Nitrogen Co-doped Carbon Quantum Dots Research Articles

Facile One-Pot Microwave-Assisted Synthesis and Ultrafast Spectroscopic Characterization of Nitrogen-Sulfur-Codoped Carbon Quantum Dots.

We report an eco-friendly, cost-effective, one-pot microwave-assisted synthesis of nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs) using citric acid and thiourea in formamide without surface passivation. The N,S-CQDs were characterized by HRTEM, FE-SEM, XRD, EDX, FTIR, Raman, and XPS, confirming monodispersed spherical particles of 4.8 nm with an amorphous carbon phase containing oxygen, nitrogen, and sulfur. The comprehensive photophysical studies of N,S-CQD employed by steady state and different time-resolved spectroscopic techniques (TCSPC, Ultrafast Time-Resolved Fluorescence Up-Conversion and Femtosecond Transient Absorption techniques). These N,S-CQDs show broad UV-visible to near-infrared absorption with peaks near 300 and 400 nm and emit strong blue photoluminescence at 360 nm excitation, with a quantum yield of ~8.4%. Time-resolved spectroscopy (TCSPC, fluorescence up-conversion, transient absorption) reveals multiexponential carrier relaxation with time constants from 0.5 ps to > 500 ps, including a 360 ps rise component and three distinct decay components, indicating complex fluorescence driven by surface defects. Ultrafast decay components correspond to thermal cooling of hot excitons, while later decays relate to carrier trapping at surface states. The tunable optical properties and carrier dynamics make N,S-CQDs promising for optoelectronic applications such as LEDs, sensors, and photodetectors, with further enhancement possible through surface engineering and defect control.

Carbon Quantum Dots Based Nanocomposite for Selective Mercury Detection.

The emergence of 2D carbon-based materials has a profound impact on various research areas, such as biosciences, electronics, optics, environmental protection, and monitoring. Mercury, a highly toxic pollutant, can cause severe health complications such as neural toxicity, insomnia, cognitive dysfunction, muscle atrophy, peripheral vision impairment, and emotional instability. A suitable 2D nanostructural interface is required to effectively monitor mercury levels in the environment. This study presents the use of synergistic nitrogen and sulfur co-doped carbon quantum dots anchored on exfoliated molybdenum disulfide for rapid detection of mercury ions. This process employs a biomass extract that facilitates the exfoliation of bulk molybdenum disulfide and also act as carbon precursor for in situ carbon quantum dot deposition on exfoliated molybdenum disulfide. The nanocomposite provides photo-physical properties and surface functionalities from both organic and inorganic components to bridge the charge transfer, resulting from selective binding of mercury (II) ions. This 2D heterojunction is capable of detecting mercury (II) ions with a response time of ≈90 s, limit of detection of 31pm, and photosensitivity of 16.6A cm-2 M-1. The interface is tested on blood samples from Labeorohita fish to detect mercury (II) toxicity in nature.

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.

Novel quantum dots-based assay for the determination of anti-hypertensive drugs minoxidil and timolol in different matrices

The present work reports a sensitive, affordable, and ecologically friendly spectrofluorimetric method for the assessment of two antihypertensive medications, namely minoxidil and timolol. Blue-emitting sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were generated by exposing soluble starch and thiourea to a 15-minute microwave treatment. The so- prepared nanodots displayed fluorescence at 276/430 nm with a quantum yield of 22 %. Inspection of the so-prepared nano-sensor verified their doping with nitrogen and sulfur, and their size was in the range of 4.5–9.03 nm. The proposed method was found to be rectilinear in the range of 0.20–5.0 and 2.0–30.0 µg/mL, with LOQs of 0.16 and 0.82 µg/mL for minoxidil and timolol, respectively. The developed method was employed to assess the concentrations of minoxidil and timolol in their pharmaceutical formulations, with %recoveries varying between 99.00 % and 101.94 %, and low RSD values (less than 2 %). The high sensitivity of the developed method allowed its use for timolol measurement in artificial aqueous humor, with % recoveries between 97.60 %.and 101.57 %. The study further examined how each analyte interacted with the prepared dots, leading to a quenching of their fluorescence. Additionally, an interference study was utilized to evaluate the specificity of the proposed approach through determining analyte levels in the existence of common additives, co-formulated drugs, and co-administered drugs. The analytical eco-scale, GAPI and AGREE assessment techniques were utilized to confirm the suggested method greenness.

