Exploring the adsorptive properties of an embryonic zeolite toward methylene blue

Abstract

Textile dyes are persistent water pollutants, requiring effective treatment strategies. This study reports the adsorption performance of embryonic zeolite precursors (EZPs) synthesized with tetrapropylammonium hydroxide as a structure-directing agent. The materials were prepared with different Si/Al ratios (50, 100, and 200) in the starting gel and tested for the removal of methylene blue (MB) from aqueous solutions. Comprehensive characterization (PXRD, SAXS, BET, FTIR, EDXRF, N₂ physisorption, and TGA/DSC) confirmed their micro/mesoporous and amorphous nature. Among them, EZTPA50 displayed the highest surface area (915 m² g⁻¹) and hierarchical porosity. Adsorption experiments revealed that EZTPA50 and EZTPA100 outperformed the crystalline counterpart H-ZSM-5. Their monolayer capacities reached 146.08 mg g⁻¹ and 122.62 mg g⁻¹, respectively. Langmuir isotherm modeling indicated monolayer coverage, while Elovich kinetics suggested heterogeneous surface chemisorption. Thermodynamic analysis showed spontaneous, endothermic, and entropy-driven adsorption for both materials. Intraparticle diffusion analysis revealed a multi-stage adsorption mechanism influenced by pore accessibility and surface heterogeneity. Thermal regeneration studies demonstrated that EZ_TPA50 retained ∼90% removal efficiency over four cycles, highlighting its structural stability and reusability. These findings position EZPs – particularly EZ_TPA50 – as promising, regenerable adsorbents for efficient dye removal, offering advantages over conventional microporous zeolites in terms of adsorption capacity, kinetics, and thermal robustness.