Sulfur Co-doped Carbon Quantum Dots Research Articles

N, S-Codoped Carbon Quantum Dots with High Inhibition Efficiency: Implications for Corrosion Mitigation of Carbon Steel in Acidic Environments.

The environmental friendliness, economic feasibility, and high efficiency of carbon quantum dots (CQDs) render them as highly promising candidates for corrosion inhibitors. The present study proposed the fabrication of nitrogen- and sulfur-codoped CQDs via an one-step hydrothermal method using l-cysteine and 4-aminosalicylic acid as precursors. The structure, particle size, and surface ligands of the prepared CQDs were determined through spectroscopy and transmission electron microscopy characterization. Subsequently, the inhibition performance of the CQDs on carbon steel in a 0.5 M sulfuric acid solution was evaluated through weight loss measurement, electrochemical methods, and surface analysis. The CQDs exhibited remarkable inhibition efficiencies of 97.9% at 293 K and 98.9% at 313 K, with a concentration of 150 ppm. In addition, the obtained CQDs demonstrated a combined physisorption and chemisorption adsorption behavior, which complied with the Langmuir adsorption isotherm. These findings provide insight into the inhibition mechanism and highlight the potential of codoped CQDs for corrosion mitigation applications in acidic environments.

Determination of sudan III using nitrogen and sulfur co-doped carbon quantum dots with fluorescence enhancement effect

Sudan III, a synthetic azo dye, is commonly used for coloring oils, waxes, and various plastics. However, its unauthorized presence in food and food products poses serious health hazards, including potential carcinogenic effects. In this study, we investigated the application of nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs) as a fluorescence sensor to detect trace amounts of sudan III. When exposed to trace amounts of sudan III, the fluorescence signal of N,S-CQDs was significantly enhanced. Under optimal conditions (pH 5.0 and an incubation time of 4 minutes), the fluorescence enhancement of N,S-CQDs showed a linear relationship with sudan III concentration in the range of 7.5 x 10-10 to 1.0 x 10-8 M, with a limit of detection of 2.0 x 10-10 M (equivalent to 0.07 ppb). The method demonstrated high accuracy (recovery from 91.5% to 103.5%), good reproducibility (RSD < 3.86%), and excellent selectivity for sudan III over other azo dyes. We successfully applied this developed method to analyze sudan III in chili sauce and chili powder samples, cross-checking differences between results less than 10% with LC-MS/MS analysis.

Nitrogen and Sulfur Co-Doped Carbon Quantum Dots as Fluorescent Nanosensors for Determination of Two Tetracycline Antibiotics in Dosage Forms and Human Plasma: Compliance With Greenness Metrics.

In this study, a novel, sensitive, and cost-effective spectrofluorimetric approach was established for the estimation of two important tetracycline antibiotics, tetracycline and doxycycline, without any pre-treatment procedures or harsh reaction conditions, for the first time. The proposed methodology is based on the quantitative quenching effect of each tetracycline and doxycycline on the native fluorescence of nitrogen and sulfur co-doped carbon quantum dots (NS-CQDs). A simple and ultrafast approach was applied to synthesize NS-CQDs using thiosemicarbazide and citric acid as starting materials after incubation in a microwave for only 1 min. Utilizing an excitation wavelength of 360 nm, NS-CQDs showed maximum emission peak at 430 nm. Calibration curves revealed excellent linearity within the ranges of 1.0-10.0 and 0.8-12.0 μg/mL with detection limits of 0.20 and 0.09 μg/mL for tetracycline and doxycycline, respectively. Due to the method's high sensitivity and selectivity, the proposed approach was applied for the determination of the studied drugs in their capsules and human plasma samples with high %recoveries. The developed approach was validated according to ICHQ2(R2) guidelines. GAPI and AGREE metric tools were used to verify the method's greenness and eco-friendliness, suggesting its use as a green substitute for the analysis of the studied drugs.

