Carbon-coated Fe3O4 nanoparticles with surface amido groups for magnetic solid phase extraction of Cr(III), Co(II), Cd(II), Zn(II) and Pb(II) prior to their quantitation by ICP-MS

Quantification of trace heavy metals in environmental water, soil and atmospheric particulates with their bioaccessibility analysis

In this work, sulfhydryl (SH) functionalized magnetic covalent organic framework (COF) was synthesized by using 4-aldehyde phenyl butadiyne (DEBD) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) as the monomers and ethanedithiol as the modifier, with the aid of thiol-alkyne "click" reaction. The prepared Fe3O4@COFTAPB-DEBD@SH exhibited relatively strong magnetism (32.8 emu g-1), good stability and selectivity to target analytes with a high sulfhydryl content (0.24 mmol g-1). Based on Fe3O4@COFTAPB-DEBD@SH, a method combining magnetic solid phase extraction with inductively coupled plasma mass spectrometry (ICP-MS) was developed for the quantitative analysis of trace metals. Under the optimal conditions, the method merited fast desorption kinetics (<2 min), adsorption kinetics (<20 min), fast phase separation (<1 min), high enrichment factor (100), and the detection limits for Cd, Hg, Pb and Bi were determined to be 1.18, 0.51, 4.91 and 0.39 ng L-1, respectively. A good resistance to complex matrices was demonstrated for the method in the analysis of soil, atmospheric particles and simulated pulmonary fluids samples. Certified reference materials (coal fly ash GBW08401 and soil GBW07427) were employed to validate the accuracy of the method. Four target metals in the range of 12.9-215 ng L-1, 0.06-24.6 μg g-1 and 0.52-33.1 ng m-3 were found in local water, soil and atmospheric particulates (PM), respectively. Additionally, artificial lysosome solution and gamble's solution were used to simulate human pulmonary fluid and the bioaccessibility of Cd, Hg, Pb and Bi in PM2.5 was evaluated to be 58.6-73.1 % and 1.3-7.1 %, respectively.

Fixed bed column adsorption systems to remove 2,4-Dichlorophenoxyacetic acid herbicide from aqueous solutions using magnetic activated carbon

The widespread use of 2,4-Dichlorophenoxyacetic acid (2,4-D) as a weedkiller has resulted in its persistence in the environment, leading to surface and groundwater pollution. In this study, the fixed bed column experiments were performed to remove 2,4-D from aqueous solutions using magnetic activated carbon derived from Peltophorum pterocarpum tree pods. The evaluation was done on effects of operating parameters such as bed depth (2-4 cm), influent flow rate (4.6-11.4 mL/min), and 2,4-D concentration (25-100 mg/L) on the breakthrough curves. The data fit well with the Yoon-Nelson and Thomas models, exhibiting high R2 values. Results indicated that lower flow rates, lower 2,4-D concentrations, and greater bed depths enhanced adsorption capacity, achieving up to 196.31 mg/g. Reusability studies demonstrated the material's potential for repeated use, while toxicity studies with Vigna radiata seeds confirmed the effectiveness of Fe3O4-CPAC in removing 2,4-D. This investigation highlights the promising application of Fe3O4-CPAC in fixed bed adsorption systems for efficient 2,4-D removal.

A new method for extraction and pre-concentration of the heavy metals using a microemulsion system in winsor II equilibrium and determination by HR-CS AAS

For the very first time, a microemulsion system in the Winsor II (WII) equilibrium was applied in a sample preparation method for extraction and pre-concentration in the determination of Pb, Cd, Co, Tl, Cu and Ni, in natural waters by high resolution continuum source atomic absorption spectrometry (HR-CS AAS). The method was optimized using the graphite furnace atomization. A simplex-centroid design for determine optimum extraction condition (77.5% aqueous phase, 5% of the oil phase, and 17.5% cosurfactant/surfactant ratio - C/S = 4) was applied. The optimized time for the sample preparations was around 30 min. The analytical performance of the optimized method using HR-CS GF AAS showed that the detection limits were: 0.09, 0.01, 0.06, and 0.05 μg L-1 for determination of Pb, Cd, Tl, and Co, respectively and the enrichment factors were between 6 and 19, considered excellent for all analytes. The RSD values were lower than 5%, demonstrating the good precision of the proposed method. When the optimized method was applied using the HR-CS F AAS, the sensibility increased 9 to 12 times for Cu and Ni, respectively. The analytical method was successfully applied for the determination of analytes in Certified Reference Material and real samples for natural waters such as Brackish water (recovery between 107 and 112%), Saline water (recovery between 83 and 94%), Produced water from oil industry (recovery between 98 and 110%) and Fresh water (recovery 80 and 87% to Cu and Ni respectively). All the results confirming the accuracy of the analytical method proposed. The repeatability of the measurements has been better 5% (n = 3), for all elements.

