Green synthesis of spongy Nano-ZnO productive of hydroxyl radicals for unconventional solar-driven photocatalytic remediation of antibiotic enriched wastewater

Herein, novel green/facile approach to synthesize spongy defective zinc oxide nanoparticles (ZnONPs) is presented using for the first time pomegranate seeds molasses as a green capping fuel/reducing mediator during an aqueous solution combustion process. The developed ZnONPs is characterized by UV-Vis. Spectrophotometry and fluorimetry, XRD, Raman spectroscopy, SEM, TEM and BET. Interestingly, pomegranate seeds molasses within a viable content of bio-capping molecules reveal a defective nanoporous ZnO NPs of smaller particle size, greater pore size/volume, and higher surface area compared to the bulky non-biogenic ZnONPs. Moreover, the biosynthesized defective ZnONPs showed narrowed band gap and higher absorption of visible photons that breed higher density of hydroxyl radicals ((OH)-O-center dot) under Solar-illumination. Even further, the bulk ZnO and the biosynthesized ZnO photocatalysts were examined in photodegrading flumequine (FL) antibiotic. The bulk ZnO gives 41.46% photodegradation efficiency compared to 97.6% for the biosynthesized ZnO. In highly acidic or highly alkaline media, FL photodegradability is greatly retarded. Scavenging experiment infers considerable contribution of holes over electrons in photodegradation reaction. The biosynthesized ZnO shows high durability in FL photodegradation after four reusing cycles. These promising findings highlight new insights for biogenic synthesis of tuned size/controlled morphology semiconductor NPs relevant to environmental remediation applications.