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

Ordered mesoporous hairbrush-like nanocarbon assembled microfibers for solid-phase microextraction of benzene series in oilfield sewage

The development of advanced functional nanomaterials for solid-phase microextraction (SPME) remains an imperative aspect of sample pretreatment. Herein, we introduce a novel SPME fiber consisting of graphene fibers modified with ordered mesoporous carbon nanotubes arrays (CNTAs) tailored for the determination of benzene series in oilfield wastewater, which is synthesized by an ionic liquid-assisted wet spinning process of graphene nanosheets, followed by a precisely controlled growth of metal-organic framework and subsequent pyrolysis treatment. The resulting robust microfiber structure resembles a "hairbrush" configuration, with a crumpled graphene fiber "stem" and high-order mesoporous CNTAs "hairs". This unique architecture significantly enhances the SPME capacity, as validated by gas chromatography-mass spectrometry. The hairbrush-like nanocarbon assembled microfibers possess structural characteristics, a high specific surface area, and numerous binding sites, offering efficient enrichment of benzene series compounds in oilfield wastewater, including benzene, ethylbenzene, m-xylene, p-xylene, and toluene. Our analysis demonstrates that these microfibers exhibit broad linear ranges (0.2-600 μg L-1), low detection limits (0.005-0.03 mg L-1), and excellent repeatability (3.2-5.5% for one fiber, 2.1-6.7% for fiber-to-fiber) for detection. When compared to commercial alternatives, these hairbrush-like nanocarbon-assembled microfibers exhibit significantly enhanced extraction efficiency for benzene series compounds.

MOF-801 based solid phase microextraction fiber for the monitoring of indoor BTEX pollution

Benzene, toluene, ethylbenzene and xylenes (BTEX) are some of the better-known indoor air pollutants, for which effective monitoring is important. The analysis of BTEX can be performed by different type of solid phase microextraction (SPME) fibers. This study presents a proposal for a low cost, convenient and environmentally friendly analytical method for the determination of BTEX in air samples using custom made SPME fibers. In this context, custom made metal organic frameworks (MOF-801) were coated on a stainless-steel wire for SPME fiber preparation. The analysis of BTEX was performed by introducing SPME fiber into an analyte-containing Tedlar bag in steady-state conditions. After the sampling step, the analytes were analyzed using gas chromatography mass spectrometry in selected ion monitoring mode. Parameters that affect the analysis results were optimized; these include desorption temperature and time, preconditioning time, extraction temperature and time, and sample volume. Under optimized conditions, analytical figure of merits of developed method were obtained, including limits of detection (LOD) (0.012 - 0.048 mg/m3), linear ranges (0.041-18 mg/m3), intraday and interday repeatability (2.08 - 4.04% and 3.94 - 6.35%), and fiber to fiber reproducibility (7.51 - 11.17%). The proposed method was successfully applied to real air samples with an acceptable recovery values between 84.5% and 110.9%. The developed method can be applied for the effective monitoring of BTEX.

A multifunctional recyclable adsorbent based on engineered MIL-125 (Ti) magnetic mesoporous composite for the effective removal of pathogens

The elimination of pathogenic bacteria from water sources is currently crucial for obtaining drinkable water. Therefore, the development of platforms with the ability to interact with pathogens and remove them is a potential future tool for medicine, food and water safety. In this work, we have grafted a layer of NH2-MIL-125 (Ti) on Fe3O4@SiO2 magnetic nanospheres for the removal of multiple pathogenic bacteria from water. The synthesized Fe3O4@SiO2@NH2-MIL-125 (Ti) nano adsorbent was characterized by FE-SEM, HR-TEM, FT-IR, XRD, BET surface analysis, magnetization tests, respectively, which illustrated its well-defined core-shell structure and magnetic behaviour. The prepared magnetic-MOF composite sorbent was attractive towards capturing a wide range of pathogens (S. typhimurium, S. aureus, E. coli, P. aeruginosa and K. pneumoniae) under experimental conditions. Influence factors such as adsorbent dosage, bacterial concentration, pH and incubation time were optimized for enhanced bacterial capture. The application of an external magnetic field removed Fe3O4@SiO2@NH2-MIL-125 (Ti) nano adsorbent from the solution along with sweeping the attached pathogenic bacteria. The non-specific removal efficiency of S. typhimurium for magnetic MOF composite was 96.58%, while it was only 46.81% with Fe3O4@SiO2 particles. For specific removal, 97.58% of S. typhimurium could be removed selectively from a mixture with monoclonal anti- Salmonella antibody conjugated magnetic MOF at a lower concentration of 1.0 mg/mL. The developed nano adsorbent may find great potential in microbiology applications and water remediation.

