Magnetic metal-organic frameworks for the extraction of trace amounts of heavy metal ions prior to their determination by ICP-AES

Benchtop volatilomics supercharged: How machine learning based design of experiment helps optimizing untargeted GC-IMS gas phase metabolomics

Gas chromatography-ion mobility spectrometry (GC-IMS) plays a significant role in both targeted and non-targeted analyses. However, the non-linear behavior of IMS and its complex ion chemistry pose challenges for finding optimal experimental conditions using existing methodologies. To address these issues, integrating machine learning (ML) strategies offers a promising approach. In this study, we propose a hybrid strategy, combining design of experiment (DOE) and machine learning (ML) for optimizing GC-IMS conditions in non-targeted volatilomic/flavoromic analysis, with saffron volatiles as a case study. To begin, a rotatable circumscribed central composite design (CCD) is used to define five influential GC-IMS factors of sample amount, headspace temperature, incubation time, injection volume, and split ratio. Subsequently, two ML models are utilized: multiple linear regression (MLR) as a linear model and Bayesian regularized-artificial neural network (BR-ANN) as a nonlinear model. These models are employed to predict the response variables of total peak areas (PAs) and the number of detected peaks (PNs) in GC-IMS. The findings show that there is a direct correlation between the factors in GC-IMS and the PNs, suggesting that MLR is a suitable approach for building a model in this scenario. However, the PAs exhibit nonlinear behavior, suggesting that BR-ANN is better suitable to capture this complexity. Notably, Derringer's desirability function is utilized to integrate the PAs and PNs, and in this scenario, MLR demonstrates satisfactory performance in modeling the GC-IMS factors.

Recent advances in metal organic frameworks-based magnetic nanomaterials for waste water treatment

Magnetic nanoparticle-incorporated metal organic frameworks (MOF) are potential composites for various applications such as catalysis, water treatment, drug delivery, gas storage, chemical sensing, and heavy metal ion removal. MOFs exhibits high porosity and flexibility enabling guest species like heavy metal ions to diffuse into bulk structure. Additionally, shape and size of the pores contribute to selectivity of the guest materials. Incorporation of magnetic materials allows easy collection of adsorbent materials from solution system making the process simple and cost-effective. In view of the above advantages in the present review article, we are discussing recent advances of different magnetic material-incorporated MOF (Mg-MOF) composite for application in photocatalytic degradation of dyes and toxic chemicals, adsorption of organic compounds, adsorption of heavy metal ions, and adsorption of dyes. The review initially discusses on properties of Mg-MOF, different synthesis techniques such as mechanochemical, sonochemical (ultrasound) synthesis, slow evaporation and diffusion methods, solvo(hydro)-thermal and iono-thermal method, microwave-assisted method, microemulsion method post-synthetic modification template strategies and followed by application in waste water treatment.

Schiff base MOFs and their derivatives for sequestration and degradation of pollutants: present and future

Removal of contaminants via adsorption and catalysis have received a significant interest as energy and money-saving solutions for treating the world's wastewater. Metal-organic frameworks (MOFs), a newly discovered class of porous crystalline materials, have demonstrated tremendous promise in the removal and destruction of contaminants for water purification. In order to improve the interactions of MOFs with the target pollutants for their selective removal and degradation, the Schiff base functionalities emerged as promising active sites. Through pre- and post-synthetic alterations, Schiff base functionalities are integrated into the pore cages of MOF adsorbent materials. To understand the adsorptive/catalytic mechanism, potential interactions between the Schiff base sites and the target pollutants are discussed. Based on cutting-edge techniques for their synthesis, this paper examines current developments in the creation of Schiff base-functionalized MOFs as innovative materials for adsorptive removal and catalytic degradation of contaminants for water remediation.

