Different materials have been used as adsorbents for removing micropollutants from industrial effluents, with vegetal-derived activated carbon being widely reported for dye removal, especially methylene blue (MB). However, its high cost and environmental concerns have driven the search for alternative adsorbents. Beyond developing new materials, understanding the interaction mechanisms between adsorbents and adsorbates is crucial. In this investigation, sodium (NaZ) and protonic (HZ) zeotypes were synthesized using diatomaceous earth (DE) residue as a silicon source and applied to MB dye adsorption. Batch experiments investigated adsorption rates, mechanisms, and thermodynamic spontaneity. The results showed rapid adsorption kinetics, with equilibrium achieved in about 5 min, following the Avrami model. The Weber and Morris model highlighted that the boundary layer significantly affects film diffusion and intraparticle diffusion. The adsorption process reached equilibrium governed by the Freundlich model, with favorable adsorption behavior for all adsorbents (nF values between 1 and 10). Additionally, the enthalpy values were found to be +39.66, + 5.70, and +21.79 kJ mol ^–1 for NaZ, HZ, and DE, respectively. This was accompanied by a decrease in Gibbs free energy with a progressive increase in temperature, indicating a more spontaneous process at higher temperatures. These results suggest that the adsorption of MB onto the synthesized zeotypes is efficient, with fast kinetics and thermodynamic favorability. The zeotypes synthesized from diatomaceous earth exhibit promising characteristics for potential large-scale applications in wastewater treatment.

The textile industry is known for its high water consumption and production of toxic effluents, including azo dyes such as Reactive Black 5 (RB-5), which are resistant to removal. Adsorption offers a promising, cost-effective solution, particularly with value-added composites made from abundant materials. This study synthesized, characterized, and applied a C/TiO₂-based composite to remove RB-5 from water. XRD analysis only confirmed anatase as the primary support, while FTIR detected adsorbate molecules on the C/TiO₂ surface, marked by the appearance of a sulfone group band. Raman and XPS analyses indicated reduced Sp² carbon content and lower graphitization after adsorption, probably due to mechanical stress. Additionally, nitrogen physisorption analysis demonstrated that the material is mesoporous, with a surface area of 56.24 m² g^-1, and a pore diameter of 9.41 nm. The composite exhibited strong affinity for anionic species like RB-5, especially at pH values below the point of zero charge (7.47). Batch studies demonstrated Avrami kinetic adsorption at a rate of 0.3023 min^-1 (at 25 °C), while temperature effects followed the Arrhenius model, with an activation energy of +41.10 kJ mol^-1. Sips isotherm data indicated a maximum adsorption capacity of 17.48 mg g^-1 at 55 °C. Thermodynamic analysis confirmed an entropically controlled, endothermic, spontaneous process at high temperatures. These aspects confirm the potential of eco-friendly C/TiO₂ composite for effective RB-5 removal from aqueous solutions.