Carbon quantum dots from natural resource: A review

Carbon quantum dots (CQDs) are a new class of fluorescence small carbon nanoparticles with a particle size of less than 10 nm and have vast applications in the field of bioimaging, biosensing and disease-detection. These are promising materials for nano-biotechnology since it has smaller particle size, excellent biocompatibility and excitation wavelength dependent photoluminescence (PL) behavior, photo induced electron transfer, chemical inertness and low toxicity. These materials have excellent fluorescent properties such as broad excitation spectra, narrow and tunable emission spectra, and high photostability against photo bleaching and blinking than other fluorescent semiconductor quantum dots. This review article demonstrate the recent progress in the synthesis, functionalization and technical applications of carbon quantum dots using electrochemical oxidation, combustion/thermal, chemical change, microwave heating, arc-discharge, and laser ablation methods from various natural resources. Natural carbon sources are used for the preparation of CQDs due to its low cost, environmental friendly and widely available.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

A facile, low-cost, green, kilogram-scale synthesis of high quality CQDs were synthesized. The throughput of CQDs is 1.4975 kg in one pot and the as-prepared CQDs have a highly crystalline hexagonal structure with remarkable solubility, stability, and biocompatibility. It showed outstanding electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

The development of large-scale synthetic methods for high quality carbon quantum dots (CQDs) is fundamental to their applications. However, the macroscopic preparation and scale up synthetic of CQDs is still in its infancy. Here, we report a facile, green, kilogram-scale synthesis of high quality fluorescent CQDs derived from poplar leaves via a one-step hydrothermal method. Notably, the throughput of CQDs can reach a level up to as high as 1.4975 kg in one pot. The structure and properties of the as-prepared CQDs were assessed through TEM, XRD, XPS and various spectroscopic methods. The obtained high quality CQDs with a photoluminescent quantum yield of 10.64% showed remarkable stability in aqueous media, rich functional groups, high photostability, consistent photoluminescence within biological pH range and low cytotoxicity. On account of these good properties, we demonstrated the multifunctional application to electrocatalytic water splitting, Fe³⁺ sensing and bioimaging. It showed remarkable electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility. This study provides a green, facile, inexpensive and large-scale method for producing high quality CQDs, which provides application value for large-scale production of CQDs.     

基于碳量子点的光电器件应用新进展

碳量子点(CQDs)作为一种新型荧光碳纳米材料,由于其较高的电子迁移率、较长的热电子寿命、极快的电子取出速度,可调的带隙宽度、较强的稳态荧光等独特的光电性质和可溶液加工、成本低廉的特点,使得CQDs在光电器件领域具有广阔的应用前景,近年来受到人们的广泛关注,重要的研究成果不断涌现。本文首先简要介绍了CQDs的合成方法、化学结构及其光电性质,然后总结了CQDs在发光二极管(LEDs)、太阳能电池(SCs)和光电探测器(PDs)等光电器件领域的研究进展,最后对CQDs的发展方向进行了展望。     

碳量子点的制备及其在能源与环境领域应用进展

碳量子点(carbon quantum dots,CQDs)作为碳纳米材料家族的新成员引起了科学家广泛关注和极大的研究兴趣。 CQDs具有优良的光学特性、生物相容性及微弱的细胞毒性,在生物医药、生物传感器及光电子设备、环境及能源等领域中具有重要的应用。 本文从CQDs的制备方法出发,介绍了近年来发展的新型制备方法,讨论了其优缺点以及对所得CQDs在组成、结构和性质等方面的影响;基于CQDs独特的光学及电化学性能,重点介绍了CQDs在环境与能源领域的应用。 此外,对CQDs研究过程中存在的若干挑战进行了分析,提出了未来发展的一些思考和建议,为拓展CQDs多方面应用提供重要参考。     

An Efficient Templating Approach for the Synthesis of Redispersible Size‐Controllable Carbon Quantum Dots from Graphitic Polymeric Micelles

Access to high‐quality, easily dispersible carbon quantum dots (CQDs) is essential in order to fully exploit their desirable properties. Copolymers based on N‐acryloyl‐D ‐glucosamine and acrylic acid prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization are self‐assembled into micelle‐like nanoreactors. After a facile graphitization process (170 °C, atmospheric pressure), each micellar template is transformed into a CQD through a 1:1 copy process. These high‐quality CQDs (quantum yield=22 %) with tunable sizes (2–5 nm) are decorated by carboxylic acid moieties and can be spontaneously redispersed in water and polar organic solvents. This preparation method renders the mass production of multifunctional CQDs possible. To demonstrate the versatility of this approach, CQDs hybridized TiO₂ nanoparticles with enhanced photocatalytic activity under visible‐light have been prepared.     

