Optical Properties Of Carbon Dots Research Articles

Optical Properties of Carbon Dots Synthesized by the Hydrothermal Method.

In this study, the optical and structural properties of carbon dots (CDs) synthesized using a hydrothermal method were investigated. CDs were prepared from various precursors such as citric acid (CA), glucose, and birch bark soot. The SEM and AFM results show that the CDs are disc-shaped nanoparticles with dimensions of ~7 nm × 2 nm for CDs from CA, ~11 nm × 4 nm for CDs from glucose, and ~16 nm × 6 nm for CDs from soot. The TEM images of CDs from CA showed stripes with a distance of 0.34 nm between them. We assumed that the CDs synthesized from CA and glucose consisted of graphene nanoplates located perpendicular to the disc plane. The synthesized CDs contain oxygen (hydroxyl, carboxyl, carbonyl) and nitrogen (amino, nitro) functional groups. CDs have strong absorption in the ultraviolet region in the range of 200-300 nm. All CDs synthesized from different precursors displayed bright luminescence in the blue-green region of the spectrum (420-565 nm). We found that the luminescence of CDs depended on the synthesis time and type of precursors. The results show that the radiative transitions of electrons occur from two levels with energies ~3.0 eV and ~2.6 eV, which are due to the presence of functional groups.

Carbon dots preserve strong blue emission in both aqueous and solid states and their application in intracellular temperature sensing and white light-emitting diodes

The emission of carbon dots is usually quenched in the solid state, thus limiting their application. Herein, we reported the structure and optical properties of carbon dots that preserve intense blue emission in both aqueous and solid states. Structural analysis indicates the obtained carbon dots are largely functionalized by sodium ion (Na+), which could keep the carbon core from direct contact and inhibit the fluorescence resonance energy transfer, leading the carbon dots still emit even after drying to solid powder. Moreover, in addition to the emission intensity, the luminescence lifetime of the aqueous carbon dots responds linearly to temperature in the physiological temperature range from 20 to 70 °C, and is stable at different pH and salinity environments, making them promising optical nanothermometers for probing intracellular temperature via dual mode (emission intensity/lifetime). The applicability of the aqueous carbon dots for intracellular temperature sensing has been demonstrated in living cell studies, while that for the solid carbon dots has been demonstrated by constructing a prototype white LEDs with high color rendering index of 95.

Exploring the Impact of Nitrogen Doping on the Optical Properties of Carbon Dots Synthesized from Citric Acid.

The differences between bare carbon dots (CDs) and nitrogen-doped CDs synthesized from citric acid as a precursor are investigated, aiming at understanding the mechanisms of emission and the role of the doping atoms in shaping the optical properties. Despite their appealing emissive features, the origin of the peculiar excitation-dependent luminescence in doped CDs is still debated and intensively being examined. This study focuses on the identification of intrinsic and extrinsic emissive centers by using a multi-technique experimental approach and computational chemistry simulations. As compared to bare CDs, nitrogen doping causes the decrease in the relative content of O-containing functional groups and the formation of both N-related molecular and surface centers that enhance the quantum yield of the material. The optical analysis suggests that the main emission in undoped nanoparticles comes from low-efficient blue centers bonded to the carbogenic core, eventually with surface-attached carbonyl groups, the contribution in the green range being possibly related to larger aromatic domains. On the other hand, the emission features of N-doped CDs are mainly due to the presence of N-related molecules, with the computed absorption transitions calling for imidic rings fused to the carbogenic core as the potential structures for the emission in the green range.

IMPROVING CARBON DOTS OPTICAL PROPERTIES OF MOLASSES USING EDTA AS A PASSIVATION AGENT WITH THE MICROWAVE METHOD

Synthesis of carbon dots from molasses using the microwave method with the addition of EDTA as a passivation agent has been carried out. Addition of EDTA to improve the optical properties of the carbon dots. The resulting carbon dots were characterized by UV, UV-Visible, PL, FTIR, and TEM lamps. A physical test of carbon dots under a UV lamp showed a change in light intensity, carbon dots with the addition of a passivation agent were brighter than those without a passivation agent. Analysis of the optical properties of carbon dots using UV-Vis spectrophotometer and photoluminescence showed a significant increase in absorbance intensity and emission intensity from 500 a.u to 3600 a.u. FTIR analysis shows the formation of carbon dots which are indicated by the presence of C=C, O-H, C-H, C-O-C, and C-N groups at certain wavenumbers. TEM analysis showed that the carbon dots produced had an average diameter of 1.8 nm. From the analysis, it is identified that the addition of EDTA can improve carbon dots’ optical properties.

