Herein, corncob waste was used as a scaffold for the fabrication of effective adsorbents. Porphyrinic zirconium metal-organic frameworks (MOFs) PCN-223 and PCN-224 constructed by different numbers of Zr6 cluster nodes were grown on the surface of the corncob. Fe (Ш) ions were implanted in the porphyrin ring by post-synthesis modification. The results showed that the extraction capacity of diuretics on PCN-224@corncob containing suitable pore size was larger than that of PCN-223@corncob. The adsorption of diuretics was further enhanced because of the electrostatic effect caused by implantation of Fe (Ш) ions. PCN-224-Fe@corncob was recyclable and selective for the extraction of furosemide (Fur) and bumetanide (Bum). Coupled in-syringe solid phase extraction (IS-SPE) with ultra-performance liquid chromatography (UPLC), an efficient, sensitive, and stable method was established. With a sensitivity between 0.6 and 1.0 μg/L and a recovery between 83.2% and 119.2%, it is used for the analysis of trace amounts of Fur and Bum in weight loss products and environmental water. The functionalized corncob has potential application for the adsorption of diuretics, and the metal ions implantation in MOFs provides a promising strategy for enhancing extraction capacity.