Formation, properties and applications of microalgae-based ZnO nanoparticles: A review

ZnO nanoparticles have many unique electronic, photonic, spintronic properties, and hence, they have been multifunctionally utilized. However, the synthesis of ZnO nanoparticles still has limits since additional chemicals, e.g., alkalis, surfactants, oxidants, or complex procedure are required. Recently, an emerging trend of green synthesis of ZnO nanoparticles without these additives has been developed. Microalgae are renewable, sustainable and economical freshwater/marine micro-organisms that can supply valuable bio-components such as phenols, tannins, alkaloids, sterols, saponins, flavonoids, tocopherols. These compounds play a reducing/chelating/capping role in the formation of green ZnO nanoparticles. Here, we review the formation, properties and applications of microalgae-based ZnO nanoparticles. Due to the biological substances present in microalgae, ZnO nanoparticles have outstanding qualities such as small size, diverse morphology, high zeta potential and chemical surface with many functional groups. Possessing these favorable characteristics, green ZnO nanoparticles have demonstrated good performance in wastewater treatment, antibacterial activity and anti-cancer performance. It is expected that microalgae-based ZnO nanoparticles not only open prospects in environmental and biomedical applications but also in sustainable agriculture and plant disease control.