A SERS-based aptasensor for ochratoxin A (OTA) is described. It is making use of Fe3O4@Au magnetic nanoparticles (MGNPs) and of Au@Ag nanoprobes modified with the Raman reporter 5,5-dithiobis-(2-nitrobenzoic acid; DTNB). Au-DTNB@Ag NPs were modified with the OTA aptamer (aptamer-GSNPs) and used as Raman signal probes. The SERS peak of DTNB at 1331 cm?1 was used for quantitative analysis. MGNPs modified with cDNA (cDNA-MGNPs) were used as capture probes and reinforced substrates. When the Au-DTNB@Ag-Fe3O4@Au complexes are formed through oligonucleotide hybridization, the Raman signal intensity of the Raman probe is significantly enhanced. If the OTA concentration in samples increases, more Raman signal probes (aptamer-GSNPs) will dissociate from the cDNA-MGNPs because more OTA aptamer is bound by OTA. This leads to a lower Raman signal after magnetic separation. Under the optimal conditions, the detection limit for OTA is 0.48 pg·mL?1 based on 3σ criterion. This is attributed to the multiple Raman signal enhancement and the good performance of the OTA aptamer. The good recovery and accuracy of the assay was confirmed by evaluating spiked samples of wine and coffee.
Graphical abstract Schematic of an aptamer based SERS assay for OTA by integrating Fe3O4@AuNPs (MGNPs) with Au-DTNB@Ag NPs with multiple signal enhancement. Aptamer modified Au-DTNB@Ag NPs are used as Raman probes, and MGNPs modified with cDNA are used as capture probes and reinforced substrates.
We report on a method for highly sensitive and selective colorimetric determination of Hg(II) via a signal amplification strategy. Cu@Au nanoparticles (NPs) are found to exhibit intrinsic peroxidase-like activity and can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine by H2O2. This is accompanied by a solution color change from colorless to green (with an absorption peak at 655 nm). The catalytic capability of the Cu@Au NPs (pale green) is strongly enhanced by a Cu@Au-Hg trimetallic amalgam (bluish), and this effect can be applied directly to the determination of Hg(II). The limit of detection as observed with the unaided eye is 10 nM, which is at least one order of magnitude lower than that of the known AuNP-based colorimetric assay. Due to excellent specificity of the amalgamation process, the assay is highly selective for Hg(II) and is not interfered by other metal ions in up to 0.5 μM concentrations. This assay was successfully applied to the determination of Hg(II) in tap water. In view of these advantages, we expect this colorimetric method to become an attractive tool for the quantitation of Hg(II) in biological, environmental, and food samples.
Graphical Abstract Cu@Au nanoparticles (NPs) exhibit intrinsic peroxidase-like activity and can catalyze the oxidation of tetramethylbenzidine (TMB) by H2O2. This is accompanied by a color change of the solution from colorless to green.
The authors describe a sensitive surface-enhanced Raman scattering (SERS)-based aptasensor for the detection of the food pathogen Vibrio parahaemolyticus. Nanostructures consisting of Fe3O4@Au particles wrapped with graphene oxide (GO) were used both as SERS substrates and separation tools. A first aptamer (apt 1) was immobilized on the Fe3O4@Au/GO nanostructures to act as a capture probe via the affinity binding of aptamer and V. parahaemolyticus. A second aptamer (apt-2) was modified with the Raman reporter molecule TAMRA to act as a SERS sensing probes that binds to the target the same way as the Fe3O4@Au/GO-apt 1. The sandwich formed between Fe3O4@Au/GO-apt 1/V. parahaemolyticus and apt 2-TAMRA can be separated with the aid of a magnet. The concentration of V. parahaemolyticus can be quantified by measurement of the SERS intensity of TAMRA. Under optimal conditions, the signal is linearly related to the V. parahaemolyticus concentration in the range between 1.4 × 102 to 1.4 × 106 cfu·mL?1, with a detection limit of 14 cfu·mL?1. Recoveries ranging from 98.5% to 105% are found when analyzing spiked salmon samples. In our perception, the assay described here is a useful tool for quantitation of V. parahaemolyticus in real samples.
