Enhanced sequestration of selenite in water by nanoscale zero valent iron immobilization on carbon nanotubes by a combined batch, XPS and XAFS investigation

In this paper, nanoscale zero-valent iron (NZVI) immobilized on carbon nanotube (CNT) composite (NZVI/CNT) was prepared, characterized and used for the sequestration of Se(IV) in water. The structural analysis revealed that NZVI were uniformly immobilized on CNT surfaces, and thus the oxidation and aggregation of NZVI was obviously minimized. Compared to bare NZVI, the NZVI/CNT exhibited much higher efficiency on Se(IV) sequestration due to the good synergistic effect between CNT adsorption and NZVI reduction. The results from X-ray absorption fine structure (XAFS) revealed that Se(IV) could be almost completely reduced into Se(0)/Se(-II) by NZVI/CNT, while partial reduction occurred on NZVI with a trace of Se(IV) adsorbed on the corrosion products. Besides, the role of pH in Se(IV) sequestration on NZVI/CNT was lower than that on NZVI due to the buffering effect of CNT. Moreover, CNT immobilization could also weaken the inhibition effect of humic acid (HA) on the removal of Se(IV) by NZVI, since CNT showed strong adsorption for HA that blocks potential reactivity. The excellent performance of NZVI/CNT offer a promising material for detoxification of Se(IV) from wastewater.