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.

Ultra-trace levels voltammetric determination of Pb2+ in the presence of Bi3+ at food samples by a Fe3O4@Schiff base Network1 modified glassy carbon electrode

In this research, a highly sensitive electrochemical sensor was developed for the square wave anodic stripping voltammetric determination of Pb²⁺ at ultra-trace levels. A Glassy carbon electrode was modified with an in-situ electroplated bismuth film and the nanocomposite of a recently synthesized melamine based covalent organic framework (schiff base network₁ (SNW₁)) and Fe₃O₄ nanoparticles (Fe₃O₄@SNW₁). The obtained results exhibit clearly that combination of Fe₃O₄@SNW₁ and in-situ electroplated bismuth film enhances the sensitivity of the modified electrode towards Pb²⁺ remarkably. A Plackett-Burman design was implemented for screening experimental factors to specify the significant variables influencing the sensitivity of the electroanalytical method. Afterward, the effective factors were optimized using Box-Behnken design (BBD). Under optimized conditions, the proposed electrode showed a linear response towards Pb²⁺ in the concentration range of 0.003-0.3 μmol L^-1 with the detection limit of 0.95 nmol L^-1. The selectivity of the fabricated electrode towards different ionic species were checked out and no serious interference was observed. At the end, the application of the designed sensor in the determination of Pb²⁺ at 10 different edible specimens were investigated and the obtained recovery values were in the range of (95.56-106.64%) indicating the successful performance of the designed sensor.

Grafting chelating groups on 2D carbon for selective heavy metal adsorption

Iminodiacetic acid (IDA) is a tridentate ligand, which can capture metal ions by forming two fused five-membered chelate rings. In this study, we fixed IDA moieties onto a two-dimensional nanocarbon, graphene oxide (GO), to obtain materials with high and selective adsorption of metal ions. The synthesis conditions for the GO-IDA composites were optimized, then their structures were characterized by infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and CHN elemental analysis. In addition, the heavy-metal removal efficiency and selectivity of the GO-IDA composites with different length alkyl linkers between the GO and IDA were investigated. An aqueous solution containing 10 metal ions (Al, As, B, Cd, Cr, Cu, Mn, Pb, Se, and Zn) was used as a model for contaminated water at pH 7, and the interactions of the ions with GO-IDA were in the order of Cu > Pb > As > B > Zn > Al ≈ Se. The interaction between Cu and GO-IDA was confirmed by XPS and extended X-ray absorption fine structure (EXAFS), which showed that Cu was coordinated to IDA.

Magnetic nanomaterials as sorbents for trace elements analysis in environmental and biological samples

This review focuses on magnetic nanomaterials as sorbents for trace elements analysis in environmental and biological samples. The design and preparation of magnetic nanomaterials with specific functional groups for trace elemental analysis are summarized, along with relevant adsorption mechanism. The application of these magnetic sorbents in different operation modes for the quantification of trace elements and their species in environmental and biological samples are discussed. The trend of development in this field is also prospected.

Enhancing arsenic sequestration on ameliorated waste molasses nanoadsorbents using response surface methodology and machine-learning frameworks

The development of a novel nanobiosorbent derived from waste molasses for the adsorptive removal of arsenic (As) has been attempted in this study. Waste molasses were chemically ameliorated through a solvothermal route for the incorporation of iron oxide, thereby producing iron oxide incorporated carbonaceous nanomaterial (IOCN). Synthesis of IOCN was confirmed through transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and atomic emission spectroscopy (AES) analysis. The surface area and porous behavior of IOCN were elucidated by Brunauer-Emmett-Teller (BET) assessments. The experimental conditions for adsorption were first modeled using response surface methodology (RSM) based on the central composite design (CCD), considering the parameters: adsorbate dosage, adsorbent dosage, pH, and contact time. RSM optimizations were improved upon using a three-layer feed-forward multilayer perceptron (MLP) based Artificial Neural Network (ANN) model. Optimization through ANN model resulted in the increase of the maximal As adsorption efficiency to ~ 96% for IOCN. The IOCN isotherm plots show the best fit for the Sips isotherm, and the reaction kinetics follows the pseudo-second-order model, indicating the chemisorption mechanism for As adsorption. Evidence for direct coordination of As to the surface of adsorbents was further confirmed by FTIR spectroscopic studies before and after As adsorption. The high adsorption efficiencies and the low-cost facile synthesis of the IOCN nanosorbent from agro-industrial waste indicate their potential for commercial applications.

