Rice Husk Ash Geopolymers Modified with Fe₃O₄ or ZnTiO₃/TiO₂ Nanoparticles for the Adsorption and Photodegradation of...

Hybrid nanomaterials integrating magnetic and semiconductor phases offer promising multifunctional platforms for wastewater remediation; however, their stabilization and recovery remain challenging. In this study, Fe₃O₄ and ZnTiO₃/TiO₂ nanoparticles were incorporated into a rice husk ash-based geopolymer matrix to develop hybrid nanocomposites for synergistic adsorption-photodegradation of methylene blue (MB) and methyl orange (MO). The materials were synthesized via alkaline activation followed by nanoparticle incorporation, and characterized by XRD, XRF, FTIR, SEM, EDX, BET surface area analysis, and pHPZC determination. XRD confirmed the presence of nanocrystalline Fe₃O₄ and ZnTiO₃/TiO₂ phases while preserving the amorphous aluminosilicate framework. Modified powders exhibited higher specific surface areas (up to 198 m² g^-1) compared to the unmodified geopolymer. Adsorption followed the Langmuir isotherm and pseudo-second-order kinetics, with spontaneous and exothermic behavior. Under UV irradiation, the ZnTiO₃/TiO₂-modified composite achieved photodegradation efficiencies up to 94% for MB and 92% for MO, whereas the Fe₃O₄-modified material combined adsorption capacity with magnetic recoverability. These results demonstrate that nanoparticle incorporation enables multifunctional performance while maintaining structural integrity of the geopolymeric matrix.