碳量子点的合成研究进展与展望

碳量子点(CQDs)呈现出的亲水性、低细胞毒性、化学及光稳定性等优异性质,使其在化学、生物医学、传感学及光电子学领域得到了广泛的关注与应用。本文重点介绍CQDs合成的最新进展,总结了宏观条件下CQDs合成的自上而下法(弧光放电、激光烧蚀、电化学等)与自下而上法(化学氧化、热分解、微波加热等),比较了不同合成方法中碳源的利用率、反应条件、产物的尺寸分布、荧光性能及应用,讨论了各种合成方法的成功之处与存在的问题。文中详细介绍了基于微反应器原理的反胶束法和模板法在CQDs尺寸可控合成领域的应用。微流控芯片技术在纳米材料合成中显现安全、高效、可控等优于宏观反应体系的优势,结合目前微流控芯片合成CQDs的研究进展,可以预期微流控芯片在不久的将来将会在CQDs的合成中得到更成功的应用。     

Self-Assembly of Semiconductor Quantum Dots using Organic Templates

Colloidal semiconductor nanocrystals, known as quantum dots (QDs), are regarded as brightly photoluminescent nanomaterials possessing outstanding photophysical properties, such as high photodurability and tunable absorption and emission wavelengths. Therefore, QDs have great potential for a wide range of applications, such as in photoluminescent materials, biosensors and photovoltaic devices. Since the development of synthetic methods for accessing high-quality QDs with uniform morphology and size, various types of QDs have been designed and synthesized, and their photophysical properties dispersed in solutions and at the single QD level have been reported in detail. In contrast to dispersed QDs, the photophysical properties of assembled QDs have not been revealed, although the structures of the self-assemblies are closely related to the device performance of the solid-state QDs. Therefore, creating and controlling the self-assembly of QDs into well-defined nanostructures is crucial but remains challenging. In this Minireview, we discuss the notable examples of assembled QDs such as dimers, trimers and extended QD assemblies achieved using organic templates. This Minireview should facilitate future advancements in materials science related to the assembled QDs.     

Electrochemistry in Carbon‐based Quantum Dots

Electrochemistry belongs to an important branch of chemistry that deals with the chemical changes produced by electricity and the production of electricity by chemical changes. Therefore, it can not only act a powerful tool for materials synthesis, but also offer an effective platform for sensing and catalysis. As extraordinary zero‐dimensional materials, carbon‐based quantum dots (CQDs) have been attracting tremendous attention due to their excellent properties such as good chemical stability, environmental friendliness, nontoxicity and abundant resources. Compared with the traditional methods for the preparation of CQDs, electrochemical (EC) methods offer advantages of simple instrumentation, mild reaction conditions, low cost and mass production. In return, CQDs could provide cost‐effective, environmentally friendly, biocompatible, stable and easily‐functionalizable probes, modifiers and catalysts for EC sensing. However, no specific review has been presented to systematically summarize both aspects until now. In this review, the EC preparation methods of CQDs are critically discussed focusing on CQDs. We further emphasize the applications of CQDs in EC sensors, electrocatalysis, biofuel cells and EC flexible devices. This review will further the experimental and theoretical understanding of the challenges and future prospective in this field, open new directions on exploring new advanced CQDs in EC to meet the high demands in diverse applications.     

Current Advances in Quantum‐Dots‐Based Photoelectrochemical Immunoassays

As a newly developed technique, photoelectrochemical (PEC) immunoassays have attracted great attention in recent years because of their low cost and desirable sensitivity. Because the detection signal originates from the photoelectric conversion of photoelectric materials, the appearance and application of quantum dots (QDs), which possess unique photophysical properties and regulated optoelectronic characteristics, has taken the development of PEC immunoassays to new heights. This review concisely introduces the general mechanism of QDs‐based photoelectric conversion for immunoassays and summarizes the current advances in QD applications in immunoassays. Given that signal strategies and photoactive materials are the key elements in PEC biosensor systems, we comprehensively highlight the state‐of‐the‐art signaling strategies and various applications of QDs in PEC immunoassays to introduce advances in QDs‐based PEC immunoassays. Finally, challenges and future developmental trends are briefly discussed     

One‐Pot Synthesis of Highly Luminescent Carbon Quantum Dots and Their Nontoxic Ingestion by Zebrafish for In Vivo Imaging

Photoluminescent carbon and/or silicon‐based nanodots have attracted ever increasing interest. Accordingly, a myriad of synthetic methodologies have been developed to fabricate them, which unfortunately, however, frequently involve relatively tedious steps, such as initial surface passivation and subsequent functionalization. Herein, we describe a green and sustainable synthetic strategy to combine these procedures into one step and to produce highly luminescent carbon quantum dots (CQDs), which can also be easily fabricated into flexible thin films with intense luminescence for future roll‐to‐roll manufacturing of optoelectronic devices. The as‐synthesized CQDs exhibited enhanced cellular permeability and low or even noncytotoxicity for cellular applications, as corroborated by confocal fluorescence imaging of HeLa cells as well as cell viability measurements. Most strikingly, zebrafish were directly fed with CQDs for in vivo imaging, and mortality and morphologic analysis indicated ingestion of the CQDs posed no harm to the living organisms. Hence, the multifunctional CQDs potentially provide a rich pool of tools for optoelectronic and biomedical applications.     

