Hollow cavity engineering of MOF-derived hierarchical nitrogen-doped In₂O₃@carbon for efficient photocatalytic degradation of tetracycline hydrochloride

The engineering of photocatalysts with hollow structures is essential for improving the absorption of visible-light irradiation to boost the photocatalytic activity of organic contaminants. This study presents a feasible cavity engineering method for the synthesis of nitrogen-doped In₂O₃@carbon spherical structures produced from In-MOF. These spherical structures feature a well-defined central void, achieved through CTAB-assisted aggregation of In₂O₃ via annealing In-MOF in an air atmosphere. The N-doped In₂O₃@carbon photocatalysts were employed for the degradation of tetracycline hydrochloride (TCH) under visible-light irradiations. The optimized N-doped In₂O₃@carbon catalyst (In₂O₃-III) exhibited 98 % degradation of tetracycline hydrochloride within 60 min of visible-light irradiation. Hollow cavity engineering may offer several active sites, a reduced band gap, and considerable benefits for the separation of electron-hole (e⁻/h⁺) pairs and light absorption capability. Furthermore, the presence of an optimal concentration of nitrogen and oxygen vacancies in the In₂O₃-III synergistically contributed to the improved visible light-driven photocatalytic degradation of tetracycline hydrochloride. Several parameters influencing the mineralization of TCH were examined, comprising catalyst type, TCH concentration, initial solution pH, catalyst dosage, inorganic anions, and radical species. Radical capturing tests and electron spin resonance studies indicate that h⁺ and O₂^•- were the principal species engaged in the degradation of TCH.