Properties Of Carbon Quantum Dots Research Articles

Enhancing the quantum yield and electrochemical properties of carbon quantum dots via optimized hydrothermal treatment using cellulose nanocrystals as precursors

Carbon quantum dots (CQDs) are receiving increasing attention due to their tunable redox activity, abundant surface functional groups, and excellent aqueous dispersion. However, their low quantum yield remains a significant impediment to their synthesis and practical application. In the present work, cellulose nanocrystals (CNCs) were utilized as precursors for the optimized hydrothermal synthesis of CQDs. Subsequently, the synthesized CQDs were electrodeposited onto a carbon-coated surface. The influence of hydrothermal temperature and time on the quantum yield and electrochemical properties of CQDs was systematically explored. The successful synthesis of CQDs displayed an average particle size of 5 nm, approximately. The quantum yield was enhanced from 14.35 % to 23.7 % as the hydrothermal temperature increased from 180 °C to 230 °C. Additionally, the electrochemical properties of the composite films were investigated. Electrochemical assessments demonstrated an increase in specific capacitance from 60.4 mF·cm−2 to 65.2 mF·cm−2 with an elevation in temperature from 180 °C to 210 °C. Remarkably, the CQDs displayed higher e CQDs, showcasing their substantial potential for supercapacitor applications.

Synthesis and luminescence properties of carbon quantum dots with core@shell structures

The luminescence stability of carbon quantum dots (CQDs) in air impedes their extensive applications. Ample –NH2 groups on the surface of a green carbon quantum dots (GCQDs) had high organic reactivity, the surface of GCQDs was modified with allyl functional groups through a simple surface substitution reaction (named as GCQD-A). The surface of the GCQD-A was continuously formed a thin organic shell by free radical copolymerization reaction with methyl methacrylate and styrene respectively, and they were named as GCQD@PMMA and GCQD@PS respectively. The allyl functional groups on the surface of GCQD-A, the shell composition of GCQD@PMMA and GCQD@PS were characterized by their 1H nuclear magnetic resonance (1H NMR) data and infrared adsorption spectra. The luminescence stabilities for GCQD@PMMA and GCQD@PS in air were greatly improved compared with that for the GCQDs. The work can provide a novel method to get stable luminescence of CQDs in air, and it will extend their application areas in solid state.

N, S-carbon quantum dots as inhibitor in pickling process of heat exchangers for enhanced performance in multi-stage flash seawater desalination

The heat exchanger in multi-stage flash seawater desalination needs to be pickled during long-term service to remove oxidation products on the copper surface. In this paper, we introduce a method for preparing carbon quantum dots from biowaste, and explore their ability to inhibit the corrosion of copper in sulfuric acid and its corrosion inhibition mechanism. Firstly, the UV–vis spectra, microstructure, tissue composition of N, S-CDs were tested by Ultraviolet-visible spectrophotometer, TEM and Fourier transform infrared. Secondly, the effectiveness of N, S-CDs in preventing corrosion was analyzed by electrochemical testing. The electrochemical test results showed that the impedance value of the solution of 200 mg/L N, S-CDs was 94,440 Ω cm2 at 298 K， with corrosion inhibition efficiencies (η) of 99.89 %, 99.77 % and 99.72 % at 298 K, 308 K, and 318 K, respectively. Moreover, SEM, XPS and AFM were used to characterize the micro-morphology and composition both before and after corrosion. It is worth noting that we used the fluorescence properties of carbon quantum dots as fluorescent probes to deeply verify the corrosion inhibition mechanism of N, S-CDs on copper.

Impact of carbon concentration on optical and zeta potential properties of carbon quantum dots

Carbon quantum dots (CQDs) are fluorescent nanoparticles with diverse applications in multiple fields. The optical and physical properties of CQDs are influenced by several factors, such as the synthesis method, surface passivation and particle size. This study explores how carbon concentration affects the properties of CQDs. The CQDs were synthesized through a carbonization process with carbon concentrations varying from 0.03 to 0.15 g/ml. The samples of CQDs were characterized by using high resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectroscopy, zeta potential, dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR). The results indicate that carbon concentration significantly impacts the optical properties and zeta potential of CQDs. Specifically, higher carbon concentrations result in increased fluorescence intensity and larger particle size. HRTEM images reveal that the average size of the CQDs is below 10 nm, consistent with DLS measurements. These findings suggest that carbon concentration can serve as a straightforward and effective parameter for tuning CQDs properties, with potential applications in bioimaging, sensing and optoelectronics.

