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 K_F) 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.

Microplastics and chlorinated phenols (CPs) are pollutants found ubiquitously in freshwater systems. Meanwhile, bioplastics are attracting much attention as alternatives to conventional plastics, but there is little data about their effect on the behaviour of pollutants. This work therefore investigates the sorption of four CPs (4-chlorophenol—4-CP, 2,4-dichlorophenol—2,4-DCP, 2,4,6-trichlorophenol—2,4,6-TCP and pentachlorophenol—PCP) on three different plastics (polyethylene (PЕg), polypropylene (PP) and polylactic acid (PLA)) using kinetics and isotherm studies. All experiments were carried out in a synthetic water matrix and in spiked Danube river water. In all cases, adsorption kinetics fitted well with the pseudo-second order rate model. Adsorption proceeded through two linear phases, corresponding to transport from the bulk solution to the external surfaces and then into the interior pores of the sorbents. Maximum adsorption capacities calculated with the Langmuir isotherm indicated that whereas adsorption of 4-CP was not significantly affected by the type of plastic present, the adsorption of 2,4-DCP, 2,4,6-TCP and PCP varied greatly, with polypropylene showing the greatest affinity for CPs adsorption. The differences observed between the adsorption behaviour of CPs in the synthetic and natural water matrices suggest further investigation is required into how the different fractions of natural organic matter impact interactions between CPs and plastics.

The subject of this study was to investigate the adsorption behavior of selected divalent metals (Cu (II), Cd (II), Pb (II)) on amino-functionalized multiwalled carbon nanotubes, MWCNT-NH2, at four selected pH values (3; 4.5, 6, 11), in order to estimate the possibility of using MWCNT-NH2 to remove ion metal from aqueous solutions at relatively low concentrations (0.01-0.1 mg L-1). The focus of the study was to determine the adsorption mechanism at the experimental conditions. The adsorption of divalent metal ions on MWCNT-NH2 was best described by the pseudo-second order kinetics model, which indicates that adsorption can be attributed to the chemical interactions between the adsorbates and the binding groups on the surface of the adsorbent. Modeling the adsorption rate by the Weber-Morris diffusion model indicated that intra-particle diffusion, although a slower step than external diffusion, is not the only limiting step in the adsorption process, and that the interaction of the investigated ions with the binding sites on the adsorbent surface also control the adsorption rate. Assessment of the impact of pH on the adsorption rate has shown that the pH value, in the investigated range, has the highest effect on the adsorption efficiency of Cu (II) and the lowest for the removal of Cd (II).