Digital image determination of copper in food and water after preconcentration and magnetic tip separation for in-cavity desorption/color development

A new analytical method for measuring copper in food and water was developed and validated, employing a solid-phase extraction (SPE) technique combined with digital-image-based (DIB) detection. A novel magnetic adsorbent of zinc ferrite/Citrullus colocynthis biochar (ZF@C.BC) was used to preconcentrate copper. A magnetic tip was used to separate the copper-loaded adsorbent from the extraction medium and to dispense it to the DIB plate. In-situ desorption and development of the spot color with iodide-starch reagent were carried out, and a digital image of the developed spots was captured using a smartphone and processed using ImageJ software. The copper adsorption capacity was 91.3 mg g-1. Desorption was effected using a 0.3 mol L-1 hydrochloric acid. The preconcentration factor was 300, the limit of detection was 4.8 μg L-1, the linearity was 16-600 μg L-1 and the sample throughput was 12 h-1. The developed approach was validated by analyzing food and water samples, confirming recoveries ≥ 91 % and 88 %, respectively, with RSD ≤ 8.4 %, n = 3.

Vortex-blending matrix solid-phase dispersion and UPLC-Q-TOF/MS were proposed to extract and examine the urushiols from Toxicodendron vernicifluum bark

Toxicodendron vernicifluum bark has been used for many years as a component in foods and as a traditional herbal medication. Unfortunately, the presence of urushiols, which induce allergies, limits its application. This study used a vortex-blending matrix solid-phase dispersion microextraction technique to extract urushiols from Toxicodendron vernicifluum bark. HPLC was used to evaluate the amounts of the extracted urushiols (15:0, 15:1, 15:2, and 15:3). The modified magnetic adsorbent was prepared through an in situ coprecipitation method and characterized using a variety of techniques. The optimized extraction conditions are as follows: using magnetic Zeolite Socony Mobil-Five as an adsorbent, a 1:2 sample/adsorbent ratio, 2.5 min of vortex-blending time, 4 mL of 0.1% (V/V) trifluoroacetic acid-methanol as the elution solvent and 8 min of ultrasound time. There was good linearity and high repeatability in the method. Furthermore, the limits of detection for the urushiols ranged from 0.20 to 0.50 μg/mL. Under the optimized conditions, 50 compounds were identified by ultra high performance liquid chromatography and quadrupole time-of-flight mass spectrometry. These compounds included 8 phenolic acids, 9 monomeric urushiols, 11 urushiol dimers, 10 other components, and 11 flavonoids. The suggested approach, which has the advantages of few stages and high extraction efficiency over existing extraction procedures, is a potentially useful method for obtaining and evaluating urushiols in raw materials or extracts.

MnFe2O4-NH2-HKUST-1, MOF magnetic composite, as a novel sorbent for efficient dye removal: fabrication, characterization and isotherm studies

Dye in industrial wastewater is one of the most serious environmental concerns due to its potentially harmful effects on human health. Many industrial dyes are carcinogenic, toxic and teratogenic. Removal and recovery of hazardous dyes from the effluents requires efficient adsorbents. In this study, magnetic adsorbent MnFe2O4-NH2-HKUST-1 was synthesized to remove methylene blue and crystal violet dyes from aqueous solutions. The synthesized adsorbent was characterized using FTIR, XRD, BET, VSM, SEM, TGA and Zeta potential techniques. The effect of different parameters such as pH, contact time, and adsorbent dosage on the removal of dyes was investigated. The dye adsorption process was investigated by UV-Vis spectrophotometry. The maximum adsorbent capacity was obtained as 149.25 mg/g for methylene blue and 135.13 mg/g for crystal violet. The adsorption equilibrium isotherm and kinetic models were plotted and results showed that the adsorption process for both dyes is a collection of physical and chemical adsorption based on langmuir and freundlich isotherm models, and follows the pseudo-second-order adsorption kinetics. This study shows that magnetic adsorbent MnFe2O4-NH2-HKUST-1 has a good potential for removal of methylene blue and crystal violet dyes from water in a short time (5 min) and it is easily separated from the solution by a magnetic field due to its magnetic property.

Functional upcycling of waste PET plastic to the hybrid magnetic microparticles adsorbent for cesium removal

Accumulation of mismanaged plastic in the environment and the appearance of emerging plastic-derived pollutants such as microplastics strongly demand technologies for waste plastic utilization. In this study, polyethylene terephthalate (PET) from waste plastic bottles was directly utilized to prepare a matrix of an adsorbent for cesium (Cs+) removal. The organic matrix of PET-derived oligomers obtained by aminolysis depolymerization was impregnated with bentonite clay and magnetite nanoparticles (Fe3O4 NPs), playing the roles as a major adsorptive medium for Cs+ removal and as a functional component to primarily provide efficient separation of the hybrid adsorbent from aqueous system, respectively. The obtained hybrid composite microparticles were next tested as an adsorbent for the removal of Cs+ cation from aqueous solutions. The adsorption process was characterized by fast kinetics reaching ca. 60% of the equilibrium adsorption capacity within 5 min and the maximum adsorption capacity toward Cs+ was found to be 26.8 mg/g. The adsorption process was primarily dominated by the cationic exchange in bentonite, which was not significantly affected by the admixture of the competing mono- and divalent cations (Na+, K+, and Mg2+). The proposed approach here exploits the sustainable utilization scenario of plastic waste-derived material to template complex multifunctional nanocomposites that can find applications for pollution cleaning and environmental remediation.

Magnetic hierarchical titanium ferrocyanide for the highly efficient and selective removal of radioactive cesium from water

Selective adsorption is the most suitable technique for eliminating trace amounts of 137Cs from various volumes of 137Cs-contaminated water, including seawater. Although various metal ferrocyanide (MFC)-functionalized magnetic adsorbents have been developed for the selective removal of 137Cs and magnetic recovery of adsorbents, their adsorption capacity for Cs remains low. Here, magnetic hierarchical titanium ferrocyanide (mh-TiFC) was synthesized for the first time for enhanced Cs adsorption. Hierarchical TiFC, comprising 2-dimensional TiFC flakes, was synthesized on SiO2-coated magnetic Fe3O4 particles using a sacrificial TiO2 shell as a source of Ti4+ via a reaction with ferrocyanide under acidic conditions. The resultant mh-TiFC exhibited the highest maximum adsorption capacity (434.8 mg g-1) and enhanced Cs selectivity with an excellent Kd value (6,850,000 mL g-1) compared to those of previously reported magnetic Cs adsorbents. This enhancement was attributed to the hierarchical structure, which reduced intracrystalline diffusion and increased the surface area available for direct Cs adsorption. Additionally, mh-TiFC (0.1 g L-1) demonstrated an excellent removal efficiency of 137Cs exceeding 99.85% for groundwater and seawater containing approximately 22 ppt 137Cs. Therefore, mh-TiFC offers promising applications for the treatment of 137Cs-contaminated water.

Application of novel adsorbents synthesized with polypyrrole in magnetic solid-phase extraction of fungicides from fresh juice and environmental water

In this work, a magnetic adsorption material based on a metal-organic framework (Fe3O4@PPy@MIL-53(Fe)) was designed and prepared, as well as used as an adsorbent for the extraction of fungicides from fresh juice and environmental water. The material was subjected to a series of characterization analyses, which showed that the material has good potential for application as an adsorbent. The main parameters such as adsorbent dosage, adsorption time, elution time, pH value, and elution solvent which could affect the experiment results were optimized. Under optimal conditions, the method exhibited linearity (R2 ≥ 0.9994) in the concentration range 10-1000 µg/L for three triazole fungicides, and LOD value ranged from 2.1 µg/L to 2.9 µg/L. In addition, the established method was applied to real samples of three fruit juices and two ambient waters, and satisfactory recoveries in the range of 78.6%-105.4% and RSDs of ≤ 5.7% were obtained.

Green magnetic carbon/alginate biocomposite beads from iron scrap waste for efficient removal of textile dye and heavy metal

The circular economy can help enhance the value of industrial waste and remediate the environment. This study considers the application of iron scrap from steel production as a free resource to produce magnetic adsorbent beads to remove methylene blue dye and lead (II) ions from wastewater. Composite beads were prepared by incorporating iron scrap and activated carbon into a calcium alginate gel using a simple 'mix and drop' synthesis. The optimized magnetic beads were stable and offered a large specific surface area. The maximum adsorption capacity of the adsorbent, calculated from the Langmuir isotherm model, was 476.19 mg g-1 for methylene blue and 163.93 mg g-1 for lead (II) ions. This study places emphasis upon the zero-waste principle and employs a scalable synthetic approach for the conversion of waste iron scrap into an adsorbent material capable of delivering significant environmental benefits.

