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This work reports the design of binary and ternary BiOI-based composites incorporating the metal–organic framework CAU-17 and the amine-functionalized microporous organic polymer MOP-CH2EDA for the removal of ciprofloxacin (CIP) from water. The materials were synthesized via an in situ solvothermal approach and systematically characterized to establish structure–property relationships. The results reveal that adsorption and photocatalysis act as coupled and sequential processes, rather than independent pathways, with the polymer component enhancing CIP pre-concentration and the BiOI/MOF interface governing photodegradation. The ternary composite BCM-10% exhibited the best performance, achieving up to 80% CIP removal under simulated solar irradiation. Scavenger experiments indicate that ·O2− is the dominant reactive species, while photogenerated holes also contribute significantly. The degradation process is strongly influenced by pH, reflecting the interplay between catalyst surface properties, reactive oxygen species generation, and CIP speciation. HPLC-MS analysis confirms the formation of multiple intermediates and highlights the complexity of the degradation pathways. Despite the improved performance of the ternary composites, the overall activity remains moderate compared to state-of-the-art photocatalysts, underscoring the limitations of current BiOI-based systems. The results emphasize that apparent kinetic behavior is strongly affected by adsorption contributions, complicating direct comparison with literature data. This study provides new insight into the design of multifunctional materials for water treatment, highlighting the importance of adsorption–photocatalysis synergy and the need for more rigorous and standardized evaluation of photocatalytic systems.