Fabrication of metal-organic framework MIL-88B films on stainless steel fibers for solid-phase microextraction of polychlorinated biphenyls

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.

Progress and prospect of adsorptive removal of heavy metal ions from aqueous solution using metal-organic frameworks: A review of studies from the last decade

The efficient removal of heavy metals (HMs) from the environment has become an important issue from both biological and environmental perspectives. Recently, porous metal-organic frameworks (MOFs), combining central metals and organic ligands, have been proposed as promising materials in the capture of various toxic substances, including HMs, due to their unique characteristics. Here we review recent progress in the field of water remediation from the perspective of primary HMs (including divalent metals and variable-valent metals) in water pollution and the corresponding MOFs (including virgin and modified MOFs, magnetic MOFs composites and so on) that can remove these metals from water. The reported values of various MOFs for adsorption of heavy metal ions were 8.40-313 mg Pb(II) g^-1, 0.65-2173 mg Hg(II) g^-1, 3.63-145 mg Cd(II) g^-1, 14.0-127 mg Cr(III) g^-1, 15.4-145 mg Cr(VI) g^-1, 49.5-123 mg As(III) g^-1, and 12.3-303 mg As(V) g^-1. The main adsorption mechanisms associated with these processes are chemical (including coordination interaction, chemical bonding and acid-base interactions) and physical (including electrostatic interaction, diffusion and van der Waals force) adsorption, which were discussed in detailed. Further efforts should be made towards expanding the repertoire of MOFs that effectively remove multiple targeted HMs, as well as exploring possible applications of MOFs in the removal of HMs from non-aqueous environments.

Recent advances in metal-organic frameworks and covalent organic frameworks for sample preparation and chromatographic analysis

In the field of analytical chemistry, sample preparation and chromatographic separation are two core procedures. The means by which to improve the sensitivity, selectivity and detection limit of a method have become a topic of great interest. Recently, porous organic frameworks, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have been widely used in this research area because of their special features, and different methods have been developed. This review summarizes the applications of MOFs and COFs in sample preparation and chromatographic stationary phases. The MOF- or COF-based solid-phase extraction (SPE), solid-phase microextraction (SPME), gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC) methods are described. The excellent properties of MOFs and COFs have resulted in intense interest in exploring their performance and mechanisms for sample preparation and chromatographic separation.

Fabrication of Metal-Organic Framework MOF-177 Coatings on Stainless Steel Fibers for Head-Space Solid-Phase Microextraction of Phenols

Direct head-space solid-phase microextraction (HS-SPME) of phenols in water is usually difficult due to its polarity and solubility in aqueous matrix. Herein we report the fabrication of metal-organic framework MOF-177 coated stainless steel fiber for the HS-SPME of phenols (2-methylolphenol, 4-methylolphenol, 2,4-dimethylolphenol, 2,4-dichlorphenol, and 3-methyl-4-chlorophenol) in environmental water samples prior to the gas chromatography-mass spectrometry detection. Several parameters affecting the extraction efficiency were optimized in the experiment, including extraction temperature and time, the pH value and salt addition. The results indicated that the coated fiber gave low detection limits (0.015-0.043 μg L^-1) and good repeatability with the RSD ranging from 2.8% to 5.5% for phenols. The recoveries are between 84.5%-98.6% with the spiked level of 10 μg L^-1 for the real water samples. The established method may afford a kind of potential enrichment material and a reference method for the analysis of methylphenols in water samples.

Recent applications of metal-organic frameworks in sample pretreatment

Metal-organic frameworks are promising materials in diverse analytical applications especially in sample pretreatment by virtue of their diverse structure topology, tunable pore size, permanent nanoscale porosity, high surface area, and good thermostability. According to hydrostability, metal-organic frameworks are divided into moisture-sensitive and water-stable types. In the actual applications, both kinds of metal-organic frameworks are usually engineered into hybrid composites containing magnetite, silicon dioxide, graphene, or directly carbonized to metal-organic frameworks derived carbon. These metal-organic frameworks based materials show good extraction performance to environmental pollutants. This review provides a critical overview of the applications of metal-organic frameworks and their composites in sample pretreatment modes, that is, solid-phase extraction, magnetic solid-phase extraction, micro-solid-phase extraction, solid-phase microextraction, and stir bar solid extraction.

