Adsorption Mechanism Of Metal Ions Research Articles

Adsorption mechanisms of metal ions (Pb, Cd, Cu) onto polyamide 6 microplastics: New insight into environmental risks in comparison with natural media in different water matrices

Microplastics (MPs) are ubiquitous in the environment and have a great potential to coexist with metal ions. This work investigated the adsorption–desorption behaviors of three divalent metal ions (Cu, Cd, Pb) on polyamide 6 (PA6) MPs and natural media (riverside soil and marine sediment) and compare their environmental risks. The result showed that the adsorption amounts of metal ions onto PA6 MPs followed the order of Cd(II) (1.210 μmol/g) < Cu(II) (2.299 μmol/g) < Pb(II) (3.756 μmol/g). The adsorption of metal ions on PA6 was significantly affected by water chemistry, including solution pH, salinity, and the concentration of citric acid (CA) and humic acid (HA). Natural water matrices (Yangtze River water and Seawater) enhanced the uptake of three metal ions by PA6 MPs. The analysis of Fourier transform-infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) highlighted the importance of amide groups in controlling the adsorption of metal ions onto PA6 MPs. Site energy distribution indicated that the adsorption of metal ions mainly involved chemisorption. The retention factor (Rf) calculated by the adsorption–desorption behavior of three heavy metal ions indicated that the risk of metal ions posed by PA6 MPs was higher than that of natural media. Among all water matrices, the metal ion/PA6 MPs combinations posed the highest environmental risk in the simulated gastric fluid. This work highlights the behavior of PA6 MPs as metal ions vectors and provides strong evidence the assessment of environmental risk posed by MPs/metal ions combinations, opening new insight into understanding the environmental impacts of MPs.

Sorption and mechanism studies of Cu2+, Sr2+ and Pb2+ ions on mesoporous aluminosilicates/zeolite composite sorbents.

The research aimed to develop a novel mesoporous aluminosilicate/zeolite composite by the template co-precipitation method. The effect of aluminosilicate (AlSi) and zeolite (NaY) on the basic properties and adsorption capacity of the resultant composite was conducted at different mass ratios of AlSi/NaY (i.e., 5/90, 10/80, 15/85, 20/80, and 50/50). The adsorption characteristics of such composite and its feedstock materials (i.e., aluminosilicates and zeolite) towards radioactive Sr2+ ions and toxic metals (Cu2+ and Pb2+ ions) in aqueous solutions were investigated. Results indicated that BET surface area (SBET), total pore volume (VTotal), and mesopore volume (VMeso) of prepared materials followed the decreasing order: aluminosilicate (890 m2/g, 0.680 cm3/g, and 0.644 cm3/g) > zeolite (623 m2/g, 0.352 cm3/g, and 0.111 cm3/g) > AlSi/NaY (20/80) composite (370 m2/g, 0.254 cm3/g, and 0.154 cm3/g, respectively). The Langmuir maximum adsorption capacity (Qm) of metal ions (Sr2+, Cu2+, and Pb2+) in single-component solution was 260 mg/g, 220 mg/g, and 161 mg/g (for zeolite), 153 mg/g, 37.9 mg/g, and 66.5 mg/g (for aluminosilicate), and 186 mg/g, 140 mg/g, and 77.8 mg/g for (AlSi/NaY (20/80) composite), respectively. Ion exchange was regarded as a domain adsorption mechanism of metal ions in solution by zeolite; meanwhile, inner-surface complexation was domain one for aluminosilicate. Ion exchange and inner-surface complexation might be mainly responsible for adsorbing metal ions onto the AlSi/NaY composite. Pore-filling mechanism was a less important contributor during the adsorption process. The results of competitive adsorption under binary-components (Cu2+ and Sr2+) and ternary-components (Cu2+, Pb2+, and Sr2) demonstrated that the removal efficacy of target metals by the aluminosilicate, zeolite, and their composite remarkably decreased. The synthesized AlSi/NaY composite might serve as a promising adsorbent for real water treatment.

