Adsorption of perfluorooctanoic acid from water by pH-modulated Brönsted acid and base sites in mesoporous hafnium oxide ceramics

Antioxidant system alterations and oxidative stress caused by polyfluoroalkyl substances (PFAS) in exposed biota: a review

Contamination of aquatic and terrestrial organisms by Perfluoroalkyl substances (PFAS), emerging contaminants, is widespread, as these compounds are present in water, soil, air, and food, owing to their environmental persistence. PFAS exposure induces biochemical process alterations associated with the disruption of the antioxidant defense system in several species. This review aims to discuss how PFAS-induced antioxidant system alterations lead to changes in biochemical processes in different organisms exposed to these pollutants. This disruption, then leads to an imbalance in antioxidant defense systems, contributing to the formation of reactive oxidative species (ROS), which, in turn, can be exacerbate oxidative stress, induce cellular damage, enhance lipid peroxidation, destabilize lysosomal membranes, and cause genotoxic effects, ultimately compromising DNA integrity. In acute tests, PFAS have led to mortality, growth inhibition, diminished behavioral and locomotor abilities, and reproductive impairment. PFAS-induced effects differ with varying species or types of substances, and further bioaccumulation through food chains exacerbates environmental contamination, carrying considerable risks. These findings demonstrate the complex and enduring impact of PFAS on environmental health, emphasizing the importance of this review in corroborating studies on sub-lethal toxicity in exposed organisms and how these effects reflect on the environment.

Graphene oxide with 1-nm-thick adlayer for efficient and near-instant removal of per- and polyfluoroalkyl substances

The environmental occurrence of anthropogenic chemicals-especially persistent micropollutants of per- and polyfluoroalkyl substances (PFAS)-raises pressing concerns for global drinking-water safety. Adsorption is an effective technology for removing PFAS but is limited by unsatisfactory adsorption capacity and efficiency. We report a strategy to attach polyamine adlayers to graphene oxide (GO) nanosheets that produces highly charged and monodispersed 2D adsorbents of a GO nanosheet sandwiched between two 1-nm-thick polyamine adlayers. This adsorbent has a high adsorption capacity for PFAS of ∼3070 mg/g-tens of times greater than that of GO and commercial activated carbon. It also provides almost instant adsorption of a variety of PFAS and reaches 57%-95% of its equilibrium capacity in a minute and removes ∼100% of PFAS from contaminated water sources within a few minutes, transforming real-life PFAS-contaminated water into safe drinking water. Experiment and theory show that the planar nature of the 2D adsorbent combined with its abundant surface adsorption sites that electrostatically attract the polar groups of the PFAS, and hydrogen bonding and hydrophobic-hydrophobic interactions with their non-polar groups, account for its ultra-high adsorption capacity and rapid removal efficiency. We also show that regeneration of the adsorbents removes the adsorbed PFAS and allows subsequent destruction, demonstrating a closed-loop treatment solution for micropollutant contamination.

Cationic covalent organic framework for the fluorescent sensing and cooperative adsorption of perfluorooctanoic acid

The contamination of water by per- and polyfluorinated substances (PFAS) is a pressing global issue due to their harmful effects on health and the environment. This study explores a cationic covalent organic framework (COF), TG-PD COF, for the efficient detection and removal of perfluorooctanoic acid (PFOA) from water. Synthesized via a simple sonochemical method, TG-PD COF shows remarkable selectivity and sensitivity to PFOA, with a detection limit as low as 1.8 µg·L⁻¹. It achieves significant PFOA adsorption exceeding 2600 mg·g⁻¹ within seconds over several cycles in batch mode and complete removal at environmentally relevant concentrations in column adsorption. Results reveal unique adsorption behavior characterized by two phases, leveraging PFOA aggregation through hydrophobic interactions. Computer simulations elucidate the mechanisms underlying TG-PD COF's sensing, adsorption, and charge transfer dynamics. Our findings position this COF design strategy as a promising solution for combating PFAS contamination in water bodies worldwide.

Effective removal of perfluorooctanoic acid from water using PVA@UiO-66-NH2/GO composite materials via adsorption

This study introduces an innovative approach using highly efficient nanocomposite materials to effectively remove PFAS from water, demonstrating remarkable adsorption capabilities. The nanocomposite was synthesized by integrating a zirconium-based metal-organic framework (MOF) called UiO-66 with graphene oxide (GO) within a polyvinyl alcohol (PVA) matrix. The resulting PVA@UiO-66/GO material features flower-like UiO-66 MOF crystals embedded in the PVA and GO matrix. Various kinetic models were applied to determine the rate constants and adsorption capacities, with the Langmuir isotherm indicating an adsorption capacity of 9.904 mg/g. Thermodynamic analysis confirmed the process's spontaneity and exothermic nature. The UiO-66-NH2/GO/PVA composite also demonstrated high reusability, maintaining substantial PFOA removal efficiency across multiple cycles, with optimal reduction occurring at approximately pH 5. Overall, the PVA@UiO-66/GO composites offer an effective, sustainable, and environmentally friendly solution for PFAS removal in water purification.

