Water-soluble Carbon Quantum Dots Research Articles

Enhancing capacitance performance of functional group assisted carbon quantum dots derived from turmeric plant waste

Supercapacitors have attracted significant attention in modern devices as a promising solution for electrical energy storage due to their remarkable capability to undergo rapid charge and discharge cycles. While various materials are employed in the construction of supercapacitors, carbon-based materials emerge as a predominant choice within the commercial realm. In present report, our intention is to develop an effective supercapacitor device derived from natural biomass. Therefore, we have synthesized water soluble, monodisperse and fluorescent carbon quantum dots (CQDs) from turmeric leaves (Curcuma caesia) via a single step hydrothermal carbonization. Further, the doctor blade technique was employed to coat a layer of CQDs on stainless steel substrate using PVA as a binder. We observed the functional groups associated with QDs triggers the fast diffusion of ions and transmission of electrons with conducting substrate and electrolyte and thereby effectively charge and discharge mechanism. The supercapacitor based on carbon quantum dots (CQDs) based electrode exhibits exceptional performance characteristics with a remarkable specific capacitance of 468 F/g and highest energy density of 78.6 Wh/kg, superior to the values reported for most carbon-based supercapacitors. Further, we demonstrated the light dependent capacitive enhancement by depositing a thin P3HT layer over CQDs. Moreover, CQDs-based supercapacitor achieves a maximum power density of 733.2 W/kg when operated in a 1 M KOH electrolyte solution and an excellent capacitive retention of about 80 % even after 5000 cycles.

Rice husk assisted carbon quantum dots synthesis for amoxicillin sensing

Recently, the green method synthesized biosensors have been used for numerous environmental and biomedical applications, especially nanomaterials-based biosensors. Herein, novel, environmentally friendly, and water-soluble carbon quantum dots (CQDs) have been synthesized from the readily available green source (rice husk) without any ionic or covalent modifications via a one-pot synthesis method. The CQDs were characterized using UV–visible spectroscopy, SEM, XPS, and Fourier transform infrared spectroscopy, and their optical properties were determined. The stability of the synthesized CQDs was determined under the effect of pH, time, and temperature and on different excitation wavelengths. The band gap energy was calculated using Tauc’s equation with the energy of 3.2 eV, which indicated that the CQDs are fluorescent, and the linear range and association constant were determined by the Stern- Volmer relation and Bensi- Hildebrand equation, respectively. The photophysical studies indicated the strong fluorescence emission with excitation dependent behaviour and the CQDs relation with amoxicillin. Hence, in this study, the sensor producing remarkable sensitivity of antibiotics with a detection limit in the nM range was proposed.

Upcycling Waste: Citrus limon Peel-Derived Carbon Quantum Dots for Sensitive Detection of Tetracycline in the Nanomolar Range.

In this work, a sustainable method was developed for the production of water-soluble carbon quantum dots employing a green approach. The synthetic protocol was employed using the microwave pyrolysis technique, while lemon peel served as a carbon precursor. Fabrication of highly fluorescent lemon-peel-derived CQDs (LP-CQDs) having inherent nitrogen functionality was validated by X-ray photoelectron spectroscopy, FTIR, X-ray diffraction, Raman spectroscopic analysis, and TEM techniques. The average particle size of fabricated LP-CQDs was 4.46 nm. LP-CQDs yielded a remarkable quantum yield of 49.5%, which displayed excellent salinity, photostability, storage time, conditions, and pH stability. LP-CQDs displayed encouraging results for tetracycline (TC) detection using a PL turn-off approach. The sensitivity of LP-CQDs toward TC was seen in a nanomolar range having a detection limit of 50.4 nM. Method validation was comprehensively studied to ensure the precision of the nanosensor. A complete analysis of different photophysical parameters of LP-CQDs was performed with TC to gain a deeper understanding of the sensing mechanism. Fabricated LP-CQDs showed fluorescence quenching toward TC, elucidated by the inner filter effect (IFE) mechanism. The synthesized nanoprobe demonstrated a lesser detection limit with a broad linear range, enabling facile, cheap, environmentally friendly, and fast detection of TC. Practicality of the detection method was assessed through analysis of real samples, resulting in satisfactory recovery percentage and relative standard deviation with respect to the developed probes. Furthermore, LP-CQDs were used as fluorescent inks and to fabricate paper-based fluorescent strips. This study lays the door for the sensing platform of LP-CQDs toward detection of TC, which may impact the potential role of environmental sustainability.

