Microwave-assisted rapid synthesis of ZnO multipod-BiOBr heterojunction on recycled PET plastic waste for photocatalytic degradation of oily wastewater

Heterojunctions based on ZnO multipod and BiOBr were developed on the floating recycled polyethylene terephthalate (PET) and they were used to investigate the photocatalytic degradation of hexane in water emulsion. Characterizations of the synthesized ZnO-BiOBr-PET photocatalysts was performed using XRD, FESEM, EDX, BET/BJH, FTIR, UV-Vis DRS, PL, WCA, and CV analyses. The FESEM results demonstrated that ZnO multipods have been synthesized during the very short time of microwave heating that effectively hosted the highly dispersed BiOBr nanoplates, particularly in the 15 %ZnO-5 %BiOBr-80 %PET sample. The BET/BJH analysis revealed the low surface areas for the synthesized samples, however, the sample with the highest ZnO multipod loading (15 %ZnO-5 %BiOBr-80 %PET) exhibited slightly enhanced surface area due to the highly dispersed BiOBr over the ZnO multipods. The fabricated samples displayed hydrophobicity and liquid marble like behaviour due to the presence of PET, while the variations in the percentages of ZnO and BiOBr strongly influenced the water contact angle. The formation of heterojunction between ZnO multipod and BiOBr was confirmed which lead to a shift in the visible light region, increased the light harvesting, and also reduced the charge carrier recombination in the composite sample of 15 %ZnO-5 %BiOBr-80 %PET. The ZnO-BiOBr-PET photocatalysts were tested for the photocatalytic degradation of hexane in a water emulsion and results indicated that 15 %ZnO-5 %BiOBr-80 %PET could degrade 92.1 % of initial hexane, retaining its performance over four successive runs with only an 11.7 % decrease in activity. Scavenger tests revealed that, in addition to hydroxyl radicals, superoxide also played a significant role in the photocatalytic degradation of hexane. This obervations indicate the efficient capturing and utilizing of O2 by this LMP even in non-oxygenated conditions.