Eco-Friendly ZnO Nanomaterial Coatings for Photocatalytic Degradation of Emerging Organic Pollutants in Water Systems: Characterization and Performance

The present study targets key limitation 'separation after the process' that is responsible for the loss of the photocatalyst in water treatment during heterogeneous photocatalysis. Therefore, eco-friendly nanostructured ZnO coatings were engineered by the doctor blade technique through the immobilization of green ZnO nanomaterials onto alumina substrate. ZnO/BPE 30 and ZnO/BPE 60 coatings were obtained from banana peel extract-based ZnO powder (ZnO/BPE). Likewise, ZnO/GTE 30 and ZnO/GTE 60 were prepared using green tea extract-based ZnO powder (ZnO/GTE). XRD characterization verified hexagonal wurtzite ZnO phase, while HRSEM analysis revealed that the flat surface of ZnO/BPE had rod-like nanostructures below 120 nm, and ZnO/GTE had spherical, porous nanoparticle networks with less than 70 nm. According to UV-vis spectrometry, all four coatings have bandgaps of ~5 eV. The highest efficiency for the solar-driven photocatalytic degradation of emerging organic pollutants was for ciprofloxacin (among pesticides clomazone and tembotrione; pharmaceuticals ciprofloxacin and 17α-ethinylestradiol; and mycotoxin zearalenone) in ultrapure water with the presence of all studied ZnO-based coatings, after 60 min of simulated solar irradiation. Its highest removal (89.1%) was achieved with ZnO/GTE 30, also having good reusability across three consecutive cycles in river water, thus supporting the application of eco-friendly, immobilized ZnO nanomaterials for wastewater treatment and environmental remediation.