Carbon nanoparticles and diatomaceous earth hybrids: A synergistic approach for methylene blue uptake

This study reports the methylene blue (MB) uptake capacity and absorption kinetics of adsorbents obtained by the hybridisation of natural diatomaceous earth with hydrophilic carbon nanoparticles at two different loadings (2 and 5 wt.%). The materials were characterized and tested as adsorbents of MB in acidic and basic pH. The effects of MB concentration (25-400 mg‧L^-1), contact time (1-120 min), and adsorbent mass (10-50 mg) on the adsorption process were investigated. The diatomite and diatomite-based adsorbents showed high uptake capacities (highest experimental adsorption capacity q_exp 464.87 mg·g⁻¹) and favorable kinetics, well described by the Elovich model, suggesting a chemisorption-driven mechanisms. The Freundlich model provides a superior fit compared to the Langmuir model, particularly for the hybrid samples, indicating a favorable and heterogeneous adsorption mechanism consistent with multilayer adsorption on non-uniform surfaces. Regenerability and reusability of the adsorbents was demonstrated over three MB adsorption-desorption cycles. Effective performance across pH 3-8 highlights their versatility for real-world water treatment applications. The hybridisation also improves the cyclability and the uptake capacities in an acid environment (pH = 3). This high uptake capacity across a broad range of pH values makes the hybrid materials versatile and easy to integrate into existing water treatment systems.