Ionic Liquid Crystals: Versatile Materials Goossens, Karel; Lava, Kathleen; Bielawski, Christopher W ...
Chemical reviews,
04/2016, Letnik:
116, Številka:
8
Journal Article
Recenzirano
This Review covers the recent developments (2005–2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive ...overview of the “state-of-the-art” in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.
Surface Modification of Water Purification Membranes Miller, Daniel J.; Dreyer, Daniel R.; Bielawski, Christopher W. ...
Angewandte Chemie (International ed.),
April 18, 2017, Letnik:
56, Številka:
17
Journal Article
Recenzirano
Odprti dostop
Polymeric membranes are an energy‐efficient means of purifying water, but they suffer from fouling during filtration. Modification of the membrane surface is one route to mitigating membrane fouling, ...as it helps to maintain high levels of water productivity. Here, a series of common techniques for modification of the membrane surface are reviewed, including surface coating, grafting, and various treatment techniques such as chemical treatment, UV irradiation, and plasma treatment. Historical background on membrane development and surface modification is also provided. Finally, polydopamine, an emerging material that can be easily deposited onto a wide variety of substrates, is discussed within the context of membrane modification. A brief summary of the chemistry of polydopamine, particularly as it may pertain to membrane development, is also described.
Cleaning up: The efficiency of polymeric water purification membranes, which are capable of removing many impurities from water but frequently suffer from fouling, can be improved by surface modification. Common techniques used to modify membrane surfaces, including grafting, coating, chemical treatment, UV irradiation, plasma treatment, and polydopamine application, are reviewed.
There has been an intense surge in interest in graphene during recent years. However, graphene‐like materials derived from graphite oxide were reported in 1962, and related chemical modifications of ...graphite were described as early as 1840. In this detailed account of the fascinating development of the synthesis and characterization of graphene, we hope to demonstrate that the rich history of graphene chemistry laid the foundation for the exciting research that continues to this day. Important challenges remain, however; many with great technological relevance.
A transformation for the ages: There has been a surge in interest in graphene in recent years; however, graphene‐like materials derived from graphite oxide were reported in 1962, and related chemical modifications of graphite were described as early as 1840. This account reveals that the rich history of graphene chemistry, the development of its synthesis and characterization, has laid the foundation for research that continues to this day.
Do not pass GO: Graphene oxide (GO) catalyzes the oxidation of various alcohols and alkenes, and the hydration of various alkynes into their respective aldehydes and ketones in good to excellent ...yields. The reactions proceed under relatively mild conditions and simple filtration was shown to be a convenient and effective method of catalyst recovery.
Harnessing the chemistry of graphene oxide Dreyer, Daniel R; Todd, Alexander D; Bielawski, Christopher W
Chemical Society reviews,
08/2014, Letnik:
43, Številka:
15
Journal Article
Recenzirano
Our understanding of the fundamental structure and bonding of graphene oxide (GO) as well as the scope of its utility have grown tremendously over the past decade. As a result, the pace of research ...efforts directed toward this carbon material continues to increase. Contemporary application now intersects a variety of disciplines and includes heterogeneous catalysis, flow reactor technologies, biomedicine and biotechnology, polymer composites, energy storage, and chemical sensors. Advances in these areas have been buoyed by improvements in the methods used to synthesize and characterize GO, as well as functionalized derivatives thereof. While the diverse uses of GO have been reviewed previously, herein we provide an overview of some of the most recent and significant developments in the field. A brief overview of GO's synthesis and characterization is also provided as well as several recently proposed structural models. The inherent reactivity of GO is described in the context of catalysis, and the utilization of GO's reactive oxygen groups and carbon framework to prepare functionalized derivatives is also discussed. Finally, we provide an outlook of potential areas where GO, its derivatives, and related materials may be expected to find utility or opportunity for further growth and study.
The chemistry of graphene oxide is revisited, and includes an update on recent developments and potential applications.
