Application of Electrochemistry for Synthesis of Quantum Dots

Nanotechnology is one of the frontier fields of research involving nanoscale manipulation of atoms and molecules. Nowadays the field focuses on developing new generation nanomaterials like quantum dots (QDs) for multitasking purposes such as energy, medical diagnostics, drug delivery, gene therapy etc. QDs, often have been described as artificial atoms and discovered for the first time in a glass matrix by Alexey Ekimov in ۱۹۸۱ [۱]. However, the first colloidal semiconductor nanocrystallite solution was synthesized by Louis Brus four years later. Mark Arthur Reed coined the term “quantum dots” for describing the photoluminescent nanostructure in ۱۹۸۸ that had fully quantized energy states [۲]. After that, many researchers began to estimate QDs for their potential applications [۳,۴]. QDs are semiconductor materials that have gained great interest due to their unique characteristics. The materials are extensively being applied in various areas such as light-emitting diodes, laser technology, solar cells, as well as biological and biomedical applications. There are different methods for synthesis of QDs.In the present study the electrochemical methods for synthesis of QDs is described. The choice of synthesis process can be an important parameter in the properties of QDs. According to the current synthesis methods of QDs as reported in literature, the synthesis of the nanostructured materials can be classified into two main groups, namely top-down and bottom-up preparation methods. Top-down routes include direct cleaving of bulk materials into nanoscale QDs by electrochemical etching, electron beam lithography techniques, laser ablation, liquid-phase exfoliation, etc. In the bottom-up methods, QDs are transformed from suitable molecular precursors under certain conditions exemplified by microwave irradiation, hydrothermal or solvothermal, pyrolysis and wet-chemical reactions. Quantum dots fabricated by electrochemical etching of a target have become one of the most popular nanodots used in many scientific disciplines as a result of its outstanding and unique set of physical and chemical properties and cost-competitive synthesis processes. Electrochemical etching contains an anodic dissolution process using electrical and*chemical reactions. In the process, the cathode and anode should be selected of the same metal to reduce unwanted electrochemical effects.Nowadays silicon (Si) is selected as one of the most promising anode candidates for electrochemical etching-based synthesis of SiQDs. Using the technique the rapid creation of SiQDs with a range of fluorescence light from blue to red and with rather narrow size dispersion is accomplished. Chen et al. synthesized photostable SiQDs by the electrochemical etching route and modified them with two components, including glutamate and polyvinyl pyrrolidone [۵]. In another research, Fu and co-workers described an electrochemical process for facile and simple synthesis of semicarbazide functionalized nitrogen-doped graphene quantum dots (GQDs) based on direct exfoliation and oxidation from graphite rods [۶]. Also, Kalita et al. reported the electrochemical synthesis of GQDs with a uniform size of ۳-۵ nm in diameter from graphene oxide (GO) at room temperature [۷]. As a result, the general principles of the electrosynthesis of QDs are formulated, the factors effecting the efficiency of the method are elucidated, the advantages of the method are evaluated and its position among other methods of QDs synthesis are established.

Keywords:

Nanotechnology , Quantum dots , Synthesis , Electrochemical methods