Magnetic Fe3O4@Mg/Al-layered double hydroxide adsorbent for preconcentration of trace metals in water matrices

A magnetic Fe₃O₄@MgAl-layered double hydroxide (MLDH) nanocomposite was successfully synthesized and applied as an effective adsorbent for preconcentration of trace As(III), Cd(II), Cr(III), Co(II), Ni(II), and Pb(II) ions from complex matrices. The quantification of the analytes was achieved using the inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The nanocomposite was then characterized using BET, FTIR, SEM, and EDS. Due to its high adsorption surface area, compared to traditional metal oxide-based adsorbents, MLDH nanocomposite exhibited high extraction efficiency. Several experimental parameters controlling the preconcentration of the trace metals were optimized using response surface methodology based on central composite design. Under optimum conditions, the linearity ranged from 0.1 to 500 µg L⁻¹ and the correlation of coefficients (R²) were higher than 0.999. The limits of detection (LODs) and quantification (LOQs) were 0.11–0.22 µg L⁻¹ and 0.35–0.73 µg L⁻¹, respectively. The intra-day (n = 10) and inter-day precisions (n = 5 working days) expressed in the form of percent relative standard deviations (%RSDs) were below 5%. The proposed method was successfully applied for the analysis of the As(III), Cd(II), Cr(III), Co(II), Ni(II), and Pb(II) ions in different environmental water samples.

Nano-clay as a solid phase microextractor of copper, cadmium and lead for ultra-trace quantification by ICP-MS

Heavy metal microextraction and determination in daily used water is accurately achieved by applying nano-clay as an extractor. The conditions for adsorption/elution of Cu(ii), Cd(ii) and Pb(ii) were investigated by adjusting the pH of samples, sample volume and the type of eluent. The nano-clay showed superior efficiency for microextraction of Cu(ii), Cd(ii) and Pb(ii) at pH 2 using 2 mL of nitric acid (1 M) as the eluent. The microextraction procedure showed high recovery% by changing the sample volume from 15 mL to 70 mL. The preconcentration factor was found to be 37.5. The LOD and LOQ were 1.8, 1.3, and 1.9 μg L^-1 and 5.3, 3.9, and 5.7 μg L^-1 for Cu(ii), Cd(ii) and Pb(ii) respectively. The addition/recovery from different water samples showed recovery% in the range 88-105 which confirms the efficiency and the accuracy of the developed solid phase microextraction using nano-clay for enrichment of Cu(ii), Cd(ii) and Pb(ii).

Deep Eutectic Solvent-Based Microextraction of Lead(II) Traces from Water and Aqueous Extracts before FAAS Measurements

Microextraction procedures for the separation of Pb(II) from water and food samples extracts were developed. A deep eutectic solvent composed of α-benzoin oxime and iron(III) chloride dissolved in phenol was applied as a phase separator support. In addition, this deep eutectic mixture worked as an efficient extractor of Pb(II). The developed microextraction process showed a high ability to tolerate the common coexisting ions in the real samples. The optimum conditions for quantitative recoveries of Pb(II) from aqueous extracts were at pH 2.0, conducted by adding 150 µL from the deep eutectic solvent. The quantitative recoveries were obtained with various initial sample volumes up to 30 mL. Limits of detection and limits of quantification of 0.008 and 0.025 µg L^-1 were achieved with a relative standard deviation (RSD%) of 2.9, which indicates the accuracy and sensitivity of the developed procedure. Recoveries from the reference materials, including TMDA 64.2, TMDA 53.3, and NCSDC-73349, were 100%, 97%, and 102%, respectively. Real samples, such as tap, lake, and river water, as well as food samples, including salted peanuts, chickpeas, roasted yellow corn, pistachios, and almonds, were successfully applied for Pb(II) analysis by atomic absorption spectroscopy (AAS) after applying the developed deep eutectic solvent-based microextraction procedures.

A novel stabilized carbon-coated nZVI as heterogeneous persulfate catalyst for enhanced degradation of 4-chlorophenol

Nano zero-valent iron (nZVI) and its composite materials have been extensively studied in the field of environmental remediation. However, the oxidation and agglomeration of nZVI limits the large-scale application of nZVI in environmental remediation. This study developed a two-step method to prepare stable carbon-coated nZVI (Fe⁰@C) which combined hydrothermal carbonization and carbothermal reduction methods and used glucose and iron oxide (Fe₃O₄) as precursors. When the carbothermal reduction temperature was 700 °C and the elemental molar ratio of carbon to iron was 22:1, stable Fe⁰@C can be generated. The nZVI particles are encapsulated by mesoporous carbon and embedded in the carbon spheres. The unique structure of carbon coating not only inhibits the agglomeration of nZVI, but also makes nZVI stable in air for more than 120 days. Not only that, the as-synthesized Fe⁰@C exhibited high catalytic activity toward the degradation of 4-chlorophenol (4-CP) by activating persulfate. Different from conventional nZVI catalysts in generation of sulfate radicals, Fe⁰@C selectively induced hydroxyl radicals for 4-CP degradation. Moreover, Fe⁰@C has been shown to efficiently degrade 4-CP by using the dissolved oxygen in water to form hydroxyl radicals. This study not only provides a simple, green method for the preparation of stabilized nZVI, but also provides the possibility of large-scale application of nZVI in the field of environmental remediation.

