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Methylation of reverse osmosis membrane for superior anti-fouling performance via blocking carboxyl groups in polyamide

Nature Water volume 3, pages 110–121 (2025)Cite this article

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An Author Correction to this article was published on 31 January 2025

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Abstract

The lifespan of reverse osmosis (RO) membranes is only several months when used for industrial wastewater treatment rather than several years for seawater desalination, dramatically increasing the maintenance cost of RO. Here, to improve the separation and anti-fouling performance and thus increase the lifespan of RO membranes, we developed a creative strategy to methylate RO membranes via grafting gaseous dimethylamine molecules onto polyamide (PA) of RO membrane during interfacial polymerization. The dimethylamine-grafted RO membrane achieved a high water permeance of 3.84 l m−2 h−1 bar−1 and a high NaCl rejection of 99.05% and exhibited unprecedented anti-fouling performance against small organic charged foulants, surpassing the upper-bound threshold of the other reported anti-fouling membranes and the well-known commercial anti-fouling RO membrane (DuPont FilmTec Fortilife CR100). Both experimental results and molecular dynamics simulation findings illustrate that the methylated PA has a lower absorption energy with small charged organic foulants than the pristine PA, which alleviates the foulantsʼ absorption with a lower areal density and a looser packing, and a much shallower penetration depth inside PA. Our work suggests that avoiding penetration of foulants inside PA and preventing pore blocking of PA by foulants are essential to improve the fouling resistance of RO membranes. This work contributes a new outlook on the RO membrane-fouling mechanism from the molecular levels using molecular dynamics simulation and also develops a simple and effective methylation approach to enhance the RO membrane-fouling resistance towards small charged foulants.

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Fig. 1: Fabrication and characterization of the DMA-modified RO membranes.
Fig. 2: Membrane surface morphologies, surface properties and separation performances.
Fig. 3: Anti-fouling properties of the pristine and the DMA-modified RO membranes.
Fig. 4: The adsorption behaviours of the positively and negatively charged small foulants including SDS and DTAB on both pristine PA and DMA-PA, along with the characteristics of the adsorbed cake layers, monitored by QCM-D.
Fig. 5: Molecular dynamics simulation of DTAB absorption on the DMA-grafted PA and the pristine PA.
Fig. 6: Side views of DTAB and SDS absorbed on the pristine PA surface and the DMA-grafted PA surface and also penetrated inside both PAs.

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Data availability

The main data supporting the findings of this study are contained within the paper. Key experimental datasets and source files for figures and extended data are attached as Supplementary Information. All other relevant data are available from the corresponding author upon reasonable request.

Code availability

All codes written for and used in this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was financially supported by Nitto Denko Corporation and National Natural Science Foundation of China (numbers 21978215 and 22378314).

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Author notes

  1. These authors contributed equally: Yiwen Qin, Pengfei Qi.

Authors and Affiliations

  1. State Key Laboratory of Separation Membranes and Membrane Processes, School of Materials Science and Engineering, Tiangong University, Tianjin, People’s Republic of China

    Yiwen Qin, Pengfei Qi, Shuang Hao, Jun Xiao, Jianxiao Wang & Yunxia Hu

  2. Institute for New Energy Materials and Low Carbon Technologies, School of Materials Science and Engineering, Tianjin University of Technology, Tianjin, People’s Republic of China

    Wenxiong Shi

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Contributions

Y.H., S.H. and Y.Q. designed the research and proposed the idea. Y.Q. carried out fabrication of RO membranes. Y.Q., J.X. and J.W. conducted the performance tests and characterization of RO membranes. P.Q. carried out the molecular dynamics simulation and the corresponding data display. Y.Q. created the initial figures and paper. W.S. participated in discussion. Y.Q., P.Q., S.H. and Y.H. co-wrote the paper.

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Correspondence to Yunxia Hu.

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Nature Water thanks Zhiping Lai, Hongjun Lin and Sanchuan Yu for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Molecular dynamics simulation of SDS absorption behaviours on the DMA-grafted PA and the pristine PA.

The distribution of SDS absorbed on the DMA-grafted PA and the pristine PA is illustrated with the top (a,b) and the side (c,d) views. The carboxyl groups of PAs are blue dots in the top view. The head groups of SDS are presented by yellow and red balls, and its tail groups are shown in green balls. Plots of the adsorption depth and the number of adsorbed SDS molecules on the DMA-grafted PA and the pristine PA (e). The adsorption energy between SDS and the PAs include LJ energy and Coul energy (f).

Extended Data Table 1 Water permeance of the pristine PA and DMA-grafted PA when fouled by DTAB and SDS and tested via molecular dynamics simulation
Full size table

Supplementary information

Supplementary Information

Supplementary methods, Figs. 1–13 and Tables 1–15.

Supplementary Table 1

Source data of the multi-cycle fouling–recovery profiles of the fabricated RO membranes when fouled by SDS and DTAB, corresponding to Supplementary Fig. 9 and Supplementary Tables 12–15.

Supplementary Data 1

1. Source files of the PA molecular models and DTAB adsorption simulations, corresponding to Fig. 5. 2. Source files of the PA molecular models and SDS adsorption simulations, corresponding to Extended Data Fig. 1. 3. Source files of the water permeation simulations, corresponding to Fig. 6. 4. Source files of the SEM, TEM and AFM images of the fabricated RO membranes, corresponding to Fig. 2, Supplementary Figs. 4 and 5 and Supplementary Table 4.

Source data

Source Data Fig. 1

Source data of the high-resolution deconvolution peaks of C 1s, N 1s and O 1s from the RO membranes.

Source Data Fig. 2

Source files of the SEM images of the RO membranes.

Source Data Fig. 3

Source data of the normalized flux profiles.

Source Data Fig. 4

Source data of the QCM-D tests.

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Qin, Y., Qi, P., Hao, S. et al. Methylation of reverse osmosis membrane for superior anti-fouling performance via blocking carboxyl groups in polyamide. Nat Water 3, 110–121 (2025). https://doi.org/10.1038/s44221-024-00371-x

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