Relations between metal ion characteristics and adsorption performance of graphene oxide: A comprehensive experimental and theoretical study

The adsorption performance of graphene oxide (GO) towards metallic hard (Na+, Mg2+), soft (Cd2+ and Pb2+) and borderline ions (Ni2+, Cu2+, Zn2+, Co2+) was studied experimentally giving the sequence of maximum Langmuir adsorption capacities Qm, mmol/g, as Na+ < Mg2+ < Co2+ < Cd2+ < Zn2+ < Ni2+ < Cu2+ < Pb2+. The results showed that the adsorption capacities Qm of hard ions were substantially lower than that of soft and borderline ones. The relationship between the Qm values of metal ions and their characteristics was studied using relative correlation analysis. The ion characteristics include atomic number AN, ionic radius r, change in ionization potential ΔIP, electronegativity Xm, atomic weight AW, covalent index Xm2r, absolute difference between electrochemical potential of the ion and that of its first stable reduced state ΔE0, absolute value of the first hydrolysis constant decimal logarithm |lgKOH|, atomic radius AR, atomic radius to atomic weight ratio AR/AW, polarization force or ionic index Z2/r and softness index σp. The Qm value exhibited positive correlation with r, △IP, Xm, Z2/r, AN/△IP, AW, Xm2/r and AN, while negative correlation was observed with △E0, |lgKOH|, σp, AR and AR/AW. The results allow the Qm values being predicted by the equation, the correlation coefficient R2 of which exceeds 0.885:Qm=0.338ΔIP-0.110|lgKOH|+0.114Z2/r+26.934σp-1.479AR-1.162Xm2r+0.115AN-3.059Density functional theory (DFT) was adopted to study the adsorption mechanism of metal ions at GO, taking Na+, Cu2+ and Pb2+ ions as examples. The results showed the adsorption energy Ead of GO-Na+ bond being negative indicating Na+ adsorption less likely resulting possibly in relatively low adsorption capacity of GO towards hard ions. The Ead values of GO bonds with Cu2+ and Pb2+ comprised the rows GO(O)-Cu2+ > GO(COOH)-Cu2+ > GO(OH)-Cu2+, and GO(COOH)-Pb2+ > GO(OH)-Pb2+ > GO(O)-Pb2+, respectively. The results provide guidelines in predicting the adsorption ability of GO adsorbent towards metal ions.

Adsorption mechanism of metal ions on activated carbon

Environmental pollution, particularly that caused by the presence of heavy metals in wastewater, is a serious problem. Therefore, heavy metals should be prevented from reaching the natural environment or removed from polluted wastewater. Adsorption is a very economical, simple, effective, highly versatile process for removing harmful pollutants from wastewater. In this study, six commercial activated carbon (AC) samples were used to evaluate the adsorption of Pb2+, Ni2+, and Zn2+. We investigated the correlation between the adsorption of metal ions on AC and the pore or surface properties of AC. Large quantities of ions in the order [Pb2+] >> [Zn2+], [Ni2+] were adsorbed on all AC samples. The results showed that the Pb2+ adsorption capacity per unit Dubinin–Polanyi (DP) surface area (SDP) is correlated with the graphite/defect (G/D) ratio of AC; the G/D ratio was analyzed via Raman spectroscopy. The adsorbability of Pb2+ on AC per unit SDP was higher in AC with a larger G/D ratio. Moreover, we found that hard and soft acids and bases contribute to adsorption. The observed correlation facilitates the determination of the adsorption capacity of Pb2+ on AC using the G/D ratio without any adsorption test.

Individual and simultaneous adsorption of Ni (II), Cd (II), and Zn (II) ions over polyamide resin: Equilibrium, kinetic and thermodynamic studies

Heavy metal pollution is a serious environmental issue worldwide with rapid increase in global industrial activities (Podder and Majumder [2016]: Water Conserv Sci Eng 1, 103–125). In this study, aromatic polyamide (PA) containing the azomethine group (Vidhyadevi et al. [2012]: Sep Sci Technol 48, 1450–1458) was used as an adsorbent for the individual and simultaneous adsorption of Ni (II), Cd (II), and Zn (II) ions from their aqueous solutions. Equilibrium, kinetic, and thermodynamic analyses of Ni (II), Cd (II), and Zn (II) ions adsorption were also carried out. The kinetic study on heavy metal ions adsorption suggests that the adsorption follows pseudo‐second‐order kinetic model. The thermodynamic study results revealed that the process is spontaneous and exothermic in nature. In the multicomponent adsorption system, adsorption of one metal ion was considerably reduced by the presence of other ions in the solution due to competition for the active sites on PA. The adsorption of heavy metal ions over PA was confirmed through FT‐IR, SEM, and EDX analyses. The adsorption capacity of PA was found significantly higher than other adsorbents. The PA could be regenerated and reused even after five cycles for the Ni (II), Cd (II), and Zn (II) ions suggesting that adsorption using the PA is a reversible process. Significance of the present work Polyamide resin (PA) is an effective adsorbent for the individual and simultaneous removal of Ni (II), Cd (II), and Zn (II). Maximum adsorption capacity of PA for Ni (II), Cd (II), and Zn (II) ions were found to be better than other commonly used adsorbents. Repeated desorption studies indicate that the PA may be reused and the adsorption is a reversible process. Adsorption mechanism of metal ions over PA is explained. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S340–S351, 2019

