Synthesis and photochemical applications of processable polymers enclosing photoluminescent carbon quantum dots

Construction of carbon nanostructures using the sodium cocoyl glycinate@NaCl system

Carbon nanomaterials are widely used in many fields due to their unique properties. However, the novel production of carbon nanostructures is still a research challenge. Here, the self-assembly system of the anion surfactant sodium cocoylonate (SC)@NaCl has successfully produced a cube-shaped carbon nanoframework. The surface morphology, graphitization degree, elemental composition, surface chemical state, formation mechanism and photoluminescence properties of the carbon nanomaterials were further investigated. The results show that the surfactant-salt system is a novel and environmentally friendly method for producing nanostructures.

Carbon Dots and Their Polymeric Nanocomposites: Insight into Their Synthesis, Photoluminescence Mechanisms, and Recent Trends in Sensing Applications

Carbon dots (CDs), a novel class of carbon-based nanoparticles, have received a lot of interest recently due to their exceptional mechanical, chemical, and fluorescent properties, as well as their excellent photostability and biocompatibility. CDs' emission properties have already found a variety of potential applications, in which bioimaging and sensing are major highlights. It is widely acknowledged that CDs' fluorescence and surface conditions are closely linked. However, due to the structural complexity of CDs, the specific underlying process of their fluorescence is uncertain and yet to be explained. Because of their low toxicity, robust and wide optical absorption, high chemical stability, rapid transfer characteristics, and ease of modification, CDs have been recognized as promising carbon nanomaterials for a variety of sensing applications. Thus, following such outstanding properties of CDs, they have been mixed and imprinted onto different polymeric components to achieve a highly efficient nanocomposite with improved functional groups and properties. Here, in this review, various approaches and techniques for the preparation of polymer/CDs nanocomposites have been elaborated along with the individual characteristics of CDs. CDs/polymer nanocomposites recently have been highly demanded for sensor applications. The insights from this review are detailed sensor applications of polymer/CDs nanocomposites especially for detection of different chemical and biological analytes such as metal ions, small organic molecules, and several contaminants.

Photoluminescent Transparent Wood with Excellent UV-Shielding Function

At present, light transmission, energy saving, environmental protection, and UV-shielding materials are very important for optimizing indoor living environment. Here, a fluorescent transparent wood (FTW) with UV-shielding function was prepared by encapsulating a carbon quantum dot and epoxy resin into a delignification wood template. FTW exhibits excellent optical transmittance (about 91%), water absorption stability (weight gain rate less than 9%), longitudinal tensile strength (139 MPa), and UV-shielding properties. Due to the photoluminescence characteristics of the carbon quantum dot and the natural cellulose skeleton of wood, FTW can show uniform luminescence under ultraviolet lamps. At the same time, it has remarkable UV-shielding performance. This kind of photoluminescent transparent wood with a UV-shielding function also has the potential to be applied to fields such as electromagnetic shielding and harmful gas detection.

Chemical- and green-precursor-derived carbon dots for photocatalytic degradation of dyes

Rapid industrialization and untreated industrial effluents loaded with toxic and carcinogenic contaminants, especially dyes that discharge into environmental waters, have led to a rise in water pollution, with a substantial adverse impact on marine life and humankind. Photocatalytic techniques are one of the most successful methods that help in degradation and/or removal of such contaminants. In recent years, semiconductor quantum dots are being substituted by carbon dots (CDs) as photocatalysts, due to the ease of formation, cost-effectiveness, possible sustainability and scalability, much lower toxicity, and above all its high capacity to harvest sunlight (UV, visible, and near infrared) through electron transfer that enhances the lifetime of the photogenerated charge carriers. A better understanding between the properties of the CDs and their role in photocatalytic degradation of dyes and contaminants is required for the formation of controllable structures and adjustable outcomes. The focus of this review is on CDs and its composites as photocatalysts obtained from different sustainable green as well as chemical precursors. Apart from the synthesis, characterization, and properties of the CDs, the study also highlights the effect of different parameters on the photocatalytic properties of CDs and their composites for catalytic dye degradation mechanisms in detail. Besides the present research development in the field, potential challenges and future perspectives are also presented.

An all-in-one nanoprinting approach for the synthesis of a nanofilm library for unclonable anti-counterfeiting applications

In addition to causing trillion-dollar economic losses every year, counterfeiting threatens human health, social equity and national security. Current materials for anti-counterfeiting labelling typically contain toxic inorganic quantum dots and the techniques to produce unclonable patterns require tedious fabrication or complex readout methods. Here we present a nanoprinting-assisted flash synthesis approach that generates fluorescent nanofilms with physical unclonable function micropatterns in milliseconds. This all-in-one approach yields quenching-resistant carbon dots in solid films, directly from simple monosaccharides. Moreover, we establish a nanofilm library comprising 1,920 experiments, offering conditions for various optical properties and microstructures. We produce 100 individual physical unclonable function patterns exhibiting near-ideal bit uniformity (0.492 ± 0.018), high uniqueness (0.498 ± 0.021) and excellent reliability (>93%). These unclonable patterns can be quickly and independently read out by fluorescence and topography scanning, greatly improving their security. An open-source deep-learning model guarantees precise authentication, even if patterns are challenged with different resolutions or devices.