A Nanograss Boron and Nitrogen Co-Doped Diamond Sensor Produced via High-Temperature Annealing for the Detection of Cadmium Ions

The high-performance determination of heavy metal ions (Cd2+) in water sources is significant for the protection of public health and safety. We have developed a novel sensor of nanograss boron and nitrogen co-doped diamond (NGBND) to detect Cd2+ using a simple method without any masks or reactive ion etching. The NGBND electrode is constructed based on the co-doped diamond growth mode and the removal of the non-diamond carbon (NDC) from the NGBND/NDC composite. Both the enlarged surface area and enhanced electrochemical performance of the NGBND film are achievable. Scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse anodic stripping voltammetry (DPASV) were used to characterize the NGBND electrodes. Furthermore, we used a finite element numerical method to research the current density near the tip of NGBND. The NGBND sensor exhibits significant advantages for detecting trace Cd2+ via DPASV. A broad linear range of 1 to 100 μg L-1 with a low detection limit of 0.28 μg L-1 was achieved. The successful application of this Cd2+ sensor indicates considerable promise for the sensitive detection of heavy metal ions.

Research progress on the magnetite nanoparticles in the fields of water pollution control and detection

Magnetite nanoparticles (MNPs) have shown increasing application in the fields of water pollution control and detection due to their perfect combination of interfacial functionalities and physicochemical properties, such as surface interface adsorption, (synergistic) reduction, catalytic oxidation, and electrical chemistry. This review presents the research advances in the synthesis and modification methods of MNPs in recent years, systematically summarizes the performances of MNPs and their modified materials in terms of three technical systems, including single decontamination system, coupled reaction system, and electrochemical system. In addition, the progress of the key roles played by MNPs in adsorption, reduction, catalytic oxidative degradation and their coupling with zero-valent iron for the reduction of pollutants are described. Moreover, the application prospect of MNPs-based electrochemical working electrodes for detecting micro-pollutants in water were also discussed in detail. This review addresses that the construction of MNPs-based systems for water pollution control and detection should be adapted to the natures of the target pollutants in water. Finally, the following research directions of MNPs and their remaining challenges are outlooked. In general, this review will inspire MNPs researchers in different fields for effective control and detection of a variety of contaminants in water.

Overview on recent advances of magnetic metal-organic framework (MMOF) composites in removal of heavy metals from aqueous system

Developing a novel, simple, and cost-effective analytical technique with high enrichment capacity and selectivity is crucial for environmental monitoring and remediation. Metal-organic frameworks (MOFs) are porous coordination polymers that are self-assembly synthesized from organic linkers and inorganic metal ions/metal clusters. Magnetic metal-organic framework (MMOF) composites are promising candidate among the new-generation sorbent materials available for magnetic solid-phase extraction (MSPE) of environmental contaminants due to their superparamagnetism properties, high crystallinity, permanent porosity, ultrahigh specific surface area, adaptable pore shape/sizes, tunable functionality, designable framework topology, rapid and ultrahigh adsorption capacity, and reusability. In this review, we focus on recent scientific progress in the removal of heavy metal ions present in contaminated aquatic system by using MMOF composites. Different types of MMOFs, their synthetic approaches, and various properties that are harnessed for removal of heavy metal ions from contaminated water are discussed briefly. Adsorption mechanisms involved, adsorption capacity, and regeneration of the MMOF sorbents as well as recovery of heavy metal ions adsorbed that are reported in the last ten years have been discussed in this review. Moreover, particular prospects, challenges, and opportunities in future development of MMOFs towards their greener synthetic approaches for their practical industrial applications have critically been considered in this review.

Multifunctional nanomaterials and nanocomposites for sensing and monitoring of environmentally hazardous heavy metal contaminants

The applications of conventional sensors are limited by the long response time, high cost, large detection limit, low sensitivity, complicated usage and low selectivity. These sensors are nowadays replaced by Nanocomposite-based modalities and nanomaterials which are known for their high selectivity and physical and chemical properties. These nanosensors effectively detect heavy metal contaminants in the environment as the discharge of heavy metals into natural water as a result of human activity has become a global epidemic. Exposure to these toxic metals might induce many health-related complications, including kidney failure, brain injury, immune disorders, muscle paleness, cardiac damage, nervous system impairment and limb paralysis. Therefore, designing and developing novel sensing systems for the detection and recognition of these harmful metals in various environmental matrices, particularly water, is of extremely important. Emerging nanotechnological approaches in the past two decades have played a key role in overcoming environmentally-related problems. Nanomaterial-based fabrication of chemical nanosensors has widely been applied as a powerful analytical tool for sensing heavy metals. Portability, high sensitivity, on-site detection capability, better device performance and selectivity are all advantages of these nanosensors. The detection and selectivity have been improved using molecular recognition probes for selective binding on different nanostructures. This study aims to evaluate the sensing properties of various nanomaterials such as metal-organic frameworks, fluorescent materials, metal-based nanoparticles, carbon-based nanomaterials and quantum dots and graphene-based nanomaterials and quantum dots for heavy metal ions recognition. All these nano-architectures are frequently served as effective fluorescence probes to directly (or by modification with some large or small biomolecules) sense heavy metal ions for improved selectivity. However, efforts are still needed for the simultaneous designing of multiple metal ion-based detection systems, exclusively in colorimetric or optical fluorescence nanosensors for heavy metal cations.

