Phase-dependent dechlorination mechanisms of organochlorines on MoS₂ electrodes : contrasting roles of 1T and 2H phases

Abstract

Organochlorine compounds (OCs), notorious for their environmental persistence and toxicity, pose significant risks to aquatic ecosystems and human health. Electrochemical dechlorination using molybdenum disulfide (MoS2), a cost-effective and efficient material, offers a promising remediation strategy. However, the distinct mechanistic roles of the metallic (1 T) and semiconducting (2H) phases in dechlorination—whether through direct electron transfer (DET) or by atomic hydrogen (H*)—remain highly controversial and poorly understood. In this study, we elucidate phase-dependent dechlorination pathways by employing florfenicol (FLO), a refractory chlorinated antibiotic, as a model pollutant. The 2H-MoS2 electrode achieved efficient dechlorination (0.98 h−1) at moderate potentials (−0.8 to −1.1 V vs. Ag/AgCl); in contrast, the 1T-MoS2 phase required a higher potential (−1.3 V) to achieve a comparable kinetic rate constant. The performance of both electrodes is competitive with previously reported expensive precious metal electrodes. Further mechanistic investigations revealed that DET dominates on 2H-MoS2, enabling two-step dechlorination, but 1T-MoS2 mainly relies on the H*-mediated pathway for one-step deep dechlorination. Density functional theory (DFT) calculations corroborated these findings, revealing that the DET pathway on 2H-MoS2 has lower energy barriers (0.53 and 1.60 eV for the first and second C–Cl bond cleavages, respectively) compared to the H* pathway (0.80 and 3.23 eV), suggesting the second C–Cl bond cleavage as the rate-limiting step. For 1T-MoS2, the H*-mediated pathway showed lower energy barriers (2.0 and 1.53 eV, respectively), supporting one-step deep dechlorination via H*. Robust performance of MoS2 electrodes was also demonstrated in complex water matrices and stability tests, underscoring their practical applicability. This work resolves outstanding controversies regarding dechlorination mechanisms on MoS2 and provides a robust foundation for the further engineering of MoS2-based materials for advanced reductive environmental applications. Graphical abstract: [Figure not available: see fulltext.]