Selective aptamer conjugation to silver-coated magnetite nanoparticles for magnetic solid-phase extraction of trace amounts of Pb2+ ions

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection. First, silver-coated magnetite core–shell nanoparticles (Fe₃O₄@Ag MNPs) were synthesized by the chemical reduction of silver ions on the surface of magnetite nanoparticles. After that, the selective DNA aptamer against Pb²⁺ was conjugated on the surface of the synthesized nanoparticles to form aptamer-modified magnetic nanoparticles (Fe₃O₄@Ag-APT). The characterization of the prepared adsorbent was performed through SEM imaging, XRD, FT-IR, EDX, and DRS instruments. The influence of the various experimental parameters on the adsorption and desorption steps in MSPE was investigated via Taguchi experimental design to optimize different parameters. Under the optimized conditions, the Pb²⁺ calibration graph was linear in the range of 33–1000 μg L⁻¹. The relative standard deviation (RSD%) of the method for six replicates containing 100 μg L⁻¹ of Pb²⁺ ions was 0.34%. Furthermore, the limit of detection (LOD) and the limit of quantification (LOQ) were 10 μg L⁻¹ and 33.3 μg L⁻¹, respectively. Finally, the applicability of the proposed method was successfully confirmed by preconcentration and determination of trace amounts of Pb²⁺ ions in tap and seawater samples. We showed a proof of concept for Fe₃O₄@Ag-APT as an efficient bio-adsorbent, offering a promising strategy for the specific binding/removal of toxic heavy metal ions.

Herein, a novel aptamer-functionalized magnetic adsorbent was developed and combined with magnetic solid-phase extraction (MSPE) for the specific enrichment of Pb²⁺ ions prior to flame atomic absorption spectrometric detection.     

Novel magnetically separable anhydride-functionalized Fe3O4@SiO2@PEI-NTDA nanoparticles as effective adsorbents: synthesis,stability and recyclable adsorption performance for heavy metal ions

In this paper, a novel adsorbent, Fe₃O₄@SiO₂@PEI-NTDA, was first prepared by the immobilization of an amine and anhydride onto magnetic Fe₃O₄@SiO₂ nanoparticles with polyethylenimine (PEI) and 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTDA) for the removal of heavy metal ions from aqueous solutions. The structure of Fe₃O₄@SiO₂@PEI-NTDA was systematically investigated; the results confirmed that amine and anhydride groups were successfully covalently grafted onto the surface of Fe₃O₄@SiO₂, which showed a homogenous core–shell structure with three layers of about 300 nm diameter (Fe₃O₄ core: 200 nm, nSiO₂ layer: 20 nm, and PEI-NTDA layer: 20 nm). The adsorption performance of Fe₃O₄@SiO₂@PEI-NTDA NPs was evaluated for single Pb²⁺ and coexisting Cd²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ions in an aqueous solution in a batch system. The amine and anhydride groups may have a synergistic effect on Pb²⁺ removal through electrostatic interactions and chelation; Fe₃O₄@SiO₂@PEI-NTDA NPs exhibited preferable removal of Pb²⁺ with maximum adsorption capacity of 285.3 mg g⁻¹ for Pb²⁺ at a solution pH of 6.0, adsorbent dosage of 0.5 g L⁻¹, initial Pb²⁺ concentration of 200 mg L⁻¹ and contact time of 3 h. The adsorption mechanism conformed well to the Langmuir isotherm model, and the adsorption kinetic data were found to fit the pseudo-second order model. Fe₃O₄@SiO₂@PEI-NTDA NPs could be recovered easily from their dispersion by an external magnetic field and demonstrated good recyclability and reusability for at least 6 cycles with a high adsorption capacity above 204.5 mg g⁻¹. The magnetic adsorbents showed high stability with a weight loss below 0.65% in the acid leaching treatment by 2 M HCl solution for 144 h. This study indicates that Fe₃O₄@SiO₂@PEI-NTDA NPs are new promising adsorbents for the effective removal of Pb²⁺ in wastewater treatment.

A magnetically separable adsorbent, anhydride-functionalized Fe₃O₄@SiO₂@PEI-NTDA, was successfully constructed for removal of heavy metal ions from aqueous solution.     