Eco-friendly thermosensitive magnetic-molecularly-imprinted polymer adsorbent in dispersive solid-phase microextraction for gas chromatographic determination of organophosphorus pesticides in fruit samples

A thermosensitive magnetic-molecularly-imprinted polymer (TMMIP) was successfully prepared in an aqueous medium. The TMMIP was applied as an effective adsorbent in dispersive solid-phase microextraction for the selective enrichment of five organophosphorus pesticides (OPPs; diazinon, fenitrothion, fenthion, parathion-ethyl, and ethion) before analysis by gas chromatography. The polymerization was performed using mixed-valence iron hydroxide nanoparticles as the magnetic support, N-isopropyl acrylamide as the thermosensitive monomer, ethion as the template, and methacrylic acid as the functional monomer. The adsorption and desorption mechanisms of OPPs depend on their interactions with the adsorbents and solution temperature. Our methodology provides good linearity (0.50-2000 µgL-1), with a correlation determination of R2 > 0.9980, low limit of detection (0.25-0.50 µgL-1), low limit of quantitation (0.50-1.50 μg L-1), and high precision (%RSD < 7%). The developed method demonstrates excellent applicability for accurately and efficiently determining OPP residuals in fruit and vegetable samples with good recoveries (93-117%).

Magnetic hydrogel based on xylan, poly (acrylic acid), and maghemite as adsorbent material for methylene blue adsorption: experimental design, kinetic, and isotherm

A magnetic hydrogel based on xylan (X), poly (acrylic acid), and maghemite (γ-Fe2O3) named HXA-Fe2O3 was synthesized, characterized, and applied as an alternative material to remove methylene blue (MB) from aqueous media by adsorption. Maghemite was synthesized by coprecipitation method and later incorporated in the hydrogel matrix synthesized by free radical polymerization. The characterization studies included FTIR, DSC, XRD, VSM, Zeta Potential, TGA, SEM, TEM, and N2 adsorption isotherms (BET). The physicochemical characterization results confirmed the intended synthesis and showed the compositional, thermal, structural, morphological, textural, and magnetic profile of the materials. The adsorption studies included experimental design, kinetic, and isotherm. A full factorial design was employed considering the factors adsorbent dosage (g L-1), pH, and ionic strength (mmol L-1 of NaCl) for adsorption capacity and removal percentage responses. As ionic strength was not significant, a Doehlert design was employed with adsorbent dosage and pH, indicating the optimal adsorption conditions. The kinetics was well described by the PSO model, while the isotherm obeyed the Sips model. Equilibrium was attained at 60 min, and the maximum experimental adsorption capacity was up to 250.26 mg g-1 at pH 8.5, adsorbent dosage of 0.2 g L-1, and 298 K. These findings show that the magnetic hydrogel produced has great potential to be applied in the adsorption of basic molecules, such as MB.

Abalone shell-based magnetic macroporous hydroxyapatite microspheres with good reusability for efficient dye adsorption

Azo dye methyl orange (MO) and shell rotting cause great environmental pollution. Most of the common dye adsorbents are difficult to produce, not environmentally friendly and it is always difficult to utilize the shell resources effectively. In this study, shell-based economical and environmentally friendly magnetic hydroxyapatite microsphere adsorbents (Fe3O4 @SiO2/HAP) were developed for the removal of MO from simulated wastewater by sol-gel and hydrothermal synthesis methods. The effects of solution pH, initial concentration, adsorption time and system temperature on the adsorption effect were investigated, and the repeat recovery performance was explored. The equilibrium adsorption data follow the Freundlich isotherm and pseudo-second-order kinetic curves, and the analysis indicates that the adsorption process is spontaneously exothermic. The adsorption capacities of MO were up to 94.48% and 88.94%, under the acidic environment of pH = 4, respectively, and had good recycling performance. The results provide a high-value utilization pathway for waste shell resources and focus on the removal of azo dyes. This is expected to provide new development ideas for the environmental hazards caused by acid dye wastewater discharged into rivers and oceans, as well as the problems of soil pollution and resource waste caused by weathering and corrosion of shells.

Green conversion of waste PET into magnetic Ni0·4Fe2·6O4/(Fe,Ni)@carbon nanostructure for adsorption and separation of dyes from aqueous media

A nanostructured core-shell composite (Ni0·4Fe2·6O4/(Fe,Ni)@carbon, NFC) comprising magnetic nano-cores encapsulated with graphitic shells (≈80 wt%) is prepared by facile and clean mechanochemical-molten salt processing approach using waste PET; providing a specific surface area of 201.9 m2 g-1, well-developed mesopores, and ferromagnetic behavior characterized by the coercivity value of 149 Oe. NFC is utilized as a high-performance adsorbent for the removal of organic dyes from their aqueous solutions. Moreover, the magnetic performance of NFC enables the facile collection of the exhausted adsorbent out of the purified water. Performances of NFC for the removal of crystal violet dye (CV), methyl orange (MO) and rhodamine B (Rh B) from their aqueous solutions are systematically investigated under different environmental conditions including the adsorbent dosage and dye concentration, as well as the solution pH and temperature, where an impressive CV removal capacity of 201.6-243.8 mg g-1 is recorded for a wide pH range of 2-10. Mechanism and kinetics involved in the adsorption process are investigated by studying the adsorption isotherms and thermodynamics. The dye adsorption of the nanocomposite material is confirmed to follow the pseudo-second-order kinetic model combined with the Langmuir isotherm model, exhibiting an excellent spontaneous and exothermic monolayer adsorption capacity of around 153 mg g-1 (for MO) for the fresh adsorbent and around 89 mg g-1 after three adsorption-regeneration cycles.

Fabricated magnetic adsorption - Forward osmosis membrane hybrid system for hydroponic irrigation from rich arsenic-containing heavy metal water stream

Solidification of soluble arsenic from extremely acidic water and direct use of recovery water have been the major challenges in global water management, with the urgent need for new treatment system development. Thus, magnetic adsorption - fertilizer drawn forward osmosis (FDFO) hybrid system with a novel adsorbent and fertilizer mixture to solve the drawbacks of each process was developed with the ultimate goals of metal removal and direct reuse for hydroponic irrigation. Magnetic metal-organic framework-based adsorbent (CMM) was synthesized with various promising capabilities, i.e., wide pH range efficiency, strong pH adjustment, good stability, fast adsorption (1 h), and oxidation (40 min), high capacity (175 and 126 mg/g for As(III), As(V)), strong magnetization (75 emu/g), complete separation by a magnet, excellent interference-tolerance and reusability. In the FDFO system, a massive water volume (50 times higher than the initial draw solution with suitable nutrients for hydroponics irrigation with acceptable NaCl levels was obtained for the first time up to now. However, low As(III) rejection (50%) required the FDFO process to improve more. After integrating with magnetic adsorption, nearly 100% of As was removed. The pH of feed solutions adjusted from extremely acidic to close to neutral conditions further solidified metal by precipitation and membrane separation processes, leading to almost no detection of metals in the final draw solution. Also, favorable nutrients and excellent reusability were obtained. This hybrid process would generally offer an environmentally sustainable and high efficiency for decontaminating As-containing heavy metal water for hydroponic irrigation.

As(III) removal from aqueous solutions using simultaneous oxidation and adsorption process by hierarchically magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite

In the present study, a magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite was synthesized by hydrothermal method and applied for As(III) removal by oxidation and adsorption process. Individual property of the entire material (i.e. magnetic property of Fe3O4, mesoporous surface property of C-dot and oxidation property of MnO2) make the composite efficient with good adsorption capacity for As(III) adsorption. The Fe3O4@C-dot@MnO2 nanocomposite had a saturation magnetization of 26.37 emu/g and it magnetically separated within 40 s. The Fe3O4@C-dot@MnO2 nanocomposite was able to reduce the 0.5 mg/L concentration of As(III) to 0.001 mg/L in just 150 min at pH 3. Pseudo-second-order kinetic and Langmuir isotherm model agreed with experimental data. The uptake capacity of Fe3O4@C-dot@MnO2 nanocomposite was 42.68 mg/g. The anions like chloride, sulphate and nitrate did not show any effect on removal but carbonate and phosphate influenced the As(III) removal rate. Regeneration was studied with NaOH and NaClO solution and the adsorbent was used for repeated five cycles above 80% removal capacity. The XPS studies proposed that As(III) first oxidized to As(V) then adsorb on the composite surface. This study shows the potential applicability of Fe3O4@C-dot@MnO2 nanocomposite to high extent and gives a suitable path for the proficient removal of As(III) from wastewater.

