基于上转换发光的碳量子点制备及应用研究

碳量子点具有易制备、低毒性、化学惰性高、荧光特性稳定等特点,和其他碳纳米材料(如富勒烯、碳纳米管和石墨烯等)一样引起了研究者的广泛关注。本文将从碳量子点的合成、特性、改性和应用等方面进行阐述,并对其受长波长光激发后可发出短波长光的这一上转换发光特性进行重点综述,为今后碳量子点的合成、改性以及应用提供一定的参考。     

Cu–N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon Dots

The broadband light‐absorption ability of carbon dots (CDs) has inspired their application in photocatalysis, however this has been impeded by poor electron transfer inside the CDs. Herein, we report the preparation of Cu–N‐doped CDs (Cu‐CDs) and investigate both the doping‐promoted electron transfer and the performance of the CDs in photooxidation reactions. The Cu–N doping was achieved through a one‐step pyrolytic synthesis of CDs with Na₂[Cu(EDTA)] as precursor. As confirmed by ESR, FTIR, and X‐ray photoelectron spectroscopies, the Cu species chelates with the carbon matrix through Cu–N complexes. As a result of the Cu–N doping, the electron‐accepting and ‐donating abilities were enhanced 2.5 and 1.5 times, and the electric conductivity was also increased to 171.8 μs cm^?1. As a result of these enhanced properties, the photocatalytic efficiency of CDs in the photooxidation reaction of 1,4‐dihydro‐2,6‐dimethylpyridine‐3,5‐dicarboxylate is improved 3.5‐fold after CD doping.     

Hot-Tailoring of Carbon Nitride Dots with Redshifted Photoluminescence for Visual Double Text Encryption and Bioimaging

The fabrication of carbon dots and their doped forms by top-down chemical cleavage has attracted considerable attention in the efforts to meet the increasing demands for optoelectronic applications ranging from biosensing to electro- and photocatalysis. However, due to strong quantum confinement effects, the size decrease often leads to an increase in the band gap, even in the emission of deep-ultraviolet (DUV) light, which greatly limits their applications. Here, we report a facile hot-tailoring strategy for fabricating carbon nitride nanodots (CNDs) with redshifted intrinsic photoluminescent (PL) emission, compared with the pristine bulk precursor. It has been found that the different leaving abilities of the C,N-containing groups during the pyrolysis stage and the chemical passivation during the liquid-collection stage played vital roles. Due to the redshifted photoluminescence and other attractive features, the as-obtained CNDs were successfully applied in visual double text encryption with higher security and also in bioimaging with photostability superior to traditional dyes. This work highlights the great potential of the hot-tailoring method in modulating carbon-based nanostructures and offsetting band-gap widening as the size decreases.     

碳量子点的荧光发射机制

碳量子点(CQDs)一般是指粒径小于10 nm的零维碳材料,因其具有优良的光学特性而在生物成像、光学器件、生物复合材料和生物传感等领域得到广泛应用,并有望成为未来应用最广泛的一种碳材料.CQDs的光学特性受粒径、表面官能团及合成的条件(如温度、溶剂的种类和pH等)的影响,为了精准调控其光学性能以及进一步扩大其应用范围,...     

Multi-Color Fluorescent Carbon Dots: Graphitized sp2 Conjugated Domains and Surface State Energy Level Co-Modulate Band Gap Rather Than Size Effects

Four types of carbon dots (CDs) with various color (blue, green, yellow, and red) emissions have been synthesized under solvent-free conditions from citric acid and different nitrogen sources (DMF, urea, ethanamide, and formamide). By detailed characterization and comparison, it is confirmed that the graphitized sp² conjugated domain and surface functional groups such as C−O and C=N play synergetic roles in adjusting the fluorescence properties. Notably, the size effect is not the dominant mechanism to achieve multi-color fluorescence emissions in this work. The structural configuration of the carbon dots further influences the energy band structure, as demonstrated in simplified energy level diagrams. An absorption peak at approximately 560 nm appears in the visible light region for red-emitting CDs, assigned to an n→π* transition of the aromatic structure, thus introducing a new surface state energy level, resulting in a reduction in the energy of electron transition and the expansion into the visible region of the UV/Vis spectrum. Taking advantage of the diverse absorption and emission properties, different CDs/TiO₂ binary composites are obtained for photocatalytic degradation of organic dyes, and it is found that the absorption range in terms of visible light and the band gap of the carbon dots make a difference to the photocatalytic performance of the composites.     

