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. 2022 Oct 20;12(10):1017.
doi: 10.3390/membranes12101017.

Polyphenylene Sulfide Ultrafine Viscous Fibrous Membrane Modified by ZIF-8 for Highly Effective Oil/Water Separation under High Salt or Alkaline Conditions

Wenlei Liu  1   2 , Lingli Yu  3   4 , Xianfeng Cui  5 , Ce Tan  1   2 , Mengen Zhang  1   2 , Di Wu  1   2 , Zhenhuan Li  1   2 , Maliang Zhang  1   2   5
Affiliations

Polyphenylene Sulfide Ultrafine Viscous Fibrous Membrane Modified by ZIF-8 for Highly Effective Oil/Water Separation under High Salt or Alkaline Conditions

Wenlei Liu et al. Membranes (Basel). .

Abstract

The oil/water separation in harsh environments has always been a challenging topic all over the world. In this study, the ZIF-8/PPS fiber membranes were fabricated via the combination of hot pressing and in situ growth. The distribution of ZIF-8 in the membranes was adjusted by changing the ZIF-8 in situ growth time, which could control the oil/water separation effect. Due to the hydrophilic nature of the ZIF-8/PPS fiber membranes, the water molecules in the oil-in-water emulsion could quickly penetrate into the fiber membrane under the drive of pressure, gravity, and capillary force, forming a water layer on the surface of the fiber membranes. The coupling of the water layer and the fiber structure prevented direct contact between the oil molecules and the fiber membrane, thereby realizing the separation of the emulsion. The results show that when the ZIF-8 in situ growth time was 10 h, the contact angle, the porosity, and the pure water flux of the ZIF-8/PPS fiber membranes were 72.5°, 52.3%, and 12,351 L/h·m2, respectively. More importantly, the separation efficiency of M10 was 97%, and the oil/water separation efficiency reached 95% after 14 cycles. This study provides a novel strategy for preparing MOFs/fiber materials for oil/water separation in harsh environments.

Keywords: ZIF-8; chemical resistance; membrane; oil/water separation; polyphenylene sulfide.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Ball and stick model of PPS structure; (b) the chemical structure of PPS.
Scheme 1
Scheme 1
Schematically illustrated fabrication of ZIF-8/PPS fiber membranes.
Scheme 2
Scheme 2
Schematic diagram of the emulsion separation experiments.
Figure 2
Figure 2
Basic properties of PPS matrix. (A) Surface SEM images of PPS fiber membranes (a: 80 °C; b: 88 °C; c: 90 °C; d: 95 °C); (B) porosity of PPS fiber membranes; (C) stress–strain curve of PPS fiber membranes.
Figure 3
Figure 3
(a) FT-IR spectra of PPS non-woven fabrics before and after treatment with nitric acid solution; (b) FT-IR spectra of ZIF-8/PPS fiber membranes obtained after different ZIF-8 in situ growth times (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h).
Figure 4
Figure 4
XPS spectra of the surface of the ZIF-8/PPS fiber membranes ((a): C1s; (b): N1s; (c): O1s; (d): Zn2p).
Figure 5
Figure 5
(a) SEM images of ZIF-8/PPS fiber membranes (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h); (b) SEM images of ZIF-8 attached to PPS fiber membranes (1: low magnification; 2: high magnification).
Figure 6
Figure 6
XRD patterns of PPS and ZIF-8/PPS fiber membranes.
Figure 7
Figure 7
The porosity of ZIF-8/PPS fiber membranes (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h).
Figure 8
Figure 8
The 3D surface roughness of ZIF-8/PPS fiber membranes (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h).
Figure 9
Figure 9
High-temperature resistance experiment diagram of PPS matrix.
Figure 10
Figure 10
(a) TG curves of PPS non-woven fabrics, PPS non-woven fabrics after nitrification, and ZIF-8/PPS fiber membranes; (b) DTG curves of PPS non-woven fabrics, PPS non-woven fabrics after nitrification, and ZIF-8/PPS fiber membranes.
Figure 11
Figure 11
Wettability of ZIF-8/PPS fiber membranes. (a) Water contact angle of ZIF-8/PPS fiber membranes (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h); (b) the changes in water droplets after standing for 2 s on different surfaces (1 and 1′: untreated PPS; 2 and 2′: nitrated PPS; 3 and 3′: ZIF-8/PPS).
Figure 12
Figure 12
Water flux and oil/water separation performance of ZIF-8/PPS fiber membranes. (a) Water flux test of ZIF-8/PPS fiber membranes (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h); (b) oil/water separation performance (M0: untreated; M4: 4 h; M8: 8 h; M10: 10 h; M12: 12 h); (c) digital photos of M10 in the separation process of chlorobenzene; (d) separation performance of ZIF-8/PPS fibers for different emulsions.
Figure 13
Figure 13
(a) PPS/ZIF-8 fiber membranes’ resistance to high alkali and salt solutions; (b) recycling performance of PPS/ZIF-8 fiber membranes.
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