Nanofiltration Membrane: Size & Charge Rejection

Nanofiltration membranes separate dissolved ions and small molecules using pores just 1–2 nanometres wide — too coarse to reject everything like reverse osmosis, but fine enough that geometry and electrostatics both matter. This simulator renders individual solute particles (a neutral glucose-size molecule, Na⁺, Cl⁻ and SO₄²⁻) drifting toward a charged nanoporous membrane in 3D, and tests each one against the pore at the moment it arrives using the Ferry steric-partitioning equation combined with a Donnan charge-exclusion factor — the same two mechanisms real membrane scientists use in the Donnan-Steric Pore Model. Adjust the pore radius, the membrane's fixed surface charge and the applied pressure, and watch rejection rates diverge by species in real time, exactly reproducing the size-and-charge selectivity that makes NF membranes useful for water softening and selective ion removal.