Mendeleev Commun., 2018, 28, 251–253 – 251 – Mendeleev Communications © 2018 Mendeleev Communications. Published by ELSEVIER B.V. on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences. Like inorganic fluorescent semiconductor nanoparticles, carbon- aceous nanoparticles or carbon quantum dots (CQDs) exhibit tunable fluorescence allowing them to be applied in bioimaging, electro-optical and photonic materials, and energy harvesting. 1 On top of excellent optical properties, CQDs are water-soluble due to surface polar groups and biocompatible. Many synthetic protocols to prepare CQDs with tunable optical properties have been elaborated, including chemical and laser ablation, electrochemical polymerization and microwave and solvothermal treatment. 2,3 Attaining stable optical properties of CQDs requires their surface passivation to prevent the undesirable transformations of reactive surface groups and the agglomeration of nanoparticles, for example, by adsorption of amino-terminated polyethylene glycol or ethyleneimine copolymers. 4 On the other hand, if CQDs are prepared directly in a nanoporous polymer matrix, the isolated nanoparticles cannot agglomerate. In this work, we studied the preparation of CQDs inside a Nafion ® membrane. Even though the Nafion structure details are debatable, 5−7 it is accepted that a hydrated Nafion membrane contains uniform (3–10 nm in diameter) spherical or cylindrical hydrophilic clusters flooded with water and surrounded with a hydrophobic perfluorinated phase. The preparation of CQDs inside hydrophilic regions should afford monodisperse nano- particles stable against aggregation. Hydrothermal treatment was used to synthesize CQDs in view of simplicity and versatility of the method. 2,3 The precursors were chosen based on the reports showing that ascorbic acid, 8 glucose 9 and glucosamine hydro- chloride 10 are prone to the formation of carbon micro- and nano- particles via hydrothermal treatment. The duration and temperature of the hydrothermal treatment † were based on our systematic study of the kinetics and mechanism of hydrothermal transformations of ascorbic acid. 11 The membranes were characterized by their equilibrium swelling in water, through-plane proton conductivity and vanadyl (VO 2+ ) permeability as described elsewhere. 12,13 The samples coding and their preparation details are given in Table 1 along with their selected physico-chemical parameters. The samples Ref, W, Asc and Glu were colorless, whereas the samples Asc/IPA and GluNH2 were yellowish and brown, respectively. When the samples were illuminated with a UV lamp, the Asc/IPA and GluNH2 ones revealed greenish fluorescence, whereas the colorless samples showed no light emission (Figure 1, Table 1). The results could be rationalized as follows: the hydrothermal treatment of a water-swollen Nafion membrane changed its morphology (no chemical transformations occurred since the IR spectra of samples Ref and W were identical). The structure evolution during the hydration of dry Nafion membranes was discussed in detail earlier, 14 and an increase in the equilibrium hydration level after hydrothermal treatment was reported. 15 We also observed a noticeable extra swelling of a Nafion membrane after the hydrothermal treatment with an increase in the hydration number (the number of water molecules per sulfonic group) from 20±1 to 33±1. This range of hydration numbers corresponds to the onset of phase inversion 14,15 and a morphology change from Synthesis of carbon quantum dots in a Nafion matrix: precursor effect on the ion transport properties Evgeny A. Karpushkin,* a Ekaterina S. Kharochkina, a Maria M. Klimenko, b Marat O. Gallyamov c and Vladimir G. Sergeyev a a Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation. Fax: +7 495 939 0174; e-mail: eukarr@gmail.com b Department of Materials Science, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation c Department of Physics, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation DOI: 10.1016/j.mencom.2018.05.007 H 2 O SO 3 – p + nanoparticle Nafion Carbon quantum dots have been prepared in a Nafion ® matrix via the hydrothermal treatment of organic precursors, and the swelling and ion transport properties of the prepared composite materials have been characterized. † A commercial Nafion 112 membrane (Sigma-Aldrich) was conditioned via sequential boiling in distilled water (1 h), aqueous H 2 O 2 (3 wt%, 1.5 h), distilled water (1 h), aqueous H 2 SO 4 (0.5 M, 1.5 h) and distilled water (1 h), 12 dried and soaked with water or an organic precursor solution for 12 h. Then, the membrane was placed in a Teflon autoclave reactor filled with water (reactor volume, 40 ml; filling degree, 90%); the reactor was closed, put in an oven pre-heated to 160 °C and kept at this temperature for 6 h. The modified specimen was rinsed with distilled water and kept in a 2.5 M aqueous solution of H 2 SO 4 for at least 24 h at room tempera- ture. W Asc Glu Glu/NH 2 Asc/IPA Figure 1 Optical microscopy images of Nafion 112 specimens after hydro- thermal treatment: (top) in white light and (bottom) under UV irradiation at 312 nm.