Synthesis and characterization of graphene quantum dots

Abstract

<jats:title>Abstract</jats:title> <jats:p>Conventional inorganic semiconductor quantum dots (QDs) have numerous applications ranging from energy harvesting to optoelectronic and bio-sensing devices primarily due to their unique size and shape tunable band-gap and also surface functionalization capability and consequently, have received significant interest in the last few decades. However, the high market cost of these QDs, on the order of thousands of USD/g and toxicity limit their practical utility in many industrial applications. In this context, graphene quantum dot (GQD), a nanocarbon material and a new entrant in the quantum-confined semiconductors could be a promising alternative to the conventional toxic QDs due to its potential tunability in optical and electronic properties and film processing capability for realizing many of the applications. Variation in optical as well as electronic properties as a function of size, shape, doping and functionalization would be discussed with relevant theoretical backgrounds along with available experimental results and limitations. The review deals with various methods available so far towards the synthesis of GQDs along with special emphasis on characterization techniques starting from spectroscopic, optical and microscopic techniques along with their the working principles, and advantages and limitations. Finally, we will comment on the environmental impact and toxicity limitations of these GQDs and their hybrid nanomaterials to facilitate their future prospects.</jats:p> <jats:p> <jats:bold>Graphical Abstract:</jats:bold> </jats:p> <jats:p><jats:fig position="anchor" fig-type="graphical" id="j_psr-2019-0013_fig_001"> <jats:caption> <jats:p>Structure of doped, functionalized and hybrid GQDs</jats:p> </jats:caption> <jats:graphic xlink:href="graphic/j_psr-2019-0013-graphabs.jpg" /> </jats:fig> </jats:p>

Advances and Trends in Chemically Doped Graphene

“…[ 1–3 ] It has been extensively explored in 0–3D (e.g., graphene quantum dots (GQDs), carbon nanotubes, and porous graphene), in many functionalized forms, as well as in combination with other materials (composites). [ 4–9 ] The typical goals are as follows: 1) exploit the unique behavior of graphene; 2) overcome the gapless symmetry of graphene as a zero bandgap material (i.e., the conduction and valence states meet at some point) that hinders its use in the electronic industry; 3) enhance the reactivity of graphene, which is naturally stable under ambient conditions owing to the delocalized π‐electron system that resists chemical modifications, for use in synthetic industry; and 4) design new materials with ideal attributes. [ 10–15 ]…”

Graphene Quantum Dots-Based Nanocomposites Applied in Electrochemical Sensors: A Recent Survey

“…The parameters used in each route can be modified to provide GQDs with desired characteristics. As there are many reviews available in the literature addressing GQDs synthesis procedures [11,[38][39][40][41]44,45], herein we will only briefly cover the main approaches to obtain GQDs and their modification through doping and functionalization. In this sense, in the next topic, we emphasize the techniques generally used to combine other materials with GQDs.…”

“…GQDs are usually obtained with functionalized oxygen-containing groups, and other functionalization can be further performed to render the desired characteristics. For instance, doping GQDs with heteroatoms, specific molecules, enzymes, nanoparticles, DNA strands, and enzymes have already been reported [8,12,39]. These modifications can be performed in the precursor (pre-modification), giving rise to functionalized GQDs, or after GQDs synthesis (post-modification).…”

“…The use of GQDs in electrochemistry is also preferred favored by their ease of production and the possibility to be doped or modified aiming at specific sensing applications [38][39][40]. These characteristics enable GQDs-based nanomaterials to have lower detection limits and higher sensitivities.…”

Electron scattering of mass-inverted in graphene quantum dots

“…GQDs are made up of a single atomic layer of nano-sized graphite. They have many of the same properties as graphene, including a large surface area, a big diameter, and superior surface grafting employing π − π conjugation and surface groups [10,11]. Recently, QDGs have been extensively discussed both theoretically [12][13][14][15][16][17][18] and experimentally [19][20][21].…”