Yolk-shell MOF-on-MOF hybrid solid-phase microextraction coatings for efficient enrichment and detection of pesticides: Structural regulation cause performance differences.

Metal-organic frameworks (MOFs) based composites with different structure-activity relationships have been widely used in the field of organic pollutant adsorption and extraction. Here, two MOF-on-MOF composites with different structures (yolk-shell and core-shell) from homologous sources were prepared by a simple in-situ growth synthesis method and structural regulation. In order to verify the effect of composite structure on the extraction capacity, the adsorption performance of the yolk-shell structure (YS-NH2-UiO-66@CoZn-ZIF) and the core-shell structured (NH2-UiO-66@CoZn-ZIF) material were compared by using them as coating material of direct immersion solid-phase microextraction (DI-SPME) to enrich six pesticides in five matrices. The results showed that because of the unique hollow hierarchical structure, high specific surface area (930.68 m2 g-1), abundant and open active sites, and synergistic and complementary adsorption forces, YS-NH2-UiO-66@CoZn-ZIF composites had the maximum adsorption amount of 36.01-66.31 mg g-1 under the same experiment condition, which was 6.81%-34.26 % higher than that of NH2-UiO-66@CoZn-ZIF. In addition, the adsorption mechanism of the prepared materials was verified and elaborated through theoretical simulations and material characterization. Under the optimized conditions, the YS-NH2-UiO-66@CoZn-ZIF-coated SPME-HPLC-UV method had a wide linear range (0.241-500 µg L-1), a good linear correlation coefficient (R2 > 0.9988), a low detection limits (0.072-0.567 µg L-1, S/N = 3) and low quantification limits (0.241-1.891 µg L-1, S/N = 10). The relative standard deviations of individual fibers and different batches of fibers were 0.47-6.20 % and 0.22-2.48 %, respectively, and individual fibers could be recycled more than 104 times. This work provided a good synthetic route and comparative ideas for exploring the in-situ growth synthesis of yolk-shell composites with reasonable structure-activity relationships.

Ultra-thin FeCoNi-LDH hollow nanoflower as solid-phase microextraction coating for targeted capture of six pesticides by electrostatic adsorption.

Pesticides are common pollutants that cause detriment to the ecological environmental safety and health of human due to their toxicity, volatility and bioaccumulation. In this work, an ultra-thin polymetallic layered double hydroxide (FeCoNi-LDH) with hollow nanoflower structure composite was synthesized using ZIF-67 as a self-sacrificial template, which was used as solid-phase microextraction (SPME) coating for the targeted capture pesticides, which could be combined with high-performance liquid chromatography (HPLC) to sensitive inspection pesticides in real water samples. Orthogonal experimental design (OAD) was applied to ensure the best SPME condition. Additionally, the adsorption properties were evaluated by chemical thermodynamics and kinetics. Under the optimized conditions, high adsorption capacity was obtained (117.0-21.5 mg g-1). A wide linear range (0.020-1000.0 µg L-1), low detection limit (0.008-0.172 µg L-1) and excellent reproducibility were obtained under the established method. This research provided a new strategy for designing hollow materials with multiple cations for the adsorption of anion or organic pollutants.

One-step solvent thermal synthesis of 3D networked MOF composites for preparation of an ultrasensitive chemosensor for hydroquinone and catechol.

Pharmaceuticals and personal care products (PPCPs) have a significant impact on the environment and human health, due to their sometimes toxic and carcinogenic characteristics. Therefore, an innovative chemosensor was constructed for ultrasensitive determination of two typical PCCPs (hydroquinone (HQ) and catechol (CC)) in several minutes. The homemade chemosensor (UiO-67@GO/MWCNTs) consisted of MOF(UiO-67), graphene oxide (GO), and multi-walled carbon nanotubes (MWCNTs) composites; it was a networked, structurally sparse, porosity-rich, homogeneous octahedral composite, and had ultra-high electrical conductivity, which provided lots of active adsorption sites, promote charge transfer, and enrich lots of molecules to be measured in a few minutes. The prepared electrochemical sensor showed good long-term stability, applicability, reproducibility, and immunity to interference for the determination of HQ and CC, with a wide linear range of response of 5.0 ~ 940 µM for both HQ and CC, and a low limit of detection with satisfactory recoveries. In addition, a new strategy of using MOF composites as the basis for electrochemical determination of organic small molecules was established, and a new platform was constructed for the quantitative determination of organic small molecules in various environmental samples.

