Dual-Emitting N/S-Doped Carbon Dots-Based Ratiometric Fluorescent and Light Scattering Sensor for High Precision Detection of Fe(III) Ions.

Precise and rapid sensing of Fe(III) under concerned facile conditions is important in environmental monitoring. Herein, a facile and label-free ratiometric sensor is constructed for selective determination of Fe(III) ions by coupling second-order scattering (SOS) and fluorescence. We were synthesized fluorescent N, S-doped carbon dots (N/S-CDs) via facile one-step hydrothermal treatment with an intensive fluorescence and a weak SOS signal and high quantum yield (32%). The fluorescence of N/S-CDs was quenched whereas the intensity of SOS was relatively increased by Fe(III) ions due to aggregation-induced fluorescence quenching or enhancement. Based on this effect, a novel fluorescent ratiometric probe with the combined fluorescence and SOS is proposed for the sensing of Fe(III) ions, and with the detection limit of 83 nM and linear range of 0.1-10 µM and 10-40 µM, respectively.

A Novel Application of Fluorine Doped Carbon Dots Combining Vortex-Assisted Liquid-Liquid Microextraction for Determination of 4-Nitrophenol with Spectrofluorimetric Method.

A simple and fast vortex-assisted liquid-liquid microextraction (VA-LLME) combining with fluorescent carbon dots have been developed for the determination 4-nitrophenol (4-NP). The high fluorescent quantum yield (58.9%) fluorine doped carbon dots (F-CDs) were synthesized using tetrafluoroterephthalic acid as a fluorine source and using citric acid as a fluorine source and using ethylenediamine as a nitrogen source via a one-step hydrothermal method. F-CDs fluorescence was effectively quenched by 4-NP due to inner filter effect (IFE) and the strong interactions between functional groups (-COOH,-OH, -NH2 and -F groups) of the F-CDs and 4-NP. In VALLME method, n-octanol was employed as extraction solvent, and vortex-mix was exploited as a gentle mix method to reduce emulsification time and improve the extraction efficiency. The detection limits, the quantification limit and relative standard deviation for the 4-NP were found as 15 nM, 50 nM and 3.5%, respectively. Moreover, the obtained F-CDs can be employed as fluorescent probe to detect 4-NP in real environmental water samples.

Mesoporous Silica for Triphase Nucleophilic Substitution Reactions.

Mesoporous silica SBA-15 is shown to be a very efficient alternative to phase transfer catalyst salts for two-phase nucleophilic substitutions. The two-phase reaction can efficiently take place in the absence of PTCs. The high catalytic activity and reaction rates can be attributed to the amphiphilic and negatively charged surface of SBA-15 as well as the rapid ingress of the reactants and egress of the products.

A ratiometric fluorescence and light scattering sensing platform based on Cu-doped carbon dots for tryptophan and Fe(III).

A new Cu-doped carbon dots (Cu-CDs) were synthesized rapidly and simply via one-step thermolysis of Na2[Cu(EDTA)] and ascorbic acid (AA) at 250°C for 2h with a high quantum yield of 9.8%. The Cu-CDs exhibits two signals of fluorescence at 396nm and second-order scattering (SOS) at 617nm under a single excitation wavelength of 308nm, and can be obviously enhanced by tryptophan (Trp) or Fe(III) leading to the ratiometric fluorescence and SOS response with a good linear wider range of 0.5-250µM and 0.1-50µM, respectively. This sensing system exhibits good selectivity and sensitivity toward Trp and Fe(III) over other analytes with a low detection limit of 275nM and 46nM, respectively. Furthermore, the proposed sensing system displays a prospective application for quantitative assay of Trp and Fe(III) in practical sample.

Feasibility of detection valence speciation of Cr(III) and Cr(VI) in environmental samples by spectrofluorimetric method with fluorescent carbon quantum dots.

