Xiaolan Zhu

Graphene Oxide-Dispersed Pristine CNTs Support for MnO2 Nanorods as High Performance Supercapacitor Electrodes

A MnO2 -CNT-graphene oxide (MCGO) nanocomposite is fabricated using graphene oxide (GO) as a surfactant to directly disperse pristine carbon nanotubes (CNTs) for the subsequent deposition of MnO2 nanorods. The resulting MCGO nanocomposite is used as a supercapacitor electrode that shows ideal capacitive behavior (i.e., rectangular-shaped cyclic voltammograms), large specific capacitance (4.7 times higher than that of free MnO2 ) even at high mass loading (3.0 mg cm(-2) ), high energy density (30.4-14.2 Wh kg(-1) ), large power density (2.6-50.5 kW kg(-1) ), and still retains approximately 94 % of the initial specific capacitance after 1000 cycles. The advanced capacity, rate capability, and cycling stability may be attributed to the unique architecture, excellent ion wettability of GO with enriched oxygen-containing functional groups, high conductivity of CNTs, and their synergistic effects when combined with the other components. The results suggest that the MnO2 -CNT-GO hybrid nanocomposite architecture is very promising for next generation high-performance energy storage devices.

Quantitative and structure analysis of pectin in tobacco by 13C CP/MAS NMR spectroscopy

A new method utilizing 13C CP/MAS NMR spectra was developed for the simultaneous quantitative and structure analysis of pectin in tobacco. The conditions of acid extraction of tobacco samples and the parameters of spectral instruments were optimized. The C-6 carbon regions of NMR spectra were studied in detail, and the chemical shift and the area of peaks were applied for the calculation of polygalacturonic acid (PGA) content, degrees of methylation (DM) and degrees of acetylation (DAc). The quantitative results showed that the average recovery was 92.5% with a RSD of 4.4–4.9%. Therefore, this NMR method could provide important information about both the amount and structure of pectins.

Separation and characterization of sucrose esters from Oriental tobacco leaves using accelerated solvent extraction followed by SPE coupled to HPLC with ion-trap MS detection

Sucrose esters (SEs) were successfully extracted from Oriental tobacco leaves using a new methodology based on accelerated solvent extraction followed by hydrophilic-lipophilic balanced cartridge cleanup step. The SEs were detected by HPLC with ion-trap MS detection using an electrospray interface operated in the positive ion mode. This methodology combines the high efficiency of extraction provided by a pressurized fluid and the highly sensitive characterization offered by ion-trap MS. Under the optimized conditions, 14 SEs were first identified among a total of 23 SEs found in Oriental tobacco leaves. Under the same conditions, only four new SEs were extracted by using traditional ultrasound-assisted extraction and liquid-solid extraction methods. The present method might be potentially useful in high-efficiency extraction and sensitive characterization of SEs from complex matrices such as tobacco leaves.

Development of a sensitive method for the quantification of urinary 3-hydroxybenzo[a]pyrene by solid phase extraction, dansyl chloride derivatization and liquid chromatography-tandem mass spectrometry detection

Analysis of the urinary metabolite of benzo[a]pyrene (BaP), 3-hydroxybenzo[a]pyrene (3-OHBaP), is useful for the biomonitoring of carcinogenic polycyclic aromatic hydrocarbons (PAHs) exposure. The determination of 3-OHBaP by liquid chromatography tandem mass spectrometry (LC-MS/MS) suffers from the poor sensitivity of detection in commonly used electrospray ionization (ESI) sources. In this study, a sensitive and selective LC-MS/MS method was developed for the determination of urinary 3-OHBaP. Following enzymatic hydrolysis of the glucuronide and sulfate conjugates, the metabolite was enriched and cleaned up by solid-phase extraction and then derivatized with dansyl chloride. The derivative was analyzed by LC-MS/MS with ESI in the positive ion mode. The derivatization of 3-OHBaP by the introduction of a dansyl group into the molecule greatly enhanced the detection sensitivity by improving both the efficiency of ESI in the positive ion mode and collision-induced dissociation in the collision cell. Good linearity was obtained in the range of 0.25–40.0 pg mL−1 with a correlation coefficient (r2) of 0.9924. The limit of detection (LOD) and lower limit of quantification (LLOQ) were 0.1 pg mL−1 and 0.25 pg mL−1, respectively. Accuracy ranged from 87.7% to 107.5%. Intra- and inter-day relative standard deviations varied from 4.6% to 8.4% and 7.2% to 10.6%, respectively. Finally, this developed method was successfully applied for the analysis of urine samples from smokers and non-smokers to measure human exposure to PAHs.

A new restriction effect of aging time on the shrinkage of ordered mesoporous carbon during carbonization

A new effect of aging time (AT) on the shrinkage of ordered mesoporous carbon (OMC) prepared by an evaporation-induced triconstituent co-assembly method has been reported. Increasing AT from 0.5 to 2.0 h can gradually reduce framework shrinkage of the OMC during carbonization. This novel effect is effective and simple for preparing the OMC with large mesopore sizes, high pore volumes and surface area.

Quantitative and Structure Analysis of Cellulose in Tobacco by 13C CP / MAS NMR Spectroscopy

SUMMARY A new method utilizing 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra was developed for the simultaneous quantitative determination and structure analysis of tobacco cellulose from hot water or acid detergent extraction. A reference spectrum of tobacco noncellulose components was subtracted from the spectrum of each sample to obtain a subspectrum of the cellulose components. The NMR spectra in combination with spectral fitting were analyzed in detail and some parameters, such as the content of cellulose, crystallinity, allomorph composition and lateral dimensions for cellulose elementary fibrils and microfibrils were determined. The quantitative results showed that the average recovery was 94.0% with a relative standard deviation (RSD) of 4.6–4.8%. The structure results obtained by the spectral fitting for the cellulose C1-region showed that the main allomorph composition in tobacco cellulose was Iβ. The cellulose crystallinity calculated by the spectral fitting in C4 -region was about 50%. The lateral dimensions for cellulose elementary fibrils and microfibrils were in the range of 3.0–6.0 nm and 6.0–13.0 nm, respectively. Therefore, this NMR method could provide important information on both amount and structure of cellulose in tobacco.

Synthesis and Solid Phase Extraction Performance Study of NNAL‐specific Molecularly Imprinted Polymers Using Dummy Templates

Dummy molecularly imprinted polymers (DMIPs) for 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanol (NNAL) were produced using three structural analogues as dummy template molecules. The chosen analogues were 4‐(acetymethylamino)‐1‐(3‐pyridyl)‐butanol, 4‐(methylamino)‐1‐(3‐pyridyl)‐1‐butanol, and 1‐(3‐pyridyl)‐1,4,‐butanediol. The molecular recognition characteristics of the produced polymers were evaluated by X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT‐IR). Interactions between NNAL and methacrylic acid should be cooperative hydrogen bonds while the nitrogen atom of the pyridine ring and the oxygen atom of the nitroso group in NNAL are two of the hydrogen‐bond acceptors. It was further demonstrated that DMIP synthesized by 4‐(acetymethylamino)‐1‐(3‐pyridyl)‐butanol had the best binding performance by XPS and FT‐IR. Then dummy molecularly imprinted solid phase extraction (DMISPE) was developed for the determination of the analyte using the hit polymer as the sorbing m...