The problem of arsenic contamination of water has affected many parts of the world including North America and Asia[1
]. Besides being classified as a Group 1 carcinogen [4
], it is also responsible for other health effects such as spontaneous abortion[5
]. The US-EPA maximum contaminant level for arsenic was reduced from 50 to 10ppb in 2001.
In a typical aquatic environment Asis predominantly found in two different oxidation states. Arseniteor As (III), which is neutral, uncharged and a soluble molecule is considered more toxic than arsenate As (V), and is more difficult to remove from aqueous media[6
]. Existing techniques for Arsenic removal include oxidation/precipitation, coagulation/coprecipitation, nanofiltration, reverse osmosis, electrodialysis, adsorption, ion exchange, foam flotation, solvent extraction and bioremediation[7
]. These well established approaches have been adapted for As removal and have their respective advantages and certain inherent limitations that include the generation of toxic waste, low arsenic removal efficiency and high cost[7
Adsorption is one of the most effective methods for As removal and myriad materials including lanthanum/iron compounds, mineral oxides, and biological materials[8
] have been studied. The use of polymeric resins, activated carbon, activated alumina, iron coated sand, hydrous ferric oxide, and natural ores have generated much interest, and novel metal modified adsorbents have demonstrated superior performance [9
]. Zirconium oxides/hydroxides have been extensively investigated as adsorbents for the removal of cationic and anionic pollutants from water. They have been shown to be effective in the removal of dyes, Flouride, uranium (IV), phosphate, mercury, and selenium[10
]. While iron oxides represent some of the most common sorbent for As removal[7
], the potential for using zirconium based compounds is also being investigated for As removal. Preliminary investigations using zirconium loaded materials such as activated charcoal, porous resin, chelating resin with lysine-Na, orange waste have shown promising results for As removal[10
]. In general, for use as an environmental adsorbent, zirconium needs to be impregnated or loaded on a support because it has poor physical properties and moreover this also lowers the overall cost of this expensive material. Therefore, the development of effective support materials is of utmost importance.
Carbon nanotubes (CNTs) are graphene sheets seamlessly rolled into cylindrical tubes. They are either single-walled (SWCNT) or multiwall carbon nanotubes (MWCNT), with the latter being relatively inexpensive[11
]. Their unique characteristics such as high aspect ratio, superior mechanical, electrical and thermal properties make them well suited for many applications. CNTs also exhibit exceptional sorption properties towards various organic compounds and inorganic ions[13
]. The potential for sidewall functionalization and surface modification make them attractive as support phases for water treatment[14
]. Effective arsenic removal with iron oxide coated MWCNT has been reported by us [9
]. Here the iron oxides were protonated forming OH2+
groups on the adsorbent surface at low pH values, and the arsenic species were removed by covalent ligand exchange.
Zirconia coated multiwall carbon nanotube was synthesized in our group and shown to remove fluoride from water and its capacity was significantly higher than other conventional sorbents [16
]. It is anticipated that Zirconium oxide supported on MWCNT may remove arsenic species through a synergistic combination of chemisorption and physisorption. The objective of this paper was to study the adsorption capacity of MWCNT–Zirconia nanohybridin the removal of arsenite and arsenate from water to meet drinking water standards.