High performance reverse osmosis membrane with a separation layer consisting of highly selective polyamide networks and porous organic cages

Abstract

Reverse osmosis (RO) membrane technology has widespread applications in many fields, such as desalination and organics removal. A long-standing goal for RO membrane technology is developing highly permeable RO membranes with high rejection. Upgrading of the separation layer microstructure is the key. One ideal design for the separation layer microstructure is that the layer is rich in fast water transport channels and meanwhile the polyamide (PA) networks are highly selective. The simplest strategy to increase fast water transport channels is introducing functional materials into the separation layer via the aqueous or organic phase addition. The organic phase addition method is more effective. However, most functional materials reported cannot be dissolved or dispersed well in the organic phase, which are not suitable for this method. Besides, the attentions that PA network received were less than functional materials in the past, though it is crucial for the rejection. This work proposes to construct the kind of separation layer mentioned above via introducing a porous organic cage (CC3), which is an intrinsically porous organic molecule with oil solubility, in the separation layer as the supplier for fast water transport channel by the organic phase addition method, and with the aid of an oil-soluble surfactant, which contributes to the formation of highly selective PA networks through surfactant-assembly regulated interfacial polymerization. Our strategy is efficient. By using a tiny amount of CC3 (0.005 % w/v) and surfactant (0.0025 % w/v), a flux of 93.6 L·m⁻²·h⁻¹ (an increase of 43.1 %), a salt rejection of 98.82 % and a water/salt selectivity of 7864 can be achieved. This performance is at high level for a desalination RO membrane. Simultaneously, the developed RO membrane exhibited an improved removal performance for organic compounds with low molecular weight (<300 Da). The organics rejection exceeded 91.00 %.