Sensitive determination of typical phenols in environmental water samples by magnetic solid-phase extraction with polyaniline@SiO2 @Fe as the adsorbents before HPLC.

A novel magnetic core-shell material polyaniline@SiO2 @Fe (PANI@SiO2 @Fe) has been successfully synthesized and investigated as an effective adsorbent for the magnetic solid-phase extraction of typical endocrine disrupting compounds such as bisphenol A, tetrabromobisphenol A, and 4-nonylphenol from water samples. The morphology of the as-prepared PANI@SiO2 @Fe was characterized by transmission electron microscopy and X-ray diffraction. The main parameters that influenced the enrichment performance such as the kind of eluent, amount of adsorbent, volume of eluent, adsorption time, elution time, ionic strength, pH, concentration of humic acid, and sample volume were investigated. Under the optimal conditions, a good linear relationship was found in the range of 0.05-100 µg/L for bisphenol A, 0.05-300 µg/L for tetrabromobisphenol A, and 0.05-250 µg/L for 4-nonylphenol, respectively. The correlation coefficients are all above 0.995. The limits of detection were in the range of 0.009-0.04 µg/L, and precisions were under 3.73% (n = 6). The real water analysis indicated that the spiked recoveries were in the range of 92.9-98.9% (n = 3). All these results indicated that the developed method was an efficient tool for the analysis of bisphenol A, tetrabromobisphenol A, and 4-nonylphenol.

Magnetic solid phase extraction of heterocyclic aromatic hydrocarbons from environmental water samples with multiwalled carbon nanotube modified magnetic polyamido-amine dendrimers prior to gas chromatography-triple quadrupole mass spectrometer.

Present study described a sensitive and efficient method for determination of heterocyclic aromatic hydrocarbons using multiwalled carbon nanotubes modified magnetic polyamido-amine dendrimers (MNPs@PAMAM-Gn@MWCNTs) as adsorbent for magnetic solid-phase extraction (MSPE) coupled with gas chromatography-triple quadrupole mass spectrometer (GC-MS/MS). Some pivotal parameters including PAMAM generation, adsorbent dosage, adsorption time, elution time and volume, pH and humic acid concentration were investigated to achieve the best adsorption efficiencies. Under the optimal conditions, 7-methylquinoline, dibenzothiophene and carbazole had good linearity in the concentration range of 0.005-20 µg L - 1, 9-methylcarbazole, 4-methyldibenzothiophene and 4,6-dimethyl dibenzothiophene had good linearity in the concentration range of 0.001-20 µg L - 1. All the correlation coefficients were higher than 0.996. The detection limits of the targets were in the range of 2.2 × 10-4-1.8 × 10-3 µg L - 1 with precisions less than 8.28% (n = 6). The enrichment factors were in the range of 141-147. The spiked recoveries were in the range of 87.0%-115.1% (n = 3). These results indicated that the method could be a reliable alternative tool for monitoring trace heterocyclic aromatic hydrocarbons in environmental water samples.

Highly efficient adsorption and mechanism of alkylphenols on magnetic reduced graphene oxide.

The influence of alkylphenols to environment cannot be ignored, as they are common product from chemical industries and potential threat to human health. Some alkylphenols are listed as persistent toxic substances (PTS) by the United Nations Environment Programme (UNEP). In this study, the optimized magnetic reduced graphene oxide (MrGO) was synthesized by a facile solvothermal method, and investigated for adsorption of three typical alkylphenols. In neutral condition, MrGO showed extremely high adsorption capacity of three typical alkylphenols, 4-heptylphenol (4-HP), 4-tert-octylphenol (4-OP), and 4-nonylphenol (4-NP), which could reach 938.9 mg g-1 (40 °C), 987.8 mg g-1 (40 °C), and 989.7 mg g-1 (20 °C), respectively. This study revealed that the adsorption process was a heterogeneous multi-layer physical adsorption, and the adsorption rates were related to the number of unoccupied vacancies on the adsorbent surface. From batch experiments and density functional theory (DFT) calculations, the main adsorption interactions between MrGO and alkylphenols were deduced to be π-π, hydrogen-bond, and hydrophobic interactions. What's more, the different affinities of MrGO towards different targets were further distinguished and explained in detail. The wonderful stability and recyclability of MrGO made it a promising cost-effective remediation candidate.

