Energy-efficient synthesis of high-quality quantum dots


In recent years, carbon quantum dots (CQDs) have attracted considerable attention as a prospective material in the fabrication of light-emitting diodes (LEDs), molecular sensors, and other advanced industrial applications. A recent article in the journal iScience focuses on the production of high quality carbon quantum dots (CQD) under exceptionally low pressure and temperature.

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​​​​​​​Study: High quality full color carbon quantum dots synthesized under unprecedentedly smooth conditions. Image Credit: Dzmitry Melnikau/Shutterstock.com

Importance of Carbon Quantum Dots (CQD)

Carbon quantum dots (CQDs), a new type of carbon nanoparticle, have emerged as potential rivals to traditional semiconductor quantum dots due to their superior optical absorption, chemical resistance, low toxicity, and ease Manufacturing. CQDs are quasi-spherical carbon nanoparticles made up of crystalline and amorphous carbon bases.

CQDs are employed in a variety of industries, including bioimaging, medical diagnostics, biomedicine, environmental sensing, electrocatalysis, and optoelectronic devices. Surface characterization and surface passivation can easily modify the physico-chemical characteristics of CQDs.

The oxygen functional groups present on CQDs can be modified depending on the synthetic technique to provide outstanding fluorescence qualities.

Carbon Quantum Dots (CQD) Manufacturing Methods

Many studies have been conducted to create innovative techniques for producing highly luminescent CQDs, which can be referred to as “top-down” or “bottom-up” techniques.

CQDs are made “top down” by deconstructing larger carbonaceous materials containing many sp2 hybridized carbon molecules, using electrodeposition, laser ablation and other energy-consuming techniques.

High temperature, high pressure and powerful oxidizing reagents are highly imperative for the “bottom-up” production of CQD from small molecular precursors to carbonize sp3 carbon into carbonaceous materials. Thus, in “bottom-up” approaches, hydrothermal and solvothermal processes are widely used.

Limitations of previously used methods

In addition to the high energy consumption in these techniques, the extreme synthesis parameters raise questions about the safety of the methods and the drop in productivity by partly converting the precursors into flammable by-products.

Additionally, the extract used to make CQDs must be free of contaminants. The introduction of contaminants into the extract has a significant impact on the fluorescence characteristics of CQDs. When these points are used for applications such as the detection of heavy metal ions, it is difficult to understand the process involved in the presence of any contaminant.

Therefore, the introduction of synthetic techniques for CQDs that are energy efficient, safe and resourceful is always needed. These unique technologies would be very helpful in boosting the use of CQDs in industry by avoiding sophisticated manufacturing operations and high energy consumption.

Image credit: Tong, Y.-J. et al. (2022).

A new soft condensation strategy for CQD development

The researchers used a moderate condensation technique to create high-quality color CQDs in this work. The acidic solution was 1,3,5-benzene tricarboxylic acid (BTCA), which has only sp2 carbon, while the basic solutions were diethylenetriamine (DETA) and other phenylenediamine compounds (PDA).

Unlike hydrothermal and solvothermal processes, which depend on high temperature and pressure, the one-pot approach suggested for the fabrication of CQD was carried out at a relatively low temperature of 85°C and at a pressure close to ambient temperature (about 1.88 bar).

The influence of solvents has been thoroughly explored to acquire the ideal reaction parameters. It was found that high quality and diverse luminescence could only be obtained when N,N-dimethylformamide (DMF) was used as the solvent, which may be related to the increased ionic strength of DMF.

Important Study Findings

The suggested moderate condensation technique produces CQDs with high QYs, high production yield, homogeneous light centers, and dominant radiative decay pathways. Additionally, the mild reaction conditions allowed detailed analysis of CQD nanostructures and condensation paths.

Based on the acquired high-quality CQDs, color LEDs and logic gate detectors were created. The results demonstrated that CQDs contained extensive adaptive strategies, providing an excellent opportunity to build advanced devices for ecological investigation, medical diagnostics, food testing, and other applications.

Prospects of the proposed strategy for the manufacture of CQDs

This study paves the way for the widespread use of CQDs by presenting an innovative moderated synthesis technique for color CQDs. This research also encourages the creation of new techniques for moderated synthesis that will make the structures of CQDs completely resolvable in the future, which will be crucial for establishing unambiguous structure-property connections.

Color CQDs were produced under moderate circumstances in this work, with an average mass yield of 69.0%. It is envisioned that future studies would use advanced structural analysis methods such as scanning tunneling microscopy (STM) to better explain the growth process.

Reference

Tong, Y.-J. et al. (2022). High-quality full-color carbon quantum dots synthesized under unprecedentedly smooth conditions. iScience. Available at: https://www.sciencedirect.com/science/article/pii/S2589004222006927

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