A magnetic metal-organic framework as a new sorbent for solid-phase extraction of copper(II), and its determination by electrothermal AAS

A zirconium metal-organic framework functionalized with a S/N containing carboxylic acid (MOF-808(Zr)-Tz) as an efficient sorbent for the ultrafast and selective dispersive solid phase micro extraction of chromium, silver, and rhodium in water samples

Metal-organic frameworks (MOFs) are good adsorbents for targeted chemicals with their adjustable properties. Herein, we prepared a zirconium based MOF (MOF-808(Zr)) and functionalized it employing 2-mercapto-4-methyl-5-thiazolacetic acid (MOF-808(Zr)-Tz). The prepared MOFs were characterized by XRD, FTIR, SEM-EDX, TGA, N2 sorption, zeta potential measurements, and elemental analysis. The surface area of MOF-808(Zr)-Tz was 1348 m2/g. Dispersive solid-phase micro-extraction (D-SPµE) method based on MOF-808(Zr)-Tz was firstly developed and applied to the extraction of chromium, silver, and rhodium in waters. The determination of the analytes was done by FAAS. The optimal pH and eluent for analytes were 7.0 and 3 mL of 2 mol L-1 HCl, respectively. The contact times were 1 min for adsorption and 3 min for elution. The LOD and PFs of the D-SPμE for analytes were 2.3 μg L-1 and 13.3 for chromium, 2.1 μg L-1 and 13.3 for silver, and 3.1 μg L-1 and 13.3 rhodium, respectively. The D-SPμE method was verified with analyses of NW-TMDA-54.6 Lake water and SPS-WW1 Batch 114 Wastewater and with spiked dam water, river water, well water, sea water, and wastewater. The recoveries of the analytes changed from 89 to 108 %. The results indicated that the method is selective, simple, effective, and rapid for extracting chromium(III), silver(I) and rhodium(III) in waters.

The Impact of Functionality and Porous System of Nanostructured Carriers Based on Metal–Organic Frameworks of UiO-66-Type on Catalytic Performance of Embedded Au Nanoparticles in Hydroamination Reaction

New methods for the preparation of metal–organic frameworks UiO-66 and NH2-UiO-66 with a hierarchical porous structure were developed using the MW-assisted technique under atmospheric pressure. The synthesized nanostructured meso-UiO-66 and meso-NH2-UiO-66 matrices were utilized as Au nanoparticle carriers. The resulting Au@meso-UiO-66 and Au@NH2-UiO-66 nanohybrids were studied in the reaction of phenylacetylene hydroamination with aniline into imine ([phenyl-(1-phenylethylydene)amine]) for the first time. Their catalytic behavior is significantly determined by a combination of factors, such as a small crystal size, micro–mesoporous structure, and functionality of the UiO-66 and NH2-UiO-66 carriers, as well as a high dispersion of embedded gold nanoparticles. The Au@meso-UiO-66 and Au@NH2-UiO-66 nanocatalysts demonstrate high activities (TOF), with conversion and selectivity values over 90. This excellent catalytic performance is comparable or even better than that demonstrated by heterogeneous systems based on conventional inorganic and inorganic supports known from the literature.

Magnetite Metal-Organic Frameworks: Applications in Environmental Remediation of Heavy Metals, Organic Contaminants, and Other Pollutants

Due to the increasing environmental pollution caused by human activities, environmental remediation has become an important subject for humans and environmental safety. The quest for beneficial pathways to remove organic and inorganic contaminants has been the theme of considerable investigations in the past decade. The easy and quick separation made magnetic solid-phase extraction (MSPE) a popular method for the removal of different pollutants from the environment. Metal-organic frameworks (MOFs) are a class of porous materials best known for their ultrahigh porosity. Moreover, these materials can be easily modified with useful ligands and form various composites with varying characteristics, thus rendering them an ideal candidate as adsorbing agents for MSPE. Herein, research on MSPE, encompassing MOFs as sorbents and Fe₃O₄ as a magnetic component, is surveyed for environmental applications. Initially, assorted pollutants and their threats to human and environmental safety are introduced with a brief introduction to MOFs and MSPE. Subsequently, the deployment of magnetic MOFs (MMOFs) as sorbents for the removal of various organic and inorganic pollutants from the environment is deliberated, encompassing the outlooks and perspectives of this field.