Simultaneous enrichment and determination of cadmium and mercury ions using magnetic PAMAM dendrimers as the adsorbents for magnetic solid phase extraction coupled with high performance liquid chromatography.

In present study, a sensitive and efficient method based on magnetic PAMAM dendrimers as the sorbents for magnetic solid-phase extraction (MSPE) coupled with high performance liquid-phase chromatography and ultraviolet variable wavelength detector (HPLC-VWD) was developed for simultaneous determination of trace cadmium and mercury ions. Sodium diethyldithiocarbamate (DDTC-Na) was used as the chelating agent during the elution process. Parameters that would affect the extraction efficiency including PAMAM generation, adsorbent dosage, adsorption time, elution time and volume, pH and coexisting ions were investigated to achieve the best adsorption efficiency. Under the optimal conditions, good linear relationship was obtained in the range of 0.05-200 µg L-1 for Cd2+ and 0.1-200 µg L-1 for Hg2+, and the limits of detection were 0.016 and 0.040 µg L-1, respectively. The spiked recoveries of Cd2+ and Hg2+ were satisfied in the range of 91.5-105% (n = 3). The proposed method was proved to be an alternative and reliable method to determine trace Cd2+ and Hg2+ in water samples.

Enrichment and sensitive determination of phthalate esters in environmental water samples: A novel approach of MSPE-HPLC based on PAMAM dendrimers-functionalized magnetic-nanoparticles.

Phthalate esters (PAEs) are an important kind of environmental endocrine disrupting chemicals, and have attracted great attention in environmental field. Present study described a new method for rapid and sensitive determination of PAEs including dibenzyl phthalate (DPhP), dibutyl phthalate (DnPP), and dicyclohexyl phthalate (DCHP) from aqueous matrices based on magnetic solid-phase extraction. Polyamidoamine (PAMAM) dendrimers-grafted magnetic-nanoparticles were synthesized and characterized, and the expected integration of more multifunctional sites of PAMAM dendrimers and rapid separation property was utilized for method development. To achieve the best extraction efficiency, several important parameters were optimized including the dosage of the adsorbent, sample pH, kind and volume of eluent, extraction time, desorption time, ionic strength. Under the optimal conditions, three phthalate esters were well enriched and simultaneously determined by high performance liquid chromatography with variable wavelength detector (VWD). Excellent linearities were observed in the range of 0.1-600 µg L-1 for DPhP and DnPP and 0.5-600 µg L-1 for DCHP, and all correlation coefficients (R2) were larger than 0.997. The limits of detection (LODs, S/N = 3) were ranged from 0.025 to 0.16 µg L-1. The spiked recoveries of PAEs in real water samples were in the range of 93.5-101.8% with satisfied relative standard deviations (RSDs) ranging from 0.9 to 4.1%. The prepared magnetic materials have shown good adsorption capability for PAEs and the developed method earned merits such as high sensitivity, simplicity, rapidness and environmental friendliness, which can be used as a robust alternative tool for monitoring PAEs in water samples.

A highly sensitive and selective chemosensor for 2,4,6-trinitrophenol based on L-cysteine-coated cadmium sulfide quantum dots.

2,4,6-Trinitrophenol (TNP) is a common explosive and widely used in military, pharmaceutical, pesticide, printing and dyeing industries. TNP in the wastewater and waste residues will enter into the environment by various ways and lead to serious threat on the environment. It is urgent to develop simple and robust analytical methods for highly sensitive and selective determination of TNP. L-cysteine-coated cadmium sulfide quantum dots (L-Cy-CdS QDs) with strong fluorescence were synthesized at room temperature and characterized by ultraviolet visible absorption spectra, transmission electron microscopy and fourier transform infrared spectrometer. TNP could quench the fluorescence of quantum dots based on the favorable electronic energy transfer, fluorescence resonance energy transfer, and electrostatic interactions. The effects of pH, reaction time and L-Cy-CdS QDs concentration on the fluorescence response were optimized. It was found that the fluorescence quenching of the quantum dots was linear with the concentration of TNP in the range of 0.05-5 µg mL-1, and the limit of detection was as low as 39 ng mL-1. The method can be applied to the quantitative detection of TNP in environmental water samples.