Fabrication of a polymeric composite incorporating metal-organic framework nanosheets for solid-phase microextraction of polycyclic aromatic hydrocarbons from water samples

In this contribution, it was discovered that even distribution of a metal-organic framework (MOF) [e.g. copper 1,4-benzenedicarboxylate (CBDC)] within polymeric matrixes (e.g. polyimide) resulted in a high-efficient coating material on the surface of a stainless steel wire (SSW). Consequently, a home-made solid phase microextraction (SPME) fiber was fabricated for fast determination of target analytes in real water samples. Scanning electron microscope images indicated that the coating possessed homogenously porous surface. Coupled with gas chromatography-mass spectrometry (GC-MS) and direct immersion SPME (DI-SPME) technique, the fiber was evaluated through the analysis of five polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. Under optimized extraction and desorption conditions, the established method based on the home-made fiber exhibited good repeatability (4.2-12.7%, n = 6) and reproducibility (0.9-11.7%, n = 3), low limits of detection (LODs, 0.11-2.10 ng L^-1), low limits of quantification (LOQs, 0.36-6.99 ng L^-1) and wide linear ranges (20-5000 ng L^-1). Eventually, the method was proven applicable in the determination of PAHs in real samples, as the recoveries were in a satisfactory range (81.7-116%).

Procedures of determining organic trace compounds in municipal sewage sludge-a review

Sewage sludge is the largest by-product generated during the wastewater treatment process. Since large amounts of sludge are being produced, different ways of disposal have been introduced. One tempting option is to use it as fertilizer in agricultural fields due to its high contents of inorganic nutrients. This, however, can be limited by the amount of trace contaminants in the sewage sludge, containing a variety of microbiological pollutants and pathogens but also inorganic and organic contaminants. The bioavailability and the effects of trace contaminants on the microorganisms of soil are still largely unknown as well as their mixture effects. Therefore, there is a need to analyze the sludge to test its suitability before further use. In this article, a variety of sampling, pretreatment, extraction, and analysis methods have been reviewed. Additionally, different organic trace compounds often found in the sewage sludge and their methods of analysis have been compiled. In addition to traditional Soxhlet extraction, the most common extraction methods of organic contaminants in sludge include ultrasonic extraction (USE), supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), and pressurized liquid extraction (PLE) followed by instrumental analysis based on gas or liquid chromatography and mass spectrometry.

Metal-Organic Framework-Polymer Composite as a Highly Efficient Sorbent for Sulfonamide Adsorption and Desorption: Effect of Coordinatively Unsaturated Metal Site and Topology

In this study, we first demonstrated the effect of two types of metal-organic framework-polymer (MOF-polymer) monoliths on in-tube solid-phase microextraction (IT-SPME) of sulfonamides. Sulfonamides were successfully adsorbed onto MIL-101(Cr)-polymer but were difficult to elute due to these sulfonamides could interact via Lewis acid-base interaction with the presence of Cr(III) coordinatively unsaturated metal sites (CUS). Moreover, the cage-type topology of MIL-101(Cr) that could produce multiple pathways thus complicates the desorption of the test analytes from the sorbent. Contrastingly, MIL-53(Al)-polymer provided weaker Al(III) CUS, and its one-dimensional channel pore structure could provide an unhindered pathway for sulfonamides transfer during elution. After optimizing the IT-SPME condition such as MOF content, pH of sample matrix, column length, extraction flow rate, and elution volume, the calculated extraction recovery of sulfonamides in MIL-53(Al)-polymer as analyzed by microemulsion electrokinetic chromatography (MEEKC) were in the range of 40%-90% with relative standard deviations (RSDs) below 5% and a reusability of at least 30 times.

A novel Schiff base network-1 nanocomposite coated fiber for solid-phase microextraction of phenols from honey samples

A novel covalent organic framework, Schiff base network-1 (SNW-1), was synthesized and used as a solid-phase microextraction (SPME) fiber coating material. The SNW-1 coated SPME fiber was fabricated by a covalent chemical cross-linking between the SNW-1 nanocomposite and a silanol-functionalized stainless steel wire substrate. Scanning electron microscopy and nitrogen isothermal adsorption results indicate that the new fiber coating exhibited a porous, homogenous surface with the Brunauer-Emmett-Teller surface of 668m²g^-1. The prepared fiber was explored for the SPME of phenols from honey samples prior to their determination by gas chromatography-mass spectrometry. The developed method had large enrichment factors (136-816), low limits of detection (0.06-0.2ngg^-1), good linearity (0.1-100.0ngg^-1) and repeatability (<9.7%) for phenols. The recoveries for spiked phenols (1.0ngg^-1 and 10.0ngg^-1) in Wolfberry, Robinia and Codonopsis honey samples were in the range of 84.2-107.2% with the relative standard deviations ranging from 3.8% to 12.7%. The developed method was suitable for the determination of phenols from honey samples.