Boron Doped Carbon Dots with Unusually High Photoluminescence Quantum Yield for Ratiometric Intracellular pH Sensing

Herein we report that boron doping in carbon dots results in increased photoluminescence (PL) quantum yield, which could be used for ratiometric intracellular pH sensing in cancer cell lines. Using a mixture of citric acid monohydrate, thiourea, and boric acid, microwave-assisted synthesis of boron doped blue emitting carbon dots (B-Cdots) with an average size of 3.5±1.0 nm was achieved. For B-Cdots, the maximum quantum yield (QY) was observed to be 25.8 % (11.1 % (w/w) H₃BO₃ input concentration), whereas, the same was calculated to be 16.9 % and 11.4 % for Cdots (synthesized from citric acid monohydrate and thiourea only) and P-Cdots (phosphorus doped carbon dots; synthesized using citric acid monohydrate, thiourea and phosphoric acid) (11.1 % (w/w) H₃PO₄ input concentration), respectively. The observed luminescence efficiencies as obtained from steady state and time-resolved photoluminescence measurements suggest an alternative emission mechanism due to boron/phosphorus doping in carbon dots. We furthermore demonstrated facile composite formation using B-Cdots and another carbon dots with orange emission in presence of polyvinyl alcohol (PVA), resulting in white light emission (0.31, 0.32; λ_ex 380 nm). The white light emitting composite enabled ratiometric pH sensing in the aqueous medium and showed favorable uptake properties by cancerous cells for intracellular pH sensing as well.     

无溶剂法大量制备高效红光碳点及其在白光器件中的应用

以邻苯二胺、 2,5-二氨基苯磺酸和三氯化铝为原料, 通过无溶剂法大量制备了高效的红色荧光碳点 (R-CDs). 制得的碳点尺寸大约为2.4 nm, 含有13%的氮元素, 主要由高度石墨化的碳核及覆盖在其表面的大量官能团构成. 在不同的波长光激发下, 碳点在乙醇溶液中表现出不依赖于激发的红光发射, 其荧光峰位于 704 nm, 最大量子产率达到22%. 由于R-CDs具有优异的光学性质, 利用其构筑了紫外光激发的碳基白色发光二极管, 其色坐标为(0.33, 0.33), 非常接近自然光. 该研究为高效红色荧光碳点的大量制备提供了一种新路径, 同时拓宽了其在白光器件中的应用.     

The Use of a Microreactor for Rapid Screening of the Reaction Conditions and Investigation of the Photoluminescence Mechanism of Carbon Dots

A microreactor is applied and reported, for the first time, in the field of research of carbon dots (CDs), including rapid screening of the reaction conditions and investigation of the photoluminescence (PL) mechanism. Various carbonaceous precursors and solvents were selected and hundreds of reaction conditions were screened (ca. 15 min on average per condition). Through analyzing the screened conditions, tunable PL emission maxima, from about 330 to 550 nm with respectable PL quantum yields, were achieved. Moreover, the relationship between different developmental stages of the CDs and the PL properties was explored by using the microreactor. The PL emission was observed to be independent of the composition, carbonization extent, and morphology/size of the CDs. This study unambiguously presents that a microreactor could serve as a promising tool for the research of CDs.     

