Comparative evaluation of H2O2 and peroxydisulfate (PDS) activation by Fe3O4/g-C3N4 composite under visible light for methyl orange degradation

Fe 3 O 4 /g-C 3 N 4 (FeCN) was prepared by thermal polymerization of melamine followed by iron oxide coprecipitation and characterized using X-ray diffraction and thermogravimetric analysis. The same catalyst was used to compare H 2 O 2 and peroxydisulfate (PDS) activation for methyl orange (MO) removal under visible light. First-order and second-order models provided comparable fits, and apparent first-order rate constants were used for comparison. H 2 O 2 /FeCN/vis performed better at the common oxidant concentration of 7.5 mM. Within the tested range, H 2 O 2 showed maximum activity at 7.5 mM, whereas PDS activity increased up to 10 mM. Apparent activation energies were 37.0 and 101.7 kJ·mol −1 for the H 2 O 2 and PDS systems, respectively, indicating stronger temperature dependence for PDS. Scavenger responses suggested reactive-species involvement, but alcohol-induced enhancement in the PDS system prevented definitive species assignments.