Abstract Abstract NbCl5 is found to be an efficient catalyst for the Pechmann condensation reaction of phenols and β-keto ester leading to the formation of coumarin derivatives in excellent yields under solvent-free conditions. The reaction protocol is simple and environmentally friendly. Keywords: Coumarins β-keto esterNbCl5 Pechmann condensationphenolssolvent-free ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of Hebei (B2011204051), the Scientific Research Foundation of Education Department of Hebei Province (2010137), and the Natural Science Foundation of the Agricultural University of Hebei (2009-001).
Abstract Achieving efficient nitrogen reduction reaction (NRR) under mild conditions is desirable but still challenging due to the lack of high-performance catalysts. Herein, we report the feasibility of a new type of two-dimensional conjugated metal–organic frameworks (cMOFs) featuring dense single-metal-atom sites, namely TM 3 (HAT) 2 monolayers (TM = transition metal from groups 4 to 10, HAT = 1,4,5,8,9,12-hexaazatriphenylene), as NRR catalysts. We construct an efficient four-step screening strategy and identify the W 3 (HAT) 2 monolayer as a candidate with considerable stability, activity, and selectivity based on density functional theory (DFT) computations. The analysis of bonding, integrated-crystal orbital Hamilton population, and Bader charge uncovers the NRR activity origin of the TM 3 (HAT) 2 monolayers and elucidates the structure–performance correlations. Meanwhile, our results show that a simple descriptor ϕ based on the inherent nature of the TM atoms can be applied to accelerate the screening of candidates without explicit DFT calculations. This work highlights a feasible strategy to prescreen and design high-performance cMOF-based electrocatalysts.
Series of β-cyclodextrin (β-CD)-based magnetic hyper-crosslinked polymers (CD-gs-MHCPs) were synthesized by crosslinking β-CD-graft-styrene (CD-gs) with different rigid crosslinkers, which delivered superior adsorption performance for triazine herbicides (THs). The adsorption mechanism study revealed that the effective adsorption of CD-gs-MHCP for THs can be ascribed to hydrogen bonds, hydrophobic interaction, π-π stacking interaction and pore adsorption. Combined CD-gs-MHCP based magnetic solid-phase extraction (MSPE) with high-performance liquid chromatography, the quantitative analysis of THs in river water and vegetable samples (zucchini, pakchoi) was successfully achieved. Under the optimal conditions, low detection limit (S/N = 3) of the four THs were obtained from 0.05 to 0.15 ng mL-1 for river water and 0.31-3.10 ng g-1 for vegetable samples. This work not only offers a new strategy for fabrication β-CD-based HCPs, but also provided a practical and effective method for efficient isolation and sensitive detection of trace THs residues in complex samples.
In order to avoid the spectral signal instability and low detection accuracy originating from “transient plasma” produced by laser-induced breakdown (LIBS) technology, the LIBS system based on three-dimensional scaffold was developed to optimize the optical fiber detection position. The spectral signal quality of samples with different contents of KCl additives (0%–100%) at 20–280 °C was analyzed. The double spectral line internal standard model of Cd and Pb elements in sediment was established. The experimental results show that the signal-to-noise ratio of Cd and Al in the sediment with 15% KCl additive at 180 °C is 1.78 and 1.39 times higher than that without additive at room temperature. The R2 of the calibration model for Cd and Pb in sediment with the double enhancement method increased from 0.938 08 and 0.948 80 to 0.963 41 and 0.952 61. The spectral line integral area bispectral line internal scale model R2 is improved to 0.990 34 and 0.988 83. The results showed that the sample heating combined with KCl additive could improve the quality of the spectral signal and increase the detection sensitivity.
Organophosphate diesters (Di-OPEs) are biotic or abiotic degradation products of organophosphate esters (OPEs). Current analytical methods focus on detecting Di-OPEs in human urine. Human exposure to Di-OPEs in environmental matrices has not been systematically studied. Soil plays an important role in the environmental migration and transformation of organic pollutants. Previous studies found that OPEs are ubiquitous in soil. However, few studies reported OPEs metabolite pollution in soil, especially in facility vegetable soil. In this study, an ultra-high performance liquid chromatography-electrostatic field orbitrap high resolution mass spectrometry (UPHLC-Orbitrap HRMS) method was developed for the determination of five Di-OPEs (bis(2-chloroethyl) phosphate (BCEP), bis(1,3-dichloro-2-propyl) phosphate (BDCP), di-n-butyl phosphate (DnBP), diphenyl phosphate (DPhP), and bis(2-ethylhexyl) phosphate (DEHP)) in the facility vegetable soil. The pretreatment process and chromatographic and mass spectrometric conditions were optimized in the present study. Comparative study of the purification effects of different solid-phase extraction columns showed that Oasis WAX cartridge had best purification efficiency for the five Di-OPEs. The cartridge was first activated using 3 mL methanol, 3 mL methanol containing 5% (v/v) ammonia, and 3 mL 0.1 mol/L sodium acetate-acetic acid buffer solution. Then, the cartridge was rinsed with 3 mL of 30% (v/v) methanol aqueous solution, and finally eluted using 8 mL methanol containing 5% (v/v) ammonia. The effects of mobile phase (with respect to solvent composition and flow rate) and column temperature on the shape and intensity of chromatographic peaks were studied. The optimized UHPLC conditions were as follows: chromatographic column, Thermo Accucore RP-MS; column temperature, 30 ℃; mobile phase, 0.2 mmol/L ammonium acetate aqueous solution and methanol; flow rate, 0.2 mL/min. In the UHPLC-Orbitrap HRMS experiment, the five Di-OPEs were analyzed in full MS mode with negative ionization. Instrumental parameters, such as sheath gas and auxiliary gas, were optimized to determine the MS conditions. The optimized Orbitrap HRMS conditions were as follows: heating electrospray ionization source (HESI), full MS mode with negative ionization; scan range, m/z 100-500; ion transfer tube temperature, 320 ℃; automatic gain control of target particle count, 1×106; sheath gas flow rate, 8.58 L/min; auxiliary gas flow rate, 17.40 L/min; spray voltage, 3.2 kV; and S-lens voltage, 50 V. The limits of detection and quantification were 0.001-0.047 ng/g and 0.004-0.156 ng/g, respectively. The correlation coefficients of the calibration curve were 0.9985-0.9999. At three spiked levels, 5.0, 25.0, and 50.0 ng/g, the recoveries of the five Di-OPEs ranged from 56.9% to 133.0% with relative standard deviations of 4.4%-18.9%. The established method was applied to the analysis of the five Di-OPEs in 16 facility vegetable soils. The detection frequencies of the five Di-OPEs exceeded 60% in all soil samples, indicating that the Di-OPEs were ubiquitous in the facility vegetable soil. The contents of the five Di-OPEs in the facility vegetable soil samples ranged from 2.53-6.94 ng/g. DnBP (1.37-3.20 ng/g) and DPhP (0.47-2.44 ng/g) were the predominant congeners in the facility vegetable soil samples, accounting for 23.4%-68.8% and 16.3%-35.9% of the five Di-OPEs, respectively. The developed method is simple, sensitive, and reproducible and can be used effectively for the determination of Di-OPEs in soil. The results of this study will be helpful for understanding the environmental behavior of Di-OPEs and their human exposure in facility vegetable soils.
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