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Journal ArticleDOI

New methods of synthesis and varied properties of carbon quantum dots with high nitrogen content

14 Feb 2014-Journal of Materials Research (Cambridge University Press)-Vol. 29, Iss: 3, pp 383-391
TL;DR: In this article, the authors present simple methods to synthesize carbon quantum dots (CQDs) with high nitrogen doping content, involving the reaction of glucose in the presence of urea under hydrothermal conditions or by microwave irradiation.
Abstract: Doping of a heteroatom such as nitrogen in carbon nanomaterials provides a means to tailor their electronic properties and chemical reactivities. In this article, we present simple methods to synthesize carbon quantum dots (CQDs) with high nitrogen doping content (18–22%), involving the reaction of glucose in the presence of urea under hydrothermal conditions or by microwave irradiation. The N-doped carbon quantum dots (N-CQDs) show high aqueous solubility and tunable photoluminescence (PL). Interaction of N-CQDs with exfoliated graphene or dimethylaniline quenches PL. Interaction of N-doped as well as undoped C-dots with electron-donating tetrathiafulvalene and electron-withdrawing tetracyanoethylene has been examined. The intense blue PL of CQDs has been exploited to produce white light by mixing the CQDs with yellow light emitting ZnO nanoparticles or graphene oxide. The N-doped CQDs exhibit superior photocatalytic activity compared to pristine CQDs.
Citations
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Journal ArticleDOI
TL;DR: Imaging of U87 cells, a human brain glioma cancer cell line, can be easily achieved with high resolution using the prepared carbon dots as probes and validates their use in imaging applications.
Abstract: In the present work, a completely green synthetic method for producing fluorescent nitrogen-doped carbon dots by using milk is introduced. The process is environmentally friendly, simple, and efficient. By hydrothermal heating of milk, we produced monodispersed, highly fluorescent carbon dots with a size of about 3 nm. Imaging of U87 cells, a human brain glioma cancer cell line, can be easily achieved with high resolution using the prepared carbon dots as probes and validates their use in imaging applications.

461 citations

Journal ArticleDOI
TL;DR: This review will give new insights into how to use different synthetic methods for tuning the structure of DFCDs, understanding the correlation between the doping and properties, and achieving new applications.
Abstract: Doping fluorescent carbon dots (DFCDs) with heteroatoms have recently become of great interest compared to traditional fluorescent materials because it provides a feasible and new way to tune the intrinsic properties of carbon quantum dots (CQDs) and graphene quantum dots (GQDs) to achieve new applications for them in different fields. Since the first report on nitrogen (N) doped GQDs in 2012, more effort is being focused on exploring different procedures for making new types of DFCDs with different heteroatoms. This mini review will summarize recent research progress on DFCDs. It first reviews various doping categories achieved up to now, looking back on the synthesis method and comparing the differences in synthesis approaches between the DFCDs and the undoped ones. Then it focuses on the advances on how the doping affects the optical properties, especially DFCDs doped with N, which have been investigated the most. Finally, different applications of DFCDs involving bio-imaging, sensing, catalysis and photoelectronic devices will be discussed. This review will give new insights into how to use different synthetic methods for tuning the structure of DFCDs, understanding the correlation between the doping and properties, and achieving new applications.

419 citations

Journal ArticleDOI
TL;DR: This state-of-the-art review will provide a platform for understanding the intricate details of heteroatom-doped CDs, a summary of the latest progress in the field, and related applications in biology and is expected to inspire further developments in this exciting class of materials.
Abstract: Heteroatom-doped carbon dots (CDs), due to their excellent photoluminescence (PL) properties, attracted widespread attention recently and demonstrated immense promise for diverse applications, particularly for biological applications. The objective of this feature article is to provide a comprehensive overview of the recent progress in the research and development of heteroatom-doped CDs and a detailed description of the influence of single or co-doping heteroatoms on their PL behavior. The most recent understanding and critical insights into the PL mechanism of heteroatom-doped CDs are also highlighted. Moreover, potential bio-related applications of heteroatom-doped CDs in biosensing, bioimaging, and theranostics are also reviewed. This state-of-the-art review will provide a platform for understanding the intricate details of heteroatom-doped CDs, a summary of the latest progress in the field, and related applications in biology and is expected to inspire further developments in this exciting class of materials.