Covalent organic framework in situ grown on the metal-organic framework as fiber coating for solid-phase microextraction of polycyclic aromatic hydrocarbons in tea

A novel MIL-88-NH2@COF composite was produced by in situ growth of covalent organic framework (COF) on the metal-organic framework (MOF) surface. To obtain a coating fiber for solid-phase microextraction (SPME), the MIL-88-NH2@COF composite physically adhered to the stainless steel wire. Combined with gas chromatography-flame ionization detection (GC-FID), various analytes such as chlorophenols (CPs), phthalates (PAEs), and polycyclic aromatic hydrocarbons (PAHs) were extracted and determined to evaluate the extraction performance of MIL-88-NH2@COF coated fibers and explore their extraction mechanism. This composite exhibit excellent extraction performance and adsorption capacity for various analytes, especially for PAHs with enrichment factor up to 9858. The SPME-GC-FID method based on MIL-88-NH2@COF fiber was established for the determination of five PAHs after the main extraction conditions were optimized. Under optimal conditions, the proposed technique showed a wide linear range (1-150 ng mL-1) with a low limit of detection (0.019 ng mL-1) and a high coefficient of determination (R2 > 0.99). The developed SPME-GC-FID method was used to determine PAHs in green tea and black tea samples, with good recoveries of 51.70-103.64% and 68.56-103.64%, respectively. It is worth mentioning that this is the first time MIL-88-NH2@COF composites have been prepared and applied to SPME. The preparation method of the composite provides a new idea in adsorbent preparation, which will contribute to the field of SPME.

In situ growth of porous organic framework on iron wire for microextraction of polycyclic aromatic hydrocarbons

In this work, a novel spherical metal organic framework (MOF) was first in situ grown on the surface of iron wire (IW), in which IW served as the substrate and metal source for MOF (type NH₂-MIL88) growth without adding additional metal salts in the process, while spherical NH₂-MIL88 provided more active sites for further construction of multifunctional composites. Subsequently, a covalent organic framework (COF) was covalently bonded to the surface of the NH₂-MIL88 to obtain the IW@NH₂-MIL88@COF fibers, which were used for headspace solid-phase microextraction (HS-SPME) of polycyclic aromatic hydrocarbons (PAHs) in milk samples prior to determination by gas chromatography-flame ionization detection (GC-FID). Compared with the fiber prepared by physical coating, the IW@NH₂-MIL88@COF fiber prepared by in situ growth and covalent bonding exhibits better stability and possesses more uniform layer. The extraction mechanism of the IW@NH₂-MIL88@COF fiber for PAHs was discussed, which mainly owed to π-π interactions and hydrophobic interactions. After optimization of the primary extraction conditions, the SPME-GC-FID method was established for five PAHs with a wide linear range (1-200 ng mL^-1), good linearity coefficient (0.9935-0.9987) and low detection limits (0.017-0.028 ng mL^-1). The relative recoveries for PAHs detection in milk samples ranged from 64.69 to 113.97%. This work not only provides new ideas for the in situ growth of other types of MOF, but also provides new methods for the construction of multifunctional composites.

Application of Functional Modification of Iron-Based Materials in Advanced Oxidation Processes (AOPs)