Adsorptive removal of aflatoxin B1 from contaminated peanut oil via magnetic porous biochar from soybean dreg

The contamination of mycotoxin in edible oil has always been a major threat to human health. In this study, magnetic soybean dreg-based biochar SDB-6-K-9@Fe₃O₄ was prepared via co-precipitation and used to remove aflatoxin B1 (AFB1) from contaminated oil. The adsorbent characterization results revealed that the Fe₃O₄ was successfully loaded to the SDB-6-K-9. The 0.45SDB-6-K-9@Fe₃O₄ had paramagnetic properties with a saturation magnetization of 45.15 emu/g, which could be quickly separated from the peanut oil using an external magnet. The maximum adsorption capacity of peanut oil contaminated with 200 ng/mL AFB1 by 50 mg 0.45SDB-6-K-9@Fe₃O₄ for 2 h reached 0.1354 mg/g, while the removal process minimally affected the quality of the oil. The adsorption behavior results followed a pseudo-second-order kinetic and fitted well with the Freundlich model. The excellent adsorption removal efficiency and facile magnetic separation of the adsorbents provide a simple and efficient method for removing contaminants from the oil.

Magnetic anaerobic granular sludge for sequestration and immobilization of Pb

The development of magnetic adsorbents with high capacity to capture heavy metals has been the subject of intense research, but the process usually involves costive synthesis steps. Here, we propose a green approach to obtaining a magnetic biohybrid through in situ grown anaerobic granular sludge (AGS) with the help of magnetite, constituting a promising adsorbent for sequestration and immobilization of Pb in aqueous solutions and soils. The resultant magnetite-embedded AGS (M-AGS) was not only capable of promoting methane production but also conducive to Pb adsorption because of the large surface area and abundant function groups. The uptake of Pb on M-AGS followed the pseudo-second order, having a maximum adsorption capacity of 197.8 mg gDS^-1 at pH 5.0, larger than 159.7, 170.3, and 178.1 mg gDS^-1 in relation to AGS, F-AGS (ferrihydrite-mediated), and H-AGS (hematite-mediated), respectively. Mechanistic investigations showed that Pb binding to M-AGS proceeds via surface complexation, mineral precipitation, and lattice replacement, which promotes heavy metal capture and stabilization. This was evident from the increased proportion of structural Pb sequestrated from the aqueous solution and the enhanced percentage of the residual fraction of Pb extracted from the contaminated soils.

Brilliant blue FCF dye adsorption using magnetic activated carbon from Sapelli wood sawdust

Sapelli wood sawdust-derived magnetic activated carbon (SWSMAC) was produced by single-step pyrolysis using KOH and NiCl₂ as activating and magnetization agents. SWSMAC was characterized by several techniques (SEM/EDS, N₂ adsorption/desorption isotherms, FTIR, XRD, VSM, and pH_PZC) and applied in the brilliant blue FCF dye adsorption from an aqueous medium. The obtained SWSMAC was a mesoporous material and showed good textural properties. Metallic nanostructured Ni particles were observed. Also, SWSMAC exhibited ferromagnetic properties. In the adsorption experiments, adequate conditions were an adsorbent dosage of 0.75 g L^-1 and a solution pH of 4. The adsorption was fast, and the pseudo-second-order demonstrated greater suitability to the kinetic data. The Sips model fitted the equilibrium data well, and the maximum adsorption capacity predicted by this model was 105.88 mg g^-1 (at 55 °C). The thermodynamic study revealed that the adsorption was spontaneous, favorable, and endothermic. Besides, the mechanistic elucidation suggested that electrostatic interactions, hydrogen bonding, π-π interactions, and n-π interactions were involved in the brilliant blue FCF dye adsorption onto SWSMAC. In summary, an advanced adsorbent material was developed from waste by single-step pyrolysis, and this material effectively adsorbs brilliant blue FCF dye.

Sulfonated magnetic multi-walled carbon nanotubes with enhanced bonding stability, high adsorption performance, and reusability for water remediation

In view of the simple and rapid conveniency of magnetic separation, magnetic nanocomposites had notably gained attention from researchers for environmental field applications. In this work, carboxylated magnetic multi-walled carbon nanotubes (c-MMWCNTs) and novel sulfonated MMWCNTs (s-MMWCNTs) were synthesized by a facile solvent-free direct doping method. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, energy dispersive X-ray, vibrating sample magnetometer, and point of zero charge analyses confirmed the successful doping of the Fe₃O₄ nanoparticles into the functionalized MWCNTs to form MMWCNTs. Besides, the bonding stabilities of both c-MMWCNTs and s-MMWCNTs were compared, and results showed that s-MMWCNTs possessed more substantial bonding stability than that of c-MMWCNTs with significantly less leaching amount of Fe₃O₄. The adsorption capacity of s-MMWCNTs was higher than that of c-MMWCNTs owing to the stronger electronegativity sulfonic group in s-MMWCNTs. Moreover, the reusability experiments proved that the adsorbent remained consistently excellent MB removal efficiency (R > 94%) even reused for twelve cycles of batch adsorption. The finding of the present work highlights the simple fabrication of novel s-MMWCNTs and its potential to be served as a promising and sustainable adsorbent for water remediation owing to its enhanced bonding stability, high adsorption performance, magnetic separability, and supreme recyclability.

Magnetic seeds promoted high-density sulfonic acid-based hydrochar derived from sugar-rich wastewater for removal of methylene blue

Methylene blue (MB) removal from dyeing wastewater using low-cost bio-derived adsorbent is a significant and challenging field. Herein, magnetic sugar hydrochar (MGHC) precursors derived from sugar-rich wastewater with small particle size and rich oxygen-containing functional groups (OCFGs) are prepared from sugar-rich aqueous solution via Fe salt-modified hydrothermal procedure. The role of Fe₃O₄ nanoparticles formed during the sugar carbonization is to provide numerous magnetic seeds to generate MGHC with core-shell structure, which reduces the particle size of hydrochar. This increases the amount of OCFGs on the surface of MGHC for bonding the sulfonic acid groups. Therefore, sulfonic acid-modified MGHC-SA shows the rapid MB adsorption rate and excellent adsorption capacity. The highest MB capacity is 869.6 mg/g at pH = 11.0 and 298 K. Additionally, the MGHC-SA can be easily recovery by magnet. And the stability of MGHC-SA was also evaluated, no degradation of adsorption performance was observed, even the adsorbent was regenerated 10 times. This study puts forward a promising way to acquire functional groups rich and easy recovery hydrochar from sugar wastewater for MB removal.

Preparation and characterization of chitosan-curdlan composite magnetized by zinc ferrite for efficient adsorption of tetracycline antibiotics in water

Tetracycline (TC) antibiotic-related water pollution directly threatens human health and ecosystems. Here, a zinc ferrite/chitosan-curdlan (ZNF/CHT-CRD) magnetic composite was prepared via a co-precipitation method to be used as a novel, green adsorbent for TC removal from water. Benefiting from a multitude of functional groups, CRD was first crosslinked with CHT and then magnetized with ZNF to provide an easy separation from the solution with an external magnetic force. The successful synthesis and magnetization of the composite were verified with different characterization techniques. The effect of solution pH and composite dosage was carefully evaluated. The optimum solution pH and composite dosage were 6 and 0.65 g/L, respectively, with complete TC removal. The adsorption process by the magnetic composite followed the pseudo-first-order kinetics and Langmuir isotherm models. The maximum adsorption capacity determined from the Langmuir model was 371.42 mg/g at 328 K. Thermodynamic parameters indicated endothermic and spontaneous adsorption. Meanwhile, the composite could be readily separated from the aqueous solution thanks to its magnetic property. Then, it was regenerated with acetone and ethanol to be reused for five more successive cycles. Interestingly, the prepared adsorbent was highly stable and performant in removing TC, maintaining approximately 90 % of its first-cycle adsorption capacity. The adsorption mechanism was primarily attributed to electrostatic and hydrogen bonding attractions. Overall, the currently developed adsorbent could be a more favorable, efficient, and cost-effective candidate than other magnetic chitosan-based composites. These features make it applicable for treating water contaminated with various pharmaceutical pollutants with high separation efficiency and easy recovery under successive adsorption-desorption cycles.

