Fe³⁺-Bridged Cellulose–Alginate Composite Gel Beads as Stable and Effective Photo-Fenton Catalysts

Cellulose pretreated by mechanical activation in the presence of FeCl3 (MAFCC) was dissolved and regenerated as a reinforcing phase for preparing a Fe3+-bridged cellulose–alginate (Alg) composite, which was formed into gel beads and subjected to ion exchange, followed by modification with polydopamine (PDA) to yield a photo-Fenton catalyst, denoted as MAFCC-Alg/Ca-Fe@PDA. Comparative characterization and studies of the catalytic degradation of methylene blue (MB) revealed that the MAFCC-Alg/Ca-Fe@PDA gel beads had outstanding mechanical properties and photo-Fenton catalytic activity, degrading 98.5% of MB in 40 min under optimized conditions. In particular, the formation of the Fe3+-bridged MAFCC-Alg gel network structure, as well as the PDA coating, contributed to the high specific surface area, compressive strength, and visible-light absorption capacity of the MAFCC-Alg/Ca-Fe@PDA porous gel beads. Moreover, MAFCC-Alg/Ca-Fe@PDA exhibited outstanding reusability and stability over five cycles without any significant decrease in catalytic activity or rupture of the gel beads. In summary, an effective synthetic route was provided to prepare a FeAlg composite catalyst having a stable structure and excellent catalytic performance and reusability.