Advanced oxidation processes (AOPs) have become a favored approach in wastewater treatment due to the high efficiency and diverse catalyzed ways. Iron-based materials were the commonly used catalyst due to their environmental friendliness and sustainability in the environment. We collected the published papers relative to the application of the modified iron-based materials in AOPs between 1999 and 2020 to comprehensively understand the related mechanism of modified materials to improve the catalytic performance of iron-based materials in AOPs. Related data of iron-based materials, modification types, target pollutants, final removal efficiencies, and rate constants were extracted to reveal the critical process of improving the catalytic efficiency of iron-based materials in AOPs. Our results indicated that the modified materials through various mechanisms to enhance the catalytic performance of iron-based materials. The principal aim of iron-based materials modification in AOPs is to increase the content of available Fe2+ and enhance the stability of Fe2+ in the system. The available Fe2+ is elevated by the following mechanisms: (1) modified materials accelerate the electron transfer to promote the Fe3+/Fe2+ reaction cycle in the system; (2) modified materials form chelates with iron ions and bond with iron ions to avoid Fe3+ precipitation. We further analyzed the effect of different modifying materials in improving these two mechanisms. Combining the advantages of different modified materials to develop iron-based materials with composite modification methods can enhance the catalytic performance of iron-based materials in AOPs for further application in wastewater treatment.

In-situ fabrication of a chlorine-functionalized covalent organic framework coating for solid-phase microextraction of polychlorinated biphenyls in surface water

The functionalization of covalent organic frameworks (COFs) identifies significant potential for developing selective coating materials for solid-phase microextraction (SPME). Herein, a chlorine-functionalized covalent organic framework (CF-COF) was in-situ synthesized by employing triformylphloroglucinol (Tp) and 2,5-dichloro-1,4-phenylenediamine (2,5-DCA) as monomers on an amino-functionalized stainless steel wire. The obtained CF-COF coated fiber exhibited a higher enrichment capacity for polychlorinated biphenyls (PCBs) than commercial fibers and non-chlorinated COF fiber, owing to a more hydrophobic surface, size-matching effect, a large number of micropores and the π-π stacking interactions between COF coating and analytes. As a practical application, the CF-COF coated fiber was applied to the headspace extraction of 17 PCBs prior to their quantification by GC/MS. The established analytical method offered a good linearity in the range of 0.1-1000 ng L^-1, low detection limits of 0.0015-0.0088 ng L^-1, and satisfactory enhancement factors (EFs) of 699-4281. The repeatability for single fiber and the fiber-to-fiber reproducibility was lower than 9.26% and 9.33%, respectively. The proposed method was verified to be sensitive, selective, and applicable for the analysis of ultra-trace PCBs in environmental surface water samples with the recoveries ranged from 78.7% to 124.0%.

On the use of metal-organic frameworks for the extraction of organic compounds from environmental samples

The determination of trace metals and organic contaminants in environmental samples, such as water, air, soil, and sediment, is until today a challenging process for the analytical chemistry. Metal-organic frameworks (MOFs) are novel porous nanomaterials that are composed of metal ions and an organic connector. These materials are gaining more and more attention due to their superior characteristics, such as high surface area, tunable pore size, mechanical and thermal stability, luminosity, and charge transfer ability between metals and ligands. Among the various applications of MOFs are gas storage, separation, catalysis, and drug delivery. Recently, MOFs have been successfully introduced in the field of sample preparation for analytical chemistry and they have been used for sample pretreatment of various matrices. This review focuses on the applications of MOFs as novel adsorbents for the extraction of organic compounds from environmental samples.

A Comprehensive Review on Metal Organic Framework Based Preconcentration Strategies for Chromatographic Analysis of Organic Pollutants

Organic pollutants (OPs) are of worldwide concern for being hazardous to human existence and natural flora and fauna in view of their contaminating nature, bio-aggregation properties and long range movement abilities in environment. Metal organic frameworks (MOFs) are a new kind of crystalline porous material, composed of metal ions and multi dentate organic ligands with well-defined co-ordination geometry exhibiting promising application respect to adsorptive evacuation of OPs for chromatographic analysis. Applications of MOFs as preconcentration material and column packing material are reviewed. Key analytical characteristics of MOF based preconcentration techniques and coupled chromatographic procedures are summarized in detail. MOF based preconcentration strategies are compared with conventional sorbent based extraction techniques for thorough evaluation of performance of MOF materials.

