Preconcentration and speciation of chromium species using ICP-OES after ultrasound-assisted magnetic solid phase extraction with an amino-modified magnetic nanocomposite prepared from Fe3O4, MnO2 and Al2O3

A series of viologen complexes containing thiophene and Br- dual fluorescent chromophores for continuous visual sensing of pH and Hg2

The mercury ion (Hg2+) is a typical high-toxicity substance that can cause severe damage to the environment and human bodies. For the detection of Hg2+, there are still significant challenges in the detection range and limit of detection (LOD). In this study, three viologen-based fluorescent probes are developed, CdCl4(Btybipy) (1), ZnBr4(Btybipy) (2), CdBr4(Btybipy) (3) (Btybipy = bis-1-thiophen-3-ylmethyl-[4,4']-bipyridinyl) through conventional solvent methods for detecting pH and Hg2+. Reversible discoloration and fluorescence response behaviour in the pH range of 4-12.8 is demonstrated by viologen-based fluorescent probes, which exhibit "ON-OFF-ON" signal changes. Compared with complex 1, it is surprising to find that complexes 2-3 display both fluorescence enhancement and fluorescence quenching simultaneously with the addition of different concentrations of Hg2+ (0-20 and 25-400 μM). There is broad linearity in the range of 0-20 and 50-300 μM with LODs of 2.14 and 3.13 nM, respectively. This occurrence of dual-signal modes is attributed to the participation of Br- and the thiophene S atom as dual chromophores in the coordination reaction of Hg2+. Dual-signal mode output, high sensitivity, wide detection range, and low LODs are exhibited by these fluorescent probes. The unique coordination reaction between Br- and the thiophene S atom with Hg2+ can provide a potential strategy for the exploitation of promising sensing platforms for monitoring Hg2+.

Bioengineered magnetic graphene oxide microcomposites for bioremediation of chromium in ex situ - A novel strategy for aggrandized recovery by electromagnetic gadgetry

Novel magnetic microcomposites consisting of graphene oxide and iron oxide was synthesized to immobilize metabolically versatile Paracoccus sp. MKU1 and Leucobacter sp. AA7 and tested for the simultaneous adsorption and enhanced biological detoxification of hexavalent chromium (Cr(VI)) from tannery wastewater. This study reports highest chromium adsorption of 272.6 mg/g and 179.3 mg/g with complete reduction of Cr(VI) to Cr(III) by the microcomposites of AA7 and MKU1 from wastewater in a bioreactor (10 L) at large-scale for first time in ex situ. Furthermore, both the microcomposites displayed an enhanced detoxification of tannery wastewater by reducing various physicochemical conditions such as ammonia, nitrate, TDS, fluoride, CaCO_3, Ca, Mg, NO₃ and SO₂ under the permissible limits. Use of electromagnetic device for magnetic microcomposites recovery from bioreactor yielded a maximum of 88% and 80.6% recovery for AA7 and MKU1, respectively. The rate of chromium recuperation achieved following desorption from the microcomposites of AA7 and MKU1 was 90.71% and 93.97%, respectively. Thus, the multifarious benefits including adsorption, metabolic detoxification, recovery, and recuperation by single functional microcomposites seems to be an intriguing and profitable approach for practicing in real-time operations to effectively remove heavy metals from the contaminated wastewater for environmental protection.

A novel ratiometric fluorescence sensor based on lanthanide-functionalized MOF for Hg2+ detection

Post-synthesis modification is an effective strategy for the preparation of rare earth organic framework materials and the derivation of high-performance functional materials. Here, we report the preparation of a dual emission Ln-MOF material (Eu-Ca-MOF) using Ca-MOF as the parent framework and introducing Eu³⁺ ions into its channels through post-synthesis modification. Eu-Ca-MOF has good photoluminescence properties and can be used as a ratiometric fluorescence sensor (I₃₈₁/I₅₉₀) to detect Hg²⁺ ions in water sensitively. The characteristic of Eu-Ca-MOF obtained is that when the material is dispersed in an aqueous solution containing Hg²⁺ ions, the characteristic emission of the ligand at 381 nm is enhanced, while the characteristic emission of Eu³⁺ at 590 nm is quenched. The peak-to-height ratio of the two emissions can be used to achieve highly sensitive detection of Hg²⁺ ions even in the presence of other potentially competing analytes. In addition, Hg²⁺ induces Eu-Ca-MOF to produce a significant ratiometric luminescence response, which changes its luminescence color from red to blue, which is beneficial to visual analysis of naked eyes. At the same time, Eu-Ca-MOF has a wider detection range (0.02-200 μM), and a lower limit detection (2.6 nM) for Hg²⁺ ions. The lanthanide compounds prepared by post-synthetic modification provide an effective synthesis strategy for photoluminescent materials.

