Yaqi Cai

Preparation of silica-magnetite nanoparticle mixed hemimicelle sorbents for extraction of several typical phenolic compounds from environmental water samples.

A novel type of superparamagnetic silica-coated (Fe3O4/SiO2 core/shell) magnetite nanoparticle modified by surfactants has been successfully synthesized and was applied as an effective sorbent material for the pre-concentration of several typical phenolic compounds (bisphenol A (BPA), 4-tert-octylphenol (4-OP) and 4-n-nonylphenol (4-NP)) from environmental water samples. Compared with pure magnetic particles, a thin and dense silica layer would protect the iron oxide core from leaching out in acidic conditions. In order to enhance their adsorptive tendency towards organic compounds, cetylpyridinium chloride (CPC) or cetyltrimethylammonium bromide (CTAB) were added, which adsorbed on the surface of the Fe3O4/SiO2 nanoparticles (Fe3O4/SiO2 NPs) and formed mixed hemimicelles. Main factors affecting the adsolubilization of analytes were optimized and comparative study on the use of CPC and CTAB-coated Fe3O4/SiO2 NPs mixed hemimicelles-based SPE was also carried out. CPC-coated Fe3O4/SiO2 NPs system was selected due to lower elution volume required and more effective adsorption of the target compounds. Under selected conditions, concentration factor of 1600 was achieved by using this method to extract 800 mL of different environmental water samples. The detection limits obtained for BPA, 4-OP and 4-NP with HPLC-FLD were 7, 14, and 20 ng/L, respectively.

Superparamagnetic Fe3O4 nanoparticles as catalysts for the catalytic oxidation of phenolic and aniline compounds

Fe(3)O(4) magnetic nanoparticles (MNPs) with diameters about 10nm were synthesized successfully and used to remove phenol and aniline from aqueous solution. The results showed that phenol and aniline could be eliminated easily from solution under acidic and neutral conditions in the presence of MNPs and H(2)O(2). When the concentrations of Fe(3)O(4) MNPs and H(2)O(2) were 5gL(-1) and 1.2M, respectively, phenol and aniline could be removed completely after 6h of reaction at 308K, and the total organic carbon (TOC) abatement efficiency for phenol and aniline were 42.79% and 40.38%. Some intermediates such as formic acid, acetic acid, fumaric acid and hydroquinone were detected during reaction. Fe(3)O(4) MNPs exhibited good stability and reusability, also showed excellent catalysis ability to eliminate some substituted phenolic and aniline compounds from solution. Fe(3)O(4) MNPs had good superparamagnetism and was readily separated from solution by applying an external magnetic field. Finally we proposed that phenol and aniline might be degraded by the hydroxyl free radicals (.OH) released from H(2)O(2) in the presence of Fe(3)O(4) MNPs as catalysts.

Evaluation of graphene as an advantageous adsorbent for solid-phase extraction with chlorophenols as model analytes

Graphene, a novel class of carbon nanostructures, possesses an ultrahigh specific surface area, and thus has great potentials for the use as sorbent materials. We herein demonstrate the use of graphene as a novel adsorbent for solid-phase extraction (SPE). Eight chlorophenols (CPs) as model analytes were extracted on a graphene-packed SPE cartridge, and then eluted with alkaline methanol. The concentrations in the eluate were determined by HPLC with multi-wavelength UV detection. Under the optimized conditions, high sensitivity (detection limits 0.1-0.4 ng/mL) and good reproducibility of CPs (RSDs 2.2-7.7% for run-to-run assays) were achieved. Comparative studies showed that graphene was superior to other adsorbents including C18 silica, graphitic carbon, single- and multi-walled carbon nanotubes for the extraction of CPs. Some other advantages of graphene as SPE adsorbent, such as good compatibility with various organic solvents, good reusability and no impact of sorbent drying, have also been demonstrated. The proposed method was successfully applied to the analysis of tap and river water samples with recoveries ranging from 77.2 to 116.6%. This work not only proposes a useful method for environmental water sample pretreatment, but also reveals great potentials of graphene as an excellent sorbent material in analytical processes.

Mixed hemimicelles solid-phase extraction based on cetyltrimethylammonium bromide-coated nano-magnets Fe3O4 for the determination of chlorophenols in environmental water samples coupled with liquid chromatography/spectrophotometry detection.

