Preparation of MOFs/chitosan positively charged nanofiltration membrane by electrospray method
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摘要: 将壳聚糖的直接成膜性与电喷雾技术结合，并引入金属有机骨架（MOFs），制备了NH2-UIO-66(Zr)/壳聚糖荷正电纳滤膜，实现对Ni2+的高效分离和富集。通过电喷雾技术可有效解决传统壳聚糖纳滤膜成膜周期长、膜层较厚、通量较低等问题。实验表明，与传统涂覆工艺相比，电喷雾法制备的壳聚糖复合膜在保持较高截留率的情况下，渗透性提高了634%。然而，单一壳聚糖基质膜受trade-off效应影响，分离性能难以进一步提升。引入NH2-UIO-66(Zr)作为填料可有效缓解trade-off效应，所制备的复合膜在不牺牲截留率的情况下，通量进一步提升38%（水通量为4.7×10-5 L·m-2·h-1·Pa-1，对NiCl2截留率为92%）。Abstract: Electrospray technology can solve the problems of long membrane formation period, thicker membrane layer and low flux of traditional chitosan nanofiltration membranes. In this study, the NH2-UIO-66(Zr)/chitosan positively charged nanofiltration membrane was successfully prepared by combining the direct membrane-forming properties of chitosan with electrospray technology and introducing metal-organic frameworks (MOFs). This membrane has achieved efficient separation and enrichment of Ni2+. The morphology, structure and properties of membrane were investigated by SEM, EDS, Zeta potential, water contact angle measurements, etc. Studies have shown that compared with the traditional coating process, the permeability of the chitosan composite membrane prepared by the electrospray method is increased by 634% and the membrane can still maintain a good rejection. However, pure chitosan matrix membranes are usually affected by trade-off effect, and it is difficult to further improve the separation performance. The introduction of NH2-UIO-66 (Zr) as a filler can effectively alleviate the trade-off effect. Hybridization improves the hydrophilicity of the separation layer and forms a special membrane surface structure, thereby increasing permeability of composite membrane. Experiments show that the limit of NH2-UiO-66(Zr) loading is 5 wt% (the ratio of MOFs to chitosan). The optimized NH2-UIO-66(Zr)/chitosan membrane has a higher flux than pristine chitosan membrane (increased by 38%). The prepared membrane exhibited a high NiCl2 rejection of 92% and a water permeability of 4.7×10-5 L·m-2·h-1·Pa-1 (test pressure: 4×105 Pa; feed concentration: 0.5 g/L). In addition, the hybrid membrane exhibits excellent mechanical strength and has the potential to separate a single solution of MgCl2, ZnCl2 and Pb(NO3)2.
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Key words:
- chitosan /
- metal-organic framework /
- nanofiltration membrane /
- electrospray
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图 1 NH2-UIO-66(Zr)的结构图(a, b)及结构式(c)
Figure 1. Schematic (a, b)and structural formula (c) of NH2-UIO-66(Zr).
图 2 电喷雾法制备MOFs/壳聚糖膜示意图。
Figure 2. Schematic diagram of MOFs/chitosan membrane prepared by electrospraying.
图 3 NH2-UIO-66(Zr)的XRD谱图(a)、 FT-IR光谱(b)、UV-vis DRS(c)光谱以及SEM图(d)
Figure 3. XRD pattern(a), FT-IR spectrum(b), UV-vis DRS spectrum(c) and SEM image(d) of NH2-UIO-66(Zr)
图 4 PSF基底(a)，MCS-0膜(b)和MCS-5膜(c)的SEM图
Figure 4. SEM images of PSF substrate(a), MCS-0 membrane(b) and MCS-5 membrane(c)
图 5 PSF基底(a)，MCS-0(b)和 MCS-5膜(c)的水接触角测试
Figure 5. Water contact angle test of PSF substrate(a), MCS-0(b) and MCS-5 membrane(c)
图 6 PSF基底，壳聚糖膜和MCS-5膜的ATR-FTIR光谱。
Figure 6. ATR-FTIR spectra of PSF substrate, chitosan membrane and MCS-5 membrane.
图 8 不同注射速度的壳聚糖膜分离性能（0.5 g/L, 4×105 Pa）。
Figure 8. Separating performance of chitosan membranes with different spraying speed (0.5 g/L, 4×105 Pa).
图 9 负载量对MCS膜分离性能的影响（0.5 g/L, 4×105 Pa）
Figure 9. Effect of loadings on the separation performance of MCS membrane (0.5 g/L, 4×105 Pa)
图 10 不同工艺制备的膜分离性能对比（0.5 g/L, 4×105 Pa）
Figure 10. Comparison of separation performance of membranes prepared by different processes (0.5 g/L, 4×105 Pa)
图 11 (a) 进料浓度（4×105 Pa）和(b)测试压力（0.5 g/L）对MCS-5分离NiCl2的影响。
Figure 11. Effect of (a) feed concentration (4×105 Pa) and (b) test pressure (0.5 g/L) on the separation performance of MCS-5 on NiCl2 solution.
图 12 MCS-5膜对不同重金属的分离性能（0.5 g/L, 4×105 Pa）
Figure 12. Separation performance of MCS-5 membrane for different heavy metals (0.5 g/L, 4×105 Pa)
表 1 Zeta电位测试
Table 1. Zeta potential test
Item Zeta potential
（pH=4）/mVZeta potential
（pH=6）/mVZeta potential
（pH=8）/mVPSF substrate −15.1±0.4 −30.88±0.82 −39.06±0.42 MCS-0 membrane 8.85±0.32 7.33±0.35 4.05±0.02 MCS-5 membrane 7.34±0.37 6.14±0.01 3.86±0.02 
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