Magnetic Solid Phase Extraction of Lead (II) and Cadmium (II) From Water Samples Using ZnO@Fe3O4 Nanoparticles Combined With Flame Atomic Absorption Spectrometry Determination

A new magnetic solid phase extraction method was developed utilizing magnetically enhanced zinc oxide (ZnO@Fe3O4) nanoparticles for the separation and enrichment of lead (II) and cadmium (II) before sample determination through flame atomic absorption spectrometry. The ZnO@Fe3O4 nanoparticles synthesized by the hydrothermal method were characterized by x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. The experimental factors like pH (6.0), eluent type and concentration (1 M nitric acid for lead (II), 1 M hydrochloric acid for cadmium (II)), adsorbent amount (150 mg for lead (II), and 200 mg for cadmium (II)), sample volume (5 mL), and extraction time (5 min for lead (II), and 10 min for cadmium (II)) were optimized. Under the optimization conditions, limits of detection of 2.36 and 7.86 µg/L for lead (II) and cadmium (II) were obtained with a wide concentration range from 50 to 5000 µg/L, respectively. The presented method was successfully applied to real water samples with spiked recoveries in the range of 99.2%-101% for lead (II) and 99.6%-100% for cadmium (II).

Polystyrene nanoplastics: optimized removal using magnetic nano-adsorbent and toxicity assessment in zebrafish embryos

Purpose

The presence of microplastics (MPs) and nanoplastics (NPs) in aquatic ecosystems has raised serious environmental and health concerns. Polystyrene is one of the most abundant plastic polymers found in the environment. Polystyrene MPs/NPs have harmful implications for human health and their removal from the environment has become a serious challenge.

Methods

In this study, we investigated the adsorptive uptake of polystyrene nanoplastics (PS NPs) from aqueous solutions using fly ash-loaded magnetic nanoparticles (FAMNPs) as the magnetic nano-adsorbent. During the factor screening study, the adsorption process was studied as a function of four variables namely pH (5-10), adsorption time (30-120 min), amount of FAMNPs (0.01-0.04 g), and stirring speed (50-200 rpm). Central composite design (CCD) and response surface methodology (RSM) were employed to establish the relationship between the variables. Furthermore, toxicity assessments of PS NPs were checked on a zebrafish model, shedding light on its potential ecological effects.

Results

Two variables namely the pH and amount of FAMNPs significantly influenced the adsorption capacity of FAMNPs and were further optimized for subsequent analysis. The optimum operational readings proposed by the model were pH (8.5), and the amount of FAMNPs (0.03 g), resulting in a good adsorption capacity of 29.12 mg/g for PS NPs. The adequacy of the proposed model was evaluated by analysis of variance (ANOVA). Zebrafish embryos exposed to PS NPs revealed physical deformations such as pericardial edema and malformed notochord.

Conclusion

The study demonstrates the effectiveness of FAMNPs in the adsorption of PS NPs from aqueous solutions, with optimal conditions identified at pH 8.5 and 0.03 g of FAMNPs using RSM. The adequacy of the model was confirmed through ANOVA analysis. Toxicity assessments on zebrafish embryos exposed to PS NPs revealed significant mortality and physical deformations, highlighting the importance of PS NPs removal for environmental health.

Graphical Abstract

Recent Developments in the Adsorption of Heavy Metal Ions from Aqueous Solutions Using Various Nanomaterials

Water pollution is caused by heavy metals, minerals, and dyes. It has become a global environmental problem. There are numerous methods for removing different types of pollutants from wastewater. Adsorption is viewed as the most promising and financially viable option. Nanostructured materials are used as effective materials for adsorption techniques to extract metal ions from wastewater. Many types of nanomaterials, such as zero-valent metals, metal oxides, carbon nanomaterials, and magnetic nanocomposites, are used as adsorbents. Magnetic nanocomposites as adsorbents have magnetic properties and abundant active functional groups, and unique nanomaterials endow them with better properties than nonmagnetic materials (classic adsorbents). Nonmagnetic materials (classic adsorbents) typically have limitations such as limited adsorption capacity, adsorbent recovery, poor selective adsorption, and secondary treatment. Magnetic nanocomposites are easy to recover, have strong selectivity and high adsorption capacity, are safe and economical, and have always been a hotspot for research. A large amount of data has been collected in this review, which is based on an extensive study of the synthesis, characterization, and adsorption capacity for the elimination of ions from wastewater and their separation from water. The effects of several experimental parameters on metal ion removal, including contact duration, temperature, adsorbent dose, pH, starting ion concentration, and ionic strength, have also been investigated. In addition, a variety of illustrations are used to describe the various adsorption kinetics and adsorption isotherm models, providing insight into the adsorption process.

Artificial intelligence and machine learning algorithms in the detection of heavy metals in water and wastewater: Methodological and ethical challenges

Heavy metals (HMs) enter waterbodies through various means, which, when exceeding a threshold limit, cause toxic effects both on the environment and in humans upon entering their systems. Recent times have seen an increase in such HM influx incident rates. This requires an instant response in this regard to review the challenges in the available classical methods for HM detection and removal. As well as provide an opportunity to explore the applications of artificial intelligence (AI) and machine learning (ML) for the identification and further redemption of water and wastewater from the HMs. This review of research focuses on such applications in conjunction with the available in-silico models producing worldwide data for HM levels. Furthermore, the effect of HMs on various disease progressions has been provided, along with a brief account of prediction models analysing the health impact of HM intoxication. Also discussing the ethical and other challenges associated with the use of AI and ML in this field is the futuristic approach intended to follow, opening a wide scope of possibilities for improvement in wastewater treatment methodologies.