Removal of arsenic(v) from aqueous solutions using sulfur-doped Fe3O4 nanoparticles

In this study, magnetic sulfur-doped Fe₃O₄ nanoparticles (Fe₃O₄:S NPs) were applied as adsorbents for the removal of As(v). Fe₃O₄:S NPs were fabricated by a two-step route, which included low-temperature mixing and high-temperature sintering. The as-prepared Fe₃O₄:S NPs could effectively remove As(v) under a wide pH range of 2–10 and presented a high As(v) adsorption capacity of 58.38 mg g⁻¹, which was much better than undoped Fe₃O₄ nanoparticles (20.24 mg g⁻¹). Adsorption experiments exhibited a pseudo-second-order model of adsorption kinetics and a Langmuir isotherm model of adsorption isotherms. Additionally, the coexisting ions such as NO₃⁻, SO₄²⁻, and CO₃²⁻ had no significant effect on As(v) adsorption and the adsorbent worked well in actual smelting wastewater. XPS and FTIR spectra of Fe₃O₄:S NPs before and after As(v) adsorption showed that Fe–OH groups played a significant role in the adsorption mechanisms. Moreover, the magnetic Fe₃O₄:S NPs adsorbents after adsorption could be rapidly separated from wastewater with an external magnetic field. Therefore, Fe₃O₄:S NPs could be an ideal candidate for the removal of As(v) from water.

Magnetic Fe₃O₄:S NPs presented a much better As(v) adsorption performance than undoped Fe₃O₄ NPs due to sulfur doping.     

Chitin/egg shell membrane@Fe3O4 nanocomposite hydrogel for efficient removal of Pb2+ from aqueous solution

The development of adsorbents by using the byproducts or waste from large-scale industrial and agricultural production is of great significance, and is considered to be an economic and efficient strategy to remove the heavy metals from polluted water. In this work, a novel chitin/EM@Fe₃O₄ nanocomposite hydrogel was obtained from a NaOH/urea aqueous system, where the proteins of egg shell membrane and Fe₃O₄ nanoparticles were chemically bonded to chitin polymer chains with the help of epichlorohydrin. Due to the existence of a large number of –NH₂, –OH, –CONH–, –COOH and hemiacetal groups, the adsorption efficiency for Pb²⁺ into the absorbent was dramatically enhanced. The experimental results revealed that the adsorption behavior strongly depends on various factors, such as initial pH, initial Pb²⁺ concentration, incubation temperature and contact time. The kinetic experiments indicated that the adsorption process for Pb²⁺ in water solution agreed with the pseudo-second-order kinetic equation. The film diffusion or chemical reaction is the rate limiting process in the initial adsorption stage, and the adsorption of Pb²⁺ into the nanocomposite hydrogel can well fit the Langmuir isotherm. Thermodynamic analysis demonstrated that such adsorption behaviors were dominated by an endothermic (ΔH° > 0) and spontaneous (ΔG° < 0) process.

A novel kind of chitin/EM@Fe₃O₄ nanocomposite hydrogel derived from the biowastes of egg shell membrane and chitin was successfully prepared for efficient removal of Pb²⁺ from wastewater solution.     

Novel easily separable core–shell Fe3O4/PVP/ZIF-8 nanostructure adsorbent: optimization of phosphorus removal from Fosfomycin pharmaceutical wastewater

A new easily separable core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent was synthesized and then examined for removal of Fosfomycin antibiotic from synthetic pharmaceutical wastewater. The removal process of Fosfomycin was expressed through testing the total phosphorus (TP). A response surface model (RSM) for Fosfomycin adsorption (as mg-P L⁻¹) was used by carrying out the experiments using a central composite design. The adsorption model showed that Fosfomycin adsorption is directly proportional to core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent dosage and time, and indirectly to initial Fosfomycin concentration. The removal increased by decreasing the pH to 2. The Fosfomycin removal was done at room temperature under an orbital agitation speed of 250 rpm. The adsorption capacity of core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent reached around 1200 mg-P g⁻¹, which is significantly higher than other MOF adsorbents reported in the literature. The maximum Langmuir adsorption capacity of the adsorbent for Fosfomycin was 126.58 mg g⁻¹ and Fosfomycin adsorption behavior followed the Freundlich isotherm (R² = 0.9505) in the present study. The kinetics was best fitted by the pseudo-second-order model (R² = 0.9764). The RSM model was used for the adsorption process in different target modes.

