New Insight into the Mechanism for the Removal of Methylene Blue by Hydrotalcite-Supported Nanoscale Zero-Valent Iron

Abstract

Nanoscale zero-valent iron (nZVI) has become a new and ecofriendly adsorbent material with promising applications. Herein, hydrotalcite-supported nanoscale zero-valent iron (nZVI@H) is synthesized for the first time and used for testing the removal of methylene blue (MB) in an aqueous solution. The successful fabrication of nZVI@H is characterized by SEM, BET, XRD, FTIR and zeta-potential analyses. The results showed that 99.6% of MB is removed using nZVI@H after 30 min of reaction at an initial MB concentration of 40 mg·L−1, while the bare nZVI is only at 71.2%. The kinetic analysis yielded that the removal process of MB using nZVI@H is consistent with the Langmuir model and the quasi-second-order kinetic model. According to the Langmuir model, the maximum adsorption of nZVI@H on MB is 81 mg·g−1. This study provides a new idea about the mechanism of MB removal, namely, MB is converted to the colorless LMB through an Fe0 redox reaction and simultaneously attached at the surface of nZVI@H through an adsorption process, and finally removed via complexation precipitation.