Mesoporous Magnetic/Polymer Hybrid Nanoabsorbent for Rapid and Efficient Removal of Heavy Metal Ions from Wastewater

As an advanced water purification technology, magnetic nanoabsorbents are highly attractive for their sustainability, robustness, and energy efficiency. However, magnetic responsiveness and high adsorptive capacity are irreconcilable during the design and synthesis of a high-performance magnetic nanoabsorbent. Here, we address this issue by designing a kind of mesoporous magnetic polymer hybrid microspheres, where functional polymers such as polyrhodanine and polypyrrole were attached to the pore walls in the interior of mesoporous Fe3O4 microspheres through in situ polymerization. Due to the integrated large saturation magnetic moment, porous structure, and dense polymer layer, the mesoporous magnetic polymer hybrid microspheres demonstrated fast magnetic responsiveness, excellent recycling performance, and high adsorption capacities toward Pb(II) ions (189 mg g-1) for polyrhodanine and Cr(VI) ions (199 mg g-1) for polypyrrole. Furthermore, their potential application in wastewater treatment was verified by a self-made magnetic separation column, where the designed magnetic nanoabsorbent exhibits significant advantages including rapid separation of heavy metal ions and high outflow. This study provided a promising magnetic polymer hybrid nanoabsorbent for realizing efficient removal of heavy metal ions from wastewater.

Effective Removal of Boron from Aqueous Solutions by Inorganic Adsorbents: A Review

Increasing levels of boron in water exceeding acceptable thresholds have triggered concerns regarding environmental pollution and adverse health effects. In response, significant efforts are being made to develop new adsorbents for the removal of boron from contaminated water. Among the various materials proposed, inorganic adsorbents have emerged as promising materials due to their chemical, thermal, and mechanical stability. This review aims to comprehensively examine recent advances made in the development of inorganic adsorbents for the efficient removal of boron from water. Firstly, the adsorption performance of the most used adsorbents, such as magnesium, iron, aluminum, and individual and mixed oxides, are summarized. Subsequently, diverse functionalization methods aimed at enhancing boron adsorption capacity and selectivity are carefully analyzed. Lastly, challenges and future perspectives in this field are highlighted to guide the development of innovative high-performance adsorbents and adsorption systems, ultimately leading to a reduction in boron pollution.

Nanoparticles and nanofiltration for wastewater treatment: From polluted to fresh water

Water pollution poses significant threats to both ecosystems and human health. Mitigating this issue requires effective treatment of domestic wastewater to convert waste into bio-fertilizers and gas. Neglecting liquid waste treatment carries severe consequences for health and the environment. This review focuses on intelligent technologies for water and wastewater treatment, targeting waterborne diseases. It covers pollution prevention and purification methods, including hydrotherapy, membrane filtration, mechanical filters, reverse osmosis, ion exchange, and copper-zinc cleaning. The article also highlights domestic purification, field techniques, heavy metal removal, and emerging technologies like nanochips, graphene, nanofiltration, atmospheric water generation, and wastewater treatment plants (WWTPs)-based cleaning. Emphasizing water cleaning's significance for ecosystem protection and human health, the review discusses pollution challenges and explores the integration of wastewater treatment, coagulant processes, and nanoparticle utilization in management. It advocates collaborative efforts and innovative research for freshwater preservation and pollution mitigation. Innovative biological systems, combined with filtration, disinfection, and membranes, can elevate recovery rates by up to 90%, surpassing individual primary (<10%) or biological methods (≤50%). Advanced treatment methods can achieve up to 95% water recovery, exceeding UN goals for clean water and sanitation (Goal 6). This progress aligns with climate action objectives and safeguards vital water-rich habitats (Goal 13). The future holds promise with advanced purification techniques enhancing water quality and availability, underscoring the need for responsible water conservation and management for a sustainable future.

Deep insights into kinetics, optimization and thermodynamic estimates of methylene blue adsorption from aqueous solution onto coffee husk (Coffee arabica) activated carbon

In the current study, an attempt was made to synthesize coffee husk (CH) activated carbon by chemical modification approach (sulphuric acid-activated CH (SACH) activated carbon) and was used as a valuable and economical sorbent for plausible remediation of Methylene blue (MB) dye. Batch mode trials were carried out by carefully varying the batch experimental variables: SACH activated carbon (SACH AC) dosage, pH, initial dye concentration, temperature, and contact time. The optimum equilibrium time for adsorption by SACH activated carbon was obtained as 60 min, and the maximum adsorption took place at 30 °C. Morphological and elemental composition, crystallinity behaviour, functional groups, and thermal stability were examined using SEM with EDX, XRD, FTIR, BET, TGA, and DTA and these tests showed successful production of activated carbon. The outcomes showed that chemical activation enhanced the number of pores and roughness which possibly maximized the adsorptive potential of coffee husk. The Box-Benken design (BBD) was used to optimize the MB dye adsorption studies and 99.48% MB dye removed at SACH AC dosage of 4.83 g/L at 30 °C for 60 min and pH 8.12, and the maximum adsorption was yielded for sulphuric acid-activated coffee husk carbon carbon with 88.1 mg/g maximum MB adsorption capacity. Langmuir- Freundlich model deliberately provided a better fit to the equilibrium data. The SACH AC-MB dye system kinetics showed a high goodness-of-fit with pseudo second order model, compared to other studied models. Change in Gibbs's free energy (ΔGo) of the system indicated spontaneity whereas low entropy value (ΔSo) suggested that the removal of MB dye on the SACH activated carbon was an enthalpy-driven process. The exothermic nature of the sorption cycle was affirmed by the negative enthalpy value (ΔHo). The adsorptive-desorptive studies reveal that SACH AC could be restored with the maximum adsorption efficiency being conserved after the fifth cycles. Overall, the outcomes revealed that sulphuric acid-activated coffee husk activated carbon (SACH AC) can be used as prompt alternative for low-cost sorbent for treating dye-laden synthetic wastewaters.

