion reactions but also important tropospheric oxidation processes, such as ozonolysis.

Ozonolysis, or the cleavage of carbon-carbon double bonds through reaction with ozone, is a reaction that plays a key role in a number of fields, including synthetic chemistry and tropospheric removal of unsaturated hydrocarbons. In the 1950s, Rudolf Criegee proposed that ozonolysis of alkenes occurs via the carbonyl oxide biradicals, now called Criegee intermediates. Criegee intermediates also have been calculated to be markers of critical chain-branching steps in hydrocarbon autoignition chemistry.

However, until 2008 no gas-phase Criegee intermediate had been observed, and rate coefficients derived from indirect measurements spanned orders of magnitude.

In the Science publication, Sandia researchers reported a new means of producing gas-phase Criegee intermediates and used this method to prepare enough CH2OO to measure its reactions with water, SO2, nitric oxide (NO), and NO2. The ability to reliably produce Criegee intermediates will facilitate studies of their role in ignition and other oxidation systems.

In particular, the present measurements show that the reactions of CH2OO with SO2 and NO2 are far more rapid than previously thought. Moreover, the Bristol and Manchester investigators demonstrated that these kinetics results imply a much greater role of carbonyl oxides in tropospheric sulfate and nitrate chemistry than models had assumed, a conclusion that will substantially impact existing atmospheric chemistry mechanisms. For example, SO2 oxidation is the source of sulfate species that nucleate atmospheric aerosols. Because the oxidation of SO2 by Criegee intermediate is much faster than modelers assumed, Criegee reactions may be a major tropospheric sulfate source, changing predictions of tropospheric aerosol formation.

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The above story is reprinted from materials provided by DOE/Sandia National Laboratories.

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Journal Reference:

O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, C. A. Taatjes. Direct Kinetic Measurements of Criegee Intermediate (CH2OO) Formed by Reaction of CH2I with O2. Science, 2012; 335 (6065): 204 DOI: 10.1126/science.1213229

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KBR to Provide Ammonia License and Engineering Services for KIMA El-Delta Fertilizer and Chemical, in Aswan, Egypt

KBR announced that it was awarded a contract by Tecnimont S.p.A. for the License and Basic Engineering Design (BED) of a new ammonia plant to be built by Chemical Industries Holding Co. (Kima) in Aswan, Egypt.

Under the terms of the contract, KBR will provide Kima with a license for its proprietary Purifier™ Ammonia Technology and related engineering services for Kima’s new plant. The plant is being built on a fast-track basis and will support regional development plans in Aswan as well as Egypt’s drive to build modern fertilizer complexes.

“KBR’s ammonia process is a benchmark in the industry as is evidenced by our global installed base,” said John Derbyshire, President, KBR Technology. “We are honored that Kima has selected KBR Technology and look forward to working closely with our EPC partner Tecnimont to deliver a world-class ammonia plant to Kima.”

 

Give support to repulsion, and you'll see attraction. We know why

 When two objects repel each other under the action of one force, we usually expect that addition of another force, also repulsive one, will accelerate separation. This intuitive view is, however, not always true. Researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw have managed to explain surprising results of experiments with mixtures, where two repulsive interactions have lead to a strong attraction.

The results of last year's experiments with mixtures carried out at the University of Stuttgart, Germany, were surprising for many researchers. In one of the systems studied, a repulsive force was acting between the system components. When a second repulsive force was introduced, an unexpected effect was observed: a strong attraction. This unusual result aroused interest of the theoreticians from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw. "Starting from the basics, we have developed a theoretical model of the system studied in Germany and successfully verified its predictions with experimental evidence. That's why we are able to explain, how superposition of two repulsive interactions transforms into attraction," says Prof. Alina Ciach from the IPC PAS.

The system modelled at the IPC PAS was a mixture of water and an oily organic liquid -- lutidine. The mixture included also salt ions. The fluid was placed between two electrically charged walls, one hydrophilic, and another one hydrophobic.

Water is miscible with lutidine only in a certain temperature range. An interesting situation arises close to the critical temperature, where the system cannot "make a decision" if the components should mix or separate. "Under these conditions, the water layer at the hydrophilic wall becomes relatively thick, similarly as the oil layer at the hydrophobic wall. And as water and oil 'dislike' each other, a force emerges to push the walls apart," explains Faezeh Pousaneh from Iran, a PhD student working at the IPC PAS under the International PhD Projects Programme of the Foundation for Polish Science.