N, N'-methylene bisacrylamide/divinyl benzene based-highly cross-linked hybrid monolithic column: Production and its applications for powerful capture of four chlorophenols.

In this paper, the role of the halogen bond in capillary monolithic column microextraction was explored for the first time. Benzene-1,3,5-tricarbohydrazide (BTH) was synthesized as a functional monomer, N, N'-methylene bisacrylamide (MBA) and divinyl benzene (DVB) were used as cross-linking agents, the hybrid monolithic column of poly (BTH-co-DVB-co-MBA) was prepared using methanol and polyethylene glycol as pore-forming agents and azodiisobutyronitrile as the initiator. Due to the existence of BTH, a large number of nitrogen atoms (Lewis base) were introduced into the monolithic column, which could form a halogen bond with chlorine-containing organic pollutants and enhance its adsorption performance. Based on the monolithic column, a sensitive and environment-friendly solid-phase microextraction technology was studied. The monolithic column was integrated with high-performance liquid chromatography (HPLC) to extract and detect four kinds of chlorophenol in real water samples. Under best conditions, the method showed excellent extraction ability and linearity, with a linear correlation coefficient of 0.9958-0.9987, a low detection limit (LOD) of 0.04-0.23 µg L-1 (S/N = 3), and relative standard deviation (RSD) less than 3.09%. The recovery rate was kept between 87.30% and 123.00%, and the RSD was less than 3.83%, which indicated that the column had powerful capture performance, high precision, and strong anti-matrix interference ability in the real sample, and had potential application value in practical work.

[Efficient enrichment of pesticides from environmental water samples by cobalt-nickel double metal hydroxide nanocage/multiwalled carbon nanotube composites].

Pesticides are widely used in agriculture to increase grain yields and prevent crop diseases and insect pests. However, pesticides pose a serious threat to ecosystems and human health owing to their high toxicity and persistence. Therefore, it is imperative to establish an efficient and sensitive detection method for pesticides in water samples. Rapid and accurate detection of trace pesticides in environmental water samples has been a challenge because of complex matrix effects and trace concentrations. Appropriate sample pretreatment is a critical step for the effective extraction of analytes and removal of interferences, and the development and design of novel and stable nanomaterial adsorbents is key to continuous innovation in sample pretreatment technology. In recent years, carboxylated multiwalled carbon nanotubes (MWCNTs-COOH) and layered double hydroxide (LDHs) have been widely used as new adsorbent materials for various pretreatment technologies because of their large specific surface area, good stability, and easy functionalization. Based on this background, MWCNTs-COOH and LDHs were combined to obtain a new efficient composite adsorbent, so that the synergistic effect of the individual components could be exploited in entirety. In this study, a zeolitic metal organic framework ZIF-67/multiwalled carbon nanotube (ZIF-67/MWCNTs) composite was prepared by a simple one-step method, and a cobalt-nickel double metal hydroxide/multiwalled carbon nanotube (CoNi-LDH/MWCNTs) hybrid material with a three-dimensional cage-like structure was synthesized by a solvothermal method using ZIF-67/MWCNTs as templates. The cage-like structure of the CoNi-LDH/MWCNTs composite, which is different from the traditional layered bimetallic hydroxide, could accelerate mass transfer. Given the excellent properties of the CoNi-LDH/MWCNTs composite, it was used as a solid-phase microextraction (SPME) coating for the efficient enrichment of six pesticides (chlorothalonil, tebuconazole, chlorpyrifos, butralin, deltamethrin, and pyridaben) and combined with high performance liquid chromatography-ultraviolet (HPLC-UV) detection for the determination of the six pesticides in real water samples. The prepared materials were characterized by scanning electron microscopy, electron dispersion spectroscopy, infrared spectroscopy, X-ray powder diffraction, and N2 adsorption/desorption. The results confirmed that the CoNi-LDH/MWCNTs composite was successfully synthesized, and that its surface area and pore volume were 281.4 m2/g and 0.49 cm3/g, respectively. An orthogonal array design was used to optimize the extraction conditions of SPME, including the extraction time, extraction temperature, stirring rate, salt effect, and desorption time. The optimal extraction conditions were as follows: extraction temperature, 40 ℃; extraction time, 30 min; stirring rate, 500 r/min; desorption time, 6 min; and salt (NaCl) mass concentration, 150 mg/L. Under optimal conditions, the method had a wide linear range (chlorothalonil: 0.015-200 µg/L, tebuconazole: 0.140-200 µg/L, chlorpyrifos: 0.250-200 µg/L, butralin: 0.077-200 µg/L, deltamethrin: 1.445-200 µg/L, pyridaben: 0.964-200 µg/L), low detection limit (0.004-0.434 µg/L), and good reproducibility. The relative standard deviations (RSDs) of single fiber and fiber-to-fiber were in the range of 0.5% to 5.7% and 0.5% to 4.8%, respectively. The spiked recoveries at two levels of 10.0 µg/L and 50.0 µg/L were in the range of 83.9%-108.2%, with RSDs less than 5.3%. Compared with other coated fibers (MWCNTs-COOH, ZIF-67, ZIF-67/MWCNTs, and silicone sealant), the CoNi-LDH/MWCNTs-coated fibers showed a better enrichment effect for pesticides, which was attributed to their high specific surface area and π-π interactions, hydrophobic interactions, cation-π interactions, and hydrogen bonding interactions between the CoNi-LDH/MWCNTs coating and the target analytes, which can enhance their ability to extract pesticides. The stability test on the SPME fibers revealed that after 128 cycles, the extraction efficiency of the CoNi-LDH/MWCNTs-coated fibers for the six pesticides decreased only slightly (< 10%), implying that the coated fibers had good stability and reusability. Therefore, this method can be used to detect pesticide residues in environmental water samples with high selectivity, sensitivity, and accuracy.