The Advance and Critical Functions of Energetic Carbon Dots in Carbon Dioxide Photo/Electroreduction Reactions

As a unique carbon-based nano material, carbon dots (CDs) have attracted great attention because of their special structures and properties, and have been widely used in various fields, such as bio-imaging technology, catalyst design, pollutant degradation, chemical analysis, clean energy development and so on. CDs are used as catalysts or cocatalysts for multiple energy conversion reactions due to their advantages of valid visible light utilization, fast transmission of charge carriers, excellent catalytic activity, and good electrical conductivity. This review first summarizes the basic structure and properties of CDs. The advance and critical functions of energetic CDs in carbon dioxide photo/electroreduction reactions are discussed in detail. Due to the excellent optical absorption, electron transfer properties and good conductivity of CDs, they can enhance catalytic activity and stability effectively. In the end, the existing problems and future development opportunities of CDs-based catalysts in CO₂ reduction reaction are proposed and outlined.

Multicolor Luminescent Carbon Dots: Tunable Photoluminescence, Excellent Stability, and Their Application in Light-Emitting Diodes

Carbon dots (CDs) are attracting much interest due to their excellent photoelectric properties and wide range of potential applications. However, it is still a challenge to regulate their bandgap emissions to achieve full-color CDs with high emissions. Herein, we propose an approach for producing full-color emissive CDs by employing a solvent engineering strategy. By only tuning the volume ratio of water and dimethylformamide (H₂O/DMF), the photoluminescence (PL) emission wavelengths of the CDs can be changed from 451 to 654 nm. Different fluorescence features of multicolor CDs were systematically investigated. XRD, SEM, TEM, Abs/PL/PLE, XPS, and PL decay lifetime characterizations provided conclusive evidence supporting the extent to which the solvent controlled the dehydration and carbonization processes of the precursors, leading to a variation in their emission color from red to blue. The as-prepared CDs exhibited excellent and stable fluorescence performance even after being heated at 80 °C for 48 h and with UV light continuously irradiated for 15 h. Based on their excellent fluorescent properties and photothermal stability, bright multicolor light-emitting diodes with a high CRI of up to 91 were obtained. We anticipate that these full-color emissive CDs are beneficial for applications in lighting, display, and other fields.

Color Conversion Light-Emitting Diodes Based on Carbon Dots: A Review

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow-green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity.

High-quality full-color carbon quantum dots synthesized under an unprecedentedly mild condition

Carbon quantum dots (CQDs) are highly promising to be applied in light-emitting, chemosensing, and other cutting-edge domains. Herein, we successfully fabricate high-quality full-color CQDs under unprecedentedly low temperature and pressure (85°C, 1.88 bar). Stable and narrow fluorescent emissions ranging from blue to green and red light were realized by simple amine engineering, which were further mixed into white-light CQDs with the absolute photoluminescent quantum yield reaching 19.2%. The average mass yield of the CQDs reached 69.0%. The optical performances demonstrated that the CQDs possessed uniform luminescent centers and dominant radiative decay channels. Component analysis further suggested that dehydrated condensation between carboxyl and amine groups directed the growth of the CQDs. By utilizing the CQDs, full-color light-emitting diodes and logic gate sensors were developed. This study paves an important step for promoting the application of CQDs by providing an energy-efficient, safe, and productive synthetic strategy.

Anhydride-Terminated Solid-State Carbon Dots with Bright Orange Emission Induced by Weak Excitonic Electronic Coupling

In this work, fluorescent solid carbon dots (CDs) welcome a new member, namely anhydride-terminated CDs, which have a photoluminescence quantum yield (PLQY) of 28% for orange-emitted CDs at 580 nm in powder form. For the first time, we revealed that the electronic coupling of the functional groups should be a crucial factor affecting the optical properties of solid CDs. Due to the negligible hydrogen bonding interaction between the anhydride groups, the electronic coupling of excitons between neighboring anhydride groups is weak, leading to a high PLQY of 28% and an immobile emission peak at 580 nm in solid state. Anhydride-terminated CDs can be partly converted into carboxyl-terminated CDs after dispersion in ethanol. However, the strong electronic coupling of carboxyl groups at high concentration generates the stacking mode of J-aggregates, giving rise to a red-shifted emission from 450 to 515 nm as well as quenched fluorescence in solid state. In comparison, a useful blue emission for solid-state CDs occurs from low sp² hybridized carbon atoms, which possess weak electronic coupling and a stationary emission band at 450 nm in both solution and solid state. By adjusting the feed ratio of the reactants, the relevant intensities between the emission from low sp² hybridized carbon atoms at 450 nm and the emission from anhydride groups at 580 nm can be controlled. As a result, single-component anhydride-terminated CD powder with tunable emission color from orange to white light can be achieved. As-prepared anhydride-terminated CDs can be used for fabricating light-emitting diodes (LEDs), white LEDs, and luminescent solar concentrators (LSCs).

A carbon dot-based Co-nanozyme with alkaline phosphatase - mechanism and application

Elevated levels of alkaline phosphatase (ALP) are associated with bone metastasis, liver cancer, prostate cancer, breast cancer, and many other diseases or stem cell marker. It is therefore of great significance to quantitatively detect the ALP levels by a rapid, highly sensitive, and easy-to-use strip paper test. In the present work, we discovered an enhancement of ALP activity upon the addition of cauliflower-derived carbon dots (CFCDs), which can be applied as a sensor for ALP. The mixed ALP and CFCDs exhibited a typical Michaelis Menten mechanism with increased V _max and reduced K _m compared to ALP alone. High-Resolution Atomic Force Microscopy (HR-AFM) reveals the dimensions of ALP, the CFCDs, and the phosphatase substrate para-nitrophenyl phosphate (pNPP), as well as the potential interactions among them. The role of the CFCDs was identified as the addition of reaction centers to ALP; in other words, a competitive activator. Besides the improved kinetics, the yield of dephosphorylated product was also increased by at least twice upon the addition of CFCDs. Taking advantage of this effect, a portable CFCD-based paper strip assay was developed to achieve sensitive detection of abnormally elevated ALP levels and visualization of cancer stem cells or proteins by phosphatase-conjugated antibodies. Our findings show great promise for disease diagnosis and bioassays related to ALP enhancement that may be used for protein or cell detection.