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.

A monolithic copolymer prepared from N-(4-vinyl)-benzyl iminodiacetic acid, divinylbenzene and N,N'-methylene bisacrylamide for preconcentration of cadmium(II) and cobalt(II) from biological samples prior to their determination by ICP-MS

A capillary monolith consisting of poly[N-(4-vinyl)-benzyl iminodiacetic acid-co-divinylbenzene-co-N,N'-methylene bisacrylamide), referred to as poly(VBIDA-DVB-Bis), has been prepared. It is shown to be an efficient sorbent for the enrichment of Co(II) and Cd(II). The two ions are completely retained by the monolith in the pH range from 4.0 to 9.0. The breakthrough curve tests were adopted to evaluate the adsorption performance of the monolith towards Co(II) and Cd(II). A dose-response model was used to describe the breakthrough curves of the two ions at different initial concentrations. The adsorption capacities for Co(II) and Cd(II) are 1.54 and 1.73 mg·m^-1 at a concentration level of 2.5 mg·L^-1, respectively. The enrichment factor is 100, and the required sample volume is 5 mL. Following elution of the two ions with 0.5 M HNO₃, they were quantified by ICP-MS. The limits of detection in a 1 mL sample are 0.35 ng·L^-1 for Co(II) and 0.44 ng·L^-1 for Cd(II). The method was applied to the determination of Co(II) and Cd(II) in spiked rice, human urine and seawater samples. Graphical abstract Schematic representation of a monolithic copolymer prepared from N-(4-vinyl)-benzyl iminodiacetic acid (VBIDA), divinylbenzene (DVB) and N,N'-methylene bisacrylamide (Bis) and its application for selective capturing of cadmium(II) and cobalt(II) from complex sample matrices prior to their determination by ICP-MS.

Green construction of Fe3O4@GC submicrocubes for highly sensitive magnetic dispersive solid-phase extraction of five phthalate esters in beverages and plastic bottles

A well-designed core-shelled Fe₃O₄@graphitic carbon (Fe₃O₄@GC) submicrocube was in situ constructed in a simple, relatively green and eco-friendly ways basing on one-step pyrolysis of low-cost waste napkins-coated Fe₂O₃ submicrocubes. The Fe₃O₄@GC submicrocubes showed unique architectures where in situ generated thin graphitic carbon layer wrapped on the surface of Fe₃O₄, resulting in excellent affinity to five phthalate esters (PAEs), good reusability and rapid magnetic separation, therefore were employed as magnetic dispersive solid-phase extraction material combined with HPLC to simultaneously detect five trace PAEs in beverages and plastic bottles. Under optimized conditions, recoveries (80.0%-112.8%), precision (RSDs ≤ 8.8%), and limits of detection (LODs) for beverages (0.09-0.28 μg L^-1) and plastic bottles (0.01-0.03 μg g^-1) were obtained. This work not only establishes an effective method for simultaneous determination of five PAEs, but also opens up a new strategy to design/construct magnetic graphitic carbon-encapsulated core-shell materials using low-cost/recyclable napkins as carbon source.

Synthesis of magnetic molecularly imprinted nanoparticles with multiple recognition sites for the simultaneous and selective capture of two glycoproteins

Magnetic molecularly imprinted nanoparticles with multiple recognition sites were prepared, which exhibited excellent selectivity for two glycoproteins simultaneously.

Vortex assisted solid-phase extraction of lead(II) using orthorhombic nanosized Bi2WO6 as a sorbent

Nanosized single crystal orthorhombic Bi₂WO₆ was synthesized by a hydrothermal method and used as a sorbent for vortex assisted solid phase extraction of lead(II). The crystal and molecular structure of the sorbent was examined using XRD, Raman, SEM and SEM-EDX analysis. Various parameters affecting extraction efficiency were optimized by using multivariate design. The effect of diverse ions on the extraction also was studied. Lead was quantified by flame atomic absorption spectrometry (FAAS). The recoveries of lead(II) from spiked samples (at a typical spiking level of 200-400 ng·mL^-1) are >95%. Other figures of merit includes (a) a detection limit of 6 ng·mL^-1, (b) a preconcentration factor of 50, (c) a relative standard deviation of 1.6%, and (d) and adsorption capacity of 6.6 mg·g^-1. The procedure was successfully applied to accurate determination of lead in (spiked) pomegranate and water samples. Graphical abstract Nanosized single crystal orthorhombic Bi₂WO₆ was synthesized and characterized by a hydrothermal method and used as a sorbent for vortex assisted solid phase extraction of lead(II). The procedure was successfully applied to accurate determination of lead in (spiked) pomegranate and water samples.