Carbon quantum dot fluorescent probe for labeling and imaging of stellate cell on liver frozen section below freezing point

The targeted labeling imaging of stellate cells on liver frozen section by immunofluorescence is a very promising visualization technique to study the distribution of stellate cells in the liver. In this study, water soluble carbon quantum dots that can emit blue, green and yellow fluorescence are synthesized by the hydrothermal method, and their sizes are 3.2, 3.7, and 4.3 nm, respectively. The three carbon quantum dots have good fluorescence stability, and the quantum yields are 36.1%, 26.3% and 21%, respectively. When the mass fraction of KCl in the blue carbon quantum dot dispersion system is 13%, it still maintains the liquid state at −30 °C. The final fluorescent probe is obtained after the carbon quantum dots are coupled with the secondary antibody, spectral characterizations confirm that the conjugate probe still maintains protein immunoactivity and has good stability. Cell experiments prove that the probe has good biocompatibility, the rabbit anti-mouse Desmin antibody is used as the primary antibody, the results of cellular immunofluorescence imaging and flow cytometry show that the probe can specifically label hepatic stellate cell at −20 °C. The results of liver frozen section experiments show that hepatic stellate cell can be specifically targeted and labeled by the fluorescent probe. This labeling technology provides an important technical means for elucidating the structure and function of the liver at the cellular level, exploring the liver pathological change, and designing and developing drug.

Turn-off fluorescence of S,N-doped carbon dots for determination of two nitro-containing drugs in dosage forms and human plasma

This study describes the development of an environmentally-friend optical nanosensor for the rapid spectrofluorimetric assessment of two nitro-compounds, namely nitrofurantoin and dantrolene in their dosage forms and plasma samples. A one-step synthetic technique successfully created very bright water-soluble carbon quantum dots doped with sulfur and nitrogen (S,N-CQDs). Carbon was derived from citric acid, while nitrogen and sulfur were obtained from thiosemicarbazide. The dimensions of the synthesized dots were measured using a high-resolution transmission electron microscope. FT-IR spectroscopy was used to determine which functional groups were located on their surfaces. The nanosensor's fluorescence emission peaked intensely at 415 nm after excitation at 345 nm with a quantum yield of about 0.52. The inherent fluorescence of the nanosensors gradually decreased upon addition of the studied analytes in increasing concentrations. The fluorescence reduction of nanosensor with the concentrations of the investigated drugs demonstrated linear correlation within the ranges of 0.5–8.0 μg/mL and 1.0–10.0 μg/mL with limits of detection of 0.14 μg/mL (0.59 μM) and 0.23 μg/mL (0.73 μM) for nitrofurantoin and dantrolene, respectively. The recommended method was used to determine the concentrations of the investigated drugs in their commercial capsules, with recoveries ranging from 97.90 % to 101.57 % and low percent RSD values less than 2 %. Moreover, the method was adapted for the in-vitro analysis of the two analytes in spiked human plasma samples with % recoveries from 95.20 % to 102.20 %. The mechanism of interaction between each analyte and the dots was also investigated. The selectivity of the approach for measuring analytes concentration in the presence of excipients, co-formulated medications, or co-administered pharmaceuticals was further evaluated through an interference study. The suggested method's validity was evaluated in accordance with ICH criteria.

Biogenic synthesis of carbon quantum dots from garlic peel bio-waste for use as a fluorescent probe for sensing of quercetin.

Highly fluorescent and water-soluble carbon quantum dots (CQDs) were synthesized from the bio-waste source of garlic peels (renovation of bio-waste into bio-asset) using a controlled carbonization method. Synthesized CQDs were characterized by various analytical methods and explored as a fluorogenic probe for the recognition of quercetin (QT). Ultraviolet-visible (UV-vis) result shows an absorption maximum at 275 nm attributed to the conjugation of C=C and C=O of CQDs and demonstrates a blue emission in the range 330-410 nm. Selectivity was performed with various biomolecules, except for QT, all others do not exhibit any considerable change in the fluorescence of CQDs. On the interaction with QT, emission was completely quenched due to Förster energy transfer (FET), confirming the high selective to QT. Effect of pH, sensitivity, and stability studies displayed excellent results under optimized conditions. The limit of detection (LOD) fluorescent probe was found to be 6.73 μM. Our approach may suggest a new platform for the development of quick and low-cost CQDs-based sensors for environmental and biological purposes.

