Fang Xu

University of Science and Technology of China, Luchow, Anhui Sheng, China

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Publications (11)27.56 Total impact

  • Hong-Wei Luo · Fang Xu
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    ABSTRACT: Although natural organic matter (NOM) is known to affect biological reduction of U(VI) and subsequent reoxidation of U(IV), the underlying mechanisms remain unclear. This study investigated the redox reactions of sulfide with NOM to form thiol functional groups, which can greatly enhance U(VI) bioreduction and U(IV) reoxidation. Results showed that humic acid (HA) was found to be more effective than fulvic acid (FA) in producing thiol groups, both U(VI) bioreduction and U(IV) reoxidation rates increased with the increase of thiols content in HA and FA. These findings suggested that among other redox sites, thiol groups in NOM may play an important role in the electron transport between uranium and microbial cells, and are of great environmental implications because they provided direct proof that thiol groups are responsible for bioremediation and immobilization of uranium when it enters into the natural environments such as soil and groundwater.
    No preview · Article · Jan 2016 · Chemosphere
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    ABSTRACT: Near-infrared (NIR)-to-visible upconversion nanotechnology has potential to be used for photodynamic therapy (PDT) because the use of NIR-irradiation provides deep tissue penetration and avoids photodamge to nomal cells, thus overcoming a major hurdle in the treatment of deep-seated tumors. In this study, a novel nano-platform of mesoporous-silica-coated NaYF4:Yb/Er upconverting nanoparticles with a large surface area of 770 m2/g and an average pore size of 2 nm, was fabricated and used for NIR-mediated PDT. Vitamin B12 (VB12), a nontoxic, easy-to-obtain and biocompatible photosensitizer, was incorporated into the mesoporous silica and used as PDT drug. There is a good overlap (545 nm) between the fluorescence emission of NaYF4:Yb/Er nanoparticles and the UV–visible absorption of VB12. Under NIR-irradiation, the visible fluorescent emission from the upconverting nanoparticles will be absorbed by the VB12 coated on their surfaces. Then, the VB12 molecules under excited-state interact with surrounding ground-state molecular oxygen, generating reactive oxygen species, leading to oxidative damage of cancer cells.
    No preview · Article · Dec 2015
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    ABSTRACT: Abstract The generation of hydroxyl radical (•OH) under solar irradiation from natural photosensitizers is widely recognized to play a key role in the photochemical degradation of biorefractory organic pollutants. Solar-light-mediated •OH production has been supposed as a green and sustainable strategy in water and wastewater treatment. In this study, an efficient visible-light-mediated •OH generation method using the photosensitization of vitamin B2 (VB2) catalyzed by dissolved iron was proposed. •OH generation was validated by electron paramagnetic resonance spectroscopy combined with spin trapping, and was further confirmed using the hydroxylation of nitrobenzene. VB2 plays a dual role of in the process of •OH generation. In the initial step, VB2 works as an excellent photosensitizer. Upon absorption of a photon, VB2 gives rise to its excited singlet state (1VB∗) and, through intersystem crossing, to its excited triplet state (3VB∗). In the subsequent step, VB2 works as an effective electron mediator to mediate O2•- generation. However, O2•- is sensitive to proton and is converted to H2O2 quickly in water. Ultimately, the •OH generation occurs through dissolved-iron catalyzed decomposition of H2O2. All ingredients involved in this process are nontoxic, environmentally benign, and easily available. Thus, this process might have potential environmental implications.
    Full-text · Article · Jun 2015 · ACS Sustainable Chemistry & Engineering
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    ABSTRACT: A phosphine-promoted [3 + 2] cycloaddition from readily accessible MBH (Morita-Baylis-Hillman) carbonate and aryl trifluoromethyl ketone is described. The use of methyl vinyl ketone-derived allylic carbonate rather than common acrylate-derived counterpart renders the reaction pathway exclusive for 5-endo process, which enables the expeditious preparation of a range of trifluoromethylated 2, 3-dihydrofuran in a chemospecific manner.
