Which of the following is effectively used to remove E. coli bacteria from water?

Silver nanoparticles exhibit potent antimicrobial properties through several mechanisms that effectively eliminate E. coli. Silver ions $\mathrm{Ag^+}$ disrupt bacterial cell membrane integrity, penetrate cells to interfere with metabolic pathways, inhibit enzyme activity, and damage DNA.

Carbon black nanoparticles primarily function as adsorbents without significant intrinsic antimicrobial effects. Titanium dioxide nanoparticles $\mathrm{TiO_2}$ require UV activation for photocatalytic generation of reactive oxygen species. Silicon nanoparticles lack effective antimicrobial properties for direct bacterial removal.

Silver nanoparticles provide direct, light-independent antimicrobial action, making them the optimal choice for E. coli removal from water.