Degradation and mineralization of oxytetracycline in pure and tap water under visible light irradiation using bismuth oxyiodides and the effect of depositing Au nanoparticles

Abstract

Different bismuth oxyiodide materials (BiOI, Bi4O5I2,Bi7O9I3and Bi5O7I) were synthesizedviathe solvothermalmethod. For BiOI, microspheres (M.S.) and nanocrystals were obtained. Decrease in the iodine loading wasachieved by varying the synthesis conditions, such as the solvent, temperature and heating time. Gold metallicnanoparticles were deposited on the surface of the BixOyIzmaterialsviathe deposition–precipitation route. Thephysical, chemical, optic and electrochemical properties of the obtained materials were assessed and compared,finding notable structural and optoelectric changes as the loading of iodine decreased in the semiconductor. Infact, lessening the iodine loading resulted, not only in the increase of the band gap value, but in the shift of thevalence band toward more oxidative potential. In contrast, no changes in the semiconductor properties of theBixOyIzmaterials were observed upon the deposition of metallic Au nanoparticles. Regarding the photocatalyticactivity, the use of BiOI M.S. led to the highest degradation and mineralization rate of the antibiotic oxyte-tracycline (OTC) upon 5 h of visible light irradiation. Deposition of Au nanoparticles reduced the photo activityof the materials, even when low metal loadings were tested. BiOI M.S. showed certain stability throughout threeconsecutive reactions cycles. High photocatalytic performance was observed when environmentally relevantconditions–i.e., tap water and Co=50μg/L–were tested. Through mass spectrometry some degradation in-termediaries were identified and a photocatalytic degradation route of OTC was proposed