Graphical abstract GO wrapped Fe3O4@Au nanostructures were synthesized as the substrate and modified with with a first aptamer (apt 1) to capture V. parahaemolyticus. TAMRA labelled aptamer 2 was then used as signal probe. The V. parahaemolyticus concentrations are closely related to the Raman intensity of TAMRA.
Magnetic Fe3O4@SiO2 core shell nanoparticles containing diphenylcarbazide in the shell were utilized for solid phase extraction of Hg(II) from aqueous solutions. The Hg(II) loaded nanoparticles were then separated by applying an external magnetic field. Adsorbed Hg(II) was desorbed and its concentration determined with a rhodamine-based fluorescent probe. The calibration graph for Hg(II) is linear in the 60 nM to 7.0 μM concentration range, and the detection limit is at 23 nM. The method was applied, with satisfying results, to the determination of Hg(II) in industrial waste water.
An electrochemical microsensor for chloramphenicol (CAP) was fabricated by introducing magnetic Fe3O4 nanoparticles (NPs) onto the surface of activated carbon fibers. This microsensor exhibited increased electrochemical response toward CAP because of the synergetic effect of the Fe3O4 NPs and the carbon fibers. Cyclic voltammograms were acquired and displayed three stable and irreversible redox peaks in pH 7.0 solution. Under optimized conditions, the cathodic current peaks at ?0.67 V (vs. Ag/AgCl). The calibration plot is linear in the 40 pM to 1 μM CAP concentration range, with a 17 pM detection limit (at a signal-to-noise ratio of 3). The sensor was applied to the determination of CAP in spiked sediment samples. In our perception, this electrocatalytic platform provided a useful tool for fast, portable, and sensitive analysis of chloramphenicol.
Graphical abstract A sensitive carbon fiber microsensor modified with Fe3O4 nanoparticles is found to display two cathodic peaks when detecting chloramphenicol at 100 mV·s?1 and at pH 7.0. The sensor was applied to the determination of chloramphenicol in sediment samples.
Graphite-like carbon nitride ? Fe3O4 magnetic nanocomposites were synthesized by a chemical co-precipitation method. The nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, FTIR spectroscopy, X-ray photoelectron spectroscopy and magnetization hysteresis loops. The nanocomposites exhibit enhanced peroxidase-like activity (compared to that of graphite-like carbon nitride or Fe3O4 NPs). More specifically, they are capable of catalyzing the oxidation of different peroxidase substrates (such as TMB, ABTS or OPD) by H2O2 to produce the typical color reactions (blue, green or orange). The nanocomposites retain their magnetic properties and can be separated by an external magnet. On the basis of these findings, a highly sensitive and selective method was applied to the determination of H2O2 and glucose (by using glucose oxidase). It was successfully applied to the determination of glucose in (spiked) human serum. Compared to other nanomaterial-based peroxidase mimetics, the one described here provides distinctly higher sensitivity for both H2O2 and glucose, with detection limits as low as 0.3 μM and 0.25 μM, respectively.
Graphical abstract The magnetic carbon nitride nanocomposite exhibits enhanced peroxidase-like activity that is much larger than that of graphite-like carbon nitride or Fe3O4 NPs alone. This finding was applied to design a highly sensitive and selective colorimetric assay for H2O2 and glucose.
