Carbon quantum dots (CQDs) as a rising star of carbon nanomaterials, by virtue of their unique physicochemical, optical and electronic properties, have displayed tremendous momentum in numerous fields such as biosensing, bioimaging, drug delivery, optoelectronics, photovoltaics and photocatalysis. In particular, the rich optical and electronic properties of CQDs including efficient light harvesting, tunable photoluminescence (PL), extraordinary up-converted photoluminescence (UCPL) and outstanding photoinduced electron transfer have attracted considerable interest in different photocatalytic applications for the sake of full utilization of the solar spectrum. This review aims to demonstrate the recent progress in the synthesis, properties and photocatalytic applications of CQDs, particularly highlighting the fundamental multifaceted roles of CQDs in photoredox processes. Furthermore, we discuss the challenges and future direction of CQD-based materials in this booming research field, with a perspective toward the ultimate achievement of highly efficient and long-term stable CQD-based photocatalysts.

Recent progress in carbon quantum dots: synthesis, properties and applications in photocatalysis

Highly fluorescent nitrogen-doped carbon dots derived from Phyllanthus acidus utilized as a fluorescent probe for label-free selective detection of Fe 3+ ions, live cell imaging and fluorescent ink.

g-C3N4/carbon dot-based nanocomposites serve as efficacious photocatalysts for environmental purification and energy generation: A review

Artificial photosynthesis is the mimicry of the natural process of solar energy conversion into chemical energy carriers. Photocatalytic systems that combine light-harvesting materials and catalysts in solution or suspension provide a promising route towards this goal. A key requirement for a sustainable solar fuel production system is a low-cost, stable and non-toxic light harvester. Photoluminescent carbon nanoparticles, carbon dots (CDs), are promising emerging light-harvesters for photocatalytic fuel production systems. CDs possess many desirable properties for this purpose, such as inexpensive, scalable synthetic routes, low-toxicity and tuneable surface chemistry. In this tutorial review, the integration of CDs in photocatalytic fuel generation systems with metallic, molecular and enzymatic catalysts is discussed. An overview of CD types, synthesis and properties is given along with a discussion of tuneable CD properties that can be optimised for applications in photocatalysis. Current understanding of the photophysical electron transfer processes present in CD photocatalytic systems is outlined and various avenues for their further development are highlighted.

/pdf/carbon-dots-as-photosensitisers-for-solar-driven-catalysis-1aqomx5zj3.pdf

Carbon dots as photosensitisers for solar-driven catalysis

Carbon dots (CDs) have tremendous potential applications in bioimaging, biomedicine, and optoelectronics. By far, it is still difficult to produce photoluminescence (PL) tunable CDs with high quantum yield (QY) across the entire visible spectrum and narrow the emission peak widths of CDs close to those of typical quantum dots. In this work, a series of CDs with tunable emission from 443 to 745 nm, quantum yield within 13-54%, and narrowed full width at half maximum (FWHM) from 108 to 55 nm, are obtained by only adjusting the reaction solvents in a one-pot solvothermal route. The distinct optical features of these CDs are based on their differences in the particle size, and the content of graphitic nitrogen and oxygen-containing functional groups, which can be modulated by controlling the dehydration and carbonization processes during solvothermal reactions. Blue, green, yellow, red, and even pure white light emitting films (Commission Internationale de L'Eclairage (CIE)= 0.33, 0.33, QY = 39%) are prepared by dispersing one or three kinds of CDs into polyvinyl alcohol with appropriate ratios. The near-infrared emissive CDs are excellent fluorescent probes for both in vitro and in vivo bioimaging because of their high QY in water, long-term stability, and low cytotoxicity.

Solvent-Controlled Synthesis of Highly Luminescent Carbon Dots with a Wide Color Gamut and Narrowed Emission Peak Widths.

Carbon dots have attracted a great deal of attention because of their high performance, cheap and facile preparation, and potential applications in a wide area. In order to broaden their applications, especially to meet specific requirements, surface engineering, including tailoring surface functional group coating and subsequent chemical modification as required, is an effective strategy for further functionalization of carbon dots. In this article, representative approaches to coating the surface with various functional groups, and strategies for conjugating specific materials onto the surface of carbon dots for functional modification via covalent bonds, electrostatic interactions and hydrogen bonds are highlighted, as well as the results from explorations of their various applications in target modulated sensing, accurate drug delivery and bioimaging at high resolution.

Carbon dots: surface engineering and applications

In this work, the carboxylate groups terminated carbon dots (−OOC-C-dots) were synthesized by the thermal pyrolysis of citric acid at 180 °C for 40 h under air. The −OOC-C-dots with excellent water solubility showed bright blue emission under excitation at 360 nm. The blue emission fluorescence of the −OOC-C-dots can be quenched by Al3+, Hg2+, Pb2+, Ni2+, Cu2+, Cr3+, Co2+, and Fe3+ ions in HNO3 solution at pH = 5.0. Most interestingly, the −OOC-C-dots exhibited highly selective response to Fe3+ in NaAc-HAc buffer solution, to Pb2+ in Britton-Robinson buffer solution, and to Hg2+ in PBS buffer solution at pH = 5.0, respectively. Moreover, good linear relationships were found between (F0-F)/F0 and the concentrations of Fe3+, Pb2+, and Hg2+ in the corresponding buffer solutions. As a result, the −OOC-C-dots can be explored as a chemosensor for the label-free detection of Fe3+, Pb2+, and Hg2+ with selectivity being switched by different buffer systems. By the proposed method, the selective detection of Fe3+, Pb2+, and Hg2+ in real water samples (mineral and tap), even in the presence of high concentration of interfering ions, was accurately achieved. Hence, a new method for the potential detection of multi-metal ions can be developed by using one carbon-dot-based chemosensor with switchable selectivity in different buffer solutions.

Yanjing Ren

Papers

Carbon dots: surface engineering and applications

The selectivity of the carboxylate groups terminated carbon dots switched by buffer solutions for the detection of multi-metal ions