Sonocatalytic decolorization of methylene blue from aqueous media by La:ZnO/GO nanocomposites

Abstract

The collaboration of graphene oxide and a rare earth element dopant has a significant effect on the catalytic performance of zinc oxide nanoparticles (ZnO). For this purpose, lanthanum-doped zinc oxide/graphene oxide (La:ZnO/GO) nanocomposites were produced. The La:ZnO/GO composites developed using various quantities of La3+ (3, 6 and 9 at.%) were used for methylene blue (MB) decomposition in the presence of ultrasound. SEM images of nanocomposites showed that the growth pattern of ZnO nanoparticles on the surface of graphene oxide changed, which can be related to lanthanum addition on the structure. In fact, by adding lanthanum, the structure of ZnO nanosheets that were aggregated in the flower form was converted into flower-like nanorods. TEM images clearly displayed La:ZnO/GO nanorods. The presence of lanthanum was confirmed by EDS analysis. La:ZnO(3 at.%)/GO nanocomposite, exhibited the highest sonocatalytic activity (93% after 80 min) and demonstrated good stability in optimized conditions (catalyst dosage 0.1 g, initial dye concentration 10 mg/L and irradiation time 80 min), which was checked out using response surface methodology from Design of Experiment software. After using a radical hydroxyl, superoxide and hole quencher results confirmed that the generated holes in the valence band of ZnO and superoxide radicals are major species for the MB oxidation process. The results demonstrated that the mineralization percentage of MB was approximately 93% of total organic carbon removal under ultrasound.