In situ anchor of multi-walled carbon nanotubes into iron-based metal-organic frameworks for enhanced adsorption of polycyclic aromatic hydrocarbons by magnetic solid-phase extraction.

In this work, a magnetic MIL-101(γ-Fe2O3)/MWCNTs composite derived from iron-based metal-organic frameworks (MIL-101(Fe)) with multi-walled carbon nanotubes (MWCNTs) was successfully synthesized by low-temperature calcination process. The composite was used as adsorbent of magnetic solid-phase extraction (MSPE) for enhanced and rapid enrichment of trace polycyclic aromatic hydrocarbons (PAHs) based on its strong π-π stacking interactions, hydrophobic and cationic-π stacking interactions. The pseudo-second-order kinetic model and Langmuir isotherm model could be applied to better describe the adsorption process. The maximum adsorption capacity for PAHs reached 93.9 mg g-1. In addition, the conditions of MSPE process were optimized by orthogonal array design (OAD). A MSPE-HPLC-UV method was established for the sensitive detection of PAHs in real water samples and exhibited wide linear range (0.05-1000 µg L-1), low detection limits (0.02-0.41 µg L-1) and high enrichment factors (44-169) for PAHs. The relative standard deviations (RSD) ranged from 0.8 to 4.0% and 1.2-7.2% for single batch and batch-to-batch, respectively, and the spiked recoveries at two levels of 10 and 50 µg L-1 ranged from 79.6 to 112% with RSD of less than 5.81%. The unique MWCNTs in situ anchor MIL-101(γ-Fe2O3) composite with an outstanding PAHs adsorption performance provides a new opportunity and promising application in removal of toxic pollutants.

Controllable in situ growth of novel octahedral TiO2 nanoparticles on nickel/titanium alloy fiber substrate for selective solid-phase microextraction of ultraviolet filters in water samples.

The nature and fabrication of fiber coatings with good adsorption capacity and selectivity play a decisive role in solid-phase microextraction (SPME). In this work, a novel SPME fiber was fabricated through hydrothermal in situ growth of octahedral TiO2 nanoparticles (TiO2NPs) on a superelastic nickel/titanium alloy (NiTi) wire substrate in acid solution. The resulting fiber coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Acid types, acid concentration as well as hydrothermal temperature and time were found to be effective route to manipulate the morphologies and composition of TiO2-based nanoflakes grown on the NiTi fiber substrates. At the concentration of 0.4 mol L-1 HCl as well as hydrothermal temperature of 150 °C and hydrothermal time of 12 h, TiO2NPs were in situ grown on the NiTi wire substrates. The obtained NiTi wire with the TiO2NPs coating (NiTi@TiO2NPs fiber) was employed to investigate the adsorption of some representative aromatic analytes in water samples coupling with high-performance liquid chromatography with UV detection (HPLC/UV). The results clearly demonstrate that the fiber exhibits good extraction selectivity for ultraviolet filters (UVFs). In view of good extraction selectivity for the selected UVFs, the key experimental parameters were optimized. Under the optimum conditions, the calibration curves were linear in the ranges of 0.05-100 µg L-1 with the correlation coefficients greater than 0.998. Limits of detection (LODs) were 0.007 to 0.064 µg L-1. Furthermore, the intra-day and inter-day repeatability of the proposed method with the single fiber varied from 4.3% to 6.1% and from 4.5% to 6.8%, respectively. The fiber-to-fiber reproducibility ranged from 5.8% to 8.2%. The developed SPME-HPLC/UV method was applied to selective preconcentration and sensitive determination of target UVFs from real water samples. Moreover, the fabricated fiber showed precisely controllable growth and 150 extraction and desorption cycles.