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.

Application of Fe3O4@CNFs combined with deep eutectic solvent-based dual microextraction: a novel and green strategy for rapid determination of pesticides in edible oil samples

A novel, green, and effective strategy employing Fe₃O₄-modified carbon nanofibers (CNFs) combined with deep eutectic solvent (DES) is proposed as an extraction agent to extract five pesticides in edible oil samples via dual microextraction modes, followed by high-performance liquid chromatography for determination. The Fe₃O₄@CNFs nanomaterial and a sequence of hydrophilic DES were prepared at first and then characterized by multiple techniques. Subsequently, the extraction performance of DES and Fe₃O₄@CNFs-DES was compared and Fe₃O₄@CNFs-DES exhibited better extraction ability. After that, several influencing parameters such as the composition of DES, the amount of Fe₃O₄@CNFs-DES, the dispersion methods, and the extraction time were investigated and optimized. Eventually, Fe₃O₄@CNFs as the solid adsorbent combined with tetrabutylammonium chloride-lactic acid-based DES as the extraction solvent were selected to extract target pesticides from oil samples. The established method received good linearity in the range 25-1000 ng·g^-1. The limits of detection for all analytes were in the range 2.25-7.50 ng·mL^-1. Satisfactory recoveries of target pesticides were obtained (ranging from 82 to 117%) with a relative standard deviation of 0.26-9.46%. The proposed method has been successfully applied to the rapid detection of target pesticides in oil samples, demonstrating its great potential for quick screening and analysis.

Preconcentrations of Cu (II) and Mn (II) by magnetic solid-phase extraction on Bacillus cereus loaded γ-Fe2O3 nanomaterials

For the simultaneous preconcentrations of Cu(II) and Mn(II), a novel preconcentration technique was developed and described. Bacillus cereus loaded magnetic ɣ-Fe₂O₃ nanoparticles were prepared and used as support materials on solid-phase extraction procedure. Important experimental parameters were investigated in details and pH 6.0, 3 mL min^-1 of flow rate, 5 mL of 1 mol L^-1 of HCl as eluent, 200 mg of biomass, and 200 mg of magnetic ɣ-Fe₂O₃ nanoparticles as support material was found as the best conditions. The preconcentrations factor were found to be 80 for Cu (II) and Mn(II). It was confirmed by the results that SPE columns could be used in 32 cycles. The LOD values calculated for Cu (II) and Mn (II) were 0.09 and 0.08 ng mL^-1, respectively. The RSD values found were less than 3.4%. The extraction recoveries were achieved as higher than 98%. The biosorption capacities of Cu (II), and Mn (II) were 26.0 mg g^-1, 30.3 mg g^-1 respectively. The approach devised for analyzing analyte concentrations in food samples proved to be successful.

Highly fluorescent N doped C-dots as sensor for selective detection of Hg2+ in beverages

In this work, nitrogen doped carbon dots (NCDs) were synthesized through one step hydrothermal reaction using citric acid and ethylenediamine as precursors. The prepared NCDs exhibit high quantum yield of 67.4%, good stability, excellent selectivity and sensitivity. It was found that the NCDs have potential as a fluorescence sensor for the detection of Hg²⁺. Under optimal conditions, good linearity between the change in NCDs fluorescence intensity and Hg²⁺ concentration was obtained in the range of 0.3 to 2.0 μM with a detection limit at 0.24 μM. The possible detection mechanism was static quenching of NCDs by Hg²⁺. The established method was successfully applied to the determination of Hg²⁺ in beverage samples. The results indicated that the NCDs-based sensor has potential for detection of Hg²⁺ in real beverage sample.

