Abstract
Pollution due to acidic and metal-enriched waters affects the quality of surface and groundwater resources, limiting their uses for various purposes. Particularly, manganese pollution has attracted attention due to its impact on human health and its negative effects on ecosystems. Applications of nanomaterials such as graphene oxide (GO) have emerged as potential candidates for removing complex contaminants. In this study, we present the preliminary results of the removal of Mn(II) ions from acidic waters by using GO functionalized with zinc oxide nanoparticles (ZnO). Batch adsorption experiments were performed under two different acidity conditions (pH1 = 5.0 and pH2 = 4.0), in order to evaluate the impact of acid pH on the adsorption capacity. We observed that the adsorption of Mn(II) was independent of the pHPZC value of the nanoadsorbents. The qmax with GO/ZnO nanocomposites was 5.6 mg/g (34.1% removal) at pH = 5.0, while with more acidic conditions (pH = 4.0) it reached 12.6 mg/g (61.2% removal). In turn, the results show that GO/ZnO nanocomposites were more efficient to remove Mn(II) compared with non-functionalized GO under the pH2 condition (pH2 = 4.0). Both Langmuir and Freundlich models fit well with the adsorption process, suggesting that both mechanisms are involved in the removal of Mn(II) with GO and GO/ZnO nanocomposites. Furthermore, adsorption isotherms were efficiently modeled with the pseudo-second-order kinetic model. These results indicate that the removal of Mn(II) by GO/ZnO is strongly influenced by the pH of the solution, and the decoration with ZnO significantly increases the adsorption capacity of Mn(II) ions. These findings can provide valuable information for optimizing the design and configuration of wastewater treatment technologies based on GO nanomaterials for the removal of Mn(II) from natural and industrial waters.
Highlights
The progressive scarcity of water resources is among the major concerns worldwide [1,2,3]
The results of this study show that graphene oxide (GO) decorated with zinc oxide nanoparticles (ZnO) nanoparticles shows a higher removal efficiency of Mn(II) ions from acidic waters compared with non-functionalized GO
The pH of point of zero charge (pHPZC) of GO/ZnO nanocomposites was 5.57, which is quite high for acidic water treatment
Summary
The progressive scarcity of water resources is among the major concerns worldwide [1,2,3]. Heavy metals can be released from natural sources, such as volcanic activities, or through anthropogenic sources, such as mining operations, because of the generation of acid mine drainage (AMD) runoffs [4,6,7]. These pollutants in AMD waters have adverse effects on the ecosystem, contaminating surface and groundwater resources in various regions [8,9]. The development of technological alternatives for the treatment and remediation of metal-enriched waters has become a key challenge to reduce the negative environmental impacts on water resources
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