Rapid microwave fabrication of highly luminescent nitrogen and phosphorous co-doped carbon quantum dots for the determination of glutathione in pharmaceutical supplements

A facile and sensitive nano-probe for spectrofluorometric glutathione (GSH) determination has been developed based on dual-doped nitrogen and phosphorus carbon quantum dots (NP@CQDs). The NP@CQDs were prepared, through a rapid, one-step microwave heating method in only 180 s with a high quantum yield (0.63) using ethylenediaminetetraacetic acid as carbon and nitrogen precursor and diammonium hydrogen phosphate as nitrogen and phosphorus dopant. The synthesised NP@CQDs had a maximum bluish fluorescence emission at 420 nm, after excitation at 360 nm. The luminescence of the prepared NP@CQDs was quenched via a static quenching mechanism by ferrous ions, while ferric ions did not affect the emission of NP@CQDs. GSH was mixed with ferric ions before adding NP@CQDs to exploit this observation. The attenuation in emission observed after adding NP@CQDs to GSH/ferric ions was directly related to the GSH concentration, as GSH worked to reduce the ferric ions present and produce ferrous ions. The proposed fluorometric method was validated in compliance with the International Council on Harmonization (ICH) guidelines. The proposed fluorescent nano-probe showed good linearity for GSH determination over a range of 0.5–10 µg/mL with % recoveries ranging between 99.50 and 101.86 %, and RSD less than 2 %. NP@CQDs were implemented for GSH determination in pharmaceutical supplementary capsules with respectable accuracy and precision. This approach is simple, reliable, accurate, specific, and it also does not require expensive chemicals or sophisticated equipment. This work opens up other uses of NP@CQDs in pharmaceutical and environmental analysis.

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.

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.

Embedded iron and nitrogen co-doped carbon quantum dots within g-C3N4 as an exceptional PMS photocatalytic activator for sulfamethoxazole degradation: The key role of Fe[sbnd]N bridge

The covalent modification of graphite-phase carbon nitride (g-C3N4) by carbon quantum dots (CQDs) is a promising way to improve its photocatalytic performance. Although CQDs can act as charge mediator for electrons storage and transfer, it is crucial to construct efficient interfaces, which serves as active sites for tight connect with g-C3N4 and fast release of electrons. Herein, a novel iron and nitrogen co-doped carbon quantum dots (Fe, N-CQDs) assembled g-C3N4 composite (FNCCN) was constructed via FeN bridge by hydrothermal and thermal polymerization methods. The FNCNN rivaled popular nitrogen-doped carbon quantum dots (N-CQDs) combined with g-C3N4 composites for peroxymonosulfate (PMS) activation and degradation of sulfamethoxazole (SMX). The SMX degradation rate (0.0963 min−1) is 5.38 and 3.15 times higher than that of g-C3N4 and N-CQDs/g-C3N4. The characterization and DFT calculation results suggest that Fe, N-CQDs was successfully incorporated into carbon matrix of g-C3N4 via FeN covalent bond, which joints the two counterparts closely and creates electron transport channels for higher electrons transfer efficiency. The FeN coordinated structure promotes PMS reduction on Fe2+ of FeN sites for HO and SO4- production and expedited photo carries separation through Fe3+/Fe2+ cycling. In addition, the degradation efficiency, ROS identification, EPR test and degradation pathway of SMX was determined, and the intermediate toxicity of degradation products was predicted. This work constructed a tight atomic-level connection between hydrophobic g-C3N4 and hydrophilic CQDs, which improved an effective strategy for accelerating electron transport and efficient photocatalytic activation of PMS.

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

Enhancing photocatalytic destruction of lignin via cellulose derived carbon quantum dots/g-C3N4 heterojunctions

Lignocellulosic biomass exhibits a promising potential for production of carbon materials. Nitrogen and phosphorus co-doped carbon quantum dots (N,P-CQDs) were fabricated via (NH4)2HPO4 assisted hydrothermal treatment of cellulose pulp fibers. The as-prepared N,P-CQDs were characterized by HRTEM, FTIR, fluorescence and UV–vis, and then incorporated into g-C3N4 (CN) through sonication and liquid deposition, forming N,P-CQDs/sonication treated g-C3N4 (C-SCN) composites, which were then explored as photocatalysts. The photocatalytic ability of C-SCN towards model lignin was further analyzed. The results showed that, the fluorescence intensity and photoluminescence performance of N,P-CQDs were much higher than that of CQDs; the heterojunction was successfully constructed between the composites of N,P-CQDs and SCN; the incorporation of N,P-CQDs enhanced the visible light absorption, but reduced the band gap of the composite heterojunction; the resultant photocatalysts exhibited a good photocatalytic ability of model lignin via catalyze the fracture of β–O–4′ ether bond and CC bond, i.e., the photocatalytic degradation ratio reached up to 95.5 %; and the photocatalytic reaction generated some valuable organics such as phenyl formate, benzaldehyde, and benzoic acid. This study would promote the high value-added utilization of lignocellulosic resources especially in the transformation of lignin, conforming the concept of sustainable development.