A magnetic nanosorbent was prepared from Fe3O4 nanoparticles and polyacrylamide using a solvothermal process. Two functions are achieved simultaneously in this process: The first consists in the formation of a carbon layer around the Fe3O4 nanoparticles, and the second one in the functionalization with an amido group. This combination allows the protection of Fe3O4 nanoparticles from dissolution in acid medium during heavy metal adsorption. The adsorbent was characterized by SEM, TEM, EDS, FTIR, TGA, and in terms of surface area. Results showed the Fe3O4 nanoparticles to be embedded in a sheet of carbon with folded surfaces which is functionalized with amido groups. The nanosorbent was applied to the enrichment of Cr(III), Co(II), Cd(II), Zn(II) and Pb(II) via magnetic solid phase extraction (mag-SPE). The effects of pH value, eluent type and sample volume were optimized. The validation of the procedure was verified by the analysis of a wheat gluten certified reference material (8418). The limits of detection for the above ions range from 1 to 110 ng L?1. The relative standard deviations are <10%. The procedure was successfully applied to the enrichment of Cr(III), Co(II), Cd(II), Zn(II) and Pb(II) from various water and food samples.
Graphical abstract Schematic of a new magnetic nanosorbent synthesized from Fe3O4 nanoparticles and polyacrylamide using a solvothermal method. The sorbent was used for the enrichment of Cr(III), Co(II), Cd(II), Zn(II) and Pb(II) in water and food samples for their ICP-MS detection.
The authors describe a highly sensitive and selective photoelectrochemical (PEC) assay for mercury(II) ions. It is based on a dual signal amplification strategy. The first enhancement results from the surface plasmon resonance (SPR) of Au@Ag nanoparticles (NPs) absorbed on MoS2 nanosheets. Here, the injection of hot electrons of Au@Ag NPs into MoS2 nanosheets produces a strong photocurrent, while background signals are strongly reduced. The second enhancement results from the use of a thymine rich ct-DNA aptamer attached to the Au@Ag-MoS2 nanohybrid. The DNA specifically binds Hg(II) ions to form thymine-Hg(II)-thymine (T-Hg-T) complexes. This leads to the formation of a hairpin-shaped dsDNA structure. The use of a CdSe quantum dot label at the terminal end of the ct-DNA further facilitates electron–hole separation. The photocurrent of the detector is measured as a function of Hg(II) concentration at a bias voltage of 0.1 V and under irradiation of 430 nm light. Due to the two-fold amplification strategy presented here, the linear range extends from 10 pmol·L?1 to 100 nmol·L?1, with a detection limit of 5 pmol·L?1 (at S/N?=?3).
Graphical Abstract The injection of hot electrons of Au@Ag into MoS2 produces a strong photocurrent, and the formation of thymine-Hg(II)-thymine further facilitates electron–hole separation by CdSe. This dual signal amplification strategy is used to detect Hg(II) ions via a photoelectrochemical assay.
The paper describes a nonenzymatic amperometric H2O2 sensor that uses a nanocomposite consisting of Co3O4 nanoparticles (NPs) and mesoporous carbon nanofibers (Co3O4-MCNFs). The Co3O4 NPs were grown in situ on the MCNFs by a solvothermal procedure. The synergetic combination of the electrocatalytic activity of the Co3O4 NPs and the electrical conductivity of MCNFs as an immobilization matrix enhance the sensing ability of the hybrid nanostructure. The oxidation current, best measured at 0.2 V (vs. SCE) is linear in the 1 to 2580 μM H2O2 concentration range, with a 0.5 μM lower detection limit (at an S/N ratio of 3). The sensor is highly selective even in the presence of common electroactive interferents. It was applied to the determination of H2O2 in spiked milk samples.
Graphical abstract Schematic of the synthesis of a nanocomposite consisting of Co3O4 nanoparticles (NPs) and mesoporous carbon nanofibers (Co3O4-MCNFs) by a solvothermal procedure. It was used as electrocatalyst for direct oxidation of H2O2.