Application of Functionalized Fe3O4 Magnetic Nanoparticles Using CTAB and SDS for Oil Separation from Oil-in-Water Nanoemulsions

Using magnetic nanoparticles (MNPs) for emulsified oil separation from wastewater is becoming increasingly widespread. This study aims to synthesize MNPs using amphiphilic coatings to stabilize the MNPs and prevent their agglomeration for efficiently breaking oil-in-water nanoemulsions. We coat two different sizes of Fe₃O₄ nanoparticles (15-20 and 50-100 nm) using cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with surfactant-to-MNP mass ratios of 0.4 and 0.8. We study the effect of various variables on the demulsification performance, including the MNP size and concentration, coating materials, and MNP loading. Based on the oil-water separation analysis, the smaller size MNPs (MNP-S) show a better demulsification performance than the larger ones (MNP-L ) for a 1000 ppm dodecane-in-water emulsion containing nanosized oil droplets (250-300 nm). For smaller MNPs (MNP-S) and at low dosage level of 0.5 g/L, functionalizing with surfactant-to-MNP mass ratio of 0.4, the functionalization increases the separation efficiency (SE) from 57.5% for bare MNP-S to 86.1% and 99.8 for the SDS and CTAB coatings, respectively. The highest SE for MNP-S@CTAB and the zeta potential measurements imply that electrostatic attraction between negatively charged oil droplets (-55.9 ± 2.44 mV) and positively charged MNP-S@CTAB (+35.8 ± 0.34 mV) is the major contributor to a high SE. Furthermore, the reusability tests for MNP-S@CTAB reveal that after 10 cycles, the amount of oil adsorption capacity decreases slightly, from 20 to 19 mg/g, indicating an excellent stability of synthesized nanoparticles. In conclusion, functionalized MNPs with tailored functional groups feature a high oil SE that could be effectively used for oil separation from emulsified oily wastewater streams.

Synthesis of azole-functionalized microspheres and their adsorption properties for gold(I) thiosulfate complex

Gold is an essential precious metal with exceptional properties. Thus, azole-functionalized microspheres (PS-3-AT) were prepared by grafting 3-amino-1,2,4-triazole (3-AT) into chloromethyl polystyrene beans (PS-Cl) and used as a novel adsorbent for the gold(I)-thiosulfate complex. The effects of initial gold concentration, thiosulfate concentration, temperature, and pH on the Au(S₂O₃)₂^3- adsorption process over PS-3-AT were investigated. In this study, PS-3-AT was considered an effective adsorbent for Au(I) recovery from a thiosulfate solution, demonstrating that PS-3-AT completely adsorbed Au(S₂O₃)₂^3- with an adsorption capacity of 39.8 kg t^-1 achieved during multistage adsorption testing. Through adsorption kinetics and isotherm studies, the pseudo-second-order and Freundlich models well describe the adsorption process of PS-3-AT for Au(I), also suggesting the exothermic nature. Furthermore, SEM, FT-IR spectroscopy, BET, and XPS techniques were used to characterize the surface and structural properties of the samples. Notably, a reliable adsorption mechanism was developed that proposed the formation of the -NH⁺Cl^- group during the grafting process and Cl^- exchange with Au(S₂O₃)₂^3- to achieve Au(I) capture. Moreover, quantum chemistry calculations and the independent gradient model (IGM) were adopted to visualize the interaction between PS-3-AT and Au(S₂O₃)₂^3- at an atomic level. The desorption ratio was 97.9% while 2 M NaCl was used as the desorbent, and regeneration with PS-3-AT was achieved after five cycles. Therefore, the facile synthetic method and adsorption properties of PS-3-AT for the gold(I)-thiosulfate complex are satisfactory, which is valuable for the development of thiosulfate gold leaching technologies.

Speciation of Hexavalent Chromium in Aqueous Solutions Using a Magnetic Silica-Coated Amino-Modified Glycidyl Methacrylate Polymer Nanocomposite

A new magnetic amino-functionalized polymeric sorbent based on glycidyl methacrylate was synthesized and used in the separation of chromium Cr(VI) oxyanions sorption from aqueous solutions in a static batch system. The kinetic and isothermal parameters of the sorption process were determined. The experimental data were best fitted by a pseudo-second-order model with R² = 0.994 and χ² = 0.004. The sorption process of Cr(VI) removal by amino-functionalized sorbent was controlled by both intraparticle diffusion and liquid film diffusion. The equilibrium results showed that the sorption process is best described by the Freundlich model, followed closely by the Sips isotherm model, with a maximum sorption capacity of 64 mg/g. Quantum chemical modeling revealed that the sorption sites on the sorbent surface are fragments with diethylenetriamine and aminopropyl silane groups that coated the magnetic nanoparticles. The calculations showed that Cr(VI) oxyanions (Cr₂O₇^2-, CrO₄^2- and HCrO₄^-) bind to both sorption sites, with diethylenetriamine centers slightly favored. The X-ray photoelectron spectroscopy (XPS) spectra demonstrate that the chromium bound to the sorbent in the form of Cr(III), indicating that the Cr(VI) can be converted on the surface of the sorbent to a less harmful form Cr(III) due to the sorbent's chemical composition.

Influence of pyrolysis temperature on biochar properties and Cr(VI) adsorption from water with groundnut shell biochars: Mechanistic approach

This study was envisaged to understand the effect of increasing pyrolysis temperature on the Cr(VI) removal potential of the groundnut shells derived biochars. The biochars were prepared at four different pyrolysis temperatures (350 °C, 450 °C, 550 °C, 650 °C) and were used unmodified to examine the adsorption potential for Cr(VI). Influence of biochar dose (1-10 g/L), pH_initial (2-10), Cr(VI)_initial (10-500 mg/L) on Cr(VI) adsorptions; adsorption kinetics and isotherms were investigated. The observations suggested that the pyrolysis temperature is the key player in deciding the physicochemical properties as well the adsorption potential of the biochars. SEM and FTIR analysis suggested significant morphological and functional transformations in biochars with increasing pyrolysis temperature. The pH_initial was found to be the most profound adsorption parameter determining the adsorption potential of the biochars. The Cr(VI) adsorption capacity of the biochars decreased with the increase of the pyrolysis temperature (142.87-31.25 mg/L) as well as the solution pH_initial. All the biochars attained 100% removal efficiency with 50 mg/L of Cr(VI)_initial and GNSB/350 achieved it in the minimum time (10 h) among all the biochars. GNSB/350 showed promising Langmuir adsorption capacity of 142.87 mg/L (pH 2, T_adsorption 30 °C, Cr(VI)_initial 10-500 mg/L). In addition, the adsorption mechanism was found to be a synergistic action of chemi/physi-sorption with monolayer adsorption. Hence, the pyrolysis temperature significantly altered the physicochemical properties of the biochars, which highly influenced the adsorption performance of biochars.

