Magnetic Alginate-Based Composite Beads Incorporating Cu/TiO₂: Synthesis, Structure-Property Relationships, and...

Magnetic alginate-based composite beads integrating Cu/TiO₂ and magnetite (Fe₃O₄) were fabricated as polymer-inorganic hybrid systems for magnetic recovery. These composite beads were generated via ionotropic gelation, a method that enabled efficient encapsulation of inorganic constituents within the sodium alginate matrix while preserving the crystalline structures of Fe₃O₄ and anatase TiO₂. The impact of Fe₃O₄ loading on the beads' structural and physicochemical attributes was systematically investigated, revealing specific structure-property relationships that dictated encapsulation efficacy, swelling behavior, bulk density, and internal morphology. Among the formulations examined, the S-1.0Fe₃O₄-SA beads demonstrated a favorable balance between structural integrity and mass-transfer accessibility. The efficacy of the composite beads was evaluated via their employment in the hydrogenation of glacial acetic acid, a representative liquid-phase reaction. Examination of the reaction products indicated the formation of ethanol and ethyl acetate; the precise product distribution depended on the Cu loading in the Cu/TiO₂ component. A moderate Cu content was observed to facilitate product formation, concurrently maintaining the structural stability of the beads. The S-1.0Fe₃O₄/SA-1.8Cu/TiO₂-0.4 catalyst exhibited the highest ethanol production (18.69 mg L^-1). Lower Cu loading resulted in insufficient active sites, whereas higher loading led to aggregation and reduced catalytic efficiency. Recycling tests revealed a gradual decrease in ethanol formation upon reuse, indicating partial catalyst deactivation, likely due to surface fouling and Cu leaching. Therefore, this study highlights the promise of alginate-based magnetic composite beads as a versatile polymer-supported platform, in which the macromolecular structure is crucial for dictating functional performance.