Multistage Microfluidic Platform for the Continuous Synthesis of III–V Core/Shell Quantum Dots

We present a fully continuous chip microreactor‐based multistage platform for the synthesis of quantum dots with heterostructures. The use of custom‐designed chip reactors enables precise control of heating profiles and flow distribution across the microfluidic channels while conducting multistep reactions. The platform can be easily reconfigured by reconnecting the differently designed chip reactors allowing for screening of various reaction parameters during the synthesis of nanocrystals. III–V core/shell quantum dots are chosen as model reaction systems, including InP/ZnS, InP/ZnSe, InP/CdS and InAs/InP, which are prepared in flow using a maximum of six chip reactors in series.     

The Unexpected Influence of Precursor Conversion Rate in the Synthesis of III–V Quantum Dots

Control of quantum dot (QD) precursor chemistry has been expected to help improve the size control and uniformity of III–V QDs such as indium phosphide and indium arsenide. Indeed, experimental results for other QD systems are consistent with the theoretical prediction that the rate of precursor conversion is an important factor controlling QD size and size distribution. We synthesized and characterized the reactivity of a variety of group‐V precursors in order to determine if precursor chemistry could be used to improve the quality of III–V QDs. Despite slowing down precursor conversion rate by multiple orders of magnitude, the less reactive precursors do not yield the expected increase in size and improvement in size distribution. This result disproves the widely accepted explanation for the shortcoming of current III–V QD syntheses and points to the need for a new generalizable theoretical picture for the mechanism of QD formation and growth.     

基于元素磷源的InP量子点的制备

以白磷作为磷源、醋酸铟为铟源、硬脂酸为表面包覆剂、十八烯为溶剂,采用胶体化学法合成了InP量子点。X射线衍射(XRD)和透射电子显微镜(TEM)分析测试显示InP量子点属于立方闪锌矿结构,并且是直径约为5 nm的球状纳米晶。紫外可见光谱和荧光光谱分析表明,InP量子点表现出明显的激子吸收和带边发射特征,荧光发射光谱在415~517 nm范围内连续可调,呈现明显的量子尺寸效应。     

Near‐Infrared Emission from Tin–Lead (Sn–Pb) Alloyed Perovskite Quantum Dots by Sodium Doping

Phase‐stable CsSn_xPb_1?xI₃ perovskite quantum dots (QDs) hold great promise for optoelectronic applications owing to their strong response in the near‐infrared region. Unfortunately, optimal utilization of their potential is limited by the severe photoluminescence (PL) quenching, leading to extremely low quantum yields (QYs) of approximately 0.3 %. The ultra‐low sodium (Na) doping presented herein is found to be effective in improving PL QYs of these alloyed QDs without alerting their favourable electronic structure. X‐ray photoelectron spectroscopy (XPS) studies suggest the formation of a stronger chemical interaction between I^? and Sn²⁺ ions upon Na doping, which potentially helps to stabilize Sn²⁺ and suppresses the formation of I vacancy defects. The optimized PL QY of the Na‐doped QDs reaches up to around 28 %, almost two orders of magnitude enhancement compared with the pristine one.     

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。     

水热法合成巯基乙胺稳定的CdTe量子点

提出了一种以水热法合成巯基乙胺稳定的CdTe量子点的简单制备路线. 在优化的反应条件下, 产物的荧光量子效率最高达到19.7%, 接近已报道的其它方法的2倍. 考察了反应条件对产物的荧光性能的影响及产物在不同pH溶液中的稳定性.     

石墨烯量子点负载银纳米粒子制备及氧还原电催化活性

银基氧还原电催化剂具有较高的电催化活性且价格相对低廉,因而受到广泛关注. 本文采用简单、预先合成的石墨烯量子点作为载体和还原剂,制得了负载于石墨烯量子点、且无保护剂和表面活性剂的表面洁净银纳米粒子（Ag NPs/GQDs）. 电化学研究表明,Ag NPs/GQDs复合电催化剂的氧还原有较高的电催化活性,氧在碱性溶液中可经4电子途径还原为水. 与商业铂碳电极（Pt/C）相比,AgNPs/GQDs电极具有高催化电流密度、良好稳定性和极佳抗甲醇性能. 该银纳米粒子对开发高性能和低成本的非铂氧还原电催化剂有潜在的应用前景.     

Non‐Blinking Semiconductor Colloidal Quantum Dots for Biology,Optoelectronics and Quantum Optics

Twinkle, twinkle: The blinking of semiconductor colloidal nanocrystals is the main inconvenience of these bright nanoemitters. There are various approaches for obtaining non‐blinking nanocrystals, one of which is to grow a thick coat of CdS on the CdSe core (see picture). Applications of this method in the fields of optoelectronic devices, biologic labelling and quantum information processing are discussed.

