Microscopic Insights into pH-dependent Adsorption of Cd(II) on Molybdenum Disulfide Nanosheets

Herein, the retention mechanisms and microstructure of Cd(II) on MoS 2 nanosheets were evaluated by batch experiments and EXAFS technology.The sorption of Cd(II) on MoS 2 was strongly affected by solution pH, contact time, and temperature, but not by the ionic strength.The solution pH could only promote the sorption capacity, but does not improve the sorption rates and change the sorption isotherms and thermodynamics in the pH range of 3.3-9.6.The pseudo-second-order model could fit the equilibrium data better and the intra-particle diffusion model showed three typical stages in the sorption process.The isotherms and thermodynamics analysis indicated that the heterogeneity sorption of Cd(II) onto MoS 2 was a spontaneous, endothermic, and irreversible process.The EXAFS spectra revealed the coexistence of two sorption types.The inner-sphere complexation was formed in the form of Cd-S bond at lower pH (3.56, 6.48), while the Cd(OH) 2 precipitation occurred in the form of Cd-O and Cd-Cd bonds at higher pH (9.57).These results provide new insights into the interaction mechanisms between metal ions and MoS 2 nanosheets.