Highly efficient solid-phase microextraction of polycyclic aromatic hydrocarbons in water based on worm-like nickel-titanium oxide nanocomposites coating grown on a nickel-titanium alloy wire by low-voltage anodization.

A novel worm-like nickel-titanium oxide nanocomposite coating was directly grown on a nickel-titanium alloy wire by low-voltage electrochemical anodization in alkaline ethylene glycol and water solution. The in situ growth of nickel-titanium oxide nanocomposites greatly depended on the volume ratio of ethylene glycol to water and temperature. Coupled to high-performance liquid chromatography with UV detection by static desorption in the mobile phase, the adsorption performance of the as-prepared fiber was evaluated for solid-phase microextraction of representative environmental analytes in water. The results indicate that the as-prepared fiber exhibits higher extraction capability for polycyclic aromatic hydrocarbons than commercial polydimethylsiloxane and polyacrylate fibers. After optimizing the extraction parameters, the calibration graphs of the developed method was linear in the range of 0.05-200 µg/L with correlation coefficients above 0.998. Limit of detection ranged from 0.013 to 0.145 µg/L for seven target analytes. Relative standard deviations of intraday and interday analyses varied from 4.0 to 5.3% and from 4.7 to 6.3% with the single fiber, respectively. The relative recoveries of 84.4-109% were achieved for highly efficient enrichment and determination of target analytes in spiked river and snow water. Moreover, the as-prepared fiber can be used more than 200 times.

Selective and efficient solid-phase microextraction of polycyclic aromatic hydrocarbons in water by robust two-dimensional zinc oxide nanosheets grown on a superelastic nickel-titanium alloy fiber prior to determination by HPLC-UV.

Oriented zinc oxide nanosheets (ZnONSs) were directly grown on pretreated nickel-titanium alloy (NiTi) fiber substrates without a traditional seeding layer of ZnO by electrochemical deposition for the first time. The fiber coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Direct growth of ZnONSs on the NiTi fiber substrate was dependent on the type of zinc salt. The adsorption performance of the ZnONSs coatings was evaluated using representative aromatic compounds as model analytes together with high performance liquid chromatography with ultraviolet detection. The as-prepared fiber shows higher extraction capability for the selected polycyclic aromatic hydrocarbons (PAHs) than for ultraviolet filters in water samples, and better extraction selectivity for PAHs. For this purpose, the important experimental parameters were optimized for the extraction of PAHs. Under the optimized conditions, the calibration curves are linear in the range of 0.03-200 µg L-1 with correlation coefficients greater than 0.999. Limits of detection ranged from 0.011 µg L-1 to 0.082 µg L-1. Intra-day and inter-day relative standard deviations (RSDs) of the developed method with a single fiber ranged from 2.69% to 4.18% and from 4.44% to 5.40%, respectively. RSDs for the fiber-to-fiber reproducibility varied between 5.57% and 7.66%. The developed method was successfully applied for selective preconcentration and determination of trace PAHs in five real water samples. Relative recoveries varied from 84.5% to 104% with RSDs between 1.65% and 8.30%. Furthermore, the as-prepared fiber is highly stable.

Modulating the selectivity of solid-phase microextraction fibers based on morphological, compositional, and size-depended control of bimetallic oxide nanostructures grown on nickel-titanium alloy substrates.