Application of sulfur-coated magnetic carbon nanotubes for extraction of some polycyclic aromatic hydrocarbons from water resources

In the present work, novel sulfur-coated magnetic carbon nanotubes (MCNTs-S) material was fabricated by S coating on the MCNTs using a simple heating procedure. TGA, EDX, XRD, TEM, and VSM were employed to characterize the as-prepared composite. Using HPLC-UV system, the produced superparamagnetic sorbent was employed for the extraction and measurement of trace levels of five polycyclic aromatic hydrocarbons (PAHs) in environmental waters. The synergistic effect of the sulfur layer and CNTs substrate is primarily responsible for the remarkable extraction efficiency of the MCNTs-S sorbent towards PAHs. The experimental factors including MCNTs-S dosage, sorption time, elution solvent, ionic strength and solution pH were explored and optimized. Considering that the ionic strength and pH do not have any impact on the PAHs extraction, as a result, there is no need the unnecessary adjustment of the water samples. The linear dynamic ranges and detection limits under optimal conditions were in the range of 0.05-0.11 ng mL^-1 and 0.2-150 ng mL^-1, respectively. The analysis of PAHs in the real samples (sea water and river water) using this approach was successfully assessed with appropriate recovery values (94.6%-99.0%).

A novel utilization of raw sepiolite: preparation of magnetic adsorbent directly based on sol-gel for adsorption of Pb(II)

The constraints of industrial separation technology for low grade sepiolite greatly limit the development and utilization of these potential resources. In this work, a novel sepiolite adsorbent loaded with copper ferrite was prepared by sol-gel method to remove Pb(II) from wastewater. The effects of various factors on Pb(II) removal ratio were investigated. The maximum adsorption capacities at 293, 313, and 333 K were 1285.32, 1325.45, and 1390.54 mg/g, respectively. The adsorption of Pb(II) by magnetic sepiolite was a spontaneous endothermic process. Besides, the adsorption process followed Langmuir isothermal adsorption model and pseudo-second-order kinetic model. The main adsorption mechanism of Pb(II) removal was electrostatic attraction, ion exchange, and surface complexation. The improvement of Pb(II) absorption indicated that the efficient removal of Pb(II) can be realized by phosphate groups introduced in the preparation process and the carbonate groups contained in gangue minerals.

Lanthanum doped magnetic polyaniline for removal of phosphate ions from water

Herein, magnetic polyaniline was modified with lanthanum nanoparticles (MPANI@La) as adsorbent, aiming to the treatment of high phosphate-containing aquatic solutions. High valent lanthanum doped with polyaniline was a promising adsorbent to uptake phosphate ions with possible electrostatic interaction and cation exchange process. The functional groups, composition, surface morphology, and magnetic property of the adsorbent were investigated using Fourier Transform-Infrared Spectroscopy (FTIR), Energy Dispersive X-ray (EDX), Scanning Electron Microscopic (SEM), and Vibrating Sample Magnetometer (VSM), respectively. During the experimental process, MPANI@La has removed phosphate ions from water >90%, with 80 mg adsorbent, and shaking for 150 min at room temperature. In this regard, the process was fitted with the Pseudo-second-order kinetic model (R2 > 0.999) and the Langmuir isotherm (R2 > 0.99). The proposed nanoparticles provided an appropriate adsorption capacity (qm) of 45.24 mg.g-1 at pH 4 for phosphate ions. Besides, the adsorbent can be used with an efficiency of 92.49% up to three times that reduced to 52.89% after ten times. In addition, the adsorption process was justified by thermodynamics which confirmed the proposed adsorption mechanism. Hence, the models were provided surface adsorption, monolayer pattern, and the physical mechanism of the phosphate removal process using MPANI@La. Hence the proposed adsorbent can be used as an alternative adsorbent in environmental water remediation.

Intelligent modelling for the elimination of lanthanides (La3+, Ce3+, Nd3+ and Eu3+) from aqueous solution by magnetic CoFe2O4 and CoFe2O4-GO spinel ferrite nanocomposites

In this research, a novel CoFe₂O₄-GO (Graphen Oxide) resulting from the combination of high applicable magnetic and organic base materials and synthesized with a simple and fast co-precipitation route was synthesized for the REEs (Rare Earth Elements) extraction. This adsorbent could remove the La³⁺, Ce³⁺, Nd³⁺ and Eu³⁺ by maximum adsorption capacity of 625, 626, 714.2, 1111.2 mg/g at optimized pH = 6, respectively. A data-driven model was obtained using Group Method of Data Handling (GMDH)-based Neural Network to estimate the adsorption capacity of these LREEs as a function of time, pH, temperature, adsorbent ζ (zeta)- potential, initial concentration of lanthanides ions, and ε which is defined by the physico-chemical properties of lanthanides. The results clearly indicated that the model estimate the experimental values with good deviation (mostly less than 10%) and it can be used for the prediction of the results from other similar researches with less than 25% deviation. The results of sensitivity analysis indicated that the adsorption capacity is more sensitive to pH of the solution, temperature, and ε. Finally, the desorption studies showed an excellent removal efficiency (97%) at least for three adsorption-desorption cycles. These results claimed that the CoFe₂O₄-GO is a highly efficient adsorbent for the REEs extraction.

Magnetic sporopollenin supported polyaniline developed for removal of lead ions from wastewater: Kinetic, isotherm and thermodynamic studies

This study evaluated the synthesis of novel binary functionaladsorbent based on sporopollenin, magnetic nanoparticles, and polyaniline to produce MSP-PANI. The MSP-PANI was applied to enhance uptake of lead ions (Pb²⁺) from wastewater samples. The functionalities, surface morphology, magnetic properties, and elemental composition of the newly synthesized nanocomposite were investigated using Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), vibration sample magnetometer (VSM), and energy-dispersive X-ray spectroscopy (EDX), respectively. The experimental condition for the adsorption process was MSP/PANI ratio 1:1, pH ∼6, adsorbent dosage 40 mg, and contact time 90 min at room temperature. Under the proposed condition, lead ions removal were obtained as 83%, 88% and 95% for MSPE, PANI, and MSP/PANI, respectively. Based on the experimental and predicted data, the adsorption was corresponded to the psudo-second-order (R² = 0.999) kinetics model, and the adsorption equilibrium corresponded to the Langmuir model (R² = 0.996). Langmuir isotherm showed the maximum adsorption capacity of MSP-PANI for lead ions was 163 mg/g and followed the monolayer pattern. Hence, thermodynamic model under Van't Hoff equation suggested that the adsorption mechanism was physio-sorption with endothermic nature. Therefore, this research can help the researchers to use magnetic nanoparticles for lead removal in highly polluted areas.

Hydroxypicolinic acid tethered on magnetite core-silica shell (HPCA@SiO2@Fe3O4) as an effective and reusable adsorbent for practical Co(II) recovery

The soaring demand and future supply risk for cobalt (Co) necessitate more efficient adsorbents for its recycling from electronic wastes, as a cheaper and less hazardous option for its production. Herein, a magnetic adsorbent covalently tethered with 5-hydroxypicolinic acid (HPCA) as Co(II) ligand was developed. The magnetic component (Fe₃O₄) was protected with silica (SiO₂), then silanized with chloroalkyl linker and subsequently functionalized with HPCA via S_N2 nucleophilic substitution (HPCA@SiO₂@Fe₃O₄). Results from FTIR, TGA, EA, and XPS confirm the successful adsorbent preparation with high HPCA loading of 2.62 mmol g^-1. TEM-EDS reveal its imperfect spherical morphology with ligands well-distributed on its surface. HPCA@SiO₂@Fe₃O₄ is hydrophilic, water-dispersible and magnetically retrievable, which is highly convenient for its recovery. The Co(II) capture on HPCA@SiO₂@Fe₃O₄ involves monodentate coordination with carboxylate (COO^-) and lone pair acceptance from pyridine (aromatic -N = ) moiety of HPCA, with minor interaction from acidic silanols (Si-O^-). The binding occurs at 2 HPCA: 1 Co(II) ratio, that follows the Sips isotherm model with competitive Q_max = 92.35 mg g^-1 and pseudo-second order kinetics (k₂ = 0.0042 g mg^-1 min^-1). In a simulated LIB liquid waste, HPCA@SiO₂@Fe₃O₄ preferentially captures Co(II) over Li(I) with α_Li(I)^Co(II)=166 and Mn(II) with α_Mn(II)^Co(II)=55, which highlights the importance of HPCA for Co(II) recovery. Silica protection of Fe₃O₄ rendered the adsorbent chemically stable in acidic thiourea solution for its regeneration by preventing the deterioration of the magnetic component. Covalent functionalization averted ligand loss, which allowed HPCA@SiO₂@Fe₃O₄ to deliver consistent and reversible adsorption/desorption performance. Overall results demonstrate the potential of HPCA@SiO₂@Fe₃O₄ as a competitive and practical adsorbent for Co(II) recovery in liquid waste sources.

