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The relative humidity (RH) determination is crucial in many fields. Based on the phosphorescent properties of room-temperature phosphorescent (RTP) carbon dots, the RTP carbon dots as a probe are expected to be used to rapidly detect relative humidity. In this study, matrix-free room-temperature phosphorescent N-doped carbon dots (N-CDs) were successfully prepared from urea, succinic acid, and acrylamide using a hydrothermal method. The as-synthesized N-CDs had good biocompatibility and water solubility. The N-CDs emitted blue fluorescence and green phosphorescence. Moreover, the N-CD powder exhibited stable phosphorescence with a phosphorescence lifetime of 158 ms (afterglow time to the naked eye for ~7 s). Because H 2 O molecules affected the afterglow time, the as-prepared N-CD test paper for the first time could be applied as a probe to monitor RH, the afterglow time of the N-CD test paper is linearly related to the RH (y = -0.0729x+7.042, R 2  = 0.998) and the RH detection range is 0%-85%. And the results were consistent with those obtained using a hygrometer. In addition, the N-CD solution could also be used as an encryption ink in the advanced information security field., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Carbon dots (CDs) emerge as excellent fluorescent nanomaterials, but the full exploitation and application of their exceptional properties in the development of fluorescence assay are still rare. In this work, cationic carbon dots (C-CDs) covered with plenty of positive charges on the surface were synthesized through a facile ultrasonic method. Negatively charged hyaluronic acid (HA) caused the aggregation of positively charged C-CDs and neutral red (NR) along its linear chain via electrostatic adsorption, leading to a remarkable Förster resonance energy transfer (FRET) from C-CDs to NR. However, the presence of hyaluronidase (HAase) resulted in the enzymolysis of HA, as well as the liberation of C-CDs and NR. The corresponding change of fluorescence color from red to green-yellow afforded a reliable ratiometric assay for HAase. Also the ratio of fluorescence intensity for C-CDs (I525) to that for NR (I630) was used for quantitative detection of HAase. The proposed sensing system was easily operated in aqueous media with a detection limit of 0.05 U/mL. This strategy provides a new approach for the wider application of some special CDs in detecting biomolecules.

A simple, sensitive and reliable dopamine (DA) biosensor was developed based on a carbon dots (CDs) and chitosan (CS) composite film modified glassy carbon electrode (CDs-CS/GCE). Under optimal conditions, the CDs-CS/GCE showed a better electrochemical response for the detection of DA than that of the glassy carbon electrode (GCE). The oxidation peak current (Ipa) of DA was linear with the concentration of DA in the range from 0.1 μM to 30.0 μM with the limit of detection as 11.2 nM (3S/N). The CDs-CS/GCE was applied to the detection of DA content in an injection solution of DA with satisfactory results.

Carbon nanodots (CDs) have been synthesized at gram scale with a high yield (41.8%) by carbonization of sucrose with oil acid in one simple step. The synthesized CDs are monodisperse with a narrow size distribution (average 1.84 nm in size), and show a high fluorescence quantum yield (21.6%) without passivation. The PL intensity of the obtained CDs is pH independent over a range of 2-8. Besides, their PL intensity remains unchanged even after six hours of UV excitation and six months of storage, exhibiting excellent stability. The obtained CDs have been used for cell imaging. The results demonstrate that the prepared CDs have great potential for real applications.

Functionalized carbon nitride quantum dots (CNQDs) are fabricated by moderate carbonization of L-tartaric acid and urea in oil acid media by a facile microwave-assisted solvothermal method. The obtained CNQDs are monodispersed with a narrow size distribution (average size of 3.5 nm), and exhibit excellent selectivity and sensitivity of fluorescence quenching for 2,4,6-trinitrophenol (TNP) with a quenching efficiency coefficient Ksv of 4.75 × 104 M−1. This sensing system exhibits a fast response time within 1 min and a wide linear response range from 0.1 to 15 μM. The limit of detection is as low as 87 nM, which is comparable or lower than the other probes. The application of the developed probe to the detection of TNP in spiked water samples yields satisfactory results. The mechanism of fluorescence quenching is also discussed. [ABSTRACT FROM AUTHOR]

