Visible-light-driven malachite green degradation by optimized mil-125(ti) immobilized in alginate hydrogel for continuous-flow remediation

Persistent organic dyes such as malachite green (MG) pose serious environmental and health risks, highlighting the urgent need for efficient and sustainable treatment strategies. This study reports a visible-light-responsive photocatalytic system based on MIL-125(Ti), a titanium-based metal–organic framework (MOF), immobilized within a hierarchically porous alginate hydrogel for continuous-flow water remediation. The optimized MIL-125(Ti), synthesized at 150°C via a controlled solvothermal route, exhibited superior crystallinity, porosity, and visible-light absorption, achieving 95% MG degradation in batch operation. Mechanistic analysis identified photogenerated holes (h⁺), superoxide radicals (•O₂⁻), and electrons (e⁻) as the dominant reactive species. To enable practical application, the optimized MOF was encapsulated into sodium alginate (SA) beads containing sodium dodecyl sulfate (SDS) and NaHCO₃, producing a robust macroporous composite. When used as packing material in a fixed-bed flow reactor, the MIL-125(Ti)/SA beads achieved 83.4% MG degradation within 90 min under visible light, maintaining excellent structural stability and reusability. This work provides a novel and scalable route for immobilized MOF photocatalysts in sustainable continuous-flow water treatment systems.