Water Nanochannels in MXene Polyamide Nanofiltration Membranes: Implications for Permeability

Over the last decade, thin-film nanocomposite (TFN) membranes have been extensively utilized in desalination and wastewater treatment. The most reported nanochannels in the TFN membranes lack sufficient observational evidence. We conducted a systematic study on the TFN membrane that incorporated two-dimensional (2D) MXene nanosheets and provided evidence that nanovoids existed in the polyamide layer surrounding the nanosheets. The nanovoids functioned as nanochannels for water, which led to a significant increase in membrane permeance by 2.8 times compared to the blank membrane. The Na2SO4 rejection of the MXene polyamide membrane is as high as 96.4% and has obvious advantages in seawater desalination. The size of the nanochannels was correlated with the quantity, size, and spreadability of MXene nanosheets. Larger water nanochannels could be formed if there is a considerable amount and size of nanosheets, and they were evenly distributed. After being subjected to a sustained pressure environment, the nanochannels remained intact and the membrane maintained its excellent permeance across varying pressures. Our work could offer a perspective on the generation of internal nanochannels in the TFN membrane and optimize nanochannels to provide better desalination performance.