Peter Oleynikov

Cobalt phosphate-modified barium-doped tantalum nitride nanorod photoanode with 1.5% solar energy conversion efficiency

Spurred by the decreased availability of fossil fuels and global warming, the idea of converting solar energy into clean fuels has been widely recognized. Hydrogen produced by photoelectrochemical water splitting using sunlight could provide a carbon dioxide lean fuel as an alternative to fossil fuels. A major challenge in photoelectrochemical water splitting is to develop an efficient photoanode that can stably oxidize water into oxygen. Here we report an efficient and stable photoanode that couples an active barium-doped tantalum nitride nanostructure with a stable cobalt phosphate co-catalyst. The effect of barium doping on the photoelectrochemical activity of the photoanode is investigated. The photoanode yields a maximum solar energy conversion efficiency of 1.5%, which is more than three times higher than that of state-of-the-art single-photon photoanodes. Further, stoichiometric oxygen and hydrogen are stably produced on the photoanode and the counter electrode with Faraday efficiency of almost unity for 100 min.

Collecting 3D electron diffraction data by the rotation method

Abstract A new method for collecting complete three-dimensional electron diffraction data is described. Diffraction data is collected by combining electron beam tilt at many very small steps, with rotation of the crystal in a few but large steps. A number of practical considerations are discussed, as well as advantages and disadvantages compared to other methods of collecting electron diffraction data.

Structure and catalytic properties of the most complex intergrown zeolite ITQ-39 determined by electron crystallography

Porous materials such as zeolites contain well-defined pores in molecular dimensions and have important industrial applications in catalysis, sorption and separation. Aluminosilicates with intersecting 10- and 12-ring channels are particularly interesting as selective catalysts. Many porous materials, especially zeolites, form only nanosized powders and some are intergrowths of different structures, making structure determination very challenging. Here, we report the atomic structures of an aluminosilicate zeolite family, ITQ-39, solved from nanocrystals only a few unit cells in size by electron crystallography. ITQ-39 is an intergrowth of three different polymorphs, built from the same layer but with different stacking sequences. ITQ-39 contains stacking faults and twinning with nano-sized domains, being the most complex zeolite ever solved. The unique structure of ITQ-39, with a three-dimensional intersecting pairwise 12-ring and 10-ring pore system, makes it a promising catalyst for converting naphtha into diesel fuel, a process of emerging interest for the petrochemical industry.

Weaving of organic threads into a crystalline covalent organic framework

Weaving organic threads Woven fabrics are inherently flexible. Liu et al. created a molecular fabric analog using metal-organic frameworks (see the Perspective by Gutierrez-Puebla). Phenanthroline ligands on a copper metal complex directed the addition of organic linkers via imine bonds to create helical organic threads with woven texture. Removing the copper allowed the strands to slide against each other and increased the elasticity of the material 10-fold. Science, this issue p. 365; see also p. 336 A metal-organic framework templates the synthesis of a material made of woven organic polymers. [Also see Perspective by Gutierrez-Puebla] A three-dimensional covalent organic framework (COF-505) constructed from helical organic threads, designed to be mutually weaving at regular intervals, has been synthesized by imine condensation reactions of aldehyde functionalized copper(I)-bisphenanthroline tetrafluoroborate, Cu(PDB)2(BF4), and benzidine (BZ). The copper centers are topologically independent of the weaving within the COF structure and serve as templates for bringing the threads into a woven pattern rather than the more commonly observed parallel arrangement. The copper(I) ions can be reversibly removed and added without loss of the COF structure, for which a tenfold increase in elasticity accompanies its demetalation. The threads in COF-505 have many degrees of freedom for enormous deviations to take place between them, throughout the material, without undoing the weaving of the overall structure.

π–π interaction of aromatic groups in amphiphilic molecules directing for single-crystalline mesostructured zeolite nanosheets

One of the challenges in material science has been to prepare macro- or mesoporous zeolite. Although examples of their synthesis exist, there is a need for a facile yet versatile approach to such hierarchical structures. Here we report a concept for designing a single quaternary ammonium head amphiphilic template with strong ordered self-assembling ability through π-π stacking in hydrophobic side, which stabilizes the mesostructure to form single-crystalline mesostructured zeolite nanosheets. The concept is demonstrated for the formation of a new type of MFI (zeolite framework code by International Zeolite Association) nanosheets joined with a 90° rotational boundary, which results in a mesoporous zeolite with highly specific surface area even after calcination. Low binding energies for this self-assembling system are supported by a theoretical analysis. A geometrical matching between the arrangement of aromatic groups and the zeolitic framework is speculated for the formation of single-crystalline MFI nanosheets.