Detection of four foodborne pathogens based on magnetic separation multiplex PCR and capillary electrophoresis

Foodborne pathogen contamination is a major safety issue for many foods and is causing concern worldwide. In this study, a detection system based on magnetic separation, multiplex PCR (MPCR) and capillary electrophoresis (CE) technologies was developed for the simultaneous detection of four foodborne pathogens. Magnetic separation technology is used to rapidly capture pathogenic bacteria in food samples, and then a combination of MPCR and CE can be used to greatly increase detection sensitivity. The detection limit for bacterial DNA reached 10^-5 -10^-7  ng μL^-1 and in the analysis of mocked food samples, the assay showed good sensitivity for bacterial detection ranging from 10¹ to 10⁵ CFU mL^-1 with excellent specificity. Compared to similar detection methodologies, this technique avoids the need for time-consuming enrichment cultures, is more sensitive, and can be used to assay simultaneously four foodborne pathogens.

Technical textiles modified with immobilized carbon dots synthesized with infrared assistance

Carbon quantum dots "CQDs" were investigated as photo-luminescent nanomaterials as it advantageous with nontoxicity to be alternative for metallic-nanomaterials in different purposes. Therefore, the presented report demonstrates an innovative strategy for industrialization of antimicrobial/fluorescent cotton textiles via exploitation of "CQDs". Unique/novel infrared-assisted technique was currently investigated for clustering "CQDs" form carboxymethyl cellulose. The successive nucleation of "CQDs" (8.0 nm) was affirmed via infra-red, Raman spectroscopy, NMR, TEM and Zeta-potential analysis. The clustered "CQDs" showed antimicrobial and fluorescent characters. The minimal inhibition concentration for "CQDs" (100 mg/mL) against E. coli and C. albicans showed pathogenic reduction of 96% and 82%, respectively. Fluorescent emission spectra for "CQDs" showed two intense peaks at 415-445 nm. "CQDs" were loaded upon pristine and cationized cotton to prepare CQDs@cotton and CQDs@cationized cotton. While, their physical/mechanical properties (air and water vapor permeabilities, tensile strength and elongation %) and thermal stability (TGA & DTG analysis) were studied. The CQDs@cationized cotton exhibited excellent antimicrobial activity with good durability as after ten repretitive washings, inhibition zone diameter against E. coli, was diminished from 21.0 mm to 14.0 mm. The fluorescent emmision intensity was diminished from 741 to 287 after 10 washing cycles. The produced cotton fabrics could be safely used in the medical and military textiles.

Insights into photoluminescence mechanisms of carbon dots: advances and perspectives

Carbon dots (CDs) are potentially useful in many areas such as bioimaging, light-emitting diodes, and sensing because of their excellent optical properties, high biocompatibility, and low toxicity. Knowledge of their photoluminescence (PL) mechanisms, which have been widely studied, is of significance in guiding the synthesis and promoting applications of CDs with tunable PL emissions. However, the intrinsic mechanism of PL emission remains unclear, and a unified mechanism has not been found because of differences in particle structures. This review generalizes the categories of CDs, noting their structural diversity. Three types of PL mechanism pertaining to structural differences are outlined: internal factors dominated emission (including the conjugation effect, the surface state, and the synergistic effect), external factors dominated emission (including the molecular state and the environment effect), and crosslink-enhanced emission. Optical applications of CDs are also briefly mentioned. Finally, the prospects for research into PL mechanisms are discussed, noting the remaining challenges and directions for future work.

Fluorescent Carbon Dots: Fantastic Electroluminescent Materials for Light-Emitting Diodes

Fluorescent carbon dots (CDs) have emerged as fantastic luminescent nanomaterials with significant potentials on account of their unique photoluminescence properties, high stability, and low toxicity. The application of CDs in electroluminescent light-emitting diodes (LEDs) have aroused much interest in recent years. Herein, the state-of-the-art advances of CD-based electroluminescent LEDs are summarized, in which CDs act as active emission layer and interface transport layer materials is discussed and highlighted. Besides, the device structure of CD-based LEDs and preparation methods of CDs are also introduced. Furthermore, the opportunities and challenges for achieving high performance CD-based electroluminescent LED devices are presented. This review article is expected to stimulate more unprecedented achievements derived from CDs and CD-based electroluminescent LEDs, thus further promoting their practical applications in future solid-state lighting and flat-panel displays.

The Rapid and Large-Scale Production of Carbon Quantum Dots and their Integration with Polymers

Carbon quantum dots (CDs) have inspired vast interest because of their excellent photoluminescence (PL) performances and their promising applications in optoelectronic, biomedical, and sensing fields. The development of effective approaches for the large-scale production of CDs may greatly promote the further advancement of their practical applications. In this Minireview, the newly emerging methods for the large-scale production of CDs are summarized, such as microwave, ultrasonic, plasma, magnetic hyperthermia, and microfluidic techniques. The use of the available strategies for constructing CD/polymer composites with intriguing solid-state PL is then described. Particularly, the multiple roles of CDs are emphasized, including as fillers, monomers, and initiators. Moreover, typical applications of CD/polymer composites in light-emitting diodes, fluorescent printing, and biomedicine are outlined. Finally, we discuss current problems and speculate on their future development.

