Photoluminescence mechanisms of red-emissive carbon dots derived from non-conjugated molecules

Hemoadhican Fiber Composite with Carbon Dots for Treating Severe Hemorrhage and Infected Wounds

Uncontrolled bleeding and infection following trauma continue to pose significant clinical challenges. This study employs hemoadhican (HD) polysaccharide, known for its superior hemostatic properties, as the foundational material to synthesize antibacterial carbon dots (H-CDs) through a hydrothermal method at various temperatures. The H-CDs exhibiting optimal antimicrobial properties were identified via in vitro antimicrobial characterization. The selected H-CDs possess nanoscale dimensions and a positive surface charge. They contain aldehyde groups and generate reactive oxygen species, which effectively eliminate bacteria. Subsequently, H-CDs were integrated into HD fibers (CDs-HD fibers) using a wet-spinning technique. The water vapor transmission rate, blood contact angle, and in vitro antimicrobial efficacy were evaluated. In a rat model of severe femoral artery hemorrhage and a noncompressible hepatic hemorrhage model, CDs-HD fibers demonstrated superior hemostatic performance compared to the commercially available QuikClot Combat Gauze. Furthermore, in a rat model of mixed bacterial wound infection, CDs-HD fibers significantly enhanced epithelial tissue remodeling and collagen deposition. In vivo studies confirmed the excellent biocompatibility of CDs-HD fibers. These findings suggest that CDs-HD fibers hold promise as a potential dressing for managing severe bleeding and preventing wound infections.

Preventive conservation of paper-based relics with visible light high-transmittance ultraviolet blocking film based on carbon dots

Paper-based relics is an important carrier for recording and preserving information, however, it faces irreversible UV-induced damage, including photocleavage, oxidation, acidification and discoloration, which seriously affects its value and lifespan. Carbon dots (CDs) possess excellent UV absorption and good chemical stability, making them suitable for UV protection. Herein, we propose a high-security and efficient method utilizing CDs films (CDFs) for preventive protection of paper against UV damage. The CDFs with high tunable UV absorbance and minimal absorbance in the visible light range, effectively shield paper from UV radiation while preserving its visual appeal. Moreover, the UV transmittance of the film can be fine-tuned to the content of CDs and can be easily removed from the paper without residue. Artificial accelerated UV aging experiments demonstrate the deceleration of acidification, oxidation, and photocleavage in the protected bamboo paper and Xuan paper. This research paces a new direction for the protection of paper and paper-based relics and artworks with emerging carbon materials, offering customizable protection effects tailored to specific preservation and exhibition requirements. This research pioneers a novel approach to preventive protection of paper and paper-based relics using emerging carbon dots materials, offering tailored protection for diverse preservation needs.

Research on Red/Near-Infrared Fluorescent Carbon Dots Based on Different Carbon Sources and Solvents: Fluorescence Mechanism and Biological Applications

Fluorescent carbon dots, especially red/near-infrared-emitting CDs, are becoming increasingly important in the field of biomedicine. This article reviews the synthesis, fluorescence mechanisms, and biological applications of R/NIR-CDs, emphasizing the importance of carbon source and solvent selection in controlling their optical properties. The formation process of CDs is classified, and the fluorescence mechanisms of CDs are summarized, involving carbon core states, surface states, molecular states, and cross-linking enhanced emission effects. This article also highlights the applications of R/NIR-CDs in bioimaging, biosensing, phototherapy, and drug delivery. The final section discusses challenges and prospects.

Preparation of pH-resistant multicolor thiol fluorescent carbon dot using cysteine and neutral red as precursors and its application in detection and adsorption of apigenin

Conventional carbon dots (CDs) typically exhibit substantial variations in fluorescence intensity across different pH. This limitation underscores the pressing need for advancements in their stability and performance under diverse environmental conditions. Herein, l-cysteine and neutral red are selected as precursors, and three kinds of CDs, which can emit red, orange, and green fluorescent light (assigned as r-CD, o-CD, g-CD, respectively), are synthesized by simply changing the reaction conditions. The pH resistance of r-CD and o-CD in acidic and alkaline environments was demonstrated. A fluorescence detection system for natural flavonoid apigenin was established with r-CD, as r-CD exhibited obviously selective quenching of apigenin, without obvious response to other analogs. The linear range of apigenin detection was divided into low concentration at 2.85-30 μmol L-1 and high concentration at 90-225 μmol L-1, demonstrating excellent anti-interference ability in complex environments. In addition, the molecularly imprinted polymer containing r-CD (r-CD@MIP) was also prepared by surface molecular imprinting technique. The maximum adsorption capacity for apigenin was 28.39 mg g-1, and the adsorption equilibrium reached in 90 min. A complete adsorption-fluorescence detection method of apigenin in actual samples was successfully established by using r-CD and r-CD@MIP. The results demonstrated that the developed CDs and detection methods have promising applications in the field of fluorescence sensing and adsorption.

Formation mechanism of lignin-derived carbon quantum dots: From chemical structures to fluorescent behaviors

Biomass-derived carbon quantum dots (CQDs) have the advantage of being green and low-cost, but their complex structure makes the study of their formation mechanism encounter a bottleneck. Lignin-derived CQDs were prepared by a two-step process of "low-temperature liquid depolymerization" coupled with "hydrothermal reaction" in a mild organic acid system. In the first step of the low-temperature acidolysis process, the lignin polymer first undergoes deethering and depolymerization reactions. During the hydrothermal process in the second step, the organic small molecules on the surface of the supernatant are enriched with reactive groups that are dehydrated, condensed, crosslinked, and carbonized under high temperature and pressure to form CQDs. On the other hand, these activated large sp2 carbon domains in the oxidized solid residue from lignin acidolysis undergo hydrothermal cleavage under high-temperature and high-pressure conditions, followed by deoxygenation and eventual decomposition into small carbon domain CQDs products. Among them, the supernatant component C1 after lignin acidolysis with abundant N-H and C-OH reactive groups is targeted as a key precursor for the formation of lignin-derived CQDs, and the resulting CQDs have both the highest QY (19.5%) and yield (16.5%). This study bridges the research gap on the formation mechanism of biomass-derived CQDs and offers a reference for the sustainable preparation of biomass-derived CQDs.