Temperature and time-controlled hydrothermal growth and sorption selectivity of titania nanowires on titanium fiber for highly efficient solid-phase microextraction

Two kinds of TiO₂ nanowires (TiO₂NWs) with different orientation were in-situ grown on Ti substrates by controlling temperature and time during the hydrothermal process. The adsorption performance was evaluated by using typical aromatic compounds as model analytes coupled to HPLC with UV detection. The results demonstrated that the TiO₂NWs coating grown at higher temperature within longer time had better affinity towards PAHs. For this purpose, the key experimental factors affecting the adsorption performance of the TiO₂NWs coating fabricated at 200 °C for 10 h were further investigated and optimized for the extraction of PAHs. Under the optimized conditions, the proposed method presented linear responses in the concentration ranges of 0.05 to 200 μg·L^-1 PAHs with correlation coefficients more than 0.998. LODs (S/N=3) were 0.008 to 0.034 μg·L^-1. Moreover, RSDs for the single fiber repeatability of the intra-day and the inter-day analyses were less than 5.6% (n=5) and 5.8%, respectively. RSDs for the fiber-to-fiber reproducibility were between 5.1% and 6.5%. Finally, the proposed method was successfully applied to the selective preconcentration and determination of trace PAHs in environmental water samples. In addition, The fabricated Ti fiber can be used at least 200 times due to its high mechanical and chemical stability.

A polythiophene/UiO-66 composite coating for extraction of volatile organic compounds migrated from ion-exchange resins prior to their determination by gas chromatography

A Poly (3,4-ethylenedioxothiophene) (PEDOT)/UiO-66 composite was electrodeposited on an etched stainless-steel wire as head-space solid-phase microextraction (HS-SPME) coating. A robust, well controlled thickness, and uniform coating of metal organic framework composites can be realized by the electrodeposited strategy. The incorporated UiO-66 not only enhanced the uniformity and stability of the composite coating, but also effectively decreased the stacking phenomenon of PEDOT and improved its extraction efficiency, which was over 100 times higher than that of the PEDOT coating without UiO-66. The composite coating was used to enrich seven types of volatile organic compounds (VOCs) in ion-exchange resins, including methyl cyclohexane, benzene, toluene, ortho-xylene, styrene, para-xylene and divinyl-benzene. The results of adsorption isotherm analysis showed that π stacking effect played dominant role between the composite coating and VOCs in the extraction process. The composite coating was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared and thermogravimetric analysis, respectively. A determination method for seven kinds of VOCs was established by HS-SPME coupled with gas chromatography-flame ionization detection (GC-FID). Under the optimal experimental conditions, the detection linear range (LRs) was 0.09-100 ng mL^-1, and the detection limit (LODs) was 0.03-0.06 ng mL^-1 (S/N = 3). The method was applied for the migration detection of VOCs in four types of ion-exchange resin, which showed satisfactory recovery (84.5-117.2%).

Headspace solid-phase microextraction sampling of endogenous aldehydes in biological fluids using a magnetic metal-organic framework/polyaniline nanocomposite

Nanoporosity, crystal structure, good thermal and mechanical stability, high surface-to-volume ratio, nanoscale cavities, and uniform pore topology have made metal-organic frameworks one of the best class of sorbents for adsorption/separation purposes. In this research, a metal-organic framework/polyaniline magnetite nanocomposite was synthesized and intercalated by polyaniline by electrophoretic deposition on the surface of a thin steel wire, to prepare a solid-phase microextraction fiber. It was coupled with gas chromatography-flame ionization detection and employed for the extraction and determination of aldehydes in biological samples. The magnetic nanocomposite was characterized using scanning electron microscopy, energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy. Under the optimal experimental conditions, the calibration curves were linear in the range of 0.01-1 and 0.1-1 µg/L for hexanal and heptanal, respectively. The limits of detections for hexanal and heptanal were 0.001 and 0.01 µg/L, respectively. Intrafiber repeatability for six replicate analyses of 0.2 µg/L of the analytes was over the range 3.5-7.1%. Interfiber (fiber-to-fiber) reproducibility, calculated by six replicate analyses of the same concentration using three different fibers, and was found to be 10.4-15.7%. The developed procedure was successfully utilized for the analysis of hexanal and heptanal in human plasma and urine samples.

