Optimized microwave-assisted synthesis and application of ZSM-5 zeolites for Cd2⁺ and Co2⁺ adsorption in the presence of competing Ca2⁺

Heavy metal contamination in water remains a major environmental concern. In this work, ZSM-5 zeolites were synthesized by a microwave-assisted route and optimized by Design of Experiments to enhance adsorption performance. Structural and textural characterization by XRD, N₂-physisorption, and SEM confirmed the formation of crystalline micro-mesoporous ZSM-5 with hierarchical features. The zeolite synthesized under the optimized conditions (Si/Al ratio of 25, tetrapropylammonium bromide concentration of 0.08 mol, and crystallization time of 8 h) demonstrated a strong ability to selectively remove Cd²⁺ at 10 µg L^-1 from aqueous solution even in the presence of a ten-fold excess of competing Ca²⁺ ions. The zeolite was further integrated into a pipette-tip microextraction format for Co²⁺ preconcentration, and the extraction procedure was independently optimized by a second DoE, assessing aspiration/dispensing strokes, sample volume, and temperature. Extraction consisted of a single procedure in which the same solution was repeatedly aspirated and dispensed through the zeolite bed to maximize contact. The regression model for tip extraction achieved R² = 0.958 and Q² = 0.892, confirming strong predictive performance and methodological robustness. These results support the use of engineered ZSM-5 as a reusable and low-impact material for monitoring and mitigating heavy-metal pollution in water.