Semiconductor-hydrophobic material interfaces as a new active site paradigm for photocatalytic degradation of perfluorocarboxylic acids

Photocatalytic innovations in PFAS removal: Emerging trends and advances

Per- and polyfluoroalkyl substances (PFAS), such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), are persistent environmental pollutants posing significant risks to ecosystems, drinking water safety, and human health. Conventional PFAS removal methods effectively mitigate contamination but face challenges such as high operational costs, energy demands, and secondary waste production. Photocatalytic methods have emerged as a promising alternative, utilizing light-activated semiconductors to generate reactive oxygen species (ROS), which facilitate the efficient degradation of PFAS into non-toxic byproducts. Advanced photocatalysts, such as titanium dioxide (TiO2), demonstrate significant potential under UV and visible light, though challenges remain, including low activity under visible light, rapid recombination of photogenerated electron-hole pairs, and inefficient carrier utilization. To address these limitations, strategies such as non-metal and metal doping and combining wide- and narrow-bandgap semiconductors have been explored to enhance light absorption, photocatalytic efficiency, and stability. Recent developments in photocatalysts, including PMR technology (80 % PFOA removal in 2 h) (Junker et al., 2024b), Bi4O7-modified Ga2O3 (59.6 % defluorination) (Chen et al., 2024), and lead-doped TiO2/rGO (98 % PFOA removal in 24 h) (Chowdhury and Choi, 2023), have improved PFAS degradation by optimizing light absorption, charge separation, and surface adsorption. Hybrid systems integrating photocatalysis with other treatment methods, such as adsorption and electrochemical oxidation, offer a path toward sustainable, efficient PFAS remediation. This review explores the latest advancements in photocatalytic technologies and highlights future directions, including the development of cost-effective, environmentally friendly materials and field-scale validation. These efforts emphasize the potential of photocatalysis as a cornerstone in achieving sustainable water treatment solutions and protecting environmental and public health.

A review on the advancement in photocatalytic degradation of poly/perfluoroalkyl substances in water: Insights into the mechanisms and structure-function relationship

Poly/perfluoroalkyl substances (PFAS) are persistent organic pollutants and ubiquitous in aquatic environment, which are hazardous to organisms and human health. Several countries and regions have taken actions to regulate or limit the production and emission of some PFAS. Even though a series of water treatment technologies have been developed for removal of PFAS to eliminate their potential adverse effects, the removal and degradation performance are usually unsatisfactory. Photocatalytic degradation of PFAS is considered as one of the most effective approaches due to the mild operation conditions and environmental friendliness. This review systematically summarized the recent advances in photocatalytic degradation of PFAS based on heterogeneous photocatalysts, including TiO2-, Ga2O3-, In2O3-, ZnO-, Bi-based, and others. Overall, two mainly degradation mechanisms were involved, including photo-oxidation (involving the holes and oxidative radicals) and photo-reduction types (by e- and reductive radicals). The band structures of the photocatalysts, degradation pathways, structure-function relationship, and impacting factors were further discussed to elucidate the essential reasons for the enhanced degradation of PFAS. Furthermore, the review identified the major knowledge gaps to solve the issues of photocatalysis in real application. This paper also propounded several strategies to promote the design and optimization of high-efficient photocatalysts, and meet the challenges to remove PFAS through photodegradation technologies.

Efficient photocatalytic degradation of perfluorooctanoic acid by bismuth nanoparticle modified titanium dioxide

Perfluorooctanoic acid (PFOA) is potentially toxic and exceptionally stable attributed to its robust CF bond, which is hard to be removed by UV/TiO2 systems. In this research, bismuth nanoparticle (Bi NP) modified titanium oxides (Bi/TiO2) were synthesized by a simple photochemical deposition-calcination method and were applied as photocatalysts for the first time to degrade PFOA. The removal rate of 50 mg/L PFOA reached 99.3 % with 58.6 % defluorination rate after 30 min of irradiation via a mercury lamp. Bi/TiO2 exhibited superior performance in PFOA degradation compared to commercial photocatalysts (TiO2, Ga2O3, Bi2O3 and In2O3). In addition, Bi/TiO2 showed high degradation activity under actual sunlight, achieved 100 % removal rate and 59.3 % defluorination rate within 2 h. Bi NPs increase the light trapping ability of Bi/TiO2 and promote the separation of photogenerated electron-hole pairs via local surface plasmon resonance (LSPR) effect, which results in more photogenerated holes (h+) and hydroxyl radicals (OH). Combined with DFT calculations and intermediate detections, the degradation reaction is initiated from the oxidation of the PFOA carboxyl group via h+, followed by the loss of the CF2 unit step by step with the participation of OH. This work presents a novel approach for the practical implementation of TiO2-based photocatalysts to achieve highly efficient photocatalytic degradation of perfluorocarboxylic acids (PFCAs).

Photocatalysts for chemical-free PFOA degradation - What we know and where we go from here?

Perfluorooctanoic acid (PFOA) is a toxic and recalcitrant perfluoroalkyl substance commonly detected in the environment. Its low concentration challenges the development of effective degradation techniques, which demands intensive chemical and energy consumption. The recent stringent health advisories and the upgrowth and advances in photocatalytic technologies claim the need to evaluate and compare the state-of-the-art. Among these systems, chemical-free photocatalysis emerges as a cost-effective and sustainable solution for PFOA degradation and potentially other perfluorinated carboxylic acids. This review (I) classifies the state-of-the-art of chemical-free photocatalysts for PFOA degradation in families of materials (Ti, Fe, In, Ga, Bi, Si, and BN), (II) describes the evolution of catalysts, identifies and discusses the strategies to enhance their performance, (III) proposes a simplified cost evaluation tool for simple techno-economical analysis of the materials; (IV) compares the features of the catalysts expanding the classic degradation focus to other essential parameters, and (V) identifies current research gaps and future research opportunities to enhance the photocatalyst performance. We aim that this critical review will assist researchers and practitioners to develop rational photocatalyst designs and identify research gaps for green and effective PFAS degradation.