Comparing solution-gate and bottom-gate nanowire field-effect transistors on pH sensing with different salt concentrations and surface modifications

Field-effect transistors (FETs) have been developed as pH sensors by using various device structures, fabrication technologies, and sensing film materials. Different transistor structures, like extended-gate (EG) FETs, floating-gate FET sensors, and dual-gate (DG) FETs, can enhance the sensor performance. In this article, we report the effects of using solution-gate and bottom-gate FET configurations on pH sensing and investigate the influence of different ionic concentrations of buffers in the measured signals. The surface charge of hafnium dioxide (HfO2) affected by the buffer pH, with/without the modification of polyethylene glycol (PEG) terminated with hydroxyl groups, and the location of applied gate voltage are vital factors to the sensor performance in pH sensing. Based on the results, the solution-gate FET exhibits good pH sensitivity even in the high ionic strength solutions of bis-tris propane (BTP), and these values of pH sensitivity are close to the Nernst limit (59.2 mV/pH). In general, silane-PEG-OH modification can reduce the deviations of measured signals in pH sensing. The performance of bottom-gate FET is inferior in the BTP buffers with high ionic solutions but suitable to be operated in low ionic concentrations, such as 0.1, 1, and 10 mM BTP buffers. The size of the ions was also studied and discussed. The solution-gate FET demonstrates excellent performance under high ionic strengths, meaning a more significant potential for detecting biological molecules under physiological conditions.

Advancing PFAS Sorbent Design: Mechanisms, Challenges, and Perspectives

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals characterized with persistence and multisurface resistance. Their accumulation in the environment and toxicity to human beings have contributed to the rapid development of regulations worldwide since 2002. The sorption strategy, taking advantage of intermolecular interactions for PFAS capture, provides a promising and efficient solution to the treatment of PFAS contaminated sources. Hydrophobic and electrostatic interactions are the two commonly found in commercially available PFAS sorbents, with the fluorous interaction being the novel mechanism applied for sorbent selectivity. The main object of this Perspective is to provide a critical review on the current design criteria of PFAS sorbents, with particular focus on their sorption and interaction mechanisms as well as limitations. An outlook on future innovative design for efficient PFAS sorbents is also provided.

Combined adsorption and electrochemical oxidation of perfluorooctanoic acid (PFOA) using graphite intercalated compound

Perfluorooctanoic acid (PFOA) is a bioaccumulative synthetic chemical containing strong C-F bonds and is one of the most common per- and polyfluoroalkyl substances (PFAS) detected in the environment. Graphite intercalated compound (GIC) flakes were used to adsorb and degrade PFOA through electrochemical oxidation. The adsorption followed the Langmuir model with a loading capacity of 2.6 µg PFOA g-1 GIC and a second-order kinetics (3.354 g µg-1 min-1). 99.4% of PFOA was removed by the process with a half-life of 15 min. When PFOA molecules broke down, they released various by-products, such as short-chain perfluoro carboxylic acids like PFHpA, PFHxA, and PFBA. This breakdown indicates the cleavage of the perfluorocarbon chain and the release of CF2 units, suggesting a transformation or degradation of the original compound into these smaller acids. Shorter-chain perfluorinated compounds had slower degradation rates compared to longer-chain ones. Combining these two methods (adsorption and in situ electrochemical oxidation) was found to be advantageous because adsorption can initially concentrate the PFOA molecules, making it easier for the electrochemical process to target and degrade them. The electrochemical process can potentially break down or transform the PFAS compounds into less harmful substances through oxidation or other reactions.

An overview on human exposure, toxicity, solid-phase microextraction and adsorptive removal of perfluoroalkyl carboxylic acids (PFCAs) from water matrices

Perfluoroalkyl carboxylic acids (PFCAs) are sub-class of perfluoroalkyl substances commonly detected in water matrices. They are persistent in the environment, hence highly toxic to living organisms. Their occurrence at trace amount, complex nature and prone to matrix interference make their extraction and detection a challenge. This study consolidates current advancements in solid-phase extraction (SPE) techniques for the trace-level analysis of PFCAs from water matrices. The advantages of the methods in terms of ease of applications, low-cost, robustness, low solvents consumption, high pre-concentration factors, better extraction efficiency, good selectivity and recovery of the analytes have been emphasized. The article also demonstrated effectiveness of some porous materials for the adsorptive removal of the PFCAs from the water matrices. Mechanisms of the SPE/adsorption techniques have been discussed. The success and limitations of the processes have been elucidated.