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Functional Carbon Materials Derived Through Hypergolic Reactions at Ambient Conditions

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Functional Carbon Materials Derived Through Hypergolic Reactions at Ambient Conditions nanomaterials Article Functional Carbon Materials Derived through Hypergolic Reactions at Ambient Conditions Nikolaos Chalmpes 1, Georgios Asimakopoulos 1, Konstantinos Spyrou 1, Konstantinos C. Vasilopoulos 1 , Athanasios B. Bourlinos 2,*, Dimitrios Moschovas 1, Apostolos Avgeropoulos 1 , Michael A. Karakassides 1 and Dimitrios Gournis 1,* 1 Department of Materials Science & Engineering, University of Ioannina, 45110 Ioannina, Greece; [email protected] (N.C.); [email protected] (G.A.); [email protected] (K.S.); [email protected] (K.C.V.); [email protected] (D.M.); [email protected] (A.A.); [email protected] (M.A.K.) 2 Physics Department, University of Ioannina, 45110 Ioannina, Greece * Correspondence: [email protected] (A.B.B.); [email protected] (D.G.); Tel.: +30-265-100-7141 (D.G.) Received: 13 February 2020; Accepted: 16 March 2020; Published: 20 March 2020 Abstract: Carbon formation from organic precursors is an energy-consuming process that often requires the heating of a precursor in an oven at elevated temperature. In this paper, we present a conceptually different synthesis pathway for functional carbon materials based on hypergolic mixtures, i.e., mixtures that spontaneously ignite at ambient conditions once its ingredients contact each other. The reactions involved in such mixtures are highly exothermic, giving-off sizeable amounts of energy; hence, no any external heat source is required for carbonization, thus making the whole process more energy-liberating than energy-consuming. The hypergolic mixtures described here contain a combustible organic solid, such as nitrile rubber or a hydrazide derivative, and fuming nitric acid (100% HNO3) as a strong oxidizer. In the case of the nitrile rubber, carbon nanosheets are obtained, whereas in the case of the hydrazide derivative, photoluminescent carbon dots are formed. We also demonstrate that the energy released from these hypergolic reactions can serve as a heat source for the thermal conversion of certain triazine-based precursors into graphitic carbon nitride. Finally, certain aspects of the derived functional carbons in waste removal are also discussed. Keywords: hypergolic reactions; fuming nitric acid; carbon nanosheets; graphitic carbon nitride; photoluminescent carbon dots 1. Introduction Hypergolic mixtures consist of two different substances that spontaneously ignite upon coming into contact at ambient conditions. One substance plays the role of a strong oxidizer (fuming HNO3, N2O4,H2O2, Cl2), whereas the other one the role of the combustible fuel (aniline, nitrile rubber, hydrazine derivatives, ionic liquids, acetylene) [1–6]. Such reactions are often used in chemistry demonstrations to show the impressive power of chemical energy, as well as ways to exploit it in real life applications (e.g., rocket propellants and fuels). The flames, smokes, sound, and motion produced by these reactions create a stunning result that captivates the senses of an observer. Interestingly, many of these reactions produce carbon, if organic fuels are used; surprisingly, in the literature, only little emphasis is given on this important aspect of hypergolic reactions [6]. Taking into consideration the central role of carbon in materials science and synthesis, hypergolic reactions can certainly provide an energy-saving and thermodynamically favoured alternative towards the direct synthesis of carbon materials at ambient conditions. In this respect, no external source of heat is required to carbonize the organic precursor, such as energy-consuming ovens operating at elevated temperature. As a matter of Nanomaterials 2020, 10, 566; doi:10.3390/nano10030566 www.mdpi.com/journal/nanomaterials Nanomaterials 2020, 10, x FOR PEER REVIEW 2 of 16 Nanomaterials 2020, 10, 566 2 of 13 is required to carbonize the organic precursor, such as energy-consuming ovens operating at elevated temperature. As a matter of fact, hypergolic reactions release sizeable amounts of energy fact,that could hypergolic be further reactions exploited release in sizeable the production amounts of of useful energy work that could(mechanical, be further electrical, exploited chemical, in the productionetc.) [7]. In addition, of useful such work reactions (mechanical, are kinetica electrical,lly chemical,favoured, etc.)thus [allowing7]. In addition, rapid product such reactions formation are kineticallyat room temperature favoured, thusand atmospheric allowing rapid pressure product (e.g., formation within few at room seconds). temperature The main and purpose atmospheric of this pressurework is to (e.g., highlight within the few importance seconds). Theof hypergolic main purpose reactions