Synthesis and modification of ZSM-5 with manganese and lanthanum and their effects on decolorization of indigo carmine dye

Hydrothermally synthesized ZSM-5 zeolite modified by manganese (Mn/ZSM-5) or lanthanum (La/ZSM-5) or mixture of both (Mn–La/ZSM-5) using impregnation technique was characterized by powder XRD, FTIR and N2 adsorption measurements. These materials were tested for discoloration (adsorption) and mineralization (in the presence of UV irradiation) of indigo carmine (IC) dye. The results indicate that MnOx incorporated ZSM-5 that showed the highest lattice volume and pore radius between all samples presented the highest photocatalytic activity, comparatively. However, the Mn-La/ZSM-5 catalyst exhibited the lowest activity even when compared with the parent ZSM-5 sample. This was in part due to evoking of Mn3O4 species at the expense of Mn2O3 ones, which were proposed to be the active sites of the reaction. This reaction was found to be acidity dependent since Mn/ZSM-5 showed significant bands at 3650 and 3619 cm−1 those in contrast appeared shapely in La/ZSM-5, whereas for Mn–La/ZSM-5 only a band at 3619 cm−1 was obtained. On the other hand, the decolorization activity showed comparable high rates for Mn/ZSM-5 and Mn–La/ZSM-5 samples (100% removal) implying that the adsorption process is more referred to acid-base site pairs where the photocatalytic activity seems to be more restricted to acidic sites. The influence of pH, catalyst amount and time on the decolorization rate of IC on Mn/ZSM-5 was thoroughly investigated and correlated with ZPC of MnOx species, various exposed species of MnOx and surface properties.