Engineering the Performance and Stability of Molybdenum Disulfide for Heavy Metal Removal.

Abstract

Molybdenum disulfide (MoS2) has recently emerged as one of the most promising water nano-based adsorbent materials for heavy metal removal with the potential to provide an alternative to conventional water decontamination technologies. In this study, we demonstrate the trade-off between mercuric removal capacity and overall MoS2 adsorbent stability, both driven by MoS2 synthesis parameters. A bottom-up hydrothermal synthesis setup at various growth temperatures was employed to grow flower-like MoS2 films onto planar alumina supports. A thorough material characterization suggests that an increase in growth temperature from 150 to 210 °C results in higher MoS2 crystallinity. Interestingly, elevated growth temperatures resulted in poor mercuric removal (525 mg g-1, K = 2.2 × 10-3 h-1), yet showed enhanced chemical stability (i.e., minimal molybdenum leaching during exposure to mercury). On the other hand, low growth temperatures produce amorphous supported MoS2, exhibiting superb mercuric removal capabilities (5158 mg g-1, K = 36.1 × 10-3 h-1) but displaying poor stability, resulting in substantial byproduct molybdate leaching. Mercuric removal by crystalline MoS2 was accomplished by adsorption and electrostatic attraction-based removal mechanisms, whereas redox reactions and HgS crystallization-based removal mechanisms were more dominant when using amorphous MoS2 for mercury removal. Overall, our study provides essential insights into the delicate balance between MoS2 mercuric removal capabilities and MoS2 degradation, both related to material synthesis growth conditions. Employment of nano-enabled water treatments in general, and MoS2 for heavy metal removal in particular, requires us to better understand these important fundamental trade-off behaviors to achieve sustainable, effective, and responsible implementation of nanotechnologies in large scale systems.