Luminescence of carbon quantum dots in amorphous carbon

Subject of study. The luminescence spectrum of amorphous protonated carbon (a-C:H) containing carbon quantum dots is studied. Aim of study. How the peak in the luminescence spectrum of a-C:H is affected by the presence of fragments with different configurations is determined. Method. The typical spectra are compared against those of the closest analogs: polycyclic aromatic hydrocarbons with a small number of aromatic rings. Main results. Bright blue fluorescence due to the presence of an ensemble of graphene islands embedded in a diamond-like matrix is experimentally observed in a-C:H [Opt. Express 19, 17935 (2011)10.1364/OE.19.017935] and similar materials. The experimental spectrum appears consistent with a theoretical spectrum generated by superposing the non-uniformly broadened spectra of three analogs, namely, acenaphthylene, pyrene, and azulene (with each spectrum being assigned different weights). This research can be generalized to a wider range of carbon materials that fluoresce at short wavelengths. Practical significance. The results from this study of the properties of carbon quantum dots in amorphous carbon can be used to develop materials for conversion of ultraviolet electromagnetic radiation into visible light.

Performance evaluation of carbon quantum dots impregnated glass ionomer cement to avoid peri-implant disease

Dental cement residues exacerbate peri-implant tissue irritation and peri-implantitis. The present study aims to evaluate the cytotoxicity, physiochemical, optical, and rheological properties of carbon quantum dots (CQDs) impregnated glass ionomer cement (GIC). Surface passivated fluorescent CQDs were synthesized using citric acid via thermal decomposition and blended with GIC. Characterization studies and rheological measurements were made to evaluate their performance. 3D-printed dental implant models cemented with GIC and GIC-CQD were compared to analyze excess cement residues. MTT assay was performed with human dental pulp stem cells (hDPSCs) and statistically analyzed using ANOVA and Tukey’s test. CQDs with a particle dimension of ∼2 nm were synthesized. The amorphous property of GIC-CQD was confirmed through XRD. The fluorescence properties of GIC-CQD showed three times higher emission intensity than conventional GIC. GIC-CQD attained maturation with a setting time extended by 64 s than GIC. Cement residue of size 2 mm was detected with a UV light excitation at a distance between 5 to 10 cm. Biocompatibility at 0.125 mg ml−1 dilution concentrations of GIC-CQD showed viability greater than 80% to hDPSCs. For the first time, we report that CQDs-impregnated GIC is a unique and cost-effective strategy for in-situ detection of excess cement rapidly using a hand-held device. A novel in-situ rapid detection method enables the dentist to identify residual cement of size less than 2 mm during the implantation. Therefore, GIC-CQD would replace conventional GIC and help in the prevention of peri-implant diseases.

Detection of ferric ions by nitrogen and sulfur co-doped potato-derived carbon quantum dots as a fluorescent probe

This paper reports the detection of ferric ions (Fe3+) based on nitrogen and sulfur co-doped carbon quantum dots. These nitrogen and sulfur co-doped carbon quantum dots were synthesized via a hydrothermal route using northern Shaanxi potatoes as carbon sources and ammonium sulfate as nitrogen and sulfur sources. The quantum yields of the carbon quantum dots were found to be 16.96% and 4.23% with and without doping, respectively. The structural details, morphology, and optical properties of carbon quantum dots were analyzed using Fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), ultraviolet-visible absorption spectroscopy (UV–vis), and fluorescence spectroscopy. The as-prepared co-doped carbon quantum dots were utilized as a fluorescent probe for detecting Fe3+ ions, where the fluorescence intensity of carbon quantum dots was remarkably quenched in the presence of Fe3+ ions. A good linear relationship for Fe3+ ion detection was obtained from 0 to 500 μmol/L with a detection limit as low as 0.26 μmol/L. Furthermore, the proposed method also provided satisfactory results in the tap water.

Engineering Nitrogen-Doped Carbon Quantum Dots: Tailoring Optical and Chemical Properties through Selection of Nitrogen Precursors.

