Toward Sustainable Photocatalysis: Addressing Deactivation and Environmental Impact of Anodized and Sol–Gel Photocatalysts

Abstract

Photocatalysis is proposed as an environmentally friendly technology that exploits solar light for environmental purification. While its effect on treated effluent quality is indeed positive, studies on its overall environmental profitability generally disregard the fact that photocatalytic materials may themselves generate pollution in their production, use, and end-of-life phases. This work addresses two distinct methods for titanium dioxide (TiO2) photocatalytic coatings preparation, that is, chemical –sol–gel, associated with spray coating– and electrochemical –anodic oxidation, which generates the oxide directly from a titanium substrate. Oxides are tested in the photocatalytic decomposition of tetracycline, an antibiotic commonly found in water. Both distilled and tap water are used as matrices. Coatings are tested multiple times to simulate real operating conditions, until photocatalytic activity is compromised. Life Cycle Assessment (LCA) is then used to quantify and compare the potential environmental impacts associated with the two different TiO2 production strategies. Eventually, the assessment is completed by considering full photocatalyst regeneration: while for Sol–Gel this only implies cleaning and re-deposition, anodizing required oxide detachment, and subsequent re-anodization. The process of oxide removal and re-anodizing, although invasive and titanium consuming, is repeated 20 times without significant loss of photocatalytic efficiency, indicating robustness and suitability for technology transfer.