The author describes the preparation of a magnetic metal organic framework of type MOF-199 containing magnetite (Fe3O4) nanoparticles carrying covalently immobilized 4-(thiazolylazo) resorcinol (Fe3O4@TAR). This material is shown to represent a viable sorbent for separation and preconcentration of Cd(II), Pb(II), and Ni(II) ions. Box-Behnken design was applied to optimize the parameters affecting preconcentration. Following elution with 0.6 mol L?1 EDTA, the ions were quantified by FAAS. The capacity of the sorbent ranged between 185 and 210 mg g?1. The limits of detection are 0.15, 0.40, and 0.8 ng mL?1 for Cd(II), Ni(II), and Pb(II) ions, respectively. The relative standard deviations are <8.5 %. The method was successfully applied to the rapid extraction of trace amounts of these ions from sea food and agri food.
Graphical abstract (a) A schematic diagram of Fe3O4 functionalization by TAR (4-(thiazolylazo) resorcinol). (b) The schematic illustration of the magnetic metal organic framework-TAR nanocomposite. H3BTC: benzene-1,3,5-tricarboxylic acid; TEA: triethylamine; 3-CPS: 3-chloropropyl triethoxysilane.
Magnetic molecularly imprinted nanoparticles (MMIPs) with improved dispersity and an increased number of adsorption sites are described. Uniform silica layers were first deposited on the surface of Fe3O4 nanoparticles (Fe3O4 NPs) in order to improve the dispersity of magnetic nanoparticles. Then, 4-formylphenylboronic acid (FPBA) as functional monomer was immobilized on the magnetic carriers to improve the efficiency of template eluting and rebinding. A thin layer of polyaniline imprinted with horseradish peroxidase (HRP) as a model glycoprotein was then placed on the magnetic nanoparticles to enhance the dispersity of the resultant MMIPs. These exhibit high adsorption capacity (62 mg g?1), a satisfactory imprinting factor ( 3.78) and short adsorption equilibrium time (40 min) toward HRP, and the limit of detection is 18.7 μg L?1. This kind of MMIPs, therefore, is deemed being a useful tool for extracting low-abundance glycoproteins from even complex samples.
Graphical abstract Schematic of the preparation of magnetic molecular imprinted nanoparticles using Fe3O4 nanoparticles as carriers, 4-formylphenylboronic acid as functional monomer, aniline as cross linker and horseradish peroxidase as template. TEOS: tetraethyl orthosilicate; APTES: 3-aminopropyltriethoxysilane; FPBA: 4-formylphenylboronic acid; HRP: horseradish peroxidase.
Magnetic microspheres (Fe3O4) were coated with polydopamine (PDA) and loaded with the metal ions Ti(IV) and Nb(V) to give a material of type Fe3O4@PDA-Ti/Nb. It is shown to be useful for affinity chromatography and for enrichment of phosphopeptides from both standard protein solutions and real samples. For comparison, such microspheres loaded with single metal ions only (Fe3O4@PDA-Ti and Fe3O4@PDA-Nb) and their physical mixtures were also investigated under identical conditions. The binary metal ion-loaded magnetic microspheres display better enrichment efficiency than the single metal ion-loaded microspheres and their physical mixture. Both multiphosphopeptides and monophosphopeptides can be extracted. The Fe3O4@PDA-Ti/Nb microspheres exhibit ultra-high sensitivity (the lowest detection amount being 2 fmol) and selectivity at a low mass ratio such as in case of β-casein/BSA (1:1000).
Graphical abstract Magnetic microspheres (Fe3O4) were coated with polydopamine (PDA) and loaded with the metal ions Ti(IV) and Nb(V) to give a material of type Fe3O4@PDA-Ti/Nb. Results showed its great potential as an affinity probe in phosphoproteome research due to rapid magnetic separation of phosphopeptides, ultrahigh sensitivity and selectivity, and remarkable reusability.
