pH responsive composite Janus cages of PS-silica-PEO are prepared using silica nanoparticles to crosslink two PAA contained di-block copolymers at an emulsion interface sequentially. Transverse channels are

in situ

created across the shell

which facilitates mass transfer. Shell is pH responsive owing to the presence of residual PAA chains tethered onto the silica nanoparticles. The Janus cages are capable to preferentially capture oil from their aqueous surroundings. The saturation absorption capacity is determined by pH and oil property. Other composite Janus cages are expected by extension the method using other copolymers and functional nanoparticles.