Magnetic porous coordination networks for preconcentration of various metal ions from environmental water followed by inductively coupled plasma mass spectrometry detection

Magnetic composites of Fe₃O₄@SiO₂@PCN-224 (MPCN-224) was obtained by one-pot method with the interaction between PCN-224 monomer and silicon layer on magnetic core. MPCN-224 exhibited a core-shell structure with the specific surface area of 1114 m² g^-1 and good adsorption performance for various metal ions. With MPCN-224 used as the sorbent, a method combing magnetic solid phase extraction (MSPE) with inductively coupled plasma mass spectrometry (ICPMS) detection was established for the enrichment and determination of trace Cr(III), Zn(II), Pb(II) and Bi(III) in environmental water samples. Under the optimized conditions, the developed method exhibited low detection limits of 0.94-11.4 ng L^-1 and wide linear range for target four metal ions. The analysis speed was fast (2/5 min for adsorption and desorption respectively). The MPCN-224 sorbent could be reused for at least 12 times, and the regeneration can be achieved easily by adjusting solution pH. The sorbent and the MSPE-ICPMS method have a great potential for adsorption and determination of trace metal ions in environmental water samples.

[Metal-organic framework UiO-67-based enrichment and purification of progesterone residues in milk]

Progesterone functions as an endocrine-disrupting compound. Imitating endogenous hormones disrupt the animals' hormone levels. The potential hazard of progesterone in milk cannot be neglected. Thus, research has focused on establishing an efficient and convenient pretreatment and analytical approach. In this study, a metal-organic framework (MOF) material UiO-67 was prepared, which possessed a large specific surface area and excellent stability. It was employed to enrich and purify trace progesterones in a complex milk matrix as a filler to integrate the solid phase extraction column. An approach based on MOF was developed using ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). This approach could simultaneously determine seven kinds of progesterone residues in milk. The element spectra of UiO-67 were first measured and analyzed using X-ray photoelectron spectroscopy. The chemical interaction between UiO-67 and progesterone was proved by comparing the changes in binding energy and relative contents of functional groups, and the adsorption efficiency of 1 mg/L and 5 mg/L progesterones by UiO-67 was studied. The adsorption efficiencies of UiO-67 for 1 mg/L and 5 mg/L progesterones were 99.73%-99.95% and 88.87%-99.23%, respectively, according to the results. It proved the efficient adsorption of UiO-67 to progesterones and ensured that subsequent studies went smoothly. Furthermore, key parameters, such as the amount of sorbent, elution solvent type, and pH value, were examined and optimized to obtain optimal extraction recovery of the progesterones. Spiked concentrations of 50 μg/L were employed for extraction optimization. All experiments were performed three times. It also evaluated the matrix effect on mass spectrum signal of the progesterones. The optimized results showed that the seven progesterones could be satisfactorily recovered when the amount of adsorbent was 40 mg, pH value of the sample solution was 5, and elution solution was 5-mL acetone. Additionally, the matrix effect of progesterone in the milk sample was <20%. The matrix effect could be neglected using the aforementioned approach to extract and purify progesterones in milk. Finally, the seven progesterones showed good linearity between 1 and 100 μg/L under the optimized conditions, with linear correlation coefficients values >0.99. The limits of detection (LODs) ranged from 0.06 to 0.30 μg/L, and limits of quantification (LOQs) ranged from 0.19 to 1.0 μg/L, respectively. At various concentration levels of progesterones in milk, the recoveries were 87.10%-105.58%, with relative standard deviations of 2.66%-9.64%. Most importantly, the approach was successfully employed to determine progesterone levels in milk samples, with results in good agreement with the standard SN/T 1980-2007. The proposed approach had the advantages of high sensitivity and satisfactory accuracy compared with the reported pretreatment and detection approaches of progesterone in milk. Satisfactory experimental results can be obtained without the calibration by isotope inner standard. Meanwhile, considering the excellent performance of MOF materials in reducing matrix interference in complex samples, such the application of materials offers a new approach. It can be employed to enrich and detect hazards in a complex matrix in the future.

