Chemical tuning of nanoporous, solid sorbents for an ideal CO2 binding requires unhindered amine functional groups on the pore walls. Although common for soluble organics, post-synthetic reduction of nitriles in porous networks often fail due to the insufficient and irreversible metal hydride penetration. Here, we synthesized a nanoporous network with pendant nitrile groups, microsphere morphology and in large scale. The hollow microspheres were easily decorated with primary amines through in situ reduction by widely available boranes. CO2 capture capacity of the modified sorbent was increased up to an eight times of the starting nanoporous network with a high heat of adsorption (98 kJ/mol). Surface area can be easily tuned between 1 and 354 m2/g. Average particle size (~50 µm) is also quite suitable for CO2 capture applications where processes like fluidized bed require spheres of micron sizes.