New Materials Based on Polyvinylpyrrolidone-Containing Copolymers with Ferromagnetic Fillers

The article investigates the peculiarities of the effect of ferromagnetic fillers (FMFs) of various natures (Ni, Co, Fe, FeCo, SmCo₅) on the formation of the structure and properties of 2-hydroxyethylmethacrylate (HEMA) with polyvinylpyrrolidone (PVP) copolymers. The composites were characterized using FTIR-spectroscopy, SEM, DMTA, magnetometry of vibrating samples, specific electrical resistivity studies, and mechanical and thermophysical studies. The formation of a grafted spatially crosslinked copolymer (pHEMA-gr-PVP) was confirmed and it was established that the FMF introduction of only 10 wt.% into the copolymer formulation increased the degree of crosslinking of the polymer network by three times. The surface hardness of composites increased by 20–25%. However, the water content decreased by 16–18% and lay within 42–43 wt.%, which is a relatively high number. The heat resistance of dry composites was characterized by Vicat softening temperature, which was 39–42 °C higher compared to the unfilled material. It was established that the obtained composites were characterized by a coercive force of 200 kA × m⁻¹ and induction of a magnetic field at the poles of 4–5 mT and 10–15 mT, respectively. The introduction of FMF particles into pHEMA-gr-PVP copolymers, which, in the dry state, are dielectrics, provides them with electrical conductivity, which was evaluated by the specific volume resistance. Depending on the FMF nature and content, as well as their orientation in the magnetic field, the resistance of filled materials could be regulated within 10²–10⁶ Ohm·m. Therefore, the modification of HEMA with PVP copolymers by ferromagnetic fillers of various natures provides the possibility of obtaining materials with unique predicted properties and expands the fields of their use, for instance as magnetic sorbents for various applications, as well as the possibilities associated with their being electrically conductive materials that can respond by changing of electrical conductivity, depending on various factors.

Remediation of Azure A Dye from Aqueous Solution by Using Surface-Modified Coal Fly Ash Extracted Ferrospheres by Mineral Acids and Toxicity Assessment

The Indian coal fly ash (CFA) is composed of 5-15% ferrous fractions. The variation in percentage depends on the source of coal and the operating conditions of the thermal power plants. The present research work reports the recovery of ferrous particles from CFA by the wet magnetic separation method. The morphological, elemental, and chemical properties of the extracted ferrous fractions were analyzed. In order to achieve surface-modified ferrospheres, the extracted ferrospheres were treated with concentrated HCl followed by sonication. The instrumental analysis reported the ferrous composition is around 16% by weight and belongs to class F. The toxicity of CFA was determined on normal human lung (BEAS-2B) cells using MTS assay. The results showed that CFA’s induced cell toxicity in a dose-dependent manner. The ferrous particles were spherically shaped with various sizes ranging from 200 nm to 7000 nm. It was crystalline in nature and is a mixture of hematite and magnetite. The particles were found to be associated with alumina, silica, oxygen, and traces of Ca, Mg, Ti, and C. The surface-modified ferrospheres were used for the remediation of Azure A dye by batch adsorption study. The removal percentage of dye was 25.03%, within 30 minutes at neutral pH, i.e., 7.2. The surface-modified ferrospheres show potential as an alternate, more economical, and reusable adsorbent for the remediation of Azure A dye in the industries or in common effluent treatment plants. Moreover, the recovery of surface-modified ferrospheres using an external magnet and the reuse of the particles make the material much economical for dye removal at an industrial scale.

Feasibility of magnetic nano adsorbent impregnated with activated carbon from animal bone waste: Application for the chromium (VI) removal

Chromium is the heavy metal which existing in the effluents cause extensive discomfort to the environmental components. Bone waste is widely generated in food processing industries and restaurants. It is now used by switching into activated carbon. By co-precipitation procedure, the activated carbon is coated with a nano adsorbent. The Fe₃O₄-BAC adsorbent potential was established in this study via several batch tests. The adsorbing adverts had super magnetic behavior, and the magnetization value was 22 emu/g. The SEM imaging of the Fe₃O₄-BAC shows an improved morphology of 100-446 nm, and the nanoparticles were monodispersed. The present investigation also delves into the study of system parameters on the removal of metal ions. Optimal adsorption has been found at the acidic pH at the contact time of 60min for the adsorbent amount of 5 g/L. Maximum capacity of adsorption by nano adsorbent was 27.86 mg/g. Thermodynamic and isotherm tests have established the process viability. In addition, the kinetic studies establish the inclination of the studied Fe₃O₄-BAC towards pseudo-first order models. Hence, Fe₃O₄-BAC could be potential adsorbent to remove chromium from an aqueous solution.

