Bismuth subcarbonate ((BiO)(2)CO3) nanospheres (150 nm in diameter) and nanosheets (5 nm thickness) were selectively synthesized in ultra-dilute bismuth nitrate solutions of 1 to 100 mu M. Bismuth ions react with carbonic acid, which is formed by CO2 dissolved in water, and (BiO)(2)CO3 nanostructures are synthesized by the reaction of BiONO3 and carbonic acid. The morphologies of the nanostructures are controlled by the reaction kinetics, proportional to the concentration of reactant ions; lower concentration leads to slower reaction and isotropic growth of nanospheres, while higher concentration causes faster reaction in the direction of higher indexed plane, and nanosheets are synthesized.