An adsorbent includes core particles containing an adsorbing material; a porous
coating layer including a polymer material that coats the core particles; and an
underlying layer containing a metal compound and disposed between the core particles
and the porous coating layer. The porous coating layer is formed by spraying and
applying a suspension or a solution containing the polymer material over the adsorbing
material, or by immersing the adsorbing material into the suspension or the solution.
