XAFS Studies of Soft-Heavy-Metal-Ion-Intercalated M_xMoS₂ (M = Hg²⁺, Ag⁺) Solids

Abstract

XAFS studies were performed on two new soft-heavy-metal-ion-intercalated materials M x -MoS 2 (M ) Hg 2+ , Ag + ). For the compound Hg 0.32 MoS 2 , EXAFS results show an average Hg coordination environment consisting of ≈2 S atoms at 2.38 Å and ≈0.2 ((35%) Hg atoms at 2.55 Å. Along with Hg XANES analysis, these data indicate that the Hg atoms in this compound are present as a mixture of mercuric and mercurous ions. Ag EXAFS analysis of the compound Ag 0.61 MoS 2 indicates a Ag coordination environment consisting of ≈2 S atoms at 2.43 Å. Ag EXAFS and XANES results for heat-treated Ag 0.61 MoS 2 indicate that the Ag coordination environment has changed to that nearly identical for silver metal with several Ag-Ag interactions detected. The results suggest that heat treatment of Ag 0.61 MoS 2 facilitates the chemical reduction of the intercalated silver ions to elemental silver. In addition, Mo EXAFS and XANES analyses indicate that both the Hg-and Ag-intercalated compounds have significant amounts of the 1T-phase of MoS 2 in them. Prolonged exposure of both of these materials to an aerobic atmosphere does not affect their Mo EXAFS. Comparison of these results with those for exfoliated and restacked MoS 2 suggests that different intercalated guest ions afford different oxidative stabilities to the host MoS 2 layers. This hypothesis is used to rationalize some inconsistencies in previous reports of M x MoS 2 XAFS studies.

MoS2 Nanosheets with Widened Interlayer Spacing for High‐Efficiency Removal of Mercury in Aquatic Systems

“…At low Hg 2+ /W‐DR‐N‐MoS 2 ratio, it was noticed that each Hg 2+ ion exchanged for two H + ions (Equation and Figure a), implying that one Hg 2+ ion probably interacted with two S atoms. The EXAFS curve‐fitting results (Figure c, Figures S18–S20 and Table S6, Supporting Information) gave the first coordination shell of 1.8 sulfur atoms at 2.38 ± 0.02 Å for Hg in the Hg 2+ ‐laden W‐DR‐N‐MoS 2 (ratio: 0.25), revealing that each Hg 2+ indeed interacted with approximately two S atoms . This also plausibly explains the shrinkage of the interlayer spacing and the reduction of the negative charge for the Hg 2+ ‐laden W‐DR‐N‐MoS 2 (Figure b and Figure S17, Supporting Information) …”

“…Accordingly, the EXAFS curve‐fitting results revealed that the coordination number of HgS bonding were gradually reduced to 1.1 with the increase of Hg 2+ /W‐DR‐N‐MoS 2 ratios (Figure c, Figures S18–S20 and Table S6, Supporting Information) . In addition, the increased negative charge on Hg 2+ ‐laden W‐DR‐N‐MoS 2 (Figure b and Table S5, Supporting Information) at high Hg 2+ /W‐DR‐N‐MoS 2 ratio suggested the probability of adsorbing counterions for charge neutrality.…”

“…To gain insight into the potential mechanism of the interactions between W‐DR‐N‐MoS 2 and Hg 2+ , we employed a diverse set of characterization methods. First, the Fourier transform infrared (FTIR) spectrum, XPS analysis, high‐angle annular dark‐field scanning TEM (HAADF‐STEM) image, and extended X‐ray adsorption fine structure (EXAFS) spectra indicated that the mercury was indeed adsorbed by W‐DR‐N‐MoS 2 and bonded by S atoms with the HgS distance similar to that of cinnabar (Figures S9–S15, Supporting Information) . Subsequently, the shrinkage of the interlayer spacing after mercury uptake (reduced to 6.3 Å, as evidenced by HRTEM image and XRD patterns in Figures S16 and S17, Supporting Information) suggested that the Hg 2+ ion spontaneously intercalated into the interlamellar spacing between the S‐Mo‐S layers during mercury uptake, and then interacted with S atoms to form a discrete HgS species.…”

Preparation and mechanism of polystyrene-molybdenum disulfide intercalation materials by a modified two-step route

“…Among them one may cite the in-situ polymerization of intercalated monomers, the exfoliation of a layered host and subsequent adsorption of polymer and reaggregation, the template synthesis of host structures in polymer-containing solutions, and the direct melt intercalation of polymers into hosts. Though the method of exfoliation and flocculation of Li x MoS 2 have been known for over a decade [21], the mechanism of guest inclusion into MoS 2 is still not well understood [5].…”

“…Many of these materials have potential applications in heterogeneous catalysis, as superconductors, as ionic or electronic conductors, in reversible battery electrodes, and in waste remediation [5]. These materials generally are comprised of a polymer or organic component (such as optically functional compounds [6]) incorporated between sheets of an inorganic host.…”