Green nanomaterials from Orange Peel Waste: chemical sensing applications and environmental remediation

Water pollution is a major environmental problem that represents a threat to human health and the natural ecosystem. Wastewater contains a wide variety of pollutants that include heavy metals, dyes, microorganisms, pharmaceuticals and other complex organic compounds. Conventional technologies used for wastewater treatment present major drawbacks, such as high operational costs, low efficiency and rigidity of use. Therefore, new innovative methods that can surpass these limitations are a major topic of research in environmental sciences. An interesting topic of research is the use of waste products in the optic of a green and circular economy, with the purpose of reusing and valorizing waste for the creation of alternative treatments for wastewater. One of these waste products is the orange fruit peel, and its properties and uses have been extensively explored in this study for many different applications. Orange wastes have increasingly been re-evaluated in the last years in an optic of circular economy to extract valuable compounds with important biological properties. In this PhD research work, the focus was to recover some of the valuable compounds contained in orange peel waste such as organic acids and flavonoids, that have a strong reducing power, and to apply them to various environmental preservation strategies. The orange peel waste was used to produce a water extract that was employed for the synthesis of three groups of green nanomaterials: plasmonic nanoparticles (Au, Ag) that were used as colorimetric sensors for heavy metal ions in water; carbon-based nanomaterials (OPE-rGO, OPE- rGO@AgNPs) that demonstrated powerful adsorbents for cationic dyes; nano iron oxides (Fe3O4- OPE) with adsorbent and photocatalytic properties, that were applied in Advanced Oxidation Processes such as Photo-Fenton reactions.