Ti-doped functionalized carbon nitride nanoparticles and hybrid TiO2/graphitic-C3N4 were prepared stepwise and applied to the detection of free residual chlorine and visible-light photocatalysis. The photocatalytic degradation rate of methylene blue by the latter could reach 24.5 times that without a catalyst. [ABSTRACT FROM AUTHOR]

In the present study, carbon nanocages (CNCs) decorated with gold nanoparticles (AuNPs) with diameters of 2–5 nm were synthesized by simply mixing their solutions. The sizes of the AuNPs are small enough to diffuse into the inside of the CNCs by electrostatic incorporation and their morphologies were characterized by transmission electron microscopy, X-ray diffraction, energy dispersive spectrometry, Raman spectrometry and ultraviolet visible absorption spectra. The AuNPs@CNCs modified electrode was prepared for simultaneous highly sensitive determination of catechol (CC) and hydroquinone (HQ). This modified electrode demonstrated fantastic eletrochemical catalytic activities towards CC and HQ by cyclic voltammetry and differential pulse voltammetry. The calibration curves showed a linear response between the peak currents and the concentrations of CC and HQ. A wide dynamic detection range of 1.0–250.0 μM and 0.1–200.0 μM with a low detection limits (S/N = 3) of 0.0986 μM and 0.0254 μM can be obtained for CC and HQ respectively. The present method was successfully employed for determination of CC and HQ in a practical sample. [ABSTRACT FROM AUTHOR]

Abstract: A visible light-driven photocatalyst, C-doped Zn3(OH)2V2O7, prepared by a hydrothermal method was studied. The as-prepared catalyst was characterized by SEM, XRD, DRS, and XPS, and exhibited efficient photocatalytic activity in the degradation of methylene blue (MB) under visible-light irradiation. Besides decoloring, the decomposition of MB was also observed, further demonstrating the performance of the photocatalyst. The carbon existing on the surface of Zn3(OH)2V2O7 nanorods was free and in carbide form. Dye degradation followed first-order kinetics, and was explained on the basis of the Langmuir–Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

Herein, iron and nitrogen co-doped carbon dots (Fe-N-CDs) were synthesized through a solvothermal method assisting with the microwave synthesis system for the first time. Multiple techniques were employed to characterize the properties of the obtained particles. The emphasis of current work was the confirmation of their intrinsic peroxidase activity due to the Fe doping, which is similar to natural ferriporphyrin. Through catalyzing the oxidization of 3,3′,5,5′-Tetramethylbenzidine (TMB) in the presence of H 2 O 2 , the Fe-N-CDs exhibited a superior catalytic performance over horseradish peroxidase (HRP), suggesting their potential applications in catalytic area. Furthermore, the Fe-N-CDs were coupled to antibody as the biocatalyst instead of HRP (commonly used in enzyme-linked immunosorbnent assay (ELISA)). Results of carcinoembryonic antigen (CEA) determination demonstrated the feasibility of this approach, a detection limit as low as 0.1 pg/mL within 5 min has been achieved. These advances may trigger research interest in Fe-N-CDs and their new applications in various fields. [ABSTRACT FROM AUTHOR]

Facile and stable nanocomposites, carbon nanocages (CNCs)-reduced graphene oxide (RGO), were developed via one-pot in situ solvothermal reaction in this study. Transmission electron microscope, scanning electron microscope, X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, atomic focus microscope, N 2 adsorption/desorption isotherms, thermogravimetric analysis and Fourier-transform infrared were performed to characterize the CNCs-RGO hybrid material. The electrochemical detections of catechol (CC) and hydroquinone (HQ) were investigated by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The excellent electrocatalytic activity and reversibility have been shown on the modified electrode toward oxidation of both CC and HQ in 0.04 M acetate buffer solution (pH = 4.0). The relationship between the oxidation peak current of CC and its concentration was linear over the range from 1 to 400 μM in the presence of 100 μM HQ, and the linear relationship between the oxidation peak current of HQ and its concentration can be obtained range from 1 to 300 μM in the presence of 100 μM CC. The detection limits (S/N = 3) for CC and HQ were 0.40 and 0.87 μM, respectively. [ABSTRACT FROM AUTHOR]