Nickel-titanium oxide nanotubes (NiTiONTs), nanoparticles, and nanopores were in situ grown on NiTi fiber substrates by controlling anodization parameters. The adsorption performance of different bimetallic oxide nanostructures was evaluated using typical aromatic compounds including chlorophenols, phthalic acid esters, ultraviolet filters (UVFs), and polycyclic aromatic hydrocarbons (PAHs) coupled to HPLC-UV. The results clearly indicate that these NiTiO nanostructures show good extraction capability for UVFs and PAHs. The extraction performance of UVFs and PAHs greatly depends on the surface morphologies and sizes of the grown NiTiO nanostructures along with their elemental compositions. Compared with NiTiO nanoparticle and nanopore coatings, the longer well-aligned NiTiONT coating exhibits better extraction capability and selectivity for PAHs than for UVFs. Therefore, the extraction parameters of the NiTi@NiTiONT fiber for PAHs were investigated and optimized. Under optimized conditions, the proposed method was linear in the range 0.05-200 µg L-1 with correlation coefficients above 0.999. Limits of detection were between 0.008 and 0.124 µg L-1. Relative standard deviations (RSDs) of the intra-day and the inter-day analyses with the single fiber varied from 4.09 to 6.33%. RSDs for fiber-to-fiber reproducibility of the proposed method with five fibers prepared in different batches were between 5.75 and 7.43%. The applicability of the proposed method was investigated by the enrichment and determination of target PAHs in environmental water samples and relative recoveries of 84.5 ± 6.5 - 116 ± 7.8% were achieved. Notably, the prepared fiber was stable up to 250 times. Graphical abstract.

Template-directed fabrication of zeolitic imidazolate framework-67-derived coating materials on nickel/titanium alloy fiber substrate for selective solid-phase microextraction.

Novel solid-phase microextraction fibers were fabricated by electrochemical deposition of cobalt on the pretreated nickel/titanium alloy (NiTi) fiber substrate and subsequent in situ growth of zeolitic imidazolate framework-67 (ZIF-67) followed by annealing treatment. The Co@ZIF-67 coating was used as a precursor and template for controlled fabrication of the Co@ZIF-67-derived coatings including Co@ZIF-67-Co3O4 and carbonaceous composite coatings. . The extraction performance of the Co@ZIF-67-derived coatings was evaluated using typical aromatic compounds coupled to high-performance liquid chromatography with UV detection. The results clearly demonstrate that the extraction selectivity is subject to the surface elemental composition of the ZIF-67-derived coatings. In view of long-term stability and good extraction selectivity, the Co@ZIF-67-C coating was selected for the enrichment and determination of polycyclic aromatic hydrocarbons (PAHs). Under the optimized conditions, the calibration curves were linear in the range of 0.05-100 µg•L-1 with the correlation coefficients above 0.998. Limits of detection were 0.005-0.042 µg•L-1. Furthermore, the intra-day and inter-day repeatability of the proposed method with the single fiber varied from 2.3% to 5.8% and from 3.3% to 6.9%, respectively. The fiber-to-fiber reproducibility ranged from 4.1% to 8.5%. The proposed method was suitable for selective enrichment and determination of target PAHs from real water samples. Moreover, the fabricated fiber showed precisely controllable growth and 150 extraction and desorption cycles.

Selective solid-phase microextraction of ultraviolet filters in environmental water with oriented ZnO nanosheets coated nickel-titanium alloy fibers followed by high performance liquid chromatography with UV detection.

Uniform and dense ZnO nanosheets (ZnONSs) as a solid-phase microextraction (SPME) fiber coating were fabricated on the surface of nickel and titanium oxide composite nanosheets (NiO/TiO2CNSs) which were in situ grown on the Nitinol (NiTi) wire in a hydrothermal procedure. The SEM micrographs illustrate that ZnONSs with the average thickness of 50 nm have been electrochemically grown on the NiTi fibers. The interconnected ZnONSs coating presents a porous nanostructure with large surface area. The as-fabricated fiber exhibits high extraction capability and excellent extraction selectivity for ultraviolet (UV) filters among the selected aromatic compounds. The main parameters affecting extraction performance were examined and optimized. Under the optimized conditions, the calibration curves were linear from 0.05 to 500 ng mL-1 with correlation coefficients above 0.999. The limits of detection (S/N = 3) ranged from 0.011 to 0.042 ng mL-1, while the limits of quanitification (S/N = 10) were in the range of 0.037-0.14 ng mL-1. Relative standard deviations (RSDs) for the single fiber repeatability were less than 7.4% (n = 5) and RSDs for the fiber-to-fiber reproducibility were below 8.2% (n = 5). The proposed method was successfully applied to the proconcentraction and determination of trace UV filters in real water samples. Moreover, the ZnONSs coating can be fabricated in highly reproducible manner with long durability.