Synthesis and applications of amino-functionalized carbon nanomaterials

Carbon-based nanomaterials (CNMs) have attracted considerable attention in the scientific community both from a scientific and an industrial point of view. Fullerenes, carbon nanotubes (CNTs), graphene and carbon dots (CDs) are the most popular forms and continue to be widely studied. However, the general poor solubility of many of these materials in most common solvents and their strong tendency to aggregate remains a major obstacle in practical applications. To solve these problems, organic chemistry offers formidable help, through the exploitation of tailored approaches, especially when aiming at the integration of nanostructures in biological systems. According to our experience with carbon-based nanostructures, the introduction of amino groups is one of the best trade-offs for the preparation of functionalized nanomaterials. Indeed, amino groups are well-known for enhancing the dispersion, solubilization, and processability of materials, in particular of CNMs. Amino groups are characterized by basicity, nucleophilicity, and formation of hydrogen or halogen bonding. All these features unlock new strategies for the interaction between nanomaterials and other molecules. This integration can occur either through covalent bonds (e.g., via amide coupling) or in a supramolecular fashion. In the present Feature Article, the attention will be focused through selected examples of our approach to the synthetic pathways necessary for the introduction of amino groups in CNMs and the subsequent preparation of highly engineered ad hoc nanostructures for practical applications.

Imidazolium-type ionic liquid-based carbon quantum dot doped gels for information encryption

Here, a strategy for the preparation of adjustable imidazolium-type ionic liquid (IL)-based carbon quantum dots (CQDs) was reported. The effect of chemical structure, including carbon chain length of the N-substitution and the type of anion, on the amphiphilicity of CQDs was systematically investigated. It was found that the hydrophobicity of CQDs can be increased with the increase of carbon chain length for substitution at the N3 position. Moreover, the amphiphilicity of CQDs was also switched by changing the hydrophilic anions to hydrophobic anions. Due to adjustable amphiphilicity, the hydrophilic and hydrophobic CQDs were used for the preparation of fluorescent hydrogels and organogels, respectively. The fluorescent CQD-doped gels showed light- and force-dual stimuli responsiveness, which provides more secure information encryption than traditional single encryption inks.

Luminescent Transparent Wood Based on Lignin-Derived Carbon Dots as a Building Material for Dual-Channel, Real-Time, and Visual Detection of Formaldehyde Gas

Formaldehyde (FA) is a widespread indoor air pollutant, and its efficient detection is a major industrial challenge. The development of a building material with real-time and visual self-detection of FA gas is highly desirable for meeting both construction and human health demands. Herein, a luminescent transparent wood (LTW) as the building material was developed for dual-channel, real-time, and visual detection of FA gas. It was fabricated by encapsulating multicolor lignin-derived carbon dots (CDs) and poly(vinyl alcohol) (PVA) into a delignified wood framework. It exhibited 85% optical transmittance, tunable room-temperature phosphorescence (RTP), and ratiometric fluorescence (FL) emission. The tunable luminescence was attributed to different CD graphitization and surface functionalization. The color-responsive ratiometric FL and delayed RTP detections of FA were displayed over the range of 20-1500 μM (R² = 0.966, LOD = 1.08 nM) and 20-2000 μM (R² = 0.977, LOD = 45.8 nM), respectively. The LTW was also used as an encapsulation film on a UV-emitting InGaN chip to form white light-emitting diodes, indicating the feasibility as an FA-responsive planar light source. The operational notion of functional LTW can expand its applications to new fields such as a stimuli-responsive light-transmitting window or planar light sources while monitoring indoor air pollutants, temperature, and humidity.

Patterned carbon dot-based thin films for solid-state devices

Carbon dot-based fluorescent nanocomposite compounds were obtained following microwave assisted thermal treatment of an aqueous mixture consisting of citric acid and urea. Thin film deposition of nanocomposites on SiO2 (100) substrates is followed by annealing, in order to render the films dissolution-resistant and processable. Optical lithography and O2 plasma etching are utilized to pattern the deposited films in the desired shapes and dimensions and a solid-state relative humidity sensor is fabricated on the SiO2 substrate. Spectroscopy and microscopy techniques are employed to characterize and monitor the whole process throughout the fabrication steps. The patterned films retain the functional groups introduced during their synthesis and continue to display hydrophilicity and PL properties. Successful patterning of these nanocomposites opens the way for the fabrication of solid-state, carbon dot-based optical and electrical devices that take advantage of the properties of carbon quantum dots.

Fluorescent Carbon Quantum Dots-Synthesis,Functionalization and Sensing Application in FoodAnalysis

Carbon quantum dots (CQDs) with stable physicochemical properties are one of theemerging carbon nanomaterials that have been studied in recent years. In addition to the excellentoptical properties such as photoluminescence, photobleaching resistance and light stability, thismaterial also has favorable advantages of good biocompatibility and easy functionalization, whichmake it an ideal raw material for constructing sensing equipment. In addition, CQDs can combinedwith other kinds of materials to form the nanostructured composites with unique properties, whichprovides new insights and ideas for the research of many fields. In the field of food analysis,emerging CQDs have been deeply studied in food composition analysis, detection and monitoringtrace harmful substances and made remarkable research progress. This article introduces andcompares the various methods for CQDs preparation and reviews its related sensing applicationsas a new material in food components analysis and food safety inspection in recent years. It isexpected to provide a significant guidance for the further study of CQDs in the field of foodanalysis and detection. CQDs; synthesis; fluorescent sensing; food analysis.