The authors describe magnetite (Fe3O4) nanoparticles modified with 3-(N,N-diethylamino) propyltrimethoxysilane (Fe3O4-PSA NPs) for use as a sorbent for dispersive solid phase extraction of pesticide residues. The Fe3O4-PSA NPs were prepared by silanizing Fe3O4 NPs and modifying them with 3-(N,N-diethylamino) propyltrimethoxysilane. Field-emission scanning electron microscopy, FTIR and zeta potential measurements were employed to characterize the modified NPs. They were then used as an adsorbent to remove acidic interferences (such as malic acid and succinic acid), which are major interferences in LC-MS/MS analysis in causing ion suppression in the MS spectra of pesticides. In addition, graphitized carbon black (GCB) was used as an adsorbent to eliminate interferences by pigments. The use of Fe3O4-PSA NPs can replace time-consuming centrifugation as used in the so-called QuEChERS (quick, easy, cheap, effective, rugged and safe) method. This improvement is particularly significant in high-throughput analysis. Following the optimization of the quantities of Fe3O4-PSA NPs and GCB, the method was applied to the determination of 56 pesticides in (spiked) fruits (apple, kiwi, orange and pear) by ultra-HPLC-MS/MS. The analytical ranges typically extend from 1 to 200 ng∙mL−1, and recoveries range from 60.2 to 130 % at different concentrations of all four kinds of fruits. The LOQs for the pesticides are 10 ng∙kg−1, which makes the method a viable tool for pesticide monitoring in fruits.
Magnetite nanoparticles modified with 3-(N,N-diethylamino) propyltrimethoxysilane (Fe3O4-PSA NPs) are shown to be useful materials for removal of acidid interferents from sample matrices. Their use can replace time-consuming centrifugation as used in the traditional QuEChERS method.
The synthesis of rattle-type nanostructured Fe3O4@SnO2 is described along with their application to dispersive solid-phase extraction of trace amounts of mercury(II) ions prior to their determination by continuous-flow cold vapor atomic absorption spectrometry. The voids present in rattle-type structures make the material an effective substrate for adsorption of Hg(II), and also warrant high loading capacity. The unique morphology, large specific surface, magnetism property and the synergistic effect of magnetic cores and SnO2 shells render these magnetic nanorattles an attractive candidate for solid-phase extraction of heavy metal ions.The sorbent was characterized by transmission electron microscopy, scanning electron microscopy, FTIR, energy-dispersive X-ray spectroscopy and by the Brunnauer-Emmett-Teller technique. The effects of pH value, adsorption time, amount of sorbent, volume of sample solutions, concentration and volume of eluent on extraction efficiencies were evaluated. The calibration plot is linear in the 0.1 to 40 μg·L?1 concentration range, and the preconcentration factor is 49. The detection limit is 28 ng·L?1. The sorbent was applied to the analysis of (spiked) river and sea water samples. Recoveries ranged from 97.2 to 100.5%.
Graphical abstract A yolk-shell structure based on a Fe3O4 core and SnO2 shell was developed as an efficient MSPE sorbent. A middle silica layer was etched by alkaline solution. The resulting sorbent was utilized for preconcentration of mercury ions from aqueous media.
Diphenyl diselenide was immobilized on chitosan loaded with magnetite (Fe3O4) nanoparticles to give an efficient and cost-effective nanosorbent for the preconcentration of Pb(II), Cd(II), Ni(II) and Cu(II) ions by using effervescent salt-assisted dispersive magnetic micro solid-phase extraction (EA-DM-μSPE). The metal ions were desorbed from the sorbent with 3M nitric acid and then quantified via microflame AAS. The main parameters affecting the extraction were optimized using a one-at-a-time method. Under optimum condition, the limits of detection, linear dynamic ranges, and relative standard deviations (for n?=?3) are as following: Pb(II): 2.0 ng·mL?1; 6.3–900 ng·mL?1; 1.5%. Cd(II): 0.15 ng·mL?1; 0.7–85 ng·mL?1, 3.2%; Ni(II): 1.6 ng·mL?1,.6.0–600. ng·mL?1, 4.1%; Cu(II): 1.2 ng·mL?1, 3.0–300 ng·mL?1, 2.2%. The nanosorbent can be reused at least 4 times.