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

A method utilizing nitrogen-doped and sulfur-doped carbon quantum dots (N, S-CQDs) as fluorescent probes for the rapid detection of Fe3+, L-ascorbic acid (AA), and alkaline phosphatase (ALP) was presented. The fluorescence intensity of N, S-CQDs nanoprobes can be rapidly and efficiently quenched by Fe3+and based on the fluorescence "turn off-on" characteristic of N, S-CQDs nanoprobes, the fluorescence signals of the N, S-CQDs/Fe3+can be recovered after the addition of AA. By coupling a fluorescent nanoprobe to an enzyme and L-ascorbic acid-2-phosphate (AA2P), a green, simple, rapid and effective fluorescent analytical method for the determination of ALP was developed. The prepared N, S-CQDs showed high sensitivity and selectivity to Fe3+, AA and ALP with the detection limit of 0.42μM, 12.7nM and 0.017 U·L-1and their optimal concentration ranges were10-600µM, 10-200μM, 0.18-54 U·L-1, respectively. The fluorescence quantum yield of N, S-CQDs (0.2mg·mL-1) at 393nm excitation wavelength was 4.41%. Additionally, the fluorescent nanoprobes have been employed to successfully measure ALP in serum samples. It is expected that the established method may offer a new approach for biomolecular detection in clinical diagnosis and pharmaceutical analysis.

Enhancing the visible light absorption of MOF-808 by surface decoration with sulfur and nitrogen co-doped carbon quantum dots: Highly efficient photocatalyst for improved photocatalytic water remediation

Metal-organic frameworks (MOFs) have aroused growing attention in the domain of photocatalysis. However, the photocatalytic performance of MOFs has been severely restricted by their fast recombination of photo-generated electrons and low utilization of solar energy. Combining MOFs with narrow-gap semiconductors can help to overcome their functional shortcomings. In this work, MOF-808 and sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were synthesized using a simple solvothermal technique. Then, novel MOF-808/S,N-CQDs(x) (MS-x) composites were fabricated through a simple solvent-deposition technique to decorate various amounts of S,N-CQDs on the surface of MOF-808. The morphology of MOF-808 and MS-0.5 composite, along with the lattice spacing, and size distribution of decorated S,N-CQDs on MOF-808 surface were investigated by SEM and HR-TEM analyses. According to the UV–Vis DRS and Tauc plots findings, MOF-808 was not photo-active in visible light region because of its large band gap energy (3.85 eV). In contrast, the photocatalytic performance of the prepared composites in Rhodamine B (RhB) degradation was significantly enhanced compared with MOF-808 under visible light irradiation. The results confirmed that S,N-CQDs play a key role in enhancing the visible light absorption efficiency. MS-0.5 composite exhibited the highest photocatalytic activity among the other composites and demonstrated high RhB photodegradation up to 89 % under visible light and 95 % under sunlight irradiation in optimal conditions. According to the kinetic studies, MS-0.5 composite had the highest rate constant, 29.67 and 6.93 times greater than S,N-CQDs and MOF-808, respectively. The scavenger tests revealed that h+ and OH radicals were the main active intermediates in the photocatalytic reaction. In addition, MS-0.5 composite exhibited excellent reusability because only a minor loss of photoactivity was observed after four reaction cycles.

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.

Lanthanum nitrogen Co-doped carbon quantum dots as optical and smartphone sensors for serotonin detection

A simple bottom up approach using hydrothermal technique was applied to prepare lanthanum and nitrogen Co-doped carbon quantum dots and were characterized by XRD, EDS, TEM, SEM FT-IR, XPS, fluorescence and UV-VIS spectroscopy to study their crystal structure, elemental and chemical composition, particle size, morphology and optical properties. It was found that morphology was spherical and particle size was 3–4 nm. EDS and XPS helps to prove the successful doping of lanthanum and nitrogen to carbon quantum dots with excitation and emission wavelengths 340 and 445 nm respectively. The intense blue color of fluorescent QDs were quenched with addition of serotonin due to the electrostatic interactions, π-π stacking interaction and may be due to complex formation between La,N-CQDs/Ser and the static quenching mechanism with inner filter effect has been observed. These La,N-CQDs were used as fluorescent probes for sensitive and selective detection of serotonin in a good linear range of 0–38 nM with low limit of detection 7.4 nM.The smartphone based portable detection was also developed for detection of serotonin providing the reliable information for analysis of color change and real sample analysis studies were also carried out. The uniqueness, high sensitivity and accuracy of the optical probe that was constructed are confirmed and this method's LOD is also highly competitive.

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.