Adsorptive removal of dyes from wastewater using a metal-organic framework: A review

Water pollution from synthetic dyes is a growing environmental concern because many dyes have carcinogenic effects on humans and aquatic life. Adsorption is a widely used technology for the separation and removal of dyes from wastewater. However, the dye removal process using conventional adsorbents is not sufficiently efficient for industrial wastewater. Metal-organic frameworks (MOFs) addresses these drawbacks. MOF showed excellent dye removal and degradation capacity owing to its multifunctionality, water-stability, large surface area, tunable pore size and recyclability. Magnetic MOFs retained excellent performance up to several consecutive cycles. Modified MOFs performed as Fenton-like catalysis process which generated abundant reactive radicals that degraded complex organic dyes into simple and less toxic forms which were further adsorbed onto the MOF. This review systematically compiles in-depth studies on the adsorptive removal of dyes from wastewater, MOF adsorption mechanisms, major influencing factors, to adsorption efficiency of MOFs. While all MOFs adsorb dyes through electrostatic attraction, the type of MOF, presence of functional groups, ligands, and pH significantly control the adsorption mechanism. Before developing an MOF, optimization and upgradation of factors and interaction between available adsorption site and adsorbate is needed. Finally, the prospects and new frontiers of MOFs in sustainable water treatment is discussed.

Preparation of yolk-shell structure NH2-MIL-125 magnetic nanoparticles for the selective extraction of nucleotides

Yolk-shell structure magnetic metal-organic framework nanoparticles were prepared via post solvothermal method and employed as a magnetic solid-phase extraction adsorbent for selective pre-concentration of 5'-ribonucleotides by π stacking interaction, hydrogen bonding, and the strong interaction between titanium ions (Ti⁴⁺) and phosphate group. The properties of the materials were confirmed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, vibrating sample magnetometer, infrared spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller analysis. The main parameters affecting the adsorption-desorption process, including adsorbent amount, incubation time, incubation temperature, sample pH, shaking speed, elution solution, and elution time, were systematically optimized. Finally, 1.0 mg of adsorbent mixed with 1.0 mL sample solution (10.0 mmol⋅L^-1 NaCl, pH 3.0) and shaken at 135 rpm for 5 min at 40 °C, washed with 1.0 mL Na₃PO₄-NH₃∙H₂O under vortex for 5 min were selected as optimized adsorption-desorption conditions. The binding performance of adsorbent towards five nucleotides was evaluated by static adsorption experiments. The data are well-fitted to the Langmuir isotherm model and the maximum adsorption capacity is 27.8 mg g^-1 for adenosine 5'-monophosphate. The limit of detection of the method is 19.44-38.41 ng mL^-1. Under the optimal conditions, the adsorbent was successfully applied to magnetic solid-phase extraction and high performance liquid chromatography determination of five nucleotides in octopus, chicken, fish, and pork samples.

Functional Hybrid Micro/Nanoentities Promote Agro-Food Safety Inspection

The rapid development of nanomaterials has provided a good theoretical basis and technical support to solve the problems of food safety inspection. The combination of functionalized composite nanomaterials and well-known detection methods is gradually applied to detect hazardous substances, such as chemical residues and toxins, in agricultural food products. This review concentrates on the latest agro-food safety inspection techniques and methodologies constructed with the assistance of new hybrid micro/nanoentities, such as molecular imprinting polymers integrated with quantum dots (MIPs@QDs), molecular imprinting polymers integrated with upconversion luminescent nanoparticles (MIPs@UCNPs), upconversion luminescent nanoparticles combined with metal-organic frameworks (UCNPs@MOFs), magnetic metal-organic frameworks (MOFs@Fe₃O₄), magnetic covalent-organic frameworks (Fe₃O₄@COFs), covalent-organic frameworks doped with quantum dots (COFs@QDs), nanobody-involved immunoassay for fast inspection, etc. The presented summary and discussion favor a relevant outlook for further integrating various disciplines, like material science, nanotechnology, and analytical methodology, for addressing new challenges that emerge in agro-food research fields.