Modulating the optical properties of carbon dots by peptide condensates.

Here, we utilized designed condensates formed by liquid-liquid phase separation (LLPS) of cationic and aromatic peptide to sequester tyrosine-based carbon dots (C-dots). The C-dots fluorescence is quenched and retrieved upon partitioning and release from condensates, allowing a spatial regulation of C-dots fluorescence which can be utilized for biosensing applications.

Predictable incorporation of nitrogen into carbon dots: insights from pinacol rearrangement and iminium ion cyclization.

Nitrogen-doped carbon dots (CDs) have attracted considerable attention across various research areas and applications due to their enhanced optical properties and photostability. However, the mechanism of nitrogen incorporation in CDs remains elusive, hampering the precise control over nitrogen-incorporated structures and the investigation of the effects of nitrogen on the electronic structure and optical properties of CDs. In this study, we employed a rational design approach, utilizing glucosamine and ethylene glycol as the carbon source and co-reagent, respectively, to synthesize N-doped CDs. Our synthesis strategy involved pinacol rearrangement and iminium ion cyclization reactions, enabling the reliable formation of N-doped CDs. Notably, the resulting CDs exhibited distinctive emissive states attributed to heteroatomic defect structures, including oxygenic and nitrogenic polycyclic aromatic hydrocarbons. To gain further insights into their energy levels and electronic transitions, we conducted comprehensive investigations, employing extended Hückel calculations and pump-probe spectroscopy. The synthesized CDs displayed great promise as bioimaging and photodynamic therapy agents, highlighting their potential for biomedical applications. Moreover, our study significantly contributes valuable insights into the rational design of N-doped CDs with controllable chemical and electronic structures, thereby paving the way for advancements in their diverse range of applications.

Optical properties of carbon dots derived from table sugar via gamma irradiation

Gamma irradiation is the only approach for green environmental synthesis that does not require further waste treatment. Therefore, gamma irradiation was employed for carbon dot production at room temperature in this study. The table sugar was utilized as a raw material without the addition of any hazardous additives. Using sugar concentrations of 4, 20, and 40% by weight, carbon dots were produced using gamma irradiation at 25 kGy. The as-synthesized carbon dots were characterized using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Utilizing UV-Visible absorption and fluorescence spectroscopy, the optical characteristics of carbon dots were investigated. The carbon dots as synthesized had a high UV absorption peak at 271 nm and adjustable fluorescence emission.

Carbon Dot - An Updated Review

These days, carbon dots (CDs) are the rising stars of nanomaterials. Carbon dots (CDs) are small carbon nanoparticles with the same type of surface passivation (less than 10 nm in size). Researchers found C-dots by accident while purifying single-walled carbon nanotubes (SWCNTs) manufactured using the arc-discharge process. Toxic metal-based quantum dots are being replaced with carbon dots (QDs). Carbon dots are currently being prepared from a variety of natural resources in order to obtain self-passivated products at a reasonable cost. Because of their superior photo physical characteristics, biocompatibility, and low toxicity, carbon dots have prospective applications in bio sensing, bio imaging, and drug administration. Different synthetic processes, precursors, salient properties, and applications were reviewed in this review, as well as some future prospects, obstacles, and possible solutions for future development. Because of their tunable optical characteristics and better biocompatibility, luminous carbon-based nanomaterials have sparked a lot of scientific interest. Different light emission properties of carbon are discussed in this review. Distinct synthesis procedures have resulted in different carbon dots (CDs). Summarized here. The optical properties of CDs that haven’t been synthesized yet surface doping and element doping can be used to further control it. CDs are being functionalized for an adjustable band gap. As a result of their luminescent with reduced cytotoxicity and tunable optical characteristics CDs have been thoroughly investigated in terms of their potential uses in biomedicine, such as analytical sensors, and instruments for bioimaging. Fluorescent carbon dots are a new type of nanomaterial from the carbon family. Green CDs, which have attracted a lot of attention from researchers because of their better water solubility, high biocompatibility, and eco-friendly nature when compared to chemically generated CDs, can be made from a variety of inexpensive and renewable resources. The presence of heteroatoms on the surface of green CDs in the form of amine, hydroxyl, carboxyl, or thiol functional groups, which can improve their physicochemical qualities, quantum yield, and likelihood of visible light absorption, eliminates the need for additional surface passivation.

