Functional group modified 1D interpenetrated metal-organic frameworks on perfluorooctanoic acid adsorption: Experimental and theoretical calculation study

Efficient removal of per/polyfluoroalkyl substances from water using recyclable chitosan-coated covalent organic frameworks: Experimental and theoretical methods

Covalent organic frameworks (COFs) demonstrate remarkable potential for adsorbing per/polyfluoroalkyl substances (PFAS). Nevertheless, the challenge of recycling powdered COFs hampers their practical application in water treatment. In this research, a quaternary amine COF with inherent positive surface charge was synthesised to adsorb perfluorooctanoic acid (PFOA) via electrostatic interactions. The COF was then combined with chitosan (CS) through a simple dissolution-evaporation process, resulting in a composite gel material termed COF@CS. The findings indicated that the adsorption capacity of COF@CS significantly surpassed that of the original COF and CS. According to the Langmuir model, COF@CS achieved a maximum PFOA capacity of 2.8 mmol g-1 at pH 5. Furthermore, the adsorption rate increased significantly to 6.2 mmol g-1 h-1, compared to 5.9 mmol g-1 h-1 for COF and 3.4 mmol g-1 h-1 for CS. Notably, COF@CS exhibited excellent removal efficacy for ten other types of PFAS. Moreover, COF@CS could be successfully regenerated using a mixture of 70% ethanol and 1 wt% NaCl, and it exhibited stable reusability for up to five cycles. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) characterisation, and theoretical calculations revealed that the quaternary amine functional group in COF served as the primary adsorption site in the composite gel material, while the protonated amino group on CS enhanced PFOA adsorption through electrostatic interaction. This study highlights the significant practical potential of COF@CS in the removal of PFAS from aqueous solution and environmental remediation.

Metal-Organic Framework-Based Composites for the Adsorption Removal of Per- and Polyfluoroalkyl Substances from Water

The increasing health risks posed by per- and polyfluoroalkyl substances (PFASs) in the environment highlight the importance of implementing effective removal techniques. Conventional wastewater treatment processes are inadequate for removing persistent organic pollutants. Recent studies have increasingly demonstrated that metal-organic frameworks (MOFs) are capable of removing PFASs from water through adsorption techniques. However, there is still constructive discussion on the potential of MOFs in adsorbing and removing PFASs for large-scale engineering applications. This review systematically investigates the use of MOFs as adsorbents for the removal of PFAS in water treatment. This primarily involved a comprehensive analysis of existing literature to understand the adsorption mechanisms of MOFs and to identify factors that enhance their efficiency in removing PFASs. We also explore the critical aspects of regeneration and stability of MOFs, assessing their reusability and long-term performance, which are essential for large-scale water treatment applications. Finally, our study highlights the challenges of removing PFASs using MOFs. Especially, the efficient removal of short-chain PFASs with hydrophilicity is a major challenge, while medium- to long-chain PFASs are frequently susceptible to being captured from water by MOFs through multiple synergistic effects. The ion-exchange force may be the key to solving this difficulty, but its susceptibility to ion interference in water needs to be addressed in practical applications. We hope that this review can provide valuable insights into the effective removal and adsorption mechanisms of PFASs as well as advance the sustainable utilization of MOFs in the field of water treatment, thereby presenting a novel perspective.

Strategies to improve adsorption and photocatalytic performance of metal-organic frameworks (MOFs) for perfluoroalkyl and polyfluoroalkyl substances (PFASs) removal from water: A review

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) represent a category of persistent and hazardous organic pollutants extensively prevalent across aquatic environments. The combination of adsorption and photocatalytic degradation has been identified as an effective approach for removing trace amounts of PFASs from water. Among the various materials explored for this purpose, metal-organic frameworks (MOFs) have structural solid tunability, and suitable modification methods could endow them with rich adsorption capabilities and excellent photocatalytic performance, which has potential for applications involving the treatment of trace, multi-chain-length PFASs in water. The research within this realm is currently in its nascent phase, and a holistic knowledge of modification methods can provide a comprehensive framework for future studies. Therefore, this review intends to (1) summarize the mechanism underlying the adsorption and photocatalytic removal of PFASs by MOFs; (2) present various modification methods aimed at enhancing the adsorption and photocatalytic performance of MOFs in alignment with the goal mentioned above; (3) provide an outlook on the prospects of utilizing MOFs for PFASs removal based on current trends and data. Ultimately, the findings from these studies will contribute to advancing knowledge in this area and facilitate the development of effective strategies for addressing PFASs contamination in water systems.