TY - JOUR
T1 - Cationic COF nanosheets engineered positively charged polyamide membranes for efficient divalent cations removal
AU - Wang, Guangzhe
AU - Wu, Tao
AU - Zhao, Junhui
AU - Shi, Benbing
AU - Gu, Tianrun
AU - Zhang, Runnan
AU - Wang, Xiaoyao
AU - Kasher, Roni
AU - Su, Yanlei
AU - Jiang, Zhongyi
N1 - Funding Information:
The authors gratefully acknowledge financial support from the Key Research and Development Program of Zhejiang Province ( 2021C03173 ), the National Natural Science Foundation of China ( 21961142013 , U20B2023 , 22008172 ), the Zhejiang Provincial Natural Science Foundation ( LGG22B060006 ) and the Ningbo Natural Science Foundation ( 2021J007 ) and Ningbo Key Research and Development Project ( 2022Z121 ). We thank the Haihe Laboratory of Sustainable Chemical Transformations for financial support.
Funding Information:
Polyacrylonitrile (PAN) support membranes were purchased from Lanjing Membrane Technology Engineering Co. LTD. (Shandong, China). Octanoic acid (98%), n-heptane (99%), and Trimesoyl chloride (99%) were provided by Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Polyethyleneimine (Mw = 70000, 30% aqueous solution) was supplied by Meryer Chemical Technology Co., Ltd. (Shanghai, China). Sodium sulfate (Na2SO4, 98%), magnesium chloride (MgCl2, 97%), magnesium sulfate (MgSO4, 99%), sodium chloride (NaCl, 99%) were obtained from Heowns Co., Ltd. (Tianjin, China). 2,4,6-Triformylphloroglucinol (C9H6O6, 98%) was received from Yanshen Technology Co., Ltd. (Jilin, China). 3,5-dicarbohydrazide-benzyltrimethylammonium bromide was synthesized in our laboratory. Polyethylene glycol (PEG) with different molecular weights was purchased from Hefei BASF Biotechnology Co., Ltd. (Anhui, China).The polyamide nanofiltration membrane was prepared with the vacuum-assisted filtration. The inner diameter of filtration device was 2 cm, the pressure was set at 1.0 MPa, and the support membrane was commercially available polyacrylonitrile (PAN) ultrafiltration membrane. Firstly, 5 ml PEI aqueous solution (0.3 g/L) was placed in the suction filter tube. After filtration, the PAN substrate membrane was placed in n-heptane solution of 0.15 g/L TMC for 60 s at room temperature. Finally, the PAN support membrane was placed in an oven at 60 °C for heat treatment for 10 min.AFM was used to accurately observe the physical structure of cCOF nanosheets. As shown in Fig. 4 (a), the AFM results show that the thickness of cCOF nanosheets are about 2 nm and the lateral size is 3-4 μm, which is conducive to the deposition and stacking of COF nanosheets on the support, forming a defect-free deposition layer of COF nanosheets [32]. The charge properties of nanosheets are the key factor to influence membrane structure. The potential of cCOF nanosheets was tested by a zeta potential analyzer. The testing results in Fig. 4 (c) show that the cCOF nanosheets have an obvious characteristic peak at 44 mv, indicating that the quaternary ammonium groups on cCOF nanosheets render obvious positive charge properties.The charge properties are the key factors that determine the ions rejection of the membrane. The zeta potentials of PA and cCOF-PA membranes are shown in Fig. 8 (a). When the deposition amount of cCOF nanosheets reached 75 μL, the zeta potential of membrane surface decreased from 69.4 mv to 46.7 mv, as the deposition volume continued to increase, the zeta potential increased. This change is consistent with the XPS results. When the proportion of carboxyl groups on membrane surface increases, the negative charge provided by carboxyl groups will weaken the positive charge of polyamide membrane. To further explore the structure-performance relationship of cCOF-PA membrane, the zeta potential of COF interlayer was also analyzed. The results in Fig. 8 (b) show that the PAN support has a typical negative charge, and its zeta potential is -25.9 mv. After the deposition of COF nanosheets, the zeta potential of membrane is continuously increased from -19.4 mv to -3.5 mv. The enhancement of the positive charge of COF interlayer can effectively fortify the electrostatic repulsion of cCOF-PA membrane toward high-valent cations.The authors gratefully acknowledge financial support from the Key Research and Development Program of Zhejiang Province (2021C03173), the National Natural Science Foundation of China (21961142013, U20B2023, 22008172), the Zhejiang Provincial Natural Science Foundation (LGG22B060006) and the Ningbo Natural Science Foundation (2021J007) and Ningbo Key Research and Development Project (2022Z121). We thank the Haihe Laboratory of Sustainable Chemical Transformations for financial support.
Publisher Copyright:
© 2023 Elsevier B.V.
PY - 2023/10/15
Y1 - 2023/10/15
N2 - Ionic covalent organic frameworks (COFs) hold great promise in regulating the structure of polyamide nanofiltration membranes for divalent ions removal. In this work, we demonstrate cationic COF (cCOF) nanosheets engineered polyamide membrane with excellent divalent cations rejection. cCOF nanosheets as versatile regulator and an interlayer accelerate the self-sealing and self-termination of interfacial polymerization between polyethyleneimine and trimesoyl chloride, endowing membranes with dense network and small thickness. Meanwhile, the quaternary ammonium groups on cCOF nanosheets increase positive charges on membranes. Through synergistic intensification of electrostatic repulsion and size sieving, the resulting cCOF-PA membranes display excellent rejection for divalent cations (MgCl2, 99.3%), superior to most reported polyethyleneimine-based polyamide membranes. This work highlights the significance of ionic COF materials in developing positively charged membranes for efficient ionic and molecular separations.
AB - Ionic covalent organic frameworks (COFs) hold great promise in regulating the structure of polyamide nanofiltration membranes for divalent ions removal. In this work, we demonstrate cationic COF (cCOF) nanosheets engineered polyamide membrane with excellent divalent cations rejection. cCOF nanosheets as versatile regulator and an interlayer accelerate the self-sealing and self-termination of interfacial polymerization between polyethyleneimine and trimesoyl chloride, endowing membranes with dense network and small thickness. Meanwhile, the quaternary ammonium groups on cCOF nanosheets increase positive charges on membranes. Through synergistic intensification of electrostatic repulsion and size sieving, the resulting cCOF-PA membranes display excellent rejection for divalent cations (MgCl2, 99.3%), superior to most reported polyethyleneimine-based polyamide membranes. This work highlights the significance of ionic COF materials in developing positively charged membranes for efficient ionic and molecular separations.
KW - Cationic covalent organic framework nanosheets
KW - Divalent cations removal
KW - Interfacial polymerization
KW - Nanofiltration
KW - Polyamide membranes
UR - http://www.scopus.com/inward/record.url?scp=85163176551&partnerID=8YFLogxK
U2 - 10.1016/j.memsci.2023.121863
DO - 10.1016/j.memsci.2023.121863
M3 - Article
AN - SCOPUS:85163176551
SN - 0376-7388
VL - 684
JO - Journal of Membrane Science
JF - Journal of Membrane Science
M1 - 121863
ER -