A ratiometric fluorescent probe for the determination of quinolone antibiotics in milk based on N and S co-doped carbon quantum dots

Quinolone antibiotics are widely used to prevent and treat diseases caused by bacterial infection. However, overuse of antibiotics may lead to their residue in the environment and food, posing potential threats to human health. In this study, a ratiometric fluorescent probe based on nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) was synthesized, which can realize the detection of moxifloxacin (MXF), gatifloxacin (GAT) and ofloxacin (OFX) in milk. After addition of these antibiotics, the fluorescence at 440 nm originating from N, S-CQDs was significantly quenched due to the fluorescence resonance energy transfer (FRET), while the fluorescence at 525 nm (MXF), 500 nm (GAT) and 515 nm (OFX) were enhanced due to aggregation induced emission (AIE). The fluorescence changes were completed within 30 s and stabilized for at least 14 days. Good linear relationships between the fluorescence intensity ratios (F525/F440 for MXF, F500/F440 for GAT and F515/F440 for OFX) and the antibiotic concentrations ranging from 0.1 to 100 mg L−1 were obtained, with R2 above 0.99. The limits of quantitation were in the range of 1.67–6.20 μg L−1, and MXF, GAT and OFX can be well identified by linear discriminant analysis. The probe enabled quantitative analysis of MXF, GAT and OFX in milk samples, with recoveries ranging from 82% to 107%. A test strip based on the ratiometric fluorescence probe was successfully applied for the detection of MXF and GAT in milk in combination with a smartphone. This method exerted high specificity and sensitivity, which has the potential to achieve in-site detection of MXF, GAT and OFX in milk.

Development of a Nanomarker for In Vivo Monitoring of Dopamine in Plants.

Dopamine, alongside norepinephrine and epinephrine, belongs to the catecholamine group, widely distributed across both plant and animal kingdoms. In mammals, these compounds serve as neurotransmitters with roles in glycogen mobilization. In plants, their synthesis is modulated in response to stress conditions aiding plant survival by emitting these chemicals, especially dopamine that relieves their resilience against stress caused by both abiotic and biotic factors. In present studies, there is a lack of robust methods to monitor the operations of dopamine under stress conditions or any adverse situations across the plant's developmental stages from cell to cell. In our study, we have introduced a groundbreaking approach to track dopamine generation and activity in various metabolic pathways by using the simple nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs). These CQDs exhibit dominant biocompatibility, negligible toxicity, and environmentally friendly characteristics using a quenching process for fluorometric dopamine detection. This innovative nanomarker can detect even small amounts of dopamine within plant cells, providing insights into plant responses to strain and anxiety. Confocal microscopy has been used to corroborate this occurrence and to provide visual proof of the process of binding dopamine with these N, S-CQDs inside the cells.

Fluorimetric determination of Vonoprazan via quenching of nitrogen and sulfur co-doped carbon quantum dots: A rapid and sustainable analytical approach.

In this study, an environmentally sustainable fluorimetric method for determination of Vonoprazan fumarate (VON) in dosage forms using nanoprobes consisting of nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs). The N, S-CQDs were prepared through a microwave-assisted method in 30 s. The resulting N, S-CQDs were characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). They exhibit fluorescence emission at 460 nm after excitation at 385 nm with a high quantum yield (60%). The analytical approach for VON determination relies on the quenching effect exerted by VON on the native fluorescence intensity of CQDs. The quenching mechanism was investigated using Stern-Volmer plots. The proposed method demonstrates linearity across a concentration range 10-80 μM (4.6-36.8μg/mL) with corresponding limits of detection and quantitation calculated as 2.17 μM (0.99 μg/mL) and 6.58 μM (3.02 μg/mL), respectively. The method has been effectively utilized for the determination of VON in the pharmaceutical samples. Statistical comparison with reported RP-HPLC has been performed to verify the accuracy and precision of the developed method. The environmental sustainability of the developed method has been thoroughly examined through various greenness metrics.

Research on photocatalytic performance and mechanism of nitrogen–sulfur co-doped carbon quantum dots and C3N4 co-modified BiOBr

Research on photocatalytic performance and mechanism of nitrogen–sulfur co-doped carbon quantum dots and C3N4 co-modified BiOBr

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.

One-pot Microwave Synthesis of Cobalt, Nitrogen, and Sulfur Co-Doped Carbon Quantum Dots for Efficient Monosodium Glutamate Determination in Food Samples