The synthesis of an easily separable novel core–shell Fe₃O₄/PVP/ZIF-8 nanostructure adsorbent and its usage for Fosfomycin pharmaceutical wastewater treatment.     

An ultra-sensitive T2-weighted MR contrast agent based on Gd3+ ion chelated Fe3O4 nanoparticles

An ultra-sensitive T₂-weighted MR imaging contrast agent was prepared based on Fe₃O₄ nanoparticles and Gd³⁺ ions (Fe₃O₄@Gd). Amino modified Fe₃O₄ nanoparticles were conjugated to diethylenetriamine pentaacetic acid, and finally coordinated with Gd³⁺ ions. The nanoparticles had a uniform morphology with a size of 100 nm and a Gd/Fe mass ratio of 1/110. The r₂ (transverse relaxivity) of the Fe₃O₄ nanoparticles increased from 131.89 mM⁻¹ s⁻¹ to 202.06 mM⁻¹ s⁻¹ after coordination with Gd³⁺ ions. MR measurements showed that the aqueous dispersion of Fe₃O₄@Gd nanoparticles had an obvious concentration-dependent negative contrast enhancement. Hepatoma cells were selected to test the cytotoxicity and MR imaging effect. The application of Fe₃O₄@Gd nanoparticles as contrast agents was also exploited in vivo for T₂-weighted MR imaging of rat livers. All the results showed the effectiveness of the nanoparticles in MR diagnosis.

An ultra-sensitive T₂-weighted MR imaging contrast agent was prepared based on Fe₃O₄ nanoparticles and Gd³⁺ ions (Fe₃O₄@Gd).     

Facile preparation of amidoxime-functionalized Fe3O4@SiO2-g-PAMAM-AO magnetic composites for enhanced adsorption of Pb(ii) and Ni(ii) from aqueous solution

In this paper, using amidoxime as a functional monomer, different generations of polyamidoxime dendrimer magnetic microspheres (Fe₃O₄@SiO₂-g-PAMAM-AO) were fabricated to adsorb Pb²⁺ and Ni²⁺ in aqueous solution. The magnetic adsorbents were characterized by FTIR, XRD, SEM, XPS, TEM, EDS, TGA and BET. The effects of different factors (such as solution pH, adsorption time, adsorption temperature, adsorbent dosage etc.) on adsorption were evaluated. Fe₃O₄@SiO₂-g-PAMAM-AO has a maximum Pb(ii) adsorption of 157.25 mg g⁻¹ (100 mg L⁻¹) at pH 5.5. Furthermore, Fe₃O₄@SiO₂-g-PAMAM-AO showed an excellent adsorption performance for the removal of Ni(ii) with a maximum adsorption capacity of 191.78 mg g⁻¹ (100 mg L⁻¹) at pH 8.0. The sorption isotherm data fitted the Freundlich isotherm model well. Adsorption kinetics analysis showed that it was best described by the pseudo-second-order rate model. Desorption experiment results showed that the adsorbent can be reused in the adsorption–desorption cycles.

In this paper, using amidoxime as a functional monomer, different generations of polyamidoxime dendrimer magnetic microspheres (Fe₃O₄@SiO₂-g-PAMAM-AO) were fabricated to adsorb Pb²⁺ and Ni²⁺ in aqueous solution.     

