Algal synthesis of ZnO-NPs: Effect of the synthesis parameters in the characteristics and properties of the nanomaterial

The Zinc Oxide Nanoparticles (ZnO-NPs) are a semiconductor material used in medicine, cosmetic, food, ceramics, manufacturing and electronics with high relevance in terms of their adsorption, photocatalytic, fluorescence, antimicrobial and toxicological properties. These properties of ZnO-NPs depend of morphological characteristics given by the methods and synthesis parameters. ZnO-NPs obtained by green synthesis using algae can exhibit different physicochemical characteristics and properties. The present review identifies and discusses the main parameters that affect the morphological characteristics and physicochemical properties of ZnO-NPs by using algae. The review includes available information in web of science database, where algal synthesis of ZnO-NPs haven been reported in thirty-three extracts of different species of algae using four zinc salts. Based on literature, it was possible to identify that pH, biological and inorganic precursors are the main parameters that affect the size, shape, and coating of nanoparticles, although other parameters also affect the morphology of ZnO-NPs such as the temperature, reaction time, drying and calcination, as well as the concentration of precursors but more research is needed to evidence their role and/or mechanisms. An important finding during review was the scarce information about the type of bioactive compounds, mechanisms, and reactions involved in algae synthesis of ZnO-NPs; having information will allow a better understanding of the synthesis parameters on the morphological characteristics of nanoparticles and the relationship between them and the properties of ZnO-NPs.