Non-enzymatic electrochemical sensors for the detection of glucose and hydrogen peroxide (H 2 O 2 ) were designed based on novel nanostructure electrocatalyst of carbon quantum dots (CQDs)/octahedral cuprous oxide (Cu 2 O) nanocomposites. The CQDs/octahedral Cu 2 O nanocomposites has been smoothly by a facile method with ultrasonic treatment and the morphologies of the synthesized materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) with Energy dispersive X-ray spectroscopy (EDS) and powder X-ray diffraction measurements (XRD). Compared to octahedral Cu 2 O, the CQDs/octahedral Cu 2 O exhibited preferable electrocatalysis to the glucose oxidation and H 2 O 2 reduction. Amperometric sensing of glucose was realized with a linear response range from 0.02 to 4.3 mM, a detection limit of 8.4 μM ( S / N = 3). The interferents of ascorbic acid (AA), uric acid (UA), dopamine (DA) and sodium chloride (NaCl) was also detected using the CQDs/octahedral Cu 2 O modified electrode, the results showed good selectivity for glucose detection. Besides, the nonenzymatic sensor also has good performance to the electrocatalytic reduction of H 2 O 2 , with a linear response range from 5 μM to 5.3 mM and a detection limit of 2.8 μM ( S / N = 3). The CQDs/octahedral Cu 2 O nanocomposites have good selectivity for the H 2 O 2 detection with the AA, NaCl and UA. [ABSTRACT FROM AUTHOR]

[Display omitted] • Matrix-free nitrogen-doped carbon dots (n-CDs) with room temperature phosphorescence are successfully synthesized using a simple hydrothermal treatment. • The n-CD powder possesses excellent phosphorescence stability. • The as-prepared n-CD-based test paper accurately monitors temperature. • The n-CD solution can be applied in information security as an encryption ink. Matrix-free nitrogen-doped carbon dots (n-CDs) with room temperature phosphorescence were successfully prepared by a simple one-step hydrothermal method. The as-prepared n-CDs exhibit good biocompatibility and water solubility and show blue fluorescence and green phosphorescence. More importantly, the n-CDs exhibit a stable phosphorescence and their phosphorescence lifetime is 139 ms. Owing to vibration, the phosphorescence intensity of the n-CD powder linearly decreases with increasing temperature. The as-prepared n-CD test paper can be applied in temperature monitoring as a probe; the monitoring results are consistent with those of a traditional thermometer. Furthermore, the n-CD solution can also be used in the field of advanced information security as an encryption ink. [ABSTRACT FROM AUTHOR]

• Novel nitrogen–fluorine co-doped carbon nanodots (N,F-CDs) were synthesized by a one-pot hydrothermal method. • The N,F-CDs were used as fluorescence probe for [ClO−] detection. • The N,F-CDs probes demonstrated high stability, high sensitivity and excellent selectivity. The detection limit was estimated to be as low as 9.6 nM. Hypochlorite ions (ClO−) are widely used in bleaching agents and disinfectants. However, high concentrations of chloride species are harmful to human health. Therefore, effective methods for the detection of ClO− ions are required. In this study, using 4-fluorophthalic acid and glycine, nitrogen–fluorine co-doped carbon nanodots (N,F-CDs) were synthesized by one-pot hydrothermal synthesis for use as a fluorescent probe for the fluorometric detection of ClO− in aqueous media, based on the inhibition of n → π* transitions. The excitation and emission peak centers of the N,F-CDs are at 387 and 545 nm, respectively. The N,F-CDs show a fast quenching response (<1 min) for ClO− and can be used in a wide pH range (pH 4–13). Under optimal conditions, the fluorescence intensity decreased with increase in the ClO− concentration from 0 to 35 μM, and a low limit of detection (9.6 nM) was achieved. This probe possesses excellent selectivity and high sensitivity and was used to analyze standardized samples of piped water, achieving a satisfactory recovery. Thus, this nitrogen–fluorine co-doped nanodot probe is promising for the detection of pollutants. [ABSTRACT FROM AUTHOR]