MoS42− intercalated NiFeTi LDH as an efficient and selective adsorbent for elimination of heavy metals

The enormous increase of heavy metal pollution has led to a rise in demand for synthesizing efficient and stable adsorbents for its treatment. Therefore, we have designed a novel adsorbent by introducing (MoS₄)²⁻ moieties within the layers of NiFeTi LDH-NO₃, via an ion exchange mechanism, as a stable and efficient adsorbent to deal with the increasing water pollution due to heavy metals. Characterization techniques such as XRD, FTIR, TGA, SEM, TEM, and Raman spectroscopy were used to confirm the formation of (MoS₄)²⁻ intercalated NiFeTi LDH and structural changes after the adsorption process. The efficiency of the material was tested with six heavy metal ions, among which it was found to be effective for toxic Pb²⁺ and Ag⁺ ions. When selectivity was studied with all six of the metal ions copresent in one solution, the material showed greater selectivity for Pb²⁺ and Ag⁺ ions with the selectivity order of Ni²⁺ < Cu²⁺ < Zn²⁺ < Fe³⁺ < Pb²⁺ < Ag⁺, with great adsorption capacities of 653 mg g⁻¹ for Pb²⁺ and 856 mg g⁻¹ for Ag⁺ metal ions. Further, the kinetics adsorption study for both the metal ions had a great correlation with the pseudo-second-order model and supported the chemisorption process via the formation of M–S bonding. The adsorption process obeyed the Langmuir model. Therefore, the MoS₄-LDH material could be a promising adsorbent for the removal of heavy metals.

Elimination of the heavy metals by using the MoS₄-LDH adsorbent.     

A luminescent Cd(ii) coordination polymer as a multi-responsive fluorescent sensor for Zn2+, Fe3+ and Cr2O72− in water with fluorescence enhancement or quenching

A luminescent Cd(ii) coordination polymer, namely {[Cd(btic)(phen)]·0.5H₂O}_n (CP-1) (H₂btic = 5-(2-benzothiazolyl)isophthalic acid, phen = 1,10-phenanthroline), was constructed through the mixed-ligand method under solvothermal conditions. CP-1 manifests a chain structure decorated with uncoordinated Lewis basic N and S donors. CP-1 exhibits high sensing towards Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions with fluorescence enhancement or quenching. CP-1 exhibited a fluorescence enhancement for Zn²⁺ ions through weak binding to S and N atoms, and a fluorescence quenching for Fe³⁺ and Cr₂O₇²⁻ ions by an energy transfer process. The binding constants were calculated as 1.812 × 10⁴ mol⁻¹ for Zn²⁺, 4.959 × 10⁴ mol⁻¹ for Fe³⁺ and 1.793 × 10⁴ mol⁻¹ for Cr₂O₇²⁻. This study shows CP-1 as a rare multi-responsive sensor material for the efficient detection of Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.

A luminescent Cd(ii) coordination polymer can act as a multi-responsive sensor for efficiently detecting Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.     

Acetylacetone functionalized magnetic carbon microspheres for the highly-efficient adsorption of heavy metal ions from aqueous solutions

Herein, Acac-C@Fe₃O₄, a magnetic carbon (C@Fe₃O₄) modified with acetylacetone (Acac), was first prepared and used as a solid-phase adsorbent for adsorbing some heavy metal ions from aqueous solution. The adsorbent was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and BET studies. Some parameters affecting the adsorption and desorption processes were studied in Pb²⁺ solution, including sample pH, contact time, initial concentration, type and connection of the desorption solution. Absorption results showed that removal of Pb²⁺ was 100% under optimal conditions at an initial concentration of 10.0 mg L⁻¹. The adsorption mechanism conformed well to a pseudo-second order kinetic model. The adsorption capacity of the sorbent also showed promising results with Hg²⁺, Cr³⁺, Fe²⁺, Cd²⁺, Mn²⁺, Zn²⁺, Cu²⁺ and Pb²⁺, where maximum adsorption capacities reached 98.0, 151.2, 188.9, 202.2, 286.3, 297.2, 305.1 and 345.3 mg g⁻¹, respectively. The Acac-C@Fe₃O₄ microsphere material was successfully applied to the adsorption of heavy metal ions in aqueous solution.

Herein, Acac-C@Fe₃O₄, a magnetic carbon (C@Fe₃O₄) modified with acetylacetone (Acac), was first prepared and used as a solid-phase adsorbent for adsorbing some heavy metal ions from aqueous solution.     