Covalent Bonding of Metal-Organic Framework-5/Graphene Oxide Hybrid Composite to Stainless Steel Fiber for Solid-Phase Microextraction of Triazole Fungicides from Fruit and Vegetable Samples

A hybrid material of the zinc-based metal-organic framework-5 and graphene oxide (metal-organic framework-5/graphene oxide) was prepared as a novel fiber coating material for solid-phase microextraction (SPME). The SPME fibers were fabricated by covalent bonding via chemical cross-linking between the coating material metal-organic framework-5/graphene oxide and stainless steel wire. The prepared fiber was used for the extraction of five triazole fungicides from fruit and vegetable samples. Gas chromatography coupled with microelectron capture detector (GC-μECD) was used for quantification. The developed method gave a low limit of detection (0.05-1.58 ng g(-1)) and good linearity (0.17-100 ng g(-1)) for the determination of the triazole fungicides in fruit and vegetable samples. The relative standard deviations (RSDs) for five replicate extractions of the triazole fungicides ranged from 3.7 to 8.9%. The method recoveries for spiked fungicides (5, 20, and 50 ng g(-1)) in grape, apple, cucumber, celery cabbage, pear, cabbage, and tomato samples were in the range of 85.6-105.8% with the RSDs ranging from 3.6 to 11.4%, respectively, depending on both the analytes and samples. The metal-organic framework-5/graphene oxide coated fiber was stable enough for 120 extraction cycles without a significant loss of extraction efficiency. The method was suitable for the determination of triazole fungicides in fruit and vegetable samples.

A porous carbon derived from amino-functionalized material of Institut Lavoisier as a solid-phase microextraction fiber coating for the extraction of phthalate esters from tea

In this work, a porous carbon derived from amino-functionalized material of Institut Lavoisier (C-NH2 -MIL-125) was prepared and coated onto a stainless-steel wire through sol-gel technique. The coated fiber was used for the solid-phase microextraction of trace levels of phthalate esters (diallyl phthalate, di-iso-butyl ortho-phthalate, di-n-butyl ortho-phthalate, benzyl-n-butyl ortho-phthalate, and bis(2-ethylhexy) ortho-phthalate) from tea beverage samples before gas chromatography with mass spectrometric analysis. Several experimental parameters that could influence the extraction efficiency such as extraction time, extraction temperature, sample pH, sample salinity, stirring rate, desorption temperature and desorption time, were investigated. Under the optimal conditions, the linearity existed in the range of 0.05-30.00 μg/L for green jasmine tea beverage samples, and 0.10-30.00 μg/L for honey jasmine tea beverage samples, with the correlation coefficients (r) ranging from 0.9939 to 0.9981. The limits of detection of the analytes for the method were 2.0-3.0 ng/L for green jasmine tea beverage sample, and 4.0-5.0 ng/L for honey jasmine tea beverage sample, depending on the compounds. The recoveries of the analytes for the spiked samples were in the range of 82.0-106.0%, and the precision, expressed as the relative standard deviations, was less than 11.1%.

In situ solvothermal synthesis of metal-organic framework coated fiber for highly sensitive solid-phase microextraction of polycyclic aromatic hydrocarbons

The present work reported a facile and simple in situ solvothermal growth method for immobilization of metal-organic framework UiO-66 via covalent bonding on amino functional silica fiber for highly sensitive solid-phase microextraction (SPME) of ten polycyclic aromatic hydrocarbons (PAHs) by coupling with gas chromatography-mass spectrometry (GC-MS) analysis. The developed SPME coated fiber has been characterized through SEM, TGA and XRD, confirmed the coating thickness of ∼25μm with high thermal and chemical stability. Under optimized conditions, the obtained method exhibited satisfactory linearity in range of 1.0-5000.0ngL(-1) for all the PAHs. The low detection limits were from 0.28ngL(-1) to 0.60ngL(-1) (S/N=3). The UiO-66 coated fibers showed good repeatability (RSDs less than 8.2%, n=5) and satisfying reproducibility between fiber to fiber (RSDs less than 8.9%, n=5). This method was successfully used for simultaneous determination of ten PAHs from Minjiang water and soil samples with satisfactory recoveries of 87.0-113.6% and 83.8-116.7%, respectively. Experimental results shows that the chemical bonding approach has dramatically improve the stability and lifetime of pure MOFs coating for SPME in sample pretreatment.