Retention of Pb(II) by a Low-Cost Magnetic Composite Prepared by Environmentally-Friendly Plasma Technique

Adsorption behavior and mechanism of Cu(II) by sodium alginate/carboxymethylcellulose/magnesium hydroxide (SC-MH) hydrogel

In the present work, an environmentally-friendly, reusable hydrogel ball characterized by its great adsorption capacity to Cu(II) was synthesized. The preparation of this hydrogel drew on sodium alginate (SA) and carboxymethyl cellulose (CMC) as primary composition elements. The endeavor brought novelty by ingeniously infusing it with slurry magnesium hydroxide (MH). The factors (pH, SC-MH amount, initial concentration, adsorption time) that are critical to adsorption were also investigated. FTIR, SEM-EDS and XPS were used to reveal the adsorption mechanism of Cu on SC-MH. The results show that the surface of SC-MH is rough, and there are a large number of gully-like structures conducive to adsorption, which are rich in hydroxyl and carboxyl groups. Under the optimum conditions, the maximum adsorption capacity reached 215.68 mg/g. Based on its high R2 value (0.999), the Langmuir model is determined to be the most appropriate for describing the adsorption behavior, indicating monolayer homogeneous adsorption. The kinetic data align well with the pseudo-second-order kinetic model. Furthermore, thermodynamic analysis reveals the adsorption process to be spontaneous and endothermic, as demonstrated by a negative ΔG and positive ΔH (38.8859 KJ/mol). The mechanism involves electrostatic attraction, chelation, Mg(OH)2 adsorption and ion exchange.

Synthesis and adsorption properties of gelatin-conjugated hematite (α-Fe2O3) nanoparticles for lead removal from wastewater

Gelatin-conjugated hematite nanoparticles (HT NPs) are prepared through the solid-state phase transformation in the presence of phosphate. Their adsorption capacity and kinetics are investigated for Pb removal in wastewater. The gelatin-conjugated HT NPs with a size of 4-6 nm exhibit an excellent Pb removal performance, with a high adsorption capacity of 169.49 mg g^-1 and a fast equilibrium adsorption kinetics, attributed to the large number of active sites and highly negative charge on the surface of HT NPs. Moreover, the magnetic property of HT NPs enables to selectively collect NPs in the wastewater by using a permanent magnet, leading to its high reusability.

A novel, recyclable magnetic biochar modified by chitosan–EDTA for the effective removal of Pb(ii) from aqueous solution

We report here the preparation process of a recyclable magnetic biochar functionalized with chitosan and ethylenediaminetetraacetic acid (E-CMBC). This prepared biochar was then evaluated regarding its adsorption performance for Pb(ii) from an aqueous solution along with the potential adsorption mechanisms behind this process. XRD and SEM analyses showed that the magnetite particles were successfully embedded into biochar and the subsequent surface coating of chitosan and ethylenediaminetetraacetic acid modification were also successful. The effects of the adsorbent dosage, ionic strength, initial solution pH, and contact time, on adsorption kinetics, adsorption isotherms, adsorption thermodynamics and regeneration performance were investigated. The removal of Pb(ii) was dramatically improved to 156.68 mg g⁻¹ compared with that by unmodified pristine biochar (10.90 mg g⁻¹) at pH 3.0. In the range of pH 2.0–5.0, the adsorption performance of Pb(ii) by E-CMBC remained above 152.50 mg g⁻¹, which suggested that the adsorption capacity of the novel sorbent was not impacted by the competing adsorption of hydrogen cations under acidic conditions. The adsorption process could be well described by the Avrami fractional-order and Langmuir models. Thermodynamic analysis proved that the adsorption process was spontaneous and endothermic. The magnetic strength of E-CMBC was measured as 3.1 emu g⁻¹, suggesting that the consumed E-CMBC could be separated from water by an external magnet. A regeneration study showed that after three cycles of adsorption–desorption, 78.60% of the sorbent was recovered and 97.26% of the adsorption capacity was retained. The adsorption mechanism investigation indicated that Pb(ii) adsorption was mainly due to the presence of functional amides and carboxyl groups of E-CMBC forming strong chemical complexation. In conclusion, E-CMBC is a novel, recyclable, and highly efficient adsorbent for removal of Pb(ii) from aqueous solution.

EDTA modified magnetic chitosan biochar was synthesized and used as an adsorbent for adsorption of Pb(ii).