CuO and CeO2 assisted Fe2O3/attapulgite catalyst for heterogeneous Fenton-like oxidation of methylene blue

In this paper, CuO and CeO₂ were screened as co-catalyst components for Fe₂O₃/attapulgite (ATP) catalyst, and three new catalysts (CuO–Fe₂O₃/ATP, CeO₂–Fe₂O₃/ATP and CuO–CeO₂–Fe₂O₃/ATP) were prepared for degradation of methylene blue (MB). The three catalysts'' characteristics were determined by BET, XRD, FT-IR, SEM and XPS. MB degradation in different systems and at different pH values was also studied. Under the conditions of H₂O₂ concentration of 4.9 mmol L⁻¹, catalyst dosage of 5 g L⁻¹, pH of 5, reaction temperature of 60 °C and MB initial concentration of 100 mg L⁻¹, the as-synthesized catalysts showed much greater reaction rate and degradation efficiency of MB than Fe₂O₃/ATP catalyst. In addition, the reusability of the as-prepared composites was evaluated. The intermediate products of MB degradation were identified by LC-MS and the possible degradation process of MB was put forward.

A novel heterogeneous catalyst CuO–CeO₂–Fe₂O₃/ATP was synthesized for MB degradation and the catalytic mechanism was put forward.     

Microwave assisted green synthesis of Fe2O3/biochar for ultrasonic removal of nonsteroidal anti-inflammatory pharmaceuticals

Iron oxide/biochar (Fe₂O₃/biochar) was prepared by green synthesis via a microwave to evaluate ultrasound-assisted adsorption capacity of Nonsteroidal Anti-inflammatory Drugs (NSAIDs) (salicylic acid, naproxen, and ketoprofen) from the water. Several techniques of characterization, including, Fourier transform infrared spectrometry, scanning electron microscopy, EDS analysis, N₂ adsorption–desorption, X-ray diffraction, and Raman spectrometry were applied. The adsorption of NSAIDs onto Fe₂O₃/biochar was performed using an ultrasonic bath. The effects of batch adsorption under various experimental parameters such as contact time (0–120 min), initial concentration (10–500 mg L⁻¹) and pH (2–12) were tested. The obtained Fe₂O₃/biochar specific surface area, mesopore volume/micropore volume, and pores size were equal to 786 m² g⁻¹, 0.409 cm³ g⁻¹, and 1.534 cm³ g⁻¹, respectively. The pseudo-second-order model could describe better all NSAID adsorptions onto Fe₂O₃/biochar. The Langmuir model agreed well with the NSAID adsorptions and the maximum adsorption capacities reached 683 mg g⁻¹, 533 mg g⁻¹ and 444 mg g⁻¹ for salicylic acid, naproxen, and ketoprofen, respectively. Fe₂O₃/biochar can be used as an excellent adsorbent for the treatment of NSAIDs in water.

Here, we have developed a simple and green microwave synthesis of iron oxide/biochar for the removal of new emergent pharmaceutical pollutants.     

Super rapid removal of copper,cadmium and lead ions from water by NTA-silica gel

Copper (Cu²⁺), cadmium (Cd²⁺) and lead ions (Pb²⁺) are toxic to human beings and other organisms. In this study, a silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple amidation procedure for the removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water. The NTA-silica gels showed rapid removal performances for the three metal ions (Pb²⁺ (<2 min), Cu²⁺ and Cd²⁺ (<20 min)) with relatively high adsorption capacities (63.5, 53.14 and 76.22 mg g⁻¹ for Cu²⁺, Cd²⁺ and Pb²⁺, respectively). At the same concentration of 20 mg L⁻¹, the removal efficiencies of the three metals by the adsorbent ranged from 96% to 99%. The Freundlich and Langmuir models were utilized to fit the adsorption isotherms. The adsorption kinetics for the three metal ions was pseudo-second-order kinetics. The removal performance of the NTA-silica gels increased in a wide pH range (2–9) and maintained in the presence of competitive metal ions (Na⁺, Mg²⁺, Ca²⁺ and Al³⁺) with different concentrations. In addition, the NTA-silica gels were easily regenerated (washed with 1% HNO₃) and reused for 5 cycles with high adsorption capacity. This study indicates that the NTA-silica gel is a reusable adsorbent for the rapid, convenient, and efficient removal of Cu²⁺, Cd²⁺, and Pb²⁺ from contaminated aquatic environments.

A silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple method for the super rapid removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water.     

Influence of Cl− ions on anodic polarization behaviour of API X80 steel in high potential/current density conditions in Na2SO4 solution

Pipeline steel has considerable risk of corrosion in the high voltage direct current interference cases. Thus, under high potential/current density conditions, the anodic polarization behaviour of X80 steel in Na₂SO₄ solution and the influence of Cl⁻ ions were investigated using reversed potentiodynamic polarization, the current interrupt method, galvanostatic polarization, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the Na₂SO₄ solution free of Cl⁻ ions, steel was passivated above 0.120 A cm⁻² and the potential increased from −0.32 V to 1.43 V. The passive film was composed of Fe₃O₄, γ-Fe₂O₃, and FeOOH. The addition of Cl⁻ ions observably influenced the passivation by attacking the passivate film. Low concentration of Cl⁻ ions (<5 mg L⁻¹ NaCl) could set higher demands of current density to achieve passivation and increase the requirement of potential to maintain passivation. A high concentration of Cl⁻ ions (>5 mg L⁻¹ NaCl) completely prevented passivation, showing strong corrosiveness. Thus, the X80 steel was corroded even under high-current-density conditions. The corrosion products were mainly composed of Fe₃O₄, α-Fe₂O₃, and FeOOH.

X80 steel gets passivated in high potential/current density conditions in Na₂SO₄ solution. Low concentration of Cl⁻ ions weakens the passivation. High concentration of Cl⁻ ions totally prevents the passivation.     

Magnetic solid-phase extraction using a mixture of two types of nanoparticles followed by gas chromatography-mass spectrometry for the determination of six phthalic acid esters in various water samples

Two types of magnetic microspheres (Fe₃O₄@MIL-100 and Fe₃O₄@SiO₂@polythiophene) were prepared and characterized as mixed sorbents for magnetic solid-phase extraction (MSPE) of six phthalic acid esters (PAEs), including dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), benzyl butyl phthalate (BBP), di-2-ethylhexyl phthalate (DEHP), and di-n-octyl phthalate (DnOP) from water samples prior to gas chromatography-mass spectrometry (GC-MS) analysis. The synthetic magnetic nanocomposites exhibited good repeatability and chemical stability, and improved extraction efficiency for the tested PAEs. The mixture of the two types of nanoparticles substantially improved the extraction efficiency of both DMP and DEP. The key parameters affecting the extraction efficiency, such as the type and the amount of sorbent, eluent (desorption solvent), adsorption and desorption time, pH of sample solution, and sample volume, were investigated and optimized, respectively. Under optimized conditions, the developed method showed satisfactory linearity in the range of 5–5000 μg L⁻¹ with coefficients of determination (R²) > 0.9935. The method detection limits (MDLs) and limits of quantitation (LOQs) were between 0.35–0.91 μg L⁻¹ and 1.1–2.9 μg L⁻¹, respectively. At three fortification levels (1.0, 10.0, and 50.0 μg L⁻¹), the mean recoveries ranged from 76.9–109.1% with favorable relative standard deviations (RSDs) < 9%. The feasibility of the method was evaluated by analysis of water samples from various sources (tap, drinking, and mineral water). The results show that the developed method is suitable for determination of trace level PAEs in water samples.

A mixture of Fe₃O₄@MIL-100 and Fe₃O₄@SiO₂@polythiophene nanoparticles exhibit high extraction efficiency for PAEs in water.     

Experimental study on the treatment of acid mine drainage by modified corncob fixed SRB sludge particles

