Danfeng Zhang

Magnetically separable CdFe2O4/graphene catalyst and its enhanced photocatalytic properties

A magnetically separable CdFe2O4/graphene (CdFe2O4/GR) photocatalyst was prepared using a one-step hydrothermal method. The photocatalytic activity was evaluated by photocatalytic oxidation of methylene blue (MB) under visible-light irradiation. Its photocatalytic activity was improved significantly by introducing graphene into CdFe2O4. The first-order kinetic constant of degradation with CdFe2O4/GR (0.00543 min−1) was 5 times that with CdFe2O4 (0.00145 min−1). The photocatalytic deactivation was investigated in the presence of individual anions (nitrate, sulfate, carbonate, and phosphate). Among the anionic species studied, carbonate exhibited the promotion effect, but others did not considerably affect the photo-degradation process. The mineralization products of MB were detected using High Performance Liquid Chromatography (HPLC) and ion chromatography. Several scavengers, the band structure obtained from UV-Vis diffuse reflectance spectrum, as well as Mott–Schottky measurement, were used to identify the roles of active species in the degradation process. The active species, i.e. holes and hydroxyl radicals, play major roles in the photo-degradation of MB. Note that the fundamental mechanism based on photo-degradation is discussed in detail, and the enhanced photocatalytic performance of CdFe2O4/GR was attributed to the improved electron–hole pair separation efficiency. The CdFe2O4/GR showed good stability after four cycles and could be easily separated by a magnet and reused, showing great potential for environmental purification of organic pollutants.

Application of ionic liquid-based dispersive liquid phase microextraction for highly sensitive simultaneous determination of three endocrine disrupting compounds in food packaging

Ionic liquid (IL) dispersive liquid-liquid microextraction (DLLME) method was successfully developed for extracting three endocrine disrupting compounds (EDCs) (bisphenol A, bisphenol AF and bisphenol AP) from the food packaging. 1-Octyl-3-methylimidazoliumhexafluorophosphate ([C8MIM][PF6]) was selected as extraction solution. The extraction procedure did not require a dispersive solvent. Three EDCs extraction kinetics were found to be very fast and the equilibrium was attained within 3.0 min following the pseudo-first-order model. The H-bonding and hydrophobic interactions play an important role in the partitioning of EDCs into IL from aqueous solution. The recovered IL could be reused for three runs without significant loss of extraction efficiencies. The spiked recoveries of three targets in food packaging were in the range of 97.8-103.1%. The limits of detection ranged from 0.50 to 1.50 ng mL(-1) (S/N=3). As a result, this method has been successfully applied for the sensitive detection of three EDCs in real samples.

Simultaneous determination of four trace level endocrine disrupting compounds in environmental samples by solid-phase microextraction coupled with HPLC

A simple, rapid, sensitive and effective method for the simultaneous determination of four endocrine disrupting compounds (EDCs) (bisphenol A (BPA), bisphenol F (BPF), bisphenol AF (BPAF) and bisphenol AP (BPAP)) in environment water samples based on solid-phase microextraction (SPME) coupled with high performance liquid chromatography (HPLC) was developed. Multi-wall carbon nanotubes (MWCNTs) adsorbents showed a good affinity to the target analytes. These compounds were rapidly extracted within 10 min. Various experimental parameters that could affect the extraction efficiencies had been investigated in detail. Under the optimum conditions, the enrichment factors of the method for the target EDCs were found to be 500. Satisfactory precision and accuracy of the method were obtained in a low concentration range of 2.0-500.0 ng mL(-1). The method detection limits were in the range of 0.10-0.30 ng mL(-1). The high pre-concentration rate and efficiency of the method ensure its successful application in extraction of trace EDCs from large volumes of environmental water samples. The extraction recoveries in real samples ranged from 85.3% to 102.5% with the relative standard deviations (n=5) less than 3.74%.

Green sample clean-up based on magnetic multiwalled carbon nanotubes for the determination of lamivudine by high performance liquid chromatography

A simple, green and efficient method for the determination of trace lamivudine (LMV) based on magnetic solid-phase extraction (MSPE) coupled with high performance liquid chromatography (HPLC) was developed. Magnetic multiwalled carbon nanotubes (MMWCNTs) were prepared by assembling Ni nanoparticles onto multiwall carbon nanotubes (Ni/MWCNTs). Due to their excellent adsorption capability, the Ni/MWCNTs were used as adsorbents for magnetic solid-phase extraction (MSPE). Various parameters affecting the extraction efficiency such as the amount of adsorbent, the pH, ionic strength and desorption conditions were optimized. The extracted LMV was desorbed using ionic liquid (IL) “Green solvents” as substitutes of volatile organic solvents. Under optimized conditions, a limit of detection (LOD) of 0.14 ng mL−1 and enrichment factor (EF) of 292 were obtained. The calibration curves showed good linearity (r2 = 0.9978–0.9993) over the concentration ranges of 0.5–500 ng mL−1. The proposed method was applied to the analysis of river water and human urine samples, and the recoveries of analytes obtained were in the range of 97.6–103.0 and 93.4–102.2%, respectively. The relative standard deviations (RSD) were less than 5.93% (n = 5). The high efficiency of the method ensures its successful application in extraction of trace LMV from large volumes of environmental water and biological fluid samples.

Simultaneous determination of endocrine disrupting compounds bisphenol F and bisphenol AF using carboxyl functionalized multi-walled carbon nanotubes modified electrode.

A novel, simple and selective electrochemical method was developed for simultaneous determination of bisphenol F (BPF) and bisphenol AF (BPAF) in aqueous media (phosphate buffer solution, pH 6.0) on carboxyl functionalized multi-walled carbon nanotubes modified glassy carbon electrode (MWCNT-COOH/GCE) using differential pulse voltammetry (DPV). In DPV, MWCNT-COOH/GCE could separate the oxidation peak potentials of BPF and BPAF present in the same solution though, at the bare GCE, the peak potentials were indistinguishable. The results showed that the electrochemical sensor exhibited excellent electrocatalytic activity towards the oxidation of the two analytes. The peak current in DPV of BPF and BPAF increased linearly with their concentration in the ranges of 0.6-1.6 mmol/L BPF and 0.6-1.6 mmol/L BPAF. The detection limits were 0.1243 mmol/L and 0.1742 mmol/L (S/N=3) correspondingly. The modified electrode was successfully used to simultaneously determine BPF and BPAF in real samples.

Nano-Al2O3-based micro solid-phase filter membrane extraction for simultaneous determination of tartrazine and sunset yellow in food

A new micro-solid-phase extraction method based on a prestructured filter membrane was developed to facilitate simultaneous analysis of tartrazine (TA) and sunset yellow (SY) with high performance liquid chromatography (HPLC). A filter membrane impregnated with nano-Al2O3 particles was proposed as a new micro-solid-phase extraction (μ-SPE) device for the preconcentration of colorants in food. The method integrated isolation and concentration in one step, and the adsorbed colorants could be easily eluted from the filter membrane for HPLC analysis. This process does not involve any additional sample treatment. The method is facile and easy to operate. The method showed good linearity, with correlation coefficients >0.9982 in the range of 1.0–200.0 ng mL−1, and low limits of detection (0.10–0.20 ng mL−1). Finally, the recovery values were 86.9–124.0% for the colorants in various food samples. The results indicated that the developed method would be a novel method for rapid determination of TA and SY at trace levels in real samples.