Magnetic UiO-66 functionalized with 4,4'-diamino-2,2'-stilbenedisulfonic as a highly recoverable acid catalyst for the synthesis of 4H-chromenes in green solvent

According to 4H-chromenes importance, we synthesized a novel magnetic UiO-66 functionalized with 4,4′-diamino-2,2′-stilbenedisulfonic as an efficient and reusable solid acid catalyst for synthesizing 4H-chromene skeletons via a one-pot three components reaction in a green solvent. The structure of the synthesized catalyst was confirmed by various techniques including FT-IR, XRD, BET, TGA, TEM, EDX, and SEM, and also the product yields were obtained in 83–96% of yields for all the reactions and under mild conditions. The reported procedure presents an environmentally friendly approach for synthesizing a significant number of 4H-chromene derivatives. Correspondingly, MOF-based catalyst makes it easy to separate from reaction media and reuse in the next runs.

Development and validation of UV chromatographic method for quantification of copper and copper nanoparticles in different matrices and pharmaceutical products

Background

The applications of Cu and CuNPs based on the earth-abundant and inexpensive Cu metal have generated a great deal of interest in recent years, including medical applications. A novel, specific, precise, accurate and sensitive reverse-phase high-performance liquid chromatography (RP-HPLC) method with UV detection has been developed and validated to quantify copper (Cu) and copper nanoparticles (CuNPs) in different biological matrices and pharmaceutical products.

Methods

The developed method has been validated for linearity, precision, sensitivity, specificity and accuracy. Cu concentration was detected in pharmaceutical products without an extraction process. Moreover, liver, serum and muscle tissues were used as biological matrices. High Cu recovery in biological samples was afforded by using citric acid as a green chelating agent, exact extraction time and pH adjustment. Cu pharmaceutical and biological samples were eluted by acetonitrile: ammonium acetate (50 mM) with 0.5 mg/ml EDTA (30:70 v:v) as an isocratic mobile phase. EDTA reacted with Cu ions forming a Cu-EDTA coloured complex, separated through the C18 column and detected by UV at 310 nm.

Results

The developed method was specific with a short retention time of 4.95 min. It achieved high recovery from 100.3% to 109.9% in pharmaceutical samples and 96.8–105.7% in biological samples. The precision RSD percentage was less than two. The method was sensitive by achieving low detection limits (DL) and quantification limits (QL).

Conclusion

The validated method was efficient and economical for detecting Cu and CuNPs by readily available chemicals as EDTA and Citric acid with C18 column, which present the best results on RP-HPLC.

Adsorptive remediation of environmental pollutants using magnetic hybrid materials as platform adsorbents

Effective separation and remediation of environmentally hazardous pollutants are burning areas of research because of a constant increase in environmental pollution problems. An extensive number of emerging contaminants in the environmental matrices result in serious health consequences in animals, humans, and plants, even at trace levels. Therefore, it is of paramount significance to quantify these undesirable pollutants, even at a very low concentration, from the natural environment. Magnetic solid-phase extraction (MSPE) has recently achieved huge attention because of its strong magnetic domain and easy separation through an external magnetic field compared with simple solid-phase extraction. Therefore, MSPE appeared the most promising technique for removing and pre-concentration of emerging pollutants at trace level. Compared to the normal solid-phase extraction, MSPE as magnetic hybrid adsorbents offers the unique advantages of distinct nanomaterials and magnetic hybrid materials. It can exhibit efficient dispersion and rapid recycling when applying to a very complex matrix. This review highlights the possible environmental applications of magnetic hybrid nanoscale materials as effective MSPE sorbents to remediate a diverse range of environmentally toxic pollutants. We believe this study tends to evoke a variety of research thrust that may lead to novel remediation approaches in the forthcoming years.