Polyamidoamine dendrimer decorated nanoparticles as an adsorbent for magnetic solid-phase extraction of tetrabromobisphenol A and 4-nonylphenol from environmental water samples.

Polyamidoamine dendrimer decorated Fe3O4 magnetic nanoparticles were successfully synthesized by Michael addition with methyl acrylate and amidation with ethylenediamine. The decorated magnetic particles were utilized as an effective adsorbent for magnetic solid-phase extraction of tetrabromobisphenol A and 4-nonylphenol at trace levels from environmental water samples. A number of parameters such as generation number, ionic strength, adsorbent dosage, eluent, adsorption time, elution volume, elution time, pH, humic acid and sample volume were optimized. Under the optimal conditions, a wide linearity was achieved in the range of 0.1-500 µg L-1 of the analytes with the correlation coefficients (R2) of 0.9985-0.9995. The limits of detection were approximately 0.011 µg L-1 of tetrabromobisphenol A and 0.017 µg L-1 of 4-nonylphenol. Satisfactory average recoveries of the analytes ranged from 93.2% to 101.1%. The results indicated that the decorated magnetic nanoparticles can be suitable for extraction of phenols from environmental water samples. The proposed method was sensitive, effective, practical and robust for the determination of tetrabromobisphenol A and 4-nonylphenol in environmental water samples.

Investigation of nanoscale zerovalent iron-based magnetic and thermal dual-responsive composite materials for the removal and detection of phenols.

In this study, well-defined magnetic and thermal dual-responsive nanomaterials were synthesized, which contained ultrafine core-shell Fe@SiO2 nanoparticles as magnetic core and poly(N-isopropylacrylamide) (PNIPAM) as thermosensitive outer shell. The fabricated nanoparticles were characterized and investigated for the adsorption of four phenolic compounds, including bisphenol A (BPA), tetrabromobisphenol A (TBBPA), 4-tert-octylphenol (4-OP) and 4-n-nonylphenol (4-NP). The experimental results demonstrated that the excellent adsorption rates were attributed to hydrophobic effect, hydrogen-bonding interaction, and electrostatic attraction. The adsorption process followed pseudo-second-order kinetics model and nonlinear isotherms, indicating heterogeneous adsorption process. The adsorption efficiency of 4-NP using Fe@SiO2@PNIPAM was more than 90% under optimized condition within 2 h. The determined maximum adsorption amounts of BPA, TBBPA, 4-OP and 4-NP were 2.43, 6.83, 24.75, and 49.34 mg g-1, respectively. Meanwhile, a magnetic solid phase extraction (MSPE) method with Fe@SiO2@PNIPAM was established to determine these four compounds simultaneously. Under the optimal conditions, the linearity ranges were in the range of 2-200, 2-300, 2-100 and 2-100 µg L-1 for BPA, 4-OP, TBBPA, and 4-NP, respectively, and the detection limits were in the range of 0.58-0.76 µg L-1, respectively. The applicability of the proposed method was evaluated by analyzing three fresh water samples, and satisfactory spiked recoveries in the range 70.9-119.9% were achieved. It was proved that these adsorbents could be easily collected and recycled owing to the appropriate magnetism. The results also demonstrated that the as-prepared adsorbents had promising potential in the enrichment and analysis of detrimental organic pollutants from water.

Magnetic solid phase extraction of typical polycyclic aromatic hydrocarbons from environmental water samples with metal organic framework MIL-101 (Cr) modified zero valent iron nano-particles.

