Molecular, Aromatic, and Amorphous Domains of N-Carbon Dots: Leading toward the Competitive Photoluminescence and Photocatalytic Properties

Abstract

Carbon dots (CDs) have become one of most promising fluorescent materials in recent days, because of their promising photoluminescence and photocatalytic properties. However, the practical applicabilities for emissive and catalytic devices are still debatable, because of the lack of fundamental understanding behind the structure–property correlations. Herein, we have developed different types of nitrogen-doped CDs (N-CDs) by varying different nitrogen-containing precursors through a simple bottom-up based carbonization technique. Depending on the nature of nitrogen atom precursor, we are able to critically control the subpopulations of various intrinsic constituents of N-CDs, i.e., aromatic domains, amorphous domains, and small molecular fluorophores inside N-CDs. Detailed structural and elemental features have been correlated with the underpinning photophysical processes by means of steady-state and time-resolved fluorescence spectroscopy. In addition, the effect of temperature on overall photoluminescence properties has been corroborated with the internal structure of N-CDs. Finally, we have investigated the photocatalytic properties and the detailed photocatalysis mechanisms by scavenging the active species originated upon light irradiation. Results suggest that photocatalytic efficiency is maximum at a larger extent of amorphous domains and in the presence of nitrogen atoms specifically located at the edges, while photoluminescence intensity is higher at larger extent of molecular fluorophores and aromatic domains. Therefore, these fundamental investigations will open up new possibilities considering the optimizations of heteroatom functionalized CDs for their on-demand applicabilities in emitting as well as photocatalytic devices.

Insight into the Multistate Emissive N, P‐doped Carbon Nano‐Onions: Emerging Visible‐Light Absorption for Photocatalysis

“…Surface states, such as À C=O and À COOH groups of CDs can induce the up-ward band bending, which leads to the effective charge separation and reduces the electron-hole recombination, resulting enhanced photocatalytic activity. [11,12] In addition to that, defined morphology can also enhance the photocatalytic efficiency by enhancing active surface sites/ effective surface area. Considering this, the hetero atom functionalized onion-like layered structure of CDs can be very much beneficial.…”

Challenges and future prospects of graphene-based hybrids for solar fuel generation: moving towards next generation photocatalysts

“…The top-down approach is mainly typical exfoliation technique, followed by cutting the larger carbon structures into ultra-small dot like structures with high crystallinity along with few surface defects by employing various physical approaches such as laser ablation, electrochemical etching, plasma treatment, and arc-discharge methods. 3,[162][163][164] On the other hand, The bottom-up synthesis approach refers to the building of dot like structure with carbon core along with various surface states, defects, and functional groups from the small molecule precursors. Based on the availability of a diversity of precursors and synthesis approaches, CDs/GQDs are provided with wide variable optoelectronic properties and performance parameters.…”

“…Furthermore, the CDs/GQDs comprise of heterogeneous distribution of aromatic domains (sp 2 hybridized carbons) embedded by amorphous regions (sp 3 hybridized carbons) along with various heteroatom functionalities, which facilitate the generation of various discrete energy levels within the CDs resulting the unique photophysical, chemical, and electronic properties. 162,163,165,166 Based on these intriguing optoelectronic properties, CDs have become potentially significant materials for photocatalytic applications. Nevertheless, the practical applicabilities of these luminescent CDs as solely photocatalysts (without co-catalyst) are still under debate due to the lack of studies for fundamental structure-property correlation.…”

“…Complex interplay between the various states of the CDs/ GQDs such as aromatic/amorphous domains along with surface states and atomic vacancies controls the overall excitonic features and charge separation kinetics. 163 In addition, tuning the surface states such as -C=O, and -COOH groups can induce the up-ward band bending resulting in effective charge separation followed by the enhanced activity. In addition to this, the defined morphologies can also enhance the photocatalytic activity of the CDs by improving the active sites and effective surface area.…”

“…Therefore, upon combining CDs/GQDs with other carbon-based materials can further increase photocatalytic performance. 162,163 Moreover, making intrinsic n-p dyad-like structures inside the CDs/GQDs by incorporating various hetero-atoms can increase visible light absorption and effective charge separation, followed by efficient photocatalysis. Therefore, further research is needed in this direction to attain superior photocatalysts.…”