The synthesis of cobalt, nitrogen and sulfur co doped carbon quantum dots (Co-NS-CQDs) has become a subject of significant research interest. These CQDs were produced using a single-step microwave method, which is considered environmentally friendly, and the entire process was completed in just 90 seconds. In this synthesis, citric acid was utilized as the carbon source, methionine served as the source for both nitrogen and sulfur, and cobaltous acetate was used to introduce cobalt ions into the CQDs structure. The synthesized carbon quantum dots (CQDs) exhibit a narrow size distribution and a high quantum yield of 51.5%, which is notably superior to non-metal-doped CQDs with a yield of 38%. Characterization of these CQDs was performed using different techniques such as transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transformation infrared spectroscopy (FTIR), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The developed CQDs have blue luminescence at emission wavelength 438 nm after excitation at 350 nm. Different factors affecting the CQDs synthesis including dialysis duration, reaction time and reaction temperature. These CQDs were utilized as a probe for the detection of monosodium glutamate (MSG) in various food products. The intensity of the fluorescence of the CQDs showed a direct and linear increase with the concentration of MSG within the range of 25–250 µg/mL. The detection and quantitation limits for MSG were 2.78 µg/mL and 8.44 µg/mL, respectively. Additionally, the developed method is environmentally friendly, as confirmed by assessments using the analytical Eco scale, Green Analytical Procedure Index (GAPI), and Analytical Greenness calculator (Agree). The proposed method presents several advantages over other reported methods in terms of convenience, rapid response, and attainment of accurate and precise results.

Photoelectrochemical quenching-recovery biosensor based on NSCQDs/Fe2O3@Bi2S3 for the detection of trypsin

BackgroundThe content of trypsin will change when pancreatic diseases occur, therefore developing a high-performance method for trypsin detection is of great significance for guiding patients on medication plans and improving their prognosis. Photoelectrochemical (PEC) analysis techniques have emerged as a solution to apply for bioassays. ResultsHerein, the Fe2O3@Bi2S3 and Nitrogen and sulfur co-doped carbon quantum dots (NSCQDs) were successfully synthesized by a hydrothermal method. Subsequently, NSCQDs/Fe2O3@Bi2S3 with a photocurrent amplification effect covered on fluorine-doped tin oxide (FTO) electrode as the substrate material and apoferritin (APO) as a bio-recognition element to quench the photocurrent of the substrate material which can be excited with light. Due to the decomposition specifically between APO and trypsin, the photocurrent response increased. The linear range for trypsin detection showed satisfied results from 2 to 1000 ng mL−1 under optimal conditions, with a detection limit of 0.42 ng mL−1 and a recovery rate of 97.41 %–103.02 %, enabling efficient quantitative analysis of trypsin. SignificanceIn this experiment, a PEC biosensor with simple operation, low detection limit, excellent selectivity and strong stability was successfully prepared, enabling quantitative analysis of trypsin in human serum samples through the quenching-recovery mechanism. It holds great significance for diagnosis and serves as a practical method for the detection of trypsin in the future.

Optimization, Kinetics, and Thermodynamics Study on the Degradation of RhB by ZnO Modified with Nitrogen and Sulfur Co-Doped Carbon Quantum Dots

Optimization, Kinetics, and Thermodynamics Study on the Degradation of RhB by ZnO Modified with Nitrogen and Sulfur Co-Doped Carbon Quantum Dots

Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe3+, Ascorbic Acid and Alkaline Phosphatase Activities

Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe3+, Ascorbic Acid and Alkaline Phosphatase Activities

Rapid environmentally benign label free detection of heparin using highly fluorescent N,S-CDs sensing probe through a turn-on mechanism

Heparin (HEP) is one of the oldest anticoagulant drugs that currently still in widespread clinical use. It lacks chromophore and not easily derivatized due to its hydrophilic nature. In this work we developed a green, selective, and sensitive fluorescence sensor for detection of HEP in its injection dosage forms. The sensor is composed of nitrogen and sulfur co-doped carbon quantum dots (N,S-CDs) semi quenched by Fe3+. The N,S-CDs were prepared using microwave assisted pyrolysis in 3.5 min and exhibited high emission at 425 nm after excitation at 350 nm with high quantum yield of 96%. Owing to the anionic nature of HEP, it could compete with N,S-CDs for Fe3+ complexation resulting in turning-on the quenched fluorescence. This fluorescence enhancement was linear over a concentration range between 6 and 20 μg/mL (R2 = 0.99) with a limit of detection of 1.41 µg/ml. The accuracy and precision of the proposed sensor were indicated by percentage recovery values between 98% −102% and %RSD less than 2, respectively. Furthermore, the proposed sensor was successfully applied for determination of HEP in injection dosage form. The developed sensor showed excellent greenness on analytical eco-scale (score 93%) and GAPI scale.

