Isolation of Homogeneous Luminophores from Citric Acid and Ethylenediamine-Based Carbon Dots: Relationship of Their Structure and Properties to pH

Abstract

Carbon dots (CDs) are one of the most promising nanomaterials for various biomedical and nanosensing applications. Carbon dots possess a unique combination of properties: stable intense photoluminescence, chemical stability, biocompatibility, low toxicity, dispersibility, and sensitivity to changes in the physicochemical parameters of the surrounding environment. CDs are relatively simple to synthesize and exhibit wide structural variability due to the large selection of synthesis methods and possible precursors, allowing optimization of their molecular composition for specific applications. In classic view, CDs are described as quasi-spherical nanoparticles consisting of a carbon core covered with various functional groups. However, during bottom-up synthesis (e.g., hydrothermal synthesis), a clearly defined carbon core may not form – the particles can have polymer structure. In such cases, CDs fractionation is performed for their effective application.
The study objects in this work are two types of CDs synthesized hydrothermally from citric acid and ethylenediamine. The CDs differed in the ethylenediamine concentration within their precursor mixture. Synthesized nanoparticles were fractionated using horizontal electrophoresis. Each fraction was characterized by photoluminescence (including time-resolved) spectroscopy, optical absorption spectroscopy, and IR spectroscopy in three pH ranges. Analysis of the obtained data allowed to identify fractions exhibiting the highest and lowest luminescence quantum yields. Furthermore, fractions that persist within the CDs upon increasing the ethylenediamine concentration were discovered. Based on changes in the CDs spectral characteristics upon protonation/deprotonation of their functional groups, conclusions regarding the molecular composition of luminophores in each fraction were drawn.
The study was carried out with the support of the Russian Science Foundation grant № 22-12-00138-П, https://rscf.ru/project/22-12-00138/.

Speaker

Anisiya A. Korepanova
Lomonosov Moscow State University, Moscow, Russia
Russia

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