The unusual behaviour of the modelled system was revealed after electric charge of the same sign was applied to both walls. A second, electrostatic, repulsion was acting then between the walls, and even so the walls were becoming attractive! "Paper and pencils were set in motion. Using purely analytical calculations, together with Faezeh, we derived specific formulae to describe the course of the phenomenon," says Prof. Ciach.

It turned out that the key element of the model was the assumption that the ions in solution move exclusively in water, while avoiding lutidine. The walls of the system under study were electrically charged, so they attracted ions. "But there is lutidine layer at the hydrophobic wall!," notices Pousaneh. "So an ion faces a dilemma: it wants to get to the wall, but the access is protected by lutidine. And the hurdle can be taken in one way only: by pulling water." As a result of the process described above, the wall surface, earlier hydrophobic, starts to behave like a hydrophilic one, becoming similar in that respect to the other wall. And two hydrophilic walls attract each other.

The team from the IPC PAS intends to continue the research on variants of the modelled systems. "Interactions similar to those described by us occur between charged colloidal particles with selective surfaces. Depending on temperature, the interactions are sometimes repulsive, sometimes attractive," says Prof. Ciach. It turns out that in a narrow temperature range, the potential has a minimum for certain distance between the particles, so it is similar to that one being responsible for arrangement of atoms in nodes of the crystal lattice. "Thus, by controlling temperature we will be able to force a colloid to develop a specific structure. Then it can be preserved and used, for instance in material engineering," stresses Prof. Ciach.

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The above story is reprinted from materials provided by Institute of Physical Chemistry of the Polish Academy of Sciences, via AlphaGalileo.

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Journal Reference:

Faezeh Pousaneh, Alina Ciach. The origin of the attraction between like charged hydrophobic and hydrophilic walls confining a near-critical binary aqueous mixture with ions. Journal of Physics: Condensed Matter, 2011; 23 (41): 412101 DOI: 10.1088/0953-8984/23/41/412101

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3-D view of 1-D nanostructures

Just 100 nanometers in diameter, nanowires are often considered one-dimensional. But researchers at Northwestern University have recently reported that individual gallium nitride nanowires show strong piezoelectricity -- a type of charge-generation caused by mechanical stress -- in three dimensions.

The findings, led by Horacio Espinosa, James N. and Nancy J. Farley Professor in Manufacturing and Entrepreneurship at the McCormick School of Engineering and Applied Science, were published online Dec. 22 in Nano Letters.

Gallium nitride (GaN) is among the most technologically relevant semiconducting materials and is ubiquitous today in optoelectronic elements such as blue lasers (hence the blue-ray disc) and light-emitting-diodes (LEDs). More recently, nanogenerators based on GaN nanowires were demonstrated capable of converting mechanical energy (such as biomechanical motion) to electrical energy.

"Although nanowires are one-dimensional nanostructures, some properties -- such as piezoelectricity, the linear form of electro-mechanical coupling -- are three-dimensional in nature," Espinosa said. "We thought these nanowires should show piezoelectricity in 3D, and aimed at obtaining all the piezoelectric constants for individual nanowires, similar to the bulk material."

The findings revealed that individual GaN nanowires as small as 60 nanometers show piezoelectric behavior in 3D up to six times of their bulk counterpart. Since the generated charge scales linearly with piezoelectric constants, this finding implies that nanowires are up to six times more efficient in converting mechanical to electrical energy.

To obtain the measurements, researchers applied an electric field in different directions in single nanowire and measured small displacements, often in pico-meter (10-12 m) range. The group devised a method based on scanning probe microscopy leveraging high-precision displacement measurement capability of an atomic force microscope.

"The measurements were very challenging, since we needed to accurately measure displacements 100 times smaller than the size of the hydrogen atom," said Majid Minary, a postdoctoral fellow and the lead author of the study.

These results are exciting especially considering the recent demonstration of nanogenerators based on GaN nanowires, for powering of self-powered nanodevices.

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The above story is reprinted from materials provided by Northwestern University.

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Journal Reference:

Majid Minary-Jolandan, Rodrigo A. Bernal, Irma Kuljanishvili, Victor Parpoil, Horacio D. Espinosa. Individual GaN Nanowires Exhibit Strong Piezoelectricity in 3D. Nano Letters, 2012; : 120103071655004 DOI: 10.1021/nl204043y

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