Recovery of Heavy Metal Ions Using Magnetic Glycine-Modified Chitosan—Application to Aqueous Solutions and Tailing Leachate

The necessity of decontaminating effluents for the dual purpose of environmental beneficiation and valorization of low-grade resources is driving the development of new sorbents. The functionalization of biopolymers is a promising strategy for improving sorption performance. Incorporating magnetic micro-particles offers an opportunity for the facilitated recovery of spent micron-size sorbent. Combining magnetic facilities and biopolymer functionalization represents a winning strategy. Magnetic glycine-grafted chitosan (G@MChs) was synthesized for the sorption of Ni(II), Zn(II), and Hg(II) before being applied to the removal of hazardous and strategic metals from tailing leachates. The sorbent was characterized using Fourier transform infrared spectroscopy and scanning electron microscopy, before and after metal sorption. The acid–base properties of functionalized sorbent were also determined (pHPZC). Uptake kinetics were studied in mono- and multi-component solutions using different equations for kinetic modeling at optimized pH (i.e., pH0: 5.5). Langmuir and Sips equations were applied to model sorption isotherms in single-component solutions. In addition, sorption isotherms in multi-component solutions were used to evaluate the preference for selected metals. Maximum sorption capacities were 0.35 mmol Hg g−1, 0.47 mmol Zn g−1, and 0.50 mmol Ni g−1. Acidified urea solution (pH 2.7) successfully desorbs metal ions from G@MChs (desorption > 90%). The sorbent was tested for the recovery of hazardous and strategic metal ions from acidic leachates of tailings. This study demonstrates the promising performance of G@MChs for the treatment of complex metal-bearing solutions.

Treatment of nano-oil polluted wastewater in an expanded bed adsorption column based on carboxymethyl cellulose-cellulose-nickel composite beads

In the present work, spherical carboxymethyl cellulose-cellulose-nickel (CMC-C-Ni) composite beads as novel adsorbent was synthesized to make a stable expanded bed adsorption (EBA) column for the treatment of the oily wastewater collected from the downstream of rapeseed industry. The morphology and structure of the CMC-C-Ni composite beads were studied by scanning electron microscopy (SEM) and optical microscope. The SEM images revealed that the synthesized composite beads were spherical with porous structure. The pore size of the beads was in the range of 90-200 nm. The physical characteristics of the CMC-C-Ni composite beads including wet density, porosity, and water content were respectively in the ranges of 1.23-1.63 g/cm³, 82.29-90.75%, and 52-76%. The factor of bed expansion in the range of 2-3 was corresponded with Richardson-Zaki equation. The results showed that by increasing the fluid viscosity, the terminal settling velocity (U_t) was reduced. The expansion index values were between 2.77 and 3.14 that were close to 4.8 (commonly utilized index in the laminar flow regimes). CMC-C-Ni composite beads were tested when the velocity of fluid was ˂ 700 cm/h, and the D_axl was found to be ˂ 1 × 10^-5 m²/s (steady state).

Smart Adsorbents for Aquatic Environmental Remediation

A noticeable interest and steady rise in research studies reporting the design and assessment of smart adsorbents for sequestering aqueous metal ions and xenobiotics has occurred in the last decade. This motivates compiling and reviewing the characteristics, potentials, and performances of this new adsorbent generation's metal ion and xenobiotics sequestration. Herein, stimuli-responsive adsorbents that respond to its media (as internal triggers; e.g., pH and temperature) or external triggers (e.g., magnetic field and light) are highlighted. Readers are then introduced to selective adsorbents that selectively capture materials of interest. This is followed by a discussion of self-healing and self-cleaning adsorbents. Finally, the review ends with research gaps in material designs.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

Magnetic aerogel: an advanced material of high importance

Magnetic materials have brought innovations in the field of advanced materials. Their incorporation in aerogels has certainly broadened their application area. Magnetic aerogels can be used for various purposes from adsorbents to developing electromagnetic interference shielding and microwave absorbing materials, high-level diagnostic tools, therapeutic systems, and so on. Considering the final use and cost, these can be fabricated from a variety of materials using different approaches. To date, several studies have been published reporting the fabrication and uses of magnetic aerogels. However, to our knowledge, there is no review that specifically focuses only on magnetic aerogels, so we attempted to overview the main developments in this field and ended our study with the conclusion that magnetic aerogels are one of the emerging and futuristic advanced materials with the potential to offer multiple applications of high value.

Recent Developments in Chitosan-Based Adsorbents for the Removal of Pollutants from Aqueous Environments

The quality of water is continuously under threat as increasing concentrations of pollutants escape into the aquatic environment. However, these issues can be alleviated by adsorbing pollutants onto adsorbents. Chitosan and its composites are attracting considerable interest as environmentally acceptable adsorbents and have the potential to remove many of these contaminants. In this review the development of chitosan-based adsorbents is described and discussed. Following a short introduction to the extraction of chitin from seafood wastes, followed by its conversion to chitosan, the properties of chitosan are described. Then, the emerging chitosan/carbon-based materials, including magnetic chitosan and chitosan combined with graphene oxide, carbon nanotubes, biochar, and activated carbon and also chitosan-silica composites are introduced. The applications of these materials in the removal of various heavy metal ions, including Cr(VI), Pb(II), Cd(II), Cu(II), and different cationic and anionic dyes, phenol and other organic molecules, such as antibiotics, are reviewed, compared and discussed. Adsorption isotherms and adsorption kinetics are then highlighted and followed by details on the mechanisms of adsorption and the role of the chitosan and the carbon or silica supports. Based on the reviewed papers, it is clear, that while some challenges remain, chitosan-based materials are emerging as promising adsorbents.

Fly Ash Coated with Magnetic Materials: Improved Adsorbent for Cu (II) Removal from Wastewater

Fly ash/magnetite material was used for the adsorption of copper ions from synthetic wastewater. The obtained material was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area, and vibrating sample magnetometer (VSM). Batch adsorption experiments were employed in order to investigate the effects of adsorbent dose, initial Cu (II) concentration and contact time over adsorption efficiency. The experimental isotherms were modeled using Langmuir (four types of its linearization), Freundlich, Temkin, and Harkins-Jura isotherm models. The fits of the results are estimated according to the Langmuir isotherm, with a maximum adsorption capacity of 17.39 mg/g. The pseudo-second-order model was able to describe kinetic results. The data obtained throughout the study prove that this novel material represents a potential low-cost adsorbent for copper adsorption with improved adsorption capacity and magnetic separation capability compared with raw fly ash.