    No preview · Article · Mar 2015 · Chinese Chemical Letters
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    ABSTRACT: Natural photosensitizer has been reported to play an important role in the sunlight-mediated degradation of organic pollutants and the self-purification of natural waters. Riboflavin (RF), a model natural photosensitizer, is widely present in-vivo and natural environments. RF has been proposed to generate reactive oxygen species (ROS) for degradation of pollutants, but it is susceptible to photodegradation because of instability of its ribose chain. In this work, the sunlight-mediated degradation of methyl orange (MO), as a model pollutant, was assessed at different pHs and initial RF concentrations. The MO photodegradation was found to be sensitized mainly by the photoproducts of RF, rather than RF itself. The highest MO photodegradation efficiency was achieved at pH 11.0. In order to further reveal its functional mechanisms, experiments were carried out in the presence of singlet oxygen (1O2) quencher (1,4-diazabicyclo[2.2.2]octane) and superoxide anion radical (O2−) quencher (1,4-benzoquinone). Only 1,4-benzoquinone was able to inhibit the photodegradation, suggesting that the photooxidation of MO was mainly initiated by O2−. The generation of O2− was further validated by electron paramagnetic resonance (EPR) spectroscopy combined with spin trapping. Possible pathways were proposed for the RF-sensitized photodegradation of MO under solar irradiation.
    Full-text · Article · Mar 2015 · Separation and Purification Technology
  • Fang Xu · Yu Xu · Rui Lu · Guo-Ping Sheng · Han-Qing Yu
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    ABSTRACT: In this study, the rationale for exploring the thermal deterioration mechanism of the bio-oil pyrolyzed from rice husk is established. This is based on identification of the unstable intermediates in the thermal deterioration process. Fourier transform infrared (FTIR) spectroscopy was used to monitor such a thermal deterioration process of bio-oil samples in thermal treatment and/or during long-term storage at ambient temperatures of 20-30 °C. Terminal olefins, as a key intermediate, so-called "signature", were identified qualitatively by using FTIR spectroscopy. A band shift observed at 880 cm(-1), which was assigned to the C-H out-of-plane deformation vibration of terminal olefins, indicates the start-up of the bio-oil thermal deterioration. A two-step pathway was proposed to describe the thermal deterioration process of bio-oil. This study suggests that the status of bio-oil could be rapidly monitored by the FTIR method.
    No preview · Article · Aug 2011 · Journal of Agricultural and Food Chemistry
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    ABSTRACT: In this work, we investigated the anaerobic decolorization of methyl orange (MO), a typical azo dye, by Shewanella oneidensis MR-1, which can use various organic and inorganic substances as its electron acceptor in natural and engineered environments. S. oneidensis MR-1 was found to be able to obtain energy for growth through anaerobic respiration accompanied with dissimilatory azo-reduction of MO. Chemical analysis shows that MO reduction occurred via the cleavage of azo bond. Block of Mtr respiratory pathway, a transmembrane electron transport chain, resulted in a reduction of decolorization rate by 80%, compared to the wild type. Knockout of cymA resulted in a substantial loss of its azo-reduction ability, indicating that CymA is a key c-type cytochrome in the electron transfer chain to MO. Thus, the MtrA-MtrB-MtrC respiratory pathway is proposed to be mainly responsible for the anaerobic decolorization of azo dyes such as MO by S. oneidensis.
    Full-text · Article · Aug 2011 · Applied Microbiology and Biotechnology
  • Fang Xu · Yu Xu · Hao Yin · Xifeng Zhu · Qingxiang Guo
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    ABSTRACT: A study was conducted to demonstrate the analysis of bio-oil obtained by biomass fast pyrolysis using low-energy electron-impact (EI) mass spectrometry (MS). The bio-oil was produced by fast pyrolysis of rice husk at the temperature of about 450 °C in a fluidized bed reactor. Mass spectral analyses were performed on a GTC TOF (MS) at a series of different electron beam energies. The source temperature was set at 220 °C and the samples were volatilized from a heated direct-insertion probe in the source. The instrument was calibrated at a mass resolution of 8000 (FWHM) using heptacosafluorotributylamine as the internal reference. Data analyses were performed automatically using the OpenLynx software within MassLynx. The objective of the study was to develop a simple method to provide the information on the molecular weight distribution of bio-oil.