Adsorption mechanisms of metal ions on the potassium dihydrogen phosphate (1 0 0) surface: A density functional theory-based investigation

The adsorption of metal ions (K+, Na+, Ca2+, Cu2+, Al3+, Cr3+) on the (1 0 0) surface of potassium dihydrogen phosphate (KDP) has been studied using density functional theory (DFT). Calculation results show that all the investigated metal ions can be spontaneously adsorbed on the surface with negative adsorption energies. The adsorption stability increases in the order of Na+ < K+ < Cu2+ < Ca2+ < Al3+ < Cr3+, and shows a consistent trend as the adsorbed metal ion valence (monovalent < divalent < trivalent). Three types of stable adsorption configurations are observed, corresponding to three different bonding mechanisms. Na+, K+ and Ca2+ ions with a large radius can form two ionic bonds and one weak covalent bond with the O and H atoms respectively. In addition, the medium-sized ion of Cu2+ forms two covalent bonds with the O and H atoms. Furthermore, Al3+ and Cr3+ ions with the smallest radius form two metal-oxygen and one metal-hydrogen covalent bonds with the surface, making one H–O bond broken. Compared with other metal ions, Al3+ and Cr3+ have the strongest interactions with the surface, which can be explained by the significant electron transfer and more stable covalent bond formations between these two ions and the surface.

Fast, selective adsorption of Cu2+ from aqueous mixed metal ions solution using 1,4,7-triazacyclononane modified SBA-15 silica adsorbent (SBA-TACN)

A new SBA-15 supported 1,4,7-triazacyclononane modified mesoporous silica adsorbent (SBA-TACN) has been synthesized using post grafting route and has thoroughly been characterized by small angle X-ray scattering (SAXS), N2 adsorption–desorption measurements, Fourier-transform infrared (FT-IR), solid-state 29Si MAS and 13C CP MAS NMR spectroscopy, transmission electron (TEM) and scanning electron microscopy (SEM), elemental analysis (EA) and thermogravimetric analysis (TGA). The synthesized material shows excellent copper (II) ion adsorption selectivity at pH 5 in mixed metal ion solution containing Cu2+, Cr3+, Ni2+, Co2+ and Li+. The copper ion adsorption capacity of the SBA-TACN can reach a maximum value of 0.67mmol/g. Possible adsorption mechanism of metal ions on SBA-TACN has been discussed. The adsorbent can be readily regenerated by HNO3–NH3 treatment.

Sorption Behavior of Cu(II), Pb(II), and Zn(II) onto Carbon Nanotubes

The sorption behavior of Cu((II), Zn(II), and Pb(II) onto multiwall carbon nanotubes (CNTs) oxidized with nitric acid was investigated. The effect of pH and metal ion concentration on their retention were studied together with more detailed information on the structural properties of CNTs, such as the surface area, the amount of acidic groups, and the pH value of the point of zero charge. The main adsorption mechanism of metal ions into CNTs is considered as a complexation with the surface oxygen-containing functional groups, and the experimental data have been fitted well by the Langmuir sorption model. The theoretical capacity of the monolayer derived from this model for Cu(II), Pb(II), and Zn(II) are 24.7, 25.6, and 14.7 mg/g, respectively. The sorption kinetic profile is fitted well for the pseudo-second order equation. The procedure for sorption of the studied metal ions shows high tolerance to the excess of alkaline and alkaline-earth metals.

Adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth

The adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth was studied as a function of their concentrations and solution pH. For that purpose, pertinent adsorption isotherm data was collected at different pH values. The amount of adsorbed zinc and cadmium ions increases while the amount of adsorbed mercury remains constant with an increase in the equilibrium pH of the solution. The adsorption mechanisms of metal ions on activated carbon cloth are discussed. Under the conditions investigated, these primarily involve adsorption of monovalent cations (Zn and Cd) or precipitation of metal hydroxides (Cd and Hg) on the activated carbon cloth tested.

The Effect of the Adsorption of Metal Ions on the Interfacial Behavior of Silicate Minerals

AbstractBecause of its importance in the fields of environmental and mineral engineering, the adsorption mechanism of metal ions on oxides has been studied rather extensively using such techniques as titration, adsorption isotherm determination, flotation and spectroscopy. However, limited work has been done to compare the behavior of hydrophilic silicates with those that are naturally hydrophobic. Our investigation was undertaken to provide a better understanding of the adsorption mechanism of selected metal ions at the solid/liquid interface through simultaneous measurements of zeta potentials, adsorption densities and turbidity on colloidal suspensions of two silicate minerals, quartz and talc, as a function of pH, to delineate the effect of hydrophobicity and surface heterogeniety on these processes.

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