Fabrication of MoS2 restrained magnetic chitosan polysaccharide composite for the photocatalytic degradation of organic dyes

Chitosan (CS) polysaccharide is expected to exhibit greater ionic conductivity, which can be attributed to its increased amino group content when it is blended with different semiconducting materials. Herein, the work used this conducting ability of chitosan and prepared a heterogeneous MoS2-induced magnetic chitosan (MF@CS) composite via the co-precipitation method, which was used to scrutinize the catalytic performance with Methylene Blue (MB) and Malachite Green (MG) dyes by visible light irradiation. The saturation magnetization value of the MF@CS composite is found to be 7.8 emu/g, which is less when compared to that of pristine Fe3O4 (55.7 emu/g) particles. The bandgap of the MF@CS composite is ∼ 2.17eV, which exceeds the bandgap (Eg) of bare MoS2 of 1.80 eV. The maximum color removal of 96.3 % and 93.4 % for MB and MG dyestuffs is recognized in the exposure of the visible spectrum, respectively. At a starting dye dosage of 30 mg/L, 0.1 g/L of MF@CS, a pH level of 8-11, and 70 min of contact with direct light. The photocatalyst provides extremely good durability for a maximum of five phases. Hence, the MF@CS matrix is a viable and appropriate substance for the efficient treatment of effluents containing dye molecules.

Synthesis of magnetic biochar composite using Vateria indica fruits through in-situ one-pot hydro-carbonization for Fenton-like catalytic dye degradation

The present study reports the synthesis, characterization, and application of sustainable magnetic biochar composite. The inedible fruits of Vateria indica, a powerful ayurvedic plant were hydrothermally transformed into magnetic biochar (BC-Fe3O4) in a single step and characterized by several sophisticated techniques. FESEM analysis portrayed fibrous irregular mesh-like biochar with surface clustered Fe3O4 nanoparticles, while the incidence of carbon, oxygen, and iron in the elemental analysis by EDS established magnetic biochar formation. Numerous peaks consistent with planes of (220), (311), (400), (422), (511), (440), and (120) also substantiated the occurrence of magnetite nanoparticles and biochar respectively, as analyzed by XRD. XPS analysis showed signals at 285.65 eV, 533.28 eV, 711.08 eV, and 724.68 eV corroborating a strong C-O bond, O1s orbit, Fe2+, and Fe3+ respectively. BC-Fe3O4 was superparamagnetic with saturation magnetization of 4.74 emu/g, as per VSM studies, while its specific surface area, pore volume, and pore diameter were 5.74 m2/g, 0.029 cm3/g, and 20.86 nm respectively. The Fenton-like degradation of methylene blue (5.0-25.0 ppm) was accomplished by synthesized BC-Fe3O4, in the presence of H2O2. Within 180 min, almost complete degradation was achieved, with first-order kinetics having rate constants between 0.0299 and 0.0167 min-1. Stability and recyclability studies performed over 7 cycles exhibited unaltered degradation between 93.98 and 97.59%. This study exhibits the exceptional characteristics and degradation capabilities of BC-Fe3O4 synthesized from a sustainable plant biomass.

Application of a novel polymer cross-linked with magnetite for efficient norfloxacin adsorption at a wide pH range

Nowadays, NOR-containing wastewater has placed huge pressure on global ecology. In this study, a chemically-modified chitosan-based polymer was cross-linked with magnetite to prepare a novel magnetic composite adsorbent named Fe3O4/CS-P(AM-SSS) for norfloxacin (NOR) removal. The preparation conditions were optimized by single factor experiments and response surface methodology. A series of characterization analyses were carried out on the morphology, structure, and properties of Fe3O4/CS-P(AM-SSS), verifying that Fe3O4/CS-P(AM-SSS) was successfully prepared. Batch adsorption experiments showed that NOR was efficiently removed by Fe3O4/CS-P(AM-SSS), with a broad pH applicability of 3-10, short adsorption equilibrium time of 60 min, maximum adsorption capacity of 268.79 mg/g, and high regeneration rate of 86% after eight adsorption-desorption cycles. Due to the three-dimensional network structure and abundant functional groups provided by modified chitosan polymer, the superior adsorption capability of Fe3O4/CS-P(AM-SSS) was achieved through electrostatic interaction, π-π stacking, hydrophobic interaction, and hydrogen bonding. Adsorption process was exothermic and well fitted by the pseudo-second-order kinetic model and the Langmuir isothermal model. The presence of cations had a slight inhibitory effect on NOR adsorption, while humic acid nearly had no effect. In model swine wastewater, 90.3% NOR was removed by Fe3O4/CS-P(AM-SSS). Therefore, with these superior characteristics, Fe3O4/CS-P(AM-SSS) was expected to be an ideal material for treating NOR-containing wastewater in the future.