Magnetization of Bauxite Residue to Enhance the Removal Efficiency Towards Heavy Metals

Bauxite residues are a mass of industrial wastes derived from aluminum metallurgy. This work provided a simple pyrolysis method to magnetize the bauxite residue to serve as a magnetic adsorbent towards heavy metals removal. The X-ray diffraction patterns and Mossbauer spectrum results confirmed the partial reduction of iron species with an obvious enhancement in magnetization. The magnetized bauxite residue exhibited excellent removal efficiencies for Cu²⁺, Cd²⁺ and Pb²⁺ with maximum adsorption capacities of 219.0 mg g^-1, 275.4 mg g^-1, and 100.4 mg g^-1, which could be quickly separated through a magnet. The adsorption equilibrium data were fitted to the Langmuir isotherm model, while the adsorption kinetics followed a pseudo-first-order model. According to the characterization results, chemical precipitation and sorption was the major mechanism for the removal of Cu²⁺, Pb²⁺, and Cd²⁺. Thus, the magnetized bauxite residue exhibited promising applications for heavy metals removal in wastewater.

Magnetic adsorbent developed with alkali-thermal pretreated biogas slurry solids for the removal of heavy metals: optimization, kinetic, and equilibrium study

Discharge of effluents containing heavy metal without adequate treatment causes contamination of water resources and creates environmental and health issues. Adsorption could be applied to remediate heavy metals from wastewater effectively. In this study, a low-cost adsorbent was prepared by magnetic modification of pretreated biogas slurry solids (BSS) to remove heavy metals such as Cu²⁺, Cd²⁺, and Pb²⁺. The temperature (423 K) and time (1.5 h) of pretreatment, the BSS to KOH ratio (1:10 w/v), and the ratio of magnetic iron nanoparticle (MIN) to pretreated BSS (PSS) (1:2 w/w) were optimized for the preparation of adsorbent. The magnetically modified pretreated biogas slurry solid (MMPSS) adsorbent was characterized by BET isotherm, FTIR, XRD, FESEM, VSM, and EDX analysis. MMPSS attained equilibrium at 60 min and showed an adsorption capacity of 26.84 mg/g, 24.79 mg/g, and 23.86 mg/g with removal percentages 89.46%, 82.63%, and 79.54% for Cu²⁺, Cd²⁺, and Pb²⁺, respectively, at 310 K and pH 6 with an initial concentration of 150 mg/L. The adsorption process followed a pseudo second-order model with an R² value above 0.9 for all metals with a well-approaching equilibrium pattern. The good fit of experimental data by the Langmuir isotherm model implied monolayer adsorption. The metal ions adsorbed onto MMPSS were able to desorb effectively in the presence of HCl and retained 83.01%, 84.66%, and 81.83% of the initial adsorption capacity for Cu²⁺, Cd²⁺, and Pb²⁺ respectively after 5 consecutive cycles.

Removal of metal ions using a new magnetic chitosan nano-bio-adsorbent; A powerful approach in water treatment

In this study, a magnetic chitosan/Al₂O₃/Fe₃O₄ (M-Cs) nanocomposite was developed by ethylenediaminetetraacetic acid (EDTA) functionalization to enhance its adsorption behavior for the removal of Cd(II), Cu(II) and Zn(II) metal ions from aqueous solution. The results revealed that the EDTA functionalization of M-Cs increased its adsorption capacity ~9.1, ~5.6 and ~14.3 times toward Cu, Cd and Zn ions. The maximum adsorption capacity followed the order of Cd(II) > Cu(II) > Zn(II) and the maximum adsorption efficiency was achieved at pH of 5.3 with the removal percentage of 99.98, 93.69 and 83.81 %, respectively, for the removal of Cu, Cd and Zn ions. The metal ions adsorption kinetic obeyed pseudo-second-order equation and the Langmuir isothermal was found the most fitted model for their adsorption isothermal experimental data. In addition, the thermodynamic study illustrated that the adsorption process was exothermic and spontaneous in nature.

Fe3O4@PDA@PANI core-shell nanocomposites as a new adsorbent for simultaneous preconcentration of Tartrazine and Sunset Yellow by ultrasonic-assisted dispersive micro solid-phase extraction

In this research, novel magnetic Fe₃O₄@PDA@PANI core-shell nanoparticles were designed and fabricated as an efficient adsorbent in the service of ultrasound-assisted dispersive micro-solid phase extraction for simultaneous preconcentration of Sunset Yellow (SY) and Tartrazine (Tar) before UV-Vis spectrophotometric detection. This adsorbent was fully characterized by Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray (EDX) analysis. To overcome the spectral overlapping of SY and Tar dyes, the derivative spectrophotometric method was successfully used for the simultaneous detection of dyes in their binary solutions. The operating parameters affecting preconcentration efficiency and spectrophotometric determination were optimized. Under optimal conditions, the limit of detections (LOD) was obtained 0.2 and 0.5 ng mL^-1 for SY and Tar, respectively. The adsorption capacity and reusability of core-shell nanoparticles were significant. The satisfactory results of analysis of a few real samples indicate that the method is very favored in the analysis of various complex matrices.

Highly efficient porous magnetic polydopamine/copper phosphate with three-dimensional hierarchical nanoflower morphology as a selective platform for recombinant proteins separation

The separation and purification of recombinant pharmaceutical proteins is a fundamental and challenging step in the biotechnology industry. Hierarchical nanostructures with unique features and high stability can be used as efficient adsorbents. In this study, hierarchical magnetic polydopamine-copper phosphate nanoflowers (Cu-PDA MNFs) were synthesized as high-performance magnetic adsorbents in a simple and low-cost method based on green chemistry. The prepared hybrid Cu-PDA MNFs revealed great performance for separating pure recombinant human growth hormone (rhGH) and the rhGH acquired from recombinant Pichia pastoris yeast fermentation. The analysis confirmed that Cu-PDA MNFs exhibited a high adsorption capacity of 257.4 mg rhGH g^-1 Cu-PDA MNFs and a fast adsorption rate for approaching the adsorption equilibrium within less than 30 min with a recovery efficiency of 74% of rhGH from the real sample. In addition, recycling tests demonstrated the stability and recyclability of Cu-PDA MNFs for at least six cycles with almost constant adsorption capacity and no toxicity. Based on these results, Cu-PDA MNFs could be considered as a promising candidate for separation and purification of rhGH. This work presents a new approach to using organic-inorganic nanoflowers as the hierarchical nanostructure for purification of pharmaceutical proteins with high performance.

A novel synthesis of sulfurized magnetic biochar for aqueous Hg(II) capture as a potential method for environmental remediation in water

Due to public health threats resulting from mercury (Hg) and its distribution in the food chain, global restrictions have been placed on Hg use and emissions. Biochar is a porous, carbonaceous adsorbent typically derived from waste biomass or organic matter, making it an eco-friendly material for aqueous mercury (Hg(II)) control. Functionalization of biochar can improve performance in pollution control applications. In this work, carbonization, magnetization, and sulfurization of biochar were combined into a single heating step to prepare sulfurized magnetic biochar (SMBC) for Hg(II) removal from water. Results indicate that SMBC prepared at 600 °C adsorbed 8.93 mg/g Hg(II), more than materials prepared at 400, 500, 700, 800, and 900 °C. Additionally, Hg(II) adsorption onto SMBC was 53.0% and 11.5% greater than onto magnetic biochar (MBC) and biochar (BC), respectively. Hg(II) adsorption is shown to be favorable in acidic conditions (pH 3.5-5), thermodynamically spontaneous, and endothermic. Adsorption results fit the pseudo-second-order (R² = 0.990 and the sum of squared error (SSE) = 5.382) and external mass transfer (R² = 0.971 and SSE = 9.422) models. The partitioning coefficients were 4.964 mg/g/μM in freshwater, 0.176 mg/g/μM in estuary water, and 0.275 mg/g/μM in seawater, highlighting the importance of salinity in environmental remediation applications. In summary, SMBC can be readily prepared with minimal processing steps. The product is a robust adsorbent for Hg(II), and it can potentially be applied to remediate contaminated water/sediment/soil in the future.