350 citations

Journal ArticleDOI
TL;DR: In this paper, the authors summarize recent progress in doping and surface functionalization of C-dots for improving their functionality, and offer insight into controlling the properties of carbon nanodots for a variety of applications.
Abstract: Distinct from conventional carbon nanostructures, such as fullerene, graphene, and carbon nanotubes, carbon nanodots (C-dots) exhibit unique properties such as strong fluorescence, high photostability, chemical inertness, low toxicity, and biocompatibility. Various synthesis routes for C-dots have been developed in the last few years, and now intense research efforts have been focused on improving their functionality. In this aspect, doping and surface functionalization are two major ways to control the chemical, optical, and electrical properties of C-dots. Doping introduces atomic impurities into C-dots to modulate their electronic structure, and surface functionalization modifies the C-dot surface with functional molecules or polymers. In this review, we summarize recent progress in doping and surface functionalization of C-dots for improving their functionality, and offer insight into controlling the properties of C-dots for a variety of applications ranging from biomedicine to optoelectronics to energy.

340 citations

Journal Article
TL;DR: This study quantifies energy transfer to and fluorescence quenching by graphene, critical properties for novel applications in photovoltaic devices and as a molecular ruler.
Abstract: Energy transfer from photoexcited zero-dimensional systems to metallic systems plays a prominent role in modern day materials science. A situation of particular interest concerns the interaction between a photoexcited dipole and an atomically thin metal. The recent discovery of graphene layers permits investigation of this phenomenon. Here we report a study of fluorescence from individual CdSe/ZnS nanocrystals in contact with single- and few-layer graphene sheets. The rate of energy transfer is determined from the strong quenching of the nanocrystal fluorescence. For single-layer graphene, we find a rate of approximately 4 ns(-1), in agreement with a model based on the dipole approximation and a tight-binding description of graphene. This rate increases significantly with the number of graphene layers, before approaching the bulk limit. Our study quantifies energy transfer to and fluorescence quenching by graphene, critical properties for novel applications in photovoltaic devices and as a molecular ruler.

304 citations

References
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Book
01 Jan 1983
TL;DR: This book describes the fundamental aspects of fluorescence, the biochemical applications of this methodology, and the instrumentation used in fluorescence spectroscopy.
Abstract: Fluorescence methods are being used increasingly in biochemical, medical, and chemical research. This is because of the inherent sensitivity of this technique. and the favorable time scale of the phenomenon of fluorescence. 8 Fluorescence emission occurs about 10- sec (10 nsec) after light absorp tion. During this period of time a wide range of molecular processes can occur, and these can effect the spectral characteristics of the fluorescent compound. This combination of sensitivity and a favorable time scale allows fluorescence methods to be generally useful for studies of proteins and membranes and their interactions with other macromolecules. This book describes the fundamental aspects of fluorescence. and the biochemical applications of this methodology. Each chapter starts with the -theoreticalbasis of each phenomenon of fluorescence, followed by examples which illustrate the use of the phenomenon in the study of biochemical problems. The book contains numerous figures. It is felt that such graphical presentations contribute to pleasurable reading and increased understand ing. Separate chapters are devoted to fluorescence polarization, lifetimes, quenching, energy transfer, solvent effects, and excited state reactions. To enhance the usefulness of this work as a textbook, problems are included which illustrate the concepts described in each chapter. Furthermore, a separate chapter is devoted to the instrumentation used in fluorescence spectroscopy. This chapter will be especially valuable for those perform ing or contemplating fluorescence measurements. Such measurements are easily compromised by failure to consider a number of simple principles."

28,073 citations

Journal ArticleDOI
02 Aug 2002-Science
TL;DR: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects.
Abstract: Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices; sensors; field emission displays and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.

9,693 citations

Journal ArticleDOI
28 Jan 2005-Science
TL;DR: The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.
Abstract: Research on fluorescent semiconductor nanocrystals (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have farreaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.

7,499 citations

Journal ArticleDOI
06 Feb 2009-Science
TL;DR: It is reported that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.
Abstract: The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

6,370 citations

Journal ArticleDOI
TL;DR: This Review summarize recent advances in the synthesis and characterization of C-dots and speculate on their future and discuss potential developments for their use in energy conversion/storage, bioimaging, drug delivery, sensors, diagnostics, and composites.
Abstract: Similar to its popular older cousins the fullerene, the carbon nanotube, and graphene, the latest form of nanocarbon, the carbon nanodot, is inspiring intensive research efforts in its own right. These surface-passivated carbonaceous quantum dots, so-called C-dots, combine several favorable attributes of traditional semiconductor-based quantum dots (namely, size- and wavelength-dependent luminescence emission, resistance to photobleaching, ease of bioconjugation) without incurring the burden of intrinsic toxicity or elemental scarcity and without the need for stringent, intricate, tedious, costly, or inefficient preparation steps. C-dots can be produced inexpensively and on a large scale (frequently using a one-step pathway and potentially from biomass waste-derived sources) by many approaches, ranging from simple candle burning to in situ dehydration reactions to laser ablation methods. In this Review, we summarize recent advances in the synthesis and characterization of C-dots. We also speculate on their future and discuss potential developments for their use in energy conversion/storage, bioimaging, drug delivery, sensors, diagnostics, and composites.

3,991 citations