Variation in the Optical Properties of Carbon Dots Fabricated by a Green and Facile Strategy for Solar-Blind UV Detection

Variation in the Optical Properties of Carbon Dots Fabricated by a Green and Facile Strategy for Solar-Blind UV Detection

Facile approach for green synthesis of fluorescent carbon dots from Manihot esculenta and their potential applications as sensor and bio-imaging agents

An eco-friendly approach for the synthesis of blue fluorescent carbon dots (CDs) using Manihot esculenta with an average size of 3–5 nm through hydrothermal method has been reported. Functionality of the prepared CDs was characterized by FT-IR spectroscopy. Structural and morphological characterisation were carried with XRD and TEM techniques, these studies exposed amorphous nature of carbons dots with spherical shape. Optical properties of CDs were examined using UV–Visible and Photoluminescence spectral techniques. Owing to strong blue fluorescence, CDs were evaluated for its ability to sense various heavy metal ions. Attributable to significant response towards Fe3+ ions among different metal ions tested (Al3+, Cu+, Co2+, Pb2+, Zn2+, Fe3+, Ca2+, Hg2+ and Mg2+), CDs were used as a selective fluorescence probe for detection of Fe3+. The bioimaging and cytotoxicity aspects of CDs on MDA MB-231 breast cancer cell lines were confirmed by localised experiments. The synthesised CDs were found to be non-toxic even at their high concentration of 500 µg/mL.

Fluorescent Carbon Dots and their Applications in Sensing of Small Organic Molecules

Background: Fluorescence-based sensing is considered highly sensitive and fluorescent probes with improved properties are always desired. Fluorescent carbon dots (CDs) are newly emerging quasi-spherical nanoparticles of less than 10 nm in size and belong to the carbon nano-material’s family. CDs have great potential as fluorescent probes and currently are under open deliberation by the researchers due to their striking properties such as low environmental hazard, high selectivity, greater sensitivity, good biocompatibility, tunable fluorescent properties and excitation dependent multicolor emission behavior. Introduction: This review demonstrates various available methods for fabrication of fluorescent CDs, capping of CDs and characterization with various techniques including UV-visible, FT-IR, and TEM. Analytical applications using CDs for the sensing of small organic molecules, specifically nitroaromatic compounds in the environmental samples are complied. Methods: The review covers literature related to synthesis and characterization of carbon dots. It includes around 171 research articles in this field. Results: Carbon dots can be synthesized using numerous routes. In all cases CDs possess spectral properties with little variation in wavelength maxima. Optical properties of CDs can be tuned by compositing these with metallic quantum dots or by modifying their surface with desired functionalities. HR-TEM is needed to see the morphology and size of particles whereas UV-Visible and FTIR are indispensable tools for this kind of research. These particles are successfully applied to sense small molecules in some matrices. Conclusion: Carbon dots are bright stars in fluorescent sensing of small molecules. However, more research is needed to determine small organic molecules in diversified areas of analysis.

Tunable upconversion emission from oil-based carbon nanodots

Optical properties of carbon dots (CDs), prepared using 10-Undeceonic acid as an organic precursor, exhibited broad range excitation wavelength-dependent photoluminescence, with maximum emission intensity at 3.5 eV. Besides conventional down-conversion PL (DCPL), CDs show excitation wavelength-dependent upconversion PL(UCPL), produced by electromagnetic radiation in the green-NIR wavelength range. The difference between the excitation energy and the UCPL peak energy is found to be constant upon varying the excitation energy, whereas the energy difference with respect to DCPL peak energy decreases linearly. UCPL/DCPL have been explained with the help of surface states, shallow and deep trap states present in the proposed CDs.

Zn-assisted modification of the chemical structure of N-doped carbon dots and their enhanced quantum yield and photostability.

This article presents the Zn-assisted synthesis of N-doped carbon dots (N-CDs) with an enhanced quantum yield (QY) and photostability. There have been intensive studies to improve or tune the optical properties of carbon dots (CDs) to meet the demand for luminescent materials in various fields, including energy conversion, photocatalysis, bioimaging, and phototherapy. For these applications, the photostability of the CDs is also a critical factor, but the related studies are relatively less common. The Zn-assisted N-CDs (denoted as Zn:N-CDs) obtained by the addition of Zn(OAc)2 to the precursors during the synthesis of N-CDs not only exhibited an enhanced quantum yield but also improved photostability compared to those of N-CDs. A comprehensive study of the chemical composition of Zn:N-CD and N-CD using X-ray photoelectron spectroscopy indicated a correlation between their chemical structure and photostability. Zn(OAc)2, which acts as a catalytic reagent, induced the modification of chemical structures at the edges of carbogenic sp2 domains, without being doped in N-CD, and the heteroatom–carbon bonds in Zn:N-CD seemed to be more resistant to light compared to those in N-CDs. The increased QY and photostability of Zn:N-CDs make them more suitable as an optical probe and they could be used in fingerprint identification. With Zn:N-CDs, the microstructure of fingerprints was confirmed clearly for a long duration effectively.

