Galvanic wastewater as a sustainable precursor of multi-purpose nanoparticles

Electroplating allow to deposit a thin metal film coating on other metal item using special baths containing not just metal salts, but a wide range of organic and inorganic components used mainly to improve the quality of the deposition and the stability of the bath. Once the baths are used they still contain a lot of metal salt and complexes, alongside the organic and inorganic additives, which might cause serious environmental hazards, as this waste need to be stock in special landfills with high probability of contamination of the surrounding environmental compartments such as soil and aquifers. The main objective of this Ph.D. is to use this waste as a precursor in order to synthesize nanoparticles with a technique called ”continuous hydrothermal flow synthesis”, or in short, ”CHFS”, a green synthesis method that employs supercritical water to decompose the metal precursor in order to form metal or metal oxide nanoparticles; the synthesis can be performed with other components called ”modifiers” that allow to change the properties of the nanoparticles such as size and shape. In this case therefore, this method is not only a simple synthesis, but at the same time it is a remediation method for galvanic wastewater. CHFS synthesis have been evaluated using both noble reagents, such as silver acetate and triethanolamine titanate for silver and titanium dioxide nanoparticles respectively. Copper and silver based wastewater were subsequently used for the synthesis of silver metal and copper (II) oxide nanoparticles. All the synthesized nanoparticles were used to deposit thin films with a deposition technique called ultrasonic spray coater, which use ultrasounds to nebulize the nanoparticles suspension which is directed on the substrate by a flow of compressed air; the solvent is evaporated by the heat released by a hotplate on which the substrate is placed. Electrically conductive thin films have been deposited using silver metal and copper (II) oxide nanoparticles, while titanium dioxide have been used to deposit thin films to which the haze was assessed via transmittance measures performed with an UV-VIS spectrophotometer equipped with an integrating sphere.