Phase-mediated mercury removal from water using multilayered molybdenum disulfide: The key role of redox mechanism

Abstract

It is crucial to distinguish the performance of different phases of molybdenum disulfide (MoS2) for Hg(II) removal owing to its distinct activity and atomic arrangement. Herein, we directionally synthesized three nanocrystalline MoS2 with metallic 1T, semiconducting 2H, and 1T/2H mixed M phase, and elucidated Hg(II) adsorption behaviors. Kinetics experiments suggested that the 1T-MoS2 exhibited the most promising performance toward Hg(II) removal over other two counterparts (2H- and M-MoS2), including highest mass transfer coefficient of 1.85 × 10−6 m s−1, an extraordinary selectivity of 3.89 × 108 mL g−1 and deep removal capability with residual concentration lower than 0.35 μg L−1. Combining various characterization tools, the phase-mediated removal mechanism was unveiled for Hg(II) onto 1T-MoS2. Specifically, Hg(II) species could be selectively captured by 1T-MoS2 via Hg-S interactions, enabling a redox reaction involving electron transfer along conductive lamellas, where Hg(II) was reduced to Hg2Cl2 crystals. Moreover, the 1T-MoS2 also demonstrated a high adsorption capacity (1622 mg g−1), a broad pH working range (1–12) and superb selectivity for Hg(II) removal. Highly practical applicability of 1T-MoS2 was confirmed for deep removal performance in various real water matrices. Great economic efficiency of the methodology was synergistically demonstrated by high adsorbent reusability (removal efficiency >99.9% over 3 cycles) and resources recovery feasibility (e.g., recyclable Hg2Cl2 products). Overall, this work has demonstrated high applicability of 1T-MoS2 for mercury removal and provides guidance for designing advanced nanoadsorbents from the perspective of crystal phase regulation.