Oil-Dispersible Green-Emitting Carbon Dots: New Insights on a Facile and Efficient Synthesis

Gianluca Minervini,Maria Lucia Curri,Marinella Striccoli,Annamaria Panniello,Angela Agostiano,Elisabetta Fanizza

doi:10.3390/ma13173716

Abstract

Carbon dots (CDs) have been progressively attracting interest as novel environmentally friendly and cost-effective luminescent nanoparticles, for implementation in light-emitting devices, solar cells, photocatalytic devices and biosensors. Here, starting from a cost-effective bottom-up synthetic approach, based on a suitable amphiphilic molecule as carbon precursor, namely cetylpyridinium chloride (CPC), green-emitting CDs have been prepared at room temperature, upon treatment of CPC with concentrated NaOH solutions. The investigated method allows the obtaining, in one-pot, of both water-dispersible (W-CDs) and oil-dispersible green-emitting CDs (O-CDs). The study provides original insights into the chemical reactions involved in the process of the carbonization of CPC, proposing a reliable mechanism for the formation of the O-CDs in an aqueous system. The ability to discriminate the contribution of different species, including molecular fluorophores, allows one to properly single out the O-CDs emission. In addition, a mild heating of the reaction mixture, at 70 °C, has demonstrated the ability to dramatically decrease the very long reaction time (i.e. from tens of hours to days) at room temperature, allowing us to synthesize O-CDs in a few tens of minutes while preserving their morphological and optical properties.

Highlights

Carbon dots (CDs) are novel photoluminescent nanoparticles, increasingly emerging as active materials in many application areas, such as optoelectronics, solar cells, catalysis, sensors and bioimaging [1,2,3,4,5,6]
Common CDs synthetic approaches rely on hydrothermal, solvothermal- or microwave-based methods, starting from a carbon precursor, that is treated at an elevated temperature and pressure in an autoclave, or exposed to microwaves [8,10,11,12,13,14]
We demonstrate the formation of blue-emitting molecular fluorophores alongside the CDs that behave as intermediates in the synthesis and contribute to their overall emission

Summary

Introduction

Carbon dots (CDs) are novel photoluminescent nanoparticles, increasingly emerging as active materials in many application areas, such as optoelectronics, solar cells, catalysis, sensors and bioimaging [1,2,3,4,5,6]. Unlike the inorganic semiconductor quantum dots, the structure of the CDs is entirely carbon-based, they are heavy-metal free, and combine good photostability and high quantum yields [2,3] with improved biocompatibility and low associated environmental risks [4,5,7]. Alongside the main carbon precursor, other components are added to the reaction mixtures to enhance surface passivation of the forming CDs, or to introduce heteroatoms in the carbogenic structure, in order to improve their photoluminescence (PL) [15,16].

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Conclusion