Equilibrium adsorption study of the adsorptive removal of Cd2+ and Cr6+ using activated carbon

The performance of activated carbon (AC) with respect to characterization, adsorption kinetics, thermodynamics, and isotherms was addressed in this study. The effects of initial concentration, pH, contact time, ion strength, and temperature on removal efficiency were also studied. The adsorption isotherms of Cd²⁺ and Cr⁶⁺ on activated carbon can fit the Langmuir model well, and correlation coefficients were above 0.99, all higher than the Freundlich and Temkin models. The maximum adsorption quantities of Cd²⁺ and Cr⁶⁺ were 19.380 and 19.305 mg g^-1 at 25 °C, respectively. The adsorption capacities of Cd²⁺ and Cr⁶⁺ are clearly pH dependent. The kinetics of the removal of Cd²⁺ and Cr⁶⁺ was in agreement with a pseudo-second-order model, and the adsorption efficiency of Cd²⁺ is higher than that of Cr⁶⁺. The thermodynamic results showed that increased temperature is favorable to adsorption. The speciation on activated carbon was mainly residual Cd²⁺ and Cr⁶⁺, and the potential ecological risk of Cd²⁺ is higher than that of Cr⁶⁺. The adsorptions of Cd²⁺ and Cr⁶⁺ on activated carbon were dominated by chelation and ion exchange, respectively.

Nanoscale zero-valent iron functionalized Posidonia oceanica marine biomass for heavy metal removal from water

Because of the excellent reducing capacity of nanoscale zero-valent iron (NZVI), it can be used as alternative materials for the removal of a variety of reducible water contaminants including toxic metals. The current paper reports the research results obtained for self-prepared biosorbent, Posidonia oceanica biomass, activated in alkaline medium and functionalized with NZVI particles. The structural characteristics, surface morphology, and binding properties of the resulting nanobiosorbent are presented. Batch comparative adsorption trials including adsorption kinetics and isothermals onto raw Posidonia, Posidonia-OH and Posidonia-OH-NZVI were investigated on three heavy metal ions: Cd(II), Pb(II), and Cu(II). The nanobiosorbent showed better properties, such as high reactivity and high uptake rate through the sorption process. The toxic metal removal has been monitored in terms of pseudo-first- and pseudo-second-order kinetics, and both Langmuir- and Freundlich-type isotherm models have been used to describe the sorption mechanism. The experimental data of all studied systems showed that the uptake kinetics follow the pseudo-second-order kinetic model and the equilibrium uptake can adopt the Langmuir-type isotherm model which assumes a monolayer coverage as the adsorption saturates and no further adsorption occurs. The thermodynamic results confirm that all sorption processes were feasible, spontaneous and thermodynamically favorable. Zeta potential data displayed that Cd(II), Pb(II), and Cu(II) tend to be reduced after exposure on the Posidonia-OH-NZVI surface. Furthermore, sorption competitions of the metals from binary and ternary systems were carried out onto Posidonia-OH-NZVI in order to gain further insight into the sorption efficiency of this material. Therefore, as a result, the proposed new nanobiosorbent could offer potential benefits in remediation of heavy metal-contaminated water as a green and environmentally friendly bionanocomposite.

Environmental Remediation and Application of Nanoscale Zero-Valent Iron and Its Composites for the Removal of Heavy Metal Ions: A Review

The presence of heavy metals in the industrial effluents has recently been a challenging issue for human health. Efficient removal of heavy metal ions from environment is one of the most important issues from biological and environmental point of view, and many studies have been devoted to investigate the environmental behavior of nanoscale zerovalent iron (NZVI) for the removal of toxic heavy metal ions, present both in the surface and underground wastewater. The aim of this review is to show the excellent removal capacity and environmental remediation of NZVI-based materials for various heavy metal ions. A new look on NZVI-based materials (e.g., modified or matrix-supported NZVI materials) and possible interaction mechanism (e.g., adsorption, reduction and oxidation) and the latest environmental application. The effects of various environmental conditions (e.g., pH, temperature, coexisting oxy-anions and cations) and potential problems for the removal of heavy metal ions on NZVI-based materials with the DFT theoretical calculations and EXAFS technology are discussed. Research shows that NZVI-based materials have satisfactory removal capacities for heavy metal ions and play an important role in the environmental pollution cleanup. Possible improvement of NZVI-based materials and potential areas for future applications in environment remediation are also proposed.