Multifaceted advances in TiO2-based photocatalysts for PFAS degradation: a critical review of mechanisms, modifications, and challenges

Abstract

The global persistence of per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals,” poses significant environmental and human health risks, driving regulatory action and intensified research into effective remediation strategies. Photocatalysis has emerged as a promising, sustainable approach for PFAS degradation via light-driven redox processes. Titanium dioxide (TiO₂) remains the benchmark photocatalyst due to its chemical stability, low toxicity, and strong oxidative potential; however, its practical application is limited by rapid electron–hole recombination, restricted visible-light absorption, and pH-dependent surface charge behavior, necessitating acidic conditions for optimal performance. These constraints reduce its efficacy against the robust carbon–fluorine bonds characteristic of PFAS and complicate large-scale deployment. Recent advances focus on multifunctional TiO₂-based systems, including metal and nonmetal doped systems, carbonaceous composites, heterojunctions, molecularly imprinted polymers, and adsorptive concentrate-and-destroy supports. Integration with advanced oxidation and reactor-level engineering approaches, such as photoelectrocatalysis (i.e., photocatalysis under applied bias) and hybrid oxidants, has further advanced photocatalytic degradation technology under broader operating conditions. This review provides a critical comparative assessment of these strategies, highlighting mechanistic insights, structure–activity relationships, and practical limitations related to pH, stability, and scalability. By consolidating recent innovations and operational considerations, this work offers guidance for the rational design of efficient, field-relevant, and sustainable photocatalytic technologies for global PFAS remediation.