Design of gradient nanopores in phenolics for ultrafast water permeation

Membrane technology is playing a pivotal role in providing potable water to our thirsty planet. However, the strong demand for highly permeable and durable membranes with affordable costs remains. Such membranes are synthesized herein by designing gradient nanopores in low-cost phenolics. The gradient nanopores are achieved by spontaneous assembly of phenolic nanoparticles with gradually enlarged sizes. These particles nucleate and grow as a result of ZnCl2-accelerated thermopolymerization of resol in the progressive downward gelating polymer. Subsequent removal of the gelated polymer and ZnCl2 exposes the gradient nanopores. The gradient nanopores endow the phenolic structures with unprecedented permselectivity when used in membrane separation, totally rejecting fine particulates down to 5 nm dispersed in water or aggressive solvents while allowing water to permeate up to two orders of magnitude faster than other membranes with similar rejections. Our work opens up an avenue for the rational design and affordable synthesis of ultrafast membranes.