Mixed hemimicelle solid-phase extraction based on magnetic halloysite nanotubes and ionic liquids for the determination and extraction of azo dyes in environmental water samples.

An effective and greener mixed hemimicelles magnetic solid phase extraction (MHMSPE) based on magnetic halloysite nanotubes (MHNTs) and ionic liquid (IL) is developed for the simultaneous enrichment and determination of anionic azo dyes in a spiked environmental water sample. In this MHMSPE, the formation of C16mimBr with mixed hemimicelles on the surface of MHNTs leads to the retention of analytes by strong hydrophobic, p-p and electrostatic interactions. This MHMSPE technique combines the advantages of MHNTs and mixed hemimicelles. Zeta potential data demonstrated that mixed hemimicelles were formed in [C16mimBr]/[MHNTs] ratios of the range from 0.15 to 1.33. Different important factors affecting the preconcentration of analytes were investigated and optimized by response surface methodology and one variable at a time. Under the optimum conditions, the limits of detection (LOD) for methyl red and methyl orange (MR and MO) were 0.042 and 0.050 µg L-1 in samples, respectively. The accuracy of the method was assessed by recovery measurements on a spiked sample, and good recoveries 85-87% for MR and 89-93% for MO, with preconcentration factors of 481 and 524, respectively. The low relative standard deviations from 1.6-3.1% for tap water and 2.5-5.4% for lake water was achieved. So far as we know, this is the first development of a mixed hemimicelles SPE based on MHNTs and IL for the extraction of trace anionic azo dyes in environment water samples.

A regenerable sorbent composed of a zeolite imidazolate framework (ZIF-8), Fe3O4 and graphene oxide for enrichment of atorvastatin and simvastatin prior to their determination by HPLC.

Graphene oxide (GO), nanosized Fe3O4 and zeolite imidazolate framework-8 (ZIF-8) were hybridized as a multifunctional sorbent for use in microextraction. The sorbent was characterized by SEM, TEM, XRD and FTIR. The composite is porous, has a high specific surface (> 600 m2·g-1) and is paramagnetic. The GO sheets are shown to act as carriers for the Fe3O4 nanoparticles and ZIF-8. The composite is a viable material for the preconcentration of atorvastatin and simvastatin from urine prior to their determination by HPLC with PDA detection. The limits of detection are 116 and 387 pg·mL-1, respectively. Recoveries from spiked urine samples range between 84.7 and 95.7%, with relative standard deviation of ≤4.5%. Enrichment factors range from 169 to 191. The method was successfully applied to the determination of atorvastatin in urine. Moreover, this sorbent is regenerable and recyclable for at least seven times without obvious decrease in performance. Graphical abstract A composite sorbent composed of a zeolite imidazolate framework, Fe3O4 and graphene oxide was applied to the extraction of statins in urine prior their determination by HPLC.

One-pot sustainable synthesis of magnetic MIL-100(Fe) with novel Fe3O4 morphology and its application in heterogeneous degradation.

A novel, rapid and simple method is described for the synthesis of magnetic MIL-100(Fe) with novel Fe3O4 morphology, which significantly improved the sustainability of conventional fabrication processes in several aspects. The magnetic MOFs were prepared (i) in one pot (instead of multiple steps), (ii) at room temperature (instead of temperatures over 150 °C), (iii) within a few hours with excellent yield (instead of in few days with low productivity) and (iv) in the absence of any corrosive inorganic acid and organic reagent. The materials were tested in the industrially demanded photocatalytic and photo-Fenton degradation of sodium sulfadiazine. The degradation results indicated that the Fe3O4 nanorods could accelerate the catalytic efficiency. The catalyst would be of potential application due to its stable catalytic activity in repeated reaction cycles and no need for regeneration. Therefore, the MIL-100(Fe) and magnetic MIL-100(Fe) proposed in this study are ideal catalysts for the heterogeneous degradation of sodium sulfadiazine.

Molecularly imprinted polymers based stir bar sorptive extraction for determination of cefaclor and cefalexin in environmental water.

Although stir bar sportive extraction was thought to be a highly efficiency and simple pretreatment approach, its wide application was limited by low selectivity, short service life, and relatively high cost. In order to improve the performance of the stir bar, molecular imprinted polymers and magnetic carbon nanotubes were combined in the present study. In addition, two monomers were utilized to intensify the selectivity of molecularly imprinted polymers. Fourier transform infrared spectroscopy, scanning electron microscopy, and selectivity experiments showed that the molecularly imprinted polymeric stir bar was successfully prepared. Then micro-extraction based on the obtained stir bar was coupled with HPLC for determination of trace cefaclor and cefalexin in environmental water. This approach had the advantages of stir bar sportive extraction, high selectivity of molecular imprinted polymers, and high sorption efficiency of carbon nanotubes. To utilize this pretreatment approach, pH, extraction time, stirring speed, elution solvent, and elution time were optimized. The LOD and LOQ of cefaclor were found to be 3.5 ng · mL-1 and 12.0 ng · mL-1, respectively; the LOD and LOQ of cefalexin were found to be 3.0 ng · mL-1 and 10.0 ng · mL-1, respectively. The recoveries of cefaclor and cefalexin were 86.5 ~ 98.6%. The within-run precision and between-run precision were acceptable (relative standard deviation <7%). Even when utilized in more than 14 cycles, the performance of the stir bar did not decrease dramatically. This demonstrated that the molecularly imprinted polymeric stir bar based micro-extraction was a convenient, efficient, low-cost, and a specific method for enrichment of cefaclor and cefalexin in environmental samples.

Adsorptive removal of trace sulfonamide antibiotics by water-dispersible magnetic reduced graphene oxide-ferrite hybrids from wastewater.

A one-pot solvothermal synthesis method was developed to prepare reduced graphene oxide (RGO) supported ferrite hybrids using graphite oxide and metal ions (Fe(3+)) as starting materials. The as-prepared composites were characterized by transmission electron microscopy(TEM), Fourier transform infrared spectrophotometer (FT-IR), X-ray powder diffraction pattern(XRD) and vibrating sample magnetometer (VSM). It was shown that Fe3O4 nanoparticles with a uniform size of ∼35nm were anchored on RGO nanosheets. Importantly, the obtained nanocomposites are effective adsorbents for the determination of three sulfonamides in wastewater. Several parameters affecting the extraction efficiency were optimized, including amount of adsorbent, extraction time, pH and desorption conditions. Compared with other adsorbents, the as-prepared RGO-Fe3O4 showed the better extraction efficiencies for the SAS due to the large surface area of RGO. A linear range from 1 to 200ng/mL was obtained with a high correlation coefficient (R(2)>0.9987), and the limits of detection for three SAs ranged from 0.43 to 0.57ng/mL. This method was successfully applied to the analysis of SAs in environmental wastewater samples, the recoveries in different sample matrices were in the range from 89.1 and 101.7% with relative standard deviations less than 8.6%. It is believed that such composites will find wide applications in the water pretreatment area.