Solvothermal Synthesis of Fluorescent Carbon Quantum Dots by Using Vanillin as Carbon Source

As a new zero-optic luminescent material, carbon quantum points are widely focused and sustained, and many researchers are trying to use simple and fast methods and stable, good carbon sources to be prepared with a good fluorescent properties of carbon quantum dots. In this paper, carbon quantum dots were synthesized by solvothermal method with vanillin as carbon source, and the effects of solvothermal temperature and time on the luminescence properties of carbon quantum dots were explored. Then, carbon quantum dots were characterized by X-ray diffraction analysis, transmission electron microscopy analysis, infrared spectrum analysis, fluorescence spectrum analysis. Research results showed that ethanol solvent with vanillin as a carbon source by solvothermal method could synthesize good water soluble carbon quantum dots with weak crystallization, and its size was about 10 nm. This carbon quantum dots had obvious excitation wavelength dependence and produce blue light, which had potential application value in ion fluorescence probe or cell labeling.

Strong Coupling of Carbon Quantum Dots in Liquid Crystals.

Carbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorption spectroscopy, and CDs display very stable and strong photoluminescence emission with a quantum yield of 35.4% and a lifetime of ∼2 ns. More importantly, we compare J-aggregate dyes with CDs in terms of their absorption line width, photostability, and ability to do strong coupling, and we conclude that highly fluorescent CDs have a bright future in the mixed light–matter states for emerging applications in future quantum technologies.

Preparation of carbon quantum dots from corn straw and their application in Cu2+ detection

Water-soluble carbon quantum dots were hydrothermally produced using corn straw as the starting material and nitric acid solution as solvent, then they were introduced as fluorescent probes for the detection of Cu2+. High-resolution transmission electron microscopy and X-ray diffraction showed that the carbon quantum dots were spherical amorphous particles with a diameter of 5 nm. The surface functional groups of carbon quantum dots were observed via Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. A new approach for Cu2+ detection was designed using carbon quantum dots based on fluorescence quenching. Linear relationships between the fluorescence variation and the Cu2+ level (1 mg·L-1 to 20 mg·L-1 and 20 mg·L-1 to 500 mg·L-1) were obtained, with coefficients of determination of 0.9960 and 0.9923, respectively. The Cu2+ detection limit was 4.26 mg·L-1. The probable quenching principle between Cu2+ and the carbon quantum dots was attributed to charge transfer.

Synthesis of silicon nanowire and crystalline carbon quantum dots heterostructure and study of photo response and photoluminescence property

Silicon nanowire based heterostrucure or nanocomposites becomes intrigued in next generation energy conversion devices. Herein, we have prepared n type silicon nanowires (n-SiNWs) and water soluble Carbon Quantum Dots (CQD) through metal assisted etching and hydrothermal method respectively. The CQD possesses very low dimensions around 2–4 nm which becomes spin coated on n type silicon nanowires. The formation of silicon nanowires/ Carbon Quantum Dots heterostructures (n-SiNW/CQD) exhibits excellent photo current properties with Ilight/IDark had apparent value within the range 1.36–3.83. The heterostructure also exhibits a strong photoluminescence spectrum in blue region.

A facile green synthesis of functionalized carbon quantum dots as fluorescent probes for a highly selective and sensitive detection of Fe3+ ions

In this study, we have reported an economical, easy, greener and non-toxic synthesis route of water soluble carbon quantum dots (CQDs) through hydrothermal treatment using gelatin as precursor. Under the UV lamp of wavelength 365 nm, the as-prepared CQDs exhibit strong blue fluorescence along with CIE coordinate index of (0.17, 0.14) and possess a quantum yield of 22.7% with rhodamine B as standard. The morphology of as-synthesized CQDs as investigated by TEM measurement confirmed their spherical shape and also revealed that their sizes varied in the scale of 0.5–5 nm. Furthermore, the CQDs showed excitation dependent fluorescence emission behaviour in range of 280 nm to 420 nm as a result of quantum confinement effect. Apart from this, in CQDs solution, the addition of Fe3+ ion lead to fluorescence quenching effect. These results revealed that the as-synthesized CQDs have a sensitive response towards the Fe3+ ion. The calculated limit of detection (LOD) is 0.2 μM with correlation coefficient R2 = 0.996 in the concentration range 0 to 50 μM. More remarkably, the application of CQDs for monitoring the trace level of Fe3+ ion in tap water yielded acceptable recoveries (103.33%-105%). Therefore, this work provides a novel additional fluorescent probe for the detection of Fe3+ ion in real world.

