Fluorescent Carbon Nanoparticles Derived from Candle Soot

Abstract

Herein, we report on the preparation, purification, and preliminary characterization of multicolor fluorescent carbon nanoparticles (CNPs) obtained from the combustion soot of candles. The CNPs are small (< 2 nm) and water soluble. Different CNPs fluoresce with different colors under a single-wavelength UV excitation.Carbon-based nanomaterials, which include carbon nanotubes, fullerenes, and nanofibers, have promising applications in nanotechnology, biosensing, and drug delivery. [1][2][3] Recently, CNPs-a new class of carbon-based nanomaterials with interesting photoluminescence properties-were isolated. [4][5][6][7][8][9][10] These nanoparticles are either nanodiamonds or materials derived from carbon nanotubes and the laser ablation of graphite. Unlike fluorescent semiconductor nanocrystals (so-called quantum dots or Qdots), the fluorescent CNPs have only been poorly studied up to now because of the lack of preparative methods and separation techniques. Herein, we report a method for efficiently preparing and isolating fluorescent CNPs from a common carbon source, namely, candle soot.Our approach includes: 1) The preparation of fluorescent CNPs from the combustion soot of candles by means of an oxidative acid treatment and 2) the purification of the fluorescent CNPs by using polyacrylamide gel electrophoresis (PAGE). Incomplete combustion produces CNPs with diameters of 20-800 nm. [11,12] These particles strongly interact with each other to form agglomerates of several micrometers. To break down such inherent interactions and produce welldispersed, individual CNPs, we adopted an oxidative acid treatment, which is commonly used for the purification of carbon nanotubes.[13] This method is known to introduce OH and CO 2 H groups to the CNP surfaces, [14] thus making the particles become negatively charged and hydrophilic.The candle soot was collected by sitting a glass plate on top of smoldering candles. The soot contained mainly elemental carbon (elemental analysis: C 91.69 %, H 1.75 %, N 0.12 %, O (calculated) 4.36 %) and was hydrophobic and insoluble in common solvents. After refluxing the candle soot with 5 m HNO 3 , it turned into a homogeneous, black aqueous suspension. Upon centrifugation, the suspension separated into a black carbon precipitate and a light-brown supernatant, which exhibited yellow fluorescence when irradiated with UV light (312 nm). The black precipitate also contained fluorescent material (even after washing it several times). For maximum recovery of this fluorescent material, both the supernatant and the precipitate were neutralized and then extensively dialyzed against water. The neutralized candle soot exhibited an excellent dispersibility in water, which lasted several months.The same procedure failed to generate visible fluorescence if an oxidant, such as HNO 3 , was not present (this happened both in the presence and in the absence of surfactants, SDS). Another oxidant (30 % H 2 O 2 /AcOH = 2:1) resulted in blue fluorescence. The oxidative acid treatment might have three functions:...

Efficient one-pot synthesis of highly monodisperse carbon quantum dots

“…Chemical methods include electrochemical synthesis, [10][11][12] combustion and acidic oxidation, 13,14 hydrothermal and pyrolysis routes, 15 supported synthesis [16][17][18] and microwave/ultrasonic synthesis. 19,20 However, some drawbacks associated these methods include extensive post-synthetic 30 purification, lack of control of CQD surface chemistry and sample polydispersity.…”

Lumineszierende Kohlenstoff‐Nanopunkte: Nanolichtquellen mit Zukunft

“…Bottom-Up-Ansätze sind z. B. Verbrennung/thermische Verfahren, [2,3,7,10,13] trägergestützte Synthesen [2,9] oder Mikrowellenverfahren, [20] bei denen C-Punkte aus molekularen Vorstufen gebildet werden. Typischerweise werden die Produkte an der Oberfläche mit Salpetersäure (HNO 3 ) oxidiert und mithilfe von Zentrifugation, Dialyse, Elektrophorese und anderen Trennungstechniken gereinigt.…”

“…Wiedergabe mit Genehmigung nach Lit. [1,2,7,9,12,17,18,20]. von Mikrodiamanten, chemische Gasphasenabscheidung (CVD), Schockwellen-oder Detonationsverfahren hergestellt.…”

“…[18] Auch C-Punkte, die durch Oxidation von Kerzenruß hergestellt wurden, trugen eine große Zahl an Carbonylgruppen auf ihrer Oberfläche und benötigten keine weitere Funktionalisierung für das Auftreten von Photolumineszenz. [7,10] Die Anregungsspektren der durch PAGE getrennten C-Punkte unterschieden sich nur geringfügig, allerdings waren die PL-Emissionsspektren eng mit den elektrophoretischen Beweglichkeiten verknüpft (Abbildung 4). Zurzeit ist noch nicht vollständig geklärt, ob die elektrophoretischen Beweglichkeiten eher mit Größen-oder Oberflächenla-dungseffekten zusammenhängen.…”

“…[6] C-Punkte, die nur COOH-Gruppen an der Oberfläche enthielten, zeigten Quantenausbeuten von 6.4 %, [19] 1.2 %, [17] 0.8 %, [7] 1.9 % [7] und 0.43 %. [13] Diese Werte sind typischerweise niedriger als bei C-Punkten mit organischen passivierenden Liganden.…”