Switchable catalysts respond to various types of stimuli in a manner that results in distinct structural or electronic changes. When each state exhibits a different activity, selectivity, or ...solubility, the corresponding catalyst may be used to control chemical reactions in a temporally- or spatially-resolved fashion. N-Heterocyclic carbenes (NHCs) are versatile scaffolds for building switchable catalysts and many examples that respond to changes in electrochemical potential or light have been introduced. Such types of switchable NHCs will be described in this Feature Article. The accompanying discussions include design considerations, characterization methodology, quantification of the underlying switching phenomena, and utility in catalytic applications. Challenges for the field as well as perspectives on potential opportunities for future development are also provided.
This Feature Article offers in-depth, design-to-application discussions of redox-switchable N-heterocyclic carbenes that have been field tested.
In this minireview, we discuss the utility of heterogeneous carbons as catalysts for facilitating a broad range of synthetic transformations. While such materials are commonly used as supports for ...transition metals that are catalytically active, carbons that are free of metals are also capable of enabling useful chemical reactions. Carbon catalysts hold promise in the development of sustainable alternatives to existing metal-dependent processes, as well as the discovery of mechanisms and transformations that are altogether new. Spanning from the 1930s to the present day, we provide a broad overview of the utility of carbon to facilitate various oxidation, reduction, and bond forming processes. Lastly, we will present some challenges for the future of the field.
Cyclic stability of the eutectic mixture of galactitol and D-mannitol. Display omitted
•A eutectic mixture of galactitol/mannitol was studied as a phase change material.•The eutectic mixture featured ...a low melting point and a high heat of fusion.•The eutectic mixture showed high cyclic and chemical stability under an atmosphere of nitrogen.•The subcooling of the eutectic mixture was improved by adding nucleating agents.
The thermophysical properties of mixtures of galactitol and mannitol were examined via differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) analysis. The aforementioned sugars were found to form a eutectic mixture at a 30:70molar ratio of galactitol and manntitol, and displayed a melting point of 153°C while maintaining a high latent heat of fusion (ΔHfus=292Jg−1). The XRD data revealed that the eutectic mixture contained the α, β, and δ forms of mannitol with the δ form being the major component. By varying the temperature ramp rates utilized in the DSC measurements from 0.5°Cmin−1 to 20°Cmin−1, the heat of crystallization as well as the crystallization temperature increased (c.f., ΔHcrys: 64Jg−1→197Jg−1; Tc: 68°C→105°C). In addition, the temperature and the enthalpy of crystallization were also improved by up to 34% through the addition of small quantities (up to 0.5wt%) of nucleating agents, such as graphite powder or silver iodide. After 100 heating/cooling cycles under an atmosphere of nitrogen, the heat of fusion of the eutectic mixture decreased by only 4% with no change in the melting point, and the mixture appeared to be chemically stable according to a Fourier transform infrared (FT-IR) spectroscopic analysis. Collectively, these data indicate that the eutectic mixture exhibits excellent cyclic stability under ambient atmospheres and offers potential for use in thermal energy storage applications.
A 4,5-dithienylimidazolium salt was found to undergo electrocyclic isomerization upon exposure to UV radiation (λ irr = 313 nm) under neutral and basic conditions; subsequent exposure to visible ...light reversed the reaction. Under ambient light and in the presence of base, the imidazolium species catalyzed transesterifications as well as amidations in a manner similar to those of previously reported N-heterocyclic carbene precatalysts. However, upon UV irradiation to effect the aforementioned photocyclization, the rate of the transesterification reaction between vinyl acetate and allyl alcohol was significantly attenuated (k vis/UV = 12.5), as was the rate of the condensation of ethyl acetate with aminoethanol (k vis/UV = 100). The rates of these reactions were successfully toggled between fast and slow states by alternating exposure to visible and UV light, respectively, thus demonstrating a rare example of a photoswitchable catalyst that operates via photomodulation of its electronic structure.
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