Nanocomposites of carbon nanosphere and graphene oxide with iron oxide as high-performance adsorbents for arsenic removal

Abstract

Arsenic is a widely distributed element in the Earth’s crust with an average terrestrial concentration of about 5 g ton-1 . Arsenic is a persistent, bio-accumulative, toxic element. The United States Environmental Protection Agency (EPA) has implemented the discharge criterion of 10 µg L -1 for arsenic as the maximum acceptable level for ground water. During the past decades, several techniques have been developed for the removal of arsenic from the wastewater, including chemical precipitation, adsorption and ion exchange, membrane and biological removal processes, and so on. Because of the good arsenic removal efficiency and the low cost, adsorption is a more popular method. In this thesis research, two ranges of iron oxide nanocomposite adsorbents have been developed and studied for their performance properties towards arsenic removal. Novel iron oxide encapsulated carbon nanospheres (FeOx-CNS) with excellent arsenic adsorption performance has been successfully synthesized. CO2 activated carbon nanospheres material (A-CNS) with high surface area (2271 m²g -1 ) and high pore volume (5.18 cm³g -1 ) was selected as the porous matrix. After surface oxidation by ammonium persulfate (APS), iron oxide was loaded into the carbon nanospheres as the effective arsenic adsorbent. Transmission electron microscopy (TEM) and Braunauer–Emmett– Teller (BET) results indicate that iron oxide nanoparticles (7-60 wt%) are well-dispersed within the mesopores. In particular, FeOx-CNS-13 composite shows most optimum performance properties, with high arsenic adsorption capacities achieved for both As(III) (416 mg g−1 ) and As(V) (201 mg g−1 ). Another range of amorphous iron oxide-graphene oxide (FeOx-GO) nanocomposites having different graphene oxide (GO) content (36-80 wt%) was prepared by coprecipitation of ferrous sulfate heptahydrate and ferric sulfate hydrate on GO sheets. The composites have been thoroughly characterized and investigated for their performance towards arsenic removal. The optimum composite, FeOx-GO-80 having the highest iron oxide content of 80 wt% shows excellent arsenic adsorption capacities for both As(III) (147 mg g−1 ) and As(V) (113 mg g−1 ), which are highest among iron oxideGO composites reported to date for arsenic removal. The high performance along with low cost and convenience in synthesis makes this range of amorphous iron oxide-GO nanocomposites promising for applications.