SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Chemical Society reviews

28

There is increasing interest in developing artificial systems that can mimic natural photosynthesis to directly harvest and convert solar energy into usable or storable energy resources. Photocatalysis, in which solar photons are used to drive redox reactions to produce chemical fuel, is the central process to achieve this goal. Despite significant efforts to date, a practically viable photocatalyst with sufficient efficiency, stability and low cost is yet to be demonstrated. It is often difficult to simultaneously achieve these different performance metrics with a single material component. The heterogeneous photocatalysts with multiple integrated functional components could combine the advantages of different components to overcome the drawbacks of single component photocatalysts. A wide range of heterostructures, including metal/semiconductor, semiconductor/semiconductor, molecule/semiconductor and multi-heteronanostructures, have been explored for improved photocatalysts by increasing the light absorption, promoting the charge separation and transportation, enhancing the redox catalytic activity and prolonging the functional life-time. The present review gives a concise overview of heterogeneous photocatalysts with a focus on the relationship between the structural architecture and the photocatalytic activity and stability.

Concepts: Photon, Chemical reaction, Light, Catalysis, Absorption, Titanium dioxide, Photocatalysis, Photocatalytic water splitting

28

In the wide area of polyoxometalate (POM) chemistry, diphosphate/diphosphonate-based POMs represent a more recent area of study. However, in this short time it has emerged to become very dynamic, as shown by the wide variety of compounds reported. Ever since the discovery of the first polyoxotungstate framework constructed from diphosph(on)ate ligands, a widespread investigation on the preparative chemistry and properties of such compounds has followed. The main focus of such a study is based on factors such as the oxidation state of the metal, the effect of pH and temperature during synthesis, and the presence of different functional groups on the diphosphonate. In this review we discuss in detail all diphosphate/diphosphonate-based POMs, beginning with early developments, subsequent growth in interest, and finally focusing on the very latest developments.

Concepts: Amine, Chemical reaction, Functional group, Electrochemistry, Carbon, Organic chemistry, Oxidation state, Focus

28

Research interest in bimetallic catalysts is mainly due to their tunable chemical/physical properties by a number of parameters like composition and morphostructure. In catalysis, numerous bimetallic catalysts have been shown to exhibit unique properties which are distinct from those of their monometallic counterparts. To meet the growing energy demand while mitigating the environmental concerns, numerous endeavors have been made to seek green and sustainable energy resources, among which hydrogen has been identified as the most promising one with bimetallic catalysts playing important roles. This tutorial review intends to summarize recent progress in bimetallic catalysts for hydrogen production, specifically focusing on that of reforming technologies as well as the relevant processes like water-gas shift (WGS) and CO preferential oxidation (PROX), and emphasizing on the fundamental understanding of the nature of catalytic sites responsible for generating high purity hydrogen and minimizing carbon monoxide formation. Meanwhile, some important synthesis and characterization methods of bimetallic catalysts developed so far are also summarized.

Concepts: Hydrogen, Catalysis, Nitrogen, Haber process, Sustainable energy, Water gas shift reaction, Hydrogen production, Partial oxidation

28

High intensity ultrasound can be used for the production of novel materials and provides an unusual route to known materials without bulk high temperatures, high pressures, or long reaction times. Several phenomena are responsible for sonochemistry and specifically the production or modification of nanomaterials during ultrasonic irradiation. The most notable effects are consequences of acoustic cavitation (the formation, growth, and implosive collapse of bubbles), and can be categorized as primary sonochemistry (gas-phase chemistry occurring inside collapsing bubbles), secondary sonochemistry (solution-phase chemistry occurring outside the bubbles), and physical modifications (caused by high-speed jets or shock waves derived from bubble collapse). This tutorial review provides examples of how the chemical and physical effects of high intensity ultrasound can be exploited for the preparation or modification of a wide range of nanostructured materials.

Concepts: Chemical reaction, Fluid dynamics, Chemistry, Acoustics, Ultrasound, Sonoluminescence, Sonochemistry, Cavitation

28

Simple ionic liquids have long been held to be designer solvents, based upon the ability to independently vary their cations and anions. The formation of mixtures of ionic liquids increases this synthetic flexibility. We review the available literature of these ionic liquid mixtures to identify how their properties change and the possibility for their application.

Concepts: Ion, Solid, Solvent, Ionic liquid, Ions, Deep eutectic solvent, Ionic liquids

28

Significant advances in colloidal synthesis made in the past two decades have enabled the preparation of high quality nanoparticles with well-controlled sizes, shapes, and compositions. It has recently been realized that such nanoparticles can be utilized as ‘artificial atoms’ for building new materials which not only combine the size- and shape-dependent properties of individual nanoparticles but also create new collective properties by taking advantage of their electromagnetic interactions. The controlled clustering of nanoparticle building blocks into defined geometric arrangements opens a new research area in materials science and as a result much interest has been paid to the creation of secondary structures of nanoparticles, either by direct solution growth or self-assembly methods. In this tutorial review, we introduce recently developed strategies for the creation and surface modification of colloidal nanoparticle clusters, demonstrate the new collective properties resulting from their secondary structures, and highlight several of their many important technological applications ranging from photonics, separation, and detection, to multimodal imaging, energy storage and transformation, and catalysis.