Mixed hemimicelles solid-phase extraction (SPE) based on cetyltrimethylammonium bromide (CTAB)-coated nano-magnets Fe3O4 was investigated for the preconcentration of four chlorophenols (CPs) in environmental water samples prior to HPLC-spectrophotometry determination in this paper. By the rapid isolating (about 5 min) of Fe3O4 nanoparticles (NPs) through placing a Nd-Fe-B strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conversional SPE method with a column can be avoided. The unique properties of Fe3O4 NPs such as high surface area and strong magnetism were utilized adequately in the SPE process. This novel separation method produced a high preconcentration rate and factor. A comprehensive study of the adsorption conditions such as the Fe3O4 NPs zeta-potential, CTAB added amounts, pH value, standing time and maximal extraction volume was also presented. Under optimized conditions, four analytes of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) were quantitatively extracted. The method was then used to determine four CPs in five real environmental water samples. High concentration factors (700) were achieved for each of the analytes, with observed detection limits ranging between 0.11 and 0.15 microg L(-1). The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (83-98%) with satisfactory relative standard deviation (RSD) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the four CPs were obtained with only a little amount of Fe3O4 NPs (0.1g) and CTAB (60 mg). To the best of our knowledge, this was the first time a mixed hemimicelles SPE method based on Fe3O4 NPs magnetic separation had been used for the pretreatment of environmental water samples.

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles.

A novel magnetic nanosized adsorbent using hydrous aluminum oxide embedded with Fe(3)O(4) nanoparticle (Fe(3)O(4)@Al(OH)(3) NPs), was prepared and applied to remove excessive fluoride from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle and hydrous aluminum oxide floc with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption capacity calculated by Langmuir equation was 88.48 mg g(-1) at pH 6.5. Main factors affecting the removal of fluoride, such as solution pH, temperature, adsorption time, initial fluoride concentration and co-existing anions were investigated. The adsorption capacity increased with temperature and the kinetics followed a pseudo-second-order rate equation. The enthalpy change (Delta H(0)) and entropy change (DeltaS(0)) was 6.836 kJ mol(-1) and 41.65 J mol(-1)K(-1), which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe(3)O(4)@Al(OH)(3) NPs as adsorbent could reach 0.3 mg L(-1) with an initial concentration of 20 mg L(-1), which met the standard of World Health Organization (WHO) norms for drinking water quality. All of the results suggested that the Fe(3)O(4)@Al(OH)(3) NPs with strong and specific affinity to fluoride could be excellent adsorbents for fluoride contaminated water treatment.

Occurrence of antibiotics in water, sediments, aquatic plants, and animals from Baiyangdian Lake in North China.

This study investigated the presence and distribution of 22 antibiotics, including eight quinolones, nine sulfonamides and five macrolides, in the water, sediments, and biota samples from Baiyangdian Lake, China. A total of 132 samples were collected in 2008 and 2010, and laboratory analyses revealed that antibiotics were widely distributed in the lake. Sulfonamides were the dominant antibiotics in the water (0.86-1563 ng L(-1)), while quinolones were prominent in sediments (65.5-1166 μg kg(-1)) and aquatic plants (8.37-6532 μg kg(-1)). Quinolones (17.8-167 μg kg(-1)) and macrolides [from below detection limit (BDL) to 182 μg kg(-1)] were often found in aquatic animals and birds. Salvinia natans exhibited the highest bioaccumulation capability for quinolones among three species of aquatic plants. Geographical differences of antibiotic concentrations were greatly due to anthropogenic activities. Sewage discharged from Baoding City was likely the main source of antibiotics in the lake. Risk assessment of antibiotics on aquatic organisms suggested that algae and aquatic plants might be at risk in surface water, while animals were likely not at risk.

Preparation of carbon coated Fe3O4 nanoparticles and their application for solid-phase extraction of polycyclic aromatic hydrocarbons from environmental water samples.

The carbon coated Fe(3)O(4) nanoparticles (Fe(3)O(4)/C) were synthesized by a simple hydrothermal reaction and applied as solid-phase extraction (SPE) sorbents to extract trace polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. The Fe(3)O(4)/C sorbents possess high adsorption capacity and extraction efficiency due to strong adsorption ability of carbon materials and large surface area of nanoparticles, and only 50 mg of sorbents are required to extract PAHs from 1000 mL water samples. The adsorption attains equilibrium rapidly and analytes are eluted with acetonitrile readily. Salinity and solution pH have no obvious effect on the recoveries of PAHs, which avoids fussy adjustment to water sample before extraction. Under optimized conditions, the detection limits of PAHs are in the range of 0.2-0.6 ng L(-1). The accuracy of the method was evaluated by the recoveries of spiked samples. Good recoveries (76-110%) with low relative standard deviations from 0.8% to 9.7% are achieved. This new SPE method provides several advantages, such as high extraction efficiency, high breakthrough volumes, convenient extraction procedure, and short analysis times. To our knowledge, this is the first time that Fe(3)O(4)/C nanoparticles are used for the pretreatment of environmental water samples.