Graphene oxide@Fe3O4-decorated iota-carrageenan composite for ultra-fast and highly efficient adsorption of lead (II) from water

The aggravated problem of lead pollution, especially in aquatic environments, necessitates the development of eminent adsorbents that could radically solve this environmental problem. Hence, a new composite was constructed based on iota carrageenan (i.Carr), graphene oxide (GO) and magnetite (Fe3O4) for removing noxious Pb2+ ions. The GO@Fe3O4-i.Carr composite was characterized by VSM, SEM, XPS, XRD, FTIR and Zeta potential. The removal of Pb2+ ions attained a quick equilibrium of almost 30 min with a removal efficiency reaching 93.68 %. The removal of Pb2+ was boosted significantly, in the order of GO@Fe3O4-i.Carr(1:1) > GO@Fe3O4-i.Carr(1:3) > GO@Fe3O4-i.Carr(3:1). Moreover, acquired experimental data fitted the pseudo 2nd order kinetic model and Freundlich isotherm model with a maximal monolayer adsorption capacity reached 440.05 mg/g. Notably, after five adsorption runs, the composite maintained its removal efficiency exceeding 74 %. The assumed adsorption mechanisms of Pb2+ onto GO@Fe3O4-i.Carr were complexation, precipitation, Lewis acid-base, and electrostatic attraction forces. Overall, the GO@Fe3O4-i.Carr composite elucidated the auspicious adsorbent criteria, comprising fast adsorption with high performance, ease-separation and tolerable recyclability, advising its feasible use to decontaminate water bodies from hazardous heavy metals.

Enhanced catalytic reduction of emerging contaminant by using magnetic CuFe2O4@MIL-100(Fe) in Fenton-based electrochemical processes

Fenton-based electrochemical processes (FEPs) using newly engineered 3D photocatalyst nanocomposites have garnered significant attention owing to their ability to remove emerging contaminants. Despite the development of numerous materials, there is still a need to enhance their efficiency, stability, and recyclability to address the limitations of FEPs. This study seeks to address this issue by investigating sustainable methods to engineer novel 3D core-shell photocatalyst composites for application in FEPs. These materials can update the photo-assisted PEFs activity, and magnetism can be helpful for the easy recyclability of the catalyst. Herein, we successfully synthesized a magnetic and photoactive CuFe₂O₄@MIL-100(Fe) (CM) composite through sustainable methods and assessed its morphological structure and physicochemical and photocatalytic properties. The catalytic performance of CM was investigated in an undivided RuO₂/air-diffusion cell to treat Cefadroxil. The results show that heterogeneous photoelectro-Fenton (HPEF) (100% in 120 min) has higher degradation efficiency than electro-Fenton (100% in 210 min) and electrooxidation (73.3% in 300 min) processes. The superior degradation efficiency of HPEF is attributed to the formation of a large amount of hydroxyl radicals indicating the excellent photocatalytic activity of the material due to the direct excitation of the Fe-O cluster, which boosts the redox reaction of Fe²⁺/Fe³⁺. Key operational parameters such as pH, catalyst concentration, current density, and CuFe₂O₄ proportion on MIL-100(Fe) in the composite were optimized in the HPEF process. The optimized composite exhibited good stability and easy recyclability, allowing high removal efficiency, which can be kept up after five cycles of 90 min. High degradation performance was observed using natural sunlight radiations. Additionally, possible catalytic degradation mechanisms in HPEFs were proposed based on radical quenching experiments. This study has significant potential to contribute to the development of more sustainable and effective water treatment strategies.

Adsorption of nitrophenol onto a novel Fe3O4-κ-carrageenan/MIL-125(Ti) composite: process optimization, isotherms, kinetics, and mechanism

Water pollution is a dreadful affair that has incessantly aggravated, exposing our planet to danger. In particular, the persistent nitro aromatic compound like nitrophenols causes anxiety to the researchers due to their hazardous impacts, excessive usage, and removal difficulty. For this purpose, a novel multi-featured composite was constructed based on κ-Carrageenan (κ-Carr), MOF (MIL-125(Ti)), and magnetic Fe3O4 for efficient adsorptive removal of o-nitrophenol (o-NP). Interestingly, BET measurements revealed the high surface area of Fe3O4-κ-Carr/MIL-125(Ti) of about 163.27 m2/g, while VSM showed its excellent magnetic property (20.34 emu/g). The comparison study pointed out the synergistic effect between Fe3O4, κ-Carr, and MIL-125(Ti), forming a composite with an excellent adsorption performance toward o-NP. The adsorption data obeyed pseudo-second-order kinetic model, and Freundlich isotherm model was better fitted than Langmuir and Temkin. Furthermore, Langmuir verified the supreme adsorption capacity of o-NP onto Fe3O4-κ-Carr/MIL-125(Ti) since the computed qmax reached 320.26 mg/g at pH 6 and 25 °C. Furthermore, the XPS results postulated that the adsorption mechanism pf o-NP proceeded via H-bonding, π-π interaction, and electron donor-acceptor interactions. Interestingly, Fe3O4-κ-Carr/MIL-125(Ti) composite retained good adsorption characteristics after reusing for five cycles, suggesting its viable applicability as an efficient, renewable, and easy-separable adsorbent for removing nitro aromatic pollutants.

