Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.

X-Ray Diffraction

Higher alcohols are important compounds with widespread applications in the chemical, pharmaceutical and energy sectors. Currently, they are mainly produced by sugar fermentation (ethanol and isobutanol) or hydration of petroleum-derived alkenes (heavier alcohols), but their direct synthesis from syngas (CO + H2) would comprise a more environmentally-friendly, versatile and economical alternative. Research efforts in this reaction, initiated in the 1930s, have fluctuated along with the oil price and have considerably increased in the last decade due to the interest to exploit shale gas and renewable resources to obtain the gaseous feedstock. Nevertheless, no catalytic system reported to date has performed sufficiently well to justify an industrial implementation. Since the design of an efficient catalyst would strongly benefit from the establishment of synthesis–structure–function relationships and a deeper understanding of the reaction mechanism, this review comprehensively overviews syngas-based higher alcohols synthesis in three main sections, highlighting the advances recently made and the challenges that remain open and stimulate upcoming research activities. The first part critically summarises the formulations and methods applied in the preparation of the four main classes of materials, i.e., Rh-based, Mo-based, modified Fischer–Tropsch and modified methanol synthesis catalysts. The second overviews the molecular-level insights derived from microkinetic and theoretical studies, drawing links to the mechanisms of Fischer–Tropsch and methanol syntheses. Finally, concepts proposed to improve the efficiency of reactors and separation units as well as to utilise CO2 and recycle side-products in the process are described in the third section.

Status and prospects in higher alcohols synthesis from syngas

I am really glad to have this opportunity to write to you, specially about a subject in which I have worked for half a century. When I was your age, if somebody had told me that I would be working in chemistry of materials most of my life, I would not have believed it. At that time, chemistry of materials meant studying something about cement, steel, sand and asbestos. It was indeed dull. I never didwell in school and college exams on questions related to this subject. Much later in my life, I got greatly interested in the subject for various reasons. First, inmy study of chemistry, I was influenced by Linus Pauling who ismy academic grandfather. His book titled ‘Nature of the Chemical Bond’ which I read when I was young made a great impression. It taught me how the structure of molecules and materials is an extremely important aspect of chemistry, and how the understanding of structure and bonding provides a basis to understand chemistry and to do new chemistry. It is because of this terrific inspiration that I started studying chemistry. It was clear at the end of my undergraduate career that I wanted to be a chemist.

Chemistry of materials

High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.

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Advances in designs and mechanisms of semiconducting metal oxide nanostructures for high-precision gas sensors operated at room temperature

Researchers show that dispersed functionalized graphene can exhibit broadband nonlinear optical absorption at fluences well below the damage threshold. An optical energy-limiting onset benchmark of 10 mJ cm−2 at a linear transmittance of 70% was obtained for nanosecond visible and near-infrared pulses. The findings shed light on the formation of practical thin films with broadband optical limiting characteristics.

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Giant broadband nonlinear optical absorption response in dispersed graphene single sheets

Free-standing, monodisperse cubic BaTiO3 colloidal nanocrystals have been prepared by a hydrothermal route at temperatures as low as 135 °C. Raman spectroscopy measurements and photoluminescence me...

Solution-Based Growth of Monodisperse Cube-Like BaTiO3 Colloidal Nanocrystals

A monoclinic tungsten trioxide nanowire array has been grown on silicon substrates using tungsten powders as source materials by thermal evaporation under specific synthesis conditions (1000 °C, 13–15 Torr, 200 sccm air flow). The morphology, chemical composition and crystal structure of the as-prepared tungsten trioxide nanowires were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and transmission electron microscopy. The nanowires were identified as monoclinic in structure, with diameters ranging from 40 to 100 nm and lengths up to 5 µm. It was found that sufficient oxygen and air flow are the major factors to influence the nanowire array growth. The nanowire array was employed directly for gas sensor fabrication using photolithography. The gas sensing experiments revealed that the nanowire array sensors are highly sensitive to NO2 (50 ppb), making the tungsten trioxide nanowire array a competitive candidate for highly sensitive gas sensor fabrication.

Growth of monoclinic WO3nanowire array for highly sensitive NO2 detection

The silica modified CeO2 gas sensing nanomaterials are synthesized using a sol-hydrothermal route. The 8%silica-CeO2 has larger specific surface areas of 83.75 m2/g and smaller crystalline size of 11.5 nm than pure CeO2, respectively. Compared to pure CeO2, the 8%silica-CeO2 based gas sensor exhibits significant enhancement NH3 gas-sensing performance. At room temperature, it shows much better gas response of 3244% to 80 ppm of NH3 gas and lower detection limit (0.5 ppm) towards NH3 gas. It is also found that the gas response of the NH3 gas sensors increases linearly with the increase of NH3 gas concentration. Moreover, the NH3 gas sensor have good reversibility, stability and selectivity. The reason of enhanced NH3 gas-sensing performance is not only because of the increased specific surface areas, but also due to the electrolytic conductivity of NH4+ and OH− on the surface.

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Enhanced NH 3 gas-sensing performance of silica modified CeO 2 nanostructure based sensors

Fischer–Tropsch synthesis of olefin-rich liquid hydrocarbons from biomass-derived syngas over carbon-encapsulated iron carbide/iron nanoparticles catalyst

Low-cost broad-band optical limiters based on nanographene have been studied, finding optical-limiting properties superior to those of current standards, carbon fullerenes (C60) solutions and carbon black suspensions. Further examination indicates that the presence of π conjugation improves the optical-limiting responses. Superior limiting performance is retained regardless of solvent viscosity and polarity, a unique feature of graphene not observed in C60 and carbon black. Graphene suspensions in organic solvents can work under 10 Hz laser pulses without losing excellent limiting performance. More significantly, outstanding limiting properties are also preserved in a gel matrix. These nanographene-based optical limiters can thus work in solutions and solid matrixes for devices used for protecting human eyes and optical sensors from high-power lasers.

Baobao Cao

Papers

Solution-Based Growth of Monodisperse Cube-Like BaTiO3 Colloidal Nanocrystals

Growth of monoclinic WO3nanowire array for highly sensitive NO2 detection

Enhanced NH 3 gas-sensing performance of silica modified CeO 2 nanostructure based sensors

Fischer–Tropsch synthesis of olefin-rich liquid hydrocarbons from biomass-derived syngas over carbon-encapsulated iron carbide/iron nanoparticles catalyst

Nonlinear optical transmission of nanographene and its composites