Comparing the Adsorption Performance of Multiwalled Carbon Nanotubes Oxidized by Varying Degrees for Removal of Low Levels of Copper, Nickel and Chromium(VI) from Aqueous Solutions

Marko Šolić,Malcolm Watson,Jasmina Nikić,Marijana Kragulj Isakovski,Jelena Tričković,Zoltan Kónya,Snežana Maletić

doi:10.3390/w12030723

Marko Šolić, Malcolm Watson + Show 5 more

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https://doi.org/10.3390/w12030723

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Journal: Water	Publication Date: Mar 6, 2020
Citations: 33	License type: CC BY 4.0

Affiliation: University of Novi Sad, University of Szeged

Abstract

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.

Highlights

IntroductionAs naturally occurring elements, can originate from both natural and anthropogenic sources
Heavy metals, as naturally occurring elements, can originate from both natural and anthropogenic sources
Taking into account all the results obtained, the following conclusions can be drawn: The Cu(II) and Ni(II) adsorption systems reach a state of equilibrium very quickly, in less than

Summary

Introduction

As naturally occurring elements, can originate from both natural and anthropogenic sources. The increasing release of these pollutants in more toxic and mobile forms has made. Water 2020, 12, 723 anthropogenic sources a worldwide issue [1]. The main anthropogenic sources of heavy metals in the aquatic environment can be attributed to urbanization, industrialization (in particular the wastewater of modern chemical plants) and certain agricultural activities [1,2]. Metal processing and mining contribute to 48% of the total release of contaminants by the European industrial sector [3]. Heavy metals cannot undergo biodegradation processes and accumulate in the environment and living organisms at all levels of the food chain, making this group of pollutants even more noteworthy. A number of health problems may result from human exposure, intake and eventual buildup of non-essential (e.g., Cr(VI) and Ni) and even essential heavy metals (e.g., Cu) [2,4,5]

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