Recoverable cellulose composite adsorbents for anionic/cationic dyes removal

GO/HEC/PGDE/Fe₃O₄ materials were successfully fabricated using environmentally-friendly hydroxyethyl cellulose (HEC), poly(ethylene glycol) diglycidyl ether (PGDE), graphene oxide (GO) and magnetic Fe₃O₄. Systematic investigations were completed to explore the influences of GO content in GO/HEC/PGDE/Fe₃O₄ and adsorption conditions on the adsorptions of cationic dyes (methylene blue (MB), crystal violet (CV)) and anionic dye acid blue 25 (AB-25). The increase of GO content can remarkably improve the adsorption capacity of GO/HEC/PGDE/Fe₃O₄ for the dyes. The three kinetic, four isothermic and three thermodynamic models were investigated to reveal the adsorption behaviors of the dyes. The formation of HEC/PGDE/Fe₃O₄ and adsorption mechanisms of the dyes by GO/HEC/PGDE/Fe₃O₄ were suggested. The GO/HEC/PGDE/Fe₃O₄ endowed with easy-fabrication, eco-friendly feature, efficient adsorption capacity of anionic/cationic dyes, convenient separation and reusability has potential applications in wastewater purification industry.

Highly efficient removal of hexavalent chromium by magnetic Fe-C composite from reed straw and electric furnace dust waste

Reed straw and electric furnace dust (EFD) waste were used to prepare magnetic Fe-C composite (EFD&C) by co-precipitation and high-temperature activation method to remove Cr(VI) from water. The magnetic EFD&C owned a large specific surface (536.61 m²/g) and a porous structure (micropores and mesopores), and had an efficient removal capacity for Cr(VI). Under conditions of pH (2), the addition amount of EFD&C (1 g/L), the adsorption time (760 min), and the temperature (45 °C), the maximum adsorption capacity reached 111.94 mg/g. The adsorption mechanism mainly attributed to chemical adsorption (redox), Cr(VI) reduced to Cr(III) by Fe(II) and Fe(0) (from Fe₃O₄ and Fe components in EFD) and surface functional groups of -OH, C = C, C-C and O-C = O (from biochar), and secondary attributed to physical adsorption, Cr(VI) and Cr(III) (from reduced Cr(VI)) adsorbed into the porous structure of EFD&C. This study provided a feasible solution for the preparation of adsorbents for adsorbing heavy metals from iron-containing metallurgical solid waste and biomass waste, which contributed to reducing the environmental pollution and lowering the cost of adsorbent preparation.

Construction of porous carbon-based magnetic composites derived from iron zinc bimetallic metal-organic framework as broadband and high-efficiency electromagnetic wave absorbers

The fabrication of broadband and high-efficiency electromagnetic (EM) wave absorbers remains a huge challenge. Metal-organic framework (MOF) with large porosity and high specific surface area has been considered as a promising precursor for the preparation of novel EM wave absorbers. In this work, porous carbon-based magnetic composites derived from iron zinc bimetallic MOF were prepared by the two-step method of solvothermal reaction and high-temperature pyrolysis. Results of micromorphology analysis demonstrated that the morphology of carbon frameworks evolved from octahedron, polyhedron, sphere to porous sphere-like shape with the increase of pyrolysis temperature. Furthermore, the EM parameters and absorbing properties of obtained composites were regulated through simply changing the pyrolysis temperature. It was noteworthy that the as-prepared Fe₃O₄/C composite pyrolyzed at 700 °C exhibited the best EM absorption performance. The minimum reflection loss was as large as -60 dB and broad absorption bandwidth reached up to 4 GHz (8-12 GHz, covering the whole X band) at a matching thickness of 2.5 mm and a filler loading ratio of 40 wt%. Furthermore, the maximum absorption bandwidth could be enlarged to 5.4 GHz via reducing the matching thickness to 1.85 mm. Additionally, the probable EM attenuation mechanisms of attained composites were proposed. The results of this study would provide a reference for the preparation of porous carbon-based composites as broadband and high-efficiency EM wave absorbers.

Anchoring ZnO on spinel cobalt ferrite for highly synergic sono-photo-catalytic, surfactant-assisted PAH degradation from soil washing solutions

In this study, the photocatalytic activity of ZnO was effectively improved via its combination with spinel cobalt ferrite (SCF) nanoparticles. The catalytic performance of ZnO@SCF (ZSCF) was investigated in coupling with UV irradiation and ultrasound (US), as a heterogeneous sono-photocatalytic process, for the decontamination of phenanthrene (PHE) from contaminated soil. Soil washing tests were conducted in a batch environment, after extraction assisted by using Tween 80. Several characterization techniques such as XRD, FESEM-EDS, BET, TEM, UV-vis DRS, PL and VSM were utilized to determine the features of the as-prepared catalysts. ZSCF showed an excellent catalytic activity toward degradation of PHE in the presence of US and UV with a significant synergic effect. It was found that more than 93% of PHE (35 mg/L) and 87.5% of TOC could be eliminated by the integrated ZSCF/US/UV system under optimum operational conditions (pH: 8.0, ZSCF: 1.5 g/L, UV power: 6.0 W and US power: 70 W) within 90 min of reaction. After five times of use, ZSCF illustrated good reusability in the decontamination of PHE (87%) and TOC (79%). Quenching tests revealed the contribution of h⁺, HO^• and e^- species during PHE degradation over ZSCF/UV/US and an S-scheme photocatalytic mechanisms was proposed for the possible charge transfer routes under the ZSCF system. This study provides the important role of SCF in enhancing the ZnO photocatalytic activity due to its high performance, easy recovery and excellent durability, which it make an efficient and promising catalyst in environmental clean-up applications.