Nitrogen‐Doped Carbon Dots: A Facile and General Preparation Method,Photoluminescence Investigation,and Imaging Applications

Carbon dots (Cdots) are an important probe for imaging and sensing applications because of their fluorescence property, good biocompatibility, and low toxicity. However, complex procedures and strong acid treatment are often required and Cdots suffer from low photoluminescence (PL) emission. Herein, a facile and general strategy using carbonization of precursors and then extraction with solvents is proposed for the preparation of nitrogen‐doped Cdots (N‐Cdots) with 3‐(3,4‐dihydroxyphenyl)‐L ‐alanine (L ‐DOPA), L ‐histidine, and L ‐arginine as precursor models. After they are heated, the precursors become carbonized. Nitrogen‐doped Cdots are subsequently extracted into N,N′‐dimethylformamide (DMF) from the carbogenic solid. A core–shell structure of Cdots with a carbon core and the oxygen‐containing shell was observed. Nitrogen has different forms in N‐Cdots and oxidized N‐Cdots. The doped nitrogen and low oxidation level in N‐Cdots improve their emission significantly. The N‐Cdots show an emission with a nitrogen‐content‐dependent intensity and Cdot‐size‐dependent emission‐peak wavelength. Imaging of HeLa cells, a human cervical cancer cell line, and HepG2 cells, a human hepatocellular liver carcinoma line, was observed with high resolution using N‐Cdots as a probe and validates their use in imaging applications and their multicolor property in the living cell system.     

Non-Metal-Heteroatom-Doped Carbon Dots: Synthesis and Properties

Carbon dots (CDs) are new materials with applications in bioimaging, optical devices, catalysis, and many other fields. Their advantages, such as ease of large-scale preparation, low-costing precursors, highly tunable photoluminescence, satisfactory biocompatibility, and photostability against photobleaching, make them competitive alternatives to conventional semiconductor-based quantum dots and organic dyes. To overwhelm other luminescent materials in applications, their functionalities still need to be improved in spite of the abovementioned advantages. In recent years, it has been proven that heteroatom doping is an effective approach to improve the optical and electronic performance of CDs by tuning their carbon skeleton matrices and chemical structures. In this review, the development of non-metal-heteroatom-doped CDs, including heteroatom categories, preparation methods, and physicochemical properties, are discussed. Progressive trends in heteroatom-doped CDs are also discussed at the end of this review.     

Solid‐State Carbon Dots with Efficient Cyan Emission towards White Light‐Emitting Diodes

Efficient cyan‐emitting solid carbon dots (CDs) were synthesized via a one‐pot hydrothermal method. The obtained solid CDs show a broad absorption from 270–460 nm with a maximum around 400 nm, and emit intense cyan light around 500 nm with an internal photoluminescence quantum efficiency of 34.1 % under 400 nm excitation. The emission maximum of the solid CDs remains unchanged under 320–400 nm excitations. Compared with dilute aqueous of CDs (2.5 mg mL^?1), the emission of solid CDs shows an obvious red‐shift of 50 nm. The red‐shift is caused by resonant energy transfer due to larger spectral overlap and smaller interparticle distance, together with a new surface state caused by aggregation in solid CDs. A lamp with white LEDs was fabricated by dropping a mixture of solid CDs, CaAlSiN₃:Eu²⁺ and silicon resin on the top of a near‐ultraviolet LED chip. Under an operating current of 20 mA, the as‐fabricated white LED generates a high‐quality, warm white light with a color rendering index of 86.1, a color temperature of 4340 K, and a luminescence efficiency of 31.3 lm W^?1.     

荧光碳点的制备及应用

荧光碳点是继富勒烯、碳纳米管及石墨烯之后最热门的碳纳米材料之一。这种纳米材料克服了传统量子点的某些缺点,不仅具有优良的光学性能与小尺寸特性,而且具有良好的生物相容性,易于实现表面功能化,在生化传感、成像分析、环境检测、光催化技术及药物载体等领域具有很好的应用潜力。本文就近年来人们对荧光碳点的研究进行了综述,简述了碳点的特性,重点介绍了荧光碳点应用的最新进展,对碳点发展过程中尚待解决的问题进行总结并对未来发展方向进行了展望。     