Recent Developments in Synthesis and Photocatalytic Applications of Carbon Dots

The tunable photoluminescent and photocatalytic properties of carbon dots (CDs) via chemical surface modification have drawn increased attention to this emerging class of carbon nanomaterials. Herein, we summarize the advances in CD synthesis and modification, with a focus on surface functionalization, element doping, passivation, and nanocomposite formation with metal oxides, transition metal chalcogenides, or graphitic carbon nitrides. The effects of CD size and functionalization on photocatalytic properties are discussed, along with the photocatalytic applications of CDs in energy conversion, water splitting, hydrogen evolution, water treatment, and chemical degradation. In particular, the enzyme-mimetic and photodynamic applications of CDs for bio-related uses are thoroughly reviewed.

CO2-triggered reversible phase transfer of graphene quantum dots for visible light-promoted amine oxidation

Carbon dots, emerging as novel photoluminescent nanomaterials, have attracted increasing attention for photocatalytic applications such as hydrogen evolution, carbon dioxide reduction, pollutant degradation and organic synthesis. However, the separation of carbon dots from the reaction system is always a cumbersome process, which may limit their applications in photocatalysis. Herein, we report the synthesis of a graphene quantum dot with CO2-switchable reversible phase transfer performance via a facile surface functionalization approach. The mechanism of this hydrophilicity and hydrophobicity alteration involves the protonation-deprotonation transformation and reversible formation of hydrophilic bicarbonate salts when CO2 is bubbled and removed. Then, the obtained graphene quantum dot was utilized as a visible-light photocatalyst for the oxidative coupling of amines. Our photocatalyst demonstrates excellent catalytic efficiency with both high reaction conversion and selectivity. Furthermore, the proposed graphene quantum dot could be recycled via a simple CO2 bubbling method.

Carbon dots: advances in nanocarbon applications

Carbon dots (C-Dots), defined by characteristic sizes of <10 nm, have become a rising star in carbon nanomaterials. C-Dots possess many unique physiochemical and photochemical properties which make them a promising platform for imaging, environmental, catalytic, biological and energy-related applications. To date, C-Dots have been investigated extensively, and their related applications have developed rapidly. However, quantitative understanding of the physiochemical properties of C-Dots still remains a difficult challenge because of their complex structures. Here, we will highlight the recent progress in the practical applications of C-Dots, with particular attention to the research in light-emitting devices, bioimaging and biodetection, catalysis, functional materials, and agriculture.

A Mini Review on Carbon Quantum Dots: Preparation, Properties, and Electrocatalytic Application

Luminescent carbon quantum dots (CQDs) represent a new form of nanocarbon materials which have gained widespread attention in recent years, especially in chemical sensor, bioimaging, nanomedicine, solar cells, light-emitting diode (LED), and electrocatalysis. CQDs can be prepared simply and inexpensively by multiple techniques, such as the arc-discharge method, microwave pyrolysis, hydrothermal method, and electrochemical synthesis. CQDs show excellent physical and chemical properties like high crystallization, good dispersibility, photoluminescence properties. In particular, the small size, superconductivity, and rapid electron transfer of CQDs endow the CQDs-based composite with improved electric conductivity and catalytic activity. Besides, CQDs have abundant functional groups on the surface which could facilitate the preparation of multi-component electrical active catalysts. The interactions inside these multi-component catalysts may further enhance the catalytic performance by promoting charge transfer which plays an important role in electrochemistry. Most recent researches on CQDs have focused on their fluorescence characteristics and photocatalytic properties. This review will summarize the primary advances of CQDs in the synthetic methods, excellent physical and electronic properties, and application in electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reduction (HER), and CO2 reduction reaction (CO2RR).

Design, Synthesis, and Functionalization Strategies of Tailored Carbon Nanodots

Over the past decades, considerable efforts have been devoted to synthesizing nanostructured materials with specific properties that ultimately shape their function. In the carbon nanotechnology era, for nanomaterials such as fullerenes, carbon nanotubes, and graphene, the main focus has been on the organic functionalization of these nanostructures, in order to tailor their processability and applicability. Carbon-based dots, quasi-spherical nanoparticles with a shape under 10 nm, have popped up into this context especially due to their versatile synthesis and intriguing properties, mainly their fluorescence emission. Even though they were discovered through the top-down route of cutting large carbon nanostructures, in recent years the ease and flexibility of the bottom-up synthesis have allowed this carbon-based class of nanomaterials to advance at a striking pace. However, the fast speed of research and publication rate have caused a few issues that affect their classification, purity criteria, and fluorescence mechanisms. As these are being progressively addressed, the true potential and applicability of this nanomaterial has started to unravel. In this Ariticle, we describe our efforts toward the synthesis, purification, characterization, and applications of carbon nanodots. Special attention was dedicated to designing and customizing the optoelectronic properties of these nanomaterials, as well as their applications in hybrid and composite systems. Our approach is centered on a bottom-up, microwave-assisted hydrothermal synthesis. We have successfully exploited a multicomponent synthetic approach, using arginine and ethylenediamine as starting materials. By controlling the reaction conditions, in just 3 min, blue-emitting carbon nanodots become accessible. We have improved this approach by designing and tuning the emissive, electrochemical, and chiroptical properties of these nanoforms. On the other hand, we have used postfunctionalization reactions as a tool for conjugation with suitable partners and for further tuning the surface chemistry. The combination of these two approaches has produced a number of carbon nanodots that can be investigated in fields ranging from biology to materials chemistry and in applications spanning from nanomedicine to energy conversion.

