Carbon nanosphere–iron oxide nanocomposites as high-capacity adsorbents for arsenic removal

Abstract

In the design of iron oxide-derived composite adsorbents for arsenic removal, the matrix selected for the encapsulation of iron oxide active material is critical to their arsenic adsorption performance. The ideal matrix should have a high surface area, high pore volume, and large pores that can accommodate the iron oxide nanoparticles while without causing the undesired pore filling or blockage. In this paper, we report the use of carbon nanospheres (size of ca. 28 nm) featuring high surface area, high pore volume, and hierarchical large mesopore/macropore structures resulting from nanosphere packing/aggregation as the matrix for the design of iron oxide composites. Iron oxide has been encapsulated into the carbon nanospheres with different contents (7–60 wt%). The composites have been systematically characterized for their structural, morphological, and textural properties, and investigated for their performance for arsenic adsorption. An optimum iron oxide content of 13 wt% has been established with high adsorption capacities of 416 and 201 mg g⁻¹ achieved for As(III) and As(V), respectively, which are highest (for As(III)) or among the highest (for As(V)) reported thus far for iron oxide-based adsorbents. These are in contrast to the typically low adsorption capacities found with iron oxide composites involving other carbon-based matrices, such as activated carbon, carbon nanotubes, and mesoporous carbons. The results confirm the high potential of this class of composite adsorbents for arsenic removal. Meanwhile, the structure–performance relationship demonstrated herein is also of value to the further design of high-performance arsenic adsorbents.