A photoelectrochemical immunosensor based on magnetic all-solid-state Z-scheme heterojunction for SARS-CoV-2 nucleocapsid protein detection

Rapid, convenient and accurate detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to timely diagnosis of coronavirus pandemic (COVID-19) and control of the epidemic. In this study, a signal-off photoelectrochemical (PEC) immunosensor was constructed for SARS-CoV-2 nucleocapsid (N) protein detection based on a magnetic all-solid-state Z-scheme heterojunction (Fe₃O₄@SiO₂@TiO₂@CdS/Au, FSTCA). Integrating the advantages of magnetic materials and all-solid-state Z-scheme heterostructures, FSTCA was implemented to ligate the capture antibody to form magnetic capture probe (FSTCA/Ab₁). It can simplify the separation and washing process to improve reproducibility and stability, while allowing immune recognition to be performed in the liquid phase instead of the traditional solid-liquid interface to improve anti-interference. Besides, the heterojunction inhibited the recombination of photogenerated electron/hole (e^-/h⁺) and promoted the light absorption to provide superior photoelectric substrate signal. The mechanism of photogenerated e^-/h⁺ transfer of FSTCA were investigated by the electron spin resonance (ESR) spectroscopy. SiO₂ spheres loaded with Au NPs utilized as an efficient signal quencher. The steric hindrance effect of SiO₂@Au labeled detection antibodies (SiO₂@Au-Ab₂) conjugates significantly diminished light absorption and hindered the transfer of photogenerated electrons, further amplifying the signal change value. Based on the above merits, the elaborated immunosensor had a wide linear range of 10 pg mL^-1-100 ng mL^-1 and a low detection limit down to 2.9 pg mL^-1 (S/N = 3). The fabricated PEC immunosensor demonstrated strong anti-interference, easy operation, and high sensitivity, showing enormous potential in clinical diagnosis of SARS-CoV-2.

Glutaraldehyde base-cross-linked chitosan-silanol/Fe3O4 composite for removal of heavy metals and bacteria

We designed and synthesised a magnetic adsorbent (Fe₃O₄@Si-OH@CS-Glu) combining chitosan-silanol groups with glutaraldehyde as a cross-linking agent, which has improved physicochemical properties and can be used to remove multiple heavy metals and bacteria from polluted water. The adsorbent was characterised with SEM, XRD, FTIR, BET, VSM, and zeta potential. Under optimum conditions, the adsorption efficiencies of Fe₃O₄@Si-OH@CS-Glu for Cr⁶⁺, As⁵⁺, Hg²⁺, and Se⁶⁺ were as high as 90.5%, 73.5%, 91.6%, and 100% respectively. In addition, Escherichia coli (gram-negative) and Staphylococcus aureus (gram-positive) can be removed after 2-4 adsorption cycles with 2.5 mg Fe₃O₄@Si-OH@CS-Glu. The main adsorption mechanism of the adsorbent for heavy metals and bacteria is electrostatic adsorption. Overall, the synthesised Fe₃O₄@Si-OH@CS-Glu adsorbent showed high removal efficiency and adsorption capacity with a stable structure and easy separation. It has promising applications for the removal of heavy metals and bacteria from water.

Synthesis of ferroferric oxide@silicon dioxide/cobalt-based zeolitic imidazole frameworks for the removal of doxorubicin hydrochloride from wastewater

Due to its low-cost, eco-friendliness and easy mode of separation biosynthesized magnetic ferroferric oxide (Fe₃O₄) can be successfully used for the removal of organic contaminants from wastewater. However, there are some challenges that to date have limited this compound's practical removal efficiency. Thus, in this study, a cobalt-based zeolitic imidazole frameworks (ZIF-67) coated biosynthesized ferroferric oxide@silicon dioxide (Fe₃O₄@SiO₂) magnetic composite (Fe₃O₄@SiO₂/ZIF-67) was prepared to address these issues and subsequently used to remove doxorubicin hydrochloride (DOX). Characterization results showed that the fabricated composite exhibited significant magnetic properties (16.1 emu·g^-1) with a size ranging between 50 and 250 nm. The amount of DOX adsorbed by the composite (90.7 mg·g^-1) was much higher than either of the component parts, which were only 35.7 and 82.5 mg·g^-1 for Fe₃O₄@SiO₂ and ZIF-67 respectively. This indicated enhanced DOX adsorption by Fe₃O₄@SiO₂/ZIF-67. The DOX adsorption best fit a pseudo-second order kinetic and Langmuir adsorption model. These studies suggested that the DOX adsorption mechanism involved a combination of electrostatic interactions, π-π stacking, hydrogen bonding and pore filling. Regeneration and application studies, exposing Fe₃O₄@SiO₂/ZIF-67 to real water samples, practically demonstrated that Fe₃O₄@SiO₂/ZIF-67 with propensity for magnetic separation and recycle is a promising nanomaterial for DOX removal.

