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Granular activated carbon (GAC) was modified with Fe–Mn binary oxide to produce a novel effective hybrid adsorbent (GAC–FeMn) for simultaneous removal of As(III) and As(V) from water. After characterization (including BET, SEM/EDS and XRD analyses) of the raw and modified GAC, FTIR analysis before and after As removal showed that ligand exchange was the major mechanism for As removal on GAC–FeMn. Sorption kinetics followed pseudo-second order kinetics for both As(III) and As(V) and were not controlled by intraparticle diffusion. Batch equilibrium experiments yielded adsorption capacities for As(III) and As(V) of 2.87 and 2.30 mg/g, and demonstrated that better sorption was achieved at low pH. Of the competitive anions investigated (PO43−, SiO32−, CO32−, SO42−, NO3−, Cl−), phosphate had the greatest negative effect on As(III) and As(V) adsorption. Three sorption/desorption cycles were conducted in continuous column tests with a real arsenic contaminated groundwater, with subsequent TCLP leaching tests confirming the stability of the spent sorbent. In the column tests, breakthrough curves were also obtained for phosphates, which were present at a relatively high concentration (1.33 mg/L) in the investigated groundwater. The phosphates limited the effective operational bed life of GAC–FeMn for arsenic removal. Nonetheless, the maximum arsenic adsorption capacities for GAC–FeMn obtained by the Thomas model during the three sorption cycles were high, ranging from 18.8 to 29.8 mg/g, demonstrating that even under high phosphate loads, with further process improvements, GAC–FeMn may provide an excellent solution for the economic removal of arsenic from real groundwaters. [ABSTRACT FROM AUTHOR]

This work investigates the possibility of applying two types of oxidized multiwalled carbon nanotubes (oxMWCNTs) as effective adsorbents for removing low concentrations of Cd(II) and Pb(II) (≤ 5 mg L−1) from aqueous media, as well as the influence of the functionalization process duration (3 h (oxMWCNT3h) or 6 h (oxMWCNT6h)) on the performance of the materials tested. Both oxMWCNTs were thoroughly characterized by SEM/EDS, TEM, FTIR, N 2 adsorption/desorption and pHpzc techniques. An extensive study of Cd(II) and Pb(II) adsorption and the mechanisms responsible was conducted by evaluating the effects of contact time, initial Cd(II) and Pb(II) concentration, pH and ionic strength. Adsorption kinetic data show that the two materials can be considered extremely effective, as less than 20 min was required to reach a state of equilibrium. Freundlich, Langmuir, Dubinin-Radushkevic and Temkin adsorption isotherm models fit the data well and suggest that the investigated adsorption processes are favorable, mainly electrostatically driven and exothermic. The maximum adsorption capacities obtained by the Langmuir model were 10.5 and 13.5 mg g−1 for Cd(II) and 23.4 and 27.9 mg g−1 for Pb(II) (thus: oxMWCNT6h > oxMWCNT3h and Pb(II) > Cd(II)). The adsorption of Cd(II) and Pb(II) is strongly and positively influenced by increasing the pH and negatively affected by increasing the ionic strength of the solutions. In general, the obtained results are very promising, with the application of oxMWCNTs proving effective for the purification of aqueous media contaminated with low concentrations of Cd(II) and Pb(II), regardless of the duration of the functionalization process. [Display omitted] • Oxidized multiwalled carbon nanotubes were used for removing low levels of Cd(II) and Pb(II) from aqueous media. • The influence of the functionalization procedure duration on the performance of the tested materials was investigated. • The study of adsorption mechanisms was conducted by evaluating the effects of different operational parameters. • The studies were performed under specific conditions (low m/V ratio, high ionic strength, low and narrow C 0 range). • The studied oxMWCNTs proved to be capable of efficiently adsorbing low levels of selected heavy metals. [ABSTRACT FROM AUTHOR]

Functionalized multiwalled carbon nanotubes (MWCNTs) have drawn wide attention in recent years as novel materials for the removal of heavy metals from the aquatic media. This paper investigates the effect that the functionalization (oxidation) process duration time (3 h or 6 h) has on the ability of MWCNTs to treat water contaminated with low levels of Cu(II), Ni(II) and Cr(VI) (initial concentrations 0.5–5 mg L−1) and elucidates the adsorption mechanisms involved. Adsorbent characterization showed that the molar ratio of C and O in these materials was slightly lower for the oxMWCNT6h, due to the higher degree of oxidation, but the specific surface areas and mesopore volumes of these materials were very similar, suggesting that prolonging the functionalization duration had an insignificant effect on the physical characteristics of oxidized multiwalled carbon nanotubes (oxMWCNTs). Increasing the Ph of the solutions from Ph 2 to Ph 8 had a large positive impact on the removal of Cu(II) and Ni(II) by oxMWCNT, but reduced the adsorption of Cr(VI). However, the ionic strength of the solutions had far less pronounced effects. Coupled with the results of fitting the kinetics data to the Elowich and Weber–Morris models, we conclude that adsorption of Cu(II) and Ni(II) is largely driven by electrostatic interactions and surface complexation at the interface of the adsorbate/adsorbent system, whereas the slower adsorption of Cr(VI) on the oxMWCNTs investigated is controlled by an additional chemisorption step where Cr(VI) is reduced to Cr(III). Both oxMWCNT3h and oxMWCNT6h have high adsorption affinities for the heavy metals investigated, with adsorption capacities (expressed by the Freundlich coefficient KF) ranging from 1.24 to 13.2 (mg g−1)/(mg l−1)n, highlighting the great potential such adsorbents have in the removal of heavy metals from aqueous solutions. [ABSTRACT FROM AUTHOR]

The role of microplastics (MPs) on the fate and transport of various pollutants in water matrices is of major concern, but it is still relatively under investigated. In order to consider the conditions in real aquatic environments, the changes to polyethylene (PE) structure during the fabrication of microplastic particles for specific uses should not be neglected. Thus, this work considers isolated PE from two types of personal care products, which are possible sources of microplastic contamination in aquatic environments. The adsorption affinity of these PE microplastics towards ionisable compounds was compared with those of standards of PE and polyethylene terephthalate (PET), using chlorinated phenols (4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) as adsorbates. The pseudo-second order kinetic model described well the sorption process for all chlorinated phenols on all four types of MPs (R² range: 0.900-0.998). The kinetic study showed that sorption rates are mainly controlled by hydrophobic interactions and molecule size. Adsorption isotherms were best described by the Freundlich model for all MPs. The obtained results indicate that MPs could serve for the transport of chlorinated phenols through ambient waters. [ABSTRACT FROM AUTHOR]