Abstract
Nanomaterials embedded in nanofiltration membranes have become a promising modification technology to improve separation performance. As a novel representation of two-dimensional (2D) nanomaterials, MXene has nice features with a strong negative charge and excellent hydrophilicity. Our previous research showed that MXene nanosheets were added in the aqueous phase, which enhanced the permeselectivity of the membrane and achieved persistent desalination performance. Embedding the nanomaterials into the polyamide layer through the organic phase can locate the nanomaterials on the upper surface of the polyamide layer, and also prevent the water layer around the hydrophilic nanomaterials from hindering the interfacial polymerization reaction. We supposed that if MXene nanosheets were added in the organic phase, MXene nanosheets would have more negative contact sites on the membrane surface and the crosslinking degree would increase. In this study, MXene were dispersed in the organic phase with the help of ultrasound, then MXene nanocomposite nanofiltration membranes were achieved. The prepared MXene membranes obtained enhanced negative charge and lower effective pore size. In the 28-day persistent desalination test, the Na2SO4 rejection of MXene membrane could reach 98.6%, which showed higher rejection compared with MXene embedded in aqueous phase. The results of a long-time water immersion test showed that MXene membrane could still maintain a high salt rejection after being soaked in water for up to 105 days, which indicated MXene on the membrane surface was stable. Besides MXene membrane showed high rejection for high-concentration brine and good mono/divalent salt separation performance in mono/divalent mixed salt solutions. As a part of the study of MXene in nanofiltration membranes, we hoped this research could provide a theoretical guidance for future research in screening different addition methods and different properties.
Highlights
Desalination of seawater and brackish water has become one of the most sustainable methods to alleviate water shortages, and brackish water contains more divalent salts such as SO4 2− and Mg2+ compared with seawater [1]
Na2 SO4 rejection of MXene membrane could reach 98.6%, which showed higher rejection compared with MXene embedded in aqueous phase
The MXene nanomaterial with strong negative charge was embedded in the organic phase, the prepared MXene nanocomposite nanofiltration membrane showed enhanced surface charge, and the effective aperture was further reduced
Summary
Desalination of seawater and brackish water has become one of the most sustainable methods to alleviate water shortages, and brackish water contains more divalent salts such as SO4 2− and Mg2+ compared with seawater [1]. Charge modification of the membrane surface can effectively improve the mono/divalent ions separation performance of the membrane. MXene was a hydrophilic nanomaterial and the embedding of MXene in the aqueous phase would cause a water layer to form on the MXene surface, which hindered the interfacial polymerization reaction and formed nanovoids [16]. We assumed that hydrophilic and negative MXene nanomaterials were embedded in the organic phase for enhanced negative charge and lower effective pore size compared with previous research. MXene nanomaterials were added in the organic phase, on the one hand for maximizing the charge effect of MXene and the charged solute and on the other hand for promoting the reaction degree of interfacial polymerization. Combined with previous research about MXene embedded in aqueous phase, we hoped that the same nanoparticles with two different methods would provide a theoretical guidance for future research in screening different addition methods and different properties
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