Determining three isoflavones from Pueraria lobata using magnetic ZIF-8 nanoparticle-based solid-phase extraction and pressurized capillary electrochromatography

In this study, magnetic functionalized ZIF-8 nanoparticles were prepared by electrostatic self-assembly using magnetic Fe₃O₄ nanoparticles as cores and ZIF-8 as shells. ZIF-8 was used as the adsorbent to efficiently extract and sensitively analyze isoflavones due to its positive charge and strong adsorption capacity. Prepared samples were investigated by SEM and TEM, BET and ζ-potential analyses, FT-IR spectroscopy, powder XRD, and vibrating sample magnetism (VSM) experiments. The synthesized ZIF-8 has a dodecahedral structure that adsorbs well. Magnetic functionalized ZIF-8/Fe₃O₄ @SiO₂ nanoparticles were prepared as a new SPE adsorbent, and a magnetic ZIF-8-pressurized capillary electrochromatography (pCEC) method was developed to separate and detect puerarin, daidzin, and daidzein (isoflavones) from Pueraria lobata by optimizing the extraction conditions, including adsorbent dosage, salt concentration, extraction time, desorption conditions, and other parameters. The developed method exhibited good linearities in the 50-2000 μg/mL concentration range for the three isoflavones, with coefficients of determination of 0.9934-0.9962. The limits of detection (LODs) for puerarin, daidzin, and daidzein were determined to be 0.02, 0.03, and 0.03 μg/mL, respectively. All analytes showed average recoveries in the 98.5-100.3% range, with relative standard deviations (RSDs, n = 6) of less than 4.0%. The developed method is convenient, enriches effectively, and shows good applications prospects for separating and analyzing components in Chinese herbal medicines.

Decoration of Citrus limon wood carbon with Fe3O4 to enhanced Cd2+ removal: A reclaimable and magnetic nanocomposite

In the present study, the activated carbon of lemon (ACL) was generated from Citrus limon wood waste and composited with Fe₃O₄ nanoparticles. The ACL/Fe₃O₄ magnetic composite was effectively used to eliminate Cd²⁺ from an aqueous solution. The active surface area values for ACL and ACL/Fe₃O₄ magnetic composite were 25.99 m²/g and 38.70 m²/g, respectively indicating the effectiveness of Fe₃O₄ nanoparticles in improving ACL active surface area. The response surface methodology with central composite design (RSM-CCD) was used to determine optimal values of pH, ACL/Fe₃O₄ dose, contact time, and Cd²⁺ concentration on the decontamination efficiency. The Langmuir and Freundlich isotherm models had more potential to describe the adsorption process using ACL and ACL/Fe₃O₄, respectively. The Langmuir-based adsorption capacity was obtained as 28.2 mg/g (ACL) and 39.6 mg/g (ACL/Fe₃O₄). A pseudo-second order (PSO) model was successfully applied to evaluate the adsorption process kinetic behavior. A higher value of α parameter for ACL/Fe₃O₄ (5.7 mg/g.min) than that of ACL (3.5 mg/g.min) indicated that the magnetic composite had a greater tendency to absorb Cd²⁺. In addition, the Weber-Morris model showed that various mechanisms such as intraparticle diffusion and boundary layer effects may have a role in the adsorption process. The study of ad(de)sorption behavior showed that the adsorbents have a good ability to adsorb Cd²⁺ and no significant change in their performance has been made up to 4 times of reuse. Our results showed that ACL modification using Fe₃O₄ nanoparticles improved the adsorption efficiency of ACL to remove Cd²⁺ from the aqueous solutions.

Polydopamine-coated magnetic nanoparticles for the determination of nitro musks in environmental water samples by stir bar sorptive-dispersive microextraction

Magnetic-based microextraction approaches have gained popularity in recent years due to the magnetic properties of the extraction phases allowing to handle them easier and more efficiently. This work describes a magnetic-based analytical method for the determination of the family of nitro musks in environmental water samples. These compounds have been of great concern due to their environmental impacts and potential health effects. The method is based on stir bar sorptive-dispersive microextraction (SBSDME) as extraction approach, prior to thermal desorption coupled to gas chromatography-mass spectrometry analysis (TD-GC-MS). For this purpose, polydopamine-coated cobalt ferrite magnetic nanoparticles (CoFe₂O₄@PDA) were used as extraction material. The main parameters involved in the extraction procedure (i.e., sorbent amount, extraction time and ionic strength) as well as in the thermal desorption step (i.e., temperature and desorption time) were evaluated in order to obtain the highest sensitivity. Under the selected conditions, the method showed good linearity, limits of detection and quantification in the low ng L^-1 range, intra- and inter-day repeatability with RSD <15%, and high enrichment factors (178-640). Finally, the method was applied to four environmental water samples of different origin. Relative recovery values ranging from 91 to 120% highlighted that the matrices under consideration do not affect the extraction process. This work constitutes the first time in which nitro musks compounds were selectively extracted by taking advantage the high potential that magnetic-based microextraction techniques offer, specially SBSDME.

