Nonpolar Cross-Stacked Super-Aligned Carbon Nanotube Membrane for Efficient Wastewater Treatment
Key Highlights :
Membrane separation technology has been widely recognized as a more advantageous technology owing to its high treatment efficiency, low footprint, and reliable effluent quality. However, its further sustainable growth has been hampered due to membrane fouling. Although great efforts have been made in the recent decades to improve the antifouling performance via various modification strategies, the obtained membranes commonly possess more complicated surface chemistry, which is unfavorable for membrane fouling control. To address this issue, researchers from Beijing Forestry University and Tsinghua University have developed a nonpolar super-aligned carbon nanotube (SACNT) membrane with a layer-by-layer cross-stacking strategy.
The polarity of molecules essentially determines their molecular interaction behavior. Nonpolar membranes may exhibit advantages in antifouling because the electric dipole moment is close to zero, which is not conducive to the deposition of pollutants on the membrane surface. However, such a fundamental interaction mechanism is rarely considered in the previous membrane fabrication and modification studies. Also, nonpolar materials have not been sufficiently concerned in previous membrane preparation studies. Although carbon nanotube had been increasingly employed for membrane fabrication, the potential beneficial effects of its nonpolar feature had been barely investigated. A few studies developed vertically aligned CNT membranes, but they are not suitable for micro-/ultra-filtration processes due to limited pore size and porosity.
The research team found that the surface chemistry of the SACNT membranes is simple and inert, thereby potentially eliminating the covalent-bonding -induced membrane fouling. Besides, the SACNT membranes exhibited a typical nonpolar wetting behavior, with high contact angles for polar liquids (water: ~124.9°–126.5°; formamide: ~80.0°–83.9°) but low contact angles for nonpolar diiodomethane (~18.8°–20.9°). Their research achieved a smoother and more uniform structure with higher permeability than commercial membranes. The SACNT membrane in municipal wastewater treatment cleaning efficiency increased by 2.3 times, oil/water separation efficiency reached 99.2%.
This study successfully proposed a novel nonpolar SACNT membrane by using a layer-by-layer cross-stacking method using the nonpolar carbon nanotubes as the raw material. This work not only provides a new solution to the problem of membrane pollution in membrane separation technology, but also improves the efficiency of municipal sewage treatment and waste water recovery, which has a broad application prospect in various fields. The nonpolar SACNT membrane has great potential in wastewater treatment and other fields, owing to its high selectivity, high permeability, and simple surface chemistry.
In conclusion, this study has demonstrated the potential of nonpolar SACNT membrane in wastewater treatment and other applications. The layer-by-layer cross-stacking method using nonpolar carbon nanotubes as the raw material offers a promising approach to fabricate nonpolar membranes with high selectivity, high permeability, and simple surface chemistry. This work provides a new solution to the problem of membrane fouling in membrane separation technology and has a broad application prospect in various fields.