Synthesis of highly luminescent carbon dots from postconsumer waste silk cloth and investigation of its electron transfer dynamics with methyl viologen dichloride

Synthesis of luminescent carbon dots (CDs) from biological waste materials is gaining more attention in the present-day scenario. We have synthesized highly luminescent (luminescence quantum yield, φ ​= ​19.1%), water-soluble CDs from a postconsumer waste silk cloth via a facile hydrothermal synthetic method. The resulting CDs are characterized and their photophysical properties are studied in detail. The electron transfer dynamics of CDs in presence of methyl viologen dichloride hydrate (MV²⁺) is systematically investigated in this work. Knowledge of the electron transfer dynamics of CDs is essential in the structural elucidation of CDs, prediction of sensing mechanisms and utilizing the CDs in energy storage devices.     

Facile Microwave‐Assisted Solid‐Phase Synthesis of Highly Fluorescent Nitrogen–Sulfur‐Codoped Carbon Quantum Dots for Cellular Imaging Applications

Carbon quantum dots (CQDs) have recently attracted significant attention for both their fundamental science and technological applications as a new class of fluorescent zero‐dimensional nanomaterials with a size below 10 nm. However, the reported methods of synthesis were generally less suitable for the large‐scale production of the CQDs with high‐fluorescent quantum yield (QY). In the paper, a novel one‐pot microwave‐assisted drying synthesis approach was presented to prepare CQDs with high QY of 61.3 % for the first time. The production yield of CQDs was 35±3 % in weight. The as‐prepared CQDs were characterized by various techniques such as TEM, AFM, XRD, XPS, FTIR spectroscopy, UV/Vis absorption spectroscopy, and fluorescence spectroscopy. The results showed that the high QY of CQDs was largely attributed to the dual doping of nitrogen and sulphur into CQDs. Such CQDs were then used as live‐cell imaging reagents due to their high QY, good water dispersibility, fine biocompatibility, high photostability, and low cytotoxicity.     

Selenium‐Doped Carbon Quantum Dots for Free‐Radical Scavenging

Heteroatom doping is an effective way to adjust the fluorescent properties of carbon quantum dots. However, selenium‐doped carbon dots have rarely been reported, even though selenium has unique chemical properties such as redox‐responsive properties owing to its special electronegativity. Herein, a facile and high‐output strategy to fabricate selenium‐doped carbon quantum dots (Se‐CQDs) with green fluorescence (quantum yield 7.6 %) is developed through the hydrothermal treatment of selenocystine under mild conditions. Selenium heteroatoms endow the Se‐CQDs with redox‐dependent reversible fluorescence. Furthermore, free radicals such as ^.OH can be effectively scavenged by the Se‐CQDs. Once Se‐CQDs are internalized into cells, harmful high levels of reactive oxygen species (ROS) in the cells are decreased. This property makes the Se‐CQDs capable of protecting biosystems from oxidative stress.     

The electrochemical behavior of core-shell CdSe/CdS magic-sized quantum dots linked to cyclodextrin for studies of the encapsulation of bioactive compounds

Semiconductor nanocrystal quantum dots have been the subject of extensive investigations in different areas of science and technology in the past years. In particular, there are few studies of magic-sized quantum dots (MSQDs), even though they exhibit features such as extremely small size, fluorescence quantum efficiency, molar absorptivity greater than traditional QDs, and highly stable luminescence in HeLa cell cultures, thereby enabling monitoring of biological or chemical processes. The present study investigated the electrochemical behavior of free CdSe/CdS MSQDs using glassy carbon electrode and CdSe/CdS MSQDs immobilized on a gold electrode modified with a self-assembled cyclodextrin monolayer. The MSQDs showed two peaks in aprotic medium. The functionalized film modifier was prepared and characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy using ferricyanide ions as a redox probe. The prepared modified electrode exhibited a stable behavior. The proposed method was successfully applied to encapsulation studies of mangiferin, a natural antioxidant compound, and cyclodextrin associated with the quantum dot, and the response was compared with that of the modified electrode without QD. The fluorescence study revealed that CdSe/CdS quantum dots emit blue light when excited by an optical source of wavelength of 350 nm and a significant increase in fluorescence and absorbance intensity is observed from the core-shell CdSe/CdS MSQDs when quantities of mangiferin are added to the solution containing thiolated cyclodextrin. CdSe/CdS MSQDs are optically and electrochemically sensitive and can be used for the detection and interaction of compounds encapsulated in cyclodextrin.     

