Nano-Adsorptive Effects Manifested In Arsenite Adsorption Onto The Nano-Sized Goethite

Goethite nanorods were synthesized to investigate the comprehensive nanoscale effects on As(III) sequestration by iron oxyhydroxide nanocrystallines. The specific adsorption-site accessible for As(III) was 12.4 sites/nm(2) on the goethite nanorods, and 6.9 sites/nm2 on the bulk phase of goethite. However, original goethite nanorods showed a weaker As(111) affinity in comparison with the bulk phase. Potent aggregation of nano-sized goethite led to a much slower rate of As(III) adsorption than its bulk relative and a very different profile of adsorption edge from its bulk phase. Surfactant activation of the nano-surface resulted in dramatic increase in both the affinity and the rate of As(III) adsorption onto the nano-sized goethite, as well as a significant improvement in As(III) adsorption over a broad pH range from 3 to 8. Both extended X-ray absorption fine structure (EXAFS) and X-ray photon spectra (XPS) found no As(Ill) oxidation on the surface of nano- or microsized goethite. Two As Fe shells, attributing to a bidentate binuclear and a monodentate surface complex between the As(III) and nano-goethite, fitted very well the experimental data of X-ray absorption fine structure (EXAFS).