Interfacial Engineering of Fluorescent Carbon Dots with Metal Oxides for Real-Time Visualization of Oxygen Vacancy Dynamics

Oxygen vacancy (Vo), as one of the most common surface defects, significantly influence the physiochemical properties of metal oxides. However, it remains a challenge for existing techniques to visualize the evolution of Vo during redox process due to its heterogeneous distribution, small size, and dynamic nature. Herein, the real-time monitoring of such microscopic interfacial events is reported by advantage of the high-contrast fluorescence response of carbon dots (H-CDs) to Vo. The green emissive H-CDs possess a unique disc-shaped structure and exceptional hydrophilicity, allowing their tight adhesion to the surfaces of Vo-rich MgO by simple mixing. Subsequently, a water involved interfacial reaction occurred between H-CDs and Vo, resulting in gradual quenching of the original green emission and simultaneously emergence of bright red fluorescence. Moreover, the spatiotemporal diffusion dynamics and reaction kinetics are investigated by confocal laser scanning microscopy, revealing the time-dependent reorganization and structural heterogeneity at the interface. The finding provides a new toolbox for in situ imaging of Vo-triggered phenomena at a microscopic level, which will be helpful in promoting the rational design of oxide materials.

Biomass-derived carbon dots with pharmacological activity for biomedicine: Recent advances and future perspectives

Carbon dots (CDs), a type of nanoparticle with excellent optical properties, good biocompatibility, and small size, are finding increasing application across the fields of biology and biomedicine. In recent years, biomass-derived CDs with pharmacological activity (BP-CDs) derived from herbal medicines (HMs), HMs extracts and other natural products with demonstrated pharmaceutical activity have attracted particular attention. Herein, we review recent advances in the development of BP-CDs, covering the selection of biomass precursors, different methods used for the synthesis of BP-CDs from natural sources, and the purification of BP-CDs. Additionally, we summarize the many remarkable properties of BP-CDs including optical properties, biocompatibility and pharmaceutical efficacy. Moreover, the antibacterial, antiviral, anticancer, biosensing, bioimaging, and other applications of BP-CDs are reviewed. Thereafter, we discuss the advantages and disadvantages of BP-CDs and Western drug-derived CDs, highlighting the excellent performance of BP-CDs. Finally, based on the current state of research on BP-CDs, we suggest several aspects of BP-CDs that urgently need to be addressed and identify directions that should be pursued in the future. This comprehensive review on BP-CDs is expected to guide the precise design, preparation, and future development of BP-CDs, thereby advancing the application of BP-CDs in biomedicine.

Advances in Shell and Core Engineering of Carbonized Polymer Dots for Enhanced Applications

ConspectusCarbon dots (CDs), as a novel type of fluorescent nanocarbon material, attract widespread attention in nanomedicine, optoelectronic devices, and energy conversion/storage due to their excellent optical properties, low toxicity, and high stability. They can be classified as graphene quantum dots, carbon quantum dots, and carbonized polymer dots (CPDs). Among these, CPDs exhibit tunable structures and components that allow fine-tuning of their optoelectronic properties, making them one of the most popular types of CDs in recent years. However, the structural complexity of CPDs stimulates deep exploration of the relationship between their unique structure and luminescent performance. As an organic-inorganic hybrid system, the diversity of self-limited quantum state carbon cores and polymer-hybrid shell layers makes understanding the underlying mechanisms and structure-property relationships in CPDs a very challenging task. In this context, elucidating the structural composition of CPDs and the factors that affect their optical properties is vital if the enormous potential of CPDs is to be realized. Achieving controllable structures with predefined optical properties via the adoption of specific functionalization strategies is the prized goal of current researchers in the field.In this Account, we describe the efforts made by our group in the synthesis, mechanism analysis, structural regulation, and functional applications of CPDs, with particular emphasis on the design of CPDs core-shell structures with tailored optoelectronic properties for applications in the fields of optoelectronics and energy. Specifically, through the rational selection of precursors, optimization of reaction conditions, and postmodification strategies for CPDs, we have demonstrated that it is possible to regulate both the carbon core and polymer shell layers, thereby achieving full-spectrum emission, high quantum yield, persistent luminescence, thermally activated delayed fluorescence, and laser action in CPDs. Furthermore, we have established structure-performance relationship in CPDs and proposed a universal strategy for synergistic interactions between hybrid carbon-based cores and surface micronanostructures. In addition, we unveiled a novel luminescence mechanism in cross-linked CPDs, specifically "cross-linking synergistically inducing quantum-state luminescence", which addresses the challenge of efficient circularly polarized luminescence in the liquid and solid phases of CPDs. Subsequently, strong cross-linking, dual-rigidity, and ordering preparation methods were introduced, thereby pioneering tunable laser emission from blue to near-infrared wavelengths. Additionally, we developed a new strategy of "confined composite nanocrystals of CPDs", leading to various high-performance hydrogen evolution catalysts for water electrolysis. The CPDs developed by this strategy not only possessed excellent optical properties but also enabled high efficiencies in field of energy conversion, thus maximizing the utilization of CPDs. Finally, we discuss important new trends in CPD research and development. Overall, this Account summarizes the latest advancements in CPDs in recent years, providing case-studies that enable deep understanding of structure-property-performance relationships and regulation strategies in CPDs, guiding the future expansion and application of CPDs.

Ru-regulated electronic structure CoNi-MOF nanosheets advance water electrolysis kinetics in alkaline and seawater media

Herein, an ion-exchange strategy is utilized to greatly improve the kinetics of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by Ru-modified CoNi- 1,3,5-Benzenetricarboxylic acid (BTC)-metal organic framework nanosheets (Ru@CoNi-MOF). Due to the higher Ni active sites and lower electron transfer impedance, Ru@CoNi-MOF catalyst requires the overpotential as low as 47 and 279 mV, at a current density of 10 mA/cm2 toward HER and OER, respectively. Significantly, the mass activity of Ru@CoNi-MOF for HER and OER are 25.9 and 10.6 mA mg-1, nearly 15.2 and 8.8 times higher than that of Ni-MOF. In addition, the electrolyzer of Ru@CoNi-MOF demonstrates exceptional electrolytic performance in both KOH and seawater environment, surpasses the commercial Pt/C||IrO2 couple. Theoretical calculations prove that introducing Ru atoms in - CoNi-MOF modulates the electronic structure of Ni, optimizes adsorption energy for H* and reduces energy barrier of metal organic frameworks (MOFs). This modification significantly improves the kinetic rate of the Ru@CoNi-MOF during water splitting. Certainly, this study highlights the utilization of MOF nanosheets as advanced HER/OER electrocatalysts with immense potential, and will paves a way to develop more efficient MOFs for catalytic applications.