Selective and fast recovery of rare earth elements from industrial wastewater by porous β-cyclodextrin and magnetic β-cyclodextrin polymers

Recovery of rare earth elements (REEs) from industrial wastewater has drawn great attention due to their potential environmental toxicity, as well as their high demand in modern technologies. In this study, we developed a magnetic composite based on the high surface area porous β-cyclodextrin polymer (P-CDP), namely P-CDP@Fe₃O₄. Both P-CDP and P-CDP@Fe₃O₄ rapidly sequester REEs such as Nd, Gd, Eu, and Y, reaching equilibrium in less than 10 min and fitting the Langmuir isotherm model with maximum adsorption capacities ranging from 7.76 to 9.59 mg/g at 25 °C when the highest initial concentration was 100 mg/L. Besides, the recovery of these REEs was not affected by competitive alkali, alkaline earth, and transition metal ions in model studies and industrial wastewater as revealed by the recovery efficiencies, which ranged from 62% to 100% indicating an excellent selectivity on both adsorbents. In addition, both adsorbents can be fully regenerated under mildly acidic conditions for at least five consecutive cycles. Moreover, P-CDP@Fe₃O₄ can be easily isolated by an external magnetic field which simplifies its synthesis and usability. It also overcomes the clogging and high backpressure issues of P-CDP, which facilitates its application for REEs recovery as compared with P-CDP. These characteristics demonstrate the promise of P-CDP and P-CDP@Fe₃O₄ for the pollution control and recovery of REEs.

Removal of mercury(II) from wastewater using a new and effective composite: sulfur-coated magnetic carbon nanotubes

A sulfur-coated magnetic multi-walled carbon nanotube (S-M-MWCNT) composite was synthesized via coating a thin S layer on M-MWCNTs via a facile heating process. The prepared superparamagnetic adsorbent was employed for the uptake of mercury(II) (Hg(II)) from aqueous solutions and then magnetically separated without filtration or centrifugation steps. The adsorption of Hg(II) increased with increasing pH and reached a plateau value in the pH range 4.5-8.0. The adsorption kinetics followed the pseudo-second-order (PSO) model and equilibrium was reached within 3 h. The isotherm data obeyed the Langmuir isotherm model, and the maximum adsorption capacity of S-M-MWCNT adsorbent was acquired as 62.11 mg g^-1. The adsorption of Hg(II) by the prepared composite is possibly controlled by the interaction between Hg(II) as a soft acid and elemental coated sulfur as a soft base. In addition, the coexist metal ions including copper(II) (Cu(II)), cadmium(II) (Cd(II)), cobalt(II) (Co(II)), lead(II) (Pb(II)), manganese(II) (Mn(II)), zinc(II) (Zn(II)), and chromium(III) (Cr(III)) had no significant effects on Hg(II) removal performance. It was found that the S-M-MWCNT composite could be reused after successive Hg(II) removal without any loss of adsorption capacity. Furthermore, the magnetic adsorbent holds high potential in the treatment of Hg-contaminated wastewater samples.

Synthesis of magnetic graphene oxide-titanate composites for efficient removal of Pb(II) from wastewater: Performance and mechanism

Magnetic graphene oxide-titanate composites (MGO@TNs) were synthesized via growing titanate nanosheets on the graphene oxide sheets with magnetite nanoparticles anchored on. The as-prepared MGO@TNs showed a hierarchical structure and large specific surface area (193.4 m²/g), which were suitable for rapid and effective adsorption of Pb(II) from wastewater. Moreover, the loaded magnetite nanoparticles guaranteed the effective magnetic separation of MGO@TNs, avoiding secondary pollution. The adsorption mechanism were illuminated to be ion exchange and surface complexation. Batch adsorption experiments showed the maximum adsorption capacity of MGO@TNs reached 322.7 mg/g for Pb(II) removal. The removal efficiency retained 89.6% after six adsorption-desorption cycles. In addition, the efficiency reached up to 99.8% when applying MGO@TNs for removal of Pb(II) from simulated realistic battery wastewater, ensuring the safe discharge of treated water. The good adsorption performance, recyclability and easy magnetic separation ability made sure that the MGO@TNs has great potential for purification of Pb(II) contaminated wastewater.

Detoxification of Aflatoxin B1 by magnetic graphene composite adsorbents from contaminated oils

Safety concerns pertaining towards fungal occurrence in oil commodities have been a significant threat to human health. In this research, magnetic composite adsorbents were fabricated for the removal of aflatoxin B₁ (AFB₁) from contaminated oils. To this goal, graphene oxides (GO) were synthesized using Hummer's method, and graphenes (rGO) were obtained by the reduction of GO by sodium borohydride. Thereafter, magnetic graphene oxides (MGO) and magnetic graphenes (MrGO) were prepared by coprecipitation of iron oxides on GO and rGO nanosheets, respectively. The as-prepared MGO and MrGO were characterized by SEM, TEM, FT-IR, XRD, VSM, and nitrogen adsorption-desorption techniques. Results showed that MGO had two-dimensional layered nanostructure with many wrinkles on its surface, and the Fe₃O₄ nanoparticles were essentially encapsulated onto the composite. The adsorption behaviors for the composite adsorbents especially for the removal of AFB₁ from contaminated oils were systematically explored by varying adsorbent dosage, contact time, adsorption temperature and initial AFB₁ concentration. The MGO adsorbent could have great potential in the application of AFB₁ removal from contaminated oils, with the merits of facile magnetic separation and high removal efficiency. However, the removal process also causes a loss of the triglyceride, pigment, and beneficial micronutrients in the oil feedstocks.

