Tuning phase compositions of MoS2 nanomaterials for enhanced heavy metal removal: performance and mechanism

Qi Han; Hao Cao; Yuchen Sun; Gang Wang; Sidney Poon; Monong Wang; Bei Liu; Yanggang Wang; Zhongying Wang; Baoxia Mi

doi:10.1039/D2CP00705C

Tuning phase compositions of MoS₂ nanomaterials for enhanced heavy metal removal: performance and mechanism†

Qi Han,‡^a Hao Cao,‡^b Yuchen Sun,^a Gang Wang,

^c Sidney Poon,^d Monong Wang,^d Bei Liu,^a Yanggang Wang,^b Zhongying Wang

*^a and Baoxia Mi

^d

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* Corresponding authors

^a Department of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
E-mail: wangzy6@sustech.edu.cn
Tel: +86-075588018040

^b Department of Chemistry and Guangdong Provincial Key Laboratory of Catalytic Chemistry, Southern University of Science and Technology, Shenzhen 518055, China

^c Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China

^d Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA

Abstract

Two-dimensional MoS₂ nanosheets have shown great potential in heavy metal remediation due to their unique properties. MoS₂ has two primary phases: 1T and 2H. Each has different physiochemical properties, but the impact of these differences on the overall material's heavy metal removal performance and associated mechanisms is rarely reported. In this study, we synthesized morphologically similar but phase-distinct MoS₂ samples via hydrothermal synthesis, which comprised dominantly either a metallic 1T phase or a semiconducting 2H phase. 1T-MoS₂ samples exhibited higher removal capacities for Ag⁺ and Pb²⁺ cations relative to 2H-MoS₂. In particular, an eight-fold increase in the Pb²⁺ adsorption capacity was observed in the 1T-MoS₂ samples (i.e. ∼632.9 mg g⁻¹) compared to the 2H-MoS₂ samples (∼81.6 mg g⁻¹). The mechanisms driving the enhanced performance of 1T-MoS₂ were investigated through detailed characterization of metal-laden MoS₂ samples and DFT modelling. We found that 1T-MoS₂ intrinsically had a larger interlayer spacing than 2H-MoS₂ because water molecules were retained between the hydrophilic 1T nanosheets during hydrothermal synthesis. The widened interlayer spacing in 1T-MoS₂ allowed the diffusion of heavy metal ions into the nanochannels, increasing the number of adsorption sites and total removal capacities. On the other hand, DFT modelling revealed the energy-favorable adsorption complex of Ag⁺ and Pb²⁺ for 1T-MoS₂, in which each metal atom was bonded with three S atoms leading to much higher adsorption energies relative to 2H-MoS₂ for Ag⁺ and Pb²⁺. This study unravels the underlying mechanisms of phase-dependent heavy metal remediation by MoS₂ nanosheets, providing an important guide for the use of 2D nanomaterials in environmental applications which include heavy metal removal, contaminant sensing, and membrane separation.

Physical Chemistry Chemical Physics

Tuning phase compositions of MoS₂ nanomaterials for enhanced heavy metal removal: performance and mechanism†

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Tuning phase compositions of MoS₂ nanomaterials for enhanced heavy metal removal: performance and mechanism

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Physical Chemistry Chemical Physics