Chitosan-based porous composites embedded with molybdenum disulfide nanosheets for removal of mercury from wastewater

Mercury-containing wastewater presents a significant environmental threat due to its high toxicity. Therefore, the urgent removal of mercury-laden wastewater is essential to protect ecosystems and public health. In this study, molybdenum disulfide (MoS2) nanosheets modified with a silane coupling agent (designated as MS) were crosslinked with natural polymer chitosan (CS) rich in −NH2 and − OH groups to develop a highly efficient and environmentally friendly MoS2-functionalized three-dimensional reticulated porous materials (denoted as MS/CTS) composite adsorbent. Following adsorption, the concentration of mercury ions in wastewater was significantly reduced from an initial level of 1000 μg∙L−1 to just 0.88 μg∙L−1, which is below the acceptable limit for drinking water. Furthermore, it showed excellent acid resistance, maintaining a removal efficiency of 99.71 % for a starting level of 587.8 mg·L−1 at a pH as low as 3.5. The adsorption capacity of composite exceeded the mathematical sum of the adsorption capacities of MS and pure chitosan adsorbent was prepared according to the same procedure without adding MS (denoted as CTS) at the same ratio. The saturated adsorption capacity fitted by Langmuir-Freundlich model is 1429.69 mg·g−1, which is very close to the experimental value of 1317.70 mg·g−1. The MS/CTS displays a selectivity for metal ions in the following order: Hg(II) > Pb(II) > Cu(II) > Cd(II), along with exceptionally high distribution coefficients (Kd) of 1.99 × 105 mL·g−1 for Hg(II). Even after five cycles of reuse, the mercury removal efficiency remained above 85 %. Mechanistic analysis indicated that both monolayer and multilayer chemical adsorption were involved in mercury removal. The high adsorption capacity was attributed to the synergistic effect of S, N, and − O functional groups. After adsorption, mercury ions existed on the surface of the adsorbent in the form of a hollow net-like Hg3S2Cl2. These findings significantly expand the application scope of MoS2/biomass composites in environmental remediation. [Display omitted]