Fabrication of core-shell MIL-125-NH2@ZIF-67/SiO2 composites with enhanced catalytic activity for nitroaromatic reduction

The high toxicity and persistence of nitroaromatic pollutants pose a serious threat to aquatic ecosystems. In this study, inert SiO 2 was employed as an "inactive enhancer" to construct core-shell MIL-125-NH 2 @ZIF-67/SiO 2 (M@Z/SiO 2 ) heterogeneous MOF catalysts via an epitaxial-wet impregnation method, enabling the efficient reduction of p -nitrophenol ( p -NP) under ambient temperature and pressure. Although SiO 2 itself lacks catalytic activity, the micro-mesoporous network it forms effectively disperses Co active sites and prevents their aggregation. The conversion rate of p -NP increased from 92.5% to 98.4% within 6   min and retained 98% activity after three consecutive cycles. Moreover, the catalyst exhibited excellent stability across a wide pH range (3-11) and in various anionic environments. Mechanistic studies revealed that the interfacial electron transfer between ZIF-67 and MIL-125-NH 2 significantly reduces the activation energy barrier of NaBH 4 . Additionally, the incorporation of SiO 2 not only enhances the mechanical stability of the composite but also optimizes pore structure and substrate mass transfer by modulating surface hydrophilicity. This work provides valuable insights for the precise design of MOF-on-MOF heterostructures and the synergistic engineering of interfacial and surface properties in environmental catalytic materials.