The process of N-doping is frequently employed to enhance the properties of carbon quantum dots. However, the precise requirements for nitrogen precursors in producing high-quality N-doped carbon quantum dots (NCQDs) remain undefined. This research systematically examines the influence of various nitrogen dopants on the morphology, optical features, and band structure of NCQDs. The dots are synthesized using an efficient, eco- friendly, and rapid continuous hydrothermal flow technique. This method offers unparalleled control over synthesis and doping, while also eliminating convention-related issues. Citric acid is used as the carbon source, and urea, trizma base, beta-alanine, L-arginine, and EDTA are used as nitrogen sources. Notably, urea and trizma produced NCQDs with excitation-independent fluorescence, high quantum yields (up to 40%), and uniform dots with narrow particle size distributions. Density functional theory (DFT) and time-dependent DFT modelling established that defects and substituents within the graphitic structure have a more significant impact on the NCQDs' electronic structure than nitrogen-containing functional groups. Importantly, for the first time, this work demonstrates that the conventional approach of modelling single-layer structures is insufficient, but two layers suffice for replicating experimental data. This study, therefore, provides essential guidance on the selection of nitrogen precursors for NCQD customization for diverse applications.

Impact of nitrogen doping on the polarization properties of carbon quantum dots

This study investigated the polarization characteristics of nitrogen-doped carbon quantum dots (CQDs) and their correlation with nitrogen doping levels through experimental and theoretical approaches. We compared carbon quantum dots with different nitrogen doping contents and discovered that with increasing nitrogen content, the lattice dimensions of the nitrogen-doped CQDs decrease while their anisotropy becomes more distinct. These changes resulted in significant variations in polarization and phase. Furthermore, the introduction of nitrogen elements was found to influence the fluorescence emission properties of the CQDs as well as the hybridization state of the carbon atoms. The findings underscored the potential to tailor the polarization properties of carbon quantum dots through controlled nitrogen doping, opening up new avenues for their application in advanced display technologies.

Hydrothermal synthesis of B, S, and N-doped carbon quantum dots for colorimetric sensing of heavy metal ions.

In this study, glucose was used as the carbon source to synthesize carbon quantum dots (CQDs) and also aimed to synthesize CQDs doped with heteroatoms such as sulphur, nitrogen, and boron to enhance their functionality. The obtained material has been characterized by several techniques. According to FL analysis, the highest peaks for CQD, N-CQD, B-CQD, and S-CQD were determined as 432 nm (ex 350), 425 (ex 350), 430 nm (ex 340 nm), and 436 nm (ex 340 nm), respectively. FTIR spectra showed different characteristic peaks for CQD, and the FTIR results show that CQDs have a unique structure. According to TEM analysis, the morphology of all CQDs was found to be spherical and monodisperse with average sizes in the range of 5-7 nm. The characterization results of CQDs show that the addition of heteroatoms changes the properties of CQDs. The synthesized CQDs were also tested as colorimetric sensors for the detection of heavy metals. It was observed that CQDs detected Fe3+ metal ions, B-CQD and S-CQD detected Fe3+ and Ag+ metal ions, and N-CQDs detected Ca2+ metal ions. Sensor studies were performed for all CQDs and linear plots were obtained against metal concentrations in the range of 0.06-1.23 μM. LOD values for CQD, N-CQD, S-CQD, and B-CQD were calculated as 0.187 μM (Fe3+), 0.391 μM (Ca2+), 0.224 μM (Fe3+)-0.442 μM (Ag+), and 0.182 μM (Fe3+)-0.174 μM (Ag+), respectively. The results show that the addition of B, N, and S atoms to CQDs plays a role in the improvement and modification of colorimetric sensor properties and has the potential to be used in sensor applications for the detection of heavy metals in areas such as the environment and health.

The effect of lignin molecular weight on the formation and properties of carbon quantum dots

Five different Mw fractionated lignins were used to prepare five types of L-CQDs for general cell imaging and to clarify the effects of lignin Mw on the formation and properties of L-CQDs.

Synthesis and Characterization of Optical Properties of Carbon Quantum Dots (CQD) Based on Mustard Green (Brassica juncea L) Leaf with Urea Addition

Carbon quantum dots (CQDs) are a class of fluorescent carbon nanomaterials. Carbon quantum dots (CQDs) were synthesized in this work from Mustard Leaves (Brassica juncea L) with the Addition of Urea via a microwave-assisted reflux method. This research aims to characterize CQDs' optical properties, energy gap, and emission under UV light computationally and experimentally. The studied optical properties obtained the maximum absorption peak observed from the UV-Vis spectrum of CQDs without urea shown at 233 nm. The UV-Vis spectrum of CQDs with the addition of urea (1 g, 1.5 g, and 2 g urea) has maximum absorption peaks at 424 nm, 422 nm, and 418 nm. The addition of urea causes a shift in the peak of the UV-Vis absorption spectrum towards red wavelengths (redshift). CQDs display bright green emissions when exposed to UV irradiation. In this work, the structures of CQDs of various forms (CQD-24, CQD-54, CQD-24-NH2, CQD-54-NH2) are theoretically studied in detail, and the results present both models (CQD-24, CQD-54) shows that the calculation results are in accordance with the experimental results, namely having a maximum UV-Vis absorption at 233 nm and in the range 200-400 nm. The results of calculations based on experiments show the same trend, namely that with the addition of urea, there is a shift in the absorption peak (redshift). The gap energy obtained also decreased with the addition of urea. CQDs solution emits yellow-green light.

