Fabrication of novel magnetic core-shell chelating adsorbent for rapid and highly efficient adsorption of heavy metal ions from aqueous solution

Inhibition photooxidation of pyrite under illumination via altering photogenerated carrier migration pathways: Role of DTC-TETA surface passivation

The oxidation of pyrite is the main cause of acidic mine drainage (AMD), which is a very serious environmental problem in numerous mining areas around the world. Previous studies have shown that passivation agents create a hydrophobic film on the surface of pyrite, effectively isolating oxygen and water. However, the presence of abundant sulfide minerals in tailings ponds may exacerbate AMD when exposed to solar radiation, due to the semiconductor properties of pyrite. It remains uncertain whether the current surface passivation coating can effectively prevent the oxidation of pyrite under light conditions. This paper is the first to investigate the passivation effect as well as the mechanism of surface passivation coating on pyrite under illumination from the perspective of materials science. The results demonstrated that the triethylenetetramine-bisdithiocarbamate (DTC-TETA) passivation coating on pyrite almost completely suppressed the photooxidation of pyrite under illumination by changing the migration path of photogenerated charge carriers. The formation of NC(S)2-Fe chelating groups provides atomic-level interface channels for DTC-TETA to transfer electrons to pyrite and creates a favorable reduction environment for pyrite. Besides, DTC-TETA coating greatly improves the electron-hole pairs recombination efficiency of pyrite, which significantly inhibits the photogenerated electron reduction of oxygen to generate reactive oxygen species (ROS). Moreover, DTC-TETA coating captures the photogenerated holes, avoiding direct oxidation of pyrite by holes. Density functional theory (DFT) calculations revealed that the DTC-TETA coating increases the adsorption energy barrier for oxygen and water. The results extend the existing knowledge on passivation mechanisms on pyrite and hold significant implications for the future screening, evaluation, and practical application of surface passivating agents.

Biosorption of halophilic fungal melanized membrane - PUR/melanin polymer for heavy metal detoxification with electrospinning technology

Eradication of heavy metal pollution has become the prime priority over the conservation of water resources in the upcoming era. Herein, the study involved the halophilic fungal melanin from Curvularia lunata showed a promising biosorbent for the removal of toxic heavy metals which shows eco-friendly, cost-effective, high stability, and adsorbent efficiency. Polyurethane blended with fungal melanin polymers, makes polymeric nanofibrous membranes through electrospinning techniques. BET isotherms revealed the raw fungal melanin holds a surface area of 3.54 m2/g exhibiting type IV isotherms. BJH results in a total pore volume of 5.79 cc/g with a pore diameter of 6.54 ± 1 nm for pores smaller than 4544.8 Å. Exhibits Eumelanin properties were characterized by FE - SEM and FTIR functional elements. ICPMS confirmed the metal adsorption proficiency on both raw and melanized membranes before and after treatments. Over 17 heavy metals, Ni2+ were adsorbed with 100% efficiency by raw melanin alone with 42.48 µg/L of Ni2+ concentration in the water sample, whereas, Cu2+, Zn2+, Co2+, Cr2+, Pb2+, Mn2+, Al3+, Mo6+, Sb3+, Ba2+, Fe2+, and Mg2+ stands next with 99%. In this study, gentle/simple application of raw fungal melanin (without PUR tailored) can detoxify the maximum concentration of heavy metals present in the water bodies which are further used for irrigation and even drinking purposes. This mycoremediation approach can be easily adapted to industrial production than other high-performance membrane materials with minimal process modification, making it a promising strategy for improving the adsorption properties used in various applications after still furthermore investigation.

Sequestration of Ni (II), Pb (II), and Zn (II) utilizing biogenic synthesized Fe3O4/CLPC NCs and modified Fe3O4/CLPC@CS NCs: Process optimization, simulation modeling, and feasibility study

The present study reports low-cost novel biogenic magnetite Citrus limetta peels carbon (Fe3O4/CLPC) nanocomposites and modified Fe3O4/CLPC@CS nanocomposites cross-linked with glutaraldehyde and subsequently employed in batch mode sequestration of heavy metals ions. Diverse techniques fully characterized them, and the influence of operating variables on adsorption reactions from aqueous solutions was investigated. The Brunauer, Emmett, and Teller (BET) surface areas of synthesized Fe3O4/CLPC and Fe3O4/CLPC@CS NCs were 53.91 and 32.16 m2/g, while the mesoporous diameters were 7.69 and 7.57 nm, respectively. The Langmuir isotherm and Pseudo second order kinetic were well-fitting and capable of explaining the adsorption reaction. The Langmuir-based monolayer adsorption (qmax) for Fe3O4/CLPC@CS NCs was 82.65, 95.24, and 64.10 mg/g, higher than Fe3O4/CLPC NCs, which were 70.92, 84.75, and 59.17 mg/g for Ni (II), Pb (II), and Zn (II), respectively. Each metal's pseudo second order correlation coefficient (R2 ≥ 0.99) reveals that nanocomposites surface binding functional groups controlled the adsorption rate via chemisorption. Further, thermodynamic results confirm that each studied metal ions' adsorption was spontaneous, endothermic, and characterized by an increase in randomness. In addition to magnetic separability, three ad-desorption cycles yielded exceptional adsorption efficacy and > 93% regenerability. The present study also reveals the effective utilization of Fe3O4/CLPC and Fe3O4/CLPC@CS NCs as cost-effective magnetic separable green adsorbents for heavy metals sequestration from electroplating wastewater.