Broadband Negative Photoconductive Response in Carbon Nanodots

Due to the broadband response and low selectivity of external light, negative photoconductivity (NPC) effect holds great potential applications in photoelectric devices. Herein, different photoresponsive carbon nanodots (CDs) are prepared from diverse precursors and the broadband response from the NPC CDs are utilized to achieve the optoelectronic logic gates and optical imaging for the first time. In detail, the mcu-CDs which are prepared by the microwave-assisted polymerization of citric acid and urea possess the large specific surface area and abundant hydrophilic groups as sites for the adsorption of H2O molecules and thereby present a high conductivity in dark. Meanwhile, the low affinity of mcu-CDs to H2O molecules permits the light-induced desorption of H2O molecules by heat effect and thus endow the mcu-CDs with a low conductivity under illumination. The easy absorption and desorption of H2O molecules contribute to the extraordinary NPC of mcu-CDs. With the broadband NPC response in CDs, the optoelectronic logic gates and flexible optical imaging system are established, achieving the applications of "NOR" or "NAND" logic operations and high-quality optical images. These findings unveil the unique optoelectronic properties of CDs, and have the potential to advance the applications of CDs in optoelectronic devices.

Efficient Quasi-2D Perovskite Based Blue Light-Emitting Diodes with Carbon Dots Modified Hole Transport Layer

Quasi-2D perovskites based blue light-emitting diodes (LEDs) suffer from its poor electroluminescence performance, mainly caused by the nonradiative recombination in in defect-rich low-n phases and the unbalanced hole-electron injection in the device. Here, we developed a highly efficient quasi-2D perovskite based sky-blue LEDs behaving recorded external quantum efficiency (EQE) of 21.07% by employing carbon dots (CDs) as additives in the hole transport layer (HTL). We ascribe the high EQE to the effective engineering of CDs: (1) The CDs at the interface of HTLs can suppress the formation of low-efficient n = 1 phase, resulting a high luminescence quantum yield and energy transfer efficiency of the mixed n-phase quasi-2D perovskites. (2) The CDs additives can reduce the conductivity of HTL, partially blocking the hole injection, and thus making more balanced hole-electron injection. The CDs-treated devices have excellent Spectral stability and enhanced operational stability and could be a new alternative additive in the perovskite optoelectronic devices.

Tailored Fabrication of Full-Color Ultrastable Room-Temperature Phosphorescence Carbon Dots Composites with Unexpected Thermally Activated Delayed Fluorescence

The development of single-system materials that exhibit both multicolor room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) with tunable after glow colors and channels is challenging. In this study, four metal-free carbon dots (CDs) are developed through structural tailoring, and panchromatic high-brightness RTP is achieved via strong chemical encapsulation in urea. The maximum lifetime and quantum yield reaches 2141 ms and 56.55%, respectively. Moreover, CDs-IV@urea, prepared via coreshell interaction engineering, exhibits a dual afterglow of red RTP and green TADF. The degree of conjugation and functional groups of precursors affects the binding interactions of the nitrogen cladding on CDs, which in turn stabilizes triplet energy levels and affects the energy gap between S1 and T1 (ΔEST) to induce multicolor RTP. The enhanced wrapping interaction lowers the ΔEST, promoting reverse intersystem crossing, which leads to phosphorescence and TADF. This strong coreshell interaction fully stabilizes the triplet state, thus stabilizing the material in water, even in extreme environments such as strong acids and oxidants. These afterglow materials are tested in multicolor, time, and temperature multiencryption as well as in multicolor in vivo bioimaging. Hence, these materials have promising practical applications in information security as well as biomedical diagnosis and treatment.

Si, O-Codoped Carbonized Polymer Dots with High Chemiresistive Gas Sensing Performance at Room Temperature

A new type of carbonized polymer dot was prepared by the one-step hydrothermal method of triethoxylsilane (TEOS) and citric acid (CA). The sensor made from carbonized polymer dots (CPDs) showed superior gas sensing performance toward ammonia at room temperature. The Si, O-codoped CPDs exhibited superior ammonia sensing performance at room temperature, including a low practical limit of detection (pLOD) of 1 ppm (Ra/Rg: 1.10, 1 ppm), short response/recovery time (30/36 s, 1 ppm), high humidity resistance (less than 5% undulation when changing relative humidity to 80 from 30%), high stability (less than 5% initial response undulation after 120 days), reliable repeatability, and high selectivity against other interferential gases. The gas sensing mechanism was investigated through control experiments and in situ FTIR, indicating that Si, O-codoping essentially improves the electron transfer capability of CPDs and synergistically dominates the superior ammonia sensing properties of the CPDs. This work presents a facile strategy for constructing novel high-performance, single-component carbonized polymer dots for gas sensing.

A Theoretical Investigation into the Oligomer Structure of Carbon Dots Formed from Small-Molecule Precursors

In-depth insights into the oligomers of carbon dots (CDs) prepared from small-molecule precursors are important in the study of the carbonization mechanism of CDs and for our knowledge of their complex structure. Herein, citric acid (CA) and ethylenediamine (EDA) were used as small-molecule precursors to prepare CDs in an aqueous solution. The structure of oligomers acquired from CA and EDA in different molar ratios and their formation process were first studied using density functional theory, including the dispersion correction (DFT-D3) method. The results showed that the energy barrier of dimer cyclization was higher than that of its linear polymerization, but the free energy of the cyclized product was much lower than that of its reactant, and IPCA (5-oxo-1,-2,3,5-tetrahydroimidazo [1,2-a]pyridine-7-carboxylic acid) could therefore be obtained under certain conditions. The oligomers obtained from different molar ratios of EDA and CA were molecular clusters formed by short polyamide chains through intermolecular forces; with the exception of when the molar ratio of EDA to CA was 0.5, excessive CA did not undergo an amidation reaction but rather attained molecular clusters directly through intermolecular forces. These oligomers exhibited significant differences in their surface functional groups, which would affect the carbonization process and the surface structure of CDs.

Mass Spectrometry-Based Analyses of Carbon Nanodots: Structural Elucidation

Carbon nanodots (CNDs) are nanomaterials with ubiquitous applications in health for diagnosis and treatments. The key to enhancing the applications of carbon nanodots in various fields lies on how deep its structure is understood. Here, we review the mass spectroscopy (MS) techniques employed for carbon nanodot analysis. We aimed to revive the use of MS to support the structural elucidation of carbon nanodots. General techniques used in nanomaterials characterization include laser desorption/ionization (LDI), matrix-assisted LDI (MALDI), inductively coupled plasma (ICP), and electrospray ionization (ESI) MS. For CNDs characterization, LDI-MS, MALDI-MS, and ESI-MS were employed. The techniques required further instrumentations of time-of-flight (TOF), for MALDI, and TOF, quadrupole (Q), and tandem (MS/MS) for ESI. LDI-MS could be applied to prove the surface and core structural composition of carbon nanodots. Meanwhile, MALDI-MS was used to elucidate the surface structures of CNDs. Finally, ESI-MS could provide significant insight into the carbon nanodots' structural composition and bonding patterns. In summary, MS could be combined with other techniques to unambiguously elucidate the structure of carbon nanodots.