Occurrence of antibiotics in eight sewage treatment plants in Beijing, China

The occurrence, removal efficiency and seasonal variation of 22 antibiotics, including eight fluoroquinolones, nine sulfonamides and five macrolides, were investigated in eight sewage treatment plants (STPs) in Beijing, China. A total of 14 antibiotics were detected in wastewater samples, with the maximum concentration being 3.1 μg L(-1) in the influent samples and 1.2 μg L(-1) in the effluent samples. The most frequently detected antibiotics were ofloxacin, norfloxacin, sulfadiazine, sulfamethoxazole, erythromycin and roxithromycin; of these, the concentration of ofloxacin was the highest in most of the influent and effluent samples. Eighteen antibiotics were detected in the sludge samples, with concentrations ranging from 1.0×10(-1) to 2.1×10(4) μg kg(-1). The dominant antibiotics found in the sludge samples were the fluoroquinolones, with ofloxacin having the highest concentration in all the sludge samples. The antibiotics could not be removed completely by the STPs, and the mean removal efficiency ranged from -34 to 72%. Of all the antibiotics, the fluoroquinolones were removed comparatively more efficiently, probably due to their adsorption to sludge. Seasonal variation of the antibiotics in the sludge samples was also studied. The concentrations of antibiotics in winter were higher than in spring and autumn. Since the total levels of the fluoroquinolones detected in the influent samples were lower than the predicted no-effect concentration (PNEC) of 8.0 μg L(-1), the residues of these antibiotics would be unlikely to have adverse effects on microorganisms involved in sewage treatment processes.

Chitosan-Coated Octadecyl-Functionalized Magnetite Nanoparticles: Preparation and Application in Extraction of Trace Pollutants from Environmental Water Samples

In the present study, chitosan-coated octadecyl-functionalized magnetite nanoparticles (Fe(3)O(4)-C(18)-chitosan MNPs) are synthesized and used as an adsorbent to extract trace analytes from environmental water samples. The magnetic nanoparticles, 20 nm in diameter, are of uniform size and have a high magnetic saturation value of 52 emu g(-1), which endue the adsorbent with a large surface area and convenience of isolation. The anionic pollutants, perfluorinated compounds (PFCs), are trapped by the octadecyl group of the interior hydrophobic layer. The positively charged chitosan polymer coating also contributes to PFC enrichment. At the same time, the coating improves the dispersibility of MNPs in aqueous solution and enhances the anti-interference ability of the adsorbent to natural organic macromolecules in complex samples by size exclusion or electrostatic repulsion. A liquid chromatography-tandem mass spectrometry system is employed in the determination of PFCs after preconcentration with the MNP adsorbent. The predominant factors affecting preconcentration are investigated and optimized. Under the selected conditions, concentration factors of 1000 are achieved by extracting the analytes from 500 mL of several environmental water samples and concentrating the eluants to 0.5 mL with a nitrogen flow. The method detection limits obtained for perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), perluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), and perfluorotetradecanoic acid (PFTA) in Gaobeidian wastewater are 0.24, 0.093, 0.24, 0.14, 0.075, 0.24, and 0.17 ng L(-1), respectively. Recoveries of PFOA, PFOS, PFNA, PFDA, PFUnDA, PFDoDA, and PFTA are in the ranges of 88-108%, 63-112%, 79-109%, 56-107%, 66-106%, 56-106%, and 66-103% for four spiked water samples with low relative standard deviation (2-8%), which indicates good method precision. The advantages of this novel adsorbent are high extraction efficiency, anti-interference, and convenient operation.

Barium alginate caged Fe3O4@C18 magnetic nanoparticles for the pre-concentration of polycyclic aromatic hydrocarbons and phthalate esters from environmental water samples

The hydrophobic octadecyl (C(18)) functionalized Fe(3)O(4) magnetic nanoparticles (Fe(3)O(4)@C(18)) were caged into hydrophilic barium alginate (Ba(2+)-ALG) polymers to obtain a novel type of solid-phase extraction (SPE) sorbents, and the sorbents were applied to the pre-concentration of polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) pollutants from environmental water samples. The hydrophilicity of the Ba(2+)-ALG cage enhances the dispersibility of sorbents in water samples, and the superparamagnetism of the Fe(3)O(4) core facilitates magnetic separation. With the magnetic SPE technique based on the Fe(3)O(4)@C(18)@Ba(2+)-ALG sorbents, it requires only 30 min to extract trace levels of analytes from 500 mL water samples. After the eluate is condensed to 0.5 mL, concentration factors for both phenanthrene and di-n-propyl-phthalate are over 500, while for other analytes are about 1000. The recoveries of target compounds are independent of salinity and solution pH under testing conditions. Under optimized conditions, the detection limits for phenanthrene, pyrene, benzo[a]anthracene, and benzo[a]pyrene are 5, 5, 3, and 2 ng L(-1), and for di-n-propyl-phthalate, di-n-butyl-phthalate, di-cyclohexyl-phthalate, and di-n-octyl-phthalate are 36, 59, 19, and 36 ng L(-1), respectively. The spiked recoveries of several real water samples for PAHs and PAEs are in the range of 72-108% with relative standard deviations varying from 1% to 9%, showing good accuracy of the method. The advantages of the new SPE method include high extraction efficiency, short analysis time and convenient extraction procedure. To the best of our knowledge, it is unprecedented that hydrophilic Ba(2+)-ALG polymer caged Fe(3)O(4)@C(18) magnetic nanomaterial is used to extract organic pollutants from large volumes of water samples.