Solid-State Fluorescent Carbon Dots with Aggregation-Induced Yellow Emission for White Light-Emitting Diodes with High Luminous Efficiencies

For practical applications of carbon dots (CDs), a major challenge is to prevent the notorious aggregation-caused quenching (ACQ) effect. Herein, a new type of CDs (CD1) has been developed that can transform from ACQ to an enhancement of fluorescence by aggregation-induced emission (AIE). The blue fluorescence of the CDs is suppressed by ACQ. However, this is accompanied by the phenomenon of AIE at a longer wavelength, resulting in the emergence and gradual enhancement of yellow fluorescence. The obtained CD1 solid powder shows a bright yellow emission with a photoluminescence quantum yield (PLQY) of 65%. The photoluminescence (PL) spectra, absorption spectra, and time-resolved PL decay curves indicate that Förster resonant energy transfer from dispersed CD1 particles to large CD1 agglomerations leads to the enhancement of yellow fluorescence. To exploit its high PLQY and strong AIE, CD1 is applied as a color-converting layer on blue light-emitting diode (LED) chips to fabricate white LEDs (WLEDs). The obtained devices show white light coordinates of (0.29, 0.38) and (0.32, 0.42), which are close to pure white light (0.33, 0.33), and luminous efficiencies of 97.8 and 93.9 lm·W^-1 and show good stability. The low cost, easy fabrication, controllability, and favorable fluorescence properties signify that CD1 of AIE will have superior performance in a variety of applications.

Organosilane-functionalized carbon quantum dots and their applications to "on-off-on" fluorometric determination of chromate and ascorbic acid, and in white light-emitting devices

Organosilane-functionalized carbon quantum dots (Si-CQDs) were synthesized by reacting glucosamine and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane in acetone. The surface morphology, crystal structure, functional groups, elemental composition, and optical properties of the Si-CQDs were characterized using TEM (HRTEM), XRD, FT-IR, XPS, UV-vis absorption and fluorescence spectroscopy. They show that N-containing groups including C=N and C-N, and Si-containing groups including Si-O-C and Si-O-Si have been formed on the surface of Si-CQDs. The element doping and surface functionalization of Si-CQDs endow their novel chemical, physical and optical properties. The Si-CQDs dispersed in acetone are almost monodisperse with an average particle diameter of 3.6 nm. The Si-CQDs dispersed in acetone display blue fluorescence (excitation/emission maxima of 380/460 nm). In contrast, the solid-state Si-CQDs exhibited yellow fluorescence (with excitation/emission maxima of 470/595 nm). The fluorescence emission spectra of acetone-suspended Si-CQDs are concentration-dependent, and the emission peak becomes red-shifted as the concentration is increased. The Si-CQDs are sensitive and selective fluorescent "on off on" nanoprobes for chromate [Cr(VI)] and ascorbic acid (AA). Fluorescence is quenched by Cr(VI) via an inner filter effect from the absorption of Si-CQDs excitation at 380 nm by Cr(VI). Upon addition of AA, fluorescence is restored because of reduction of Cr(VI) by AA. Under optimal conditions (excitation/emission wavelength of 380/460 nm), the response is linear in the 0.4-160 μM Cr(VI) concentration range, and the detection limit is 34 nM. The respective data for AA are 1-80 μM and 84.6 nM. The practical use of the nanoprobe for Cr(VI) determination in real river water samples is also demonstrated successfully. Their concentration-dependent fluorescence, good thermal stability and self-crosslinking behavior also make the Si-CQDs a candidate material for white light-emitting diodes that displays color conversion and can act as an encapsulation layer in a blue light-emitting diode (LED) chip. Graphical abstract One-pot solvothermal synthesis of organosilane-functionalized carbon quantum dots (Si-CQDs) with blue fluorescence in solution, yellow fluorescence in solid state and concentration-dependent fluorescence property, and their applications for chromate (Cr(VI)) and ascorbic acid dual determinations and white light-emitting device. Graphical Abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have changed the poor quality graphical abstract into the jpg and pdf.

Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Highly active photocatalysts driving chemical reactions are of paramount importance toward renewable energy substitutes and environmental protection. As a fascinating Aurivillius phase material, Bi₂ MoO₆ has been the hotspot in photocatalytic applications due to its visible light absorption, nontoxicity, low cost, and high chemical durability. However, pure Bi₂ MoO₆ suffers from low efficiency in separating photogenerated carriers, small surface area, and poor quantum yield, resulting in low photocatalytic activity. Various strategies, such as morphology control, doping/defect-introduction, metal deposition, semiconductor combination, and surface modification with conjugative π structures, have been systematically explored to improve the photocatalytic activity of Bi₂ MoO₆ . To accelerate further developments of Bi₂ MoO₆ in the field of photocatalysis, this comprehensive Review endeavors to summarize recent research progress for the construction of highly efficient Bi₂ MoO₆ -based photocatalysts. Furthermore, benefiting from the enhanced photocatalytic activity of Bi₂ MoO₆ -based materials, various photocatalytic applications including water splitting, pollutant removal, and disinfection of bacteria, were introduced and critically reviewed. Finally, the current challenges and prospects of Bi₂ MoO₆ are pointed out. This comprehensive Review is expected to consolidate the existing fundamental theories of photocatalysis and pave a novel avenue to rationally design highly efficient Bi₂ MoO₆ -based photocatalysts for environmental pollution control and green energy development.

