Doping and Surface Modification of Carbon Quantum Dots for Enhanced Functionalities and Related Applications

Abstract

Carbon quantum dots (CQDs) are a unique class of 0D nanomaterials, featured by a graphitic core and shell layers saturated with hydrogen atoms and functional groups. CQDs are prepared through top‐down and bottom‐up strategies from natural and synthetic precursors. CQDs can be modified through chemical (e.g., surface functionalization/passivation, doping, etc.) and physical (e.g., core–shell architecture, composite material blending, etc.) strategies to control their properties. This review highlights the effect of such modifications on the photophysical properties of CQDs, such as photoluminescence (PL), absorbance, and relaxivity. The dependence of PL upon the size, orientation at the edges, surface and edge functionalization, doping, excitation wavelength, concentration, pH, aggregate formation, etc., are summarized along with the supporting theoretical evidence available in the literature. Also, this review outlines the recent advancements, and future prospective of optical (e.g., sensing, bioimaging, and fluorescent ink) and catalytic applications (e.g., photocatalysis and electrocatalysis) of CQDs enhanced through physical and chemical modifications of their structure and composition.

Carbon Dots in Bioimaging, Biosensing and Therapeutics: A Comprehensive Review

“…[ 86,87 ] These new surface states inhibit or eliminate the original O ‐states and promote radiative recombination, leading to higher QYs and doped CDs with excitation‐independent emissions. [ 84 ] In addition to intrinsic property control achieved by element doping, post‐synthetic modifications involving non‐covalent and covalent coupling strategies can be used to further tune the functional properties of CDs ( Table 2 ). [ 88,89 ]…”

“…[82] Advances in synthesis and surface modification technologies make CDs appealing platforms for engineering of biological probes with improved brightness, tunable fluorescence, enhanced water-solubility, and biocompatibility. [83][84][85] For example, heteroatom doping can endow CDs regulated structural defects and enhanced optical properties. [86,87] These new surface states inhibit or eliminate the original O-states and promote radiative recombination, leading to higher QYs and doped CDs with excitation-independent emissions.…”

“…[86,87] These new surface states inhibit or eliminate the original O-states and promote radiative recombination, leading to higher QYs and doped CDs with excitation-independent emissions. [84] In addition to intrinsic property control achieved by element doping, post-synthetic modifications involving non-covalent and covalent coupling strategies can be used to further tune the functional properties of CDs (Table 2). [88,89] Non-covalent strategies generally refers to modification methods that utilize non-specific forces such as electrostatic interaction, complexation/chelation, hydrogen bonding, hydrophobic interactions and π-π stacking.…”

Carbon Dots from Natural Sources for Biomedical Applications

“…Several mechanisms have been put forward to explain the PL of CDs, including surface groups, surface passivation, the quantum confinement effect, defects and surface states, fluorophores with varying degrees of π-conjugation, and electronhole recombination. [4] The isolation of sp 2 domains entrenched within the sp 3 environment resulted in PL. The excitonic state generated by high-density p electrons in sp 2 hybridized islands is the reason for band gaps that form broad emission wavelengths from UV to near-infrared.…”

Recent advances in solid‐state supercapacitors: From emerging materials to advanced applications

“…CQDs are a new class of CNPs 397‐404 . Jian et al synthesized CQDs/polypyrrole (PPy) composite electrodes by electrochemical deposition and assembled an SSC using PVA/LiCl GPE.…”