Reuse of Agro-industrial Green Bean Pod Residue for the Production of Original Catalytic Composites and Application in Fenton Reactions

During the research, the structure of bean pod residues (BPRs) was evaluated as a support medium to fix magnetite (Fe 3 O 4 ) and pyrite (FeS 2 ) particles, forming composites capable of acting as catalysts for Fenton reactions. The respective iron particles were synthesized through coprecipitation and hydrothermal methods that allowed the synthesis of these particles and led to the formation of BPR/Fe 3 O 4 and BPR/FeS 2 composites. The success of the methodologies used was confirmed from the characterization analyses using the FTIR, XRD, SEM–EDS, and TG techniques. The high catalytic potential of BPR/Fe 3 O 4 and BPR/FeS 2 was verified after use for the degradation of the aqueous mixture of four textile dyes using the Fenton (36.20%/53.33%), photo-Fenton (94.69%/90.86%), sono-Fenton (73.70%/58.98%), and sono-photo-Fenton (74.01%/62.22%). The BPR/Fe 3 O 4 showed greater catalytic activity and, therefore, its reuse capacity was evaluated through the photo-Fenton system with solar radiation. It was evidenced that the material is stable, having a high potential for reuse. Thus, it can be stated that a new applicability was granted to bean pod waste, appearing as an alternative to solve solid waste problems. Linked to this, the proposed immobilization of iron particles, which are commonly placed in suspension for catalysis of Fenton reactions, helped to fill in yet another gap, which still exists in the literature on AOP treatments. Graphical Abstract