Oriented ZnO nanoflakes on nickel-titanium alloy fibers for solid-phase microextraction of polychlorinated biphenyls and polycyclic aromatic hydrocarbons.

ZnO nanoflakes (ZnONFs) were electrochemically grown on a nickel-titanium alloy (NiTi) wire for use in solid-phase microextraction. Prior to the growth of ZnONFs, the NiTi wire was hydrothermally treated for in-situ growth of TiO2/NiO nanoflakes as a seeding base. The applied potential was used to control the dimensions of vertically oriented hexagonal ZnONFs. After annealing at 600 °C, the resulting fiber display fairly selective affinity for polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons. The fibers were applied to the preconcentration of PCBs which then were quantified by HPLC with UV detection. Compared to commercial polydimethylsiloxane coatings, the new coating displays high extraction capability, rapid extraction kinetics and superior cycling stability. This is assumed to be due to its high surface-to-volume ratio, double-sided open access structure, and enhanced structural stability. The assay excels by (a) a wide analytical range (0.10 to 200 µg L-1 of PCBs), (b) low limits of detection (20-17 ng L-1), and (c) low standard deviations for the single fiber repeatability (<9.8%) and for the fiber-to-fiber reproducibility (<7.5%). Satisfactory accuracy and precision were achieved when PCBs were determined by this method in spiked rain water, river water and wastewater samples. Graphical abstract ZnO nanoflakes were fabricated on a superelastic nickel-titanium alloy wire in desired orientation with enhanced extraction capability and good extraction selectivity. The fabricated fiber was suitable for the determination of PCBs in environmental water samples.

An effective strategy for controlled fabrication and self-assembled modification of template-supported silica nanosheets on a superelastic nickel-titanium alloy fiber for highly efficient solid-phase microextraction.

Silica nanosheets (SiO2NSs) were successfully fabricated on the superelastic nickel-titanium alloy (NiTi) wire as a novel fiber for solid-phase microextraction (SPME). Before sol-gel coating, the NiTi wire was hydrothermally treated in alkaline solution for the in situ growth of NiO/TiO2 nanosheets (NiO/TiO2NSs). The sol-gel coating of SiO2 on the surface of NiO/TiO2NSs template was investigated and a thin shell of SiO2 was found to cover NiO/TiO2NSs, which can enlarge the effective surface area of the SiO2 coating. This SiO2 capped NiO/TiO2NSs coated NiTi (NiTi@NiO/TiO2@SiO2NSs) fiber shows good extraction selectivity for polycyclic aromatic hydrocarbons (PAHs) and enhanced mechanical stability. After the self-assembled modification of SiO2NSs by phenyltrichlorosilane, the NiTi@NiO/TiO2@SiO2NSs@Ph fiber shows higher extraction capability for non-polar PAHs. Thus, the conditions for the extraction of PAHs were investigated and optimized coupled to HPLC with UV detection. Under the optimized conditions, the analytical parameters of the SPME-HPLC methods with the NiTi@NiO/TiO2@SiO2NSs and the NiTi@NiO/TiO2@SiO2NSs@Ph fibers were determined and compared. The SPME-HPLC method with the NiTi@NiO/TiO2@SiO2NSs@Ph fiber was developed for the concentration and the determination of PAHs in environment water samples. The relative recovery of PAHs in real water samples spiked at 5 µg L-1, 10 µg L-1 and 30 µg L-1 ranged from 88.1% to 109%. Furthermore, this fiber is stable due to the chemical bonding between different coatings and NiTi substrates. The fabrication of the NiO/TiO2@SiO2NSs@Ph coating on the NiTi fiber substrate is precisely controllable.

Electrophoretic deposition strategy for the fabrication of highly stable functionalized silica nanoparticle coatings onto nickel-titanium alloy wires for selective solid-phase microextraction.