Sleep deprivation boosts O2·- levels in the brains of mice as visualized by a Golgi apparatus-targeted ratiometric fluorescence nanosensor

Sleep deprivation (SD) is highly prevalent in the modern technological world. Emerging evidence shows that sleep deprivation is associated with oxidative stress. At the organelle level, the Golgi apparatus actively participates in the stress response. In this study, to determine whether SD and Golgi apparatus stress are correlated, we rationally designed and fabricated a novel Golgi apparatus-targeted ratiometric nanoprobe called Golgi dots for O2·- detection. This probe exhibits high sensitivity and selectivity in cells and brain slices of sleep-deprived mice. Golgi dots can be readily synthesized by coprecipitation of Golgi-F127, an amphiphilic polymer F127 modified with a Golgi apparatus targeting moiety, caffeic acid (CA), the responsive unit for O2·-, and red emissive carbon nanodots (CDs), which act as the reference signal. The fluorescence emission spectrum of the developed nanoprobe showed an intense peak at 674 nm, accompanied by a shoulder peak at 485 nm. As O2·- was gradually added, the fluorescence at 485 nm continuously increased; in contrast, the emission intensity at 674 nm assigned to the CDs remained constant, resulting in the ratiometric sensing of O2·-. The present ratiometric nanoprobe showed high selectivity for O2·- monitoring due to the specific recognition of O2·- by CA. Moreover, the Golgi dots exhibited good linearity with respect to the O2·- concentration within 5 to 40 μM, and the limit of detection (LOD) was ~ 0.13 μM. Additionally, the Golgi dots showed low cytotoxicity and an ability to target the Golgi apparatus. Inspired by these excellent properties, we then applied the Golgi dots to successfully monitor exogenous and endogenous O2·- levels within the Golgi apparatus. Importantly, with the help of Golgi dots, we determined that SD substantially elevated O2·- levels in the brain.

Facile preparation, optical mechanism elaboration, and bio-imaging application of fluorescent cellulose nanocrystals with tunable emission wavelength

Interfacing cellulose nanocrystals (CNCs) with fluorescent materials provides more possibilities for constructing of sensory/imaging platforms in biomedical applications. In this work, by harnessing the efficient extraction accompanied modification of CNCs and adjustable optical properties of carbon dots (CDs), we report the constructions and emission wavelength tuning of fluorescent CNCs (F-CNCs) composed of CNC nano-scaffolds and CDs. The as-prepared CNCs are densely decorated with citric acid (CA), which plays the role of carbon source for the in-situ synthesis of CDs on CNCs. For the F-CNCs carrying blue, green, and red emissive CDs, ethylenediamine (EDA), urea, and thiourea are the N or N/S sources. Fingerprints of chemical groups, morphological characters, and redox activities are resolved to elaborate the optical mechanisms of CDs with varying emission colors. The emission wavelength is adjusted by either changing the particle size or introducing new emission centers. Both are primarily achieved via precursor engineering. The F-CNCs reveal quantum yields (QYs) >22 % and negligible fluorescence quenching (< 6 %) upon continuous excitation as long as 24 h. Benefited from their cell membrane penetration capability, the F-CNCs with different emission wavelengths were challenged for multiplexed cytoplasm imaging.

Hydrophobic Mn-Doped Solid-State Red-Emitting Carbon Nanodots with AIE Effect and Their Hydrogel Composites for Color-Changing Anticounterfeiting

The aggregation-caused quenching has always limited the high concentration and solid-state applications of carbon nanodots. While the aggregation-induced emission effect, dominated by intramolecular motion, may be an effective means to solve this problem. Here, hydrophobic solid-state red-light carbon nanodots (M-CDs) with 95% yield are synthesized by a one-step hydrothermal method using 2,2'-dithiodibenzoic acid as the carbon source and manganese acetate as the dopant source. The disulfide bond of 2,2'-dithiodibenzoic acid serves as the symmetry center of molecular rotation and Mn catalyzes the synthesis of M-CDs, which promotes the formation of the central graphitic carbon structure. The M-CDs/agar hydrogel composites can achieve fluorescence transition behavior because of the special fluorescence transition properties of M-CDs. When this composite hydrogel is placed in water, water molecules contact with M-CDs through the network structure of the hydrogels, making the aggregated hydrogels of M-CDs fluorescence orange-red under 365 nm excitation. While in dimethyl sulfoxide, water molecules in the hydrogels network are replaced and the M-CDs fluoresce blue when dispersed, providing a potential application in information encryption. In addition, high-performance monochromatic light-emitting diode (LED) devices are prepared by compounding M-CDs with epoxy resin and coating them on 365 nm LED chips.

Carbon Quantum Dots for Long-Term Protection against UV Degradation and Acidification in Paper-Based Relics

Paper-based cultural relics constitute a significant and invaluable part of human civilization and cultural heritage. However, they are highly vulnerable to environmental factors such as ultraviolet (UV) photodegradation and acidification degradation, posing substantial threats to their long-term preservation. Carbon quantum dots (CQDs), known for their outstanding optical properties, high water solubility, and good safety, offer a promising solution for slowing down UV damage and acidification of paper-based relics during storage and transportation. Herein, we propose a feasible strategy for the simple preparation of CQDs with high dispersion stability, excellent UV absorption, room-temperature phosphorescence, and photostability for the safety protection of paper. Accelerated aging experiments were conducted using UV and dry-heat aging methods on both CQD-protected paper and unprotected paper, respectively, to evaluate the effectiveness of CQD protection. The results demonstrate a slowdown in both the oxidation and acid degradation processes of the protected paper under both UV-aging and dry-heat aging conditions. Notably, CQDs with complex luminescence patterns of both fluorescence and room-temperature phosphorescence also endue them as enhanced optical anticounterfeiting materials for multifunctional paper protection. This research provides a new direction for the protection of paper-based relics with emerging carbon nanomaterials.

