Preparation of magnetic covalent triazine frameworks by ball milling for efficient removal of PFOS and PFOA substitutes from water

• Published in: Environmental science. Nano 2022-04, Vol.9 (4), p.1466-1475
• Main Authors: Wang, Wei, Shao, Haipei, Sun, Chang, Jiang, Xiangzhe, Zhou, Shuangxi, Yu, Gang, Deng, Shubo
• Format: Article
• Language: English
• Subjects: Adsorption; Air bubbles; Amines; Amorphous materials; Analytical methods; Anions; Ball milling; Covalence; Fourier transforms; Iron oxides; Mass ratios; Ocean bottom seismometers; Perfluorooctane sulfonic acid; Perfluorooctanoic acid; Photoelectron spectroscopy; Photoelectrons; Pollutant removal; Pollutants; Quaternary ammonium salts; Removal; Sodium; Sodium chloride; Substitutes; Triazine; Trimers; Wastewater pollution; Wastewater treatment; X ray photoelectron spectroscopy
• ISSN: 2051-8153; 2051-8161
• DOI: 10.1039/d1en01158h

Difficult separation of covalent organic frameworks (COFs) greatly limits their application in wastewater treatment. For the first time, the ball-milling method was used to prepare recyclable magnetic covalent triazine frameworks (CTF/Fe 3 O 4 ), and little influence on the structure and adsorption performance of CTFs after ball-milling was observed. We synthesized crystalline CTF1 and amorphous CTF2 materials and then investigated the effect of CTF/Fe 3 O 4 mass ratios on the removal of two typical PFOS and PFOA substitutes including sodium p -perfluorous nonenoxybenzene sulfonate (OBS) and hexafluoropropylene oxide trimer acid (HFPO-TA). CTF2/Fe 3 O 4 exhibited higher adsorption performance than CTF1/Fe 3 O 4 due to the additional quaternary amine groups as highly efficient adsorption sites, achieving adsorption capacities of 1.18 mmol g −1 for OBS and 1.02 mmol g −1 for HFPO-TA, with their adsorption equilibrium within 3 h. The adsorption mechanisms were investigated through Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), and anionic exchange, electrostatic attraction and accumulation on the air bubble surfaces on the adsorbent were proposed. Additionally, the spent CTF2/Fe 3 O 4 was well regenerated by the mixture of NaCl and methanol solution and showed relatively stable adsorption for OBS and HFPO-TA within 5 cycles. This study provides a feasible method to make recyclable COF powders for efficient removal of pollutants from wastewater. Recyclable magnetic COFs/Fe 3 O 4 synthesized using ball-milling showed fast and high adsorption for two PFOS and PFOA substitutes in water.