Nanomaterial-Based Advanced Oxidation/Reduction Processes for the Degradation of PFAS

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.

Internal electric field triggered charge redistribution in CuO/Fe2O3 composite to regulate the peroxymonosulfate activation for enhancing the degradation of organic pollutants

Herein, we adopt a feasible method to synthesize the CuO/Fe2O3 composite with heterostructure. Owing to the significant differences in work functions, an internal electric field is built at the interface of heterojunction after the combination of CuO with Fe2O3, which can reduce interface resistance and accelerate charge transfer. Interestingly, under the induction of electrostatic interaction provided by internal electric field, the CuO/Fe2O3 composite will form electron-rich and electron-deficient active zones. More importantly, the peroxymonosulfate (PMS) can be oxidized by the CuO with electron-deficient active zone to generate SO5•‒, subsequently converting into 1O2. Meanwhile, the Fe2O3 component with electron-rich active zone can provide electrons for PMS to achieve the heterolysis of Fe-O-O, thereby producing the high-valent metal complex (namely ≡ Fe5+=O). Consequently, the CuO/Fe2O3-2-mediated PMS system with good anti-interference ability displays excellent performance in wastewater treatment. Benefiting from the electrophilic reaction of 1O2 and ≡ Fe5+=O, various typical organic pollutants can be ultimately mineralized into CO2, H2O and other nontoxic by-products by the CuO/Fe2O3-2-mediated PMS system. In short, current work shares some novel insights into the effect of internal electric field on PMS activation, which can provide valuable references for future research.

Dual action of non-metal doped C2N and Ti3C2T2 heterojunction enhances the catalytic activity of electrochemical simultaneous oxidation of hydrogen peroxide and peroxymonosulfate:A theoretical study

Electrochemical advanced oxidation processes (EAOPs) are energy-efficient methods for generating activated radicals like HO• and SO4•-, which enable the degradation of difficult-to-mineralize chlorinated organic compounds. This study explored the catalytic activity and reaction mechanism of EAOPs under a dual strategy involving non-metal doped C2N (X@C2N (X = O, F, Si)) and a heterostructured build (X@C2N/Ti3C2T2) using first principles calculation. The non-metal doping and the heterojunction construction can make H2O2 and PMS spontaneously adsorb (Eads < 0), with negative Gibbs free energy for their oxidation to HO• and SO4•-, significantly enhancing catalytic activity. The catalytic activity of the X@C2N catalysts was in the order of O@, F@, and Si@C2N. The loading of Ti3C2T2 improved the stability and activity of the material, while Ti3C2F2 and Ti3C2O2 proved superior as heterojunction carriers compared to Ti3C2(OH)2. Notably, O@C2N/Ti3C2F2 is proved to be an appropriate catalyst for simultaneous hydrogen peroxide (ΔGmax = -0.90 eV) and peroxymonosulfate (ΔGmax = -0.99 eV) oxidation reactions, achieving non-selective generation of oxidants in electrochemistry. 2,4-D can be effectively degraded by surface-generated HO• and SO4•-, with the reactivity of SO4•- towards 2,4-D greater than that of HO•. This research highlights the potential of combining heteroatom doping with heterojunction catalyst formation to enhance EAOPs for environmental remediation.

Mobilization of poly- and perfluoroalkyl substances (PFAS) from heterogeneous soils: Desorption by ethanol/xanthan gum mixture

Remediating soils contaminated by per- and polyfluoroalkyl substances (PFAS) is a challenging task due to the unique properties of these compounds, such as variable solubility and resistance to degradation. In-situ soil flushing with solvents has been considered as a remediation technique for PFAS-contaminated soils. The use of non-Newtonian fluids, displaying variable viscosity depending on the applied shear rate, can offer certain advantages in improving the efficiency of the process, particularly in heterogeneous porous media. In this work, the efficacy of ethanol/xanthan mixture (XE) in the recovery of a mixture of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), and perfluorobutane sulfonate (PFBS) from soil has been tested at lab-scale. XE's non-Newtonian behavior was examined through rheological measurements, confirming that ethanol did not affect xanthan gum's (XG) shear-thinning behavior. The recovery of PFAS in batch-desorption exceeded 95 % in ethanol, and 99 % in XE, except for PFBS which reached 94 %. 1D-column experiments revealed overshoots in PFAS breakthrough curves during ethanol and XE injection, due to over-solubilization. XE, (XG 0.05 % w/w) could recover 99 % PFOA, 98 % PFBS, 97 % PFHxS, and 92 % PFOS. Numerical modeling successfully reproduces breakthrough curves for PFOA, PFHxS, and PFBS with the convection-dispersion-sorption equation and Langmuir sorption isotherm.

IMPACT: Innovative (nano)Materials and processes for advanced catalytic technologies to degrade PFOA in water

We hereby report the development of a novel electrochemical method to degrade perfluorooctanoic acid (C7F15COOH, PFOA). At the center of the approach are bimetallic Pd-Ru nano-catalyst materials called IMPACT: Innovative (nano)Materials and Processes for Advanced Catalytic Technologies. IMPACT uses flavonoid-sequestered Pd-Ru, allowing the development of specialized electrodes with tunable properties to sequentially degrade PFOA in wastewater samples into a sustainable byproduct via an indirect electrochemical method. Electron transfers at RuOxHy species stabilize the Pd component of the nano-catalysts, enabling the degradation process via PFOA deprotonation, chain shortening, decarboxylation, hydrolysis, fluoride elimination, and CF2 flake-off mechanism. IMPACT enabled the observation of redox peaks at -0.26 V and 0.56 V for the first time, with accompanying reduction peaks at -0.5V and 0.29 V, respectively. These redox peaks, which correlated with the concentrations of PFOA (20, 50, 100, 200, and 400. mg L-1), were verified and confirmed using electrochemical simulations. Control experiments did not show degradation of PFOA in the absence of Pd-Ru nano-catalyst. The degradation in wastewater was obtained within 3 h with an efficiency of 98.5%. The electrochemical degradation products of PFOA were identified using High-resolution desalting paper spray mass spectrometry (DPS-MS) and collision-induced dissociation (CID) analysis. The results yielded C2F5COOH, C3F7COOH, and C6F13OH with dissociation losses of CF2O or CO2. IMPACT introduces a novel nano-catalyst with high efficiency and a reliable capability that defluorinates strong C-F bonds that are components of recalcitrant organics in myriad environmental matrices.

Preparation of Cobalt-Nitrogen Co-Doped Carbon Nanotubes for Activated Peroxymonosulfate Degradation of Carbamazepine

Cobalt-nitrogen co-doped carbon nanotubes (Co3@NCNT-800) were synthesized via a facile and economical approach to investigate the efficient degradation of organic pollutants in aqueous environments. This material demonstrated high catalytic efficiency in the degradation of carbamazepine (CBZ) in the presence of peroxymonosulfate (PMS). The experimental data revealed that at a neutral pH of 7 and an initial CBZ concentration of 20 mg/L, the application of Co3@NCNT-800 at 0.2 g/L facilitated a degradation rate of 64.7% within 60 min. Mechanistic investigations indicated that the presence of pyridinic nitrogen and cobalt species enhanced the generation of reactive oxygen species. Radical scavenging assays and electron spin resonance spectroscopy confirmed that radical and nonradical pathways contributed to CBZ degradation, with the nonradical mechanism being predominant. This research presents the development of a novel PMS catalyst, synthesized through an efficient and stable method, which provides a cost-effective solution for the remediation of organic contaminants in water.