Amido-Functionalized Magnetic Metal-Organic Frameworks Adsorbent for the Removal of Bisphenol A and Tetracycline

In this paper, amido-functionalized MOFs with core/shell magnetic particles (Fe₃O₄@MIL-53(Al)-NH₂) was prepared by the solvothermal method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), Vibrating Sample Magnetometer (VSM) and UV/VIS spectrophotometer. The influence of different factors on the adsorption effect of the pollutant, including adsorbent amounts, adsorption time, ionic strength and pH, were explored. It was found that the amine-decorated Fe₃O₄@MIL-53(Al)-NH₂ were efficient for removal of contaminant, with the adsorption capacity for bisphenol A (234.1 mg/g) and tetracycline (84.8 mg/g) under the optimized conditions. The adsorption kinetics and the equilibrium adsorption data indicated that the adsorption process of BPA and TC was more compatible with the pseudo-second-order kinetic model and the Langmuir model, respectively. The thermodynamic values show the adsorption of the mentioned contaminant was spontaneous and endothermic. Moreover, the Fe₃O₄@MIL-53(Al)-NH₂ adsorbent had good regeneration and reusability capacity after five cyclic utilization. All these results show Fe₃O₄@MIL-53(Al)-NH₂ adsorbent could be a potential candidate for future water purification.

Preparation of polyacrylonitrile/polyindole conducting polymer composite and its use for solid phase extraction of copper in a certified reference material

A polyacrylonitrile/polyindole (PAN/PIN) [50, 50] conducting polymer composite was chemically synthesized using FeCl₃ as an oxidizing agent in chloroform solution and nitrogen atmosphere at 10 °C. The formation of the composite was supported by Fourier transform infrared spectroscopy. The morphological properties of the composite were investigated by atomic force microscopy and scanning electron microscopy. The thermal properties of the composite were examined by using thermogravimetric analyses. It was found that the composite had good thermal stability. The conducting polymer composite was used for the first time as an adsorbent for solid phase extraction of Cu (II). The optimum pH was found to be 7. The adsorption and elution shaking times were 5 and 15 min, respectively. The elution was done with 5 mL of 2 mol L^-1 HNO₃. The accuracy of the developed method was confirmed by analyzing certified reference material (TMDA-70.2 Lake Water).

Determination of color additive tartrazine (E 102) in food samples after dispersive solid phase extraction with a zirconium-based metal-organic framework (UiO-66(Zr)-(COOH)2)

A new and rapid dispersive solid phase extraction method by using a green-synthesised UiO-66(Zr)-(COOH)₂ (Zr-BTeC) adsorbent with body-centred cubic (bcu) topology was developed for determination of tartrazine in food samples. Zr-BTeC was used for the first time as an adsorbent for tartrazine. It was synthesised and characterised by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller surface area analysis, and zeta potential measurements. Tartrazine was determined at 405 nm spectrophotometrically. Experimental conditions were optimised in order to achieve quantitative recoveries. The sample acidity was found to be 0.02 mol L^-1 HCl. The amount of Zr-BTeC was 10 mg. Both adsorption and elution contact times were only 5 s without the need for vortexing. Elution was with 2 mL of 0.5 mol L^-1 NH₃. A sample volume of 45 mL was selected as optimum. The adsorption capacity for tartrazine with Zr-BTeC was found to be 185 mg g^-1 and the adsorbent was reusable up to 40 cycles. The tartrazine concentrations found by the developed method in food supplements were compared with the results obtained by HPLC method for the same samples. Statistical analysis results showed that there are insignificant differences between the results of the two methods (p = .05). The method was successfully applied to the determination of tartrazine in spiked chewing gums, lemon flavoured icing glaze, and jelly samples.

Evolution of Environmentally Friendly Strategies for Metal Extraction

The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed.

