Removal of Trace Arsenic To Meet Drinking Water Standards Using Iron Oxide Coated Multiwall Carbon Nanotubes

Abstract

This study presents the removal of trace level arsenic to meet drinking water standards using an iron oxide-multi-walled carbon nanotube (Fe-MWCNT) hybrid as a sorbent. The synthesis was facilitated by the high degree of nanotube functionalization using a microwave assisted process, and a controlled assembly of iron oxide was possible where the MWCNT served as an effective support for the oxide. In the final product, 11 % of the carbon atoms were attached to Fe. The Fe-MWCNT was effective in arsenic removal to below the drinking water standard levels of 10 µg L−1. The absorption capacity of the composite was 1723 µg g−1 and 189 µg g−1 for As(III) and As(V) respectively. The adsorption of As(V) on Fe-MWCNT was faster than that of As(III). The pseudo-second order rate equation was found to effectively describe the kinetics of arsenic adsorption. The adsorption isotherms for As(III) and As(V) fitted both the Langmuir and Freundlich models.

Adsorption of arsenic on multiwall carbon nanotube–zirconia nanohybrid for potential drinking water purification

“…This was somewhat different from the iron oxide coated MWCNTs where the former protonated forming OH 2 + groups on the adsorbent surface at low pH values, and the arsenic species were removed by covalent ligand exchange with OH and OH 2 + functional groups [9]. …”

“…99% of As(V) and 92% of As(III) were removed after 60 minutes of contact. Relative to MWCNT-ZrO 2 nearly twice the amount of both As(III) and As(V) were removed in the presence Fe-MWCNT[9] after 10 mins of contact, with (80–99)% removed after only 30mins of contact. The kinetics of As(III) and As(V) adsorption using the MWCNT-ZrO 2 was relatively slower compared to that observed with iron oxide coated MWCNT[9].…”

“…The adsorption capacity, estimated by the Langmuir isotherm model was 2000 μg g −1 and 5000 μg g −1 for As(III) and As(V) respectively. These values were significantly higher than the q m values obtained with Fe-MWCNT[9]. The Langmuir constant, b, the ratio of the adsorption rate constant to the desorption rate constant, is an indication of the affinity of the sorbent material toward arsenic[27].…”

“…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.…”

“…The potential for sidewall functionalization and surface modification make them attractive as support phases for water treatment[14–16]. Effective arsenic removal with iron oxide coated MWCNT has been reported by us [9, 17]. Here the iron oxides were protonated forming OH 2 + groups on the adsorbent surface at low pH values, and the arsenic species were removed by covalent ligand exchange.…”