Nanoadsorbants for the Removal of Heavy Metals from Contaminated Water: Current Scenario and Future Directions

Nano silica-mediated stabilization of heavy metals in contaminated soils

Soil contamination with heavy metals presents a substantial environmental peril, necessitating the exploration of innovative remediation approaches. This research aimed to investigate the efficiency of nano-silica in stabilizing heavy metals in a calcareous heavy metal-contaminated soil. The soil was treated with five nano-silica levels of 0, 100, 200, 500, and 1000 mg/kg and incubated for two months. The results showed that nano-silica had a specific surface area of 179.68 m 2 / g . At 1000 mg/kg, the DTPA-extractable concentrations of Pb, Zn, Cu, Ni, and Cr decreased by 12%, 11%, 11.6%, 10%, and 9.5% compared to the controls, respectively. Additionally, as the nano-silica application rate increased, both soil pH and specific surface area increased. The augmentation of nano-silica adsorbent in the soil led to a decline in the exchangeable (EX) and carbonate-bound fractions of Pb, Cu, Zn, Ni, and Cr, while the distribution of heavy metals in fractions bonded with Fe-Mn oxides, organic matter, and residue increased. The use of 1000 mg/kg nano-silica resulted in an 8.0% reduction in EX Pb, 4.5% in EX Cu, 7.3% in EX Zn, 7.1% in EX Ni, and 7.9% in EX Cr compared to the control treatment. Overall, our study highlights the potential of nano silica as a promising remediation strategy for addressing heavy metal pollution in contaminated soils, offering sustainable solutions for environmental restoration and ecosystem protection.

An Updated Overview of Magnetic Composites for Water Decontamination

Water contamination by harmful organic and inorganic compounds seriously burdens human health and aquatic life. A series of conventional water purification methods can be employed, yet they come with certain disadvantages, including resulting sludge or solid waste, incomplete treatment process, and high costs. To overcome these limitations, attention has been drawn to nanotechnology for fabricating better-performing adsorbents for contaminant removal. In particular, magnetic nanostructures hold promise for water decontamination applications, benefiting from easy removal from aqueous solutions. In this respect, numerous researchers worldwide have reported incorporating magnetic particles into many composite materials. Therefore, this review aims to present the newest advancements in the field of magnetic composites for water decontamination, describing the appealing properties of a series of base materials and including the results of the most recent studies. In more detail, carbon-, polymer-, hydrogel-, aerogel-, silica-, clay-, biochar-, metal-organic framework-, and covalent organic framework-based magnetic composites are overviewed, which have displayed promising adsorption capacity for industrial pollutants.

Network-Polymer-Modified Superparamagnetic Magnetic Silica Nanoparticles for the Adsorption and Regeneration of Heavy Metal Ions

Superparamagnetic magnetic nanoparticles (MNPs, Fe3O4) were first synthesized based on a chemical co-precipitation method, and the core-shell magnetic silica nanoparticles (MSNPs, Fe3O4@SiO2) were obtained via hydrolysis and the condensation of tetraethyl orthosilicate onto Fe3O4 seed using a sol-gel process. Following that, MSNPs were immobilized using a three-step grafting strategy, where 8-hloroacetyl-aminoquinoline (CAAQ) was employed as a metal ion affinity ligand for trapping specific heavy metal ions, and a macromolecular polymer (polyethylenimine (PEI)) was selected as a bridge between the surface hydroxyl group and CAAQ to fabricate a network of organic networks onto the MSNPs' surface. The as-synthesized MSNPs-CAAQ nanocomposites possessed abundant active functional groups and thus contained excellent removal features for heavy metal ions. Specifically, the maximum adsorption capacities at room temperature and without adjusting pH were 324.7, 306.8, and 293.3 mg/g for Fe3+, Cu2+, and Cr3+ ions, respectively, according to Langmuir linear fitting. The adsorption-desorption experiment results indicated that Na2EDTA proved to be more suitable as a desorbing agent for Cr3+ desorption on the MSNPs-CAAQ surface than HCl and HNO3. MSNPs-CAAQ exhibited a satisfactory adsorption capacity toward Cr3+ ions even after six consecutive adsorption-desorption cycles; the adsorption efficiency for Cr3+ ions was still 88.8% with 0.1 mol/L Na2EDTA as the desorbing agent. Furthermore, the MSNPs-CAAQ nanosorbent displayed a strong magnetic response with a saturated magnetization of 24.0 emu/g, and they could be easily separated from the aqueous medium under the attraction of a magnet, which could facilitate the sustainable removal of Cr3+ ions in practical applications.