Revealing the synergetic interaction between amino and carbonyl functional groups and their effect on the electronic and optical properties of carbon dots.

Nitrogen and oxygen-based functionalized carbon dot (CDs) surfaces have attracted significant attention due to their ability to tailor the optical and electronic properties of CDs. However, the complex synthesis process and structure of the functionalized CDs hinder an in-depth understanding of their mechanism, limiting their potential applications. Herein, we report CDs functionalized with amino and carbonyl functional groups and reveal the mechanism of interaction between the amino and carbonyl groups and the CDs' optical and electronic properties. Both Time-dependent Density Functional Theory (TD-DFT) and experimental studies revealed that the synergetic effects between amino and carbonyl groups significantly shift the absorption peaks to the NIR region and strengthen their absorption intensity. Furthermore, their absorption and bandgap energy could be tuned by optimizing the amino to carbonyl ratio on CDs surfaces. This study suggests that amino and carbonyl groups synergistically tailor the CDs' optical and electronic properties through frontier orbital hybridization and high charge transfer. This knowledge opens a new avenue for tailoring the desired optical and electronic properties of CDs for any application.

Carbon Dots: Synthesis, Properties and Applications.

Carbon dots (CDs) are known as the rising star of carbon-based nanomaterials and, by virtue of their unique structure and fascinating properties, they have attracted considerable interest in different fields such as biological sensing, drug delivery, photodynamic therapy, photocatalysis, and solar cells in recent years. Particularly, the outstanding electronic and optical properties of the CDs have attracted increasing attention in biomedical and photocatalytic applications owing to their low toxicity, biocompatibility, excellent photostability, tunable fluorescence, outstanding efficient up-converted photoluminescence behavior, and photo-induced electron transfer ability. This article reviews recent progress on the synthesis routes and optical properties of CDs as well as biomedical and photocatalytic applications. Furthermore, we discuss an outlook on future and potential development of the CDs based biosensor, biological dye, biological vehicle, and photocatalysts in this booming research field.

SWCNT/ZnO nanocomposite decorated with carbon dots for photoresponsive supercapacitor applications

In this work, we report the fabrication of an optically responsive hybrid supercapacitor. The hybrid electrode material for the supercapacitor was synthesized by attaching carbon dots (CDs) on the SWCNT/ZnO nanocomposites. The optical properties of CDs and ZnO have been explored by operating the supercapacitor under illuminated conditions (UV light). It was observed that the areal capacitance of the fabricated supercapacitor got enhanced by ∼ 41.38% at 50 mV/s scan rate under UV light. The photo-charging and galvanostatic discharging of the device were also examined. The maximum photo-charged areal capacitance value was calculated to be 1.53 mF/cm2 at a current density of 1.25 μA/cm2, whereas the values of areal energy density and areal power density at this current density value were 19.85×10-3 μWh/cm2, and 0.0953 μW/cm2, respectively. The working mechanism of the supercapacitive system has also been explored. It is observed that the overall capacitance of the hybrid electrode is a combination of both electric double layer capacitance (EDLC) and pseudocapacitance. The EDLC and pseudocapacitance contributions were confirmed by using the Dunn method, and the values of the individual capacitance contributions are 69.35 and 30.65% for EDLC and pseudocapacitance, respectively. Further, it was observed that the pseudocapacitance phenomenon was dominated by the diffusion of the ions in the electrode material. The diffusivity of the electrolytic ions was calculated to be 0.13 and 0.14 mm2/s for the oxidation peaks, whereas 1 and 0.07 mm2/s for the reduction peaks, respectively. Moreover, the reaction mechanism of the system has also been explored, and the occurrence of intercalation of K+ ions in the defects of ZnO has been confirmed with justified explanations.

