Reversible Phase Transfer of Carbon Dots between an Organic Phase and Aqueous Solution Triggered by CO₂

Abstract

Carbon dots (CDs) have attracted increasing attention in applications such as bio-imaging, sensors, catalysis, and drug delivery. However, unlike metallic and semiconductor nanoparticles, the transfer of CDs between polar and non-polar phases is little understood. A class of amine-terminated CDs is developed and their phase transfer behavior has been investigated. It is found that these CDs can reversibly transfer between aqueous and organic solvents by alternatively bubbling and removing CO at atmospheric pressure. The mechanism of such CO -switched phase transfer involves reversible acid-base reaction of amine-terminated CDs with CO and the reversible formation of hydrophilic ammonium salts. By using the CDs as catalysts, the phase transfer is applied in the Knoevenagel reaction for efficient homogeneous reaction, heterogeneous separation, and recycling of the catalysts.

Mapping the Surface Groups of Amine-Rich Carbon Dots Enables Covalent Catalysis in Aqueous Media

“…This approach opens new synthetic opportunities via tailored CD synthesis or post-functionalization protocols and enables advanced applications such as catalytic transformations. [20][21][22][23][24] In particular, the appeal of CDs as nano-catalysts relate to their straightforward synthesis, cost-efficiency, and safety that, combined with high solubility in water, may allow their use even in biological or quasi-biological environments. [25][26][27][28][29] Despite their high potential, only exploratory applications of CDs as…”

“…ll catalysts have been reported relying on simple acid-base or hydrogen-bonding activation modes. [20][21][22][23] Aminocatalysis represents one of the most versatile strategies in covalent organocatalytic transformations. The robustness of its activation modes, via enamine or iminium-ion intermediates, has been implemented in several synthetic applications addressing the requirements of step economy and metal-free catalysis.…”

Carbon Dots as Nano-Organocatalysts for Synthetic Applications

“…For all these reasons, the "bottom-up" approach is usually the preferred route for preparing catalytically active carbon nanoparticles. 25,26,[40][41][42] Besides, it has been shown that hetero-doping may enhance the photophysical and electronic features of CDs, by generating new energy levels and promoting radiative combination, therefore facilitating the process of designing and customizing of effective nanostructured photocatalysts. 1,4,5 One of the most important examples of doping is the widely investigated nitrogen incorporation, leading to the preparation of N-doped-CDs.…”

Carbon dot/TiO2nanocomposites as photocatalysts for metallaphotocatalytic carbon–heteroatom cross-couplings

“…The superficial carboxylic acid, hydroxy, or amino functionalities were exploited in acid-base, hydrogen bond, or amine-catalysed reactions. [12][13][14][15] CDs are also promising metal-free photocatalysts for pollutant degradation, H 2 evolution and CO 2 conversion, owing to their photostability, light-harvesting ability and electron-transfer efficiency. [16][17][18][19] The high solubility of CDs in water makes them a suitable alternative to hydrophobic organic materials, such as carbon nitride and graphite.…”