Co-adsorption of methylene blue/Pb(II) from aqueous solutions using sulfonated mesoporous diatomite

Water contamination by heavy metals and organic dyes poses a significant threat to environmental and human health, particularly in developing countries. In this study, a cost-effective and eco-friendly mesoporous diatomite-based adsorbent functionalized with sulfonate groups (DE-SO₃) was developed to enhance adsorption performance. The adsorbents were systematically evaluated for the simultaneous removal of Pb(II) and methylene blue (MB) from aqueous solutions under various operational conditions. Characterization confirmed the successful sulfonation and its impact on surface properties, improving adsorption efficiency. Equilibrium adsorption followed the Langmuir isotherm model, with maximum adsorption capacities of 178.57 mg/g for Pb(II) and 392.16 mg/g for MB in single systems. In the mixed systems, competitive adsorption slightly reduced these capacities to 149.25 mg/g for Pb(II) and 354.61 mg/g for MB. Kinetic studies indicated that adsorption was primarily governed by a chemisorption process, following the pseudo-second-order model. Additionally, the adsorbent demonstrated good regeneration potential over multiple cycles. A comparative analysis with existing adsorbents highlighted the superior performance of DE-SO₃. These findings emphasize the potential of sulfonated diatomite as a promising, sustainable solution for wastewater treatment, addressing both heavy metal and organic dye contamination.