Influence of Aminosilane Structure on 5-Fluorouracil Adsorption and Retention in Zeolites

5-Fluorouracil (5-FU) can cause ocular adverse effects due to its presence in lacrimal fluid during treatment. To explore potential drug-scavenging materials for reducing excess 5-FU exposure, we investigated the adsorption and retention of 5-FU in zeolites and silane-functionalized zeolites. Seven commercial zeolites with different framework structures were evaluated for 5-FU adsorption from phosphate-buffered saline (PBS). Among the unmodified materials, Beta-type zeolite (ZF) exhibited the highest adsorption ratio (14.76%). To enhance drug-capturing performance, zeolites were functionalized with amino-containing silanes, including APTMS, APTES, AEPMS, and AHPMS. Functionalization altered both adsorption and retention behavior depending on the zeolite framework and silane structure. AEPMS increased 5-FU adsorption in several zeolites, whereas APTMS- and APTES-functionalized ZF exhibited the highest retention. After 24 h of immersion in PBS, the retention ratio increased from 7.63% for unmodified ZF to 98.47% and 98.25% for APTMS- and APTES-functionalized ZF, respectively. The silane structure that maximized adsorption differed from that conferring the highest retention, indicating distinct structure–property relationships. These results identify amino-functionalized zeolites as promising materials for capturing 5-FU and supporting their potential use as drug-scavenging materials in ophthalmic applications.