It is possible to increase ion occupancy within a CNT by placing a rim of partial charges at the NT ends. In molecular dynamics simulations Joseph et al57 demonstrated a fourfold increase in ion occupancy in a CNT 2.2 nm in diameter and 1.3 nm long, using a partial charge of ±0.38 e placed at the NT rim atoms. Fornasiero et al37 were able to control ion transport through fabricated CNT pores 0.8 to 2.6 nm in diameter embedded in a Si3N4 matrix. Following Joseph et al, their NT ends were terminated with negatively charged carboxylic groups. By varying the solution pH they were able to modulate the NT tip charges so that the membrane would either reject ions or permeate ions. In addition, they found that an increase in the number of multivalent ions in the solution decreased the rejection capability toward monovalent ions.