Study on preparation methodology of zero-valent iron decorated on graphene oxide for highly efficient sonocatalytic dye degradation

Various preparation methodologies (stirring, hydrothermal, and high energy ball milling methods) were used to prepare zero-valent iron (ZVI) catalysts decorated on graphene oxide (GO) for highly efficient sonochemical dye degradation, and their dye degradation efficiencies were compared. For the effective activation of ZVI, N,S co-doped GO (N,S-GO) prepared by high-energy ball milling synthesis was also tested. According to the preparation methodologies, the ZVI catalysts showed different degrees of surface passivation, morphologies, and zeta-potentials because of the different degrees of aerial oxidation of ZVI, which are the key factors determining their activities in sonocatalytic dye degradation. The ZVI catalysts on GO prepared using the stirring and hydrothermal methods showed a high oxidation state with low sonocatalytic activity. In contrast, the ZVI catalysts on GO prepared using the high-energy ball milling method exhibited moderate sonocatalytic activity due to moderate passivation. The ZVI on N,S-GO prepared by stepwise high-energy ball milling synthesis showed the maximum activity (100% removal efficiency within 1 min) due to the minimum aerial oxidation. The rapid generation of •OH radicals by high-energy sonication, the existence of mixed-valence states of iron via activation, and N,S-doping facilitated electron transfer for the dye degradation process. The complete mineralization and degradation pathway of crystal violet dye was confirmed by electrospray ionization-mass spectrometry. The effects of the preparation methodologies (stirring, hydrothermal, and high-energy ball milling methods) of zero-valent iron (ZVI) on graphene oxide (GO) and N,S co-doped GO (N,S-GO) for the sonocatalytic degradation of various dyes were investigated. [Display omitted] •The methodology-dependent activation of ZVI on GO or N,S-GO was induced.•High-energy ball milling activated ZVI on GO or N,S-GO by surface passivation.•100% dye removal efficiency via sonocatalytic degradation occurred within one min.•ESI-Mass spectrometry confirmed the mineralization and degradation pathway of CV.