Photoluminescent Carbon Quantum Dots: Synthetic Approaches and Photophysical Properties

Abstract

A number of synthetic methodologies and applications of carbon quantum dots (CQDs) have been reported since they were first discovered nearly two decades ago. Unlike metal‐based or semiconductor‐based (e. g., metal chalcogenides) quantum dots (MSQDs), CQDs have the unique feature of being prepared through a variety of synthetic protocols, which are typically understood from considerations of reaction models and photoluminescence mechanisms. Consequently, this brief review article describes quantum dots, in general, and CQDs, in particular, from various viewpoints: (i) their definition, (ii) their photophysical properties, and (iii) the superiority of CQDs over MSQDs. Where possible, comparisons are made between CQDs and MSQDs. First, however, the review begins with a general brief description of quantum dots (QDs) as nanomaterials (sizes≤10 nm), followed by a short description of MSQDs and CQDs. Described subsequently are the various top‐down and bottom‐up approaches to synthesize CQDs followed by their distinctive photophysical properties (emission spectra; quantum yields, Φs).

Solid-State Phosphors from Coal-Derived Carbon Quantum Dots

“…The synthesis of CQDs involves either the top-down approach ,,− using fairly high-cost starting materials such as graphite, graphene, carbon nanotubes, and photonic crystals, or the bottom-up approach ,,,− using diverse organic molecules (e.g., glucose, ascorbic acid, citric acid, urea, etc.) as building blocks.…”

Green synthesis of CQDs for determination of iron and isoniazid in pharmaceutical formulations

“…[2][3][4][5][6][7][8][9][10] At present, the preparation methods of CQDs are divided into two categories: top-down and bottom-up, mainly including the electrochemical method, laser resection method, arc discharge method, microwave method, hydrothermal method and template method. 11,12 Among them, the hydrothermal method has low requirements for reaction precursors, can easily be used to prepare large quantities, and is one of the most commonly used methods in the laboratory. The precursors employed by researchers to synthesize CQDs include natural components such as gelatin, 13 orange juice, 14 pear juice, 15 sucrose, 16 honey, 17 and orange peel, 18 in addition to some organic reagents like citric acid and ethylenediamine.…”

Novel selenium-doped carbon quantum dots derived from algae effectively enhanced the delivery and accumulation of selenium in tomato plants (Lycopersicum esculentum) via foliar application

“…Multiple lines of synthesis methods have been used to prepare CQDs, which could be classified as top-down processes and bottom-up processes, 22 respectively, and lead to CQDs with different physicochemical properties such as their size, functional groups and surface charges. 23 Precursors are also needed to be extensively considered in the preparation of nanomaterials from renewable, environmentally friendly, and non-toxic materials. 24,25 Therefore, great efforts have been made to synthesize CQDs using natural biomass such as wheat bran, 26 food waste, 27 and tea residue.…”