Adsorption isotherms and kinetics for Pb(ii) ion removal from aqueous solutions with biogenic metal oxide nanoparticles

This study investigates the sorption removal of lead(ii) ions using zinc oxide (ZnO) and copper(ii) oxide (CuO) nanoparticles synthesized through a wet burning method with the aid of plant extract from Serratula coronata L. The effect of plant collection time on polyphenol content was investigated and optimal conditions were determined. The structural and chemical properties of the nanoparticles were studied by scanning electron microscopy, energy dispersive analysis, X-ray phase analysis, and X-ray photoelectron spectroscopy. A comparative analysis of lead ion sorption on the surface of synthesized nanoparticles was conducted. The kinetic study revealed that the sorption process follows a pseudo-second-order mechanism, and the Freundlich sorption model provides a better fit for the experimental data. ZnO and CuO nanoparticles exhibited significant sorption capacities, with values of 163.6 and 153.8 mg g-1, respectively.

Valorization of Fibrous Plant-Based Food Waste as Biosorbents for Remediation of Heavy Metals from Wastewater-A Review

Mobilization of heavy metals in the environment has been a matter of concern for several decades due to their toxicity for humans, environments, and other living organisms. In recent years, use of inexpensive and abundantly available biosorbents generated from fibrous plant-based food-waste materials to remove heavy metals has garnered considerable research attention. The aim of this review is to investigate the applicability of using fibrous plant-based food waste, which comprises different components such as pectin, hemicellulose, cellulose, and lignin, to remove heavy metals from wastewater. This contribution confirms that plant-fiber-based food waste has the potential to bind heavy metals from wastewater and aqueous solutions. The binding capacities of these biosorbents vary depending on the source, chemical structure, type of metal, modification technology applied, and process conditions used to improve functionalities. This review concludes with a discussion of arguments and prospects, as well as future research directions, to support valorization of fibrous plant-based food waste as an efficient and promising strategy for water purification.

Biofabricated copper ferrite nanoparticles: a potential nanosorbent for the removal of Pb (II) ions from aqueous media

In the present study, we describe a facile strategy for the easy removal of the heavy metal ion, Pb (II) using biosynthesized copper ferrite (CuFe₂O₄) Nanoparticles (Nps) prepared via a cost-effective and eco-friendly method usingPimenta dioicaleaf extract. The structural characterization was performed using UV-Visible, FT-IR, XRD, XPS, TG, SEM - EDS and TEM techniques. Various characterization techniques showed that the biosynthesized CuFe₂O₄nanoparticles have spherical shape with minimum aggregation and possess a size range between 7 and 16 nm. Batch experiments were carried out to analyze the adsorption efficiency of CuFe₂O₄Nps by varying different experimental conditions such as pH, adsorbent dose and initial metal ion concentration. From the atomic absorption spectroscopy results, the optimum removal efficiency (99.69%) occurred at a contact time of 90 min in the solution having pH 6 with 0.06 g of nanoadsorbent. The experimental data were analyzed using adsorption isotherm and fitted with kinetic models. In the present study, we report the the highest removal efficiency of 99.69% for Pb (II) ions with minimum experimental parameters which is greater than other similar reported studies. The novel CuFe₂O₄nanosorbent synthesized in the present study is highly effective in eliminating toxic pollutants. They also possess outstanding recycling characteristics for the effective removal of Pb (II) ions from aqueous media.This cost-effective and ecofriendly strategy could be utilized for addressing the emerging water contamination.

