# Light-Induced Advanced Oxidation Processes as PFAS Remediation Methods: A Review
###### Abstract  
PFAS substances, which have been under investigation in recent years, are certainly some of the most critical emerging contaminants. Their presence in drinking water, correlated with diseases, is consistently being confirmed by scientific studies in the academic and health sectors. With the aim of developing new technologies to mitigate the water contamination problem, research activity based on advanced oxidation processes for PFAS dealkylation and subsequent mineralization is active. While UV radiation could be directly employed for decontamination, there are nevertheless considerable problems regarding its use, even from a large-scale perspective. In contrast, the use of cheap, robust, and green photocatalytic materials active under near UV-visible radiation shows interesting prospects. In this paper we take stock of the health problems related to PFAS, and then provide an update on strategies based on the use of photocatalysts and the latest findings regarding reaction mechanisms. Finally, we detail some brief considerations in relation to the economic aspects of possible solutions. PFAS substances; emerging contaminants; water decontamination; photocatalysts; advanced oxidation processes +
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In recent years, different technologies have been developed aiming to purify water contaminated with PFAS compounds. Photolysis has been considered but given the C-F bond strength of around 480 kJ/mol [7], impractical wavelengths shorter than 250 nm are needed to drive efficient cleavage. Physical adsorption and redox process have been also investigated. Physical adsorption processes using powdered activated carbon (PAC) and granulated activated carbon (GAC) are the most studied and used techniques for PFAS removal from water. These techniques present the limitation of only transferring PFAS molecules from one medium to another, and therefore require further treatments downstream [5]. In this respect, redox processes present potential advantages towards PFAS degradation, enforcing continuous defluorination of the chain and thus featuring degradation to shorter and safer molecules and ultimately to mineralization [1; 3; 8]. Several efforts to develop cost-effective photocatalytic pathways are currently under investigation, although the overall photocatalytic defluorination and degradation mechanisms are quite complex and still need to be detailed. Novel photocatalytic materials in combination with various illumination sources have been tested for PFAS degradation, with relevant results. High degradation and defluorination efficiencies were achieved in neutral pH conditions, with photocatalyst materials (such as In\({}_{2}\)O\({}_{3}\) nanoporous nanospheres [9; 10] and Ga\({}_{2}\)O\({}_{3}\) needle- and sheaf-like nanostructures [11]) which have drawbacks in terms of biocompatibility, availability, and cost. So far, the most likely solutions rely on the use of either Fe\({}^{2+}\)/H\({}_{2}\)O\({}_{2}\) or TiO\({}_{2}\)/O\({}_{3}\) combined with UV light under acidic pH [5]. The challenge here relies on the development of low-toxicity, efficient, and cost-effective materials preferably featuring an optical energy gap compatible with the near UV-visible range (between 350 and 500 nm), therefore providing the possibility of employing lower-cost radiation sources such as artificial visible light illumination, or concentrated sunlight, a clean and renewable resource. In this review, an analysis of current literature on the applications of advanced oxidation processes for PFAS remediation in water is proposed, focusing on the materials and methods employed with an eye on economic viability. This report starts with a brief overview of PFAS applications and environmental and health concerns, as well as a comparison of conventional vs. emerging treatment methods and related analytical techniques.