ZnO Nanoadsorbents: A potent material for removal of heavy metal ions from wastewater

Abstract

The skyrocketing progress in industrialization is increasing the concentration of heavy metals in water resources. Most of the heavy metals are highly toxic and even a trace amount of these heavy metals in water resources can be ruthless for humans and aquatic biomes. Therefore, the alleviation of heavy metals from industrial effluents is a matter of serious concern. The adsorption is one of the widely used methods to remove such nonbiodegradable heavy metals due to its simple design as well as economical and eco-friendly nature. Over the last decade, nanoadsorbents has drawn a significant attention to remediate heavy metals contaminated water due to their high surface area to volume ratio, which provides a huge number of active sites for the adhesion of heavy metals. Among different nanoadsorbent materials, ZnO is quite promising for heavy metals remediation due to its excellent biocompatibility, low toxicity, negative zeta potential resulted due to the surface modifications during growth process and redox reactions resulted due to the generation of effeicient photoinduced electron hole pairs in ZnO NPs. Here in this article, we will systematically review the use of ZnO nanostructures for removing poisonous heavy metal ions from water. Various ZnO-based nanostorbents such as pristine ZnO NPs, doped ZnO nanostrutes, ZnO nanocomposites, and surface-modified ZnO NPs are reviewed thoroughly along with the comparisons of their maximum adsorption capacity for different heavy metal ions (Cd2+, Hg2+, As3+, Pb2+, Cr6+, Ni2+, Co2+, and Cu2+) in a tabular form.