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      Covalent functionalization of graphene by azobenzene with molecular hydrogen bonds for long-term solar thermal storage

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          Abstract

          Reduced graphene oxide-azobenzene (RGO-AZO) hybrids were prepared via covalent functionalization for long-term solar thermal storage. Thermal barrier (Δ E a ) of cis to tran reversion and thermal storage (Δ H) were improved by molecular hydrogen bonds (H-bonds) through ortho- or para-substitution of AZO. Intramolecular H-bonds thermally stabilized cis- ortho-AZO on RGO with a long-term half-life of 5400 h (Δ E a = 1.2 eV), which was much longer than that of RGO- para-AZO (116 h). RGO- para-AZO with one intermolecular H-bond showed a high density of thermal storage up to 269.8 kJ kg −1 compared with RGO- ortho-AZO (149.6 kJ kg −1) with multiple intra- and intermolecular H-bonds of AZO according to relaxed stable structures. Thermal storage in experiment was the same order magnitude to theoretical data based on Δ H calculated by density functional theory and packing density. Photoactive RGO-AZO hybrid can be developed for high-performance solar thermal storage by optimizing molecular H-bonds.

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          Generalized Gradient Approximation Made Simple.

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            Diazonium functionalization of surfactant-wrapped chemically converted graphene sheets.

            Surfactant-wrapped chemically converted graphene sheets obtained from reduction of graphene oxide with hydrazine were functionalized by treatment with aryl diazonium salts. The nanosheets are characterized by X-ray photoelectron spectroscopy, attenuated total reflectance infrared spectroscopy, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The resulting functionalized nanosheets disperse readily in polar aprotic solvents, allowing alternative avenues for simple incorporation into different polymer matrices.
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              Azobenzene photoswitching without ultraviolet light.

              Most azobenzene-based photoswitches use UV light for photoisomerization. This can limit their application in biological systems, where UV light can trigger unwanted responses, including cellular apoptosis. We have found that substitution of all four ortho positions with methoxy groups in an amidoazobenzene derivative leads to a substantial (~35 nm) red shift of the n-π* band of the trans isomer, separating it from the cis n-π* transition. This red shift makes trans-to-cis photoswitching possible using green light (530-560 nm). The cis state is thermally stable with a half-life of ~2.4 days in the dark in aqueous solution. Reverse (cis-to-trans) photoswitching can be accomplished with blue light (460 nm), so bidirectional photoswitching between thermally stable isomers is possible without using UV light at all. © 2011 American Chemical Society
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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                19 November 2013
                2013
                : 3
                Affiliations
                [1 ]School of Materials Science and Engineering, Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University , Tianjin 300072, China
                [2 ]Shimane Institute for Industrial Technology, Hokuryo-cho , Mastue, Shimane 690-0816, Japan
                Author notes
                Article
                srep03260
                10.1038/srep03260
                3832871
                Copyright © 2013, Macmillan Publishers Limited. All rights reserved

                This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/

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