Extraction of Metal Ions with Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are crystalline porous materials composed of metal ions or clusters coordinated with organic linkers. Due to their extraordinary properties such as high porosity with homogeneous and tunable in size pores/cages, as well as high thermal and chemical stability, MOFs have gained attention in diverse analytical applications. MOFs have been coupled with a wide variety of extraction techniques including solid-phase extraction (SPE), dispersive solid-phase extraction (d-SPE), and magnetic solid-phase extraction (MSPE) for the extraction and preconcentration of metal ions from complex matrices. The low concentration levels of metal ions in real samples including food samples, environmental samples, and biological samples, as well as the increased number of potentially interfering ions, make the determination of trace levels of metal ions still challenging. A wide variety of MOF materials have been employed for the extraction of metals from sample matrices prior to their determination with spectrometric techniques.

Postsynthetic functionalization of water stable zirconium metal organic frameworks for high performance copper removal

In this work, a water stable zirconium metal-organic framework functionalized with thiol groups was synthesized by a solvent-assisted ligand incorporation technique. The composites were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, specific surface area measurement and field emission scanning electron microscopy. The prepared material was then used as a novel adsorbent for Cu(ii) removal from water. The experimental parameters associated with adsorption capability, such as the initial solution pH, contact time, and the presence of competing cations were investigated in detail. Under the optimal conditions, the adsorption follows a pseudo-second-order kinetics, and the equilibration time for the adsorption is 15 min. The Langmuir adsorption model was in better correlation with the isothermal adsorption data than the Freundlich model. The maximum Cu(ii) adsorption capacity reached up to 42.70 mg g^-1. Quantitative recovery of Cu(ii) was achieved by using 0.1 mol L^-1 HCl. The prepared adsorbent has fast adsorption efficiency, high adsorption capacity, and exceptional stability up to 50 adsorption/desorption cycles. It can be used as a promising candidate material for heavy metal ion removal and water treatment.

Adsorption of DNA by using polydopamine modified magnetic nanoparticles based on solid-phase extraction

A polydopamine magnetic composite (PDA@Fe₃O₄) was prepared for the extraction of human genomic DNA and characterized by transmission electron microscopy, X-ray diffraction, FT-IR spectrometer, zeta potential and vibrating sample magnetometry. PDA@Fe₃O₄ based on magnetic solid phase extraction (MSPE) method have highly efficient capture of genomic deoxyribonucleic acid (DNA)and gene fragments ranging from about 100 bp to 200 bp. Compared with commercial beads (Shenggong, China) and spin column nucleic acid extraction kit (Tiangen, China), the PDA coated magnetic nanoparticles display superior genomic DNA extraction capacity (116 mg/g) and yield (90.2%). The isolation protocol used the solutions (composed of PEG and NaCl) with a specific pH for the binding and release of DNA. The procedure can be attributed to the charge switch of amino and hydroxyl groups on surface of the magnetic particle. The extracted DNA with high quality (A260/A280 = 1.82 ± 0.04) can be directly used as template for polymerase chain reaction (PCR) followed by agarose gel electrophoresis. The results showed the new composite to be an ideal adsorbent for separation of DNA which had the advantage of its low cost, high extraction capacity and yield.

Structural design of a high sensitivity biomass cellulose-based colorimetric sensor and its in situ visual recognition mechanism for Cu2

A novel biomass cellulose-based colorimetric sensor (DAC-PDH) was prepared by a Schiff base reaction between the aldehyde groups of dialdehyde cellulose (DAC) and the amino groups of 2,6-pyridine dihydrazide (PDH). The as-prepared sensor (DAC-PDH) showed selective recognition of Cu²⁺ and a visual colour change from white to green. The visual limit of detection for Cu²⁺ was 10^-7 mol/L. Furthermore, DAC-PDH responded to Cu²⁺ within 30 s by the method of dynamic condition. The sensor possessed the properties of a high density of functional groups (CO, NH, NH₂), a large external surface area, a short transit distance and flexibility; thus, Cu²⁺ can be rapidly absorbed and enriched on the DAC-PDH through multi-dentate ligand chelation between Cu²⁺ and the carbonyl groups (CO) and the amino groups (NH, NH₂) of DAC-PDH. The as-prepared DAC-PDH colorimetric sensor exhibits promising prospects for in situ identification of Cu²⁺.

