Encapsulation/capture of S-nZVI particles by PANa-PAM hydrogel limits their leakage and improves Cr(VI) removal

Sulfide-modified zero-valent iron (S-nZVI) has been shown to be an effective material for removal of various contaminants from wastewater. However, the release of this powder material into the environment brings some hidden troubles to its application. Therefore, poly(sodium acrylate)-poly(acrylamide) (PANa-PAM) hydrogel was used in this study to capture S-nZVI particles within their frameworks, and encapsulate them from being released into the environment. The structure and composition characterization of the composites (S-nZVI@H) showed that the S-nZVI particles were tightly encapsulated by the cross-linked network frameworks of the PANa-PAM hydrogel. The content of Fe in S-nZVI@H was 123.77 mg/g, and only 6.34% were leached out after being used three times in a row. The maximum removal capacity of Cr(VI) by S-nZVI@H was 9.24 mg/g. Moreover, SnZVI@H showed excellent reusability and stability. The proposed mechanism of Cr(VI) removal by S-nZVI@H can be described as uptake-reduction-codeposition. The synergistic effect of PANa-PAM hydrogel and S-nZVI particles realized stabilization and solidification of Cr(VI). These results demonstrate that the encapsulation of SnZVI particles by PANa-PAM hydrogel not only limited their leakage to the environment, but also facilitated the removal of Cr(VI).