A new strategy for the immobilization of phenyl-functionalized silica nanoparticles onto nickel-titanium alloy wires is presented. The homogeneous and compact silica nanoparticle coating was achieved on the hydrothermally treated nickel-titanium wires with large surface area by electrophoretic deposition, and followed by self-assembled modification of phenyltrichlorosilane. Coupled to high-performance liquid chromatography with ultraviolet detection, the extraction performance of the fabricated fiber was evaluated using typical aromatic compounds in direct-immersion mode of solid-phase microextraction. Due to its high extraction efficiency and good selectivity for ultraviolet filters, the novel fiber was employed to investigate the key factors affecting the extraction of ultraviolet filters. Under the optimized conditions, the proposed method presented linear ranges from 0.05 to 300 µg/L with correlation coefficients higher than 0.999 and limits of detection from 0.005 to 0.058 µg/L. Relative standard deviations were below 4.3 and 5.6% for intraday and interday analyses at the spiking level of 50 µg/L ultraviolet filters with the single fiber, respectively. The proposed method was successfully applied to the selective concentration and sensitive detection of target ultraviolet filters from environmental water samples. Furthermore, the developed fiber can be used at least 200 times, and fabricated in a precisely controllable manner.

Hydrothermally grown and self-assembled modified titanium and nickel oxide composite nanosheets on Nitinol-based fibers for efficient solid phase microextraction.

A novel titanium and nickel oxide composite nanosheets (TiO2/NiOCNSs) coating was in situ grown on a Nitinol (NiTi) wire by direct hydrothermal treatment and modified by self-assembly of trichlorophenylsilane for solid phase microextraction (SPME). TiO2/NiOCNSs were radially oriented and chemically bonded to the NiTi substrate with double-faced open access sites. Moreover the phenyl modified TiO2/NiOCNSs (TiO2/NiOCNSs-Ph) coating exhibited original surface supporting framework favorable for effective SPME. The extraction performance of TiO2/NiOCNSs-Ph coated NiTi (NiTi-TiO2/NiOCNSs-Ph) fiber was investigated for the concentration and detection of ultraviolet (UV) filters, polycyclic aromatic hydrocarbons (PAHs), phthalate acid esters and polychlorinated biphenyls coupled to HPLC with UV detection. The novel fiber exhibited better selectivity for UV filters and PAHs and presented greater extraction capability compared to commercial polydimethylsiloxane and polyacrylate fibers. Under the optimized conditions for SPME of UV filters, the proposed method presented linear ranges from 0.1 to 300µg/L with correlation coefficients of higher than 0.999 and limits of detection from 0.030µg/L to 0.064µg/L. Relative standard deviations (RSDs) were below 7.16% and 8.42% for intra-day and inter-day measurements with the single fiber, respectively. Furthermore RSDs for fiber-to-fiber reproducibility from 6.57% to 8.93% were achieved. The NiTi-TiO2/NiOCNSs-Ph fiber can be used up to 200 times. The proposed method was successfully applied to the preconcentration and determination of trace target UV filters in different environmental water samples. The relative recoveries from 87.3% to 104% were obtained with RSDs less than 8.7%.

Rapid in situ growth of oriented titanium-nickel oxide composite nanotubes arrays coated on a nitinol wire as a solid-phase microextraction fiber coupled to HPLC-UV.

An oriented titanium-nickel oxide composite nanotubes coating was in situ grown on a nitinol wire by direct electrochemical anodization in ethylene glycol with ammonium fluoride and water for the first time. The morphology and composition of the resulting coating showed that the anodized nitinol wire provided a titania-rich coating. The titanium-nickel oxide composite nanotubes coated fiber was used for solid-phase microextraction of different aromatic compounds coupled to high-performance liquid chromatography with UV detection. The titanium-nickel oxide composite nanotubes coating exhibited high extraction capability, good selectivity, and rapid mass transfer for weakly polar UV filters. Thereafter the important parameters affecting extraction efficiency were investigated for solid-phase microextraction of UV filters. Under the optimized conditions, the calibration curves were linear in the range of 0.1-300 µg/L for target UV filters with limits of detection of 0.019-0.082 µg/L. The intraday and interday precision of the proposed method with the single fiber were 5.3-7.2 and 5.9-7.9%, respectively, and the fiber-to-fiber reproducibility ranged from 6.3 to 8.9% for four fibers fabricated in different batches. Finally, its applicability was evaluated by the extraction and determination of target UV filters in environmental water samples.

3-D graphene-supported mesoporous SiO2 @Fe3 O4 composites for the analysis of pesticides in aqueous samples by magnetic solid-phase extraction with high-performance liquid chromatography.