A new proposal for the determination of polychlorinated biphenyls in environmental water by using host-guest adsorption

Polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants whose wide industrial use has been banned over the years in most countries due to their persistence and bioaccumulation. In fact, the International Agency for Research on Cancer defined them in 2016 as carcinogenic to humans based on sufficient evidence of an increased risk of cancer, being children and pregnant or lactating women the most vulnerable population subgroups. In this work, a new alternative for the determination of polychlorinated biphenyls (PCB28, PCB52, PCB101, PCB138, PCB153, and PCB180) in water samples has been developed by using a cyclodextrin-containing silica microparticulated material as an adsorbent in solid-phase extraction. Gas chromatography coupled to an electron capture detector has been used in the quantification step. The methodology allows quantifying polychlorinated biphenyls at very trace levels, with limits of detection between 0.2 and 1.7 ng L^-1. Other parameters such as the repeatability, with coefficients of variation lower than 11%, were likewise established. To end, real water samples were analyzed, and the results were comparable with those obtained with a reference method. The proposed methodology can be utilized for assessing the presence of these compounds in the environment and can come in handy for evaluation and remediation purposes.

Development of a needle trap device packed with titanium-based metal-organic framework sorbent for extraction of phenolic derivatives in air

We developed a novel method of needle trap device packed with titanium-based metal-organic framework for the extraction of phenolic derivatives in air followed by gas chromatography-flame ionization detector analysis. The synthetized adsorbent was packed inside a 22-gauge spinal needle. This method was first tested at laboratory scale, and then was used for field sampling of phenolic derivatives in air. A glass chamber placed on a heater at 60°C was used to provide different concentrations of phenolic derivatives. The desorption conditions and breakthrough volume were optimized using response surface methodology. The limit of detection and limit of quantitation of the proposed method were estimated to be in the range of 0.001-0.12 and 0.003-0.62 ng/mL, respectively, indicating a high sensitivity for the suggested sampler. Storing the packed needle trap device in a refrigerator at 4˚C for 60 days did not dramatically affect the storage stability. Our findings indicated that there was a high correlation coefficient (R²  = 0.99) between the measurement results of this method and the NIOSH recommended method (XAD-7 sorbent tube). Therefore, it can be concluded that the needle trap device packed with titanium-based metal-organic framework can be used as a efficient method for extraction of phenolic derivatives in air.

Recent Applications and Newly Developed Strategies of Solid-Phase Microextraction in Contaminant Analysis: Through the Environment to Humans

The present review aims to describe the recent and most impactful applications in pollutant analysis using solid-phase microextraction (SPME) technology in environmental, food, and bio-clinical analysis. The covered papers were published in the last 5 years (2014–2019) thus providing the reader with information about the current state-of-the-art and the future potential directions of the research in pollutant monitoring using SPME. To this end, we revised the studies focused on the investigation of persistent organic pollutants (POPs), pesticides, and emerging pollutants (EPs) including personal care products (PPCPs), in different environmental, food, and bio-clinical matrices. We especially emphasized the role that SPME is having in contaminant surveys following the path that goes from the environment to humans passing through the food web. Besides, this review covers the last technological developments encompassing the use of novel extraction coatings (e.g., metal-organic frameworks, covalent organic frameworks, PDMS-overcoated fiber), geometries (e.g., Arrow-SPME, multiple monolithic fiber-SPME), approaches (e.g., vacuum and cold fiber SPME), and on-site devices. The applications of SPME hyphenated with ambient mass spectrometry have also been described.

Metal–Organic Frameworks as Key Materials for Solid-Phase Microextraction Devices—A Review

Metal–organic frameworks (MOFs) have attracted recently considerable attention in analytical sample preparation, particularly when used as novel sorbent materials in solid-phase microextraction (SPME). MOFs are highly ordered porous crystalline structures, full of cavities. They are formed by inorganic centers (metal ion atoms or metal clusters) and organic linkers connected by covalent coordination bonds. Depending on the ratio of such precursors and the synthetic conditions, the characteristics of the resulting MOF vary significantly, thus drifting into a countless number of interesting materials with unique properties. Among astonishing features of MOFs, their high chemical and thermal stability, easy tuneability, simple synthesis, and impressive surface area (which is the highest known), are the most attractive characteristics that makes them outstanding materials in SPME. This review offers an overview on the current state of the use of MOFs in different SPME configurations, in all cases covering extraction devices coated with (or incorporating) MOFs, with particular emphases in their preparation.