Development of magnetic porous coordination polymer adsorbent for the removal and preconcentration of Pb(II) from environmental water samples

A novel porous coordination polymer adsorbent (BTCA-P-Cu-CP) based on a piperazine(P) as a ligand and 1,2,4,5-benzenetetracarboxylic acid (BTCA) as a linker was synthesized and magnetized to form magnetic porous coordination polymer (BTCA-P-Cu-MCP). Fourier transform infrared (FTIR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), field emission scanning electron microscope(FESEM), energy-dispersive X-ray spectroscopy(EDS), CHN, and Brunauer-Emmett-Teller(BET) analysis were used to characterize the synthesized adsorbent. BTCA-P-Cu-MCP was used for removal and preconcentration of Pb(II) ions from environmental water samples prior to flame atomic absorption spectrometry(FAAS) analysis. The maximum adsorption capacity of BTCA-P-Cu-MCP was 582 mg g^-1. Adsorption isotherm, kinetic, and thermodynamic parameters were investigated for Pb(II) ions adsorption. Magnetic solid phase extraction (MSPE) method was used for preconcentration of Pb(II) ions and the parameters influencing the preconcentration process have been examined. The linearity range of proposed method was 0.1-100 μg L^-1 with a preconcentration factor of 100. The limits of detection and limits of quantification for lead were 0.03 μg L^-1 and 0.11 μg L^-1, respectively. The intra-day (n = 7) and inter-day (n = 3) relative standard deviations (RSDs) were 1.54 and 3.43% respectively. The recoveries from 94.75 ± 4 to 100.93 ± 1.9% were obtained for rapid extraction of trace levels of Pb(II) ions in different water samples. The results showed that the BTCA-P-Cu-MCP was steady and effective adsorbent for the decontamination and preconcentration of lead ions from the aqueous environment.

Adsorption of 2,4-dichlorophenoxyacetic acid in an aqueous medium on nanoscale MIL-53(Al) type materials

MIL-53(Al) type materials were prepared using MW-activation. They show high adsorption capacities in the adsorption of 2,4-dichlorophenoxyacetic acid in an aqueous medium and demonstrate faster adsorption rates as compared to an activated carbon.

Study on the copper(II)-doped MIL-101(Cr) and its performance in VOCs adsorption

The metal-organic framework (MOF) materials, MIL-101(Cr), and copper-doped MIL-101(Cr) (Cu@MIL-101(Cr)) were prepared through hydrothermal method and were used to remove volatile organic compounds (VOCs) in this study. Morphological characterization demonstrated that MIL-101(Cr) and Cu-3@MIL-101(Cr) were octahedral crystal, with specific surface area of 3367 and 2518 m²/g, respectively. The results of XRD, TG, and FTIR showed that the copper doping procedure would not alter the skeleton structure, but it would affect the crystallinity and thermal stability of MIL-101(Cr). Besides, MIL-101(Cr) and Cu-3@MIL-101(Cr) displayed good removal efficiencies on benzene sorption, and the maximum sorption capacity was 103.4 and 114.4 mg/g, respectively. In competitive adsorptions, the order of adsorption priority on Cu-3@MIL-101(Cr) was as follows: ethylbenzene > toluene > benzene. Hence, it could be concluded that MIL-101(Cr) and copper-doped MIL-101(Cr) demonstrated good performance in VOCs adsorption and showed a promising potential for large-scale applications in the removal of VOCs. Graphical abstract ᅟ.

