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      An efficient on-board metal-free nanocatalyst for controlled room temperature hydrogen production†

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          Abstract

          Positively charged functionalized carbon nanodots (CNDs) with a variety of different effective surface areas (ESAs) are synthesized via a cheap and time effective microwave method and applied for controlled hydrogen production via hydrolysis of sodium borohydride.

          Abstract

          Positively charged functionalized carbon nanodots (CNDs) with a variety of different effective surface areas (ESAs) are synthesized via a cheap and time effective microwave method and applied for the generation of hydrogen via hydrolysis of sodium borohydride. To the best of our knowledge, this is the first report of metal-free controlled hydrogen generation. Our observation is that a positively charged functional group is essential for the hydrolysis for hydrogen production, but the overall activity is found to be enhanced with the ESA. A maximum value of 1066 ml g –1 min –1 as the turnover frequency is obtained which is moderate in comparison to other catalysts. However, the optimum activation energy is found to be 22.01 kJ mol –1 which is comparable to well-known high cost materials like Pt and Ru. All of the samples showed good reusability and 100% conversion even after the 10th cycle. The effect of H + and OH is also studied to control the on-board and on-demand hydrogen production (“on–off switching”). It is observed that H 2 production decreases inversely with NaOH concentration and ceases completely when 10 –1 M NaOH is added. With the addition of HCl, H 2 production can be initiated again, which confirms the on/off control over production.

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          Nitrogen-doped, carbon-rich, highly photoluminescent carbon dots from ammonium citrate.

          The synthesis of water-soluble nitrogen-doped carbon dots has received great attention, due to their wide applications in oxygen reduction reaction, cell imaging, sensors, and drug delivery. Herein, nitrogen-doped, carbon-rich, highly photoluminescent carbon dots have been synthesized for the first time from ammonium citrate under hydrothermal conditions. The obtained nitrogen-doped carbon dots possess bright blue luminescence, short fluorescence lifetime, pH-sensitivity and excellent stability at a high salt concentration. They have potential to be used for pH sensors, cell imaging, solar cells, and photocatalysis.
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            Nitrogen-doped carbon quantum dots: facile synthesis and application as a "turn-off" fluorescent probe for detection of Hg2+ ions.

            A facile, economical and straightforward hydrothermal strategy is used to prepare highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) by using folic acid as both carbon and nitrogen sources. The as-prepared N-CQDs have an average size of 4.5 ± 1.0 nm and exhibit excitation wavelength-dependent fluorescence with the maximum emission and excitation at 390 and 470 nm, respectively. Furthermore, due to the effective quenching effect of Hg(2+) ions, such N-CQDs are found to serve as an effective fluorescent sensing platform for lable-free sensitive detection of Hg(2+) ions with a detection limit of 0.23 μM. The selectivity experiments reveal that the fluorescent sensor is specific for Hg(2+) even with interference by high concentrations of other metal ions. Most importantly, the N-CQDs-based Hg(2+) ions sensor can be successfully applied to the determination of Hg(2+) in tap water and real lake water samples. With excellent sensitivity and selectivity, such stable and cheap carbon materials are potentially suitable for monitoring of Hg(2+) in environmental application.
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              Superionic conductivity in lithium-rich anti-perovskites.

              Lithium ion batteries have shown great promise in electrical energy storage with enhanced energy density, power capacity, charge-discharge rates, and cycling lifetimes. However common fluid electrolytes consisting of lithium salts dissolved in solvents are toxic, corrosive, or flammable. Solid electrolytes with superionic conductivity can avoid those shortcomings and work with a metallic lithium anode, thereby allowing much higher energy densities. Here we present a novel class of solid electrolytes with three-dimensional conducting pathways based on lithium-rich anti-perovskites (LiRAP) with ionic conductivity of σ > 10(-3) S/cm at room temperature and activation energy of 0.2-0.3 eV. As temperature approaches the melting point, the ionic conductivity of the anti-perovskites increases to advanced superionic conductivity of σ > 10(-2) S/cm and beyond. The new crystalline materials can be readily manipulated via chemical, electronic, and structural means to boost ionic transport and serve as high-performance solid electrolytes for superionic Li(+) conduction in electrochemistry applications.
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                Author and article information

                Journal
                Chem Sci
                Chem Sci
                Chemical Science
                Royal Society of Chemistry
                2041-6520
                2041-6539
                01 April 2017
                30 January 2017
                : 8
                : 4
                : 2994-3001
                Affiliations
                [a ] Materials Research Centre , Indian Institute of Science , Bangalore-560012 , India . Email: santra.saswati@ 123456gmail.com ; Email: nanda@ 123456mrc.iisc.ernet.in
                [b ] Department of Basic Science and Humanities , Techno India – Batanagar , Kolkata 700141 , India
                Author information
                http://orcid.org/0000-0002-1643-6621
                http://orcid.org/0000-0001-9496-1408
                Article
                c7sc00162b
                10.1039/c7sc00162b
                5380114
                291964b8-3bb2-4e0e-8d68-1445d4d46300
                This journal is © The Royal Society of Chemistry 2017

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unported License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 12 January 2017
                : 29 January 2017
                Categories
                Chemistry

                Notes

                †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00162b


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