Investigating the Effect of Reaction Time on Carbon Dot Formation, Structure, and Optical Properties.

Nikolaos Papaioannou,Andrei Sapelkin,Maria-Magdalena Titirici

doi:10.1021/acsomega.9b01798

Nikolaos Papaioannou, Andrei Sapelkin + Show 1 more

Open Access

https://doi.org/10.1021/acsomega.9b01798

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Abstract

Carbon dots, a young member of the carbon nanomaterial family, are quasi-spherical nanoparticles, which have fluorescent properties as their key characteristic. A wide range of starting materials and synthetic routes have been reported in the literature, divided into two main categories: a top-down and bottom-up approach. Moreover, a series of different parameters that affect the properties of carbon dots have been investigated, including temperature, starting pH, as well as precursor concentration. However, the effect of reaction time has not been extensively monitored. In our study, a biomass derivative was treated hydrothermally with varying reaction times to draw a solid formation mechanism. In addition, we monitored the effect of reaction time on optical and structural characteristics, as well as the chemical composition of our materials. Our key findings include a four-stage formation mechanism, a higher level of crystallinity, and an increasing brightness over reaction time.

Highlights

Carbon dots (CDs) are a new class of nanomaterials, which have attracted tremendous attention due to their unique photoluminescent (PL) properties, biocompatibility, and low toxicity.[1,2] they appear as rising candidates to replace the metal-based quantum dots in various applications such as bioimaging[3−5] and biosensing,[6,7] drug delivery,[8] and photocatalysis.[9]
We identified a fourstage formation mechanism, which leads to smaller particle size CDs with a higher level of crystallinity
transmission electron microscopy (TEM) showed a decrease in particle size, while a higher level of monodispersity over reaction time was attained

Summary

Introduction

Carbon dots (CDs) are a new class of nanomaterials, which have attracted tremendous attention due to their unique photoluminescent (PL) properties, biocompatibility, and low toxicity.[1,2] they appear as rising candidates to replace the metal-based quantum dots in various applications such as bioimaging[3−5] and biosensing,[6,7] drug delivery,[8] and photocatalysis.[9]. Top-down strategy refers to the breaking down of large-sized carbonaceous materials by laser ablation,[13] arc discharge,[12] acidic oxidation,[14] or electrochemical approaches.[15] The bottom-up strategy refers to synthetic approaches from molecular precursors through thermal or combustion treatments,[2,16,17] microwave synthetic routes,[18,19] and other solution-based synthetic methods.[20,21] Precursors such as saccharides,[22] amino acids,[23] and biopolymers[17] are among the most common in this strategy. Structural and optical characteristics of CDs have gained vast attention in the research community since their first discovery in 2004.12,24,25 Many parameters have been examined including reaction temperature,[26−29] precursor concentration,[30] the addition of any doping elements,[31−34] and the ratio between the starting materials.[2,35] there are only a few published reports assessing the effect of the reaction time to monitor how their properties evolve.[30,36,37]

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