Comparative study on the efficiency of mercury removal from aqueous medium using MoS2-based nanocomposites

Abstract

Achieving the efficient and reversible remediation of mercury-polluted water through the application of advanced sorbents is highly advantageous but remains a challenging technical endeavor. The study provides a comparative investigation into the adsorption capabilities of Hg using two MoS₂ (molybdenum disulfide) based nanocomposites: reduced graphene oxide/molybdenum disulfide (rGO/MoS₂) and magnesium–aluminum layered double hydroxide/molybdenum disulfide (Mg-Al LDH/MoS₂). Synthesis of the nanocomposites was achieved via a simple hydrothermal approach, followed by their characterization using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller surface area analysis methodologies. To determine the effectiveness of mercury adsorption, experiments were designed to examine the influence of several factors, including the amount of adsorbent, pH value, ionic strength, initial mercury ion concentration, and the duration of contact. The isotherm data were adjusted to the Langmuir, Freundlich and Temkin. The adsorption of Hg²⁺ onto the rGO/MoS₂ and Mg-Al MgAl Mg-Al LDH/MoS₂ was consistent with the Langmuir model, indicating monolayer adsorption. Results revealed that both rGO/MoS₂ and Mg-Al LDH/MoS₂ exhibited high adsorption capacities of 544.5 and 282.9 mg.g⁻¹ respectively, rGO/MoS₂ showcasing superior performance due to its enhanced surface area and synergistic effect between rGO and MoS₂. The thermodynamic parameters derived from van’t Hoff plots confirm the spontaneous and endothermic characteristics of the adsorption process. The interaction pathway of Hg2⁺ ions with the nanocomposites involves Hg-S complexation alongside electrostatic attraction. The adsorption kinetics followed the pseudo-second order model. The process of analyte diffusion was jointly influenced by both intraparticle diffusion and film diffusion mechanisms. Both nanocomposites demonstrated robust reusability, retaining over 94 % adsorption capacity for at least 5 cycles. The feasibility of the as-prepared adsorbents for real-world applications was assessed by evaluating its performance in authentic water matrices, including deionized water, tap water, well water, and river water, obtained from diverse sources. This comparative study opens the possibility to use of these nanocomposites for efficient Hg²⁺ removal from polluted water, providing insights for the development of advanced materials in environmental remediation.