In view of the characteristics of high content of SO₄²⁻, Fe²⁺ and Mn²⁺ in acid mine drainage and low pH value, based on the microbial immobilization technology, the single factor test and the orthogonal test were set respectively to determine the optimum alkaline H₂O₂ modification conditions for corncob. Then combining with sulfate reducing bacteria sludge, the modified corncob immobilized SRB sludge particles were prepared to treat acid mine drainage. On this basis, three dynamic column test models, including Column 1 without corncob particles, Column 2 with unmodified corncob particles, and Column 3 with modified corncob particles, were constructed. Through dynamic experiments, the three dynamic columns were compared to study the efficacy of AMD and their ability to resist changes in pollution load. The results of the orthogonal experiment showed that: when the corncob modified time was 24 h, the concentration of NaOH was 6% and the concentration of H₂O₂ was 1.5%, the prepared immobilized particles performed best. The results of the dynamic test showed that the treatment effect of Column 3 on AMD was better than that of Column 1 and 2. In the dynamic tests before and after the increase of pollution load, the highest removal percentages of SO₄²⁻, Mn²⁺, Fe²⁺ in Column 3 were 72.65%, 56.72%, 62.47% and 62.58%, 30.07%, 46.87% respectively, the average COD emission was 234 mg L⁻¹ and 102.75 mg L⁻¹, the effluent pH value was 6.96 and 6.65. In the dynamic tests before and after the increase of pollution load, the highest removal percentages of SO₄²⁻, Mn²⁺, Fe²⁺ in Column 2 were 52.94%, 46.93%, 72.55% and 48.92%, 26.43%, 43.23% respectively, the average COD emission was 508.14 mg L⁻¹ and 152.88 mg L⁻¹, the effluent pH value was 6.56 and 6.36. The high COD value of Column 2 is due to the organic matter leakage and poor metabolic activity of SRB contained in immobilized particles. Therefore, it indicated that Column 3 could better treat pollutants and resist changes of pollution load.

A cost-effective system for acid mine drainage removal was developed with the key role of alkaline H₂O₂ modified corncob and sulfate reducing bacteria.     

Adsorption mechanism of polyethyleneimine modified magnetic core–shell Fe3O4@SiO2 nanoparticles for anionic dye removal

In this paper, polyethyleneimine modified magnetic core–shell Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂/PEI) were innovatively synthesized and investigated using various techniques such as TEM, TGA, FT-IR, XRD, VSM and XPS. The adsorption performance based on the removal of the anionic dyes Methyl orange and Congo red from aqueous solution was studied systematically. The results showed that the adsorption rate of anionic dyes MO and CR increased rapidly then decreased gradually as the pH increased, the adsorption capacity of Fe₃O₄@SiO₂/PEI for MO was better than that for CR, and the maximum adsorption capacity for MO and CR was 231.0 mg g⁻¹ at pH 4 and 134.6 mg g⁻¹ at pH 6, respectively. The equilibrium adsorption capacities for MO and CR increased rapidly in the initial 40 min, and reached equilibrium in approximately 180 min, while the adsorption capacity for MB was relative low even negligible, demonstrating the strong adsorptive affinity of Fe₃O₄@SiO₂/PEI toward anionic compounds. Both of the adsorption processes followed the pseudo-second-order kinetics model and the Freundlich isotherm model. The mechanism of adsorption was mainly related to electrostatic attraction and the number of active sites occupied by anionic dyes. This study provides valuable guidance and is an effective method for the removal of anionic dyes from aquatic environments.

In this paper, polyethyleneimine modified magnetic core–shell Fe₃O₄@SiO₂ nanoparticles (Fe₃O₄@SiO₂/PEI) were innovatively synthesized and investigated using various techniques such as TEM, TGA, FT-IR, XRD, VSM and XPS.     

Unusual semiconductor–metal–semiconductor transitions in magnetite Fe3O4 nanoparticles

Magnetite (Fe₃O₄) nanoparticles were successfully prepared by a co-precipitation method. Rietveld refinement on the X-ray diffraction pattern confirmed the development of a single-phase cubic spinel structure with space group Fd$\bar{3}$m. However, ⁵⁷Fe Mössbauer spectroscopy suggested the presence of Fe³⁺ and Fe^2.5+ (mixed Fe³⁺ and Fe²⁺) ions at the tetrahedral and octahedral sites of the inverse spinel structure, respectively. Impedance spectroscopy measurements showed a discontinues variation in the temperature dependence of the sample''s resistive behavior, indicating the appearance of semiconductor–metal–semiconductor like transitions between the temperature range of 293 and 373 K. A similar dual transition was also observed from the dielectric and conductivity measurements around the same temperature regions. The observed unusual transition is explained in term of the competitive effects among the hopping of localized/delocalized and short-range/long-range charge carriers present in the sample. Moreover, the prepared sample exhibits colossal dielectric permittivity (∼10⁶), reduced tangent loss (∼0.2) and moderate conductivity (>10⁻⁶ S cm⁻¹) values, making Fe₃O₄ nanoparticles a potential candidate for electromagnetic absorbing materials.

