Simultaneous electrokinetic energy conversion and organic molecular sieving by two-dimensional confined nanochannels

With the development of nanofabrication and nanomaterials, electrokinetic nanofluidic energy conversion has been studied in nanometre-scale, even sub-1-nm channels, which can sieve organic molecules. However, achieving simultaneous nanofluidic energy conversion and organic molecular sieving still remains a challenge. In this work, functional MXene-based membranes were prepared for simultaneous electrokinetic energy conversion and organic molecular sieving. The surface charges of MXene-based membranes were successfully transferred from negative to positive by functionalizing poly (diallyldimethylammonium chloride) (PDDA) polycation chain. The positively charged PDDA-MXene (PMXene) composite membranes displayed good rejection (greater than 99 %) for positively charged methylene blue (MB) molecules. The streaming currents through PMXene and MXene membranes were opposite, indicating the successful modification of the surface charge in the nanochannels of the membranes. In addition, the output current improved around four times from ∼ 95 nA (50 kPa) to ∼ 380 nA (150 kPa) through the PMXene membranes. The flux and rejection of the membranes can also be enhanced by tuning the applied pressure and the thickness of the membranes. Given the superior selective transport of ions and molecules, functional MXene-based membranes can offer many exciting opportunities for self-powered and energy recovery systems during the separation process.