MOF-derived Fe3O4@PC-supported biosynthesized silver nanoparticles: a highly efficient and magnetically separable catalyst for methyl orange reduction.

In this study, a novel magnetic Ag/Fe3O4@PC nanocomposite was successfully fabricated by immobilizing biosynthesized silver nanoparticles onto an Fe3O4/porous carbon (Fe3O4@PC) support derived from the iron-based metal-organic framework MIL-88B(Fe), using onion peel extract as a green reducing and stabilizing agent. The synthesized nanocomposite was comprehensively characterized by XRD, FE-SEM, N2 adsorption-desorption, FTIR, VSM, and TGA analyses, confirming the successful formation of a mesoporous magnetic catalyst with uniformly dispersed Ag nanoparticles. The catalyst exhibited a specific surface area of 161 m2 g-1 and a saturation magnetization of 61 emu g-1, enabling rapid magnetic separation after the catalytic reaction. Under the optimized reaction conditions, approximately 96% of methyl orange was reduced within 2 min, following pseudo-first-order kinetics with an apparent rate constant of 0.036 s-1. The catalyst also exhibited excellent activity toward crystal violet, achieving up to 99% reduction. Furthermore, the catalyst demonstrated excellent reusability, exhibiting only a slight decline in catalytic efficiency after three consecutive cycles, while maintaining comparable performance in tap water (95.8%) compared with distilled water. The outstanding catalytic performance is attributed to the synergistic integration of uniformly dispersed Ag nanoparticles, a mesoporous carbon framework, and magnetic Fe3O4 support, which collectively facilitate rapid electron transfer, abundant accessible active sites, and efficient catalyst recovery. Overall, these findings demonstrate that the developed Ag/Fe3O4@PC nanocomposite is a highly efficient and magnetically recoverable catalyst with strong potential for practical wastewater treatment applications.