Photostable yellow emissive carbon dots for iron-mediated reversible sensing of biothiols and cellular imaging

The different levels of biothiols in cells can not only screen cancer cells but also play a selective role in killing cancer cells. Therefore, accurate monitoring of biothiol in cancer cells is of great research significance. Herein, novel yellow emission CDs (Y-CDs) were prepared by a simple hydrothermal method using 2, 5-dihydroxyterephthalic acid (DHTA) as precursors. The Y-CDs as a highly efficient dual-mode sensor could detect Fe3+ and biothiols by colorimetric and fluorescence signals. Especially, with the addition of L-Cysteine, the quenched fluorescence could be quickly restored within 2 min and the detection limit was as low as 31.65 nM. Additionally, this sensor was utilized to sense biothiols in actual samples and living cells due to its eminent biocompatibility. Finally, the Y-CDs were successfully applied not only as fluorescent ink for message encryption but also as a portable solid hydrogels sensor for the detection of Fe3+ and biothiols. Therefore, these results suggested that Y-CDs could serve as a promising sensor for Fe3+ and biothiol detection in early cancer screening.

Red-Emissive Center Formation within Carbon Dots Based on Citric Acid and Formamide

The formation of red-emissive optical centers in carbon dots based on citric acid and formamide was investigated by varying the synthesis parameters with focus on finding optimal─necessary and sufficient─amount of precursors to decrease byproduct amount and to increase the chemical yield of red-emissive carbon dots. The emission is observed at 640 nm excited at 590 nm and quantum yield reaches up 19%. A high chemical yield of carbon dots of 26% was achieved at an optimal molar ratio of citric acid to formamide of 1:4.

Bandgap tailoring and enhancing the aromatization in cysteine-based carbon dots

Cysteine, as a non-aromatic precursor, was used to produce Nitrogen (N) and Sulfur (S) sources for preparing N, S-doped carbon dots (CDs) with tunable luminescence emission. Despite the tremendous investigations, the photoluminescence (PL) mechanism of CDs is still unclear due to its complex core-shell structure, variety of surface functional groups, and structure dependency. This study focuses on controlling aromatization and graphitization processes during the hydrothermal synthesis on CDs by using Citric Acid (CA) and Ammonium persulfate. Detailed characterizations by FTIR spectroscopy, XPS, and HR-TEM are provided to suggest both chemical and bandgap structures. Results reveal that the red-shift of PL occurred due to the graphitization and increasing content of graphitic nitrogen in the core, as well as the Pyridinic and Amine groups creating sub-bands on the surface. These findings resolve the controversy on the PL mechanism of Cysteine-based CDs and provide a general guide for increasing the aromatization and graphitization degree from non-aromatic precursors which clarify the mechanism exploration and structural analysis of other types of CDs.

Surface Modification Functionalized Carbon Dots

Carbon dots (CDs) smaller than 10 nm constitute a new type of fluorescent carbon-based nanomaterial. They have attracted much attention owing to their unique structures and excellent photoelectric properties. Primitive CDs usually comprise carbon and oxygen and are synthesized in one step from various natural products or synthetic organic compounds, usually via microwave or hydrothermal methods. However, the uniformity of surface functional groups often make CDs lack the diversity of active sites required for specific applications. Therefore, the functionalization of CDs by specific groups is a powerful strategy for improving their photophysical and photochemical properties. This paper reviews surface modification strategies to overcome these shortcomings. Functionalizing CDs using covalent or non-covalent modification can give them unique properties and broaden their applicability.

Molecular Engineering of Highly Fluorinated Carbon Dots: Tailoring Li+ Dynamics and Interfacial Fluorination for Stable Solid Lithium Batteries

Fluorinated carbon dots (FCDs) have garnered interest owing to their distinct physicochemical properties. Nevertheless, intricate synthesis procedures and quite low fluorine doping levels limit its development and application. Herein, we propose a facile approach based on the Claisen-Schmidt reaction to realize gram-scale synthesis of highly fluorinated carbon dots (up to 20.79 at. %) at room temperature and atmospheric pressure, and a comprehensive exploration of the specific reaction mechanism is conducted. Furthermore, in consideration of the high fluorine content, good dispersibility, and compatibility with polymer electrolyte, the synthesized FCDs are utilized as an additive for PEO-based solid electrolytes of a Li battery to improve its ionic conductivity, interface stability, and mechanical properties. The introduction of FCDs can not only reduce the crystallinity of PEO and enhance the interaction of polymer chains, but also facilitate the establishment of uninterrupted pathways and in situ fluorination at the interface, which is substantiated by both theoretical calculations and experimental findings. As a result, the lithium symmetrical battery can operate stably for 1000 h at a current density of 0.4 mA cm-2. Simultaneously, the LiFePO4/Li battery utilizing the composite electrolyte exhibits a capacity of 130.3 mAh g-1 over 300 cycles while maintaining a capacity retention rate of 95.10%. This study develops a strategy for synthesizing highly fluorinated carbon dots, which demonstrate a useful influence on PEO electrolytes, thus boosting the advancement of FCDs and solid-state batteries.

Dye-Derived Red-Emitting Carbon Dots for Lasing and Solid-State Lighting

Carbon dots are carbon-based nanoparticles renowned for their intense light-emitting capabilities covering the whole visible light range. Achieving carbon dots emitting in the red region with high efficiency is extremely relevant due to their huge potential in biological applications and in optoelectronics. Currently, photoluminescence in such an energy interval is often associated with polyheterocyclic molecular domains forming during the synthesis that, however, present low emission efficiency and issues in controlling the optical features. Here, we overcome these problems by solvothermally synthesizing carbon dots starting from Neutral Red, a common red-emitting dye, as a molecular precursor. As a result of the synthesis, such molecular fluorophore is incorporated into a carbonaceous core while retaining its original optical properties. The obtained nanoparticles are highly luminescent in the red region, with a quantum yield comparable to that of the starting dye. Most importantly, the nanoparticle carbogenic matrix protects the Neutral Red molecules from photobleaching under ultraviolet excitation while preventing aggregation-induced quenching, thus allowing solid-state emission. These advantages have been exploited to develop a fluorescence-based color conversion layer by fabricating polymer-based highly concentrated solid-state carbon dot nanocomposites. Finally, the dye-based carbon dots demonstrate both stable Fabry-Perot lasing and efficient random lasing emission in the red region.

Carbon dots from alcohol molecules: principles and the reaction mechanism

Carbon dots (CDs) have attracted significant attention in the energy, environment, and biology fields due to their exceptional physicochemical properties. However, owing to the multifarious precursors and complex reaction mechanisms, the production of carbon dots from organic molecules is still a mysterious process. Inspired by the color change of sodium hydroxide ethanol solution after standing for some time, in this work, we thoroughly investigated the reaction mechanism from alcohol molecules to carbon dots through a lot of experiments and theoretical calculations, and it was found that the rate-controlling reaction is the formation of aldehydes, and it is also confirmed that there is a self-catalysis reaction, which can accelerate the conversion from alcohol to aldehyde, further facilitating the final formation of CDs. After the rate-controlling reaction of alcohol to aldehyde, under strongly alkaline conditions, an aldol reaction occurs to form unsaturated aldehydes, followed by further condensation and polymerization reactions to form long carbon chains, which are cross-linked and dehydrated to form carbon dots with a carbon core and surface functional groups. Additionally, it is found that the reaction can be largely accelerated with the assistance of electricity, which indicates the great prospect of industrial production. Furthermore, the obtained CDs with rich functional groups can be utilized as electrolyte additives to optimize the deposition behavior of Na metal, manifesting great potential towards safe and stable Na metal batteries.