Facile preparation of taurine modified magnetic chitosan nanocomposites as biodegradable adsorbents toward methylene blue

A novel magnetic Fe₃O₄@chitosan@taurine adsorbent (MCT) was prepared by surface modification of magnetic chitosan nano-composites with taurine-glutaraldehyde solution. The adsorbents were characterized by FTIR, SEM, TEM, XRD, TGA and VSM techniques, respectively. According to the FTIR spectrum of MCT, the characteristic peaks of the SO₃^-group on MCT were observed to have a shift after adsorption of the cationic dye, which indicates that there may be electrostatic attraction between the MCT and the cationic dye. Moreover, the saturation magnetization of MCT was found to be 20.797 emu g^-1, suggesting that MCT has sufficient magnetic response to meet the need of magnetic separation. The adsorption properties of cationic dyes by MCT were further investigated by using methylene blue (MB) as a representative. The adsorption behaviour of MB by MCT was well described by the pseudo-second order kinetic model and the Langmuir isotherm model, respectively. The maximum adsorption capacity of MB calculated from the Langmuir model fitting was 204.1 mg g^-1 at pH 5 and 384.6 mg g^-1 at pH 9, respectively, and the adsorption equilibrium could be reached within 10 min. Besides, the negative values of ΔG° and ΔH° suggested that the adsorption process was spontaneous and exothermic, and the good reusability indicated that MCT could act as a recyclable adsorbent for dye adsorption. All of these results illustrate that MCT has great potential for practical application in removal of cationic dyes from aqueous solutions.

Thiol-methyl-modified magnetic microspheres for effective cadmium (II) removal from polluted water

For effective removal of cadmium (II) (Cd(II)) from polluted water, a magnetic adsorbent of Fe₃O₄@SiO₂ core-shell microspheres modified with methyl-protected thiol groups (Fe₃O₄@SiO₂-SH-Protected) was synthesized and characterized by scanning electron, transmission electron, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopies, as well as X-ray diffraction, Raman spectroscopy, and magnetic measurements. Characterization results showed that thiol groups on the surface of Fe₃O₄@SiO₂ material were protected to avoid disulfide formation. Batch adsorption experiments were conducted by varying the contact time, initial pH, solid-liquid ratio, temperature, Cd(II) concentrations, and interfering cations. Fe₃O₄@SiO₂-SH-Protected material exhibited much higher adsorption capacity than Unprotected forms and other adsorbents due to methyl group protection. The maximum adsorption capacity calculated from the Langmuir fitting was 27.5 mg·g^-1 (pH 7, 25 °C), and the adsorption kinetics followed a pseudo-second-order model, and adsorption mainly dominated by film diffusion processes. Thermodynamic parameters indicated that the adsorption process was a spontaneous, endothermic, and positive entropic process. Cd(II)-loaded on the adsorbent was easily desorbed with 0.1 M HCl and the adsorbent stable in 0.1 M HCl for long times, showing good reusability and stability.

Efficient removal of acetochlor pesticide from water using magnetic activated carbon: Adsorption performance, mechanism, and regeneration exploration

In this study, MnFe₂O₄ supported activated carbon magnetic adsorbent (MnFe₂O₄@AC) was successfully prepared by a simple one-pot solvothermal method and used for the adsorption and removal of acetochlor from aqueous media. Results showed that MnFe₂O₄@AC with a MnFe₂O₄/AC mass ratio of 1:2 was characterized by good magnetism and high acetochlor adsorption capacity over a wide ranging pH, ionic strength, and humic acid concentration in an aqueous solution. Acetochlor was adsorbed on MnFe₂O₄@AC mainly by hydrogen bonding, π-π interactions, and pore-filling via film, intraparticle, and pore diffusion steps. Adsorption reaction generally approached an equilibrium after 10 h, with the adsorption capacity being ca. 226 mg g^-1 for 0.2 g L^-1 adsorbent at 25 °C. Adsorbate (acetochlor) degradation and adsorbent regeneration were simultaneously achieved through heat-activated peroxymonosulfate (PMS) oxidation catalyzed by MnFe₂O₄ on the AC surface with >90% degradation efficiency at ≥9.6 mM PMS concentration at 70 °C within 12 h. However, the adsorption capacity of the regenerated adsorbent decreased by 50% of its original capacity. This needs to be addressed in future studies. MnFe₂O₄@AC adsorbent has the advantages of high adsorption capacity, good magnetism, and catalyzation, which are promising for adsorption, separation, and degradation for the effective removal and treatment of acetochlor as well as other organic contaminants in different types of waters.

As(V) adsorption by a novel core-shell magnetic nanoparticles prepared with Iron-containing water treatment residuals

A novel core-shell magnetic nanoparticle was synthesized through heterogeneous nucleation technique and utilized to remove As(V) from water. Both the magnetic core and the coating material, amorphous FeOOH shell, were prepared with iron-containing water treatment residuals (WTRs), also called iron sludge. The bare magnetic nanoparticles (MNPs) and coated magnetic nanoparticles (c-MNPs) were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Brunauer-Emmett -Teller analysis (BET), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The c-MNPs, mainly consisting of maghemite (γ-Fe₂O₃) as the magnetic core and amorphous FeOOH as the coating material, could be easily separated from water through a hand-held magnet, the saturation magnetization of which is 36.4 emu/g. Freundlich adsorption isotherm model could better described the As(V) adsorption behavior of c-MNPs than Langmuir model, and kinetic data could be described well by the pseudo-second order model. The maximum As(V) adsorption capacity of c-MNPs (26.05 mg/g) was more than twice that of MNPs (12.74 mg/g). At 25 °C, 0.2 g/L of the c-MNPs could reduce the As(V) from 400 μg/L to below the maximum contaminant level (MCL) of 10 μg/L over a broad pH ranging from 4 to 8. The c-MNPs still exhibited effective adsorption in the presence of co-existing anions including nitrate, chloride, carbonate, and sulfate, whereas, silicate and phosphate had a negative influence on the As(V) adsorption. Throughout five consecutive cycles, the adsorbents could still maintain high As(V) adsorption capacity.

Efficient removal of various coexisting organic pollutants in water based on β-cyclodextrin polymer modified flower-like Fe3O4 particles

HYPOTHESIS

The construction of porous β-cyclodextrin polymer (β-CDP) modified flower-like Fe₃O₄ particles (CDP@Fe₃O₄) is expected to remove various organic pollutants from water, based on the larger specific surface area of flower-like Fe₃O₄ particles and the active sites provided by β-CDP. With the help of various noncovalent interactions, the removal ability of CDP@Fe₃O₄ for various water-soluble and water-insoluble organic pollutants were systematically studied.

EXPERIMENTS

CDP@Fe₃O₄ were successfully synthesized and applied for the simultaneous removal of various organic pollutants with different electrical properties, structure and hydrophobicity. Adsorption efficiency, adsorption process, adsorption mechanism and the reusability of CDP@Fe₃O₄ for single pollutant and mixed pollutants were comprehensively investigated.

FINDINGS

CDP@Fe₃O₄ exhibited excellent adsorption capabilities for various pollutants. Importantly, when these pollutants were coexisting, CDP@Fe₃O₄ still maintained a comparable removal ability for various pollutants. Efficient removal of organic pollutants was attributed to varieties of noncovalent interactions between organic pollutants and CDP@Fe₃O₄, including hydrophobic interactions, hydrogen bonds, π-π and electrostatic interactions. These results revealed that the excellent adsorption ability and convenient regeneration make CDP@Fe₃O₄ being a potential candidate in various complex organic wastewater purification.

