Adsorption, antibacterial, and antibiofilm properties of kaolin-based materials

Abstract

The critical environmental challenges associated with mercury pollution are attributed to its toxicity, persistence, and tendency to bioaccumulate throughout the food chain. Adsorption has been reported to be the preferred mercury remediation method due to its favorable characteristics relative to other conventional methods, such as ion exchange and chemical precipitation; however, most conventional adsorbents lack selectivity, capacity, and multifunctional advantages. In this thesis, kaolin–molybdenum disulfide (MoS2) composites engineered with two distinct morphologies, three-dimensional (3D) flower-like MoS2 (F-MoS2) and two-dimensional MoS2 (2D-MoS2), were synthesized and evaluated for mercury removal from aqueous solutions to address the shortcomings mentioned above. Commercial kaolin was initially calcined and subjected to sequential acid–base treatments to enhance its pore structure and expose additional active sites. MoS2 was hydrothermally synthesized and composited with the kaolin (to enhance dispersibility and stability) to obtain K–F-MoS2 and K–2D-MoS2 composites. Comprehensive physicochemical characterizations, including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Transmission electron microscopy, Brunauer–Emmett–Teller surface analysis, zeta potential measurements, X-ray photoelectron spectroscopy, and Energy-dispersive spectroscopy, confirmed well-defined 2D and 3D flower-like architectures and demonstrated their structural integrity following Hg2+ adsorption. K–F-MoS2 exhibited significantly higher performance than K–2D-MoS2 with maximum Langmuir capacities of 161.4 and 76.8 mg/g, respectively. The adsorption isotherms were best described by the Langmuir model for K–F-MoS2 and the Freundlich model for K–2D-MoS2. Both composites followed the pseudo-second-order kinetic model, indicating chemisorption-driven uptake, and mechanistic investigations confirmed Hg2+ binding was predominantly through covalent surface complexation with sulfur atoms on MoS2. Thermodynamic studies establish the endothermic nature of the adsorption process. Both adsorbent samples were tested for antibacterial and antibiofilm activities. K–F-MoS2 and K–2D-MoS2 exhibited antibacterial activity against S. aureus and E. coli (BL21) and inhibited biofilm formation. These findings demonstrate that kaolin–MoS2 hybrid systems are promising multifunctional materials for Hg2+ remediation and antimicrobial protection with good applicability.