Fabrication of Zwitterionic Polymer-Functionalized Onion-like Carbon Nanoparticles as Aqueous Lubricant Additives

Onion-like carbon (OLC) is a kind of carbon material with a graphene-like structure and large interlayer spacing, favorable to a good lubricating performance. Herein, a facile method is presented for the preparation of functionalized OLC nanoparticles from candle soot with surface modification. The OLC nanoparticles are collected from combustion soot with candle burning via a simple heat treatment, and then the zwitterionic polymer (polyethylenimine-quaternized derivative, PEIS) can self-assemble onto the OLC surface with epigallocatechin gallate via Michael addition and Schiff-base reaction, thus obtaining PEIS-functionalized OLC nanoparticles (PEIS@OLC). The grafting zwitterionic polymer PEIS endows the OLC nanoparticles with good hydrophilic performance, so the as-obtained PEIS@OLC exhibits outstanding dispersion and lubricating property as a water-based lubricant additive. Compared to pure water, the average coefficient of friction decreases to 0.110 from 0.512, and the corresponding wear volume is reduced by 61.02% with 1.5 wt % addition. The improved lubricating property is mainly due to the synergetic effect of the protective film induced by the tribochemical reaction and the hydration film of zwitterionic polymer PEIS. Besides, the OLC nanoparticles could also display the nanoscale rolling and repairing effects at the friction contact interface, resulting in reduction of friction and wear.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

The Preparation of Golgi Apparatus-Targeted Polymer Dots Encapsulated with Carbon Nanodots of Bright Near-Infrared Fluorescence for Long-Term Bioimaging

As a vital organelle in eukaryotic cells, the Golgi apparatus is responsible for processing and transporting proteins in cells. Precisely monitoring the status of the Golgi apparatus with targeted fluorescence imaging technology is of enormous importance but remains a dramatically challenging task. In this study, we demonstrate the construction of the first Golgi apparatus-targeted near-infrared (NIR) fluorescent nanoprobe, termed Golgi-Pdots. As a starting point of our investigation, hydrophobic carbon nanodots (CNDs) with bright NIR fluorescence at 674 nm (fluorescence quantum yield: 12.18%), a narrow emission band of 23 nm, and excellent stability were easily prepared from Magnolia Denudata flowers using an ultrasonic method. Incorporating the CNDs into a polymer matrix modified with Golgi-targeting molecules allowed for the production of the water-soluble Golgi-Pdots, which showed high colloidal stability and similar optical properties compared with pristine CNDs. Further studies revealed that the Golgi-Pdots showed good biocompatibility and Golgi apparatus-targeting capability. Based on these fascinating merits, utilizing Golgi-Pdots for the long-term tracking of the Golgi apparatus inside live cells was immensely successful.

A double rare earth doped CD nanoplatform for nanocatalytic/starving-like synergistic therapy with GSH-depletion and enhanced reactive oxygen species generation

Cancer has been one of the principal diseases threatening human health in the world. Traditional chemotherapy, radiotherapy and surgery in clinical applications have some disadvantages, such as inefficiency, low specificity, and serious side effects. Therefore, some emerging synergistic therapies have been developed for more accurate diagnosis and more efficient treatment of cancer. Herein, novel Ce-Gd@CDs-GOx nanozymes were obtained by combining magnetic resonance/fluorescence (MR/FL) imaging and nanocatalytic/starving-like synergistic therapy for tumor tissue imaging and efficient cancer treatment. The as-prepared Ce-Gd@CDs-GOx nanozymes with a diameter of 25.0 ± 0.8 nm exhibited favorable physiological stability, negligible toxicity, bright fluorescence and strong T1-weighted MR imaging (MRI) performance (10.97 mM-1 s-1). Moreover, the nanozymes could not only cut off the nutrient supply of tumor cells, but also generate ROS to synergistically enhance antitumor efficacy. The coexistence of Ce3+/Ce4+ in Ce-Gd@CDs-GOx endowed them with attractive capacity for alleviating hypoxia and enhancing GSH consumption to induce the apoptosis of tumor cells. Furthermore, most of the 4T1 cells treated with Ce-Gd@CDs-GOx nanozymes were damaged in the CCK-8 and Calcein-AM/PI staining assays, indicating the excellent efficiency of intracellular synergistic therapy. In summary, this study offered a promising strategy to design a nanoplatform for MR/FL imaging-guided nanocatalytic and starvation-like synergistic therapy of cancer.

Colorful Triplet Excitons in Carbon Nanodots for Time Delay Lighting

Time delay lighting offers an added period of buffer illumination for human eyes upon switching off the light. Long-lifetime emission from triplet excitons has outstanding potential, but the forbidden transition property due to the Pauli exclusion principle makes them dark, and it stays challenging to develop full-color and bright triplet excitons. Herein, triplet excitons emission from ultraviolet (UV) to near infrared (NIR) in carbon nanodots (CNDs) is achieved by confining multicolor CNDs emitters in NaCNO crystal. NaCNO crystal can isolate the CNDs, triplet excitons quenching caused by the excited state electrons aggregation induced energy transfer is suppressed, and the confinement crystal can furthermore promote phosphorescence of the CNDs by inhibiting the dissipation of the triplet excitons due to non-radiative transition. The phosphorescence from radiative recombination of triplet excitons in the CNDs covers the spectral region from 300 nm (UV) to 800 nm (NIR), the corresponding lifetimes can reach 15.8, 818.0, 239.7, 168.4, 426.4, and 127.6 ms. Furthermore, the eco-friendly luminescent lampshades are designed based on the multicolor phosphorescent CNDs, time delay light-emitting diodes are thus demonstrated. The findings will motivate new opportunities for the development of UV to NIR phosphorescent CNDs and time delay lighting applications.