Adsorption mechanism of rhein-coated Fe3O4 as magnetic adsorbent based on low-field NMR

In the present study, a magnetic adsorbent, rhein-coated magnetic Fe₃O₄ nanoparticle (RMNP), for Pb²⁺ and Mg²⁺ had been developed, and adsorption mechanism was studied via low-field NMR. RMNP was characterized by TEM, FTIR, and XRD. RMNP could adsorb and remove Pb²⁺ and Mg²⁺ from water and was successfully applied to remove Pb²⁺ and Mg²⁺ from wastewater, with satisfactory recovery rates and high adsorption capacities. The calculated maximum adsorption capacity for Mg²⁺ and Pb²⁺ was approximately 69.3 and 64.9 mg g^-1 of RMNP, respectively, which was better than some results reported. Low-field NMR results showed that Pb²⁺ or Mg²⁺ enhanced the T₂ relaxation time of RMNP, which suggested that RMNP selectively coordinated with Pb²⁺ or Mg²⁺ and led to the aggregation of RMNP, furthermore removal of Pb²⁺ or Mg²⁺ from water. The standard curves for △T₂-cation concentration exhibited good line correlation. The linear ranges were from 4.2 × 10^-6 to 2.0 × 10^-4 mol L^-1 for Pb²⁺ and from 5.0 × 10^-6 mol L^-1 to 1.0 × 10^-4 mol L^-1 for Mg²⁺, respectively. The limits of detection were 1.4 × 10^-6 mol L^-1 for Pb²⁺ and 2.1 × 10^-6 mol L^-1 for Mg²⁺, respectively. In short, low-field NMR could clearly display the interaction between RMNP and Pb²⁺ or Mg²⁺, even be used to detect Pb²⁺ or Mg²⁺ in suitable condition. Besides, this method could be expanded to study the interaction between other magnetic adsorbents and analytes.

La(OH)3-modified magnetic sodium carboxymethyl cellulose for sequential removal of pollutants: adsorption of phosphate and subsequent photocatalytical reduction of Cr(VI)

In this study, La(OH)₃-modified magnetic sodium carboxymethyl cellulose (La-MC) was prepared as adsorbents for phosphate, which exhibited excellent adsorption performance up to 62.98 mg P/g and magnetic property for easy recovery. The recovered adsorbents after phosphate sorption were subsequently used for photocatalytic reduction of Cr(VI) and possessed good photocatalytic activity. This work provided an excellent reference for developing a new way of extending life cycle of adsorbents by combining phosphate adsorption with photocatalysis for sequential removal of pollutants from water in the future.

Removal of aflatoxin B1 from contaminated peanut oils using magnetic attapulgite

The efficient magnetic adsorbent (Fe₃O₄@ATP) was prepared by precipitation through the dispersion of Fe₃O₄ nanoparticles on the natural attapulgite (ATP) and then tested as an adsorbent for aflatoxin B₁ (AFB₁) removal from contaminated oils. The adsorbent characterization results revealed that the Fe₃O₄ were incorporated into the ATP, affording the Fe₃O₄@ATP composite. This magnetic composite displayed a good ability to eliminate AFB₁ from contaminated oils with a removal efficiency of 86.82% using a 0.3% dosage. The Fe₃O₄@ATP possessed paramagnetic character with a saturation magnetization of 50.86 emu/g, enabling its easy separation from the medium using an external magnet. The adsorption process followed the pseudo-second-order model and fitted the Freundlich isotherm well. Moreover, the thermodynamic studies showed that AFB₁ adsorption onto Fe₃O₄@ATP was exothermic and spontaneous. The novelty of this study lies in the fabrication of magnetic composite adsorbents for AFB₁ elimination from oils.

Fabrication and characterization of magnetically responsive Fe3O4@TiO2 core-shell adsorbent for enhanced thallium removal

Thallium (Tl) contamination in natural waters can pose a severe risk to human health. In this study, a magnetically responsive Fe₃O₄@TiO₂ core-shell adsorbent was developed for the effective removal of thallium(I) from water. The isoelectric point of the adsorbent surface was decreased from 6.0 to 4.8 due to the loading of nano-sized TiO₂, leading to an enhanced electrostatic interaction between the adsorbent and Tl(I) ions in a wider pH range. The Fe₃O₄@TiO₂ magnetic adsorbent exhibited a threefold higher BET specific surface area compared to pristine Fe₃O₄ particles. The kinetics study showed that approximately 82% of the maximum Tl(I) loading amount could be achieved within 30 min at the initial Tl(I) concentration of 8 mg/L and adsorbent dosage of 0.1 g/L. The adsorption of Tl(I) was significantly increased with increasing solution pH. The experimental data was better fitted by the Langmuir and Temkin isotherms than the Freundlich isotherm and the maximum adsorption capacity of the magnetic adsorbent was 101.5 mg/g at pH 7.0. The interference of co-existing cations in the Tl(I) adsorption followed the subsequence: Cu²⁺ > Mg²⁺ > Ca²⁺ > Na⁺. The hydroxyl groups bonded on titanium atoms might play a key role in the uptake of Tl(I) ions. During the adsorption, the Tl(I) ions can be effectively adsorbed on the adsorbent surface via the formation of Ti-O-Tl linkages. Graphical Abstract.

Adsorption of Sr(II) ions and salicylic acid onto magnetic magnesium-zinc ferrites: isotherms and kinetic studies

Magnetic magnesium-zinc spinel ferrite Mg_1 - xZn_xFe₂O₄ (where x = 0.4, 0.6, and 0.8) was investigated as adsorbent for the efficient removal of Sr(II) ions and salicylic acid (SA) contaminants from aqueous medium. The characterization of ferrites was carried out using XRD, VSM, BET, SEM, and EDS. The surface charge of magnetic adsorbents was measured by the drift method. The determination of SA and Sr(II) ion concentrations in the solution phase was carried out by UFLC and complexometry, respectively. It was shown that varying of the Zn(II) content affected the adsorption capacities of magnesium-zinc ferrites. The increasing of zinc content from x(Zn²⁺) = 0.4 to x(Zn²⁺) = 0.6 increased the adsorption of Sr(II) ions from 50 to 65 mg/g, and then it was decreased to 36 mg/g for the sample with x(Zn) = 0.8. The Mg_0.4Zn_0.6Fe₂O₄ sample demonstrated the maximum adsorption capacity of 74 mg/g. The adsorption isotherm for Sr(II) was fitted by the Dubinin-Radushkevich, Langmuir, Freundlich, and Sips models. The adsorption kinetics of Sr(II) was analyzed by PFO, PSO, and Elovich models. The adsorption kinetics of SA was also investigated. It was demonstrated that the Mg_0.2Zn_0.8Fe₂O₄ sample exhibited 90% removal of salicylic acid from the water solutions. The results demonstrated that magnetic Mg-Zn ferrites with spinel structure are good sorbents for the removal of SA and Sr(II) ions from aqueous solution.

Performance and mechanism of polypeptidylated hemoglobin (Hb)/iron oxide magnetic composites for enhanced dye removal

Composites of polypeptidylated hemoglobin supported on different iron oxide weights (0.5:1 and 1:1) were developed and demonstrated to function as efficient adsorbents for Eriochrome black-T dye removal. The synthesis of these adsorbents were performed through N-carboxyanhydride (NCA) polymerization at low temperature (4 °C) and near-neutral pH for 24 h followed by chemical co-precipitation. The synthesized adsorbents were found to exhibit BET surface area (54-87 m²/g), pore volume (0.30-0.35 cm³/g), average pore diameter (160-218 Å) and average pore width (136-171 Å). The developed adsorbents were tested in a batch dye adsorption system. Adsorption was found to follow pseudo-second order kinetics and the Langmuir adsorption capacities were 123, 204 and 217 mg/g for Fe₃O₄, 0.5:1 and 1:1 adsorbent samples, respectively. Chemical regeneration was successfully carried out using methanol and the reusability of the adsorbents were demonstrated with a decrease in adsorption capacities from ∼49 to ∼33 mg/g after the fourth reuse.

A simple magnetic solid-phase extraction method based on magnetite/graphene oxide nanocomposite for pre-concentration and determination of melamine by high-performance liquid chromatography

In this study, a clean and simple magnetic solid-phase extraction (MSPE) procedure using magnetite/graphene oxide nanocomposite as an adsorbent was developed for melamine separation and preconcentration from water and dairy products. After synthesis and characterization of the adsorbent, adsorption isotherms and kinetic studies of the adsorption were carried out. The analyte quantification was performed by reversed phase high-performance liquid chromatography after elution of the preconcentrated analytes from the adsorbent surface. Several factors affecting the extraction/preconcentration procedure such as pH, adsorbent amount, extraction time, sample volume, type, and volume of eluent were investigated. The optimizing of some important parameters was assessed by employing a response surface method. The constructed calibration curve in the optimized conditions is linear in the working range of 0.10-100 μg L^-1 with a correlation coefficient of 0.9999. The detection limit, limit of quantification, and enrichment factor are 0.03 μg L^-1, 0.10 μg L^-1, and 500, respectively. The melamine relative recoveries from different real samples are between 97.20 and 103.10% with relative standard deviations of 1.07-4.98%.