    No preview · Article · Mar 2009 · Energy & Fuels
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    ABSTRACT: A highly selective and sensitive LC-MS-MS method was developed and validated to quantify tiopronin in human plasma, using fudosteine as the internal standard (IS). L-Cysteine and 1,4-dithiothreitol (DTT) were used as the reducer and the stabilizer to release and stabilify tiopronin from a dimmer and mix forms with endogenous thiols in the treatment of plasma samples. After a simple liquid-liquid extraction with ethyl acetate in acidic condition, the post-treatment samples were analyzed on a C(18) column interfaced with a triple-quadruple tandem mass spectrometer using negative electrospray ionization. Methanol and water (40:60, v/v) were used as the isocratic mobile phase, with 0.2% formic acid and 1.0 mM tris (hydroxymethyl) aminomethane (Tris) in water. The method was validated to demonstrate the specificity, lower limit of quantification, accuracy and precision of measurements. The assay was linear over the concentration range 0.078-10 microg/mL. The correlation coefficients for the calibration curves ranged from 0.9980 to 0.9990. The intra- and inter-day precisions, calculated from quality control samples, were not more than 10.49%. The method was employed in a pharmacokinetic study after oral administration of 200 mg tiopronin tablets to 24 healthy volunteers.
    No preview · Article · Jan 2009 · Biomedical Chromatography
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    ABSTRACT: In this study, a rapid, sensitive and reproducible liquid chromatography–tandem mass spectrometry method for the determination of levonorgestrel in human plasma, was developed and validated. With a structural analogue norethindrone as the internal standard, levonorgestrel was extracted from plasma using ethyl acetate. The organic layer was evaporated to dryness and the residue was reconstituted in mobile phase. An aliquot of 20μL was chromatographically analyzed on a Phenomenex Luna C18 column with water and acetonitrile as the mobile phase. Selected reaction monitoring was specific for mass detection employing positive electrospray ionization. The calibration standards were linear over the concentration range 0.625–40ngmL−1. The intra- and inter-day precision over the entire concentration range were less than 8.16%. The method was found to be suitable for application to a pharmacokinetic study after oral administration of 1.5mg levonorgestrel tablet to 20 healthy female volunteers.
    No preview · Article · Oct 2008 · Chromatographia
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    ABSTRACT: A simple and sensitive HPLC/MS/MS method was developed and evaluated to determine the concentration of ritodrine (RTD) in human plasma. Liquid-liquid extraction with ethyl acetate was employed as the sample preparation method. The structural analogue salbutamol was selected as the internal standard (IS). The liquid chromatography was performed on a Hanbon Sci. & Tech. Lichrospher CN (150 mm x 4.6 mm, i.d., 5 microm) column (Hanbon, China) at 20 degrees C. A mixture of 0.03% acetic acid and methanol (50:50, v/v) was used as isocratic mobile phase to give the retention time 3.60 min for ritodrine and 2.94 min for salbutamol. Selected reaction monitoring (SRM) in positive ionization mode was employed for mass detection. The calibration functions were linear over the concentration range 0.39-100 ng mL(-1). The intra- and inter-day precision of the method were less than 15%. The lower limit of quantification was 0.39 ng mL(-1). The method had been found to be suitable for application to a pharmacokinetic study after oral administration of 20mg ritodrine hydrochloride tablet to 18 healthy female volunteers. The half-life is 2.54+/-0.67 h.
    No preview · Article · Jun 2008 · Journal of Chromatography B