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.

A comprehensive review on magnetic carbon nanotubes and carbon nanotube-based buckypaper for removal of heavy metals and dyes

Industrial effluents contain several organic and inorganic contaminants. Among others, dyes and heavy metals introduce a serious threat to drinking waterbodies. These pollutants can be noxious or carcinogenic in nature, and harmful to humans and different aquatic species. Therefore, it is of high importance to remove heavy metals and dyes to reduce their environmental toxicity. This has led to an extensive research for the development of novel materials and techniques for the removal of heavy metals and dyes. One route to the removal of these pollutants is the utilization of magnetic carbon nanotubes (CNT) as adsorbents. Magnetic carbon nanotubes hold remarkable properties such as surface-volume ratio, higher surface area, convenient separation methods, etc. The suitable characteristics of magnetic carbon nanotubes have led them to an extensive search for their utilization in water purification. Along with magnetic carbon nanotubes, the buckypaper (BP) membranes are also favorable due to their unique strength, high porosity, and adsorption capability. However, BP membranes are mostly used for salt removal from the aqueous phase and limited literature shows their applications for removal of heavy metals and dyes. This study focuses on the existence of heavy metal ions and dyes in the aquatic environment, and methods for their removal. Various fabrication approaches for the development of magnetic-CNTs and CNT-based BP membranes are also discussed. With the remarkable separation performance and ultra-high-water flux, magnetic-CNTs, and CNT-based BP membranes have a great potential to be the leading technologies for water treatment in future.

Adsorptive Removal of Cd, Cu, Ni and Mn from Environmental Samples Using Fe3O4-Zro2@APS Nanocomposite: Kinetic and Equilibrium Isotherm Studies

In this study, Fe₃O₄-ZrO₂ functionalized with 3-aminopropyltriethoxysilane (Fe₃O₄-ZrO₂@APS) nanocomposite was investigated as a nanoadsorbent for the removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions from aqueous solution and real samples in batch mode systems. The prepared magnetic nanomaterials were characterized using X-ray powder diffraction (XRD), scanning electron microscopy/energy dispersion x-ray (SEM/EDX) Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Factors (such as adsorbent dose and sample pH) affecting the adsorption behavior of the removal process were studied using the response surface methodology. Under optimized condition, equilibrium data obtained were fitted into the Langmuir and Freundlich isotherms and the data fitted well with Langmuir isotherms. Langmuir adsorption capacities (mg/g) were found to be 113, 111, 128, and 123 mg/g for Cd, Cu, Ni and Mn, respectively. In addition, the adsorption kinetics was analyzed using five kinetic models, pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models. The adsorbent was successfully applied for removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions in wastewater samples.

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.

Nanocomposites for Electrochemical Sensors and Their Applications on the Detection of Trace Metals in Environmental Water Samples

The elevated concentrations of various trace metals beyond existing guideline recommendations in water bodies have promoted research on the development of various electrochemical nanosensors for the trace metals' early detection. Inspired by the exciting physical and chemical properties of nanomaterials, advanced functional nanocomposites with improved sensitivity, sensitivity and stability, amongst other performance parameters, have been synthesized, characterized, and applied on the detection of various trace metals in water matrices. Nanocomposites have been perceived as a solution to address a critical challenge of distinct nanomaterials that are limited by agglomerations, structure stacking leading to aggregations, low conductivity, and limited porous structure for electrolyte access, amongst others. In the past few years, much effort has been dedicated to the development of various nanocomposites such as; electrochemical nanosensors for the detection of trace metals in water matrices. Herein, the recent progress on the development of nanocomposites classified according to their structure as carbon nanocomposites, metallic nanocomposites, and metal oxide/hydroxide nanocomposites is summarized, alongside their application as electrochemical nanosensors for trace metals detection in water matrices. Some perspectives on the development of smart electrochemical nanosensors are also introduced.