A simple and fast spectrofluorimetric method coupled with fluorescent carbon quantum dots have been developed for the detection and speciation chromium(VI) and chromium(III). The high fluorescence quantum yield (QY: 20.5%) carbon quantum dots (CQDs) were synthesized from natural kelp by hydrothermal method. The fluorescence of CQDs was effectively quenched by Cr(VI) due to inner filter effect (IFE) and the strong interactions between the functional groups on the CQDs surface and Cr(VI). Cr(III) species after oxidation of this species to Cr(VI) using KMnO4 as the oxidant were also detected by the proposed method. Under optimal conditions, the Cr(VI) could be detected with the range from 0.01 to 50 µM and a limit of detection 0.52 µM. And the synthesized CQDs were utilized as fluorescent probe to determinate Cr(III) and Cr(VI) in environmental water samples with satisfactory recoveries in the range of 94%-107%.

Magnetic Solid Phase Extraction Based on Oleic Acid Coated Fe3O4 for the Determination of Benzo[α]pyrene in Cigarette Smoke Coupled with High-Performance Liquid Chromatography.

In this work, a simple and effective method based on magnetic solid-phase extraction combined with high-performance liquid chromatography was developed for the determination of benzo[α]pyrene (BaP) in cigarette smoke. Oleic acid coated Fe3O4 (Fe3O4-OA) was synthesized and directly used as an efficient sorbent for the first time in magnetic solid-phase extraction (MSPE) procedure for the clean-up of BaP in cigarette smoke extracts. The synthesized Fe3O4-OA was characterized by transmission electron microscopy, X-ray diffraction and Fourier transformed infrared spectroscopy. The extraction via Fe3O4-OA was dispersed in the extracts of cigarette smoke followed by the magnetic isolation, acetonitrile-tetrahydrofuran (ACN-THF; v/v = 9:1) was used for desorption of the analyte. The effects of important parameters such as the amount of adsorbent, solution pH, the content of acetonitrile, temperature and sorption time were investigated. The method showed good linearity for the determination of BaP in the concentration range of 0.5-50 ng mL-1 with a regression coefficient (R2) of 0.9987. The limit of detection and limit of quantification for BaP were obtained to be 0.12 and 0.41 ng mL-1, respectively. The mean recoveries were in the range from 81.0% to 97.6% at low, medium, high spiked levels, and the relative standard deviations were in the range of 2.7-6.8%. Combined with high-performance liquid chromatography and fluorescence detection, a simple and effective method was developed for the analysis of BaP in cigarette smoke.

Ortho effects on the change in electronic absorption spectrum of pyridinium salts of saturated bromohydrocarbon.

The quaterisation process of 1,2-dibromoethane and pyridine is in situ traced by electronic absorption spectrum. Two absorption peaks, induced by mono- and bis-pyridinium salt of 1,2-dibromoethane, appear at 429 nm and 313 nm, respectively. To explain the phenomena, several kinds of alkyl bromides with special structures were selected and compared by experimental measurement and theoretical calculation. The results indicate that for mono-pyridinium salt of 1,2-dibromoethane, the electron donor property of ortho-bromine group increases the electron cloud density of the carbon atom associated with pyridinium cation, which induces red-shift of absorption wavelength.

Particle-wire-tube mechanism for carbon nanotube evolution.

The synthesis of carbon nanotubes (CNTs) has been proved to be greatly promoted by vapor metal catalysts, but the fast reaction feature and the required high-temperature environment involved in CNT evolution usually make it difficult for an insight into the evolution mechanism. Here, we successfully freeze the synthetic reaction at intermediary stages and observe the detailed morphologies and structures of the obtained intermediates and various objects related to carbon nanotubes. It is unveiled that there is a kindred evolution linkage among carbon nanoparticles, nanowires, and nanotubes in the vapor catalyst-involved synthetic processes: tiny carbon nanoparticles first form from a condensation of gaseous carbon species and then self-assemble into nanowires driven by an anisotropic interaction, and the nanowires finally develop into nanotubes, as a consequence of particle coalescence and structural crystallization. The function of metals is to promote the anisotropic interactions between the nanoparticles and the structural crystallization. An annealing transformation of carbon nanoparticles into nanotubes is also achieved, which gives further evidence for the evolution mechanism.