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. 2023 Jul 10;10(10):nwad191.
doi: 10.1093/nsr/nwad191. eCollection 2023 Oct.

Unique fluorophilic pores engineering within porous aromatic frameworks for trace perfluorooctanoic acid removal

Chi Zhang  1 , Junchao Dong  1 , Panpan Zhang  1 , Lei Sun  2 , Liu Yang  1 , Wenjian Wang  1 , Xiaoqin Zou  1 , Yunning Chen  1 , Qingkun Shang  1 , Danyang Feng  1 , Guangshan Zhu  1
Affiliations

Unique fluorophilic pores engineering within porous aromatic frameworks for trace perfluorooctanoic acid removal

Chi Zhang et al. Natl Sci Rev. .

Abstract

Perfluorooctanoic acid (PFOA), a representative of per/polyfluorinated alkyl substances, has become a persistent water pollutant of widespread concern due to its biological toxicity and refractory property. In this work, we design and synthesize two porous aromatic frameworks (PAF) of PAF-CF3 and PAF-C2F5 using fluorine-containing alkyl based monomers in tetrahedral geometry. Both PAFs exhibit nanosized pores (∼1.0 nm) of high surface areas (over 800 m2 g-1) and good fluorophilicity. Remarkable adsorption capacity (˃740 mg g-1) and superior efficiency (˃24 g mg-1 h-1) are achieved toward the removal of PFOA with 1 μg L-1 concentration owing to unique C-F···F-C interactions. In particular, PAF-CF3 and PAF-C2F5 are able to reduce the PFOA concentration in water to 37.9 ng L-1 and 43.3 ng L-1, below EPA regulations (70 ng L-1). The reusability and high efficiency give both PAFs a great potential for sewage treatment.

Keywords: adsorption removal; fluorophilicity; halogen interactions; perfluorooctanoic acid; porous aromatic frameworks.

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Figures

Figure 1.
Figure 1.
(a) Synthetic routes of PAF-CF3 and PAF-C2F5; (b) infrared (IR) spectra of as-synthesized monomer 1 ((4-bromo-3-trifluoromethylphenyl)tris(4-bromophenyl)methane), monomer 2 ((4-bromo-3-pentafluoroethylphenyl)tris(4-bromophenyl)methane), PAF-CF3 and PAF-C2F5; (c) 13C and (d) 19F NMR spectra of PAF-CF3 (red) and PAF-C2F5 (blue).
Figure 2.
Figure 2.
(a) Adsorption isotherms of PAF-CF3 and PAF-C2F5 for PFOA and the Langmuir fits (PAF dosage: 200 mg L−1, [PFOA]0 = 10-1000 mg L−1), and (b) kinetics of PFOA (200 μg L−1) adsorption on PAF-CF3 and PAF-C2F5 (PAF dosage: 500 mg L−1), inset in (b) is the corresponding pseudo-second-order plots.
Figure 3.
Figure 3.
Solid state 19F NMR spectra of PFOA, PAF-CF3 and PFOA@PAF-CF3 (a), and PAF-C2F5 and PFOA@PAF-C2F5 (b).
Figure 4.
Figure 4.
Kinetics of PFOA (1 μg L−1) adsorption (a) and pseudo-second-order plots (b) of PAF-CF3 and PAF-C2F5 (PAF dosage: 10 mg L−1); (c) removal degrees and remaining contents of PFOA (1 μg L−1) adsorbed by GAC, PAC, PAF-1, PAF-CF3 and PAF-C2F5 after 9 h (adsorbent dosage: 10 mg L−1); (d) a summary of adsorption capacities and rates of reported materials for PFOA removal; (e) removal/recovery degrees of PFOA during regeneration tests (removal experiment: [PAF-CF3] = 500 mg L−1, [PFOA]0 = 200 μg L−1, 24 h; recovery experiment: PAF-CF3 was soaked in methanol for 24 h); (f) kinetics curves of PFOA (200 μg L−1) adsorption on PAF-CF3 and PAF-C2F5 (PAF dosage: 500 mg L−1) in the presence of humic acid (20 mg L−1).
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