LC-MS determination of catecholamines and related metabolites in red deer urine and hair extracted using magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) composite

A novel analytical methodology for the extraction and determination of catecholamines (dopamine, epinephrine and norepinephrine) and their metabolites DL-3,4-dihydroxyphenyl glycol and DL-3,4-dihydroxymandelic acid by LC-MS is developed and validated for its application to human and animal urine and hair samples. The method is based on the preliminary extraction of the analytes by a magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) composite. This is followed by a <9 min chromatographic separation of the target compounds in an Onyx Monolithic C₁₈ column using a mixture of 0.01% (v/v) heptafluorobutyric acid in water and methanol at 500 µL min^-1 flow rate. Detection limits within range from 0.055 to 0.093 µg mL^-1, and precision values of the response and retention times of analytes were >90%. Accuracy values comprised the range 79.5-109.5% when the analytes were extracted from deer urine samples using the selected MMWCNT-poly(STY-DVB) sorbent. This methodology was applied to real red deer urine and hair samples, and concentrations within range from 0.05 to 0.5 µg mL^-1 for norepinephrine and from 1.0 to 44.5 µg mL^-1 for its metabolite 3,4-dihydroxyphenyl glycol were calculated. Analyses of red deer hair resulted in high amounts of 3,4-dihydroxyphenyl glycol (0.9-266.9 µg mL^-1).

Synthesis of magnetic functionalized MWCNT nanocomposite through surface RAFT co-polymerization of acrylic acid and N-isopropyl acrylamide for removal of cationic dyes from aqueous solutions

In this study, magnetic multi-walled carbon nanotube (MMWCNT) composites were prepared via surface reversible addition fragmentation chain transfer (RAFT) co-polymerization of acrylic acid (AA) and N-isopropyl acrylamide (NIPAM) in the presence of Fe₃O₄ nanoparticles. First, a novel RAFT agent (RA) was prepared and then immobilized onto the surface of MWCNT to fabricate RA-g-MWCNT. Then, Fe₃O₄ nanoparticles were attached onto the surface of RA-g-MWCNT. Finally, RAFT co-polymerization of AA and NIPAM monomers was carried out via Fe₃O₄-g-RA-g-MWCNT RAFT agent. The structure and morphology of the prepared polymer-coated MWCNT was examined by FTIR, SEM, TEM, XRD, VSM, and TGA. The adsorption behaviours of the cationic dyes were studied. The equilibrium isotherm and kinetics of cationic dyes were investigated. Thermodynamics investigations also depicted that the adsorptions of cationic dyes were spontaneous and endothermic in nature. The synthesized dye adsorbent with high adsorption capacities, reusability, and easy recovery makes it as a good candidate for wastewater treatment.

Effective adsorption of malachite green using magnetic barium phosphate composite from aqueous solution

Magnetic Ba₃(PO₄)₂/Fe₃O₄-nanoparticle (called BPFN) was prepared, characterized, and developed as a low-cost adsorbent for malachite green (MG) from aqueous solution. Factors such as adsorption temperature, pH of solution, dosage of adsorbent, adsorption kinetics and isotherms were investigated. The maximum adsorption capacity obtained in this work was 1639mgg^-1 at 45°C and pH6. The adsorption process fitted the pseudo-first-order kinetic model and Langmuir isotherm model. Evidences from zeta potential, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) data revealed that the adsorption process was driven by electrostatic attraction, the interaction between Lewis base N(CH₃)₂ in MG and Lewis acid Ba sites of BPFN. In addition, the BPFN could be easily regenerated by a magnet and the adsorption capacity maintained at 70% after five cycles. The present study suggests that the BPFN had high potential of removing MG from wastewater.

Preparation of La-modified magnetic composite for enhanced adsorptive removal of tetracycline

Composite adsorbents usually outperform single component adsorbents as they could combine the properties and advantages of each component. In this research, rare earth element Lanthanum was introduced into magnetic substrate by a method of chemical co-precipitation to enhance its adsorption capability. It was found that the La-modified magnetic composite with a presumed La and Fe₃O₄ molar ratio at 1:50 had a better adsorption performance for tetracycline than the magnetic adsorbents at other molar ratios. The La-modified magnetic composite was characterized by scanning electron microscope, X-ray diffractometer, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results showed that the magnetic adsorbent was nano-sized, and the introduction of La did not change the crystal structure of magnetic substrate. The adsorptive removal of tetracycline was favorable at neutral pH conditions. Kinetic experiments indicated that most of the uptake occurred within the initial 120 min. Chemisorption occurred in the process while rate-determining step might be diffusive in nature. An empirical model (Langmuir model) was applied in this paper, and fitting result indicates that the q _max value of the magnetic composite reached as much as 145.9 mg/g for the uptake of tetracycline at 298 K. The above indicates that method of La doping could significantly enhance the adsorption capability of an intentionally designed composite adsorbent.

