Arsenic Removal from Drinking Water Using Carbon Nanotubes

Background

Studies have found Carbon Nanotubes (CNTs) can effectively remove arsenic levels to a tolerable for humans (Ntim & Mitra, 2012). CNTs form nanoscale pores from the entanglement of hundreds of tubes that are held together by Van der Waal forces. CNTs “provide large external surface areas that can immobilize contaminants including bacteria and viruses” (Upadhyayula et al., 2009). They are known for their strength, as well as their unique electrical and thermal properties. The structure and function of CNTs allows for this high adsorption of contaminants. They can be formed with either single or multi-wall properties.

Single-wall CNTs are one sheet of graphene, whereas multi-wall CNTs are multiple layers of graphene sheets (Naghizadeh et al., 2012). Although the internal structure of the CNTs does not adsorb the contaminants on account of its massive size, the interstitial pore spacing between the tube bundles provides sufficient space for metal ions, such as arsenic, to attach. The metal ions attach to the bundles, grooves, and exterior of the CNT. Pristine CNTs also possess cytotoxic abilities that prohibit the growth of pathogens on their structure. CNTs are ideal for removal because this capability is unlike other carbon-based adsorbents. The CNTs also can be functionalized allowing for surface modification with covalent and non-covalent attachment of functional groups as shown in Figure 1. The non-covalent bonds can be used to make the CNTs more water-soluble, therefore preferred. Slightly water soluble CNTs can be used for practical treatment purposes by enhancing their chance for surface contact (Upadhyayula et al., 2009).

Figure 1.

(a) acid-functionalized MWCNT, (b) iron-oxide coated hybrid (Fe-MWCNT) (Ntim and Mitra, 2011)

As a result of CNTs structural and functional capabilities, it has been sought after as an adsorbent to remove contaminants in water. In order to gage the success of the current usage of CNTs, a range of applications for heavy metal and arsenic removal have been summarized. This article outlines several studies that have examined different forms of CNT and their treatment of arsenic contaminated water.

The scope of this article describes the adsorbent capacities of CNTs on different types of heavy metals. This is the focus of the article because future research is based off of these literary reviews.