Description:
Goethite is a commonly found iron (hydr)oxides that is known to significantly influence on the transport and fate of arsenic in soil and sediment. Although the presence of defects in goethite has been proved, the underlying impact of these defects in goethite on arsenic immobilization remains unclear. In this study, goethite samples with abundant, sufficient, and sparse defects were synthesized to evaluate their arsenic adsorption capacities. The characteristics of defect in goethite were investigated by EXAFS, HAADF-STEM-EDS mapping, VSM, ESR, and XPS. The characterization analysis revealed that the defects in as-synthesized goethite primarily existed in the form of Fe vacancies. Batch experiments demonstrated that the adsorption capacities of defect-rich goethite for the As(V) and As(III) removal were 10.2 and 22.1 times larger than those of defect-poor goethite, respectively, thereby indicating the considerable potential of defect-rich goethite for arsenic immobilization. The origin of the impact of Fe defect on arsenic immobilization was experimentally and theoretically elucidated using density functional theory (DFT) calculations and charge distribution-multisite complexation (CD-MUSIC) modeling. The enhanced adsorption of goethite was attributed to the improvement of the As affinity constant as well as the site density due to the Fe vacancy defect, thus considerably promoting the arsenic immobilization