Recombinant Organophosphorus acid anhydrolase (OPAA) enzyme-carbon quantum dot (CQDs)-immobilized thin film biosensors for the specific detection of Ethyl Paraoxon and Methyl Parathion in water resources

Organophosphates pesticide (OP) toxicity through water resources is a large concern globally among all the emerging pollutants. Detection of OPs is a challenge which needs to be addressed considering the hazardous effects on the health of human beings. In the current research thin film biosensors of recombinant, Organophosphorus acid anhydrolase (OPAA) enzyme along with carbon quantum dots (CQDs) immobilized in thin films were developed. OPAA-CQDs thin film biosensors were used for the specific detection of two OPs Ethyl Paraoxon (EP) and Methyl Parathion (MP) in river water and household water supply. Recombinant OPAA enzyme was expressed in E. Coli, purified and immobilized on the CQD containing chitosan thin films. The CQDs used for this purpose were developed by a one-pot hydrothermal method from phthalic acid and Tri ethylene diamine. The properties of CQDs, OPAA and thin films were characterized using techniques like XPS, TEM, XRD, enzyme activity and CLSM measurements. Biosensing studies of EP and MP were performed by taking fluorescence measurements using a fiber optic spectrometer. The analytical parameters of biosensing were compared against an estimation carried out using the HPLC method. The biosensing performance indicates that the OPAA-CQDs thin film-based biosensors were able to detect both EP and MP in a range of 0–100 μM having a detection limit of 0.18 ppm/0.69 ppm for EP/MP, respectively with a response time of 5 min. The accuracy of estimation of EP/MP when spiked in water resources lie in the range of ∼100–102% which clearly indicates the OPAA-CQD based thin film biosensors can function as a point-of-use method for the detection of OP pesticides in complex water resources.

Solvent-Dependent Photoluminescence Emission and Colloidal Stability of Carbon Quantum dots from Watermelon Peels.

Waste peels are considered an environmental burden and typically disposed in landfills. The aim of this study was to investigate the effects of various solvents on the luminescence properties of carbon quantum dots (CQDs). Watermelon peels were recycled and reuse as precursors for the synthesis of biomass CQDs via a green carbonization method. The colloidal stability, surface charge, and particle size were characterized using zeta potential and dynamic light scattering (DLS). DLS revealed that the size of the CQDs was approximately 5.80 ± 0.4nm to 9.74 ± 0.8nm. The high-resolution transmission electron microscopy (HRTEM) results demonstrated a correlation with the DLS results. The optical properties were characterized by photoluminescence (PL) and UV-Visible (UV-Vis) spectroscopy. PL measurements at different excitation wavelengths revealed that the CQDs emissions were influenced by the polarity of the solvents. Meanwhile, the Fourier transform infra-red (FTIR) results showed the presence of oxygen-containing groups on the surface of the CQDs. These results deepen our understanding of the solvent-dependent behavior and colloidal stability of the CQDs.

Studying the structural and optical properties of carbon quantum dots prepared by electro-chemical method

Studying the structural and optical properties of carbon quantum dots prepared by electro-chemical method

Machine-learning analysis to predict the fluorescence quantum yield of carbon quantum dots in biochar

