ROS-Mediated Aquaculture Wastewater Remediation Using TeO.sub.2-Deposited ZnO Nanotubes

The current study focuses on utilizing TeO.sub.2-deposited ZnO nanotubes fabricated via a solution-free thermo-mechanical method for aquaculture wastewater remediation. The phase, crystallite size, and morphological studies of the fabricated TeO.sub.2-deposited ZnO nanotubes were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD of TeO.sub.2-deposited ZnO nanotubes (0.5 wt%, 3 wt%, 5 wt%) exhibited crystallite size of 10-20 nm. FE-SEM shows that TeO.sub.2 nanoparticles are uniformly deposited on the surface of ZnO. The photocatalytic studies confirm the higher photocatalytic activity of 3 wt% and 5 wt% TeO.sub.2-deposited ZnO (about 90% and 94.5%) and 80% for pristine ZnO towards the photodegradation of 2,4-dichlorophenol in aqueous medium under both UV and sunlight. The antibacterial activity of synthesized samples was investigated against Gram-positive (Bacillus subtilis MTCC 441 strain) and an aquatic fish pathogenic Gram-negative (Aeromonas salmonicida strain MTCC 1522) bacteria applying the disc diffusion method. This assay showed that 5 wt% TeO.sub.2-deposited ZnO exhibited excellent antibacterial activity compared to pristine ZnO NPs. Reactive oxygen species (ROS) determination assay confirmed that the 2,4-dichlorophenol degradation by TeO.sub.2-deposited ZnO was due to the generation of superoxide radicals. The mechanism of both pollutant degradation and antimicrobial activity is studied in terms of scavenging of produced ROS in the aqueous medium by a scavenger test using histidine and ascorbic acid. The reusability of the TeO.sub.2-deposited ZnO nanotubes was also studied, and it showed stability up to three cycles with a negligible loss of efficiency. The synthesized materials could also be applicable for preparation of electrochemical devices to track bacteria.