Green synthesis, characterization, and application of metal oxide nanoparticles for mercury removal from aqueous solution

In this work, a novel surface-modified, green-based wheat straw-supported magnetite nanoparticles (Fe₃O₄-NPs) were synthesized via the green synthesis method, and the adsorption of mercury (Hg(II)) ion from aqueous solutions was methodically investigated. The synthesized wheat straw-supported magnetite (Fe₃O₄-WSS) NPs were characterized using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopic (SEM) methods. FT-IR and TGA confirmed that the surface of Fe₃O₄-NPs was functionalized well. The XRD analysis revealed the existence of magnetite in the synthesized wheat straw-supported Fe₃O₄-NPs of 19.83 nm average crystalline size. SEM analysis showed Fe₃O₄-NPs were almost spherical, with an average particle size of 22.48 nm. Adsorption studies were carried out to investigate the adsorption of Hg(II) ions onto Fe₃O₄-WSS NPs and the effect of various adsorption parameters such as pH, time, adsorbent dosage, and Hg(II) ion concentration. The optimum adsorption conditions were obtained: pH of 6, contact time of 45 min, adsorbate of 40 mg/L, and adsorbent of 1 g. A maximum of 98.04% Hg(II) ion removal efficiency was obtained at these optimum conditions. FT-IR analysis also indicated that surface functional groups such as C = C,-OH, and C-C of the newly produced Fe₃O₄-NPs led to the more efficient removal of Hg(II) from aqueous solution. The synthesized nano-adsorbent showed an excellent adsorption capability of 101.01 mg/g. Hg(II) ions adsorption onto Fe₃O₄-WSS NPs fitted well with the Langmuir adsorption isotherm model. Therefore, these reasonable findings reveal that Fe₃O₄-WSS NPs are an efficient and promising adsorbent for Hg(II) removal from aqueous water environments.

Cosmetic wastewater treatment technologies: a review

Over the past three decades, environmental concerns about the water pollution have been raised on societal and industrial levels. The presence of pollutants stemming from cosmetic products has been documented in wastewater streams outflowing from industrial as well as wastewater treatment plants. To this end, a series of consistent measures should be taken to prevent emerging contaminants of water resources. This need has driven the development of technologies, in an attempt to mitigate their impact on the environment. This work offers a thorough review of existing knowledge on cosmetic wastewater treatment approaches, including, coagulation, dissolved air flotation, adsorption, activated sludge, biodegradation, constructed wetlands, and advanced oxidation processes. Various studies have already documented the appearance of cosmetics in samples retrieved from wastewater treatment plants (WWTPs), which have definitely promoted our comprehension of the path of cosmetics within the treatment cycle; however, there are still multiple blanks to our knowledge. All treatments have, without exception, their own limitations, not only cost-wise, but also in terms of being feasible, effective, practical, reliable, and environmentally friendly.

Development of Cyanine 813@Imidazole-Based Doped Supported Devices for Divalent Metal Ions Detection

A NIR cyanine@imidazole derivative Cy1 was synthesized and evaluated as a metal ion sensor in solution. Cy1 was shown to be very sensitive to all metal ions tested, presenting a blue shift in the absorption from 668 nm to 633 nm, followed by a change in colour from pale green to blue with Zn2+, Cd2+, Co2+, Ni2+ and Hg2+ ions. Despite the blue shift in the absorption, a decrease at 633 nm (with a colour change from pale green to colourless), as well as a quenching in the emission intensity at 785 nm were observed for Cu2+ ions. The results show the formation of sandwich complexes of two ligands per metal ion with the highest association constant observed for Cu2+ (Log Kass.abs = 14.76 ± 0.09; Log Kass.emis. = 14.79 ± 0.06). The minimal detectable amounts were found to be 31 nM and 37 nM, with a naked eye detection of 2.9 ppm and 2.1 ppm for Hg2+ and Cu2+ ions, respectively. These results prompted us to explore the applicability of Cy1 by its combination with nanomaterials. Thus, Cy1@ doped MNs and Cy1@ doped PMMA nanoparticles were synthesized. Both nanosystems were shown to be very sensitive to Cu2+ ions in water, allowing a naked-eye detection of at least 1 ppm for Cy1@ doped MNs and 7 ppm for Cy1@ doped PMMA. This colourimetric response is an easy and inexpensive way to assess the presence of metals in aqueous media with no need for further instrumentation.