Graphical abstract Fe3O4-chitosan composite was modified with diphenyl diselenide as a sorbent for separation of metal ions by effervescent salt-assisted dispersive magnetic micro solid-phase extraction.
This review (with 144 refs.) focuses on the recent advances in the preparation and application of magnetic micro/nanoparticles. Specifically, it covers (a) methods for preparation (such as by coprecipitation, pyrolysis, hydrothermal, solvothermal, sol-gel, micro-emulsion, sonochemical, medium dispersing or emulsion polymerization methods), and (b) applications such as magnetic resonance imaging, magnetic separation of biomolecules (nucleic acids; proteins; cells), separation of metal ions and organic analytes, immobilization of enzymes, biological detection, magnetic catalysis and water treatment. Finally, the existing challenges and possible trends in the field are addressed.
Graphical abstract This review focuses on the recent advances in the preparation and application of magnetic micro/nano particles. Finally, the existed problems and possible trends in the field were discussed. a: Fe3O4@SiO2-PVAm: polyvinyl amine-coated Fe3O4@SiO2 b: CTS/MMT-Fe3O4 microsphere: chitosan/montmorillonite-Fe3O4 microsphere c: MTAMs: magnetic targeted antibiotic microspheres d: SM: the code of iron oxide-silica composite microspheres e: PSt: poly styrene f: gamma-PGA- PLA: poly(gamma-glutamic acid) and poly(lactide) g: poly(-MMA–DVB–GMA) microspheres: poly(methylmethacrylate–divinylbenzene–glycidylmethacrylate) microspheres h: AEAPS: N-(2-aminoethyl)-3-aminopropyltrimethoxysilane
Magnetite nanoparticles were surface-modified with mercaptoacetic acid (MAA), complexed with Zn(II), and then treated with the dual Schiff base (referred to as imine-based ligand; IBL; obtained by reaction of p-aminobenzoic acid and 2,3-butanedione) to give particles with an architecture of type Fe3O4@MAA@IBL. These are shown to be viable sorbents for magnetic solid phase extraction of organochlorine pesticides (OCPs) from seawater samples. Efficient extraction of the OCPs probably is due to lone pair-π, π-complexation and π-interactions. The sorbent was characterized by transmission electron microscopy, scanning electron microscopy, FT-IR and energy-dispersive X-ray spectroscopy. The effects of the volumes of sample, sorbent dosage and eluent, adsorption and desorption times, and the salinity of the sample on the extraction efficiencies were optimized. The OCPs (heptachlor, aldrin, dieldrin, p,p’-DDE and p,p’-DDT) were quantified by gas chromatography with microelectron capture detection. Under optimal conditions, the limit of detections range was between 1.0 and 1.9 ng L?1. The enrichment factors are between 84.1 and 99.9 %. The sorbent was applied to the rapid extraction of trace quantities of OCPs from seawater samples and gave good relative recoveries (78 to 108 %) and relative standard deviations (<8.3 %).
Graphical Abstract Fe3O4 nanoparticles were functionalized with mercaptoacetic acid. The carboxylate was coordinated with Zn(II) and the ligands were immobilized via coordination with Zn(II). The lone pair-π, π-complexation and π-interaction of modified magnetite nanoparticles made this sorbent effective for extraction of organochlorine pesticides.