Preparation of microwave-activated magnetic bio-char adsorbent and study on removal of elemental mercury from flue gas

In this study, novel activated magnetic bio-char adsorbents were proposed to remove the element mercury (Hg⁰) from flue gas. Microwave activation and Mn-Fe mixed oxides impregnation assisted by ultrasound treatment were applied on the modification of renewable cotton straw chars. The influence of different preparation methods, loading value of Mn-Fe, molar ratio of Mn/Fe, calcining temperature, reaction temperature and individual flue gas ingredients (O₂, NO, SO₂ and H₂O) on removal of Hg⁰ was investigated in a fixed bed system. The characterization results reveal that microwave activation is advantageous for the development of the pore structure, and ultrasound treatment can optimize the dispersion of Mn and Fe active ingredients. MnFe4%(3/10)/CSWU700 adsorbent exhibits the optimal Hg⁰ removing performance. O₂, NO, low concentration of SO₂ (<600 ppm) and low concentration of H₂O (<2%) are found to be favourable for the capture of Hg⁰, while high concentrations of SO₂ and H₂O inhibit the removal of Hg⁰. Chemical adsorption acts a pivotal part in the process of Hg⁰ removal. Mn and Fe active ingredients are consumed in large quantities during the Hg⁰ capture. In addition, chemisorbed oxygen (O_β) also plays an indispensable in the oxidation process of Hg⁰. Furthermore, the magnetic adsorbent MnFe4%(3/10)/CSWU700 presents a good regeneration performance and adsorption capacity.

Carbothermal preparation of magnetic-responsible ferrihydrite based on Fe-rich precipitates for immobilization of arsenate and antimonate: Batch and spectroscopic studies

The present study provides the starch-mediated carbothermal preparation of magnetic-responsible ferrihydrite (MFHP) based on Fe-rich precipitates which is recovered by mine drainage for immobilization of arsenate and antimonate in water. Fe K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) represented partial transformation from ferrihydrite to magnetite in MFHP due to the carbothermal reduction process, resulting in an effective saturation magnetism (= 19.2 emu/g). As and Sb K-edge EXAFS revealed that arsenate ion combines onto the surface of MFHP as inner-sphere binuclear bidentate surface complex, and antimonate forms inner-sphere mononuclear bidentate complex. In addition, the leachability by toxicity characteristic leaching procedure (TCLP) implies the environmental friendly preparation method for preparing magnetic-responsible adsorbents using mining waste.

Study on adsorption properties and mechanism of thallium onto titanium‑iron magnetic adsorbent

Thallium (Tl) contamination caused by the industrial wastewater leakage has become a serious environmental problem due to thallium's high toxicity. In this study, a novel titanium‑iron magnetic nano-sized adsorbent was synthesized and applied for the effective removal of thallium(I). The physicochemical properties of the adsorbent were investigated by a series of techniques such as scanning electron microscope (SEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). About 83% of equilibrium adsorption capacity could be accomplished within the initial 30 min. The adsorption of Tl(I) was found to be highly dependent on solution pH. The maximum adsorption capacity of Tl(I) was 111.3 mg/g at pH 7.0. The presence of such co-existing cations as Na⁺, Mg²⁺, Ca²⁺ and Cu²⁺ could have a certain influence on the uptake of Tl(I). The adsorption mechanism was proposed as a surface complexation process of Tl(I) ions by binding to deprotonated sites of hydroxyl groups on the adsorbent surface. The prepared magnetic adsorbent would be suitable for effectively treating thallium-containing water due to its promising adsorption ability towards Tl(I) and ease in operation.

Preparation of magnetic hydrogel microspheres of lignin derivate for application in water

A low-cost and well-separated approach is introduced for adsorption pollutants in water. Chemical modified lignin is prepared with diethylenetriamine to enhance the reaction activities, then used to prepare lignin derivate magnetic hydrogel microspheres (LDMHMs) via blending with Fe₃O₄. The LDMHMs are successful prepared by the determination of FT-IR data, and the morphology shown from SEM imagine indicates the LDMHMs are in nanosized. The prepared LDMHMs are used as adsorbents for organic dyes, such as methylene blue (MB), methyl orange (MO) and malachite green (MG), the plateaus data are 43 mg/g, 39 mg/g and 155 mg/g, respectively. For inorganic pollutions, such as Pb²⁺, Hg²⁺ and Ni²⁺, the plateaus data are 33 mg/g, 55 mg/g and 23 mg/g, respectively. The adsorption data of unmodified lignin are 2.6 mg/g (Pb²⁺), 3.3 mg/g (Hg²⁺), 2.1 mg/g (Ni²⁺), 8 mg/g (MB), 10 mg/g (MG) and 2 mg/g (MO) in the same condition. The adsorbents are recycled by magnetic separation, regenerating from acid condition and reused for multiple cycles. The regeneration ratios are all above 90%, indicating a highly reusability and further reducing the cost of the treatment.

Thermal conversion of pineapple crown leaf waste to magnetized activated carbon for dye removal

Pineapple crown leaf was successfully converted to the magnetized activated carbon (MAC) as an attractive solution to overcome separation problems. The activated carbon (AC) was produced by an innovative method combining KOH activation and microwave heating while the magnetization process was prepared by a co-precipitation method. In this sense, the activation stage was studied at different impregnation ratio. The resulted magnetic adsorbent was further tested its feasibility for methyl violet dye removal. The result shows that MAC consists of both micropores and mesopores with more oxygen-containing functional groups, indicating it can be used to remove dye from contaminated water. The increase of impregnation ratio led to an increase in the MAC porosity and a decrease in the magnetic property. The adsorption behavior of methyl violet dye onto MAC was well described by the Redlich-Peterson isotherm model.

Experimental and theoretical investigations of Cs+ adsorption on crown ethers modified magnetic adsorbent

Carboxyl Fe₃O₄ nanoparticles (Fe₃O₄@R-COOH) modified with 18-Crown-6 ether functional groups have been prepared via an amidation reaction and used as bifunctional adsorbent for Cs⁺. The adsorbent has a superparamagnetic property, allowing an easy recycling, and a high capacity of Cs⁺ adsorption on the crown ether. The adsorption isotherms and kinetic behaviors agree well with the Langmuir and the pseudo-second-order models. The material exhibits a high selectivity for Cs⁺ in the solution with co-existing cations (NH₄⁺, Rb⁺, K⁺, Na⁺ and Li⁺). A theoretical calculation according to density functional theory (DFT) is used to estimate the structure of Cs⁺ adsorption on crown ether, demonstrating an exothermic process and showing a good agreement with the experimental observations. The adsorption behavior is affected not only by the size of macrocyclic crown ethers, but also by the chelating symmetry and the binding energy. The newly developed adsorbent has a potential application for removing cesium out of wastewater and salt lakes.

Synthesis of novel sepiolite-iron oxide-manganese dioxide nanocomposite and application for lead(II) removal from aqueous solutions

In this study, the sepiolite-iron oxide-manganese dioxide (Sep-Fe₃O₄-MnO₂) nanocomposite was synthesized and applied as a magnetically separable adsorbent for removal of Pb(II) ions from water in a batch system. The effects of initial Pb(II) concentration, adsorbent dosage, contact time, pH value, and temperature were investigated to optimize the conditions for maximum adsorption. The equilibrium adsorption data were analyzed with the Langmuir, Freundlich, and Temkin models. The adsorption process closely agreed with the Langmuir adsorption isotherm, and the monolayer saturation adsorption value was achieved as 131.58 mg g^-1. The adsorption kinetics follow the pseudo-second-order (PSO) model that illustrated the rate controlling step might be chemisorption. Thermodynamic investigations for the removal process were conducted by determining the values of ∆G°, ∆H°, and ∆S°. The adsorption behavior of Pb(II) on the Sep-Fe₃O₄-MnO₂ was a spontaneous and endothermic process. Several consecutive adsorption-desorption cycles confirmed that the proposed Sep-Fe₃O₄-MnO₂ nanocomposite could be reused after successive lead removal. Furthermore, the practical application of the adsorbent was successfully realized by the treatment of real Pb-contaminated water samples.