Nitrogen-doped carbon dots encapsulated in the mesoporous channels of SBA-15 with solid-state fluorescence and excellent stability

A simple and low-cost approach is developed, by which nitrogen-doped carbon dots (NCDs) with a negative potential are assembled inside the mesoporous channels of SBA-15 via capillary force. The unique confined microenvironment leads to a strong interaction between confined NCDs and the inner surface of SBA-15, thus effectively avoiding the aggregation of NCDs. The resultant composite (NCDs-in-SBA-15) exhibits blue fluorescence similar to the NCD aqueous solution, and shows excellent structural, thermal and photostability. Solid NCDs-in-SBA-15 still emits fluorescence even after heat treatment at 400 °C under ambient atmosphere. In addition, NCDs-in-SBA-15 possesses remarkable resistance to acid/alkali solvents. Furthermore, NCDs-in-SBA-15 shows superior selectivity and adsorption capacity to Fe3+. The facile approach and these advantageous performances could make CDs meet the requirements of fluorescent materials in the solid state and then have wider applications.

Photoluminescent functionalized carbon dots for CRISPR delivery: synthesis, optimization and cellular investigation

Gene therapy using clustered regularly interspaced short palindromic repeat plasmids (pCRISPR) reduces mistakes in gene editing and prevents engendering integrational mutagenesis that has been seen in available genome engineering technologies. Developing an ideal and traceable nanocarrier, which can accurately and efficiently transfer this complex into the cytosol and which facilitates the journey towards the nucleus, is a fascinating area of research. Polyethylenimine (PEI) functionalized carbon dots (CD-PEI) were fabricated by one-step microwave assisted pyrolysis with an average size around 3 nm. This CD-PEI showed good potential for intracellular delivery of genetic materials (∼70%). Also, this CD-PEI with passive surface modification with low molecular PEI (2 kDa) has a very high quantum yield, as high as 40% with low cytotoxicity. The expression rate of the pCRISPR was around 15% in the HEK-293 cell which is comparable with the pristine PEI. Furthermore, the CD-PEI demonstrated good properties, such as high quantum yield, biocompatibility and tunable emission wavelengths, suggesting the potential application of photoluminescent functionalized CDs as a suitable, traceable nanocarrier for CRISPR delivery.

Covalently functionalized carbon nanoparticles with a chiral Mn-Salen: a new nanocatalyst for enantioselective epoxidation of alkenes

The first nanocatalyst, obtained via “step-by-step” functionalization of CNPs, for enantioselective epoxidation of non-functionalized alkenes is reported here.

Catalysis with carbon nanoparticles

Carbon nanoparticles represent a new class of nanocatalysts able to catalyze different reactions. This review collects the catalytic applications of these nanoparticles.

Carbon Quantum Dots Encapsulated Molecularly Imprinted Fluorescence Quenching Particles for Sensitive Detection of Zearalenone in Corn Sample

An eco-friendly and efficient one-step approach for the synthesis of carbon quantum dots (CDs) that encapsulated molecularly imprinted fluorescence quenching particles (MIFQP) and their application for the determination of zearalenone (ZEA) in a cereal sample are described in this study. CDs with high luminescence were first synthesized, and then encapsulated in the silica-based matrix through a non-hydrolytic sol-gel process. The resulting ZEA-imprinted particles exhibited not only an excellent specific molecular recognition of ZEA, but also good photostability and obvious template binding-induced fluorescence quenching. Under the optimized conditions, the fluorescence intensity of MIFQP was inversely proportional to the concentration of ZEA. By validation, the detection range of these fluorescence quenching materials for ZEA was between 0.02 and 1.0 mg L-1, and the detection limit was 0.02 mg L-1 (S/N = 3). Finally, the MIFQP sensor was successfully applied for ZEA determination in corn with recoveries from 78% to 105% and the relative standard deviation (RSD %) was lower than 20%, which suggests its potential in actual applications.

Tailored synthesis of polymer-brush-grafted mesoporous silicas with N-halamine and quaternary ammonium groups for antimicrobial applications

Antimicrobial mesoporous materials with polymer brushes on the surface were prepared, and their structure and antimicrobial performance investigated. Poly ((3-acrylamidopropyl) trimethylammonium chloride) (PAPTMAC) modified mesoporous silica was prepared by a polymer-brush-grafted method through treatment with the initiator 4,4'-azobis (4-cyanovaleric acid) (ACVA) and polymerized with (3-acrylamidopropyl) trimethylammonium chloride (APTMAC). A covalent bond was formed between mesoporous silica and N-halamine precursor; N-H bonds were successfully transformed to N-Cl bonds after chlorination. Morphology and structure of mesoporous silica were affected to some extent after modification. The surface area of the polymerized sample decreased, but was sufficient for further applications. Compare to the original sample, antimicrobial properties of the polymerized samples with quaternary ammonium groups (QAS) increased slightly. After exposure to dilute household bleach, the chlorinated samples showed excellent antimicrobial properties against 100% of S. aureus (ATCC 6538) (7.63 log) and E. coli O157:H7 (ATCC 43895) (7.52 log) within 10 min. The prepared mesoporous silicas with effective antimicrobial properties could be very useful for potential application in water filtration.

Carbon quantum dot-based fluorescent vesicles and chiral hydrogels with biosurfactant and biocompatible small molecule

In recent years, it is heartening to witness that carbon quantum dots (CQDs), a rising star in the family of carbon nanomaterials, have displayed tremendous applications in bioimaging, biosensing, drug delivery, optoelectronics, photovoltaics and photocatalysis. However, the investigations toward self-assembly of CQDs are still in their infancy. The participation of CQDs can bring additional functions to supramolecular self-assemblies, with photoluminescent property as the most exciting aspect. Here, we introduce CQDs into two types of classic colloidal systems containing low molecular weight surfactant and gelator to construct fluorescent vesicles and chiral hydrogels. The CQD-based vesicles were constructed through electrostatic interaction between the positively charged CQDs with peripherally substituted imidazolium cations and a negatively-charged biosurfactant, i.e., sodium deoxycholate (NaDC). The chiral hydrogels were prepared by increasing the concentration of NaDC and addition of a tripeptide (glutathione, GSH). It was found that both the hydrogels and corresponding xerogels are highly photoluminescent. A solid sensing system was prepared by coating a uniform layer of the hydrogel onto the silica gel plates by doctor blade technique followed by air-drying, which was then utilized to semiquantitatively detect Cu2+ in aqueous solutions.