Self-Assembly Fabrication of Honeycomb-like Magnetic-Fluorescent Fe3O4-QDs Nanocomposites for Bimodal Imaging

Magnetic-fluorescent nanocomposites have a tremendous potential in biomedicine realms as a revolutionary dual-modality probe tool for more accurate medical detection. However, complicated and inefficient postprocesses pose obstacles to obtaining high-quality magnetic-fluorescent nanocomposites. Thus, the fabrication of magnetic-fluorescent functional nanocomposites via a simple, effective, and ideal method remains a challenge and is still waiting to be tapped. The new synthesis approaches are becoming impending demands and probably enable us to address these above-mentioned problems. In this contribution, we present a novel self-assembly synthesis route for the construction of magnetic-fluorescent bimodal imaging nanocomposites rather than adopting sophisticated postpreparative processes. The Fe₃O₄ and quatum dots (QDs) nanocomposites were cross-linked fleetly by cerium(III) ion driven coordination bonds in which the cerium(III) ions served as the cross-connecting node and the carboxylate groups acted as bridging ligands. The potential application for dual-modality imaging capability was validated on tumor-bearing mice. This ingenious strategy was extremely efficient and handy for the magnetic-fluorescent Fe₃O₄-QDs nanocomposite construction. Significantly, our cerium(III) ion driven self-assembly method probably has a wide applicability for nanoparticles and organic molecules containing carboxyl groups but extensive explorations are still necessary.

A new route for manufacturing poly(aminophosphonic)-functionalized poly(glycidyl methacrylate)-magnetic nanocomposite - Application to uranium sorption from ore leachate

A high-energy ball milling of magnetite nanoparticles with amino-phosphonic functionalized poly(glycidyl methacrylate) polymer is used for manufacturing a highly efficient magnetic sorbent for U(VI) sorption from aqueous solutions. The Uranyl ions were adsorbed through the binding with amine and phosphonic groups as confirmed by Fourier Transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The maximum sorption capacity (up to 270 mg U g^-1) occurred at pH = 3-4; Langmuir isotherm well describes the sorption process. Small-size particles allow achieving fast uptake (within ≈90 min of contact); and the kinetic profiles are modeled by the pseudo-second order rate equation. Uranium is successfully desorbed from loaded sorbent using 0.25 M NaHCO₃ solution: Sorbent can be recycled with minimal decrease in sorption and desorption efficiency for at least 6 cycles. The sorbent is efficiently used for U(VI) recovery from the acidic leachates of U-bearing ores (after precipitation pre-treatment). Sorption capacity approaches 190 mg U g^-1 despite the presence of high concentrations of Fe and Si: the sorbent has a marked preference for U(VI) (confirmed by distribution ratios and selectivity coefficients).

A bioinspired metal-organic approach to cross-linked functional 3D nanofibrous hydro- and aero-gels with effective mixture separation of nucleobases by molecular recognition

The direct reaction between Cu(CH3COO)2 and uracil-1-acetic acid in water gives rise to the formation of a hydrogel consisting of entangled nanometric ribbons of a crystalline antiferromagnetic 1D Cu(ii) coordination polymer (CP) decorated with biocompatible uracil nucleobases. This hydrogel is the precursor for the preparation of a meso/macroporous ultralight aerogel that shows a remarkable Young's modulus. As a proof-of-concept of the molecular recognition capability of the terminal uracil moieties anchored at Cu(ii) CP chains, this material has been tested as the selective stationary phase for the separation of nucleobase derivatives in HPLC columns.

Treatment of oil refinery effluent using bio-adsorbent developed from activated palm kernel shell and zeolite

This study investigated the potential of palm kernel shell (PKS) as a biomass feed for adsorbent production. This work aims at synthesizing green adsorbent from activated PKS by integrating iron oxide and zeolite. The newly developed adsorbents, zeolite-Fe/AC and Fe/AC, were analyzed for surface area, chemical composition, magnetic properties, crystallinity, and stability. The adsorbent efficiency in removing effluent from the palm oil mill was evaluated. The influence of operating parameters, including adsorbent dosage, H2O2, reaction time, and initial solution pH for adsorption performance was studied. The Fourier transform infrared analysis revealed that the adsorbents contain functional groups including OH, N-H, C[double bond, length as m-dash]O and C[double bond, length as m-dash]C, which are essential for removing pollutants. The SEM-EDX analysis shows holes in the adsorbent surface and that it is smooth. The adsorption study revealed that under optimized conditions, by using 4 g L-1 of adsorbent and 67.7 mM H2O2, zeolite-Fe/AC was able to remove 83.1% colour and 67.2% COD within 30 min. However, Fe/AC requires 5 g L-1 of adsorbent and 87.7 mM to remove 86.8 percent and 65.6 percent, respectively. This study also showed that zeolite-Fe/AC has higher reusability compared to Fe/AC. Among Freundlich and Temkin models, the experimental data were found to be best fitted with the Langmuir isotherm model. The kinetic analysis revealed that for both adsorbents, the adsorption process fitted the pseudo-second-order model (R 2 = 0.9724). The finding reflects monolayer adsorption of zeolite-Fe/AC and Fe/AC. This study thus demonstrates the applicability of low-cost green adsorbents produced from PKS to treat oil refinery effluent and other recalcitrant wastewaters.

Novel reusable functionalized magnetic cobalt ferrite nanoparticles as oil adsorbents

Magnetic nanoparticles are amongst the most promising adsorption materials for oil spill clean-up due to their high surface area, ease of functionalization with high oil affinity and facile separation after the cleaning process with an external magnetic field. In this work, we successfully synthesized magnetic cobalt ferrite nanoparticles (CoFe2O4 NPs) that were electrostatically stabilized and functionalized with various alkoxysilanes for effective oil adsorption and oil spill removal. Additionally, the adsorption capacity of CoFe2O4 NPs was determined, and the possibility of their reuse assessed. Prepared samples showed high oil adsorption capacities between 2.6 and 3.5 g of oil per g of nanoparticles and were successfully collected with an external magnet. Furthermore, the samples showed excellent properties after regeneration, as their adsorption capacity decreased by less than 3% after reuse. All the prepared samples were thoroughly characterized to better understand their behaviour and the differences in the use of various silanes were highlighted.