Metal-Organic Frameworks for Food Safety

Food safety is a prevalent concern around the world. As such, detection, removal, and control of risks and hazardous substances present from harvest to consumption will always be necessary. Metal-organic frameworks (MOFs), a class of functional materials, possess unique physical and chemical properties, demonstrating promise in food safety applications. In this review, the synthesis and porosity of MOFs are first introduced by some representative examples that pertain to the field of food safety. Following that, the application of MOFs and MOF-based materials in food safety monitoring, food processing, covering preservation, sanitation, and packaging is overviewed. Future perspectives, as well as potential opportunities and challenges faced by MOFs in this field will also be discussed. This review aims to promote the development and progress of MOF chemistry and application research in the field of food safety, potentially leading to novel solutions.

Recent advances in microextraction procedures for determination of amphetamines in biological samples

Amphetamine and its related derivatives have stimulant and hallucinogenic properties. Illegal use of these drugs is an increasing global problem resulting in significant public health and legal problems. Deaths have been reported after intake of these drugs due to overdose. It is important to determine the type and concentration of illicit drugs in biological samples. These compounds are found in complex matrices at low concentration levels. The microextraction techniques are dominant sample preparation procedure and they are widely accepted as the most labor-intensive part of the bioanalytical process. For this purpose, a survey of recent published advances in microextraction procedures for quantification of amphetamines in biological samples found in the different databases from 2008 to date will be conducted.

Activated carbon/metal-organic framework nanocomposite: Preparation and photocatalytic dye degradation mathematical modeling from wastewater by least squares support vector machine

Herein, Kiwi peel activated carbon (AC), Materials Institute Lavoisier (MIL-88B (Fe), and AC/MIL-88B (Fe) composite were synthesized and used as catalysts to degrade Reactive Red 198. The material properties were analyzed by the FTIR, BET-BJH, XRD, FESEM, EDX, TGA, and UV-Vis/DRS. The BET surface area of AC, MIL-88B (Fe) and AC/MIL-88B (Fe) was 1113.3, 150.7, and 199.4 m²/g, respectively. The band gap values (E_g) estimated by Tauc plot method, were obtained 5.06, 4.19 and 3.79 eV for AC, MIL-88B (Fe) and AC/MIL-88B (Fe), respectively. The results indicated that the AC/MIL-88B (Fe) composite had higher photocatalytic activity (99%) than that of pure AC (79%) and MIL-88B (Fe) catalysts (87%). The decolorization kinetic was matched well with the second-order model. Moreover, the data were modeled using least squares support vector machine which optimized with Cuckoo optimization algorithm. The optimal parameters were found 0.837 and 3.49e+02 based on σ² and γ values, respectively. The mean square error (MSE) and correlation coefficient (R²) values were obtained 3.97 and 0.948. Therefore, the attained data, materials characterization and prediction of modeling validate the composite form of MIL-88B(Fe) with new AC, had better photocatalytic activity in comparison with the individual form.

Dispersive micro-solid phase extraction based on Fe3O4@SiO2@Ti-MOF as a magnetic nanocomposite sorbent for the trace analysis of caffeic acid in the medical extracts of plants and water samples prior to HPLC-UV analysis

In this work, Fe₃O₄@SiO₂@Ti-MOF-NCs, as an efficient sorbent, have been synthesized in a laboratory and utilized for extracting CA in the medical extracts of plants and water samples before their analysis by HPLC.

Determination of Enantiomeric Excess by Solid-Phase Extraction Using a Chiral Metal-Organic Framework as Sorbent

Metal-organic frameworks (MOFs) have recently attracted considerable attention because of their fascinating structures and intriguing potential applications in diverse areas. In this study, we developed a novel method for determination of enantiomeric excess (ee) of (±)-1,1′-bi-2-naphthol by solid-phase extraction (SPE) using a chiral MOF, [Co(l-tyr)]_n(l-tyrCo), as sorbent. After optimization of the experimental conditions, a good linear relationship between the ee and the absorbance of the eluate (R² = 0.9984) was obtained and the standard curve was established at the concentration of 3 mmol L⁻¹. The ee values of (±)-1,1′-bi-2-naphthol samples can be rapidly calculated using the standard curve after determination of the absorbance of the eluate. The method showed good accuracy, with an average error of 2.26%, and is promising for ee analysis.