Speciation of chromium in waters using dispersive micro-solid phase extraction with magnetic ferrite and graphite furnace atomic absorption spectrometry

The combination of a solid-phase microextraction process with graphite furnace atomic absorption spectrometry provides a very sensitive determination method for determining chromium in waters. Freshly prepared ferrite particles are used to retain the chromium species, and then separated by a magnet without the need for a centrifugation step. The solid phase is suspended in water and directly introduced into the graphite furnace to obtain the analytical signal. The complexation of Cr(III) with ethylenediaminetetraacetate allows the selective retention of Cr(VI), and thus the speciation of the metal. The procedure is sensitive (0.01 µg L⁻¹ detection limit when using a 10 mL sample aliquot) and reproducible (5% relative standard deviation for five consecutive experiments at the 0.3 µg L⁻¹ level). The reliability of the procedure is verified by analysing five certified water samples.

Nanomaterials in speciation analysis of metals and metalloids

Nanomaterials have draw extensive attention from the scientists in recent years mainly due to their unique and attractive thermal, mechanical and electronic properties, as well as high surface to volume ratio and the possibility for surface functionalization. Whereas mono functional nanomaterials providing a single function, the preparation of core/shell nanoparticles allows different properties to be combined in one material. Their properties have been extensively exploited in different extraction techniques to improve the efficiency of separation and preconcentration, analytical selectivity and method reliability. The aim of this paper is to provide an updated revision of the most important features and application of nanomaterials (metallic, silica, polymeric and carbon-based) for solid phase extraction and microextraction techniques in speciation analysis of some metals and metalloids (As, Cr, Sb, Se). Emphasis will be placed on the presentation of the most representative works published in the last five years (2015-2019).

Polystyrene-divinyl benzene microspheres with amino methyl phosphonic acid functional hairy brushes for the sorption and speciation of chromium prior to inductively coupled plasma mass spectrometric determination

This article describes the synthesis and application of a novel sorbent for Cr(III) and Cr(VI) speciation prior to their quantitation by inductively coupled plasma mass spectrometry. The sorbent consists of polystyrene-divinyl benzene microbeads that were graft-coated with poly(oligo (ethylene glycol) methacrylate)-block-poly(glycidyl methacrylate). The particles were finally modified with phosphomethylated triethylene tetramine. The resulting microbeads are shown to be a viable sorbent for Cr(VI). The total concentration of chromium was determined after oxidation of Cr(III) to Cr(VI) with KMnO₄ using the novel sorbent. The Cr(III) amount was then calculated by subtracting the concentration of Cr(VI) from that of total chromium. The optimum conditions for batch type sorption were established. Under optimal conditions, the limit of detection and quantification are 0.015 μg L^-1 and 0.050 μg L^-1, respectively. The kinetics and isotherms of the sorption of Cr(VI) were investigated. Following desorption with 0.1 M hydroxylamine hydrochloride, the method was successfully applied to spiked real water samples and a certified reference material. Graphical abstract Schematic presentation of a method for the sorption and speciation of chromium using amino methyl phosphonic acid functional brushes on polystyrene-divinyl benzene microspheres.

Magnetic nanostructures for preconcentration, speciation and determination of chromium ions: A review

Magnetic nanoparticles based solid-phase extraction is a new analytical technique based on the use of magnetic sorbents for the preconcentration and quantification of different inorganic and organic species. The present review concentrates on recent developments that have been built in magnetic nanostructures-based solid phase extraction, speciation and quantification of chromium ions. Besides, a description of the preparation, characterization as well as applications of various types of magnetic nanostructures, either with an inorganic or organic coating of the magnetic core, is presented. In addition, the most important analytical characteristics such as preconcentration factor, linear range, and limits of detection were carefully reported and compared. On the other hand, the removal of the chromium ions by magnetic solid phase extraction was not discussed in the review.