Flammulina velutipes-derived carbon dots for fluorescence detection and imaging of hydroxyl radical

Monitoring hydroxyl radical (•OH) fluctuation is of great importance to study some relative pathological processes and to predict early diagnosis of diseases. Efficient •OH-responsive fluorescent sensors based on carbon dots (CDs) have been reported, but most researches have focused on the new strategies for the synthesis and doping of the CDs. Herein, a kind of biomass CDs (F-CDs) with Flammulina velutipes (F. velutipes) as the carbon source was prepared by a one-step hydrothermal method without any additional modification. The prepared F-CDs have remarkable sensitivity and selectivity and there is a good linear relationship from 0 to 12 μM with a low detection limit of 95 nM for quantitative •OH assay. With excitation-independent emission, favourable biocompatibility and low toxicity, the F-CDs can penetrate cell membranes as •OH-responsive fluorescent sensors to detect intracellular •OH in A549 cells stimulated by phorbol 12-myristate 13-acetate (PMA) and successfully monitor the •OH concentration levels by the corresponding fluorescence change. Given the combined benefits of the green and eco-friendly approach, the F-CDs show promise as novel theranostics tools for early detection and treatment of related diseases.

Carbon Dots: Classically Defined versus Organic Hybrids on Shared Properties, Divergences, and Myths

Carbon dots are defined as small carbon nanoparticles with effective surface passivation via organic functionalization. The definition is literally a description of what carbon dots are originally found for the functionalized carbon nanoparticles displaying bright and colorful fluorescence emissions, mirroring those from similarly functionalized defects in carbon nanotubes. In literature more popular than classical carbon dots are the diverse variety of dot samples from "one-pot" carbonization of organic precursors. On the two different kinds of samples from the different synthetic approaches, namely, the classical carbon dots versus those from the carbonization method, highlighted in this article are their shared properties and apparent divergences, including also explorations of the relevant sample structural and mechanistic origins for the shared properties and divergences. Echoing the growing evidence and concerns in the carbon dots research community on the major presence of organic molecular dyes/chromophores in carbonization produced dot samples, demonstrated and discussed in this article are some representative cases of dominating spectroscopic interferences due to the organic dye contamination that have led to unfound claims and erroneous conclusions. Mitigation strategies to address the contamination issues, including especially the use of more vigorous processing conditions in the carbonization synthesis, are proposed and justified.

Polyoxometalate functionalizing CeO2 hollow nanospheres as enhanced oxidase mimics for ascorbic acid colorimetric sensing

Phosphotungstic acid covered with CeO₂ hollow nanospheres (CeO₂@PTA HNSs) has been successfully prepared by a simple method, serving as highly efficient nanozymes for ascorbic acid (AA) colorimetric sensing. In virtue of the unique hollow nanostructures, oxide defects and synergic effects of CeO₂ and PTA, the proposed CeO₂@PTA HNSs present remarkable intrinsic oxidase-like activity and help capture electrons from 3,3',5,5'-tetramethylbenzidine (TMB). Due to the reducibility of AA, a promising colorimetric sensing platform based on CeO₂@PTA HNSs has been constructed for quantitative analysis of AA. The present colorimetric detection exhibits a low limit of detection, good selectivity and stability, as well as reliability in orange juice and milk. This work provides a simple surface defect engineering to prepare high-performance oxidase mimics in the application of colorimetric biosensing.

Organic disulfide-modified folate carbon dots for tumor-targeted synergistic chemodynamic/photodynamic therapy

Carbon dots (CDs) have great potential for cancer diagnosis and treatment. Photodynamic therapy and chemodynamic therapy are promising treatments mediated by reactive oxygen species (ROS), which have the advantages of being minimally invasive, having no multi-drug resistance, and having no systemic toxic side effects. However, the tumor microenvironment (TME) and poor targetability often reduce the therapeutic effect. In this work, we have successfully prepared folate-based carbon dots (FCP-CDs) from folic acid (FA), citric acid (CA), and polyethyleneimine (PEI) for tumor-targeting. The surface of FCP-CDs was modified using organic disulfide, 3,3'-dithiodipropionic acid (DTPA), and a photosensitizer (PS) pyropheophorbide-a (PPa) to form a tumor microenvironment-responsive nanoplatform, FCP-CDs@DTPA@PPa (named FCPPD), for synergistic cancer therapy. The results showed that FCPPD effectively preserved the tumor target specificity of folic acid and the photodynamic therapeutic (PDT) activity of PPa, and could provide additional chemodynamic therapeutic (CDT) function by reacting with hydrogen peroxide (H₂O₂) to generate ˙OH. The introduction of DTPA, which contains disulfide bonds, endows FCPPD with an excellent ability to deplete glutathione (GSH) in tumors via intracellular redox reactions, amplifying intracellular oxidative strain and enhancing ROS-based therapeutic effects. Systematic in vitro and in vivo studies under various conditions have shown that the obtained FCPPD nanoparticles have good biocompatibility and could be a promising therapeutic agent for imaging-guided PDT/CDT combination therapy.

Hydrothermally Derived Green Carbon Dots from Broccoli Water Extracts: Decreased Toxicity, Enhanced Free-Radical Scavenging, and Anti-Inflammatory Performance

Biomass carbon dots (CDs) derived from natural plants possess the advantages of low cost, photostability, and excellent biocompatibility, with potential applications in chemical sensing, bioimaging, and nanomedicine. However, the development of biomass CDs with excellent antioxidant activity and good biocompatibility is still a challenge. Herein, we propose a hypothesis for enhancing the antioxidant capacity of biomass CDs based on precursor optimization, extraction solvent, and other conditions with broccoli as the biomass. Compared to broccoli water extracts, broccoli powders, and broccoli organic solvent extracts, CDs derived from broccoli water extracts (BWE-CDs) have outstanding antioxidant properties due to the abundant C═C, carbonyl, and amino groups on their surface. After optimization of the preparation condition, the obtained BWE-CDs exhibit excellent free-radical scavenging activity with an EC₅₀ of 68.2 μg/mL for DPPH^• and 22.4 μg/mL for ABTS^•+. Cytotoxicity and zebrafish embryotoxicity results indicated that BWE-CDs have lower cytotoxicity and better biocompatibility than that of CDs derived from organic solvents. In addition, BWE-CDs effectively scavenged reactive oxygen species (ROS) in A549 cells, 293T cells, and zebrafish, as well as eliminating inflammation in LPS-stimulated zebrafish. Mechanistic studies showed that the anti-inflammatory effect of BWE-CDs was dependent on the direct reaction of CDs with free radicals, the regulation of NO levels, and the upregulation of the expression of SOD and GPX-4. This work indicates that the antioxidant activity of CDs could be enhanced by using solvent extracts of biomass as precursors, and the obtained BWE-CDs exhibit characteristics of greenness, low toxicity, and excellent antioxidant and anti-inflammatory activities, which suggests the potential promising application of BWE-CDs as an antioxidant nanomedicine for inflammatory therapy.