Magnetic dispersive solid-phase extraction of triazole and triazine pesticides from vegetable samples using a hydrophilic-lipophilic sorbent based on maltodextrin- and β-cyclodextrin-functionalized graphene oxide

Maltodextrin- and β-cyclodextrin-functionalized magnetic graphene oxide (mGO/β-CD/MD), a novel hydrophilic-lipophilic composite, was successfully fabricated and used for the co-extraction of triazines and triazoles from vegetable samples before HPLC-UV analysis. mGO/β-CD/MD was synthesized by chemical bonding of β-CD and MD to the surface of mGO, using epichlorohydrin (ECH) as a linker. The successful synthesis of mGO/β-CD/MD was confirmed by characterization tests, including attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), vibrating sample magnetometry (VSM), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), and Barrett-Joyner-Halenda (BJH) analyses. The hydrophobic cavity of β-CD and a large number of hydroxyl groups on the MD structure contributed to the co-extraction of mentioned pesticides with a wide range of polarity. Under the optimized condition (sorbent amount, 30 mg; desorption time, 10 min; desorption solvent volume, 300 μL; desorption solvent, methanol/acetonitrile (1:1) containing 5% (v/v) acetic acid; extraction time, 20 min; and pH of sample solution, 7.0), good linearity within the range 1.0-1000 μg L^-1 (r² ≥ 0.992) was achieved. Extraction efficiencies were in the range 66.4-95.3%, and the limits of detection were 0.01-0.08 μg L^-1. Relative recoveries for spiked samples were obtained in the range 88.4-112.0%, indicating that the matrix effect was insignificant, and good precisions (intra- and inter-day) were also achieved (RSDs < 9.0%, n = 3). The results confirmed that the developed method was efficient for the determination  of trace amounts of pesticides in potato, tomato, and corn samples.

Multi-ion imprinted polymers (MIIPs) for simultaneous extraction and preconcentration of Sb(III), Te(IV), Pb(II) and Cd(II) ions from drinking water sources

Simultaneous extraction and preconcentration of several potentially toxic metal ions have received great attention because of their toxicological effects on aquatic life and human beings. Multi-ion imprinted polymers (MIIP) have proved to be promising adsorbents with excellent specific recognition performance than single-ion imprinted polymer. Therefore, in this study, the MIIP strategy was employed for simultaneous extraction and enrichment of Sb(III), Cd(II), Pb(II) and Te(IV) ions from drinking water sources. MIIPs was used as a sorbent material in ultrasound-assisted dispersive solid phase extraction combined with inductively coupled plasma optical emission spectrometry (UA-DSPE/ICP-OES). The experimental parameters that affect the extraction efficiency and recovery of Sb(III), Cd(II), Pb(II) and Te(IV) were investigated using response surface methodology. Under optimum conditions, the enhancement factors, linear range, limit of detection (LOD) and limit of quantification (LOQ) were 37.7-51.1, 0.04-100 µg L^-1, 0.011-0.28 µg L^-1, 0.037-093 µg L^-1, respectively. The intra-day (n = 10) and inter-day (n = 5) precision expressed as relative standard deviations (%RSDs,) were 3% and 5%, respectively. The proposed UA-DSPE/ICP-OES method was applied for preconcentration and determination of the trace metal ions in environmental samples. Furthermore, the accuracy of the method was evaluated using spiked recovery experiments and the percentage recoveries ranged from 95% to 99.3%.

Application of novel nanomagnetic metal-organic frameworks as a catalyst for the synthesis of new pyridines and 1,4-dihydropyridines via a cooperative vinylogous anomeric based oxidation

Herein, a new magnetic metal-organic frameworks based on Fe3O4 (NMMOFs) with porous and high surface area materials were synthesized. Then, NMMOFs were characterized by FT-IR, XRD, SEM, elemental mapping, energy dispersive X-ray (EDS), TG, DTG, VSM, and N2 adsorption-desorption isotherms (BET). Fe3O4@Co(BDC)-NH2 as a magnetic porous catalyst was applied for synthesis of novel fused pyridines and 1,4-dihydropyridines with pyrazole and pyrimidine moieties as suitable drug candidates under ultrasonic irradiation. The significant advantages of the presented methodology are mild, facile workup, high yields, short reaction times, high thermal stability, and reusability of the described NMMOFs catalyst.