Ultrasound Assisted Adsorptive Removal of Cr, Cu, Al, Ba, Zn, Ni, Mn, Co and Ti from Seawater Using Fe2O3-SiO2-PAN Nanocomposite: Equilibrium Kinetics

This work reports the preparation and application of Fe2O3-SiO2-PAN nanocomposite for the removal of Cr3+, Cu2+, Al3+, Ba2+, Zn2+, Ni2+, Mn2+, Co2+, and Ti3+ from seawater. X-ray diffraction (XRD), scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscope (TEM), and Brunauer-Emmett-Teller (BET) characterized the synthesized composite. The following experimental parameters (Extraction time, adsorbent mass and pH) affecting the removal of major and trace metals were optimized using response surface methodology (RSM). The applicability of the RSM model was verified by performing the confirmation experiment using the optimal condition and the removal efficiency ranged from 90% to 97%, implying that the model was valid. The adsorption kinetic data was described by the pseudo-second order model. The applicability of the materials was tested on real seawater samples (initial concentration ranging from 0.270–203 µg L−1) and the results showed satisfactory percentage efficiency removal that range from 98% to 99.9%. The maximum adsorption capacities were found to be 4.36, 7.20, 2.23, 6.60, 5.06, 2.60, 6.79, 6.65 and 3.00 mg g−1, for Cr3+, Cu2+, Al3+, Ba2+, Zn2+, Ni2+, Mn2+, Co2+, and Ti4+, respectively.

Efficient discovery and capture of new neuronal nitric oxide synthase-postsynaptic density protein-95 uncouplers from herbal medicines using magnetic molecularly imprinted polymers as artificial antibodies

In the scope of stroke treatment, new neuronal nitric oxide synthase-postsynaptic density protein-95 uncouplers from herbal medicines were discovered and captured. To do so, highly selective magnetic molecularly imprinted polymers with a core-shell structure were prepared as artificial antibodies. According to the results of computational simulations, we designed and synthesized various polymers with varying amounts and types of template, functional monomer, cross-linker, and solvent. Characterization and performance tests revealed that the most appropriate artificial antibodies showed uniform spherical morphologies, large adsorption capacities, fast-binding kinetics, high selectivity, and quick separation. These artificial antibodies were then used as sorbents for dispersive magnetic solid-phase extraction coupled with high-performance liquid chromatography and mass spectrometry to capture and identify structural analogs to ZL006 from extracts of Scutellariae radix, Psoraleae fructus, and Trifolium pratense. Furthermore, according to the neuroprotective effect and coimmunoprecipitation test, Baicalein, Neobavaisoflavone, Corylifol A, and Biochanin A can be the potential uncouplers of neuronal nitric oxide synthase-postsynaptic density protein-95. Therefore, this present study contributes valuable information for the discovery of neuronal nitric oxide synthase-postsynaptic density protein-95 uncouplers from herbal medicines.

Selective adsorption and determination of hexavalent chromium ions using graphene oxide modified with amino silanes

Novel adsorbents are described for the preconcentration of chromium(VI). Graphene oxide (GO) was modified with various amino silanes containing one, two, or three nitrogen atoms in the molecule. These include 3-aminopropyltriethoxysilane (APTES), N-(3-trimethoxysilylpropyl)ethylenediamine (TMSPEDA), and N1-(3-trimethoxysilylpropyl)diethylenetriamine (TMSPDETA). The resulting GO derivatives were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray fluorescence spectrometry (EDXRF). Adsorption studies show that these GO based sorbents are highly selective for Cr(VI) in the presence of Cr(III) at pH 3.5. Although the amino silanes applied in modification of GO contain different numbers of nitrogen atoms, the maximum adsorption capacities of GO derivatives are very similar (13.3-15.1 mg·g-1). Such results are in accordance with spectroscopy studies which show that the amount of amino silanes attached to GO decreases in the order of APTES > TMSPEDA > TMSPDETA. The APTES-modified GO was applied to selective and sensitive extraction of Cr(VI) ions prior to quantitation by low-power EDXRF using the Cr Kα line. The Cr(VI) ions need not be eluted from the solid adsorbent. The method has a 0.17 ng·mL-1 detection limit, and the recovery is 99.7 ± 2.2% at a spiking level of 10 ng·mL-1. The method was successfully applied to the determination of Cr(VI) in water samples. Graphical abstractGraphene oxide adsorbents modified with various amino silanes are described for the preconcentration and speciation of trace and ultratrace levels of chromium ions.