Disclosed herein is a method of making a polymeric material for selective adsorption of a gas. The method comprises dissolving a monomer comprising a functional group having an affinity for the gas in a solvent with a cross-linker and an initiator; emulsifying the solution in a liquid which is inimiscible with the first solvent; and agitating and heating the enmulsion to cause polymerization of the monomer into a cross-linked polymer having nanocavities with functional groups covalently-incorporated on walls thereof. Also disclosed are polymeric particles, an apparatus for forming the particles and a method of adsorbing a selected gas