Metal-organic framework material has been paid more attention because of its good physical and chemical properties. Nanoscale zero valent iron is also in the center of concern recently. Combination of their merits will give impressive results. Present study firstly synthesized a new magnetic nanomaterial nano-scale zero valent iron-functionalized metal-organic framworks MIL-101 (Fe@MIL-101) by co-precipitation method. The morphology and structure of the as-prepared Fe@MIL-101 were characterized by transmission electron microscopy and X-ray diffraction, etc. The experimental results showed that Fe@MIL-101 earned good adsorption ability to polycyclic aromatic hydrocarbons. The limits of detection of developed magnetic solid phase extraction were all below 0.064µgL-1 and precision can be expressed as relative standard deviation (RSD, %) and which was better than 4.4% (n=6). The real water analysis indicated that the spiked recoveries were satisfied, and Fe@MIL-101 earned excellent reusability. All these demonstrated that Fe@MIL-101 exhibited excellent adsorption capability to polycyclic aromatic hydrocarbons and would be a good adsorbent for development of new monitoring methods for environmental pollutants.

Iron-based magnetic molecular imprinted polymers and their application in removal and determination of di-n-pentyl phthalate in aqueous media.

Iron-based magnetic molecular imprinted polymers (Fe@SiO2@MIP) were synthesized for highly selective removal and recognition of di-n-pentyl phthalate (DnPP) from water. Well-defined core-shell Fe@SiO2 nanoparticles (less than 70 nm) were decorated on MIPs reticular layers to endow DnPP-MIPs with magnetic property for the first time. Five other phthalic acid esters including dimethyl phthalate, diethyl phthalate, dipropyl phthalate, di-n-butyl phthalate and di-iso-octyl phthalate were used to investigate the adsorptive selectivity to DnPP. The designed experiments were carried out to explore the adsorption kinetics, isotherms and thermodynamics and the results demonstrated that the adsorption was a spontaneous, exothermal and physical adsorption process. The materials were proved to be excellent adsorbents in removal of DnPP with an adsorption capacity as high as 194.15 mg g-1 in optimal condition. Furthermore, a magnetic solid phase extraction with Fe@SiO2@MIP coupled to high-performance liquid chromatography method was successfully developed for the determination of DnPP, and the proposed method achieved a good linear range of 0.5-250 µg l-1 with a correlation coefficient (R2) of 0.999 and low limit of detection (LOD) of 0.31 µg l-1. These materials exhibited excellent capacity in removal and highly sensitive identification of DnPP from aqueous environment samples, and opened a valuable direction for developing new adsorbents for the removal and enrichment of important pollutants.

Simultaneous determination of cadmium, lead and mercury ions at trace level by magnetic solid phase extraction with Fe@Ag@Dimercaptobenzene coupled to high performance liquid chromatography.

Pollution resulted from heavy metal ions have absorbed much attention, and it is of great importance to develop sensitive and simultaneous determination method for them with common technologies without highly sensitive instruments. We prepared a new and functional core-shell magnetic nano-material, Fe@Ag@dimercaptobenzene (Fe@Ag@DMB), by a one-step method with sodium borohydride as the reducing agent and transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) were used for characterisation. The mercapto functional groups on the newly synthesised magnetic nanoparticles could interact with Cd2+, Pb2+, and Hg2+ ions in water samples and then efficient extraction for Cd2+, Pb2+, and Hg2+ ions was achieved. DDTC-Na solution was a good elutent for elution of these ions from Fe@Ag@DMB nanoparticles. Based on these, a sensitive method was developed for simultaneous preconcentration and determination of the aforementioned ions using magnetic Fe@Ag@DMB nanoparticles as the magnetic solid phase extraction adsorbent prior to high performance liquid chromatography coupled with variable wavelength detection. Under the optimal conditions, the detection limits of the three metal ions were in the range of 0.011-0.031µgL-1, and precisions were below 2.37% (n=6). The proposed method was evaluated with real water samples, and excellent spiked recoveries achieved indicated that the developed method would be a promising tool for monitoring these heavy metal ions in water samples.