Bio-safety assessment of carbon quantum dots,N-doped and folic acid modified carbon quantum dots: A systemic comparison

The carbon quantum dots(CQDs) and their functionalized materials are promising in biomedical field because of their unique properties;meanwhile,a growing concern has been raised about the potential toxicity of these modified materials in biosystem.In this study,we synthesized original CQDs and two common functionalized CQDs including N-doped CQDs(NCQDs) and folic acid-modified CQDs(FACQDs),and compared the toxicity and biocompatibility with each other in vitro and in vivo.L929,C6 and normal cell MDCK were selected to detect the adverse reaction of these materials in vitro.No acute toxicity or obvious changes were noted from in vitro cytotoxicity studies with the dose of these CQD materials increasing to a high concentration at 1 mg/mL.Among these materials,the FA-CQDs show a much lower toxicity.Moreover,in vivo toxicity studies were performed on the nude mice for 15 days.The experimental animals in 10 or 15 mg/kg groups were similar with animals treated by phosphate buffer solution(PBS) after 15 days.The results of the multifa rious biochemical parameters also suggest that the functionalized products of CQDs do not influence the biological indicators at feasible concentration.Our findings in vitro and in vivo through toxicity tests demonstrate that CQDs and their modified materials are safe for future biological applications.     

野酸枣氮掺杂荧光碳量子点高灵敏检测Hg2+

以天然产物野酸枣和色氨酸为原料,通过水热法一步合成量子产率为16.9%的氮掺杂荧光碳量子点。该碳量子点具有良好的水溶性和耐光性,在高盐环境中也呈现出了较高的稳定性。应用荧光光谱、透射电子显微镜(TEM)、傅里叶变换红外光谱(FTIR)和X射线光电子能谱(XPS)对碳量子点进行了表征。此外,Hg^2+能够有效地猝灭碳量子点的荧光,猝灭机理为电子转移的动态猝灭。基于此,可将碳量子点作为荧光探针检测Hg^2+。方法对Hg^2+的检测范围为1~50 nmol/L,检出限为0.26 nmol/L,能够应用于实际水样中Hg2+含量的测定。     

Surface and Interface Chemistry in Colloidal Quantum Dots for Solar Applications Studied by X‐Ray Photoelectron Spectroscopy

Control of the surface and interface chemistry of colloidal quantum dots (CQDs) is critical to achieving a product with good air stability and high performing optoelectronic devices. Through various surface passivation treatments, vast improvements have been made in fields such as CQD photovoltaics; however devices have not currently reached commercial standards. We show how X‐ray photoelectron spectroscopy (XPS) can provide a better understanding of exactly how surface treatments act on CQD surfaces, and the effect of surface composition on air stability and device performance.. We illustrate this with PbS‐based CQDs, using XPS to measure oxidation processes, and to quantify the composition of the topmost surface layer after different surface treatments. We also demonstrate the use of synchrotron radiation‐excited depth‐profiling XPS, a powerful technique for determining the surface composition, chemistry and structure of CQDs. This review describes our recent progress in characterization of CQD surfaces using SR‐excited depth profiling XPS and other photoemission techniques.     

中温煤沥青基碳量子点的制备与结构解析

以中温煤沥青为碳源，采用HNO₃预处理结合球磨过程及双氧水氧化刻蚀的方法制备沥青基荧光碳量子点，以CQDs的收率和荧光量子产率为目标，获得最优制备条件：反应时间6 h、H₂O₂加入量100 mL （c-CQDs），此时，CQDs收率和荧光量子产率分别为6.3%和11.2%，且尺寸均匀、粒径分布在4-14 nm。延长反应时间至8 h （a-CQDs），碳量子点团聚；H₂O₂用量增加至120 mL （b-CQDs）则导致碳量子点氧化过度，颗粒小且杂乱无章。对不同条件下所制备的CQDs进行XPS、红外光谱、热重、¹³C NMR、Raman和晶相分析，探究反应条件对CQDs结构的影响规律。结果表明，就碳含量而言，a-CQDs > b-CQDs > c-CQDs，氧元素含量则为b-CQDs > c-CQDs > a-CQDs。各CQDs结构中C主要以芳碳形式存在，c-CQDs的C=O、O-C=O含量最高，而b-CQDs的C-O含量最高，¹³C NMR分析发现CQDs中表征平均芳环尺寸大小的X_b约为0.5，相应地，其平均芳环数约为3。