Characterization and Mechanistic Study of Heavy Metal Adsorption by Facile Synthesized Magnetic Xanthate-Modified Chitosan/Polyacrylic Acid Hydrogels

A simple method was used to synthesize magnetic xanthate-modified chitosan/polyacrylic acid hydrogels that were used to remove heavy metal ions from an aqueous solution. Xanthate modification of chitosan significantly improved adsorption performance: individual adsorption capacities of the hydrogel for Cu(II), Cd(II), Pb(II), and Co(II) ions were 206, 178, 168, and 140 mg g^-1, respectively. The magnetic hydrogels had good regeneration ability and were effectively separated from the solution by use of a magnet. Adsorption kinetic data showed that the removal mechanism of heavy metal ions from the solution by magnetic hydrogels occurs mainly by chemical adsorption. The equilibrium adsorption isotherms were well-described by the Freundlich and Langmuir equations. Positive values were found for the Gibbs standard free energy and enthalpy, indicating an increase in the disorder at the solid-liquid interface during adsorption. Magnetic xanthate-modified chitosan-based hydrogels that exhibit high adsorption efficiency, regeneration, and easy separation from a solution have broad development prospects in various industrial sewage and wastewater treatment fields.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Novel eco-friendly spherical porous adsorbent fabricated from Pickering middle internal phase emulsions for removal of Pb(II) and Cd (II)

Spherical porous materials prepared from the emulsion template used in the water treatment have displayed a vast prospect, as the high surface area, abundant porous structure, convenient operation and excellent adsorption performance. But the tedious fabrication process, high consumption of organic solvent and surfactant limited the application widely. Herein, a facile and eco-friendly spherical porous adsorbent (SPA) is fabricated from the green surfactant-free (corn oil)-in-water Pickering medium internal phase emulsions (Pickering MIPEs) via the convenient ion crosslinking procedure. The Pickering MIPEs synergistically stabilized with the semi-coke (SC), which is the natural particle produced from the shale oil distillation, and sodium alginate (SA) has excellent storage and anti-coalescence stability. The as-prepared porous adsorbent possessed the abundant pore structure, which provided favorable conditions for effective mass transfer in adsorption, and could be tuned by varying the SA dosage. The saturation adsorption capacities of Pb(II) and Cd(II) can be achieved with 460.54 and 278.77 mg/g within 45 min at 25°C, respectively. Overall, this study supplied a viable and eco-friendly route for fabricating the spherical porous adsorbent with a tunable porous structure for heavy metal ion wastewater.

Magnetic Adsorbents for Wastewater Treatment: Advancements in Their Synthesis Methods

The remediation of water streams, polluted by various substances, is important for realizing a sustainable future. Magnetic adsorbents are promising materials for wastewater treatment. Although numerous techniques have been developed for the preparation of magnetic adsorbents, with effective adsorption performance, reviews that focus on the synthesis methods of magnetic adsorbents for wastewater treatment and their material structures have not been reported. In this review, advancements in the synthesis methods of magnetic adsorbents for the removal of substances from water streams has been comprehensively summarized and discussed. Generally, the synthesis methods are categorized into five groups, as follows: direct use of magnetic particles as adsorbents, attachment of pre-prepared adsorbents and pre-prepared magnetic particles, synthesis of magnetic particles on pre-prepared adsorbents, synthesis of adsorbents on preprepared magnetic particles, and co-synthesis of adsorbents and magnetic particles. The main improvements in the advanced methods involved making the conventional synthesis a less energy intensive, more efficient, and simpler process, while maintaining or increasing the adsorption performance. The key challenges, such as the enhancement of the adsorption performance of materials and the design of sophisticated material structures, are discussed as well.

Crescent-shaped micromotor sorbents with sulfonic acid functionalized convex surface: The synthesis by A Janus emulsion strategy and adsorption for Li. JOURNAL OF HAZARDOUS MATERIALS 2022;422:126870. [PMID: 34425430 DOI: 10.1016/j.jhazmat.2021.126870]

Self-propelled micromotor (SPM) plays a vital role in recycling of lithium (Li⁺) from wastewater in battery industry. In this work, a crescent-shaped micromotor sorbent (CSMSs) with sulfonic group on convex surface was prepared by Janus emulsion to extract Li⁺. Using sodium p-styrene sulfonate as a functional monomer, well-designed CSMSs was prepared by UV-induced monomer interfacial polymerization, and their pit size can be controlled by adjusting the ratio of two incompatible oils (ethoxylated trimethylolpropane triacrylate and liquid paraffin). In addition, MnO₂ nanoparticles, which embedded into concave interface, generated O₂ bubbles in the presence of H₂O₂, and constant circular or line motion of CSMSs was observed. Zeta potential of CSMSs was -51.66 eV at pH = 10, and strong electrostatic attraction between sulfonate groups and Li⁺ endowed the maximum monolayer adsorption capacity of 31 mg g^-1 at 25 °C. Self-propelled effect further enhanced kinetic performance for Li⁺, and equilibrium time can be reduced from original 10-6.0 h, suggesting autonomous movement achieves rapid mixing and mass transportation. After three adsorption/desorption cycles, the adsorption capacity of the material remains above 90%. This simple and large-scale preparation strategy provided a synthetic method for functional and Janus SPM, as well as sorbents for Li⁺ enrichment.

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

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