Water-Soluble Carbon Quantum Dots Modified by Amino Groups for Polarization Fluorescence Detection of Copper (II) Ion in Aqueous Media

Industrialization is serious for changing the environment and natural water composition, especially near cities and manufacturing areas. Logically, the new ultrasensitive technology for precise control of the quality and quantity of water sources is needed. Herein, an innovative method of polarization fluorescence analysis (FPA) was developed to measure the concentration of heavy metals in water. The approach was successfully applied for precise tests with reduced analysis time and increased measurement efficiency among laboratory methods. Based on this work, the investigations established the new type of carbon quantum dots (CQDs) with controllable fluorescence properties and functionalized amino—groups, which is appropriate for FPA. The parameters of one and two-step microwave synthesis routes are adjusted wavelength and fluorescence intensity of CQDs. Finally, under optimized conditions, the FPA is showed the detection of copper (2+) cations in water samples below European Union standard (2 mg/L). Moreover, in comparison with fluorescence quenching, polarization fluorescence is proved as a convenient, simple, and rapid test method for effective water safety analysis.

A facile approach to synthesis carbon quantum dots-doped P25 visible-light driven photocatalyst with improved NO removal performance

The water-soluble carbon quantum dots (CQDs) and a novel composite photocatalyst CQDs/P25 have been prepared by a one-step electrochemical-microwave method. The experimental result shows that the photocatalytic degradation of NO by this new kind of CQDs/P25 composite reaches 71%, which is approximately 1.65 times than that of the pure P25 at room temperature. The initial concentration of NO pollutants is 10 ppm. The photocatalytic efficiency of the composite catalyst achieves the highest when the content of CQDs is 1%. It can be concluded that the CQDs extend the light absorption range and adjust the band gap of pure P25. The high photocatalytic performance of this new kind of photocatalyst can be mainly attributed to the unique up-conversion fluorescence property, nanometer size effect and surface activity effect.

A facile one step hydrothermal synthesis of carbon quantum dots for label -free fluorescence sensing approach to detect picric acid in aqueous solution

In this work, a facile one step approach has been applied for the synthesis of nitrogen and sulphur co-doped water soluble carbon quantum dots (NS-CQDs) through hydrothermal treatment of L-Lysine and thiourea. The obtained NS-CQDs have a high quantum yield (QY) of 53.19 % and emit strong blue fluorescence under UV light excitation of wavelength 365 nm. The morphology of NS-CQDs is spherical in shape and their sizes are distributed in the range 5–8 nm with average diameter 6.86 nm. Moreover the NS-CQDs show excitation dependent emission behavior due to quantum confinement effect. Additionally, NS-CQDs serve as a fluorescent probe for the selective and sensitive detection of picric acid (PA) in aqueous solution. A good linear response to PA in the concentration range 1–10 μM with a detection limit 0.24 μM has been obtained. The high selectivity of PA by NS-CQDs is suggested to arise from fluorescence resonance energy transfer (FRET) mechanism. Finally these NS-CQDs fluorescent probes have been examined in real water sample by measuring the concentration of PA in tap water.

Crosslinking induced photoluminescence quenching in polyvinyl alcohol-carbon quantum dot composite

Highly luminescent and water-soluble carbon quantum dots (CQDs) have been integrated into polyvinyl alcohol (PVA) recently to realize composites with synergistic functionalities. The effects of chemical interactions between CQDs and PVA matrix on the changes in optical properties of CQDs or physicochemical properties of PVA are yet to be investigated fully. Herein, we first synthesized CQDs with different surface chemistry via varying the molar ratio between citric acid (CA) and ethylenediamine and then embedded the CQDs into PVA with or without additional CA crosslinking. Infrared and UV–vis studies on CQDs and composites showed that condensation between CQDs and PVA induced a redshift in the absorption peak originating from CQDs’ surface fluorophore groups. Interestingly, CA crosslinking significantly increased the water resistance, but it quenched the photoluminescence of composites. The quenching effects were reduced by using CQDs having less reactivity with CA.

