Subject Number : S-16-CT-0084
Support Type : Collaborative research
Proposal Title (English) : Analysis of fluorescent carbon nanoparticles
Username (English) : Till Thomas Meiling1
Affiliation (English) : 1) University of Potsdam, Germany
1. Summary
Carbon dot (CD) is a comprehensive term for all types of luminescent, surface-functionalized small nanoparticles in the nanometer range (d ≤ 10 nm) which consist mainly of sp2/sp3 hybridised carbon atoms. CDs share common advantages with quantum dots (QDs), such as high photostability, large two-photon cross sections as well as suitability for bio-imaging. However, in contrast to QDs, CDs are non-toxic, non-blinking, typically biocompatible and soluble in water. Due to their promising properties, CDs have already been implemented as proof of principle in various applications (e.g. chemical sensing, optoelectronic devices like LEDs and bio-imaging). Since carbon can be found in every organic matter, CDs can be easily prepared from readily accessible materials, leading to various existing synthesis methods. However, these synthesis methods are typically expensive and depend on complex and time-consuming processes or severe synthesis conditions and toxic chemicals. Therefore, our work focused on development of new, reliable, economic, and environmentally-friendly one-step synthesis to obtain nitrogen-doped carbon dots (N-CDs) in high yield (approx. 80% w/w) with well-defined and reproducible photoluminescence (PL) properties via microwave-assisted hydrothermal treatment of Tris- EDTA (TE) buffer and various carboxylic acids as nitrogen- and carbon source, respectively [1]. The topic of this research project was the analysis and characterization of three as-synthesized N-CD types by various methods (e.g. TGA, TEM and EDX).

2. Experimental
N-CD samples were synthesized in our laboratory (University of Potsdam) and brought along in solution or as freeze-dried powder. EDX microanalyses was performed on a JSM-7800F and TGA-50 (Shimadzu Corporation, Tokyo, Japan) and an connected TA-60WS Thermal Analysis Workstation (Shimadzu Corporation, Tokyo, Japan). Measurements were performed in alumina (Al2O3) cells under atmospheric pressure and air as flow gas, heating occurred from room temperature (approx. 25°C) up to 1000°C with a linear heating rate of 10K/min.

3. Results and Discussion
Figure 1 shows the TGA traces of two different CD types obtained from TE buffer mixed with citric acid
Fig. 1: TGA spectra of two CD types: CA-N-CND (left) and N-CND (right).

(left) or acetic acid (right), respectively. The EDX microanalyses shows significant differences in the synthesized CDs elemental compositions; depending on starting materials used (Figure 2 (right)).

Fig. 2: EDX-TEM image of a CA-N-CND samples carbon content (left). Elemental composition in wt% of three CD types (right), as obtained by EDX microanalyses.

The performed analyses play an important part in our attempt to gain a better understanding about the influence of elemental composition and chemical structure on PL properties of CD nanoparticles. Especially, as PL properties (e.g. emission wavelength, emission full width at half maximum, and PL quantum yield) can vary significantly between different CD types.

4. Literature

[1] Till T. Meiling et al.: Scientific Reports; 6:28557, 1-9, 06/2016

Acknowledgment
I am grateful to Prof. Olaf Karthaus for advice and collaboration on the every stage of this work and his hospitality during my visit to CIST, Japan.

5. Publication: In preparation: “Fluorescent carbon nanoparticles – Influence of carboxylic acids and reaction conditions on the photoluminescence properties of nitrogen-doped carbon nanodots.”