Three-dimensional graphene-supported mesoporous silica@Fe3 O4 composites (mSiO2 @Fe3 O4 -G) were prepared by modifying mesoporous SiO2 -coated Fe3 O4 onto hydrophobic graphene nanosheets through a simple adsorption co-condensation method. The obtained composites possess unique properties of large surface area (332.9 m(2) /g), pore volume (0.68 cm(3) /g), highly open pore structure with uniform pore size (31.1 nm), as well as good magnetic separation properties. The adsorbent (mSiO2 @Fe3 O4 -G) was used for the magnetic solid-phase extraction of seven pesticides with benzene rings in different aqueous samples before high-performance liquid chromatography. The main parameters affecting the extraction such as adsorbent amount, volume of elution solvent, time of extraction and desorption, salt effect, oscillation rate were investigated. Under the optimal conditions, this method provided low limits of detection (S/N = 3, 0.525-3.30 µg/L) and good linearity (5.0-1000 µg/L, R(2) > 0.9954). Method validation proved the feasibility of the developed adsorbent, which has a high extraction efficiency and excellent enhancement performance for pesticides in this study. The proposed method was successfully applied to real aqueous samples, and satisfactory recoveries ranging from 77.5 to 113.6% with relative standard deviations within 9.7% were obtained.

Growth of cedar-like Au nanoparticles coating on an etched stainless steel wire and its application for selective solid-phase microextraction.

A novel cedar-like Au nanoparticles (AuNPs) coating was fabricated on an etched stainless steel (SS) wire by direct chemical deposition and used as an efficient and unbreakable solid phase microextraction (SPME) fiber. The etched SS wire offers a rough surface structure for subsequent growth of AuNPs in chloroauric acid solution. As a result, the uniform cedar-like AuNPs coating with larger surface area was tightly attached to the etched SS wire substrate. The AuNPs coated etched SS fiber (AuNPs/SS) was examined for SPME of ultraviolet (UV) filters, phthalate esters and aromatic hydrocarbons coupled to high-performance liquid chromatography with UV detection. The fabricated fiber exclusively exhibited excellent extraction efficiency and selectivity for some aromatic hydrocarbons. Influential parameters of extraction and desorption time, temperature, stirring rate and ionic strength were investigated and optimized. The limits of detection ranged from 0.008 µg L(-1) to 0.037 µg L(-1). The single fiber repeatability varied from 3.90% to 4.50% and the fiber-to-fiber reproducibility ranged from 5.15% to 6.87%. The recovery of aromatic hydrocarbons in real water samples spiked at 2.0 µg L(-1) and 20 µg L(-1) ranged from 94.38% to 106.2% with the relative standard deviations below 6.44%. Furthermore the growth of the cedar-like AuNPs coating can be performed in a highly reproducible manner. This fabricated fiber exhibits good stability and withstands at least 200 extraction and desorption replicates.

Fabrication and application of zinc-zinc oxide nanosheets coating on an etched stainless steel wire as a selective solid-phase microextraction fiber.

A novel zinc-zinc oxide (Zn-ZnO) nanosheets coating was directly fabricated on an etched stainless steel wire substrate as solid-phase microextraction (SPME) fiber via previous electrodeposition of robust Zn coating. The scanning electron micrograph of the Zn-ZnO nanosheets coated fiber exhibits a flower-like nanostructure with high surface area. The SPME performance of as-fabricated fiber was investigated for the concentration and determination of polycyclic aromatic hydrocarbons, phthalates and ultraviolet (UV) filters coupled to high performance liquid chromatography with UV detection (HPLC-UV). It was found that the Zn-ZnO nanosheets coating exhibited high extraction capability, good selectivity and rapid mass transfer for some UV filters. The main parameters affecting extraction performance were investigated and optimized. Under the optimized conditions, the calibration graphs were linear over the range of 0.1-200µgL(-1). The limits of detection of the proposed method were 0.052-0.084µgL(-1) (S/N=3). The single fiber repeatability varied from 5.18% to 7.56% and the fiber-to-fiber reproducibility ranged from 6.74% to 8.83% for the extraction of spiked water with 50µgL(-1) UV filters (n=5). The established SPME-HPLC-UV method was successfully applied to the selective concentration and sensitive determination of target UV filters from real environmental water samples with recoveries from 85.8% to 105% at the spiking level of 10µgL(-1) and 30µgL(-1). The relative standard deviations were below 9.7%.