Nanocapsule controlled interfacial polymerization finely tunes membrane surface charge for precise molecular sieving.

• Nanocapsule controlled interfacial polymerization is used to tune surface charge precisely. • Tune the charge by encapsulating and disintegrating the functional modifier. • The membrane achieves high retention performance of positively charged salts. • The membrane shows higher than 90% rejection on charged materials in a wide pH range. Angstrom-scale molecular sieving with tunable membrane surface charge is urgently needed. Conventional methodologies cannot control the surface charge with high resolution and scalability. For the first time, a nanocapsule controlled interfacial polymerization (NCIP) is proposed to precisely tune the membrane properties by encapsulation and disintegration of charge mediative agent in the nanofiltration membrane formation process. The angstrom-scale molecular sieve membranes can be customized by the NCIP to achieve 3.82-time enhanced pure water permeability (from 3.24 to 12.37 L‧m−2‧bar−1‧h−1). The charge tunable surface can alter the Na+ rejection from 90.51% to 27.43% while maintaining Mg2+ retention at a high level (>90.18%), so that effectively separates these ions. The targeted filtration of similar-sized amino acids (131–147 g mol−1) can be effectively achieved in a wide pH range by precisely controlling the membrane's isoelectric point instead of tediously and costly adjusting solution chemistry. This unique strategy may provide a paradigm shift in the precise sieving of small, especially bioactive high-value-added molecules in mild conditions. [ABSTRACT FROM AUTHOR]