Greenness of magnetic nanomaterials in miniaturized extraction techniques: A review

Green analytical chemistry principles should be followed, as much as possible, and particularly during the development of analytical sample preparation methods. In the past few years, outstanding materials such as ionic liquids, metal-organic frameworks, carbonaceous materials, molecularly imprinted materials, and many others, have been introduced in a wide variety of miniaturized techniques in order to reduce the amount of solvents and sorbents required during the analytical sample preparation step while pursuing more efficient extraction methods. Among them, magnetic nanomaterials (MNMs) have gained special attention due to their versatile properties. Mainly, their ability to be separated from the sample matrix using an external magnetic field (thus enormously simplifying the entire process) and their easy combination with other materials, which implies the inclusion of a countless number of different functionalities, highly specific in some cases. Therefore, MNMs can be used as sorbents or as magnetic support for other materials which do not have magnetic properties, the latter permiting their combination with novel materials. The greenness of these magnetic sorbents in miniaturized extractions techniques is generally demonstrated in terms of their ease of separation and amount of sorbent required, while the nature of the material itself is left unnoticed. However, the synthesis of MNMs is not always as green as their applications, and the resulting MNMs are not always as safe as desired. Is the analytical sample preparation field ready for using green magnetic nanomaterials? This review offers an overview, from a green analytical chemistry perspective, of the current state of the use of MNMs as sorbents in microextraction strategies, their preparation, and the analytical performance offered, together with a critical discussion on where efforts should go.

Review of the distribution and detection methods of heavy metals in the environment

Heavy metals can be enriched in living organisms and seriously endanger human health and the ecological environment, which has evolved into a significant global environmental problem. Based on summarizing the spatial distribution of heavy metals in the environment, this review introduces heavy metal detection technologies such as inductively coupled plasma mass spectrometry/atomic emission spectrometry, atomic absorption spectrometry, atomic fluorescence spectrometry, and laser-induced breakdown spectrometry. It summarizes their respective advantages, characteristics, and applicability. Besides, atmospheric pressure discharge plasma as a potential heavy metal detection technology is also introduced and discussed in this review. The current research mainly focuses on improving the analytical performance and optimizing the practical application. Furthermore, this review not only summarizes the advantages of atmospheric pressure discharge plasma in the field of element analysis but also summarizes the principal scientific and technical problems to be solved urgently.

Amperometric determination of heavy metal using an HRP inhibition biosensor based on ITO nanoparticles-ruthenium (III) hexamine trichloride composite: Central composite design optimization

A novel horseradish peroxidase (HRP) enzyme inhibition biosensor based on indium tin oxide (ITO) nanoparticles, hexaammineruthenium (III) chloride (RUT), and chitosan (CH) modified glassy carbon electrode (GCE) was developed. The biosensor fabrication process was investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The amounts of ITO nanoparticles and RUT were optimized using a 2² central composite design for the optimization of electrode composition. The detection limits were determined as 8 nM, 3 nM, and 1 nM for Pb²⁺, Ni²⁺, and Cd²⁺, respectively. The inhibition calibration curves of the biosensor were found to be within the range of 0.009-0.301 µM with a sensitivity of 11.97 µA µM^-1 cm^-2 (0.85 µA µM^-1) for Pb²⁺, 0.011-0.368 µM with a sensitivity of 10.84 µA µM^-1 cm^-2 (0.77 µA µM^-1) for Ni²⁺, and 0.008-0.372 µM with a sensitivity of 10.99 µA µM^-1 cm^-2 (0.78 µA µM^-1) for Cd²⁺. The type of HRP inhibition by Pb²⁺, Ni²⁺ and Cd²⁺ was investigated by the Dixon and Cornish-Bowden plots. The effects of possible interfering species on the biosensor response were examined. The analysis of Pb²⁺, Ni²⁺, and Cd²⁺ in tap water was demonstrated using the HRP/ITO-RUT-CH/GCE with satisfactory experimental results. The proposed method agreed with the atomic absorption spectrometry results.