Biochar nanoparticles have recently attracted attention, owing to their environmental behavior and ecological effects. However, biochar has not been shown to contain carbon quantum dots (< 10 nm) with unique photovoltaic properties. Therefore, this study utilized several characterization techniques to demonstrate the generation of carbon quantum dots in biochar produced from 10 types of farm waste. The generated carbon quantum dots had a quasi-spherical morphology and high-resolution lattice stripes with lattice spacings of 0.20–0.23 nm. Moreover, they contained functional groups with good hydrophilic properties, such as amino and hydroxyl groups, and elemental O, C, and N on the surface. A crucial determinant of the photoluminescence properties of carbon quantum dots is their fluorescence quantum yield. Therefore, the relationship between the biochar preparation parameters and the fluorescence quantum yield was investigated using six machine learning analytical models based on 480 samples. Among the models, the gradient-boosting decision-tree regression model exhibited the best predictive performance (R2 > 0.9, RMSE <0.02, and MAPE <3), and was used for the analysis of feature importance; compared to the properties of the raw material, the production parameters had a greater effect on the fluorescence quantum yield. Additionally, four key features were identified: pyrolysis temperature, residence time, N content, and C/N ratio, which were independent of farm waste type. These features can be used to accurately predict the fluorescence quantum yield of carbon quantum dots in biochar. The relative error range between the predicted and the experimental value of fluorescence quantum yield is 0.00–4.60 %. Thus, the prediction model has the potential to predict the fluorescence quantum yield of carbon quantum dots in other types of farm waste biochar, and provides fundamental information for the study of biochar nanoparticles.

Synthesis, characterization, photoluminescent properties of carbon quantum dots and its applications in wastewater treatment

Carbon-based nanomaterials are currently gaining attention in wastewater treatment. They have gained a prime position in membrane filtration to degrade pollutants. One of the most recent additions to the field of carbon-based nanomaterials is quantum dots (QDs). Due to their exceptional qualities, QDs are among the most promising carbon-based nanomaterials at the forefront of the wastewater treatment research field. Nonetheless, most quantum dots were not sustainably fabricated. Therefore, this study aims to evaluate the carbon-based carbon quantum dots derived from biomass wastes (rubber seed shells) where the properties, behaviour and photoluminescence characteristics were evaluated through several characterization analyses. The QDs were characterized using Fourier-transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), field emission scanning electron microscope (FESEM) equipped with energy-dispersive X-ray spectroscopy (EDX), photoluminescence spectroscopy, zeta potential analyser and Raman spectroscopy. The morphological analysis revealed multi-layered planes with highly porous and uneven surfaces, consisting of a large number of oxygen-functional groups (hydroxyl, carboxyl, carbonyl). The mapping results showed a large uniform distribution of carbon and oxygen elements on the surface of QDs with a more signified composition of wt% carbon (72.4%) compared to oxygen elements, with 23.6%. The spectroscopic and photoluminescence studies confirmed the fabrication of high-quality carbon quantum dots with blue-greenish fluorescence emissions. These results have shown promising biomass-based QDs that can be applied in wastewater treatment based on their unique characteristics. Thus, the derived biomass-based QDs can be viewed as a promising and cost-effective adsorbent for wastewater and water treatment.

Effect of Hydrothermal Reaction Temperature on Fluorescent Properties of Carbon Quantum Dots Synthesized from Lemon Juice for Adsorption Applications

Photoluminescent carbon quantum dots (CQDs) were synthesized from lemon juice precursors via single-step, hydrothermal techniques under different temperatures to control the optical properties. The synthesized CQDs were characterized by PL, illuminated UV analyzer chamber, UV–vis spectroscopy, X-ray diffractometer, Fourier-transformed infrared spectrophotometry, and zeta potential techniques. The results show that the synthesized CQDs had an excellent blue–green emission extending up to the infrared region with high quantum yield (Φ) in the range of 14%–41%. The effect of reaction temperature and the aging of CQDs on the emission spectra of CQDs are also investigated. Furthermore, the adsorption effect of the synthesized CQDs was evaluated on methylene blue (MB) dyes. The result indicated the synthesized CQDs have excellent adsorbent properties with a removal efficiency of 60%–82% and an extremely fast adsorption rate of 6 × 10−2 min−1 for MB dyes.

Nitrogen-Doped Carbon Quantum Dots for Biosensing Applications: The Effect of the Thermal Treatments on Electrochemical and Optical Properties

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]0+, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

(Keynote, Digital Presentation) First-Principles Study of Optical and Electronic Properties of Carbon Quantum Dots

We study the optical and electronic properties of carbon-based quantum dots using first-principles calculations. Based on time-dependent density functional theory we calculated absorption and emission of carbon quantum dots, we focus on the influence of surface (edge) functional groups. We can show that nitrogen groups on the carbon edges are decisive for the emission properties of small carbon quantum dots and could give rise to charge-carrier multiplication which has been suggested by recent experiments. Moreover, we explain the stability, with regard to the absorption in the optical range, of carbon quantum dots under ambient conditions. Here, we demonstrate that surface oxidation does only influence the absorption in the visible light range but does give rise to variation in the UV absorption.