Multiple Stimuli-Response Polychromatic Carbon Dots for Advanced Information Encryption and Safety

Optical information encryption and safety have aroused great attention since they are closely correlated to data protection and information safety. The development of multiple stimuli-response optical materials for constructing large-capacity information encryption and safety is very important for practical applications. Carbon dots (CDs) have many gratifying merits, such as polychromatic emission, diverse luminous categories, and stable physicochemical properties, and are considered as one of the most ideal candidates for information protection. Herein, carbon core, functional groups, solvents, and other crucial factors are reviewed for outputting polychromatic emission of multiple luminous categories. In particular, substrate engineering strategies have been emphasized for their critical role in yielding excellent optical features of multiple luminous categories. High-capacity information encryption and safety strategies are reviewed by relying on the rich optical properties of CDs, such as polychromatic emission, multiple luminous categories of fluorescence, afterglow, and upconversion, as well as external-stimuli-assisted optical changes. Some perspectives for preparing excellent CDs and further developing information security strategies are proposed. This review provides a good reference for the manipulation of polychromatic CDs and the development of next-generation information encryption and safety.

In Vivo and In Vitro Biodistribution of Inulin-Tethered Boron-Doped Amine-Functionalized Carbon Dots

Carbon dots (CDs) are considered a potential substance for use in biomarker applications due to their exceptional light stability. However, there are several unsolved uncertainties about CD toxicity in vitro and in vivo. In this study, a redesigned derivative of the natural polysaccharide inulin is connected with boron-doped amine-functionalized carbon dots (In@BN-CDs) through carbodiimide coupling to improve the biocompatibility of the nanoformulation. The toxicity and biodistribution of ln@BN-CDs in vivo and in vitro were explored in detail. The In@BN-CDs were tested after a single inhalation dosage of 10, 7, 5, 3, and 1 mg/kg. We explored a dose- and time-dependent technique of collecting blood samples and then centrifuged the blood samples and obtained serum samples, which were then analyzed for fluorescence inspection; findings showed that the fluorescence intensity decreased with time. Similarly, In@BN-CDs were effectively used as in vitro toxicity and fluorescent probes for cellular imaging in living cells due to their biocompatibility and cell membrane accessibility. The biocompatibility and efficacy of In@BN-CDs as fluorescent imaging agents have been demonstrated. The data suggest that the usage of In@BN-CDs in vitro and in vivo should be examined.

Investigation into Red Emission and Its Applications: Solvatochromic N-Doped Red Emissive Carbon Dots with Solvent Polarity Sensing and Solid-State Fluorescent Nanocomposite Thin Films

In this work, a NIR emitting dye, p-toluenesulfonate (IR-813) was explored as a model precursor to develop red emissive carbon dots (813-CD) with solvatochromic behavior with a red-shift observed with increasing solvent polarity. The 813-CDs produced had emission peaks at 610 and 698 nm, respectively, in water with blue shifts of emission as solvent polarity decreased. Subsequently, 813-CD was synthesized with increasing nitrogen content with polyethyleneimine (PEI) to elucidate the change in band gap energy. With increased nitrogen content, the CDs produced emissions as far as 776 nm. Additionally, a CD nanocomposite polyvinylpyrrolidone (PVP) film was synthesized to assess the phenomenon of solid-state fluorescence. Furthermore, the CDs were found to have electrochemical properties to be used as an additive doping agent for PVP film coatings.

A comprehensive model of nitrogen-free ordered carbon quantum dots

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.

Achieving High-Efficiency Large-Area Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) are semitransparent windows that are able to generate electricity from sunlight absorption. LSCs have shown huge promise for realizing building-integrated photovoltaics (BIPV). Unfortunately, to date, the power conversion efficiency (PCE) of LSCs is still very low which dramatically hampers their practical applications. In this Perspective, We summarize and review the latest developments of LSCs by looking at different structures. Among others, we focus more on the next developments in the field of LSCs, i.e., the possibility of high PCE, large area, mass production, and durability needed for future industrial development. We hope to promote the application of uniform testing standards and to draw attention to industrial development, toxicity, and durability. Then, we will provide a critical assessment of the field of LSCs. Finally, the challenge and solution will be discussed.

One-Pot Synthesis of Dual Color-Emitting CDs: Numerical and Experimental Optimization towards White LEDs

Carbon Dots (CDs) are fluorescent carbon-based nanoparticles that have attracted increasing attention in recent years as environment-friendly and cost-effective fluorophores. An application that can benefit from CDs in a relatively short-term perspective is the fabrication of color-converting materials in phosphor-converted white LEDs (WLEDs). In this work we present a one-pot solvothermal synthesis of polymer-passivated CDs that show a dual emission band (in the green and in the red regions) upon blue light excitation. A purposely designed numerical approach enables evaluating how the spectroscopic properties of such CDs can be profitable for application in WLEDs emulating daylight characteristics. Subsequently, we fabricate nanocomposite coatings based on the dual color-emitting CDs via solution-based strategies, and we compare their color-converting properties with those of the simulated ones to finally accomplish white light emission. The combined numerical and experimental approach can find a general use to reduce the number of experimental trial-and-error steps required for optimization of CD optical properties for lighting application.

Ethanol Solution Plasma Loads Carbon Dots onto 2D HNb3O8 for Enhanced Photocatalysis

Layered metal oxoacids hold potential as photocatalysts due to their facile exfoliation to two-dimensional (2D) nanosheets with a large surface area and a short migration distance for photoexcited charge carriers. However, the utilization of electrons in photocatalytic processes is restricted by the competitive trapping of electrons by metal ions. In this work, we attempt to improve the utilization of photogenerated electrons over exfoliated HNb₃O₈ nanosheets by solution plasma activation. On dispersing exfoliated HNb₃O₈ nanosheets in ethanol solution plasma, the defects in HNb₃O₈ can be engineered, and carbon dots (CDs) can be anchored on the surface of HNb₃O₈ nanosheets in situ. In comparison with pristine HNb₃O₈ nanosheets, the rate of photocatalytic hydrogen evolution can be increased by 317.7 times over the HNb₃O₈/C heterojunction, and the apparent quantum efficiency of hydrogen production can be as high as 5.05%. The reason for the high photocatalytic performance is explored by the comparison of activation between plasma-in-ethanol and plasma-in-water, which reveals that CD anchoring and defect engineering indeed promote charge separation and hence lead to enhanced photocatalytic activity. This work provides an alternative approach to synthesize CDs and activate 2D-layered compounds with MO₆ (M = Nb, Ti, and W) octahedral building blocks in the host layer for enhanced photocatalytic evolution of hydrogen.