Zongsu Wei

Per- and polyfluoroalkyl substances (PFAS) are widely detected in the water environment at levels posing significant risks to the ecosystem and human health. While these “forever chemicals” are considered highly resistant to natural photolysis, this study demonstrates the unexpected decomposition of perfluoroalkyl carboxylic acids (PFCAs) and hexafluoropropylene oxide dimer acid (GenX) under simulated solar light in a catalyst-free environment, with GenX exhibiting up to 49.1% degradation and 21.2% defluorination within 5 h. The probe experiment and electron spin resonance spectroscopy, together with a subpicosecond transient absorption spectrometer, confirm the production of hydrogen radicals from the photoexcitation of water at acidic and neutral pH. The hydrogen radical-driven reactions are inconsistent with the widely proposed hydrated electron-dominated defluorination, and we have theoretically elaborated the PFAS decomposition pathways supported by the identified decarboxylated shorter-chain PFCAs and hydrodefluorinated intermediates in mass spectrometry analysis. It is also concluded that light above 300 nm may degrade PFCAs through a long, continuous photolysis treatment (e.g., >24 h) but is still insufficient for defluorination; instead, the hydrogen radical-driven defluorination is primarily attributed to UV wavelengths below 300 nm. This study contributes a comprehensive and fundamental perspective on PFAS photolysis, and the obtained results will inform new strategies by applying simulated solar light for sustainable PFAS remediation.

Photocatalytic hydrogen evolution and pollutant degradation are both promising strategies for clean energy production and environmental remediation, yet their integration for synchronous wastewater-to-energy conversion is fundamentally hindered by inefficient charge utilization and severe interfacial redox competition. Herein, a quantum-dot-bridged dual-defect interface engineering strategy is developed to synchronize photocatalytic oxidation and hydrogen evolution for wastewater-to-energy conversion. This is realized by constructing Ti3C2 MXene quantum dots anchored on sulfur-vacancy-rich MoS2 coupled with oxygen-defective CeO2 (TMMC), forming a hierarchical S-scheme heterostructure with accelerated interfacial charge transport. The optimized catalyst achieves a hydrogen evolution rate of 12.17 mmol g⁻1 h⁻1 with 98.6% norfloxacin removal and maintains high stability under continuous operation. In pollutant-containing systems, hydrogen production reaches 274.35 μmol g⁻1 h⁻1 and further increases to 405.93 μmol g⁻1 h⁻1 upon low-dose peroxymonosulfate addition. Mechanistically, Ce-O-Mo interfacial coupling induces asymmetric charge redistribution and a built-in electric field for directional carrier separation, while spatially separated sulfur and oxygen vacancies regulate proton reduction and oxidant activation, respectively, mitigating interfacial redox competition. This work establishes defect-coordinated interfacial engineering as a general paradigm for regulating charge utilization and reaction selectivity in integrated photocatalytic systems.

Sustainable biochar materials are promising alternatives to activated carbon for PFAS removal, yet they are facing the same challenges of poor short-chain PFAS capture and low regeneration potential. The diverse biochar properties also complicated the interpretation of PFAS removal mechanisms. To this end, we comprehensively investigated 17 biochar of varying physicochemical characteristics for their adsorption of two legacy long-chain PFAS and two emerging short-chain PFAS. While batch adsorption tests confirmed the importance of hydrophobic/electrostatic interactions, divalent cation (e.g., Ca²⁺) bridging of PFAS anions and biochar surface groups is also found essential. Likewise, micropore filling played a larger role in the adsorption of short-chain PFAS, which were prone to displacement by long-chain PFAS. Finally, spent wheat straw biochar could be effectively reactivated through 900 °C N₂ thermolysis with complete PFAS degradation, which surprisingly enhanced the adsorption of short-chain PFAS in three cycles due to micropore formation. The findings from this study underscore the importance of pore structure and indigenous ionic species in guiding biochar selections for PFAS removal, informing new strategies in the future design and engineering of biochar adsorbents toward both short- and long-chain PFAS.

Per- and polyfluoroalkyl substances (PFAS) are highly resistant to conventional degradation methods due to the exceptional stability of their C-F bonds. As a result, current degradation technologies often rely on high energy inputs and excessive use of additives while largely overlooking strategies that focus on lowering the reaction energy barrier by directly activating PFAS molecules or ions. This Perspective presents a new angle to PFAS degradation by emphasizing the predegradation activation of PFAS molecules. We systematically examine a range of molecular activation mechanisms facilitated by catalyst surface complexation, solvents, salts, and air-water microinterfaces. These methods destabilize PFAS molecules by elongating C-F bonds or altering surface electronic structures and charge distributions, thereby overcoming the activation barriers (ΔG^‡) for subsequent defluorination reactions. Additionally, we outline future directions that incorporate multimodal activation and emerging data technologies, such as intelligent reactor design and machine-learning-guided optimization, with the goal of bridging fundamental molecular insights and practical engineering applications. Molecular activation thus offers a transformative pathway to overcome kinetic and energetic challenges, paving the way for energy-efficient, cost-effective, and broadly applicable solutions to eliminate these persistent "forever chemicals" from the environment.

Advanced oxidation processes involve radical-induced reactions to degrade organic contaminants, and understanding their reaction mechanisms is essential for optimizing and controlling treatment performance. However, the transient nature and complex kinetics of radical systems, characterized by highly branched pathways, make full quantitative mechanism elucidation challenging. Here, the decay kinetics of sulfate and carbonate radicals (SO₄^•- and CO₃^•-) were investigated through direct testing of mechanistic hypotheses against observations from time-resolved spectroscopy with a two-loop self-consistent approach. We found that four elementary reactions (SO₄^•- self-termination and reactions with persulfate PS, H₂O, and hydroxyl radical ^•OH) dominate the decay kinetics of SO₄^•- in UV/PS systems. In the presence of HCO₃^- near neutral solutions, the kinetics of CO₃^•- can be described by its self-termination reaction alone. For comparison, in UV/H₂O₂/HCO₃^- systems, two elementary reactions (CO₃^•- self-termination and its reaction with H₂O₂) dictate the chemical dynamics of CO₃^•-. This differential involvement results in 2 orders of magnitude discrepancy in the CO₃^•- lifetime (9.07 ms and 70.2 μs, respectively) between the two systems. For the first time, direct evidence was presented to discern the elementary reactions involved and quantify the contribution of each elementary reaction to overall radical consumption.

Increased awareness of pervasive per- and polyfluoroalkyl substances (PFAS) contamination and the need for zero-pollution treatment solutions necessitate the scientific and engineering community to respond urgently and systematically. Existing approaches lack reproducible and standardized methods to report the technological treatment capabilities. Consequently, it is difficult to compare innovations and accurately assess their potential. In this Perspective, we shed light on hurdles encountered in the lab-scale research and development of aqueous PFAS destruction technologies with a focus on chemical methods and offer recommendations for overcoming them. Best practices are provided for developing robust PFAS laboratory protocols covering crucial aspects such as experimental planning, sample storage and analysis, and waste management. Further, we present five criteria to standardize reporting on performance and advances in PFAS degrading technologies: 1) scope, 2) defluorination efficiency, 3) relative energy consumption, 4) material stability, and 5) unit process considerations. Through the dissemination of these insights, we aim to foster progress in the development of highly effective treatment solutions.