Engineered Hierarchical Porous HKUST-1/HZSM-5 Composite for the Co-Adsorption of Hexavalent Chromium and Cephalexin from Aqueous Media

A hierarchical porous HKUST-1/HZSM-5 composite was synthesized via a facile hydrothermal method and applied for capturing hexavalent chromium (Cr(VI)) and cephalexin (CEP) from aqueous media. Comprehensive material characterizations pre- and post-adsorption, including N 2 physisorption, FTIR, PXRD, TGA/DTG, XPS, FESEM, EDS, elemental mapping, and TEM analyses, confirmed successful composite integration, high crystallinity, and thermal stability. Integrating hierarchical HZSM-5 significantly modified the HKUST-1 morphology and pore architecture, generating a hierarchical micro/mesoporous structure with a mesopore volume of 0.492 cm 3 /g, compared to 0.034 cm 3 /g for pristine HKUST-1. This enhanced total pore volume (0.767 cm 3 /g) and mean pore diameter (18.436 nm) facilitated mass transfer and superior adsorption performance. Batch adsorption experiments ascertained the effects of adsorbent dose, pH, ionic strength, contact time, initial pollutant concentration, and temperature. The adsorption process followed pseudo-second-order kinetics ( R 2 > 0.930), which signifies chemisorption as the dominant rate-controlling mechanism, enabling rapid contaminant removal within 30 min. Equilibrium data were best described by the Redlich-Peterson isotherm model ( R 2 > 0.980), suggesting heterogeneous surface adsorption involving both monolayer and nonideal interactions. The composite demonstrated exceptional maximum uptake capacities of 1053.3 mg/g for Cr(VI) and 902.7 mg/g for CEP (at 0.1 g/L adsorbent dose, pH 7.0 ± 0.1, and temperature 298 ± 1 K), significantly outperforming bare HKUST-1 and HZSM-5. Thermodynamic analyses revealed a spontaneous, exothermic process driven by pore-filling, complexation, electrostatic attraction, hydrogen bonding, and π–π electron donor–acceptor/stacking interactions. The composite maintained robust capacities during binary coadsorption experiments despite competitive effects, and exhibited satisfactory performance in spiked real-water matrices, confirming practical applicability. Furthermore, the material presented excellent reusability, with capacity losses of only 21.0 and 13.5% for Cr(VI) and CEP, respectively, after five consecutive adsorption–desorption cycles. The remarkable uptake capacity, hierarchical porosity, and robust stability highlight HKUST-1/HZSM-5 as a highly efficient adsorbent for advanced wastewater remediation.