Combined adsorption and solar driven photocatalysis processes for the removal of persistent contaminants from water by highly porous nanocomposite aerogels

Abstract

Water is a very important resource for human and ecosystem. However, in recent years the presence of pollutants, such as pharmaceuticals, cosmetics, personal cares, dyes, and pesticides deriving from industrial, agricultural, and human practices is object of growing concern as these substances persist in the environment and are not removed by wastewater treatment plants (WWTPs). In fact, the latter are among the main sources of such pollution since they are not designed to remove persistent organic contaminants that are eventually discharged into receiving water bodies. Thus, many substances, their metabolites and/or transformation products once in the environment, can propagate through different environmental compartments or can accumulate in plants and others organism posing a risk to the environment and human health, as the ecotoxicological effects of the presence of these molecules in the environment are often unknown. Advanced oxidation processed (AOPs) are the most promising techniques that could solve this problem. In fact, during AOPs processes are generate hydroxyl radicals (OH•) highly reactive and capable of oxidising these contaminants. Among all these processes, heterogeneous photocatalysis has been widely investigated for this purpose due to its ability to mineralize many organic compounds using the solar light as light source. The photocatalysts is generally dispersed in a slurry reactor as suspended powder resulting in disadvantages, such as the necessity to separate particles from the treated water, the damage of the recirculation pumps used for the process and toxicity problems related either to the release of the metal in solution or to the generation of by-products or intermediates that are more toxic than the starting materials. Therefore, possible solutions could include dispersing the photocatalyst into highly porous nanocomposite aerogels (HP-NcAs) and conducting ecotoxicological experiments to assess the materials and solutions compatibility undergoing photocatalytic treatment. The process will be then optimised to develop a sustainable, low environmental impact technology for the degradation of organic pollutants using UV, VIS and sunlight. The HP-NcAs are easy-to-handle, highly efficient composite materials to be used as an alternative to conventional catalysts in solar driven-photocatalysis with the benefit of maximising the specific photo-activatable surface area compared with other media (ceramics, films and sponge) and preventing the nanoparticles aggregation in aqueous matrix. Therefore, in this work, aerogel/photocatalyst composite systems based on syndiotactic polystyrene (sPS) and semiconductors such as N-TiO2 (NdT), ZnO, ZnO/NdT and Fe0-ZnS were prepared and tested in the degradation processes of model pollutants, such as atrazine (ATZ), thiacloprid (THI) and tetrachloroethylene (PCE) under UV, Visible and solar irradiation. In addition, ecotoxicological experiments were carried out to evaluate the adverse toxicity effects of materials and solutions generated by the degradation process. [edited by Author]