Herein, we report the existence of a novel semiconductor–metal–semiconductor type transition in Fe₃O₄ nanoparticles by employing impedance spectroscopy techniques.     

Metal (Cd,Cr, Ni,Pb) removal from environmentally relevant waters using polyvinylpyrrolidone-coated magnetite nanoparticles

Water pollution is a major global challenge given the increasing growth in industry and human population, and certain metals can be highly toxic and contribute to this significantly. In this study, polyvinylpyrrolidone-coated magnetic nanoparticles (PVP–Fe₃O₄ NPs) were used to remove metals (Cd, Cr, Ni, and Pb) from synthetic soft water and sea water in the presence and absence of fulvic acid. Nanoparticle (NP) suspensions were added to water media at a range of metal concentrations (0.1–100 mg L⁻¹). Removal at different time points (1.5, 3, 6, 12, 24 hours) was also evaluated. Results showed that 167 mg L⁻¹ PVP–Fe₃O₄ NPs could remove nearly 100% of four metals at 0.1 mg L⁻¹ and more than 80% at 1 mg L⁻¹. The removal decreased as the initial metal concentration increased, although essentially 100% of the Pb was removed under all conditions. The kinetic adsorption fitted well to the pseudo-second-order model and in general, the majority of metal adsorption occurred within the first 1.5 hours. These NPs are a reliable method to remove metals under a wide range of environmentally relevant conditions. Our previous research showed the NPs effectively removed oil from waters, so these NPs offer the possibility of combined in situ remediation of oil and metals.

PVP–Fe₃O₄ NPs synthesized with no organic solvents, low toxicity reactants and low temperature/energy requirements could remove Cd, Cr, Ni, Pb efficiently in the different synthetic water media under environmentally relevant conditions.     

Computer-aided design of magnetic molecularly imprinted polymer nanoparticles for solid-phase extraction and determination of levetiracetam in human plasma

Analytical methods should be accurate and specific to measure plasma drug concentration. Nevertheless, current sample preparation techniques suffer from limitations, including matrix interference and intensive sample preparation. In this study, a novel technique was proposed for the synthesis of a molecularly imprinted polymer (MIP) on magnetic Fe₃O₄ nanoparticles (NPs) with uniform core–shell structure. The Fe₃O₄@MIPs NPs were then applied to separate and enrich an antiepileptic drug, levetiracetam, from human plasma. A computational approach was developed to screen the functional monomers and polymerization solvents to provide a suitable design for the synthesized MIP. Different analysis techniques and re-binding experiments were performed to characterize the Fe₃O₄@MIP NPs, as well as to identify optimal conditions for the extraction process. Adsorption isotherms were best fitted to the Langmuir model and adsorption kinetics were modeled with pseudo-second-order kinetics. The Fe₃O₄@MIP NPs showed reasonable adsorption capacity and improved imprinting efficiency. A validated colorimetric assay was introduced as a comparable method to a validated HPLC assay for the quantitation of levetiracetam in plasma in the range of 10–80 μg mL⁻¹ after extraction. The results from the HPLC and colorimetric assays showed good precision (between 1.08% and 9.87%) and recoveries (between 94% and 106%) using the Fe₃O₄@MIP NPs. The limit of detection and limit of quantification were estimated to be 2.58 μg mL⁻¹ and 7.81 μg mL⁻¹, respectively for HPLC assay and 2.32 μg mL⁻¹ and 7.02 μg mL⁻¹, respectively for colorimetric assay. It is believed that synthesized Fe₃O₄@MIP NPs as a sample clean-up technique combined with the proposed assays can be used for determination of levetiracetam in plasma.

A novel molecularly imprinted polymer on Fe₃O₄ nanoparticles was applied to extract antiepileptic drug; levetiracetam from plasma for TDM purposes.