Recent Advances in Nanomaterials for Analysis of Trace Heavy Metals

In an effort to achieve high sensitivity analysis methods for ultra-trace levels of heavy metals, numerous new nanomaterials are explored for the application in preconcentration processes and sensing systems. Nanomaterial-based methods have proven to be effective for selective analysis and speciation of heavy metals in combination with spectrometric techniques. This review outlined the different types of nanomaterials applied in the field of heavy metal analysis, and concentrated on the latest developments in various new materials. In particular, the functionalization of traditional materials and the exploitation of bio-functional materials could increase the specificity to target metals. The hybridization of multiple materials could improve material properties, to build novel sensor system or achieve detection-removal integration. Finally, we discussed the future perspectives of nanomaterials in the heavy metal preconcentration and sensor design, as well as their respective advantages and challenges. Despite impressive progress and widespread attention, the development of new nanomaterials and nanotechnology is still hampered by numerous challenges, particularly in the specificity to the target and the anti-interference performance in complex matrices.

Determination and Analysis of Trace Elements in Five Kinds of Traditional Chinese Medicine in High Blood Pressure Medicinal Food by ICP-AES

Objective. To establish a method for analysis of microelements in five kinds of traditional Chinese medicine in high blood pressure medicinal food, mainly including manganese, cobalt, selenium, iron, magnesium, and other 15 elements. Methods. The samples were digested using a microwave digestion instrument through NHO3-H2O2 solution, and then, the elements were synthesized by inductively coupled plasma atomic emission spectrometry (ICP-AES). Results. The content of cobalt, manganese, zinc, copper, and nickel in the high blood pressure diet foods is higher, the RSD is between 0.005% and 4.82%, and the recovery rate ranges from 93.40% to 106.5%. The precision and recovery of the detection method are higher. Conclusion. The experiment result is better. Medicinal foods curing high blood pressure contain a number of micronutrients that are beneficial to the human body. This experiment provides some meaningful basis for the prevention and treatment of cardiovascular diseases such as hypertension.

Using PVA/CA/Au NPs electrospun nanofibers as a green nanosorbent to preconcentrate and determine Pb2+and Cu2+in rice samples, water sources and cosmetics

Polyvinyl alcohol (PVA)/citric acid (CA)/Au NPs electrospun nanofibers was synthesized and applied as a green and efficient sorbent to extract and preconcentrate Pb²⁺and Cu²⁺from water sources, rice samples and cosmetics before FAAS.

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.

Fast and Selective Removal of Aqueous Uranium by a K+-Activated Robust Zeolitic Sulfide with Wide pH Resistance

For the nuclear industry, uranium is not only an important strategic resource but also a serious global contaminant with radiotoxicity and high chemotoxicity. It is very important to efficiently capture uranium from complex aqueous solutions for further treatment and disposal of nuclear wastes. Herein, we first demonstrate the suitability of a three-dimensional (3D) water-stable K⁺-exchanged zeolitic sulfide, namely K@GaSnS-1, for the remediation of radioactive and toxic uranium by ion exchange. In comparison to the pristine compound GaSnS-1, the K⁺-activated porous sulfide K@GaSnS-1 exhibits faster [UO₂]²⁺ ion uptake kinetics, following the pseudo-second-order adsorption model. Further studies indicate that K@GaSnS-1 shows high exchange capacity (q_m^U = 147.6 mg/g) and wide pH resistance (pH 2.75-10.87). In particular, it can efficiently capture [UO₂]²⁺ ion even when excessive amounts of Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions are present. The highest distribution coefficient value K_d, signifying the affinity and selectivity for [UO₂]²⁺ ion, reaches as high as 1.24 × 10⁴ mL/g. More importantly, the uranium in corresponding exchanged samples can be facilely and effectively eluted by a low-cost and eco-friendly method. These merits of K@GaSnS-1 make it promising for the effective and selective removal of uranium from complex contaminated water.

Mixed-Metal MOFs: Unique Opportunities in Metal-Organic Framework (MOF) Functionality and Design

Mixed-metal metal-organic frameworks (MM-MOFs) can be considered to be those MOFs having two different metals anywhere in the structure. Herein we summarize the various strategies for the preparation of MM-MOFs and some of their applications in adsorption, gas separation, and catalysis. It is shown that compared to homometallic MOFs, MM-MOFs bring about the opportunity to take advantage of the complexity and the synergism derived from the presence of different metal ions in the structure of MOFs. This is reflected in a superior performance and even stability of MM-MOFs respect to related single-metal MOFs. Emphasis is made on the use of MM-MOFs as catalysts for tandem reactions.

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.