In situ synthesis of Prussian blue@MXene membranes for high-efficient ion sieving in desalination

Two-dimensional (2D) materials membranes show great potential for water desalination, whose performance can be further improved by introducing nanoporous crystals into the narrow and tortuous interlayer channels. Here, we constructed a new membrane using Prussian blue (PB)@MXene nanosheets synthesized in situ at room temperature as building blocks, presenting a significantly enhanced water desalination performance. Briefly, the negatively charged MXene nanosheets anchored Fe³⁺ as nucleation sites through electrostatic interactions, and then coordinated with [Fe(CN)₆]^4- at room temperature to produce PB crystals. By utilizing microfluidic synthesis approach, the residence time and reaction amount of Fe³⁺ and [Fe(CN)₆]^4- in the flow channel were precisely controlled, which was beneficial for regulating crystal size to tune the interlayer spacing. The membranes were fabricated by vacuum filtration of PB@MXene nanosheets on the surface of porous substrate. The resulting PB@MXene membrane exhibited an enhanced water permeance of up to 61.6 mol m⁻² h⁻¹ and salt rejection of 98.1 %, increasing by 63.4 % and 13.9 % respectively compared with those of MXene membrane. Interestingly, the iron ions could be replaced with other metal ions such as cobalt and nickel atoms, to generate Prussian blue analogs, thereby varying the pore size of crystal to improve water permeance. Such a facile fabrication approach for PB@MXene membranes provides new insights into the development of advanced materials to construct 2D membrane for desalination.