The article describes a bienzyme visual system for aptamer-based assay of Hg(II) at nanomolar levels. The detection scheme is based on the finding that Hg(II) ions captured by aptamer-functionalized magnetic beads are capable of inhibiting the enzymatic activity of uricase and thus affect the formation of H2O2 and the blue product, i.e., oxidized tetramethylbenzidine. This strategy allows for a visual detection of Hg(II) at nanomolar levels without additional amplification procedure. Measuring the absorbance at 650 nm, the logarithmic calibration plot is linear in the concentration range of 0.5–50 nM and the limit of detection (LOD) is 0.15 nM. This is as low as the LOD obtained by atomic fluorescence spectrometry (AFS). The ions K+, Mg2+, Na+, Ca2+, Cu2+, Zn2+, Fe3+, Al3+, Co2+, AsO2?, Ni2+, Cd2+ and Pb2+ do not have a significant effect on color formation. The method was applied to the analysis of (spiked) river water, lake water, mineral water, tap water and certified reference water samples, and the results agreed well with those obtained by AFS or certified values, with recoveries ranging from 97% to 109%. The relative standard deviation for five parallel detections at a 10 nM Hg(II) level is 5.2%.
Graphical abstract A bienzyme-based visual aptasensor was fabricated for label-free detection of nanomolar Hg2+ in water samples without any amplification or enrichment procedure.
A highly sensitive electrochemical sensor is described for the determination of H2O2. It is based on based on the use of polyaniline that was generated in-situ and within 1 min on a glassy carbon electrode (GCE) with the aid of the Fe(II)/H2O2 system. Initially, a 2-dimensional composite was prepared from graphene oxide and polyamidoamine dendrimer through covalent interaction. It was employed as a carrier for Fe(II) ions. Then, the nanocomposite was drop-coated onto the surface of the GCE. When exposed to H2O2, the Fe(II) on the GCE is converted to Fe(III), and free hydroxy radicals are formed. The Fe(III) ions and the hydroxy radicals catalyze the oxidation of aniline to produce electroactive polyaniline on the GCE. The resulting sensor, best operated at a working potential as low as 50 mV (vs. SCE) which excludes interference by dissolved oxygen, has a linear response in the 500 nM to 2 mM H2O2 concentration range, and the detection limit is 180 nM. The sensor was successfully applied to the determination of H2O2 in spiked milk and fetal bovine serum samples.
Graphical abstract Schematic presentation of a sensitive electrochemical sensor employed for detection of H2O2 in sophisticated matrices by using graphene oxide-PAMAM dendrimer as initiator container and Fe2+/H2O2 system as signal enhancer.
An amino acid derived ionic liquid, Fe3O4 nanoparticles and graphene oxide (GO) were used to prepare a material for the magnetic solid phase extraction (MSPE) of the ions Al(III), Cr(III), Cu(II) and Pb(II). The material was characterized by Fourier transform infrared spectral (FT-IR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), magnetic analysis and isoelectric point (pI) analysis. It is shown to be a viable sorbent for the separation of these metal ions. Single factor experiments were carried out to optimize adsorption including pH values, ionic strength, temperature and solution volume. Following desorption with 0.1 M HCl, the ions were quantified by inductively coupled plasma optical emission spectrometry. Under the optimum conditions, the method provides a linear range from 10 to 170 μg· L?1 for Al(III); from 4.0 to 200 μg· L?1 for Cr(III); from 5.0 to 170 μg· L?1 for Cu(II); and from 5.0 to 200 μg· L?1 for Pb(II). The limits of detection (LOD) are 6.2 ng L?1 for Al(III); 1.6 ng L?1 for Cr(III); 0.52 ng L?1 for Cu(II); and 30 ng L?1 for Pb(II). Method performance was investigated by determination of these ions in (spiked) environmental water and gave recoveries in the range of 89.1%–117.8%.
Graphical abstract The graph shows that Al(III), Cr(III), Cu(II), Pb(II) are not adsorbed quantitatively by Fe3O4-SiO2. On the other hand, Cr(III) and Pb(II) are adsorbed quantitatively by Fe3O4-SiO2-GO while Al(III) and Cu(II) are not quantitatively retained. However, 3D–Fe3O4-SiO2-GO-AAIL adsorb all these 4 metal ions quantitatively.