Removal of Cs+ from water and soil by ammonium-pillared montmorillonite/Fe3O4 composite

To remove cesium ions from water and soil, a novel adsorbent was synthesized by following a one-step co-precipitation method and using non-toxic raw materials. By combining ammonium-pillared montmorillonite (MMT) and magnetic nanoparticles (Fe₃O₄), an MMT/Fe₃O₄ composite was prepared and characterized. The adsorbent exhibited high selectivity of Cs⁺ and could be rapidly separated from the mixed solution under an external magnetic field. Above all, the adsorbent had high removal efficiency in cesium-contaminated samples (water and soil) and also showed good recycling performance, indicating that the MMT/Fe₃O₄ composite could be widely applied to the remediation of cesium-contaminated environments. It was observed that the pH, solid/liquid ratio and initial concentration affected adsorption capacity. In the presence of coexisting ions, the adsorption capacity decreased in the order of Ca²⁺>Mg²⁺>K⁺>Na⁺, which is consistent with our theoretical prediction. The adsorption behavior of this new adsorbent could be expressed by the pseudo-second-order model and Freundlich isotherm. In addition, the adsorption mechanism of Cs⁺ was NH₄⁺ ion exchange and surface hydroxyl group coordination, with the former being more predominant.

Magnetically recoverable TiO2-WO3 photocatalyst to oxidize bisphenol A from model wastewater under simulated solar light

A novel magnetically recoverable, visible light active TiO₂-WO₃ composite (Fe₃O₄@SiO₂@TiO₂-WO₃) was prepared to enable the photocatalyst recovery after the degradation of bisphenol A (BPA) under simulated solar light. For comparison, the photocatalytic activity of other materials such as non-magnetic TiO₂-WO₃, Fe₃O₄@SiO₂@TiO₂, TiO₂, and the commercial TiO₂ P25 was also evaluated under the studied experimental conditions. The structure and morphology of the synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and electron dispersion spectroscopy (EDS). Moreover, Brunauer-Emmett-Teller (BET) surface area and magnetic properties of the samples were determined. The Fe₃O₄@SiO₂@TiO₂-WO₃ and TiO₂-WO₃ led to a BPA degradation of 17.50 and 27.92 %, respectively, after 2 h of the simulated solar light irradiation. Even though their activity was lower than that of P25, which degraded completely BPA after 1 h, our catalysts were magnetically separable for their further reuse in the treatment. Furthermore, the influence of the water matrix in the photocatalytic activity of the samples was studied in municipal wastewater. Finally, the identification of reaction intermediates was performed and a possible BPA degradation pathway was proposed to provide a better understanding of the degradation process. Graphical abstract ᅟ.

Degradation of p-Nitrophenol using magnetic Fe0/Fe3O4/Coke composite as a heterogeneous Fenton-like catalyst

A Coke supported Fe₃O₄ and Fe⁰ composite (Fe⁰/Fe₃O₄/Coke) was prepared for the first time with the aim of evaluating its ability to be used as heterogeneous catalyst for the Fenton degradation of p-Nitrophenol (p-NP). A four factor Box-Behnken design (BBD) coupled with response surface methodology (RSM) was applied to evaluate the effects of several operating parameters, namely Fe⁰/Fe₃O₄/Coke dosage, reaction temperature, initial pH and H₂O₂ concentration, on the removal efficiency of p-NP. A significant quadratic model (p-value<0.0001, R²=0.9952) was derived using analysis of variance (ANOVA). Optimum conditions were determined to be 1.3g/L catalyst, 32°C, pH3.1 and 11.3mM H₂O₂. 100% of p-NP (100mg/L) conversion and 81% of COD removal were achieved after 120min of reaction time, respectively, under the optimum conditions, which agreed well with the modeling prediction. The recyclability of Fe⁰/Fe₃O₄/Coke was also investigated after three successive runs, in which p-NP degradation performances showed a slight difference with the first oxidation cycle with an acceptable iron leaching. Moreover, according to the main intermediate products identified by gas chromatography-mass spectrometry (GC-MS), a possible pathway of p-NP degradation was proposed based on hydrogen radicals ([H]) or hydroxyl radicals (•OH) mechanism.

Recycling of iron and silicon from drinking water treatment sludge for synthesis of magnetic iron oxide@SiO₂ composites

More attention has been paid to the deterioration of water bodies polluted by drinking water treatment sludge (DWTS) in recent years. It is important to develop methods to effectively treat DWTS by avoiding secondary pollution. We report herein a novel investigation for recovery of Si and Fe from DWTS, which are used for the synthesis of two iron oxide@SiO2 composites for adsorption of reactive red X-3B (RRX-3B) and NaNO2. The results show that Fe(3+) (acid-leaching) and Si(4+) (basic-leaching) can be successfully recovered from roasted DWTS. Whether to dissolve Fe(OH)3 precipitation is the key point for obtaining Fe3O4 or γ-Fe2O3 particles using the solvothermal method. The magnetic characteristics of Fe3O4@SiO2 (390.0 m(2) g(-1)) or Fe2O3@SiO2 (220.9 m(2) g(-1)) are slightly influenced by the coated porous SiO2 layer. Peaks of Fe-O stretching vibration (580 cm(-1)) and asymmetric Si-O-Si stretching vibrations (1080 cm(-1)) of Fe3O4@SiO2 indicate the successful coating of a thin silica layer (20-150 nm). The adsorption capacity of RRX-3B and NaNO2 by Fe3O4@SiO2 is better than that of Fe2O3@SiO2, and both composites can be recycled through an external magnetic field. This method is an efficient and environmentally friendly method for recycling DWTS.