Carbon dots (CDs), as a new type of carbon-based nanomaterial, have attracted broad research interest for years, because of their diverse physicochemical properties and favorable attributes like good biocompatibility, unique optical properties, low cost, ecofriendliness, abundant functional groups (e.g., amino, hydroxyl, carboxyl), high stability, and electron mobility. In this Outlook, we comprehensively summarize the classification of CDs based on the analysis of their formation mechanism, micro-/nanostructure and property features, and describe their synthetic methods and optical properties including strong absorption, photoluminescence, and phosphorescence. Furthermore, the recent significant advances in diverse applications, including optical (sensor, anticounterfeiting), energy (light-emitting diodes, catalysis, photovoltaics, supercapacitors), and promising biomedicine, are systematically highlighted. Finally, we envisage the key issues to be challenged, future research directions, and perspectives to show a full picture of CDs-based materials.

Carbon Dots: A New Type of Carbon-Based Nanomaterial with Wide Applications

Visible-light-driven photocatalytic degradation of diclofenac by carbon quantum dots modified porous g-C3N4: Mechanisms, degradation pathway and DFT calculation.

The Blue Laser Diode

Graphene quantum dots (GQDs) are carbon-based, nanoscale particles that exhibit excellent chemical, physical, and biological properties that allow them to excel in a wide range of applications in nanomedicine. The unique electronic structure of GQDs confers functional attributes onto these nanomaterials such as strong and tunable photoluminescence for use in fluorescence bioimaging and biosensing, a high loading capacity of aromatic compounds for small-molecule drug delivery, and the ability to absorb incident radiation for use in the cancer-killing techniques of photothermal and photodynamic therapy. Recent advances in the development of GQDs as novel, multifunctional biomaterials are presented with a focus on their physicochemical, electronic, magnetic, and biological properties, along with a discussion of technical progress in the synthesis of GQDs. Progress toward the application of GQDs in bioimaging, biosensing, and therapy is reviewed, along with a discussion of the current limitations and future directions of this exciting material.

Graphene Quantum Dots and Their Applications in Bioimaging, Biosensing, and Therapy.

Nitrogen-doped graphene and graphene quantum dots: A review onsynthesis and applications in energy, sensors and environment.

Quantum dots have innate advantages as the key component of optoelectronic devices. For white light-emitting diodes (WLEDs), the modulation of the spectrum and color of the device often involves various quantum dots of different emission wavelengths. Here, we fabricate a series of carbon quantum dots (CQDs) through a scalable acid reagent engineering strategy. The growing electron-withdrawing groups on the surface of CQDs that originated from acid reagents boost their photoluminescence wavelength red shift and raise their particle sizes, elucidating the quantum size effect. These CQDs emit bright and remarkably stable full-color fluorescence ranging from blue to red light and even white light. Full-color emissive polymer films and all types of high-color rendering index WLEDs are synthesized by mixing multiple kinds of CQDs in appropriate ratios. The universal electron-donating/withdrawing group engineering approach for synthesizing tunable emissive CQDs will facilitate the progress of carbon-based luminescent materials for manufacturing forward-looking films and devices.

https://advances.sciencemag.org/content/advances/6/40/eabb6772.full.pdf

Full-color fluorescent carbon quantum dots

Facile synthesis of fluorescent graphene quantum dots from coffee grounds for bioimaging and sensing

A dual-mode colorimetric/fluorescence pH sensor was fabricated from carbon dots (CDs). It exhibited a pH response via both fluorescence and visible colorimetric observation. The CDs solution changed from red to yellow when the pH changed from acid to alkaline. Meanwhile, the color of pH test paper that incorporated the CDs changed from purple-red to orange and then to yellow. The CD fluorescence maximum was at 630 nm in acid solution and 590 nm under neutral and alkaline conditions. The fluorescence of the pH test paper changed from red to orange and then to yellow, which was better than that of the pure CDs solution. The CDs exhibited highly selective and reversible fluorescence quenching with respect to Cu2+ ions because of strong binding and fast chelating kinetics. There was a linear relationship between fluorescence quenching and Cu2+ concentration, suggesting the other promising practical usage of this sensing system. The versatile CDs-based pH sensor thus provides a basis for developing sustainable...

Rationally Designed Efficient Dual-Mode Colorimetric/Fluorescence Sensor Based on Carbon Dots for Detection of pH and Cu2+ Ions

Herein, solar-driven GQDs loaded BiVO4 heterostructure catalysts were fabricated and employed to degradate carbamazepine (CBZ) under simulated solar light. The as-prepared ternary catalysts (GQD/m-BiVO4/t-BiVO4) were thoroughly characterized by TEM, HRTEM, XRD, XPS, UV-vis, Raman and PL. The characterization results demonstrated that GQDs are well-dispersed on binary BiVO4 support, and the optical properties of the composites are improved with GQDs loaded. The photocatalytic activities of the novel composite catalysts were significantly increased by incorporation of GQDs on original BiVO4 semiconductor. In particular, the 1.0 wt% GQD loaded catalysts exhibited the highest photocatalytic activity for CBZ, and the mineralization degree of CBZ with the catalysts could achieve more than 95%. In addition, the transformation products (TPs) of CBZ during the catalysis processes were tentatively identified, and hydroxyl radicals were regarded as the predominant active species. From the results of density functional theory (DFT) calculations and evolution of TPs, hydroxylation and cleavage of amide group on the heterocycle may be the main initial photocatalytic degradation channels for CBZ under the catalysis of GQD/BiVO4.

Simulated solar driven catalytic degradation of psychiatric drug carbamazepine with binary BiVO4 heterostructures sensitized by graphene quantum dots

Sustainable, inexpensive, and environmentally friendly biomass waste can be exploited for large-scale production of carbon nanomaterials. Here, alkali lignin was employed as a precursor to synthesize carbon quantum dots (CQDs) with bright green fluorescence through a simple one-pot route. The prepared CQDs had a size of 1.5-3.5 nm, were water-dispersible, and showed wonderful biocompatibility, in addition to their excellent photoluminescence and electrocatalysis properties. These high-quality CQDs could be used in a wide range of applications such as metal-ion detection, cell imaging, and electrocatalysis. The wide range of biomass lignin feedstocks provide a green, low-cost, and viable strategy for producing high-quality fluorescent CQDs and enable the conversion of biomass waste into high-value products that promote sustainable development of the economy and human society.

Weitao Li

Papers

Full-color fluorescent carbon quantum dots

Facile synthesis of fluorescent graphene quantum dots from coffee grounds for bioimaging and sensing

Rationally Designed Efficient Dual-Mode Colorimetric/Fluorescence Sensor Based on Carbon Dots for Detection of pH and Cu2+ Ions

Simulated solar driven catalytic degradation of psychiatric drug carbamazepine with binary BiVO4 heterostructures sensitized by graphene quantum dots

Sustainable Synthesis of Bright Green Fluorescent Nitrogen-Doped Carbon Quantum Dots from Alkali Lignin.