Abstract
Due to the unique properties of carbon nanotubes (CNTs), they have attracted great research attention as an emergent technology in many applications including water and wastewater treatment. However, raw CNTs have few functional groups, which limits their use in heavy metal removal. Nevertheless, their removal properties can be improved by oxidation processes that modify its surface. In this study, we assessed the capacity of oxidized and double-oxidized multiwalled carbon nanotubes (MWCNTs) to remove heavy metals ions from acidic solutions. The MWCNTs were tested for copper (Cu), manganese (Mn), and zinc (Zn) removal, which showed an increment of 79%, 78%, and 48%, respectively, with double-oxidized MWCNTs compared to oxidized MWCNTs. Moreover, the increase in pH improved the sorption capacity for all the tested metals, which indicates that the sorption potential is strongly dependent on the pH. The kinetic adsorption process for three metals can be described well with a pseudo-second-order kinetic model. Additionally, in multimetallic waters, the sorption capacity decreases due to the competition between metals, and it was more evident in the removal of Zn, while Cu was less affected. Besides, XPS analysis showed an increase in oxygen-containing groups on the MWCNTs surface after oxidation. Finally, these analyses showed that the chemical interactions between heavy metals and oxygen-containing groups are the main removal mechanism. Overall, these results contribute to a better understanding of the potential use of CNTs for water treatment.
Highlights
Water scarcity has become a major problem worldwide
It can be inferred that according to the intensity of the signal, raw multiwalled carbon nanotubes (MWCNTs) have a higher amount of C=C bonds, and when MWCNTs were oxidized, these bonds were broken, resulting in the formation of new bonds [49]
Our results showed that double-oxidized MWCNTs have a high capacity to remove metals from acidic waters
Summary
Water scarcity has become a major problem worldwide. Population growth, urbanization, pollution, and climate change are some of the main factors responsible for water scarcity [1,2,3]. Chile has a variable climate and, a diverse industrial activity along it [4], i.e., mining activity is very common in the central and northern regions of Chile. The mining industry consumes around 7.2% of all water used in Chile and represents more than 50% of the water used in northern regions [4,5,6]. Mining activity results in widespread pollution related to acid generation and heavy metal release known as acid mine drainage (AMD), which adversely affects the quality of surface and ground water resources [7,8]. New alternatives to improve the water availability are becoming increasingly necessary
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