Tailoring magnetic and mechanical properties of mesoporous single-phase Ni-Pt films by electrodeposition

Homogeneous mesoporous Ni-rich Ni-Pt thin films with adjustable composition have been synthesised by one-step micelle-assisted electrodeposition. The films exhibit a face-centred cubic solid solution (single phase) and their magnetic and mechanical properties can be tuned by varying the alloy composition. In particular, the Curie temperature (T_C) is shown to decrease with the Pt content and thin films with a T_C close to room temperature (i.e. Ni₅₈Pt₄₂) and below can be produced. Hysteresis loops show a decrease of saturation magnetisation (M_s) and coercivity (H_c) with decreasing Ni content. A comparison of porous and dense films reveals significantly lower saturation magnetic field strength for porous films. Concerning mechanical properties, mainly two trends can be observed: a decrease of the Young's modulus of the nanoporous films with respect to dense films by 10% in average and a progressive increase of Young's modulus with the Ni content from 4.2 GPa to 5.7 GPa in both types of films. The tunability of properties and facility of synthesis make this alloy a promising material for microelectromechanical systems (MEMS).

Magneto-ionic control of magnetism in two-oxide nanocomposite thin films comprising mesoporous cobalt ferrite conformally nanocoated with HfO2

Advances in nanotechnology require of robust methods to fabricate new types of nanostructured materials whose properties can be controlled at will using simple procedures. Nanoscale composites can benefit from actuation protocols that involve mutual interfacial interactions on the nanoscale. Herein, a method to create nanoscale composite thin films consisting of mesoporous cobalt ferrite (CFO) whose pore walls are nanocoated with HfO2 is presented. Porous CFO films are first prepared by sol-gel. Atomic layer deposition is subsequently used to conformally grow a HfO2 layer at the surface of the pore walls, throughout the thickness of the films. The magnetic properties of uncoated and HfO2-coated CFO mesoporous films are then modulated by applying external voltage, via magneto-ionic effects. The CFO-HfO2 composite films exhibit an enhanced magnetoelectric response. The magnetic moment at saturation of the composite increases 56% upon the application of -50 V (compared to 24% for CFO alone). Furthermore, dissimilar trends in coercivity are observed: after applying -50 V, the coercivity of the composite film increases by 69% while the coercivity of the CFO alone decreases by 25%. The effects can be reversed applying suitable positive voltages. This two-oxide nanocomposite material differs from archetypical magneto-ionic architectures, in which voltage-driven ion migration is induced between fully-metallic and oxide counterparts. The synthesized material is particularly appealing to develop new types of magnetoelectric devices with a highly tunable magnetic response.

Enhancing the Removal of Sb (III) from Water: A Fe3O4@HCO Composite Adsorbent Caged in Sodium Alginate Microbeads

To remove antimony (Sb) ions from water, a novel composite adsorbent was fabricated from ferriferous oxide and waste sludge from a chemical polishing process (Fe3O4@HCO) and encapsulated in sodium alginate (SAB). The SAB adsorbent performed well with 80%–96% removal of Sb (III) ions within a concentration range of 5–60 mg/L. The adsorption mechanism of Sb (III) was revealed to be the synergy of chemisorption (ion exchange) and physisorption (diffusion reaction). The adsorption isotherms and kinetics conformed to the Langmuir isotherm and the pesudo-second-order kinetic model. Both initial pH and temperature influenced the adsorption performance with no collapse of microbeads within solution pH range 3–7. Most importantly for practical applications, these microspheres can be separated and recovered from aqueous solution by a magnetic separation technology to facilitate large-scale treatment of antimony-containing wastewater.

Synthesis of Fe3O4@PVBC-TMT nanoparticles for the efficient removal of heavy metals ions

Core–shell magnetic Fe₃O₄@PVBC–TMT (Fe₃O₄@polyvinylbenzyl chloride–trithiocyanuric acid) nanoparticles containing trithiocyanuric acid groups were fabricated and employed for the fast removal of heavy metals from an aquatic environment. The morphology, structure and properties of Fe₃O₄@PVBC–TMT nanoparticles were characterized by a series of modern analytical tools. The adsorption behavior of the Fe₃O₄@PVBC–TMT nanoparticles for heavy metals ions in aqueous solutions was investigated by batch experiments. The maximum removal capacities of the Fe₃O₄@PVBC–TMT nanoparticles toward Mn²⁺, Ni²⁺, Cu²⁺, Cd²⁺ and Pb²⁺ ions were 127.4, 146.6, 180.5, 311.5, and 528.8 mg g⁻¹, respectively. Importantly, it is found that Pb²⁺ ions can be completely and quickly removed by the Fe₃O₄@PVBC–TMT nanoparticles. The equilibrium was established within 6 min, and the removal efficiencies were found to be 99.9%, 99.8% and 99.5% for Pb²⁺ ions at the initial concentrations of 100 mg L⁻¹, 200 mg L⁻¹ and 300 mg L⁻¹, respectively. It is hoped that the core–shell magnetic Fe₃O₄@PVBC–TMT nanoparticles may find application in wastewater treatment.

Core–shell Fe₃O₄@PVBC–TMT nanoparticles were fabricated and served as a valid magnetic adsorbent for the removal of heavy metals ions.

