Structural design of core-shell ZIF-8@NH2-MIL-125 photocatalyst for synergistic adsorption-photocatalytic degradation of tetracycline hydrochloride

The development of a green, efficient, and reusable photocatalyst is of great importance for pollution remediation. Herein, a series of core-shell ZIF-8@NH2-MIL-125 composites (ZM-X) were prepared by epitaxial growth method. The in-situ homogeneous encapsulation of NH2-MIL-125 by ZIF-8 was achieved through the structural modulation, and the formed core-shell architecture exhibited outstanding synergistic effect of adsorption and photocatalysis for eliminating tetracycline hydrochloride (TCH), which dramatically enhanced the photocatalytic reaction rate. The results show that the TCH adsorption capacity of optimized ZIF-8@NH2-MIL-125 (ZM-2) is 70.25 mg g–1, which can be fitted well the pseudo-second-order and Langmuir isotherm modes. Under 100 min of visible light irradiation, the ZM-2 has the best synergistic removal rate on TCH (92.9%) compared with other samples, which is 6.5 times higher than of pristine NH2-MIL-125 (14.3%). The results of quenching experiments and ESR analysis clearly demonstrate that the superoxide radical (·O2–) dominates the TCH photodegradation reaction. In addition, ZM-2 can effectively remove TCH in different types of water systems (e.g., ultrapure water, tap water, lake water and actual pharmaceutical wastewater) through adsorption-photocatalytic synergy. Therefore, the novel core-shell material designed in this study has significant potential for environmental purification applications.