Antibiotics are pervasive contaminants in aqueous systems that pose an environmental threat to aquatic life and humans. Typically, antibiotics are developed to counteract bacterial infections; however, their prolonged and excessive use has provoked unintended consequences. The presence of excessive amounts of antibiotics and anti-inflammatory, anti-depressive, and contraceptive drugs in hospital and industrial wastewater poses a significant threat to the ecosystem, with groundwater containing drug concentrations of <1 mg/L to hundreds of µg/L. According to the literature, 33,000 people die directly from drug-resistant bacterial infections in Europe annually, which costs EUR 1.5 billion in health care and productivity loss. Consequently, the continuous spread of antibiotics in the ecosystem has led to greater interest in developing a sustainable method for effective antibiotic removal from wastewater. This critical review aims to present and discuss recent advances in the photocatalytic degradation of widely used drugs by ZnO-based nanostructures, namely (i) antibiotics; (ii) antidepressants; (iii) contraceptives; and (iv) anti-inflammatories. This study endows a comprehensive understanding of the degradation of antibiotics using ZnO-based nanomaterials (bare, doped, and composites) for effective treatment of wastewater containing antibiotics. In addition, the operational conditions and mechanisms involved during the photocatalytic degradation process are systematically discussed. Finally, particular emphasis is devoted to future challenges and the corresponding outlook with respect to toxic effects following the utilization of ZnO-based nanomaterials.

Tricobalt tetraoxide (Co₃O₄), a spinel-structured nanoparticle which possesses mixed oxidation states, has been synthesized via a Punica granatum (P. granatum, pomegranate) seed extract-mediated green reaction and has been investigated for its superior catalytic activity in three applications, which include (i) photodegradation of textile dye effluents (TDE) collected from the dyeing industry, Tiruppur, Tamil Nadu, India, (ii) catalytic hydrogenation of nitro-aromatic pollutants such as 4-nitrophenol and 4-nitroaniline, and (iii) antibacterial potential in biomedical applications. Prior to the application studies, the synthesized Co₃O₄ spinel nanoparticles (Co₃O₄-NPs) were characterized by well-known established techniques such as X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), and Raman and FT-IR spectroscopies. We have also discussed the probable mechanism and kinetic studies of the catalytic activity of the Co₃O₄-NPs. Finally, we concluded that the design and development of novel, economic and green synthesis-mediated catalysts such as Co₃O₄-NPs can exhibit efficient catalytic activity in diverse fields, which is necessary for environmental remediation.