V workshop on oxide based materials

Fe3O4 was prepared and stabilized in nanometric size using a bio-organic substance (BOS) extracted from compost of green and food waste [1]. BOS (namely CVT230 type) was previously characterized in term of composition, functional groups, average molecular weight and size, and it evidenced photocatalytic properties (tested in homogeneous reactions) and surfactant behaviours given by the simultaneous presence of apolar fragments and functional groups such as COOH, Ph-OH, and so on. These groups modify their charge depending on working pH, thus modifying their interaction with polar and/or charged substrates. This feature was used to form a stable interaction with a cationic dye (Crystal Violet, CV) in order to test the possibility of capturing a potential cationic pollutant via adsorption mechanism and, subsequently, to test its photocatalytic abatment. The synthesis of BOS- Fe3O4 samples, containing different amounts of organic species, was carried out following a procedure already developed with humic substances [2] in order to obtain crystalline, regularly shaped and sized magnetic iron oxide, whose magnetic properties were tested through magnetization measurements. Materials characterization was carried out through gas-volumetric N2 adsorption at 77K to study specific surface area and porosity, X-Ray Diffraction to confirm the presence of Fe3O4 phase, Scanning and High-Resolution Electron Microscopies to check crystalinity, particles size and aggregation, Energy-dispersive X-ray spectroscopy to check the elemental composition of the outermost layer of the materials, Thermo-Gravimetric Analysis to quantify the biosurfactant amount present in the materials, FTIR spectroscopy (ATR mode) to check the vibrational features of materials. Dye adsorption carried out at 25°C indicates that adsorption is almost irreversible, and depends strongly on working pH (the adsorbed amount increases sharply in the pH interval between 9 and 10). The photocatalytic properties of BOS species were tested in a Pyrex stirred batch reactor (500 mL) equipped with a medium pressure 125W mercury lamp surrounded by a Pyrex glass jacket in which circulated cooling water keeping the temperature inside the reactor constant (25°C). Samples were irradiated under continuous gas (air or nitrogen) bubbling in order to keep the suspension stable. At various reaction times fixed amount of suspension were sampled, the nanoparticles were magnetically separated and the CV left in solution was evaluated by means of UV-vis spectroscopic measurements. The obtained results evidence a CV abatement of more than 40% after 13 hours of irradiation, thus encouraging further investigation in this direction.