Recent advances in exploitation of nanomaterial for arsenic removal from water: a review

Recently, increasing research efforts have been made to exploit the enormous potential of nanotechnology and nanomaterial in the application of arsenic removal from water. As a result, there are myriad of types of nanomaterials being developed and studied for their arsenic removal capabilities. Nevertheless, challenges such as having a complete understanding of the material properties and removal mechanism make it difficult for researchers to engineer nanomaterials that are best suited for specific water treatment applications. In this review paper, a comprehensive review will be conducted on several selected categories of nanomaterials that possess promising prospects in arsenic removal application. The synthesis process, material properties, as well as arsenic removal performance and removal mechanisms of each of these nanomaterials will be discussed in detail. Fe-based nanomaterials, particularly iron oxide nanoparticles, have displayed advantages in arsenic removal due to their super-paramagnetic property. On the other hand, TiO₂-based nanomaterials are the best candidates as photocatalytic arsenic removal agents, having been reported to have more than 200-fold increase in adsorption capacity under UV light irradiation. Zr-based nanomaterials have among the largest BET active area for adsorption-up to 630 m² g^-1-and it has been reported that amorphous ZrO₂ performs better than crystalline ZrO₂ nanoparticles, having about 1.77 times higher As(III) adsorption capacity. Although Cu-based nanomaterials are relatively uncommon as nano-adsorbents for arsenic in water, recent studies have demonstrated their potential in arsenic removal. CuO nanoparticles synthesized by Martinson et al were reported to have adsorption capacities up to 22.6 mg g^-1 and 26.9 mg g^-1 for As(V) and As(III) respectively. Among the nanomaterials that have been reviewed in this study, Mg-based nanomaterials were reported to have the highest maximum adsorption capacities for As(V) and As(III), at 378.79 mg g^-1 and 643.84 mg g^-1 respectively. By combining desired properties of different nanomaterials, composite nanomaterials can be made that have superior potential as efficient arsenic removal agents. Particularly, magnetic composite nanomaterials are interesting because the super-paramagnetic property, which allows efficient separation of nano-adsorbents in water, and high adsorption capacities, could be achieved simultaneously. For instance, Fe-Mn binary oxide nanowires have shown promising As(III) adsorption capacity at 171 mg g^-1. Generally, nanomaterials used for arsenic removal face severe degradation in performance in the presence of competing ions in water, especially phosphate ions. This study will contribute to future research in developing nanomaterials used for arsenic removal that are highly efficient, environmentally friendly and cost-effective by providing a thorough, structured and detailed review on various nanomaterial candidates that have promising potential.