Synthesis of carbon quantum dots with green luminescence from potato starch

Water-soluble carbon quantum dots (CQDs) are synthesized via an acid assisted ultrasonic route using the biomass carbon precursor of potato starch as the raw material.

Carbon quantum dots: An innovative additive for water lubrication

Water soluble carbon quantum dots (CQDs) were prepared and used as lubricant additives in deionized (DI) water. The impacts of CQDs on the tribological properties of water were evaluated for both Si3N4-on-steel and Si3N4-on-Si3N4 contacts. Experimental results show that the coefficient of friction (COF) reduced in the two types of tribopairs after the addition of CQDs. Maximum reductions in COF were found to be 30% and 14% for the Si3N4-steel and Si3N4-Si3N4 contacts, respectively. In terms of wear behaviors, the CQDs notably improved tribofilm formation on the Si3N4 disk surface for the Si3N4-Si3N4 contacts, confirming that the nanoparticles increase friction while providing better protection from wear. This research will help to expand the application of CQDs as promising additives in water-based lubricants.

Bioinspired Synthesis of Carbon Dots/g-C3N4 Nanocomposites for Photocatalytic Application

This study reports a fast and green preparative strategy to synthesize water soluble and fluorescent carbon quantum dots (CQDs) through hydrothermal method by using low cost organic waste of human fingernails as the carbon precursor for the first time. The coupling of CQD with pure carbon nitride (g-C3N4) was further explored to enhance the latter’s performance in photocatalysis of 2,4-dicholorophenol (2,4-DCP), a toxic and recalcitrant compound mostly released from industrial effluent. Such coupling overcame the weakness of pure g-C3N4 in photocatalysis process by broadening its visible light absorption and promoting the charge separation. As a result, the removal rate of CQD/ g-C3N4(10) was up to 71.53%, which was approximately 1.5 times higher than that of pure g-C3N4 under sunlight irradiation. The morphological structure, optical properties and chemical compositions of CQDs/g-C3N4 composites were characterized using various spectroscopic techniques including field emission scanning electron microscopy (FESEM), Energy Dispersive X-Ray (EDX) and Ultraviolet-visible diffuse reflectance spectra (UV-DRS).

Hemostatic bioactivity of novel Pollen Typhae Carbonisata-derived carbon quantum dots

BackgroundPollen Typhae Carbonisata (PTC) is a type of calcined herb drug that has been used as a hemostatic medicine to promote hemostasis for thousands of years. In this study, we discovered and separated novel water-soluble carbon quantum dots (CQDs, named PTC-CQDs) from aqueous extracts of PTC. These PTC-CDs were characterized using transmission electron microscopy (TEM) and high-resolution TEM, as well as Fourier transform infrared, ultraviolet–visible, and fluorescence spectroscopy. Then, we assessed the anti-hemorrhagic effects and related hemostatic mechanisms of the obtained PTC-CQDs.ResultsThe PTC-CQDs separated from PTC are spherical, monodisperse, and have a narrow size distribution between 2 and 8 nm. In the pharmacology experiment, remarkable anti-hemorrhage effects of PTC-CQDs were revealed. Additionally, the rats showed a profound decrease in activated partial thromboplastin time and increase in fibrinogen and PLT after PTC-CQDs treatment.ConclusionsThese results indicated the explicit hemostasis effect of PTC-CQDs, which not only provided a new idea for the material research of PTC, but have also provided new insights into potential biomedical and healthcare applications of CQDs in the field of haemorrhage control and laid a solid foundation for future drug discovery.

Ellagic acid-functionalized fluorescent carbon dots for ultrasensitive and selective detection of mercuric ions via quenching

The authors report on a strategy for the fabrication of water soluble carbon quantum dots (CDs) functionalized with ellagic acid. They also demonstrate highly selective detection of Hg2+ ions in aqueous media via fluorescence quenching. The CDs were prepared via a one-step technique using tannic acid as the carbon source and directly surface functionalized during nanoparticle synthesis. Following photoexcitation at 210nm they exhibit excitation-independent emission that peaks at 340nm. The CDs display strong affinity for Hg2+ and binding result in quenching of fluorescence. This effect can be used to quantify Hg2+ in concentration down to 10pM and with detection limit as low as 0.24pM. The ultrasensitive detection of Hg2+ ions is demonstrated by analyzing Hg2+-spiked water and tap-water samples.