On the Colloidal Stability of Nitrogen-Rich Carbon Nanodots Aqueous Dispersions

Abstract

The present survey reports on the colloidal stability of aqueous dispersions of nitrogen-rich carbon nanodots (N-CDs). The N-CDs were synthesized by thermally induced decomposition of organic precursors and present an inner core constituted of a β - C 3 N 4 crystalline structure surrounded by a surface shell containing a variety of polar functional groups. N-CDs size and structure were checked by combined analysis of XRD (X-ray Diffraction) and TEM (Transmission Electron Microscopy) measurements. FTIR (Fourier-Transform Infrared Spectroscopy) experiments revealed the presence of carboxyl and amide groups on N-CDs surface. Towards a better understanding of the relation between colloidal stability and surface charge development, zetametry experiments were applied in N-CDs dispersions at different pHs and constant ionic strength. The increase of the absolute values of zeta potential with the alkalinization of the dispersion medium is consistent with the deprotonation of carboxyl groups on N-CDs surface, which agrees with the macroscopic visual observations of long-term colloidal stability at pH 12. The saturation value of N-CDs surface charge density was evaluated by means of potentiometric-conductometric titrations. The difference between carboxyl-related surface charge and the one determined by zeta potential measurements point to the presence of oxidized nitrogen functionalities onto the N-CDs surface in addition to carboxyl groups. These novel results shed light on the electrostatic repulsion mechanism that allows for the remarkable colloidal stability of N-CDs dispersions.

Plant Part-Derived Carbon Dots for Biosensing

“…CDs have several advantages including good photostability [4], good solvent dispersion [5], easy functionalization or modification [6], a simple synthesis process [7], tunable FL excitation and emission [8], and high sensitivity and selectivity [9], compared to FL organic dyes and other quantum dots [10][11][12][13][14]. In addition, CDs exhibit robust chemical stability [15], inertness [16], stable colloidal solution [17], and photobleaching resistance [18]. Up to now, the exploration of CDs with extraordinary potential has led to intensive studies.…”

Carbon Nanotubes, Graphene, and Carbon Dots as Electrochemical Biosensing Composites

“…Nitrogen-rich carbon dots (N-CDs) have been reported to be well dispersed in aqueous solutions in large concentrations. Fiuza et al discussed the potential of N-CDs to have tunable isoelectric points based on varying colloidal stability, solution pH, and ionic strength [132]. This possibility opens the door for its use as effective electrochemical sensing composites to better control the deposition of catalytically active NPs on these carbon supports by attaching them to the surface using Coulombic attraction.…”

“…Scheme 7.Various functionalizations for modification of carbon dots. Reproduced with permission from ref [132]…”

Review on green carbon dot-based materials for the photocatalytic degradation of dyes: fundamentals and future perspective

“…[22][23][24][25][26] In addition, CDs exhibit high photobleaching resistance, chemical stability, stable colloidal solution, and inertness. [27][28][29][30] Researchers have studied the CDs synthesis by both top-down and bottom-up approaches with the help of both chemical and green precursors. 31 The photocatalytic dye degradation is often performed using metals or complexes, non-metals, semiconducting materials, metal oxides such as ZnS, WO 2 , ZnO, SrO 2 , CdS, and TiO 2 doped with CDs as catalysts.…”