The pore volume and BET surface area of bio-MOF-1(a), Zn-8(ad)(4)(BPDC)(6)O center dot 2Me(2)NH(2), is systematically modified via postsynthetic cation exchange with either tetramethylammonium, tetraethylamonium, or tetrabutylammonium cations to yield Zn-8(ad)(4)(BPDC)(6)O center dot 2Me(2)NH(2) (b), Zn-8(ad)(4)(BPDC)(6)O center dot 2Et(4) (c), Zn-8(ad)(4)(BPDC)(6)O center dot 2Bu(4)N (d), respectively. The impact that pore volume and BET surface area have on CO2 capacity is evaluated, and it is found that materials with intermediate porosity (b and c) have the largest CO2 capacities under the conditions studied.