     

氮掺杂石墨烯量子点/钯纳米复合材料的研究

铂基催化剂因具有高催化活性、高稳定性而成为极其重要的能源转化催化剂。本文采用水热法合成氮掺杂石墨烯量子点支撑的钯纳米复合材料(Pd@N-GQDs),并将其用于碱性介质中甲醇的电催化氧化反应。实验结果表明,相比同类型材料钯负载于石墨烯纳米片(Pd@GS)、钯负载于石墨烯量子点(Pd@GQDs)和商业钯黑催化剂(Pd@C),Pd@N-GQDs纳米材料具有很高的催化活性和稳定性,并可减少催化剂材料中贵金属的使用量。     

Bottom-Up Synthesis,Dispersion and Properties of Rectangular-Shaped Graphene Quantum Dots

Carbon nanomaterials have attracted the attention of the scientific community for more than 30 years now; first with fullerene, then with nanotubes and now with graphene and graphene related materials. Graphene quantum dots (GQDs) are nanoparticles of graphene that can be synthesized following two approaches, namely top-down and bottom-up methods. The top-down synthesis used harsh chemical and/or physical treatments of macroscopic graphitic materials to obtain nanoparticles, while the second is based on organic chemistry through the synthesis of polycyclic aromatic hydrocarbons exhibiting various sizes and shapes that are perfectly controlled. The main drawback of this approach is related to the low solubility of carbon materials that prevents the synthesis of nanoparticles containing more than few hundreds of sp² carbon atoms. Here we report on the synthesis of a family of rectangular-shaped graphene quantum dots containing up to 162 sp² carbon atoms. These graphene quantum dots are not functionalized on their periphery in order to keep the maximum similarity with nanoparticles of pure graphene. We chose water with sodium deoxycholate surfactant to study their dispersion and their optical properties (absorption, photoluminescence and photoluminescence excitation). The electronic structure of the particles and of their aggregates are studied using Tight-Binding (TB). We observe that the larger particles ( GQD 3 and GQD 4 ) present a slightly better dispensability than the smaller ones, probably because the larger GQDs can accommodate more surfactant molecules on each side, which helps to stabilize their dispersion in water.     

发光碳量子点的合成、性质和应用

基于碳量子点具有良好的水溶性、化学惰性、低毒性、易于功能化和抗光漂白性等优异性能,碳量子点和其它的碳纳米材料（如富勒烯、碳纳米管和石墨烯等）同样引起了研究者广泛的关注。 碳量子点可以通过很多较为廉价的一步法进行大规模的制备,包括化学氧化法、超声法、微波法和激光烧蚀法等。 本文主要介绍了不同碳量子点的合成方法,以及依赖于碳量子点尺寸和波长等性质的发光性能,并且讨论了碳量子点在生物成像、光催化、能量转换/储存、光电子、光限幅和传感器等方面的应用。     

Analytical Applications of Enzymatic Growth of Quantum Dots

We have developed an analytical assay to detect the enzymatic activity of acetylcholine esterase and alkaline phosphatase based on the generation of quantum dots by enzymatic products. Acetylcholine esterase converts acetylthiocholine into thiocholine. The latter enhances the rate of decomposition of sodium thiosulfate into H₂S, which in the presence of cadmium sulfate yields CdS quantum dots showing a time dependent exponential growth, typical of autocatalytic processes. This assay was also applied to detect acetylcholine esterase inhibitors. Alkaline phosphatase hydrolyzes thiophosphate and yields H₂S, which instantly reacts with Cd²⁺ to give CdS quantum dots. The formation of CdS quantum dots in both reactions was followed by fluorescence spectroscopy and showed dependence on the concentration of enzyme and substrate.     

硅量子点支撑钯纳米粒子的可控制备

采用微乳法制备烯丙胺修饰的硅量子点(Si QDs),通过紫外-可见吸收光谱、荧光光谱和红外光谱对其光学性能进行了表征,通过透射电镜(TEM)对其形貌进行了表征,测得其荧光量子产率为10.06%,荧光寿命τ1=3.1982ns,τ2=12.4527ns。依据Si QDs的光学性质,制备了Si QDs支撑Pd纳米粒子材料(Si QDs/Pd)。通过量子点的浓度实现了Pd纳米粒子形貌和尺寸的有效控制。结果表明制备的Pd纳米材料具有较好的分散性,在有机催化和能源转化领域具有潜在的应用价值。     

CdSe Spherical Quantum Dots Stabilised by Thiomalic Acid: Biphasic Wet Synthesis and Characterisation

CdSe quantum dots stabilised by thiomalic acid have been synthesised by an aqueous biphasic ligand exchange reaction in air. The materials are completely water‐soluble and were found to be stable over a long time. X‐ray diffraction and transmission electron microscopy reveal the formation of CdSe nanocrystals with cubic structure (a=0.6077 nm; spatial group: F‐43m). The average particle size is about 5 nm. Energy dispersive X‐ray analysis shows that the nanocrystals are nonstoichiometric, with a Cd/Se ratio varying between 60/40 and 70/30, and indicates the presence of Cd²⁺ ions at the nanocrystal surface. Diffuse reflectance infrared Fourier transform measurements suggest that thiomalic acid chelates CdSe through the thiol group and one carboxylic function, while the second COOH group is semi‐free. A complex‐like structure is proposed, in which thiomalic acid forms a five‐membered chelate ring with the Cd²⁺ ions present on the nanocrystal surface. Chelate effect accounts for the easiness of ligand exchange and is expected to additionally stabilise the nanosystem.     

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.     

White‐Light‐Emitting Edge‐Functionalized Graphene Quantum Dots

Graphene quantum dots (GQDs) have received considerable attention for their potential applications in the development of novel optoelectronic materials. In the generation of optoelectronic devices, the development of GQDs that are regulated in terms of their size and dimensions and are unoxidized at the sp² surfaces is desired. GQDs functionalized with bulky Fréchet’s dendritic wedges at the GQD periphery were synthesized. The single‐layered, size‐regulated structures of the dendronized GQDs were revealed by atomic force microscopy. The edge‐functionalization of the GQDs led to white‐light emission, which is an uncommon feature.