of this in workthe area is toof highlightcarbon materials the importance synthesis. of hypergolicTo this aim, reactions we provide in the examples area of carbon of hypergolic materials reactions synthesis. that To thisdirectly aim, lead we provideto the formation examples of hypergolicdifferent types reactions of functional that directly carbon lead tomaterials the formation at ambient of diff erentconditions. types ofFunctional functional carbon carbon materials atinclude ambient carbon conditions. nanosheets Functional [8], grap carbonhitic carbon materials nitride include [9], and carbon phot nanosheetsoluminescent [8], carbon graphitic dots carbon [10]. nitrideIn one [case,9], and we photoluminescent show that the reaction carbon of dots disposab [10]. Inle one nitrile case, gloves we show (acrylonitrile that the reaction butadiene of disposable rubber) nitrilewith fuming gloves nitric (acrylonitrile acid (100% butadiene HNO3) rubber)results in with carbon fuming nanosheets, nitric acid thus (100% offering HNO a3) way results to transform in carbon nanosheets,this waste plastic thus o intoffering a valuable a way to product. transform Moreover, this waste the plastic heat intoproduced a valuable fromproduct. the ignition Moreover, of the theglove heat can produced be further from utilized the ignition for the of thepreparation glove can of be other further important utilized forcarbon the preparation materials, ofsuch other as importantgraphitic carbon carbon nitride materials, by suchin-situ as graphiticheating of carbon a suitable nitride molecular by in-situ precursor. heating of In a suitableanother molecular case, the precursor.Girard’s reagent In another T case,(a hydrazide the Girard’s derivative) reagent T (a is hydrazide treated derivative)with fuming is treated nitric with acid fuming to afford nitric acidaqueous-dispersible to afford aqueous-dispersible photoluminescent photoluminescent carbon dots. carbonThe choice dots. of The Girard’s choice reagent of Girard’s T as reagent hypergolic T as hypergolicfuel is novel fuel in is the novel literature in the literature and was and merely was merelybased basedon the on fact the that fact hydrazine that hydrazine derivatives derivatives are arecommon common ingredients ingredients in inhypergolic hypergolic mixtures. mixtures. The The molecular molecular structure structure of of each each combustible fuel (nitrile(nitrile rubberrubber andand Girard’sGirard’s reagent reagent T) T) is is shown shown in in Scheme Scheme1. 1. Lastly, Lastly, we we show show practical practical applications applications of theof the derived derived functional functional carbons carbons in wastein waste removal, removal, such such as hexavalentas hexavalent chromium chromium and and organic organic dyes. dyes. Scheme 1. Molecular structures of the disposable nitrile glove (left) and Girard’s reagent T (right). Scheme 1. Molecular structures of the disposable nitrile glove (left) and Girard’s reagent T (right). 2. Materials and Methods 2. Materials and Methods All procedures were performed in a safety hood with a ceramic tile bench. For the synthesis of carbonAll nanosheets, procedures a were medium performed size disposable in a safety nitrile hood glove with (ca. a ceramic4 g, DURAGLOVE tile bench.® For, Penang, the synthesis Malaysia) of wascarbon placed nanosheets, inside a largea medium test tube size (diameter: disposable 3 cm; nitrile length: glove 20 cm),(ca. followed4 g, DURAGLOVE by the quick®, additionPenang, Malaysia) was placed inside a large test tube (diameter: 3 cm; length: 20 cm), followed by the quick of 10 mL fuming HNO3 (100%, Sigma–Aldrich, St. Louis, MO, USA). Upon contact, nitric acid and nitrileaddition glove of 10 were mL spontaneously fuming HNO ignited,3 (100%, releasing Sigma–Aldrich, brown gases St. Louis, (nitrogen MO, oxides) USA). andUpon an contact, intense flame.nitric Afteracid and reaction nitrile completion, glove were carbon spontaneously foam was ignited, formed releasing (minor residues brown ofgases unreacted (nitrogen glove oxides) were and simply an cutintense out). flame. The foam After was reaction crashed completion, into a fine powdercarbon foam and copiously was formed washed (minor with residues dimethylformamide of unreacted (DMF),glove were tetrahydrofuran simply cut out). (THF), The a saturatedfoam was ethylenediaminetetraaceticcrashed into a fine powder acid(EDTA) and copiously aqueous washed solution with dimethylformamide (DMF), tetrahydrofuran (THF), a saturated ethylenediaminetetraacetic (EDTA: chelating agent), water, and finally with acetone prior to drying at 80 ◦C for a day. The obtained acid(EDTA) aqueous solution (EDTA: chelating agent), water, and finally with acetone prior to powderNanomaterials is thereafter 2020, 10, x FOR denoted PEER asREVIEW C-GLOVE (yield: 5%). The overall procedure is visualized in Figure3
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