Special Issue on the 40th Anniversary of University of Macau

Special Issue on the 40th Anniversary of University of Macau

A Green and Simple Carbon-dot-based Fluorescent Probe for Selective and Sensitive Detection of Ranitidine Hydrochloride

Herein, a novel fluorescent probe was designed and synthesized for the selective and sensitive detection of ranitidine hydrochloride based on the quenched fluorescence signal of carbon dots (CDs). The one-step hydrothermal treatment of Urtica dioica extract was used to prepare CDs. The as-synthesized CDs exhibited excellent water dispersibility and had a blue color under UV light irradiation (365 nm) with 12.49% of quantum yield (QY). The structural and optical properties of CDs were investigated using UV-Vis spectrophotometer, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The as-synthesized CDs were used as a simple, sensitive, and inexpensive probe for the detection of ranitidine hydrochloride in pharmaceutical samples. The absorption spectrum of ranitidine overlapped with the excitation spectrum of CDs and the fluorescence intensity of CDs effectively decreased with the increase of ranitidine concentration due to the inner filter effect (IFE). A fluorometric assay was formed based on these findings that had a linear response in the ranitidine hydrochloride concentration range of 0.167 to 14.03 µg. mL-1 with a detection limit as low as 0.081 µg. mL-1. This new sensing assay was green and had beneficial features such as simplicity, rapidity, inexpensiveness, and ease of operation without the need for further modification. Using the suggested method, ranitidine hydrochloride was successfully measured in the pharmaceutical preparations.

Carbon Dot/Polymer Composites with Various Precursors and Their Sensing Applications: A Review

Carbon dots (CDs) have generated much interest because of their significant fluorescence (FL) properties, extraordinary photophysical attributes, and long-term colloidal stability. CDs have been regarded as a prospective carbon nanomaterial for various sensing applications because of their low toxicity, strong and broad optical absorption, high chemical stability, rapid transfer properties, and easy modification. To improve their functionality, CD/polymer composites have been developed by integrating polymers into CDs. CD/polymer composites have diversified because of their easy preparation and applications in sensing, optoelectronics, semiconductors, molecular delivery, and various commercial fields. Many review articles are available regarding the preparation and applications of CDs. Some review articles describing the production and multiple applications of the composites are available. However, no such article has focused on the types of precursors, optical properties, coating characteristics, and specific sensing applications of CD/polymer composites. This review aimed to highlight and summarize the current progress of CD/polymer composites in the last five years (2017–2021). First, we overview the precursors used for deriving CDs and CD/polymer composites, synthesis methods for preparing CDs and CD/polymer composites, and the optical properties (absorbance, FL, emission color, and quantum yield) and coating characteristics of the composites. Most carbon and polymer precursors were dominated by synthetic precursors, with citric acid and polyvinyl alcohol widely utilized as carbon and polymer precursors, respectively. Hydrothermal treatment for CDs and interfacial polymerization for CDs/polymers were frequently performed. The optical properties of CDs and CD/polymer composites were almost identical, denoting that the optical characters of CDs were well-maintained in the composites. Then, the chemical, biological, and physical sensing applications of CD/polymer composites are categorized and discussed. The CD/polymer composites showed good performance as chemical, biological, and physical sensors for numerous targets based on FL quenching efficiency. Finally, remaining challenges and future perspectives for CD/polymer composites are provided.

One-step hydrothermal method for preparing carbon dots and its determination of lead (II)

As a new type of carbon nanomaterials, carbon dots have attracted great interest due to their non-toxic, low preparation cost and unique photoluminescence properties. They have been widely studied and shown great potential in many fields. Here, nitrogen doped fluorescent carbon dots were prepared by one-step hydrothermal method using Epiphyllum leaves as raw materials. Ultraviolet-visible absorption spectrometer and fluorescence spectrometer were used to study the optical properties of carbon dots. The elemental composition and morphology of the surface of carbon dots were analyzed by transmission electron microscope, Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer. The results show that the prepared carbon dots are uniformly dispersed in the aqueous solution, emit blue fluorescence, and the average particle size is 4.2 nm. The carbon dots have good light stability and strong anti-photobleaching ability. Continuous spectral scanning of the carbon dots can keep the fluorescence intensity basically unchanged within 30 minutes. In the concentration of 0∼f molL-1 NaCl solution, the strength is not affected by the ionic strength. In the pH range of 4∼ 8, the fluorescence intensity of carbon dots is basically stable. The heavy metal ion pb2+ has a quenching effect on the fluorescence of carbon dots, and has a good linear relationship in the range of 0.5*200 μm. Therefore, a simple and green method for pb2+ has been developed.