Nitrogen and sulfur co-doped coal-based carbon quantum dots enhance the photocatalytic hydrogen evolution of Co-Fe-P derived from MOF

In order to explore the functional application of coal and realize the high-value application of low-quality coal. Therefore, low-cost coal as a carbon source into environmental protection, high-value coal-based carbon quantum dots (CQDs). This study employed high-sulfur coal as the carbon source and urea as the nitrogen source to successfully synthesize nitrogen and sulfur co-doped coal-based carbon quantum dots (NSCQDs) via a one-pot hydrothermal method. These NSCQDs were utilized as co-catalysts to assist the photocatalytic water splitting and hydrogen evolution of metal phosphides (Co-P and Fe-P). The obtained catalysts were subjected to systematic structural and property analyses, and the photocatalytic hydrogen evolution activity and stability were investigated, along with an analysis of the photocatalytic mechanism. The results revealed that the novel composite photocatalyst exhibited high hydrogen evolution activity, with a maximum hydrogen evolution rate of 28.41 mmol·g−1·h−1 at pH 10. Under a wavelength of 520 nm, the apparent quantum efficiency (AQE) reached 4.93%, and the solar-to-hydrogen (STH) conversion efficiency reached 0.46%. The semiconductor type (n-type) of the monophasic catalyst was determined through Mott-Schottky analysis, and the band structure was analyzed accordingly. The conduction and valence band positions for Co-P were determined to be -0.44 eV and 1.31 eV, respectively, while those for Fe-P were found to be -0.51 eV and 1.17 eV, respectively. Based on these results, it is inferred that an S-type heterojunction is formed between Co-P and Fe-P, and NSCQDs enhanced photocatalytic hydrogen evolution as an auxiliary catalyst. This research advances the synthesis of coal-based carbon quantum dots and provides the key information for the photocatalytic decomposition of water and hydrogen evolution using coal-based CQDs.

Facile synthesis of nitrogen, sulfur co-doped carbon quantum dots for selective detection of mercury (II)

Facile synthesis of nitrogen, sulfur co-doped carbon quantum dots for selective detection of mercury (II)

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots (NSCQDs) nanoparticles on the surface of sheet cobalt-based metal-organic framework (Co-MOF) and graphitic carbon nitride (g-C3N4, CN). The structure and properties of the obtained catalysts were systematically analyzed. NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region. The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254 μmol/(g·h) at pH = 9. At the same time, NSCQDs synergy Co-MOF/CN composites have good stability. After four cycles of hydrogen production, the performance remains relatively stable. The transient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts. The semiconductor type (n-type semiconductor) of the single-phase catalyst was determined by the Mott–Schottky test, and the band structure was analyzed. The conductive and valence bands of CN are −0.99 and 1.72 eV, respectively, and the conduction and valence bands of Co-MOF are −1.85 and 1.33 eV, respectively. The mechanism of the photocatalytic reaction can be inferred, that is, Z-type heterojunction is formed between CN and Co-MOF, and NSCQDs was used as cocatalyst.

Facile synthesis of NS-doped carbon dots as sensitive “ON-OFF-ON” fluorescent sensor for Cu2+ and GSH detection

In this paper, a novel nitrogen and sulfur co-doped carbon quantum dots (NS-CQDs) were successfully prepared by a dehydration exothermic carbonization method. The NS-CQDs exhibited uniform size distribution, splendid photostability, and bright fluorescence emission with a fluorescence quantum yield of 24.1 %. It was found that Cu2+ could quench the fluorescence at 467 nm based on the static quenching effect when Cu2+ was added to the NS-CQDs. At this time, the fluorescence sensor changed from the “ON” state to the “OFF” state. When glutathione (GSH) was further introduced into the NS-CQDs/Cu2+ system, the fluorescence intensity of NS-CQDs was amazingly restored through the coordination reaction between GSH and Cu2+. The fluorescence sensor changed from the “OFF” state to the “ON” state. Therefore, NS-CQDs as an “ON-OFF-ON” fluorescence sensor was designed for sequential detection of Cu2+ and GSH. Furthermore, this study successfully demonstrated the sensor’s ability to selectively detect Cu2+ and GSH within a wide concentration range. Specifically, the detection range for Cu2+ was 0.1 μM−200.0 μM with a detection limit of 0.07 μM, while the range for GSH was 0.6 μM−180.0 μM with a detection limit of 0.1 μM. Most importantly, the NS-CQDs nanosensor could reliably monitor Cu2+ and GSH levels in human serum samples, with significant potential for practical applications.