新型水溶性多色荧光碳点的制备及细胞成像研究

以鸡蛋清和牛奶分别与葡萄糖进行水热反应,制备水溶性多色荧光碳点,通过膜和柱层析分离纯化,利用透射电子显微镜(TEM)、紫外吸收光谱(UV)、荧光光谱(FL)、红外光谱(FTIR)等技术对所制备碳纳米粒子的粒径大小、吸收光谱、发光性质、表面基团进行表征。将所制备的碳点与小鼠黑色素瘤细胞共孵育,进行细胞成像应用评价。结果表明:制备的两种水溶性荧光碳点平均粒径分别为2.5 nm和4.9 nm,可在紫外灯下发出明亮的荧光,紫外最大吸收波长为250 nm。基于鸡蛋清或牛奶与葡萄糖反应制备的多色荧光碳量子点具有良好水溶性,其荧光光谱最大发射波长分别在410 nm和400 nm处,同时在660~800 nm激发波长范围内具有上转换性质,且荧光发射光谱随着激发光波长的增加发生红移。红外光谱表明存在—COOH、—NH2和—OH基团。细胞成像结果表明,在405 nm或488 nm激光照射下,所制备的碳点在细胞内的荧光成像清晰可见,而且在碳点浓度小于2.5 mg/mL时,均表现出较低的细胞毒性。     

Applicability Evaluation of Bright Green‐Emitting Carbon Dots in the Solid State for White Light‐Emitting Diodes

Self‐quenching‐resistant and bright green‐emitting carbon dots (CDs) in the solid state were synthesized via a facile hydrothermal method. Their structure, optical properties together with their thermal and photostabilities, as well as their applicability in white LEDs were investigated. The obtained CDs have nearly spherical shape with a size around 4–5 nm. The resulting powder CDs show excitation‐independent emission behavior, and can be excited over a broad range from 300–450 nm. Under optimal excitation at 400 nm, the resultant powder CDs yield bright and broad green emission around 505 nm with full width at half maximum (FWHM) of about 110 nm and under 360 nm excitation with lifetime of 15.8 ns. A potential application of the green‐emitting CDs was evaluated by constructing a white light‐emitting diode lamp. The fabricated white LED lamp emitted bright, warm white light with excellent color rendering properties (a color rendering index of 86.9 and a correlated color temperature of 3863 K).     

聚胺界面修饰改善碳量子点可见光光敏化性能

在新兴能源的存储与转化技术中,碳量子点作为新一代光吸收组分得到越来越广泛的关注。然而目前关于对碳量子点复合体系界面的改性,进而有效提高碳量子点光敏化性能的研究还较少。在本研究工作中,我们通过一种简单的静电自组装的方法构建催化体系,碳量子点能够很好地分散在枝状聚乙烯亚胺修饰的二氧化钛表面,其中碳量子点在复合体系中质量分数约为5%(w, mass fraction)时,展现出最优的可见光还原对硝基苯胺的活性。整体活性相比没有经过修饰的二氧化钛/碳量子点复合体系以及作为参比的枝状聚乙烯亚胺修饰的二氧化硅/碳量子点复合体系均有较明显的提高。结构与光谱研究表明,碳量子点与聚乙烯亚胺修饰的二氧化钛形成了较好的界面接触;进一步通过对比二氧化硅复合体系与二氧化钛复合体系表明,枝状聚乙烯亚胺可作为电子传输通道,能够有效地促进光生电子的分离与传递。因此,得益于良好的界面接触与有效地光生载流子的传递,相比未修饰的复合体系,枝状聚乙烯亚胺修饰的二氧化钛/碳量子点展现出更好地光催化反应活性。此研究工作中界面优化的手段,可将二氧化钛/碳量子点复合体系进一步拓展到其他宽带隙半导体光催化体系并设计构建有效的碳量子点基的半导体光吸收体系。     

从量子点的角度审视碳点的研究进展

碳点不仅具有类似于传统量子点的强发光和小尺寸特性,还表现出传统量子点无法比拟的水相分散性和生物相容性等优势.作为量子点领域的一个新兴分支,碳点的结构、合成化学和光电性质与传统量子点显著不同,也为量子点的发展提供了新的机遇和挑战.随着碳点领域的迅速发展和不断深化,越来越有必要在一些基本概念上与传统量子点比较,并从传统量子点的角度澄清碳点的独特特征和关键挑战.本综述主要聚焦于基本结构、合成化学、光学性质和应用研究等四个方面,从传统量子点基础概念的角度来重新审视碳点领域的研究进展和挑战.     

