Porous spherical g-C₃N₄/geopolymer composite for photo-Fenton-like degradation of tetracycline hydrochloride

Porous metakaolin-based geopolymer spheres were produced using a direct molding method. To enhance the photocatalytic degradation of tetracycline in water, a low-cost non-metallic catalyst (g-C₃N₄) was incorporated as a functional solid additive. The g-C₃N₄ was synthesized through the thermal condensation of melamine at 550 °C. Given the pH buffering capacity of the alkaline geopolymer, the composite catalyst was pre-treated to achieve a near-neutral pH. The resulting composite photocatalysts (GG) with 0.63 wt% g-C₃N₄ content demonstrated 49.36 % photocatalytic degradation of tetracycline within 3 h, with a higher pH environment further enhancing the degradation process. Notably, the composite photocatalysts (GG-N), when not subjected to alkali removal, exhibited an impressive 91.57 % photo-Fenton-like degradation of tetracycline. The synergistic catalytic degradation mechanism of the composite catalysts was thoroughly investigated. Furthermore, the porous spherical g-C₃N₄/geopolymer composite, with a diameter of 7.44 mm, can be easily reused without causing secondary pollution, providing a promising approach for the practical application of non-metallic catalyst/geopolymer composites in co-catalytic organic degradation. © 2025 Elsevier Ltd