Green “turn-off” luminescent nanosensors for the sensitive determination of desperately fluorescent antibacterial antiviral agent and its metabolite in various matrices

Nitazoxanide (NTX) is an antimicrobial drug that was used for the treatment of various protozoa. However, during the coronavirus pandemic, NTX has been redirected for the treatment of such virus that primarily infect the respiratory tract system. NTX is now used as a broad-spectrum antiviral agent. In this study, a highly sensitive and green spectrofluorometric method was developed to detect NTX in various dosage forms and its metabolite, tizoxanide (TX), in human plasma samples using nitrogen and sulfur co-doped carbon quantum dots nanosensors (C-dots). A simple and eco-friendly hydrothermal method was used to synthetize water soluble C-dots from citric acid and l-cysteine. After excitation at 345 nm, the luminescence intensity was measured at 416 nm. Quenching of C-dots luminescence occurred upon the addition of NTX and was proportional to NTX concentration. Assessment of the quenching mechanism was performed to prove that inner filter effect is the underlying molecular mechanism of NTX quenching accomplished. After optimizing all experimental parameters, the analytical procedure was evaluated and validated using the ICH guidelines. The method linearity, detection and quantification limits of NTX were 15 × 10–3–15.00 µg/mL, 56.00 × 10–4 and 15 × 10–3 µg/mL, respectively. The proposed method was applied for the determination of NTX in its commercial pharmaceutical products; Nanazoxid® oral suspension and tablets. The obtained % recovery, relative standard deviation and % relative error were satisfactory. Comparison with other reported spectrofluorimetric methods revealed the superior sensitivity of the proposed method. Such high sensitivity permitted the selective determination of TX, the main metabolite of NTX, in human plasma samples making this study the first spectrofluorimetric method in literature that determine TX in human plasma samples. Moreover, the method greenness was assessed using both Eco-Scale and AGREE approaches to prove the superiority of the proposed method greenness over other previously published spectrofluorimetric methods for the analysis of NTX and its metabolite, TX, in various dosage forms and in human plasma samples.

Rapid microwave synthesis of N and S dual-doped carbon quantum dots for natamycin determination based on fluorescence switch-off assay

Green, one-pot, quick, and easily synthesized nitrogen and sulfur co-doped carbon quantum dots (N,S-CDs) were obtained from cheap and readily available chemicals (sucrose, urea, and thiourea) using a microwave-assisted approach in about 4 min and utilized as a turn-off fluorescent sensor for estimation of natamycin (NAT). First, the effect of N and S doping on the microwave-synthesized CDs’ quantum yield was carefully studied. CDs derived from sucrose alone failed to produce a high quantum yield; then, to increase the quantum yield, doping with heteroatoms was carried out using either urea or thiourea. A slight increase in quantum yield was observed upon using thiourea with sucrose, while an obvious enhancement of quantum yield was obtained when urea was used instead of thiourea. Surprisingly, using a combination of urea and thiourea together results in N,S-CDs with the highest quantum yield (53.5%), uniform and small particle size distribution, and extended stability. The fluorescent signal of N,S-CDs was quenched upon addition of NAT due to inner filter effect and static quenching in a manner that allowed for quantitative determination of NAT over a range of 0.5–10.0 μg ml−1 (LOD = 0.10 μg ml−1). The N,S-CDs were applicable for determination of NAT in aqueous humor, eye drops, different environmental water samples, and bread with excellent performance. The selectivity study indicated excellent selectivity of the prepared N,S-CDs toward NAT with little interference from possibly interfering substances. In-silico toxicological evaluation of NAT was conducted to estimate its long-term toxicity and drug-drug interactions. Finally, the preparation of N,S-CDs, and analytical procedure compliance with the green chemistry principles were confirmed by two greenness assessment tools.

N, S-doped carbon quantum dot for long persistence phosphor assisted all-weather solar cells

Traditional solar cells can only work during the daytime. The solar cells that can harvest energy in all weather conditions are favorable to solving the energy crisis and ecological issues. We present a novel quantum dot-sensitized all-weather solar cell (AW-SC) that can harvest energy in both day and night conditions. The AW-SC consists of a TiO2/long persistence phosphor (LPP) photoanode sensitized by nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs) and a Pt counter anode. The N and S doping reduces the band gap of CQDs and enhances the charge injection into the TiO2 layer, resulting in better solar cell performance. The LPP enables the AW-SC to store unabsorbed light from visible to infrared wavelengths and emit green fluorescence to excite the N, S-CQDs in the dark. The optimal AW-SC achieves a power conversion efficiency (PCE) of 18.7% in the dark.