Water-stable metal-organic frameworks for aqueous removal of heavy metals and radionuclides: A review

Heavy metals and radionuclides in water are a global environmental issue, which has been receiving considerable attention worldwide. Water-stable MOFs are green and recyclable materials to eliminate the environmental impacts caused by the hazardous heavy metal ions and radionuclides in water. This paper presents a systematical review on the current status of water-stable MOFs that capture and convert a wide range of heavy metal ions (e.g., As(III)/As(V), Pb(II), Hg(II), Cd(II), and Cr(III)/Cr(VI)) and radionuclides (e.g., U(VI), Se(IV)/Se(VI) and Cs(I)) in aqueous solution. Water-stable MOFs and MOF-based composites exhibit the superior adsorption capability for these metal species in water. Significantly, MOFs show high selectivity in capturing target metal ions even in the presence of multiple water constituents. Mechanisms involved in capturing metal ions are described. MOFs also have excellent catalytic performance (photocatalysis and catalytic reduction by formic acid) for Cr(VI) conversion to Cr(III). Future research is suggested to provide insightful guidance to enhance the performance of the MOFs in capturing target pollutants in aquatic environment.

Core-shell Fe3O4 polydopamine nanoparticles as sorbent for magnetic dispersive solid-phase extraction of copper from food samples

In the present study, core-shell Fe₃O₄ polydopamine nanoparticles were synthesized and used for the first time as an adsorbent for the vortex assisted magnetic dispersive solid phase extraction of copper from food samples. After elution, copper in the solutions was determined by FAAS. The adsorbent was characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area, and zeta potential measurements. Various parameters affecting the magnetic dispersive solid-phase extraction were evaluated. The optimum pH and magnetic adsorbent amount were found to be 5 and 40 mg, respectively. Elution was made by 3 mL of 2 mol L^-1 HNO₃.The major advantage of the method is the fast equilibration during adsorption without the need for vortexing or shaking. The preconcentration factor and detection limit of the method were found to be 150 and 0.22 mg L^-1, respectively. The precision (as RSD%) and adsorption capacity of the method were 3.7% and 28 mg g^-1, respectively. The method was successfully verified by analyzing four certified reference materials (SPS-WW1 Batch 114 Wastewater, TMDA-53.3 Lake water, BCR-482 Lichen and 1573a Tomato Leaves) and by addition/recovery tests of copper standard solution in organic baby food, muesli, macaroni, honey, and milk samples.

Zwitterion-functionalized polymer microspheres as a sorbent for solid phase extraction of trace levels of V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II) prior to their determination by ICP-MS

This paper describes the preparation of zwitterion-functionalized polymer microspheres (ZPMs) and their application to simultaneous enrichment of V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II) from environmental water samples. The ZPMs were prepared by emulsion copolymerization of ethyl methacrylate, 2-diethylaminoethyl methacrylate and triethylene glycol dimethyl acrylate followed by modification with 1,3-propanesultone. The components were analyzed by elemental analyses as well as Fourier transform infrared spectroscopy, and the structures were characterized by scanning electron microscopy and transmission electron microscopy. The ZPMs were packed into a mini-column for on-line solid-phase extraction (SPE) of the above metal ions. Following extraction with 40 mM NH₄NO₃ and 0.5 M HNO₃ solution, the ions were quantified by ICP-MS. Under the optimized conditions, the enrichment factors (from a 40 mL sample) are up to 60 for the ions V(V), As(III), Sb(III) and Hg(II), and 55 for Cr(III) and Sn(IV). The detection limits are 1.2, 3.4, 1.0, 3.7, 2.1 and 1.6 ng L^-1 for V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II), respectively, and the relative standard deviations (RSDs) are below 5.2%. The feasibility and accuracy of the method were validated by successfully analyzing six certified reference materials as well as lake, well and river waters. Graphical abstract Zwitterion-functionalized polymer microspheres (ZPMs) were prepared and packed into a mini-column for on-line solid-phase extraction (SPE) via pump 1. Then V(V), Cr(III), As(III), Sn(IV), Sb(III) and Hg(II) ions in environmental waters were eluted and submitted to ICP-MS via pump 2.

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.