水热法新型水溶性荧光碳点的制备及其性能研究

以阿拉伯糖和磷酸酪蛋白肽进行水热反应,制备水溶性多色荧光碳点,利用透射电子显微镜(TEM)、紫外吸收光谱(UV)、荧光光谱(FL)、红外光谱(FTIR)和X射线衍射(XRD)等对所制备碳点的粒径大小、吸收光谱、发光性质、表面基团等进行表征,并考察了其性能和对不同金属离子的识别作用。结果表明:制备的荧光碳点平均粒径为4.62 nm,其紫外最大吸收波长为281 nm,XRD峰值约为21°,可在紫外灯下发出明亮的荧光,最大发射波长为414 nm,且呈荧光多元发射。红外光谱分析表明存在—COOH,—NH2和—OH基团。该荧光碳点具有良好的性能,且对Cu2+和Fe3+有较强的选择性识别作用,其原因可能是荧光碳点的聚合导致粒径增大从而使荧光强度减弱。该碳点有望作为荧光探针用于检测分析和生物成像等领域。     

有机硅功能化碳纳米球:合成及可见光催化活性

以柠檬酸为碳源,3-氨丙基三乙氧基硅烷（APTES）为功能化试剂,乙二醇为溶剂,溶剂热法制备了具有上下转换发光性质的有机硅功能化的碳纳米球（SiCNs）。利用X射线衍射（XRD）、透射电镜（TEM）、红外光谱（FTIR）、X射线光电子能谱（XPS）、紫外可见漫反射光谱（UV-Vis DRS）和光致发光光谱（PL）等对合成的SiCNs进行了表征。结果表明,在APTES与柠檬酸质量比为2.0时,180℃反应5 h可以制备出尺寸分布在30~50 nm之间均一球形的SiCNs。可见光辐射下,以亚甲基蓝（MB）为目标降解物研究了SiCNs样品的光催化降解活性,通过活性物种的分析对催化降解体系的光催化机理进行了探讨。结果表明,可见光照射120 min,SiCNs样品对MB溶液的降解率可以达到99%,经过5次循环使用降解率仍保持在96%以上。SiCNs样品展现了优异的可见光催化活性及良好的稳定性。     

有机硅功能化碳纳米球:合成及可见光催化活性

以柠檬酸为碳源,3-氨丙基三乙氧基硅烷(APTES)为功能化试剂,乙二醇为溶剂,溶剂热法制备了具有上下转换发光性质的有机硅功能化的碳纳米球(SiCNs)。利用X射线衍射(XRD)、透射电镜(TEM)、红外光谱(FTIR)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis DRS)和光致发光光谱(PL)等对合成的SiCNs进行了表征。结果表明,在APTES与柠檬酸质量比为2.0时,180℃反应5 h可以制备出尺寸分布在30~50 nm之间均一球形的SiCNs。可见光辐射下,以亚甲基蓝(MB)为目标降解物研究了SiCNs样品的光催化降解活性,通过活性物种的分析对催化降解体系的光催化机理进行了探讨。结果表明,可见光照射120 min,SiCNs样品对MB溶液的降解率可以达到99%,经过5次循环使用降解率仍保持在96%以上。SiCNs样品展现了优异的可见光催化活性及良好的稳定性。     

Circularly Polarized Luminescence of Achiral Carbon Dots in Bi-Solvent Systems Triggered by Supramolecular Self-Assembly

An innovative strategy for circularly polarized luminescence (CPL) of carbon dots (CDs) has been developed: The achiral CDs displayed contrary supramolecular chirality and opposite CPL in two different bi-solvent systems, which are due to the formation of self-assembled helical nanostructures with two diverse assembly modes (P and M) in aggregate state via intermolecular π-π interactions and differential hydrogen bonding (H-bonding) without the need of any additional element of chirality.