Facile synthesis of functionalized polyglycidyl methacrylate-magnetic nanocomposites for enhanced uranium sorption

Designing and fabricating nanocomposite magnetic sorbents (with more accessible active sites for achieving high sorption capacities, selectivity and rapid kinetics) has become an impending challenge in the removal of radionuclides. Two core-shell multifunctional magnetic-nanocomposites have been prepared suitably to be used as sorbents using facile two-step processes. In the first step, after synthesis of parent PGMA microparticles (by a dispersion polymerization method), the grafting of aminoalkylcarboxylate and aminoalkylphosphonic ligands (via an intermediary amination step of PGMA) allows increasing sorption capacities due to the specific reactivity of carboxylate and phosphonate groups, giving iminodiacetate (IDA-PGMA) and iminodiphosphonate (IDP-PGMA), respectively. In the second step, functionalized-PGMA was ball-milled with pre-formed magnetic nanoparticles using high-energy planetary milling, resulting in a magnetic nanocomposite structure (M-IDA-PGMA and M-IDP-PGMA). These sorbents were characterized by elemental analysis, FTIR, XRD, pHZPC, TEM, and VSM. The magnetic nanocomposite sizes were around 10.0 nm. The super paramagnetic properties of the hybrid materials make their solid/liquid separation quite easy using an external magnetic field. These materials were investigated for uranium sorption. Optimum pH was found to be close to 4.0; the maximum monolayer chemisorption capacities reach 122.9 and 147.0 mg g-1 for M-IDA- and M-IDP-PGMA, respectively. The adsorption activation energies were calculated from the Arrhenius equation. The sorption is spontaneous, endothermic and controlled by entropic change. Sorbents were tested for U(vi) removal from a real acidic leachate of ores collected in the El-Sella mining area. Finally, sodium bicarbonate revealed efficiency for uranium desorption and the re-use of sorbents was successfully tested for five cycles.

Fabrication of magnetic lignosulfonate using ultrasonic-assisted in situ synthesis for efficient removal of Cr(Ⅵ) and Rhodamine B from wastewater

A novel and eco-friendly one-step approach has been developed to fabricate magnetic lignosulfonate (MLS) with high performance in wastewater treatment. The obtained MLS was characterized by FTIR, XRD, SEM, TEM, VSM. The results showed that MLS had a good magnetic behavior in an applied magnetic field and its saturation magnetization intensity was up to 43.98 emu/g. Moreover, MLS exhibited excellent adsorption properties for Cr(Ⅵ) (57.14 mg/g) and Rhodamine B (22.47 mg/g). Simultaneously, the adsorption kinetics and adsorption isotherm experiments indicated that the data was agreed well with the pseudo-second-order and Langmuir model, respectively. After five regeneration cycles, the desorption efficiencies of Cr(Ⅵ) and Rhodamine B could reach more than 70% and 85%, respectively. Hence, the magnetic lignosulfonate is a promising material as a highly adsorptive and recyclable adsorbent for removing metal ions and cationic pollutants in wastewater.

Extraction of plasmid DNA by use of a magnetic maghemite-polyaniline nanocomposite

We describe the use of a hybrid magnetic nanocomposite (HMNC) for the extraction and purification of plasmid DNA (pDNA) from Escherichia coli aqueous solutions. The HMNC, which was synthesized via emulsion polymerization, was characterized by transmission electron microscopy, scanning electron microscopy, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering and magnetic measurements. The results confirmed the incorporation of polyaniline (Pani) in its conducting form onto a core formed by the magnetic iron oxide, with the hybrid particles presenting an average size of (95 ± 30) nm and a saturation magnetization of 30 emu/g. The yield, purity and quality of the pDNA purified by using the Pani HMNC were evaluated by UV-Vis spectroscopy, agarose gel electrophoresis, and Polymerase Chain Reaction (PCR), respectively. An average yield of ~6.9 μg was obtained in the DNA extraction process, with the collected material presenting a good purity (a ₳260/280 ratio in the 1.68-1.82 range) and an excellent quality, as confirmed by subsequent PCR assays. Hence, this HMNC appears as a promising material for use in pDNA purification protocols, and we suggest that this novel HMNC-based methodology can be of general interest and find widespread application in different biomedical procedures.

Simple synthesis and characterization of l-Cystine functionalized δ-FeOOH for highly efficient Hg(II) removal from contamined water and mining waste

l-Cystine functionalized δ-FeOOH nanoparticles (Cys-δ-FeOOH) were prepared by a cheap and straightforward method for using as an adsorbent of Hg(II) in aqueous solution. X-ray diffraction (XRD), attenuated total reflectance infrared spectroscopy (ATR-IR), and Raman spectroscopy confirmed that Cys-δ-FeOOH was successfully synthesized. Cys-δ-FeOOH with 14 nm crystal size, 34 m² g^-1 surface area, and 9 nm pore size were produced. The functionalization of the δ-FeOOH surface with cysteine decreases the point of zero charge of the iron oxyhydroxide from 8.4 in δ-FeOOH to 5.7 in Cys-δ-FeOOH, which is beneficial for the adsorption of Hg(II) near neutral pH. The maximum Hg(II) adsorption capacity of the δ-FeOOH and Cys-δ-FeOOH at pH 7 were found to be 35 mg g^-1 and 217 mg g^-1, respectively. The kinetics data were best fitted by a pseudo-second-order model, suggesting chemical adsorption on the surface and pores of Cys-δ-FeOOH nanoparticles. Finally, δ-FeOOH and Cys-δ-FeOOH filters were constructed for purifying mercury-contaminated water. The filters were highly efficient to treat mercury-contaminated water from a Brazilian river, reducing the concentration of mercury in water to values below the allowed limits by the current legislation.

Graphene oxide enhanced polyacrylamide-alginate aerogels catalysts

Biomass aerogel is a promising catalyst and has attracted extensive attention. However, most of the biomass aerogels are fragile, which limits their practical application. Herein, we significantly enhance the mechanical property of biomass aerogel catalysts by 30 times through incorporating graphene oxide into polyacrylamide and Cu-cross-linked alginate formed supper-strong double network aerogels. In addition to enhance the mechanical property, the graphene oxide also significantly increases the catalytic activity. Graphene oxide enhancement for biomass aerogel catalyst provides a new method to develop next generation supper catalysts.