Selective adsorption of Pb (II) over the zinc-based MOFs in aqueous solution-kinetics, isotherms, and the ion exchange mechanism

Two series of metal-organic frameworks (MOFs) with similar formula units but different central metal ions (M) or organic linkers (L), M-BDC (BDC = terephthalate, M = Zn, Zr, Cr, or Fe), or Zn-L (L = imidazolate-2-methyl, BDC, BDC-NH₂), were prepared and employed as the receptors for adsorption lead ions. It was found that the Zn-BDC exhibited a much higher adsorption capacity than the other M-BDC series with various metal ions which have very closely low capacities at same conditions. Furthermore, the Zn-L (L = imidazolate-2-methyl, BDC, BDC-NH₂) still have highly efficient adsorption capacity of lead ions, although the adsorption capacity varies with different ligand, as well as the adsorption rate and the equilibrium pH of the solution. This significant high adsorption over Zn-L, different from other M-BDC series with various metal ions (Zr, Cr, or Fe), can be explained by ion exchange between the central metal ions of Zn-L and lead ion in solution. Based on the analysis of FT-IR, X-ray diffraction pattern, the nitrogen adsorption isotherms, the zeta potentials, and the results, a plausible adsorption mechanism is proposed. When equivalent Zn-L were added to equal volume of aqueous solution with different concentration of lead ion, the content of zinc ion in the solution increases with the increase of the initial concentration of lead ions. The new findings could provide a potential way to fabricate new metal organic frameworks with high and selective capacities of the heavy metal ions.

Rapid magnetic solid-phase extraction of Congo Red and Basic Red 2 from aqueous solution by ZIF-8@CoFe2 O4 hybrid composites

Core-shell metal-organic framework materials have attracted considerable attention mainly due to their enhanced or new physicochemical properties compared with their single-component counterparts. In this work, a core-shell heterostructure of CoFe2 O4 -Zeolitic Imidazolate Framework-8 (ZIF-8@CoFe2 O4 ) is successfully fabricated and used as an solid-phase extraction adsorbent to efficiently extract Congo Red and Basic Red 2 dyes from contaminated aqueous solution. Vibrating sample magnetometry indicates that the saturated magnetization of ZIF-8@CoFe2 O4 is 3.3 emu/g, which is large enough for magnetic separation. The obtained hybrid magnetic metal-organic framework based material ZIF-8@CoFe2 O4 can remove the investigated dyes very fast within 1 min of the contact time. The adsorbent ZIF-8@CoFe2 O4 also shows a good reusability. After regeneration, the adsorbent can still exhibit high removal efficiency (∼97%) toward Congo Red for five cycles of desorption-adsorption. This work reveals the great potential of core-shell ZIF-8@CoFe2 O4 sorbents for the fast separation and preconcentration of organic pollutants in aqueous solution before high-performance liquid chromatography analysis.

Copper selective self-sorting polymeric resin with mixed-mode functionality for column preconcentration and atomic absorption spectrometric determination

A new approach for the synthesis of a highly Cu(ii) selective mixed-mode solid phase extractant is proposed.

Rapid Determination of Clenbuterol in Pork by Direct Immersion Solid-Phase Microextraction Coupled with Gas Chromatography-Mass Spectrometry

Direct immersion solid-phase microextraction (DI-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was developed for rapid analysis of clenbuterol in pork for the first time. In this work, a low-cost homemade 44 µm polydimethylsiloxane (PDMS) SPME fiber was employed to extract clenbuterol in pork. After extraction, derivatization was performed by suspending the fiber in the headspace of the 2 mL sample vial saturated with a vapor of 100 µL hexamethyldisilazane. Lastly, the fiber was directly introduced to GC-MS for analysis. All parameters that influenced absorption (extraction time), derivatization (derivatization reagent, time and temperature) and desorption (desorption time) were optimized. Under optimized conditions, the method offered a wide linear range (10-1000 ng g(-1)) and a low detection limit (3.6 ng g(-1)). Finally, the method was successfully applied in the analysis of pork from the market, and recoveries of the method for spiked pork were 97.4-105.7%. Compared with the traditional solvent extraction method, the proposed method was much cheaper and fast.