CO2 capture from humid flue gases and humid atmosphere using a microporous coppersilicate

Grabbing CO2 from wet gas streams It is a challenge to extract CO2 from typical gas streams, such as the flue gas from a power plant. This is because any water in the stream tends to prevent CO2 absorption and may also degrade the absorbing material. Datta et al. developed a microporous copper silicate that avoids these problems. Most other materials have sites that absorb both water and CO2 at the same sites, and in that fight, the water tends to win. Although their material still absorbs water, it has separate sites for the CO2 absorption. It also shows good stability despite the absorbed water and can be reused. Science, this issue p. 302 A material with different sites for CO2 and water absorption can extract CO2 from moist gas streams. Capturing CO2 from humid flue gases and atmosphere with porous materials remains costly because prior dehydration of the gases is required. A large number of microporous materials with physical adsorption capacity have been developed as CO2-capturing materials. However, most of them suffer from CO2 sorption capacity reduction or structure decomposition that is caused by co-adsorbed H2O when exposed to humid flue gases and atmosphere. We report a highly stable microporous coppersilicate. It has H2O-specific and CO2-specific adsorption sites but does not have H2O/CO2-sharing sites. Therefore, it readily adsorbs both H2O and CO2 from the humid flue gases and atmosphere, but the adsorbing H2O does not interfere with the adsorption of CO2. It is also highly stable after adsorption of H2O and CO2 because it was synthesized hydrothermally.

WO3 nanorods created by self-assembly of highly crystalline nanowires under hydrothermal conditions.

WO3 nanorods and wires were obtained via hydrothermal synthesis using sodium tungstate as a precursor and either oxalic acid, citric acid, or poly(methacrylic acid) as a stabilizing agent. Transmission electron microscopy images showed that the organic acids with different numbers of carboxylic groups per molecule influence the final sizes and stacking nanostructures of WO3 wires. Three-dimensional electron diffraction tomography of a single nanocrystal revealed a hexagonal WO3 structure with preferential growth along the c-axis, which was confirmed by high-resolution transmission electron microscopy. WO3 nanowires were also spin-coated onto an indium tin oxide/glass conducting substrate, resulting in the formation of a film that was characterized by scanning electron microscopy. Finally, cyclic voltammetry measurements performed on the WO3 thin film showed voltammograms typical for the WO3 redox process.

Precession electron diffraction using a digital sampling method

A software-based method for collecting precession electron diffraction (PED) patterns is described. The PED patterns are obtained on a computer controlled transmission electron microscope. A series of electron diffraction (ED) patterns are collected as still ED frames at equal intervals, while the electron beam is precessed by one period (360°) around the optical axis. A PED pattern is obtained by combining the different ED frames, which resembles the sampling of a conventional PED pattern. Since intermediate ED frames are collected, it is possible to perform different post-processing strategies on the ED data. This can be used for geometric corrections to obtain accurate integrated intensities. The alignments and data collection are fully automated and controlled by software. The data quality is comparable to what can be achieved using specialized hardware for precession. The PED data can be used for structure solution and refinement with reasonably good R-values.

Scanning reciprocal space for solving unknown structures : energy filtered diffraction tomography and rotation diffraction tomography methods

Abstract Structure solutions of CaFe2O4 from energy filtered and unfiltered precession electron diffraction tomography and rotation electron diffraction tomography data, collected on two different microscopes, are reported. The collected data are analysed with three available software packages (ADT3D, PETS and EDT-PROCESS) and the obtained results are compared. In all cases the structure solution is successfully achieved. Energy filtered precession electron diffraction tomography, performed here for the first time, gives sharper diffraction peaks and less background compared to the unfiltered data and the final recovered model is closer to the X-ray refinement. Simultaneously the first crystal structure solution obtained from the rotation electron diffraction tomography data is reported.

Solving Approximant Structures Using a “Strong Reflections” Approach

A new general approach for solving τ-related approximants in an inflation series is derived. The strongest reflections from an approximant with known structure are used to deduce the structure of other approximants in the series. The structure model deduced in such a way is close enough to the true structure and a more accurate structure can be obtained from the refinement of such a model. The method is applied to m-Al 13 Co 4 , (C2/m, a = 15.173 Å, b = 8.109 Å, c = 12.349 Å and β = 107.84°) 1 and the inflation related τ 2 -Al 13 Co 4 2.