Nanoparticle-assisted Photocatalytic and SonoPhotocatalytic treatment of contaminated industrial wastewater

Textile wastewater represents one of the major sources of water pollution worldwide due to its high content of organic compounds, surfactants, and, most notably, synthetic dyes. These molecules, characterized by high chemical stability and low biodegradability, are responsible for the persistent coloration of the effluents and may cause toxic and ecotoxicological effects on aquatic ecosystems. Therefore, the efficient removal of dyes from textile effluents remains a critical environmental and technological challenge. Following this purpose, this Master Thesis work investigated the degradation of textile dyes exploiting photocatalysis and photosonocatalysis. Among different photocatalysts, nanoparticles (NPs) of ZnO capped with oleic acid (Ol-ZnO) were chosen because of their good photocatalytic activity, non-toxicity and low price. NPs were synthetized via the co-precipitation method and subsequently characterized to well know their hydrodynamic diameter and Zeta potential. First tests investigated the adsorption of six different dyes, provided by a dyeing company, on the nanoparticles. The quantitative results clearly highlight the remarkable efficiency of Ol-ZnO nanoparticles in removing dyes from aqueous solutions. ZnO wide band limits its catalytic capability within the absorption of the UV spectrum and causes fast electron–hole recombination. For this reason, first degradation studies were conducted on six different dyes from the same dyeing company, using a specific lamp which could emit radiation with a high UV content. Aiming to develop an innovative and sustainable process able to degrade textile dyes, studies were focused on the use of a different lamp which can simulate solar light, with its precise UV radiation percentage (around 4%). The effect of the starting concentration was investigated and each test was carried out for three hours to better understand nanoparticles behavior over time. Results were obtained by analyzing the samples with a spectrophotometer, coupled with specific calibration curves previously prepared for each dye. Therefore, dyes which showed worst degradation under solar light were tested investigating the synergy between luminous radiation and ultrasound. The device used to generate ultrasound let us explore the effects of different intensities on the solutions containing dyes and nanoparticles, useful to find the best conditions of the process. Lastly, all the results were compared to understand which degradation process could be deeper investigated aiming to find an innovative and sustainable way of treating textile industries wastewater.