ABSTRACT
In this study, geopolymer catalysts were synthesized by incorporating different TiO2 (0, 7, and 14 wt%) and Fe2O3 content (0, 7, 14, and 20 wt%) into porous metakaolin-based geopolymer granules. TiO2- and Fe2O3-immobilized geopolymer granules were applied for photocatalytic removals of imidacloprid under UV-C irradiation. The analysis of the surface morphology of the Fe2O3 catalyst revealed its larger surface area predominated with meso- and macro-pores thus providing a larger area for photocatalysis. Meanwhile, the TiO2 catalyst had TiO2 nanoparticles filled up those mesopores and macropores in geopolymer resulting in its denser structure therefore limiting access of imidacloprid to the reactive sites. To maximize its photocatalytic activities, Fe2O3 and TiO2 could be immobilized into porous geopolymer matrix up to 20 and 14 wt%, respectively. The developed porous geopolymer had relatively stable imidacloprid adsorption capacities regardless of the TiO2 and Fe2O3 contents in their texture. After UV irradiation, their removal efficiencies were 94.85-100% and the photocatalytic degradation increased with the increase in TiO2 content (from 0 to 14 wt%) and Fe2O3 content (from 14 to 20 wt%). Nevertheless, Fe2O3-immobilized geopolymer granules posed a significantly higher kinetic rate (1.966 h-1) compared to that of TiO2 (0.154 h-1) at the same catalyst content (14 wt%). The newly developed Fe2O3-immobilized porous geopolymer catalysts could be effectively reused over 10 successive cycles during which the imidacloprid could be completely removed.