Concepts: Nanoparticle, Nanotechnology, Sol-gel, Colloid, Materials science, Ceramic engineering, Colloidal crystal, Colloid-facilitated transport

28

Endohedral metallofullerenes (EMFs), a new class of hybrid molecules formed by encapsulation of metallic species inside fullerene cages, exhibit unique properties that differ distinctly from those of empty fullerenes because of the presence of metals and their hybridization effects via electron transfer. This critical review provides a balanced but not an exhaustive summary regarding almost all aspects of EMFs, including the history, the classification, current progress in the synthesis, extraction, isolation, and characterization of EMFs, as well as their physiochemical properties and applications in fields such as electronics, photovoltaics, biomedicine, and materials science. Emphasis is assigned to experimentally obtained results, especially the X-ray crystallographic characterizations of EMFs and their derivatives, rather than theoretical calculations, although the latter has indeed enhanced our knowledge of metal-cage interactions. Finally, perspectives related to future developments and challenges in the research of EMFs are proposed. (381 references).

Concepts: Electron, Chemistry, Science, Carbon, Physical chemistry, Materials science, Fullerene, Metallofullerene

28

The advances in micro- and nanofabrication technologies enable the preparation of increasingly smaller mechanical transducers capable of detecting the forces, motion, mechanical properties and masses that emerge in biomolecular interactions and fundamental biological processes. Thus, biosensors based on nanomechanical systems have gained considerable relevance in the last decade. This review provides insight into the mechanical phenomena that occur in suspended mechanical structures when either biological adsorption or interactions take place on their surface. This review guides the reader through the parameters that change as a consequence of biomolecular adsorption: mass, surface stress, effective Young’s modulus and viscoelasticity. The mathematical background needed to correctly interpret the output signals from nanomechanical biosensors is also outlined here. Other practical issues reviewed are the immobilization of biomolecular receptors on the surface of nanomechanical systems and methods to attain that in large arrays of sensors. We then describe some relevant realizations of biosensor devices based on nanomechanical systems that harness some of the mechanical effects cited above. We finally discuss the intrinsic detection limits of the devices and the limitation that arises from non-specific adsorption.

Concepts: Mass, Materials science, Young's modulus, Elasticity, Sensors, The Reader, Surface chemistry, Biosensor

27

Carbocyclic nucleosides are nucleoside analogues in which the furanosidic moiety has been replaced by a carbocycle. Several members of this family have been isolated from natural sources and include a 5-membered ring carbocycle. The aim of this review is to examine critically the different methodologies for the enantioselective construction of 3- to 6-membered rings, with a particular focus on 5-membered rings and their modifications. The procedures for bonding the heterocyclic moiety and the carbohydrate are treated separately. The methods for synthesising the carbocyclic moiety mainly focus on the construction of the cycle, although precise details about the functionalisation are provided in some cases. The selected methods aim to provide an overview of the synthesis of carbocycles related to the synthesis of carbocyclic nucleosides. The methods of synthesis of 5-membered rings are classified into two types: methods in which the cyclopentane ring is formed by ring closing reactions (C[double bond, length as m-dash]C and C-C formation) and methods that start from preformed 5-membered rings, based mainly on cycloaddition reactions. With respect to the methods of synthesis of 3-, 4- and 6-membered ring carbocyclic nucleosides, a selection of the more relevant enantioselective procedures is presented in a systematic manner.

Concepts: Natural selection, Chemical reaction, Nucleoside, Cyclopropane

27

It is increasingly apparent that many important classes of molecular framework material exhibit a variety of interesting and useful types of structural disorder. This tutorial review summarises a number of recent efforts to understand better both the complex microscopic nature of this disorder and also how it might be implicated in useful functionalities of these materials. We draw on a number of topical examples including topologically-disordered zeolitic imidazolate frameworks (ZIFs), porous aromatic frameworks (PAFs), the phenomena of temperature-, pressure- and desorption-induced amorphisation, partial interpenetration, ferroelectric transition-metal formates, negative thermal expansion in cyanide frameworks, and the mechanics and processing of layered frameworks. We outline the various uses of pair distribution function (PDF) analysis, dielectric spectroscopy, peak-shape analysis of powder diffraction data and single-crystal diffuse scattering measurements as means of characterising disorder in these systems, and we suggest a number of opportunities for future research in the field.

Concepts: Function, Temperature, Thermodynamics, Materials science, Set theory, Powder diffraction, Statistical mechanics, Thermal expansion