Carbon Dots from Sugars and Ascorbic Acid: Role of the Precursors on Morphology, Properties, Toxicity, and Drug Uptake

There is the need for reproducible, simple, high-yielding synthetic protocols aimed at obtaining carbon dots (CDs) with controlled fluorescence, photothermal and photochemical behavior, surface properties, biocompatibility, tumor targeting ability, drug absorption biodistribution, and tumor uptake. This Letter describes a systematic study on the effect of glucose, fructose, and ascorbic acid as starting materials for the preparation of highly luminescent CDs, characterized by a blue emission. Their composition and morphology are investigated by titration of OH surface groups, spectroscopic techniques, and high-resolution transmission electron microscopy (HR-TEM), and their toxicity was tested toward HeLa cells. CDs made using fructose were toxic, while those made from glucose and ascorbic acid showed good biocompatibility. The reproducible and simple synthetic procedure yields luminescent biomass-derived CDs for combined cancer therapy and diagnostics. Their doxorubicin (DOX) drug uptake was measured by spectrofluorimetry, indicating a crucial role of the morphologies of the CDs in controlling DOX loading. The glucose derived CDs showed up to 28% w/w of DOX loading.

Carbon-based hybrid nanogels: a synergistic nanoplatform for combined biosensing, bioimaging, and responsive drug delivery

Nanosized crosslinked polymer networks, named as nanogels, are playing an increasingly important role in a diverse range of applications by virtue of their porous structures, large surface area, good biocompatibility and responsiveness to internal and/or external chemico-physical stimuli. Recently, a variety of carbon nanomaterials, such as carbon quantum dots, graphene/graphene oxide nanosheets, fullerenes, carbon nanotubes, and nanodiamonds, have been embedded into responsive polymer nanogels, in order to integrate the unique electro-optical properties of carbon nanomaterials with the merits of nanogels into a single hybrid nanogel system for improvement of their applications in nanomedicine. A vast number of studies have been pursued to explore the applications of carbon-based hybrid nanogels in biomedical areas for biosensing, bioimaging, and smart drug carriers with combinatorial therapies and/or theranostic ability. New synthetic methods and structures have been developed to prepare carbon-based hybrid nanogels with versatile properties and functions. In this review, we summarize the latest developments and applications and address the future perspectives of these carbon-based hybrid nanogels in the biomedical field.

Modulation of the photoluminescence in carbon dots through surface modification: from mechanism to white light-emitting diodes

Carbon dots (CDs) have emerged as a new type of fluorescent material because of their unique optical advantages, such as high photoluminescence quantum yields (QYs), excellent photo-stability, excitation-dependent emissions, and low toxicity. However, the photoluminescence mechanism for CDs remains unclear, which limits their further practical application. Here, CDs were synthesized via a solvothermal route from citric acid and urea. Through the oxidation and reduction treatment of pristine CDs, the origin of the photoluminescence and the involved mechanism were revealed. We found that the blue/green/red emissions originated from three diverse emitting states, i.e. the intrinsic state, and C=O- and C=N-related surface states, respectively. Based on the as-prepared CDs, a pH sensor depending on the radiometric luminescence detection was developed. Furthermore, we constructed CD/PVP (PVP, polyvinylpyrrolidone) composite films, which exhibited white light emission with photoluminescence QYs of 15.3%. The white light emission with different correlated color temperatures (CCTs), from 4807 K to 3319 K, was obtained by simply changing the amount of PVP solution. Benefiting from the white light-emitting solid-state films, single-component white light-emitting diodes were fabricated with an average color rendering index value (Ra) of 80.0, luminous efficiency of 10.2 lm W^-1, and good working stability, thus indicating a promising potential for practical lighting applications.

Carbon dots with efficient solid-state red-light emission through the step-by-step surface modification towards light-emitting diodes

Carbon dots with efficient solid-state red-light emission through step-by-step surface modification.

Bright, stable, and tunable solid-state luminescence of carbon nanodot organogels

Stable, bright, and tunable solid-state luminescence was achieved in carbon nanodots through engineering photon reabsorption.

Full-Color Emission Polymer Carbon Dots with Quench-Resistant Solid-State Fluorescence

Polymer carbon dots (PCDs) represent a new class of carbon dots (CDs) possessing sub-fluorophores and unique polymer-like structures. However, like small molecule dyes and traditional CDs, PCDs often suffer from self-quenching effect in solid state, limiting their potential applications. Moreover, it is hard to prepare PCDs that have the same chemical structure, exhibiting full-color emission under one fixed excitation wavelength by only modulating the concentration of the PCDs. Herein, self-quenching-resistant solid-state fluorescent polymer carbon dots (SSFPCDs) are prepared, which exhibit strong red SSF without any other additional solid matrices, while having a large production yield (≈89%) and a considerable quantum yield of 8.50%. When dispersed in water or solid matrices in gradient concentrations, they can exhibit yellow, green, and blue fluorescence, realizing the first SSFPCDs with the same chemical structure emitting in full-color range by changing the ratio of SSFPCDs to the solid matrices.